No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Interaction between climate, volcanism, and isostatic rebound in Southeast Alaska during the last deglaciation
... Distal tephra records in marine cores, which provide high temporal resolution to test causality between volcanism and changes in sea-level and/or ice volume over numerous glacial cycles (e.g., Schindlbeck et al., 2018), indicate that periods of enhanced volcanism occurred following deglaciation (Kutterolf et al., 2019). More proximal terrestrial and marine tephra records have provided compositional and volumetric data for studying magma system response to deglaciation, but only for the time period sincẽ 20 ka (Watt et al., 2013;Praetorius et al., 2016;Rawson et al., 2016). Such records can be hampered by the under-recording of relatively small-scale eruptions (Kiyosugi et al., 2015) and the poor preservation of tephras during glacial periods (Watt et al., 2013). ...
... While a general hypothesis has been agreed upon (i.e., deglaciation leads to enhanced eruption rates), the assumptions and limitations of studies that test this hypothesis are seldom reported. Testing whether ice loading reduces rates of volcanism implies that eruptible magma ascent is suppressed and/or magma recharge is prevented at the time of ice loading (e.g., Praetorius et al., 2016;Rawson et al., 2016). Such a condition implies that there is a steady-state flux of magma from the mantle to the surface via the crust over the~10-100 kyr time periods of interest ( Figure 1C), and that deviations from regular eruptive rates or compositions can be interpreted as being driven by external processes (i.e., ice loading). ...
... Alternatively, the finding may indicate that biases in eruption records have affected numerous volcanoes similarly. Whereas some tephra records only permit investigation of post-LGM volcanic activity (e.g., Praetorius et al., 2016), sampling of Pleistocene volcanic edifices allows longer eruption records to be constructed that may permit investigation of eruption rate changes during older glacial/interglacial transitions. The observation of increased eruptive rates following deglaciation over multiple glacial-interglacial cycles at any given volcano would strengthen support for causality between ice unloading and eruption rates. ...
One of the fundamental questions that underpins studies of the interactions between the cryosphere and volcanism is: do causal relationships exist between the ice volume on a volcano and its eruption rate? In particular, it is critical to determine whether the decompression of crustal magma systems via deglaciation has resulted in enhanced eruption rates along volcanic arcs in the middle to high latitudes. Evidence for such a feedback mechanism would indicate that ongoing glacier retreat could lead to future increases in eruptive activity. Archives of eruption frequency, size, and style, which can be used to test whether magma generation and eruption dynamics have been affected by local ice volume fluctuations, exist in the preserved eruptive products of Pleistocene-Holocene volcanoes. For this contribution, we have reviewed time-volume-composition trends for 33 volcanoes and volcanic groups in arc settings affected by glaciation, based on published radiometric ages and erupted volumes and/or compositions of edifice-forming products. Of the 33 volcanic systems examined that have geochronological and volumetric data of sufficient resolution to compare to climatic changes since ∼250 ka, increases in apparent eruption rates during post-glacial periods were identified for 4, with unclear trends identified for a further 12. Limitations in the geochronological and eruption volume datasets of the case studies make it difficult to test whether apparent eruption rates are correlated with ice coverage. Major caveats are: 1) the potential for biased preservation and exposure of eruptive materials within certain periods of a volcano’s lifespan; 2) the relative imprecision of geochronological constraints for volcanic products when compared with high-resolution climate proxy records; 3) the reliance on data only from immediately before and after the Last Glacial Termination (∼18 ka), which are rarely compared with trends throughout the Pleistocene to test the reproducibility of eruptive patterns; and 4) the lack of consideration that eruption rates and magma compositions may be influenced by mantle and crustal processes that operate independently of glacial advance/retreat. Addressing these limitations will lead to improvements in the fields of geochronology, paleoclimatology, and eruption forecasting, which could make valuable contributions to the endeavours of mitigating future climate change and volcanic hazards.
... The Alexander Archipelago is highlighted by the red box on the main figure. Orange dots indicate locations of marine sediment cores: 51-JPC (Caissie et al., 2010), SO202-27-6 (Maier et al., 2018, U1419 (Walczak et al., 2020), EW0408-85JC (Davies et al., 2011;Mix, 2014, Praetoruis et al., 2015), EW0408-66JC (Praetorius and Mix, 2014;Praetorius et al., 2016), EW0408-26JC (Praetorius and Mix, 2014;Praetorius et al., 2016), EW0408-40JC (Addison et al., 2010), MD02-2496 (Cosma et al., 2008), and JT96-09 (Kienast and McKay, 2001). Blue dots indicate location of terrestrial study sites: Sanak Island (Misarti et al., 2012), Kodiak Island (Mann and Peteet, 1994), Finger Glacier (Mann, 1986), Haida Gwaii Mathewes and Clague, 2017), Calvert Island (Darvill et al., 2018), and Puget Sound (Porter and Swanson, 1998). ...
... The Alexander Archipelago is highlighted by the red box on the main figure. Orange dots indicate locations of marine sediment cores: 51-JPC (Caissie et al., 2010), SO202-27-6 (Maier et al., 2018, U1419 (Walczak et al., 2020), EW0408-85JC (Davies et al., 2011;Mix, 2014, Praetoruis et al., 2015), EW0408-66JC (Praetorius and Mix, 2014;Praetorius et al., 2016), EW0408-26JC (Praetorius and Mix, 2014;Praetorius et al., 2016), EW0408-40JC (Addison et al., 2010), MD02-2496 (Cosma et al., 2008), and JT96-09 (Kienast and McKay, 2001). Blue dots indicate location of terrestrial study sites: Sanak Island (Misarti et al., 2012), Kodiak Island (Mann and Peteet, 1994), Finger Glacier (Mann, 1986), Haida Gwaii Mathewes and Clague, 2017), Calvert Island (Darvill et al., 2018), and Puget Sound (Porter and Swanson, 1998). ...
... Blue box shows extent of study area from Lesnek et al. (2018Lesnek et al. ( , 2020. Orange dots represent locations of marine sediment cores: EW0408-66JC and EW0408-26J (Praetorius and Mix, 2014;Praetorius et al., 2016) and EW0408-40JC (Addison et al., 2010). Blue dots indicate locations of relevant terrestrial study sites: Gastineau Channel (Miller, 1973), Pleasant Island (Hansen and Engstrom, 1996), Hummingbird Lake (Ager, 2019), Shuká Káa (Lesnek et al., 2018), and El Capitan Cave (Wilcox et al., 2019). ...
The late-Pleistocene history of the coastal Cordilleran Ice Sheet remains
relatively unstudied compared to chronologies of the Laurentide Ice Sheet.
Yet accurate reconstructions of Cordilleran Ice Sheet extent and the timing
of ice retreat along the Pacific Coast are essential for paleoclimate
modeling, assessing meltwater contribution to the North Pacific, and
determining the availability of ice-free land along the coastal Cordilleran
Ice Sheet margin for human migration from Beringia into the rest of the
Americas. To improve the chronology of Cordilleran Ice Sheet history in the
Alexander Archipelago, Alaska, we applied 10Be and 36Cl dating to
boulders and glacially sculpted bedrock in areas previously hypothesized to
have remained ice-free throughout the local Last Glacial Maximum (LLGM;
20–17 ka). Results indicate that these sites, and more generally the coastal northern Alexander Archipelago, became ice-free by 15.1 ± 0.9 ka (n = 12 boulders; 1 SD). We also provide further age constraints on deglaciation along the southern Alexander Archipelago and combine our new ages with data from two previous studies. We determine that ice retreated from the outer coast of the southern Alexander Archipelago at 16.3 ± 0.8 ka (n = 14 boulders; 1 SD). These results collectively indicate that
areas above modern sea level that were previously mapped as glacial refugia
were covered by ice during the LLGM until between ∼ 16.3 and
15.1 ka. As no evidence was found for ice-free land during the LLGM, our
results suggest that previous ice-sheet reconstructions underestimate the
regional maximum Cordilleran Ice Sheet extent, and that all ice likely
terminated on the continental shelf. Future work should investigate whether
presently submerged areas of the continental shelf were ice-free.
... Shaded light blue areas are ice sheet extents at ∼17.3 cal ka BP (Dyke, 2004). Black dots indicate locations of marine sediment cores: SO202-27-6 (Maier et al., 2018), EW0408-85JC (Davies et al., 2011;Praetorius and Mix, 2014;Praetorius et al., 2015), EW0408-22JC (Praetorius et al., 2016), and MD02-2946 Hendy and Cosma, 2008;Taylor et al., 2014). Yellow dots indicate locations of terrestrial CIS chronology: APGC = Alaska Peninsula Glacier Complex (Misarti et al., 2012), Kodiak Island (Mann and Peteet, 1994), Mt. ...
... HL = Hummingbird Lake (Ager et al., 2019), EC = El Capitan Cave (Wilcox et al., 2019). Modern glacier extents (white) are from version 6 of the Randolph Glacier Inventory (NSIDC, 2005(NSIDC, , updated 2018. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) ...
... Similarly, terrestrial 14 C ages from Kodiak Island, southern Alaska (Mann and Peteet, 1994), and the Alaska Peninsula Glacier Complex (Misarti et al., 2012) indicate initial glacier retreat ∼17 ka (Fig. 1). Ice-rafted debris records from the Southeast Alaska margin (Praetorius et al., 2016), the Vancouver Island shelf ( Fig. 12g; , and the coastal Gulf of Alaska (Praetorius and Mix, 2014) show a period of intense iceberg calving around North Pacific beginning between ∼18 and 17 ka. Likewise, observations of surface freshening in the central Gulf of Alaska ( Fig. 12c; Davies et al., 2011;Maier et al., 2018) suggest widespread calving of the western CIS beginning ∼18 ka. ...
Understanding marine-terminating ice sheet response to past climate transitions provides valuable long-term context for observations of modern ice sheet change. Here, we reconstruct the last deglaciation of marine-terminating Cordilleran Ice Sheet (CIS) margins in Southeast Alaska and explore potential forcings of western CIS retreat. We combine 27 new cosmogenic ¹⁰ Be exposure ages, 13 recently published ¹⁰ Be ages, and 25 new ¹⁴ C ages from raised marine sediments to constrain CIS recession. Retreat from the outer coast was underway by 17 ka, and the inner fjords and sounds were ice-free by 15 ka. After 15 ka, the western margin of the CIS became primarily land-terminating and alpine glaciers disappeared from the outer coast. Isolated alpine glaciers may have persisted in high inland peaks until the early Holocene. Our results suggest that the most rapid phase of CIS retreat along the Pacific coast occurred between ~17 and 15 ka. This retreat was likely driven by processes operating at the ice-ocean interface, including sea level rise and ocean warming. CIS recession after ~15 ka occurred during a time of climatic amelioration in this region, when both ocean and air temperatures increased. These data highlight the sensitivity of marine-terminating CIS regions to deglacial climate change.
... An abrupt ~5°C warming into the Holocene is seen in cores EW0408-85JC (33), JT96-09PC (34), and ODP (Ocean Drilling Program) 1019 (35). The magnitude of the abrupt warming into the Holocene is slightly reduced in EW0408-66JC (36) relative to the other margin sites, and core EW0408-87JC in the Pacific subpolar gyre shows a more gradual warming into the Holocene that peaks at ~10 ka. Most cores show peak early Holocene warmth until ~9 ka, when a ~1°C cooling trend is initiated, reaching a Holocene minimum near ~6 ka, followed by warming near ~4 ka. ...
... Data were reported in notation, 18 (42). Published records of Nps and Gb 18 O from cores EW0408-85JC (55), EW0408-26JC (17), and EW0408-66JC (17) were used for the 18 O sw-ivc records in these cores (33,36). The (73). ...
... Measurements of Uk′37 from EW0408 cores in the GOA were conducted at the Oregon State University in Fredrick Prahl's laboratory. Data from cores EW0408-66JC and EW0408-26JC/TC were published by Praetorius et al. (36). Data from EW0408-85JC were published by Praetorius et al. (33). ...
Columbia River megafloods occurred repeatedly during the last deglaciation, but the impacts of this fresh water on Pacific hydrography are largely unknown. To reconstruct changes in ocean circulation during this period, we used a numerical model to simulate the flow trajectory of Columbia River megafloods and compiled records of sea surface temperature, paleo-salinity, and deep-water radiocarbon from marine sediment cores in the Northeast Pacific. The North Pacific sea surface cooled and freshened during the early deglacial (19.0-16.5 ka) and Younger Dryas (12.9-11.7 ka) intervals, coincident with the appearance of subsurface water masses depleted in radiocarbon relative to the sea surface. We infer that Pacific meltwater fluxes contributed to net Northern Hemisphere cooling prior to North Atlantic Heinrich Events, and again during the Younger Dryas stadial. Abrupt warming in the Northeast Pacific similarly contributed to hemispheric warming during the Bølling and Holocene transitions. These findings underscore the importance of changes in North Pacific freshwater fluxes and circulation in deglacial climate events.
... Most attention has been focused on the volcanic history surrounding the Mt. Edgecumbe volcanic field (MEVF) (Fig. 1), especially late Pleistocene tephra deposits ranging in age from 14,600 to 13,100 calibrated years before present (cal yr BP) (Riehle et al., 1992;Begét and Motyka, 1998;Addison et al., 2010;Praetorius et al., 2016). These tephras provide unique geochronological constraints during an important time period, when the Cordilleran Ice Sheet was actively retreating (Taylor et al., 2014), and when human migration is hypothesized to have occurred along coastal Alaska (Lesnek et al., 2018). ...
... These tephras provide unique geochronological constraints during an important time period, when the Cordilleran Ice Sheet was actively retreating (Taylor et al., 2014), and when human migration is hypothesized to have occurred along coastal Alaska (Lesnek et al., 2018). Additionally, the timing of these deposits during deglaciation of the Cordilleran Ice Sheet provides initial clues as to the eruption mechanism, possibly driven by ice sheet retreat itself (Praetorius et al., 2016). However, there is currently no widely accepted geochronological marker during this important time period in southernmost Southeast Alaska. ...
... Postglacial tephra deposits from the MEVF near Sitka, Alaska (Fig. 1), have been well studied in both terrestrial and marine environments (Riehle et al., 1992;Begét and Motyka, 1998;Addison et al., 2010;Praetorius et al., 2016). At least 12 postglacial tephra deposits have been identified from the MEVF with compositions ranging from basalt to rhyolite (Praetorius et al., 2016) and thereby represent a potential source for the Baker Island tephra. ...
Three new tephras have been identified in Southeast Alaska. An 8-cm-thick black basaltic tephra with nine discrete normally graded beds is present in cores from a lake on Baker Island. The estimated age of the tephra is 13,492 ± 237 cal yr BP. Although similar in age to the MEd tephra from the adjacent Mt. Edgecumbe volcanic field, this tephra is geochemically distinct. Black basaltic tephras recovered from two additional sites in Southeast Alaska, Heceta Island and the Gulf of Esquibel, are also geochemically distinct from the MEd tephra. The age of the tephra from Heceta Island is 14,609 ± 343 cal yr BP. Whereas the tephras recovered from Baker Island/Heceta Island/Gulf of Esquibel are geochemically distinct from each other, similarities in the ages of these tephras and the MEd tephra suggest a shared eruptive trigger, possibly crustal unloading caused by retreat of the Cordilleran Ice Sheet. The submerged Addington volcanic field on the continental shelf, which may have been subaerially exposed during the late Pleistocene, is a possible source for the Southeast Alaska tephras.
... Other late Quaternary Insular Belt volcanoes are scattered across the Alexander archipelago in southeast Alaska between the Mount Edgecumbe volcanic field (MEV) on Kruzof Island (Riehle et al. 1992;Praetorius et al. 2016;Grapenthin et al. 2022) and the edge of Dixon Entrance at the Canadian border. They include Tlevak Strait-Suemez Island Volcano near Prince of Wales Island (Brew 1990;Riehle et al. 1992), the drowned cinder cone near Misty Fjords National Monument (Karl et al. 2013;Kheiry 2013), and the submerged Addington basaltic volcanic field (Wilcox et al. 2019) in southeast Alaska. ...
... We interpret the relationship between deglaciation and volcanism around Milbanke Sound as causal rather than merely coincidental. There is some evidence globally for glacial-volcanic activity related to changing loads and stresses in the crust (Nakada and Yokose 1992;Riehle et al. 1992;Watt et al. 2013;Conway et al. 2015Conway et al. , 2023Maccaferri et al. 2015;Praetorius et al. 2016;Mora and Tassara 2019). Wilson and Russell (2020) presented a potential mechanism for deglacial volcanism and pumping caused by the CIS loading and unloading, given a background level of melting and volcanic activity in the Garibaldi-Cascades Arc. ...
Kitasu Hill and MacGregor Cone formed along the Principe Laredo Fault on British Columbia’s central coast as the Wisconsinan ice sheet withdrew from the Coast Mountains. These small-volume Milbanke Sound Volcanoes (MSV) provide remarkable evidence for the intimate relationship between volcanic and glacial facies. The lavas are within-plate, differentiated (low MgO < 7%) Ocean Island Basalts, hawaiites, and mugearites that formed from ∼1% decompression melting of asthenosphere with residual garnet. Kitasu Hill, on glaciated bedrock, formed between 18 and 15 cal ka BP. Dipping, poorly stratified, admixed hyaloclastite, and glacial diamicton with large plutonic clasts and pillow breccia comprise its basal tuya platform (0–43 masl). Subaerial nested cinder cones, with smaller capping lava flows, sit atop the tuya. New marine samples show McGregor Cone formed subaerially but now sits submerged at 43–200 mbsl on an eroded moraine at the mouth of Finlayson Channel. Seismic data and cores reveal glaciomarine sediments draping the cone’s lower slopes and show beach terraces. Cores contain glaciomarine diamictons, ice-rafted debris, delicate glassy air fall tephra, and shallow, sublittoral, and deeper benthic foraminifera. Dates of 14.1–11.2 cal ka BP show volcanism spanned ∼2000 years during floating ice shelf conditions. The MSV have similar proximal positions to the retreating ice sheet, display mixed volcano-glacial facies, and experienced similar unloading stresses during deglaciation. The MSV may represent deglacially triggered volcanism. The dates, geomorphic and geological evidence, constrain a local relative sea level curve for Milbanke Sound and show how ice gave way to fire.
... In the event that La Niña-like conditions occurred in HS1, they would contribute to a cooling of the Northeastern Pacific and a warming of the Northwestern Pacific, similar to how ENSO dynamics affect North Pacific SSTs today. Given the limited reconstructions regarding paleo-ENSO variability on abrupt millennial-scale events (i.e., HS1 and YD), there is no consensus whether the mean state of the tropical Pacific in HS1 resembles more La Niña-like (Lea et al., 2000;Xiong et al., 2018;Zhou et al., 2016) LI ET AL. (Bard et al., 2000) using the calibration equation of Prahl et al. (1988); (c) TEX 86 -SST record from core SO201-2-12KL (Meyer et al., 2016); (d) TEX 86 -SST record from core LV63-41-2 (this study), error bars are standard error (±1.7°C) of the regional calibration equation (Seki et al., 2014); (e) U ′ 37 -SST record from core SO202-27-6 (Maier et al., 2018;Méheust et al., 2018); (f) U ′ 37 -SST record from core EW0408-26JC (Praetorius et al., 2016); (g) An average Northeastern Pacific δ 18 O sw-ivc record (Praetorius et al., 2020), with blue shading denoting negative anomalies (lower salinity) and orange shading denoting positive anomalies (higher salinity); (h) Chemical index of alteration (magenta) and terrigenous mass accumulation rate (red brown) of core MD06-3054 from the western Philippine Sea, proxies for the local precipitation (Xiong et al., 2018); (i) SST difference between the western and eastern tropical Pacific (Zhou et al., 2016). HS1 = Heinrich Stadial 1. 9 of 11 or more El Niño-like conditions (Koutavas & Joanides, 2012;Koutavas et al., 2002). ...
... Organic ) based sea surface temperature (SST) reconstructions from the subarctic Pacific since the last ice age in comparison to NGRIP ice core δ 18 O. (a) TEX 86 -SST record from core SO201-2-114KL(Meyer et al., 2016); (b) U ′ 37 -SST records from cores SO201-2-77KL and SO201-2-85KL(Max et al., 2012); (c) TEX 86 -SST record from core SO201-2-12KL(Meyer et al., 2016); (d) TEX 86 -SST record from core LV63-41-2 (this study), error bars are standard error (±1.7°C) of the regional calibration equation(Seki et al., 2014); (e) U ′ 37 -SST record from core LV29-114-3(Max et al., 2012); (f) U ′ 37 -SST record from core PC-01(Harada et al., 2004); (g) U ′ 37 -SST record from core MD01-2412(Harada, Ahagon, et al., 2006); (h) U ′ 37 -SST record from core EW0408-85JC(Praetorius et al., 2015) on the revised age model fromPraetorius et al. (2020); (i) U ′ 37 -SST record from core EW0408-87JC(Praetorius et al., 2020); (j) Composite U ′ 37 -SST records from cores EW0408-66JC and EW0408-26JC, a correction of +1°C was added to the original paleotemperature of core EW0408-66JC(Praetorius et al., 2016); (k) U ′ 37 -SST record from core SO202-27-6(Maier et al., 2018;Méheust et al., 2018); (l) U ′ 37 -SST record from core JT96-09PC(Kienast & McKay, 2001) on the revised age model fromPraetorius et al. (2020); (m) U ′ 37 -SST record from core ODP 1019(Barron et al., 2003;Herbert, 2003) on the revised age model fromPraetorius et al. (2020); (n) NGRIP ice core δ 18 O on the GICC05 age model(Rasmussen et al., 2006). All TEX 86 data were calibrated to SST using the regional calibration equation ofSeki et al. (2014), and all U ′ 37 data were re-calibrated to SST based on the calibration equation ofPrahl et al. (1988). ...
The phase relationships of sea surface temperature (SST) changes between the North Pacific and North Atlantic during deglacial millennial‐scale climate events have been of great interest. However, uncertainties remain partly due to the sparsity of deglacial SST records in the North Pacific. This study presents a new high‐resolution TEX86L ${\mathrm{T}\mathrm{E}\mathrm{X}}_{86}^{L}$‐SST record spanning the entire last deglaciation from core LV63‐41‐2 retrieved from the Northwestern Pacific off the Kamchatka Peninsula, which allows us to explore regional SST change patterns and associated driving mechanisms by compiling previously published SST data in the subarctic Pacific. The subarctic Pacific SST changes during the Bølling‐Allerød and Younger Dryas show in‐phase relationships in response to the North Atlantic SST variations, suggesting a dominant control of atmospheric teleconnections between both oceans. During Heinrich Stadial 1 (HS1) when the North Atlantic exhibited significant cooling, the subarctic Pacific SST developments are complex, showing gradual warming from the Last Glacial Maximum to HS1 in the Northwestern Pacific and cooling at the onset of HS1 in the Northeastern Pacific. We suggest that the inconsistent phase responses resulted from the combined effects of multiple processes, which involve an enhanced poleward advection of warm subtropical waters, cold meltwater inputs from the retreating Cordilleran Ice Sheet into the Northeastern Pacific, and a persistent La Niña‐like state in the tropical Pacific.
... Here we find that initial deoxygenation in the North Pacific immediately after the Cordilleran ice sheet (CIS) retreat 4 was associated with increased volcanic ash in seafloor sediments. Timing of volcanic inputs relative to CIS retreat suggests that regional explosive volcanism was initiated by ice unloading 5,6 . We posit that iron fertilization by volcanic ash [7][8][9] during CIS retreat fuelled ocean productivity in this otherwise iron-limited region, and tipped the marine system towards sustained deoxygenation. ...
... (2) The basalt-andesite-dacite cluster represents the main volcanic rock and lava series of the AA, although it is common elsewhere too. Some deglacial terrestrial and marine tephra found on the southern Alaska margin belong to this cluster 6,83 . (3) The basalt (alkaline) cluster is mainly found in the NCVF 84 , as well as some volcanic centres in the Bering Sea. ...
North Pacific deoxygenation events during the last deglaciation were sustained over millennia by high export productivity, but the triggering mechanisms and their links to deglacial warming remain uncertain1–3. Here we find that initial deoxygenation in the North Pacific immediately after the Cordilleran ice sheet (CIS) retreat⁴ was associated with increased volcanic ash in seafloor sediments. Timing of volcanic inputs relative to CIS retreat suggests that regional explosive volcanism was initiated by ice unloading5,6. We posit that iron fertilization by volcanic ash7–9 during CIS retreat fuelled ocean productivity in this otherwise iron-limited region, and tipped the marine system towards sustained deoxygenation. We also identify older deoxygenation events linked to CIS retreat over the past approximately 50,000 years (ref. ⁴). Our findings suggest that the apparent coupling between the atmosphere, ocean, cryosphere and solid-Earth systems occurs on relatively short timescales and can act as an important driver for ocean biogeochemical change.
... Specifically, a recent field of research is devoted to understanding how long-period rotational tide (i.e, monthly to multiyear pole tides and LOD changes) acts on volcanoes, as short-periodic (commonly semi-diurnal to fortnightly tides) forcing influences shallow volatile-saturated magma reservoir or hydrothermal environments (Sottili et al., 2007;Sottili and Palladino, 2012;Petrosino et al., 2018) whilst low-frequency, rotational tidal oscillations are compatible with the resonance time of the lithosphere (Zaccagnino et al., 2020) and with differential stress changes on wall rocks of magma chambers located within the shallow 20 km of the Earth's crust (Sottili et al., 2015;Lambert and Sottili, 2019). Moreover, over the last years, the detection of Milankovitch periodicities in volcanic explosive activity through the Pleistocene-Holocene (Kutterolf et al., 2013(Kutterolf et al., , 2019Praetorius et al., 2016) led to the formulation of a variety of hypotheses on the possible cause-and-effect relationships among orbital forcing, climate changes and volcanism. For instance, the glacio-eustatism hypothesis links the observed Milankovitch periodicities in volcanic activity to crustal stress changes associated with ice age mass redistribution and sea level changes (Rampino and Self, 1993;Ryan et al., 2004;Watt et al., 2013;Praetorius et al., 2016;Rawson et al., 2016). ...
... Moreover, over the last years, the detection of Milankovitch periodicities in volcanic explosive activity through the Pleistocene-Holocene (Kutterolf et al., 2013(Kutterolf et al., , 2019Praetorius et al., 2016) led to the formulation of a variety of hypotheses on the possible cause-and-effect relationships among orbital forcing, climate changes and volcanism. For instance, the glacio-eustatism hypothesis links the observed Milankovitch periodicities in volcanic activity to crustal stress changes associated with ice age mass redistribution and sea level changes (Rampino and Self, 1993;Ryan et al., 2004;Watt et al., 2013;Praetorius et al., 2016;Rawson et al., 2016). This hypothesis seems to be corroborated by evidence for a subaerial volcanism increase during the last deglaciation phase (Huybers and Langmuir, 2009;Jull and Mc Kenzie, 1996) and during the Messinian salinity crisis in the Mediterranean area (Sternai et al., 2017) whilst the impact of Milankovitch cycle-caused sea level fluctuations on the volcanic construction process at mid-ocean ridges remains an area of active research (e.g., Olive et al., 2015;Goff, 2020). ...
In this paper, we examine the origins and the history of the hypothesis for an influence of tidal forces on volcanic activity. We believe that exploring this subject through a historical perspective may help geoscientists gain new insights in a field of research so closely connected with the contemporary scientific debate and often erroneously considered as a totally separated niche topic. The idea of an influence of the Moon and Sun on magmatic processes dates back to the Hellenistic world. However, it was only since the late 19th century, with the establishment of volcano observatories at Mt. Etna and Vesuvius allowing a systematic collection of observations with modern methods, that the “tidal controversy” opened one of the longest and most important debates in Earth Science. At the beginning of the 20th century, the controversy assumed a much more general significance, as the debate around the tidal influence on volcanism developed around the formulation of the first modern theories on the origins of volcanism, the structure of the Earth’s interior and the mechanisms for continental drift. During the same period, the first experimental evidence for the existence of the Earth tides by Hecker (Beobachtungen an Horizontalpendeln über die Deformation des Erdkörpers unter dem Einfluss von Sonne und MondVeröffentlichung des Königl, 1907, 32), and the Chamberlin–Moulton planetesimal hypothesis (proposed in 1905 by geologist Thomas Chrowder Chamberlin and astronomer Forest Ray Moulton) about the “tidal” origin of the Solar System, influenced and stimulated new researches on volcano-tides interactions, such as the first description of the “lava tide” at the Kilauea volcano by Thomas Augustus Jaggar in 1924. Surprisingly, this phase of gradual acceptance of the tidal hypothesis was followed by a period of lapse between 1930 to late 1960. A new era of stimulating and interesting speculations opened at the beginning of the seventies of the 20th century thanks to the discovery of the moonquakes revealed by the Apollo Lunar Surface Experiment Package. A few years later, in 1979, the intense volcanism on the Jupiter’s moon Io, discovered by the Voyager 1 mission, was explained by the tidal heating produced by the Io’s orbital eccentricity. In the last part of the paper, we discuss the major advances over the last decades and the new frontiers of this research topic, which traditionally bears on interdisciplinary contributions (e.g., from geosciences, physics, astronomy). We conclude that the present-day debate around the environmental crisis, characterized by a large collection of interconnected variables, stimulated a new field of research around the complex mechanisms of mutual interactions among orbital factors, Milankovitch Cycles, climate changes and volcanism.
... There has been a great deal of debate regarding the driving forces underlying changes in atmospheric CO 2 concentration. Research over the last several decades has indicated that globally synchronous variation in volcanism plays an important role in generating glacial/interglacial CO 2 variability (Jull and McKenzie, 1996;McGuire et al., 1997;Jellinek et al., 2004;Nowell et al., 2006;Huybers and Langmuir, 2009;Tolstoy, 2015;Praetorius et al., 2016). In the high-latitude glaciated regions, in particular, the deglaciation-associated increase in subaerial volcanic eruptions has been suggested to influence CO 2 variation (i.e., Zielinski et al., 1996;Maclennan et al., 2002;Bay et al., 2004;Licciardi et al., 2007;Narcisi et al., 2010;Brown et al., 2014). ...
... However, the temporal pattern of volcanic eruption frequency in global MORs does not appear to adhere to the ideal theory. Similar to subaerial volcanic eruptions in the high-glaciated regions (Maclennan et al., 2002;Narcisi et al., 2010;Huybers and Langmuir, 2009;Praetorius et al., 2016), sedimentary records of volcanic and hydrothermal activity at global ocean ridges including the CIR are a large increase during the last deglaciation, peaking between ~18 and ~ 7 kyr BP, with a much lower number of eruptions prior to this (Fig. 8). That is, the results combined with the previous data suggest that the last deglaciation (i.e., Termination I) was characterized by enhanced hydrothermal/volcanic eruptions. ...
Sedimentary evidence for enhanced volcanic eruption during the glacial/interglacial transition in the volcanically active mid-ocean ridges is still lacking. Here, we present the sedimentary records of enhanced deglacial volcanic activity in a well-dated sediment core from the middle part of Central Indian Ridge (CIR), which can provide clue for comprehensively understanding of the temporal relation of increase in submarine volcanism relative to glacial/interglacial transition. Notably, the 35-kyr sediment core used in this study contains continuous, discernible pyroclastic deposit layers (0.5–5 cm thick), which are composed mainly of angular and curved fluidal shards with vesicles, possibly suggesting volatile-rich ridge eruptions. High-resolution elemental profiles of the core provide definite records of at least 17 volcanic eruptions during the past 35 kyr. Interestingly, volcanism was sparse during the Last Glacial Maximum (LGM), but increased significantly during the last deglaciation after ~18 kyr BP. The last deglaciation-associated volcanic eruptions in the CIR may be linked to decompression melting during the LGM sea-level lowstand, reaffirming an influence of sea level variability on global ocean ridge magmatism. Combining the previous results, furthermore, simultaneous strengthening of submarine and subaerial volcanic eruptions during the last deglaciation could have accelerated the rise of atmospheric CO2, with the ensuing warming constituting positive feedback upon deglaciation.
... The idea that refugia for plants and animals existed along the western edge of the CIS has long been a subject of discussion and research (e.g., Heusser, 1960Heusser, , 1989Worley, 1980;Wheeler and Guries, 1982;Heaton et al., 1996;Heaton and Grady, 2003;Lacourse and Mathewes, 2005;Reimchen and Byun, 2005;Carrara et al., 2007). These investigations provide strong biological evidence for the existence of refugia in southeastern Alaska, composed (Misarti et al., 2012); C -Cook Inlet; K -Kodiak Island (Peteet and Mann, 1994); P -Patton Seamounts marine coring sites (de Vernal and Pedersen, 1997;Méheust et al., 2018); E -EW0408-85JC marine coring site (Barron et al., 2009;Davies et al., 2011;Praetorius et al., 2016). of terrestrial and marine ecosystems robust enough to support a genetically distinct population of brown bears, implying long-term isolation from other populations (Heaton et al., 1996). ...
... The crustal adjustments during deglaciation included forebulge lateral migration, isostatic rebound, and perhaps major earthquakes caused by nearby fault movements along the Queen Charlotte-Fairweather Fault system on the outer shelf (Carlson et al., 1988). These events may have triggered the multiple volcanic eruptions on Kruzof Island soon after local deglaciation (Addison et al., 2010;Praetorius et al., 2016). ...
The Cordilleran Ice Sheet covered most of southeastern Alaska during the Last Glacial Interval (LGI: Marine Isotope Stage 2). Ice began to recede from western Alexander Archipelago ∼17,000 ± 700 yr BP. In this study, pollen analysis and radiocarbon dating of three sediment cores were used to reconstruct, for the first time, the postglacial development of vegetation in the northwestern Alexander Archipelago during the past ∼15,240 cal yr. Hummingbird Lake (HL), on southwestern Baranof Island, yielded a sediment core with one of the longest dated records from southeastern Alaska. The earliest part of the HL pollen record (∼15,240–14,040 yr BP) indicates that the earliest vegetation was pine (Pinus contorta subsp. contorta) parkland with willows (Salix), heaths (Ericaceae), sedges (Cyperaceae), grasses (Poaceae), herbs and ferns. Starting at ∼14,040 yr BP, alder (Alnus) rapidly colonized the area as pine populations declined. By 11,400 yr BP, Sitka spruce (Picea sitchensis) colonized the area, and soon became the dominant conifer. Mountain hemlock (Tsuga mertensiana) also colonized the area by ∼11,400 yr BP, followed by western hemlock (Tsuga heterophylla) at ∼10,200 yr BP. By ∼9200 yr BP, western hemlock had become the dominant tree species in the area. During the late Holocene yellow cedar (Chamaecyparis nootkatensis) became established. Two marine sediment cores were also analyzed for pollen, with the oldest core from Lower Sitka Sound, between Kruzof and Baranof Islands. The lower part of the core consists of interlayered tephras and freshwater lake muds that are estimated to be ∼14,000 to 13,150 yr BP. Pollen evidence indicates that the early postglacial vegetation around Sitka Sound was pine parkland with alders and abundant ferns. Damage to vegetation around Sitka Sound by volcanic eruptions is suggested by abrupt, large shifts in percentages of alder and pine pollen, and fern spores in samples adjacent to tephra layers. A marine sediment core from Slocum Arm, a fiord on the western coast of Chichagof Island, has a basal age of ∼10,000 yr BP. The pollen record is similar to the Holocene pollen record at Hummingbird Lake. The sequence of vegetation changes interpreted from the three northwestern Alexander Archipelago pollen records is similar to those from other well-dated sites in southeastern Alaska, although chronologies differ between sites.
... The annual rise in temperature due to climate change has previously been linked to many problems such as sea level rise, floods, droughts etc. however recent addition of increased volcanoes and earthquakes to its list is alarming [7,8]. The climate change has led to a hypothesis that deglaciation in volcanic terrains and earthquake prone zones can increase volcanism and earthquake frequency respectively by depressurizing the shallow mantle causing isostatic rebound. ...
... The climate change has led to a hypothesis that deglaciation in volcanic terrains and earthquake prone zones can increase volcanism and earthquake frequency respectively by depressurizing the shallow mantle causing isostatic rebound. [7,8]. Both are consistent with their hypotheses that isostatic rebound is associated with ice unloading that increases seismic activity. ...
Our entire planet is experiencing the dangers of global warming that have gone beyond what implied by climate change. Recently 2017 has been declared all time second warmest year by NOAA on record for the entire globe, while a BBC report from Alaska “a great thaw of America is coming” suggests that the steady rising trend of summer temperatures every year, making the thaw deeper hence causing the permafrost to become less stable, for which human activity has been the major cause of rise in temperature for past few decades.
Regional studies of Alaska show that global warming due to climate change cannot just trigger volcanic eruptions, tsunamis, and landslides but can also enhance earthquake activity due to rapid melting of glaciers. Because when glaciers melt, the unloading can cause a bounce back also called isostatic rebound which can reactivate the pre-existing faults hence increases seismic activity. The study involves statistical techniques such as Pearson’s correlation coefficient and Regression analysis to establish a link between global warming with the subsurface movement of tectonic plates. The paper also suggests subsurface depth estimates affected due to soaring temperatures causing frequent tectonic disturbances –earthquakes based on a case study from Alaska.
The study has showed using Pearson’s correlation coefficient and regression analysis that shallow depths regions of Alaska are sensitive to postglacial stresses (energy accumulated) due to regional rise in temperature infuriating earthquakes as compared to the intermediate zones. Furthermore it also cues that due to constant rise in temperature since 2000 the effect of temperature has probably started influencing the subsurface beyond shallow depth earthquakes zones in Alaska.
... An enhanced volcanic activity has been observed due to deglaciation in Arctic has led to a hypothesis that the unloading of the glaciated ice in a volcanic terrains can increase volcanism through decompression melting in the shallow mantle or storage time reduction in crustal magma. Recently, the enhanced deglacial volcanic activity in Southeast Alaska sourced from Mount Edgecumbe Volcanic field has been correlated with the rapid isostatic adjustment, occurred following a retreat of regional glaciers [6]. The finding is consistent with the hypothesis that isostatic rebound is associated with ice-unloading which increases the volcanism [6], that can possibly influence the frequency of the earthquakes as well. ...
... Recently, the enhanced deglacial volcanic activity in Southeast Alaska sourced from Mount Edgecumbe Volcanic field has been correlated with the rapid isostatic adjustment, occurred following a retreat of regional glaciers [6]. The finding is consistent with the hypothesis that isostatic rebound is associated with ice-unloading which increases the volcanism [6], that can possibly influence the frequency of the earthquakes as well. ...
The impact of human induced climate change on the rising temperature cannot be neglected. According to the Intergovernmental Panel on Climate Change (IPCC) 2012 report, the mean temperature roughly rises up to 3?C relative to 1990. Permafrost in Siberia and Alaska has started to thaw for the first time since it formed 11,000 years ago, has caused by the recent rise in temperature over the past six decades. The melting rate of glaciers has become significantly higher, causing a noticeable rise (0.19meters) in the sea level globally. Climate change can trigger catastrophes such as earthquakes, volcanic eruptions, tsunamis and landslides due to melting glaciers and rising in sea level. The melting of glaciers driven by global warming warns us of a seismically turbulent future. When glaciers melt, the massive weight on the Earth's crust reduces and the crust bounces back in what scientists call an "isostatic rebound". The process can reactivate faults and lift pressure on magma chambers that feed volcanoes, hence increases seismic activity. The paper discusses the correlation between rise in temperature due to global warming and earthquake frequency using Pearson's correlation coefficient and regression analysis based on a case study from Alaska.
... Local geological controls probably modulate the climatic effects on volcanism (e.g. 12,14,38 ). However, the more important difference may be that the compiled record contains contributions from a wide range of latitudes. ...
... Location latitude may play a crucial role as volcanism at sites closer to the ice sheets may react differently from near-equatorial volcanism (e.g. 38,39 ). ...
It is a longstanding observation that the frequency of volcanism periodically changes at times of global climate change. The existence of causal links between volcanism and Earth's climate remains highly controversial, partly because most related studies only cover one glacial cycle. Longer records are available from marine sediment profiles in which the distribution of tephras records frequency changes of explosive arc volcanism with high resolution and time precision. Here we show that tephras of IODP Hole U1437B (northwest Pacific) record a cyclicity of explosive volcanism within the last 1.1 Myr. A spectral analysis of the dataset yields a statistically significant spectral peak at the ~100 kyr period, which dominates the global climate cycles since the Middle Pleistocene. A time-domain analysis of the entire eruption and δ18O record of benthic foraminifera as climate/sea level proxy shows that volcanism peaks after the glacial maximum and ∼13 ± 2 kyr before the δ18O minimum right at the glacial/interglacial transition. The correlation is especially good for the last 0.7 Myr. For the period 0.7-1.1 Ma, during the Middle Pleistocene Transition (MPT), the correlation is weaker, since the 100 kyr periodicity in the δ18O record diminishes, while the tephra record maintains its strong 100 kyr periodicity.
... Even though some of the precipitation may fall as snow in the ablation zone due to the cooling, large part of it will still be rain, which would act as an additional melting agent through a pathway that is detailed in the text. Finally, we have also highlighted that enhanced glacier melting in conjunction with volcanic eruptions has also been inferred from other records from Alaska during the Bølling interstadial (Praetorius et al., 2016). D. Conclusions: robustness, validity, reliability. ...
... We would also like to stress that we now provide more compelling evidence suggesting that the events recorded in the GISP2 sulfate record are predominantly originated at high northern latitudes (see comparison between Antarctic and Greenlandic ice cores - Figure S1) and primarily from Iceland. In fact a new study has shown a substantial decrease in volcanic activity in North America starting around 13.2-13.1 ka BP (Praetorius et al., 2016). This implies that, given the general paucity of tropical eruptions after ca. 13 ka BP, Iceland must have been the largest contributor in terms of aerosol deposition in GISP2 ice cores. ...
... Furthermore, the relatively limited spatial extent of the macro-tephra fallout and the short-term nature of these events make it difficult to identify and link a geologic record of a climate response to a given volcanic eruption. Nevertheless, it is likely volcanism may be an important source of abrupt climate forcing, which may help to trigger instabilities in the climate system (Praetorius et al., 2016). Guo et al. (2008) opined that the global climate system experienced a series of drastic changes during the Cenozoic. ...
... Williamson and Bell (2012) also inferred similar climatic conditions and flash-flood events from the Palaeogene lava field of NW Scotland. Praetorius et al. (2016) have suggested while direct radiative-forcing effects from individual eruptions are unlikely to lead to long-term cooling due to the relatively short residence time of volcanic aerosols into the upper atmosphere (1-3 yrs.), a prolonged increase in the frequency of eruptions could lead to either warming or cooling perturbations through ice-albedo, sea-ice, or CO 2 feedbacks. Modeling studies suggest hemispheric cooling for decades -centuries can be initiated by the effects of multiple eruptions, or sea-ice feedbacks. ...
Explosive volcanic events often produce pyroclastic materials that can be recognized from the geological record. These discrete pyroclastics form regional marker beds. Here we report the occurrence of a tephra layer interbedded within very thick coal beds near Mukah, Sarawak, Borneo. Traceable for tens of kilometers in the Mukah area of Sarawak, this tephra layer can be considered as regional stratigraphic marker with precise chronostratigraphic control. Systematic sedimentological, mineralogical, geochemical and zircon U-Pb geochronological studies have revealed a major effusive volcanic event during the latest Middle Miocene, presumably contemporaneous and/or related to a magmatic event of an earlier phase of the Mt. Kinabalu pluton or magmatism in West Sarawak or East Sabah. The volcanic event had promoted catastrophic flooding of coastal swamps and fall-out from the ash clouds that formed a regionally monotonous tephra layer across the Serravallian- Tortonian boundary. In conjunction with the regional occurrences of trap rocks, structural trends and known tectonic events, we constrained the regional depositional environments, and climate. The tephra layer was deposited in a coastal plain-swamp,- seasonal, shallow, high-moderate energy fluvial channel-lacustrine environmental setting, wherein atmospheric fallout and eroded material from regoliths formed over older basement and volcanic rocks of the hinterland which were mixed to produce the tephra layer. This tephra layer is sandwiched between the very thick coal beds. A pre-existent volcanic chamber that was active for a long time, also experienced periodic explosive activity from probably the same magma chamber and conduit and including a major explosive activity that recycled early-formed crystals and felsic magma (rhyolite-dacite) during the major effusive event are also recognized. Our findings provide robust evidence for the prevalence of intensive chemical weathering under a wet-humid climate, and relative tectonic quiescence before the major effusive event, and the existence of vast, monotonously gently-sloping coastal plains and luxuriant vegetation akin to the present.
... These species are indicative of a pack ice habitat. Along the southern Alaskan coast, ice-rafted debris vanishes in marine core samples abruptly around 14,700 cal yr BP, marking the retreat of glaciers onto land or into sheltered fjords in the Gulf of Alaska region (Davies et al., 2011;Praetorius et al., 2016). Others have tracked diatoms and ice-rafted debris as a proxy for sea-ice, potentially pushing its disappearance into the Younger Dryas (Barron et al., 2009;Addison et al., 2012). ...
... Isostatic adjustment appears to have triggered a sequence of volcanic activity in southeast Alaska, which further accelerated deglaciation. A recent analysis of core data from the coast of Chicagof Island suggests up to 22 individual eruptions of the Mount Edgecumbe volcanic field occurred during deglaciation; 19 fall within a peak period from 14,600e13,100 cal yr BP (Praetorius et al., 2016). The spatial extent of associated tephras is not well constrained, though based on other marine cores and terrestrial deposits the affected areas are to the east and north of Mount Edgecumbe. ...
Recent archaeological and paleoecological work along both interior and coastal routes for early colonization of the New World has suggested that the interior route was impossible, leaving the coastal route as the only colonization route taken by Clovis ancestors. We review the geological, paleoecological, and archaeological record for Eastern Beringia and adjacent areas. Spatio-temporal patterning of known sites and evaluation of early interior and coastal route radiocarbon, luminescence, and cosmogenic dating, along with new analyses of obsidian distribution and adaptive strategies of early Beringians, indicate this assessment is premature and the interior route remains a viable hypothesis.
... On a worldwide scale tectonic earthquakes produce movement between several large plates formed of the earth's crust or rock layer (about 15 in total) The material in the earth's mantle moves as a result of the heat produced at the earth's core which in turn drives that heat, A sudden slide that releases a massive amount of energy is what causes the earthquake the point where earthquakes begin and break the plates underground is known as focus and above the focus on the surface of the earth is called the epicenter, [3], During plate movement one plate gets submerged into the molten magma and another plate is moved across the top of it This plate rises up due to the heat of molten magma the plates keep on moving until they get stuck against each other Most earthquakes take place on the boundaries of the plates where one plate is forced further into the earth crust while another plate is move [4]. [5] Reported that significant increases in air temperature in the distant part may have been related to changes that occurred in geological activity. It remains a matter of speculation to point out that the climate change expected to occur in the coming decades could lead to similar geological changes. ...
Based on a study for 16 years of earthquake data in Sulaymaniyah city from 2005 to 2021 almost 11000 earthquakes were recorded, the degree intensity (4.4 Richter) was chosen to be the critical degree for the earthquake and for humans to feel it, After 2005 there was an increase in the number of earthquakes until 2012, in 2013 it was the peak witch reached 238 hitting, in 2014 there was a significant decreasing and kept down, climate change data focused on months of August, October, November and December, changes that occurred in number of sunny hours were studied there was a significant change in 2005 with value (15.5 hours) which gradually decreased to (10.4 hours), there wasn't a clear evidence linked sunny hours to occurrence of earthquakes, Rainfall tends to increase relatively in some years in December as well as (and 2018) that were consecutive (67, 118, 98.3, 103.6, 185.8 and 315.1 mm) but no evidence connect rainfalls to earthquake occurrence, Temperatures in the months of the study were relatively similar in terms of rise and fall, but the month of December differed slightly in the years 2012 to 2017.No changes noted in October and November in atmospheric pressure values but in December there was a relative increase in most years of study, evaporation rates in December after 2016 there was a relative increase in evaporation rates.
... ka), and the late Younger Dryas (12.3-11.7 ka). (A) Seawater δ 18 O values (in SMOW) calculated from benthic foraminifera off the coast of Alaska(Grebmeier et al. 1990;Praetorius et al., 2015Praetorius et al., , 2016; (B) snail shell δ 18 O values (in PDB) of Succinea shells from central Alaska; and (C) North Greenland Ice Core Project (NGRIP Members, 2004) and North Greenland Eemian Ice Drilling (NEEM; Masson-Delmotte et al., 2015) Greenland ice core δ 18 O values in SMOW. Box extremes represent lower and upper quartiles. ...
The isotope values of fossil snail shells can be important archives of climate. Here, we present the first carbon (δ ¹³ C) and oxygen (δ ¹⁸ O) isotope values of snail shells in interior Alaska to explore changes in vegetation and humidity through the late-glacial period. Snail shell δ ¹³ C values were relatively consistent through the late glacial. However, late-glacial shell δ ¹³ C values are 2.8‰ higher than those of modern shells. This offset is best explained by the Suess effect and changes in the δ ¹³ C values of snail diet. Snail shell δ ¹⁸ O values varied through the late glacial, which can be partially explained by changes in relative humidity (RH). RH during the snail growing period was modeled based on a published flux balance model. Results suggest a dry period toward the beginning of the Bølling–Allerød (~14 ka) followed by two distinct stages of the Younger Dryas, a wetter stage in the early Younger Dryas from 12.9 to 12.3 ka, and subsequent drier stage in the late Younger Dryas between 12.3 and 11.7 ka. The results show that land snail isotopes in high-latitude regions may be used as a supplementary paleoclimate proxy to help clarify complex climate histories, such as those of interior Alaska during the Younger Dryas.
... The study area is underlain by Mesozoic sedimentary, metasedimentary, metavolcanic, and intrusive volcanic rocks of the Baranof Accretionary Complex and Wrangellia Terrane, parts of an accreted volcanic arc complex (Gehrels & Berg, 1992;Karl et al., 2015). Pleistocene glaciation has sculpted the bedrock into broad, steep-sided valleys and fjords, with the most recent glaciers beginning to retreat ∼14.6 ka (Praetorius et al., 2016). Glaciation also left behind a thin layer of till up to elevations of ∼1,000 m, which is overlain by ∼1 m thick Late Pleistocene tephras that were erupted from the Mt. ...
Landslides influence the global carbon (C) cycle by facilitating transfer of terrestrial C in biomass and soils to offshore depocenters and redistributing C within the landscape, affecting the terrestrial C reservoir itself. How landslides affect terrestrial C stocks is rarely quantified, so we derive a model that couples stochastic landslides with terrestrial C dynamics, calibrated to temperate rainforests in southeast Alaska, United States. Modeled landslides episodically transfer C from scars to deposits and destroy living biomass. After a landslide, total C stocks on the scar recover, while those on the deposit either increase (in the case of living biomass) or decrease while remaining higher than if no landslide had occurred (in the case of dead biomass and soil C). Specifically, modeling landslides in a 29.9 km² watershed at the observed rate of 0.004 landslides km⁻² yr⁻¹ decreases average living biomass C density by 0.9 tC ha⁻¹ (a relative amount of 0.4%), increases dead biomass C by 0.3 tC ha⁻¹ (0.6%), and increases soil C by 3.4 tC ha⁻¹ (0.8%) relative to a base case with no landslides. The net effect is a small increase in total terrestrial C stocks of 2.8 tC ha⁻¹ (0.4%). The size of this boost increases with landslide frequency, reaching 6.5% at a frequency of 0.1 landslides km⁻² yr⁻¹. If similar dynamics occur in other landslide‐prone regions of the globe, landslides should be a net C sink and a natural buffer against increasing atmospheric CO2 levels, which are forecast to increase landslide‐triggering precipitation events.
... Instead, explosive (rhyolitic) eruptions from Deception Island generated by magma injection processes (Geyer et al., 2019) could have been triggered by increased crustal and magma chamber stress, associated with isostatic rebound, and increased magma interaction with sea water, associated with localised changes in sea level, during the Mid-to Late Holocene (cf. Forte and Castro, 2019;Maclennan et al., 2002;Praetorius et al., 2016;Satow et al., 2021). Further work is needed on the South Shetland Islands to investigate the relationship between Holocene deglaciation and volcanic activity. ...
To provide insights into glacier-climate dynamics of the South Shetland Islands (SSI), NW Antarctic Peninsula, we present a new deglaciation and readvance model for the Bellingshausen Ice Cap (BIC) on Fildes Peninsula and for King George Island/Isla 25 de Mayo (KGI) ~62°S. Deglaciation on KGI began after c. 15 cal. ka BP and had progressed to within present-day limits on the Fildes Peninsula, its largest ice-free peninsula, by c. 6.6–5.3 cal. ka BP. Probability density phase analysis of chronological data constraining Holocene glacier advances on KGI revealed up to eight 95% probability ‘gaps’ during which readvances could have occurred. These are grouped into four stages – Stage 1: a readvance and marine transgression, well-constrained by field data, between c. 7.4 and 6.6 cal. ka BP; Stage 2: four probability ‘gaps’, less well-constrained by field data, between c. 5.3 and 2.2 cal. ka BP; Stage 3: a well-constrained but restricted ‘readvance’ between c. 1.7 and 1.5 cal. ka BP; Stage 4: two further minor ‘readvances’, one less well-constrained by field data between c. 1.3 and 0.7 cal. ka BP (68% probability), and a ‘final’ well-constrained ‘readvance’ after <0.7 cal. ka BP. The Stage 1 readvance occurred as colder and more negative Southern Annular Mode (SAM)-like conditions developed, and marginally stronger/poleward shifted westerly winds led to more storms and precipitation on the SSI. Readvances after c. 5.3 cal. ka BP were possibly more frequent, driven by reducing spring/summer insolation at 62°S and negative SAM-like conditions, but weaker (equatorward shifted) Westerlies over the SSI led to reduced storminess, restricting readvances within or close to present day limits. Late Holocene readvances were anti-phased with subaquatic freshwater moss layers in lake records unaffected by glaciofluvial inputs. Retreat from ‘Neoglacial’ glacier limits and the recolonisation of lakes by subaquatic freshwater moss after 1950 CE is associated with recent warming/more positive SAM-like conditions.
... During the Holocene, Riehle et al. (1992) report two eruptions at 5.8 and 4.2 ka that created thin rhyolite ash layers on Kruzof Island, which they attribute to Crater Ridge. Praetorius et al. (2016) document a period of increased volcanism from 14.6 to 13.1 ka with a recurrence of about 1.5 events per century that they attribute to last glacial maximum ice loss as reported for, for example, Iceland (e.g., Jull & McKenzie, 1996;Maclennan et al., 2002;Pagli & Sigmundsson, 2008) and California (Jellinek et al., 2004). This activity ranged from basaltic to late erupting rhyolite, the latter also found in adjacent marine sediment cores in tephra-fall and pyroclastic flow deposits (Addison et al., 2010). ...
Plain Language Summary
In April 2022, a cluster of earthquakes, detected near Mt. Edgecumbe in Southeast Alaska, suggested magmatic activity. As the volcano is near the major Queen‐Charlotte Fairweather fault that separates the Pacific and North American plates, similar earthquakes were previously assumed to be tectonic. Since magmatic activity at volcanoes is often accompanied by ground deformation, we analyzed available satellite radar data going back to fall of 2014. This reveals ongoing crustal motion toward the satellite of up to 7.1 cm/yr starting in August 2018. Modeling of the deformation suggests that magma sourced from gently dipping tabular body at 20 km depth is pooling at about 10 km depth. Since the nearest seismograph is 25 km away, we record only large seismicity, which increases in July 2019, but we perhaps missed some lower energy seismicity due to this distance. We believe that we are observing magma rising through malleable crust into an existing magmatic system and that the observed earthquakes are created as the overlying rock adjusts to the increased magmatic pressure. The observed activity is rare, especially in similar tectonic settings, and presents an opportunity to better understand the reactivation of dormant volcanoes.
... In volcanic arcs, the effects of glaciation on eruptive chemistry and volcanic output are more likely to be driven by changes in crustal stress and rheological conditions (Geyer and Bindeman, 2011). Several different groups have suggested that hydrothermal alteration weakens host rock and glacial loading and unloading produce changes in the crustal lithosphere stress field that inhibit or drive magma storage and transport (e.g., Jellinek et al., 2004;Geyer and Bindeman, 2011;Praetorius et al., 2016;Rawson et al., 2016;Wilson and Russell, 2020). Over long time-scales crustal loading may impede dyke formation and enhance sill production, while unloading favors dyke formation and enhances magma transport into the eruption region (Gudmundsson, 1986;Sigvaldason et al., 1992;Gee et al., 1998;Glazner et al., 1999;McLeod and Tait, 1999;Jellinek and DePaolo, 2003;Jellinek et al., 2004;Andrew and Gudmundsson, 2007;Albino et al., 2010;Wilson and Russell, 2020). ...
In contrast to water and air, ice is the most dynamic enveloping medium and unique environment for volcanic eruptions. While all three environments influence volcanic activity and eruption products, the cryospheric eruption environment is unique because: 1) it supports rapid changes between those environments (i.e. subglacial, subaqueous, subaerial), 2) it promotes a wide range of eruption styles within a single eruption cycle (explosive, effusive), 3) it creates unique edifice-scale morphologies and deposits, and 4) it can modulate the timing and rates of magmatism. The distinctive products of cryospheric eruptions offer a robust means of tracking paleoclimate changes at the local, regional and global scale. We provide a framework for understanding the influence of the cryosphere on glaciovolcanic systems, landforms and deposits.
... While a willow/sedge and pine parkland expanded across the deglaciated landscape by around 15,000 cal BP (Ager, 2019), ice unloading triggered a coinciding period of intense volcanism. The Mount Edgecumbe volcanic field alone produced at least 22 individual eruptions, 19 of which were between 14,600 and 13,100 cal BP (Praetorius et al., 2016); mounting evidence suggests that there were additional eruptions elsewhere in the region (Wilcox et al., 2019). Absent the weight of the ice sheet, the uplifted crustal forebulge under the outer islands collapsed during the Younger Dryas, flooding whatever refugia may have existed on the western coastal plain, an intensely erosive process (Barrie et al., 2021). ...
Human behavioral ecology has proven a valuable theoretical framework for evaluating the archaeological record of human population expansion the world over. To evaluate hypotheses for the late Pleistocene human colonization of the Americas, we need to address a typical assumption built into those models: static landscape knowledge. By taking landscape knowledge as the predicting variable, rather than a constant, we can explore the behavioral mechanisms involved in the interaction of humans with new and unfamiliar environments. Acknowledging the process of adaptation produces contrasting and readily testable hypotheses for human population expansion. As a case study, we use an ideal free distribution model to test competing hypotheses for the colonization of Southeast Alaska. Our results indicate that Southeast Alaska was likely colonized by humans prior to their appearance in the extant archaeological record in the early Holocene. The locations of our oldest archaeological sites in the early Holocene are best explained as the result of a well-established population matching their settlement locations to rising sea level.
... Medial and distal tephra layers may be used to investigate the long-term geochemical evolution of the volcanicmagmatic system, for example the compositions of tephra preserved in marine cores from the Izu-Bonin forearc record the temporal evolution in magma composition during the transition from extensional back arc to arc volcanism (Bryant et al. 2003). Finally, tephrochronology has been used to investigate the link between climate and volcanism, revealing an increase in volcanic activity following glacial unloading in places such as Chile (Rawson et al. 2015) and Alaska (Praetorius et al. 2016). Further examples of tephrochronology applications can be found in Lowe et al. (2015) and Lane et al. (2017). ...
Layers of volcanic ash (tephra) can be used as isochronous markers linking different sedimentary archives and allowing detailed analysis of the relative timing of climatic or evolutionary events. Conversely, high-resolution sedimentary tephra archives can shed light on the geochemical evolution of magmatic systems. The last ~110 kyrs of activity at the Campi Flegrei volcanic field is punctuated by several large eruptions, including the caldera forming Campanian Ignimbrite (~40 ka) and Neapolitan Yellow Tuff (~15 ka) eruptions and the more recent Pomici Principali (~12.1 ka) and Agnano-Monte Spina (~4.5 ka) all of which are preserved in distal settings several hundred kilometres away. In addition, there are a number of important distal Campi Flegrei caldera tephra layers for which the source eruption is not known (X-5 at ~105 ka and X-6 at ~109 ka) or only recently established (Y-3; ~29 ka), indicating the occurrence of large eruptions that are unknown or poorly constrained from proximal deposits. In this contribution we discuss the dispersal and age significance of these 7 key Campi Flegrei caldera eruptions. The value of distal tephra layers is dependent on the ability to identify a distinctive geochemical fingerprint for each layer, for example, the Campanian Ignimbrite and Neapolitan Yellow Tuff events tapped zoned magma chambers and thus produced unique and compositionally variable tephra layers. Micron-beam major and trace element analyses of distal and proximal volcanic glasses allow direct distal-distal and proximal–distal tephra comparisons. In addition, good stratigraphic and chronological control is important in order to identify and correlate tephra with confidence. Here, we discuss the distinctive geochemical compositions of each of the 7 highlighted Campi Flegrei caldera marker tephra layers.
... Large volcanic activity can increase atmospheric CO 2 , forcing global warming, followed by the glacial termination and the onset of deglaciation, where the retreat of ice sheets further intensifies the reduction in albedo and results in increased volcanism (Huybers and Langmuir, 2009;Praetorius et al., 2016;Kutterolf et al., 2019). In this study, anomalous Hg/TOC ratios were associated with increased atmospheric CO 2 ( Fig. 5; Hönisch et al., 2009;Lisiecki, 2010;Chalk et al., 2017). ...
Volcanoes are a significant component of the Earth system, influencing the interaction between oceans and the atmosphere over large spatial and temporal scales. Being a volcanically dynamic region, the Tropical Western Pacific (TWP) can significantly impact variations in global climate. However, high-resolution continuous records of volcanic activity in this region are lacking, resulting in significant uncertainties regarding the coupling between the deep earth, climate changes, and atmospheric CO2 in the TWP. To address this issue, mercury (Hg) levels, isotopic compositions, and Hg/total organic carbon (Hg/TOC) ratios were determined at site U1486 to track volcanic activity throughout the mid-Pleistocene transition (MPT) from 1.3 Myr to 0.6 Myr. Our results of anomalously high Hg concentrations and Hg/TOC ratios provide evidence of time-varying volcanism throughout the MPT. Mercury isotopes in the Hg-enriched sediments were characterized by near-zero Δ¹⁹⁹Hg values, which is consistent with volcanism acting as the primary source of Hg to the sediments. Spectral analysis of the Hg/TOC ratio showed significant periodicity at ~100 kyr and ~ 23 kyr as well as a weaker signal at ~41 kyr consistent with Milankovitch cycles. A cross spectral analysis of Hg/TOC and the LR04 δ¹⁸O stack record suggests that the peak in volcanism lags the temperature minimum by ~6 kyr, and occurs prior to the δ¹⁸O minimum known as the glacial termination by ~14 ± 2 kyr. The records of volcanic activity in this site are also consistent with a prominent rise in atmospheric CO2 and negative excursion of benthic carbon isotopes throughout the MPT. This study provides direct sedimentary evidence in the TWP of the feedback between volcanic activity, climate change and atmospheric CO2.
... However, the establishment of the willow-sedge and pine parklands on land (Ager, 2019) was tempered by intense volcanism; the Mount Edgecumbe volcanic field alone was responsible for 22 individual eruptions in central southeastern Alaska, 19 within a peak interval between 14,600 and 13,100 cal. yr B.P. (Praetorius et al., 2016). There is mounting evidence for further eruptions from other volcanic fields in the southern part of southeastern Alaska at the end of that interval (Wilcox et al., 2019a;T.A. Ager, 2021, personal commun.). ...
We leverage a data set of >720 shell-bearing marine deposits throughout southeastern Alaska (USA) to develop updated relative sea-level curves that span the past ~14,000 yr. This data set includes site location, elevation, description when available, and 436 14C ages, 45 of which are published here for the first time. Our sea-level curves suggest a peripheral forebulge developed west of the retreating Cordilleran Ice Sheet (CIS) margin between ca. 17,000 and 10,800 calibrated yr B.P. By 14,870 ± 630 to 12,820 ± 340 cal. yr B.P., CIS margins had retreated from all of southeastern Alaska’s fjords, channels, and passages. At this time, isolated or stranded ice caps existed on the islands, with alpine or tidewater glaciers in many valleys. Paleoshorelines up to 25 m above sea level mark the maximum elevation of transgression in the southern portion of the study region, which was achieved by 11,000 ± 390 to 10,500 ± 420 cal. yr B.P. The presence of Pacific sardine (Sardinops sagax) and the abundance of charcoal in sediments that date between 11,000 ± 390 and 7630 ± 90 cal. yr B.P. suggest that both ocean and air temperatures in southeastern Alaska were relatively warm in the early Holocene. The sea-level and paleoenvironmental reconstruction presented here can inform future investigations into the glacial, volcanic, and archaeological history of southeastern Alaska.
... Eventually a rising packet of mantle will intersect the mantle's solidus and begin to melt (Figure 4, arrow). This process does not require Earth-like plate tectonics and could be caused by an impact (e.g., Jones et al., 2002;Roberts & Barnouin, 2012) or by unloading of the crust due to ice removal (e.g., Maclennan et al., 2002;Praetorius et al., 2016). (Hirschmann, 2000), as well as the solidi for the first hypothetical exoplanet starting composition (HEX1) and the second hypothetical exoplanet starting composition (HEX2) (lines are solid over the range of experimental conditions and dashed where extrapolated). ...
For rocky exoplanets, knowledge of their geologic characteristics such as composition and mineralogy, surface recycling mechanisms, and volcanic behavior are key to determining their suitability to host life. Thus, determining exoplanet habitability requires an understanding of surface chemistry, and understanding the composition of exoplanet surfaces necessitates applying methods from the field of igneous petrology. Piston‐cylinder partial melting experiments were conducted on two hypothetical rocky exoplanet bulk silicate compositions. HEX1, a composition with molar Mg/Si = 1.42 (higher than bulk silicate Earth's Mg/Si = 1.23) yields a solidus similar to that of Earth's undepleted mantle. However, HEX2, a composition with molar Ca/Al = 1.07 (higher than Earth Ca/Al = 0.72) has a solidus with a slope of ∼10°C/kbar (vs. ∼15°C/kbar for Earth) and as result, has much lower melting temperatures than Earth. The majority of predicted adiabats point toward the likely formation of a silicate magma ocean for exoplanets with a mantle composition similar to HEX2. For adiabats that do intersect HEX2's solidus, decompression melting initiates at pressures more than 4x greater than in the modern Earth's undepleted mantle. The experimental partial melt compositions for these exoplanet mantle analogs are broadly similar to primitive terrestrial magmas but with higher CaO, and for the HEX2 composition, higher SiO2 for a given degree of melting. This first of its kind exoplanetary experimental data can be used to calibrate future exoplanet petrologic models and predict volatile solubilities, volcanic degassing, and crust compositions for exoplanets with bulk compositions and ƒO2 similar to those explored herein.
... ka, there would have likely been greater earthquake activity. Evidence of enhanced volcanic frequency during this same time interval is apparent off southeast Alaska, adjacent to the Queen Charlotte fault (Praetorius et al., 2016). The increased earthquake and volcanic activity would then have resulted in increased development of submarine failures and turbidites adjacent to the fault, but there is little evidence of this within the cores collected along the fault. ...
The active Pacific margin of the Haida Gwaii and southeast Alaska has been subject to vigorous storm activity, dramatic sea-level change, and active tectonism since glacial times. Glaciation was minimal along the western shelf margin, except for large ice streams that formed glacial valleys to the shelf break between the major islands of southeast Alaska and Haida Gwaii. Upon deglaciation, sediment discharge was extensive, but it terminated quickly due to rapid glacial retreat and sea-level lowering with the development of a glacio-isostatic forebulge, coupled with eustatic lowering. Glacial sedimentation offshore ended soon after 15.0 ka. The shelf became emergent, with sea level lowering by, and possibly greater than, 175 m. The rapid transgression that followed began sometime before 12.7 ka off Haida Gwaii and 12.0 ka off southeast Alaska, and with the extreme wave-dominated environment, the unconsolidated sediment that was left on the shelf was effectively removed. Temperate carbonate sands make up the few sediment deposits presently found on the shelf.
The Queen Charlotte fault, which lies just below the shelf break for most of its length, was extensively gullied during this short period of significant sediment discharge, when sediment was transported though the glacial valleys and across the narrow shelf through fluvial and submarine channels and was deposited offshore as sea level dropped. The Queen Charlotte fault became the western terminus of the glacio-isostatic forebulge, with the fault acting as a hinged flap taking up the uplift and collapse along the fault of 70+ m. This may have resulted in the development of the distinctive fault valley that presently acts as a very linear channel pathway for sediment throughout the fault system.
... An outstanding question to be addressed is why Makushin's eruptive volumes became smaller (Bean 1999) and more mafic in the past~1800 years (Fig. 9), compared with the voluminous andesitic magmas that erupted in the early Holocene. It is possible that de-glaciation at the end of the Pleistocene triggered stress unloading of the edifice, allowing greater volumes of recharge magma triggering eruptions of the andesites (Praetorius et al. 2016). However, the relationship between ice load and volcanic activity is complex, and comprehensive studies of the effects of deglaciation on volcanism in the Aleutians are lacking (Geyer and Bindeman 2011 Table Top Mountain, and Wide Bay cone, after McConnell et al. (1998). ...
Makushin stratovolcano, Alaska, produced three, highly explosive, andesitic eruptions between ~ 9292 and 6215 yBP. Those eruptions are informally named the CFE (“crater-forming eruption”), Nateekin, and Driftwood Pumice, and they deposited significant tephra fallout in the present-day port of Dutch Harbor and City of Unalaska area. The focus of this study is to examine the geochemistry and petrology of those eruptions to better understand Makushin volcano hazards, andesite petrogenesis and eruption triggering by mafic recharge processes. The CFE, Nateekin, and Driftwood Pumice samples range from basaltic andesite to dacite but are predominantly andesitic (SiO2 = 55.6 to 63.5 wt%). The CFE deposits are slightly compositionally stratified, with the top CFE samples slightly more mafic (55 to 60 wt% SiO2) than the basal deposits (58 to 60 wt% SiO2). Disequilibrium mineral compositions and textures in the CFE, Nateekin, and Driftwood Pumice samples, combined with two pyroxene thermometry and An-rich plagioclase microlites (An80) found only in the top of the CFE deposits, provide evidence for repetitive mafic recharge triggering those eruptions, consistent with prior studies. We compare the Makushin geochemical data with data from select satellite vents and cones in the Makushin Volcanic Field (MVF) from prior studies, to examine possible genetic relationships. The geochemical data and Rhyolite-MELTS models run at crustal storage conditions (2 kbar, fO2 = Ni-NiO, and 1.5 and 3.5 wt% H2O) indicate that no single parental magma supplies the MVF satellite cones and Makushin volcano. Instead, two component mixing models better fit the MVF geochemical array. Our Makushin results compare well with models of predominantly andesitic volcanoes that require mafic recharge to mobilize the andesites and trigger eruptions.
... Based on the Reykjanes Peninsula postglacial volcanism study, Guðmundsson (1986) suggested that the rapid uplift and bending of the crust above the magma reservoirs, during the glacial unloading, favor the formation of ridges and shield volcanoes. Since that time, the mechanical effects of deglaciation on volcanism and the connection between glacial loading/unloading and volcanic activity have been discussed, analyzed, or modeled by many (Jull and McKenzie, 1996;Slater et al., 1998;Zielinksi, 2000;Maclennan et al., 2002, Sinton et al., 2005Andrew and Guðmundsson, 2007;Huybers and Langmuir, 2009;Sturkell et al., 2003;Praetorius et al., 2016). Glacial unloading is thought to have been responsible for an increase in magma melting rates below the base of the crust, due to enhanced mantle decompression (Maclennan et al., 2002;Sinton et al., 2005), in combination with unloading by subglacial erosion (Sternai et al., 2016). ...
Southern Iceland is one of the main outlets of the ice-sheet, and is subject to seismicity of both tectonic and volcanic origins, along the South Iceland Seismic Zone (SISZA sedimentary complex spanning Marine Isotopic Stage 6 to the present includes evidence of both activities. It includes a continuous sedimentary record since the Eemian interglacial period, controlled by a rapid deglaciation, followed by two marine glacioisostasy-forced transgressions, separated by a regression phase connected to an intra-MIS 5e glacial advance. This record has been constrained by tephrostratigraphy and dating. Analysis of this record has provided better insights into the interconnections between hydrology, volcanic and tectonic activity during deglaciations, and glaciations. Low-intensity earthquakes recurrently affected the water-laid sedimentation during the early stages of unloading, accompanying rifting events, dyke injection, and fault reactivations. During full interglacials periods, earthquakes were significantly less frequent, but of higher magnitudes, along the SISZ, in consequence to stress accumulation, favoured by low groundwater levels and more limited magma production. Occurrence of volcanism and seismicity in Iceland is mostly related to rifting events, but subglacial one seems to have been moreover related to stress unlocking related to limited or full unloading/deglaciation events. Major eruptions were mostly located at the melting margin of the ice-sheet.
... In the past few decades, it has been proposed that climate changes may affect volcanic activity (Kutterolf et al., 2019, and references therein). Studies of several glaciated regions worldwide (e.g., Sigvaldason et al., 1992;MacLennan et al., 2002;Nowell et al., 2006;Rawson et al., 2015;Praetories et al., 2016) showed a significant increase in subaerial volcanic activity during postglacial warming. Huybers and Langmuir (2009) analyzed a global record of subaerial volcanic eruptions back to the last glacial period and showed an increase in eruption frequency of at least 50% during deglaciation. ...
Established theories ascribe much of the observed long‐term Cenozoic climate cooling to atmospheric carbon consumption by erosion and weathering of tectonically uplifted terrains, but climatic effects due to changes in magmatism and carbon degassing are also involved. At timescales comparable to those of Milankovitch cycles, late Cenozoic building/melting of continental ice sheets, erosion, and sea level changes can affect magmatism, which provides an opportunity to explore possible feedbacks between climate and volcanic changes. Existing data show that extinction of Neo‐Tethyan volcanic arcs is largely synchronous with phases of atmospheric carbon reduction, suggesting waning degassing as a possible contribution to climate cooling throughout the early to middle Cenozoic. In addition, the increase in atmospheric CO2 concentrations during the last deglaciation may be ascribed to enhanced volcanism and carbon emissions due to unloading of active magmatic provinces on continents. The deglacial rise in atmospheric CO2 points to a mutual feedback between climate and volcanism mediated by the redistribution of surface masses and carbon emissions. This may explain the progression to higher amplitude and increasingly asymmetric cycles of late Cenozoic climate oscillations. Unifying theories relating tectonic, erosional, climatic, and magmatic changes across timescales via the carbon cycle offer an opportunity for future research into the coupling between surface and deep Earth processes.
... Here we assume little or no change in the surface-ocean reservoir age at our North Pacific sites. Based on correlation and tephrochronology, near-surface reservoir ages are constrained to be relatively constant (within a few hundred years) in this region during the deglacial interval 69,84 . ...
During the last deglaciation (19,000–9,000 years ago), atmospheric CO2 increased by about 80 ppm. Understanding the mechanisms responsible for this change is a central theme of palaeoclimatology, relevant for predicting future CO2 transfers in a warming world. Deglacial CO2 rise hypothetically tapped an accumulated deep Pacific carbon reservoir, but the processes remain elusive as they are underconstrained by existing tracers. Here we report high-resolution authigenic neodymium isotope data in North Pacific sediment cores and infer abyssal Pacific overturning weaker than today during the Last Glacial Maximum but intermittently stronger during steps of deglacial CO2 rise. Radiocarbon evidence suggestive of relatively ‘old’ deglacial deep Pacific water is reinterpreted here as an increase in preformed 14C age of subsurface waters sourced near Antarctica, consistent with movement of aged carbon out of the deep ocean and release of CO2 to the atmosphere during the abyssal flushing events. The timing of neodymium isotope changes suggests that deglacial acceleration of Pacific abyssal circulation tracked Southern Hemisphere warming, sea-ice retreat and increase of mean ocean temperature. The inferred magnitude of circulation changes is consistent with deep Pacific flushing as a significant, and perhaps dominant, control of the deglacial rise of atmospheric CO2.
... GIA potentially plays a role in modulating climate cycles. Postglacial rebound acts to reduce the pressure in the mantle, and this has been implicated in promoting terrestrial volcanism (Sigmundsson et al., 2010;Schmidt et al., 2013;Praetorius et al., 2016). Huybers and Langmuir (2009) argue that the CO 2 release associated with increased volcanism during the last deglaciation may have been sufficient to promote further ice melt, raising the possibility that glacial rebound, CO 2 release, and ice dynamics are part of a positive feedback loop. ...
Glacial isostatic adjustment (GIA)
describes the response of the solid Earth, the gravitational field, and the
oceans to the growth and decay of the global ice sheets. A commonly studied
component of GIA is postglacial rebound, which specifically relates to
uplift of the land surface following ice melt. GIA is a relatively rapid
process, triggering 100 m scale changes in sea level and solid Earth
deformation over just a few tens of thousands of years. Indeed, the
first-order effects of GIA could already be quantified several hundred years
ago without reliance on precise measurement techniques and scientists have
been developing a unifying theory for the observations for over 200 years.
Progress towards this goal required a number of significant breakthroughs to
be made, including the recognition that ice sheets were once more extensive,
the solid Earth changes shape over time, and gravity plays a central role in
determining the pattern of sea-level change. This article describes the
historical development of the field of GIA and provides an overview of the
processes involved. Significant recent progress has been made as concepts
associated with GIA have begun to be incorporated into parallel fields of
research; these advances are discussed, along with the role that GIA is
likely to play in addressing outstanding research questions within the field
of Earth system modelling.
... GIA potentially plays a role in modulating climate cycles. Postglacial rebound acts to reduce the pressure in the mantle, and this has been implicated in promoting terrestrial volcanism (Sigmundsson et al., 2010;Praetorius et al., 2016). Huybers and Langmuir (2009) argue that the CO 2 release associated with increased volcanism during the last deglaciation may have been sufficient to promote further ice melt, raising the possibility that glacial rebound, CO 2 release, and ice dynamics are part of a positive feedback loop. ...
Glacial Isostatic Adjustment (GIA) describes the response of the solid Earth, the gravitational field, and consequently the oceans to the growth and decay of the global ice sheets. It is a process that takes place relatively rapidly, triggering 100 m-scale changes in sea level and solid Earth deformation over just a few tens of thousands of years. Indeed, the first-order effects of GIA could already be quantified several hundred years ago without reliance on precise measurement techniques and scientists have been developing a unifying theory for the observations for over 200 years. Progress towards this goal required a number of significant breakthroughs to be made, including the recognition that ice sheets were once more extensive, the solid Earth changes shape over time, and gravity plays a central role in determining the pattern of sea-level change. This article describes in detail the historical development of the field of GIA and an overview of the processes involved. Significant recent progress has been made as concepts associated with GIA have begun to be incorporated into parallel fields of research; these advances are discussed, along with the role that GIA is likely to play in addressing outstanding research questions within the field of Earth system modelling.
... To account for re-gional surface-water reservoir ages of 880 ± 80 yrs, a constant R of 470 ± 80 yrs was applied to all planktonic foraminiferal dates (Davies-Walczak et al., 2014). Correlation of marine tephra layers that have also been dated on land suggest that near-surface marine reservoir ages in this region may vary by at most a few hundred years (Praetorius et al., 2016). To generate age-depth relationships for the cores, we apply a Bayesian probabilistic model (BChron; Haslett and Parnell, 2008) to the remaining calibrated planktonic foraminiferal dates, assuming constant reservoir ages with respect to a changing atmosphere (Davies-Walczak et al., 2014). ...
High-resolution sedimentary records on two cores from the Gulf of Alaska margin allow development of a ∼17,400-yr reconstruction of paleomagnetic secular variation (PSV). General agreement between the two records on their independent chronologies confirms that local PSV is recorded, demonstrating that such archives, notwithstanding complexities due to variable sedimentary regimes, deposition rates, and diagenetic conditions, provide meaningful information on past changes of the geomagnetic field. Comparisons with other independently dated sedimentary paleomagnetic records from the NE Pacific indicate largely coherent inclination records that in combination create a NE Pacific sedimentary inclination anomaly stack (NEPSIAS) capturing the common signal over an area spanning >30° longitude and latitude from Alaska through Oregon to Hawaii. Comparisons of NEPSIAS with high quality declination records from the northern North Atlantic (NNA) show that negative (shallow) inclination anomalies in NEPSIAS are associated with eastward NNA declinations while positive (steep) inclination anomalies in NEPSIAS are associated with westward NNA declinations. Comparison of these directional records to regional geomagnetic intensities over the past ∼3000 yrs in North America and back nearly 8000 yrs in the Euro/Mediterranean region, are consistent with a driving mechanism of oscillations in the relative strength of the North American and Euro/Mediterranean flux lobes. The persistence of these dynamics through the Holocene implicates a long-lived organizing structure likely imposed on the geomagnetic field by the lower mantle and/or inner core. These observations underscore a fundamental connection between directional PSV in the North Pacific with that of the North Atlantic, supporting the potential for long-distance correlation of directional PSV as a chronostratigraphic tool.
... Research in Iceland has shown that with thinning ice cover, magma production has increased at depth as a response to decompression of the underlying mantle (Jull & McKenzie 1996;Schmidt et al. 2013). Moreover, there is evidence that, worldwide, volcanism is most frequent in deglaciating regions as the overburden pressure of the ice is first reduced and then removed (Huybers & Langmuir 2009;Praetorius et al. 2016). Unloading of the WAIS from the WARS therefore offers significant potential to increase partial melting and eruption rates throughout the rifted terrain. ...
The West Antarctic Ice Sheet overlies the West Antarctic Rift System about which, due to the comprehensive ice cover, we have only limited and sporadic knowledge of volcanic activity and its extent. Improving our understanding of subglacial volcanic activity across the province is important both for helping to constrain how volcanism and rifting may have influenced ice-sheet growth and decay over previous glacial cycles, and in light of concerns over whether enhanced geothermal heat fluxes and subglacial melting may contribute to instability of the West Antarctic Ice Sheet. Here, we use ice-sheet bed-elevation data to locate individual conical edifices protruding upwards into the ice across West Antarctica, and we propose that these edifices represent subglacial volcanoes.We used aeromagnetic, aerogravity, satellite imagery and databases of confirmed volcanoes to support this interpretation. The overall result presented here constitutes a first inventory of West Antarctica's subglacial volcanism. We identified 138 volcanoes, 91 of which have not previously been identified, and which are widely distributed throughout the deep basins of West Antarctica, but are especially concentrated and orientated along the > 3000 km central axis of the West Antarctic Rift System.
Insular evolution on archipelagos generates a significant proportion of global biodiversity, yet islands are among the ecosystems most sensitive to accelerating anthropogenic disturbance, introductions of non‐native species, and emerging pathogens, among other conservation challenges. The Alexander and Haida Gwaii archipelagos along North America's North Pacific Coast support a disproportionate number of endemic taxa compared to other high‐latitude terrestrial ecosystems. In this region, endemics in Canada are explicitly protected, but in the United States, endemics have been operationally ignored. We reviewed regional research on terrestrial mammals and endemics from 2000–2022 to guide wildlife management. Elevated regional endemism is due to a combination of deep and shallow temporal processes (i.e., long‐term refugial isolation vs. recent colonization). With adequate sampling, genomic analyses are well‐suited to identifying nuanced patterns of divergence and endemism, thereby facilitating a deeper understanding of regional diversity. We identified 18 mammalian endemics in Southeast Alaska, USA, at varying taxonomic scales, but research effort has significant taxonomic biases and sampling infrastructure remains inadequate. Of the 66 terrestrial and aquatic mammal species in Southeast Alaska, only 55% are represented by ≥10 archived samples over the last 2 decades. Across taxa, major spatial and temporal sampling gaps limit interpretations of wildlife responses to changing environmental conditions. The Tongass National Forest is spread across an island archipelago, and climate change is projected to have disproportionate impacts on island endemics worldwide. In this case, the United States Forest Service is not closely monitoring endemic taxa, as was required by the Tongass Land Management Plan in 1997. Our review underscores a need for increased consideration of how endemism can be incorporated into land and wildlife management across the Alexander Archipelago. Moving forward, we encourage state and federal agencies, Indigenous communities, and international collaborators to continue to partner with natural history biorepositories to ensure strategic wildlife sampling infrastructure is built and made accessible to the broader scientific community as part of the land management process.
Perturbations in stratospheric aerosol due to explosive volcanic eruptions are a primary contributor to natural climate variability. Observations of stratospheric aerosol are available for the past decades, and information from ice cores has been used to derive estimates of stratospheric sulfur injections and aerosol optical depth over the Holocene (approximately 10,000 BP to present) and into the last glacial period, extending back to 60,000 BP. Tephra records of past volcanism, compared to ice cores, are less complete, but extend much further into the past. To support model studies of the potential impacts of explosive volcanism on climate variability over across timescales, we present here an ensemble reconstruction of volcanic stratospheric sulfur injection (VSSI) over the last 130,000 years that is based primarily on terrestrial and marine tephra records. VSSI values are computed as a simple function of eruption magnitude, based on VSSI estimates from ice cores and satellite observations for identified eruptions. To correct for the incompleteness of the tephra record we include stochastically generated synthetic eruptions, assuming a constant background eruption frequency from the ice core Holocene record. While the reconstruction often differs from ice core estimates for specific eruptions due to uncertainties in the data used and reconstruction method, it shows good agreement with an ice core based VSSI reconstruction in terms of millennial-scale cumulative VSSI variations over the Holocene. The PalVol reconstruction provides a new basis to test the contributions of forced vs. unforced natural variability to the spectrum of climate, and the mechanisms leading to abrupt transitions in the palaeoclimate record with low-to-high complexity climate models. The PalVol volcanic forcing reconstruction is available at https://doi.org/10.26050/WDCC/PalVolv1 (Toohey, Schindlbeck-Belo, 2023).
Founding populations of the first Americans likely occupied parts of Beringia during the Last Glacial Maximum (LGM). The timing, pathways, and modes of their southward transit remain unknown, but blockage of the interior route by North American ice sheets between ~26 and 14 cal kyr BP (ka) favors a coastal route during this period. Using models and paleoceanographic data from the North Pacific, we identify climatically favorable intervals when humans could have plausibly traversed the Cordilleran coastal corridor during the terminal Pleistocene. Model simulations suggest that northward coastal currents strengthened during the LGM and at times of enhanced freshwater input, making southward transit by boat more difficult. Repeated Cordilleran glacial-calving events would have further challenged coastal transit on land and at sea. Following these events, ice-free coastal areas opened and seasonal sea ice was present along the Alaskan margin until at least 15 ka. Given evidence for humans south of the ice sheets by 16 ka and possibly earlier, we posit that early people may have taken advantage of winter sea ice that connected islands and coastal refugia. Marine ice-edge habitats offer a rich food supply and traversing coastal sea ice could have mitigated the difficulty of traveling southward in watercraft or on land over glaciers. We identify 24.5 to 22 ka and 16.4 to 14.8 ka as environmentally favorable time periods for coastal migration, when climate conditions provided both winter sea ice and ice-free summer conditions that facilitated year-round marine resource diversity and multiple modes of mobility along the North Pacific coast.
We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at https://doi.org/10.1594/PANGAEA.936747
(Mulitza et al., 2021a). The database contains 2106 published and previously unpublished stable isotope downcore records with 361 949 stable isotope
values of various planktic and benthic species of Foraminifera from 1265 sediment cores. Age constraints are provided by 6153 uncalibrated
radiocarbon ages from 598 (47 %) of the cores. Each stable isotope and radiocarbon series is provided in a separate netCDF file containing
fundamental metadata as attributes. The data set can be managed and explored with the free software tool PaleoDataView. The atlas will provide
important data for paleoceanographic analyses and compilations, site surveys, or for teaching marine stratigraphy. The database can be updated with
new records as they are generated, providing a live ongoing resource into the future.
We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at https://doi.pangaea.de/10.1594/PANGAEA.936747 (Mulitza et al., 2021). The database contains 2,108 published and previously unpublished stable isotope downcore records with 362,067 stable isotope values of various planktonic and benthic species of foraminifera from 1,265 sediment cores. Age constraints are provided by 6,153 uncalibrated radiocarbon ages from 598 (47 %) of the cores. Each stable isotope and radiocarbon series is provided in a separate netCDF file containing fundamental meta data as attributes. The data set can be managed and explored with the free software tool PaleoDataView. The atlas will provide important data for paleoceanographic analyses and compilations, site surveys, or for teaching marine stratigraphy. The database can be updated with new records as they are generated, providing a live ongoing resource into the future.
Large volcanic eruptions occurring in the last glacial period can be detected in terms of their deposited sulfuric acid in continuous ice cores. Here we employ continuous sulfate and sulfur records from three Greenland and three Antarctic ice cores to estimate the emission strength, the frequency and the climatic forcing of large volcanic eruptions that occurred during the second half of the last glacial period and the early Holocene, 60–9 ka years before AD 2000 (b2k). The ice cores are synchronized over most of the investigated interval making it possible to distinguish large eruptions with a global sulfate distribution from eruptions detectable in one hemisphere only. Due to limited data resolution and to a large variability in the sulfate background signal, particularly in the Greenland glacial climate, we only detect Greenland sulfate depositions larger than 20 kg km−2 and Antarctic sulfate depositions larger than 10 kg km−2. With those restrictions, we identify 1113 volcanic eruptions in Greenland and 740 eruptions in Antarctica within the 51 ka period – where the sulfate deposition of 85 eruptions is defined at both poles (bipolar eruptions). Based on the relative Greenland and Antarctic sulfate deposition, we estimate the latitudinal band of the bipolar eruptions and assess their approximate climatic forcing based on established methods. The climate forcing of the five largest eruptions is estimated to be higher than −70 W m−2. Twenty-seven of the identified bipolar eruptions are larger than any volcanic eruption occurring in the last 2500 years and 69 eruptions are estimated to have larger sulfur emission strengths than the VEI-7 Tambora eruption that occurred in Indonesia in 1815 AD. The frequency of eruptions larger than the typical VEI-7 (VEI-8) eruption by the comparison of sulfur emission strength is found to be 5.3 (7) times higher than estimated from geological evidence. Throughout the investigated period, the frequency of volcanic eruptions is rather constant and comparable to that of recent times. During the deglacial period (16–9 ka b2k), however, there is a notable increase in the frequency of volcanic events recorded in Greenland and an obvious increase in the fraction of very large eruptions. For Antarctica, the deglacial period cannot be distinguished from other periods. These volcanoes documented in ice cores provide atmospheric sulfate burden and climate forcing for further research on climate impact and understanding the mechanism of the Earth system.
Volcanic landslides are controlled by a combination of magmatic, tectonic and surficial processes, the last of which is predominantly influenced by climate. In this chapter, we consider the influences of present and geologically recent climates on the occurrence of volcanic landslides. We begin by summarizing Quaternary climatic variability to illustrate the wide range of conditions and rates of change experienced by modern edifices. A focus on geologically recent volcanoes is prudent because both their morphologies and evidence of the climatic conditions affecting them are typically better preserved; pre-Quaternary climates similarly affected edifices that are now largely lost from the geomorphic record. We then review the climatic factors that condition and possibly trigger volcanic landslides, the challenges in dating landslides and climatic changes, and the difficulties in determining triggers of volcanic landslides. Finally, case studies of present and past climate influences on volcanic landslides collected from scientific literature–covering both subaerial and coastal settings–illustrate several key points: edifice collapses were numerous at the end of the last glaciation; current glacial retreat is conditioning volcanic slope failure in some specific settings; shallow landslides in volcanic environments appear to be increasing due to changes in weather extremes; and sea level fluctuation plays a role in volcanic island collapses. As knowledge on climate variability, volcanic, and surficial processes progresses, the understanding of how climate and its changes affect volcanic landslides will further improve.
Deglacial sea surface conditions in the subarctic North Pacific and marginal seas are the subject of increasing interest in paleoceanography. However, a cohesive picture of near-surface oceanography from which to compare inter and intra-regional variability through the last deglaciation is lacking. We present a synthesis of sea surface temperature covering the open North Pacific and its marginal seas, spanning the past 20 ka using proxy records from foraminiferal calcite (δ¹⁸O and Mg/Ca) and coccolithophore alkenones (Uk’37). Sea surface temperature proxies tend to be in agreement through the Holocene, though Uk’37 records are often interpreted as warmer than adjacent δ¹⁸O or Mg/Ca records during the Last Glacial Maximum and early deglaciation. In the Sea of Okhotsk, Holocene discrepancies between δ¹⁸O and Uk’37 may be the result of changes in near-surface stratification. We find that sea-surface warming occurred prior to the onset of the Bølling-Allerød (14.7 ka) and coincident with the onset of the Holocene (11.7 ka) in much of the North Pacific and Bering Sea. Proxy records also show a cold reversal roughly synchronous with the Younger Dryas (12.9–11.7 ka). After the onset of the Holocene, the influence of an intensified warm Kuroshio Current is evident at higher latitudes in the Western Pacific, and an east-west seesaw in sea surface temperature, likely driven by changes in the strength of the North Pacific Gyre, characterizes the open interglacial North Pacific.
The evidence for periods of increased volcanic activity following deglaciation, such as following ice sheet retreat after the Last Glacial Maximum, has been examined in several formerly glaciated areas, including Iceland, Alaska, and the Andean Southern Volcanic Zone. Here we present new evidence supporting the theory that during episodes of cooling in the Holocene, Icelandic volcanic activity decreased. By examining proximal and distal tephra records from Iceland spanning the last 12,500 years, we link two observed tephra minima to documented periods of climatic cooling and glacial advance, at 8.3 to 8 and 5.2 to 4.9 cal kyr BP. We simulate these periods in atmosphere-ocean and ice sheet models to assess the potential validity of the postglacial ‘unloading effect’ on Icelandic volcanic systems. We conclude that an increase in glacial cover may have decreased shallow magma ascent rates, thus limiting eruption potential and producing apparent quiescent periods in proximal and distal tephra records. However, several major uncertainties remain regarding the theory, including geographical and temporal preservation biases and the importance of any unloading effects against other factors, and these will require more prolonged investigation in future research.
Prehistoric Holocene eruptions of Changbaishan volcano in Northeast China are poorly dated, with the exception of the AD 946 Millennium eruption (ME). Poorly refined age estimates for the earlier eruptions present problems for the reconstruction of the eruptive history of the volcano. The Qixiangzhan eruption (QE) is a major controversial event in terms of its eruptive timing (ranging from ~88 kyr to ~4 kyr) and style (effusive or explosive). As a result of the imprecise age estimates for the eruption, a geomagnetic field excursion recorded within the QE comendite has been variably correlated with a number of different excursion events observed elsewhere. In this study, a visible early Holocene tephra was identified in Yuanchi Lake, ~30 km east of the Changbaishan volcanic vent, and was dated to 8831‐8100 cal yr BP using Bayesian age modelling. Glass shard compositions enable the correlation of this tephra with the poorly dated QE, as well as with a tephra (SG14‐1058) recorded in Lake Suigetsu, in central Japan. These correlations confirm that the QE was explosive, and that the ash from Qixiangzhan eruption (QEA) can serve as an important early Holocene marker bed across East Asia. In addition, we propose an age of ~8100 cal yr BP for the QE based on the precise date of the Suigetsu SG14‐1058 tephra. Our results also confirm that the geomagnetic field excursion recorded in the Qixiangzhan comendite dates to ~8100 cal yr BP.
Volcanic activity can have a notable impact on glacier behaviour (dimensions and dynamics). This is evident from the palaeo-record, but is often difficult to observe for modern glaciers. However, documenting and, if possible, quantifying volcanic impacts on modern glaciers is important if we are to predict their future behaviour (including crucial ice masses such as the West Antarctic Ice Sheet) and to monitor and mitigate glacio-volcanic hazards such as floods (including jökulhlaups) and lahars. This review provides an assessment of volcanic impacts on the behaviour of modern glaciers (since AD 1800) by presenting and summarising a global dataset of documented examples. The study reveals that shorter-term (days-to-months) impacts are typically destructive, while longer-term (years-to-decades) are more likely protective (e.g., limiting climatically driven ice loss). However, because these events are difficult to observe, particularly before the widespread availability of global satellite data, their frequency and importance are likely underestimated. The study also highlights that because the frequency and nature of volcano-glacier interactions may change with time (e.g., glacier retreat may lead to an increase in explosive volcanic activity), predicting their future importance is difficult. Fortunately, over coming years, continued improvements in remotely sensed data will increase the frequency, and enhance the quality, of observations of volcanic impacts on glaciers, allowing an improved understanding of their past and future operation.
Volcanic eruptions can impact the mass balance of ice sheets through changes in climate and the radiative properties of the ice. Yet, empirical evidence highlighting the sensitivity of ancient ice sheets to volcanism is scarce. Here we present an exceptionally well-dated annual glacial varve chronology recording the melting history of the Fennoscandian Ice Sheet at the end of the last deglaciation (∼13,200–12,000 years ago). Our data indicate that abrupt ice melting events coincide with volcanogenic aerosol emissions recorded in Greenland ice cores. We suggest that enhanced ice sheet runoff is primarily associated with albedo effects due to deposition of ash sourced from high-latitude volcanic eruptions. Climate and snowpack mass-balance simulations show evidence for enhanced ice sheet runoff under volcanically forced conditions despite atmospheric cooling. The sensitivity of past ice sheets to volcanic ashfall highlights the need for an accurate coupling between atmosphere and ice sheet components in climate models.
Widespread ash dispersal poses a significant natural hazard to society, particularly in relation to disruption to aviation. Assessing the extent of the threat of far-travelled ash clouds on flight paths is substantially hindered by an incomplete volcanic history and an underestimation of the potential reach of distant eruptive centres. The risk of extensive ash clouds to aviation is thus poorly quantified. New evidence is presented of explosive Late Pleistocene eruptions in the Pacific Arc, currently undocumented in the proximal geological record, which dispersed ash up to 8000 km from source. Twelve microscopic ash deposits or cryptotephra, invisible to the naked eye, discovered within Greenland ice-cores, and ranging in age between 11.1 and 83.7 ka b2k, are compositionally matched to northern Pacific Arc sources including Japan, Kamchatka, Cascades and Alaska. Only two cryptotephra deposits are correlated to known high-magnitude eruptions (Towada-H, Japan, ca 15 ka BP and Mount St Helens Set M, ca 28 ka BP). For the remaining 10 deposits, there is no evidence of age- and compositionally-equivalent eruptive events in regional volcanic stratigraphies. This highlights the inherent problem of under-reporting eruptions and the dangers of underestimating the long-term risk of widespread ash dispersal for trans-Pacific and trans-Atlantic flight routes.
Significance
Antarctic ice cores provide a precise, well-dated history of increasing atmospheric CO 2 during the last glacial to interglacial transition. However, the mechanisms that drive the increase remain unclear. Here we reconstruct a key indicator of the sources of atmospheric CO 2 by measuring the stable isotopic composition of CO 2 in samples spanning the period from 22,000 to 11,000 years ago from Taylor Glacier, Antarctica. Improvements in precision and resolution allow us to fingerprint CO 2 sources on the centennial scale. The data reveal two intervals of rapid CO 2 rise that are plausibly driven by sources from land carbon (at 16.3 and 12.9 ka) and two others that appear fundamentally different and likely reflect a combination of sources (at 14.6 and 11.5 ka).
In the Arctic region, Iceland is an important source of dust due to ash production from volcanic eruptions. In addition, dust is resuspended from the surface into the atmosphere as several dust storms occur each year. During volcanic eruptions and dust storms, material is deposited on the glaciers where it influences their energy balance. The effects of deposited volcanic ash on ice and snow melt were examined using laboratory and outdoor experiments. These experiments were made during the snow melt period using two different ash grain sizes (1 ϕ and 3.5 ϕ) from the Eyjafjallajökull 2010 eruption, collected on the glacier. Different amounts of ash were deposited on snow or ice, after which the snow properties and melt were measured. The results show that a thin ash layer increases the snow and ice melt but an ash layer exceeding a certain critical thickness caused insulation. Ash with 1 ϕ in grain size insulated the ice below at a thickness of 9–15 mm. For the 3.5 ϕ grain size, the insulation thickness is 13 mm. The maximum melt occurred at a thickness of 1 mm for the 1 ϕ and only 1–2 mm for 3.5 ϕ ash. A map of dust concentrations on Vatnajökull that represents the dust deposition during the summer of 2013 is presented with concentrations ranging from 0.2 up to 16.6 g m−2.
The SIMAN coefficient is the average ratio obtained when each variable in a set of multivariate data is divided by the larger value for that variable in either of two samples. By dividing by the larger value for any one measurement, trace elements (or minute quantities) can be compared along with major elements (or large quantities) with each type of variable influencing the SIMAN coefficient to the same degree. SIMAN coefficients produce a similarity matrix of comparisons between analyses of all samples. The comparison of any two samples results in a coefficient that remains unchanged by later addition of other samples to the data set. The coefficient is related to the analytical precision of replicates and is probably best used where the variability within classes is low. It has been used successfully in volcanic ash correlation with trace element and major element data.
The oceans mediate the response of global climate to natural and anthropogenic forcings. Yet for the past 2,000 years-a key interval for understanding the present and future climate response to these forcings-global sea surface temperature changes and the underlying driving mechanisms are poorly constrained. Here we present a global synthesis of sea surface temperatures for the Common Era (ce) derived from 57 individual marine reconstructions that meet strict quality control criteria. We observe a cooling trend from 1 to 1800 ce that is robust against explicit tests for potential biases in the reconstructions. Between 801 and 1800 ce, the surface cooling trend is qualitatively consistent with an independent synthesis of terrestrial temperature reconstructions, and with a sea surface temperature composite derived from an ensemble of climate model simulations using best estimates of past external radiative forcings. Climate simulations using single and cumulative forcings suggest that the ocean surface cooling trend from 801 to 1800 ce is not primarily a response to orbital forcing but arises from a high frequency of explosive volcanism. Our results show that repeated clusters of volcanic eruptions can induce a net negative radiative forcing that results in a centennial and global scale cooling trend via a decline in mixed-layer oceanic heat content.
Significance
Several areas of earth science require knowledge of the fluctuations in sea level and ice volume through glacial cycles. These include understanding past ice sheets and providing boundary conditions for paleoclimate models, calibrating marine-sediment isotopic records, and providing the background signal for evaluating anthropogenic contributions to sea level. From ∼1,000 observations of sea level, allowing for isostatic and tectonic contributions, we have quantified the rise and fall in global ocean and ice volumes for the past 35,000 years. Of particular note is that during the ∼6,000 y up to the start of the recent rise ∼100−150 y ago, there is no evidence for global oscillations in sea level on time scales exceeding ∼200 y duration or 15−20 cm amplitude.
Due to their outstanding resolution and well-constrained chronologies, Greenland ice-core records provide a master record of past climatic changes throughout the Last Interglacial–Glacial cycle in the North Atlantic region. As part of the INTIMATE (INTegration of Ice-core, MArine and TErrestrial records) project, protocols have been proposed to ensure consistent and robust correlation between different records of past climate. A key element of these protocols has been the formal definition and ordinal numbering of the sequence of Greenland Stadials (GS) and Greenland Interstadials (GI) within the most recent glacial period. The GS and GI periods are the Greenland expressions of the characteristic Dansgaard–Oeschger events that represent cold and warm phases of the North Atlantic region, respectively. We present here a more detailed and extended GS/GI template for the whole of the Last Glacial period. It is based on a synchronization of the NGRIP, GRIP, and GISP2 ice-core records that allows the parallel analysis of all three records on a common time scale. The boundaries of the GS and GI periods are defined based on a combination of stable-oxygen isotope ratios of the ice (δ18O, reflecting mainly local temperature) and calcium ion concentrations (reflecting mainly atmospheric dust loading) measured in the ice. The data not only resolve the well-known sequence of Dansgaard–Oeschger events that were first defined and numbered in the ice-core records more than two decades ago, but also better resolve a number of short-lived climatic oscillations, some defined here for the first time. Using this revised scheme, we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the Last Glacial period that are represented in the Greenland ice records. The final product constitutes an extended and better resolved Greenland stratotype sequence, against which other proxy records can be compared and correlated. It also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations.
Volcanic ash layers preserved within the geologic record represent precise time markers
that correlate disparate depositional environments and enable the investigation of synchro- nous and/or asynchronous behaviors in Earth system and archaeological sciences. However, it is generally assumed that only exceptionally powerful events, such as supereruptions (≥450 km3 of ejecta as dense-rock equivalent; recurrence interval of ~105 yr), distribute ash broadly enough to have an impact on human society, or allow us to address geologic, climatic, and cul- tural questions on an intercontinental scale. Here we use geochemical, age, and morphological evidence to show that the Alaskan White River Ash (eastern lobe; A.D. 833–850) correlates to the “AD860B” ash (A.D. 846–848) found in Greenland and northern Europe. These occur- rences represent the distribution of an ash over 7000 km, linking marine, terrestrial, and ice-core records. Our results indicate that tephra from more moderate-size eruptions, with recurrence intervals of ~100 yr, can have substantially greater distributions than previously thought, with direct implications for volcanic dispersal studies, correlation of widely distrib- uted proxy records, and volcanic hazard assessment.
Some proposed mechanisms for transmission of major climate change events between the North Pacific and North Atlantic predict
opposing patterns of variations; others suggest synchronization. Resolving this conflict has implications for regulation of
poleward heat transport and global climate change. New multidecadal-resolution foraminiferal oxygen isotope records from the
Gulf of Alaska (GOA) reveal sudden shifts between intervals of synchroneity and asynchroneity with the North Greenland Ice
Core Project (NGRIP) δ18O record over the past 18,000 years. Synchronization of these regions occurred 15,500 to 11,000 years ago, just prior to and
throughout the most abrupt climate transitions of the last 20,000 years, suggesting that dynamic coupling of North Pacific
and North Atlantic climates may lead to critical transitions in Earth’s climate system.
Northern Hemisphere summer temperatures over the past 8000 years have
been paced by the slow decrease in summer insolation resulting from the
precession of the equinoxes. However, the causes of superposed
century-scale cold summer anomalies, of which the Little Ice Age (LIA)
is the most extreme, remain debated, largely because the natural
forcings are either weak or, in the case of volcanism, short lived. Here
we present precisely dated records of ice-cap growth from Arctic Canada
and Iceland showing that LIA summer cold and ice growth began abruptly
between 1275 and 1300 AD, followed by a substantial intensification
1430-1455 AD. Intervals of sudden ice growth coincide with two of
the most volcanically perturbed half centuries of the past millennium. A
transient climate model simulation shows that explosive volcanism
produces abrupt summer cooling at these times, and that cold summers can
be maintained by sea-ice/ocean feedbacks long after volcanic aerosols
are removed. Our results suggest that the onset of the LIA can be linked
to an unusual 50-year-long episode with four large sulfur-rich explosive
eruptions, each with global sulfate loading >60 Tg. The persistence
of cold summers is best explained by consequent sea-ice/ocean feedbacks
during a hemispheric summer insolation minimum; large changes in solar
irradiance are not required.
Cultured planktonic foraminifera, Orbulina universa (symbiotic) and Globigerina bulloides (nonsymbiotic), are used to reexamine temperature:δ18O relationships at 15°–25°C. Relationships for both species can be described by linear equations. Equations for O. universa grown under low light (LL) and high light (HL) share a slope of −4.80 (0.21‰ °C−1) with a HL-LL offset of −0.33‰ due to symbiont photosynthetic activity. The effect of [CO32−] on O. universa is −0.002‰ µmol−1 kg−1 and is insensitive to temperature. For G. bulloides, ontogenetic effects produce size-related trends in temperature:δ18O, whereby larger shells are enriched in 18O relative to smaller specimens. The O. universa temperature:δ18O relationships are more accurate than previously published equations for describing plankton tow data. Our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic Cibicidoides data below 10°C. Temperature:δ18O relationships for G. bulloides provide good agreement with field data for this species from the northeast Pacific.
The IntCal09 and Marine09 radiocarbon calibration curves have been revised utilizing newly available and updated data sets from 14C measurements on tree rings, plant macrofossils, speleothems, corals, and foraminifera. The calibration curves were derived from the data using the random walk model (RWM) used to generate IntCal09 and Marine09, which has been revised to account for additional uncertainties and error structures. The new curves were ratified at the 21st International Radiocarbon conference in July 2012 and are available as Supplemental Material at www.radiocarbon.org. The database can be accessed at http://intcal.qub.ac.uk/intcal13/. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.
We present a new common stratigraphic timescale for the North Greenland Ice Core Project (NGRIP) and GRIP ice cores. The timescale covers the period 7.9–14.8 kyr before present and includes the Bølling, Allerød, Younger Dryas, and early Holocene periods. We use a combination of new and previously published data, the most prominent being new high-resolution Continuous Flow Analysis (CFA) impurity records from the NGRIP ice core. Several investigators have identified and counted annual layers using a multiparameter approach, and the maximum counting error is estimated to be up to 2% in the Holocene part and about 3% for the older parts. These counting error estimates reflect the number of annual layers that were hard to interpret, but not a possible bias in the set of rules used for annual layer identification. As the GRIP and NGRIP ice cores are not optimal for annual layer counting in the middle and late Holocene, the timescale is tied to a prominent volcanic event inside the 8.2 kyr cold event, recently dated in the DYE-3 ice core to 8236 years before A. D. 2000 (b2k) with a maximum counting error of 47 years. The new timescale dates the Younger Dryas-Preboreal transition to 11,703 b2k, which is 100–150 years older than according to the present GRIP and NGRIP timescales. The age of the transition matches the GISP2 timescale within a few years, but viewed over the entire 7.9–14.8 kyr section, there are significant differences between the new timescale and the GISP2 timescale. The transition from the glacial into the Bølling interstadial is dated to 14,692 b2k. The presented timescale is a part of a new Greenland ice core chronology common to the DYE-3, GRIP, and NGRIP ice cores, named the Greenland Ice Core Chronology 2005 (GICC05). The annual layer thicknesses are observed to be log-normally distributed with good approximation, and compared to the early Holocene, the mean accumulation rates in the Younger Dryas and Bølling periods are found to be 47 ± 2% and 88 ± 2%, respectively.
Oxygen isotope data from planktonic and benthic foraminifera, on a high-resolution age model (44 14C dates spanning 17,400 years), document deglacial environmental change on the southeast Alaska margin (5933.32N, 1449.21W, 682 m water depth). Surface freshening (i.e., δ18O reduction of 0.8‰) began at 16,650 170 cal years B.P. during an interval of ice proximal sedimentation, likely due to freshwater input from melting glaciers. A sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14,790 380 cal years B.P. Abrupt warming and/or freshening of the surface ocean (i.e., additional δ18O reduction of 0.9‰) coincides with the Blling Interstade of northern Europe and Greenland. Cooling and/or higher salinities returned during the Allerd interval, coincident with the Antarctic Cold Reversal, and continue until 11,740 200 cal years B.P., when onset of warming coincides with the end of the Younger Dryas. An abrupt 1‰ reduction in benthic δ18O at 14,250 290 cal years B.P. likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater, a regional megaflood event, or brine formation associated with sea ice. Two laminated opal-rich intervals record discrete episodes of high productivity during the last deglaciation. These events, precisely dated here at 14,790 380 to 12,990 190 cal years B.P. and 11,160 130 to 10,750 220 cal years B.P., likely correlate to similar features observed elsewhere on the margins of the North Pacific and are coeval with episodes of rapid sea level rise. Remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia.
The abundance and chemistry of the planktonic foraminifera
Neogloboquadrina pachyderma (sinistral coiling) have long been used as
tools for monitoring polar surface ocean changes and for correlating
these changes to atmospheric and thermohaline circulation fluctuations.
However, due to its remote habitat, very little is known about how
modern N. pachyderma (s.) respond to changing environmental conditions
in the polar seas. Modern samples of N. pachyderma (s.) from the
Northeast Water Polynya provide a means for studying how environmental
conditions affect the vertical distribution and chemistry of this
species. Highest abundances of N. pachyderma (s.) were associated with
the chlorophyll maximum in the surface 20-80 m, where they are
exploiting their primary food source. Evidence suggests that the
addition of a calcite crust modifies the calcite tests of some N.
pachyderma (s.) between 50 and 200 m, increasing shell density and
modifying shell chemistry. The shell mass of encrusted forms is 3-4
times greater than the nonencrusted forms between 50 and 200 m. The
oxygen isotope composition of N. pachyderma (s.) shells increase by
1.5‰ in response to local water column gradients. The
δ13C values of N. pachyderma (s.) are basically
invariant with depth in this region, are consistently 1.0‰
depleted in comparison with the δ13C for equilibrium
calcite, and remain basically constant during the shell-thickening
process. Mass balance calculations suggest that encrustation occurs at
all depths, but abundance counts suggest that the process occurs mostly
at the depth of the main pycnocline. Sediment fluxes of N. pachyderma
(s.) occur during a 2-week bloom event and decrease to almost zero below
complete ice cover. The decoupling of the processes controlling
abundances and shell chemistry explain the discrepancies between
transfer function and isotopically derived paleotemperature estimates of
surface conditions, in some oceanic settings. The ability of
δ18O to record surface ocean conditions will depend on
vertical water column gradients, as evidenced by the differences in
core-top calibrations between the North and South Atlantic.
The eruption of Mt Pinatubo in June 1991 caused the largest perturbation
this century to the participate content of the stratosphere. The
radiative influence of the injected particles put an end to several
years of globally warm surface temperatures. At the same time, the
combined effect of volcanic particles and anthropogenic reactive
chlorine has led to record low levels of stratospheric ozone.
To better understand the process of crustal contamination/assimilation, 23 Pb isotopic compositions and 12 concentrations have been measured on lavas and basement rocks from the Edgecumbe volcanic field, SE Alaska. Measured isotopic ratios have the following ranges: 206 Pb / 204 Pb = 18.477-19.161; 207 Pb / 204 Pb = 15.562-15.679; 208 Pb / 204 Pb = 38.17-38.85. While the data form well-constrained linear arrays on Pb-Pb diagrams, no simple correlation exists with major element composition. Basaltic lavas ( 51 wt% SiO 2 ) are characterized by two isotopic groups. The olivine basalt ( 48% SiO 2 ) is more radiogenic than the plagioclase basalt (48-51%) which also shows more heterogeneity. In the silica range 52-55%, Pb isotopic ratios increase significantly but remain fairly constant in the range 55-70% SiO 2 . Lead concentrations vary from 1 ppm in the basalts to 7 ppm in the rhyodacites. Analyzed basement rocks are more radiogenic than any of the lavas ( 206 Pb / 204 Pb = 19.20; 207 Pb / 204 Pb = 15.65; 208 Pb / 204 Pb = 38.86. The Pb isotopic data are qualitatively consistent with the contamination process described by et al . (1984). However, because of fundamental differences in the mixing relations between the Sr system studied earlier and the Pb system, the new Pb data have revealed details of the process not apparent from the Sr data alone. In particular, it has been shown that the parent magma was more primitive than originally assumed, and that two contamination events are recorded in the lavas. The first event, involving a mafic parent and different crustal contaminants, produced the intermediate and siliceous hybrids in cupolas located above the main basaltic chamber. The types of country rock intruded as well as the degree of partial fusion achieved in individual cupolas controlled the range of hybrid compositions produced while the eruption sequence was determined by the order in which the cupolas were tapped. The second contamination event produced the plagioclase basalt, the most voluminous basaltic unit, by mixing the mafic parent with the olivine basalt, an independent, primary magma. Our results suggest crustal contamination models that assume bulk assimilation of crustal end members may be too simplistic.
The northern Cordilleran volcanic province encompasses a broad area of Neogene to Quaternary volcanism in northwestern British Columbia, the Yukon Territory, and adjacent eastern Alaska. Volcanic rocks of the northern Cordilleran volcanic province range in age from 20 Ma to ca. 200 yr B.P. and are dominantly alkali olivine basalt and hawaiite. A variety of more strongly alkaline rock types not commonly found in the North American Cordillera are locally abundant in the northern Cordilleran volcanic province. These include nephelinite, basanite, and peralkaline phonolite, trachyte, and comendite. The most MgO-rich nephelinites, basanites, and alkaline basalts from throughout the northern Cordilleran volcanic province show trace element abundances and isotopic compositions that are consistent with an asthenospheric source region similar to that for average oceanic island basalt and for post-5 Ma alkaline basalts from the Basin and Range. Our petrologic observations help constrain the origin of northern Cordilleran volcanic province magmatism as well as lithosphere changes between the four major basement terranes that underlie the province. Results from phase equilibria calculations and the spatial distributions of volcanic rock types and magmatic inclusions are more consistent with the existence of thicker lithosphere beneath Stikinia, which underlies the southern part of the northern Cordilleran volcanic province, than beneath the Cache Creek and Yukon-Tanana terranes, which underlie the northern part of the northern Cordilleran volcanic province. Our results support a model for initiation of northern Cordilleran volcanic province magmatism due to incipient rifting of the northern Cordillera, driven by changes in relative plate motion between the Pacific and North American plates ca. 15-10 Ma.
The INternational focus group on Tephrochronology And Volcanism (INTAV) of the International Union for Quaternary Research (INQUA) has conducted an intercomparison of tephrochronology laboratories with electron-beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries. This assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community. The intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation. Participating laboratories were each supplied with a mount containing three samples for analysis: (1) rhyolitic Lipari obsidian ID3506, (2) phonolitic Sheep Track tephra from Mt. Edziza, British Columbia, Canada, and (3) basaltic Laki 1783 A.D. tephra. A fourth sample, rhyolitic Old Crow tephra, was also distributed.
Acidity peaks in Greenland ice cores have been used as critical reference horizons for synchronizing ice-core records, aiding the construction of a single Greenland Ice Core Chronology (GICC05) for the Holocene. Guided by GICC05, we examined sub-sections of three Greenland cores in the search for tephra from specific eruptions that might facilitate the linkage of ice core records, the dating of prehistoric tephras and the understanding of the eruptions. Here we report the identification of 14 horizons with tephra particles, including 11 that have not previously been reported from the North Atlantic region and that have the potential to be valuable isochrons. The positions of tephras whose major element data are consistent with ash from the Katmai AD 1912 and Öraefajökull AD 1362 eruptions confirm the annually-resolved ice core chronology for the last 700 years. We provide a more refined date for the so-called "AD860B" tephra, a widespread isochron found across NW Europe, and present new evidence relating to the 17th century BC Thera/Aniakchak debate that shows N. American eruptions likely contributed to the acid signals at this time. Our results emphasize the variable spatial and temporal distributions of volcanic products in Greenland ice that call for a more cautious approach in the attribution of acid signals to specific eruptive events.
In tectonic settings where decompression melting drives magmatism, there is compelling evidence that changes in ice loading or water loading across glacial-interglacial cycles modulate volcanic activity. In contrast, the response of subduction-related volcanoes remains unclear. A high-resolution postglacial eruption record from a large Chilean stratovolcano, Mocho-Choshuenco, provides new insight into the arc magmatic response to ice-load removal. Following deglaciation, we identify three distinct phases of activity characterized by different eruptive fluxes, sizes, and magma compositions. Phase 1 (13–8.2 ka) was dominated by large dacitic and rhyolitic explosive eruptions. During phase 2 (7.3–2.9 ka), eruptive fluxes were lower and dominated by moderate-scale basaltic andesite eruptions. Since 2.4 ka (phase 3), eruptive fluxes have been elevated and of more intermediate magmas. We suggest that this time-varying behavior reflects changes in magma storage time scales, modulated by the changing crustal stress field. During glaciation, magma stalls and differentiates to form large, evolved crustal reservoirs. Following glacial unloading, much of the stored magma erupts (phase 1). Subsequently, less-differentiated magma infiltrates the shallow crust (phase 2). As storage time scales increase, volcanism returns to more evolved compositions (phase 3). Data from other Chilean volcanoes show a similar tripartite pattern of evacuation, relaxation, and recovery, suggesting that this could be a general feature of previously glaciated arc volcanoes.
A rigorous detection of Milankovitch periodicities in volcanic output across the Pleistocene-Holocene ice age has remained elusive. We report on a spectral analysis of a large number of well-preserved ash plume deposits recorded in marine sediments along the Pacific Ring of Fire. Our analysis yields a statistically significant detection of a spectral peak at the obliquity period. We propose that this variability in volcanic activity results from crustal stress changes associated with ice age mass redistribution. In particular, increased volcanism lags behind the highest rate of increasing eustatic sea level (decreasing global ice volume) by 4.0 +/- 3.6 k.y. and correlates with numerical predictions of stress changes at volcanically active sites. These results support the presence of a causal link between variations in ice age climate, continental stress field, and volcanism.
A predictive model for locating sites in southern Southeast Alaska was developed based on shell-bearing raised marine deposits. Fieldwork included coring of select-raised marine strata, measuring their elevations,
and radiocarbon dating the associated shell samples within the cores. A subset of the data was used to produce a relative sea-level curve spanning the Holocene. The relative sea-level curve suggests that sites favorable for habitation between 9200 and 7000 14C yr B.P. should be found 16–22 ± 1 m above present zero tide. The sea-level curve and new high-resolution digital elevation models allowed reconstruction of past shorelines at various elevations. Surveys to test the model found and recorded over 70 archaeological sites from present sea level up to 32 m above present zero tide. Eleven new sites were within the targeted elevation range and radiocarbon dated to 9280–6890 14C yr B.P. Initial investigations indicate these older sites are rich in microblade and pebble tool technology. The new early Holocene sites indicate more extensive early maritime settlement of Alaska than implied by previous studies and contribute to our understanding of the early movement of people into North America.
C �2015 Wiley Periodicals, Inc.
Global climate and the concentration of atmospheric carbon dioxide (CO2) are correlated over recent glacial cycles. The combination of processes responsible for a rise in atmospheric CO2 at the last glacial termination (23,000 to 9,000 years ago), however, remains uncertain. Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO2 and methane (CH4) records of the last deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO2-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination, given the strong covariance of CO2 levels and Antarctic temperatures. Our data establish a contribution from an abrupt, centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
Tephra layers preserved within the Greenland ice-cores are crucial for the independent synchronisation of these high-resolution records to other palaeoclimatic archives. Here we present a new and detailed tephrochronological framework for the time period 25,000–45,000 a b2k that brings together results from 4 deep Greenland ice-cores. In total, 99 tephra deposits, the majority of which are preserved as cryptotephra, are described from the NGRIP, NEEM, GRIP and DYE-3 records. The major element signatures of single glass shards within these deposits indicate that 93 are basaltic in composition all originating from Iceland. Specifically, 43 originate from Grimsvötn, 20 are thought to be sourced from the Katla volcanic system and 17 show affinity to the Kverkfjöll system. Robust geochemical characterisations, independent ages derived from the GICC05 ice-core chronology, and the stratigraphic positions of these deposits relative to the Dansgaard-Oeschger climate events represent a key framework that provides new information on the frequency and nature of volcanic events in the North Atlantic region between GS-3 and GI-12. Of particular importance are 19 tephra deposits that lie on the rapid climatic transitions that punctuate the last glacial period. This framework of well-constrained, time-synchronous tie-lines represents an important step towards the independent synchronisation of marine, terrestrial and ice-core records from the North Atlantic region, in order to assess the phasing of rapid climatic changes during the last glacial period.
We apply a coupled energy-balance/ice-sheet climate model in an
investigation of northern hemisphere ice-sheet advance and retreat over
the last glacial cycle. When driven only by orbital insolation
variations, the model predicts ice-sheet advances over the continents of
North America and Eurasia that are in good agreement with geological
reconstructions in terms of the timescale of advance and the spatial
positioning of the main ice masses. The orbital forcing alone, however,
is unable to induce the observed rapid ice-sheet retreat, and we
conclude that additional climatic feedbacks not explicitly included in
the basic model must be acting. In the analyses presented here we have
parameterized a number of potentially important effects in order to test
their relative influence on the process of glacial termination. These
include marine instability, thermohaline circulation effects, carbon
dioxide variations, and snow albedo changes caused by dust loading
during periods of high atmospheric aerosol concentration. For the
purpose of these analyses the temporal changes in the latter two
variables were inferred from ice core records. Of these various
influences, our analyses suggest that the albedo variations in the
ice-sheet ablation zone caused by dust loading may represent an
extremely important ablation mechanism. Using our parameterization of
"dirty" snow in the ablation zone we find glacial retreat to be strongly
accelerated, such that complete collapse of the otherwise stable
Laurentide ice sheet ensues. The last glacial maximum configurations of
the Laurentide and Fennoscandian complexes are also brought into much
closer accord with the ICE-3G reconstruction of Tushingham and Peltier
(1991,1992) and the ICE-4G reconstruction of Peltier (1994) when this
effect is reasonably introduced.
Novarupta erupted in Alaska on 6th June 1912 and was the biggest of the
21st century. It erupted for 60 hours and sent an ash cloud over 32,000m
into the air. People were stranded for several days, houses destroyed,
villages abandoned and food supplies disrupted for a long period after
the eruption. Ash was recorded to have travelled over 9,500km away in
Africa, demonstrating potentially global impacts. The eruption occurred
when Alaska had very little aviation industry, today however the
airspace above Alaska is one of the busiest in the world. The eruption
in Iceland in 2010 which disrupted the European airspace for several
weeks and closed it completely for five days, brought to light just how
disruptive a volcanic eruption can be, even in countries where volcanic
activity is not considered a hazard. It was an expensive event for the
aviation industry and caused much disruption. Simulations of a Katmai
scale eruption were run in the ‘present-day’, using the PUFF
ash fall model. Simulations were run for one week from the start the
eruption. A ‘worst-case’ scenario is presented based on data
from 2005-2009. It is a hypothetical eruption started on 17th January
2005 and it shows that ash is likely to cause havoc in North America,
Europe and parts of Asia. At least 43 airports on average would be
severely affected each day of the simulation, leading to several of the
major air routes being affected. Where financial data is available, an
estimated cost of this event is presented. A 500 hr simulation is
presented to demonstrate the possible global effects that could occur
within three weeks of an eruption. It shows ash being transported across
the equator at high altitudes to the southern hemisphere in Asia as well
as the whole of the northern hemisphere being engulfed. The complex
implications an eruption like this would have on national and
international infrastructures is presented. The results could aid
further scientific studies, governmental bodies and industries on the
effects of volcanic eruptions and provide information for hazard
management.
New radiocarbon dates on charcoal incorporated in proximal airfall deposits indicate the largest late Pleistocene eruption from the Mt. Edgecumbe volcanic field in Southeast Alaska occurred ca. 11,250 ± 5014C yr B.P. The more precise dating of the principal Edgecumbe tephra layer greatly improves its utility as a tephrochronologic marker horizon in southeastern Alaska.
Several lines of evidence have previously been used to suggest that ice retreat after the last glacial maximum (LGM) resulted in regionally-increased levels of volcanic activity. It has been proposed that this increase in volcanism was globally significant, forming a substantial component of the post-glacial rise in atmospheric CO2, and thereby contributing to climatic warming. However, as yet there has been no detailed investigation of activity in glaciated volcanic arcs following the LGM. Arc volcanism accounts for 90% of present-day subaerial volcanic eruptions. It is therefore important to constrain the impact of deglaciation on arc volcanoes, to understand fully the nature and magnitude of global-scale relationships between volcanism and glaciation.
In recent years, increased awareness of the considerable potential offered by tephrochronology in palaeoclimatic studies has fuelled a renewed interest in the tephra record preserved within the Greenland ice-cores. This renewal has occurred in tandem with the development of continuous flow analysis techniques, which provide high-resolution volcanic aerosol records. These chemical records are of considerable value for identifying tephra horizons composed of glass shards and also provide the basis for a new high-precision ice-core timescale, thus allowing ages to be assigned to volcanic events. Tephra horizons of glass shards in the ice-cores play a critical role for (1) testing and building chronological frameworks for the ice-cores and other sequences, (2) synchronising disparate palaeoclimatic sequences and testing phase relationships, (3) atmospheric pathway reconstruction, and (4) verifying the source of volcanic aerosol peaks. Here we review the results of over 25 years of research into tephra horizons in the GRIP, GISP2 and NGRIP cores. We provide high-precision ages for horizons based on recently developed timescales and draw together geochemical characterisations of the products of 45 volcanic events deposited on the Greenland ice sheet and identified in the cores. There is a clear disparity between the number of volcanic aerosol peaks and the number of tephra horizons of glass shards identified thus far. However, this synthesis highlights the critical role of the Greenland ice-cores, firstly in the reconstruction of the history of Icelandic volcanic eruptions, and secondly the considerable value of some tephra horizons in facilitating the correlation of these key climatic archives to North Atlantic marine sequences. Other noteworthy issues include the potential of these cores to preserve tephra horizons from more distal volcanic sources such as North America, to resolve the debate surrounding the Thera eruption, and the observation that some tephra horizons are preserved within the ice without coeval volcanic aerosol signals.
Large regions of Yukon Territory and Alaska remained ice-free through glaciations of the late Cenozoic. This ice-free region hosts sedimentary archives that span the last 3 million years. Most of these records are preserved in windblown silt (loess) that has aggraded over multiple glacial-interglacial cycles and contain abundant distal volcanic ash (tephra) beds. Chester Bluff, on the Yukon River in Yukon Charley Rivers National Preserve, exposes a 10 m bedrock terrace overlain by fluvial gravels and outburst flood deposits. This sequence is mantled by loess up to 40 m thick and includes approximately 20 distinct tephra beds, almost exclusively with Type II characteristics, indicating a Wrangell Volcanic Field (WVF) source. Two Type I beds (Aleutian Arc source) that are present at Chester Bluff, the Old Crow tephra (140 000 +/- 10 000) and GI tephra (560 000 +/- 80 000), provide age control on the sequence. The loess at Chester Bluff is normally magnetized, indicating a Brunhes age (
Seafloor geology plays a major role in habitat formation and can be used to remotely identify key habitats for some commercially important fish species. We have used a combination of side-scan sonar mosaics, multibeam bathymetry, and backscatter data, and in situ observations and video from the submersible Delta to investigate marine benthic habitats in the Eastern Gulf of Alaska. The intent of this paper is to review the results of previous marine benthic habitat mapping efforts completed by us along the transform plate boundary of Alaska and to present new information that show how volcanic, plutonic, and glacial submarine geomorphology can be used to identify potentially important discrete habitat areas. Demersal shelf rockfish, a seven-species management complex of nearshore rockfish, including yelloweye rockfish (Sebastes ruberrimus), are found in rugged and highly rugose geomorphologic features. Eroded volcanic edifices, lava fields, and a pit crater, as well as a small shutterridge, deformed and differentially eroded sedimentary bedrock, and highly fractured and faulted plutonic rock outcrops are features that attract adult rockfish. Volcanic edifices that lie along the leaky (magma-conducting) Fairweather transform fault system intercept ocean currents, in turn producing upward eddies that bring nutrients to species residing on the features. We show that geologic processes such as fault deformation, volcanism, and glaciation are critical to the development of Essential Fish Habitats (EFH) for demersal shelf rockfish. Our work is the first attempt to determine a common geologic link between desperate commercial fishing areas in SE Alaska, USA, and to suggest how tectonic and glacial processes, including sea level rise and transgression, can be used to identify seafloor geologic characteristics as surrogates for marine groundfish habitats.
Theoretical approaches to computing gravitationally self-consistent sea-level changes in consequence of ice growth and ablation are comprised of two parts. The first is a mapping between variations in global sea level and changes in ocean height (required to define the surface load), and the second is a method for computing global sea-level change arising from an arbitrary surface loading. In Mitrovica & Milne (2003) (Paper I) we described a new, generalized mapping between sea-level change and ocean height that takes exact account of the evolution of shorelines associated with both transgression and regression cycles and time-dependent marine-based ice margins. The theory is valid for any earth model. In this paper we extend our previous work in three ways. First, we derive an efficient, iterative numerical algorithm for solving the generalized sea-level equation. Secondly, we consider a special case of the new sea-level theory involving spherically symmetric earth models. Specifically, we combine our iterative numerical formulation with viscoelastic Love number theory to derive an extended pseudo-spectral algorithm for solving the new sea-level equation. This algorithm represents an extension of earlier methods developed for the fixed-shoreline case to precisely incorporate shoreline migration processes. Finally, using this special case, we quantitatively assess errors incurred in previous efforts to extend the traditional (fixed shoreline) sea-level equation of Farrell & Clark (1976) to treat time-dependent shorelines. We find that the approximations adopted by Johnston (1993) and Milne (1998) to treat transgression and regression at shorelines introduce negligible (~1 per cent) error into predictions of post-glacial relative sea-level histories. In contrast, the errors associated with the Peltier (1994) sea-level equation are an order of magnitude larger, and comparable to the error incurred using the traditional sea-level theory. Furthermore, our numerical tests verify the high accuracy of the Milne (1998) approximation for treating the influence of grounded, marine-based ice.
During the last deglaciation, changes in freshwater fluxes were associated with changes in ice-sheet melting or calving rates that caused changes in rates of sea-level rise, as well as with routing of continental runoff that changed the location of freshwater flux relative to sites of deepwater formation without necessarily changing sea level. Modeling studies have established the sensitivity of the Atlantic meridional overturning circulation (AMOC) to increases in the freshwater budget at the sites of deepwater formation. A large fraction of the Northern Hemisphere ice sheets drained into the North Atlantic, so that establishing variations in the freshwater flux derived from these ice sheets is important for establishing their role in causing changes in the AMOC. Here we review the geologic evidence constraining the sources of sea-level rise and locations of freshwater discharge between the Last Glacial Maximum (LGM) and the Holocene. The LGM was terminated by an abrupt 10-15 m sea-level rise at ~19 ka, which was likely sourced from widespread retreat of Northern Hemisphere ice sheets in response to high-northern-latitude insolation forcing. Subsequent sea-level rise of ~15 m between 19 ka and 14.5 ka can be attributed to continued retreat of the Laurentide (LIS) and Scandinavian (SIS) ice sheets, with an additional freshwater forcing was delivered by Heinrich event 1 at ~17 ka. The source of the abrupt acceleration in sea-level rise ~14.5 ka (meltwater pulse 1a of 15-25 m sea-level rise in less than 700 years) remains widely debated. Geochemical, ice margin and far-field sea-level records all point to a small Northern Hemisphere ice-sheet contribution (e.g.,
Predictions of glaciation-induced changes in the Earth's rotation vector exhibit sensitivities to Earth structure that are unique within the suite of long-wavelength observables associated with glacial isostatic adjustment (henceforth GIA), and, despite nearly a quarter of a century of research, these sensitivities remain enigmatic. Previous predictions of present-day true polar wander (TPW) speed driven by GIA have indicated, for example, a strong sensitivity to variations in the thickness of the elastic lithosphere and the treatment (phase or chemical?) of the density discontinuity at 670-km depth. Nakada recently presented results that suggest that the predictions are also sensitive to the adopted rheology of the lithosphere; however, his results have introduced an intriguing paradox. In particular, predictions generated using a model with an extremely high-viscosity lithospheric lid do not converge to results for a purely elastic lithosphere of the same thickness. Mitrovica (as cited by Nakada) has suggested that the paradox originates from an inaccuracy in the traditional rotation theory (e.g. Wu & Peltier) associated with the treatment of the background equilibrium rotating form upon which any load- and rotation-induced perturbations are superimposed. We revisit these issues using a new treatment of the linearized Euler equations governing load-induced rotation perturbations on viscoelastic earth models. We demonstrate that our revised theory, in which the background form of the planet combines a hydrostatic component and an observationally inferred excess ellipticity, resolves the apparent paradox. Calculations using the revised theory indicate that earlier predictions based on earth models with purely elastic lithospheric lids are subject to large errors; indeed, previously noted sensitivities of TPW speed predictions to the thickness and rheology (elastic versus viscous) of the lithosphere largely disappear in the application of the new theory. Significant errors are also incurred by neglecting the stabilizing influence of the Earth's excess ellipticity. Finally, we demonstrate that the contribution from rotational feedback on predictions of present-day rates of change of the geoid (sea surface) and crustal velocities are overestimated by the traditional rotation theory, and this has implications for analyses of ongoing satellite (e.g. GRACE) missions and geodetic GPS surveys.
Modern analyses of sea level changes due to glacial isostatic adjustment (GIA) are based on the classic sea level equation derived by Farrell & Clark (1976, Geophys. J.R. astr. Soc., 46, 647-667). The connection between global sea level variations and changes to ocean height that is assumed within this equation breaks down in the presence of a time-varying shoreline geometry. We present a generalized sea level equation that overcomes this difficulty. We also derive analytic expressions for, and present schematic illustrations of, the error in the ocean height change over finite time intervals introduced in published efforts to incorporate shoreline evolution into the theory of GIA-induced sea level change. This comparison includes studies of shoreline migration due to either local sea level changes or the growth and ablation of marine-based ice. We conclude that the theories applied by Johnston (1993, Geophys. J. Int., 114, 615-634), Milne (1998, PhD thesis, University of Toronto, Toronto) and co-workers are more accurate than the procedure advocated by Peltier (1994, Science, 265, 195-201 1998a, Geophys. Res. Lett., 25, 3955-3958 1998b, Rev. Geophys., 114, 615-634), although an improvement in the latter has recently been reported (Peltier & Drummond (2002, Geophys. Res. Lett., 29, 10.1029/2001GL014273). Our generalized theory is valid for any Earth model. In a companion paper we derive the equations necessary to treat the special case of a spherically symmetric, linear viscoelastic and rotating Earth, and we quantify errors associated with previous work.
The recently collected Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project ice cores from Summit, Greenland, provide lengthy and highly resolved records of the deposition of both the aerosol (H2SO4) and silicate (tephra) components of past volcanism. Both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism-climate system. The continuous time series of volcanic SO42- for the last 110,000 years show a strong relationship between periods of increased volcanism and periods of climatic change. The greatest number of volcanic SO42- signals, many of very high magnitude, occur during and after the final stages of deglaciation (6000-17,000 years ago), possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins (sea level change). The increase in the number of volcanic SO42- signals at 27,000-36,000 and 79,000-85,000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation, respectively. A comparison of the electrical conductivity of the GISP2 core with that of the volcanic SO42- record for the Holocene indicates that only about half of the larger volcanic signals are coincident in the two records. Other volcanic acids besides H2SO4 and other SO42- sources can complicate the comparisons, although the threshold level picked to make such comparisons is especially critical. Tephra has been found in both cores with a composition similar to that originating from the Vatnaöldur eruption that produced the Settlement Layer in Iceland (mid-A.D. 870s), from the Icelandic eruption that produced the Saksunarvatn ash (~10,300 years ago), and from the Icelandic eruption(s) that produced the Z2 ash zone in North Atlantic marine cores (~52,700 years ago). The presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras. The presence of both rhyolitic and basaltic shards in the Z2 ash in the GISP2 core and the composition of the basaltic grains lend support to multiple Icelandic sources (Torfajökull area and Katla) for the Z2 layer. Deposition of the Z2 layer occurs at the beginning of a stadial event, further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions.
This contribution summarizes and brings up to date the recommendations made by the IUGS Subcommission on the Systematics of
Igneous Rocks for the classification of volcanic rocks when modal analyses are lacking. The classification is on a non-genetic
basis using the total alkali-silica (TAS) diagram, and is as nearly consistent as possible with the QAPF modal classification.
The diagram is divided into 15 fields, two of which contain two root names which are separated according to other chemical
criteria, giving the following 17 root names: basalt, basaltic andesite, andesite, dacite, rhyolite, trachybasalt, basaltic
trachyandesite, trachyandesite, trachyte, trachydacite, picrobasalt, basanite, tephrite, phonotephrite, tephriphonolite, phonolite
and foidite. Using Na-K criteria, trachybasalt may be further divided into the sub-root names hawaiite and potassic trachybasalt,
basaltic trachyandesite into the sub-root names mugearite and shoshonite, and trachyandesite into the sub-root names benmoreite
and latite.
Pleistocene basalt of the Mount Edgecumbe volcanic field (MEF) is subdivided into a plagioclase type and an olivine type. Olivine basalt crops out farther inboard from the nearby Fairweather transform than plagioclase basalt. Th/La ratios of plagioclase basalt are similar to those of mid-ocean-ridge basalt (MORB), whereas those of olivine basalt are of continental affinity. The olivine basalt has higher 87Sr/86Sr ratios than the plagioclase basalt.We model rare earth element (REE) contents of the olivine basalt, which resemble those of transitional MORB, by 10–15% partial melting of fertile spinel–plagioclase lherzolite followed by removal of 8–13% olivine. Normative mineralogy indicates melting in the spinel stability field. REE contents of an undersaturated basalt (sample 5L005) resemble those of Mauna Loa tholeiite and are modelled by 5–10% partial melting of fertile garnet lherzolite followed by 10% olivine removal. Plagioclase basalt resembles sample 5L005 in REE contents but is lower in other incompatible-element contents and 87Sr/86Sr ratios. Plagioclase basalt either originated in depleted garnet lherzolite or is a mixture of sample 5L005 and normal MORB; complex zoning of plagioclase and colinear Sc and Th contents are consistent with magma mixing.We conclude that olivine basalt originated in subcontinental spinel lherzolite and that plagioclase basalt may have originated in suboceanic lithosphere of the Pacific plate. Lithospheric melting seemingly requires vertical flow of mantle material, although there is no direct evidence at the MEF for crustal extension that might provide a mechanism for mantle advection. In any case, most MEF magmas are subalkaline because of moderately high degrees of partial melting at shallow depth.
Acidity profiles along well dated Greenland ice cores reveal large
volcanic eruptions in the Northern Hemisphere during the past 10,000 yr.
Comparison with a temperature index shows that clustered eruptions have
a considerable cooling effect on climate, which further complicates
climatic predictions.
Volcanic eruptions are an important natural cause of climate change on many timescales. A new capability to predict the climatic response to a large tropical eruption for the succeeding 2 years will prove valuable to society. In addition, to detect and attribute anthropogenic influences on climate, including effects of greenhouse gases, aerosols, and ozone-depleting chemicals, it is crucial to quantify the natural fluctuations so as to separate them from anthropogenic fluctuations in the climate record. Studying the responses of climate to volcanic eruptions also helps us to better understand important radiative and dynamical processes that respond in the climate system to both natural and anthropogenic forcings. Furthermore, modeling the effects of volcanic eruptions helps us to improve climate models that are needed to study anthropogenic effects. Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e-folding residence time of about 1 year. Large ash particles fall out much quicker. The radiative and chemical effects of this aerosol cloud produce responses in the climate system. By scattering some solar radiation back to space, the aerosols cool the surface, but by absorbing both solar and terrestrial radiation, the aerosol layer heats the stratosphere. For a tropical eruption this heating is larger in the tropics than in the high latitudes, producing an enhanced pole-to-equator temperature gradient, especially in winter. In the Northern Hemisphere winter this enhanced gradient produces a stronger polar vortex, and this stronger jet stream produces a characteristic stationary wave pattern of tropospheric circulation, resulting in winter warming of Northern Hemisphere continents. This indirect advective effect on temperature is stronger than the radiative cooling effect that dominates at lower latitudes and in the summer. The volcanic aerosols also serve as surfaces for heterogeneous chemical reactions that destroy stratospheric ozone, which lowers ultraviolet absorption and reduces the radiative heating in the lower stratosphere, but the net effect is still heating. Because this chemical effect depends on the presence of anthropogenic chlorine, it has only become important in recent decades. For a few days after an eruption the amplitude of the diurnal cycle of surface air temperature is reduced under the cloud. On a much longer timescale, volcanic effects played a large role in interdecadal climate change of the Little Ice Age. There is no perfect index of past volcanism, but more ice cores from Greenland and Antarctica will improve the record. There is no evidence that volcanic eruptions produce El Nino events, but the climatic effects of El Nino and volcanic eruptions must be separated to understand the climatic response to each.
Chester Bluff (CB), in Yukon Charley Rivers National Preserve (YCNP), Alaska, contains an extensive middle to late Pleistocene tephra record within thick loess deposited on a terrace. The regionally prominent Old Crow (OC) tephra (140710ka), GI tephra (560780ka) of Fairbanks, the Preido Hill (PrH) tephra of the Klondike, and VT tephra (77.874.1ka) of both the Klondike and Fairbanks were found at CB. The presence of these tephra beds will aid in correlating disparate paleoenvironmental records across eastern Beringia. There are 15 new tephra beds; 11 from the Wrangell volcanic field (WVF) and/or Hayes volcano, one from the Aleutian-Arc Alaska Peninsula (AAAP) and three unclassified beds. CB is normally magnetized, indicating the entire sequence is of Bruhnes age (o780 ka). Also present are at least two interglacials, one late–Middle Pleistocene, the other early–Middle Pleistocene. At least five more organic horizons representing interstadials or interglacials are present. Collectively, sediments at CB span most of the middle to late Pleistocene (i.e. 780 to o77.874.1 ka). The bluffs represent the most extensive middle-to-late Pleistocene sedimentary record yet established for Yukon or Alaska.
The tephrochronological record of the 1400–1640 m depth (∼10 000–16 000 calendar ice core years before present) of the NGRIP ice core has been established by particle screening of selected samples. Ash was identified in 20 samples. Correlation with ice, marine and terrestrial records from volcanic source regions in the northern hemisphere positively identifies the Saksunarvatn Ash and the Vedde Ash (Ash Zone 1). Major element chemistry of the remaining identified ash layers mainly points towards an Icelandic origin. This tephrochronological record provides new important marker horizons for correlating the timing of the climatic changes associated with the Last Glacial Termination within the North Atlantic region, as well as outlining more details concerning the frequency and composition of volcanic eruptions occurring at this deglaciation. Copyright © 2005 John Wiley & Sons, Ltd.
We present a complete derivation of the equation governing long-term sea-level variations on a spherically symmetric, self-gravitating, Maxwell viscoelastic planet. This new ‘sea-level equation’ extends earlier work by incorporating, in a gravitationally self-consistent manner, both a time-dependent ocean–continent geometry and the influence of contemporaneous perturbations to the rotation vector of the planet. We also outline an efficient, pseudo-spectral, numerical methodology for the solution of this equation, and present a variety of predictions, based on a suite of earth models, of relative sea level (RSL) variations due to glacial isostatic adjustment (GIA). These results show that the contribution to the predicted RSL signal from GIA-induced perturbations to the rotation vector can reach 7–8 m over the postglacial period in geographic regions where the rotationally induced signal is a maximum. This result is sensitive to variations in the adopted lower-mantle viscosity and is relatively insensitive to variations in the adopted lithospheric thickness. We also show that the rotationally induced component of RSL change is sufficient to influence previous estimates of Late Holocene melting eventsand ongoing sea-level change due to GIA which were based on a RSL theory for a non-rotating Earth. In particular, estimates of Antarctic melting over the last 5 kyr, based on the amplitude of sea-level highstands from the Australian region, may require an adjustment downwards of the order of 0.5 m of equivalent sea-level rise. Furthermore, present-day rates of sea-level change are perturbed by as much as ∼0.2 mm yr−1 by the rotational component of sea-level change, and this has implications for GIA corrections of the global tide gauge record. Over the period from the last glacial maximum to the present, we predict a distinctly non-monotonic variation in the rotation-induced component of RSL. This is in agreement with our previouspreliminary study (Milne & Mitrovica 1996), but contrasts significantly with predictions presented by Han & Wahr (1989) and Bills & James (1996). We demonstrate that the disagreement arises as a consequence of approximations adopted in the latter studies. We furthermore refute an assertion by Bills & James (1996) that previously published constraints on mantle viscosity and ice-sheet histories which did not incorporate a rotation-induced RSL component are ‘largely invalidated’ by this omission.