No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The 1500-year climate oscillation in the midlatitude North Pacific during the Holocene
Abstract
Suborbital climate variability during the last glacial period was characterized by a periodicity of 1,470 years, but the expression and spatial distribution of the ~1,500-year oscillation during interglacials are not clear. Here we generated a multi-decade-resolution record of alkenone sea-surface temperatures (summer SST) off central Japan in the northwestern Pacific during the Holocene. The SST record showed centennial and millennial variability with an amplitude of ~1°C through the entire Holocene. Spectral analysis shows that SST variation was expressed in 1560-, 880- and 620-year periods, and the ~1,500 year periodicity was the most pronounced. The SST minima correlate with reduced North Atlantic Deep Water formation events (Bond events) and with SST maxima at the California margin. These findings indicate that the mean latitude of the Northern Westerly and the intensity of the North Pacific High varied through a 1,500-year cycle, and that a climatic link existed between the mid-latitude North Pacific and the high-latitude North Atlantic. The regular pacing at 1,500- year intervals through both the Holocene and the last glacial suggests that the oscillation was a response to external forcing rather than an internal oscillation in the climate system.
Supplementary resource (1)
Data
January 2009
... As regards the role of climate during the Late Holocene, the Pyrenees has been under the influence of regional variability expressed as millennial-scale oscillations, known as Bond events or cycles [12][13][14][15][16][17][18]. Such climate variability could have resulted in cool and wet winters during Bond events 3 to 0 (4.2, 2.7, 1.2 cal kyr BP, and during the Little Ice Age) in the The outcropping geological materials of the area constitute two major entities: the substratum, consisting of Paleozoic materials ranging in age from Cambro-Ordovician to Devonian periods with rocks of variable composition such as amphibole quartz-gabbro, quartz-diorites, and fine-grained tonalites with amphibole, biotite, and accessory quantities of pyroxenes, and the covering deposits from the Pleistocene and the Holocene (Quaternary). ...
... Different studies with paleoenvironmental and archaeological data have improved knowledge of the evolution of the landscape on the southern slopes of the Pyrenees [2,4,5,7,[15][16][17][18]38,39]. This research in Clots de Rialba is the first paleoenvironmental study in this valley contributing to a deeper understanding of this knowledge. ...
... A visual representation of the age-depth model is presented in Figure 4. nearby areas have shown the growing importance of the agro-livestock system since the Neolithic period, and especially during the Bronze and Roman periods [14,29,37]. Different studies with paleoenvironmental and archaeological data have improved knowledge of the evolution of the landscape on the southern slopes of the Pyrenees [2,4,5,7,[15][16][17][18]38,39]. This research in Clots de Rialba is the first paleoenvironmental study in this valley contributing to a deeper understanding of this knowledge. ...
Vegetation landscape dynamics are derived from the relationships established between anthropic activities and climate conditions over time. Paleoenvironmental research in the Pyrenees range (north-eastern Iberian Peninsula) has revealed what these dynamics were like in some regions during the Holocene. However, some fields of biogeography still present questions that need to be addressed, such as the patterns of Fagus sylvatica and Abies alba and the importance of the fire regime during the Meghalayan (late Holocene). We present a multiproxy study performed in a sedimentary record from the Clots de Rialba peat bog, located at 2093 m a. s. l. (Lleida, southern slope of the Pyrenees mountain range), that covers the last c. 3500 years. Analyses were performed on the organic matter content, pollen, non-pollen palynomorphs, and sedimentary charcoals larger than 150 μm. The palynological spectra revealed a maximum extension of Abies alba at about 3500 cal yr BP in the Bronze Age, while Fagus sylvatica showed its maximum extent between 3300 and 2800 cal yr BP. A dominance of Pinus was detected throughout the studied period. Other taxa such as cereals, herbaceous plants, aquatic plants, and coprophilous fungi have also been discussed to identify anthropic pressure and climate pulses. In addition, the study of sedimentary charcoals reveals the main forest fire episodes and their recurrences, some of them linked to anthropogenic activities and/or climate variations. These anthropogenic activities would include the use of opening and maintaining forest fires in deforestation in order to obtain pastures and spaces dedicated to cereal agriculture and the appearance of some taxa linked to or introduced by human communities.
... This millennial oscillation, to our knowledge, has not been documented previously in biotic lake proxies in the region, although a 1400-year cycle was reported from lake records and peatland initiation dates in adjacent interior western Canada (Campbell et al. 2000). (Berger 1978); b speleothem stable carbon isotope data from Oregon Caves National Monument (Ersek et al. 2012); c Moss Lake diatom-based convective mixing proxy (detrended D:A ratio, this study); d North Pacific sea surface temperature anomalies, off Japan (residuals from 3rd order polynomial fitting) (Isono et al. 2009); e comparison of the Moss Lake wavelet power at period 1375 year (blue dotted line, this study) and long-term peat absorption at Lynch's Crater, Northern Australia (pink line, Turney et al. 2004); f sediment record of flooding activity at Lake Pallcacocha, Ecuador (Moy et al. 2002); g TSI data (total solar irradiance) (Steinhilber et al. 2012). Bold lines in b, c, d, f, g show a consistent lowpass filtering to highlight millennial-scale dynamics in the records. ...
... Based on presentday teleconnections, colder, wetter, windier episodes in the PNW may have been associated with weaker or less frequent El Niño events. Considering these teleconnections on a much larger spatial scale, we also note a good match between the 1500-year Holocene fluctuations reported in mid-latitude North Pacific sea surface temperatures (Isono et al. 2009) and the PNW records ( Fig. 8b-d). This match further supports a wider pattern of millennial dynamics linked to PDOlike variability in the coupled Pacific Ocean-atmosphere system. ...
... This match further supports a wider pattern of millennial dynamics linked to PDOlike variability in the coupled Pacific Ocean-atmosphere system. Cooling in the high-resolution MD01-2421 record off Japan, in opposition to warming on the Californian Pacific margin, reflects variation in the North Pacific sub-tropical gyre system (Isono et al. 2009;Barron et al. 2003). SST cooling anomalies at this location are linked to weakening of the Kuroshio Extension jet associated with a weaker subarctic gyre or stronger subtropical gyre (Isono et al. 2009), which in turn may be associated with PDOlike dynamics, as well as the North Pacific Gyre Oscillation (NPGO). ...
A diatom record from Moss Lake, Washington, USA spans the last 14,500 cal year and revealed Holocene climate change in the Pacific Northwest (PNW), including evidence for periodicities related to ocean-atmosphere teleconnections and/or variations in solar output. Three main climate phases were identified: (i) Late Pleistocene to early Greenlandian (until 10,800 cal year BP, spanning GI-1, GS-1), with a cold climate and low diatom abundance; (ii) early Greenlandian to Northgrippian (10,800–7500 cal year BP), shifting to a warmer climate; and (iii) late Northgrippian and Meghalayan from 7500 cal year BP onwards, with a cooler, moist climate. These climate shifts are in good agreement with the pollen record from the same core and other regional studies. Fluctuations in Discostella pseudostelligera and Aulacoseira taxa suggest climate cycles of different frequency and amplitude throughout the record. Spectral and wavelet analyses revealed periodicities of approximately 1400 and 400–500 years. We interpret the ~ 1400-year and ~ 400–500-year cycles to reflect alternating periods of enhanced (and reduced) convective mixing in the water column, associated with increased (and decreased) storms, resulting from ocean–atmosphere teleconnections in the wider Pacific region. The ~ 1400-year periodicity is evident throughout the Late Pleistocene and late Northgrippian/Meghalayan, reflecting high-amplitude millennial shifts from periods of stable thermal stratification of the water column (weak wind intensity) to periods of convective mixing (high wind intensity). The millennial cycle diminishes during the Greenlandian, in association with the boreal summer insolation maximum, consistent with suppression of ENSO-like dynamics by enhanced trade winds. Ocean–atmosphere teleconnection suppression is recorded throughout the PNW, but there is a time discrepancy with other records, some that reveal suppression during the Greenlandian and others during the Northgrippian, suggesting endogenic processes may also modulate the Moss Lake diatom record. The large amplitude of millennial variability indicated by the lake data suggests that regional climate in the PNW was characterised over the longer term by shifting influences of ocean–atmosphere dynamics and that an improved understanding of the external forcing is necessary for understanding past and future climate conditions in western North America.
... The details of radiocarbon dating and cellulose analysis are described in Text S2 in the Supporting Information S1. Map showing the locations of the study site (MHWL) and the reference sites, that is, BKB-2 (Sakurai et al., 2021), MD01-2,421 (Isono et al., 2009), PC-6 (Minoshima et al., 2007, KH-84-3-9, KH-84-3-33, KH-86-2-9, D-GC-6 (Koizumi et al., 2006), and HO76-P1 (Shimada et al., 2004), as well as the mean positions of the summer (June-August) westerly jet and the ranges of variation for the 30 years from 1988 to 2017 (yellow shade) of the summer westerlies, the Kuroshio, Kuroshio Extension, Oyashio, Tsushima Warm Current (TWC), Soya Warm Current (SWC), and Tsugaru Warm Current (TGWC). The letter "T" indicates the town of Teshio. ...
... The correspondence between cellulose δ 18 O and the indices of the TWC was poor before 2,300 years BP (Figure 3e), suggesting that there was another factor determining cellulose δ 18 O. The variations of Sphagnum δ 18 O and Δδ 18 O vp-sp in the MHWL sites before 2,300 years BP were consistent with SST in the Kuroshio-Oyashio transition area (Figure 3; MD01-2,421 by Isono et al., 2009). The Pacific SST at MD01-2,421 is a good indicator of the strength of the Kuroshio and its extension, which form part of the subtropical gyre circulation driven by the development of the North Pacific High (NPH; Yamamoto et al., 2004). ...
... On the other hand, the spatial distributions of the Zoku-Jomon, Satsumon, and Ainu cultures (inland cultures) stayed in Hokkaido Island, although the northern and southern margins shifted latitudinally (Figure 4). The (Isono et al., 2009) and the cellulose δ 18 O values at sites MHWL and BKB-2. We assumed that the BKB-2 value reflected the WJ, while the MHWL value reflected both the WJ and the TWC. ...
In Hokkaido, northern Japan, densely populated societies of hunter‐fisher‐gatherer cultures persisted over the Holocene until the 19th century. We used the cellulose δ¹⁸O values of Sphagnum and vascular plants in peat cores from Rishiri Island to understand paleoclimate changes in Hokkaido over the past 4,400 years and discuss the impacts of climate changes on the development of the cultures. The cellulose δ¹⁸O values showed multi‐centennial and millennial variations, reflecting the intensity of the Tsushima Warm Current and the summer position of the westerly jet. The marine hunter‐fisher cultures responded to changes in the strength of Tsushima Warm Current and coastal primary production. In contrast, the inland cultures responded to changes in the latitudinal position of the summer westerlies. This implies that human societies of different lifestyles responded differently to climate changes.
... The Pacific SST at the offshore of central Japan is a good indicator of the strength of the Kuroshio and its extension, which form part of the subtropical gyre circulation. The SST at Site 01-2421 off central Japan (Isono et al., 2009) was elevated around 300, 800, 1000, 1200, and 1400 CE and lower around 500, 1600, and 1800-1900 CE (Figure 11). The SST at Site PC-6 exhibited a similar changing pattern to that of MD01-2421, with some differences that were likely associated with the intrusion of the Tsugaru Warm Current (Figure 11; Minoshima et al., 2007). ...
... The SST record at Site 01-2421 off central Japan shows a precession 23,000-and 1,500-year cycles (Isono et al., 2009;Yamamoto et al., 2004). The SST record is characterized by cooling around 400 and 1800 years CE ( (Isono et al., 2009) andPC-6 (Minoshima et al., 2007) in the Kuroshio-Oyashio transition zone. ...
... The SST record at Site 01-2421 off central Japan shows a precession 23,000-and 1,500-year cycles (Isono et al., 2009;Yamamoto et al., 2004). The SST record is characterized by cooling around 400 and 1800 years CE ( (Isono et al., 2009) andPC-6 (Minoshima et al., 2007) in the Kuroshio-Oyashio transition zone. Vertical bars indicate a 1σ interval in sample value. ...
The cellulose δ¹⁸O of plant tissues in peat is a potential climate proxy. However, understanding what is driving the shifts in δ¹⁸O of cellulose is required for its application. Here, we analyzed the δ¹⁸O values of Sphagnum and vascular plant cellulose, as well as the δ¹⁸O and δD values of pore water, in a 4‐m‐long peat core from the Bekanbeushi ombrotrophic bog to understand paleoclimatic changes in northern Japan over the past 2,000 years. The cellulose δ¹⁸O values of Sphagnum were lower than those of vascular plant tissues, although both draw water from the same layer. Whereas the cellulose δ¹⁸O values of Sphagnum more directly reflect those of precipitation, those of vascular plants become enriched through transpiration. Thus, the difference between vascular plants and Sphagnum (Δδ¹⁸Ovp–sp) is a potential proxy for relative humidity. Cellulose δ¹⁸O of Sphagnum revealed centennial variations with maxima around 800, 1300, and 1500 CE and minima around 500, 1000, 1700, and 1900 CE. The Δδ¹⁸Ovp–sp was inversely correlated with Sphagnum cellulose δ¹⁸O, indicating that the axis of summer westerlies was more frequently located to the north and the climate was moist in the former periods, whereas the axis of summer westerlies was generally located to the south and the climate was dry in the latter periods. These results suggest a warm and moist climate during the former periods due to frequent rainy summers driven by strong East Asian summer monsoon activity, and the opposite conditions in the latter periods.
... The summer climate of northern Japan is influenced by the summer position of the westerly winds and the strength of the Tsushima Warm Current (TWC). The position of the westerly winds is linked to the oceanic subarctic boundary between the subtropical Kuroshio and subarctic Oyashio currents in the Pacific (Figure 1) (e.g., Yamamoto et al., 2004;Yamamoto et al., 2005;Isono et al., 2009;Yamamoto, 2009). Yamamoto et al. (2005) and Isono et al. (2009) identified the southern summer position of the Kuroshio-Oyashio transition (KOT) in the Oldest Dryas and Younger Dryas periods due to the weaker North Pacific High, a northward shift of the KOT at the end of the Younger Dryas period, the northernmost position at 8 ka and the gradual southward shift during the Middle and Late Holocene. ...
... The position of the westerly winds is linked to the oceanic subarctic boundary between the subtropical Kuroshio and subarctic Oyashio currents in the Pacific (Figure 1) (e.g., Yamamoto et al., 2004;Yamamoto et al., 2005;Isono et al., 2009;Yamamoto, 2009). Yamamoto et al. (2005) and Isono et al. (2009) identified the southern summer position of the Kuroshio-Oyashio transition (KOT) in the Oldest Dryas and Younger Dryas periods due to the weaker North Pacific High, a northward shift of the KOT at the end of the Younger Dryas period, the northernmost position at 8 ka and the gradual southward shift during the Middle and Late Holocene. The TWC flows northwards as a branch of the Kuroshio Current along the eastern margin of the Sea of Japan (Figure 1). ...
... When the westerly jet is located north of the study site, southerly winds bring moisture from the south, inducing more precipitation at the study site ( Figure 2). Thus, a FIGURE 6 | Changes in the glycerol dialkyl glycerol tetraether-based mean annual temperatures (MATs) obtained using different calibrations (averages and 1σ range), U K 37 '-based sea surface temperature (SST) at sites MD01-2421 (Yamamoto et al., 2004;Yamamoto et al., 2005;Isono et al., 2009;Yamamoto, 2009) and PC-6 (Minoshima et al., 2007) in the Kuroshio-Oyashio transition zone, temperature index of diatoms (Td') and relative abundance of Fragilariopsis doliola, and Tsushima Warm Current species in cores KH-84-3-9, KH-84-3-33, KH-86-2-9, and D-GC-6 (Koizumi et al., 2006) over the last 17 ka. northward shift in the position of the westerly jet increases the δD of precipitated water, and the associated higher fraction of summer-to-annual precipitation further increases the δD. ...
The summer climate of northern Japan since the last glacial period has likely been determined by atmospheric and oceanic dynamics, such as changes in the North Pacific High, the position of the westerlies, the Kuroshio Current, the Tsushima Warm Current (TWC), and the East Asian summer monsoon. However, it is unclear which factor has been most important. In this study, we analyzed leaf wax δ¹³C and δD and glycerol dialkyl glycerol tetraethers (GDGTs) in sediments from Lake Kushu, Rebun Island, northern Japan, and discuss changes in climate over the past 17,000 years. The GDGT-based temperature, the averaged chain length, δ¹³C and δD of long-chain n-fatty acids indicated that the climate was cold during the Oldest Dryas period ∼16 ka and warm in the early Middle Holocene from ∼9 to 6 ka. This climate change is consistent with the sea surface temperature in the Kuroshio–Oyashio transition, but inconsistent with changes in the TWC in the Sea of Japan. The results imply that the summer climate of northern Japan was controlled mainly by changes in the development of the North Pacific High via changes in the position of the westerly jet and East Asian summer monsoon rainfall, whereas the influence of the TWC was limited over a millennial timescale.
... Temperature reconstructions of intermediate waters (500-600 m water depth) in the WPWP have revealed a cooling of 2.1 ± 0.4°C during the mid-to-late Holocene (Rosenthal et al., 2013). The cooling of the intermediate waters is accompanied by a cooling of the WPWP thermocline (Dang et al., 2020) and surface water temperatures (Linsley et al., 2010), a contraction of the WPWP (Moffa-Sanchez et al., 2019) and a southward shift of Kuroshio extension (Isono et al., 2009). The concordant decrease of the BWTs in the southern YS and intermediate/thermocline water temperatures in the WPWP might imply that the temperature signal of the low-latitude source waters was transmitted by the Kuroshio Current, which flows northward along the western side of the Okinawa Trough and carries large amounts of heat (and temperature signal) from the tropics to mid-latitudes (Wu et al., 2012 and references therein), into the YS (Figures 2a-2d) via its intermediate/thermocline waters. ...
... (d) Alkenone-derived sea surface temperature (U k' 37 -SST) estimates from site ODP 1202B (Ruan et al., 2015). (e) Alkenone-derived sea surface temperature (U k' 37 -SST) estimates from site MD01-2421 which is located in the extension of the Kuroshio Current (Isono et al., 2009). (f) δ 18 O N. incompta from site SK-2 off Japan (Sagawa et al., 2014). ...
... The ∼700-800 and ∼1,500 year spectral signals have been found in both the southern YS BWT and the WPWP intermediate water temperature and have also been observed in other Holocene records from the western Pacific (Hao et al., 2017;Isono et al., 2009;Jian et al., 2000;Khider et al., 2014;J. Park, 2017;Sagawa et al., 2014), and the Atlantic (Debret et al., 2009 and references therein). ...
Plain Language Summary
The Yellow Sea (YS) is a semi‐closed marginal sea located in the northwestern Pacific Ocean. During the winter season, the Yellow Sea Warm Current (YSWC) is driven by northwesterly winds, flowing into the southern YS along the west flank of the central trough. The YSWC, a continuation of the Kuroshio Current, brings warm equatorial Pacific water into the YS, leading to milder winters in the surrounding coastal cities compared with other cities on the same latitude in China. The YSWC is sensitive to changes in ocean‐atmosphere dynamics. However, its evolution during the Holocene is not well understood. We reconstruct the winter season temperature changes of the YSWC during the last 8.8 kyr. We found warm temperatures during the mid‐Holocene (8.8‐5 ka) and a gradual cooling trend over the last 5 kyr, which coincides with subsurface water temperature changes in the Western Pacific Warm Pool (WPWP). We suggest that the tropical subsurface water temperature changes of the WPWP are most likely transmitted via the Kuroshio Current into the YS. Our results shed new light on our understanding of the role played by the WPWP water masses in regulating subtropical ocean dynamics and climate during the mid‐to‐late Holocene.
... In general, precipitation increases (decreases) in summer (winter) (Liu, Gu, et al., 2019;Li et al., 2020), while ocean currents are strengthened (suppressed) by monsoons that flow in the same (converse) direction; for example, the northeast-directed Kuroshio Current intensifies (weakens) due to the northward summer (southward winter) monsoons and dominates the current circulation pattern in the western and northwestern Pacific (Chen & Sheu, 2006;Hu et al., 2015;Wang & Oey, 2016;Wu et al., 2003). Paleoclimate and paleocurrent studies of the Holocene suggest that climate changes (e.g., Asian monsoon and El Niño activity) have generated obvious multicentennial-millennial variations in regional precipitation (Li et al., 2017;Xie et al., 2013;Zhu et al., 2017) and Kuroshio Current intensity (Isono et al., 2009;Ujiie & Ujiie, 1999;Zheng et al., 2016). Based on these observations and paleoclimate studies, we hypothesize that the shelf mud supply, transport, and sedimentation have responded sensitively to climate-driven evolutions of precipitation in river basins and ocean currents not only in modern times but also during the Holocene. ...
... The spatial distributions of the Taiwan River-dominated (yellow areas) and Changjiang River-dominated (green areas) Holocene mud are shown (Liu et al., 2007;Liu et al., 2008) as well as the locations of sediment cores (circles) and ocean currents (arrows). (c) Holocene variations in the Kuroshio Current recorded by the detrended U K 0 37 -derived sea surface temperature (DSST) (Isono et al., 2009) and ΔSST between the north and south based on planktonic foraminiferal data (Jian et al., 2000). Because appropriate proxies are not available to reconstruct the Holocene Kuroshio onshore intrusion current variation, the Kuroshio Current based on the modern antiphase relationship of intensities between Kuroshio onshore intrusion current and Kuroshio Current is used. ...
... This similarity indicates that an ocean current shear front has occurred over the last 8.0 ka. Nevertheless, recent oceanographic and paleoclimatic studies revealed that climate oscillations (e.g., Asian monsoon and El Niño activity) generated centennial variations in the intensities of ocean currents during the mid-late Holocene (Hu et al., 2015;Isono et al., 2009;Zheng et al., 2016). Because the velocity shear between different ocean currents due to different intensities is vital in driving the formation of shear fronts (Liu, Qiao, et al., 2018;Wang et al., 2007), we infer that the current shear fronts could migrate frequently in the north-south direction because of climate-driven changes in the relative intensities between the Min-Zhe longshore current and Kuroshio onshore intrusion current during different centennial phases of the Holocene. ...
Shelf mud is an important sink for fluvial sediment, and it is sensitive to variations in river discharge and ocean circulation, which are significantly influenced by climate change. However, the evolution of shelf mud in response to climate change during the Holocene is poorly understood. Here, we present high‐resolution sedimentary records of heavy minerals and mass accumulation rates (MARs) from the East China Sea shelf to study the response mechanisms of the Holocene shelf mud supply, transport, and sedimentation to the climate‐driven variations in fluvial discharge and ocean currents. The results indicate that the shelf mud primarily originates from the Changjiang (Yangtze) River and has been mainly transported by wind‐driven longshore currents in suspension since approximately 8.0 ka. A comparison of the MARs with several shelf mud sedimentation‐rate records and climate changes during the Holocene on millennial timescales showed that strong (weak) precipitation in the river basin, which is positively linked with Asian summer monsoon and El Niño‐driven storms, could intensify (weaken) the fluvial sediment supply, thereby increasing (decreasing) the shelf mud deposition flux. On multicentennial timescales, changes in the relative intensities of different ocean currents due to climate oscillations during the Holocene could generate frequent migrations of the current shear front (a hydrodynamic barrier), which has trapped an abundance of suspended materials on the shoreward side and resulted in rapid mud sedimentation (~2.3 g/cm²/year) at different sites during different periods. Therefore, our study highlights that the Holocene shelf mud evolution responds sensitively to climate changes on different timescales.
... e The Intertropical Convergence Zone (ITCZ) record (Haug et al. 2001). f The western Pacific SST (Isono et al. 2009). g 65° N July insolation (Berger and Loutre 1991) decreased events at 3900-3500 years BP, 1700-1300 years BP, and 500-0 years BP (Fig. 6d). ...
... The red vectors indicate the anticyclonic anomaly generated over northwestern Pacific Ocean and northern Asia. The red and blue circle indicates our study site (BLC Lake) and the location of the reconstructed western Pacific SST mentioned in the text, respectively (Isono et al. 2009) 1 3 northern Asia (Fig. 7c). Again, the distinct anti-cyclonic anomaly transports more water vapor from western Pacific Ocean, which induces more precipitation in the southwestern Loess Plateau through the EASM circulation . ...
... Furthermore, changes in the western Pacific SST can also influence the intensity of monsoon circulation and thus monsoon rainfall in the southwestern Loess Plateau by increasing evaporation and moisture availability (Wang et al. 2000;Isono et al. 2009). Instrumental data and model simulations have indicated that increased SST in the western Pacific Ocean would enhance the upper convection above the sea surface, which would provide more moisture transports and result in more precipitation in East Asian monsoon region (Huang and Li 1987;Soman and Slingo 1997;Zhou and Yu 2005;Cai et al. 2010). ...
Numerous paleoclimate records on reconstructed monsoon precipitation isotopes (δDp and δ18Op) have been published to infer past hydroclimate changes in Asian monsoon region. However, there are still debates on whether or not these reconstructed δDp or δ18Op can represent changes of monsoon precipitation. In this study, we report a ~ 5000 year record of leafwax hydrogen isotope (δDwax) from a 6.67-m-long sediment core collected in Beilianchi (BLC) Lake in the southwestern Chinese Loess Plateau. Based on analyses of the instrumental precipitation isotopes, precipitation amounts, and moisture sources, we find that δDp in the southwestern Chinese Loess Plateau shows distinct negative correlation with amounts of summer (from April to September) monsoon precipitation at inter-annual scales. This is further supported by the observed negative relation between precipitation amounts and regional lake-sediments and speleothems inferred δDp (or δ18Op) values at decadal scales over the past 60 years. Therefore, our reconstructed ~ 35-year resolution monsoon precipitation, inferred from δDwax, reveals a long-term decrease since the mid-Holocene. Superimposed on this trend, there are several multi-centennial to millennial-scale fluctuations for increased monsoon precipitation at 4500–4000 years BP, 2900–2400 years BP and 1200–700 years BP and decreased precipitation at 3900–3000 years BP, 2200–1300 years BP, and 500–0 years BP. Reanalyses of instrumental data and Kiel Climate Model on regional atmosphere circulations show that moisture of this region is mainly derived from the western Pacific Ocean through the East Asian summer monsoon circulation at inter-annual to inter-decadal, and millennial timescales. We conclude that monsoon rainfall in the southwestern Chinese Loess Plateau is likely connected with changes in sea surface temperatures and migrations of the ITCZ in the western Pacific Ocean.
... The colour map shows the annual mean SST, and the bathymetric contours (1000 and 2000 m) are also shown. (b) Map showing the locations B-3GC (Jian et al., 2000), Mulyoungari (Park et al., 2016), MD01-2421 (Isono et al., 2009), BN-1 (Jo et al., 2017), Mt. Logan (Fisher et al., 2008), and V21-30 (Koutavas and Joanides, 2012), which are selected Holocene climate archives used in this study. ...
... (a) total solar irradiance (Steinhilber et al., 2009), (b) volcanic forcing (Kobashi et al., 2017), (c) Mt. Logan ice core δ 18 O (Fisher et al., 2008), (d) Mg/Ca-derived SST record from the Japan Sea (PC09, this study), (e) alkenone-derived SST records from the western North Pacific (MD01-2421) (Isono et al., 2009), (f) stalagmite δ 18 O records from Baeg-nyong Cave (BN-1) in the eastern Korean Peninsula (Jo et al., 2017), (g) blue dotted line representing the dry period in Jeju Island off the southern Korean Peninsula (Mulyoungari) (Park et al., 2016) water. Interestingly, off Hokkaido at the northern end of the TWC the warm molluscan assemblages increased during 7200-5000, 4200-3200, 2500-2300, and 1000-900 cal. ...
... Unlike these records, our SST records in the Japan Sea (PC09) do not show such obvious shift from the mid to the late Holocene. As a different feature, the SST records in the Japan Sea have varied synchronously with the SST at Site MD01-2421, at the northern end of the Kuroshio Current, although the SST variability was somewhat smaller (< 1°C) and was superimposed onto a long-term SST decrease (Isono et al., 2009) (Figs. 1b, 9d, e). ...
Cyclic changes in volume transport of the Tsushima Warm Current (TWC) have been argued from diatom records in the southern Japan Sea off the Japanese islands during the Holocene. Although this phenomenon has not yet been confirmed by various proxy data, determining whether or not these oceanographic changes occurred is crucial for clarifying the nature of oceanographic changes in the southern Japan Sea. Here, we conducted a coupled analysis of Mg/Ca ratios and oxygen isotopes (δ18O) in shallow-dwelling Neogloboquadrina incompta from 13 core-top sediments in southern Japan, and developed a new equation for Mg/Ca temperature calibration (Mg/Ca = 0.311 × exp (0.07 × T)) as a proxy for spring sea surface temperature (SST). Using the newly developed, species-specific Mg/Ca-paleothermometry, we reconstructed SST variability for the past 6800 years from core YK10-7-PC09 in the southern Japan Sea. The Mg/Ca-derived SST record clearly represented five warmer periods at 6200–6000, 4900–4500, 4200–3800, 2600–2100, and 900–400 cal. year BP, almost consistent with previously published diatom records. These warmer events also corresponded to the periods in which warm molluscan assemblages increased at the northern end of the TWC, suggesting that periods of higher SST can be seen as reflecting the increased volume transport of the TWC. We interpreted the results of a model study showing that higher solar irradiance provoked positive Arctic Oscillation (AO)-like spatial patterns and the negative phase of the Pacific Decadal Oscillation (PDO) to mean that increased (reduced) TWC volume transport on the multi-centennial to millennial time scales was caused by high (low) solar insolation via a potential link between AO and PDO. Given that larger and more frequent volcanic eruptions occurred in the mid Holocene than in the late Holocene, volcanic forcing on the TWC volume transport changes would have been more significant during the former, as seen in the highly variable SST from this period and distinct decreases in SST around ~5900 cal. year BP and ~6400 cal. year BP. The millennial-scale fluctuations seen in SSTs in the southern Japan Sea would have had a large impact on the evolution of vegetation and human adaptation in the northern Japanese islands, adjacent to the Japan Sea, over the last 6800 years.
... yr BP. Similar results are also obtained from a pollen record of the Toushe basin in Taiwan province of China and SST variations along the Japanese coast (Isono et al., 2009;Huang et al., 2020; Figure 6d). Quantitative integration analysis of pollen records from China and adjacent areas shows that temperature and precipitation began to decrease simultaneously since about 4200 cal. ...
... Subsequently, weak trade winds cause a weakening of subtropical circulation, indicating that low SSTs may spread from the tropical western Pacific to the northwest Pacific along with ocean currents; this is reflected in the low SSTs along the Japanese coast during the period 5100-4500 cal. yr BP (Isono et al., 2009;Figure 6d). A weak Kuroshio current may also reduce the transport capacity of water vapor to the coastal region. ...
Our knowledge about the interaction between human activities and the environment in the middle-late Holocene remains incomplete. Core C1 in Lake Chaohu from the middle and lower reaches of Yangtze River (MLYR), eastern China, provides an opportunity to investigate vegetation and climate changes, human activities, and East Asian summer monsoon (EASM) evolution since 5100 cal. yr BP. These variables are assessed based on radiocarbon dating, pollen and charcoal records, and magnetic susceptibility (χlf), median grain size and TP. Results reveal a hiatus in sedimentation between 2080 and 730 cal. yr BP in the western part of Lake Chaohu, which is common in most lakes in the MLYR. Evergreen and deciduous broadleaved mixed forest retreated gradually after 3650 cal. yr BP, and was replaced by secondary Pinus forest after at least 730 cal. yr BP. Intense agricultural activities and vegetation clearance are first detected at 2520 cal. yr BP. Human settlements expanded from the lake front wetlands (during the period 2520–2080 cal. yr BP) to remote high-altitude areas (2080–100 cal. yr BP), and then returned to the lake front to reclaim the wetlands and lake (after 400 cal. yr BP). A gradual trend of recessional EASM strength from 4300 cal. yr BP and centennial-scale variations of EASM during the period 5100–3650 cal. yr BP are revealed. The reduction of summer insolation, southward shift of the ITCZ, and El Niño Southern Oscillation may control the intensity of EASM and climate on a large regional scale.
... (d) Mg/Ca-derived SST records from the Japan Sea (Horikawa et al., 2019). (e) Alkenone-derived SST records from the Northwest Pacific off Japan (Isono et al., 2009). (f-g) Typhoon records on the coast of South China Sea (Zhou et al., 2019) and southwest Japan (Woodruff et al., 2009). ...
... An increase in sea surface temperature (SST) at ca. 4.5 cal. kyr BP has also been reported for the northwestern Pacific off central Japan (Isono et al., 2009;Fig. 6e). ...
Reconstructing the long-term history of tropical cyclones is key to understanding their driving mechanisms and to enable better predictions of future extreme storm events. However, the available history of typhoons, based on sedimentary records in the northwest Pacific basin, remains very limited. In this study, we conducted multi-proxy analyses of sedimentary profiles collected from a chenier ridge on the north bank of Hangzhou Bay, East China. We applied evidences from the lithology, grain size, and marine micro-fossils on sediments in these profiles, dated using OSL and AMS ¹⁴C, to reveal the mid-Holocene sedimentary environmental evolution and obtain records of extreme storm events. The lithology and foraminiferal assemblages indicate an aggradational succession from intertidal to supratidal flats incorporating two layers of storm deposits preserved in the chenier ridge. The lower layer of storm deposits was formed in the intertidal flats at ca. 6.0 cal. kyr BP, while the upper layer was formed in the supratidal flats at ca. 5.2–4.9 cal. kyr BP. The storm deposits are characterized by coarsened grain size and the prevalence of allochthonous foraminiferal species, including E. advenum, A. annectens, and A. compressiuscula which occur in the inner and middle shelf of East China Sea. The extreme storm events at ca. 6.0 and 5.2–4.9 cal. kyr BP recorded at the chenier ridge have also been described at different sites on the southeast coast of Hangzhou Bay. Together with previously reported storm deposits at ca. 4.5 cal. kyr BP, we suggest that these mid-Holocene extreme typhoon events on the East China coast resulted from global climate changes driven by solar irradiance.
... Because of the restricted N. bicapitata distribution in the open ocean, abundant N. bicapitata suggests strengthening Kuroshio inflow into the East China Sea. During the early to middle Holocene, Kuroshio intensified due to strengthening the Subtropical Gyre by precessional forcing (Isono et al. 2009;Yamamoto 2009). ...
... An event at 7 ka ago was the most prominent. Subsequently, Kuroshio intensity might have weakened during the late Holocene due to its southward migration by precessional forcing controlling the strength of the North Pacific subtropical gyre (Isono et al. 2009;Yamamoto 2009). However, a sudden increase in N. bicapitata, representative diatom species dwelling in the open ocean with high SST, was observed near the core top of KY07-04 PC01 (Fig. 3). ...
We investigated diatom assemblages for the last 19 ka in a piston core KY07-04 PC01 collected from the northern Okinawa Trough, East China Sea. Most of the diatom taxa in the Core KY07-04 PC01 were subtropical to temperate marine species throughout the core. Pronounced turnover of major diatom groups from periphytic to planktonic taxa occurred during deglaciation between 17 and 14 ka ago. During the Last Glacial Maximum (LGM) to early deglaciation, the representative taxa were Paralia spp., a periphytic diatom abundant in continental shelves of the modern East China Sea covering the Chinese Coastal Water. Relative abundances of Paralia spp. rapidly decreased during 15–14 ka ago, corresponding to sea-level rise, displaced by planktonic taxa such as Thalassionema . Thalassionema nitzschioides varieties living in subtropical water increased since 12 ka and have reached the present level at 8 ka ago, suggesting strengthening the influences of Kuroshio water in the northern East China Sea during the early to middle Holocene. Warm planktonic diatom taxa such as Nitzschia bicapitata also gradually increased from 12 to 8 ka ago. Near the core top, a sudden increase in N. bicapitata might relate to the intensifying Kuroshio during the latest Holocene.
... This study uses two methods, including east-west SST contrast over the subtropical North Pacific and PDO-related precipitation anomalies in East Asia, to investigate the PDO variability during the Holocene. Since the temporal resolution of SST records over the subtropical North Pacific is relatively low (e.g., Barron et al., 2003;Caissie et al., 2010;Harada et al., 2006Harada et al., , 2014Isono et al., 2009;Jonas et al., 2017;Kennett et al., 2000;Kienast and Mckay, 2001;Kim et al., 2004;Max et al., 2012;Nan et al., 2017;Praetorius et al., 2015;Ruan et al., 2017;Sawada and Handa, 1998;Seki et al., 2004), this study focuses on the mean state of PDO-like changes at a millennial timescale during the Holocene. Mechanisms of the PDO-like variability at a millennial timescale during the Holocene are also analyzed using simulation results. ...
... (4) observed SSTs around the core sites are significantly correlated with the instrumental PDO index (Fig. 1a, histogram). Among the various records from the subtropical North Pacific (e.g., Barron et al., 2003;Caissie et al., 2010;Harada et al., 2006Harada et al., , 2014Isono et al., 2009;Jonas et al., 2017;Kennett et al., 2000;Kienast and Mckay, 2001;Kim et al., 2004;Max et al., 2012;Nan et al., 2017;Praetorius et al., 2015;Ruan et al., 2017;Sawada and Handa, 1998;Seki et al., 2004), only two SST records meet all the four criteria to reconstruct the PDO-like index: marine core MD01-2412 (Harada et al., 2006) and core ODP1019C (Barron et al., 2003) (Fig. 1b). ...
Sea surface temperatures (SSTs) in the North Pacific exert a great influence on global climate and ecosystem changes. The Pacific Decadal Oscillation (PDO) is the leading mode of decadal SST variability in the North Pacific. The Pacific Decadal Oscillation (PDO)-like variability at a millennial timescale during the Holocene is still poorly understood. In this study, the millennial-scale PDO-like variability during the Holocene is explored using model–data comparisons. To reduce the uncertainties caused by differential age controls, this study reconstructs the Holocene PDO-like index using two types of published proxy records, including 1) east–west SST contrast in the extratropical North Pacific and 2) PDO-related precipitation anomalies in East Asia. These two reconstructions reveal coherent changes in the PDO-like pattern during the Holocene, showing positive phases between 10.4 and 8.5 ka BP and 3.5–3.0 ka BP, and negative phases between 8.5 and 3.5 ka BP and 3.0–0.2 ka BP. Climate simulations suggest that the millennial-scale PDO-like variability is predominantly controlled by orbital forcing during the Holocene, leading to a positive phase of the PDO-like regime during the early Holocene. The positive phase of the PDO-like regime between 3.5 and 3.0 ka BP was probably caused by the internal feedback of the climate system, which the climate simulations fail to capture.
... And hereafter, synchronous temperature decreases responding to these cooling events had been widely reported during the Holocene, in particular from the northern hemisphere high-latitude regions (Risebrobakken et al., 2003;Mayewski et al., 2004;Viau et al., 2006;Wanner et al., 2011;Marsicek et al., 2018). In addition, responses to the North Atlantic cooling events had also been observed from the East Asian monsoon records (Wang et al., 2005;Yu et al., 2011;An et al., 2012;Wang et al., 2012;Hao et al., 2017;Kang et al., 2018) and paleo-environmental archives from the western Pacific marginal-sea and open-ocean regions (Jian et al., 2000;Sun et al., 2005;Isono et al., 2009;Kubota et al., 2010;Wang et al., 2011;Kim and Lim, 2014;Ruan et al., 2015). ...
... Superimposing on the millennial-scale variations, several centennial-scale cold events were observed from the south YS SST records (Fig. 3a, b). To better reveal the centennial-scale changes during the Holocene, low-frequency variability was removed by subtracting the 1500-yr moving average according to Isono et al. (2009), and therefore detrended south YS SSTs from A03-B and YS01 (Fig. 4a, b) were obtained. As displayed in Fig. 4, a series of rapid cooling events, with amplitude of 0.5-1.0°C, ...
Sea surface temperature (SST) of the modern Yellow Sea (YS) is sensitive to forcing by both the East Asian monsoon and the North Pacific western boundary current, however, detailed mechanisms for explaining the Holocene SST evolution remains to be understood. Here we present two decadal sampling resolution alkenone SST records from the south YS spanning the last 8.9 kyr to understand forcing mechanisms on different timescales. The results show that the two sites from the south YS experienced SST variations on millennial timescale, displaying mean high values of 16.5 °C (A03-B) and 15.2 °C (YS01) from 7.7 to 5.9 ka, followed by low values of 16.4 °C (A03-B) and 14.8 °C (YS01) from 5.9 to 2.9 ka, then by high values of 16.9 °C (A03-B) and 15.5 °C (YS01) from 2.9 to 0.6 ka. After the entrance of the YS Warm Current at about 7.5 ka, evolution of the south YS SSTs paralleled the pattern of the main Kuroshio Current intensity, i.e., low (high) SST coeval with weak (strong) Kuroshio Current, suggesting that millennial-scale SST variations in the south YS were primarily controlled by the Kuroshio Current. Superimposing on the millennial variations, seven abrupt centennial-scale cold events were observed during the Holocene, with SST oscillations broadly coeval with those of North Atlantic ice-rafted detritus and East Asian winter monsoon rather than SSTs from the Okinawa Tough and Indo-Pacific warm pool. Hence, we propose that the East Asian winter monsoon was the top-down conveyor transmitting North Atlantic cooling signals to the south YS on centennial timescale. Thus, our study reveals both high- and low-latitude climate forcing on the evolution of the south YS SST during the Holocene, with low-latitude forcing on millennial-scale and high-latitude forcing on centennial-scale.
... The C ), (b) alkenone-based sea surface temperature (SST) record from core SO201-2-12KL ( Max et al., 2012), (c) alkenone-inferred water temperature for the growing season in Lake Sihailongwan (data below 10°C are excluded), (d) alkenone-based summer temperature record from Lake Qinghai ( Hou et al., 2016), (e) alkenone-based SST record from core MD01-2421 ( Isono et al., 2009), and (f) pollen-based summer temperature record (5-point running average) from Lake Suigetsu ( Nakagawa et al., 2003). A 250- year correction has been applied to adjust the chronology (Shen et al., 2010). in unreliable reconstructed temperature values in lacustrine stud- ies. ...
... Second, the alkenone-inferred temperature dur- ing the YD decreased by only 2-4°C, which is much less than observed in Greenland ice cores (Alley, 2000;Buizert et al., 2014). This could be explained by temperature records from Greenland ice cores being highly weighted toward the winter sea- son ( Buizert et al., 2014;Denton et al., 2005), while the alkenone- based temperature reconstruction is biased toward summer ( Hou et al., 2016;Isono et al., 2009;Max et al., 2012;Nakagawa et al., 2003; Figure 5). ...
Abrupt temperature changes during the last deglaciation are well recognized in Greenland ice cores and in deep-sea sediment records. On the continent
of monsoonal Asia, however, only a few terrestrial temperature reconstructions extend to the Younger Dryas (YD). This hampers the understanding of
how the Asian monsoon system responded to large-scale boundary changes in ice-sheet dynamics and reorganizations of atmospheric–oceanic circulation
between the last deglaciation and the Holocene. Here, we report an alkenone-inferred temperature record from varved sediments of the maar lake
Sihailongwan, northeastern China. Alkenone provides temperatures that represent the water temperature during the growing season when the lake is
ice-free. Annually laminated sediments provide a reliable time control. Reconstructed temperatures reveal a distinctive pattern of variations during the
last deglaciation: a temperature increase of 6°C at the onset of the Bølling–Allerød, two cold intervals (during the Older Dryas and the intra-Allerød
cold period), a relatively minor temperature decrease of 1–3°C during the YD, and a rapid temperature increase of 4–5°C at the early Holocene. The
reconstructed temperature records from Lake Sihailongwan and adjacent regions indicate that summer (or growing season) temperature changes were
smaller than is evident in Greenland ice core records that are weighted toward winter.
... The C 37 /C 38 ratio has been used to estimate different haptophyte species (e.g. Chu (Max et al., 2012), (c) alkenone-inferred water temperature for the growing season in Lake Sihailongwan (data below 10°C are excluded), (d) alkenone-based summer temperature record from Lake Qinghai (Hou et al., 2016), (e) alkenone-based SST record from core MD01-2421 (Isono et al., 2009), and (f) pollen-based summer temperature record (5-point running average) from Lake Suigetsu (Nakagawa et al., 2003). A 250year correction has been applied to adjust the chronology (Shen et al., 2010). in unreliable reconstructed temperature values in lacustrine studies. ...
... Second, the alkenone-inferred temperature during the YD decreased by only 2-4°C, which is much less than observed in Greenland ice cores (Alley, 2000;Buizert et al., 2014). This could be explained by temperature records from Greenland ice cores being highly weighted toward the winter season (Buizert et al., 2014;Denton et al., 2005), while the alkenonebased temperature reconstruction is biased toward summer (Hou et al., 2016;Isono et al., 2009;Max et al., 2012;Nakagawa et al., 2003; Figure 5). ...
Abrupt temperature changes during the last deglaciation are well recognized in Greenland ice cores and in deep-sea sediment records. On the continent of monsoonal Asia, however, only a few terrestrial temperature reconstructions extend to the Younger Dryas (YD). This hampers the understanding of how the Asian monsoon system responded to large-scale boundary changes in ice-sheet dynamics and reorganizations of atmospheric–oceanic circulation between the last deglaciation and the Holocene. Here, we report an alkenone-inferred temperature record from varved sediments of the maar lake Sihailongwan, northeastern China. Alkenone provides temperatures that represent the water temperature during the growing season when the lake is ice-free. Annually laminated sediments provide a reliable time control. Reconstructed temperatures reveal a distinctive pattern of variations during the last deglaciation: a temperature increase of 6°C at the onset of the Bølling–Allerød, two cold intervals (during the Older Dryas and the intra-Allerød cold period), a relatively minor temperature decrease of 1–3°C during the YD, and a rapid temperature increase of 4–5°C at the early Holocene. The reconstructed temperature records from Lake Sihailongwan and adjacent regions indicate that summer (or growing season) temperature changes were smaller than is evident in Greenland ice core records that are weighted toward winter.
... A range of DACP indications of Pacific origin (Figures 1b and 3) suggest that the event may have extended to areas quite distant from the key regions of the NAO. Climatic oscillations similar to that of IRD cyclicity of 1470 years in the North Atlantic (Bond et al., 1997(Bond et al., , 2001 have been reported in the North Pacific Gyre system (Isono et al., 2009), with a possibility of a climatic link between the North Pacific Gyre Oscillation (NPGO; Di Lorenzo et al., 2008) and the North Atlantic component of the thermohaline circulation (Isono et al., 2009). The low-frequency NPGO is driven by the central tropical Pacific El Niño mode of sea surface temperatures (SST) and affects the climate variability over Eurasia and North America (Di Lorenzo et al., 2008, 2010. ...
... A range of DACP indications of Pacific origin (Figures 1b and 3) suggest that the event may have extended to areas quite distant from the key regions of the NAO. Climatic oscillations similar to that of IRD cyclicity of 1470 years in the North Atlantic (Bond et al., 1997(Bond et al., , 2001 have been reported in the North Pacific Gyre system (Isono et al., 2009), with a possibility of a climatic link between the North Pacific Gyre Oscillation (NPGO; Di Lorenzo et al., 2008) and the North Atlantic component of the thermohaline circulation (Isono et al., 2009). The low-frequency NPGO is driven by the central tropical Pacific El Niño mode of sea surface temperatures (SST) and affects the climate variability over Eurasia and North America (Di Lorenzo et al., 2008, 2010. ...
... Multiple frequency patterns of millennial-scale periodicities are also identified in other geological periods 18,19,21,22,[57][58][59][60][61] (Table 1), including the well-documented ' ~ 1470-yr cycle' of Bond events in the Holocene and the DO events in last glacial [1][2][3][4][5][6] , and the ~ 4500-6000-yr periodicities of Heinrich events 62 . A recent study also pointed out existence of DO-like ~ 1.5-kyr oscillations with AM by half-precession, precession and short eccentricity cycles during the Late Jurassic 22 . ...
Understanding climate variability and stability under extremely warm ‘greenhouse’ conditions in the past is essential for future climate predictions. However, information on millennial-scale (and shorter) climate variability during such periods is scarce, owing to a lack of suitable high-resolution, deep-time archives. Here we present a continuous record of decadal- to orbital-scale continental climate variability from annually laminated lacustrine deposits formed during the late Early Cretaceous (123–120 Ma: late Barremian–early Aptian) in southeastern Mongolia. Inter-annual changes in lake algal productivity for a 1091-year interval reveal a pronounced solar influence on decadal- to centennial-scale climatic variations (including the ~ 11-year Schwabe cycle). Decadally-resolved Ca/Ti ratios (proxy for evaporation/precipitation changes) for a ~ 355-kyr long interval further indicate millennial-scale (~ 1000–2000-yr) extreme drought events in inner-continental areas of mid-latitude palaeo-Asia during the Cretaceous. Millennial-scale oscillations in Ca/Ti ratio show distinct amplitude modulation (AM) induced by the precession, obliquity and short eccentricity cycles. Similar millennial-scale AM by Milankovitch cycle band was also previously observed in the abrupt climatic oscillations (known as Dansgaard–Oeschger events) in the ‘intermediate glacial’ state of the late Pleistocene, and in their potential analogues in the Jurassic ‘greenhouse’. Our findings indicate that external solar activity forcing was effective on decadal–centennial timescales, whilst the millennial-scale variations were likely amplified by internal process such as changes in deep-water formation strength, even during the Cretaceous ‘greenhouse’ period.
... These synthesized records include inferred SSTs from δ 18 O, alkenone, and Mg/Ca (Andrews et al., 1999;Antonarakou et al., 2015;Arz et al., 2003;Bard et al., 2000;Barron et al., 2003a;Benway et al., 2006;Bolliet et al., 2011;Cacho et al., 1999Cacho et al., , 2001Came et al., 2007;Castañeda et al., 2004Castañeda et al., , 2010F. Chang et al., 2015;Doose-Rolinski et al., 2001;Elmore et al., 2015;Emeis & Dawson, 2003;Eynaud et al., 2009;Fan et al., 2018;Farmer et al., 2008;Flower et et al., 1994;Huguet et al., 2006;Ijiri et al., 2005;Isono et al., 2009;Keigwin & Jones, 1995;Keigwin et al., 2005;Kennett et al., 2007;M. Kienast et al., 2001;Kim et al., 2004Kim et al., , 2007Kim et al., , 2012Kristjánsdóttir et al., 2017;Kubota et al., 2010;Lea et al., 2003;Marchitto et al., 2010;Martrat et al., 2003Martrat et al., , 2007Martrat et al., , 2014McClymont et al., 2012;Minoshima et al., 2007;Mohtadi et al., 2014;Moossen et al., 2015;Overpeck et al., 1996;Pelejero et al., 1999;Praetorius et al., 2015;Rühlemann et al., 1999;Riethdorf et al., 2013;Rigual-Hernández et al., 2017;Rodrigo-Gámiz et al., 2014;Rodrigues et al., 2010;Rosenthal et al., 2003;Sachs, 2007;Saraswat et al., 2013;Schmidt, Chang, et al., 2012;Schmidt, Weinlein, et al. 2012b;Schmidt & Lynch-Stieglitz, 2011;Schmidt et al., 2004;Schwab et al., 2012;Sejrup et al., 2011;Shintani et al., 2011;Staubwasser et al., 2003;Steinke et al., 2008;Stott et al., 2007;Sun et al., 2005;Thornalley et al., 2010;Tierney et al., 2016;Tiwari et al., 2015;Weldeab et al., 2005Weldeab et al., , 2007Werner et al., 2013;Yamamoto et al., 2013;Zhao et al., 1995;Ziegler et al., 2008). ...
Variations of the sea surface temperature (SST) and primary productivity in the northeast Pacific have far‐reaching implications. In addition to influencing the regional and global temperature and hydroclimate, these conditions also control marine ecosystems and their services, which subsequently impact regional economies. Yet, our understanding of the variability and controls of northeast Pacific SST and productivity on timescales exceeding observational records remains limited. Here, we use marine sediment records from seven locations, spanning 25.2°N–59.6°N, in the northeast Pacific to characterize the millennial‐scale variability of SST and productivity from 9,000 to 1,000 years BP. We explore the dynamics of their spatiotemporal evolution and compare these data with transient climate model outputs to identify potential drivers. Through a heat budget analysis and optimal fingerprinting analysis, we characterize the spatial pattern of forcings. We find that SST varied spatially in the northeast Pacific, with higher latitudes exhibiting greater magnitude changes than lower latitudes, which differs from previous work suggesting regional synchronicity and coherence during the Holocene. Our analysis did not find evidence for coherent variability of primary producer community nor carbon export, highlighting the difficulty of identifying the complex interactions between environmental conditions, producers, and carbon export. Model‐proxy disagreement demonstrates the need for higher resolution model frameworks, but shows nonetheless that observed variability in the proxy records can be explained by a combination of greenhouse gas and orbital forcing. We suggest that the complex SST variations and marine ecosystem responses to forced changes are important factors that can drive disagreements in model projections.
... 本可以忽略，isoGDGTs主要来自于海洋奇古菌 [37][38][39][40] (c)δ 18 O records of GISP2 ice core [46] Fig.8 (a)δ 18 O records from Dongge Cave stalagmites, China [2] ; (b)Ti contents from from the sediment sequence of Lake Huguang Maar [5] ; (c)The differences between TEX H 86 SSTs in QH-CL11 and U K' 37 SSTs in MD01-2421 [47] ; (d)The differences between U K' 37 north SSTs and U K' 37 SSTs in MD01-2421 [9,17,47] ; (e)The differences between U K' 37 SSTs in MD97-2151 and U K' 37 SSTs in MD01-2421 [47][48] ; (f)The differences between U K' 37 SSTs in MD97-2151 and TEX H 86 SSTs in QH-CL11 [48] ...
... ka (Jian, 1998). During the Holocene, the mean latitude of the KCE varied in response to millennial/suborbital scale (∼1,500year) forcing associated with changes in sea surface temperature and North Atlantic thermohaline circulation (Isono et al., 2009;Jian et al., 2000). The Pleistocene behavior of the KCE is less well-known compared to its Holocene behavior, but studies do indicate that in the last 600 ka the KCE underwent large changes in its velocity and latitudinal location in response to middle Pleistocene climate instability (Ito & Horikawa, 2000;Kawahata & Ohshima, 2002;Ujiié, 2003;Yamane, 2003). ...
The Kuroshio Current (KC) and Kuroshio Current Extension (KCE) form a western boundary current as part of the North Pacific Subtropical Gyre. This current plays an important role in regulating weather and climate dynamics in the Northern Hemisphere in part by controlling the delivery of moisture to the lower atmosphere. Previous studies indicate the KCE responded dynamically across glacial and interglacial periods throughout the Pliocene‐Pleistocene. However, the response of the KCE during Pleistocene super‐interglacials has not been examined in detail. We present a ∼2.2 Ma record of X‐ray fluorescence elemental data from Ocean Drilling Program Hole 1207A and employ hierarchical clustering techniques to demonstrate paleoenvironmental changes around the KCE. Time‐frequency analysis identifies significant heterodyne frequencies, which suggests there were nonlinear interactions between high‐latitude and low‐latitude climate regulating expansion and contraction of the North Pacific Subtropical Gyre prior to the onset of the Mid‐Pleistocene Climate Transition (MPT). We observe two periods of elevated ln Ca/Ti, which may represent sustained warmth with northward migrations of the KCE in the northwestern Pacific. These intervals correspond to Marine Isotope Stages 29‐25, 15, and 11‐9 and occur around recent climatic transitions, the MPT and Mid‐Brunhes Event. Northward expansion of the subtropical gyre during these exceptionally warm interglacials would have delivered more heat and moisture to the high latitudes of the northwest Pacific. Furthermore, enhanced evaporation from the warm KCE vented to the lower atmosphere may have preconditioned the Northern Hemisphere for ice volume growth during two of the most recent periods of climate transition.
... Concerning the role of climate (Fig. 1), the northern Iberian Peninsula has been under the influence of regional climatic variability, such as the succession between Stadials and Interstadials (Dansgaard et al., 1982;Johnsen et al., 1992;Rasmussen et al., 2014;Seierstad et al., 2014), the Heinrich events (Heinrich, 1988;Bond et al., 1992;Hemming, 2004) and the Bond cycles (Bond et al., 1997;Bond et al., 2001;Mayewski et al., 2004;Wanner and Bütikofer, 2008;Isono et al., 2009;Wanner et al., 2011). Several studies have examined the impact that this climate variability has had on the Cantabrian region through isotopic analyses of cave speleothems (Domínguez-Villar et al., 2008, 2017Moreno et al., 2010a;Baldini et al., 2015Baldini et al., , 2019Smith et al., 2016;Rossi et al., 2018). ...
Our aim with this paper is to provide insight into the landscape dynamics of the Cantabrian region (northern Iberian Peninsula) from the Last Glacial Period to the present. We present a multiproxy approach performed in a sedimentary record from La Molina peat bog, located at 484 m a. s. l. in Puente Viesgo, Cantabria (Latitude: 43.26° N; Longitude: 3.97° W), that covers the last c. 17,550 years. Analyses were performed on the organic matter, pollen and sedimentary charcoals, which have been used to characterise the fire regime at a local level. The results revealed a steppe-like formation from the basis of the sequence to the Bølling-Allerød chronozone, when the spread of woody species is detected. The dry and cold conditions of the Younger Dryas caused the decrease of mesophilous taxa until the onset of the Holocene. From that point onwards, a mixed deciduous formation composed of Betula and deciduous Quercus was established in the region. Besides, a series of biomass pulses was detected during the early Holocene, probably linked to intervals of increased rainfall. Fire episodes detected at the 9.3 and the 8.2 ka events created forest openings and probably favoured the establishment of Corylus, most likely also helped by a climate shift. There was a lack of fire activity until the Neolithic, when the fire signal increased probably linked to grazing and agricultural practices and triggered deeper changes in the Cantabrian plant landscape structure.
... In light of the current difficulty, as stated above, to directly track this NPSG branch, we are only able to include existing SST records from its upstream regions, for example, sites 8-10 across the KE and Kuroshio-Oyashio Interfrontal Zone (Fig. 1a), to further reinforce the identified changes in the overall KC/NPSG circulation. In particular, these independent paleorecords display a general cooling trend 48,78,79 , essentially indicating a southward displacement of the KE, and the NPC as a result, toward the late Holocene (Fig. 4b). Due to such migration, the SST records from the modern NPC location, if available, would document its position more likely than its strength. ...
The North Pacific Subtropical Gyre circulation redistributes heat from the Western Pacific Warm Pool towards the mid- to high-latitude North Pacific. However, the driving mechanisms of this circulation and how it changed over the Holocene remain poorly understood. Here, we present alkenone-based sea surface temperature reconstructions along the Kuroshio, California and Alaska currents that cover the past ~7,000 years. These and other paleorecords collectively demonstrate a coherent intensification of the boundary currents, and thereby the basin-scale subtropical gyre circulation, since ~3,000–4,000 years ago. Such enhanced circulation during the late Holocene appears to have resulted from a long-term southward migration of the Intertropical Convergence Zone, associated with Holocene ocean cooling. Our results imply that the North Pacific Subtropical Gyre circulation could be weakened under future global warming. Long-term variability of the North Pacific Subtropical Gyre (NPSG) circulation is not well understood. Here, the authors present data from different boundary currents that shows an enhanced NPSG circulation since ~3000-4000 years ago, linked to a southward migration of the Intertropical Convergence Zone.
... Published records of planktic foraminiferal Mg/Ca and 18 O calcite (24,29,82,87,(123)(124)(125)(126)(127), U K′ 37 (112,113,(128)(129)(130)(131)(132)(133)(134)(135) covering the Holocene (0 to 10 ka) and LGM (19 to 21 ka) were collated for the North Pacific, spanning both the subpolar and subtropical gyres. All age models are as given in the original publication. ...
Although the Pacific Ocean is a major reservoir of heat and CO2, and thus an important component of the global climate system, its circulation under different climatic conditions is poorly understood. Here, we present evidence that during the Last Glacial Maximum (LGM), the North Pacific was better ventilated at intermediate depths and had surface waters with lower nutrients, higher salinity, and warmer temperatures compared to today. Modeling shows that this pattern is well explained by enhanced Pacific meridional overturning circulation (PMOC), which brings warm, salty, and nutrient-poor subtropical waters to high latitudes. Enhanced PMOC at the LGM would have lowered atmospheric CO2—in part through synergy with the Southern Ocean—and supported an equable regional climate, which may have aided human habitability in Beringia, and migration from Asia to North America.
... We compiled Mg/Ca and U K' 37 sea surface temperature (SST) data from across the North Pacific (Mg/Ca: Reitdorf et al., 2013;Gebhardt et al., 2008;Rodriguez Sanz et al., 2013;Taylor et al., 2015;Sagawa et al., 2006;Sagawa et al., 2008;Pak et al., 2012;Kubota et al., 2010;. U K' 37: Minoshima et al., 2007Seki, 2004;Harada et al., 2004;Harada, 2006;Inagaki et al., 2009;Herbert et al., 2001;Sawada et al., 1998;Yamamoto et al., 2004;Isono et al., 2009). All age models are as given in the original publication. ...
Plain language summary
Despite the North Pacific's importance in the global climate system, changes in the circulation of this region since the last ice age are poorly understood. Today, the North Pacific Ocean has distinct properties north and south of ~40°N: To the south, the warm surface waters form a circulation cell that moves clockwise (the subtropical gyre); to the north, the cold surface waters form a circulation cell that moves anticlockwise (the subpolar gyre). This difference in surface ocean circulation north and south of ~40°N is determined by the wind patterns. Here, using a compilation of oxygen isotopes measured in the carbonate shells of fossil plankton from sediment cores across the basin, which tracks changes in the spatial pattern of temperature, we reconstruct how the position of the boundary between the gyres changed since the last ice age. Our results show that the boundary between the gyres was shifted southward by ~3° during the last ice age; this indicates that the westerly winds were also shifted southward at this time. Using numerical simulations of the climate, we find that this ice age shift in the westerly winds is primarily due to the presence of a large ice sheet over North America.
... These currents meet each other off the northeast coast of the Kanto area to form the subarctic front with the most pronounced latitudinal gradients of SST in the North Pacific (Kida et al., 2016). The temperature in this area is susceptible to global changes in atmospheric and oceanic circulations (e.g., Haneda et al., 2019;Suganuma et al., 2018) because the latitudinal position of the subarctic front is controlled by the changes in the distribution of atmospheric pressure systems, including the behavior of the ENSO, the monsoon intensity, and the position of westerly jets, which are associated with the insolation variability in the Northern Hemisphere (Isono et al., 2009;Oba et al., 2006;Yamamoto et al., 2005). ...
The regional paleoenvironmental record of Tokyo, central Japan, is required to enrich our understanding of climate change in East Asia and its impact on Japanese civilizations. Previous studies have generated paleotemperature records based on the analysis of shell mounds along the coast of Tokyo Bay and pollen from terrestrial borehole cores. However, a continuous, high time-resolution, quantitative paleotemperature record does not exist. A piston core was recovered from Tokyo Bay from which 22 mollusk shells were extracted. An age model for the core, determined via accelerator mass spectroscopy (AMS) ¹⁴C dating of the shells and a scoria layer from the Hoei eruption (1707 CE), showed that the core contains continuous record from ca. 2400 BCE. We analyzed the alkenone unsaturation ratios (UK’37) to reconstruct the variations in the paleotemperature. The temperature during the Meghalayan was generally warmer than that at present exhibiting a declining trend, which roughly matches the changes in the orbital-forcing summer insolation and the millennial-scale latitudinal shift of the subarctic front in the northeastern Pacific Ocean. The largest cold period, which occurred ca. 2300 BCE and had a minimum temperature of 19.5 °C, interrupted the warm conditions. This cold period may correspond to the global cooling/drying “4.2 ka BP event,” which marks the boundary between the Northgrippian and Meghalayan. Our results also revealed that several cold periods occurred, which may have been caused by decreases in solar activity or large volcanic eruptions. Particularly, large decadal to centennial-scale cold periods were observed ca. 440 BCE and 100 CE during the Yayoi era (ca. 900 BCE–300 CE). The coldest period after the establishment of a centralized system of government (ca. 300 CE–present) was recorded ca. 1050 CE, which may have been caused by the combination of a strong El-Niño mode and reduced solar activity. These climate change events can all be linked and, therefore, may be the potential causes of significant periods of famine and civil war in Japanese history, which eventually led to major shifts in Japanese social systems.
... The North Pacific Ocean contains the Kuroshio Current (Fig. 1b), which strongly affects East Asian and global climates by transporting large amounts of heat and water from low to middle latitudes (e.g., Kida et al., 2016). Isono et al. (2009) argued that the North Pacific Subtropical Gyre and Kuroshio Current responded to abrupt climate changes in the North Atlantic on a millennial scale during the Holocene. However, the Holocene record is not sufficiently long to elucidate the behavior of the North Pacific during the entire interglacial period under an orbital configuration characterized by phasing of obliquity maxima with precession minima and low eccentricity. ...
Marine isotope stage (MIS) 19 has been suggested as the best orbital analogue of the present interglacial period. Thus, its paleoenvironmental reconstruction will provide valuable information on future climate change, excluding anthropogenic impacts. The Kuroshio Current, the largest western boundary current in the northwestern Pacific, transports large amounts of heat and water poleward and strongly influences both East Asian and global climates. However, the responses of the Kuroshio Current to the variable intensity of the Atlantic meridional overturning circulation (AMOC) under this orbital configuration remain unknown. Here, we provide new centennial-scale resolution oxygen isotope (δ18O) records throughout MIS 19 using benthic, as well as subsurface and surface planktonic foraminifera from the Chiba composite section, a marine succession sequence in central Japan, to reconstruct detailed paleoceanographic variations in the northwestern Pacific and reveal the response of the Kuroshio Current to climate variability in the North Atlantic under this orbital configuration. The vertical water temperature structure and its gradient (ΔT) based on δ18O profiles elucidates the latitudinal oscillations of the Kuroshio Extension Front (KEF) on a millennial scale during the late MIS 19 and MIS 20–19 transition in association with AMOC disruption/reactivation due to freshwater discharges into the North Atlantic. The power spectra of the surface δ18O and ΔT show half-precession periodicity throughout MIS 19, which probably originated from equatorial insolation at equinoxes co-occurring with the orbital perihelion. This periodicity was especially strong during MIS 19c, during which paleoceanographic records from the North Atlantic show minor variations in the AMOC and freshwater discharge. Our results suggest that millennial-scale oceanographic variation and stability along the KEF under this orbital configuration are influenced by both North Atlantic climate variability and tropical insolation forcing.
... 考察 2485 年温度曲线, 我们 发现它可以划分成 4 个变化阶段: 阶段Ⅰ(250 BC~ 了地球气候系统. 北大西洋深海沉积[3] 、阿拉斯加湖 泊[1] 、希腊 Ptolemais 盆地[38] 、中国九洲台黄土[39] 、 北太平洋中纬度海表温度[40] 等均记录了 1500 a 的变 化周期. 阿拉伯海 74K1 孔还发现了 1450 和 1150 a ...
... The teleconnected dynamic processes such as the El NiñoeSouthern Oscillation (ENSO) and the Pacific decadal oscillation (PDO) could operate a link to solar activity through changes in the sea surface temperature pattern (Sun et al., 2013). The quasi-periodicities of 1750e2041 years may relate to the millennial-scale climatic oscillation recognized in a numbers of oceanic and terrestrial sites (Bond et al., 1997;Yu et al., 2003;Isono et al., 2009). Interestingly, the d 13 C 27e31 time series shows an opposite pattern of variation compared with the stalagmite oxygen isotope record from Water cave (Tan, 2007) and Nuanhe cave , about 150 km away from Lake Xiaolongwan ( Figs. 1 and 8). ...
... A large number of Holocene climate reconstructions reveal a climatic pattern far from stable throughout the Holocene. The most prominent feature is a series of decadal-to-centennial scale oscillations and/or abrupt events (Andrews et al. 1997;Axford et al. 2009;Bügelmayer-Blaschek et al. 2016;Bond et al. 2001Bond et al. , 1997Chen et al. 2015;Dixit et al. 2014;Fleitmann et al. 2003Fleitmann et al. , 2008Hou et al. 2012;Isono et al. 2009;Liu et al. 2014;Mayewski et al. 2004;Moros et al. 2006;Owen et al. 2016;Schulz and Paul 2002;Shao et al. 2006;Soon et al. 2014;Wang et al. 2005;Wanner et al. 2011;Zhou et al. 2007). These previous studies show that there are at least eight large and rapid climatic events, not counting the Little Ice Age (LIA), recorded in the North Atlantic drift ice records throughout the Holocene, including events at 8. 2, 9.4, 10.3 and 11.1 ka in the early Holocene (Bond et al. 2001(Bond et al. , 1997. ...
Numerous Holocene paleo-proxy records exhibit a series of centennial-millennial scale rapid climatic events. Unlike the widely acknowledged 8.2 ka climate anomaly, the likelihood of a significant climate excursion at around 9.2 cal ka BP, which has been notably recognized in some studies, remains to be fully clarified in terms of its magnitude and intensity, as well as its characteristics and spatial distributions in a range of paleoclimatic records. In this study, a peat sediment profile from the Dajiuhu Basin in central China was collected with several geochemical proxies and a pollen analysis carried out to help improve understanding of the climate changes around 9.2 cal ka BP. The results show that the peat development was interrupted abruptly at around 9.2 cal ka BP, when the chemical weathering strength decreased and the tree-pollen declined. This suggests that a strong drier regional climatic event occurred at around 9.2 cal ka BP in central China, which was, in turn, probably connected to the rapid 9.2 ka climate event co-developing worldwide. In addition, based on the synthesis of our peat records and the other Holocene hydrological records from Asian summer monsoon (ASM) region, we further found that the 9.2 ka event probably constituted the strongest abrupt collapse of the Asian monsoon system during the full Holocene interval. The correlations between ASM and the atmospheric ¹⁴C production rate, the North Atlantic drift ice records and Greenland temperature indicated that the weakened ASM event at around 9.2 cal ka BP could be interpreted by the co-influence of external and internal factors, related to the changes of the solar activity and the Atlantic Meridional Overturning Circulation (AMOC).
... In contrast, the Holocene temperature trend for the U K' 37 -inferred SSTs shows a steep increase from 21.5 to 24.5 °C during the transition period from the YD to the early Holocene followed by a ~1.5 °C decline throughout the early to middle Holocene and a very abrupt temperature drop to 21.7 °C at around 4 kyr. This is well in line with temperature records from the Japanese margin (Isono et al., 2009) and the Tohoku area with similar declines in U K´3 7 -, Td´ (a diatom-based proxy for SST), Mg/Ca-and δ 18 O-SST records (Sagawa et al., 2006;Oba et al., 2006). A similar decrease in SST, inferred from planktonic foraminiferal assemblages, occurs at the Okinawa Trough at ~4 kyr (Jian et al., 2000) and was interpreted to result from a weakened KC associated with stronger winter monsoonal winds and an associated shift of the main axis of the KC. ...
The Kuroshio Current (KC) and Oyashio Current (OC) are the two major western boundary currents of the Pacific Ocean and their interplay exerts a major control on the climate evolution of the northwestern Pacific region as well as East Asia. Although millennial scale variations in the strength and flow pattern of the KC are well documented, only little is known on the long-term evolution of this ocean current and its role in affecting regional and global climate over geological time scales. Here, we present surface and thermocline temperature records covering the last two glacial-interglacial cycles of IODP (Integrated Ocean Drilling Program) Site C0011, SE of Japan, using the lipid paleothermometers TEXH86 (tetraether index of tetraethers consisting of 86 carbon atoms), UK´37 (unsaturated ketone index) and LDI (long-chain diol index). Lower average water temperatures (20.1–20.7 °C in TEXH86, 21.6–22.0 °C in UK´37, and 20.7–21.9 °C in LDI) during marine isotope stages (MIS) 2 and 6 are considered to indicate a reduction in warm water mass export from the Western Pacific Warm Pool (WPWP) to northern mid-latitudes via the KC due to decreased subtropical gyre circulation in the North Pacific. A synchronous southward displacement of the KC/OC interfrontal zone resulted in an overall stronger influence of colder and more polar waters at Site C0011. MIS 1, 3 and 5 are characterized by generally higher water temperatures (21.7–22.1 °C in TEXH86, 23.2–24.3 °C in UK´37, and 23.1–24.3 °C in LDI), likely reflecting an increased northward transport of subtropical waters to the study site. Higher Holocene than Eemian water temperatures are attributed to a stronger KC and the formation of its short meander south of Japan, whereas a less strong KC during the Eemian likely favored the formation of the large meander path. Better correlations between the different lipid paleothermometers during cold MIS are considered to indicate more similar production seasons and habitat depths of the biological proxy sources with the latter factor likely driven by thermocline shoaling.
The Qilian Mountains (QLM) act as an “ecological security barrier” in western China, impacting the downstream ecosystems and water resource utilization. However, the hydrological evolution of the QLM during the last millennium remains controversial, and their ecological response to climate change is poorly understood. We present a pH record based on the brGDGTs (branched glycerol dialkyl glycerol tetraethers) of a 14 C -dated sediment core from Lake Maozangtianchi in the QLM. We combined this record with element contents determined by scanning XRF and grain size to reconstruct the summer monsoon precipitation variability over the last 900 years. We also reconstructed the history of eco-environmental changes from the total n-alkane contents. On centennial scales, local precipitation exhibited peaks during the intervals of 1100‒1300 CE and 1750‒2000 CE, as well as between 1400‒1750 CE. Additionally, abrupt decreases in precipitation occurred during the transition from the Medieval Warm Period (MWP) to the Little Ice Age (LIA) (1300‒1400 CE). This pattern coherent with other hydroclimatic records from the monsoonal margin of northern China, likely resulted from the combined impact of the El Niño‒Southern Oscillation on tropical Pacific sea-surface temperatures and the meridional shift of the Intertropical Convergence Zone. In addition, a coupled relationship between plant biomass in the Lake Maozangtianchi watershed and fluctuations in monsoon precipitation was observed, with higher plant biomass during 1100‒1200 CE, 1750‒1900 CE, and 1950‒2000 CE, and lower biomass during 1200‒1400 CE and 1900‒1950 CE. However, during 1400‒1750 CE, plant biomass exhibited a minor increasing trend, deviating from its usual correlation with monsoon precipitation. Despite precipitation usually being the primary climatic factor influencing plant biomass in the QLM, during the LIA, nutrients transported by dust and decreased evapotranspiration became pivotal in bolstering plant growth. Our research emphasizes the significant moderating effects of exogenic dust on vegetation changes in alpine ecosystems.
The alpine grasslands and meadows of the Tibetan Plateau are critical for maintaining biodiversity, carbon storage, and regional ecological balance. However, the ecological response of the Tibetan Plateau to climate change and anthropogenic activity is poorly understood. We selected two alpine lakes at different altitudes on the northeastern Tibetan Plateau and used n-alkanes from lacustrine sediments to probe the process of ecological response to climate change (temperature and precipitation) during typical climatic periods of the past millennium, as well as impacts on the ecosystem caused by anthropogenic activities. Our results showed that mid- and long-chain n-alkanes in Lake Dalzong and Lake Bihu sediments, which could be used to evaluate plant biomass variations, were mainly derived from terrestrial plants around the watershed. For both the low-altitude Lake Dalzong (3120 m above sea level (a.s.l.)) and the high-altitude Lake Bihu (4360 m a.s.l.), plant biomass of the watershed increased with enhanced temperature and precipitation during the Medieval Warm Period (MWP), whereas they decreased during the Little Ice Age (LIA), under conditions of lower temperature and precipitation. A further comparison with regional climatic records indicates that temperature and precipitation may have played a more important role in plant biomass changes in the low- and high-altitude regions in the northeastern Tibetan Plateau, respectively. In addition, during the Current Warm Period (CWP), when temperature and precipitation were higher than that in the MWP, plant biomass was lower than that in the MWP in both the Lake Dalzong and Lake Bihu watersheds. The intensification of regional grazing activities and the increase in religious rituals were the primary factors contributing to CWP vegetation degradation. This study highlights the fact that a progressively warmer and wetter climate will not offset the negative impacts of anthropogenic activities on vegetation.
Coastal evolution is influenced by past sea-level changes and resultant shifts from fluvial- to marine-dominant environments and the accompanying significant geochemical and isotopic changes in the water mass and sediments. We investigated the elemental and isotopic features of coastal sedimentary cores (27 m in length) from a small paleo-bay located on the southern coast of Korea to determine such geochemical variability and specify past changes in the bay environment and anoxic conditions and possible links to past climate changes. We analyzed total organic carbon (TOC), total sulfur (TS), their isotopes (δ13CTOC and δ34STS), and pyrite. The δ13CTOC values ranging from −25 to −19‰ (a proxy for terrestrial influence) were lower than average (−22.5‰) before 8300 cal yr BP and since 500 cal yr BP, while the intervening Early to Late Holocene showed higher δ13CTOC values, indicating a shallow coastal environment. The δ34STS values fluctuating between −35 and +5‰ resembled sedimentation rate change. Based on the changes in the ratios of TOC to TS (C/S ratios), sedimentation rate, and δ34STS, we found five possible periods with higher salinity and intensified anoxic conditions at millennial timescales: 8900–8200, 7950–6500, 5200–4300, 3500–2600, and 2000–1100 cal yr BP. These intensified anoxic conditions seem to have been influenced by increased air temperature and sea-surface temperature conditions, which could have intensified the intensity of thermal stratification (less ventilation and mixing) between surface and bottom waters and resultant anoxic conditions.
Drought is the deadliest natural disaster on Earth due to its long duration, wide spatial coverage and direct connection with the food supply for human beings. Drought develops slowly and thus is called a silent killer. This paper reviews the history of research on droughts and mega-droughts. Interannual droughts are in many places driven by the El Nino-Southern Oscillation, multi-decadal mega-droughts are often driven by the Atlantic Multi-Decadal Oscillation, while centennial mega-droughts are often driven by the Global Inter-Centennial Oscillation. More generally, droughts are affected by multiple factors including global sea surface temperature anomalies, local land-atmosphere feedbacks, internal atmospheric variability and external forcings from outside the climate system. Possible future research directions are also suggested. © 2022 Environment and Climate Change Canada. Published by Informa UK Limited, trading as Taylor & Francis Group.
Coastal currents play a key role in regulating alongshore sediment transport, and their relationships with winter storms (burst of the East Asian winter monsoon) and formation of the coastal mud deposits on the eastern China shelf have been established, based on which the evolution of the East Asian winter monsoon has been widely explored. Unlike that of coastal deposits, the formation of offshore deposits on the eastern China shelf is very complex and highly debated, leading to enormous challenges on paleoclimate reconstructions based on these deposits. In this study, cross-front sediment transport under a variable Yellow Sea Warm Current (YSWC) was explored using remote sensing imagery and sedimentary records (seismic profile and sediment grain size) from the North Yellow Sea (NYS). The results indicate that, although the offshore mud deposit in the western NYS is formed by winter storms through triggering cross-front transport of coastal sediment around the Shandong Peninsula, the winter storm signal was completely obscured by that of the YSWC, which might determine the flux of cross-front sediment transport on a millennial scale. The 1500 y sub-orbital climate variability cycle could also be observed in distal muds after 2.8 ka. By comparing the sediment composition within the same mud deposit or between adjacent mud deposits in the NYS, we found that the response of cross-front sediment transport to the YSWC varied spatially, which may be a reason for discrepancies observed in previous winter monsoon reconstructions on the eastern China shelf. Therefore, as indicated by this study, offshore deposits on the eastern China shelf are not suitable for inversions of the winter monsoon. In addition, mud deposits on the eastern China shelf are also dramatically affected by other dynamic factors, including typhoons and river flooding; thus, deeply exploring the dynamic characteristics and formation mechanism of these deposits are prerequisites for paleoclimate reconstruction.
In general, although the climate during the Holocene has been warm, nine well-recognized cold events with an average time interval of more than one thousand years have been highlighted. The forcing mechanism of these cold events with millennial-scale cycles is still widely discussed. In the present study, two different Solar System dynamical processes collectively driven by all eight planets were considered together: the solar inertial motion and the combined planetary tidal force acting on the Sun. In this context, an attempt was made to analyze their effects on solar activity and Holocene North Atlantic cold events at the millennial-scale. These two Solar System dynamical processes were proxied by the distance between the Sun and the Solar System barycenter (DS–S) and the intensity of the combined planetary tidal force (IP–S), respectively. Using the ensemble empirical mode decomposition (EEMD) method, time series data of Solar System dynamics proxies (i.e., DS–S, and IP–S), solar activity proxies (i.e., ¹⁴C and ¹⁰Be), and a proxy of Holocene North Atlantic cold events (i.e., hematite-stained grains) were decomposed into several intrinsic mode functions (IMFs). After extracting IMF components containing millennial-scale cycles, a correlation analysis was performed. As a result, it was found that the solar inertial motion had ∼2,300- and ∼1,000-year cycles and the combined planetary tidal force had a ∼1,500-year cycle, while the solar activity and Holocene North Atlantic cold events proxies had ∼2,300-, ∼1,500-, and ∼1,000-year cycles, respectively. The correlation analysis revealed that the millennial-scale periodic components of the two Solar System dynamics proxies were largely correlated with that of solar activity and Holocene North Atlantic cold events, suggesting that the solar inertial motion and combined planetary tidal force may work together to impact solar activity, and thus the climate in the North Atlantic. Consequently, solar activity was weaker and the North Atlantic temperature was cooler when the Sun was far from the Solar System barycenter and/or the combined planetary tidal force was weakened. This might indicate the involvement of Solar System dynamics on Holocene North Atlantic cold events at the millennial-scale.
Proxy reconstructions from marine sediment cores indicate peak temperatures in the first half of the last and current interglacial periods (the thermal maxima of the Holocene epoch, 10,000 to 6,000 years ago, and the last interglacial period, 128,000 to 123,000 years ago) that arguably exceed modern warmth1,2,3. By contrast, climate models simulate monotonic warming throughout both periods4,5,6,7. This substantial model–data discrepancy undermines confidence in both proxy reconstructions and climate models, and inhibits a mechanistic understanding of recent climate change. Here we show that previous global reconstructions of temperature in the Holocene1,2,3 and the last interglacial period⁸ reflect the evolution of seasonal, rather than annual, temperatures and we develop a method of transforming them to mean annual temperatures. We further demonstrate that global mean annual sea surface temperatures have been steadily increasing since the start of the Holocene (about 12,000 years ago), first in response to retreating ice sheets (12 to 6.5 thousand years ago), and then as a result of rising greenhouse gas concentrations (0.25 ± 0.21 degrees Celsius over the past 6,500 years or so). However, mean annual temperatures during the last interglacial period were stable and warmer than estimates of temperatures during the Holocene, and we attribute this to the near-constant greenhouse gas levels and the reduced extent of ice sheets. We therefore argue that the climate of the Holocene differed from that of the last interglacial period in two ways: first, larger remnant glacial ice sheets acted to cool the early Holocene, and second, rising greenhouse gas levels in the late Holocene warmed the planet. Furthermore, our reconstructions demonstrate that the modern global temperature has exceeded annual levels over the past 12,000 years and probably approaches the warmth of the last interglacial period (128,000 to 115,000 years ago).
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.
A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format.
=== Open access article: https://rdcu.be/b3y6w ===
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.
The subpolar NE Atlantic Ocean experiences seasonal fluxes of labile organic matter (phytodetritus) which are expected to strongly influence the composition of benthic foraminiferal assemblages and benthic foraminiferal accumulation rates. We studied export production over the last 12 kyr at a sampling resolution of approximately 250–300 years through an investigation of bathyal benthic foraminiferal assemblages (>63 μm) at Ocean Drilling Program (ODP) Site 980 on the Feni Drift (55°29′N, 14°42′W, 2179 m water depth).
During the last 12 kyr, faunas at Site 980 were dominated (~75%) by Cassidulina obtusa, Nonionella iridea, Bolivina difformis, Trifarina pauperata, Alabaminella weddellensis, Stainforthia fusiformis, Cassidulina laevigata and Eilohedra vitrea. The absolute and relative abundances and diversity of these and other species varied significantly. In the interval ~12–10 ka, A. weddellensis, S. fusiformis and T. pauperata had higher % abundance (named here ‘H10 species’), but this is not reflected in a higher accumulation rate, suggesting that surface productivity was low, at highly variable conditions. Species at lower % abundance during this time include B. difformis, C. laevigata, C. obtusa, E. vitrea and N. iridea (so-called ‘L10 species’). The ‘8.2 ka cold event’ was characterized by increased carbonate dissolution (reflected in decreases in the absolute abundance, benthic foraminifera accumulation rate, weight % coarse fraction, and presence of poorly preserved/fragmented benthic foraminifera). Peaks in the relative abundance of species which, in our opinion, exploited phytodetritus (‘phytodetritus species’: N. iridea, A. weddellensis, C. obtusa, and rare Epistominella exigua) occurred at 8.0 ka, 7.0 ka, 6.3–5.6 ka, 4.7 ka, 4.3–3.4 ka and 2.4 ka. These peaks generally correspond to peaks in absolute abundance (number of specimens per gram, accumulation rate), indicating increases in the seasonality of export productivity. However, the ‘phytodetritus species’ do not covary in absolute and relative abundance over the studied interval, suggesting that they have somewhat different ecological requirements.
There appears to be no simple relationship between changes in the degree of seasonality of export productivity (i.e., abundance of ‘phytodetritus species’) and records of palaeoclimatic/palaeoceanographic proxies, suggesting that bentho-pelagic coupling (arrival of food on the seafloor with local surface productivity) might not have been straightforward in this region. Site 980 is located in the hydrodynamically active area of Feni Drift, and during the Holocene, currents might have winnowed and removed fine-grained organic matter, making it unavailable to benthic organisms. Alternatively, there may have been changes in remineralization and/or mid-water competition for food, so that the fraction of the organic flux that reached the seafloor may have varied. Holocene benthic foraminiferal assemblages thus reflect highly dynamic conditions in export productivity and arrival of organic matter at the seafloor.
Systematic comparisons of proxy-based reconstructions and climate model simulations of past millennium temperature variability offer insights into climate sensitivity and feedback mechanisms, besides allowing model evaluation independently from the period covered by instrumental data. Such simulation–reconstruction comparisons can help to distinguish more skillful models from less skillful ones, which may subsequently help to develop more reliable future projections. This study evaluates the low-frequency simulation–reconstruction agreement within the past millennium through assessing the amplitude of temperature change between the Medieval Climate Anomaly (here, 950–1250 CE) and the Little Ice Age (here, 1450–1850 CE) in PMIP3 model simulations compared to proxy-based local and continental-scale reconstructions. The simulations consistently show a smaller temperature change than the reconstructions for most regions in the Northern Hemisphere, but not in the Southern Hemisphere, as well as a partly different spatial pattern. A cost function analysis assesses how well the various simulations agree with reconstructions. Disregarding spatial correlation, significant differences are seen in the agreement with the local temperature reconstructions between groups of models, but insignificant differences are noted when compared to continental-scale reconstructions. This result points toward a limited possibility to “rank” models by means of their low-frequency temperature variability alone. The systematically lower amplitude of simulated versus reconstructed temperature change indicates either too-small simulated internal variability or that the analyzed models lack some critical forcing or have missing or too-weak feedback mechanisms. We hypothesize that too-cold initial ocean conditions in the models—in combination with too-weak internal variability and slow feedbacks over longer time scales—could account for much of the simulation–reconstruction disagreement.
To help further understand the long-term dynamics of environments and ecosystems and those modern situations which have been identified by observations, paleo studies on the last centuries to millennia using coastal sediments play important roles. Here I introduce three coastal paleo studies in the Seto Inland Sea and the Bungo Channel, Japan, which I and collaborators have performed so far : ocean warming trend in the Bungo Channel ; decadal-scale marine ecosystem variability in the Bungo Channel and the Seto Inland Sea ; and long-term dynamics of Japanese sardine and anchovy populations.
From the studies on benthic foraminiferal Mg/Ca-based bottom water temperature reconstruction in the eastern Bungo Channel over the last 200 years, we found an onset of the ocean warming trend in the early 20th century and the highest temperature stage seen in the late 20th century over the last 200 years in the bottom water. Fossil diatom and pigment records from the Bungo Channel and Beppu Bay showed decadal-scale variations in primary productivity, which are likely due to their responses to variations in nutrient supply from shelf slope regions off the Bungo Channel associated with Pacific decadal climate variability. This phenomenon is potentially linked to the recent oligotrophication in the Seto Inland Sea. On the basis of fish scale records reconstructed from Beppu Bay sediments, we found that multidecadal alternations between Japanese sardine and anchovy as seen in the catch records during the 20th century were unstable for the last 2800 years. Paleo records rather show centennial and millennial scale variations in fish populations, indicating that there may be a wide variety of sardine and anchovy population dynamics in response to centennial to millenial climate modes before the observational era. Therefore, the paradigm for Pacific climate/marine ecosystem decadal variability, such as regime shifts based on modern observations, may be transient. These paleo studies on the past centuries and millennia using Japanese coastal sediments have improved our understanding of long-term dynamics of climate and marine ecosystems and these modern situations. For projections and management of marine environments and ecosystems, there still remain many things for coastal paleo researchers on the past centuries and millennia to do.
In this data article, a dataset of paleoclimatic records ranging from 22 to 9 thousand years before present is reported, which is related to the research article entitled “Breakpoint lead-lag analysis of the last deglacial climate change and atmospheric CO2 concentration on global and hemispheric scales” published in the journal of Quaternary International by Liu et al. (2018). In the dataset, 4 δ¹⁸O records derived from Greenlandic ice cores, 2 δD records and 7 δ¹⁸O records derived from Antarctic ice cores, 32 UK’37 records and 26 Mg/Ca records derived from marine deposits, and 17 δ¹⁸O records derived from cave stalagmites were collected and collated. General and statistical characteristics of these 88 proxy records are showed here. All of the data are stored in separate Microsoft Excel spreadsheets that are available for researchers.
Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.
Total organic carbon (TOC) and calcium carbonate (CaCO3) concentrations were determined for 304 samples, and biomarkers were analyzed for 101 samples from Core 167-1016C-1H. TOC varies between 1% and 2%, and CaCO3 is typically 1%-4%, with peaks reaching 14%. Paleotemperature estimated from U37(k') varies from 8.5°to 17.5°C. The U37(k') variation implies that Core 167-1016C-1H covers oxygen isotope Stages 1-6. Peaks of diatom-derived C(25:1) HBI alkene concentrations occur during warming intervals, suggesting intensified upwelling during deglaciation. The concentrations of haptophyte-derived alkenones and diatom-derived C(25:1) HBI alkene vary out of phase, which presumably resulted from the changes in the mode of nutrient supply to surface mixed layer. Maximal CaCO3 contents (>10%) were observed in both warming and cooling intervals. The peak in cooling interval relates to an alkenone maximum, whereas the peaks in warming intervals do not. This implies that carbonate production is not the only factor controlling carbonate compensation depth at this site, and it suggests considering the changes in North Pacific deep-water chemistry. Petroleum-type compounds are present in Site 1016 sediments. Their concentrations are maximized in the warming intervals that correspond to the timing of destruction of a huge tar mound off Point Conception. The tarry material was presumably transported by the Arguello Fan system to Site 1016.
The significance of the apparent 1470 years cycle in the recurrence of the Dansgaard-Oeschger (DO) events, observed in the Greenland ice cores, is debated. Here we present statistical significance tests of this periodicity. The detection of a periodicity relies strongly on the accuracy of the dating of the DO events. Here we use both the new NGRIP GICC05 time scale based on multi-parameter annual layer counting and the GISP2 time scale where the periodic-ity is most pronounced. For the NGRIP dating the recurrence times are indistinguishable from a random occurrence. This is also the case for the GISP2 dating, except in the case where the DO9 event is omitted from the record.
Twelve years of sea surface height (SSH) data from multiple satellite altimeters are used to investigate the low-frequency changes and the interconnections of the Kuroshio Extension (KE) jet, its southern recirculation gyre, and their mesoscale eddy field. The dominant signal is characterized by the steady weakening of the KE jet/recirculation gyre from 1993 to 1996, followed by a gradual strengthening after 1997. During the weakening period of 1993-96, the KE path migrated southward in general, and this path migration reversed in direction during the strengthening period of the KE jet and recirculation gyre after 1997. By hindcasting the SSH signals using linear vorticity dynamics, it was found that weakening (strength- ening) in the KE jet and recirculation gyre is consistent with westward propagation of negative (positive) SSH anomalies generating in the eastern North Pacific and strengthening during their westward propaga- tion. When the KE jet and recirculation gyre were in a weak mode during 1996-2001, the regional eddy kinetic energy level was observed to be higher than when the jet and recirculation gyre were in a strong mode. This negative correlation between the mean flow intensity and the level of regional eddy kinetic energy is found in both the SSH data and the linear vorticity model to result from the migration of the KE jet inflow over the Izu-Ogasawara Ridge. When it is forced southward by the impinging negative SSH anomalies, the KE jet inflow rides over the ridge through a shallow segment, leading to large-amplitude downstream meanders. Impinging of positive SSH anomalies, on the other hand, strengthens the recircu- lation gyre and forces the inflow northward where it passes through a deep channel, minimizing the path perturbations in the downstream region.
Here we present a high-resolution marine sediment record from the El Niño region off the coast of Peru spanning the last 20,000 years. Sea surface temperature, photosynthetic pigments, and a lithic proxy for El Niño flood events on the continent are used as paleo–El Niño–Southern Oscillation proxy data. The onset of stronger El Niño activity in Peru started around 17,000 calibrated years before the present, which is later than modeling experiments show but contemporaneous with the Heinrich event 1. Maximum El Niño activity occurred during the early and late Holocene, especially during the second and third millennium B.P. The recurrence period of very strong El Niño events is 60–80 years. El Niño events were weak before and during the beginning of the Younger Dryas, during the middle of the Holocene, and during medieval times. The strength of El Niño flood events during the last millennium has positive and negative relationships to global and Northern Hemisphere temperature reconstructions.
Holocene and latest Pleistocene oceanographic conditions and the coastal climate of northern California have varied greatly, based upon high-resolution studies (ca. every 100 years) of diatoms, alkenones, pollen, CaCO3%, and total organic carbon at Ocean Drilling Program (ODP) Site 1019 (41.682°N, 124.930°W, 980 m water depth . Marine climate proxies (alkenone sea surface temperatures [SSTs] and CaCO3%) behaved remarkably like the Greenland Ice Sheet Project (GISP)-2 oxygen isotope record during the Bølling-Allerod, Younger Dryas (YD), and early part of the Holocene. During the YD, alkenone SSTs decreased by >3°C below mean Bølling-Allerod and Holocene SSTs. The early Holocene (ca. 11.6 to 8.2 ka) was a time of generally warm conditions and moderate CaCO3 content (generally >4%). The middle part of the Holocene (ca. 8.2 to 3.2 ka) was marked by alkenone SSTs that were consistently 1-2°C cooler than either the earlier or later parts of the Holocene, by greatly reduced numbers of the gyre-diatom Pseudoeunotia doliolus (<10%), and by a permanent drop in CaCO3% to <3%. Starting at ca. 5.2 ka, coastal redwood and alder began a steady rise, arguing for increasing effective moisture and the development of the north coast temperate rain forest. At ca. 3.2 ka, a permanent ca. 1°C increase in alkenone SST and a threefold increase in P. doliolus signaled a warming of fall and winter SSTs. Intensified (higher amplitude and more frequent) cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature (enhanced El Niño-Southern Oscillation [ENSO] cycles) have characterized the Site 1019 record since about 3.5 ka.
A detailed stable-isotope record is presented for the full length of the Greenland Ice-core Project Summit ice core covering the last 250,000 years according to a graduated timescale. It appears that the climatic stability of the Holocene is the exception rather than the rule; the last interglacial is also noted to have lasted longer than is implied by the deep-sea SPECMAP record. This discrepancy may be accounted for if the climate instability at the outset of the last interglacial delayed the melting of the Saalean ice sheets in America and Eurasia.
Paleoclimatic time series are often unevenly spaced in time, making it difficult to obtain an accurate estimate of their red-noise spectrum. A Fortran 90 program (REDFIT) is presented that overcomes this problem by fitting a first-order autoregressive (AR1) process, being characteristic for many climatic processes, directly to unevenly spaced time series. Hence, interpolation in the time domain and its inevitable bias can be avoided. The program can be used to test if peaks in the spectrum of a time series are significant against the red-noise background from an AR1 process. Generated and paleoclimatic time series are used to demonstrate the capability of the program.
Evidence from North Atlantic deep sea cores reveals that abrupt shifts punctuated what is conventionally thought to have been
a relatively stable Holocene climate. During each of these episodes, cool, ice-bearing waters from north of Iceland were advected
as far south as the latitude of Britain. At about the same times, the atmospheric circulation above Greenland changed abruptly.
Pacings of the Holocene events and of abrupt climate shifts during the last glaciation are statistically the same; together,
they make up a series of climate shifts with a cyclicity close to 1470 ± 500 years. The Holocene events, therefore, appear
to be the most recent manifestation of a pervasive millennial-scale climate cycle operating independently of the glacial-interglacial
climate state. Amplification of the cycle during the last glaciation may have been linked to the North Atlantic's thermohaline
circulation.
We have generated a high-resolution record of alkenone sea surface temperature (SST) between 10–24 ka from Core MD01-2421 off central Japan, in the northwestern Pacific. The cooling by 5°C from 21 ka to 12.8 ka implies the equatorward shift of the subarctic boundary in the northwestern Pacific by ∼2.8° in latitude. This shift was a result of the stronger summer Okhotsk High. The Okhotsk High was likely enhanced by the combined effects of El Niño-like conditions in the tropical Pacific and the heating of the land surface of northeastern Siberia.
The late Quaternary records of alkenone sea surface temperature (SST) in the Japan and California margins showed orbital-scale anti-phase SST variations between the two margins. This east-west seesaw-like change agreed well with the long-term El Niño-Southern Oscillation (ENSO) behavior predicted by the Zebiak-Cane ENSO model [ Clement et al., 1999 ] as regards both the timing and frequency during 0–60 ka and 120–145 ka, and is attributed to the precession-controlled change in tropical ENSO behavior. This anti-phase SST change was not clearly demonstrated during 60–120 ka. This finding suggests that the influence of tropical climatic dynamics on the mid-latitude North Pacific varied in response to glacial-interglacial cycles.
The El Niño-Southern Oscillation (ENSO) is the most potent source of interannual climate variability. Uncertainty surrounding the impact of greenhouse warming on ENSO strength and frequency has stimulated efforts to develop a better understanding of the sensitivity of ENSO to climate change. Here we use annually banded corals from Papua New Guinea to show that ENSO has existed for the past 130,000 years, operating even during "glacial" times of substantially reduced regional and global temperature and changed solar forcing. However, we also find that during the 20th century ENSO has been strong compared with ENSO of previous cool (glacial) and warm (interglacial) times. The observed pattern of change in amplitude may be due to the combined effects of ENSO dampening during cool glacial conditions and ENSO forcing by precessional orbital variations.
Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene "thermal maximum." Since approximately 5400 years ago, a trend toward drier conditions is evident from the data, with high-amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the "Little Ice Age." These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The Cariaco Basin record exhibits strong correlations with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global teleconnections among regional climates.
Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in
solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production
rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of
drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment
of the North Atlantic's “1500-year” cycle. The surface hydrographic changes may have affected production of North Atlantic
Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.
The variability of El Niño/Southern Oscillation (ENSO) during the Holocene epoch, in particular on millennial timescales, is poorly understood. Palaeoclimate studies have documented ENSO variability for selected intervals in the Holocene, but most records are either too short or insufficiently resolved to investigate variability on millennial scales. Here we present a record of sedimentation in Laguna Pallcacocha, southern Ecuador, which is strongly influenced by ENSO variability, and covers the past 12,000 years continuously. We find that changes on a timescale of 2-8 years, which we attribute to warm ENSO events, become more frequent over the Holocene until about 1,200 years ago, and then decline towards the present. Periods of relatively high and low ENSO activity, alternating at a timescale of about 2,000 years, are superimposed on this long-term trend. We attribute the long-term trend to orbitally induced changes in insolation, and suggest internal ENSO dynamics as a possible cause of the millennial variability. However, the millennial oscillation will need to be confirmed in other ENSO proxy records.
Many palaeoclimate records from the North Atlantic region show a pattern of rapid climate oscillations, the so-called Dansgaard-Oeschger events, with a quasi-periodicity of approximately 1,470 years for the late glacial period. Various hypotheses have been suggested to explain these rapid temperature shifts, including internal oscillations in the climate system and external forcing, possibly from the Sun. But whereas pronounced solar cycles of approximately 87 and approximately 210 years are well known, a approximately 1,470-year solar cycle has not been detected. Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard-Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of approximately 87 and approximately 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation. For Holocene conditions, similar events do not occur. We conclude that the glacial 1,470-year climate cycles could have been triggered by solar forcing despite the absence of a 1,470-year solar cycle.
In 1996/1997, a 14C-AMS system (model 4130-AMS) manufactured by High Voltage Engineering Europe (HVEE), B.V., The Netherlands, was installed at the Center for Chronological Research (CCR), Nagoya University. The system provides highly precise and accurate 14C determinations as well as C values for graphite targets (1.5 mg carbon and 3 mg iron powder) prepared from standards and samples. One sigma errors in 14C ages typically range from ±20 to ±40 yr for materials younger than 8000 BP, depending on absolute 14C ages or 14C counting uncertainties. Standard deviations of 13C/12C ratios range from ±0.1‰ to ±0.9‰. For relatively young samples, accuracies of less than 10‰ are obtained using IAEA reference materials and FIRI test samples. Background levels on the 14C-AMS system range from 52 to 54 ka BP for a pure graphite powder. The HVEE 14C-AMS system at the CCR has been used routinely to date samples with a variety of research applications.
Solar (heliomagnetic), geomagnetic and oceanic forcing all play a role in atmospheric 14CO2 change. Here we assign the variance associated with certain periodicities in a single year (0-450 cal. BP) and a Holocene bidecadal (0-11400 cal. BP) 14CO2 record to specific forcing factors. In the single-year time series the variance in the 2-6-year periodicity range is attributable to El Niño-Southern Oscillation (ENSO) ocean perturbations. A 10-11-year component is partially tied to solar modulation of the cosmic ray flux, and multidecadal variability may relate to either solar modulation or instability of the North Atlantic thermohaline circulation. For the early Holocene bidecadal 14C record we derive a 512-year atmospheric 14C periodicity which relates to instabilities in North Atlantic thermohaline circulation. North Atlantic deep water formation increased near the start, instead of the termination, of the Younger Dryas interval. The ubiquitous 206-year 14C cycle is assigned either to solar modulation, or to solar modulation modified by a climate (ocean) response. The latter modification is discussed as part of a hypothetical mechanism explaining postulated climate-14C relationships in which a minor solar- induced Maunder Minimum climate change is amplified by salinity effects on North Atlantic thermoha line circulation.
The 3-km-long Greenland Ice Sheet Project 2 (GISP2) ice core presents a 100,000+- year detailed oxygen isotope profile covering almost a full glacial-interglacial cycle. Measurements of isotopic fluctuations in snow, frost, and atmospheric water vapor samples collected during summer field seasons (up to 200/00) are compatible with the large and abrupt 18O/16O changes observed in accumulated firn. Snow pit delta18O profiles from the GISP2 summit area, however, show rapid smoothing of the 18O/16O signal near the surface. Beyond about 2-m depth the smoothed delta18O signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate. The longer climate fluctuations also have regional and often global significance. In the older part of the record, corresponding to marine isotope stages (MIS) 5a to 5d, the effect of orbital climate forcing via the 19- and 23-kyr precession cycles and the 41-kyr obliquity cycle is obvious. From the end of MIS 5a, at about 75,000 years B.P., till the end of the glacial at the Younger Dryas-Preboreal transition, at 11,650 years B.P., the O18O/16O record shows frequent, rapid switches between intermediate interstadial and low stadial values. Fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1.5 kyr, a broad peak at 4.0 kyr, and additional shorter periods. Detailed comparison of the GISP2 18O/16O record with the Vostok, Antarctica, deltaD record; Pacific Ocean foraminiferal 18O/16O; Grande Pile, France, tree pollen; and insolation indicates that a counterpart to many of the rapid 18O/16O fluctuations of GISP2 can be found in the other records, and that the GISP2 isotopic changes clearly are the local expression of climate changes of worldwide extent. Correlation of events on the independent GISP2 and SPECMAP time scales for the interval 10,000-50,000 years B.P. shows excellent chronometric agreement, except possibly for the event labeled 3.1. The glacial to interglacial transition evidently started simultaneously in the Arctic and the Antarctic, but its development and its expression in Greenland isotopes was later suppressed by the influence of meltwater, especially from the Barents Sea ice sheet, on deep water formation and ocean circulation. Meltwaters from different ice sheets bordering the North Atlantic also influenced ocean circulation during the Bølling-Allerød interstadial complex and the Younger Dryas and led to a distinct development of European climate and Greenland 18O/16O values. The Holocene interval with long-term stable mean isotopic values contains several fluctuations with periods from years to millennia. Dominant is a 6.3-year oscillation with amplitude up to 3 to 40/00. Periodicities of 11 and 210 years, also found in the solar-modulated records of the cosmogenic isotopes 10Be and 14C, suggest solar processes as the cause of these cycles. Depression of 18O/16O values (cooling) by volcanic eruptions is observed in stacked GISP2 delta18O records, but the effect is small and not likely to trigger major climate changes.
Evidence gleaned from the instrumental record of climate data identifies a robust, recurring pattern of ocean-atmosphere climate variability centered over the midlatitude North Pacific basin. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal timescales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, and 1977; the last two reversals correspond to dramatic shifts in salmon production regimes in the North Pacific Ocean. This climate pattern also affects coastal sea and continental surface air temperatures, as well as streamflow in major west coast river systems, from Alaska to California.
The chronology of interdecadal climatic regime shifts is examined, using instrumental data over the North Pacific, North America and the tropical oceans, and reconstructed climate records for North America. In the North Pacific and North America, climatic regime shifts around 1890 and in the 1920s with alternating polarities are detected, whose spatial structure is similar to that of the previously‐known climatic shifts observed in the 1940s and 1970s. Sea‐surface temperatures in the tropical Indian Ocean‐maritime continent region exhibit changes corresponding to these four shifts. Spectra obtained by the Multi‐Taper‐Method suggest that these regime shifts are associated with 50–70 year climate variability over the North Pacific and North America.
The leading mode of the empirical orthogonal functions of the air‐temperature reconstructed from tree‐rings in North America exhibits a spatial distribution that is reminiscent of instrumentally observed air‐temperature differences associated with the regime shifts. The temporal evolution of this mode is characterized by a 50–70 year oscillation in the eighteenth and nineteenth centuries. This result, combined with the results of the analyses of the instrumental data, indicates that the 50–70 year oscillation is prevalent from the eighteenth century to the present in North America.
A 4-day superrotation 60-times faster than the planetary rotation (243 days) is observed in Venus' atmosphere. Although it has been difficult to reproduce the extraordinary phenomenon in GCMs, the superrotation is reproduced by meridional circulation and planetary-scale waves with phase velocities slower than 50 m s-1 in our improved GCM. Thermally induced waves produce equatorward momentum fluxes in the middle atmosphere, while the planetary-scale pattern of two different gravity and Rossby waves with the same frequency is found to produce the equatorward momentum flux in the lower atmosphere. These processes play crucial roles in dynamics of the simulated Venus superrotation.
The most prominent Holocene climatic event in Greenland ice-core proxies, with approximately half the amplitude of the Younger Dryas, occurred ˜8000 to 8400 yr ago. This Holocene event affected regions well beyond the North Atlantic basin, as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane. Widespread proxy records from the tropics to the north polar regions show a short-lived cool, dry, or windy event of similar age. The spatial pattern of terrestrial and marine changes is similar to that of the Younger Dryas event, suggesting a role for North Atlantic thermohaline circulation. Possible forcings identified thus far for this Holocene event are small, consistent with recent model results indicating high sensitivity and strong linkages in the climatic system.
The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000–0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The 14 C age–cal age information, produced by many laboratories, is converted to Δ 14 C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured l4 C ages and the errors therein, regional 14 C age differences, tree–coral 14 C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs . single-year 14 C results. Changes in oceanic deepwater circulation, especially for the 16,000–11,000 cal BP interval, are reflected in the Δ 14 C values of INTCAL98.
Cores 255 and B-3GC from the southern and northern Okinawa Trough, respectively, were studied for determining the variability of the Kuroshio Current on centennial scales during the Holocene based on detailed AMS C-14 dates, stable isotope, and planktonic foraminiferal distribution. The main flow of the Kuroshio Current was inferred to reenter the Okinawa Trough at similar to7.3 calendar (cal.) kyr BP, leading to abrupt changes in sedimentation rate, remarkably increased abundance of the Kuroshio Current indicator Pulleniatina obliquiloculata, increased sea surface temperature (SST) and depth of thermocline (DOT). During similar to4.6-2.7 cal. kyr BP, the abundance of P, obliquiloculata sharply decreased, corresponding to a decreases in SST and DOT, implying that the influence of the Kuroshio Current weakened at that time, possibly as a result of the intensified winter monsoon. Significantly, the Kuroshio Current proxies (e.g. the difference in SST between the southern and northern Okinawa Trough) disp
1] Many paleoclimatic data reveal a $1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system; oscillatory modes within the Earth system can be expected to be far more irregular in period.
Decadal fluctuations in salinity, nutrients, chlorophyll, a variety of zooplankton taxa, and fish stocks in the Northeast Pacific are often poorly correlated with the most widely-used index of large-scale climate variability in the region - the Pacific Decadal Oscillation (PDO). We define a new pattern of climate change, the North Pacific Gyre Oscillation (NPGO) and show that its variability is significantly correlated with previously unexplained fluctuations of salinity, nutrients and chlorophyll. Fluctuations in the NPGO are driven by regional and basin-scale variations in wind-driven upwelling and horizontal advection – the fundamental processes controlling salinity and nutrient concentrations. Nutrient fluctuations drive concomitant changes in phytoplankton concentrations, and may force similar variability in higher trophic levels. The NPGO thus provides a strong indicator of fluctuations in the mechanisms driving planktonic ecosystem dynamics. The NPGO pattern extends beyond the North Pacific and is part of a global-scale mode of climate variability that is evident in global sea level trends and sea surface temperature. Therefore the amplification of the NPGO variance found in observations and in global warming simulations implies that the NPGO may play an increasingly important role in forcing global-scale decadal changes in marine ecosystems.
Cultures of the marine coccolithophorid, Emiliania huxleyi, were grown in the laboratory at five temperatures (8°, 10°, 15°, 20°, 25°C) and monitored by capillary gas chromatography for their long-chain, unsaturated lipid compositions. The long-chain lipids of this plant comprise a series of C37, C38 and C39 di-, tri- and, in cells grown below 15°C, tetra-unsaturated methyl and ethyl ketones and a methyl and ethyl ester of a di-unsaturated C36 fatty acid. Systematic changes in the degree of unsaturation and in the overall carbon chain length distribution of the alkenones and in the proportion of fatty acid esters relative to alkenones are noted as a function of growth temperature. We present temperature calibrations for these changes in the lipid composition of laboratory cultures and compare these results with the compositions of this biomarker series measured in a variety of sediments accumulating beneath warm (⩾25°C) and cold (⩽12°C) surface waters in the tropical and temperate North Pacific Ocean, respectively. The comparisons demonstrate 1) this series of biomarkers is deposited in these oceanic sediments with minimal evidence of alteration to its original composition and 2) the strain of E. huxleyi used in this laboratory calibration is representative of the “average” marine phytoplankton supplying this novel series of biomarkers to contemporary sediments in these two environments and a wide variety of other oceanic environments. The long-chain alkenones constitute a major component (8.0 ± 2.9%) of the total organic carbon content of living cells of E. huxleyi. The high cellular abundance of these compounds appears to be relatively constant and independent of the growth temperature of the plant. These biomarkers provide a well-designed and useful geochemical tool for assessing variations not only in surface water temperatures but potentially also in the productivity of an important group of marine phytoplankton in oceans of the recent and distant past.
Sinking particles collected from year-long time-series sediment traps at 1674, 4180, 5687 and 8688 m depths, the underlying bottom sediment at 9200 m depth, and suspended particles from surface and subsurface waters in the northwestern North Pacific off Japan were analyzed for long-chain alkenones and alkyl alkenoates (A&A) which are derived mainly from Gephyrocapsacean algae, especially Emiliania huxleyi and Gephyrocapsa oceanica. Alkenone temperature records in sediment trap samples at 1674 m were almost similar to observed sea surface temperatures (SST) with a time delay of one half to one full month. However, alkenone temperatures in trap samples were about slightly lower than measured SST in late spring to early fall. The lowering might be caused by formation of the seasonal thermocline. Nevertheless, these temperature drops observed in trap samples were smaller than those actually observed in a subsurface layer off central Japan. Vertical profiles of A&A concentrations and alkenone temperatures in suspended particles collected from the subsurface waters in early fall indicated that these compounds were produced mostly in a surface mixed layer above the depth of the chlorophyll maximum even in warm seasons. These results suggested that alkenone temperatures strongly reflected SST rather than the temperatures of thermocline waters in these study areas even in such a warm season. Pronounced maxima in A&A fluxes found in sediment trap samples at 1674 m in late spring to summer showed that A&A productions were highest during the periods of spring bloom, according to a time delay between alkenone temperatures and observed SST. Seasonal patterns of alkenone records in trap samples at 4180 and 5687 m could also preserve SST signals well, suggesting that A&A in deep sea waters were mainly derived from primary products in the surface layer. A&A fluxes tended to decrease with water depth, and the ratios of A&A to particulate organic carbon (POC) rapidly decreased in underlying bottom sediment. This clearly indicates that A&A were decomposed and diluted by other refractory organic materials in either the water column or the sediment–water interface. However, A&A compositions were consistently uniform between the trap samples and the underlying bottom sediments, so that A&A could not qualitatively alter during early diagenetic processes.
Alkenone sea surface temperature (SST) records were generated from the Ocean Drilling Program's (ODP) Sites 1014 and 1016 to examine the response of the California Current System to global climate change during the last 136 ka. The temperature differences between these sites (ΔSSTNEP=SSTODP1014–SSTODP1016) reflected the intensity of the California Current and varied between 0.4 and 6.1 °C. A high ΔSSTNEP (weaker California Current) was found for late marine isotope stage (MIS) 2 and early MIS 5e, while a low ΔSSTNEP (stronger California Current) was detected for mid-MIS 5e and MIS 1. Spectral analysis indicated that this variation pattern dominated 23- (precession) and 30-ka periods. Comparison of the ΔSSTNEP and SST based on data from core MD01-2421 at the Japan margin revealed anti-phase variation; the high ΔSSTNEP (weakening of the California Current) corresponded to the low SST at the Japan margin (the southward displacement of the NW Pacific subarctic boundary), and vice versa. This variation was synchronous with a model prediction of the tropical El Niño-Southern Oscillation behavior. These findings suggest that the intensity of the North Pacific High varied in response to precessional forcing, and also that the response has been linked with the changes of tropical ocean–atmosphere interactions.
Evidence has been accumulating in many fields of investigation pointing to a notably warm climate in many parts of the world, that lasted a few centuries around A.D. 1000–1200, and was followed by a decline of temperature levels till between 1500 and 1700 the coldest phase since the last ice age occurred. There has been some controversy as to whether this climatic variation was geeat enough to be significant in connection with the balance of Nature or the economy of Man. It is time to marshal the evidence and attempt a numerical assessment of the climatic values involved in some area for which there are enough data to permit it. This is attempted here and provides an illustration of how data from the realms of botany, historical document research and meteorology may be used to confirm, correct and amplify each other.Changes of prevailing temperature and rainfall in England between periods of 50–150 years duration around 1200 and around 1600 are found which, on all the evidence at present available, probably amounted to 1.2–1.4°C and 10% respectively. Changes in some reasons of the year may have exceeded these ranges of the annual mean. The changes indicated are small enough to account for earlier impressions in some quarters that there has been no significant change of climate in the last 2,500 years, yet they are big enough to be surprising in terms of previous meteorological knowledge and undoubtedly upsetting for the human economies of those times (and perhaps of any time).It is by quantitative assessment of climatic values for epochs, such as the one here treated, for which some sort of extreme character is indicated by reliably dated evidence, that palaeoclimatology may hope to progress. The time-scale of the epoch here studied appears similar to that of several earluer climatic oscillations of known importance to the history of the European fauna and flora, which for obvious reasons cannot be submitted to equally close meteorological analysis. It is essential that the geographical distribution of climatic values arrived at, should be examined (as is done here) for consistency and the possibility of a reasonable interpretation in terms of the condition of the wind and ocean circulations.
Seasonal and depth variations in alkenone flux and molecular and isotopic composition of sinking particles were examined using a 21-month time-series sediment trap experiment at a mooring station WCT-2 (39°N, 147°E) in the mid-latitude NW Pacific to assess the influences of seasonality, production depth, and degradation in the water column on the alkenone unsaturation index UK′37. Analysis of the underlying sediments was also conducted to evaluate the effects of alkenone degradation at the water–sediment interface on UK′37. Alkenone sinking flux and UK′37-based temperature showed strong seasonal variability. Alkenone fluxes were higher from spring to fall than they were from fall to spring. During periods of high alkenone flux, the UK′37-based temperatures were lower than the contemporary sea-surface temperatures (SSTs), suggesting alkenone production in a well-developed thermocline (shallower than 30 m). During low alkenone flux periods, the UK′37-based temperatures were nearly constant and were higher than the contemporary SSTs. The nearly constant carbon isotopic ratios of C37:2 and C38:2 alkenones suggest that alkenones produced in early fall were suspended in the surface water until sinking. The alkenone sinking flux decreased exponentially with increasing depth. The decreasing trend was enhanced during the periods of high alkenone flux, suggesting that fresh and labile particles sank from spring to fall, while old and stable particles sank from fall to spring. The UK′37-based temperature usually increased with increasing depth. The preservation efficiency of alkenones was ∼2.7–5.2% at the water–sediment interface. Despite the significant degradation of the alkenones, there was little difference in UK′37 levels between sinking particles and the surface sediment.
The oxygen isotope record from the Greenland Ice Sheet Project 2 (GISP2) ice core was reanalyzed in the frequency and time domains. The prominent 1470-year spectral peak, which has been associated with the occurrence of Dansgaard-Oeschger interstadial events, is solely caused by Dansgaard-Oeschger events 5, 6, and 7. This result emphasizes the nonstationary character of the oxygen isotope time series. Nevertheless, a fundamental pacing period of ∼1470 years seems to control the timing of the onset of the Dansgaard-Oeschger events. A trapezoidal time series model is introduced which provides a template for the pacing of the Dansgaard-Oeschger events. Statistical analysis indicates only a ≤3% probability that the number of matches between observed and template-derived onsets of Dansgaard-Oeschger events between 13 and 46 kyr B.P. resulted by chance. During this interval the spacing of the Dansgaard-Oeschger onsets varied by ±20% around the fundamental 1470-year period and multiples thereof. The pacing seems unaffected by variations in the strength of North Atlantic Deep Water formation, suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period.
Direct observations of sunspot numbers are available for the past four centuries, but longer time series are required, for example, for the identification of a possible solar influence on climate and for testing models of the solar dynamo. Here we report a reconstruction of the sunspot number covering the past 11,400 years, based on dendrochronologically dated radiocarbon concentrations. We combine physics-based models for each of the processes connecting the radiocarbon concentration with sunspot number. According to our reconstruction, the level of solar activity during the past 70 years is exceptional, and the previous period of equally high activity occurred more than 8,000 years ago. We find that during the past 11,400 years the Sun spent only of the order of 10% of the time at a similarly high level of magnetic activity and almost all of the earlier high-activity periods were shorter than the present episode. Although the rarity of the current episode of high average sunspot numbers may indicate that the Sun has contributed to the unusual climate change during the twentieth century, we point out that solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades.
A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates: Science, v. 278
- G Bond
- W Showers
- M Cheseby
- R Lotti
- P Allmasi
- P Priore
- P Cullen
- H Hajdas
- I Bonani
Bond, G., Showers, W., Cheseby, M., Lotti, R., Allmasi,
P., deMenocal, P., Priore, P., Cullen, H., Hajdas, I.,
and Bonani, G., 1997, A pervasive millennial-scale
cycle in North Atlantic Holocene and glacial climates: Science, v. 278, p. 1257-1266, doi: 10.1126/
science.278.5341.1257.
Holocene variability of the Kuroshio Current in the Okinawa Trough, northwestern Pacifi c Ocean: Earth and Planetary Science Letters
- Z Jian
- P Wang
- Y Saito
- J Wang
- U Pfl Aumann
- T Oba
- X Cheng
Jian, Z., Wang, P., Saito, Y., Wang, J., Pfl aumann, U., Oba,
T., and Cheng, X., 2000, Holocene variability of the
Kuroshio Current in the Okinawa Trough, northwestern Pacifi c Ocean: Earth and Planetary Science
Letters, v. 184, p. 305-319, doi: 10.1016/S0012-821X(00)00321-6.
The early medieval warm epoch and its sequel: Palaeogeography, Palaeoclimatology, Palaeoecology
- H H Lamb
Lamb, H.H., 1965, The early medieval warm epoch and
its sequel: Palaeogeography, Palaeoclimatology,
Palaeoecology, v. 1, p. 13-37, doi: 10.1016/0031-0182(65)90004-0.
A Pacifi c interdecadal climate oscillation with impacts on salmon production: Bulletin of the American Meteorological Society
- N J Mantua
- S R Hare
- Y Zhang
- J M Wallace
- R C Francis
Mantua, N.J., Hare, S.R., Zhang, Y., Wallace, J.M.,
and Francis, R.C., 1997, A Pacifi c interdecadal
climate oscillation with impacts on salmon
production: Bulletin of the American Meteorological Society, v. 78, p. 1069-1079, doi:
10.1175/1520-0477(1997)078<1069:APICOW>
2.0.CO;2.
Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions: Geochimica et Cosmochimica Acta
- F G Prahl
- L A Muehlhausen
- D L Zahnle
Prahl, F.G., Muehlhausen, L.A., and Zahnle, D.L., 1988,
Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions: Geochimica et Cosmochimica Acta, v. 52, p. 2303-2310, doi: 10.1016/0016-7037(88)90132-9.
Timing of abrupt climate change: A precise clock: Geophysical Research Letters, v. 30
- S Rahmstorf
Rahmstorf, S., 2003, Timing of abrupt climate change: A
precise clock: Geophysical Research Letters, v. 30,
1510, doi: 10.1029/2003GL017115.
Production and transport of long-chain alkenones and alkyl alkenoates in a sea water column in the northwestern Pacifi c off central Japan: Marine Chemistry, v. 59
- K Sawada
- N Handa
- T Nakatsuka
Sawada, K., Handa, N., and Nakatsuka, T., 1998, Production and transport of long-chain alkenones
and alkyl alkenoates in a sea water column in the
northwestern Pacifi c off central Japan: Marine
Chemistry, v. 59, p. 219-234, doi: 10.1016/S0304-4203(97)00074-1.