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![The (modern) Arctic Ocean and Nordic Seas in Polar map projection for orientation (top), and the Greenland-Scotland Ridge, with shallow depths highlighted in grey (bottom). DS: Denmark Strait; FBC: Faroe Bank Channel; FSC: Faroe-Shetland Channel; IFG: Iceland-Faroe Gap. Areas depicted in grey could not be passed by icebergs of >470 m total thickness, areas in white were blocked by any ice thicker than 720 m. Ice sheets from Greenland, Iceland and Scandinavia calved into this region. Red arrows indicate examples of deep iceberg scourmarks (800-1200 m water depth) or ice shelf traces (Lomonossov Ridge, close to 1000 m) [Color figure can be viewed at wileyonlinelibrary.com].](profile/Walter-Geibert/publication/360110925/figure/fig1/AS:1148319439032322@1650792097226/The-modern-Arctic-Ocean-and-Nordic-Seas-in-Polar-map-projection-for-orientation-top.jpg)
The (modern) Arctic Ocean and Nordic Seas in Polar map projection for orientation (top), and the Greenland-Scotland Ridge, with shallow depths highlighted in grey (bottom). DS: Denmark Strait; FBC: Faroe Bank Channel; FSC: Faroe-Shetland Channel; IFG: Iceland-Faroe Gap. Areas depicted in grey could not be passed by icebergs of >470 m total thickness, areas in white were blocked by any ice thicker than 720 m. Ice sheets from Greenland, Iceland and Scandinavia calved into this region. Red arrows indicate examples of deep iceberg scourmarks (800-1200 m water depth) or ice shelf traces (Lomonossov Ridge, close to 1000 m) [Color figure can be viewed at wileyonlinelibrary.com].
Source publication
Hillaire-Marcel et al. bring forward several physical and geochemical arguments against our finding of an Arctic glaciolacustrine system in the past. In brief, we find that a physical approach to further test our hypothesis should additionally consider the actual bathymetry of the Greenland–Scotland Ridge (GSR), the density maximum of freshwater at...
Contexts in source publication
Context 1
... include here a complete map of the Greenland-Scotland Ridge (GSR, Fig. 1), based on modern bathymetry. It shows that the majority of the GSR is shallower than 500 m (ca. 400-420 m in peak glacials). Only small parts of the Denmark Strait, the Iceland-Faroe Gap and Faroe Bank Channel are deeper than 500 m, up to approximately 750 m (ca. 650-670 m in peak glacials). Consequently, it is not necessary to cover ...
Context 2
... a couple of larger icebergs also block the Faroe Bank Channel and the Faroe-Shetland Channel, the GSR is blocked almost entirely. There is evidence for sufficiently thick grounded ice in the Nordic Seas (NS): iceberg scourmarks of 800 m and more are known from both north ( Blischke et al., 2019) and south (Kuijpers and Werner, 2007) of the GSR (Fig. 1), which is no surprise because the Greenland, Iceland and the Scandinavian ice sheets were calving into the NS, presumably creating an iceberg armada retained by the sill, immobilised by falling sea levels, and waiting for sea-level rise, their slow melting, or a salinity increase that modified iceberg freeboard, for their ...
Citations
... In this respect, a striking feature of the 230 Th xs distribution in sedimentary sequences is the widely observed "subsurface" 230 Th xs peak (Huh et al., 1997), which was tentatively assigned to the last deglaciation by Hoffmann and McManus (2007), based on 14 C-derived chronologies (Darby et al., 1997;Poore et al., 1999aPoore et al., , 1999b. This peaking "subsurface" 230 Th xs -value is generally higher than that of the surface sample and was thought to be related to sediment focusing due to the rapid sea level rise at the end of the last deglaciation (Hoffmann and McManus, 2007) or some 230 Th xs intensifications associated with an extremely low sedimentation rate (Geibert et al., 2022). Hoffmann and McManus (2007) concluded that 230 Th xs sedimentary fluxes, as estimated from 14 C-based chronologies, had been in balance with the production of this isotope in the water column (henceforth the " 230 Th-rain") since the Marine Isotope Stage 3 (MIS 3). ...
... In contrast to the sediment-focusing model which has been used to interpret the subsurface 230 Th xs peak (Hoffmann and McManus, 2007), Geibert et al. (2022) suggested that the subsurface 230 Th xs peak might be linked to extremely low sedimentation rate considering that "Even fine particle fluxes generating sedimentation rates < 1 mm/1000 years lead to > Fig. 8. Post-LGM 230 Th xs inventories vs 230 Th production in the overlying water column ( 230 Th-rain) in cores from Lomonosov and Mendeleev ridge areas. Inventories are estimated to mostly represent sediment and 230 Th xs accumulation during the last ~9 ka; the 230 Th-rain is calculated since the end of the LGM (~18 ka). ...
... Additionally, the absence of excess 230 Th corresponded to the absence of cosmogenic 10 Be in several cores, suggesting that the absence of excess 230 Th was coeval with intervals where the Arctic Ocean was shielded from the input of cosmogenic nuclides, potentially by circum-Arctic ice shelves (Geibert et al., 2021). The fresh Arctic hypothesis (Geibert et al., 2021) has generated significant discussion about both the interpretation of excess 230 Th and cosmogenic 10 Be in Arctic sediments Geibert et al., 2022a) and the evidence supporting or refuting this hypothesis from outside the Arctic Ocean (Spielhagen et al., 2022;Geibert et al., 2022b). Importantly, any significant contribution of highlatitude, 18 O-depleted freshwater should be readily traceable in Arctic δ 18 O sw , provided that our signal carriers (benthic foraminifera and ostracodes) were present to trace intervals of freshwater input. ...
... In addition, ostracodes inhabit both fresh and marine environments and experience large faunal transitions in many locations, yet no freshwater ostracodes have been observed from Arctic Ocean sediments Poirier et al., 2012). Instead, terrigenous material dilution provides an alternative explanation consistent with all observations, including low excess 230 Th, low-to-absent 10 Be, and limited microfossil abundance (e.g., Hillaire-Marcel et al., 2022; but see rebuttal by Geibert et al., 2022a). ...
The oxygen isotopic composition of benthic foraminiferal tests (δ18Ob) is one of the pre-eminent tools for correlating marine sediments and interpreting past terrestrial ice volume and deep-ocean temperatures. Despite the prevalence of δ18Ob applications to marine sediment cores over the Quaternary, its use is limited in the Arctic Ocean because of low benthic foraminiferal abundances, challenges with constructing independent sediment core age models, and an apparent muted amplitude of Arctic δ18Ob variability compared to open-ocean records. Here we evaluate the controls on Arctic δ18Ob by using ostracode Mg/Ca paleothermometry to generate a composite record of the δ18O of seawater (δ18Osw) from 12 sediment cores in the intermediate to deep Arctic Ocean (700–2700 m) that covers the last 600 kyr based on biostratigraphy and orbitally tuned age models. Results show that Arctic δ18Ob was generally higher than open-ocean δ18Ob during interglacials but was generally equivalent to global reference records during glacial periods. The reduced glacial–interglacial Arctic δ18Ob range resulted in part from the opposing effect of temperature, with intermediate to deep Arctic warming during glacials counteracting the whole-ocean δ18Osw increase from expanded terrestrial ice sheets. After removing the temperature effect from δ18Ob, we find that the intermediate to deep Arctic experienced large (≥1 ‰) variations in local δ18Osw, with generally higher local δ18Osw during interglacials and lower δ18Osw during glacials. Both the magnitude and timing of low local δ18Osw intervals are inconsistent with the recent proposal of freshwater intervals in the Arctic Ocean during past glaciations. Instead, we suggest that lower local δ18Osw in the intermediate to deep Arctic Ocean during glaciations reflected weaker upper-ocean stratification and more efficient transport of low-δ18Osw Arctic surface waters to depth by mixing and/or brine rejection.
... The "Fresh Arctic" hypothesis (Geibert et al., 2021) has generated significant discussion about both the interpretation of 385 excess 230 Th and cosmogenic 10 Be in Arctic sediments (Hillaire-Marcel, 2022;Geibert et al., 2022a) and the evidence supporting or refuting this hypothesis from outside the Arctic Ocean (Spielhagen et al., 2022;Geibert et al., 2022b). ...
The oxygen isotopic composition of benthic foraminiferal tests (δ18Ob) is one of the preeminent tools for correlating marine sediments and interpreting past terrestrial ice volume and deep-ocean temperatures. Despite the prevalence of δ18Ob applications to marine sediment cores over the Quaternary, its use is limited in the Arctic Ocean because of low benthic foraminiferal abundances, challenges with constructing independent sediment core age models, and an apparent muted amplitude of Arctic δ18Ob variability compared to open ocean records. Here we evaluate the controls on Arctic δ18Ob by using ostracode Mg/Ca paleothermometry to generate a composite record of the δ18O of seawater (δ18Osw) from fourteen sediment cores in the intermediate to deep Arctic Ocean (700–2700 m) covering the last 600 kyr. Results show that Arctic δ18Ob was generally higher than open ocean δ18Ob during interglacials but was generally equivalent to global reference records during glacial periods. The reduced glacial-interglacial Arctic δ18Ob range resulted in part from the opposing effect of temperature, with intermediate-to-deep Arctic warming during glacials counteracting the whole-ocean δ18Osw increase from expanded terrestrial ice sheets. After removing the temperature effect from δ18Ob, we find that the intermediate-to-deep Arctic experienced large (≥ 1 ‰) variations in local δ18Osw, with generally higher local δ18Osw during interglacials and lower δ18Osw during glacials. Both the magnitude and timing of low local δ18Osw intervals are inconsistent with the recent proposal of freshwater intervals in the Arctic Ocean during past glaciations. Instead, we suggest that lower local δ18Osw in the intermediate-to-deep Arctic Ocean during glaciations reflected weaker upper ocean stratification and more efficient transport of low-δ18Osw Arctic surface waters to depth by mixing and/or brine rejection.
The presence of a late Quaternary ice sheet/ice shelf over the East Siberian Sea has been proposed in several papers. Here, we further document its duration/resilience based on the sedimentary, bulk mineralogical, and geochemical (organic matter content and its stable isotopic composition, U‐Th series) properties of a core raised from the southernmost Mendeleev Ridge. The chronostratigraphy of the studied core was mainly built from the ²³⁰ Th excess ( ²³⁰ Th xs ) distribution and decay downcore. At the core‐top, peaking ²³⁰ Th xs values during the early MIS 3 and mid‐MIS 1 encompassing an MIS 2 hiatus were observed. As documented in several papers, these peaks suggest seasonally open ice conditions over proximal continental shelves. Below, the interval spanning MIS 4 and possibly MIS 5d records major ice‐rafting events illustrated by overall high coarse‐fraction contents. Underlying MIS 5e, down to MIS 11, the sediment depicts relatively low sand (1.7±2.5 dw%), high clay (33.5±4.7 dw%), and very low organic carbon (0.10±0.06 dw%) contents, and low δ ¹³ C org values (−24.3±0.9‰). This section is interpreted as recording fine sediment transport by deep currents and/or meltwater plumes below a resilient ice cover, only interrupted by a few short‐duration events. These events include (i) detrital carbonate pulses assigned to deglacial events along the NW Laurentide Ice Sheet margin (Termination (T) III), and (ii) intervals with some planktonic foraminifer occurrences, likely relating to their advection from open areas of the Arctic Ocean (MIS 5e, 9 and 11). All Terminations, but TII and the early MIS 3, show peaking Mn/Al values linked to the submergence of Arctic shelves under a rising sea level. We conclude that the resilient ice cover, likely an ice shelf, has been present over the southern Mendeleev Ridge during most of the interval after the Mid‐Pleistocene Transition and was favoured by the low summer insolation of the MIS 14 to 10 interval.
