Deep Ocean storage of heat and CO2 in the Fram Strait, Arctic Ocean during the last glacial period

Ezat, Mohamed; Rasmussen, Tine L.; Hain, Mathis P.; Greaves, Mervyn; Rae, J. W. B.; Zamelczyk, Katarzyna; Marchitto, Thomas M.; Szidat, Sönke; Skinner, Luke C

doi:10.1002/essoar.10506998.1

Cited by 2 publications

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“…2012; Ezat et al . 2021; Spielhagen & Mackensen 2021). This could indicate low melting rates and continued perennial to near‐perennial sea ice cover over the shelf and slope of NE Greenland (Spielhagen & Mackensen 2021.…”

Section: Discussionmentioning

confidence: 99%

Northeast Greenland: ice‐free shelf edge at 79.4°N around the Last Glacial Maximum 25.5–17.5 ka

Rasmussen

Pearce

Andresen

et al. 2022

Boreas

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The size of the last glacial ice sheet on the Northeast (NE) Greenland shelf and its interaction with ocean circulation have been the subject of debate. Here we provide insights into the extent of the ice sheet around the Last Glacial Maximum (LGM) and investigate timing and strength of changes in the flow of Atlantic Water. The study is based on a multiproxy investigation of a marine sediment core, gravity core DA17-NG-ST01-019G, from 323-m water depth at the NE Greenland shelf edge at 79.4°N. We present benthic and planktic foraminiferal distribution data, AMS-14 C dates, sedimentological (ice-rafted debris (IRD) and grain sizes), and geochemical (XRF) data in combination with geophysical (sub-bottom profiler) data. The oldest sediments at the study site are dated to 25.5-17.5 ka, encompassing the time frame from the beginning of the LGM to the early deglaciation. This part is overlain by sediments from the late deglaciation and Holocene. The deposits dating from the LGM are very rich in both planktic and benthic foraminifera and macrofossils of excellent preservation. The faunas show that the site generally was affected by a strong flow of relatively warm subsurface Atlantic Water during the LGM and Early Holocene. Conditions turned more polar with cold bottom water flow in the Middle-Late Holocene (c. 7.5 ka to Recent) with presence of mainly agglutinated benthic foraminiferal species. Our data from the LGM also indicate that the deposits were mixed by iceberg scouring, confirmed by the geophysical data showing extensive ploughing of the sediments on the outer shelf area. The results further indicate that the Greenland Ice Sheet did not reach to the edge of the NE Greenland shelf at 79.4°N during the LGM 24-18 ka.

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Section: Discussionmentioning

confidence: 99%

Northeast Greenland: ice‐free shelf edge at 79.4°N around the Last Glacial Maximum 25.5–17.5 ka

Rasmussen

Pearce

Andresen

et al. 2022

Boreas

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“…2 and 3), non-conservative processes (changing seawater εNd via input of Nd sourced from local sediment) may mask the εNd record of export to the NE Atlantic 24,34 . This dense water could also have exited the Nordic Seas via the Denmark Strait, as has been previously suggested 18,35 ; however, no suitable εNd records have yet been obtained from the Denmark Strait.…”

Section: Connectivity To the Atlanticmentioning

confidence: 74%

“…The temperature over much of the deep to intermediate Nordic Seas during the LGM was ~1 to 2 o C warmer than the modern 11,13 , suggesting a lower net of cooling of high salinity NAC waters and a reduced heat release to the atmosphere. Although more recent evidence suggests there were periodically cooler bottom water temperatures during the LGM in the Nordic Seas (e.g., near Svalbard 18,20 ), which may reflect periodic and localized higher efficiency cooling. We infer that the overall efficiency of surface to deep water transformation was likely less than it is today, with moderately ventilated overflows and deep waters 16,32 .…”

Section: Last Glacial Maximum Homogeneitymentioning

confidence: 98%

“…Several proxy studies indicate a persistent overflow from the Nordic Seas into the glacial Atlantic Ocean 8,15,16 . However, warmer waters (~ 1 to 2 o C warmer than the modern) in the intermediate to deep Nordic Seas and Arctic 11,17,18 indicate a reduced heat release to the atmosphere and less net cooling of the NAC waters, which could be due to subsurface expansion and deepening of the NAC 13,19 . This does not support widespread deep-water formation by brine rejection or modern-like open-ocean convection, which would produce cooler waters at depth.…”

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confidence: 99%

“…This does not support widespread deep-water formation by brine rejection or modern-like open-ocean convection, which would produce cooler waters at depth. Nevertheless, periodic cooler bottom water temperatures have been observed in LGM-aged sediments near Svalbard and in the Lofoten Basin 18,20 . Less efficient deep-water formation via convective processes, upwelling, slow modification and return of Atlantic waters, or small-scale brine formation at shelf edges could be consistent with studies to date.Ultimately, the question of Nordic Seas deep-water formation during the LGM and its geographical extent remains an open debate which has not yet been fully constrained by proxy studies.…”

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Active Nordic Seas deep-water formation during the last glacial maximum

et al. 2022

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The Nordic Seas are the primary location where the warm waters of the North Atlantic Current densify to form North Atlantic Deep Water, which plays a key part in the modern Atlantic Meridional Overturning Circulation. The formation of dense water in the Nordic Seas and Arctic Ocean and resulting ocean circulation changes were likely driven by and contributed to the regional and global climate of the last glacial maximum (LGM). Here, we map the source and degree of mixing of deep-water in the Nordic Seas, and through the Arctic Gateway (Yermak Plateau) over the last 35 thousand years using neodymium isotopes (εNd) measured on authigenic phases in deep-sea sediments with a high spatial and temporal resolution. We find that a large-scale reorganisation of deep-water formation in the Nordic Seas took place between the LGM (23-18 thousand years ago) and the rapid climate shift that accompanied the subsequent deglaciation (18-10 thousand years ago). We show that homogeneous εNd signatures across a wide range of sites support LGM deepwater formation in the Nordic Seas. In contrast, during the deglaciation disparate and spatially variable εNd values are observed leading to the conclusion that deep-water formation may have been reduced during this time. Deep-water formation processes in the Nordic Seas regulate the global climate via the redistribution of heat by the surface ocean and the capacity of the deep ocean to store carbon 1 . At present the Atlantic Meridional Overturning Circulation (AMOC) links polar and sub-polar climate with the formation of North Atlantic Deep Water (NADW), a major component of the global oceanic thermohaline circulation. The densest northern-sourced waters in the modern AMOC are formed in the Nordic Seas, primarily by deep convection and gradual transformation of North Atlantic surface waters 2 .These dense waters formed in the modern Nordic Seas overflow the Greenland-Scotland Ridge (GSR), eventually contributing to NADW accumulating carbon and nutrients as it flows throughout the deep ocean 2 (Fig. 1). The extent, mechanism, and importance of deep-water formation in the Nordic Seas during glacial periods and periods of ice rafting during meltwater events (Heinrich Events/Heinrich Stadials) are still not adequately understood. The canonical view is that the glacial AMOC was displaced from the Nordic Seas to south of Iceland in the form of a fast and shallow overturning cell forming Glacial North Atlantic Intermediate Water and that there was Southern-sourced water in the deep (> 2.5 km) Atlantic e.g,3 . Contrary to this several studies e.g.4,5 argue for the presence of glacial NADW and speculate that this dense water may have been sourced from the Nordic Seas. Keigwin and Swift 6 similarly suggest that a Northern-sourced water mass may have been present in the deep (~ 5000 m) Atlantic, which could plausibly have been sourced from the Nordic Seas 7 . However, proposed scenarios of LGM deep-water formation in the Nordic Seas range from near-cessation to vigorous present-day-like deep-water f...

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Deep Ocean storage of heat and CO2 in the Fram Strait, Arctic Ocean during the last glacial period

Abstract: Late Pleistocene glaciations were characterized by millennial-and decadal-scale variations in global/regional climate and atmospheric carbon dioxide levels (i.e., pCO 2 ), superimposed on gradual longer-term trends of increasing ice volume and decreasing atmospheric pCO 2 (e.g.,

Cited by 2 publications

References 38 publications

Northeast Greenland: ice‐free shelf edge at 79.4°N around the Last Glacial Maximum 25.5–17.5 ka

Northeast Greenland: ice‐free shelf edge at 79.4°N around the Last Glacial Maximum 25.5–17.5 ka

Active Nordic Seas deep-water formation during the last glacial maximum

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