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Tracking Southern Ocean sea ice extent with winter water: a new method based on the oxygen isotopic signature of foraminifera


Lund, DC and Chase, Z and Kohfeld, KE and Wilson, EA, Tracking Southern Ocean sea ice extent with winter water: a new method based on the oxygen isotopic signature of foraminifera, Paleoceanography and Paleoclimatology, 36, (6) Article e2020PA004095. ISSN 2572-4517 (2021) [Refereed Article]

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2021. American Geophysical Union. All Rights Reserved.

DOI: doi:10.1029/2020PA004095


Southern Ocean sea ice plays a central role in the oceanic meridional overturning circulation, transforming globally prevalent watermasses through surface buoyancy loss and gain. Buoyancy loss due to surface cooling and sea ice growth promotes the formation of bottom water that flows into the Atlantic, Indian, and Pacific basins, while buoyancy gain due to sea ice melt helps transform the returning deep flow into intermediate and mode waters. Because northward expansion of Southern Ocean sea ice during the Last Glacial Maximum (LGM; 1923 kyr BP) may have enhanced deep ocean stratification and contributed to lower atmospheric CO2 levels, reconstructions of sea ice extent are critical to understanding the LGM climate state. Here, we present a new sea ice proxy based on the 18O/16O ratio of foraminifera (δ18Oc). In the seasonal sea ice zone, sea ice formation during austral winter creates a cold surface mixed layer that persists in the sub-surface during spring and summer. The cold sub-surface layer, known as winter water, sits above relatively warm deep water, creating an inverted temperature profile. The unique surface-to-deep temperature contrast is reflected in estimates of equilibrium δ18Oc, implying that paired analysis of planktonic and benthic foraminifera can be used to infer sea ice extent. To demonstrate the feasibility of the δ18Oc method, we present a compilation of N. pachyderma and Cibicidoides spp. results from the Atlantic sector that yields an estimate of winter sea ice extent consistent with modern observations.

Item Details

Item Type:Refereed Article
Keywords:sea ice, Antarctic, Southern Ocean, proxy, winter water
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Chemical oceanography
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the earth sciences
UTAS Author:Chase, Z (Professor Zanna Chase)
ID Code:150278
Year Published:2021
Funding Support:Australian Research Council (DP180102357)
Web of Science® Times Cited:3
Deposited By:Oceans and Cryosphere
Deposited On:2022-06-06
Last Modified:2022-08-24
Downloads:5 View Download Statistics

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