Reversal of ocean gyres near ice shelves in the Amundsen Sea caused by the interaction of sea ice and wind

Zheng, Yixi, Stevens, David P. ORCID:, Heywood, Karen J. ORCID:, Webber, Benjamin G.M. ORCID: and Queste, Bastien Y. (2022) Reversal of ocean gyres near ice shelves in the Amundsen Sea caused by the interaction of sea ice and wind. Cryosphere, 16 (7). pp. 3005-3019. ISSN 1994-0416

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Floating ice shelves buttress the Antarctic Ice Sheet, which is losing mass rapidly mainly due to ocean-driven melting and the associated disruption to glacial dynamics. The local ocean circulation near ice shelves is therefore important for the prediction of future ice mass loss and related sea-level rise as it determines the water mass exchange, heat transport under the ice shelf and resultant melting. However, the dynamics controlling the near-coastal circulation are not fully understood. A cyclonic (i.e. clockwise) gyre circulation (27 km radius) in front of the Pine Island Ice Shelf has previously been identified in both numerical models and velocity observations. Mooring data further revealed a potential reversal of this gyre during an abnormally cold period. Here we present ship-based observations from 2019 to the west of Thwaites Ice Shelf, revealing another gyre (13 km radius) for the first time in this habitually ice-covered region, rotating in the opposite (anticyclonic, anticlockwise) direction to the gyre near Pine Island Ice Shelf, despite similar wind forcing. We use an idealised configuration of MITgcm, with idealised forcing based on ERA5 climatological wind fields and a range of idealised sea ice conditions typical for the region, to reproduce key features of the observed gyres near Pine Island Ice Shelf and Thwaites Ice Shelf. The model driven solely by wind forcing in the presence of ice can reproduce the horizontal structure and direction of both gyres. We show that the modelled gyre direction depends upon the spatial difference in the ocean surface stress, which can be affected by the applied wind stress curl filed, the percentage of wind stress transferred through the ice, and the angle between the wind direction and the sea ice edge. The presence of ice, either it is fast ice/ice shelves blocking the effect of wind or mobile sea ice enhancing the effect of wind, has the potential to reverse the gyre direction relative to ice-free conditions.

Item Type: Article
Additional Information: Funding Information: This work is from the Thwaites-Amundsen Regional Survey and Network (TARSAN) project, a component of the International Thwaites Glacier Collaboration (ITGC), with ITGC contribution no. ITGC-059. Support was received from the National Science Foundation and Natural Environment Research Council (NERC grant NE/S006419/1). Logistics were provided by the NSF-US Antarctic Program and NERC British Antarctic Survey. This work is also funded by the European Research Council (H2020-EU.1.1.) under research grant Climate-relevant Ocean Measurements and Processes on the Antarctic continental Shelf and Slope (COMPASS, grant agreement ID 741120). Yixi Zheng is supported by the China Scholarship Council and the University of East Anglia.
Uncontrolled Keywords: water science and technology,earth-surface processes ,/dk/atira/pure/subjectarea/asjc/2300/2312
UEA Research Groups: Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
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Depositing User: LivePure Connector
Date Deposited: 22 Nov 2023 04:39
Last Modified: 23 Jul 2024 02:17
DOI: 10.5194/tc-16-3005-2022


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