Preprints
https://doi.org/10.5194/tc-2021-390
https://doi.org/10.5194/tc-2021-390
 
18 Jan 2022
18 Jan 2022
Status: a revised version of this preprint was accepted for the journal TC and is expected to appear here in due course.

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

Yixi Zheng1, David P. Stevens2, Karen J. Heywood1, Benjamin G. M. Webber1, and Bastien Y. Queste3 Yixi Zheng et al.
  • 1Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
  • 2Centre for Ocean and Atmospheric Sciences, School of Mathematics, University of East Anglia, Norwich NR4 7TJ, UK
  • 3Department of Marine Sciences, University of Gothenburg, Box 460, 405 30 Göteborg, Sweden

Abstract. 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 the 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. 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 ERA-5 climatological wind fields and simplified sea ice conditions from MODIS satellite images, 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 the mobile sea ice enhancing the effect of wind, has the potential to reverse the gyre direction relative to ice-free conditions.

Yixi Zheng et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-390', Anonymous Referee #1, 28 Jan 2022
    • AC1: 'Reply on RC1', Yixi Zheng, 22 Apr 2022
  • RC2: 'Comment on tc-2021-390', Anonymous Referee #2, 22 Feb 2022
    • AC2: 'Reply on RC2', Yixi Zheng, 22 Apr 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-390', Anonymous Referee #1, 28 Jan 2022
    • AC1: 'Reply on RC1', Yixi Zheng, 22 Apr 2022
  • RC2: 'Comment on tc-2021-390', Anonymous Referee #2, 22 Feb 2022
    • AC2: 'Reply on RC2', Yixi Zheng, 22 Apr 2022

Yixi Zheng et al.

Yixi Zheng et al.

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Short summary
New observations reveal the Thwaites gyre in a habitually ice-covered region in the Amundsen Sea for the first time. This gyre rotates anticlockwise, despite the wind here favours clockwise gyres like the Pine Island Pay gyre – the only other ocean gyre reported in this region. We use an ocean model to suggests that sea ice alters the wind stress felt by the ocean and hence determines the gyre direction and strength. These processes may also be applied to other gyres in polar oceans.