Detecting eddies around Antarctica

Image of the Month - July 2023

Polar seas are complex areas for altimetry data, since they are, at least part of the time, covered with ice, which reflects the altimeter radar beam differently than open water. In these regions, sea surface height can however be obtained from radar altimetry in sea ice leads, open water crevices between iced areas. Retrieving sea level information requires specific processing of the altimeter's radar waveforms.
The Southern Ocean around Antarctica is moreover an energetic region, with eddies playing a role in the heat and nutrient transport across the different current fronts. Sea level anomalies gridded datasets encompassing those seasonnally-ice covered regions have been computed and released for Arctic and Antarctic regions. From those, Eddy Kinetic Energy (EKE) and mesoscale eddies detection can be processed.

From these, it appears that  eddies are distributed evenly in the subpolar Southern Ocean, but their amplitude, following the pattern of the Eddy Kinetic Energy is different. Eddies have low amplitude and density in the pack ice, while the northern part of the Marginal Ice Zone is favorable for mesoscale eddies, especially cyclonic. In this region, we expect to see genesis of fronts due to sea ice melt and upwelling generated from interactions between the wind and the sea ice.  It must be mentionned that all of the eddies aren't detected by the method, since eddies are smaller at high latitude, and many fall under detection level. However, the ones detected can give hints on the general interactions in the region. 

Polar regions are very sensitive, and less observed by in situ instruments than lower latitudes. Satellites which do observe them (not all altimetry satellites) are bringing important clues on the iced regions, their dynamics and ultimately their evolution.

See also:

Reference:

  • Auger, M., Sallée, J.-B., Thompson, A. F., Pauthenet, E. and Prandi, P. (2023). Southern Ocean ice-covered eddy properties from satellite altimetry. Journal of Geophysical Research: Oceans, 128, e2022JC019363. https://doi.org/10.1029/2022JC019363