Interaction Between Antarctic Circumpolar Current Eddies and the Sea Ice Edge: Influence on Sea Ice Extent

Multi-decadal expansion in the winter maximum sea ice extent (SIE) around Antarctica was interrupted by contraction, beginning in 2016 and continuing into 2019. This unexpected behavior motivates a closer look at factors controlling the position of the outer ice margin.We analyzed sea ice concentration (SIC) estimates derived from passive microwave sensors with differing resolutions (SSM/I, AMSR-E and AMSR2) to identify spatial and temporal statistics of the sea ice edge defined by 15% SIC. The low-pass filtered position of the ice edge is similar in different products, with the maximum northward position determined by proximity to the relatively warm waters of the Antarctic Circumpolar Current. Higher resolution SIC products reveal greater spatial detail along the convoluted margin, resulting in a relatively longer sea ice perimeter. Spectral analysis does not identify statistically significant peaks in length scales along the margin; however, visual comparison with geostrophic velocities and sea surface temperature inferred from satellite altimetry suggests that advection of sea ice by mesoscale eddies is an important mechanism for deforming the ice edge in some regions, such as the Bellingshausen Sea. We analyze a high-resolution (dx=5 km), coupled ocean-sea ice model which realistically represents the annual expansion of sea ice to quantify the dynamic and thermodynamic roles of eddies in sea-ice mass balance and SIE. These eddy effects on the sea ice edge are not well represented in coarser-grid ocean reanalysis products such as ECCO-2, motivating an investigation of how to represent eddy/sea-ice interactions in global climate models.