Understanding recent changes in Antarctic sea ice seasonality

Changes in the timing of Antarctic sea ice retreat and advance have been analyzed over 1979-2012, based on satellite sea ice concentration retrievals. The Ross Sea showed large trends towards earlier sea ice advance and later retreat whereas the Bellingshausen and Amundsen Seas showed opposite trends.

Since 2016, however, we find the occurrence of anomalously late advance and early retreat in the Ross and Weddell Seas and anomalously early advance and late retreat, west of the Peninsula. Trends in the timing of sea ice retreat and advance are consequently weaker over 1979-2022, than over 1979-2012. Here, we investigate the possible role of ocean thermodynamics and wind-driven ice drift in causing such anomalies and resulting trend weakening, using satellite and reanalysis data.

In most of the seasonal zone, anomalies in the date of advance strongly correlate with anomalies in the previous seasonal maximum sea surface temperature (SST) and in the previous date of retreat. This suggests that anomalies in the date of advance are caused by summer ocean heat uptake anomalies, themselves constrained by anomalies in the previous date of retreat. In a large outer band of the seasonal ice zone, however, anomalies in the timing of sea ice advance seem linked to anomalies in the magnitude of winter southerlies, suggesting a possible role for ice drift anomalies there.

By contrast, we find no clear correspondence between anomalies in the date of retreat and anomalies in winds or SST. We will provide more analysis to disentangle the thermodynamic and dynamic mechanisms causing anomalies in the date of retreat, based on a sea ice concentration budget decomposition.