A significant transition of Antarctic sea ice variability in response to the shoaling of the Circumpolar Deep Water

As a crucial component of the Earth’s climate system, Antarctic sea ice has shown significant variability over the satellite era. Here, we identify a remarkable decadal transition in the total Antarctic sea ice extent (SIE). The stage from 1979 to 2006 is characterized by high-frequency (i.e., seasonal to interannual) temporal variability in SIE and zonal asymmetry in sea ice concentration (SIC), which is primarily under the control of the Amundsen Sea Low (ASL). After 2007, however, sea ice changes exhibit a more spatially homogeneous pattern in SIC and a more temporally long-lasting mode in SIE. Further analysis reveals that sea ice-ocean interaction plays a major role in the low-frequency (i.e., multiannual) variability of Antarctic sea ice during 2007-2022. The related physical process is inferred to be a strong coupling between the surface and the subsurface ocean layers, involving enhanced vertical convection and downward delivery of the surface anomalies related to ice melt and freeze, thus maintaining the SIE anomalies for a longer time. Furthermore, this process mainly occurs in the Amundsen-Bellingshausen Sea (ABS) sector, and the weakened subsurface ocean stratification is the key factor triggering the coupling process in this region. We find that the Circumpolar Deep Water (CDW) over the ABS sector continued to shoal before 2007 and remained stable thereafter. It is speculated that the shoaling of the CDW may be a possible driver leading to the weakening of the subsurface stratification.