Satellite‐Derived Volume Budget of Antarctic Sea Ice

In recent years, the Antarctic has seen a notable shift in sea ice trends: Where sea ice extent and volume were increasing on average, they have shown an unprecedented decline since 2016. Understanding the drivers of this shift is crucial to determining the impacts of climate change on sea ice and improving modeling of Antarctic sea ice evolution. In this study, we introduce the CryoSat-2 Antarctic Ocean (CSAO) Sea Ice Thickness (SIT) product. We find there is good agreement between CSAO sea ice thickness estimates with the airborne measurements from Operation IceBridge and with ASPeCt shipborne observations, with mean biases of −0.68 and −0.25 m, attributed to an underestimation in snow depth in the CSAO SIT. We use this new SIT product along with satellite sea ice drift and concentration data to create the first observational budget of pan-Antarctic sea ice volume (SIV). We present a budget decomposition of seasonal dynamic and thermodynamic changes in SIV across the pan-Antarctic from 2014 to 2020. Our budget indicates a sharp 27% decrease in September SIV between September 2014 and September 2016, consistent with previous literature, with the largest seasonal decline occurring between 2015 and 2016. Thermodynamic growth is a critical determinant of the winter SIV, showing consistent decline since 2016, most notably and consistently in the Weddell Sea, while dynamic processes maintain the winter ice edge. The 2014–2016 decline in SIV also shows significant spatial variability across the Antarctic.