Impact of winds and Southern Ocean SSTs on Antarctic sea ice trends and variability

Antarctic sea ice extent (SIE) has slightly increased over the satellite observational period (1979 to present) despite global warming. Several mechanisms have been invoked to explain this trend, such as changes in winds, precipitation, or ocean stratification, yet there is no widespread consensus. Additionally, fully coupled earth system models run under historic and anthropogenic forcing generally fail to simulate positive sea ice extent trends over this time period. In this work, we quantify the role of winds and Southern Ocean SSTs on sea ice trends and variability with an earth system model run under historic and anthropogenic forcing that nudges winds over the polar regions and Southern Ocean SSTs north of the sea ice to observations from 1979 to 2018.

Simulations with nudged winds alone capture the observed interannual variability in sea ice extent and the observed long-term trends from the early 1990s onwards, yet for the longer 1979-2018 period simulate a negative SIE trend, in part due to faster-than-observed warming at the global and hemispheric scale in the model. Simulations with both nudged winds and SSTs show no significant SIE trends over 1979-2018, in agreement with observations. At the regional scale, simulated sea ice shows higher skill compared to the pan-Antarctic scale both in capturing trends and interannual variability in all nudged simulations. We additionally find negligible impact of the initial conditions in 1979 on long term trends.