Exploring the role of ocean preconditioning as a driver of Antarctic sea ice loss events

Antarctic sea ice expanded during much of the late 20^th and early 21^st century, in contrast to the rapid loss of sea ice observed in the Arctic over the same period. However, since the mid-2010s, Antarctic sea ice has produced a series of record minima, with 2022 – 2025 collectively producing the lowest four extents on record. Climate models with adequate global warming have struggled to reproduce the general increase in sea ice coverage prior to 2016 and only very rarely simulate losses of the magnitude seen thereafter, raising concerns about their capability in simulating realistic variability in Antarctic sea ice state. Moreover, climate models have significant Southern Ocean biases, in particular an overestimation of Southern Ocean convection, which is a related source of low confidence in sea ice variability. Understanding the relationship between sea ice variability and the Southern Ocean state is particularly important because several recent studies have suggested that warming in the subsurface ocean is a significant driver of the repeated sea ice lows seen in the Antarctic since 2016.

In this study, we identify a series of substantial sea ice loss events within model output from simulations produced using a regional Southern Ocean circumpolar configuration of NEMO-SI3. We also characterise the modelled ocean salinity and temperature profiles leading up to each ice loss event. We then run a series of sensitivity studies where we either directly modify the ocean state or change parameters that impact the subsurface ocean. We will present results exploring how the magnitude of ice loss events is impacted by these changes in ocean state and discuss the implications of these results for the role of the ocean as a driver of Antarctic sea ice change and variability.