The Role of the Atmosphere during the 2023 Antarctic Sea Ice Minimum

Abstract. In February 2023, Antarctic sea ice extent reached a record minimum, yet the mechanisms driving this event remain debated.
Here we use a coupled ocean–sea ice model (NEMO-SI3) forced by two different atmospheric reanalyses, ERA5 and JRA-55-
do, to investigate the drivers of the 2023 minimum and assess the sensitivity of inferred mechanisms to reanalysis choice. Both
simulations capture exceptionally low February sea ice extent during the 2022/23 melt season, though neither atmospheric5
reanalysis reproduces 2023 as a record minimum, with JRA-55-do showing closer agreement with observations. Substantial
regional differences emerge between the two simulations in February 2023: JRA-55-do produces greater sea ice coverage in
the Amundsen–Bellingshausen and Ross sectors, while ERA5 yields higher concentrations in the Weddell and Indian Ocean
sectors. We further investigate the atmospheric differences between the atmospheric reanalyses - differences in downwelling
longwave radiation are the strongest disparity in October, whereas shortwave radiation is the primary disparity in February-10
suggesting a role for these atmospheric differences in the differing sea ice outcome between the two simulations. Much of the
existing literature attributes the 2023 minimum to mechanisms inferred from a single reanalysis, most commonly ERA5. Our
results demonstrate that reanalysis choice produces markedly different regional sea ice responses, with implications for the
interpretation of both thermodynamic and dynamical drivers. We therefore recommend caution when diagnosing real-world
sea ice events from reanalysis-forced simulations and that multiple reanalysis products could be employed to improve the15
robustness of inferred mechanisms