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. Bothsimulations capture exceptionally low February sea ice extent during the 2022/23 melt season, though neither atmospheric5reanalysis reproduces 2023 as a record minimum, with JRA-55-do showing closer agreement with observations. Substantialregional differences emerge between the two simulations in February 2023: JRA-55-do produces greater sea ice coverage inthe Amundsen–Bellingshausen and Ross sectors, while ERA5 yields higher concentrations in the Weddell and Indian Oceansectors. We further investigate the atmospheric differences between the atmospheric reanalyses - differences in downwellinglongwave radiation are the strongest disparity in October, whereas shortwave radiation is the primary disparity in February-10suggesting a role for these atmospheric differences in the differing sea ice outcome between the two simulations. Much of theexisting literature attributes the 2023 minimum to mechanisms inferred from a single reanalysis, most commonly ERA5. Ourresults demonstrate that reanalysis choice produces markedly different regional sea ice responses, with implications for theinterpretation of both thermodynamic and dynamical drivers. We therefore recommend caution when diagnosing real-worldsea ice events from reanalysis-forced simulations and that multiple reanalysis products could be employed to improve the15robustness of inferred mechanisms