Austral autumn is a critical but under-observed season in the Southern Ocean, when the transition toward rapid sea ice formation is influenced by atmospheric forcing, upper-ocean dynamics, and subsurface heat supply. In the Ross Sea, direct observations during March-April remain sparse, limiting our understanding of how atmospheric variability modulates sea-ice and ocean conditions during this seasonal transition. Here, we investigate a recurrent embayment-like low-sea-ice-concentration feature in the Ross Sea during the austral autumns of 2021–2025. We combine sea-ice concentration data, atmospheric reanalysis, numerical simulations from a high-resolution ocean–sea ice–ice shelf coupled model and BGC-Argo observations. The results show that the ice embayment recurred in multiple years with a relatively stable spatial pattern. The occurrence of this feature is associated with cyclones, which enhances sea ice divergence and induces Ekman pumping that provides a dynamical pathway for the upward transport of relatively warm subsurface water.
Heat budget analysis based on the model simulations further indicates that temperature variability in the surface and subsurface layers is controlled by a combination of horizontal advection, vertical advection, and vertical diffusion. These processes suggest that the intrusion and upward transport of Circumpolar Deep Water can provide an important oceanic heat source that helps maintain low sea ice concentration in the embayment during the ice formation season. BGC-Argo observations show that upper-ocean chlorophyll concentrations are generally higher inside the ice embayment than outside it, implying a potential biogeochemical response to reduced sea ice cover and enhanced subsurface nutrient supply along with the Ekman pumping. Overall, this study highlights a coupled atmosphere-ice-ocean mechanism for the generation of a relatively stable low-ice-concentration area in the Ross Sea, and provides insights into the coupled physical processes on ecosystem production in Antarctic marginal seas in the autumn season.
 

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