Temporal Dynamics of Open Ocean Polynyas Influenced by Sea Ice and Climatic Impacts in the West Cosmonaut Sea

Abstract

Open ocean polynyas, regions of open water surrounded by sea ice, frequently occur in the West Cosmonaut Sea, an Antarctic marginal sea in the southern Indian Ocean sector. These polynyas play a crucial role in regional energy exchange and influence Antarctic atmospheric processes. This study examines the spatial and temporal distribution of the West Cosmonaut Sea polynyas (WCP) from 1979 to 2023, using sea ice concentration (SIC) data collected from May to August. Our results reveal that a pronounced winter sea ice decline promotes the embayment shape formation, precursor to WCP with open water encircled on three sides by sea ice, mainly open on the northeast side. Statistical analysis identifies regions between 62.0–67°S and 28.0–50.0°E, centered near 65°S, 41°E, as hotspots of polynya occurrence. The annual mean WCP area ranges from 2.0 × 10³ to 0.7 × 10⁵ km², with maximum yearly extents between 3.6 × 10³ to 1.5 × 10⁵ km². The yearly accumulated lasting time spans 3–20 days, exhibiting interannual variability with periodicities of 2–3 years and 4–8 years, partially modulated by the Southern Annular Mode. Since 1987, the duration of WCP events has markedly increased, though a decline has been observed since 2012, likely linked to variations in SIC within the embayment. Enhanced wind stress curl supports WCP formation, increases precipitation, and contributes to polynya closure. WCP dynamics amplify evaporation, latent and sensible heat flux, further highlighting the complex interplay between the atmosphere and the ocean in the Antarctic.