Boundary Currents in the Bransfield Strait: Near-Surface Interbasin Water Volume and Heat Exchange

Marta Veny ^* Borja Aguiar-González ^* Alex Ruiz-Urbaneja Tania Pereira-Vázquez Laia Puyal-Astals Ángeles Marrero-Díaz

• University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain

The Bransfield Strait, located between the Bellingshausen and Weddell seas, serves as a natural laboratory for studying boundary current dynamics and interbasin exchange in polar regions of the world ocean. Using 30 years (1993–2022) of multi-platform satellite data (altimetry, sea surface temperature, air temperature, sea ice coverage, and wind stress), this study examines the near-surface spatiotemporal variability of the Bransfield Current and Antarctic Coastal Current. The Bransfield Current consistently strengthens up to King George Island across all seasons, with volume transport (0-100 m depth) increasing from 0.24–0.33 Sv in the western transect to 0.52–0.64 Sv in the eastern transect in the Bransfield Strait, exhibiting limited seasonal variability, while decreasing downstream as it recirculates around the SSI. In contrast, the Antarctic Coastal Current displays pronounced seasonality, with volume transport oscillating between 0.19–0.38 Sv in the western transect and 0.05–0.33 Sv in the eastern transect in the Bransfield Strait. Heat transport analyses reveal significant asymmetries: the Bransfield Current contributes up to 5.44x1012 W eastward in summer based on a hydrographic climatology constructed from CTD, MEOP, and Argo float measurements (0–100 m depth) and 6.67x1011 W using remotely-sensed sea surface temperature (0–10 m depth). Complementary to this, while smaller in magnitude, the Antarctic Coastal Current peaks at 2.13x1012 W (0–100 m depth) and 2.67x1011 W (0–10 m depth) westward in summer, respectively. Notably, the net heat transport balance approaches zero during winter, likely reflecting periods of reduced interbasin heat exchange driven by homogeneous temperatures and sea ice coverage. Seasonal shifts in near-surface volume and heat balances, driven by wind stress and temperature gradients, highlight the critical role of these boundary currents in shaping local hydrography and sea ice dynamics. Lastly, the evaluation of two global ocean reanalysis products (GLORYS12V1 and HYCOM) reveals their inability to accurately represent the Bransfield Strait circulation, emphasizing the need for high-resolution observational data and improved models to better resolve boundary current dynamics. These findings establish a comprehensive baseline for assessing climate-driven changes in the near-surface layers of the boundary currents that exchange water masses with distinct properties between basins in the Antarctic Peninsula region.