Summer circulation and water masses transport in Bransfield Strait, Antarctica: An evaluation of their response to combined effects of Southern Annular Mode and El Niño–Southern Oscillation

Bransfield Strait, situated in the northern Antarctic Peninsula, is a critical area for studying the impacts of climate change. This complexity arises from the convergence of distinct water masses: Transitional Zonal Water with Weddell influence (TWW), and Transitional Zonal Water with Bellingshausen influence (TBW). This study aims to give a long–term description of Bransfield Strait circulation during austral summers through high-quality hydrographic data from 2003 to 2019, altimetry data and the global eddy–resolving ocean reanalysis product GLORYS12v1. Findings reveal a cyclonic ocean circulation pattern within Bransfield Strait, characterized by the northeastward Bransfield Current along the South Shetland Islands and extending to Elephant Island, and the southwestward Antarctic Coastal Current entering near 62.40°S and 55.00°W. GLORYS12v1 and altimetry datasets revealed that: part of the Bransfield Current leaves the eastern basin between King George and Clarence Islands and recirculation around the South Shetland Islands, and provides the first robust estimate over an extended period that TBW is transported between King George and Elephant Islands and feeds Bransfield Current. Our results highlight links between the strength of TBW transport and variability in climate modes, quantifying their magnitude and variability due to wind forcing modulation by combined effects of Southern Annular Mode and El Niño–Southern Oscillation indices (jointly called the SEI index). For instance, time-averaged years of SEI negative conditions reveal 0.10 Sv of TBW entering the Bransfield Strait between King George and Elephant Islands. On the other hand, under SEI positive conditions, the TBW transport increases to 0.31 Sv. These observed changes are crucial for advancing our understanding of regional circulation patterns and their underlying mechanisms, as they directly influence the physical and biogeochemical properties of the region.