Identifying Changes in Ice-Ocean-Atmosphere Fluxes in Antarctic Bottom Water

The Southern Ocean plays a crucial role in global climate regulation through its influence on the oceanic and atmospheric circulation. Due to the very cold temperatures in the polar Southern Ocean, salinity exerts a fundamental control on vertical mixing, water mass renewal, and the global overturning circulation. Thus, understanding the causes and consequences of salinity changes in the Southern Ocean is not only essential for understanding changes in regional climate dynamics but also implications the changes have on the global climate system. We here investigate spatial and temporal changes in the salinity of Antarctic Bottom Water (AABW) from historic hydrographic data to understand the coupled system of freshwater inputs and salinity changes in the Southern Ocean. Using a novel database of seawater isotopes and noble gases as tracers, combined with in-situ salinity measurements, we identify freshwater sources in AABW within the Weddell Sea, and their changes over time. We find that AABW has freshened and become enriched in δ¹⁸O from 1995 to 2016, suggesting a coupled relationship between reduced sea ice export from the Weddell Sea continental shelf, increased sea ice melting, and reduced basal melting of the adjacent Filchner-Ronne Ice Shelf. The observed decline in meteoric water contributions, including basal melt, further supports this inference, suggesting that declines in sea ice export from the continental shelf significantly impact AABW formation and export.