Persistent Warming and Reduced Freshening of the Abyssal Southern Ocean

Antarctic Bottom Water has thinned, warmed, freshened, and spread more slowly into the global ocean since 1970. Yet, the physical drivers of these changes and their broader implications remain incompletely understood. Here we combine up‐to‐date observations (1985–2024) with ocean model simulations extending to 2050 to quantify ongoing and projected abyssal ocean changes. Between 1985 and 2024 and below 3,000 m depth, isopycnals descended at a rate of −95 5 m . The water that previously occupied these depths has been replaced by warmer overlying layers resulting in warming of 0.02 0.02 C . Freshening of −0.002 0.003 g also occurred, due to meltwater‐driven changes in the continental shelf source waters. Under continued glacial melt, model projections indicate that Antarctic Bottom Water thinning and abyssal Southern Ocean warming will persist, while abyssal freshening is expected to slow and eventually reverse as the shelf‐to‐abyss connection weakens. Observations indicate this transition is already underway. These results suggest that ongoing meltwater input is already altering long‐term abyssal salinity trends, while continued warming of the deep Southern Ocean could further enhance its contribution to regional sea level rise.