Abstract

Recent observations reveal that Antarctic Bottom Water is thinning, warming, freshening, and spreading more slowly  northward into the abyssal ocean. Using the most-up-to-date historical data (1985-2024) alongside simulations out to 2050, I review and assess abyssal ocean changes that are ongoing and projected. Between 1985-2024, isopycnals below 3000 m have descended at a rate of -95±5 m/decade, and have been replaced by warmer water, resulting in warming of 0.02±0.02 °C/decade. Freshening of -0.002±0.003 g/kg/decade also occurred, due to meltwater-driven changes in the continental shelf waters.  Projections, in line with the latest observations, suggest thinning and warming will persist in response to continued glacial melt. However, freshening slows and even reverses. Meltwater makes shelf waters too light to reach the deep ocean, weakens the shelf-to-abyss connection, alters long-standing trends, and doubles the deep ocean contribution to Southern Ocean sea level rise.