Southern Ocean layer turns saltier after decades of freshening

Researchers report that Antarctic Intermediate Water, a layer of the Southern Ocean lying roughly 2,300 to 4,000 feet deep, has become saltier, denser and deeper since 2016, reversing decades of freshening. The study, published on 28 Oct 2026 in Nature Climate Change, attributes the shift to reduced freshwater from melting Antarctic sea ice, which had kept the layer fresh through summer melt from 1995 to 2015. The team, led by researchers including Bishakhdatta Gayen of the University of Melbourne, analyzed Argo float data, satellite records and atmospheric datasets covering 2004 to 2024. The layer carries heat, carbon, oxygen and nutrients northward into the Indian, Pacific and Atlantic oceans.