Antarctic Ocean Layer Reverses as Meltwater Declines

Antarctic Intermediate Water became saltier, denser and deeper from 2016 to 2024 as Antarctic meltwater input fell, according to a new study, reversing a decades-long trend of freshening. The researchers said the change could affect how the Southern Ocean stores and moves heat and carbon, though its persistence and wider effects are not yet known. The study, published in Nature Climate Change, found that the water layer freshened from 1995 to 2015, when summer sea-ice melt added freshwater to the ocean. From 2016 through 2024, reduced meltwater input coincided with the layer becoming saltier, denser and deeper. The study links the shift to declining Antarctic sea ice, but the observed changes do not by themselves establish how long the reversal will last. Antarctic Intermediate Water forms in the Southern Ocean and spreads northward through the Atlantic, Indian and Pacific oceans, carrying heat, carbon and other materials. Researchers examined observations from Argo floats, which measure ocean conditions at depth, together with satellite and atmospheric data. The reporting on the study describes a shared analysis of those observations, rather than independent replication of...