A layer of Southern Ocean water is becoming saltier
· BehindLines newsroom
The retreat of Antarctic sea ice is also transforming the ocean below the surface. A study published on 28 October in Nature Climate Change describes a reversal in the trend since 2016: Antarctic Intermediate Water is becoming saltier and denser after several decades of change in the opposite direction.
Seasonal melting supplies an ocean layer
According to the University of Melbourne, this water mass helps redistribute heat and carbon in the ocean. The word “intermediate” refers to its position within the ocean's structure; it is not a reservoir of fresh drinking water.
The researchers link its transformation to changes in sea ice. Until 2015, expanding sea ice supported an increasing supply of meltwater during the southern summer. That input reduced salinity and helped separate layers of different densities.
Sea ice losses observed from 2016 reduced this seasonal supply. The study associates this change with saltier, denser water. The University of Melbourne's announcement also says that the layer deepens over the period from 2016 to 2024.
Observations, with consequences still to be clarified
The team combined ocean measurements from the Argo programme with satellite observations and reanalysis data. Argo relies on an international network of around 4,000 autonomous floats, the university notes.
These findings concern the properties of a water mass. They do not mean that all ocean circulation has reversed, or that a major ocean current has already stopped.
The authors consider effects on heat transport and carbon storage, with possible distant repercussions over years or decades. The scale and timing of those effects remain uncertain.
The central finding is therefore an observed change in how the Southern Ocean works. Turning that observation into regional forecasts for sea levels or storms requires further research.