Overview

• Surface salinity in the Southern Ocean has reversed a decades-long freshening trend since 2015, with levels now rising sharply.
• Researchers used ESA satellite observations and robotic underwater instruments to confirm that saltier surface water sinks and stirs warmer deep currents toward the ice.
• This vertical mixing creates a positive feedback loop that accelerates sea ice melt and reduces the ocean’s reflective surface.
• Antarctic sea ice has shrunk by an area roughly the size of Greenland over the past decade, coinciding with the unexpected return of the Maud-Rise Polynya in the Weddell Sea.
• Scientists say the drivers of the salinity surge remain uncertain and are calling for immediate updates to climate models and expanded continuous ice–ocean monitoring.