Overview

• Since 2015 surface salinity south of 50° latitude has surged, reversing decades of freshening and weakening the ocean’s stratification
• Saltier surface waters draw deep heat upward in a feedback loop that has driven Antarctic sea ice to record lows and reopened the Maud Rise polynya
• Summers with extreme ice loss now produce more than twice as many icebergs, exposing ice shelves and threatening species like emperor penguins and krill
• The Southern Ocean retains excess heat for up to three years after low-ice summers, compounding warming and challenging existing climate models
• The U.S. Department of Defense will stop delivering SSMIS microwave data after July 31, jeopardizing long-term monitoring of future sea ice extremes