Overview

• Recent June 2025 satellite and Argo float data confirm a sudden reversal from decades of surface freshening to rising salinity south of 50° latitude.
• Saltier surface waters have weakened stratification, allowing deep ocean heat to reach the surface and melt Antarctic ice from below.
• Antarctic sea ice is now in steep decline, reaching record low extents and revealing large polynyas including the Maud Rise opening unseen since the 1970s.
• The reinforcing salinity-heat feedback loop poses risks for global climate by potentially accelerating sea level rise and altering weather patterns.
• Scientists urge continuous high-resolution monitoring and updates to climate models to anticipate future shifts in the Southern Ocean system.