What it is
For decades the surface of the polar Southern Ocean (south of 50 degrees S) had been freshening, a change that strengthened stratification, trapped subsurface heat below, and may have helped Antarctic sea ice expand. Using satellite observations, this study shows that since about 2015 the circumpolar surface has instead grown saltier. That shift has weakened upper-ocean stratification and coincides with a dramatic decline in Antarctic sea ice coverage. Rising salinity also allowed the Maud Rise polynya in the Weddell Sea to reappear for the first time since the mid-1970s.
Why it matters
Antarctic sea ice dropped to record lows in recent years after decades of stability, a swing that climate models did not anticipate and that alters how much sunlight the polar ocean reflects. By identifying rising surface salinity since 2015 as a physical mechanism, this work offers an explanation for the regime shift rather than treating it as noise. The authors also show satellites can now track these salinity and ice changes in near real time, giving early warning of a possible transition to persistently reduced sea ice.
Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.
Filed underSouthern Ocean, Antarctic sea ice, ocean salinity, satellite observations, polar climate