The Southern Ocean absorbs nearly half of human-made CO₂ and most of the ocean’s excess heat, making it a key player in regulating Earth’s climate. Yet this remote region is changing rapidly (warming, freshening, and losing sea ice) with the causes still uncertain.

Salinity is central to these processes, influencing ocean circulation, carbon and heat storage, and sea level rise. However, measuring it accurately has long been a challenge. Cold waters and contamination close to sea ice edge interfere with satellite signals, making it difficult to monitor changes over time.

Now, a new satellite-based Sea Surface Salinity (SSS) product developed for the Southern Ocean offers a major step forward. It provides  salinity maps from 2011 to 2023  on a 25 km EASE-SL grid, improving the quality near cold waters and sea ice edges.

The new satellite SSS product accurately captures the Antarctic Circumpolar Current and reproduces seasonal and inter-annual variability consistent with regional models. Satellite observations reveal a marked increase in SSS across the Southern Ocean since 2016, indicating weakened upper-ocean stratification linked to Antarctic sea-ice retreat and the reappearance of the Maud Rise polynya. Incorporating these observations into data-assimilating models will improve representation of key Southern Ocean processes, such as sea-ice dynamics, ocean mixing, and bottom-water formation, critical for reliable climate projections.