Study links Antarctic sea ice decline to rising Southern Ocean salinity

Left · 2A paper published on Wednesday 28 October documented a sharp increase in salinity in a vast layer of the Southern Ocean that encircles Antarctica and extends from 2,300 to 4,000 feet deep. 1 2 Left · 1The shift reverses decades of freshening. According to the report, it echoes ocean changes usually associated with major global climate shifts over millennia, but it is happening in just a few years. 1 Left · 2Co-author Bishakhdatta Gayen, of the University of Melbourne and the Centre for Atmospheric and Oceanic Sciences in Bengaluru, said the study combined six independent datasets covering 2004 to 2024, including readings from Argo floats that measure properties such as density and salinity at different depths. 1 2

Left · 2The researchers link the change to the decline in Antarctic sea ice since 2016. Sea ice reached its highest extent in the satellite record in 2014, dropped to a record low two years later, and hit another low in 2023, when it was about 1 million square miles below the 1981–2010 average. 1 2 Left · 2As the ice dwindles, less freshwater is available during the melt season, which makes the layer, known as Antarctic Intermediate Water, saltier. Gayen also pointed to a 2025 study that detected increasing surface salinity linked to declining sea ice. 1 2 Left · 2The layer spreads north into the Indian, Pacific and Atlantic oceans, carrying heat, carbon, oxygen and nutrients toward the tropics and beyond the equator. Gayen said changes to its density, thickness and salinity could affect how the ocean stores and redistributes heat. 1 2

Left · 2Gayen said more monitoring is needed because impacts are potentially "knocking on your door" within five years. He said these could include increased storm frequency and ocean heat loss, as identified by a 2024 study. 1 2 Left · 2Michael Meredith, an oceanographer with the British Antarctic Survey, said the research shows sea-ice loss since 2016 is already affecting the properties and circulation of deep ocean waters. He called the Southern Ocean "the key juncture for all the world’s oceans" and said it plays a "massive role" in absorbing human carbon dioxide emissions. 1 2 Left · 2Meredith said it is not yet clear whether the shift is permanent, because it rests on a relatively short observational record. He added that global climate models used to guide policy still struggle to reflect recent sea ice losses, saying "Our climate models need to catch up." 1 2

Left · 2The report places the finding alongside earlier research. A review earlier this year said the "speed and persistence" of the sea ice decline suggests the ocean around Antarctica may be moving into a new state. Other work found that deep Southern Ocean circulation has slowed, whereas Meredith said the upper circulation can affect climate within years to decades. 1 2