Salinity spike in Southern Ocean layer hits 4,000 feet deep
Researchers report a rapid reversal in water chemistry linked to the decline of Antarctic sea ice since 2016.
By Anthony Shevchenko ·
Scientists have identified a sharp increase in salinity within a major layer of the Southern Ocean, a change they attribute to the rapid decline of Antarctic sea ice since 2016. The shift occurs in a water mass that circulates around the continent and extends into other ocean basins, marking a departure from decades of historical trends.
A paper published Wednesday documents the salinity rise in Antarctic Intermediate Water, a layer situated between 2,300 and 4,000 feet deep. The water had been getting fresher for decades, but the new data shows this trend has reversed. The current changes mirror ocean shifts that typically unfold over thousands of years, yet they are occurring over a period of just a few years.
Bishakhdatta Gayen, a professor at the University of Melbourne and the Centre for Atmospheric and Oceanic Sciences in Bengaluru, India, co-authored the study. He explained that this water layer spreads northward into the Indian, Pacific, and Atlantic oceans. It carries heat, carbon, oxygen, and nutrients toward the tropics and across the equator, meaning local changes can have global reach.
The study analyzed six independent datasets to track changes from 2004 to 2024. The primary source of data was Argo floats, devices that drift through the ocean, descend to specific depths to measure density and salinity, and then resurface to transmit the readings. Gayen noted that a separate 2025 study also found increasing surface salinity linked to the loss of sea ice.
Satellite records show Antarctic sea ice reached its highest extent in 2014 before dropping to a record low in 2016. The ice remained well below 2014 levels and hit another low in 2023. At that point, the ice area was approximately 1 million square miles below the 1981 to 2010 average, representing a loss equivalent to four times the size of Texas. As the ice melts, less freshwater enters the ocean, increasing the salt concentration of the intermediate layer.
Changes in the density and thickness of this water layer influence how heat moves between the ocean surface and deeper waters. Gayen stated that these alterations could affect how the ocean stores and redistributes heat. He added that more monitoring is required because the impacts of these changes are potentially arriving within five years.
