Antarctic waters are getting saltier, and that’s damaging the region’s sea ice. Scientists still don’t know why salinity in the Southern Ocean has risen, but the situation is alarming.
Since 2015, Antarctica’s sea-ice area has been shrinking. By July of last year the region lost a massive ice chunk larger than Western Europe, with no signs of recovery in sight.
Researchers recently linked the drop in Antarctic sea ice to an unexplained rise in salinity around the continent. Their findings were published in the journal PNAS.
“The situation is paradoxical, as we usually associate ice melting with ocean freshening. This indicates deeper structural changes in the Southern Ocean—not just in the sea ice, but also in the ocean beneath it,” said lead author Alessandro Silvano, a senior research fellow at the University of Southampton in the UK, in an interview with Live Science.
The Roots of the Paradox Go Beyond Climate Change
Polar sea ice melts in summer and refreezes in winter, cycling between annual minimums and maximums. In Antarctica, that ice shields the continent’s more vulnerable inland ice from warming, reflects some solar energy back into space, and traps carbon dioxide beneath the ocean surface.
Satellites have been tracking changes in sea-ice extent since 1979. Arctic sea ice has declined by more than 12 percent per decade since then. Antarctic sea ice, however, continued to grow and hit a record high in 2014—until that trend reversed and a sharp decline took hold in 2016.
For the study, scientists used data from the European Space Agency’s Soil Moisture and Ocean Salinity satellite, which detects subtle changes in microwave brightness at the ocean surface caused by salinity. That signal is complex and only recently became interpretable thanks to advanced algorithms.
By examining daily readings from 2011 through 2023, researchers found that sea-ice melt and the opening of giant polynyas (like the Mod Ice Hole in the Weddell Sea) coincided with a sharp rise in salinity. The team was skeptical of the result until floating-buoy data confirmed it.
The Mystery’s Resolution Lies Ahead
In short, some unknown process is making the water saltier. “The exact reasons remain unclear. One theory suggests that salt stored in deeper ocean layers has been brought to the surface. This process could be driven by changes in ocean circulation or by atmospheric influences,” Silvano explained.
The increase in salinity is likely to drive stronger warming of surface waters and even faster ice melt.
“The fact that this change in salinity contradicts what we expect from climate change indicates that there are processes we do not fully understand, which may not be accounted for or represented in our climate models,” said Ariaan Purich, a climate researcher focused on Antarctica at Monash University in Australia, who was not involved in the study.
Silvano and his colleagues are now investigating what specifically caused the sharp salinity increase in 2015 and whether that year marks a turning point. The team is also analyzing how the process may affect global climate, ocean circulation, and the carbon cycle.
