The waters of Antarctica are becoming saltier, leading to the deterioration of its sea ice. Scientists are still unsure why salinity levels in the Southern Ocean have risen, but the overall situation is quite alarming.
Since 2015, the area of sea ice in Antarctica 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.
Recently, researchers linked the reduction in Antarctic sea ice to an unexplained increase in salinity in the waters surrounding the continent. The findings of this new study 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 (UK), in an interview with Live Science.
The Roots of the Paradox Go Beyond Climate Change
The sea ice that surrounds the Earth’s poles melts in the summer and freezes in the winter, fluctuating between minimums and maximums. In Antarctica, this ice protects the more fragile continental ice from warming, reflects some solar energy back into space, and traps carbon dioxide beneath the ocean’s surface.
Since 1979, satellites have been tracking changes in the extent of sea ice on our planet. Since then, Arctic sea ice has been declining by more than 12 percent each decade. However, Antarctic sea ice continued to grow steadily, reaching a historical maximum in 2014—until this trend suddenly reversed with a sharp decline that intensified in 2016.
During the study, scientists utilized data from the European Space Agency’s (ESA) Soil Moisture and Ocean Salinity satellite, which measures subtle changes in microwave brightness reflected from the ocean’s surface due to increased salinity. This signal is complex and requires the application of cutting-edge algorithms for interpretation, making its analysis possible only recently.
By examining daily readings from 2011 to 2023, researchers found that the melting of sea ice and the formation of giant polynyas within it (such as the Mod Ice Hole in the Weddell Sea) coincided with a sharp increase in salinity. The team was shocked by this result and doubted its validity until it was confirmed by data from floating buoys.
The Mystery’s Resolution Lies Ahead
So, 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 atmospheric influences,” Silvano explained.
The increase in salinity is likely to lead to stronger warming of surface waters and even faster ice melting.
“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 (Australia), who was not involved in the study.
Currently, Silvano and his colleagues are focused on investigating what specifically caused the sharp increase in salinity in 2015 and whether this can be considered a turning point. The team is also analyzing how this process may impact global climate, ocean circulation, and the carbon cycle.