American researchers have documented an unprecedented loss of salinity in the waters off Western Australia. Fueled by climate-altered winds, this silent transformation threatens major ocean currents and the global marine food chain.
Seawater isn’t just « salty »—it’s primarily stratified . Its salt content determines its density, and therefore how water layers stack, how currents transport heat around the globe, and how nutrients rise to the surface to feed marine life. That’s why what researchers at the University of Colorado Boulder detected off the coast of Western Australia deserves serious attention.
According to their study published in February 2026 in Nature Climate Change, the waters of the southern Indian Ocean are losing their salt at an unprecedented rate in the Southern Hemisphere . And the causes are directly linked to climate change.
Evaporation that no longer compensates
Historically, the waters off the southwest coast of Australia were among the saltiest in the region. The reason is simple: evaporation exceeded rainfall, naturally concentrating salt at the surface. But this balance is now shifting.
By analyzing sixty years of oceanographic observations and numerical simulations, the team led by Weiqing Han , professor of atmospheric and oceanic sciences, established that the surface area of salt water in this zone had decreased by 30% in six decades . A figure that the authors themselves describe as astonishing.
To illustrate the scale of this upheaval, the study’s lead author, Gengxin Chen , a researcher at the Chinese Academy of Sciences, offers a striking comparison: each year, the equivalent of 60% of Lake Tahoe’s volume is added to the region in the form of fresh water. Or, he explains, enough to supply the entire American population with drinking water for over 380 years .
Climate winds that redistribute fresh water
The source of this fresh water is not local rainfall. Researchers have identified a larger-scale mechanism: climate change is altering major wind patterns over the Indian Ocean and the tropical Pacific. These altered winds are diverting ocean currents to carry more fresh water from a naturally low-salinity area—the Indo-Pacific freshwater reservoir , a vast tropical region stretching from the eastern Indian Ocean to the western Pacific, where abundant rainfall constantly dilutes surface waters.
This reservoir is not isolated from the rest of the world. It is connected to the thermohaline circulation , this vast system of currents sometimes compared to a planetary conveyor belt, which transports heat, salt, and fresh water between ocean basins. Disturbances in the salt concentration of the southern Indian Ocean can therefore, through a domino effect, influence this mechanism all the way to the North Atlantic.
A threat to global currents and marine life
When the salt level drops, surface water becomes less dense and tends to stay at the surface, strengthening the separation between the surface and deeper layers . This phenomenon limits vertical mixing—the essential process by which cold, nutrient-rich water rises from the depths to the sunlit surface.
The consequences are twofold. On the one hand, surface marine organisms are deprived of nutrients , compromising the productivity of ecosystems. On the other hand, heat concentrates at the surface, exacerbating warming for species already under pressure.
« Changes in salt levels could affect plankton and seagrass beds, » Chen points out. « These are the foundations of the marine food chain. Changes that affect them can have profound repercussions for the biodiversity of our oceans. »
This study is part of a broader picture: other studies have already shown that melting ice in Greenland and the Arctic adds freshwater to the North Atlantic, weakening the existing circulation system. The expansion of the Indo-Pacific reservoir would constitute additional pressure , this time from the south, on a climatic mechanism whose weakening is increasingly worrying scientists.
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source : la provence
