Until now, scientists did not have enough data to detect the warming trend, but the study's results have generated concern.
Heat circulation processes in the ocean are approaching Antarctica and threatening the ice shelves surrounding the continent, according to a study led by the University of Cambridge, United Kingdom, released this Tuesday.
The university, in collaboration with the University of California, United States, compiled long-term measurements, collected by ships and floating robotic devices, showing that a comparatively warm mass called "circumpolar deep water" has expanded and moved towards the Antarctic continental shelf over the past 20 years.
Until now, scientists did not have enough data to detect the warming trend, but the study's results have generated concern.
"It's worrying because this warm water can flow under the Antarctic ice shelves, melting them from below and destabilizing them," said Joshua Lanham, lead author of the study, quoted in a statement.
Sea ice shelves play an important role in containing the polar ice caps and glaciers of Antarctica, which together store enough fresh water to raise sea levels by about 58 meters, according to the press release about the study.
Researchers highlight that, for the first time, a change in temperature has been observed that climate models indicated was due to global warming, but which insufficient data had prevented from being confirmed.
Previous observations of the ocean surrounding Antarctica came from ship data, but the records were very spaced out in time, nothing compared to the detailed and continuous data collected by the global Argo network, made up of autonomous floats that drift through the upper layer of the ocean.
“In the past, ice masses were protected by a layer of cold water, preventing them from melting. Now it seems that ocean circulation has changed, and it’s almost as if someone has turned on the hot water tap,” said Sarah Purkey, one of the study’s lead authors.
And this expansion of comparatively warm water makes sense, he argues, pointing out that more than 90% of the excess heat from global warming is stored in the ocean, with the Antarctic Ocean absorbing most of the heat generated by human activity.
The researchers responsible for the study also warn that the discovery has implications not only for the melting of Antarctica, but for the entire world.
According to Ali Mashayek, one of the study's lead authors, "the Southern Ocean plays a key role in regulating global heat and carbon storage, so changes in heat distribution in this region have broader implications for the global climate system."
Around the poles, extremely cold and dense water forms and sinks to the deeper layers of the ocean. As this dense water sinks, it absorbs heat, carbon, and nutrients, setting in motion a global "conveyor belt" of currents, including the current that regulates temperature in Europe, the "Atlantic Meridional Overturning Circulation" (AMOC), which transports warm water from the tropics to the North Atlantic, where it cools, becomes denser, sinks, and keeps the ocean circulation functioning.
Climate models indicate that warmer air temperatures and the influx of freshwater from melting glaciers and polar ice caps are reducing the formation of this dense water in the North Atlantic, which could lead to a weakening of the AMOC.
Similar changes have been predicted for the Antarctic Ocean. But scientists warn that these are no longer scenarios suggested by models; it is something that is happening and is already observable.
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