In Antarctica, the ice sheet is rebuilding at an unusually slow rate, having reached an “extraordinarily low” level in February. According to the European Copernicus Observatory, the ice deficit in Antarctica is equivalent to five times the area of mainland France.
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“An unprecedented and worrying event”: After a historic thaw in February, the Antarctic plate is struggling to recover despite the onset of winter in the Southern Hemisphere, a phenomenon that could accelerate global warming and threaten many species in the Southern Ocean.
About 2.5 million km², that is to say, five times the surface of mainland France: this is the deficit of the layer recorded by the European Copernicus observatory at the end of June, compared to the average of 1991-2020.
On February 16 of this year, Antarctic sea ice, which is formed by the freezing of salt water in the ocean, had already reached its lowest extent since satellite measurements began 45 years ago, with a total area of 2 .06 million km².
Since then, it has been rebuilding at an unusually slow rate, despite the onset of winter in the Southern Hemisphere. In June, the ice sheet covered 11.5 million km2 (17% less than average). An “extraordinarily low” extent, according to Ed Blockley, who heads the Polar Climate Group at the metofficethe British weather service.
“An unprecedented and worrying event,” confirms Jean-Baptiste Sallée, an oceanographer and climatologist at the French National Center for Scientific Research (CNRS). “We are witnessing something never seen before, with a plaque that is not growing at its natural rate. The question is: have we entered a new regime? But it is still too early to tell.”
Until recently, the Antarctic ice sheet seemed to have escaped the effects of global warming. For 35 years, it had remained stable or even increased slightly, and in September 2014 it even broke a record in terms of its size, with more than 20 million km2, for the first time since 1979.
“In 2015, everything turned around: we lost in two or three years what we had gained in 35 years,” explains François Massonnet, a climatologist at the Catholic University of Louvain (Belgium). “Since 2016, records have been broken almost every year, and it seems that these records are not independent of each other.”
One hypothesis, he believes, is that it is a self-perpetuating phenomenon: the ocean heats up more strongly in summer, due to the lack of sea ice. Then, “when winter returns, you have to release all the excess heat so that sea ice can form,” explains François Massonnet. This thinner ice also melts more quickly when summer returns.
A threat to the ecosystem
This plate retreat “is consistent with climate change that is beginning to have an impact on the Antarctic layer,” says Jean-Baptiste Sallée. But researchers are reluctant to make a formal link to global warming, given how difficult climate models have had in the past to predict changes in the plate.
Be that as it may, the reduction in sea ice is likely to exacerbate global warming. The darker ocean reflects less sunlight than white ice, so it will store more heat.
As the pack ice melts, it will also lose its role as a buffer between the waves and the ice cap of the Antarctic continent, risking accelerating the flow of freshwater glaciers into the ocean.
Finally, the retreat of the sea ice threatens the rich ecosystem that it supports. Far from being a frozen desert, “packed ice forms terraces, tunnels and labyrinths that serve as shelters where animals can hide from predators,” explains Sara Labrousse, a polar ecology researcher at the CNRS.
In particular, it is home to the krilla shrimp-like crustacean that grazes on algae on the ice before being eaten by numerous predators including whales, seals, and penguins.
“Pack ice is also a resting, molting and breeding area for many marine mammals and birds,” adds Sara Labrousse.
According to the researcher, when the plate breaks too early, young seals with little fat and poorly waterproof fur can die of hypothermia when they fall into the water.
The retreat of the layer “can endanger populations,” he warns.
*With AFP; adapted from its original in French
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