Antarctic ice faces difficulty to recover – 7/9/2023 – Environment

After a historic meltdown in February, the Antarctic ice sheet 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.

The Antarctic ice sheet had a deficit of 2.5 million km^two at the end of June, an area slightly smaller than that of Argentina (2.78 million km^two), compared to the average between 1991 and 2020, according to the European observatory Copernicus.

On February 16, Antarctic sea ice —which is formed by the freezing of salt water in the ocean— reached its lowest extent since satellite measurements began 45 years ago, with a total area of ​​2.06 million km^two.

Since then, it has been recovering at an unusually slow pace, despite the onset of winter in the southern hemisphere.

The sea ice surface in June was 11.5 million km^two (17% less than average).

An “extraordinarily low” extent, according to Ed Blockley, who heads the Polar Climate group at the Met Office, the UK’s weather service.

“An unprecedented and worrying event”, confirms Jean Baptiste Sallée, oceanographer and climatologist at the French National Center for Scientific Research (CNRS). “It’s something we’ve never seen before. The question is: are we entering a new regime? It’s too early to answer”, he emphasizes.

Until recently, the Antarctic ice sheet seemed to escape the effects of global warming.

For 35 years, it has remained stable or even slightly increased, reaching a record length of over 20 million km.^two in September 2014, for the first time since 1979.

“In 2015, everything changed. In two or three years, what was gained in 35 (years) was lost”, explains François Massonnet, a climatologist at the Catholic University of Leuven, in Belgium.

“Since 2016, we have broken records almost every year and these records are not independent of each other”, he adds.

One hypothesis would be, according to him, that it is a self-sustaining phenomenon. The ocean heats up more strongly during the summer, due to the lack of ice. So, “when winter comes back, it first needs to release all the excess heat before sea ice forms,” ​​he explains. This thinner ice melts faster when summer returns.

refuge zone

Sea ice retreat “is consistent with climate change starting to impact the Antarctic ice sheet,” says Sallée.

But researchers are reluctant to make a formal link to global warming because of the difficulty they’ve had in the past working on climate models to predict changes in the Antarctic ice sheet.

Reducing sea ice could exacerbate global warming. The darker ocean reflects less of the sun’s rays than white ice, so it stores more heat.

As it melts, the ice sheet will also lose its role as a buffer between waves and the ice cap on the Antarctic continent, which could accelerate the flow of freshwater glaciers into the ocean.

Lastly, shrinking sea ice threatens the rich ecosystem it supports.

“The ice forms terraces, tunnels and labyrinths that serve as refuges where animals can hide from predators”, explains Sara Labrousse, researcher of polar ecology at CNRS.

The cap is home to krill, a shrimp-like crustacean that feeds on ice algae before being eaten by whales, seals or penguins.

“Sea ice is also a resting, molting and breeding area for many marine mammals and birds”, adds Labrousse.

When the ice breaks very early in the season, young seals —which have little fat and poorly waterproof fur— can die of hypothermia when they fall into the water, according to the researcher.

The reduction of sea ice “may put different populations at risk”, he warns.