Something strange is happening to Antarctic sea ice. The areal expanse of drift ice surrounding the continent is not only at an all-time low for this time of year, surpassing a record just set in 2022, but ice extent has reached all-time lows throughout the year.
What happened here is different than the Arctic sea ice expanse, says Mark Serreze, a climate scientist and director of the US National Snow and Ice Data Center, or NSIDC, in Boulder, Colorado. The other pole of the earth, he says (SN: 9/25/19). Not much has happened to Antarctica’s sea ice until the last few years. But it just crashed.
NSIDC uses satellite data, collected daily, to keep a close eye on the spread of sea ice at both poles. For most of 2023, the sea ice ring around Antarctica repeatedly made new historic lows, remaining well below its average extent from 1981 to 2010. On Feb. 21, at the hemisphere’s height of summer the southern sea, the sea ice extent has touched an all-time low since records began in 1978, of 1.79 million square kilometers. That’s 130,000 square kilometers about the size of New York state, less than the previous record low, reached on February 25, 2022.
Even as the Southern Hemisphere transitioned into winter, Antarctic sea ice remained at record levels. As of June 27, ice was strewn across about 11.7 million square kilometers of ocean. This is about 2.6 million square kilometers below the 1981-2010 average and about 1.2 million square kilometers below the previous lowest extent on record for June 27, set for 2022.
Unlike Arctic ice, whose decline is known to be closely linked to global warming, it has been more difficult to analyze the reasons for changes in Antarctic sea ice extent. This difficulty has made it unclear whether the changes are the result of natural variability or if something big has changed, Serreze says.
Recent years have made scientists think (SN: 06/27/17). We were losing control, Serreze says. It’s not yet clear whether this year’s extension is part of a larger trend, she notes. But the longer it persists, the more likely something big is going on.
The Arctic and Antarctic regions are antipodes, so to speak, in their geographical location. The ice in the Arctic Ocean is confined to a relatively small body of water surrounded by land. Antarctica, by contrast, is a landmass surrounded by ocean, meaning that the sea ice around the continent is much more mobile than in the north, with a larger seasonal range as it expands over the southern hemispheres in winter and narrows in summer. Climate simulations have, as a result, consistently predicted that the Arctic would experience greater sea ice losses as the planet warms, at least initially, while Antarctica would be slower to respond.
As for why Antarctic ice has tracked so low this year there are a few possible culprits. Regional climate patterns, particularly an air pressure pattern known as the meridional annular mode that shifts the direction of winds blowing around the continent, can compact or spread sea ice cover around Antarctica. And other regional patterns, such as El Nio’s meridional oscillation, can affect both oceanic and air circulation at high southern latitudes.
Right now, scientists are most concerned with what lies beneath the ice (SN: 12/13/21). There is growing evidence that there has been some kind of change in ocean circulation that is bringing more heat to the region, affecting the ice cover, Serreze says. There are a lot of people looking into this; they were really quick to get the data. We need to figure out what the hell is going on in the ocean.
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Image Source : www.sciencenews.org