The extent of sea ice is often considered an indicator of the state of the corresponding polar region, especially in light of global climate change. Therefore, special emphasis is placed on the minimum and maximum extents in February and September. However, while a clear downward trend is evident for the Arctic, the Antarctic shows a far more variable course. But in this 2021/22 season, the extent of the expansion has amazed even experts.
As reported by the US National Snow and Ice Data Center (NSIDC), Antarctic sea ice extent in February dropped to what is now the lowest daily level since satellite record-keeping began in 1979. According to the most recent measurements, the area of total sea ice on February 25 was 1.924 million square kilometers, lower than the previous low, recorded on March 3, 2017. At that time, an extent of 2,110 million square kilometers was reported. This means that this year’s trend of the minimum extent since measurements began has come true, and the value is about 1 million square kilometers below the 1981-2010 average.
A closer look at the individual Antarctic regions shows that this year’s record low was mainly driven by losses in the area between the Amundsen and the Ross seas. On the eastern side of the Antarctic Peninsula, in the Weddell Sea, large areas also have not formed a closed ice sheet and are therefore considered ice-free. In the other areas, the declines are rather moderate. “This year, none of the individual regions (except for the Ross Sea, ed.) have record low extents. But all are below average (…),” the NSIDC says in a statement on its website.
Why sea ice extent reached such a low this year, after previous years had shown a moderately positive trend, is not yet well understood. One possibility could be a mis-estimation of the natural variability of Antarctic sea ice in research models. “Natural variability is higher than the models indicate and that natural variability may still dominate the Antarctic sea ice trends,” the NSIDC says. A recent study looking at sea-ice extent prior to the use of satellite imagery concluded that the oceanic and atmospheric conditions that influence sea-ice extent actually undergo large variations on the order of decades, and therefore the variability in sea-ice extent is also likely to be much greater than previously thought. This must now be incorporated into the forecast models and can thus help to more precisely identify possible courses of sea ice.
Antarctic sea ice provides the habitat for many of the species of animals and plants that live in and around Antarctica. Seals and penguins in particular depend on the white surface of the sea, as they can rest on it somewhat safely. In addition, the pack ice areas at their edges drive food webs. And more accurate prediction of sea ice extent is also important for research. This is because such information is of great importance, especially for the planning of supply trips to research stations and expedition such as the on-going Endurance22.
Dr Michael Wenger, PolarJournal
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