For a long time, the Antarctic sea ice was considered relatively stable and less affected by climate change than its Arctic counterpart. But now the Antarctic sea ice has reached a new record low: At the beginning of February 2023, only 2.20 million square kilometers of the Southern Ocean were covered by sea ice – such a low value has never been documented in the southern summer since satellite measurements began. An accelerated meltdown has already become apparent in recent years.
Similar to the Arctic Ocean, the extent of sea ice around the Antarctic continent fluctuates over the course of the year. In the southern hemisphere, ice melt peaks in January and February – during the southern summer. However, the seasonal fluctuations are significantly stronger than in the far north: because the Antarctic sea ice is thinner overall, it thaws completely in some places in summer, but then quickly grows back again in the very cold winters. Overall, the sea ice area around the Antarctic fluctuates between a winter maximum of around 18 to 20 million square kilometers and a minimum of around three million square kilometers at the end of southern summer.
Summer record low
Despite these large seasonal fluctuations, the Antarctic sea ice seemed to be little affected by climate change for a long time. This has only changed in recent years. At the beginning of 2022, the sea ice area shrank to a record minimum of just 2.27 million square kilometers. But this year the sea ice area has decreased again: “On February 8, 2023, with an extent of 2.20 million square kilometers, the previous record minimum from 2022 was already undercut,” reports sea ice physicist Christian Haas from the Alfred Wegener Institute , Helmholtz Center for Polar and Marine Research (AWI).
The Antarctic sea ice has thus reached an all-time low. Such a small area has never been measured since satellite measurements began around 40 years ago – and it could go further: “Since the sea ice melt in the Antarctic is expected to continue into the second half of February, we cannot yet say when the new one will start negative record will be reached and how much additional sea ice will melt by then,” says Haas. The sharp decline in sea ice was already apparent in December 2022 and the trend has continued since then.
Rapid decline only in recent years
The ice melt is particularly pronounced in the West Antarctic Bellingshausen and Amundsen Seas, the Bellingshausen Sea is almost ice-free. The research ship Polarstern is currently also located there to research traces of past ice ages and interglacial periods. “I have never experienced such an extreme ice-free situation here before. The continental shelf, which is the size of Germany, is completely ice-free,” reports expedition leader and AWI geophysicist Karsten Gohl. “These conditions are obviously beneficial for research on the ship, but it makes you think that this change has happened in such a short time.”
The summer sea ice extent in Antarctica has been below the long-term trend for several years. “The rapid decrease in sea ice over the past six years is very astonishing because the ice cover had hardly changed in the previous thirty-five years,” says Haas. “It is unclear whether this is the beginning of the rapid end of summer sea ice in Antarctica, or whether it is just a new phase with lower but still stable sea ice coverage in the summer.” In the southern summer, the researchers see warmer than average air temperatures west and east of the Antarctic Peninsula, and natural climate fluctuations, the so-called Southern Annular Mode (SAM), also play a role. In a positive phase of the SAM, an abnormally low air pressure develops over Antarctica. As a result, the shielding west wind belt is tightening around Antarctica. This, in turn, causes more warmer deep water to rise and be washed onto the Antarctic shelf, where it melts the sea ice and ice shelves from below.
Historical photographs also show how much the Antarctic sea ice and climate have changed compared to previous centuries: 125 years ago, the Belgian research ship Belgica was involuntarily frozen in the massive pack ice of the Bellingshausen Sea for more than a whole year don’t get out of the ice. Today, on the other hand, the research vessel Polarstern can operate in an almost ice-free Bellingshausen Sea.
Source: Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, sea ice portal