In a new study from the British Antarctic Survey, scientists report that the Weddell Sea has lost one-third of its summer ice cover in the last five years. Summer sea ice has declined by one million square kilometers, an area twice the size of Spain, in the Weddell Sea along the coast of Antarctica.
Many animals such as penguins and seals depend on the sea ice that surrounds Antarctica for finding food and breeding.
The researchers analyzed satellite records and weather data from over the last four decades to investigate the dramatic decline of summer ice in the Weddell Sea. The experts found that much of the ice was lost as a result of severe storms in the Antarctic summer of 2016 and 2017.
The summer sea ice was also influenced by the re-emergence of a polynya – an area of open water in the middle of the contiguous pack ice – which had not appeared since the mid-1970s.
“Antarctic sea ice continues to surprise us. In contrast to the Arctic, sea ice around the Antarctic had been increasing in extent since the 1970s, but then rapidly decreased to record low levels, with the greatest decline in the Weddell Sea,” said study lead author Professor John Turner.
“In summer, this area now has a third less sea ice, which will have implications for ocean circulation and the marine wildlife of the region that depend on it for their survival.”
The size of Antarctica doubles in the wintertime when the surrounding ocean freezes. By late September, sea ice extent reaches over 18 million square kilometers. Most Antarctic sea ice melts in the spring and summer, but the Weddell Sea retains a large amount of ice.
According to the study, a series of intense storms developed in the Weddell Sea in December of 2016 that drew warm air toward the Antarctic and melted a substantial amount of sea ice. The resulting lack of ice cover exposed this region of the Southern Ocean to more sunlight, leading to unusually warm water temperatures that have persisted ever since.
The combination of strong winds and warmer ocean temperatures created the polynya, and this large area of open water has also contributed to the decline in summer sea ice.
If the dramatic changes in ice cover continue in the Weddell Sea, there will be major consequences throughout the Antarctic food chain. Many species, including algae, krill, seabirds, seals, and whales, are highly adapted to the presence of sea ice. Changes in ice cover will affect nutrients and reduce the essential habitat needed by vast numbers of animals for breeding and feeding.
“The dramatic decline in sea ice observed in the Weddell Sea is likely to have significant impacts on the way the entire marine ecosystem functions,” said study co-author Professor Eugene Murphy. “Understanding these wider consequences is of paramount importance, especially if the decline in ice extent continues.”
The sea ice in Antarctica is highly variable from year to year, so the scientists are not yet sure if ice in the Weddell Sea may recover, or whether this is a signal of the long-term decline of sea ice.
The study is published in the journal Geophysical Research Letters.