Emperor penguins not only share with polar bears the title as icons of their respective polar regions, but also a strong dependence on sea ice. And it’s precisely this habitat, which for a long time had shown itself to be fairly resistant to the warming of the polar regions, that has declined in recent years in large parts around Antarctica. This led to a massive breeding loss last year among emperor penguins in the Bellingshausen Sea, a study shows. And the outlook is unlikely to be much better for greater success this breeding season.
The discovery made by Dr. Peter Fretwell, Dr. Norman Ratclliff, and Audet Boutet of the British Antarctic Survey BAS during the analysis of satellite images from the eastern Bellingshausen Sea shocked the three researchers despite their many years of experience with emperor penguins: four of the five known breeding colonies had disappeared completely in the course of the breeding season even before the chicks had fledged. According to the experts, this likely means a complete breeding failure for the birds in these colonies and the loss of several thousand chicks, as the latter are still too small to survive in the icy waters. The reason for the failure, according to analysis of satellite imagery and sea ice data, is the loss of sea ice in the region, which was up to 100 percent during the breeding season in the southern winter of 2022. The team has now published the results of the study in the journal Nature Communications Earth & Environment.
Analysis of satellite images taken in the region during the austral winter of 2022 by the Sentinel-2 satellites as part of the European Space Agency ESA’s “Copernicus” mission showed that the sea ice had broken up again in some places soon after it had formed. The emperor penguins breeding at these sites thus lost the solid ground they need for their chicks. These usually hatch between July and August. However, the sea ice broke up again just two months later, which was much too early for the little chicks. Their plumage protects them from wind at this point in their development, but not from freezing water temperatures. According to Dr. Peter Fretwell, who has studied emperor penguins for years, “The loss of sea ice in this region during the Antarctic summer made it very unlikely that the chicks would survive.” According to the team of authors, individual fledglings may have escaped onto stranded icebergs, but this could not be verified due to the low resolution of the satellite imagery.
According to the authors, the four affected colonies are not among the largest colonies, but are still estimated to include between 630 and 3,500 breeding pairs. Moreover, not much is known about the colonies. Their remote location and the previously very dense ice conditions had hardly allowed direct visits. Only the colony at Rothschild Island had been visited directly so far. The remaining colonies had only been seen as brown patches by air or on satellite imagery over the past 14 years.
But for Dr. Peter Fretwell and his two team members, it’s clear that sea ice loss has left all four colonies in misery, an event never before observed on this scale. Complete breeding failures have been recorded at individual colonies since satellite observations of the colonies began in 2009, Fretwell, Ratcliff and Boutet write. “There has been no record of a widespread failure of breeding emperor penguins due to a regional sea ice loss affecting multiple sites before fledging in early December.,” they write in the study. “Our findings of probable breeding failure across multiple (…) sites in a single season are unprecedented.”
Move or Disappear – What Happens in 2023?
The results of the study do not bode well for the breeding success of emperor penguins this austral winter. That’s because Antarctic sea ice is well on its way to an all-time low. Although it will take a few more weeks to reach maximum sea ice extent (around mid-September, editor’s note), it is already clear that the area will fall further below the 30-year average. For sea ice experts, the decline is no surprise, yet the extent is. Negative records have been chasing each other since 2016, after years of stable development. The reasons for this are quite diverse. “Year-to-year changes in sea ice extent are linked to natural atmospheric patterns such as El Niño-Southern Oscillation, the strength of the southern hemisphere jet stream, and regional low-pressure systems,” explains Dr. Caroline Holmes from BAS. Much more effort is therefore needed to increase research investment in the Southern Ocean and to seek broader collaborations, a call made by some 300 researchers at the recently concluded SOOS symposium.
This year’s negative record is likely to have affected many of the colonies that rely on stable ice conditions. However, several scenarios are possible, as in some areas hardly any sea ice had ever built up. In those areas, it is likely that the emperor penguins have moved to new locations. But elsewhere, the birds may have been taken by surprise by breaking sea ice in the middle of their breeding season, and suffered a fate similar to that of the Bellingshausen Sea population. Researchers like Dr. Peter Fretwell will not know for sure until they have analyzed the satellite images, which, given the volume, is likely to take some time. In any event, the outlook for the icons of Antarctica is bleak.
Dr Michael Wenger, PolarJournal
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