How Antarctica’s melting sea ice killed thousands of emperor penguins chicks

The study, ‘Record low 2022 Antarctic sea ice led to catastrophic breeding failure of emperor penguins’, was published on August 24 in the journal Communications Earth & Environment. It was conducted by Peter T Fretwell and Norman Ratcliffe of the British Antarctic Survey (Cambridge) and Aude Boutet, an independent researcher based in Paris.

Since 2016, the Antarctic sea ice extent — the total region with at least 15% sea-ice cover — has been shrinking with the total area of frozen water around the continent reducing to new record low levels almost every year. This puts more than 90% of emperor penguin colonies at risk as they may go extinct by the end of this century, if Earth continues to get warmer at the present rate.

“Our findings show a clear link between negative sea ice anomalies and emperor penguin breeding failures that may represent a snapshot of a future, warming Antarctica where such events become more frequent and widespread, with grave consequences for emperor penguin population viability,” the research added.

Sea-ice and the emperor penguin breeding cycle

The role of stable sea ice in the emperor penguin breeding cycle is crucial. “Emperor penguins spend their whole breeding cycle on the sea ice. They need it to last from early April until late December,” Fretwell told The Indian Express in an email.

The birds arrive from the sea to their preferred breeding sites on sea-ice in late March to April. They court and mate, and then lay eggs in May and June. Eggs hatch in August after which parent emperor penguins take turns to feed their chick. “The chick grows quickly and by December starts to lose its grey downy feathers and replaces them with sleek black waterproof adult plumage,” Fretwell added.

By late December or early January, the fledgling period comes to an end, leading chicks to go into the water and look for food themselves. Therefore, the sea ice on which emperor penguins breed needs to remain stable between April to January to ensure successful breeding.

The findings

Researchers observed five emperor penguin colonies located in the Bellingshausen Sea region, west of the Antarctic Peninsula, using satellite images taken between 2018 and 2022. Through those images, they analysed the activity of birds by tracking their excrement, called guano, which leaves a distinct brown trace on the white sea ice. The examined colonies were at Rothschild Island, Verdi Inlet, Smyley Island, Bryant Coast and Pfrogner Point.

The fallout began when the sea-ice extent around Antarctica hit a record low in 2022. The Bellingshausen Sea region was the worst affected — during November, some parts saw a 100% loss in sea-ice extent. As a result, four out of five colonies witnessed complete breeding failure.

Only at one colony in Rothschild Island, the most northerly site, some breeding was successful because icebergs may have helped to stabilise the sea-ice, giving chicks the time to fledge.

“We believe up to 10,000 chicks (7000-10,000) would have perished in the Bellingshausen Sea. Around the continent, this number would have been much higher as around 30% of all colonies (there are 62 known emperor penguin colonies) were affected by early sea ice loss. But as yet we have calculated the number,” said Fretwell.

Emperor penguins are known to tackle breeding failures caused by the localised disappearance of sea ice by moving to alternative, more stable, sites the next year, the study said. However, given the large-scale shrinking of the sea ice extent, such a strategy will not be possible.

“That’s why this (Bellingshausen Sea) regional failure is so difficult (for the penguins) because they can’t just go to the nearest colony… A 1,500km region in length has lost almost all its sea ice. We have no real idea what happens if there’s no ice,” Fretwell told The Guardian.

Antarctic sea ice extent shrinking

Like last year, the Antarctic sea ice extent has diminished to a new record low in 2023. But this time, the ice cover is exceptionally low. Throughout July 2023, sea ice averaged 13.5 million sq km, the lowest extent observed for this time of year since the continuous satellite record began in late 1978, according to a NASA Earth Observatory report.

Credit: Climate Analyzer

Although it’s currently the winter season in the Southern Hemisphere, ice growth has been really slow in Antarctica. The development has raised alarm among scientists and experts as the drop in sea ice could have grave global consequences.

For instance, less sea ice exposes more of the continent’s ice to the open ocean, leading it to melt and break off more easily. This will contribute to rising sea levels, which can affect millions of people living in coastal regions.

Decline in the ice sheet also causes a spike in sea surface temperatures as sea ice reflects solar rays back into space and thwarts heat from getting absorbed in the oceans. Warmer oceans mean more difficulty in the formation of ice and a wide range of other consequences.

The reasons behind this year’s record low ice covers aren’t clear yet though. There is a lack of satellite data and scientists haven’t been able to confirm if the drop in sea ice is due to either natural variability or climate change.

“A lot of people have discussed if this is a transition to a new sea ice state. And I think it’s really too early to tell, still, based on the fact that Antarctic sea ice is very variable,” Lettie Roach, a polar climate scientist who studies Antarctic sea ice at Columbia University, told Wired magazine.

“Climate models show very large variability in Antarctic sea ice, but this should perhaps be taken with a pinch of salt, because the models generally struggle to simulate the past changes in Antarctic sea ice.”