Antarctic Sea Ice Collapse Triggers Unprecedented Emperor Penguin Breeding Failure

In the central and eastern Bellingshausen Sea, west of the Antarctic Peninsula, the sea ice that emperor penguins depend on vanished entirely in November 2022. Satellite images showed it going well before the year's chicks could have grown waterproof feathers, and researchers at the British Antarctic Survey now say it caused a breeding failure of a kind they have never recorded.

The study, published in Communications Earth & Environment, looked at five colonies: Rothschild Island, Verdi Inlet, Smyley Island, Bryan Peninsula and Pfrogner Point. All were found within the last 14 years using satellite imagery, and all had been shown to return to the same spot each year. The only earlier breeding failure on record among them was at Bryan Peninsula in 2010. This time, the researchers say it is highly probable that no chicks survived from four of the five. The team worked from images captured by the European Commission's Copernicus Sentinel-2 mission, which has monitored the area continuously since 2018.

The timing explains the damage. Emperor penguins need stable sea ice firmly attached to the shore from April through January. Eggs are laid in the Antarctic winter, in May and June, and hatch about 65 days later. But chicks do not have waterproof feathers until December or January. When the ice broke up before then, chicks were displaced into the water. Dr Peter Fretwell, the study's lead author, said the loss of ice during the Antarctic summer made it very unlikely that displaced chicks would survive, and added: "We have never seen emperor penguins fail to breed, at this scale, in a single season."

The wider ice record is bleak. At the start of December 2022, Antarctic sea ice extent matched the all-time low set in 2021, and by the end of that month it was the lowest in the 45-year satellite record. Since 2016, Antarctica has had the four lowest extents on record, with the two lowest in 2021/22 and 2022/23. In the Bellingshausen Sea, ice did not begin re-forming until late April 2023. Between 2018 and 2022, 30% of the 62 known emperor colonies were affected by partial or total ice loss.

Penguins have a fallback. After earlier ice losses, colonies have moved to more stable sites the following year. Scientists say that cannot work when the habitat across a whole region is hit, as happened here. The findings fit predictions, based on current warming trends, that more than 90% of emperor colonies will be quasi-extinct by the end of the century.

The trend has not eased. As of 20 August 2023, sea ice extent was 2.2 million square kilometres below the 1981-2022 average of 17.9 million, and well below the previous winter low of 17.1 million set on the same date in 2022. The missing area is larger than Greenland, or roughly ten times the size of the United Kingdom. Dr Caroline Holmes, a BAS polar climate scientist, said areas that should be freezing are remarkably still largely ice-free.

The researchers are careful about attribution. Holmes noted that year-to-year changes are tied to natural patterns, including El Nino-Southern Oscillation, the southern hemisphere jet stream and regional low-pressure systems, and that years of targeted observation and modelling will be needed to say how much each contributes. Still, she said the run of record lows and the warming of the subsurface Southern Ocean point strongly to human-induced warming worsening these extremes. Dr Jeremy Wilkinson, a BAS sea ice physicist, said the paper reveals the link between sea ice loss and ecosystem annihilation, and that politicians must act. He noted Arctic sea ice is likely to be absent in the 2030s.

What to watch is whether the ice around the Bellingshausen colonies holds in the coming breeding seasons, and whether the colonies return to sites that have now failed.