A penguin apocalypse is unfolding in Commonwealth Bay, Antarctica, as tens of thousands of birds are cut off from their food supply by a stranded iceberg. The iceberg in question, B09B, has altered the penguins’ frigid environment, resulting in a mass of deaths. The finding is a worrying sign for other penguin colonies confronted with climate change.

When the explorer Douglas Mawson established a base at Cape Denison at the head of Commonwealth Bay in 1912, he complained about the noise of the Adélie penguin colony, estimated to contain 100,000 birds. Considering the location is the windiest place on Earth, the birds must have been loud.

However, Professor Chris Turney of the University of New South Wales recently found numbers around a tenth of that, and many were not even trying to hatch eggs. In Antarctic Science, Turney and his co-authors attribute the difference to the iceberg B09B, grounded offshore, filling the bay with ice. The penguins of Cape Denison now have an almost impossibly long walk to the ocean to feed.

In normal times, the sea ice is driven offshore, leaving gaps into which the penguins can dive to feed. However, powerful winds now sweep down from the Antarctic highlands and freeze the waters of Commonwealth Bay.

The cause of the penguin's suffering is, as Turney put it to IFLScience, the size of a small country. B09B broke off the Ross Ice Shelf in 1987 and in December 2011 became frozen to the seabed at the mouth of Commonwealth Bay. The sea ice is now blocked, and has built up to form what is called “fast ice," which is ice fastened to the shore by some blockage. 

The paper reports there was still some open water off the glacier a year after the fateful stranding, but by January 2012 “fast ice extended around 12 nautical miles (22 kilometers) offshore from Cape Denison.” A long way for penguins to waddle.

It is not clear whether the 5,500 surviving penguins pairs have found rare cracks in the ice to jump through, or if they are journeying all the way to the edge.

What the authors were able to determine was that the surviving birds are not doing well. In December 2013, “Hundreds of abandoned eggs were noted, and the ground was littered with the freeze-dried carcasses of the previous season’s chicks,” they wrote.

^{One of the few healthy-looking penguins left at Cape Denison. Australasian Antarctic Expedition 2013-2014}

Turney told IFLScience: “We have no idea how long B09B will stay there. It could move this year, or it could be there for decades to centuries.”

Based on long-abandoned rookeries, "There is some evidence that this might have happened in the past," Turney added. Nevertheless, the fear is that global warming will cause an increase in iceberg calving, creating situations such as the one at Cape Denison all around Antarctica. Already, Turney noted, it appears that icebergs have become drastically more frequent off the Antarctic Peninsula, the area of the continent most affected by climate change.

Turney said the penguins appear unable to move to new colonies and there is no prospect for rescuing them by carving holes in the ice, as these would rapidly freeze over.