Changing Life: Sea Ice

Sea ice is more than just a layer of frozen ocean: it is a vibrant, essential habitat for many Antarctic species.

Each winter, an area of the Southern Ocean roughly the size of the United States freezes around the Antarctic coastline. This sea ice provides a protective layer over the ocean: a cover that insulates it against the strong winds and cold temperatures above, and creates a sheltered habitat for life to flourish. 

Sea ice is an important habitat for Antarctic krill, particularly in the larval and juvenile stages of life. Krill larvae have been seen scraping sea ice algae from the underside of the ice to eat, and juvenile krill find shelter from predators and strong currents in small ridges and caverns under the ice. Krill are an essential food source for Antarctic penguins, seals, whales, and many other marine creatures.

Emperor penguins breed, incubate their eggs and raise their young on the sea ice. They need a solid, stable platform of sea ice for around 9 months each year, to allow their chicks to mature and become independent before the sea ice breaks apart. 

Any change in sea ice can be catastrophic for emperor penguin colonies. Too little sea ice means there is not enough space to breed, raise chicks, hide from predators and rest while molting (replacing their damaged feathers). Too much sea ice, and the distance between their colony and the open water where they feed becomes too large. A longer journey between the colony and feeding grounds can lead to exhaustion and starvation for emperor penguins whose job is to feed themselves and their young. Even when the amount of sea ice is just right, if it breaks up before the chicks are fledged and independent, entire generations can be lost.

By 2019, almost all of the penguins had abandoned the colony. While it’s normal for penguin colonies to fluctuate in size from year to year, change on this scale is extremely unusual, and unprecedented at Halley Bay.

Emperor penguins face significant threats to their survival due to the warming climate, and other human activities. If we continue with ‘business as usual’ greenhouse gas emissions, 80 percent of Antarctica’s emperor penguins will be gone by 2100, and they will be doomed to eventual extinction. 

In 2021 the U.S. Fish and Wildlife Service proposed the emperor penguin for protection under the Endangered Species Act. It is currently recognised as Near Threatened on the IUCN Red List.

It’s not just emperor penguins that are being affected. On the Antarctic Peninsula, many Adélie penguin colonies have declined by 50-80 percent since the 1970s. Some Adélie penguin colonies in the northern part of the Peninsula have vanished entirely. 

Chinstrap penguin colonies have faced similar declines on the nearby South Shetland Islands, according to a study released in February 2020. The collapse of a number of penguin colonies in this area appears to be linked to reduced availability of krill in nearby waters, which may be related to diminishing sea ice cover across the region. This is an area of current research. Both Adélie and chinstrap penguin populations remain strong in other areas of Antarctica and the subantarctic, and they are not at imminent risk of extinction.

In the global ocean, everything is connected. Antarctic life interacts with the rest of the ocean, including sea ice, in many ways that benefit humans. For example, sea ice algae absorbs carbon from the atmosphere, helping to reduce the greenhouse effect. Great whales feed on the Antarctic krill that grow under sea ice. As they travel north to breed they fertilize the ocean with their lifegiving feces, which add vital nutrients to the ocean.

Exactly how changes in Antarctic sea ice and the broader Antarctic marine environment will affect humans remains a great unknown. This uncertainty is part of why it is so important that we protect these fragile ecosystems from the unpredictable changes caused by the climate crisis: we may not know yet what we’ve got to lose. It’s not too late to act – now is the time.