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  • Writer's pictureXochitl Clare

Krill at crisis: Scientists point to sea ice as critical habitat for Antarctic krill

Updated: Apr 11, 2022

Photo by Vincent van Zeijst / Wikimedia Commons | Article by Xochitl Clare, Santa Cruz, CA, February 23, 2017

As a budding marine biologist, when asked if I could conduct research anywhere in the world, one of my answers has always been Antarctica. To most this answer is puzzling. The planet’s polar regions do not immediately appear to be teeming with life in comparison to reef ecosystems and seem to provide little playing ground for a biologist. However, much insight can be drawn from studying Antarctica by looking under the surface—literally.

It wasn’t until I took my first oceanography classes in college that I learned about the Antarctic Circumpolar Current (ACC) that flows completely around the globe. Circling Antarctica in the Southern Ocean to flowing through the Atlantic, Indian, and Pacific Oceans—current cycling driven by the ACC can have long term global influences on our climate, oceans, and all those within it.

While ice sheet formation on the continent remains a mystery, a new study published by Nature Geoscience by scientists in McGill University's Department of Earth and Planetary Sciences supports beliefs that both ocean circulation patterns and global climate change caused rapid formation of Antarctica’s ice sheets about 34 million years ago.

The formation of an ice-covered Antarctica began with the deepening of Drake’s Passage, the body of water between South American and Antarctica that pushed warm water northward and caused an increase in rainfall, pushing carbon dioxide levels in the atmosphere low enough for the formation of ice sheets in the Antarctic. Because the ACC also influences levels of atmospheric carbon dioxide, it has been also shown to control glacial activity and global sea level rise.

The Antarctic has remained cold due to the presence of the ACC. A team of MIT and University of Washington researchers explain in a Nature Geoscience paper published last May, that old reservoirs of deep cold water in the ACC to rise and create a slow-moving band around the continent.

Diagram of the outflow of ACC (darker blue) from Euro-Argo Education.

Thanks to climate shifts millions of years ago, sea ice is now the home to both plant and animals of at all trophic levels and serves as the foundation of overlapping communities.

Sea ice is especially important for Antarctic krill, arguably the base of the Antarctic food web. Only up 2.4 inches (6 centimeters) long and weighing up to .071 oz. (2 grams), this swimming crustacean feeds directly on phytoplankton and sets the record as the most abundant animal species on the planet (biomass of 125-725 million metric tons).

Antarctic krill (Photo by Flip Nicklin)

Many animal species in Antarctica including whales, seals, penguins, fish, squid, and seabirds depend on krill for survival, making Antarctic ecosystems unusually fragile. In their early life stages, krill dwell underneath seasonal “pack ice” during the winter. Reduction of pack ice during warmer winters lead to sharp declines in krill and scarce food conditions. This poses greater risks for humpback, fin, minke, and blue whales who feed almost exclusively on krill.

“If the Antarctic ecosystem is seen as a heart, pumping its red streams of krill, then for the last century it has been a heart in fibrillation” reports Kenneth Brower from National Geographic during his time at the British Antarctic Survey station in 2013.

Brower also reports that the Southern Ocean which was once home to 200,000 krill feeding blue whales a century ago, now has only a few hundred left. Stark declines in krill could mean massive marine mammal extinctions in our time as well as the crash of one of our planet’s most unique ecosystems.

Other scientists are not so quick to claim the ongoing krill crisis to be completely climate change driven. Krill biologist So Kawaguchi from the Australian Antarctic Division asserts that “we still don’t have a full grasp of how krill interact with ice…and [that] this interaction could further change as the environment changes” in an interview with Climate Central.

Regardless, more research done on oceanographic properties of the Southern Ocean is needed to understand which parts of the environment may largely influence marine life.

Antarctic krill in distress are far from the average person’s day-to-day concerns. Yet, it is important to remember that as the currents in the Southern Ocean effect ocean patterns 4,436 miles (7,122 kilometers) away here in the Pacific—some of the world’s smallest organisms, such as krill and their phytoplankton counterparts have been proven to impact some of the world’s largest.

Oceanographic technological advances have allowed us to gain a greater biogeographical understanding of our oceans that was once inconceivable. It is now up to the biologists, physicists, chemists, and geologist to put these tools to use. We are only at the tip of the iceberg.

For more information check out these articles:

1. “Scientists think they finally know how Antarctica was formed, and it contains ‘an interesting lesson’ about our future” by Lindsay Dodgson, Feb 4, 2017, Business Insider

2. “Life in Antarctica Relies on Shrinking Supply of Krill” by Kenneth Bower, Aug. 17, 2013, National Geographic

3. “Instantaneous movement of krill swarms in the Antarctic Circumpolar Current”, Geraint A. Tarling and Sally E. Thorpe, May 1, 2014, Limnology and Oceanography, Vol. 59, Issue 3

4. “Krill, Currents, and Sea Ice” by Stephen Nicol, Feb. 1, 2006, BioScience

About the author: Xochitl Clare will be receiving her Ph.D. in Marine Biology at the University of California, Santa Barbara (23'). Xochitl wrote this piece while double majoring in Marine Biology & Theater Arts at UC Santa Cruz (17'). Her current research covers eco-physiology and global change biology. Xochitl is also passionate about multi-media science communication.

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