Life is much more abundant in Antarctica during winter than scientists had previously thought, according to a USC researcher. The sea ice that forms around the continent is filled with pores that serve as a giant “nursery” for krill, a shrimp-like crustacean that is a food source for fish, squid, penguins and whales, marine biologist Cornelius Sullivan said in a report scheduled to be released today by the National Science Foundation.
“The sea ice itself is literally full of living organisms, which is a very surprising discovery because we tend to think of ice as being devoid of living organisms,” Sullivan said in a telephone interview. “We thought they would freeze or their metabolic rates would be reduced so much that they would be in a kind of suspended animation. But this sea ice biota has evolved a metabolism that allows them to be active and growing, even at temperatures below freezing.”
And when the ice melts in the Antarctic spring, the fresh water that is released “keeps phytoplankton in the surface water in a nutrient-rich, very light environment where they can bloom and become very productive, which results in a rich food source for higher organisms,” he said. Marine life is attracted from long distances to feed on these organisms, he said.
The six- to eight-foot thick sea ice extends outward from the Antarctic continent for about 1,000 miles in the winter, covering roughly 11 million square miles or three times the area of the United States. By the summer, however, more than 80% of the ice melts.
As far back as the beginning of the century, whalers and sealers reported an abundance of marine life at the edge of the sea ice. At the beginning of this decade, the National Academy of Sciences recommended that the National Science Foundation establish a program to discover the source of this biological abundance and the mechanism by which it is produced.
Researchers also wanted to find out what happens to krill in the winter. “Some researchers thought they settled to great depths in the ocean, and others thought they simply shriveled up for lack of food,” Sullivan said.
The foundation established a 47-member team of researchers to explore the problem, headed by Sullivan and David Ainley of the Point Reyes Bird Observatory north of San Francisco. The team has periodically visited the Antarctic for the last six years, the most recent visit occurring from June through August at the height of the austral winter.
The researchers deployed instruments and collected water samples from their ship in the Weddell Sea near the South Orkney Islands, 800 miles southeast of the tip of South America. They also left the ship to drill cores through the ice to collect samples, and even swam under the ice to obtain biological specimens.
They found that the ice is permeated “like Swiss cheese” with pores that range in size from the diameter of a human hair to that of an arm, Sullivan said. Algae and bacteria grow on the surface of ice crystals in the pores. At the latitudes they studied, the plants received five to six hours of light per day in mid-winter.
The plants and bacteria serve as a food source for the krill. Living in the pores also protects the krill from predators, he added, although the researchers spotted at least one type of fish in the larger pores. Most of the krill they observed in the ice were in larval and juvenile stages, he said, suggesting the idea of a nursery.