WASHINGTON - Icebergs that break off Antarctica and drift away turn out to be hotspots of life in the cold southern ocean, researchers report. Climate warming has led to an increase in the number of icebergs breaking away from the Antarctic in recent years, and a team of researchers set out to study the impact the giant ice chunks were having on the environment.
Turns out, the melting ice also dumps particles scraped off Antarctica into the ocean, providing a pool of nutrients that feed plankton and tiny shrimplike creatures known as krill.
Indeed, the researchers led by Kenneth L. Smith Jr., of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., found an increase in life forms surrounding a pair of icebergs they studied.
The abundance extended more than four kilometres away from the drifting ice, they report in this week's online edition of the journal Science.
"Just as water-holes become "hotspots" in the desert, drifting icebergs are like oases in Antarctic's ocean," helping promote life, said Russell R. Hopcroft of the Institute of Marine Science at the University of Alaska, Fairbanks.
It has been known that biological productivity is increased near the edge of an ice pack, Hopcroft said, but it's an aspect of floating icebergs that has not been previously considered. Hopcroft was not part of the research team.
Smith said he was surprised at the amount of sealife surrounding the icebergs, though "there had been anecdotal observations in the past of increased seabird abundance around icebergs."
By promoting life surrounding them, the icebergs also may have an impact on reducing the excess carbon in the atmosphere -- at least somewhat countering the greenhouse warming that helped make them break free in the first place, Smith suggested.
"One important consequence of the increased biological productivity is that free-floating icebergs can serve as a route for carbon dioxide drawdown and sequestration of particulate carbon as it sinks into the deep sea," Smith said in a statement.
"While the melting of Antarctic ice shelves is contributing to rising sea levels and other climate change dynamics in complex ways, this additional role of removing carbon from the atmosphere may have implications for global climate models that need to be further studied," he added.
Kristen St. John, a professor or geology and environmental science at James Madison University in Harrisonburg, Va., said the surprising aspect of the report is the scale at which it is happening.
It has been known that icebergs deposit material from land into the ocean as they melt, but the amount of the impact in this case was significant, she said.
Lack of iron is known to limit biological activity in the southern ocean, she said, and "if icebergs are transporting iron-rich minerals to offshore marine settings it is logical that the icebergs are ... helping the base of the food chain, which then can have positive effects all the way up the food chain," she said.
However, St. John cautioned that bedrock in different source areas has different rock and mineral types so every source will not be the same.
"This study is fascinating and should prompt others to pay greater attention to the organic content of the drifting ice," said St. John, who was not part of the research team.
Smith said he is organizing a new study to make more detailed measurements of the amount of iron and other nutrients released.
Walker Smith of the Virginia Institute of Marine Science of the College of William and Mary, said the study "confirms what has been known in a fragmentary sense."
"What is novel about the study is the use of radium isotopes to establish clearly the influence of" the material in the water and estimating the area it influenced, said Smith, who was also not part of the research team.
The researchers closely studied icebergs W-86 and A-52 in the Weddell Sea, adjacent to Antarctica and southeast of the southern tip of South America. They collected samples of the water around the ice and used a remotely operated submarine to study the undersides of the ice.
The work was supported by the National Science Foundation and the David and Lucille Packard Foundation.
