Islands of Life

A warmer world creates a new iceberg ecology

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Norbert Wu

Weddell seals, a mother and pup, under a breathing hole, Antarctica

Freighter captains avoid them as potential catastrophes; climate scientists see them as a bellwether of global warming. But now marine biologists have a more positive take on the thousands of icebergs that have broken free from Antarctica in recent years. These frigid, starkly beautiful mountains of floating ice turn out to be bubbling hot spots of biological activity. And in theory, at least, they could help counteract the buildup of greenhouse gases that are heating the planet.

That's the conclusion of a recent report in the online journal Science Express. Oceanographer Kenneth Smith Jr., of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., led a team of scientists that studied two bergs, one about 1.25 miles (2 km) long and the other closer to 13 miles (21 km), in the Weddell Sea, which lies between the Antarctic continent and the southern Atlantic, near the tip of Argentina.

The ice, it turns out, is not as pristine as it looks: as it flowed to the sea over many thousands of years, it picked up mineral- rich dust that settled out of the atmosphere. As they melt, the bergs are releasing that highly nutritious dust, which feeds phytoplankton, a microscopic form of oceanic plant life on which shrimplike krill feed. The result, says Smith: "There is an accumulation of organisms around icebergs, and this goes through the food chain up to seabirds." The iceberg ecosystem could extend to seals and penguins as well, although there's no proof of that yet. With an estimated 1,000 icebergs in the Weddell Sea, the overall boost in biological productivity in the chilly waters could be enormous.

Not only that, but most of the krill surrounding the bergs die natural deaths and float to the bottom of the sea--taking with them the globe-warming carbon dioxide pulled from the atmosphere by the phytoplankton they fed on. That CO2, once absorbed, is kept from doing any more harm. It's not enough to cancel out human-generated greenhouse gases, but it doesn't hurt. [This article contains a complex diagram. Please see hardcopy or pdf.]