Icebergs can be biological hot spots.

Material scraped off land by glaciers and carried to sea by icebergs nourishes life in frigid Antarctic waters.

Late in 2005, oceanographers conducted separate biological surveys near two large icebergs in the South Atlantic. One, an ice mass about 2 kilometers long and 0.5 km wide, drifted more than 120 km in 8 days, says Kenneth L. Smith Jr., an oceanographer at the Monterey Bay Aquarium Research Institute in Moss Landing, Calif. Currents earthed the other iceberg--30.8 square kilometers in area--about 531 km during an 18-day period.

Smith and his colleagues assayed the ocean around each iceberg from about 20 meters to 9 km away. Phytoplankton, the organisms at the base of the ocean's food chain, were about five times as abundant near the bergs as they were in distant waters, the scientists report online and in an upcoming Science. Populations of aquatic predators were similarly enhanced in waters near the bergs, Smith notes. The data suggest that the zone of increased biological productivity extended about 3.7 km from each iceberg.

Chemical analyses of water samples suggest that the near-berg population booms were fueled by nutrients, such as iron, that dissolved into the sea as each iceberg melted and released bits of soil and rock.

Satellite images of the region at the time of the surveys showed 89 icebergs that each covered more than 0.1 [km.sup.2]. Even though the bergs together occupied less than 0.5 percent of the ocean's surface, the thriving ecosystems around them covered about 39 percent of the sea, the team estimates.--S.P.