Ice Adrift From Warming Scrapes Antarctic Seabed Bare

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Warming is reducing the area and time that seasonal sea ice covers the sea surface, Barnes said.

The winter ice decays as winter temperatures rise, releasing slabs of iceberg to drift in the sea.

These icebergs can vary dramatically in size—from the size of fists to small countries, Barnes said.

Once freed from the fast ice, icebergs are blown by winds and carried by sea currents until they smash into the seabed in shallow depths.

"They not only kill virtually everything underneath on the seabed—mainly animals—but crush rock and reshape the seabed," Barnes said.

Vulnerable animals include Antarctic worms, sea spiders, and urchins, the scientists said.

(Related photos: "Giant, Unknown Animals Found off Antarctica" [March 28, 2008])

An Unfamiliar Look

Researchers studied the ice scouring over a five-year period, regularly monitoring markers placed at varying depths along the seafloor.

Made of molded concrete and plastic, the markers deformed and splintered when they encountered the force of a drifting iceberg.

The variety in iceberg sizes creates a range of damaged areas on the seafloor, Barnes said.

In shallow waters, researchers measured damaged areas a few meters by a meter. At deeper regions, however, they found impacted areas up to 0.62 mile (a kilometer), he said.

Smale added that icebergs can ground out at depths of up to 550 yards (500 meters), which means much of polar seabed could be susceptible to ice scouring.

The impact is dramatic, Barnes said. "Diving on the big ice scours after they have happened is like visiting a completely new area, everything looks unfamiliar," he said.

Life is able to eventually rebound in the deadly wake of a scrubbing, but the process takes a while, Barnes said.

"Antarctic animals grow very slowly—in fact, they do virtually everything very slowly—so re-colonization is not quick," he said.

Part Biodiversity, Part "Black Pools of Death"

By clearing out the seafloor, however, the scouring also enables a wide range of species to live, Barnes said.

"Think of it like a forest," he said. "The weedy species that are normally crowded out and out-competed by the dominant species persist where big trees fall and create a clearing."

The research can help expand awareness about the impact of warming temperatures, said a marine biologist not affiliated with the study.

"It is a nice story about what sea ice can do to marine life and sediment characteristics on the seafloor, a place where the general public would not associate processes happening on the surface with what is happening on the bottom of the ocean," said Kathleen Conlan at the Canadian Museum of Nature in Ottawa.

Conlan, who has conducted research on ice scouring in the eastern Canadian Arctic, agreed that its effect on marine life could be varied.

In some areas, it can promote diversity, where it turned over nutrient-rich sediments and pushed out dominant grazers, such as sea urchins.

In other locations, however, the result could be catastrophic, "producing black pools of death," she said.

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