Shifted Ice Cap Unexpectedly Reveals Life

Three years ago, a huge section of an Antarctic ice sheet broke off and floated away. Now scientists have had a chance to look at what was under the shelf and have discovered huge mats of bacteria and clams. It's a cold seep, a rare phenomenon where methane bubbles up from under the seabed, and the first found in the Antarctic.

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In Antarctica, a freak act of nature has uncovered something strange. Three and a half years ago a floating ice shelf along the coast suddenly disintegrated, and that gave scientists a chance to look at the ocean floor beneath it. To their surprise, they found life unlike anything else in the Antarctic. NPR's Christopher Joyce reports.

CHRISTOPHER JOYCE reporting:

The Larsen B ice shelf was like a huge floating pancake attached to the Antarctic coastline along the Weddell Sea. Fed by glaciers on shore, it covered an area about the size of Lake Ontario, until warm weather caused it to rupture into a flotilla of icebergs. Marine geologists wondered what had been underneath that shelf. From aboard a research ship, they sent down a robotic vehicle with a video camera. For weeks they didn't see anything alive. They packed up, and on the way home they watched the final day's video. Team leader Eugene Domack of Hamilton College recalls what they saw.

Mr. EUGENE DOMACK (Hamilton College): We found the area covered by a white pustular mat. It's as if someone laid down a thin layer of cheese on the seafloor. It looked very different than anything we had ever seen before.

JOYCE: They were totally surprised. Normally bottom dwellers of the deep ocean feed on what you might call manna from heaven, dead animals and other organic matter that rains down from the surface. But with an ice shelf overhead for thousands of years, that food supply would have been cut off. Even light wouldn't have reached the bottom. But there it was, a bubbling, undulating carpet of something alive. It covered half an acre, and that was only half the story.

Mr. DOMACK: Later, as the video footage played out, we came across a large mud volcano, and large--I'm talking maybe about a meter and a half high and several meters across, which was completely surrounded by large clams. These are good-sized clams. And there were 40, 50 of these clustered around a central vent, which was spewing out fluid and fine mud grains.

JOYCE: What they'd found was a cold seep. It's unusual. It's like the hydrothermal vents in the ocean that spew out superheated water and chemicals. But cold seeps are cold; in this case, 2 degrees below freezing. James Barry is a marine biologist at the Monterey Bay Aquarium Research Institute in California.

Mr. JAMES BARRY (Marine Biologist, Monterey Bay Aquarium Research Institute): Hey, it's a pretty special community, I think, in the sense that these are extreme communities to begin with, and you might think of this as an extreme among extremes. So it's very interesting.

JOYCE: Barry says animals in cold seeps depend on methane gas bubbling up from under the seafloor. Methane reacts with seawater to create sulfide, which some bacteria can live on. That's what the cheesy mat was, bacteria. Barry thinks the big clams have bacteria in their gills that turn sulfide into food.

Domack describes his discovery in the journal Eos published by the American Geophysical Union. He says the cold seep is in danger of being buried in falling sediment or colonized by other animals, so he's going back this year to check. And this time, he says, he's hoping to bring back some of those big clams in his bucket. Christopher Joyce, NPR News.

MELISSA BLOCK (Host): This is NPR, National Public Radio.

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