Ice shelves normally lose mass when entire icebergs break off, events that occur years or even decades apart.
The rapid disintegration of both shelves within 12 years indicates global warming was a major factor (related news: "Giant Ice Shelf Breaks Off in Canadian Arctic" [December 29, 2006]).
"The collapse of the Larsen A and B ice shelves and other ice shelves at the peninsula is definitely due to global warming," Julian Gutt, a marine ecologist with the Alfred Wegener Institute for Polar and Marine Research in Germany, told National Geographic News.
Despite being dire signs of warming temperatures, the ice shelves' collapse offers a rare opportunity to study an ocean environment that Gutt describes as the least disturbed in the world by humankind.
The region serves as a model to study and understand how pristine ecosystems respond to sudden environmental changes, he said.
Using a camera-equipped remotely operated vehicle, the scientists spent ten weeks peering into the relatively shallow—about 650 feet (200 meters) deep—waters once covered by the Larsen shelves.
What they found were creatures such as sea cucumbers and sea lilies that are more commonly known to thrive in waters ten times as deep, Gutt said.
The scientists therefore believe life under ice shelves is similar to the deep sea: resource-poor and inhabited by only the hardiest of creatures.
"We also found the first hints of a shift in the species composition," Gutt said.
For example, fast-growing sea squirts, which would not have thrived under ice cover, were found latched onto the seabed that had been capped by the Larsen B ice shelf.
"They are abundant, and they need maybe only three to four years until they reach their final size, and so this fits quite well with the period," Gutt said.
The scientists also observed juvenile slow-growing animals called glass sponges, mostly in the area of the former Larsen A ice shelf. This indicates the slow pace of the ecosystem shift at the seafloor.
The transition to a fully mature community may take hundreds to thousands of years, Gutt noted.
"The original fauna will simply disappear, locally get extinct, and new animals will invade," he said.
But in the water column, he noted, change is happening more quickly.
Researchers observed abundant krill—open-water crustaceans that are near the base of the marine food chain. Minke whales were seen feasting on the krill.
"The whole system, including the minke whales, is quite opportunistic," Gutt said. "As soon as the conditions are favorable in the open ocean, they invade and they benefit."
Poles and Climate
Ronald O'Dor is the senior scientist for the Census of Marine Life, a ten-year global initiative to assess the diversity and abundance of ocean life.
The census helped organize the expedition, which is the first of several that will take place in the Arctic and Antarctic as part of International Polar Year.
The multinational collaboration, which officially runs from March 2007 to March 2009, aims to advance scientific understanding of the polar regions, including how the poles interact with global climate systems.
O'Dor, who was not on the Polarstern expedition, said he was impressed at how many species have colonized the Larsen region since the ice shelves collapsed.
In particular he noted the presence of blue Antarctic ice fish and sea stars—organisms that would not have thrived under the ice.
"Considering the temperatures at which everything is happening down there," he said, "it really seemed lush with these invasive species."
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