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Antarctic Icebergs Teeming With Life, Study Says

John Roach
for National Geographic News
June 21, 2007
 
Looking for some lively action in the Antarctic? Check out an iceberg.

The oblong chunks of free-floating ice are hotspots for ocean denizens, a new study says.

Anecdotal scientific observations suggest marine plants, shrimplike crustaceans, and seabirds—big players in the ocean food chain—congregate on and around the chunks of ice.

Icebergs are proliferating in the Antarctic as rising temperatures shrink and split the continent's ice shelves, leading scientists to wonder what effect this has on the marine environment.

(See related: "Singing Iceberg Recorded in Antarctica" [November 29, 2005].)

Sparse Observations

A study in 2002 actually found Connecticut-sized icebergs in Antarctica's Ross Sea reduced activity of marine life there by 70 percent.

"That was catastrophically bad for the ecosystem," said Kevin Arrigo, a biological oceanographer at Stanford University in California who led the 2002 research.

But the new study, in which Arrigo did not participate, found the exact opposite around much smaller icebergs in the Weddell Sea, on the other side of the continent.

There melting icebergs release terrestrial nutrients into the sea, which allow tiny marine plants called phytoplankton to bloom.

Shrimplike crustaceans called krill congregate around the icebergs to feast on the plants, and seabirds flock in to eat the krill.

This thriving web of marine life extends out 2.3 miles (3.7 kilometers) from each iceberg and then dwindles.

"These species are the same that are in the surrounding waters, it's just a concentration of them around the iceberg because it's an enriched area," said lead study author Kenneth Smith, a senior scientist at the Monterey Bay Aquarium Research Institute in Moss Landing, California.

"It's the first time anybody's actually documented increased biological activity around the icebergs," Arrigo of Stanford said.

Spiraling Icebergs

Smith and his colleagues used satellite images to select the two icebergs in their study and then sailed to the remote targets aboard a research vessel.

The icebergs were up to 12 miles (19 kilometers) long and more than 120 feet (37 meters) high. One extended nearly a thousand feet (305 meters) below the sea surface.

The researchers sampled and imaged the surrounding waters with an array of instruments, including a remotely operated vehicle (ROV).

As the team worked, the oblong chunks of ice spiraled as they drifted east and northeast. Waterfalls cascaded off the larger of the icebergs, indicating rapid melting.

Based on lab work, Smith said the team assumes the meltwater has a large component of iron, which seeds the phytoplankton to grow.

Further studies may determine if the concentration of marine life remains in the wake of the icebergs as they drift further out into the oceans around Antarctica.

(See a map of the region.)

Smith and colleagues' study will appear tomorrow in the journal Science.

Carbon Sink

The researchers counted 89 icebergs of similar size in the general area. They calculated the increase in icebergs has increased biological productivity in the region by nearly 40 percent.

This rise in activity, the researchers add, may play a role in soaking up the carbon dioxide that is causing Earth's temperature to rise.

This carbon is stored in the thriving food chain that surrounds the icebergs.

"It could possibly be a very important source of [carbon dioxide] drawdown from the atmosphere," Smith said.

Stanford's Arrigo agreed the iceberg biological activity may have some effect on the global carbon budget, but said it amounts to only "a blip."

That's because the area investigated is one of the few areas in the whole Antarctic where there is a lot of calving icebergs and melting icebergs, Arrigo said.

Icebergs in the Ross Sea, he noted, aren't melting much and thus not concentrating marine life around them like those in the Weddell Sea.

Total biological production in the seas around Antarctica, he added, is less than 10 percent of the total production worldwide.

"The amount that would be associated with these icebergs would be a small fraction of that," Arrigo said, "so we're talking about a pretty small number."

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