Iceberg Threatens Penguin Survival in Antarctic

A huge iceberg that broke off from Antarctica last year has had a devastating impact on wildlife by virtually wiping out the tiny plants and animals that form the foundation for the food chain upon which all other creatures depend.

The production of phytoplankton in the normally nutritious waters of Antarctica's Ross Sea is down 90 percent, and what little there is came too late in the season to do much good, according to Stanford University scientists who have been monitoring the area through NASA satellites.

"It's absolutely horrendous," geophysicist Kevin Arrigo says of the impact on the production of phytoplankton, the primary food source for krill, tiny shrimp-like crustaceans that are eaten by just about everything from whales to fish which in turn are consumed by penguins and other birds. Thus the collapse of the entire food chain is possible, if not certain.

Double Whammy

There's a double whammy effect at work here, because an earlier huge berg broke loose from the Ross Ice Shelf in 2000 and the impact from that event had left sea life in the area reeling. Arrigo and his Stanford colleague, Gert L. van Dijken, thought the legacy from the earlier berg, called B-15, was "really big" when they were studying it two years ago.

"But it was just dwarfed by what we saw this past year," Arrigo says. The scientists published their findings in a recent issue of the American Geophysical Union's Geophysical Research Letters.

The most recent berg, called C-19, is more than twice the size of the state of Rhode Island. It is so huge that it blocked sea ice in the Ross Sea, thus reducing the amount of sunlight reaching the water, a critical factor in the production of phytoplankton. Less sunlight means less photosynthesis, and a dramatic reduction in phytoplankton.

"Not only is it down 90 percent, but whatever production there was happened really late in the season and a lot of these animals, like penguins, time it so that their chicks hatch right at the time that the Ross Sea is most productive, which is December.

"And now, suddenly, we don't have a peak in production until March, and the peak is 90 percent below the normal peak. So in terms of the food supply, there's almost nothing there this past year," Arrigo says.

Uncertain Causes

It's still too soon to tell just how devastating all of this will be for the larger animals in the region, including the rare Adelie penguins, but earlier research suggests that it could be catastrophic. Arrigo participated in three cruises through the region from 1996 through 1998, when he was with NASA, to verify the measurements taken by NASA's SeaStar satellite, a process called "ground truthing."

Another iceberg had broken off from Ross in 1989, and the scientists were able to get a firsthand look at the impact from that berg. Arrigo said some entire colonies of penguins had disappeared. The berg itself ended up right where one of the biggest rookeries had been.

"The birds can't get around this thing," he says. "It would be like swimming around the state of Rhode Island. They just can't do it."

What happened to them is not known, but it is probable that they were forced to relocate to an area that is farther away from their food resource, leaving them even more vulnerable.

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