Iceberg Threatens Penguin Survival in Antarctic

Oct. 23, 2003 -- 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.

The calving of three giant icebergs from the Ross Ice Shelf over a relatively brief span of 14 years seems to be a significant increase over such activity in past decades, and it comes at a time of dramatic changes in Antarctica. Scientists have documented warming trends in some areas of the continent, in some cases by as much as 6 degrees, but Arrigo doesn't believe the intense level of activity in the Ross Sea has anything to do with global warming.

"There's no evidence that anything is warming up there," he says, referring to the Ross Sea, which is at a higher latitude, 77 degrees south, than the Antarctic Peninsula, where the warming trend has been found. It's still very, very cold in the Ross Sea.

‘Iceberg Graveyard’

Unlike people who have studied this kind of thing in the past, Arrigo and his colleagues have a continuous flow of critical data throughout the year, thanks to NASA. The satellite's SeaWIFFS instrument (Sea-viewing Wide Field of View Sensor) and other sensors aboard other satellites measure everything from light coming from the sea to sea water temperatures.

Phytoplankton contains green chlorophyll, so by measuring the intensity of the "greenness" of the water, the scientists can estimate the rate of phytoplankton production.

That gave them the basis for their dire predictions about the impact of C-19, which incidentally has finally moved on after lodging for awhile on a sand bar. Driven by currents, the berg has drifted into an area Arrigo calls an "iceberg graveyard" about 600 miles from the productive area that is so important to marine organisms.

But its legacy will linger on. The damage has been done.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.