Monday, June 25, 2007

Sea Life Thrives Near Icebergs

Scientists have documented that global warming is causing the Antarctic ice sheet to shrink, with large chunks breaking off and forming free-floating icebergs in a trend that could portend substantial rises in global sea levels.

Now, a team of California-based researchers has discovered that those new islands of ice are breeding grounds for life in the Weddell Sea. As the icebergs melt, they release bits of rock, dirt and other debris, which enhance the growth of phytoplankton. Those microscopic plants attract krill -- small crustaceans that feed on them -- and the krill draw fish and fishing birds, and so on up the food chain, creating what the scientists call "hot spots" for ocean life.

"As global warming continues, you would expect to see more and more icebergs and hence more and more hot spots," said lead researcher Kenneth Smith of the Monterey Bay Aquarium Research Institute.

The phytoplankton also absorb the greenhouse gas carbon dioxide, so the hot spots probably need to be factored into global climate-change models to account for their role in removing carbon from the atmosphere, Smith said.

The researchers based their conclusions on data gathered around two icebergs in the southern Atlantic Ocean, including one that was 1,000 feet deep. They documented a "halo" effect of enhanced populations of phytoplankton, krill and other life as far as two miles from the icebergs. Their findings were published online last week in the journal Science.

-- Christopher Lee

Colo. Elk Lose Fear of Predators

Elk in Siberia that hear recorded calls of bears, tigers or wolves tend to cluster together, become vigilant and in many cases bolt in a near panic. Yet elk in Colorado's Rocky Mountain National Park that hear the recordings continue to graze with nonchalance.

A sign of American toughness?

Hardly. Rather, it is good scientific evidence that fear of predators is not hardwired into animals' brains but is maintained by ongoing exposure to the risk posed by those predators. The large carnivores that once attacked elk in Colorado have been gone for decades, and with those predators went the fear that once sent the elk fleeing.

Those findings, from research led by Joel Berger of the Wildlife Conservation Society in Teton Valley, Idaho, stand to help conservation biologists as they reintroduce predators such as wolves into areas where those animals have disappeared.

Berger conducted experiments in 19 areas around the world, including some where native predators of caribou, moose and elk -- such as wolves, grizzly bears and Siberian tigers -- remain in place, and others where those predators had been chased away or killed off years ago.

The results, published in the June 9 early online issue of Conservation Biology, show not only that fear dissipates in the absence of predators but also that it returns in areas where the predators have been reintroduced -- including Grand Teton and Yellowstone national parks, where wolf populations have been replenished at a cost of tens of millions of dollars.

The data are timely, scientists say, because plans are afoot to allow large numbers of wolves to be hunted in some U.S. areas where they were reintroduced. The results suggest it may be important to keep those populations high enough so that prey species maintain proper vigilance levels.

-- Rick Weiss

Case of Missing Carbon Solved

About 8 billion tons of carbon are created every year by vehicles, industry, and burning forests and other natural occurrences, and we could not survive if the carbon stayed where it was. Scientists have known for some time that about 40 percent accumulates in the atmosphere and oceans absorb about 30 percent. The rest is assumed to be taken up by trees and plants in the northern forests and the tropics.

Computer models predicted that about 2.4 billion tons should be taken up by the northern forests, but ground-based studies have tracked only half that amount -- creating one of the bigger mysteries of climate studies. In an effort to better understand how the "carbon sink" works, scientists at the National Center for Atmospheric Research analyzed air samples that had been collected over decades by aircraft around the world but had never been studied.

The samples collected above the tropics contained less carbon than expected; those taken above the northern forests had more than expected. The conclusion: Intact tropical forests are far more effective at removing carbon from the air than ever predicted.

The tropics are still net emitters of carbon, since forest is being cleared at a fast rate. But instead of releasing 1.8 billion tons of carbon yearly, the tropics are releasing only 100 million tons, the researchers found. That means their trees have been capturing much more carbon than was believed.

"Our study will provide researchers with a much better understanding of how trees and other plants respond to industrial emissions of carbon dioxide, which is a critical problem in global warming," said Britton Stephens, leader of an international team. "This will help us better predict climate change and identify possible strategies for mitigating it."

-- Marc Kaufman

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