Mother Nature comes through at the South Pole

- but at what price? The International Herald Tribune explains

ROSS ISLAND, Antarctica — Cape Royds, home to the southernmost colony of penguins in the world, is a rocky promontory overlaid with dirty ice and the stench of pinkish guano. Beyond the croaking din of chicks pestering parents for regurgitated krill lies the Ross Sea, a southern extension of the Pacific Ocean that harbors more than one-third of the world’s Adélie penguin population and a quarter of all emperor penguins, and which may be the last remaining intact marine ecosystem on Earth.

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The penguin colony is one of the longest-studied in the world. Data on its resident Adélie penguins was first acquired during the 1907-9 expedition of Ernest Shackleton, the eminent British explorer, whose wooden hut stands preserved nearby.

“This is penguin nirvana,” David Ainley, an ecologist with the consulting firm H. T. Harvey and Associates who has been studying Ross Sea penguins for 40 years, said on a morning in January. “This is where you want to be if you’re a pack ice penguin.”

Of the species that stand to be most affected by global warming, the most obvious are the ones that rely on ice to live. Adélie penguins are a bellwether of climate change, and at the northern fringe of Antarctica, in the Antarctic Peninsula, their colonies have collapsed as an intrusion of warmer seawater shortens the annual winter sea ice season.

In the past three decades, the Adélie population on the peninsula, northeast of the Ross Sea, has fallen by almost 90 percent. The peninsula’s only emperor colony is now extinct. The mean winter air temperature of the Western Antarctic Peninsula, one of the most rapidly warming areas on the planet, has risen 10.8 degrees Fahrenheit in the past half-century, delivering more snowfall that buries the rocks the Adélie penguins return to each spring to nest — and favoring penguins that can survive without ice and breed later, like gentoos, whose numbers have surged by 14,000 percent.

The warmer climate on the Antarctic Peninsula has also upended the food chain, killing off the phytoplankton that grow under ice floes and the krill, a staple of the penguin diet, that eat them, by as much as 80 percent, according to a new study published this month in The Proceedings of the National Academy of Sciences.

But in the Ross Sea a reverse trend is occurring: Winter sea ice cover is growing, and Adélie populations are actually thriving. The Cape Royds colony grew more than 10 percent every year, until 2001, when an iceberg roughly the size of Jamaica calved off the Ross Sea ice shelf and forced residents to move 70 kilometers north to find open water. (The iceberg broke up in 2006, and the colony of 1,400 breeding pairs is now recovering robustly.) Across Ross Island, the Adélie colony at Cape Crozier — one of the largest known, with an estimated 230,000 breeding pairs — has increased by about 20 percent.

Climate change has created a paradise for some pack ice penguin colonies and a purgatory for others, but the long-term fate of all Adélie and emperor penguins seems sealed, as relentless warming eventually pulls their rug of sea ice out from under them. Some scientists attribute the recent sea ice growth in the Ross Sea to the persistent ozone hole, a legacy of the human use of chlorofluorocarbons that cools the upper atmosphere over the continent, increasing the temperature difference with the lower atmosphere and equator, and over the last 30 years has delivered significantly brisker westerly winds in the summer and autumn. The warming of Earth’s middle latitudes is having a similar effect, increasing that temperature difference and sending stronger winds that push sea ice off the coast and expose pockets of open water, called polynyas, that give nesting Adélie penguins easier access to food.

Meanwhile, consumers’ appetite for Chilean sea bass (Antarctic and Patagonian toothfish) may also be benefiting Ross Sea penguins, as fishing fleets from southern nations converge on one of the last remaining refuges of the fish (Dissostichus mawsoni). A fishery in the Ross Sea that opened in 1996 and was certified sustainable in December by the Marine Stewardship Council, could ultimately serve Adélie penguins by reducing competition for Antarctic silverfish (Pleuragramma antarcticum), a sardine-size fish that the penguins and toothfish enjoy. Dr. Ainley and colleagues have reported seeing fewer killer whales in the southern Ross Sea since 2002. The whales feed on toothfish, and fewer sightings suggest that the fishery is already altering the ecosystem.

Researchers witnessed Ross Sea penguin colonies thrive during the 1970s when commercial whaling removed 20,000 Antarctic minke whales, also a food competitor of Adélies, from the penguins’ wintering area. Adélie populations eventually leveled off after 1986, after an international moratorium on whaling began (and remained static until the more recent influences of climate change). Japanese whaling of minkes resumed right after the moratorium was instituted, purportedly for science, a claim that conservation groups dispute and that has incited a confrontation in the Ross Sea between the Japanese fleet and the Sea Shepherd Conservation Society, an antiwhaling vigilante group.

http://www.nytimes.com/2011/05/10/science/10penguins.html