July 23, 2007 Climate change is nothing new. For thousands, perhaps millions of years, Antarctica's massive ice sheet - 5.5 million square miles - has advanced and retreated as the earth's atmosphere cooled and warmed. Yet, until recently, there was no precise way to measure the shifting interface between ice and open water.
By estimating the age of Adélie penguin remains using radiocarbon dating, University of North Carolina Wilmington Steven D. Emslie has determined a history of penguin colony locations that spans the last 45,000 years, the longest record now known for any species of penguin. He has charted the ancient penguin colonies' population shifts with climate change data and sea-ice extent to create a new and reliable method of dating ice movement.
Adélie penguins return to the same nesting site year after year and leave behind a wealth of debris, including bone, tissue, feathers, feces and eggshells, almost perfectly preserved in Antarctica's frigid, dry atmosphere. Emslie, a marine ornithologist in the Department of Biology and Marine Biology, has even found an entirely mummified penguin in the debris that dates to ~1000 years old. These penguin remains are the focus of two recent articles by Emslie, the second of which appeared as the cover story in the July 10 issue of the Proceedings of the National Academy of Sciences, a leading scientific journal in the U.S.
The first article describes the method Emslie developed to measure the advance and retreat of the Ross Ice Shelf, part of a large glacier that extends into the Ross Sea, by locating and dating the presence of Adélie penguin colonies. Published with Larry Coats and Kathy Licht in the January 2007 edition of Geology, and entitled "A 45,000 year record of Adélie penguins and climate change in the Ross Sea, Antarctica," the article examines the effects of climate change on Adélie penguins over millennia.
Adélie penguins are the smallest and most widely distributed penguins in Antarctica. They nest in ice-free areas along the coast of the open sea, their historical colonies marking the edge of the sea and its advancing and retreating ice sheets with the debris they leave behind. Using the locations of these ancestral colonies, Emslie determined that the Ross Ice Shelf advanced northward in the Ross Sea until about 13,000 years ago, when it began retreating at the end of the last ice age.
The Antarctic ice sheet plays a critical role in global climate control by reflecting sunlight into space and cooling the earth's temperatures and oceans.
The second article, published July 10, is a companion to the one published in Geology, and documents an apparent dietary shift in penguins that occurred 200 years ago in conjunction with the historic depletion of krill-eating seals and whales in the Southern Ocean. Adélie penguins are known to feed primarily on krill in Antarctica today. However, Emslie's research indicates that this krill diet is a recent adaptation to changing marine conditions, in this case brought about by humans. The former diet of penguins, prior to seal and whale depletions, was based on fish, a food resource also now depleted in the Southern Ocean. With krill biomass now undergoing large decreases as well, mainly due to the effects of human-induced climate warming and krill fisheries combined, the penguins are rapidly losing their options for prey.
Emslie's research has been funded by the National Science Foundation, the National Geographic Society and NASA.
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