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Ancient Elephants in Antarctica

 


Ancient Elephants in Antarctica
Prehistoric remains of the southern seal species shed new light on climate change thousands of years ago

About the Photo: In her laboratory, Brenda Hall displays some of the remains she and her team discovered. While elephant seals and penguins remain the primary focus of the team's research, another perplexing discovery may soon bring a new marine animal into the mix. While searching for elephant seal skeletons, Brenda Hall's team discovered the mummified remains of 15 leopard seals grouped near the Ross Sea. Normally considered solitary hunters, the leopard seal grouping may prove to be even more perplexing than the elephant seal discovery.
 

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Southern elephant seals that grow up to 20 feet long and weigh in at 4 tons aren't creatures you search for armed only with digging spoons and tweezers. But, then again, elephant seals weren't really what University of Maine glacial geologist Brenda Hall had set out to find.

In 1994, Hall and her scientific team were conducting research in Antarctica that they hoped would lead to better understanding of how the world's climate has changed over time. By comparing ancient beaches that were created by the slow retreat of glaciers throughout thousands of years, they compiled information about sea level and glacial movement along the windswept coastline of the Ross Sea in Antarctica.

Combing the barren landscape for tiny particles of organic matter, they hoped to find something large enough to allow for accurate carbon dating of the ancient shoreline.

What they found were elephant seals.

The tiny samples of skin and fur recovered from the first dig sites eventually led the researchers to much larger remains, including entire seal carcasses frozen and mummified by the southernmost continent's frigid winds. Tests showed some of the remains to be as much as 7,000 years old, but it was the location of the discovery that attracted the attention of biologists and climatologists alike.

"It took a while to identify what we had found. We didn't expect to find elephant seals because they don't live in the Ross Sea," says Hall. "Even foraging individuals are extremely rare that far south today, (yet) we had found evidence of a large population molting and breeding there as recently as 1,000 years ago. This is important to understanding climate conditions, because there has got to be a change in climate for the seals to have lived there."
 

Elephant seals are picky when it comes to choosing sites to breed and molt, refusing to haul themselves out of the water unless the shoreline is completely clear of sea ice. Current conditions in the Ross Sea leave the seals' former breeding grounds choked with sea ice year round, relegating the current population of southern elephant seals to subantarctic locales farther north.

Hall and her colleagues published a paper in The Proceedings of the National Academy of Sciences in June that points to the seal remains as evidence for a warming period in the region, which they believe occurred between 2,300 and 1,100 years ago.

Important to more than just elephant seal researchers, Hall's findings shed new light on the stability of Antarctic ice shelves, according to longtime UMaine researcher George Denton.

"The critical question that she is helping to answer is: How stable are the huge southern Antarctic ice shelves? Ice shelves are what hold together Antarctica's two major ice sheets, and marine-based ice shelves like that found in the Ross Embayment have been disintegrating rapidly over the last decade," says Denton.

"If a big ice shelf were to give way, the results could be catastrophic. Through her discovery of elephant seal remains over a widespread area where they do not exist today, she shows evidence not only that a warming occurred, but that the Ross Ice Shelf survived that event. It's important because it speaks to the staying capacity of the ice shelf in the face of global warming."

Denton, an internationally recognized authority in Antarctic research and Hall's former faculty adviser at UMaine, was the first to discover elephant seal remains in the Antarctic while working with Robert Nichols of Tufts University as an undergraduate research assistant in 1958. Carbon dating showed the remains of the solitary animal to be more than 4,000 years old, but the find was lost among many other new discoveries in the early days of Antarctic research. Now more than 40 years later, the use of animal remains as clues to past changes in the environment is coming to the fore.
 

Hall is the first to admit that she is no seal biologist, but she has become something of an expert on southern elephant seals since she plucked the first few flakes of frozen skin from the sand nearly 12 years ago. And while it may seem a bit unusual for a geologist to be using seals to tell a story about climate change, stranger still is the fact that penguins seem to be backing it up.

Hall is working closely with Carlo Baroni, a researcher from the University of Pisa in Italy and an expert in the status of past and present populations of Adelie penguins. Together, they are working to determine how data on ancient populations of southern elephant seals and penguins in the Ross Sea can be combined to create a more accurate picture of climate conditions in the region.

"What we have found is that when the penguins disappeared, the elephant seals began to arrive in full force. While no sea ice at all is good for elephant seals, it is bad for Adelie penguins," says Hall. "Combining the two species to look at sea ice patterns in the Ross Sea is helping us to get at what the climate has been like over time."

Hall's efforts in this and other projects have earned her no small amount of recognition, including her recent selection as a distinguished young scientist by the National Academy of Sciences (NAS). Selected by a committee of NAS members, Hall and other future science leaders will be attending the NAS Kavli Frontiers of Sciences Symposium in November to build a collaborative network to address some of the most pressing questions in science.

With a recent National Science Foundation grant, Hall also will be part of a three-pronged effort to strengthen the team's initial findings regarding the Ross Sea elephant seals. While Hall seeks to answer questions regarding the age of elephant seal colonies on Victoria's Land and to look for clues regarding where the populations may have gone, another group from the University of California - Santa Cruz will be using stable isotopes to determine foraging patterns for the ancient colonies. And researchers at the University of Durham in the United Kingdom will be analyzing samples of the seals' DNA.

"For something that we never set out to find, the project really seems like something that will have some major results in the long term," says Hall. "Aside from the occasional sighting of an individual seal, no one had reason to believe that a group of elephant seals had been that far south because most of the evidence tiny fragments of skin and tufts of hair was so small. Once we knew it was there, the seals became a lot easier to find."
 

By David Munson
November-December, 2006

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