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
"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
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