The modern Ross Sea coast is much too cold for southern elephant seals to survive. The region is so dry that there is almost no snow on the ground and the only visible vegetation is lichens and algae.
The shore is locked in ice year-round, and the ice opens up a few kilometers offshore for only one to two months.
"If you visit this place, it's hard to ever imagine it being warmer," Hall said.
But the latest evidence shows that elephant seals did live in the Ross Sea area thousands of years ago.
What's more, during the two periods when elephant seals were present, other Antarctic denizens, Adélie penguins, apparently disappeared from the region.
The penguins prefer a colder climate than the elephant seals, so their disappearance is another clue that temperatures were warmer at those times.
Hall says the most recent warming period was likely the warmer of the two, "based on the fact that the elephant seals were most abundant and occupied the most southern sites."
Critter Climate Records
Climatologists know little about the climate history of certain areas of the Antarctic, because there are very few records.
Using animal remains as clues to climate history is an uncommon technique and is not what Hall's team originally set out to do.
The team was in the region a few years ago studying the age of the beaches when they happened to notice bits of skin and hair in the beach sediment.
The team wasn't sure what creatures' remains they had found, so they sent samples to laboratories for DNA testing. The results were puzzling.
"We thought, This is really strange. If they are elephant seals, what are they doing here?" Hall said.
The team later found several naturally mummified adult males and pups in the region.
Hall believes the presence of multiple seals across different age groups means the animals definitely lived and bred in the region and were not there by accident.
Hall also says her findings of a warmer South Pole in the past do not detract from evidence that the region's dramatic warming trend over the last 30 years is being driven by human contributions (related video: "Antarctica's Big Meltdown").
"One way to look at it is there are natural Earth cycles and man-made cycles. I've been looking at natural cycles," she said.
"If we know the past, we can better predict into the future and maybe understand what we do that may interfere with the natural cycle."
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES