- Scientists found an abandoned Adélie penguin colony at Cape Irizar, off the south Antarctic coast, in 2016.
- Penguins hadn't been seen in that part of Antarctica in over a century, but the nesting site had fresh bodies, as well as mummified corpses, bones, and poop.
- In a new study, a researcher report solving the mystery: The penguin remains had been buried under the ice for hundreds, if not thousands, of years. But snow had recently melted to reveal the colony.
- By dating the mummies, the author, Steve Emslie, discovered Cape Irizar had been occupied by Adélies three times during the last 5,000 years, before being driven out by encroaching sea ice 800 years ago.
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Rumors reached Steve Emslie's ears that fresh penguin poop had been spotted at a remote cape overlooking the Ross Sea in Antarctica.
That surprised Emslie, because there weren't supposed to be any Adélies at this remote headland, named Cape Irizar. The last time penguins had been spotted there was nearly 120 years ago.
Emslie has been studying Adélie penguin migrations for years. He knew where the birds liked to nest, and what parts of the Antarctic coast they couldn't occupy because snow covered up their preferred beaches.
So in 2016, after finishing up work at a nearby research station, Emslie's team went to investigate: "We had one extra day, so we thought we should check it out," he told Business Insider.
Not only did they find lots of guano (penguin excrement), but they also discovered a barren, rocky landscape peppered with bones and carcasses. Some of those corpses had been mummified by the dry, cold Antarctic air. But others seemed fresh — with feathers and skin still intact.
"I thought to myself, 'That's strange, did we miss a colony?'" Emslie said. "It looked like a modern colony that had been abandoned for a season."
In a study published last month, Emslie finally laid out the answer to this penguin puzzle.
His team used radiocarbon dating to determine that the carcasses they found weren't fresh at all, but rather ancient bodies that melting Antarctic snow had revealed to the fresh air for the first time in centuries.
A penguin graveyard
Most of the bones and carcasses Emslie's team found belonged to penguin chicks.
Cape Irizar was once a nesting ground, according to Emslie, which explains why his team found so many pebble mounds there (Adélie parents collected pebbles from nearby beaches to build their nests).
The researchers excavated three of those mounds to collect eggshells, skin, feathers, bones to date in their lab at the University of North Carolina, Wilmington, where Emslie is a professor and ornithologist.
They discovered the penguin remains were between 800 and 5,000 years old — the creatures had been buried beneath the snow until rising temperatures in the southern Antarctic thawed their icy grave.
"I've never seen a site like it," Emslie said.
Three waves of penguin occupation
The myriad ages of the remains suggest that Cape Irizar had been occupied by penguins three times in the last 5,000 years, Emslie wrote in the study, published in the journal Geology.
"Penguins like to come back to same place every year to nest," Emslie said, adding, "but if conditions change so they can't nest there anymore, they'll move on."
Adélies currently can't get to Cape Irizar because steep ice cliffs and sea ice block access to the beach.
But that ice wasn't always present.
Adélies lived there between 5,145 and 2,750 years ago, then again between 2,340 and 1,375 years ago, and finally between 1,100 and 800 years ago.
Those dates seems to align with a changing climate, Emslie said.
About 800 years ago, when the planet underwent a cooling period called the Little Ice Age, the area of snow and ice surrounding their colony expanded, forcing the penguins to abandon Cape Irizar for good.
Whatever dead were left behind got buried, until recently summer thawing exposed them for scientists like Emslie to find.
A warming planet reveals hidden remains
This isn't the first time thawing polar ice and glaciers have revealed unprecedented findings. In 1991, Italians hiking on the melting Val Senales Valley glacier found Ötzi the Iceman, a human ancestor who had been perfectly preserved for 5,300 years.
But Cape Irizar is the first case of ice melt revealing remains in the Antarctic, according to Emslie.
"It's a true sign of the warming facing the planet right now," he said. "Even in the coldest region on Earth we're seeing ice melt on a scale that reveals remains."
Unlike glaciers in western Antarctica, which are thawing at unprecedented rates, southern Antarctica's melt speed has been slower.
But rising global temperatures have finally caught up to Cape Irizar, and other capes like it abutting the Ross Sea. Satellite imagery collected over the last few decades reveal decreasing snow cover, and the average annual temperature in the Ross Sea has increased by up to 2 degrees Celsius (3.4 degrees Fahrenheit) since the 1980s.
As temperatures rise, glaciers melt, which sends rivulets of water flowing over the capes during the summer.
Those meltwater rivers thaw the snow below, and exposes findings like the Adélie penguin colony.
Emslie said he'd like to go back to the Cape Irizar area soon.
"There are other caves emerging from under the melting snow nearby that are worth checking to see if they had penguins," he said.
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