Scientists Uncover a Frozen History in 6,000 Years’ Worth of Penguin Poop, Revealing Past Ecology on Antarctica

Penguin poop is stinky but useful. In Antarctica, the birds’ nutrient-rich guano allows mosses and other organisms to flourish in an otherwise inhospitable place. And, since poop stains on the ice are sometimes visible from space, scientists have used the birds’ feces to identify multiple previously unknown penguin colonies using satellite imagery.

Now, researchers have found yet another way to put penguin poo to good use. Adélie penguin guano is helping them study 6,000 years of environmental and biological changes along the coast of Antarctica’s Ross Sea.

They describe their novel methods, as well as their findings, in a new paper published March 5 in the journal Nature Communications.

For the study, researchers visited ten active and abandoned Adélie penguin colonies along a 435-mile stretch of the Ross Sea coastline. They dug roughly 2.5-foot-deep pits into the ground, then excavated the sediment from each one. In the end, they had 156 samples that were full of penguin poop and eggshells, as well as feathers, hair and skin cells from other animal species.

“We started digging down through the layers and, as you go down, you’re going back through time,” says study lead author Jamie Wood, an ecologist at the University of Adelaide in Australia, to Cosmos magazine’s Coco Veldkamp.

From the samples, they were able to generate 94 billion DNA sequences, which offered some unexpected insights into the region’s past. For example, they were surprised to find DNA from southern elephant seals, which used to breed on the Antarctic continent but now breed on sub-Antarctic islands.

Earlier research suggests elephant seals began vanishing from the Ross Sea coastline roughly 1,000 years ago. They likely disappeared from the region as the world’s climate cooled, which allowed sea ice to proliferate, as two of the study authors write for the Conversation. As a result, the seals could no longer reach their normal breeding sites on the continent. Opportunistic Adélie penguins moved in and took over.

The recent DNA analysis adds to our understanding of the creatures’ disappearance: Cape Hallett, located on the northern tip of the Hallett Peninsula, was likely one of the last places southern elephant seals bred on Antarctica before they abandoned the continent.

“There was no previous evidence of southern elephant seal occupation from Cape Hallett until we found their DNA in sediments,” says study co-author Chengran Zhou, a geneticist at BGI Research in China, in a statement. “Cape Hallett is now the northernmost possible former breeding site identified from the Ross Sea region.”

Scientists also gleaned new insights into how the diets of Adélie penguins have changed over time.

Today, the black and white birds that live along the southern Ross Sea primarily eat Antarctic silverfish, a small, abundant fish that scientists consider a keystone species. But 4,000 years ago, Adélie penguins living in the same area ate a different type of fish: the bald notothen.

Why did the penguins make the switch? As with the southern elephant seals, scientists suggest Adélie penguins were probably responding to changing sea ice conditions.

The team also used the DNA to estimate Adélie population trends over time. For instance, the data suggest that several active colonies along the Ross Sea have expanded over the last century—a finding that aligns with past research on growing Adélie colonies in East Antarctica.

Zooming out, the researchers say that investigating how animals responded to past environmental and climatic changes could help them understand how best to protect and support them, now and into the future.

“By analyzing the historical distribution and diet of Adélie penguins and southern elephant seals, we can predict their responses to future climate change and develop effective conservation strategies,” says study co-author Li Qiye, also a geneticist at BGI Research, to the South China Morning Post’s Holly Chik.

The study also demonstrates that ancient DNA found in sediment—which scientists call “sedaDNA”—is a useful tool for exploring ancient ecosystems. Even the oldest bits of DNA they studied from 6,000 years ago were well-preserved, with the icy continent acting as a giant freezer to protect genetic material—which suggests scientists should dig even deeper.

“It should be possible to obtain much older DNA from sediments on land in Antarctica—maybe even one-million-year-old DNA,” the study authors write in the Conversation.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.