Poop, stomach oil and ostrich eggshells keep records of Earth’s ancient climate
May 7, 2026
5 min read
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Poop, stomach oil and ostrich eggshells keep records of Earth’s ancient climate
Peering into Earth’s climate past is getting ever more bizarre
By Hannah Richter edited by Sarah Lewin Frasier
Stinky samples of Snow Petrels‘ 50,0000-year-old regurgitated stomach oil can reveal ancient Antarctic conditions.
Ewan Wakefield/Durham University
Erin McClymont’s laboratory has six kitchen freezers, each alarmed. This is for self-preservation: when the power goes out or an appliance breaks down, she needs to act quickly to prevent the nauseating smell of old fish from seeping out. The source of that stench: solidified blocks of 50,000-year-old regurgitated stomach oil from Antarctic Snow Petrels, hunks of which line each freezer’s shelves.
“One of my colleagues who did some of the original sampling..., he’s been on field work where they’ve had to dump their coats at the end because they can’t get the smell out,” says McClymont, a paleoclimatologist at Durham University in England. The blocks “are revolting.”
The solidified oil is an indirect record, or proxy, of the past that scientists rely on “because we don’t have a time machine,” says Tyler Karp, a paleoecologist at the University of Chicago. Researchers trying to understand Earth’s climate and ecosystems need to trace rainfall, ice coverage, fire and other factors over thousands or millions of years—far longer than human records. But the most common proxies, including tree rings, pollen and ice cores containing pockets of ancient air, have already been well studied. To learn something new, researchers have to get creative.
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So scientists like McClymont look for clever ways to study obscure features of the past, such as her research focus of how the Antarctic environment has changed over tens of thousands of years. Sea ice makes drilling samples from the Antarctic seafloor particularly hard to do, so her collaborators found a more obscure polar record to explore: seabird stomach oil. Snow Petrels spit out the oil in front of their nests, primarily to ward off predators with its smell and stickiness. That vomit accretes in layers across avian generations, trapping 50,000 years’ worth of data about the birds’ diet and the sea ice environment.
Solidified Snow Petrel stomach oil.
Dominic Hodgson/British Antarctic Survey
Seabird oil is a good proxy because it’s composed of waxes and fats, which degrade more slowly than proteins and carbohydrates do. Chunks can be radiocarbon-dated and biopsied to determine the source of their carbon and nitrogen—a process that first requires using a large saw to cut through what feels like “a mild cheddar: slightly soft and squishy,” McClymont says. As sea ice shrinks and expands, the surface ocean warms or cools. That in turn affects how nutrients cycle and where different species can live, which shows up in the birds’ regurgitations.
Such methods have revealed that as Antarctic ice sheets expanded during the last glacial maximum, sea ice got pushed farther offshore, forcing krill to move out of the petrels’ feeding ranges. The finding suggests that Snow Petrels are capable of temporarily adapting to different food sources and might do so again during future climate changes.
Sampling Snow Petrel stomach oil.
Zhongxuan Li/Durham University
Tripti Bhattacharya, a paleoclimatologist at Syracuse University, also takes advantage of waxy substances—though much less smelly ones. She puts fossilized, freeze-dried sediments through a “glorified espresso machine” to extract the hydrophobic outer coating of ancient leaves, called leaf wax. As plants use rainwater to grow, their leaves pick up the rain’s characteristic ratio of hydrogen isotopes—atoms with the same number of protons and different numbers of neutrons. Hydrogen isotope ratios, specifically, can be traced back to reveal how much and when water fell onto a plant.
Bhattacharya found that the last time carbon dioxide levels in the atmosphere went above 400 parts per million, as present-day levels do, southern California had rainy summers; today it has rainy winters. The finding helps explain the hot, humid environment that made California suitable for tropical animals such as crocodiles three million years ago. Climate change likely won’t bring crocs back to the West Coast, but ecologists can use the ancient weather data to forecast the kinds of species that might thrive in a similar future. “Proxy data might seem like this obscure scientific thing, but