Using Sediment Cores to Study Past Arctic Wildfires

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Will Daniels, a geosciences researcher in associate professor Isla Castaneda’s geochemistry lab, has received a coveted National Science Foundation postdoctoral fellowship to address the question of wildfires in Arctic regions, which he and other scientists report are increasing in Greenland, across Canada and elsewhere in the Arctic today.

The two-year award that begins next spring includes a salary and $25,000 in research funds. It will allow Daniels to “take my current research reconstructing climate change in the Arctic over the past 3 million years, in a new direction by and adding reconstruction of wildfires over the same period.” Until then, he will explore the relationship of climate change, fire and woolly mammoth extinction on Alaska’s St. Paul Island.

For the larger wildfire study, Daniels will test the hypothesis that during the warm mid-Pliocene about 3 million years ago, when there was no permafrost in the Arctic, the occurrence of wildfires was controlled mainly by temperature. But after the Mid-Pleistocene Transition about 1.5 million years ago, the climate-fire link was fundamentally altered because permafrost became established and Arctic sea ice formed. As the global climate cooled and the Arctic grew drier, lack of moisture may have become a more important factor determining tundra wildfire prevalency.

Daniels says this research will improve Arctic fire models by reconstructing fire activity over a wider range of climate variations than before. He will study warm climate states such as the Pliocene which was about 6 degrees Celsius warmer than today, and colder climates such as the Last Glacial Maximum which was about 6 degrees colder than today. “Ultimately we want to know what will fires do in the future,” the geoscientist adds.

Scientists are curious, Daniels says, whether Arctic warming, which is advancing faster than in other regions, contributes to more fires. Looking backward and comparing fire activity in both warm and cooler past periods can help to fill in the picture. “It’s a paradox because the colder periods tend to be drier which appears to be conducive to burning,” he says. More than that, “it’s important to determine whether fires will be more common, because tundra burning would have large ramifications for the global carbon cycle.” 

Arctic soils store “a tremendous amount” of carbon, Daniels points out, an estimated three times more than is stored in the atmosphere. If the organic matter there burns, it will release large amounts of carbon dioxide (CO₂) into the atmosphere. “Increased fire abundance in the Arctic will lead to increased CO₂ emissions globally.

For the reconstruction, he will use sediment cores collected in 2009 from Lake El’gygytgyn “Lake E” in Siberia by an international research team that included lead U.S. scientist and paleo-climate expert Julie Brigham-Grette, geosciences chair. She and colleagues retrieved the longest core samples ever collected in the Arctic, more than 30 times longer than records from the Greenland Ice Sheet. Lake E was formed 3.6 million years ago when a meteor more than a half-mile in diameter hit the Earth and gouged out the 11-mile wide crater, the scientists point out.

Because the cores include sediments from both warm and cold periods in the same record, Daniels says, it will allow him the unusual opportunity to compare fire incidence in the two situations. He will use a couple of methods to measure the concentrations of fire biomarkers at different periods. One is a “suite of lipids” called polycyclic aromatic hyrdrocarbons (PAH) that are byproducts of combustion. Another useful chemical marker called levoglucosan is produced from burning cellulose in plants.

One challenge to this sort of investigation, Daniels explains, is that fires are time-limited, discrete events and the signature in the sediment record can be short-lived, only detectable in a very small, narrow band of the core. “You’d need to look at every centimeter of the core, which we can’t do.”

Another challenge has to do with fire location. In a typical such study, Daniels says past fire activity is reconstructed by counting charcoal fragments. But this method is limited because charcoal is only deposited in close proximity to a fire. If a fire occurred adjacent to Lake El’gygytgyn it may be detected, “but if that fire was far away there’s no charcoal record in the sediment.” But Daniels can overcome this limitation by measuring PAHs, which travel farther from the fire in smoke and are deposited over a wider geographic area.

He will analyze the PAH samples with the gas chromatograph mass spectrometer on campus but will send levoglucosan samples to be analyzed a at a laboratory in Potsdam, Germany, Daniels says. In the end, his research will improve the use of fire biomarker applications in paleofire research, and provide important clues about how aridity, temperature, permafrost, and vegetation interact to determine the frequency of Arctic wildfires.