Carbon up to nearly 10,000 years old has been found in Southeast Alaska’s glacial ecosystems, and researchers say at least some of it is likely deposited by the combustion of fossil fuels.
According to Jason Fellman, a Post-Doctoral Research Fellow at the University of Alaska Southeast, carbon in glacial ecosystems could come from a variety of sources: the decomposition of plant matter exposed by a glacier’s recession, such as the sheared trees recently uncovered at the Mendenhall Glacier; algae on top of a glacier (which would produce younger carbon); and dust. Or it could come from helicopters, planes, cars and coal-fired factories.
“The net result of mixing all those sources is that you do get this old carbon coming out, some portion of which is likely fossil fuel,” said Eran Hood, Assistant Professor in UAS’ Environmental Science Program.
Although fossil fuels’ aerosol deposits would be a new addition to a glacier, its carbon retains characteristics that allow researchers to date it. Hood said people have found fossil fuel combustion as a contributing source of carbon on glaciers around the world.
Hood, Fellman and others traced certain aspects of the carbon (in science-language, they used isotopic signatures) in order to figure out where it more likely originated.
“You can get a good idea of who is eating whom,” Fellman said.
In August of 2012, Fellman collected fish and aquatic insects from the upper Herbert River, the lower Herbert River and from a non-glacial tributary that drains into the Herbert. August is when glacial runoff is at its peak.
They also collected water, leaf litter and bacteria from rocks.
They isolated all the carbon in each sample to find its average age. Because that age is an average, some parts of it could be much older. Some are younger, Fellman said.
On the upper Herbert, one sample had a radiocarbon age of almost 10,000 years old. Fellman also found bacteria that had been consuming carbon averaging 1,900 years old, and an insect (a midge) averaging 100 years.
Fish and invertebrates’ carbon age varied, he said. Some averaged 6,800 years old.
Their research so far suggests that the old carbon may be coming from the surface of the glacier instead of beneath it — in other words, fossil fuels are a more likely source of old carbon than old trees and soil.
Part of what’s tricky right now is figuring out to what extent microbes and other inhabitants of glacial streams are consuming fossil fuel byproducts, Hood said.
“It’s a really tricky question to simplify,” he said. “It could be that they’re consuming (fossil fuel byproducts,) but we just don’t know.”
Also unknown is what effect that may have; it may not necessarily be bad, Fellman said.
Streams without glacial influence, like Fish Creek or Peterson Creek, have much younger carbon.
Fellman hopes future studies will confirm the older carbon’s origin and lead to an idea of how modern-day glacial retreat will affect the glacial ecosystems. Dissolved organic carbon, common in glacial ecosystems, is a good thing ecologically.
Aerosol deposits may also contribute to higher rates of glacial melt; Hood, however, said he doesn’t know the extent to which that’s happening in Southeast.
Southeast Alaska’s glaciers are retreating at a “dramatic” rate, with “some of the highest levels of ice-mass loss on Earth to date,” Fellman said.
“If glaciers continue to recede at the current rate you’re likely to see less glacial inputs over time,” he said. “Carbon’s ability to be used by the aquatic biota in the streams is going to change based on where it’s coming from … It’s kind of like ice cream. You have Ben and Jerry’s type ice cream coming from the glacier. You might also have Fred Meyer ice cream (coming from plants growing where the glacier has receded) … As glaciers recede, there’s less Ben and Jerry’s available, and more of Fred Meyer’s.”
Fellman also plans to collect more snow and rain samples, and to analyze them for black carbon (soot). They’ll also continue their research this summer.
Peter Raymond, Maura Bozeman, John Hudson, Mayumi Arimitsu, the University of Alaska Southeast, Yale University, Aquatics Alaska and the United States Geological Survey also contributed to the research.
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