Glacial Carbon may Hold Record of Environmental Change

New clues as to how the Earth's remote ecosystems have been influenced by the Industrial Revolution are frozen in glaciers, according to a paper in the March issue of Nature Geoscience.

"Remote regions are often perceived as being pristine and devoid of human influence," said Aron Stubbins, the study's lead author and an assistant professor at the Skidaway Institute of Oceanography. "Glaciers show us that burning fuels has an impact upon the natural functioning of ecosystems far removed from industrial activity."

Glaciers provide a great deal of carbon to downstream ecosystems, and many scientists believe the source of this carbon is from ancient forests and peatlands that were overrun by glaciers. However, the carbon comes mainly from contemporary biomass and the burning of fossil fuels that gets deposited on the surface of glaciers. Once it's deposited by snow and rain, carbon-containing dissolved organic matter (DOM) in the glacial ice moves with the glacier and is eventually delivered downstream, where it provides food for microorganisms at the base of the marine food web.

"These findings imply that the deposition of this ancient fossil-fuel organic carbon is ubiquitous, with important implications to the functioning of different ecosystems," said Peter Raymond, professor of ecosystem ecology at the Yale School of Forestry & Environmental Studies.

Glaciers and ice sheets together represent the second-largest reservoir of water on Earth, with glacier ecosystems covering 10 percent, yet the carbon dynamics underpinning those ecosystems remain poorly understood.

"Increased understanding of glacier biogeochemistry is a priority, as glacier environments are among the most sensitive to climate warming and the effects of industrial pollution," he said.

Glacier ice loss is accelerating globally, driven in part by the deposition of carbon in the form of soot or "black carbon," which darkens glacier surfaces and increases the absorption of light and heat. The burning of biomass and fossil fuels by people around the globe are the major sources of black carbon.

Stubbins and his fellow scientists have conducted much of their research at the Mendenhall Glacier near Juneau, Alaska. The researchers' findings also reveal how the ocean may have changed over past centuries. The microbes that form the very bottom of the food web are particularly sensitive to changes in the quantity and quality of the carbon entering the marine system.

Since the study found that the organic matter in glacier outflows stems largely from human activities, it means that the supply of glacier carbon to the coastal waters of the Gulf of Alaska is a modern, post-industrial phenomenon. "When we look at the marine food webs today, we may be seeing a picture that is significantly different from what existed before the late 18th century," he said. "It is unknown how this manmade carbon has influenced the coastal food webs of Alaska and the fisheries they support."

Source: Yale University