Glaciers provide a window into human impact on the global carbon cycle

Science Daily: New clues as to how Earth's remote ecosystems have been influenced by the industrial revolution are locked, frozen in the ice of glaciers. That is the finding of a group of scientists, including Robert Spencer of the Woods Hole Research Center. The research will be published in the March 2012 issue of Nature Geoscience.

Globally, glacier ice loss is accelerating, driven in part by the deposition of carbon in the form of soot or "black carbon," which darkens glacier surfaces and increases their absorption of light and heat. The burning of biomass -- trees, leaves and other vegetation around the globe, often in fires associated with deforestation -- and fossil fuel combustion, are the major sources of black carbon.

Spencer and his fellow scientists have conducted much of their research at the Mendenhall Glacier near Juneau, Alaska. Mendenhall and other glaciers that end their journey in the Gulf of Alaska receive a high rate of precipitation, which exacerbates the deposition of soot, but also makes for a good research site.

"We are finding this human derived signature in a corner of the U.S. that is traditionally viewed as being exceptionally pristine," Spencer notes. "The burning of biomass and fossil fuels has an impact we can witness in these glacier systems although they are distant from industrial centers, and it highlights that the surface biogeochemical cycles of today are universally post-industrial in a way we do not fully appreciate."

The key to the process is carbon-containing dissolved organic matter (DOM) in the glacial ice. Glaciers provide a great deal of carbon to downstream ecosystems. Many scientists believe the source of this carbon is the ancient forests and peatlands overrun by the glaciers. However, thanks to new evidence from radiocarbon dating and ultra-high resolution mass spectrometry, Spencer and his colleagues believe that the carbon comes mainly from the burning of fossil fuels and contemporary biomass. Once the organic matter that contains black carbon is deposited on the glacier surface by snow and rain, the resultant DOM moves with the glacier and is eventually delivered downstream in meltwaters where it provides food for microorganisms at the base of the aquatic food web....

The Mendenhall Glacier in 2006, shot by Stephen Kellam, public domain