The Earth's remote ecosystems may have been far more influenced by the industrial revolution than thought, say researchers from the Skidaway Institute of Oceanography.
The National Science Foundation (NSF)-funded team examined carbon-containing dissolved organic matter (DOM) in glacial ice, and concludes that its source isn't, as was widely believed, ancient forests and peatlands overrun by the glaciers.
The team conducted most of its research at the Mendenhall Glacier near Juneau, Alaska, which receives large amounts of rain and snow. This strips the atmosphere of organic materials, then dumps them on the glaciers.
As a result, these Alaskan glaciers are among the most sensitive to global emissions of soot.
And, says Aron Stubbins, it appears that the carbon comes mainly from modern biomass and fossil fuel burning that makes its way onto the glaciers' surfaces.
Once deposited by snow and rain, the DOM moves with the glacier and is eventually delivered downstream where it provides food for microorganisms at the base of the aquatic food web.
"In warmer ecosystems like in the temperate or tropical zones, once this atmospheric organic material makes landfall it is quickly consumed by plants, animals and microbial populations," he says.
"But in cold glacier environments, these carbon 'signals' are preserved."
Indeed, says the team, the results show that some aquatic systems previously thought to be pristine have, in fact, been affected by human activities for a century or more.
The findings also reveal that the ocean may have changed over past centuries as a result of this process, as the microbes that form the bottom of the food web are sensitive to changes in the quantity and quality of carbon entering the marine system.
The scientists found that the organic matter in glacier outflows stems largely from human activities. This means that the supply of glacial carbon to the coastal waters of the Gulf of Alaska is a modern, post-industrial phenomenon.
"When we look at marine food webs today, we may be seeing a picture that is significantly different from what existed before the late 18th century," says Stubbins.
"It's unknown how this man-made carbon has influenced the coastal food webs of Alaska, for example, and the fisheries they support."