Researchers: Organic Material in Glacial Ice a Reason for Concern
A team of researchers, including three from Old Dominion University, reports in the influential journal Nature Geoscience this week that their analysis of organic matter in glacial ice raises new concerns about biomass burning and fossil fuel use by humans.
The first author of the paper is Aron Stubbins, a former researcher in the Department of Chemistry and Biochemistry at ODU who is now an assistant professor at Skidaway Institute of Oceanography in Savannah, Ga. Current ODU researchers who are co-authors of the paper are Patrick Hatcher, the Batten Chair in Physical Sciences; Hussain Abdulla, a postdoctoral researcher in chemistry and biochemistry; and Rachel Sleighter, a Ph.D. graduate from ODU who is a manager for the Hatcher Research Group.
Hatcher, a geochemist, is the director of the College of Sciences Major Instrument Cluster (COSMIC) Laboratory at ODU. Contributions of the university to this research project include analysis done with the $1.3 million ultra-high-resolution Fourier transform ion cyclotron mass spectrometer (FTIC-MS), which anchors COSMIC.
The key to the research findings 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 sources of this carbon are forests and peat lands overrun long ago by the glaciers. However, Stubbins and his colleagues believe the carbon comes mainly from contemporary biomass and fossil fuel burning that gets deposited on the glacier surfaces.
As they report in Nature Geoscience, they examined the radiocarbon age and chemical composition of DOM in snow, glacier surface water, ice and glacier outflow samples to determine the origin of the organic matter. "Low levels of compounds derived from vascular plants indicate that the organic matter does not originate from forests or peat lands. Instead, we show that the organic matter on the surface of glaciers is radiocarbon depleted, consistent with an anthropogenic aerosol source."
Once deposited on the glacier surface 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 marine food web.
"In vibrant ecosystems like in the temperate or tropical zones, once this atmospheric organic material makes landfall it is quickly consumed by the plants, animals and microbial populations," said Stubbins. "However, in frigid glacier environments, these carbon signals are preserved and stand out.
"Remote regions are often perceived as being pristine and devoid of human influence," Stubbins continued. "Glaciers show us that no area goes untouched by industry. Instead, burning fuels has an impact upon the natural functioning of ecosystems far removed from industrial activity."
Glaciers and ice sheets together represent the second-largest reservoir of water on the planet, and glacier ecosystems cover 10 percent of the Earth, 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," said Stubbins.
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. Biomass and fossil fuel burning by people around the globe are the major sources of that black carbon.
Much of the research for this project was done 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. High levels of rain and snow act to strip the atmosphere clean of organics, dumping them on the glacier. Consequently, these glaciers are among the most sensitive to global emissions of soot.
The researchers' findings also reveal how the oceans 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," said Stubbins. "It is unknown how this man-made carbon has influenced the coastal food webs of Alaska and the fisheries they support."
A warming climate will increase the outflow of the glaciers and the accompanying input of dissolved organic material into the coastal ocean. This will be most keenly felt in glacially dominated coastal regions, such as those off of the Gulf of Alaska, Greenland and Patagonia. These are the areas that are experiencing the highest levels of glacier ice loss.
"Although it is not known to what extent organic material deposition has changed and will continue to alter glacially dominated coastal ecosystems or the open ocean, it is clear that glaciers will continue to provide a valuable and unique window into the role that the deposition of organic material plays in our changing environment," Stubbins said.
Stubbins' collaborators also included Eran Hood and Andrew Vermilyea from the University of Alaska Southeast; Peter Raymond and David Butman from Yale University; George Aiken, Robert Striegl and Paul Schuster from the U.S. Geological Survey; Peter Hernes from the University of California-Davis; Durelle Scott from Virginia Tech; and Robert Spencer from Woods Hole Research Center.
This work is being done with support from the National Science Foundation.