Glacial ice has provided scientists new clues as to how the Earth's remote ecosystems have been influenced by the industrial revolution. 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. Robert Spencer of the Woods Hole Research Center 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 US that is traditionally viewed as being exceptionally pristine,” Spencer noted. “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,” he said. 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. “In frigid glacier environments any input stands out, making glaciers ideal sentinel ecosystems for the detection and study of anthropogenic perturbation,” said Spencer referring to the reason why glaciers record the impact of human emissions. “However, the deposition of this organic material happens everywhere and in vibrant ecosystems such as those found in temperate or tropical regions, once this organic material makes landfall it is quickly consumed in the general milieu of life,” he stated.
