The Greenland ice sheet (GrIS) is the largest expanse of glacial ice in the Northern Hemisphere and is capable of contributing significant quantities of meltwater and associated material to the surrounding North Atlantic and Arctic Oceans. Surface derived meltwater drains to the bottom of the ice sheet and interacts with overridden soils, vegetation and bedrock. This meltwater fuels biogeochemical processes beneath the ice initiated by subglacial microbial communities prevalent in glacial systems with water at their base. Since microbial communities consume and produce unique fractions of dissolved organic matter, the composition of organic compounds in glacial runoff can be used to explore microbial processes under the ice. We have explored the link between microbial communities, overridden soils and surface derived meltwater with a novel suite of complementary tools, including ultrahigh resolution mass spectrometry, bulk organic carbon concentrations and radiocarbon content. Our preliminary data suggests that these communities have a particularly significant impact on the composition of dissolved organic matter exported in the early melt season. This signature is diluted relative to plant derived organic matter later in the season as the flux of surface derived meltwater increases. Here, we propose to build on our promising early results by determining organic matter source, quantity and age in glacial runoff from a larger glacier over the 2010 melt season. These additional samples will allow us to explore the impact of catchment size on DOM export and reactivity in ice dominated regions and to assess the role of large ice masses in delivery of labile substrates to downstream ecosystems and nearby coastal oceans.
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