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Woods Hole Oceanographic Institution

Sarah B. Das

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Publications
»Antarctic meltwater flux, GRL, 2013
»Tropical Pacific influence on W. Antarctic marine aerosols, J. Climate, 2013
»Thwaites Glacier, Antarctica accumulation, GRL, 2013
»ACCMIP multi-model global nitrogen and sulfur deposition dataset, ACP, 2013
»Influence of ice sheet geometry and supraglacial lakes on seasonal ice flow, TC, 2013
»Greenland Iron Export, Nature Geosc, 2013
»Greenland Organic Carbon Export, GCA, 2013
»Amundsen Coast Sea Ice and Polynya Variability, JGR, 2013
»Ice Core 10Be Records, EPSL, 2012
»Antarctic Ice Sheet Surface Melting, JGR, 2012
»Greenland discharge isotope mixing model, J. Glac., 2011
»Future Science Opportunities in Antarctica and the Southern Ocean, NRC Report, 2011
»Greenland Ice Sheet DOM, GCA, 2010
»Ice Sheet Hydrofracture and Water-transport Model, GRL, 2009
»Greenland Supraglacial Lake Drainage, Science, 2008
»Greenland Seasonal Speedup, Science, 2008
»West Antarctica Holocene Climate, JGR, 2008
»Greenland Accumulation, J. Climate, 2006
»Melt Layer Formation, J. Glac, 2005
»Whillans Ice Stream Deceleration, GRL, 2005
»Siple Dome Temperature Variability, Annals Glac., 2002
»Patagonian Icefield SAR, JGR, 1996


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Bhatia, M.P., S.B. Das, L. Xu, M.A.Charette, J.L. Wadham, and E.B. Kujawinski, Organic carbon export from the Greenland ice sheet, GCA, 2013, doi: http://dx.doi.org/ 10.1016/j.gca.2013.02.006

Glacial meltwater exports a unique type of organic carbon to marine systems, distinct from non-glacially derived riverine export, potentially capable of stimulating downstream marine primary productivity. Here, we describe for the first time the bulk-level dissolved organic carbon (DOC) and particulate organic carbon (POC) isotopic composition of glacial meltwater draining the Greenland Ice Sheet (GrIS). These data, in conjunction with an earlier study that investigated the molecular-level composition of GrIS dissolved organic matter, collectively describe the concentration, radiocarbon content, and lability of organic carbon in subglacial discharge from a land-terminating outlet glacier during a melt season. By scaling up our measurements across the ice sheet, we estimate that the annual DOC flux from the GrIS (0.08 Tg/y) is equivalent to that from a small Arctic river (discharge (Q) < 50 km3/y), and that the annual POC flux from the GrIS (0.9 Tg/y) may be comparable to that of a large Arctic river (Q > 200 km3/y). The DOC flux is derived primarily from beneath the glacier (subglacial) (>75%) in the early season, and from surface ice-melt (up to 100%) transmitting through the subglacial environment at the peak of the meltseason. The POC flux is primarily derived from the subglacial environment throughout the meltseason. The early season (low flow) glacier discharge contains higher DOC concentrations (0.5 – 4.1 mg L-1), and exports more enriched carbon (Δ14CDOC ~ -250‰) compared to the peak season (high flow) discharge, when the concentrations are lower (0.1 – 0.6 mg L-1) and the Δ14C is more depleted (Δ14CDOC ~ -400‰). Conversely, the POC export (1.4 – 13.2 mg L-1, Δ14CPOC ~ -250‰) shows no temporal variation in either concentration or radiocarbon content throughout the meltseason. Dissolved ion loads in concomitant samples reflected the seasonal evolution of the subglacial drainage system, confirming the influence of subglacial hydrology on the composition of the bulk carbon pools. Based on this work, we conclude that (1) different mechanisms control the DOC and POC flux from glacial systems; (2) chemically-distinct DOC pools are accessed by seasonally-evolving hydrological flow-paths; and (3) the GrIS can deliver labile carbon, which may also be 14C-depleted, to downstream proglacial and marine environments.

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