Greenland Ice Sheet exports labile organic carbon to the Arctic oceans

Lawson, Emily C. and Wadham, Jemma L. and Tranter, Martyn and Stibal, Marek and Lis, Greg P. and Butler, Catriona E.H. and Laybourn-Parry, Johanna and Nienow, Peter and Chandler, David and Dewsbury, Paul (2014) Greenland Ice Sheet exports labile organic carbon to the Arctic oceans. Biogeosciences, 11 (14). pp. 4015-4028. ISSN 1726-4170

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Abstract

Runoff from small glacier systems contains dissolved organic carbon (DOC) rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr−1). We report high and episodic fluxes of POC and DOC from a large (> 600 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70–89% on average), is sourced from the ice sheet bed, and contains a significant bioreactive component (9% carbohydrates). A major source of the “bioavailable” (free carbohydrate) LMW–DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW–DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (26–53%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the approximately two-fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating a supply limitation in suspended sediment in runoff. Scaled to the GrIS, the combined DOC (0.13–0.17 TgC yr−1 (±13 %)) and POC fluxes (mean = 0.36–1.52 TgC yr−1 (±14 %)) are of a similar order of magnitude to a large Arctic river system, and hence may represent an important OC source to the near-coastal North Atlantic, Greenland and Labrador seas.

Item Type: Article
Keywords: Glacier, carbon, bioavailable, microbes, Greenland Ice Sheet
Schools/Departments: University of Nottingham UK Campus > Faculty of Social Sciences > School of Geography
Identification Number: https://doi.org/10.5194/bg-11-4015-2014
Related URLs:
URLURL Type
http://www.biogeosciences.net/11/4015/2014/bg-11-4015-2014.htmlPublisher
http://www.nottingham.ac.uk/geography/people/emily.lawsonAuthor
Depositing User: Lawson, Dr Emily
Date Deposited: 17 Oct 2014 13:27
Last Modified: 16 Sep 2016 17:15
URI: http://eprints.nottingham.ac.uk/id/eprint/27608

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