Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of American Chemical Society for personal use, not for redistribution. The definitive version was published in Environmental Science & Technology 48 (2014): 14248–14257, doi:10.1021/es501732h.
Runoff from glaciers and ice sheets has been acknowledged as a potential source of bioavailable dissolved organic matter (DOM) to downstream ecosystems. This source may become increasingly significant as glacial melt rates increase in response to future climate change. Recent work has identified significant concentrations of bioavailable carbon and iron in Greenland Ice Sheet (GrIS) runoff. The flux characteristics and export of N-rich DOM are poorly understood. Here, we employed electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to determine the elemental compositions of DOM molecules in supraglacial water and subglacial runoff from a large GrIS outlet glacier. We provide the first detailed temporal analysis of the molecular composition of DOM exported over a full melt season. We find that DOM pools in supraglacial and subglacial runoff are compositionally diverse and that N-rich material is continuously exported throughout the melt season as the snowline retreats further inland. Identification of protein-like compounds and a high proportion of N-rich DOM, accounting for 27-41% of the DOM molecules identified by ESI FT-ICR MS, may suggest a microbial provenance and high bioavailability of glacially-exported DOM to downstream microbial 16 communities.
This research was funded by the Natural Environment Research Council UK (NERC) grant NE/E004016/1 (to J. L. Wadham) and a NERC CASE studentship to E. C. Lawson (NERC DTG/GEOG SN1316.6525) co-sponsored by Dionex Corporation (part of Thermo Fisher Scientific). Support to J. L. Wadham was also provided by the Leverhulme Trust via a Phillip
Leverhulme award and a Leverhulme Trust Research Fellowship. Support to M. P. Bhatia and E. B. Kujawinski was provided by a WHOI Clark Arctic Research Initiative Grant.
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