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    Assessing the Role of Photochemistry in Driving the Composition of Dissolved Organic Matter in Glacier Runoff

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    Author
    Holt, Amy D.
    Kellerman, Anne M.
    Li, Wenbo
    Stubbins, Aron
    Wagner, Sasha
    McKenna, Amy
    Fellman, Jason B.
    Hood, Eran
    Spencer, Robert G. M.
    Keyword
    Dissolved organic matter (DOM)
    Glacier runoff
    Photochemistry
    Juneau Icefield
    Greenland Ice Sheet
    Metadata
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    URI
    http://hdl.handle.net/11122/12858
    Abstract
    Dissolved organic matter (DOM) in glacier runoff is aliphatic-rich, yet studies have proposed that DOM originates mainly from allochthonous, aromatic, and often aged material. Allochthonous organic matter (OM) is exposed to ultraviolet radiation both in atmospheric transport and post-deposition on the glacier surface. Thus, we evaluate photochemistry as a mechanism to account for the compositional disconnect between allochthonous OM sources and glacier runoff DOM composition. Six endmember OM sources (including soils and diesel particulate matter) were leached and photo-irradiated for 28 days in a solar simulator, until >90% of initial chromophoric DOM was removed. Ultrahigh-resolution mass spectrometry was used to compare the molecular composition of endmember leachates pre- and post-irradiation to DOM in supraglacial and bulk runoff from the Greenland Ice Sheet and Juneau Icefield (Alaska), respectively. Photoirradiation drove molecular level convergence between the initially aromatic-rich leachates and aromatic-poor glacial samples, selectively removing aromatic compounds (−80 ± 19% relative abundance) and producing aliphatics (+75 ± 35% relative abundance). Molecular level glacier runoff DOM composition was statistically indistinguishable to post-irradiation leachates. Bray-Curtis analysis showed substantial similarity in the molecular formulae present between glacier samples and post-irradiation leachates. Post-irradiation leachates contained 84 ± 7.4% of the molecular formulae, including 72 ± 17% of the aliphatic formulae, detected in glacier samples. Our findings suggest that photodegradation, either in transit to or on glacier surfaces, could provide a mechanistic pathway to account for the disconnect between proposed aromatic, aged sources of OM and the aliphatic-rich fingerprint of glacial DOM.
    Date
    2021-11-04
    Publisher
    American Geophysical Union
    Type
    Article
    Peer-Reviewed
    Yes
    Citation
    Holt, A. D., Kellerman, A. M., Li, W., Stubbins, A., Wagner, S., McKenna, A., et al. (2021). Assessing the role of photochemistry in driving the composition of dissolved organic matter in glacier runoff. Journal of Geophysical Research: Biogeosciences, 126, e2021JG006516. https://doi. org/10.1029/2021JG006516
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    Hood, Eran

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