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Glaciers as a source of ancient and labile organic matter to the marine environment
Hood, E.; Fellman, J.; Spencer, R.G.M.; Hernes, P.J.; Edwards, R.; D’Amore, D.; Scott, D. (2009). Glaciers as a source of ancient and labile organic matter to the marine environment. Nature (Lond.) 462(7276): 1044-1047. https://dx.doi.org/10.1038/nature08580
In: Nature: International Weekly Journal of Science. Nature Publishing Group: London. ISSN 0028-0836; e-ISSN 1476-4687, more
Peer reviewed article  

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Keyword
    Marine/Coastal

Authors  Top 
  • Hood, E.
  • Fellman, J.
  • Spencer, R.G.M.
  • Hernes, P.J.
  • Edwards, R.
  • D’Amore, D.
  • Scott, D.

Abstract
    Riverine organic matter supports of the order of one-fifth of estuarine metabolism(1). Coastal ecosystems are therefore sensitive to alteration of both the quantity and lability of terrigenous dissolved organic matter (DOM) delivered by rivers. The lability of DOM is thought to vary with age, with younger, relatively unaltered organic matter being more easily metabolized by aquatic heterotrophs than older, heavily modified material(2-4). This view is developed exclusively from work in watersheds where terrestrial plant and soil sources dominate streamwater DOM. Here we characterize streamwater DOM from 11 coastal watersheds on the Gulf of Alaska that vary widely in glacier coverage (0-64 per cent). In contrast to non-glacial rivers, we find that the bioavailability of DOM to marine microorganisms is significantly correlated with increasing (14)C age. Moreover, the most heavily glaciated watersheds are the source of the oldest (similar to 4 kyr (14)C age) and most labile (66 per cent bioavailable) DOM. These glacial watersheds have extreme runoff rates, in part because they are subject to some of the highest rates of glacier volume loss on Earth(5). We estimate the cumulative flux of dissolved organic carbon derived from glaciers contributing runoff to the Gulf of Alaska at 0.13 +/- 0.01 Tg yr(-1) (1 Tg = 10(12) g), of which similar to 0.10 Tg is highly labile. This indicates that glacial runoff is a quantitatively important source of labile reduced carbon to marine ecosystems. Moreover, because glaciers and ice sheets represent the second largest reservoir of water in the global hydrologic system, our findings indicate that climatically driven changes in glacier volume could alter the age, quantity and reactivity of DOM entering coastal oceans.

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