Letter

Nature 462, 1044-1047 (24 December 2009) | doi:10.1038/nature08580; Received 11 March 2009; Accepted 2 October 2009

Glaciers as a source of ancient and labile organic matter to the marine environment

Eran Hood1, Jason Fellman2,6, Robert G. M. Spencer3,6, Peter J. Hernes3, Rick Edwards4, David D’Amore4 & Durelle Scott5

  1. Environmental Science and Geography Program, University of Alaska Southeast, Juneau, Alaska 99801, USA
  2. Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA
  3. Department of Land, Air and Water Resources, University of California Davis, Davis, California 95616, USA
  4. Pacific Northwest Research Station, USDA Forest Service, Juneau, Alaska 99801, USA
  5. Biological Systems Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA
  6. Present addresses: School of Plant Biology, University of Western Australia, Crawley, Western Australia, 6009, Australia (J.F.); Department of Plant Sciences, University of California Davis, Davis, California 95616, USA (R.G.M.S.).

Correspondence to: Eran Hood1 Correspondence and requests for materials should be addressed to E.H. (Email: eran.hood@uas.alaska.edu).

Riverine organic matter supports of the order of one-fifth of estuarine metabolism1. 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 material2, 3, 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 14C age. Moreover, the most heavily glaciated watersheds are the source of the oldest (~4kyr 14C 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 Earth5. We estimate the cumulative flux of dissolved organic carbon derived from glaciers contributing runoff to the Gulf of Alaska at 0.13±0.01Tgyr-1 (1Tg = 1012g), of which ~0.10Tg 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.