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

• Published in: Nature (London) Vol. 462; no. 7276; pp. 1044 - 1047
• Main Authors: Hood, Eran, Fellman, Jason, Spencer, Robert G. M., Hernes, Peter J., Edwards, Rick, D’Amore, David, Scott, Durelle
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 24.12.2009; Nature Publishing Group
• Subjects: Age; Alaska; Animal and plant ecology; Animal, plant and microbial ecology; Aquatic ecosystems; Bioavailability; Biogeochemistry; Biological and medical sciences; Carbon; Carbon - analysis; Coastal; Coastal ecosystems; Creeks & streams; Dissolved organic carbon; Dissolved organic matter; Earth, ocean, space; Ecosystem; Environmental aspects; Exact sciences and technology; External geophysics; Forest soils; Fresh Water - chemistry; Fundamental and applied biological sciences. Psychology; Glaciers; Glaciohydrology; Humanities and Social Sciences; Humic Substances - analysis; Ice Cover - chemistry; letter; Marine; Marine Biology; Marine ecosystems; Marine environment; Marine microorganisms; Measurement; Microorganisms; multidisciplinary; Oceans; Pacific Ocean; Physical and chemical properties of sea water; Physics of the oceans; Properties; Rivers; Runoff; Runoff rates; Science; Science (multidisciplinary); Sea water ecosystems; Spectrometry, Fluorescence; Synecology; Terrigenous sediments; Water Movements; Watersheds; Pacific Ocean; Northeast Pacific; North American Pacific; Gulf of Alaska; North Pacific; Alaska; INE, USA, Alaska, Alaska Gulf; glaciers; Microbial activity; Heterotrophy; runoff; Impact study; Bioavailability; Ocean dynamics; biogeochemistry; drainage basins; marine environment; Flux density; Source localization; organic materials; dissolved materials; primary productivity; Material balance
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature08580

Glacier runoff as a carbon source Biogeochemical cycling along coastlines is influenced by the influx of terrestrial organic matter and nutrients from rivers. Coastal ecosystems are therefore sensitive to any alteration in the amount and reactivity of dissolved organic matter (DOM) delivered. The Gulf of Alaska drainage basin contains more than 10% of the mountain glaciers on Earth and its annual runoff is the second greatest discharge of freshwater into the Pacific Ocean. A survey of streamwater DOM content in samples from eleven coastal watersheds along the Gulf of Alaska during peak glacial runoff now shows that the bioavailability of DOM to marine microorganisms is significantly correlated with increasing age, in contrast to the norm in non-glacial rivers. The findings suggest that glacial runoff is a quantitatively important source of labile reduced carbon to marine ecosystems and that climatically driven changes in glacier volume could alter the age, quantity and reactivity of DOM entering coastal oceans. Coastal ecosystems are sensitive to changes in the quantity and lability of terrigenous dissolved organic matter (DOM) delivered by rivers. The lability of DOM is thought to decrease with age, but this view stems from work in watersheds where terrestrial plant and soil sources dominate streamwater DOM. Here, glaciated watersheds on the Gulf of Alaska are shown to be a source of old but labile dissolved organic matter, suggesting that glacial runoff is an important source of labile reduced carbon to marine ecosystems. 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 , 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 14 C age. Moreover, the most heavily glaciated watersheds are the source of the oldest (∼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 ∼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.