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Sunlight controls water column processing of carbon in arctic fresh waters

Science  22 Aug 2014:
Vol. 345, Issue 6199, pp. 925-928
DOI: 10.1126/science.1253119

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Illuminating the pathway to destruction

Arctic lakes are an important source of atmospheric CO2 and therefore play a role in climate change. It is thus vital to know how the rapid Arctic warming will affect them. Cory et al. now show that light is the biggest culprit in the breakdown of carbon from thawing permafrost soils (see the Perspective by Tranvik). This carbon then moves out into Arctic lakes and streams. Contrary to previous expectations, these photochemical processes cause much more destruction of the organic molecules in fresh water than bacterial respiration does.

Science, this issue p. 925; see also p. 870

Abstract

Carbon in thawing permafrost soils may have global impacts on climate change; however, the factors that control its processing and fate are poorly understood. The dominant fate of dissolved organic carbon (DOC) released from soils to inland waters is either complete oxidation to CO2 or partial oxidation and river export to oceans. Although both processes are most often attributed to bacterial respiration, we found that photochemical oxidation exceeds rates of respiration and accounts for 70 to 95% of total DOC processed in the water column of arctic lakes and rivers. At the basin scale, photochemical processing of DOC is about one-third of the total CO2 released from surface waters and is thus an important component of the arctic carbon budget.

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