Mobilization and Processing of Ancient Organic Matter from Thawing Permafrost in the Siberian Arctic
Abstract
Permafrost soils in the Arctic contain vast quantities of ancient organic matter, equivalent to roughly twice as much carbon as is currently in the atmosphere or four times as much as is in aboveground biomass globally. If thawed, the decomposition of this aged organic carbon would release the greenhouse gases CO2 and CH4 to the atmosphere, fueling a positive feedback between permafrost thaw and global warming. We suggest that interannual trends in the age of dissolved organic carbon (DOC) in Arctic streams and rivers during the late-summer period of maximum active layer depth may be a sensitive indicator of permafrost thaw at the watershed scale. That is, if warming is causing widespread increases in active layer depth, we would predict that the age of DOC in Arctic streams and rivers would be increasing over time. Prior to this study, the oldest published DOC ages that we know of are approximately ~7000 years. Here we present data, collected in summer 2010 and 2011, for small streams draining a permafrost exposure along the Kolyma River in northeast Siberia. In these streams, DOC concentrations were exceptionally high (100-340 mg/L) and DOC ages were very old (18,000 - 31,000 years), indicating the potential for ancient DOC to be mobilized and transported downstream when permafrost thaws. Particulate organic carbon in these streams was of similar age, with maximum ages approaching 40,000 years. Measurements of biological oxygen demand demonstrated that the organic carbon in these streams was remarkably labile, indicating that once released to streams and rivers much of the ancient organic matter would re-enter the active carbon cycle. To date, the data do not exist to know whether temporal trends in DOC age are already presenting an unambiguous signal of widespread terrestrial change in the Arctic, but we suggest that observations of stream water DOC age may be one of our more powerful means of identifying significant feedbacks in the Arctic's carbon cycle.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGC43C0939H
- Keywords:
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- 0428 BIOGEOSCIENCES / Carbon cycling;
- 0475 BIOGEOSCIENCES / Permafrost;
- cryosphere;
- and high-latitude processes;
- 0744 CRYOSPHERE / Rivers;
- 1621 GLOBAL CHANGE / Cryospheric change