Ancient low-molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw.
Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere. Here, we demonstrate that ancient dissolved organic carbon (DOC) leached from 35,800 y B.P. permafrost soils is rapidly mineralized to CO2. During 200-h experiments in a novel high-temporal-resolution bioreactor, DOC concentration decreased by an average of 53%, fueling a more than sevenfold increase in dissolved inorganic carbon (DIC) concentration. Eighty-seven percent of the DOC loss to microbial uptake was derived from the low-molecular-weight (LMW) organic acids acetate and butyrate. To our knowledge, our study is the first to directly quantify high CO2 production rates from permafrost-derived LMW DOC mineralization. The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearby inland waters.
National Research Program, US Geological Survey, Boulder, CO 80303; Environmental Studies Program, University of Colorado, Boulder, CO 80302; draketw@gmail.com.
Travis W
TW
Drake
National Research Program, US Geological Survey, Boulder, CO 80303;
Kimberly P
KP
Wickland
Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL 32306;
Robert G M
RG
Spencer
Environmental Studies Program, University of Colorado, Boulder, CO 80302; Department of Civil, Environmental and Architectural Engineering, University of Colorado, Boulder, CO 80302.
Diane M
DM
McKnight
National Research Program, US Geological Survey, Boulder, CO 80303;
Robert G
RG
Striegl
D000143:Acids / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis*; D008970:Molecular Weight; D009930:Organic Chemicals / Q000032:analysis*; D065946:Permafrost
D000143:Acids; D009930:Organic Chemicals; D002245:Carbon Dioxide
Pleistocene; carbon dioxide; dissolved organic carbon; organic acids; permafrost