title: Large amounts of labile organic carbon in permafrost soils of northern Alaska.
abstract: Permafrost-affected soils of the northern circumpolar region represent 50% of the terrestrial soil organic carbon (SOC) reservoir and are most strongly affected by climatic change. There is growing concern that this vast SOC pool could transition from a net C sink to a source. But so far little is known on how the organic matter (OM) in permafrost soils will respond in a warming future, which is governed by OM composition and possible stabilization mechanisms. To investigate if and how SOC in the active layer and adjacent permafrost is protected against degradation, we employed density fractionation to separate differently stabilized SOM fractions. We studied the quantity and quality of OM in different compartments using elemental analysis,13C solid-phase nuclear magnetic resonance (13C-NMR) spectroscopy, and14C analyses. The soil samples were derived from 16 cores from drained thaw lake basins, ranging from 0 to 5500 years of age, representing a unique series of developing Arctic soils over time. The normalized SOC stocks ranged between 35.5 and 86.2 kg SOC m-3, with the major amount of SOC located in the active layers. The SOC stock is dominated by large amounts of particulate organic matter (POM), whereas mineral-associated OM especially in older soils is of minor importance on a mass basis. We show that tremendous amounts of over 25 kg OC per square meter are stored as presumably easily degradable OM rich in carbohydrates. Only about 10 kg OC per square meter is present as presumably more stable, mineral-associated OC. Significant amounts of the easily degradable, carbohydrate-rich OM are preserved in the yet permanently frozen soil below the permafrost table. Forced by global warming, this vast labile OM pool could soon become available for microbial degradation due to the continuous deepening of the annually thawing active layer.
authors: Lehrstuhl für Bodenkunde, TU München, Freising-Weihenstephan, 85356, Germany.
authors: Carsten W
authors: CW
authors: Mueller
authors: Institute of Geology and Mineralogy, University of Cologne, Cologne, 50674, Germany.
authors: Janet
authors: J
authors: Rethemeyer
authors: Department of Horticulture, Cornell University, Ithaca, NY, 14853, USA.
authors: Jenny
authors: J
authors: Kao-Kniffin
authors: Lehrstuhl für Bodenkunde, TU München, Freising-Weihenstephan, 85356, Germany.|Department of Soil Science of Temperate Ecosystems, University of Göttingen, Göttingen, Germany.
authors: Sebastian
authors: S
authors: Löppmann
authors: Department of Geography, University of Cincinnati, Cincinnati, OH, 45221, USA.
authors: Kenneth M
authors: KM
authors: Hinkel
authors: Department of Soil Science, University of Wisconsin-Madison, Madison, WI, 53706, USA.
authors: James
authors: J
authors: G Bockheim
keywords: 
  14
  C
  ; 13C-CPMAS NMR spectroscopy; density fractionation; drained thaw lake basin; free particulate organic matter; mineral-associated organic matter; occluded organic matter