From GRL/AGU Journal Highlights 6/22/10:
Less warming risk from permafrost thaw
Soil found in the Arctic stores half of the world's soil organic carbon (SOC) and twice as much carbon as is in the atmosphere. Rising temperatures in the Arctic are thawing the permafrost; some of the soil carbon then degrades into greenhouse gases that are remobilized into the carbon cycle, exerting positive [negative to minimal according to several empirical studies] feedback on global warming.
Vonk et al.'s objective was to find out what happens to terrestrial SOC after it is released from Arctic landmasses to coastal waters. The authors chose northernmost Scandinavia to conduct their study due to its sensitivity to the warming climate.
The molecular radiocarbon fingerprint of suspended particulate matter and surface sediments collected during spring flood 2005 in the Kalix River-Bothnian Bay system reveals that there are two distinct SOC pools, which exhibit different susceptibilities to degradation upon settling from the surface water to the underlying sediments. The exported SOC distributed by rivers and streams consists of a young pool that is released from recent plant material and the upper soil layers of peatlands and an older pool that originates from deeper mineral soil layers.
The data reveal that the young pool, with an inferred high degradation rate, would be expected to add greenhouse gases to the atmosphere, while the carbon from the older pool, which is tightly bound to mineral particles that protect it from degradation, would resettle in coastal sediments. Therefore, thaw-released mineral organic carbon may, relative to peat organic carbon, preferentially end up in coastal sediments instead of the atmosphere. The results suggest that researchers should reevaluate the assumption that there is a simple direct link between thawing of permafrost and the addition of greenhouse gases to the atmosphere.
Title: Selective preservation of old organic carbon fluvially released from sub-Arctic soils
Authors: Jorien E. Vonk, Bart E. van Dongen, and Örjan Gustafsson: Department of Applied Environmental Science and Bert Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL042909, 2010 http://dx.doi.org/10.1029/2010GL042909