PERMASOM - Organic matter in permafrost: molecular composition and associated response to increasing temperature

The release of CO2 to the atmosphere from the mineralization of soil organic matter (SOM) in thawing permafrost is one of the largest potential feedback mechanisms on the climate system. This positive feedback, i.e. it will aggravate climate changes, is d ue to the fact that SOM decomposes faster at higher temperatures. The key question is how much faster. Recent research suggests that it might not decompose at the same speed as non-frozen soils because of contrasting molecular composition. The temperature sensitivity of SOM decomposition is embedded in the terrestrial C modules of global earth system models as simple rate-multiplier functions. Slight modifications of function parameters can have profound effects on greenhouse gas (GHG) flux estimates and thereby feedback effects on predicted climate changes. The main objective of the proposal is to determine the intrinsic sensitivity of arctic and permafrost soil organic matter to temperature changes, and to assess the associated greenhouse-gas feedbacks in an earth system model. Here, we propose collecting permafrost (and non-permafrost control) soil samples in Norway and Russia, conducting incubation experiments to determine potential mineralization rates and temperature sensitivity functions. In additi on, we will perform advanced molecular characterizations of the soil sample SOM in order to test the hypothesis of a link between temperature sensitivity and SOM composition, as recently much debated in high-profile publications. Finally, we will test the improved temperature sensitivity parameters in terms of GHG production in the land cover scheme of the Norwegian earth system model BCM. This project will thereby contribute to reducing uncertainties in future climate change predictions through improved parameterization of SOM turnover algorithms for permafrost soils.