Impact of active layer thickening on vertical soil organic matter GHG emissions in a dynamic vegetation model

With climate change happening at a faster rate at high-latitudes than the global average, it is important to understand the warming-induced permafrost thaw effect on high-latitude GHG emissions. As permafrost soils contain nearly half of the global soil C pool a change to active layer depths could substantially increase GHG emissions from the soil and hence the concentrations in the atmosphere. Here we present a version of the dynamic vegetation model LPJ-GUESS updated to include a new multi-layer soil organic matter scheme that makes it possible to simulate organic matter dynamics at all soil depths. Together with improved soil physics, hydrology, and snow representation, this new version of LPJ-GUESS can closely simulate the current best estimates of Arctic soil C at depths (e.g. NCSCDv2.2) making it possible to simulate emissions of CO₂, CH₄, and N₂O as the active layer thickens. We also present preliminary estimates of how the Arctic soil thermodynamics and biogeochemistry could change under different future scenarios, including overshoot scenarios, to see if the Arctic C balance will act as a net source or sink of greenhouse gases.