Modelling the carbon cycle in permafrost in a simplified thermal soil model coupled with iLOVECLIM

During the Last Glacial Maximum (LGM, 21000 years ago), atmospheric CO₂ concentrations were approximately 100 ppm lower than during the pre-industrial period, yet the mechanisms responsible for this difference remain poorly understood. Several hypotheses have been proposed, involving ocean circulation, the marine biosphere, or continental carbon stocks, but none has been able to fully explain this difference. Carbon stored in permafrost soils may represent a significant and still poorly constrained component of this missing carbon reservoir.

This study investigates the role of permafrost as a long-term carbon reservoir from the LGM to the present using a modelling approach. A simple soil thermal model (FROG) is used to simulate permafrost extent, depth, active layer thickness and soil carbon content down to 1000 meters depth. The model is coupled to iLOVECLIM, an intermediate-complexity Earth System Model coupling atmosphere, ocean, and biosphere components. This approach allows transient simulations to be performed over several thousand years, which is necessary to better represent carbon cycle evolution during glacial–interglacial cycles.

Simulations are conducted for present-day and LGM climate conditions. The model produces spatially explicit estimates of permafrost extent, active layer thickness, and soil carbon distribution for both periods. Results indicate substantial differences in permafrost depth and spatial coverage between the LGM and present day. Model results are compared with available observational datasets for permafrost and soil carbon, as well as outputs from other climate models.