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Respiration in frozen soils is limited to thawed substrate withinthe thin water films surrounding soil particles. As temperatures decrease andthe films become thinner, the available substrate also decreases, withrespiration effectively ceasing at −8 °C. Traditional exponentialscaling factors to model this effect do not account for substrateavailability and do not work at the century to millennial timescalesrequired to model the fate of the nearly 1100 Gt of carbon in permafrostregions. The exponential scaling factor produces a false, continuous loss ofsimulated permafrost carbon in the 20th century and biases in estimates ofpotential emissions as permafrost thaws in the future. Here we describe a newfrozen biogeochemistry parameterization that separates the simulated carboninto frozen and thawed pools to represent the effects of substrateavailability. We parameterized the liquid water fraction as a function oftemperature based on observations and use this to transfer carbon betweenfrozen pools and thawed carbon in the thin water films. The simulatedvolumetric water content (VWC) as a function of temperature is consistentwith observed values and the simulated respiration fluxes as a function oftemperature are consistent with results from incubation experiments. Theamount of organic matter was the single largest influence on simulated VWCand respiration fluxes. Future versions of the parameterization shouldaccount for additional, non-linear effects of substrate diffusion in thinwater films on simulated respiration. Controlling respiration in frozen soilsbased on substrate availability allows us to maintain a realistic permafrostcarbon pool by eliminating the continuous loss caused by the originalexponential scaling factors. The frozen biogeochemistry parameterization is auseful way to represent the effects of substrate availability on soilrespiration in model applications that focus on century to millennial timescales in permafrost regions

A parameterization of respiration in frozen soils based on substrate availability