Autumn destabilization of deep porewater CO(2) store in a northern peatland driven by turbulent diffusion

The deep porewater of northern peatlands stores large amounts of carbon dioxide (CO(2)). This store is viewed as a stable feature in the peatland CO(2) cycle. Here, we report large and rapid fluctuations in deep porewater CO(2) concentration recurring every autumn over four consecutive years in a boreal peatland. Estimates of the vertical diffusion of heat indicate that CO(2) diffusion occurs at the turbulent rather than molecular rate. The weakening of porewater thermal stratification in autumn likely increases turbulent diffusion, thus fostering a rapid diffusion of deeper porewater CO(2) towards the surface where net losses occur. This phenomenon periodically decreases the peat porewater CO(2) store by between 29 and 90 g C m(−2) throughout autumn, which is comparable to the peatland’s annual C-sink. Our results establish the need to consider the role of turbulent diffusion in regularly destabilizing the CO(2) store in peat porewater.