Stochastic Modeling of Carbon Photo-mineralization along Arctic Rivers

Abstract:

Permafrost soil stores twice the amount of carbon found in current atmosphere, leading to increasing concern about climate feedbacks due to thawing of organic carbon stored in arctic permafrost. Current climate models assume that CO₂ outgassing occurs only at the site of thawing, overlooking the flushing of dissolved organic carbon (DOC) from soils into surface waters, downstream transport, and the associated opportunities for photochemical transformations. To better understand the mechanisms producing CO₂ and the effect of water flow on riverine photo-mineralization of DOC, we developed a stochastic particle-tracking model that characterizes the migration of DOC in arctic rivers and the concurrent photo-mineralization during downstream transport. We calibrated the model against field tracer measurements, and then applied the model to analyze the effects of river geometry and flow on rates of photo-mineralization of DOC to CO₂ in the Kuparuk River, Alaska. We found that rates of photo-mineralization were dependent on vertical mixing in the water column and average residence times. When flow paths are restricted to areas near and beneath the river bed, where both flow velocity and light availability are low, the overall photo-mineralization of DOC is reduced. Using this model will improve our understanding of the interactions between hydrological and photochemical controls on CO₂ production in surface waters, and provide tools that can be used more generally to assess redistribution and transformation of carbon in arctic and global climate models.