Predicting Time and Spatial Scales for the Degradation of Dissolved Organic Carbon (DOC) in Five Large Arctic Rivers: The Fate of Permafrost Under a Warming Climate

Abstract:

Under current climate scenarios the mobilization and remineralization of permafrost organic carbon (OC) could be one of the most significant climate feedbacks from the terrestrial ecosystem to the atmosphere, yet time and spatial scales over which this might occur on a pan-Arctic scale is poorly understood. To develop a simplistic, yet empirical framework that can explore, and predict dissolved organic carbon (DOC) degradation patterns across five large Arctic Rivers we leverage relatively simple optical methods, developed for rapid analysis of DOC, combined with known physical catchment characteristics. Specifically, we use fluorescence to estimate the concentration of relatively “labile” versus “refractory” DOC sources, and assuming first order kinetics introduce a robust DOC lability index (%DF). We then show that the mean slope of the catchment can predict the flux of DOC delivered to the Arctic Ocean, and estimate the extent of terrestrial DOC degradation on a pan-Arctic scale. Next, we estimate relevant DOC exposure (t_E) and processing (t_P) time scales, and show that the outcome of an individual thaw event depends critically on the ratio between t_E:t_p, regardless of the spatial regime over which the reaction occurs. Finally, we provide strong evidence that the mean catchment slope, and to what extent the catchment remains continuously frozen (i.e. % continuous permafrost) are key variables to predict the fate of Arctic River DOC under a warming climate.