The magnitude, source, and implication of DIC flux from major pan-arctic rivers to the Arctic Ocean

The response of Arctic carbon (C) stocks to climatic change is of increasing concern. However, there remains considerable uncertainty about the flux of dissolved inorganic C (DIC) from land to the Arctic Ocean. We have determined DIC flux from the 6 largest pan-arctic watersheds using measurements collected during the PARTNERS (Pan Arctic River Transport of Nutrients, Organic Matter and Suspended Sediment; 2003-2006) and Arctic-GRO (Arctic Great Rivers Observatory; 2009-current) projects, which have a unique focus on consistent sampling and analytical methods across the pan-arctic, and a sampling regime that captures previously under-reported ice-out and under-ice periods. Within rivers, there is as much as a 5-fold seasonal variation in DIC concentration, while flow-weighted concentrations vary more than 3-fold between rivers. The total DIC flux from these 6 watersheds, which deliver greater than 50% of the freshwater discharge to the Arctic Ocean, is approximately 30 Tg C yr-1. This is double the flux of dissolved organic C to the Arctic Ocean in these rivers, and more than 6 times current estimates of particulate organic C flux. Analyses of major ion (Ca, Na, Mg) and Sr composition indicates that the majority of DIC in these rivers is derived from the weathering of carbonate rocks, with rivers on the North American plate having the highest proportion of DIC derived from carbonate drainage. Given the dramatic effect of climate change in the Arctic it is imperative that we establish the magnitude and flux of contemporary C stocks in this landscape to enable the detection of future changes.