Distribution of Dissolved Organic Carbon in the Source Waters of the Trans Polar Drift: Inferences on Terrigenous DOC Dynamics in the Eastern Arctic Ocean

The fate of terrigenous dissolved organic carbon (tDOC) delivered to the Arctic Ocean by rivers remains poorly constrained on both spatial and temporal scales. Previous studies in the western Arctic have shown tDOC removal to be an active but slow process. Here we present observations of DOC measured in the Polar Surface Layer (PSL) from a recent field expedition to the outer shelf and deep basins of the eastern Eurasian and western Canadian Arctic Ocean. Mean DOC concentrations were higher over the Eurasian basins (94±17 µM C) than in the Canadian Basin (64±4.5 µM C), suggesting differing controls on DOC variability between the two systems. To examine the role that freshwaters have on the observed DOC variability, the variables salinity and δ18O were used to calculate the fraction of freshwater due to river runoff and sea-ice melt present in the PSL. Regression of DOC against salinity over the Eurasian basins had a zero-salinity intercept of 331 µM C, which is significantly lower than the estimated riverine source in the region of 724 µM C indicative of active removal of tDOC. To obtain the timescale of this removal process, we applied an age model using measurements of dissolved 228Ra/226Ra, an isotopic tracer of water mass age. The coupling of the Ra age model with DOC distributions indicates that the tDOC removal rate for the eastern Eurasian Arctic is higher than the rate previously reported for the western Arctic. Causes for the differences in these rates will be considered.