Evidence for terrigenous dissolved organic nitrogen in the Arctic deep sea

To trace the fate of terrigenous dissolved organic nitrogen (DON) in the Arctic Ocean, principal-components analyses (PCA) was used on a data set of 13 amino acids released via hydrolyses from a total of 110 water samples from Russian rivers, adjacent near-shore locations, and the Laptev Sea. The first component of the PCA distinguished significantly between terrigenous DON from the rivers (1.2 +/- 0.1) and marine-derived DON in the deep central Arctic Ocean (-1.1 +/- 0.2). The significance of this distinction was validated with amino acid data from seawater and river samples from other regions. The second PCA component correlated significantly with the proportion of D-alanine, a tracer for microbial degradation. The percentage of terrigenous DON in the Arctic Ocean was assessed from the first PCA component. The model was calibrated using data from the rivers (100% terrigenous) and the deep central Arctic Ocean (similar to0% terrigenous) as end members. Terrigenous DON accounted for 28 +/- 13% of the total DON on the Laptev Sea shelf, which is in good agreement with independent, lignin-based estimates. High proportions of terrigenous DON (up to 100%) were calculated for the continental slope down to 2,000 in depth and are probably due to downward convection of brine-enriched shelf waters. The model presented here provides the first direct evidence of terrigenous DON in the deep sea. The model may be directly applied to trace the fate of terrigenous DON in other terrestrially dominated marine environments.