| Summary: | Little is known about the distribution and dynamics of dissolved organic nitrogen (DON) within Arctic Ocean surface waters, though seasonal inputs from both rivers and marine phytoplankton production are likely important. Here we combine multiple datasets to provide the first quasi-synoptic view of DON concentrations in the summertime Arctic Ocean Polar Surface Layer (PSL) and western Arctic shelves, and infer controlling processes. Distributions indicate inputs of DON by Arctic rivers followed by net consumption of up to 70% of this terrigenous material across the resulting salinity gradients over time scales of years. Coupling of DON losses to PSL residence times indicates first order decay constants (?) of 0.15 ± 0.07 yr? 1 and 0.08 ± 0.01 yr? 1 for terrigenous DON in the eastern and western Arctic systems, respectively. Riverine delivery of both inorganic and organic nitrogen have only a minor (< 15%) impact on Arctic shelf export production. In the Pacific Ocean-influenced Chukchi Sea, net biological production of ~ 2 ?M DON, representing ~ 8% of net community production, is observed in surface waters following seasonal sea-ice retreat. These findings highlight the contrasting roles and locations of terrigenous versus marine derived DON in the cycling of nitrogen in the surface Arctic Ocean.
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