Nutrients, organic carbon and organic nitrogen in the upper water column of the Arctic Ocean: implications for the sources of dissolved organic carbon

Particulate and dissolved organic carbon and nitrogen were analyzed for shelf, slope and basin samples collected during the 1994 Arctic Ocean Section. Concentrations of organic carbon and nitrogen were highest in the surface water and decreased dramatically below 100 m. Over the shelf 40–50% of the organic material was present in the particulate phase, while in the slope and basin waters >-90% of the organic material was present in the dissolved phase. The halocline layer over the Chukchi plateau contained high concentrations of inorganic nutrients but no significant elevation of either organic carbon or organic nitrogen. Highest concentrations of total organic carbon were found in the surface water of the Makarov and Amundsen Basins between 80 and 90° N. The C:N ratio of the dissolved organic material in the upper 100 m ranged from 9 to 25, with highest ratios along the Makarov flank of the Lomonosov Ridge. We suggest that a major portion of the carbon-rich organic material in surface waters is derived from Eurasian shelf riverine inputs, which tend to flow in perimeter currents along the slope and ridges. Our preliminary dissolved organic carbon (DOC) budget suggests that the three major sources of DOC in the central Arctic are in situ production (56%), river run-off (25%), and Pacific water (19%).