ARCTIC SEDIMENTS (SVALBARD) - PORE-WATER AND SOLID-PHASE DISTRIBUTIONS OF C, N, P AND SI

Pore water and solid phase distributions of C, N, P and Si in sediment s of the Arctic Ocean (Svalbard area) have been investigated. Concentr ations of organic carbon (C-org) in the solid phase of the sediment va ried from 1.3 to 2.8% (mean 1.9%), with highest concentrations found a t shallow stations south/southwest of Svalbard. Relatively low concent rations were obtained al the deeper stations north/northeast of Svalba rd. Atomic carbon to nitrogen ratios in the surface sediment ranged fr om below 8 to above 10. For some stations, high C/N ratios together wi th high concentrations of C-org suggest that sedimentary organic matte r is mainly of terrigenous origin and not from overall biological acti vity in the water column. Organic matter reactivity (defined as the to tal sediment oxygen consumption rate normalized to the organic carbon content of the surface sediment) correlated with water depth at all in vestigated stations. However, the stations could be divided into two s eparate groups with different reactivity characteristics, representing the two most dominant hydrographic regimes: the region west of Svalba rd mainly influenced by the West Spitsbergen Current, and the area eas t of Svalbard where Arctic polar water set the environmental condition s. Decreasing sediment reactivity with water depth was confirmed by th e partitioning between organic and inorganic carbon of the surface sed iment. The ratio between organic and inorganic carbon at the sediment- water interface decreased exponentially with water depth: from indefin ite values at shallow stations in the central Barents Sea, to approxim ately 1 at deep stations north of Svalbard. At stations east of Svalba rd there was an inverse linear correlation between the organic matter reactivity (as defined above) and concentration of dissolved organic c arbon (DOG) in the pore water. The more reactive the sediment, the les s DOC existed in the pore water and the more total carbonate (C-t or S igma CO2) was present. This observation suggests that DOC produced in reactive sediments is easily metabolizable to CO2. Sediment accumulati on rates of opaline silica ranged from 0.35 to 5.7 mu mol SiO2 m(-2) d (-1) (mean 1.3 mu mol SiO2 m(-2) d(-1)), i.e. almost 300 times lower t han rates previously reported for the Ross Sea, Antarctica. Concentrat ions of ammonium and nitrate in the pore water at the sediment-water i nterface were related to organic matter input and water depth. In shal low regions with highly reactive organic matter, a pool of ammonium wa s present in the pore water, while nitrate concentrations were low. In areas where less reactive organic matter was deposited at the sedimen t surface, the deeper zone of nitrification caused a build-up of nitra te in the pore water while ammonium was almost depleted. Nitrate penet rated from 1.8 to greater than or equal to 5.8 cm into the investigate d sediments. Significantly higher concentrations of ''total'' dissolve d nitrogen (defined as the sum of NO3, NO2, NH4 and urea) in sediment pore water were found west compared to east of Svalbard. The differenc es in organic matter reactivity, as well as in pore water distribution patterns of ''total'' dissolved nitrogen between the two areas, proba bly reflect hydrographic factors (such as ice coverage and production/ import of particulate organic material) related to the dominant water mass (Atlantic or Arctic Polar) in each of the two areas.