Different benthic size-compartments and their relationship to sediment chemistry in the deep Eurasian Arctic Ocean

During the Arctic Expedition ARK VlII/3 (August to September 1991) with RV 'Polarstern', the macrofauna, meiofauna, foraminifera, bacteria were sampled and sediment chemistry was deter- mined at 13 stations along a transect from the Barents Sea slope across the deep Arctic Eurasian Basins towards the Lomonosov Ridge. Water depths ranged from 258 to 4427 m. In general, higher values for all benthic compartments as well as total organic carbon (TOC) and total hydrolysable amino acids (THAA) were recorded for the Barents Sea slope than for the deeper stations in the basins and the ridge slopes. The only signiEicant correlation found was between macrofaunal abundance and depth. Bac- terial and all faunal abundances as well as bacterial and macrofaunal biomass decreased significantly with increasing latitude. Although correlations between food items such as TOC and THAA and the fauna were weak, significant relationships between the bacterial and faunal size-classes reflected a distinct food chain typical of oligotrophic systems. The smallest compartments-bacteria, meiofauna and foraminifera-were more abundant than the macrofauna in the central Arctic Ocean. Macrofauna biomass dominated the biomass on the Barent Sea shelf and slope and on the Lomonosov Ridge, but bacterial biomass was equally or even more important on the Gakkel Ridge and in the deep basins. The results reveal the Eurasian Basin as one of the most oligotrophic regions in the World Ocean. Although primary production is low, recent foraminiferal investigations have revealed that benthic communities in the central Arctic Ocean are driven by the sedimentation of fresh organic material. Lateral transport of organic material from the Siberian shelf may provide additional food. The various benthic compart- ments compete either for fresh organic matter or for refractory material that is transferred to higher levels of the food chain by bacterial mineralisation.