Description: During the Arctic Expedition ARK VIII/3 (August to September 1991) with RV Polarstern, the macrofauna, meiofauna, foraminifera, bacteria were sampled and sediment chemistry was determined 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 significant correlation found was between macrofaunal abundance and depth. Bacterial 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 compartments compete either for fresh organic matter or for refractory material that is transferred to higher levels of the food chain by bacterial mineralisation.

Description: To test the pore density in benthic foraminifera as a potential proxy for bottom-water oxygenation, pore density analyses were carried out on tests of living (rose Bengal-stained) specimens of the deep-infaunal and anoxia-tolerant foraminiferal species Globobulimina turgida. Three stations within and two stations below the oxygen minimum zone (OMZ) off Namibia were investigated and compared to in situ-measured bottom-water oxygen content (BW-O2). Pore density was first conventionally assessed by rather time-consuming manual pore counting on SEM photographs and measurement of the analyzed test areas. To significantly shorten the measurement time we tested and evaluated an automation of the pore density measurement using the image analysis software package analySIS (version 5.0, Olympus Soft Imaging Solutions). Pore density data from automated analyses are compared to manually acquired data from G. turgida. Our study shows almost identical results for both manually and automatically acquired data. Consequently, we assume that the new technique provides an alternative and more rapid method to analyze the pore density of foraminifera. For both methods, our results show a distinct negative linear correlation (automatically analyzed pore density: τ = −0.50, p 〈 0.001; manually analyzed pore density: τ = −0.49, p 〈 0.001) between pore density and BW-O2, suggesting that G. turgida increases its pore density in response to decreasing oxygen. Thus, we suggest that, similar to other recently described low-oxygen-tolerant benthic foraminiferal species, G. turgida may improve its O2 uptake by increasing pore density to survive in low-oxic environments. This morphological adaption might be useful for future studies to establish an independent proxy for BW-O2. In addition, pore density has been compared to in situ-measured bottom-water nitrate concentration (BW-NO3−). Our investigation of the pore density-to-BW-NO3− relationship for G. turgida suggests that nitrate seems to be a minor factor influencing pore density in this species compared to BW-O2. Add to CiteULike