Beschreibung: This is the first study to present the patterns and environmental controls of benthic biomass size spectra, carbon demand, and production along the entire bathymetric gradient from the shelf to the abyssal depths in the Arctic Ocean. The materials were collected at 17 stations (76 - 5561 m) in the eastern Fram Strait, in the Atlantic passage to the Arctic Ocean, in the vicinity of the productive Marginal Ice Zone, with concentrations of sediment-bound chloroplastic pigments (indicating food availability from phytodetritus sedimentation) higher than in other deep-sea localities at similar depths. Meiobenthic and macrobenthic individuals were measured using image analysis to assess their biovolume, biomass, annual production, and carbon demand. Benthic biomass in the area was clearly higher than that in the High Arctic locations and comparable to that in the lower-latitude North Atlantic. Biomass and annual production were significantly negatively correlated with water depth, with stronger bathymetric clines in macrofauna than in meiofauna and the increasing dominance of meiofauna with increasing depth. A bimodal shape in the size spectra was observed only at the shallow stations, while at depths below 2000 m, an additional trough was present in the macrofaunal part of the spectrum. The entire range of the spectra (i.e., the number of size classes) decreased with increasing depth, especially in the macrofaunal part of the spectrum. Similar slope values in the normalized spectra indicated that the distribution of the biomass across the present size classes was consistent from the shelf to the abyssal depths, irrespective of the decreasing amount of food availability. The fragmented macrofaunal size spectra documented at the two stations were probably due to physical disturbances at the sediment-water interface (e.g., intense bioturbation of holothurians and strong near-bottom currents). Benthic carbon demand declined from 50.7 gC m-2 y-1 at the shelf to 11.5 gC m-2 y-1 at the slope to 2.2 gC m-2 y-1 at the abyssal depths, and its partitioning among meiofauna and macrofauna changed with water depth, with meiofauna contributions increasing from 50 % at the shelf to over 90 % at the deepest station. The estimated total benthic carbon demand exceeded the vertical Corg fluxes, suggesting that the studied system can be particularly sensitive to future changes in productivity regimes and associated organic matter fluxes.

Beschreibung: Deep-sea benthic communities and their structural and functional characteristics are regulated by surface water processes. Our study focused on the impact of changes in water depth and food supplies on small-sized metazoan bottom-fauna (meiobenthos) along a bathymetric transect (1200–5500 m) in the western Fram Strait. The samples were collected every summer season from 2005 to 2009 within the scope of the HAUSGARTEN monitoring program. In comparison to other polar regions, the large inflow of organic matter to the sea floor translates into relatively high meiofaunal densities in this region. Densities along the bathymetric gradient range from approximately 2400 ind. 10 cm-2 at 1200 m to approximately 300 ind. 10 cm-2 at 4000 m. Differences in meiofaunal distribution among sediment layers (i.e., vertical profile) were stronger than among stations (i.e., bathymetric gradient). At all the stations meiofaunal densities and number of taxa were the highest in the surface sediment layer (0–1 cm), and these decreased with increasing sediment depth (down to 4–5 cm). However, the shape of the decreasing pattern differed significantly among stations. Meiofaunal densities and taxonomic richness decreased gradually with increasing sediment depth at the shallower stations with higher food availability. At deeper stations, where the availability of organic matter is generally lower, meiofaunal densities decreased sharply to minor proportions at sediment depths already at 2–3 cm. Nematodes were the most abundant organisms (60–98%) in all the sediment layers. The environmental factors best correlated to the vertical patterns of the meiofaunal community were sediment-bound chloroplastic pigments that indicate phytodetrital matter.