Biomass and bioturbation in surface sediments of the Arctic Ocean

Little is known about the benthic communities of the Arctic Ocean's slope and abyssal plains. Here we report on benthic data collected from box cores along a transect from Alaska to the Barents Abyssal Plain during the Arctic Ocean Section of 1994. We determined: (1) density and biomass of the polychaetes, foraminifera and total infauna; (2) concentrations of potential sources of food (pigment concentration and percent organic carbon) in the sediments; (3) surficial particle mixing depths and rates using downcore 210Pb profiles; and (4) surficial porewater irrigation using NaBr as an inert tracer. Metazoan density and biomass vary by almost three orders of magnitude from the shelf to the deep basins (e.g. 47 403 individuals m**-2 on the Chukchi Shelf to 95 individuals m**-2 in the Barents Abyssal Plain). Water depth is the primary determinant of infaunal density, explaining 39% of the total variability. Potential food concentration varies by almost two orders of magnitude during the late summer season (e.g. the phaeopigment concentration integrated to 10 cm varies from 36.16 mg m**-2 on the Chukchi Shelf to 0.94 mg m**-2 in the Siberia Abyssal Plain) but is not significantly correlated with density or biomass of the metazoa. Most stations show evidence of particle mixing, with mixing limited to <=3 cm below the sediment-water interface, and enhanced pore water irrigation occurs at seven of the nine stations examined. Particle mixing depths may be related to metazoan biomass, while enhanced pore water irrigation (beyond what is expected from diffusion alone) appears to be related to total phaeopigment concentration. The data presented here indicate that Arctic benthic ecosystems are quite variable, but all stations sampled contained infauna and most stations had indications of active processing of the sediment by the associated infauna.