Biomass of foraminifera in the St. Anna Trough, Russian Arctic continentalmargin

The abundance of large agglutinated tests in brown oxidized mud has suggest ed that high biomasses of foraminifera occur in troughs on the western Arct ic Eurasian shelf. To verify this, we measured foraminiferal biomass (proto plasmic volume) at seven stations close to 80 degrees N in the St. Anna Tro ugh, a shelf depression open to the Arctic Basin. The abundance of arenaceo us tests was high owing to good postmortem preservation within a thick (30 cm) surface oxidized layer of the sediment. Foraminiferal biomass was moder ate (range = 0.06-1.7 g/m(2)) compared with common shelf values and increas ed with increasing water depth. The foraminiferal contribution to the bioma ss of the benthic community was negligible on the slopes of the trough but below 500 m water depth, where the macrofauna is scarce, the foraminifera:m acrofauna ratio reached 0.3, The bulk of the foraminiferal biomass consiste d of specimens approximately 2 mm in diameter. The volume of cytoplasm in t ests of the dominant foraminiferan Reophax pilulifer increased in response to the summer pulse of organic detritus.