The role of the benthic biota in sedimentary metabolism and sediment-waterexchange processes in the Goban Spur area (NE Atlantic)

We provide an overview of the role of biological processes in the Benthic b oundary layer (BBL) and in sediments on the cycling of particulate organic material in the Goban Spur area (Northeast Atlantic). The benthic fauna, se diment and BBL characteristics were studied along a transect ranging from 2 08 to 4460m water depth in different seasons over 3 years. Near-bottom flow velocities are high at the upper part of the slope (1000-1 500m), and high numbers of filter-feeding taxa are found there such that or ganic carbon normally passing this area during high flow conditions is prob ably trapped, accumulated, and/or remineralised by the fauna. Overall metabolism in shelf and upper slope sediments is dominated by the m acrofauna. More than half of the organic matter flux is respired by macrofa una, with a lower contribution of metazoan meiofauna (4%) and anoxic and su boxic bacterial mineralisation (21%); the remainder (23%) being channelled through nanobiota and oxic bacteria. By its feeding activity and movement, the macrofauna intensely reworks the sediments on the shelf and upper slope . Mixing intensity of bulk sediment and of organic matter are of comparable magnitude. The benthos of the lower slope and abyssal depth is dominated by the microb iota, both in terms of total biomass (> 90%) and carbon respiration (about 80%). The macrofauna (16%), meiofauna (4%) and megafauna (0.5%) only margin ally contribute to total carbon respiration at depths below 1400m. Because large animals have a lower share in total metabolism, mixing of organic mat ter within the sediments is reduced by a factor of 5, whereas mixing of bul k sediment is one to two orders of magnitude lower than on the shelf. The f ood quality of organic matter in the sediments in the shallowest part of th e Goban Spur transect is significantly higher than in sediments in the deep er parts. The residence time of mineralisable carbon is about 120 d on the shelf and compares well with the residence time of the biota. In the deepes t station, the mean residence time of mineralisable carbon is more than 300 0 d, an order of magnitude higher than that of biotic biomass. (C) 2001 Pub lished by Elsevier Science Ltd.