Material supply to the European continental slope: A budget based on benthic oxygen demand and organic supply

Two sites were selected adjacent to the Northeast Atlantic continental shelf to examine material supply to and loss from the benthos. At both a bathyal mid-slope (2000 m water depth) and an abyssal (4800 m water depth) site an in situ technique was used to measure sediment community oxygen consumption. At the mid-slope site a sediment trap mooring provided a measure of the annual vertical flux of material, whereas at the abyssal site, vertical Bur was deduced from data obtained nearby. At the mid-slope site, vertical flux was similar to values determined elsewhere in the mesotrophic Northeast Atlantic, but oxygen demand was somewhat higher than values reported for other comparable regions. Vertical Aux was, however, sufficient to fuel only 20% of the benthic oxygen demand. A strong seasonal signal was seen from time lapse photographs of the seabed in terms of the quantity of phytodetritus lying on it, but no significant seasonal variation in oxygen consumption was detected. Similarly, on fine spatial scales (between cores) the existence of a detrital layer appeared to have no effect on oxygen demand. It is concluded that substantial quantities of material are transported down slope to this mid-slope region, to provide the organic carbon required by the sediment and that this may be assumed to be the case for the entire particulate pool, including the inorganic fraction. In contrast to the bathyal station, at the deep site on the Porcupine Abyssal Plain, the organic carbon required to fuel benthic oxygen demand was similar to the estimated vertical supply.