Benthic response to the sedimentation of particulate organic matter at the BIOTRANS station, 47°N, 20°W

Abstract

The benthic response to the sedimentation of particulate organic matter (POM) was investigated during 1985–1990 at 47°N, 20°W (BIOTRANS station). The first noticeable annual sedimentation of phytodetritus, as indicated by chlorophyll a concentrations in the sediment, occurred as early as late April-early May. Maximum amounts were found in June–July. Two different sedimentation pulses to the sea bed are described that demonstrate interannual variation: the occurrence of salp faecal pellets early in the year 1988 and the massive fall out of a plankton bloom in summer 1986, which deposited approximately 15 mmol C m−2. The benthic reaction to POM pulses was quite diverse. The mega-, macro- and meiobenthos showed no change in biomass, whereas bacterial biomass doubled between March and July. This corresponds to a seasonal maximum of total adenylate biomass. The relative abundance of Foraminifera among the meiobenthos increased during the summer. Benthic activity (ATP, ratio ATP/ETSA), as well as in situ sediment community oxygen consumption rates (SCOC), showed distinct seasonal maxima in July–August of 0.75 mmol C m−2 day−1. Based on SCOC and the carbon demand for growth, a benthic carbon consumption of 0.94 mmol C m−2 day−1 was estimated. This represents about 1.1% of spring bloom primary production and 9.6% of the export flux beneath the 150 m layer, measured during the North Atlantic Bloom Experiment. Bacteria and protozoans colonizing the epibenthic phytodetrital layer were responsible for 60–80% of the seasonal increase in SCOC. The strong reaction of the smaller benthic size groups (bacteria, protozoans) to POM pulses stresses their particular importance for sediment-water interface flux rates.