HYDROLYTIC ENZYMATIC-ACTIVITY IN DEEP-SEA SEDIMENTS

Hydrolytic activities of five enzymes were measured in deep-sea sediment cores at three stations under in situ temperature and pressure in the NE-Atlantic in March/April and July/August 1992. Generally, activity profiles declined vertically in the upper 10 cm of the cores. Experiments under in situ pressure were not significantly different from measurements under surface conditions. The ranking of potential activity rates in the top sediment horizon was: aminopeptidase > esterase > chitobiase > beta-glucosidase > alpha-glucosidase with ratios of 687/174/11/3/1. This is similar to ratios obtained in marine aggregates from the upper mixed layer, thus supporting the idea of pelagic-benthic coupling in the open ocean. The vertical activity profiles show that the biochemical composition, and thereby the nutritive quality of the degradable material, changed with depth in the sediment cores. About 518 mg carbon was potentially mobilized in the 0-1 cm sediment horizon per square meter per day. This contrasts with the input of particulate organic carbon to the sea floor in this area of only 2.74 mg C m(2) d(-1), determined by sediment traps, which indicates that the deep-sea benthic community can rapidly utilize sedimenting particulate organic material and highlights the importance of extracellular enzyme activity in the sediment biogeochemical loop.