Benthic-pelagic coupling in the oligotrophic Cretan sea

During the EU-MAST2 project CINCS (pelagic-benthic Coupling IN the oligotro phic Cretan Sea), sediment community oxygen consumption (SCOC) was measured during the winter and summer of 1995. Satellite CZCS images showed a diffe rent phytoplankton biomass in the surface water during these two periods. S COC was measured in-situ with a benthic lander at depths ranging from 40 to about 1600 m. In conjunction to the SCOC measurements, microbial biomass a nd chlorophyll content of the surface layer of the sediment were also deter mined. SCOC, microbial biomass and the chlorophyll concentration displayed similar spatial and temporal trends, i.e. a steady decrease with increasing water depth in both seasons, with lower values occuring below 40 m depth d uring the summer. In winter SCOC ranged from 438 mu mol m(-2) h(-1) at 40 m depth to 37 mu mol m(-2) h(-1) at 1570 m which is equivalent to carbon min eralisation varying from 107 to 9 mg C m(-2) d(-1), respectively. SCOC valu es in the summer were about half the winter values except at the 40 m stati on where the opposite was found. Shortterm deployments of a sediment trap 4 m above the sea floor showed diminished vertical fluxes of phytodetritus w ere lower in summer at all stations including 40 m depth. It is argued, par tially on the basis of oxygen microprofiles, that the enhanced sedimentary concentration and decreased vertical flux of chlorophyll in summer at 40 m are primarily caused by benthic primary production. The results from the ot her stations shaw that in an highly oligotrophic sea such as the Cretan Sea , pelagic-benthic coupling exists although the amplitude of the seasonal si gnal is small. Moreover, the bathymetric trends in benthic microbial biomas s and SCOC indicate that there is no substantial horizontal transport of la bile organic material down the slope. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.