SEASONAL SEDIMENTATION OF AUTOCHTHONOUS MATERIAL FROM THE EUPHOTIC ZONE OF A COASTAL SYSTEM

The seasonal sedimentation of particulate matter across the pycnocline was recorded in the Kattegat during the period of stratification (Mar ch-October 1989). The proportion of viable phytoplankton cells of the total carbon flux (63 g C m(-2)) was low (18%). Faecal pellets contrib uted on average less than 5%. The major component of the sinking matte r consisted of detrital material (amorphous particles with few recogni zable components) which was estimated mainly to originate from the act ivity of microzooplankton. The average C/N ratio of the particulate bi ogenic matter trapped at the pycnocline was 8.6, but only 6.4 for the suspended particulate organic matter in the mixed layer indicating tha t nitrogen is more effectively recycled than carbon in the euphotic zo ne. This mechanism allows for an additional new organic carbon product ion of 33% compared to that which can be estimated from the external l oading of nitrogen. Over the entire period the average daily vertical flux of carbon corresponded to 14% of the phytoplankton biomass indica ting a high efficiency in the transport of organic material from the e uphotic zone to the bottom. (C) 1995 Academic Press Limited