WINTER DISTRIBUTION OF ALGAL PIGMENTS IN SMALL-SIZE AND LARGE-SIZE PARTICLES IN THE NORTHEASTERN ATLANTIC

Particles were collected by filtration on GF/F filters and by vertical hauls of 50 mu m mesh-sized net throughout the water column (50-1700 m) in the northeastern Atlantic in January 1989 during the Medatlante I cruise, in the framework of the French JGOFS program. Particles were analysed for their organic carbon and algal chlorophyll and carotenoi d pigments by highperformance liquid chromatography coupled with UV ab sorbance and fluorescence detection. Complementary analyses were perfo rmed on a surface sample for sterols and fatty acids by gas chromatogr aphy and gas chromatography/mass spectrometry. Organic carbon concentr ations were 2-3 orders of magnitude higher in GF/F (10-50 mu g l(-1)) than in net particles (0.01-0.06 mu g l(-1)). The same ratio was encou ntered for pigments: 4-603 ng l(-1) and 0.003-0.037 ng l(-1), respecti vely. Among 11 GF/F samples collected between 500 and 1700 m, four sam ples contained pigments in detectable amounts (4-106 ng l(-1)). Their pigment distribution pattern was close to deep GF/F samples, but diffe red from the pigment pattern of deep net-collected particles, mainly c omposed of fecal pellets. This latter sinking material was enriched in chlorophyll degradation pigments and showed higher values of the rati o (sum of carotenoids)/(sum of chlorophylis) than those observed in sm all-size particles. The combined information from pigments, sterols an d fatty acids shows that Prymnesiophytes in a post bloom situation con tributed to a major part of the surface autotrophs. Two processes of r apid transfer of organic matter between the surf ace and the deep Medi terranean water are discussed: fecal pellets of herbivorous plankton a nd sedimentation of aggregates partly linked to the presence of Prymne siophytes.