Winter distribution of algal pigments in small- and large-size particles in the northeastern Atlantic

Particles were collected by filtration on GF/F filters and by vertical hauls of 50 μm mesh-sized net throughout the water column (50–1700 m) in the northeastern Atlantic in January 1989 during the Medatlante t cruise, in the framework of the French JGOFS program. Particles were analysed for their organic carbon and algal chlorophyll and carotenoid pigments by high-performance liquid chromatography coupled with UV absorbance and fluorescence detection. Complementary analyses were performed on a surface sample for sterols and fatty acids by gas chromatography and gas chromatography/mass spectrometry. Organic carbon concentrations were 2–3 orders of magnitude higher in GF/F (10–50 μg l−1) than in net particles (0.01−0.06μg l−1). The same ratio was encountered for pigments: 4–603 ng l−1 and 0.003−0.037 ng l1¯, respectively. Among 11 GF/F samples collected between 500 and 1700 m, four samples contained pigments in detectable amounts (4–106 ng l−1). Their pigment distribution pattern was close to deep GF/F samples, but differed from the pigment pattern of deep net-collected particles, mainly composed of fecal pellets. This latter sinking material was enriched in chlorophyll degradation pigments and showed higher values of the ratio (sum of carotenoids)/(sum of chlorophylls) than those observed in small-size particles. The combined information from pigments, sterols and fatty acids shows that Prymnesiophytes in a post bloom situation contributed to a major part of the surface autotrophs. Two processes of rapid transfer of organic matter between the surface and the deep Mediterranean water are discussed: fecal pellets of herbivorous plankton and sedimentation of aggregates partly linked to the presence of Prymnesiophytes.