Size distribution and abundance of phytoplankton in the Pacific Equatorial upwelling

In January 1991, the Equatorial Pacific enrichment area covered a belt more than 11000 km long, with surface nitrate concentration ... near the Galapagos Islands, decreasing westwards and desappearing beyond 167°E. In this area, the amount of chlorophyll a (Chla) did not change significantly from one end of the upwelling to the other, and was very low everywhere ... Schematically, in spite of the typical longitudinal gradients of temperature and nutrients, all data of chlorophyll, size distribution and cell numbers clearly indicate that an extreme monotony characterizes the distribution of phytoplankton all along the enrichment area due to the Equatorial upwelling, covering 11 million km2 for mean upwelling conditions. (D'après résumé d'auteur

Actes du colloque Tour du Monde Jean Charcot

La biomasse des organismes inférieurs à 35 microns a été évaluée dans les eaux oligotrophes du bassin nord fidjien (océan Pacifique sud-ouest) en septembre-octobre 1985 (croisière Proligo). Cette biomasse a été évaluée de deux façons; d'une part globalement à partir de mesures d'ATP pour la biomasse totale, et de mesures chl#a$ pour la biomasse des autotrophes; d'autre part à partir de comptages en épifluorescence et après coloration pour évaluer l'importance des différents taxons : eubactéries, cyanobactéries, hétéroflagellés et ciliés hétérotrophe

Effect of El Nino southern oscillation events on the distribution and abundance of phytoplankton in the Western Pacific Tropical Ocean along 165°E

The distribution of physical and chemical parameters and their impact on the biomass and abundance of phytoplankton in the Western Pacific ocean were compared in two opposing situations : the El Nino Southern Oscillation (ENSO) event of 1987 and the no-ENSO period of 1988. During El Nino conditions (september 1987), maximum cell abundance was recorded at 10°S at the boundary between the South Equatorial current (SEC) and the South Equatorial countercurrent (SECC). In September 1988, after the return of non-ENSO conditions, a well-established Equatorial upwelling produced an increase in the surface layer nutrient supply over 7° of latitude. This in turn caused an increase in phytoplankton populations in the upper layer, with chlorophyll concentrations ... Integrated over 120 m, the cyanobacteria and microalgae populations were respectively 4.7. and 3.2 times larger than the year before. On the other hand, transient nutrients inputs such as those observed at 10°S in September 1987 caused a large increase in cyanobacteria populations (4.4. times) compared with those in neighbouring zones, and a somewhat smaller increase in microalgae populations (1.3 times

Zooplankton of Tikehau atoll (Tuamotu archipelago) and its relationship to particulate matter

The standing stock and taxonomic composition of zooplankton (> 200 microns) were monitored in the lagoon of Tikehau atoll from April 1985 to April 1986. These data were supplemented by two 10 d studies on the variability, structure and functioning of the pelagic ecosystem. The biomass of animals > 2000 comprised 50% of the total biomass of all organisms from 35 to >2000 microns. The zooplankton populations were characterized by successive blooms of copepods, larvaceans, pteropods and salps, probably arising from the periodic input of detritus from the reef during windy period. As a result, the ecosystem was not in a steady state and the data for the fluxes of organic matter are presented separately for april 1985 and april 1986. Using the C:N:P ratio method, net growth efficiencies, K2, were calculated for total mezoplankton, mixed copepods, and two planktonic species, #Undinula vulgaris$ and #Thalia democratica

Proceedings of the international colloquium photosynthesis and remote sensing

The in vivo specific absorption coefficient of phytoplankton a*ph (lambda) was measured along an equatorial transect in the Pacific Ocean during the JGOFS-cruise in Octobre 1994 in order to validate bio-optical models of primary production. The fiber filter technique was used on board, as well as spectrofluorometry for pigment determination and flow cytometry for cells counting. The a*ph (435-441 nm) walues strongly decreased from oligotrophic to mesotrophic waters (between 170°E and 153°W). This zonal variation reflected a change in phytoplankton composition, dominated by #Prochlorococcus$ in the oligotrophic zone and by picoeucaryotes in the mesotrophic one. Such variations in a*ph have to be taken into account for estimating primary production of the equatorial Pacific Ocean from ocean colour imagery. (Résumé d'auteur