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

The impact of terrigeneous inputs on the Bay of Ouinne (New Caledonia) phytoplankton communities : a spectrofluorometric and microscopic approach

The impact of terrigeneous inputs on the phytoplankton composition was studied during a 2.5 months daily survey in the Bay of Ouinne, a deep cove on the south-eastern coast of New Caledonia. Surface waters benefited from nutrients originating from nearby land drainage and the Ouinne river outflow during periods of heavy rain. The nutrient composition mirrored the composition of the drained soils, with concentrations reaching 3-4 mu M for nitrate and 0.13 mu M for phosphate at the river mouth. In addition to nutrient inputs, significant quantities of particulate matter (inorganic and organic compounds) were discharged into the lagoon during heavy rain periods, resulting in transitory decreases of the photic layer depth and enrichments of the water column through remineralization processes. Changes in contributions of the main phytoplankton groups in response to terrigeneous inputs were shown by chlorophyll and phycobiliprotein spectrofluorometric analyses. While dry periods were marked by the dominance of pico-(Prochlorococcus, and high-phycourobilin (PUB) Synechococcus) and microcyanobacteria (Trichodesmium spp.), developments of various eukaryote populations resulted from land drainage occurring during the wet periods. This was indicated by the increase of accessory chlorophyll pigments that doubled at a depth of 15 m: chlorophyll b (chlorophytes), chlorophyll c(1) + c(2) (associated with diatoms and dinoflagellates), chlorophyll c(3) (associated with c(1) and/or c(2) in prymnesiophytes, chrysophytes and/or pelagophytes). In addition, Synechococcus with a high phycoerythrobilin (PEB) content also appeared to be stimulated by river outputs. Finally, microscopic observations of the > 35 mu m net plankton confirmed the greater presence of diatoms and dinoflagellates during periods of rain compared to Trichodesmium, particularly in the surface layer. (c) 2005 Elsevier Ltd. All rights reserved

Programme PROPPAC : hydrologie, nutrients, chlorophylle et zooplancton des campagnes SURTROPAC 07 à 13 (1987-1989)

Ce recueil présente les données de sels nutritifs, oxygène dissous, chlorophylle et zooplancton obtenues deux fois par an lors de la radiale SURTROPAC, de 20°S à 10°N le long 165°E. Les campagnes couvrent la période comprise entre janvier 1987 (SURTROPAC 07) et décembre 1989 (SURTROPAC 13). Les données sont présentées sous forme de coupes 20°S - 10°N et sous forme de tableaux. (Résumé d'auteur