A simple and rapid device for measuring planktonic primary production by in situ sampling, and 14C injection and incubation

A system (LET GO) is described that enables measurements of primary production at sea after #in situ incubation, with 14C being injected at depth immediately after enclosure of the sample. Each incubation cell, about 200 ml, is made of two transparent plexiglass cups facing each other. Mechanical energy to operate the system is provided by the tension of the nylon line between the drifting buoy, which holds the experimental equipment, and a weight at the bottom : when the line is strained, the two cups enclose the water sample, and the 14C is delivered by a syringe. Absence of metallic or rubber parts ensures that toxicity effects are minimized and that reliable results can be expected. Furthermore, #in situ incubations can start 1 or 2 min after arrival on station, leaving the research vessel and winches available for other tasks. These points make it possible to make #in situ$ 14C incubations during most oceanographic cruises and to increase greatly the acquisition rate of primary production data. The LET GO device has been tested in parallel with the conventional technique. Both techniques showed similar vertical patterns. Carbon fixation measured with the LET GO, however, was greater by a factor 1.3. (Résumé d'auteur

Indices biochimiques et milieux marins

La chlorophylle a est l'indice de la biomasse du phytoplancton le plus utilisé en océanographie. Cependant, sa relation avec la production primaire est encore mal connue, particulièrement en milieu océanique. Au cours d'une étude de 13 jours consécutifs en un point fixe situé à l'équateur dans le Golfe de Guinée, à 4°W, la synthèse de la chlorophylle est mesurée chaque jour en parallèle avec la fixation photosynthétique du carbone : les échantillons sont prélevés avant le lever du jour, tamisés sur filet de 200 um de vide de maille, et placés en incubation "in situ" du lever au coucher du soleil. Les teneurs maximales de chlorophylle sont toujours observées à 50 m. La quantité de chlorophylle par flacon augmente dans la journée de 150 à 200% entre 20 et 30 m, mais seulement de 40 à 50% à 50 m. Le rapport (carbone fixé)/(Chla accumulée) s'établit autour de 150 près de la surface, et entre 50 et 100 à 50 m. (D'après résumé d'auteur

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

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