BIOSOPE: Biogeochemistry and Optics South Pacific Experiment

Objectives: The objectives of the BIOSOPE (Biogeochemistry Optics South Pacific Experiment) project was to study, during the austral summer, the biological, biogeochemical and bio-optical properties of different trophic regimes in the South East Pacific: the eutrophic zone associated with the upwelling regime of the chilean coast ; the mesotrophic area associated with the plume of the Marquises Islands in the HNLC (High Nutrient Low Chlorophyll) waters of this subequatorial area; and the extremely oligotrophic area associated with the central part of the South Pacific gyre which presents the interesting particularity of being far away from any desert dust (iron) source.

Implementation plan: The BIOSOPE cruise (October 21 – December 12, 2004) mainly relied on observations acquired along a ~8000 km transect from Marquises Islands towards the Chilean coast. 21 “short” stations (~8 hours each) have been investigated for the measurement of core biogeochemical parameters (stocks and fluxes) and of optical properties which are required for the calibration and validation of ocean color remote sensing data. An intensive sampling was also undertaken for the characterization of functional and taxonomic diversity (flow cytometry, microscopy, molecular biology) of the various studied systems. The detailed investigation of 6 “long” stations (2 to 6 days of occupation), located along the trophic gradient allowed to complete these observations by in situ measurements of primary production and of assimilation of various nutrients (N, P, Si), by sampling the particulate flux (drifting sediment traps) and finally by high frequency measurements of hydro-bio-optical characteristics, thus allowing the diurnal scale the functioning of the various systems at the diurnal to be studied. Detail of the various measurement undertaken can be found at : http://www.obs-vlfr.fr/proof/php/x_datalist.php?xxop=biosope