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Large- to submesoscale surface circulation and its implications on biogeochemical/biological horizontal distributions during the OUTPACE cruise (southwest Pacific)

By Louise Rousselet, Alain DE VERNEIL, Andrea DOGLIOLI, Anne PETRENKO, Solange Duhamel, Christophe Maes and Bruno Blanke

Abstract

International audienceThe patterns of the large-scale, meso-and sub-mesoscale surface circulation on biogeochemical and biological distributions are examined in the western tropical South Pacific (WTSP) in the context of the OUTPACE cruise (February-April 2015). Multidisciplinary original in situ observations were achieved along a zonal transect through the WTSP and their analysis was coupled with satellite data. The use of Lagrangian diagnostics allows for the identification of water mass pathways, mesoscale structures, and submesoscale features such as fronts. In particular, we confirmed the existence of a global wind-driven southward circulation of surface waters in the entire WTSP, using a new high-resolution altimetry-derived product, validated by in situ drifters, that includes cyclogeostrophy and Ekman components with geostrophy. The mesoscale activity is shown to be responsible for counter-intuitive water mass trajecto-ries in two subregions: (i) the Coral Sea, with surface exchanges between the North Vanuatu Jet and the North Cale-donian Jet, and (ii) around 170 • W, with an eastward pathway , whereas a westward general direction dominates. Fronts and small-scale features, detected with finite-size Lyapunov exponents (FSLEs), are correlated with 25 % of surface tracer gradients, which reveals the significance of such structures in the generation of submesoscale surface gradients. Additionally , two high-frequency sampling transects of biogeochem-ical parameters and microorganism abundances demonstrate the influence of fronts in controlling the spatial distribution of bacteria and phytoplankton, and as a consequence the microbial community structure. All circulation scales play an important role that has to be taken into account not only when analysing the data from OUTPACE but also, more generally, for understanding the global distribution of biogeochemical components

Topics: [SDE]Environmental Sciences
Publisher: 'Copernicus GmbH'
Year: 2018
DOI identifier: 10.5194/bg-15-2411-2018
OAI identifier: oai:HAL:hal-02024259v1
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