From large to submesoscale circulation during the OUTPACE cruise (Southwest Pacific)

International audience; The circulation within the Southwest Pacific Ocean is today well established from a climatological point of view. The northern branch of the anticyclonic South Pacific gyre creates the South Equatorial current, a major westward current controlling the circulation in the Southwest Pacific. The complex topography as well as the barotropic instabilites cause intense mesoscale activity that is well observed with satellites but strongly undersampled with in situ observations. The ocean dynamics at mesoscale can have an important impact on the ecosystem of this oligotrophic region, and in particular on the development of species involved in the biological carbon pump. We use the in situ dataset of the OUTPACE cruise (ADCP, TSG, SVP data) to validate satellite data (altimetry, Sea Surface Temperature, Chlorophyll-a concentration) that allow to characterize the overall conditions during the cruise. In particular we used specifically designed high resolution (1/8) regional altimetric product (summing Absolute Geostrophic currents and Ekman currents) produced by CLS (with support from CNES) to study the circulation at different scale : large, mesoscale and submesoscale. Lagrangian numerical experiments performed with this altimetric product allow us to identify the general surface circulation. Mesoscale activity is examined through structure identification to determine its influence on the water masses encountered during the cruise. Finally the computation of Finite Size Lyapunov Exponents (FSLE), a Lagrangian diagnostic that identify frontal areas, allow to quantify the impact of these structure on the surface distribution of biogeochemistry quantities (temperature, salinity, chlorophyll..). Our results show that despite the strong mesoscale activity in this area, the meso- and submesoscale structures had a small, but non-negligable, influence on the water masses sampled during the cruise. Meso- and submesoscale participate in the surface distribution of tracers such as SST, SSS or chlorophyll-a but also of some micro-organismes such as bacteria or Prochlocorococcus.