High-resolution Bio-Argo and Argo Measurements to Reveal Specific Oceanic Processes.
Antoine Poteau, Sorbonne Universités, UPMC Univ Paris 06, INSU-CNRS, Laboratoire d'Océanographie de Villefranche, Villefranche-sur-mer, France, Herve Claustre, Laboratoire d'Océanographie de Villefranche CNRS/UPMC, Villefranche sur Mer, France, Nathan Briggs, Sorbonne Universités, UPMC Univ Paris 06, INSU-CNRS, Laboratoire d'Océanographie de Villefranche, Villefranche sur mer, France, Fabrizio D'Ortenzio, Observatoire Océanologique de Villefranche, Villefranche Sur Mer, France, Catherine Schmechtig, OSU Ecce Terra, UMS 3455, CNRS and Université Pierre et Marie Curie, Paris 6, 4 place Jussieu 75252, Paris, France, Louis M Prieur, Sorbonne Universités, UPMC Univ Paris 06, INSU-CNRS, Laboratoire d'Océanographie de Villefranche, 181 Chemin du Lazaret, 06230, Villefranche-sur-mer, France and Emmanuel Boss, University of Maine, Orono, ME, United States
Abstract:
Together with temperature and salinity measurements, Bio-Argo profiling floats now measure a significant range of biogeochemical (e.g. O2, NO3) and bio-optical variables (Chla, backscattering coefficient and radiometry). To transmit the very large amount of data acquired by this new generation of floats, it was required to substitute the Argos telemetry (Argo program) with iridium telemetry. The obvious consequence is not only a much greater flexibly on data transmission but also on data acquisition thanks to the two-way communication allowed by iridium. Our group has now deployed and managed over 100 Bio-Argo floats of this type. In particular we have set up high-resolution mode of acquisition for certain periods of time or for dedicated portions of the water column. Here we illustrate with three examples the potential of conducting high-resolution measurement to identify and explore certain oceanic processes.
(1) High resolution measurements of pressure, temperature and salinity (every 2 s) when the float is finishing its ascent (without any pump action) in the upper 10 m layer are analyzed with respect to sea state. We particularly focus on the study of the speed anomaly as compared to a nominal speed expected for a calm sea state. By comparison between speed anomaly of a float in the Mediterranean Sea and concurrent sea state measurements by a weather buoy in the same area, we suggest that float behaviour can be an indicator of sea state.
(2) Each year, in response to springtime phytoplankton blooms, the resolution of bio-optical variables (backscattering and Chla) in the top 1000 m was increased to at least 1 m (every 10 s) for all floats in the North Atlantic and Southern Ocean. This resolution allowed accurate estimation of the concentration of large phytoplankton aggregates and revealed systematic differences in bulk aggregate sinking rate between ocean basins.
(3) Finally we continuously record all the variables at a 10 min resolution during the float drift at 1000m. This allows us to characterize some events at this depth that can be related to bottom currents, high mixing or massive export of aggregates.
