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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 13
Biogeosciences, 15, 4103-4124, 2018
https://doi.org/10.5194/bg-15-4103-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue: Interactions between planktonic organisms and biogeochemical...

Biogeosciences, 15, 4103-4124, 2018
https://doi.org/10.5194/bg-15-4103-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Jul 2018

Research article | 05 Jul 2018

Intermediate water flows in the western South Pacific: as revealed by individual Argo floats trajectories and a model re-analysis

Simon Barbot1, Anne Petrenko1, and Christophe Maes2 Simon Barbot et al.
  • 1Aix Marseille Université, CNRS/INSU, IRD, Université du Sud Toulon-Var, Mediterranean Institute of Oceanography (MIO), UM 110, 13288 Marseille, France
  • 2Laboratoire d'Océanographie Physique et Spatiale (LOPS), CNRS, Ifremer, IRD, UBO, Brest, France

Abstract. Thanks to the autonomous Argo floats of the OUTPACE cruise (Oligotrophy to UlTra-oligotrophy PACific Experiment) and of the THOT (TaHitian Ocean Time series) project, some features of intermediate-flow dynamics, at around 1000 m depth, within the central and western South Pacific Ocean (around 19° S, 156° E–150° W) are described. In the Coral Sea, we highlight minima in dissolved oxygen of 140 µmol kg−1 that are associated with the signature of a southward transport of waters between two zonal jets: from the North Vanuatu Jet to the North Caledonia Jet. This transport takes place in the core of a cyclonic eddy or via the path between a cyclonic eddy and an anticyclonic one, highlighting the importance of mesoscale dynamics in upper thermocline and surface layers. Further east, we observe a strong meridional velocity shear with long-term float trajectories going either eastward or westward in the lower thermocline. More interestingly, these trajectories also exhibit some oscillatory features. Those trajectories can be explained by a single Rossby wave of 160-day duration and 855 km wavelength. Considering the thermohaline context, we confirm the meridional shear of zonal velocity and highlight a permanent density front that corresponds to the interface between Antarctic intermediate waters and North Pacific deep waters. Hence both circulation and thermohaline contexts are highly prone to instabilities and wave propagation.

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In the context of the OUTPACE cruise and THOT project in the western South Pacific Ocean, we use individual float trajectories in order to understand the intermediate-flow dynamics, from 300 to 1000 m depth. We highlight two main features: exchanges of water between parallel jets entering the Coral Sea through eddies and intermediate-wave influence of the currents in the frontal area connecting the Antarctic intermediate water (AAIW) and North Pacific deep water (NPDW) masses.
In the context of the OUTPACE cruise and THOT project in the western South Pacific Ocean, we use...
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