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

Barbot, Simon; Petrenko, Anne; Maes, Christophe

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 inline-formulam depth, within the central and western South Pacific Ocean (around 19inline-formula S, 156inline-formula E–150inline-formula W) are described. In the Coral Sea, we highlight minima in dissolved oxygen of 140 inline-formulaµmol 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 inline-formulakm 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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Barbot, Simon / Petrenko, Anne / Maes, Christophe: Intermediate water flows in the western South Pacific: as revealed by individual Argo floats trajectories and a model re-analysis. 2018. Copernicus Publications.

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