Transport and Mixing from Observed Tracer Fields Structuration by Mid-depth Zonal Jets in the Tropical Pacific Ocean.

Audrey Delpech1, Sophie E Cravatte2, Frederic Marin2, Yves Morel1, Claire Menesguen3 and Elodie Kestenare1, (1)Laboratoire d’Etudes Géophysiques et d’Océanographie Spatiale, LEGOS – UMR 5566 CNES-CNRS-IRD-UPS, Toulouse, France, (2)LEGOS, Université de Toulouse, (IRD, CNES, CNRS, UPS), Toulouse, France, (3)Laboratoire d'Océanographie Physique et Spatiales, LOPS – UMR 6523 Ifremer-CNRS-IRD-UBO, Brest, France
The circulation in the tropical regions is singular and quite different from the rest of the ocean. Below the thermocline and down to the sea floor, systems of alternating intense and narrow zonal jets are found at the basin scale. The origin and transport properties of these jets remain in many ways an open question; all the more crucial since their usual underestimation in ocean global circulation models has been identified as a potential bias for tracers budgets.
Thanks to a large dataset available in the tropical Pacific Ocean, this study investigates the potential role of the jets in shaping water mass properties across the basin. The correspondence between zonal velocity and different tracers (oxygen, salinity and potential vorticity), gathered from many cross-equatorial cruises sections, is analyzed. It is shown that the close equatorial jets advect oxygen rich waters from the western boundary and participate in the ventilation of the eastern tropical Pacific. In addition, unexpected alternating frontal and uniform regions of tracer properties, coinciding with eastward and westward jets respectively, are found below 1000 m, with a striking zonal and temporal coherence throughout the basin. These staircase profiles may reveal the presence of alternating regions of enhanced and inhibited isopycnal mixing at the jets scale, suggesting that the jets also contribute to the erosion of water masses.
The dynamics of the jets formation and maintenance is also investigated; it is shown from idealized numerical simulations how the intraseasonal variability, as propagating equatorial waves, can provide an energy source for the generation of such alternating zonal jets.