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https://doi.org/10.5194/egusphere-2024-2548
https://doi.org/10.5194/egusphere-2024-2548
30 Aug 2024
 | 30 Aug 2024

Turbulent dissipation from AMAZOMIX off the Amazon shelf along internal tides paths

Fabius Kouogang, Ariane Koch-Larrouy, Jorge Magalhaes, Alex Costa da Silva, Daphne Kerhervé, Arnaud Bertrand, Evan Cervelli, Jean-François Ternon, Pierre Rousselot, James Lee, Marcelo Rollnic, and Moacyr Araujo

Abstract. The Amazon shelf-break is a key region of the ocean where strong internal tides (ITs) are generated, which may have a key role to play on both Climate and Ecosystem, via its vertical mixing. AMAZOMIX survey (2021) collected microstructure and hydrographic (ADCP/CTD-O2) profiles to quantify mixing, associated processes and their impact on marine ecosystems. Measurements are obtained over M2 tidal period (12 h) inside and outside of both the ITs generation sites and propagation beams, respectively at mode-1 distances (90 km and 210 km) from the shelf-break to evaluate the IT impact on mixing.

Hydrography analysis showed strong step-like characteristics (~20–40 m thick) and vertical displacements (20–60 m) triggered by ITs, as well as the signatures of high modes up to 5–6 on generation sites and IT pathways.

The results of the microstructure analysis coupled with those of the hydrography revealed important mixing associated with a competition of processes between the semidiurnal shear of ITs and the baroclinic shear of the mean current (BC). Closer to the generation sites, mixing is stronger within [10-6,10-4] W.kg-1, with a greater contribution (~65 %) from ITs shear than BC shear. It is reduced but nevertheless considerable between [10-8, 10-6] W.kg-1 along the IT pathways, owing to equal contributions from ITs and BC shear. At a distance of ~225 km, mixing was still higher within [10-7,10-6] W.kg-1 because of the increased contribution (~65 %) of ITs shear, where IT beams may intersect and interact with background circulation. Mixing in no-tidal fields was fairly minimal ([10-8,10-7] W.kg-1), owing to a minor contribution (~50.4 %) of BC shear from the North Brazil Current.

Finally, the nutrient flux estimations showed that ITs mixing could reach the surface (by a large tidal diffusivity of [10-4,10-1] m-2.s-1). This resulted in high vertical fluxes of nitrate ([10-2, 10-0] mmol N m-2.s-1) and phosphate ([10-3, 10-1] mmol P m-2.s-1), which can stimulate chlorophyll production, biodiversity and cool surface water, so influencing the whole ecosystem and climate in this river-ocean continuum region. This study provides a guide for the mixing parameterization in future numerical simulation (e.g., in physical-biogeochemical coupled models) in the Amazon region in order to include the impact of the IT turbulence on the whole ecosystem (i.e., from physics to biological production).

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Fabius Kouogang, Ariane Koch-Larrouy, Jorge Magalhaes, Alex Costa da Silva, Daphne Kerhervé, Arnaud Bertrand, Evan Cervelli, Jean-François Ternon, Pierre Rousselot, James Lee, Marcelo Rollnic, and Moacyr Araujo

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2548', Anonymous Referee #1, 10 Sep 2024
  • RC2: 'Comment on egusphere-2024-2548', Anonymous Referee #2, 28 Oct 2024
  • RC3: 'Comment on egusphere-2024-2548', Anonymous Referee #3, 14 Nov 2024
Fabius Kouogang, Ariane Koch-Larrouy, Jorge Magalhaes, Alex Costa da Silva, Daphne Kerhervé, Arnaud Bertrand, Evan Cervelli, Jean-François Ternon, Pierre Rousselot, James Lee, Marcelo Rollnic, and Moacyr Araujo
Fabius Kouogang, Ariane Koch-Larrouy, Jorge Magalhaes, Alex Costa da Silva, Daphne Kerhervé, Arnaud Bertrand, Evan Cervelli, Jean-François Ternon, Pierre Rousselot, James Lee, Marcelo Rollnic, and Moacyr Araujo

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Short summary
The first time direct measurements of turbulent dissipation from AMAZOMIX revealed high energy dissipations within [10-6,10-4] W.kg-1 caused at 65 % apart from internal tides in their generation zone, and [10-8,10-7] W.kg-1 caused at 50.4 % by mean circulation of surrounding water masses far fields. Finally, estimates of nutrient fluxes showed a very high flux of nitrate ([10-2, 10-0] mmol N m-2.s-1) and phosphate ([10-3, 10-1] mmol P m-2.s-1), due to both processes in Amazon region.