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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/npg-2019-47
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/npg-2019-47
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 18 Sep 2019

Submitted as: research article | 18 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Nonlinear Processes in Geophysics (NPG).

Effects of upwelling duration and phytoplankton growth regime on dissolved oxygen levels in an idealized Iberian Peninsula upwelling system

João H. Bettencourt1, Vincent Rossi2, Lionel Renault1, Peter Haynes3, Yves Morel1, and Véronique Garçon1 João H. Bettencourt et al.
  • 1LEGOS, University of Toulouse, CNES, CNRS, IRD, UPS, Toulouse 31400, France
  • 2MIO (UM 110, UMR 7294), CNRS, Aix-Marseille Univ., Univ. Toulon, IRD, 13288, Marseille, France
  • 3Department of Applied Mathematics and Theoretical Physics, University of Cambridge, England

Abstract. We apply a coupled modelling system composed of a state-of-the-art hydrodynamical model and a low complexity biogeochemical model to an idealized Iberian Peninsula upwelling system to identify the main drivers of dissolved oxygen variability and to study its response to changes in the duration of the upwelling season and in phytoplankton growth regime. We find that the export of oxygenated waters by upwelling front turbulence is a major sink for nearshore dissolved oxygen. In our simulations of summer upwelling, when phytoplankton population is generally dominated by diatoms whose growth is largely enhanced by nutrient input, net primary production and air-sea exchange compensate dissolved oxygen depletion by offshore export over the shelf. A shorter upwelling duration causes relaxation of upwelling winds and a decrease in offshore export, resulting in a slight increase of net dissolved oxygen enrichment in the coastal region as compared to longer upwelling durations. When phytoplankton is dominated by groups less sensitive to nutrient inputs, growth rates decrease and the coastal region becomes net heterotrophic. Together with the physical sink, this lowers the net oxygenation rate of coastal waters, that remains positive only because of air-sea exchanges. These findings help disentangling the physical and biogeochemical controls of dissolved oxygen in upwelling systems and, together with projections of increased duration of upwelling seasons and phytoplankton community changes, suggest that the Iberian coastal upwelling region may become more vulnerable to hypoxia and deoxygenation.

João H. Bettencourt et al.
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João H. Bettencourt et al.
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Short summary
We used a oxygen model and an hydrodynamic model of the Iberian upwelling to study the interplay between upwelling wind duration and phytoplankton growth and its impact on oxygen levels. When wind duration increases, marine currents remove oxygen from the coast, that is replenished by a fast phytoplankton growth. When phytoplankton growth is slow, the oxygen removal dominates and the coastal region looses oxygen. This can increase the future risk of upwelling regions becoming oxygen poor.
We used a oxygen model and an hydrodynamic model of the Iberian upwelling to study the interplay...
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