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

Type Article
Date 2020
Language English
Author(s) Bettencourt João H.1, Rossi Vincent2, Renault Lionel5, Haynes Peter3, Morel Yves1, Garçon Véronique4
Affiliation(s) 1 : LEGOS, University of Toulouse, CNES, CNRS, IRD, UPS, Toulouse 31400, France
2 : MIO (UM 110, UMR 7294), CNRS, Aix-Marseille Univ., Univ. Toulon, IRD, 13288, Marseille, France
3 : Department of Applied Mathematics and Theoretical Physics, University of Cambridge, England
Source Nonlinear Processes in Geophysics Discussions (2198-5634) (Copernicus GmbH), 2020 , Vol. 27 , N. 2 , P. 277–294
DOI 10.5194/npg-2019-47
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.

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Bettencourt João H., Rossi Vincent, Renault Lionel, Haynes Peter, Morel Yves, Garçon Véronique (2020). Effects of upwelling duration and phytoplankton growth regime on dissolved oxygen levels in an idealized Iberian Peninsula upwelling system. Nonlinear Processes in Geophysics Discussions, 27(2), 277–294. Publisher's official version : https://doi.org/10.5194/npg-2019-47 , Open Access version : https://archimer.ifremer.fr/doc/00516/62747/