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Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 11, 6389-6400, 2014
https://doi.org/10.5194/bg-11-6389-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
26 Nov 2014
Wind-induced upwelling in the Kerguelen Plateau region
S. T. Gille1, M. M. Carranza1, R. Cambra*,2, and R. Morrow2 1Scripps Institution of Oceanography, University of California, San Diego, USA
2Laboratoire d'Etudes en Géophysique et Océanographie Spatiale, Observatoire Midi-Pyrénées, 31400 Toulouse, France
*now at: Laboratoire Atmosphères, Milieux, Observations Spatiales, Institute Pierre-Simon Laplace, Paris, France
Abstract. In contrast to most of the Southern Ocean, the Kerguelen Plateau supports an unusually strong spring chlorophyll (Chl a) bloom, likely because the euphotic zone in the region is supplied with higher iron concentrations. This study uses satellite wind, sea surface temperature (SST), and ocean color data to explore the impact of wind-driven processes on upwelling of cold (presumably iron-rich) water to the euphotic zone. Results show that, in the Kerguelen region, cold SSTs correlate with high wind speeds, implying that wind-mixing leads to enhanced vertical mixing. Cold SSTs also correlate with negative wind-stress curl, implying that Ekman pumping can further enhance upwelling. In the moderate to high eddy kinetic energy (EKE) regions surrounding Kerguelen, we find evidence of coupling between winds and SST gradients associated with mesoscale eddies, which can locally modulate the wind-stress curl. This coupling introduces persistent wind-stress curl patterns and Ekman pumping around these long-lived eddies, which may modulate the evolution of Chl a in the downstream plume far offshore. Close to the plateau, this eddy coupling breaks down. Kerguelen has a significant wind shadow on its downwind side, which changes position depending on the prevailing wind and which generates a wind-stress curl dipole that shifts location depending on wind direction. This leads to locally enhanced Ekman pumping for a few hundred kilometers downstream from the Kerguelen Plateau; Chl a values tend to be more elevated in places where wind-stress curl induces Ekman upwelling than in locations of downwelling, although the estimated upwelling rates are too small for this relationship to derive from direct effects on upward iron supply, and thus other processes, which remain to be determined, must also be involved in the establishment of these correlations. During the October and November (2011) KErguelen Ocean and Plateau compared Study (KEOPS-2) field program, wind conditions were fairly typical for the region, with enhanced Ekman upwelling expected to the north of the Kerguelen Islands.

Citation: Gille, S. T., Carranza, M. M., Cambra, R., and Morrow, R.: Wind-induced upwelling in the Kerguelen Plateau region, Biogeosciences, 11, 6389-6400, https://doi.org/10.5194/bg-11-6389-2014, 2014.
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Short summary
The Kerguelen Plateau supports a strong spring chlorophyll bloom, in contrast with most of the Southern Ocean. Throughout the Southern Ocean, including in the Kerguelen area, wind can determine oceanic vertical velocities that may bring nutrients to the surface and contribute to the development of blooms. The Kerguelen Island itself generates a wind shadow that locally enhances upwelling velocities to the north of the main axis of the winds, and chlorophyll is high in this upwelling region.
The Kerguelen Plateau supports a strong spring chlorophyll bloom, in contrast with most of the...
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