Satellite observations of chlorophyll, phytoplankton biomass, and Ekman pumping in nonlinear mesoscale eddies

Authors

  • P. Gaube,

    Corresponding author
    1. College of Earth Ocean and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, USA
    2. Now at Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
    • Corresponding author: P. Gaube, Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institute, Mail Stop 9, Woods Hole, MA 02543, USA. (pgaube@whoi.edu)

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  • D. B. Chelton,

    1. College of Earth Ocean and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, USA
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  • P. G. Strutton,

    1. Institute for Marine and Antarctic Studies and Australian Research Council, Center of Excellence for Climate System Science University of Tasmania, Hobart, Tasmania, Australia
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  • M. J. Behrenfeld

    1. Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, USA
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Abstract

[1] Nonlinear mesoscale eddies can influence biogeochemical cycles in the upper ocean through vertical and horizontal advection of nutrients and marine organisms. The relative importance of these two processes depends on the polarity of an eddy (cyclones versus anticyclones) and the initial biological conditions of the fluid trapped in the core of the eddy at the time of formation. Eddies originating in the eastern South Indian Ocean are unique in that anticyclones, typically associated with downwelling, contain elevated levels of chlorophyll-a, enhanced primary production and phytoplankton communities generally associated with nutrient-replete environments. From analysis of 9 years of concurrent satellite measurements of sea surface height, chlorophyll, phytoplankton carbon, and surface stress, we present observations that suggest eddy-induced Ekman upwelling as a mechanism that is at least partly responsible for sustaining positive phytoplankton anomalies in anticyclones of the South Indian Ocean. The biological response to this eddy-induced Ekman upwelling is evident only during the Austral winter. During the Austral summer, the biological response to eddy-induced Ekman pumping occurs deep in the euphotic zone, beyond the reach of satellite observations of ocean color.

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