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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 5, issue 2
Biogeosciences, 5, 495-507, 2008
https://doi.org/10.5194/bg-5-495-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Biogeochemistry and Optics South Pacific Experiment...

Biogeosciences, 5, 495-507, 2008
https://doi.org/10.5194/bg-5-495-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  07 Apr 2008

07 Apr 2008

Particle optical backscattering along a chlorophyll gradient in the upper layer of the eastern South Pacific Ocean

Y. Huot1, A. Morel1, M. S. Twardowski2, D. Stramski3, and R. A. Reynolds3 Y. Huot et al.
  • 1CNRS, Laboratoire d'Océanographie de Villefranche, 06230 Villefranche-sur-mer, France; Université Pierre et Marie Curie-Paris 6, Laboratoire d'Océanographie de Villefranche, 06230 Villefranche-sur-mer, France
  • 2Department of Research, WET Labs, Inc., 165 Dean Knauss Dr., Narragansett, RI 02882, USA
  • 3Marine Physical Laboratory, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0238, USA

Abstract. The particulate scattering, bp, and backscattering, bbp, coefficients are determined by the concentration and physical properties of suspended particles in the ocean. They provide a simple description of the influence of these particles on the scattering of light within the water column. For the remote observation of ocean color, bbp along with the total absorption coefficient govern the amount and spectral qualities of light leaving the sea surface. However, for the construction and validation of ocean color models measurements of bbp are still lacking, especially at low chlorophyll a concentrations ([Chl]). Here, we examine the relationships between spectral bbp and bp vs. [Chl] along an 8000 km transect crossing the Case 1 waters of the eastern South Pacific Gyre. In these waters, over the entire range of [Chl] encountered (~0.02–2 mg m3), both bbp and bp can be related to [Chl] by power functions (i.e. bp or bbp=α[Chl]β). Regression analyses are carried out to provide the parameters α and β for several wavelengths throughout the visible for both bbp and bp. When applied to the data, these functions retrieve the same fraction of variability in bbp and bp (coefficients of determination between 0.82 and 0.88). The bbp coefficient fall within the bounds of previous measurements at intermediate and high [Chl] recently published. Its dependence on [Chl] below ~0.1 mg m−3 is described for the first time with in situ data. The backscattering ratio (i.e. bbp/bp) with values near 0.01 for all stations appears to be spectrally neutral and not significantly dependent on [Chl]. These results should foster the development of improved forward models of the mean optical properties for oceanic Case 1 waters as well as inverse models based upon them.

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