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Particle optical backscattering along a chlorophyll gradient in the upper layer of the eastern South Pacific Ocean
1CNRS, Laboratoire d'Océanographie de Villefranche, 06230 Villefranche-sur-mer, France; Université Pierre et Marie Curie-Paris6, Laboratoire d'Océanographie de Villefranche, 06230 Villefranche-sur-mer, France
2Dept. 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 m−3), 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 (determination coefficients 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. At these low and decreasing [Chl] a continuous trend with data at higher [Chl] is observed, i.e. a decrease in bbp. The backscattering ratio (i.e. bbp/bp) with values averaging 0.008 is found to have a weak dependence 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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Citation: Huot, Y., Morel, A., Twardowski, M. S., Stramski, D., and Reynolds, R. A.: Particle optical backscattering along a chlorophyll gradient in the upper layer of the eastern South Pacific Ocean, Biogeosciences Discuss., 4, 4571-4604, 2007. Bibtex EndNote Reference Manager
