Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 5 2 2008 10.5194/bg-5-495-2008 http://www.biogeosciences.net/5/495/2008/ http://www.biogeosciences.net/5/495/2008/bg-5-495-2008.html http://www.biogeosciences.net/5/495/2008/bg-5-495-2008.pdf 495 507 2008-04-07 Particle optical backscattering along a chlorophyll gradient in the upper layer of the eastern South Pacific Ocean Y. Huot huot@obs-vlfr.fr A. Morel M. S. Twardowski D. Stramski R. A. Reynolds CNRS, 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 Department of Research, WET Labs, Inc., 165 Dean Knauss Dr., Narragansett, RI 02882, USA Marine Physical Laboratory, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0238, USA 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. Ahn, Y. H., Bricaud, A., and Morel, A.: Light backscattering efficiency and related properties of some phytoplankters, Deep-Sea Res. Pt., 39, 1835–1855, 1992. Antoine, D., Morel, A., Gordon, H. R., Banzon, V. F., and Evans, R. H.: Bridging ocean color observations of the 1980s and 2000s in search of long-term trends, J. Geophys. Res., 110, C06009, doi:10.1029/2004JC002620, 2005. Bader, H.: The hyperbolic distribution of particle sizes, J. Geophys. Res., 75, 2822–2830, 1970. Balch, W. M., Drapeau, D. T., Fritz, J. J., Bowler, B. C., and Nolan, J.: Optical backscattering in the arabian sea - continuous underway measurements of particulate inorganic and organic carbon, Deep-Sea Res. Pt. I, 48, 2423–2452, 2001. Behrenfeld, M. J., Boss, E., Siegel, D. A., and Shea, D. M.: Carbon-based ocean productivity and phytoplankton physiology from space, Global Biogeochem. Cy., 19, GB1006, doi:10.1029/2004GB002299, 2005. Boss, E., Twardowski, M. S., and Herring, S.: Shape of the particulate beam attenuation spectrum and its inversion to obtain the shape of the particulate size distribution, Appl. Opt., 40, 4885–4893, 2001. Clark, G. L., and Ewing, G. C.: Remote spectroscopy of the sea for biological production studies, in: Optical aspect of oceanography, edited by: Jerlov, N. G., and Nielsen, E. S., Academic, New York, 494, 1974. Gao, Y., Fan, S.-M., and Sarmiento, J. L.: Aeolian input to the ocean through precipitation scavenging: A modeling perspective and its implication for natural iron fertilization in the ocean, J. Geophys. Res., 108, 4221, doi:10.1029/2002JD002420, 2003. Gordon, H. R., Brown, O. B., and Jacobs, M. M.: Computed relationships between inherent and apparent optical properties of a flat homogeneous ocean, Appl. Opt., 14, 417–427, 1975. Gordon, H. R. and Morel, A.: Remote assessment of ocean color for interpretation of satellite visible imagery: A review, Lecture notes on coastal and estuarine studies, Springer Verlag, Heidelberg, Germany, 114 pp., 1983. Gordon, H. R., Brown, O. B., Evans, R. H., Brown, J. W., Smith, R. C., Baker, K. S., and Clark, D. K.: A semianalytic radiance model of ocean color, J. Geophys. Res., 93, 10 909–10 924, 1988. IOCCG: Remote sensing of inherent optical properties: Fundamentals, tests of algorithms, and applications, in: Reports of the International Ocean-Colour Coordinating Group, edited by: Lee, Z.-P., No. 5, IOCCG, Dartmouth, Canada, 126, 2006. Lee, Z. P., Carder, K. L., and Arnone, R. A.: Deriving inherent optical properties from water color: A multiband quasi-analytical algorithm for optically deep waters, Appl. Opt., 41, 5755–5772, 2002. Loisel, H. and Morel, A.: Light scattering and chlorophyll concentration in case 1 waters: A reexamination, Limnol. Oceanogr., 43, 847–858, 1998. Maritorena, S., Siegel, D. A., and Peterson, A. R.: Optimization of a semianalytical ocean color model for global-scale applications, Appl. Opt., 41, 2705–2714, 2002. Morel, A.: Diffusion de la lumière par les eaux de mer. Resultats expérimentaux et approche théorique., AGARD lectures series, 3.1.1–3.1.76, 1973. Morel, A. and Prieur, L.: Analysis of variations in ocean color, Limnol. Oceanogr., 22, 709–722, 1977. Morel, A. and Bricaud, A.: Theoretical results concerning the optics of phytoplankton, with special references to remote sensing applications, in: Oceanography from space, edited by: Gower, J. F. R., Plenum, New York, 313–327, 1981. Morel, A. and Bricaud, A.: Inherent properties of algal cells including picoplankton: Theoretical and experimental results., in: Photosynthetic picoplankton, edited by: Platt, T. and Li, W. K. W., Canadian bulletin of fisheries and aquatic sciences, 521–559, 1986. Morel, A.: Optical modeling of the upper ocean in relation to its biogenous matter content (case 1 waters), J. Geophys. Res., 93, 10 749–10 768, 1988. Morel, A. and Ahn, Y.-H.: Optics of heterotrophic nanoflagellates and ciliates: A tentative assessment of their scattering role in oceanic waters compared to those of bacterial and algal cells, J. Mar. Res., 49, 177–202, 1991. Morel, A. and Maritorena, S.: Bio-optical properties of oceanic waters: A reappraisal, J. Geophys. Res., 106, 7163–7180, 2001. Morel, A., Gentili, B., Chami, M., and Ras, J.: Bio-optical properties of high chlorophyll case 1 waters and of yellow-substance-dominated case 2 waters, Deep-Sea Res. Pt. I, 53, 1439–1459, 2006. Morel, A., Gentili, B., Claustre, H., Babin, M., Bricaud, A., Ras, J., and Tièche, F.: Optical properties of the "Clearest" Natural waters, Limnol. Oceanogr., 52, 217–229, 2007. O'Reilly, J. E., Maritorena, S., Mitchell, B. G., Siegel, D. A., Carder, K. L., Garver, S. A., Kahru, M., and McClain, C. R.: Ocean color chlorophyll algorithms for SeaWiFS, J. Geophys. Res., 103, 24 937–24 953, 1998. Petzold, T. J.: Volume scattering functions for selected ocean waters, Scripps Institution of Oceanography, Visibility Lab, San Diego, 85, 1972. Ras, J., Claustre, H., and Uitz, J.: Spatial variability of phytoplankton pigment distributions in the subtropical South Pacific ocean: Comparison between in situ and predicted data, Biogeosciences, 5, 353–369, 2007. Reynolds, R. A., Stramski, D., and Mitchell, B. G.: A chlorophyll-dependent semianalytical reflectance model derived from field measurements of absorption and backscattering coefficients within the southern ocean, J. Geophys. Res., 106, 7125–7138, 2001. Snyder, W. A., Arnone, R. A., Davis, C. O., Goode, W., Gould, R. W., Ladner, S., Lamela, G., Rhea, W. J., Stavn, R., Sydor, M., and Weidemann, A.: Optical scattering and backscattering by organic and inorganic particulates in U.S. Coastal waters, Appl. Opt., 47, 666–677, 2008. Stramska, M., Stramski, D., Hapter, R., Kaczmarek, S., and Ston, J.: Bio-optical relationships and ocean color algorithms for the north polar region of the Atlantic, J. Geophys. Res., 108, 3143, doi:10.1029/2001JC001195, 2003. Stramska, M., Stramski, D., Kaczmarek, S., Allison, D. B., and Schwarz, J.: Seasonal and regional differentiation of bio-optical properties within the north polar Atlantic, J. Geophys. Res., 111, C08003, doi:10.1029/2005JC003293, 2006. Stramski, D. and Kiefer, D. A.: Light scattering by microorganisms in the open ocean, Prog. Oceanogr., 28, 343–383, 1991. Stramski, D., Boss, E., Bogucki, D., and Voss, K. J.: The role of seawater constituents in light backscattering in the ocean, Prog. Oceanogr., 61, 27–56, 2004. Stramski, D., Reynolds, R. A., Babin, M., Kaczmarek, S., Lewis, M. R., Röttgers, M., Sciandra, A., Stramska, M., Twardowski, M. S., Franz, B. A., and Claustre, H.: Relationships between the surface concentration of particulate organic carbon and optical properties in the eastern South Pacific and eastern Atlantic oceans., Biogeosciences, 5, 171–201, 2008. Sullivan, J. M., Twardowski, M. S., Donaghay, P. L., and Freeman, S. A.: Use of optical scattering to discriminate particle types in coastal waters, Appl. Opt., 44, 1667–1680, 2005. Twardowski, M. S., Boss, E., Macdonald, J. B., Pegau, W. S., Barnard, A. H., and Zaneveld, J. R. V.: A model for estimating bulk refractive index from the optical backscattering ratio and the implications for understanding particle composition in case i and case ii waters, J. Geophys. Res., 106, 14 129–14 142, 2001. Twardowski, M. S., Claustre, H., Freeman, S. A., Stramski, D., and Huot, Y.: Optical backscattering properties of the "clearest" natural waters, Biogeosciences, 4, 1041–1058, 2007. Ulloa, O., Sathyendranath, S., and Platt, T.: Effect of the particle-size distribution on the backscattering ratio in seawater, Appl. Opt., 33, 7070–7077, 1994. Whitmire, A. L., Boss, E., Cowles, T. J., and Pegau, W. S.: Spectral variability of the particulate backscattering ratio, Opt. Express., 15, 7019–7031, 2007.