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www.biogeosciences-discuss.net/6/8075/2009/
doi:10.5194/bgd-6-8075-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
Optical characterization of an eddy-induced diatom bloom west of the island of Hawaii
1Ocean Physics Laboratory, Department of Geography, University of California, Santa Barbara, CA 93106, USA
2Sea Engineering Inc., 200 Washington St. Suite 210, Santa Cruz, CA 95060, USA
3Dept. of Research, WET Labs Inc., Narragansett, RI, 02882, USA
Abstract. Optical properties are used to characterize the biogeochemistry of cyclonic eddy Opal in the lee of Hawaii. The eddy featured an intense diatom bloom. Our results show that the ratio of chlorophyll concentration to particulate beam attenuation coefficient, [chl]/cp, is not a good indicator of the changes in particle composition through the water column. The ratio is controlled primarily by the variation in chlorophyll concentration per cell with depth (photoadaptation), so that its values increase throughout the Deep Chlorophyll Maximum Layer (DCML). Below the DCML, high values of [chl]/cp suggest that remineralization might be another important controlling factor. On the other hand, the backscattering ratio (particle backscattering to particle scattering ratio, b~bp) clearly indicates a shift from a small phytoplankton to a diatom dominated community. Below an upper layer characterized by constant values, the b~bp ratio showed a rapid decrease to a broad minimum within the DCML. The higher values below the DCML are consistent with enhanced remineralization below the eddy-induced bloom. The DCML was characterized by a layer of "healthy" diatoms underlying a layer of "senescent" diatoms. These two layers are characterized by similar optical properties, indicating some possible limitations in using optical measurements to fully characterize the composition of suspended material in the water column. An inverse relationship between b~bp and [chl]/cp, also reported by others, is observed as deep as the DCML. There, [chl]/cp increases whereas b~bp remains similar to values found in the empty frustule layer. This is a further indication that [chl]/cp might not be a good alternative to the backscattering ratio for investigating changes in particle composition with depth in Case I waters.
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Citation: Nencioli, F., Chang, G., Twardowski, M., and Dickey, T. D.: Optical characterization of an eddy-induced diatom bloom west of the island of Hawaii, Biogeosciences Discuss., 6, 8075-8100, doi:10.5194/bgd-6-8075-2009, 2009. Bibtex EndNote Reference Manager XML
