Abstract
Two coccolithophore blooms in the Gulf of Maine were studied in 1988 and 1989. Each bloom was about 50,000 km2 in area and confined to the top 20 m of the water column. Maximal cell concentrations were 2,000 cells ml−1 and coccolith densities of 3 × 105 ml−1 were observed. The coccolith : cell ratio was highest in the bloom center (region of most intense reflectance) and lowest at the bloom periphery, an indication of varying organic vs. inorganic C production. Chlorophyll concentrations were generally low within the bloom and no relation could be observed between major nutrients and coccolithophore abundance. Backscattered light was profoundly affected by coccolith density and was slightly wavelength‐dependent. We calculated total backscattering as well as backscattering (bb) caused exclusively by coccoliths and derived the algorithm relating coccolith density to backscattering. Although cells were efficient light absorbers, coccoliths showed negligible light absorption. Diffuse attenuation was lowest in the green and blue‐green part of the visible spectrum. At the center of the bloom, coccoliths contributed >75% of the backscattering signal and > 50% of the beam attenuation signal. The most accurate way to estimate coccolith concentrations via remote sensing is to measure water‐leaving radiance in the green wavebands.
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