Title:
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Evolution and structure of a shelf coccolithophore bloom in the Western English Channel : a satellite, airborne and ship study
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The physical factors associated with the development, advection and disappearance of a bloom of the coccolithophore Emiliania huxleyi were investigated with AVHRR satellite imagery (thermal and visible bands) in the Western English Channel in June 1992 from an early reflective stage to a mature and dissipative phase (3-4 weeks life time). The physical processes that appeared important in patch evolution and structure were, differential stratification in an area of weak tidal currents, initial zero wind conditions (allowing local bloom development), later strengthening NE winds (driving the bloom within a coastal warm surface current), entrainment of the bloom water into the anticyclonic tidal circulation around the Isles of Scilly and finally bloom dispersal by mixing and flow divergence. Ship and airborne surveys simultaneous to the satellite images investigated the extent to which the bloom changed the local optical properties (red beam attenuation coefficient, PAR diffuse attenuation coefficient, in situ reflectance spectra (415-660nm) and Airborne Thematic Mapper reflectance), and examined the distribution of the different E.huxleyi standing stocks (detached coccoliths, empty coccospheres and living E.huxleyi cells). The bloom vertical structure was characterised by sections of temperature, chlorophyll a, inorganic nutrients, particulate organic and inorganic carbon, C/N atom-ratio and non-coccolithophore phytoplankton species. The results were analysed in relation to the life history strategy of E.huxleyi, the regional redistribution of phytoplankton and chemical constituents, the biological impact of the bloom irradiance field, the development of coccolithophore optical algorithms and the differences between oceanic and shelf coccolithophore blooms. The satellite time series of the present work is so far the most comprehensive remote sensing report of a coccolithophore bloom. The simultaneous sea-truth measurements show for the first time a section of hydrographic, biological and optical properties of a bloom of Emiliania huxleyi.
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