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The optical properties of mineral particles suspended in seawater were calculated from the Mie scattering theory for different size distributions and complex refractive indices of the particles. The ratio of the spectral backscattering coefficient to the sum of the spectral absorption and backscattering coefficients of seawater, b(b)(lambda)/[a(lambda) + b(b)(lambda)], was analyzed as a proxy for ocean reflectance for varying properties and concentrations of mineral particles. Given the plausible range of variability in the particle size distribution and the refractive index, the general parameterizations of the absorption and scattering properties of mineral particles and their effects on ocean reflectance in terms of particle mass concentration alone are inadequate. The variations in the particle size distribution and the refractive index must be taken into account. The errors in chlorophyll estimation obtained from the remote sensing algorithms that are due to the presence of mineral particles can be very large. For example, when the mineral concentration is 1 g m(-3) and the chlorophyll a concentration is low (0.05 mg m(-3)), current global algorithms based on a blue-to-green reflectance ratio can produce a chlorophyll overestimation ranging from approximately 50% to as much as 20-fold.

Photosynthetic and optical properties of the marine chlorophyte Dunaliella tertiolecta Butcher were studied in response to irradiance fluctuations caused by surface-wave focusing. The experimental conditions simulated the prominent features of the light field (high average irradiance, spectral composition and statistical properties) in the uppermost few meters of the water column under sunny surface conditions. The properties of algae grown under high-frequency fluctuations were compared with control cells grown under constant light at the same average irradiance (∼800 μmol quantams). No significant differences were found for a number of parameters, including growth rate, cellular chlorophyll a and pigment ratios, photosynthetic unit size and density of Photosystem I reaction centers, the rate of photosynthesis at the growth irradiance, dark respiration, and in vivo fluorescence of chlorophyll a per cell. Photosynthetic parameters were not affected by whether the incident light for oxygen exchange measurements was fluctuating or constant. This was the case whether the cells had been previously acclimated to either fluctuating or constant irradiance. Such a photosynthetic response indicates that cells are accomplishing a time integration of the fluctuating light. In addition, although D. tertiolecta is capable of dramatically changing its optical properties in response to low or high growth irradiance levels, the refractive index of the cells, the efficiency factors for light absorption and scattering by individual cells, and chlorophyll-specific absorption and scattering coefficients of cell suspensions, were all very similar under high irradiance, whether or not wave focusing was present. [ABSTRACT FROM AUTHOR]