The effect of a phytoplankton bloom on the change with depth of photosynthetically available radiation (PAR), the spectral downwelling irradiance in coastal waters, and the phytoplankton ability to absorb PAR in the sea is estimated. The 10-fold increase in the chlorophyll a concentration (from 0.4 to 4.0 mg/m³) during a diatom/ dinoflagellate bloom leads to a decrease in water transparency and a narrowing of the photosynthesis zone. As a consequence, the average PAR within the phytoplankton habitat layer is almost halved. A diatom/dinoflagellate bloom is accompanied by changes in the downwelling irradiance spectrum at the same PAR level (optical depths). The penetrating irradiance maximum near the bottom of the euphotic zone shifts to longer wavelengths (~550–600 nm) as compared to background conditions (~500–550 nm). The increase in diatom/dinoflagellate biomass and the concomitant change in the downwelling irradiance spectrum are accompanied by a decrease in the specific absorption coefficient of phytoplankton pigments up to about three times that under background conditions at the same optical depths. The downwelling irradiance spectrum at fixed optical depths and the ability of cells to absorb light change slightly as compared to background conditions when coccolithophores bloom.

中文翻译：

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沿海水域浮游植物的开花和光合有效辐射

估算了浮游植物开花对光合有效辐射（PAR）的深度，沿海水域光谱下降辐射辐照度以及浮游植物吸收海洋中PAR的能力的影响。叶绿素a浓度增加10倍（从0.4到4.0 mg / m ³）期间，硅藻/鞭毛藻的花开导致水透明度降低和光合作用区变窄。结果，浮游植物栖息层内的平均PAR几乎减半。硅藻/鞭毛藻的开花伴随着在相同PAR水平（光学深度）下的下行辐射光谱的变化。与背景条件（〜500–550 nm）相比，在常光区底部附近的穿透辐射最大值移至更长的波长（〜550–600 nm）。硅藻/双鞭毛生物量的增加以及下降流辐照度谱的变化伴随着浮游植物色素的比吸收系数的降低，最高可达背景条件下在相同光学深度的三倍。