Absorption of light by phytoplankton, detritus, and dissolved organic substances in the coastal region of the Black Sea (July–August 2002)

Abstract

We present some results of our investigations of the concentrations of pigments and the biooptical characteristics of suspended and dissolved organic substances in the coastal region of the sea near the coast of the Crimea. Under the conditions of variable meteorological situation, we observe well-pronounced variations of the concentrations of pigments in the surface layer and their different vertical profiles. The inhomogeneity of the distribution of pigments in depth is accompanied by a decrease in the specific coefficients of absorption of light by phytoplankton. In the analyzed case, the contribution of "detritus" to absorption does not vary with depth and its maximum values are observed under the storm conditions. The dependences of the absorption of light by phytoplankton and suspended substances on the content of pigments and of the absorption of light by dissolved organic substances on the wavelength are established. These dependences are well described by power and exponential functions.The existing algorithms used for the evaluation of the concentrations of pigments according to the satellite data inaccurately describe their actual values in the Black Sea [1]. Among the factors affecting the spectral properties of upwelling radiation, one can mention the absorption of light by suspended substances and organic compounds dissolved in seawater. The absorption of light by suspended substances can be split into the absorption by phytoplankton pigments and absorption by "detritus" in the form of a "decolorized" suspension consisting of the detritus of organic origin, inorganic suspension, and cell membranes of plankton. The optical properties of phytoplankton are determined by the concentrations of photosynthetically active chlorophyll A and auxiliary pigments whose quantitative and qualitative composition varies depending on the abiotic conditions of the habitat and the taxonomic composition of the phytoplankton population. This affects the relationship between the spectral characteristics of phytoplankton and the concentration of chlorophyll A. Moreover, the spectra of the light-absorbing components of the suspension have different shapes and, hence, their relative contributions to the total absorption undergo significant changes [1, 2], which can lead to ambiguous estimates of the productivity of waters according to the satellite data. Hence, to create a regional satellite algorithm aimed at the evaluation of the content of chlorophyll A according to the spectra of upwelling radiation, it is necessary to know the dependences of the coefficients of absorption of light by all components of the suspension on the concentration of chlorophyll A at different wavelengths and the contributions of all component to the total absorption of light.To solve this problem, we study the space and time variations of the concentration of chlorophyll A and the biooptical properties of the suspension and dissolved organic substances in the coastal region of the Crimea in summer. Materials and MethodsThe present work was carrie...

Inter-Annual Variability of the Seawater Light Absorption in Surface Layer of the Northeastern Black Sea in Connection with Hydrometeorological Factors

“…In the Black Sea, the first studies of spectral absorption were associated with phytoplankton and focused on the problems of utilization of solar radiation during photosynthesis [9][10][11]. First measurements of spectral absorption by seawater components, including CDOM, at a modern level, were carried out at the beginning of this century; recently, they were aimed at developing satellite algorithms for the separate determination of absorption by chlorophyll and yellow substance [12,13].…”