For the first time, spectral bio-optical properties of Lake Teletskoye were measured. The variability of the spectral light absorption coefficients by all optically active components is presented. The contribution of each optically active component to the total light absorption at a wavelength of 440 nm was assessed. It has been established that colored organic matter makes the main contribution to the absorption of light (about 85% of the total).
Results of measurements of the spectral light absorption coefficients of all in water optically active components and spectral downwelling irradiance in the Black and Azov Seas, as well as Lake Teletskoye were analysed. The regional specificity of water areas in terms of light absorption by suspended particles and colored dissolved organic matter, water transparency and spectral characteristics of downwelling irradiance has been revealed. Dependences of the euphotic zone and spectral characteristics of light on the total non-water light absorption by particles and colored dissolved organic matter have been revealed and described by power function.
A three-band satellite algorithm for retrieval of the bio-optical properties of surface waters, developed for the Black Sea, was adapted to the waters of the Southern Ocean (Atlantic region) on the basis of spectral light absorption coefficients of all optically active components (phytoplankton, non-algal particles and coloured dissolved organic matter) measured during the scientific cruises RV “Akademic Msctislav Keldysh” in austral summer 2020 and 2022. The accuracy of the regional algorithm was estimated by comparison with the in situ data. The advantage of the regional algorithm in comparison with the standard one in the range of low values of bio-optical parameters of water was shown, and an approach to further refinement of the algorithm to ensure correct assessment in waters with a relatively high content of optically active components was discussed.
The spectral light absorption coefficient by phytoplankton pigments, non-algal particles and colored dissolved organic matter were compared in optically contrasting waters of different trophic status. Contribution of optically active components to the total light absorption at 440 nm, as well as the effect of non-water total light absorption on water transparency, were evaluated.
During the scientific expedition "European Arctic - 2020" on the R/V "Akademik Mstislav Keldysh" (cruise No. 80), the concentration of chlorophyll a, spectral coefficients of light absorption by phytoplankton pigments, non-algal particles and colored dissolved organic matter have been measured in the euphotic layer of the Norwegian and the Barents Seas, and in the Arctic Ocean from July 28 to August 23, 2020. High variability of bio-optical properties, heterogeneity of the studied water area in terms of the relative contribution of colored dissolved organic matter to the total lightu absorption was revealed. Relationship between the total light absorption at 438 and 490 nm in the surface layer and the photosynthesis zone has been obtained.
Spectral bio-optical properties of Black Sea coastal waters (near Sevastopol) with different trophic status were analysed. In summer 2020-2021, the chlorophyll a concentration (Ca) differed by an order between stations, located in the apex of the Sevastopol Bay and at a distance ~2 miles from the Sevastopol Bay. At the station located in the apex of the Sevastopol Bay, effected by river runoff (the most trophic waters), the total particulate light absorption at wavelength 438 nm (aP(438)) increased by an order compared to station located at a distance of ~2miles zone from the Bay. The contribution of the light absorption by non-algal particles to the ap(438) was not depended on water trophic status. With a rise of water trophic status the coefficient of colored dissolved organic matter absorption increased by ~2.2 times, and the coefficient of total non-water absorption (atot(438)) increased by ~4 times. The spectral features of downwelling irradiance depended on the atot(438). The increasing of atot(438) of about 10 times resulted in shift of ~50 nm to the longer wavelength domain of the spectrum.
The regional full spectral primary production model accuracy has been assessed based on the comparison results of calculation with the data of measurements of chlorophyll a concentration and primary production (gross) in the surface layer of the western and eastern regions of the sea in September and December curried out in the scientific cruises in the period from 2005 to 2016. The comparison showed a good agreement between measured and calculated primary production data. The assimilation number is considered as one of the criteria for the assessment of the accuracy of the primary production model.
Based on the field measurements of the light absorption spectra of phytoplankton pigments, the non-algal suspended matter, the colored dissolved organic matter and ocean color product, remote sensing reflectance, reconstructed from MODIS instruments from Aqua and Terra measurements, regression equations were obtained to restore the main biooptical characteristics in Sea of Azov: total concentration of chlorophyll a and pheopigments, coefficients of light absorption by phytoplankton pigments, non-living organic matter and coefficient of light backscattered by particles suspended at 438 nm. The daily 2D maps of these parameters were constructed in the surface layer from 2000 to 2018.
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