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 vertical distribution of chlorophyll a concentration (Ca) was uniform in the upper mixed layer (UML). In UML the Ca values varied between stations from 0.8 to 1.8 mg m-3 and decreased to 0.06-0.25 mg m-3 in the layer below maximum temperature gradient. The values of phytoplankton light absorption coefficient varied more than in twice in accordance with Ca variability. The shapes of phytoplankton light absorption spectra slightly changed. The characteristics of phytoplankton light absorption in UML were typical for the winter phytoplankton community which is dominated by Bacillariophyceae and Dinophyceae. In the layer below thermocline, phytoplankton light absorption spectra with a pronounced local absorption maximum at wavelength ~ 550 nm were obtained. The local maximum at ~ 550 nm likely indicates the domination of C-phycoerythrin-containing cyanobacteria Synechococcus spp. in the biomass of the phytoplankton community below the thermocline. The contribution of non-algal particles to total particulate light absorption at wavelength ~ 438 in the layer below thermocline was more than 2 times higher than in the UML.
Results of long-term biooptical monitoring and parameterization of light absorption by phytoplankton, non-algal particles ( αNAP(λ)) and colored dissolved organic matter (αCDOM(λ)) in coastal surface waters of the Black Sea near Sevastopol have been presented. Seasonal differences in the relationship between phytoplankton light absorption coefficients and chlorophyll a concentrations, which are associated with annual dynamics in the intracellular pigment concentration and composition in the surface layer of the sea, have been revealed. The αNAP(440) was on ~order increased from off-shore waters to the Sukharnaya Balka, but the αNAP(440) contribution to the total particulate absorption was the same (~ 20-49% based on IQR) at all stations reflecting the correlated variations in phytoplankton and NAP absorption coefficients at ~440 nm. The obtained slope coefficient (SNAP) values varied from 0.010 to 0.014 nm -1 . The CDOM light absorption increased significantly (almost in order) from off-shore waters to the Sukharnaya Balka, but the contribution of αCDOM(440) to total light absorption by particles and dissolved matter changed in the opposite direction: decreased from 40 - 70% to 25 – 45%. The ranges of SCDOM variability in all investigated areas were close (0.017 to 0.020 nm-1 based on IQR). The median of SCDOM was 0.018-0.019 nm-1 . The obtained in this research results will be used for adaptation of the regional algorithms of remote assessment of water quality and productivity indicators for coastal waters near Sevastopol.
Bio-optical studies were carried out in coastal waters around the Crimea peninsula in different seasons 2016. It was shown that variability of chlorophyll a concentration (Chl-a), light absorption by suspended particles (ap(λ)), phytoplankton pigments (aph(λ)), non-algal particles (aNAP(λ)) and by colored dissolved organic matter (aCDOM(λ)) in the Crimea coastal water was high (~order of magnitudes) in all seasons 2016. Relationships between ap(440), aph(440) and Chl-a were obtained and their seasonal differences were analyzed. Spectral distribution of aNAP(λ) and aCDOM(λ) were parameterized. Seasonality in aCDOM(λ) parameterization was revealed, but - in aNAP(λ) parameterization was not revealed. The budget of light absorption by aph(λ), aNAP(λ) и aCDOM(λ) at 440 nm was assessed and its seasonal dynamics was analyzed.
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