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).
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.
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.
Based on the data of shipborne measurements performed in the Atlantic sector of the Southern Ocean in January 2020, the Hydrolight hydrooptical model was configured to take into account the presence of the phycoerythrin pigment in phytoplankton cells. The use of this model will allow to validate and adjust the bio-optical algorithms for assessing the concentration of chlorophyll-a in the presence of phycoerythrin.
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.
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.
The work is devoted to the study of the effect of phycoerythrin pigment on the seawater optical properties in the Atlantic sector of the Southern Ocean. The investigation was carried out in the 79th expedition of the R / V “Akademik Mstislav Keldysh” in January 2020. At some stations, a high content of phycoerythrin was registered in the fluorescence spectra of seawater, the light absorption spectra by suspended particles, and in the remote sensed reflectance spectra of seawater. In particular, the fluorescence of this pigment induced by solar radiation was recorded in ocean color data. The presence of phycoerythrin can lead to uncertainties of the chlorophyll-a concentration estimates from satellite data retrieved with standard algorithms.
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.
For the first time light absorption by all optically active components (phytoplankton, non-algal particles and colored dissolved organic matter) has been measured in the Sea of Azov. Regional bio-optical properties have been shown for winter and spring seasons.
Dependence of fluorescence intensity and light absorption on chlorophyll a concentration was investigated in designated layers of euphotic zone of the Black Sea in October 2017, when waters were seasonally stratified. Chlorophyll a specific light absorption was obtained to decrease with depth (from layer to layer), which resulted in a change of coefficient of relationship between concentration of chlorophyll a and its fluorescence intensity.
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.
Variability in light absorption by colored dissolved organic matter (ܽαCDOM(λ)),by non-algal particles (αNAP(λ)), and by colored detrital matter (αCDM(λ)) were analyzed in the coastal and deep water regions in the Black sea at the same season (Autumn) to avoid the impact of seasonal variability. The CDOM, NAP and CDM light absorption were parameterized. As result of the parameterization the two parameters were obtained (coefficient et 490 nm and slope coefficient (S):αCDOM(490) and ܵSCDOM;αNAP(490) and SNAP ; αCDM(490) and ܵSCDM. The CDOM contributed mainly in the ܽαCDM(490) in both coastal (79 ± 13%) and deep water (88 ± 6%) regions. It was observed high (in ~order) variability in the αNAP(490) in coastal waters due to resuspension of sediments from the bottom at shallow stations. The average αSNAP values were 0.010 nm-1 in coastal and 0.012 nm-1 in deep water regions. For all dataset the relationship between of ܽαCDM(490) and ܵSCDM was described by power function. This equation can be used for refining of the regional algorithm of ܽαCDM(λ) assessment in the Black Sea based on satellite data. The obtained in this research relative absorption of NAP and CDOM could be used for remote assessment of αNAP (λ) and ܽαCDOM(λ) in the Black Sea.
To assess an effect of optically active components (OAC) on water transparency and the spectral features of downwelling irradiance (Ed(λ))in coastal waters several scenarios have been simulated: blooms of planktonic microalgae (with the exception of coccolithophore blooms), resuspension of sediments, incoming of suspended and dissolved organic matter with river/coastal run off. General and specific effects of OAC variability on (Ed(λ)) have been revealed. The general effects are: the OAC increase resulted in decrease of water transparency and narrowing of euphotic layer, which in turn led to decreasing in photosynthetic available radiation (PAR) averaged within the mixed layer from the surface down to the bottom altering the light condition of plankton and benthic algae. Specific effects caused by the differences in the shape of light absorption coefficient spectrum of the OAC are: in the scale of optical depths, the spectral features of (Ed(λ)) varied depending on the relative content of OAC; shift of penetrating irradiance to the longer wavelengths was amplified from phytoplankton to non-algal particles, to colored dissolved organic matter. Values of chlorophyll a concentration and Kd at particular wavelength or spectrally average Kd are not sufficient for correct assessment of underwater light. An additional indicator characterizing the ratio between OAC is required.
Variability of the bio-optical properties of the Crimean coastal waters in June 2016 has been analyzed. The type of vertical distribution chlorophyll a concentration and phytoplankton light absorption coefficients and spectra shape differed between shallow and deeper water. In the deeper water seasonal stratification divided euphotic zone into layers with different environmental conditions. In the deeper part of the euphotic zone (below the thermocline) phytoplankton absorption spectra had local maximum at ~ 550 nm, which was likely to be associated with high abundance of cyanobacteria (Synechococcus sps.) in the phytoplankton community. The concentration of chlorophyll a specific light absorption coefficient of phytoplankton decreased with depth (especially pronounced in the blue domain of the spectrum). In the shallow water the vertical distributions of all absorption properties were relatively homogeneous due to vertical water mixing. In the shallow water non-algal particles light absorption coefficient and its contribution to total particulate absorption were higher than those in the deeper water. The non-algal particles (NAP) and colored dissolved organic matter (CDOM) light absorption spectra were well described by an exponential function with a slope averaging 0.010 nm-1 (SD = 0.001 nm-1) and 0.022 nm-1 (SD = 0.0060 nm-1), correspondingly. The CDOM absorption at 440 nm and slope coefficient varied significantly across the investigated area, which was possibly associated with the terrestrial influences. The assessment of the contribution of phytoplankton, NAP and CDOM to total light absorption showed that CDOM dominated in the absorption at 440 nm.
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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