This work precedes the field experiment on Lake Teletskoye, which is scheduled for August 10-20, 2023. The main goal of the work is to get an information of the regional features and seasonal variability of the optically active characteristics of the water upper layer of Lake Teletskoye based on the Level-2 standard products of the OLCI optical scanner.
The results of hydrological and hydrooptical measurements carried out in the spring (April 22–May 17) and summer (July 29–August 10) 2021 in the north-eastern part of the Black Sea during cruises 116th and 117th of the R/V Professor Vodyanitsky are presented. It is shown that in spring, when there was an intensive rivers run-off, the area with a high content of total suspended matter was a strip up to 40 km wide, stretched along the coast of the Krasnodar Krai. In summer, when the river run-off was weakened, the maximum values of the total suspended matter concentration were noted in a relatively narrow coastal strip no more than 20 km wide. Maximum turbidity was noted in the surface layer in spring and in summer it descended into the layer of seasonal thermocline, halocline and pycnocline. The consistency of the horizontal distributions of the total suspended matter concentration and temperature had a significant level deeper than the seasonal thermocline – in the spring in the layer from 20 to 35 m, in the summer in the layer from 15 to 70 m, while a direct correlation was observed, i.e. at these depths, warmer waters were characterized by increased turbidity. The maximum level of consistency between the horizontal fields of the total suspended matter concentration, salinity and density in spring was observed in the upper 20–25 m layer, while the correlation was inverse, i.e. at these depths, less saline and denser waters were characterized by increased turbidity, which is explained by intensive river run-off. In summer, the nature of the correlation was preserved, and the best consistency of the horizontal fields of the total suspended matter concentration, salinity and density was observed in the surface 10-m layer and deeper than the seasonal halocline and pycnocline in the 20–40 m layer.
Using the results of the 4D IOPs model, an estimate of the lower boundary of the photosynthesis zone in the deep water region of the Black Sea was obtained. For the year warm period, its value significantly differs downward (by 5–10 m) from that obtained in earlier paper. At the cold period, this difference in estimates is smaller and amounts to 2–3 m. The main reason is the more correct consideration of the light absorption profile of dissolved organic matter, which increases with depth.
Studies were carried out on August 14, 2019, in the shallow part of the Kazachya Bay (Sevastopol, Black Sea) under cloudless sky conditions. At the selected point of the Zostera noltii Hornemann canopy, at a depth of 42 cm, with coordinates 44° 57′26″ N, 33° 40′33″ E, measurements of photosynthetically active radiation intensity (IPAR) were taken. During the entire period of research, the plants were in a vertical state. The Z. noltii biomass (mdry) distribution along the canopy height (z) was found to change unevenly, increasing with depth (mdry(z) = 0.0001Z3.881; R2 = 0.95), and this is reflected in the vertical distribution of IPAR. IPAR was observed to decrease with the depth of the canopy, the manner of this decrease being largely dependent on solar altitudes. The measurement results show a significant influence of the Fresnel effect on IPAR values.
Based on the results of hydrological and hydrooptical measurements carried out in the winter of 2020 (November 27 – December 16) off the Crimea coast during the 115th cruise of the R/V Professor Vodyanitsky, the vertical structure of the coefficients of linear relationships between the horizontal distributions of temperature, salinity, density and total suspended matter concentration with a discreteness of 1 m in depth was analyzed. It is shown that the closest linear correlation are founded between temperature, salinity and total suspended matter concentration within the upper quasihomogeneous layer. In this layer, the values of the correlation coefficients between these parameters have a negative sign and exceed 0,75 in absolute value. Below the upper quasi-homogeneous layer, in the layer of high vertical gradients of thermohaline parameters, these connections noticeably weaken, while in the temperature and density fields they change sign and become positive. At the depths of the cold intermediate layer, linear connections increase again. The estimates of the relationships between the distribution of the fluorescence intensity of phycocyanin and phycoerythrin with thermohaline parameters revealed in most cases a low correlation level. A high direct correlation with the values of R ~ 0,65 – 0,75 was revealed only between the distributions of the phycocyanin fluorescence intensity and the temperature distribution under the main thermocline in the 65 – 70 m layer.
The results of hydrological, hydro-optical and biological studies carried out in autumn 2020 near the coast of Crimea during the 114th cruise of the R/V «Professor Vodyanitsky» are presented. Comparison of the vertical profiles of chlorophyll «a» obtained by different methods has been made. A high convergence was revealed between the fluorescent in situ method for determining the concentration of chlorophyll «a» upon excitation in the blue region of the spectrum and the standard biological in vitro method. The necessity of the simultaneous use of both methods for determining the concentration of chlorophyll «a» and its spatial distribution in sea areas is shown.
The purpose of the work was to build a regional algorithm for reconstructing the vertical diffuse attenuation coefficient at 380, 443, 490, 510, 555, 590 and 620 nm for Lake Baikal based on quasi-synchronous in situ measurements and the standard ocean color Level-2 OLCI product. For the first time, the spatial distribution of the diffuse attenuation coefficient was obtained at seven wavelengths in the upper layer of Lake Baikal.
The results of hydro-hydro-optical measurements performed in the spring of 2019 in the northern part of the Black Sea off the coast of the Crimea and the Caucasus are presented. It is shown that the maximum concentration of total suspended matter was observed off the coast of the Kerch Peninsula and in the Feodosiya Gulf, which was associated with the coastal transport of the Rim Current of freshened and turbid Azov Sea waters from the Kerch Strait. Minimums of the concentration of total suspended matter were observed at the southern boundary of the polygon in the area of the cyclonic gyre identified by the survey data, and in the southwestern part of the polygon, where the cyclonic meander was recorded. In the vertical structure of the concentration of total suspended matter in the upper 200-meter layer, three main maximums were observed, the depth of which is associated with the features of the circulation and thermohaline waters structure. One maximum was observed in the layer of seasonal thermocline and pycnocline in the eastern part of the polygon. The second maximum was traced below the cold intermediate layer core in the layer of the main pycnocline and halocline in the central part of the polygon at stations located on the periphery of the cyclonic gyre. The third maximum was found in the entire area of the polygon under the main pycnocline and halocline in the sub-oxygen zone.
The paper presents a joint analysis of direct measurements of bio-optical, hydro-optical and hydrodynamic characteristics performed on a section through the Lomonosov equatorial undercurrent in December 2019 along 26 degrees of west longitude. The vertical structure of the temperature and salinity of seawater, the speed and direction of the currents, the concentration of chlorophyll-a and the fluorescence of dissolved organic matter (DOM), and light beam attenuation coefficient at 525 and 625 nm were analyzed. The obtained sections show a low content of the main optically active components of seawater. The maximum values of all the analyzed optical parameters were recorded on a pycnocline at depths of 60-80 meters, where phytoplankton cells develop, which mainly determine the variability of the optical characteristics of the region.
Photosynthetically active radiation (PAR) intensity (IPAR) measurements were carried out in a shallow waters section of Tolstiy cape, Sevastopol, the Crimean Peninsula, at a depth of 63 cm along the profile of Cystoseira crinita (Desf.) Bory canopy (canopy height 25-30 cm) at different solar elevation angles in sounding mode on August 27, 2019. During the entire study period the C. crinita thalli were in inclined state. The greater part of the plants mass [67.07% (SD = 9.62, CV = 0.14)] was located in the upper 10 cm layer of the canopy. The PAR vertical intensity profile in the Cystoseira crinita canopy may change during daylight hours. The equations describing the IPAR distribution in the canopy depth at different times of day are provided. Conditions that would typically develop at 9 a.m., made the PAR intensity decrease linearly in the canopy from 657.6 μE . m-2 . s-1 in its upper part up down to 123.45 μE . m-2 . s-1 in its lower part at a depth of 20 cm. At 11 a.m., a high level of PAR intensity (564.98 – 828.12 μE . m-2 . s-1) was observed throughout the canopy. At 6 p.m., with the Sun low on the horizon, the lowest PAR level would be recorded (2.59 – 269.41 μE . m-2 . s-1).
The profiles of the light attenuation coefficients, reconstructed using a model based on statistics of bio-argo floats and regional satellite product, as well as measured under natural conditions in the Black Sea, were compared. Additionally, we compared the values of the attenuation coefficient of photosynthetically active radiation – Kd(PAR), obtained on the basis of spectral measurements of horizontal irradiance, with the results of direct measurements of Kd(PAR) on the shelf and the deep-sea parts of the Black Sea. The effects of meteorological conditions, cloudiness on PAR attenuation in the upper and lower the sea layers are demonstrated.
The results of hydrological and hydro-optical researches carried out in the autumn of 2018 in the Black Sea northern part off the coast of the Crimea and the Caucasus are presented. The features of the spatial distribution of the total suspended matter and their relationship with hydrological parameters are revealed. It is shown that the minimum concentration of the total suspended matter was observed in the western part of the study area. An increase in the concentration of total suspended matter was noted off the coast of the Caucasus, which is associated with the alongshore transport of the Rim Current of turbid and freshened waters of numerous rivers (Rioni, Inguri, etc.). The highest concentrations of suspended matter were found in the coastal zone to the south of the Kerch Peninsula due to the agitation of the bottom and coastal suspensions under the influence of storm conditions. The vertical structure of the concentration of total suspended matter was characterized by a well-pronounced maximum, the depth of which was close to the depth of maximum vertical gradients of temperature and density. The greatest depths of maximum concentration of suspended matter and vertical temperature gradients (40–45 m) were observed to the west of the Heraclean Peninsula in the anticyclonic gyre, the minimum (up to 5–10 m) – in the open deep-sea survey part closer to the central parts of the large-scale Eastern cyclical gyre.
A comparison of phytomass vertical distributions (Wdry(z)/S0) and photosynthetically active radiation (PAR) in Zostera noltii Hornemann canopy in a shallow waters conditions was made. It was found out that between PAR values and Wdry(z)/S0 there is a high inverse relationship of two types – power and exponential. In both cases, the correlation coefficient reaches the value of R2=0.995. The averaged vertical PAR distribution in the canopy is well described by a fourth order polynomial function, with a correlation coefficient of R2=0.998.
The information capabilities of spectral measurements of underwater irradiance in the upper layer of Lake Baikal were demonstrated. It allowed to obtain the spectra of the vertical light attenuation coefficient, to restore the spectral structure of the incident solar radiation, including changes of photosynthetically active radiation with depth, and to calculate a number of primary bio-optical characteristics of water: spectra of the CDM absorption coefficient and the light backscattering coefficient, as well as the chlorophyll-a concentration.
Based on the daily means values of surface temperature and remote sensing reflectance coefficient Rrs(555), monthly mean values of chlorophyll "a" concentration from the array of satellite measurements with high spatial resolution COPERNICUS, monthly mean temperature and salinity values of the climatic hydrological oceanographic database created at the Marine Hydrophysical Institute and calculated geostrophic current velocities are analyzed regional features of the spatial distribution of the monthly average climatic values of these parameters off the coast of the Crimea. The patterns of Rim Current manifestation in the bio-optical and thermohaline fields are revealed. Shown, that maximum propagation of water transported by Rim Current to the west in climatic fields of bio-optical and thermohaline parameters is observed in February. Rim Current manifestation in bio-optical and thermohaline fields in the form of "tongues" water with increased values of temperature, chlorophyll "a" concentration and Rrs(555) coefficient and decreased salinity values, most clearly expressed to the west of the Crimean Peninsula.
In the paper a joint analysis of direct measurements of the seawater vertical diffuse attenuation coefficient with a satellite product was carried out for several stations on the northwestern shelf of the Black Sea in late April and early May 2017. An attempt to model the empirical spectrum of the seawater vertical diffuse attenuation revealed a number features of that were explained by the peculiarity of the vertical structure, namely, by the presence of an optically active layer, which is typical for the considered period of time and is associated with the thermocline formation process.
The results of studying the natural fouling of flat quartz glasses, as well as fouling on the beam attenuation coefficient (BAC) meters’ flat surfaces of objective lens and triple-prism are presented, using the method of spectrophotometry under the same conditions during the plant cover formation. The method based of the obtained empirical data is proposed for registration the biofouling contribution.
On the basis of daily means of sea surface temperature, concentration of chlorophyll "a", diffuse attenuation coefficient Kd(490) and remote sensing reflectance Rrs(555) from the array of satellite measurements with high spatial resolution COPERNICUS spatial-temporal features of seasonal and inter-annual variability of these parameters on the Black Sea surface analyzed. Shown, that in 2017, the main maximums of the Chl-a concentration and the coefficients of diffuse attenuation Kd(490) were observed in November-December. The second maximum of Chl-a and Kd(490) in the northern coastal zone of the sea was observed from February to June, in the in the deep sea – from February to March, near the sea southern coasts – from February to April. The main maximum of remote sensing reflectance Rrs(555) was observed in June-July. Shown, that in 2017 the sea surface temperature was higher than the climatic norm, the largest anomalies were observed mainly on the northwestern shelf and in the zone of the Eastern large-scale cyclonic gyre. Anomalies of Chl-a and Kd(490) during the year were predominantly negative, and the appearance of positive anomalies was observed in April to the west and to the east from the Crimean coasts. The Rrs(555) values for almost the whole year were close to the climatic norm except for June, when they were several times higher than climatic values.
The results of hydro-optical investigations performed in the spring-summer period of 2017 in the northern part of the Black Sea are considered. It is shown that during the spring survey (22.04.17 - 6.05.17), low concentrations of the total suspended matter were observed in the surface layer. The subsurface maximum in the vertical distributions of the total suspended matter concentrations was not present. In summer (14.06.17 - 4.07.17), due to intensive coccolithophore bloom, a higher content of suspended particles was observed. It was found that in summer the vertical structure of the total suspended matter concentration was characterized by a well-pronounced maximum at the depth close to the depth of vertical temperature and density gradients maxima.
The methods of determination of concentration and scattering by suspended particles in seawater are compared. The methods considered include gravimetric measurements of the mass concentration of suspended matter, empirical and analytical calculations based on measurements of the light beam attenuation coefficient (BAC) in 4 spectral bands, calculation of backscattering by particles using satellite measurements in the visible spectral range. The data were obtained in two cruises of the R/V "Professor Vodyanitsky" in the deep-water part of the Black Sea in July and October 2016., Spatial distribution of scattering by marine particles according to satellite data is in good agreement with the contact measurements.
By the beam attenuation measurements in the photic layer of the Black Sea the total suspended matter (TSM) content was calculated. The main features of the TSM spatial distribution were identified. The relationship between the TSM vertical distribution and the thermohaline structure is shown.
A method allowing to obtain estimates of dissolved organic and suspended matter content in Black Sea waters using beam attenuation coefficient (BAC) measurements in two spectral channels is proposed. It makes possible to assess the composition, bio-productivity and ecological state of waters in real time, and to validate the data of satellite scanners. The method is based on retrieval the spectral distribution of BAC by orthogonal functions. Full spectral distribution in range 416 – 677 nm allows to select spectral sites with a dominant contribution of certain substance in BAC and to obtain the content of yellow substance and suspended matter using specially designed optimization technique. Calculated values are in good agreement with the satellite data obtained from MODIS scanner.
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.
The results of the beam attenuation spectra measurements performed in August and September 2015 in the area of wastewater discharge in the southern part of the Heracleian Peninsula of the Black Sea are presented. The studies were conducted by sounding beam attenuation meter, developed in the Department of Optics and Biophysics of MHI RAS. Methods of measurement allowed to detect the presence of flooded streams pollutants in water in a real time.
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