Vol 40, No 6 (2024)
Analysis of observations and methods of calculating Hydrophysical fields in the ocean
Investigation of the relationship between partial pressure of carbon dioxide and sea surface temperature in the cyclic seasonal variations in the Black Sea
Abstract
Purpose. The purpose of the study consists in describing the parameterization based on the field data which take into account the relationship between the variability of pCO2 sw and the state of surface water layer depending on the sea surface temperature and allowing for geographical location and seasonality at the example of the Black Sea.
Methods and Results. The main seasonal trends of changes in pCO2 related to the variations in sea surface temperature are proposed based on special processing of direct measurement data on pCO2 of the surface layer obtained in the cruises of R/V “Professor Vodianitsky” in 2015–2023 and at the stationary observation point of the Black Sea hydrophysical subsatellite polygon (BSHSP), Katsiveli, in 2012–2022. The basic approach consists in describing the variations in pCO2 sw distribution over the sea surface using the linear approximations (trends) for three fixed seasons represented by four months (January – April, May – August and September – December) in each of the grid cells. It is shown that both in the coastal zone and in the open sea, the hysteresis dependences of pCO2 upon the sea surface temperature are manifested: the ratios of partial pressure and temperature during the periods of spring warming and autumn cooling are different. The reason for the observed hysteresis is related to a shift of the pCO2 sw fluctuation phase and a temperature change of about 1.5–2 months.
Conclusions. The dependence of pCO2 upon the sea surface temperature in an autumn-winter period turns out to be close to the dependences typical for the oceanic conditions in mid latitudes of the Northern Hemisphere (the Atlantic and Pacific oceans). This can indicate the universal mechanisms of influence of the sea surface temperature (SST) upon pCO2 sw both for the local conditions in the Black Sea and for the open ocean during a certain seasonal period. Besides, such a similarity of dependences can mean that, most likely, SST directly conditions a value of pCO2 sw, whereas biological activity is not a determining factor. The obtained results can be used for describing and studying the variations of the CO2 sea – air fluxes in the Black Sea.
805-820
Spatial and temporal dynamics of pH and total alkalinity of the Sea of Azov waters in 1950–2020
Abstract
Purpose. The purpose of the study consists in analyzing the spatial-temporal dynamics of pH and total alkalinity of the Sea of Azov waters in 1950–2020.
Methods and Results. Statistical analysis of the data on the Sea of Azov for 1950–2020 derived from the oceanographic database of the Southern Scientific Center of RAS made it possible to determine the average long-term values of the parameters under consideration in the Taganrog Bay, the open part of the Sea of Azov and the Kerch Strait by seasons. For the first time, the long-term changes in pH andtotal alkalinity of the Sea of Azov waters, as well as the distribution features of these parameters in theregions affected by the river runoffs are shown.
Conclusions. Two zones of Alk low values of seawater with the salinity ranges 2–4 and 11–13 ‰ were established in the Taganrog Bay. In these regions, under significant supersaturation of water with calcium carbonate the processes of chemogenic calcite formation are potentially possible. One zone of the increased pH values with the salinity range 4–6 ‰ coincides with the area of maximum phytoplankton productivity. In the Taganrog Bay, a pH increase in summer and autumn was noted, that can be explained by the growing production of organic matter against the background of salinity decrease starting from the second half of the 1970s, and by a rise of water temperature in the first decade of the 2000s. The open part of the sea and the Kerch Strait are characterized by a general trend towards a decrease in pH values, except for the period of an intensive river runoff. The general pattern of Alk distribution in the Sea of Azov consists in its relatively elevated values in the Taganrog Bay (especially in the regions with salinity range 5–8 ‰) which decrease towards the open sea and then increase towards the Kerch Strait. The average Alk value in the Taganrog Bay tended to decrease during the low-water periods (1972–1978 and 2011–2020) against the background of its general increase over the past seventy years. A noticeable growth of the average Alk values was noted during the period of increasing average water temperature in the Sea of Azov at the beginning of the 21st century.
821-837
Climatic variability of the Black Sea thermohaline characteristics (1950–2023)
Abstract
Purpose. The purposes of the study are to create a new climatic array of thermohaline fields in the Black Sea, to estimate (on its basis) the climate changes during the last decades and to compare them with the global climatic tendencies in the World Ocean.
Methods and Results. A new climate array of thermohaline fields in the Black Sea (MHI-2024) with a 1/6° × 1/4° spatial grid has been created in Marine Hydrophysical Institute of RAS based on statistical processing of more than 123 thousand hydrological stations in 1950‒2023 and using the methods of optimal interpolation. The climate atlas and the digital array are the open access products and can be used in climate studies, mathematical modeling, as well as in solving various applied problems. The deviations of initial data and averaged values from the climatic fields in the MHI-2024 array have constituted a basis for calculating the parameters of temporal variability at different scales and for forming the time series of average monthly/annual anomalies. It is revealed that after 2015, sea warming in the 0–100 m layer steadily exceeded the natural background of interannual variability, at that its maximal increase fell on the summer-autumn seasons. Since about 2010–2012, a sharp salinity growth has been observed which does not yet surpasses the standard deviation (SD) of interannual variability. The highest salinity increase in course of a seasonal cycle occurs in spring and autumn, i. e. when the water balance in the basin is maximal.
Conclusions. The Black Sea is related to the areas with the increased rates of climate changes, such as tropical parts of the World Ocean. The high temperature rise in the Black Sea over the past 40 years is the second in intensity as compared to that of the Arctic seas. Salinity growth in the Black Sea over a 70-year period is close to that in the areas of subtropical anticyclonic gyres, where over last 20 years, sharp salinification, atypical for the ocean, was observed. The current warm and saline stage of hydrologic state of the Black Sea is similar to the conditions in 1960–1970, but with greater oscillation amplitude. The obtained results are of a wide range of applications including the formation of general ideas on the carbon cycle mechanisms in the Azov-Black Sea basin.
838-852
“Bloom” of сoccolithophores in the Black Sea based on remote sensing data obtained in 1998–2023: Intensity and frequency
Abstract
Purpose. Monitoring of coccolithophore “blooms” is becoming increasingly important due to their influence on the biogeochemical cycles. The purpose of the study is to analyze the frequency, intensity and area of Gephyrocapsa huxleyi “bloom” in different sub-regions of the Black Sea, as well as to assess the affect of environmental factors on the intensity and interannual variability of “bloom”.
Methods and Results. Based on the satellite data and using the regional algorithms, the values of chlorophyll a concentration, the particulate backscattering coefficient and the coefficient of light absorption by colored detrital matter were retrieved with a two-week averaging for different Black Sea sub-regions for the period 1998–2023. Application of the normalized anomalies made it possible to reveal the annual cycles of variability of these parameters, as well as to identify their common patterns and variability features in particular sub-regions of the sea.
Conclusions. It has been revealed that in early June in all the regions of the sea, the “bloom” of Gephyrocapsa huxleyi was regularly observed; at that it was characterized by a year-to-year variability in its intensity and area. High light intensity in the sea upper mixed layer is a key factor for a shift in the phytoplankton species structure and for the transition to Gephyrocapsa huxleyi dominance and “bloom” due to the physiologically determined capacity for of these algae to grow at an extremely high light intensity with no inhibition, whereas at similar light conditions the growth of other plankton microalgae is suppressed. In most sub-regions of the Black Sea, the “bloom” of Gephyrocapsa huxleyi is not followed by an increase in the phytoplankton biomass, only species structure of phytoplankton changes. The exception is the coastal waters affected by the river runoffs: the “bloom” there is observed when the phytoplankton biomass increases. In the coastal waters during a cold period (December, February), the Gephyrocapsa huxleyi abundance sometimes increases due to a decrease of nutrient supply that results from weakening of the river runoffs and/or increasing stability of the water column. Decrease in phytoplankton supply with nutrients contributes to the competitive growth of coccolithophores as compared to other types of phytoplankton. The development of Gephyrocapsa huxleyi “bloom” in different seasons can reflect its genetic and physiological plasticity.
853-877
Experimental and field research
Biogeochemical characteristics of the surface layer and CO2 fluxes in the ocean – atmosphere system in the fjords of Western Spitsbergen
Abstract
Purpose. The study is purposed at assessing and analyzing spatial variability and seasonal dynamics of the carbonate system parameters in the fjords of Western Spitsbergen based on the results of field research in the spring (April) and summer (August) seasons, 2023.
Methods and Results. The physical and chemical parameters of water, such as total alkalinity, pH and nutrient component contents are studied. The samples are analyzed in the chemical analytical laboratory of the Russian Scientific Center at the Spitsbergen (RSCS). pH is measured using a Mettler Tolledo Seven Compact S220 laboratory pH-meter, and total alkalinity – by direct titration of a seawater sample with a 0.02 hydrochloric acid solution (the equivalence point is determined visually). The concentrations of phosphates and silicates, as well as chlorophyll a are measured by standard spectrometric methods. The carbonate system parameters, and CO2 flux direction and speed are computed within the Program Developed for CO2 System calculations. The revealed seasonal dynamics and variability of the carbonate system parameters are closely related to the atmospheric conditions, water mass seasonal variability and intensity of bioproductivity. The estimates of carbon dioxide flux obtained using the data for August 2023 permit to conclude that during this period it is absorbed in Grønfjord (–1.52 ... –4.76 mmol m–2·day–1) and Isfjord (–0.12 ... –1.0 mmol m–2·day–1), whereas in Billefjord a local area with positively directed CO2 flux (1.2–2.6 mmol m–2·day–1) is noted.
Conclusions. The studies carried out in the fjords have resulted in revealing seasonal fluctuations in the carbonate system parameters and the carbon dioxide fluxes similar to those in other inner fjords of Spitsbergen. The obtained results highlight the importance of the carbonate system parameters in understanding the biogeochemical balance and the state of marine ecosystems in the context of climate change.
878-890
Suspended matter of the deep-water part of the Black Sea
Abstract
Purpose. The purpose of the work is to research the suspended matter (SM) flux in the deep part of the Black Sea, its variability and transformation of composition under the anaerobic conditions based on the data of 2021–2022.
Methods and Results. The data were obtained using the sediment traps installed at five horizons at the transect Cape Chersonesos – Bosphorus Strait in the Black Sea. The automatic deep-sea sedimentation observatory (AGOS) was installed during the 119th cruise of the RV «Professor Vodyanitsky» and lifted during the 124th cruise in 2022. The research covered all the seasons in 2021–2022. To collect the material, two types of traps were included in AGOS: to determine the SM vertical distribution and to study its seasonal variation. The processing was carried out by the method common for all the samples, including filtration, drying, gravimetric analysis for calculating suspended particulate matter fluxes, as well as determination of the organic and inorganic carbon contents by the coulometric titration method in the laboratory of Marine Hydrophysical Institute of RAS. The study made it possible to obtain the data both on the vertical distribution of SM flux and its seasonal variation. The patterns of distribution of SM, as well as organic and inorganic carbon involved in its composition were revealed.
Conclusions. The dynamics of SM and carbon fluxes are determined by different processes including the physical and biogeochemical ones. The SM fluxes are distributed unevenly over depth and change seasonally in course of a year. Analysis of the integral trap data shows that at different depths the SM flux changes within 62–99 mg·m‒2·day‒1. At depths 218 and 1568 m it reaches its peak intensity. Its decrease depends on various biogeochemical processes, namely dissolution, oxidation and mineralization. The increase of SM flux, in its turn, can be related both to the deep-sea currents, and to the physical and chemical sorption processes. The seasonal changes in SM flux are represented by two peaks: its maximum falls on the period July – September and its minimum – on March. The carbon concentration in SM also varies with depth and seasonal variations which are conditioned mainly by the biological processes. The lag between the peaks of coccolithophore bloom at the surface and the maximum values of the inorganic carbon flux recorded by the trap can be explained by the sedimentation rates.
891-904
Mathematical modeling of marine systems
Distribution and vertical fluxes of particulate organic matter in the Black Sea based on the results of numerical modeling
Abstract
Purpose. The work is purposed at studying the spatial distribution, temporal variability and fluxes of particulate organic matter in the Black Sea based on numerical modeling.
Methods and Results. A model of the lower trophic level of the Black Sea ecosystem is applied to estimate the spatial distribution and vertical fluxes of particulate organic matter in the upper 200-meter layer. To extend the study to the whole thickness of the Black Sea, a model consisting of an equation for the evolution of particulate organic matter concentration in the layer from 200 m to the bottom was developed. The hydrodynamic and thermodynamic fields resulted from the previously performed reanalysis, are used as the coefficients of this equation and the equations of ecosystem model. The modeling was carried out for the period 2016–2020. The concentrations and vertical fluxes of particulate organic matter are obtained on a regular grid and with time resolution 1 day. The particulate organic carbon fluxes derived from numerical modeling are compared with the results of processing the samples collected by the sediment traps at two points in the Black Sea. The simulation results are in a fairly good qualitative and quantitative agreement with the measurement results.
Conclusions. A model for calculating the particulate organic matter content in the deep layers of the Black Sea was developed. The modeling results have shown that due to the biological processes, the particulate organic matter concentration in the surface layer of the Black Sea significantly exceeds the one in the deep-sea layer. The magnitude of vertical particulate organic matter fluxes in the surface layer is conditioned mainly by the suspended matter concentration, whereas in the deep-sea layer – by the value of vertical velocity. Based on the modeling results, the carbon flux directed from the water column to the bottom was classified as a result of suspended matter settling. The main part of this flux falls on the shelf zone of the sea.
905-917
Automation of scientific research of seas and oceans
Results of monitoring of greenhouse gas concentrations and variations in the Earth’s crust deformations at Cape Schultz in winter period, 2023–2024
Abstract
Purpose. The purpose of the study is to monitor climatic changes in the southern part of Primorsky Krai related to the variations in meteorological parameters, greenhouse gas flows, and the affect of catastrophic deformation processes of the Earth's crust.
Methods and Results. At the marine experimental station “C. Shultz”, complex measurements are continuously performed by a stationary hardware and software measuring complex for gas-deformation monitoring. The measuring complex consisting of several laser interference measuring devices (laser strainmeters, laser nanobarograph and laser meter of hydrosphere pressure variations) and a stationary closed-type gas analyzer for measuring the carbon dioxide and water vapor concentrations in the atmosphere, is briefly described. All the field measurement data obtained using the complex, are assembled in a common database for subsequent research. During the measurements performed in winter, 2023–2024 and spring, 2024, new data on the manifestations and interactions of different geospheric processes were obtained. In winter, an excess of carbon dioxide content in the atmosphere and its decrease in early spring were recorded, that was due to a seasonal change of the prevailing wind direction. The monitoring has resulted in revealing a daily frequency of the carbon dioxide concentration. At the same time, the effect of daily variations in the atmospheric air temperature upon the daily variations in carbon dioxide concentration was recorded. The deformation monitoring made it possible to record a catastrophic earthquake which caused a tsunami in the Sea of Japan. Calculation of the magnitude of the revealed deformation anomaly of the earthquake permitted to determine the magnitude of the Earth’s crust displacement which led to the occurrence of a tsunami wave. Complex processing of data shows the data correlation induced by micro-deformations the Earth’s crust and the variations in atmospheric pressure, carbon dioxide and water vapor in the atmosphere at tidal harmonics.
Conclusions. Comprehensive monitoring of the greenhouse gas concentrations and the variations in crustal deformations made it possible to identify the dependencies of short-period oscillations during the gas-deformation inter-geospheric interactions. The latest data on the changes in greenhouse gas concentrations in winter in the southern part of Primorsky Krai have been obtained.
918-935