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Project titleBeryllium-7 in the Black Sea: spatiotemporal variability and processes that determine it

AffiliationFederal State Budget Scientific Institution Federal Research Centre "Marine Hydrophysical Institute of RAS",

KeywordsBeryllium-7, tracer, Black Sea, numerical modeling, spatiotemporal variability, control processes, sedimentation flux.

Annotation
This project is aimed at developing a three-dimensional model of beryllium-7 transport in the Black Sea waters, developed earlier by the participants of the proposed project, and identifying regions in which this radionuclide can be used as a tracer of processes that determine the transport of dissolved or suspended substances. The relevance of research is due to two reasons. The first reason is that various pollutants continuously enter the marine environment, including passive and conservative impurities represented by radionuclides, heavy metals and persistent organic compounds. In high concentrations, these substances have a negative impact on the functioning of the ecosystem. In this regard, the calculation of the concentration fields of such substances is of great scientific and practical interest. Beryllium-7 is a natural radionuclide of cosmogenic origin, which is formed in the atmosphere and enters the marine environment with a stream of "wet" and "dry" atmospheric fallout. This radionuclide in the marine environment behaves as a passive and conservative impurity. Thus, data on the spatial and temporal variability of the beryllium-7 content are extremely useful in developing models for the transport of passive and conservative impurities at the stage of their validation. The second reason is that beryllium-7 is an ideal tracer in the study of processes occurring in the active layer of seas and oceans on time scales from synoptic to seasonal. In the marine environment, beryllium-7 is distributed between dissolved and adsorbed on suspension forms. Potentially, beryllium-7 is the most convenient tracer in the study of the processes that determine the transport of dissolved impurities, and quite promising in the study of the transport of suspended impurities, but before using it in one role or another, it is necessary to quantify the contribution of sedimentation processes to the vertical transport of this radionuclide and identify regions where this contribution is low or high, depending on the objectives. In practice, mathematical models are the most convenient tool for identifying such regions when considering the entire Black Sea area. In the course of the project, the model will be improved by using the technology of nested grids (nesting). For the coastal zone of the Black Sea, it will be possible to carry out calculations with a spatial resolution of about 500 m. The accuracy of impurity concentration calculations will be ensured by increasing the accuracy of circulation modeling by assimilating field data on the hydrological structure of waters. The computing complex will be transferred to the CMF platform, which provides parallel operation of the basin model of the sea and the nested model of the coastal zone. Within the framework of the project, for the first time, comprehensive studies of the vertical structure of the beryllium-7 concentration field will be carried out using field and model data, quantitative estimates of the contribution of sedimentation to the vertical transport of this radionuclide for the entire Black Sea area will be obtained.

Expected results
Expected results: 1. For the first time, field data on the vertical distribution of beryllium-7 in the marine environment and bottom sediments in the Black Sea shelf zone will be obtained (approximately 18 stations). 2. For the first time, comprehensive studies of sedimentation flows of beryllium-7 in the waters of the Black Sea will be carried out using field and model data. For the first time, maps of the spatial distribution of the contribution of sedimentary flows to the vertical transport of beryllium-7 for the entire Black Sea area will be obtained and analyzed. 3. For the first time, a qualitative and quantitative analysis of the influence of various processes on the seasonal variability of the vertical flow and the vertical distribution of beryllium-7 in the shelf and deep water zones of the Black Sea will be carried out according to numerical experiments. 4. A new version of the domestic three-dimensional thermohydrodynamic model of the Black Sea circulation will be proposed, combined with the passive and conservative admixture transfer model developed and developed at the Marine Hydrophysical Institute. Passive and conservative impurities in the marine environment can be represented by substances of various nature and origin. These can be radionuclides (cesium-137, strontium-90, etc.), heavy metals (mercury, cadmium, lead) and persistent organic pollutants (PCBs, pesticides, etc.). At high concentrations, these substances have a negative impact on the functioning of the ecosystem. In this regard, the development and improvement of models that make it possible to calculate the concentration fields of such substances entering the marine environment from various sources is of great scientific and practical interest. In particular, these data are necessary in the development of measures to prevent the development of dangerous phenomena for the ecosystem. Beryllium-7 enters the marine environment from the atmosphere and behaves in the marine environment as a passive and conservative impurity. Data on the content of this radionuclide and its spatiotemporal variability are extremely useful in the development of models for the transfer of passive and conservative impurities. The radionuclide itself is also of great interest, since, according to the available literature data (Kadko et al., 1996, 2011, 2019; Haskell et al., 2015a, 2015b, 2016; Kadko, 2017), it is the most convenient tracer in the study of processes determining the inflow and transport of substances in the active layer of seas and oceans on time scales from synoptic to seasonal. At the same time, in the marine environment, beryllium-7 is distributed between dissolved and adsorbed on suspension forms, and the determination of areas in which this radionuclide can be used as a tracer of processes that determine the transport of dissolved or suspended substances is of great practical interest. The results obtained during the implementation of the project fully correspond to the world level in this field of research. Haskell, W.Z., Hammond, D.E., Prokopenko, M.G., 2015b. A dual-tracer approach to estimate upwelling velocity in coastal Southern California. Earth planet. Sci. Lett. 422, 138–149. https://doi.org/10.1016/j.epsl.2015.04.015. Haskell, W.Z., Kadko, D., Hammond, D.E., Knapp, A.N., Prokopenko, M.G., Berelson, W.M., Capone, D.G., 2015a. Upwelling velocity and eddy diffusivity from 7Be measurements used to compare vertical nutrient flux to export POC flux in the eastern tropical South Pacific. Mar. Chem. 168, 140–150. https://doi.org/10.1016/j.marchem.2014.10.004 Haskell, W.Z., Prokopenko, M.G., Hammond, D.E., Stanley, R.H.R., Berelson, W.M., Baronas, J.J., Fleming, J.C., Aluwihare, L., 2016. An organic carbon budget for coastal Southern California determined by estimates of vertical nutrient flux, net community production and export. Deep Sea Res. Part I: Oceanogr. Res. Pap. 116, 49–76. https://doi.org/10.1016/j.dsr.2016.07.003. Kadko, D., 2017. Upwelling and primary production during the U.S. GEOTRACES East Pacific zonal transect. Glob. Biogeochem. Cycles 31, 218–232. https://doi.org/10.1002/2016GB005554. Kadko, D., Aguilar-Islas, A., Bolt, C., Buck, C.S., Fitzsimmons, J.N., Jensen, L.T., Landing, W.M., Marsay, C.M., Rember, R., Shiller, A.M., Whitmore, L.M., Anderson, R.F., 2019. The residence times of trace elements determined in the surface Arctic Ocean during the 2015 US Arctic GEOTRACES expedition. Mar. Chem. 208, 56–69. https://doi.org/10.1016/j.marchem.2018.10.011. Kadko, D., Johns, W., 2011. Inferring upwelling rates in the equatorial Atlantic using 7Be measurements in the upper ocean. Deep Sea Res. Part I: Oceanogr. Res. Pap. 6 (58), 647–657. https://doi.org/10.1016/j.dsr.2011.03.004. Kadko, D., Landing, W.M., Buck, C.S., 2020. Quantifying atmospheric trace element deposition over the ocean on a global scale with satellite rainfall products. Geophys. Res. Lett 47. https://doi.org/10.1029/2019GL086357 Kadko, D., Olson, D., 1996. Beryllium-7 as a tracer of surface water subduction and mixed-layer history, Deep Sea res. Part I: Oceanogr. Res. Pap. 2 (43), 89–116. https://doi.org/10.1016/0967-0637(96)00011-8. Kadko, D., Prospero, J., 2011. Deposition of 7Be to Bermuda and the regional ocean: environmental factors affecting estimates of atmospheric flux to the ocean. J. Geophys. Res. 116, C02013 https://doi.org/10.1029/2010JC006629

Annotation of the results obtained in 2022
In the first year of the project implementation, in the course of expeditionary research, sea water samples (24 stations, 64 samples) and bottom sediments (35 stations, 60 samples) in the Black Sea were taken. Based on the results of samples processing, new data on the spatial variability of the vertical distribution of beryllium-7 in dissolved and adsorbed forms, as well as on the content of beryllium-7, cesium-137, radium-226, and lead-210 in bottom sediments were obtained. Using these data, quantitative estimates of a number of parameters were carried out: the distribution coefficient of beryllium-7 between dissolved and adsorbed forms on particulate matter, the rate of sedimentation of particulate matter, the rate of sedimentation, the flow of suspended matter, and the contribution of sedimentation processes to the vertical transport of beryllium-7 was also estimated. It has been established that the value of the distribution coefficient of beryllium-7 in the surface layer of the Black Sea waters varies in space by 5 times, with depth the value of the coefficient increases by 0.3–10 times relative to its value in the surface layer. Most (56–81%) of beryllium-7, which enters the upper quasi-homogeneous layer in winter, undergoes radioactive decay without leaving it. The contribution of sedimentation processes to the vertical transfer of beryllium-7 from the upper quasi-homogeneous layer to the underlying layers varies from 1.5 to 31.3%. The maximum values of the contribution are observed in the coastal zone, the minimum - in the deep water. The rate of sedimentation and sedimentation flow in the study region varies in the ranges from 0.3 to 4.7 mm/year and from 162 to 3111 g/m2, respectively. The maximum velocities are noted in the coastal zones, the minimum - on the shelf (deep water areas were not considered). The data necessary for carrying out numerical experiments and validating the results obtained have been prepared. The MHI model has been improved by adding a data assimilation procedure. A program code has been implemented for joint modeling of beryllium-7 transport in the Black Sea both in the entire basin with a resolution of 1.6 km and in the coastal zone of Crimea with a resolution of 0.56 km. Preliminary numerical experiments were carried out, which made it possible to determine the choice of boundary conditions and perform the selection of coefficients. Thus, ERA5 atmospheric reanalysis data were chosen as atmospheric forcing. When performing high-resolution calculations, the Dirichlet conditions were implemented for the equations of motion on the open part of the lateral boundaries (velocity components calculated from the model with a coarser resolution were set for each calculated time moment). For sections of the boundary where water flowed into the region, temperature, salinity (Dirichlet conditions) were set; for sections of the boundary where water flowed out of the area, Orlansky's conditions (Orlanski, 1976) were set to determine T and S at the open boundary. These conditions were discretized using the central explicit numerical scheme (Kantha et al., 1990) to calculate the perturbation transfer rate. The adjusted values of the horizontal turbulent viscosity and diffusion coefficients, as well as the time step, were νH = 5 10E5 cm2/s, κH = 3 10E5 cm2/s, and 10 s, respectively. A test calculation was carried out for modeling the hydrodynamics of water and the transfer of beryllium-7 in the zone of the Southern coast of Crimea for the period June 30 - July 21, 2016. The results of the validation of the data obtained in the course of the numerical experiment indicate that in the seaward part both models show close values of the concentration of beryllium-7 that fall within the measurement error themselves, while near the coast the model of the coastal zone provides more accurate data.

Publications

1. Demyshev S.G., Dymova O.A., Miklashevskaya N.A. Особенности изменчивости плотности доступной потенциальной энергии и работы силы плавучести в верхнем 300-м слое Черного моря по результатам численного моделирования Physical Oceanography, - (year - 2023)

2. Dymova O., Markova N. Numerical Estimation of the Black Sea Circulation near the Continental Slope Using SKIRON and ERA5 Atmospheric Forcing Environmental Sciences Proceedings, 25(1), 61 (year - 2023) https://doi.org/10.3390/ECWS-7-14305

3. Kremenchutskii D.A., Batrakov G.F. Seasonal variations in total deposition velocity and washout ratio of fine aerosols revealed from beryllium-7 (7Be) measurements in Sevastopol, the Black Sea region Atmospheric Pollution Research, Volume 14, Issue 3, 101698 (year - 2023) https://doi.org/10.1016/j.apr.2023.101698

4. Markova N.V., Dymova O.A. Влияние вихревой и бассейновой динамики на формирование противотечений в северо-восточной части Черного моря Волны и вихри в сложных средах: 13-ая международная конференция – школа молодых ученых; 30 ноября – 02 декабря 2022 г., Москва: Сборник материалов школы. – М.: ООО «ИСПО-принт», 2022. – С.170-173., С.170-173. (year - 2022)

5. Kremenchutskii D.A., Batrakov G.F. Поток бериллия-7 из атмосферы в г. Севастополь Сборник тезисов докладов Всероссийской конференции, посвященной памяти академика Александра Михайловича Обухова «ТУРБУЛЕНТНОСТЬ, ДИНАМИКА АТМОСФЕРЫ И КЛИМАТА». М.: Физматкнига, 2022 – С. 131., С. 131. (year - 2022)

6. - Победителем «молодежного» конкурса 2022 года Президентской программы РНФ стал Дмитрий Кременчуцкий! Морской гидрофизический институт РАН, - (year - )