Search

The Black Sea contains the largest volume of sulphidic water in the world. The position of the upper boundary of hydrogen sulfide is associated with the supply of oxygen, which is used for the oxidation of organic matter and reduced compounds of several chemical elements, such as sulfur, manganese, iron, nitrogen, etc. Climate change and anthropogenic impact dramatically affect the biogeochemical regime of the Black Sea. The depth of the oxygen layer of the sea depends on vertical mixing, which transfers dissolved oxygen from the upper euphotic layer to deeper layers, and the consumption of dissolved oxygen for the oxidation of autochthonous organic matter (OM) produced in the sea and allochthonous OM delivered with coastal runoff, and for the reduced forms of the listed elements.The study uses the BROM biogeochemical model, which describes biogeochemical processes in the water column. The BROM benthic-pelagic biogeochemical model combines a relatively simple ecosystem model with a detailed biogeochemical model for the water column, bottom boundary layer, and upper sediment, with a focus on changes in oxygen regime and redox conditions. BROM considers the interrelated transformations of chemical elements (N, P, Si, C, O, S, Mn, Fe) and organic matter (OM) in terms of nitrogen according to the Redfield ratio between the main nutrients.In this work, we used the previously combined BROM-2DBP model within the FABM framework. In order to more accurately reproduce the fine structure of the redox layer by the model, the parameterization of the change in the vertical velocity of the suspended matter due to aggregation with Mn(IV) oxide was introduced:WCi=WCi0+WMe∗Mn(IV)/(Mn(IV)+0.1) ,where WCi is the total vertical velocity, WCi0 is the own vertical velocity of the suspended matter, Mn(IV) is the concentration of Mn(IV) oxide.The hydrophysical forcing was hourly temperature, salinity, and orthogonal components of currents data for 2010 on a point with coordinates 43.5 °N. 37.75 °E from “Copernicus” portal. To take into account stationary recovery conditions, the upper 350 m were used in the calculations. The obtained data were compared with the field observations of the expedition aboard the R/V Knorr in March 2003. The obtained vertical distributions of hydrochemical parameters (a) are consistent with the existing hydrochemical structure of the Black Sea. Dissolved oxygen has a similar distribution in the model and observations, occupying the upper 70 m layer, its origin was located higher than the appearance of hydrogen sulfide at about 150 m. Within the redox layer, nitrate, Mn(IV), Mn(III ), Fe(III), elemental sulfur and a minimum of phosphate. Below the redox layer, the model reproduced the maxima of Mn(II) and Fe(II). Hydrogen sulfide appears at a horizon of about 80 m.The introduced parametrization of the additional vertical velocity of suspended matter makes it possible to more accurately reproduce the processes of a relatively thin redox layer by taking into account its aggregation with Mn(IV) oxide, which, in turn, can shift the redox layer lower or higher, depending on the availability of Mn(IV) oxide.

Progressive permafrost thawing leads to excessive transport of organic matter (OM) from the land and massive bubbling methane (CH4) release from degrading subsea permafrost in the Arctic shelf. The “extreme” aragonite under-saturation in the vast East Siberian Arctic Shelf (ESAS) reflects seawater acidity levels much higher than those projected in this region for the end of this century, as these are currently based only on atmospheric CO2.(Semiletov et al., 2016). The changes in the carbonate system can be explained by an excessive production of carbon dioxide connected due to mineralization of land origin OM or /and oxidation of methane in the areas of intensive seeping.Here, we analyze consequences of CH4 oxidation on the carbonate system state in the methane seepage areas. We used biogeochemical model BROM coupled with a vertical 2 Dimensional Benthic-Pelagic Model 2DBP and bubble fate model (Yakushev et al., 2021). BROM is a detailed biogeochemical model for the water column, benthic boundary layer (BBL), and sediments. BROM considers interconnected transformations of species (N, P, Si, C, O, S, Mn, Fe) and resolves OM in nitrogen currency. BROM includes a module describing the carbonate equilibrium; this allows BROM to be used to calculate pH and carbonates saturation states, as well as processes of formation and dissolution of carbonates. The model's alkalinity variations take into account changes connected with redox reaction consuming or releasing proton. Methanogenesis and aerobic and anaerobic methane oxidation are also parameterized. The gas bubble fate module parameterizes bubbles rising and dissolution. An application of the model allowed to estimate connection between an intensity of CH4 release in the area (Shakhova et al., 2015) and changes in the carbonate system and to evaluate a volume of water affected. This research was funded by the Research Council of Norway: 315317 BEST-Siberian.References:Semiletov et al. (2016) Acidification of East Siberian Arctic Shelf waters through addition of freshwater and terrestrial carbon. Nat. Geosci., 9 (2016), pp. 361-365, 10.1038/NEGO2695Shakhova N et al . ( 2015) The East Siberian Arctic Shelf: towards further assessment of permafrost-related methane fluxes and role of sea ice. Phil. Trans. R. Soc. A373: 20140451.http://dx.doi.org/10.1098/rsta.2014.0451Yakushev E., Blomberg A.E.A., Eek E., Protsenko E., Totland C., Staalstrøm A., Waaru I.-K. Modeling of biogeochemical consequences of a CO2 leak in the water column with bottom anoxia. International Journal of Greenhouse Gas Control. 2021. 111: 103464.

Microplastics (MPs) are plastic fragments less than 5 mm in size. At present, all natural environments, including the World Ocean, are polluted with MPs from the poles to the equator.The study tests the hypothesis that seasonality of processes in the marine ecosystem can affect the vertical transport of MPs in the water column (through changes in density due to biofouling and absorption and excretion of MP particles by zooplankton). The work used the biogeochemical model OxyDep (Yakushev et al., 2011) to reproduce the seasonality of marine ecosystem. BioPlast (Berezina et. al. 2021) considers processes of MPs degradation, biofouling, ingestion of particles by zooplankton and MPs in detritus. OxyDep biogeochemical module and MP module BioPlast were coupled with ROMS-20 (20 km resolution) 3D transport model using the FABM framework (Bruggeman & Bolding, 2014). The applied models describe the transformation of MPs and reproduce in detail the effect of ecosystem and biogeochemical processes on its vertical and horizontal transport, as well as on its burying in sediments.MPs were supplied to the Arctic Ocean from rivers flowing into the White, Barents, Kara and East Siberian Seas, as well as from the Atlantic Ocean, excluding any other sources. It was shown that within 8 years MPs spreads throughout the Arctic Ocean, except for the Canadian Basin. Several numerical experiments were conducted, MPs of Atlantic origin dominate in the western part of the Arctic Ocean. According to the upper estimate, the MPs from the North Atlantic occupies almost the entire water area of the Arctic Ocean. At the same time, the concentrations of MP covered with biofilm, MP in zooplankton, and MP in detritus are quite low compared to the virgin form of MP. A short-term purification of the surface layer from MP due to biofouling and sedimentation with detritus was observed in the estuarine zones and in the Fram Strait. This is partly due to the low productivity of the Arctic Ocean and the short period of phytoplankton blooms, and partly to the limitations of the BioPlast model. Further work will be devoted to the analysis of other sources of microplastics in the Arctic Ocean, such as the supply of MPs through the Bering Strait and local sources associated with maritime activity on the Northern Sea Route.The development of the described model is of great importance, especially for the Arctic region, where regular observations of MPs are not available, and the ecosystem is extremely vulnerable to anthropogenic impact.

Plastic is recognized as a threat to marine ecosystems and estimating the level of plastic and microplastics (MP) pollution of the World Ocean is nowadays the goal of many studies. However, the use of different methods for sampling and analysis of MPs leads to the problem of comparing the results obtained. Studies on surface MP pollution of the surface sea water are based on the application of the manta or neuston nets that collect water from the upper 10-20 cm layer (the “surface” MP) or submersible pumping systems, that collect water from the water layer 3-5 m below the sea surface (the “subsurface” MP). These two techniques allow to collect particles of different size fraction, i.e. >300 µm for the surface MP and >100 µm for subsurface MP. The aim of this work was to study the distribution of surface and subsurface MPs and to reveal an influence of oceanographic conditions on their spatial distribution as an example of the open ocean waters of the Central Atlantic and coastal water in Norwegian fjords. It was shown that microplastics found in the surface and subsurface layers differ not only in the size of the items found, but also in morphology, types of polymers, abundance, weight concentration and their spatial distribution. Different hydrodynamic processes affect the fate of plastic occurring exactly at the sea surface and several meters deeper. MPs inhabiting the subsurface waters (about 3-5 m depth) have buoyancy close to neutral and appear to be suspended in the surface mixed layer and are readily transported from the sources to the distant regions by ocean currents. Subsurface turbulence is probably the main process that maintains the MPs in the near-surface part of the water column. In contrast, the surface MPs (which are captured by sampling with surface nets) have positive buoyancy and its spatial distribution is significantly influenced by water dynamics, wind and waves, which led to a more scattered distribution on the ocean surface. It was shown that surface and subsurface microplastics differ significantly in a number of properties and, apparently, they should be considered as two independent groups that may have different sources, and their distribution is driven by different hydrophysical processes. Thus, MPs data collected using both methods simultaneously could provide additional information about MPs fate in the ocean.

Among other marine environmental problems, the issue of marine litter accumulation in the World Oceans is of increased interest. It is relevant not only in areas with direct intense anthropogenic pressure, but also in remote and presumably pristine areas, such as the Arctic Sea. As the concentration of plastic waste in the marine environment increases, it can have impacts on various components of the marine ecosystem, at sea, on the seafloor, on the coasts and in particular in accumulation areas, while it also can negatively affect human social and economic activities. To reduce the release of plastic debris into the marine environment, litter occurrence and pathways need to be studied in order to identify litter sources, requiring monitoring studies that provide comparable results. Here we present the results of studies of the level of pollution by floating marine debris carried out using ship-based visual observations through a harmonised methodology, developed to obtain comparable data. The observations were carried out in the White Sea, Barents Sea and the Kara Seas during a research cruise of the Floating University project by the Shirshov Institute of Oceanology Russian Academy of Sciences in 2021. The studies included training and involvement of a large number of students as observers. Floating macro litter was observed in all study areas along the vessel’s route. In total 2500 km route and 19,8 km2 were covered with observations. The concentration of litter varied on observed transects from 0 to 226 items/km2, with a mean value of 10.1 items/km². 95% of registered items were made of plastic, the most common were unidentified, weathered plastic objects that could indicate the long presence of litter items in the environment.

The present study addresses spatial and temporal distribution of floating microplastics in the Kara Sea. The studies were carried out in two cruises: on board the R/V «Akademik Mstislav Keldysh» in October 2020 and 2021, and the cruise on the R/V «Akademik Ioffe» as part of the MIPT Floating University in July-August 2021. A neuston net was used for sampling surface microplastics, each catch lasted an average of 30 minutes. Only particles up to 0.5 mm in size (detection limit with the naked eye) are considered in this work. In total, 85 samples were processed, including the samples in Kara Gates, estuaries of the Ob, Yenisei, Pyasina rivers, Baydaratskaya Bay, the central and northern parts of the Kara Sea (the northernmost point is 82.5 °N). All particles were analyzed on a Fourier transform infrared-spectrometer «Perkin Elmer spectrum two».A number of trends have been found. First, microplastics concentrations in plumes of Siberian Rivers were significantly lower than in the sea water (0-0,032 items/m3 in summer and 0-0,02 items/m3 in autumn). Second, higher concentrations were observed in the sea water (it can be noted that microplastic particles were found at the northernmost point of the expedition route). There was a local maximum in the Kara Gates Strait (1,53 items/m3), which can be explained by the local hydrophysics features, as well as by the general intensification of the processes in straits. Also a noticeable decrease of the microplastics concentration in the autumn in the same areas. Chemical composition of microplastics was diversified , all polymers with positive buoyancy were found: polyethylene, polypropylene, polystyrene and polyurethane foam. The most common were polyethylene and polypropylene, which correspond the level of their use. Particles of all morphological types were found. There was no significant seasonal variability in the polymer composition.Brief conclusions: Although the Great Siberian Rivers are one of the main sources of microplastics in the Kara Sea, they seem to dilute the total number of particles. The most considerable contribution is made by the Barents Sea waters coming from the Kara Gates Strait. A similar conclusion can be made due to the observed decrease in the concentrations of microplastics when moving eastward from the Kara Gates. There is a slowdown in the rate of microplastics inflow in the autumn period. There is no seasonal changes in the polymer composition of microplastic particles and their morphological composition.

Climate change and anthropogenic impact drastically affect the biogeochemical regime of the Black Sea, the contains the largest in the world volume of sulfidic water. The volume of the oxic layer of the sea depends on vertical mixing, that transports dissolved oxygen (DO) from the upper euphotic layer in the deeper layers and dissolved oxygen consumption for oxidation organic matter (OM). Changes in the Sea hydrodynamic properties due to warmer winters restricts renovation of the Black Sea Cold Intermediate Layer and therefore the DO flux to the deeper layers. The main goal of this study was to model upper 350 m with emphasis on redox layer.In the study we use the benthic-pelagic biogeochemical BROM model combined with 2DBP model for vertical and horizontal transport via FABM. BROM combines a relatively simple ecosystem model with a detailed biogeochemical model considering interconnected transformations of chemical species (N, P, Si, C, O, S, Mn, Fe). OM dynamics include parameterizations of production (via photosynthesis and chemosynthesis) and decay via oxic mineralization, denitrification, metal reduction, sulfate reduction and methanogenesis.Hydrophysical forcing (temperature, salinity and northward and eastward sea water velocity) was hourly data for year 2010 for a point with coordinates 43.5 °N. 37.75 °E from the E.U. Copernicus Marine Service Information “Copernicus”. The data is the result of a reanalysis calculation based on the NEMO hydrodynamic numerical model.The 2DBP/BROM model was applied for the 350 m water column with bottom boundary positioned in sulfidic layer. A steady-state solution was reached after 50 calculation years. The results of calculations were compared with the data of field observations of the expedition on the RV "Knorr" in March 2003. The obtained vertical distributions of hydrochemical characteristics are consistent with the existing understanding of the hydrochemical structure of the Black Sea. The dissolved oxygen has the similar structure in the model and observations occupying the upper 70 m layer, its onset was positioned shallower than the appearance of hydrogen sulfide at appr. 80. In the limits of the redox layer there were reproduced maxima of nitrite, Mn(IV), Mn(III), Fe(III), elemental sulfur and phosphate minimum. Below the redox layer the model reproduced maxima of Mn(II) and Fe(II).Calculated seasonal variability in the upper layer shows seasonality in development of phytoplankton and corresponding changes dissolved oxygen and nutrients. Organic matter distributions changes in accordance with seasonality of its production and destruction. At the same time, the redox layer remains practically unchanged during the year.At the present the BROM model is applied for the Black Sea and satisfactory validated against the data of observations. The calculated seasonal dynamics of the biogeochemical properties of the Black Sea will be used as an initial condition for studying of effects of changing in mixing (considering modeling interannual changes with difference in hydrodynamical scenarios) and allochthonous OM delivery on the biogeochemical structure of the Sea.This study was funded by the Ministry of Science and Higher Education of the Russian Federation, theme 13.2251.21.0008.

In this work we analyze how seasonal production and degradation of organic matter, and corresponding changes in the plankton ecosystem affect microplastics (MP) density and ability for transportation and burying in sediments. This is simulated with a coupled hydrodynamical-biogeochemical model that provides a baseline scenario of the seasonal changes in the planktonic ecosystem and changes in the availability of particulate and dissolved organic matter. We use a biogeochemical model OxyDep that simulates seasonal changes of phytoplankton (PHY), zooplankton (HET), dissolved organic matter (DOM) and detritus (POM). A specifically designed MP module BioPlast considers MP particles as free particles, particles with biofouling, particles consumed by zooplankton and particles in detritus, including fecal pellets. A 2D coupled benthic-pelagic vertical transport model 2DBP was applied to study the effect of seasonality on lateral transport of MP and its burying in the sediments. OxyDep and MP modules were coupled with 2DBP using Framework for Aquatic Biogeochemical Modelling (FABM). The model was applied to numerically predict the spatial distribution of MP in the water column and sediments after being discharged into the aquatic environment. We have used documented concentrations of MP (fibres) in the treated wastewater from a large wastewater treatment plant with discharge to the Bekkelaget basin in the Inner Oslofjord, Norway. Numerical experiments confirm, that biogeochemical cycling leads to seasonality in the vertical and horizontal transport of MP of neutral buoyancy from its source, with higher accumulation in the sediment during the summer-autumn period, while cleaning of the upper water layers resembles the winter period. That means that MP of neutral buoyancy could be transported to a smaller distance in summer, compared with winter. Transport of light density floating MP into the deep layers and the sediments can be explained by influence of biogeochemical processes. High density MPs are affected by the biogeochemical processes to a very small degree and tend to accumulate in the sediments close to the source point. Thus, we confirm that the “biological pump” can be one of the important drivers controlling the quantity and the distribution of MP in the water column. The biological pump can deplete MP from the surface water and accelerate MP burying in summer period compared to the winter.The reported study was funded by RFBR according to the research project № 20-35-90056.

The flowing into the White Sea Northern Dvina River is the largest river in the European Arctic, and in contrast to other Arctic rivers, it runs through the populated regions with developed industry. Observations on seasonal variability of microplastics were organized in the Northern Dvina River mouth. The samples were collected every month from September to November 2019 and from May to October 2020 with a Neuston net that was togged 3 nautical miles in the Korbel’nyy Branch of the River delta. Surface plastic with dimensions ranging from 0.5 to 5 mm was analyzed. Chemical composition of the plastic particles was determined using an FT-IR spectrometery in Norway (Oslo) and Russia (Arkhangelsk). The majority of the microplastics were identified as polyethylene (PE) 52.63%, followed by polypropylene (PP) 36.84% and Ethylene Ethyl Acrylate Copolymer (EEA) 10.53%. It was found that the average concentration of microplastics was 0.0054 items/m3, that is close to the average concentration of surface microplastics observed in the in the open Barents Sea, 0.005 items/m3 (Yakushev et al. 2021). No detectable seasonal variability of the microplastics content in the waters of the Northern Dvina was found. With an assumption that the concentration of microplastics is the same in all the depths, we can assess how the amount of delivering to the sea microplastics changes throughout the year. The microplastics input rate during the spring flood period in May turned out to be maximum, 37.76 items/second. The minimum input rate can be in September with a value of to 5.28 items/second. The data obtained allow us to conclude that the Northern Dvina River is be one of the main sources of microplastic pollution of the White and Barents Seas. This work was partly funded by the Norwegian Ministry of Climate and Environment project RUS-19/0001 “Establish regional capacity to measure and model the distribution and input of microplastics to the Barents Sea from rivers and currents (ESCIMO)” and the Russian Foundation for Basic Research, research projects 19-55-80004.

The fate of microplastics (MP) in seawater is heavily influenced by the biota: the density of MP particles can be changed due to biofouling, which affects sinking, or MP can be digested by zooplankton and transferred into fecal pellets with increased sinking rate. We hypothesize that seasonal production and degradation of organic matter, and corresponding changes in the plankton ecosystem affect the MP capacity for transportation and burying in sediments in different seasons. This is simulated with a coupled hydrodynamical-biogeochemical model that provides a baseline scenario of the seasonal changes in the planktonic ecosystem and changes in the availability of particulate and dissolved organic matter. In this work, we use a biogeochemical model OxyDep that simulates seasonal changes of phytoplankton (PHY), zooplankton (HET), dissolved organic matter (DOM) and detritus (POM). A specifically designed MP module considers MP particles as free particles (MPfree), particles with biofouling (MPbiof), particles consumed by zooplankton (MPhet) and particles in detritus, including fecal pellets (MPdet). A 2D coupled benthic-pelagic vertical transport model 2DBP was applied to study the effect of seasonality on lateral transport of MP and its burying in the sediments. OxyDep and MP modules were coupled with 2DBP using Framework for Aquatic Biogeochemical Modelling (FABM). A depletion of MP from the surface water and acceleration of MP burying in summer period compared to the winter was simulated numerically. The calculations confirm the observations that the “biological pump” can be one of the important drivers controlling the quantity and the distribution of MP in the water column.

Plastic pollution is globally recognised as a threat to marine ecosystems, habitats, and wildlife, and it has now reached remote locations such as the Arctic Ocean. Nevertheless, the distribution of microplastics in the Eurasian Arctic is particularly underreported. Here we present analyses of 60 subsurface pump water samples and 48 surface neuston net samples from the Eurasian Arctic with the goal to quantify and classify microplastics in relation to oceanographic conditions. In our study area, we found on average 0.004 items of microplastics per m3 in the surface samples, and 0.8 items per m3 in the subsurface samples. Microplastic characteristics differ significantly between Atlantic surface water, Polar surface water and discharge plumes of the Great Siberian Rivers, allowing identification of two sources of microplastic pollution (p

The main objectives of this work were the acquisition of new data on floating marine macro litter (FMML) and natural floating objects in the Arctic seas, an initial assessment of the level of pollution by FMML and an analysis of potential sources. The results of this study present the first data on FMML distribution in Russian Arctic shelf seas in relation to oceanographic conditions (i.e. position of water masses of different origin as described by temperature, salinity, dissolved oxygen and pH). The main finding of this study is that FMML was found only in the water of Atlantic origin, inflowing from the Barents Sea, where FMML average density on the observed transects was 0.92 items/ km2. Eastern parts of the study, Kara Sea, Laptev Sea and East Siberian Sea were practically free from FMML. No input from rivers was detected, at least in autumn, when the observations were performed.

To investigate the impacts of fish farm emissions, we coupled the biogeochemical C-N-P-Si-O-S-Mn-Fe transformation model BROM with a 2-Dimensional Benthic-Pelagic transport model (2DBP), considering vertical and horizontal transport in the water and upper 5 cm sediments along a 10000 m transect centered on a fish farm. The 2DBP model had 25 m horizontal resolution and was forced by hydrophysical model data for the Hardangerfjord in western Norway. The model predicted significant impacts on seafloor biogeochemistry up to 500 meters from the fish farm (e.g., increased organic matter in sediments, oxygen depletion in water and sediments, denitrification, metal and sulfur reduction) as well as detectable decreases in oxygen and increases in ammonia, phosphate and organic matter in the water near to the fish farm cages. The model results are compared with field data from the Hardangerfjord in August 2016 and indicated satisfactory model performance.