Northwestern Black Sea Shelf Research Articles

STATE-OF-THE-ART 3D ACQUISITION AND IMAGING IN ULTRA-SHALLOW WATER IN THE NORTHWESTERN PART OF THE BLACK SEA

Background. The paper discusses the acquisition and imaging (PSDM+FWI) of 3D seismic data in the ultra-shallow waters of the Black Sea's northwestern shelf, focusing on the Dolfin Inner shelf license areas. Despite depths ranging from 14m to 40m, an efficient acquisition setup has been chosen to navigate seafloor obstacles. Methods. GeoStreamer data has allowed more advanced imaging options. Access to separated wavefield components has permitted us to include advanced processing technologies. The data underwent advanced processing, including 3D wavefield separation, deghosting, demultiple, and machine learning-guided denoising. Results. Results demonstrate the final migration velocity model's (with FWI) ability to capture high and low velocity contrasts critical for depth imaging. Separated wavefield imaging (SWIM) enhances imaging of the seafloor providing a very good match with bathymetry data. SWIM also allows acquiring high-resolution images of the shallow water area, which opens up the possibility of using this data for wind farm siting and hydrogen exploration. Сonclusions. Comparing 2D and 3D seismic data emphasizes the latter's superior quality, crucial for evaluating the Dolfin Inner shelf area's hydrocarbon potential. Next study will focus on the exploration in the Outer Shelf and adjacent deepwater domains, highlighting the Black Sea's Ukrainian waters as a promising frontier for oil and gas exploration. The acquired 3D seismic data plays a pivotal role in advancing this exploration, contributing valuable insights in a cost-effective manner.

An Assessment of Potential Beam Trawling Impact on North-Western Black Sea Benthic Habitats Aiming at a Sustainable Fisheries Management

The North-Western Black Sea shelf is extremely vulnerable to disturbances of its habitats and ecosystems. In the past 10 years, this area has become targeted by beam trawl fisheries for the invasive gastropod Rapana venosa (Valenciennes, 1846), with a potentially destructive impact on the area’s soft bottoms. Not many studies have been performed in the region, and most investigations have focused on gear selectivity and by-catch rates. In this context, our novel research aimed, on the one hand, to assess and quantify the actual impact of beam trawling and, on the other hand, to propose effective spatial/temporal management measures for a sustainable zonation of the North-Western Black Sea shelf (marine zone of the Danube Delta Biosphere Reserve). The methodology used integrated beam trawl catch dynamics information, VMS data, geophysical investigations, and macrozoobenthos sampling. Our findings show that beam trawling activities can cause changes in the benthic habitat structure (lower number of taxa, lower values of ecological indicators, and an overall non-GES status). Further in-depth investigations are needed to underpin the ecosystem-based management of this marine protected area (MPA), aiming to allow the recovery of the affected benthic habitats, by alternating defined areas undergoing fishing with biological recovery polygons.

The precision of the migration image of the depth section on the seismometry observations on northwestern Black Sea shelf

For many years, the Institute of geophysics has been developing original versions of the finite-difference migration and wavefield modeling techniques for a valid reproduction of the geological cross-section. The modeling provides a practical test of the accuracy of the reproduction of various geological structure features on a migration result and a way to define, in the observed field, the waves which can be used to produce a migration image of the geologic environment efficiently.
 In 2013, the Institute conducted a marine seismic investigation with reflection CDP (Common Deep Point) profiles on the continental slope of the NW part of the Black Sea. The registered wavefields were processed using full-wave finite-difference post-stack migration. The efficiency and validity of the processing methods for various geological structures were evaluated with the help of finite-difference modeling of the wavefield based on solving the wave equation on a grid with a seven-point pattern.
 The study validates the precision of marine seismic data processing using full-wave finite-difference post-stack migration with the help of wavefield modeling.

Locating the southern boundary of the East European Platform within the north-western Black Sea shelf according to gravimetric data

The work is devoted to the problem of determining the position of the border of the East European Platform (EEP) and the Scythian Plate (SP), which is of great economic importance in dividing the north-western shelf of the Black Sea into more and less promising areas for hydrocarbons. An analysis of the allocation of the juncture of EEP and SP using 23 literature sources published from 1985 to 2020 was performed. The essential differences in drawing the relevant line by different authors are shown. A method for determining the position of the southern boundary of the EEP within the north-western shelf of the Black Sea is proposed, based on the integrated use of gravimetry data — characteristic features of the gravity field (Δgf.a.) and the results of systematic two-dimensional density modeling. The outcome of modelling allowed determining the position and nature of the EEP and SP junction in the section of the earth’s crust, which turned out to be a transcrustal fracture of the southern falling with angles of inclination from 83.5° to 85.5° in different parts of the shelf. According to calculations of the exit points of the faults on the basement surface superimposed on the scheme Δgf.a made it possible to identify the spatial position of the junction of EEP and SP and its extension outside the modeling area for the entire study area. It is established that this line has a zigzag character, changing direction at the intersection with submeridional faults. It is shown that the formation of the southern boundary of EPS was controlled, except for the submeridional component characteristic of EPS, by three other systems — latitude, directions NE-SW and NW-SE, which are observed for tectonic elements of SP in Pridobruzha and Crimea. The correctness of the determination of the boundary position by gravimetric data is confirmed by the results of seismic stratigraphy and thermometry previously obtained by other researchers.

A Multi-Proxy Approach to Reconstruct Hypoxia on the NW Black Sea Shelf over the Holocene

Coastal hypoxia is a worldwide concern. Even though seasonal hypoxia has been reported on the northwestern Black Sea shelf since the 1970s, little is known about oxygenation in this area over the Holocene. With a multiproxy approach, this work aimed to detect potential hypoxic events in two gravity cores. Our results demonstrate that the most common proxies of hypoxia are irrelevant for the Black Sea coastal environment. For instance, the Ammonia-Elphidium index appears to be inappropriate. We assume a salinity bias due to the influence of freshwater inputs. Likely, the redox sensitivity of vanadium is obscured by the dominant supply of detrital elements. However, the size distribution of framboidal pyrites gives clear indications of the oxygenation of the water column. Indeed, the absence of framboidal pyrites in the core located at the Danube mouth suggests permanent oxic conditions over the last 2 ka. On the contrary, in the core located in the Odessa Bay, the two observed ranges of pyrite sizes evidence an alternation between anoxic (mean diameter 3–6 ± 1–2 µm) and hypoxic or oxic (mean diameter 6–10 ± 3–5 µm) conditions in bottom waters over the last 7 ka. Therefore, this proxy reveals different oxygenation levels for these proximal sites.

Rhyolites of the Kiliya-Zmeinyi uplift on the Black Sea shelf: geochemical evidence of a non-subduction boundary between the East European Platform and the Scythian Plate

The geochemistry of rhyolites uncovered at shallow depth by a borehole on the Kiliya-Zmeinyi uplift of the Black Sea northwestern shelf northeast of Zmeinyi island, in the junction zone of the East European platform and the Scythian plate, has been studied for the first time. This zone is considered by many geologists and geophysicists as a Late Paleozoic collisional suture that had been formed due to subduction of oceanic crust of the ocean, which adjoined the East European platform from the south, under the Scythian plate; it is traced from Dobrudzha to the Caspian Sea and named North Crimean. To check the subduction nature of the boundary between the East European platform and the Scythian plate, igneous rocks’ geochemical characteristics beeng indicators of various geodynamic regimes were used. A petrogeochemical comparison of rhyolites from the borehole in Zmeinyi area with acid igneous rocks known nearby has been carried out, namely with: 1) Late Permian subalkaline granites and rhyolites Turcoaia of the Macin zone of Northern Dobruja; 2) Triassic and / or Triassic-Jurassic trachyrhyolites and rhyolites of the Tulcea zone of Northern Dobruja and the Tatarbunar complex of the Pre-Dobruja depression. Some acid rocks of various ages and genesis from the southernmost margin of the Scythian plate (southwestern Crimea on- and offshore) were taken additionally for comparison. According to the distribution of rare earth elements, the position on the discriminant geochemical diagrams and the shape of curves on the multicomponent spider diagrams, the rhyolites of the Kiliya-Zmeinyi uplift exhibit not subduction but intraplate geochemical features closest to those of granites and rhyolites Turcoaia of the Macin zone of Northern Dobruja. Considering that the latter are reputed to be Late Permian, one can assume the same age for the rhyolites from the borehole in Zmeinyi area. Taking into account section features, geophysical information and geochemical similarity of magmatism, Kiliya-Zmeinyi uplift of the northwestern shelf seems to be a continuation of the Northern Dobruja structure into the Black Sea; it was a part of the hypothetical Late Paleozoic Euxinian orogen near its northern boundary. An absence of subduction geochemical properties in the studied presumably Late Permian rhyolites indicates that the junction zone of the East European platform and the Scythian plate in the Ukrainian shelf area is not a Late Paleozoic suture, but rather represents a thrust of the Euxinian orogen.

Heavy Metals in the Bottom Sediments of the Black Sea Northwestern Shelf in Recent Years

Purpose. The study is aimed at investigating metal accumulation in the 0–2 cm layer of the bottom sediments of the Black Sea northwestern shelf over 2000–2020, and at identifying the sea bottom areas subjected to the increased anthropogenic load through comprehensive assessment of the degree of their pollution taking into account their granulometric composition. Methods and Results. The bottom sediments were sampled annually from the 0–2 cm depth at the same stations. The detected metal concentrations were compared with their content in the Earth crust and the background values. The dynamics and trends of the individual metals’ content in the shelf bottom sediments were assessed for the whole period of observations. The notion of the average characteristic concentration of an element is introduced; the procedure for its calculation is represented. The pollution of bottom sediments was analyzed with the regard for the element average characteristic concentration in the bottom sediments of various granulometric types. Increase in the average content of lead, zinc and chromium was revealed from the beginning of the observation period to 2020. The seasonal dynamics of these elements was found in the whole water area under study (as well as the iron content at some areas). Conclusions. Multiple cases of the lead, manganese and chrome concentrations exceeding their content in the Earth crust were recorded; as for zinc and copper, such cases were few and sporadic. The tendencies in variation of the bottom sediments content were determined: the average long-term values of the lead concentration increased by 1.2 times, those of zinc – by 1.6 times, and those of chrome – by 2 times; the concentrations of iron, manganese and copper remained essentially the same. Seasonal dynamics of the zinc, chromium, lead and iron content was shown. For a number of metals, the cases when their absolute content exceeded their average characteristic concentration in the corresponding type of the bottom sediments had been found. The regions subjected to a multi-faceted anthropogenic load were identified; the areas of possible local inflow of the monitored elements were revealed. The bottom sediments sampled in 2019 were the most polluted.

Tyazhelyye metally v donnykh osadkakh shel'fa severo-vostochnoy chasti Chernogo morya v sovremennyy period

Purpose. The study is aimed at investigating metal accumulation in the 0–2 cm layer of the bottom sediments of the Black Sea northwestern shelf over 2000–2020, and at identifying the sea bottom areas subjected to the increased anthropogenic load through comprehensive assessment of the degree of their pollution taking into account their granulometric composition. Methods and Results. The bottom sediments were sampled annually from the 0–2 cm depth at the same stations. The detected metal concentrations were compared with their content in the Earth crust and the background values. The dynamics and trends of the individual metals’ content in the shelf bottom sediments were assessed for the whole period of observations. The notion of the average characteristic concentration of an element is introduced; the procedure for its calculation is represented. The pollution of bottom sediments was analyzed with the regard for the element average characteristic concentration in the bottom sediments of various granulometric types. Increase in the average content of lead, zinc and chromium was revealed from the beginning of the observation period to 2020. The seasonal dynamics of these elements was found in the whole water area under study (as well as the iron content at some areas). Conclusions. Multiple cases of the lead, manganese and chrome concentrations exceeding their content in the Earth crust were recorded; as for zinc and copper, such cases were few and sporadic. The tendencies in variation of the bottom sediments content were determined: the average long-term values of the lead concentration increased by 1.2 times, those of zinc – by 1.6 times, and those of chrome – by 2 times; the concentrations of iron, manganese and copper remained essentially the same. Seasonal dynamics of the zinc, chromium, lead and iron content was shown. For a number of metals, the cases when their absolute content exceeded their average characteristic concentration in the corresponding type of the bottom sediments had been found. The regions subjected to a multifaceted anthropogenic load were identified; the areas of possible local inflow of the monitored elements were revealed. The bottom sediments sampled in 2019 were the most polluted.

Osobennosti techeniy na severo-zapadnom shel'fe Chernogo morya po rezul'tatam chislennogo modelirovaniya

Purpose. The work is aimed at studying the features of currents on the Black Sea northwestern shelf based of the reanalysis results, and at analyzing the reasons of these features. Methods and Results. To analyze the currents on the northwestern shelf, applied were the results of physical reanalysis of the Black Sea fields performed by the authors earlier, namely, the arrays of hydrodynamic fields on a regular grid with the 21-year duration (1992–2012). Surface currents on the northwestern shelf of the Black Sea are directed mainly to the southwest. Throughout the whole year (except for the summer months when the wind effect weakens), an intensive compensatory current directed to the south is formed along the western coast. The waters near the western coast are highly horizontally stratified that is caused by fresh water inflowing with the river runoffs. In winter seasons, the stratification is most pronounced, whereas in summer, the horizontal density gradient decreases. The horizontal density stratification leads to the following: starting from the depth ~ 20 m, the pressure gradient changes its sign and the along-coastal jet countercurrent directed to the north, occurs. Conclusions. The performed studies have shown that the water circulation on the Black Sea northwestern shelf is determined mainly by the following factors: the wind-induced water flows across the shelf boundary and strong horizontal water stratification near the western coast resulted from the river runoffs. As the currents on the sea surface are directed mainly to the southwest, the compensatory current directed to the south is formed near the western coast. Due to the strong horizontal stratification resulted from the river runoffs, a countercurrent directed to the north is formed in the subsurface layer near the western coast. In case the seawater flows to the shelf are extremely high, the countercurrent may be absent.

Features of Currents on the Black Sea Northwestern Shelf Based on the Numerical Simulation Results

Purpose. The work is aimed at studying the features of currents on the Black Sea northwestern shelf based of the reanalysis results, and at analyzing the reasons of these features. Methods and Results. To analyze the currents on the northwestern shelf, applied were the results of physical reanalysis of the Black Sea fields performed by the authors earlier, namely, the arrays of hydrodynamic fields on a regular grid with the 21-year duration (1992–2012). Surface currents on the northwestern shelf of the Black Sea are directed mainly to the southwest. Throughout the whole year (except for the summer months when the wind effect weakens), an intensive compensatory current directed to the south is formed along the western coast. The waters near the western coast are highly horizontally stratified that is caused by fresh water inflowing with the river runoffs. In winter seasons, the stratification is most pronounced, whereas in summer, the horizontal density gradient decreases. The horizontal density stratification leads to the following: starting from the depth ~ 20 m, the pressure gradient changes its sign and the along-coastal jet countercurrent directed to the north, occurs. Conclusions. The performed studies have shown that the water circulation on the Black Sea northwestern shelf is determined mainly by the following factors: the wind-induced water flows across the shelf boundary and strong horizontal water stratification near the western coast resulted from the river runoffs. As the currents on the sea surface are directed mainly to the southwest, the compensatory current directed to the south is formed near the western coast. Due to the strong horizontal stratification resulted from the river runoffs, a countercurrent directed to the north is formed in the subsurface layer near the western coast. In case the seawater flows to the shelf are extremely high, the countercurrent may be absent.

Структура угруповання фіто- та зоопланктону шельфових вод північно-західної частини Чорного моря влітку 2019 року

The article presents the results of studies of phyto- and zooplankton of North-Western Black Sea shelf in the summerof 2019. For phytoplankton, 117 taxa from 13 classes were noted, Bacillariophyceae and Dinophyceae dominated.The average abundance was 123 thousand cells*L-1, the average biomass was 713 mg*m-3. Pseudosolenia calcar-avis(Schultze) B.G. Sundstrom, 1986 and Tripos muelleri Bory de Saint-Vincent, 1826. dominated by biomass. The spatialdistribution of chlorophyll-α concentration approximately coincides with the distribution of phytoplankton biomass. Forzooplankton, 30 taxa were noted, the basis of diversity belongs to Copepoda and Cladocera. The average abundance was 10816 ind* m-3, the average biomass was 607 mg* m-3. The genera Acartia, Oithona, Centropages, Penilia avirostrisand various species of the family Podonidae dominated at all the stations. In transitional waters, the contributionof freshwater phytoplankton species to biomass did not exceed 2%, the basis of biomass was formed by marine species.Despite this, in ShW_UA_1 there was a significant negative correlation between biomass and salinity (r = -0.87). Inthe shelf waters of the marine zone, the contribution of freshwater species to the total biomass did not exceed 0.1%,the correlation between salinity and biomass was absent (r = 0.26). At most offshore stations, brackish and freshwaterzooplankton taxa were absent. There was no significant correlation between salinity and zooplankton biomass. As weapproach the estuaries, the biomass of zooplankton decreases with increasing abundance. There is a high negativecorrelation between the ratio of zooplankton abundance to its biomass and the distance to the nearest estuary (r = - 0.90),for phytoplankton this correlation is r = - 0.534. For most offshore stations and horizons, water quality by phytoplanktonindicators can be assessed as GES, by zooplankton indicators, as non-GES.

Исследование формирования и распространения речного плюма Дуная на основе численного моделирования

The relevance of the studied circulation caused by the water river runoff deals with the anthropological impact on the ecological state of the shelf. River waters, entering into the sea, form mesoscale structures in the delta’s area, characterized by low salinity with a high level of suspended matter and dissolved organic matter. Such structures are called “plume” in modern literature. In this case, the inertial motion of the plume is free to form a rounded area or “bulge” like anticyclonic circulation type of flow. The purpose of this work is to investigate the propagation of freshened waters, formed by the river inflow, the formation of the waters hydrological structure regularities, dynamics of the buoyancy current, and thermohaline front formation on the base of numerical modeling. Numerical modeling is used to study the formation of a river plume and downward propagation of buoyancy current on the shelf without taking into account the tides forcing. A three-dimensional σ-coordinate numerical model was used, adapted for the shelf and estuaries. The calculations were carried out for a rectangular box area. The influence of changes in the main parameters of the runoff, the mouth geometry and wind forcing are considered to development of the plume and the alongshore propagation of buoyancy current. The obtained modeling results for the conditions of the Northwestern Black Sea shelf and the Danube discharge are consistent with the estimates of plume characteristics based on the archival hydrological observations data of water temperature and salinity. The results of this work can be used for further study of hydrological processes in the region of river mouths, the peculiarities of the plumes formation and evolution, assessment of the suspended matter, biogenic elements and microplastics transport in the sea and ocean coastal zones.

Features of water circulation on the Black Sea northwestern shelf based on physical reanalysis results

The paper studies the main features of water circulation on the northwestern shelf (NWS) of the Black Sea. The study is based on a physical reanalysis performed previously. The result of reanalysis is a set of hydrodynamic fields for a period of twenty years on a regular grid with a discreteness of one day. To analyze the general properties of the currents on the NWS, the fields were averaged over a monthly period, and further analysis used the monthly average values of them. Spreading of the rivers outflow and wind stress are basic mechanisms, which controls the flow structure in the upper layer of the NWS. Surface currents are directed mainly to the southwest. Along the western coast, a compensatory current is formed, directed to the south, with the exception of the summer months, when the effects of wind are significantly weakened. A characteristic feature of the waters near the western shore is the strong horizontal stratification caused by fresh water with rivers outflow, mainly the Danube. An interesting feature of the circulation on the NWS is presence of a subsurface coastal jet counter-flow directed to the north. The center of this counter-flow is located approximately on the horizon of 20 meters. Its depth may vary, but the counter-flow itself is observed throughout the year.

Heavy Metalspatial Distribution and Pollution Assessment in the Surface Sediments of the North � Western Black Sea Shelf

22 surface sediment samples were collected in August 2018 from the Romanian inner shelf (Nord-Western Black Sea). Concentrations of some metals (Al, Cr, Cu, Ni, Zn, As, Pb, and Hg), TOC content, and grain size of sediment samples were determined by specific techniques. The order of accumulation of heavy metals was Zn]Cr]Ni]Cu]Pb]As]Hg. Multivariate analysis indicated that As, Ni, Cu, Zn, Pb, and Hg concentrations had similar behavior and they were positively correlated with the clay content, whereas Al and Cr concentrations presented close patterns and they were negatively correlated with the water depth. Sediment pollution assessment indices (enrichment factor, contamination factor, and geo-accumulation index) suggested no/low pollution for most of the metals analyzed, excepting for Pb and Hg (moderate pollution). Values of pollution indices highlighted a higher sediment pollution with Pb and Hg along the Danube�s plume direction, in the oil platform area (eastern edge of the Portita Bay), and partially in the Constanta and Mangalia area, suggesting the influence of port activities, tourism, urban wastewater discharges, oil and gas extraction.

Controls on the shuttling of manganese over the northwestern Black Sea shelf and its fate in the euxinic deep basin

Manganese (Mn) is an essential micronutrient for phytoplankton and its cycling interacts with that of iron (Fe). Continental shelf sediments are a key but poorly quantified source of Mn to marine waters. In this study, we investigate Mn release from shelf sediments, its lateral transport (“shuttling”) in the oxic water column over the northwestern Black Sea shelf and its fate in the adjacent euxinic deep basin. We find a high release of Mn from organic-rich, bioirrigated coastal sediments, but negligible mobilization and release of Mn from sediments in offshore shelf regions, because of a low input of organic matter. Most Mn in the water column is present in dissolved form. We suggest that this dissolved Mn is released from coastal sediments and subsequently transported offshore through physical processes. Surface sediments at open shelf and shelf edge stations are highly enriched in Mn when compared to coastal and deep basin stations. Only part of the surface enrichment can be explained by oxidation of porewater Mn. The remainder of this enrichment is likely the result of oxidative removal of dissolved Mn from the water column and deposition as Mn oxides. Using X-ray spectroscopy we show that Mn in surface sediments in this area predominately consists of Mn(IV) oxides (phyllo- and/or tectomanganates). A key difference between Mn versus Fe shuttling is the form in which the metal is transported: while dissolved Mn dominates in the water column over the shelf, most Fe is present in particulate form. Sediment trap data indicate that the vertical transport of both Mn and Fe through the euxinic water column is correlated and is associated with the sinking flux of biogenic particulate matter following the spring and fall phytoplankton blooms. In the sediments of the euxinic basin, Mn is enriched when compared to a detrital Mn background and its burial correlates with that of Fe. This suggests that Mn could be incorporated in pyrite in the euxinic water column. Our results highlight the critical role of organic matter input as a driver of Mn and Fe shuttling over the Black Sea continental shelf and particulate matter as the carrier of Mn and Fe into the euxinic basin.

First records of blue crab Callinectes sapidus (Rathbun 1869) on the north-western Black Sea shelf

Recently, there have been regular reports and notes of blue crab C. sapidus (Rathbun, 1896) findings in different regions of the Black Sea and Azov Sea. There is an assumption that this species will be common for the Black Sea benthic fauna. There are already more than fifteen previously published reported records of the blue crab from the Black Sea and Azov Sea. In 2019 three individuals of blue crab (one male and two female) were captured by Khizhnyak dredge and bottom beam trawls in the north-western part of the Black Sea (Ukrainian part). This is the first record for the C. sapidus from this region.

HISTORY OF THE GEOLOGICAL DEVELOPMENT OF THE BLACK SEA NORTHWEST SHELF IN THE LATE NEOPLEISTOCENE-HOLOCENE

Research results are presented into the geological history of the Black Sea’s northwestern shelf during the late Neopleistocene and Holocene. The principal goal was to reconstruct the age, character of transformation, and changes in Black Sea level and salinity focusing on the Neopleistocene-Holocene boundary using evidence from conjugate paleontological (foraminifers, ostracods, mollusks), lithological, and ecostratigraphic analyses of bottom sediments supplemented by radiocarbon dating.Samples were collected during geological survey of the northwestern Black Sea shelf, and data have been entered into electronic databases for use in future paleo-oceanographic reconstructions.The Early Neoeuxinian lake level rose from -100 m to -39 m bsl following the Late Neoeuxinian transgression due to Caspian inflow. It was brackish (5-12 psu), never freshwater, and it transformed into the Black Sea around 9.0 ka BP with the Mediterranean transgression, which was progressive, gradual, and oscillatory, not catastrophic or fast. The first wave of in-migrating Mediterranean organisms was weak and synchronous with the first (Bugazian) transgression phase. It slowed and even stopped during the following Kolchidian regressive phase, then stabilized during the second (Vityazevian) wave of migration, reaching its maximum during the Kalamitian and Dzhemetinian transgressive phases (third and fourth migration waves). The oscillating character of the Mediterranean transgression and re-colonization of the Late Neoeuxinian lake by marine fauna can be clearly traced on the inner shelf only due to the low amplitude of the sea-level and salinity changes. It is almost invisible on the outer shelf of the Black Sea, below isobath -100 m.

Sea ice modeling in the Sea of Azov for a study of long-term variability

This study deals with an attempt to use the NEMO modeling framework to investigate the long-term variability of the sea-ice fields in the Sea of Azov. A coupled ocean-ice model is used to perform a simulation by using an earlier developed configuration of cascading sea basins (Azov, Black, and Marmara). Various features of geographical location cause the formation of sea ice in the waters of the Sea of Azov and in the coastal area of the north-western Black Sea shelf. For a preliminary accuracy assessment, the simulation results are compared with the data based on satellite observations. The restricted amount of the data for the rather small area under study, as well as the features of the regional weather conditions, produce rather low accuracy of the available data products based on the satellite data. At the same time, the available data from coastal weather stations, as well as archived observations, produce a fairly adequate pattern of the simulated variability of the sea-ice conditions in the basin.

A thermobaric mechanism for the formation of low velocity zones in the crystalline crust of the northwestern Black Sea shelf: a new type of traps for abiogenic methane

Seismic studies of the NW Black Sea shelf have delineated low-velocity zones (LVZs) in the crystalline crust at depths of 6—16 km. For the first time, this paper presents a novel thermodynamic mechanism for their formation. The active temperature regime and deep geodynamic processes of the region provide evidence in favour of this mechanism. The LVZs are mainly associated with the thermal decompaction of rocks, which is not compensated by deep pressures. The rocks of such zones are characterized by an increase in fracturing and porosity and decrease in density, elastic parameters and thermal conductivity. As the rocks are permeable and hygroscopic they are able to more freely transform, absorb and localize mantle hydrocarbon-bearing fluids which, in turn, further destroy rock matter. Within the LVZs the existence of hydrocarbons is confirmed by the occurrence about 3200 activegas seeps and 8 gas and gas condensate fields. For the first time, the spatial coexistence was revealed between LVZs and a degassing tube to which hydrocarbon fields are related. LVZs zones should be considered as a new search criteria for thermobaric traps. Favou­rable conditions exist for the accumulation of abiogenic methane at a depth of 6—16 km that can substantially expand the hydrocarbon potential of the shelf in usage modern drilling technology.

Assimilation of Satellite Observations of the Chlorophyll-a Concentration and the Calculated Data on the Marine Environment Dynamics in the Adaptive Model of the Ecosystem of the Black Sea Northwestern Shelf

Assimilation of Satellite Observations of the Chlorophyll-a Concentration and the Calculated Data on the Marine Environment Dynamics in the Adaptive Model of the Ecosystem of the Black Sea Northwestern Shelf