Northwestern Black Sea Shelf Research Articles

A post Younger Dryas Black Sea regression identified from sequence stratigraphy correlated to core analysis and dating

The north-western Black Sea shelf is the widest continental shelf of the Black Sea, where the Danube delta/prodelta system includes important records on the Black Sea water level fluctuations. This study integrates newly acquired high-resolution single channel seismic reflection profiles and Calypso piston cores recovered along a transect extending from the Danube delta deep into its deep sea fan. The correlated results provide information on the Late Quaternary architecture of the Danube Black Sea shelf and on the role of global glacio-eustatic fluctuations on the building of the Danube delta/prodelta. The sedimentary sequences in the Black Sea are strongly affected by water level changes. For the whole duration of Late Glacial–Holocene period, the level of the Black Sea was controlled by the regional climate modifications rather than the global eustatic changes. The seismic sequences recognized on a very high-resolution seismic profile were dated by two Calypso piston cores. Based on the obtained data, during the Last Glacial Maximum the Black Sea was a land locked lake with the level below −120 m. In the course of the deglaciation the lake level rose up to −40 m, which is confirmed by occurrence of the prodelta lobes formed after the rise in water level originated from the melt water. Following the Younger Dryas, 11 000–8500 14C BP, there occurred a new level lowering to the level of −100 m, identified by the forced regression deposits recorded on the Romanian shelf. This last lowstand previously recognized by a pronounced shoreline with a characteristic beach profile and a belt of coastal dunes is also indicated by the prodelta at −100 m depth. All these coastal features as well as the incised anastomosed channel system remained preserved on the shelf resulting from a rapid ultimate transgression starting immediately after 8500 14C BP.

Recovery or decline of the northwestern Black Sea: A societal choice revealed by socio-ecological modelling

During recent decades anthropogenic activities have dramatically impacted the Black Sea ecosystem. High levels of riverine nutrient input during the 1970s and 1980s caused eutrophic conditions including intense algal blooms resulting in hypoxia and the subsequent collapse of benthic habitats on the northwestern shelf. Intense fishing pressure also depleted stocks of many apex predators, contributing to an increase in planktivorous fish that are now the focus of fishing efforts. Additionally, the Black Sea's ecosystem changed even further with the introduction of exotic species. Economic collapse of the surrounding socialist republics in the early 1990s resulted in decreased nutrient loading which has allowed the Black Sea ecosystem to start to recover, but under rapidly changing economic and political conditions, future recovery is uncertain. In this study we use a multidisciplinary approach to integrate information from socio-economic and ecological systems to model the effects of future development scenarios on the marine environment of the northwestern Black Sea shelf. The Driver–Pressure–State-Impact-Response framework was used to construct conceptual models, explicitly mapping impacts of socio-economic Drivers on the marine ecosystem. Bayesian belief networks (BBNs), a stochastic modelling technique, were used to quantify these causal relationships, operationalise models and assess the effects of alternative development paths on the Black Sea ecosystem. BBNs use probabilistic dependencies as a common metric, allowing the integration of quantitative and qualitative information. Under the Baseline Scenario, recovery of the Black Sea appears tenuous as the exploitation of environmental resources (agriculture, fishing and shipping) increases with continued economic development of post-Soviet countries. This results in the loss of wetlands through drainage and reclamation. Water transparency decreases as phytoplankton bloom and this deterioration in water quality leads to the degradation of coastal plant communities ( Cystoseira, seagrass) and also Phyllophora habitat on the shelf. Decomposition of benthic plants results in hypoxia killing flora and fauna associated with these habitats. Ecological pressure from these factors along with constant levels of fishing activity results in target stocks remaining depleted. Of the four Alternative Scenarios, two show improvements on the Baseline ecosystem condition, with improved waste water treatment and reduced fishing pressure, while the other two show a worsening, due to increased natural resource exploitation leading to rapid reversal of any recent ecosystem recovery. From this we conclude that variations in economic policy have significant consequences for the health of the Black Sea, and ecosystem recovery is directly linked to social–economic choices.

High frequency sea level fluctuations recorded in the Black Sea since the LGM

This paper presents a 3D geometric interpretation of very high resolution seismic Chirp profiles acquired on the Romanian shelf during ASSEMBLAGE European Project. The results provide a solid record of the Black Sea Last Glacial Maximum (LGM) water level fluctuations. This pseudo-3D seismic interpretation shows that the Black Sea lacustrine shelf deposits form a significant basinward-prograding wedge system. On top of these prograding sequences is a set of sand dunes that delineates a wave cut-terrace like feature around the isobath − 100 m. Landward of this dune field are small depressions containing barkhan-like bodies. The upper part of the last prograding sequence is incised by anastomosed channels which end in the Danube (Viteaz) canyon which are also built on the lacustrine prograding wedge. Ten stratigraphic units were distinguished and correlated with analyses of cores retrieved from this area. The results demonstrate that the first eight sequences represent lacustrine prograding wedges, the ninth sequence is the dune system itself and the tenth is a marine mud drape which covers the entire continental shelf. The lacustrine prograding wedges represent a lowstand deposit characterised by forced regression-like reflectors mapped from the pseudo-3D seismic data. Their hinge point corresponds to the wave erosion surface mapped around − 100 m isobath on the multibeam mosaic. Dated cores give age control on this lowstand period, which lasted from 11 to 8.5 kyr 14C BP as implied by: (1) the continuously dry climatic conditions in the region inferred by high percentages of herbs and steppe elements determined from ASSEMBLAGE cores and, (2) the formation of dunes between 10 and 8.5 kyr 14C BP on the desiccated north-western Black Sea shelf at − 100 m and (3) all of these covered by a marine mud drape confirming that the dune system is no longer active. The buried, anastomosed fluvial channels that suddenly disappear below 90 m depth, and a unique wave-cut terrace between 95 and 100 mbsl on the outer shelf are also consistent with a major lowstand base-level at around − 100 m water depth. Preservation of sand dunes and the occurrence of small, buried incised valleys mark a rapid transgression within less than a century during which ravinement processes related to the water level rise had no time to significantly erode the seafloor.

Nutrient budgets for European seas: A measure of the effectiveness of nutrient reduction policies

Socio-economic development in Europe has exerted increasing pressure on the marine environment. Eutrophication, caused by nutrient enrichment, is evident in regions of all European seas. Its severity varies but has, in places, adversely impacted socio-economic activities. This paper aims to evaluate the effectiveness of recently adopted policies to reduce anthropogenic nutrient inputs to European seas. Nitrogen and phosphorus budgets were constructed for three different periods (prior to severe eutrophication, during severe eutrophication and contemporary) to capture changes in the relative importance of different nutrient sources in four European seas suffering from eutrophication (Baltic Proper, coastal North Sea, Northern Adriatic and North-Western Black Sea Shelf). Policy success is evident for point sources, notably for P in the Baltic and North Seas, but reduction of diffuse sources has been more problematic.

Dynamics of the coastal North Black Sea area in Late Pleistocene and Holocene and early human dispersal

Based on detailed surveys, the reconstructions of coastal and marine environments of the North-Western Black Sea shelf were carried out for the time spans of ca 25, 18, 12, 10–7, and 7–4 ka BP. During the great part of Late Pleistocene and Early Holocene the Black Sea remained a land-locked basin of the Caspian type, which became colonised by early modern humans starting from ca 40 ka. The subsequent evolution of coastal landscapes was generally conditioned by the gradual rise of sea-level and increasing temperature and precipitation, resulting in the formation of coastal wetland landscapes, which became the main source of Late Palaeolithic and Mesolithic subsistence. The initial indications of farming activities are coeval with the Kalamitian stage, being conditioned by the increased temperature and precipitation combined with the formation of fertile soils under Altithermal conditions. The data fail to indicate a catastrophic breakthrough of Mediterranean water that could have had any effect on the subsistence or migrations of early farming communities.

Paleogeographic reconstructions of sea-level change and coastline migration on the northwestern Black Sea shelf over the past 18 kyr

The paper discusses the main questions of Black Sea level change during the Late Pleistocene to Holocene based on high-resolution lithological-genetic and paleogeolographic analyses of the northwest Black Sea shelf and Prichernomorean limans (estuaries). Based on the study of ancient coastlines (wave-generated coastal landforms such as beaches) with radiocarbon dating, a paleogeographic map of the northwest shelf is constructed for the period from 18 to 9.2kyrBP.Statistical data processing instrumental observations show a direct and robust relationship between sea level and river discharge at intra-annual and multi-annual periodicities. Periodicity of sea-level change at different frequencies and lengths is calculated using spectral and wavelet analysis. For the periodicity investigations, analysis included the composition and salinity of bottom sediments of two cores reconstructed from the Dnieper River discharge for the past 4000 years, and data from instrumental observations for the period of 1818–2001. The results indicate statistically significant periods of sedimentation rhythms, Dnieper discharge, and sea-level change, which are defined by their common climatic and astrophysical factors of variability. There is a relationship between the generations of coastal landforms of Dzharylgach Island and the Holocene transgressive–regressive phases of the Black Sea. The data support an oscillatory model of sea-level development for the last 18kyr. Five regressions: Drevnechernomorian, Tyraian, Khadzhibeian, Olbian (Phanagorean), and Medieval, are identified in the Holocene.

Environmental monitoring in a gas production area on the northwestern Black-Sea shelf

The results of long-term seasonal oceanographic observations conducted by YugNIRO from 1955 to 1991 in standard cross-sections on the northwestern shelf of the Black Sea and data obtained by monitoring oil and chemical pollution of the marine environment from 1987 to 1993 in the area of gas deposit development are systematized and statistically treated. The oceanographic conditions of pollution field formation in this region are studied. The dynamics and distribution of total concentrations of oil products and microelements (Hg, Cu, Pb, Cd, and Cr) in water and bottom sediments are examined in the areas in Karkinitskii Bay where permanent offshore platforms are operated. The obtained results are compared with data on the background environmental pollution of the Black Sea and World Ocean. A hypothesis is offered to elucidate the possible causes and mechanisms through which offshore gas production affects the hydrochemical conditions on the shelf. The monitoring data are said to be a necessary information basis for the prediction of pollution dynamics in Karkinitskii Bay with the use of a box-type hydroecological model of petroleum hydrocarbon biotransformations in water, and approaches for the use of these data for this purpose are outlined.

Numerical studies on the dynamics of the Northwestern Black Sea shelf

The Northwestern Black Sea shelf dynamics are studied with numerical simulations based on the Princeton Ocean Model. The study focus is on buoyancy and wind driven flows and on the transport and fate of low salinity waters that are introduced through riverine sources (the Danube, Dnestr and Dnepr Rivers), under the seasonal changes in atmospheric forcing. The study is part of the DANUBS project (NUtrient management in the DAnube basin and its impact on the Black Sea). The numerical simulations show that the coastal circulation is greatly influenced by river runoff and especially that of the Danube, which is dominant with monthly averaged values ranging from 5,000 m3 to 10,000 m3. The transport of low-salinity waters associated with the Danube runoff is greatly influenced by wind stress, topographic effects and basin-scale circulation patterns, such as changes in the position of the Rim Current.

Nitrogen budget of the northwestern Black Sea shelf inferred from modeling studies and in situ benthic measurements

A 3D eddy-resolving coupled biogeochemical-hydrodynamical model and in situ obser- vations are used to investigate benthic processes on the Black Sea's NW shelf. Measurements of ben- thic fluxes (oxygen, nutrients, redox compounds) with in situ flux chambers are analyzed in regard to sediment dynamics on the shelf. The seasonal/interannual and spatial variability of benthic processes is explained in terms of 3D ecohydrodynamics. The space/time distribution of benthic fluxes depended on the position of the river plume and the associated primary production, intensity of ver- tical mixing and water depth. Model results and in situ observations reveal the presence of a region of intense benthic recycling and high benthic nutrient fluxes nearshore and in the northern part of the shelf. The model estimates that this region covers about 15% of the shelf area and is connected to the high productivity and high sedimentation caused by river input of organic matter. On the off- shore shelf, covering about 85% of the shelf area, benthic nutrient regeneration is low due to low pro- ductivity. Benthic mineralization pathways (aerobic respiration, denitrification, sulfate reduction, methanogenesis) are quantified. In the high flux region, more than 55% and in the offshore low flux region more than 80% of the organic matter is decomposed by aerobic respiration. In the high flux region, sulfate reduction is the main anaerobic pathway, whereas denitrification is more important on the low flux offshore shelf. At the shelf edge, under the influence of anoxic waters, more than 60% of organic matter is remineralized by sulfate reduction. Little organic matter is decomposed by methanogenesis. A mass balance of particulate organic carbon (POC) and particulate organic nitro- gen (PON), integrated over the whole shelf and year, shows that 3.7 to 4.2 × 10 6 t of POC reach the sediments, while model results give a value of 1.4 × 10 6 t C. The annual ammonium benthic outflux is estimated at 85 × 10 3 and 174 × 10 3 t N by in situ data and the model, respectively. The amount of nitrogen lost by burial and denitrification estimated from in situ observations is 57 × 10 3 and 324 × 10 3 t N, respectively. Therefore, NW shelf Black Sea sediments are an efficient sink for riverine nitrogen, trapping about 50% of the annual river discharge in total inorganic N.

In situmacrofaunal respiration rates and their importance for benthic carbon mineralization on the northwestern Black Sea shelf

Abstract Benthic fauna assemblages and organic carbon mineralization processes were studied in the northwestern Black Sea along a transect from the well-oxygenated shelf to the (deep) anoxic basin. Bivalves dominated the coenoses at the three oxygenated stations, but with decreasing macrofaunal biomass at increasing water depth. The previously well-described zonation of macrofaunal communities for the northwestern shelf of the Black Sea was also found in this study (Mytilus galloprovincialis coenosis at Station 1 (62 m), Modiolus phaseolinus coenosis at Station 2 (77 m) and 3 (100 m)). The highest meiofauna density was found at the transition from oxic to anoxic bottom waters (Station 4, 130 m, < 5 μM O2). Reduced predation and sufficient food supply are suggested to be of importance at that site. The weight-specific fauna-mediated respiration rate of the mussel community was independent of water depth and always around 14 nmol O2 mg ww-1 d-1. Thus indicating that the mussel communities on the northwester...

Microbial reefs in the Black Sea fueled by anaerobic oxidation of methane.

Massive microbial mats covering up to 4-meter-high carbonate buildups prosper at methane seeps in anoxic waters of the northwestern Black Sea shelf. Strong 13C depletions indicate an incorporation of methane carbon into carbonates, bulk biomass, and specific lipids. The mats mainly consist of densely aggregated archaea (phylogenetic ANME-1 cluster) and sulfate-reducing bacteria (Desulfosarcina/Desulfococcus group). If incubated in vitro, these mats perform anaerobic oxidation of methane coupled to sulfate reduction. Obviously, anaerobic microbial consortia can generate both carbonate precipitation and substantial biomass accumulation, which has implications for our understanding of carbon cycling during earlier periods of Earth's history.

Danube River Sediment Input and its Interaction with the North-western Black Sea

The influence of the river Danube is determinant to the sedimentation of the north-western and western Black Sea area. After 1970, following the building of the Iron Gates dam, the Danube River sediment discharge diminished to 30–40% of its previous value. After a 12 000-year evolution, marked by active progradation, the Danube delta has become mainly inactive over the last few decades partly due to interventions of man-made origin. The deficit of sediment influx has led to the intense erosional processes of the deltaic littoral. On the Black Sea north-western shelf, two main areas (with contrasting sedimentary processes) have been identified: the internal, Danube sediment-fed shelf and the external, sediment-starved shelf. The modern highstand sedimentary history of the north-western Black Sea deep area is marked by the cessation of the Danube deep-sea fan active development. The main depositional units within the north-western Black Sea are described.

Seasonal Dynamics of the Sulphate Reduction Rate on the North-western Black Sea Shelf

The microbial sulphate reduction rate (SRR) in the surface layer (0–30 cm) of shallow water sediments of the north-western Black Sea shelf has been measured using the 35S radioisotopic technique. It was shown that SRR is accompanied by changes of salt composition of porewaters and isotopic (δ 34S) composition of sulphate. The hydrogen sulphide-derived minerals are formed in the solid phase of sediments. An expected exponential dependence of the isotopic composition of reduced sulphur compounds on the SRR was observed. In near-shore sediments, terrestrial organic carbon (δ 13C≈−26‰) as well as marine phytoplankton organic carbon (δ 13C≈−22‰) are associated with the SR processes. In August 1995 and May 1997–1998, anoxic conditions in near-bottom waters of coastal areas were not detected. The average value of H 2S production in nearshore sediments varied from 3·62 mmol S m −2 day −1 in spring to 8·89 mmol S m −2 day −1 in summer 1995; these fluxes were twice as high as those measured in spring 1997 and 1998.

Biogeochemical cycle of methane in the northwestern shelf of the Black Sea

Seasonal investigations of methane distribution and rates of its oxidation and generation in the water column and sediments of the Black Sea northwestern shelf were carried out within the framework of the interdisciplinary projects "European River-Ocean Systems" (EROS-2000, EROS-21) and "Biogenic Gases Exchange in the Black Sea" (BigBlack) in August 1995, May 1997, and December 1999. Experiments that involved the addition of 14CH3COONa and 14CO2 to sediment samples showed the main part of methane to be formed from CO2. Maximum values of methane production (up to 559 mumol/(m2 day)) were found in coastal sediments in summer time. In winter and spring, methane production in the same sediments did not exceed 3.6-4.2 mumol/(m2 day). The delta 13C values of methane ranged from -70.7 to -81.8@1000, demonstrating its microbial origin and contradicting the concept of the migration of methane from cold seeps or from the oil fields located at the Black Sea shelf. Experiments that involved the addition of 14CH4 to water and sediment samples showed that a considerable part of methane is oxidized in the upper horizons of bottom sediments and in the water column. Nevertheless, it was found that, in summer, part of methane (from 6.8 to 320 mumol/(m2 day)) arrives in the atmosphere.

Synthesis of ecosystemic and ecoscreening modelling in solving problems of ecological safety

The traditional approach to modeling the state of complex ecological systems assumes realization of a series of numerical experiments with a dynamic model. The results obtained are difficult to evaluate for multicomponent systems. To give an integrated estimation of the state of an ecosystem as a whole is quite a complicated task. The synthesis of dynamic modeling for aggregated and averaged components of an ecosystem and ecoscreening approach for risk estimation is one way of overcoming this difficulty. The annual variations of the basic components of the ecological system (concentrations of phytoplankton, zooplankton, macroalgae, fish, nutrients, suspended and dissolved organic matter, and hydro-optical characteristics) are calculated from full dynamic modelling. The annual variations of ecological risk from effects on an ecological system are calculated based on the synthesis of the two approaches. This method was developed for prediction of variations of risk estimation for the north-western Black Sea shelf. The annual variations of risk are calculated when the ecological system is submitted to regular pollution and emergency situations. More accurate estimation of risk is reached by step wise application of each one of the approaches.

Spatial distribution in sediment characteristics and benthic activity on the northwestern Black Sea shelf

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 181:25-39 (1999) - doi:10.3354/meps181025 Spatial distribution in sediment characteristics and benthic activity on the northwestern Black Sea shelf Jeroen W. M. Wijsman1,*, Peter M. J. Herman1, Marian-Traian Gomoiu2 1Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands 2National Institute of Marine Geology and Geo-ecology, Constanta branch, Mamaia 304, RO-8700 Constanta, Romania *E-mail: wijsman@cemo.nioo.knaw.nl ABSTRACT: The influence of the River Danube as a major source of nutrients and suspended solids to the continental shelf of the Black Sea has been analyzed. In the framework of the EC project EROS-2000, sediment cores from 33 stations on the northwestern continental shelf were sampled in August 1995. Spatial patterns in structural sediment characteristics, macrobenthos composition and benthic mineralization rates were examined using ordination techniques. Three general areas could be distinguished according to the distribution of abiotic sediment characteristics and macrobenthos community: (1) The area just in front of the Danube Delta where large amounts of nutrients and suspended solids are discharged. High sedimentation rates of fine-grained sediments and high benthic mineralization rates characterized this area. The macrobenthos community was dominated by deposit feeders. (2) The northern part of the continental shelf where an anticyclonic gyre is located. The majority of the Danube discharges are transported to this region. This area was characterized by low sedimentation rates. However, the deposited material contained a larger fraction of fresh organic matter compared to the delta area, resulting in high benthic mineralization rates. Suspension feeders dominated the macrobenthos community. (3) The southern part of the continental shelf was characterized by low sedimentation rates and low rates of benthic mineralization. In this area suspension feeders dominated the macrobenthos community. Oxygen fluxes into the sediment ranged between 2 and 52 mmol O2 m-2 d-1 (average 21 mmol O2 m-2 d-1) decreasing with water depth. Macrobenthos accounted for 20% of the total benthic oxygen consumption. In the northern part of the continental shelf and in the coastal stations, microorganisms, and micro- and meiobenthos dominated benthic community respiration, while macrobenthos became relatively more important in terms of oxygen consumption in the southern part of the continental shelf. KEY WORDS: Black Sea · Danube · Macrobenthos · Benthic oxygen flux · Ordination · Benthic-pelagic coupling Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 181. Publication date: May 18, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Inter-annual variability of the hydrological-chemical characteristics in the north-western Black Sea shelf area over recent decades (1960–1990)

A number of significant hydrologicla and chemical parameters of the Black Sea shelf area have been identified and investigated: the inter-annual variability of the mean annual and seasonal (winter and summer) values of the air and seawater temperatures and salinity in the vicinity of Odessa; silicon and phosphate concentrations averaged over the north-western Black Sea shelf area (NWBS); discharges of the Danube and Dnieper rivers; mean surface and near-bottom oxygen concentrations in summer acquired through the analysis of the summarized data collected at three oceanographic stations occupied between Bolshoi Fontan and the Tendra isthmus from the early 1950s up to date. From these data, the variability of the areas subject to oxygen deficit in the near-bottom layer of the NWBS shelf during the summers of 1973–1994 has been assessed. Predominant oscillation periods and trends in the inter-annual variability of the studied parameters have been revealed and their relationship and climatic dependence has been demonstrated.

Hydrocarbon Generation History and Petroleum Potential of Sedimentary Basins on Northwestern Black Sea Shelf&amp;nbsp; :ABSTRACT

Hydrocarbon Generation History and Petroleum Potential of Sedimentary Basins on Northwestern Black Sea Shelf&amp;nbsp; :ABSTRACT

Environmental changes in the western Black Sea related to anthropogenic and natural conditions

Abstract The Black Sea northwestern shelf (NWS) ecosystem has been subjected to the strongest anthropogenic pressure of the entire Black Sea as about 80% of the freshwater runoff is discharged there. This paper presents a review of the global environmental changes related mainly to increased eutrophication in the western Black Sea basin. A case study (CoMSBlack 92a cruise) attempts to highlight the interaction of some natural and anthropogenic factors responsible for specific chemical and biological features in the western Black Sea environment. The significance of processes located near the Danube river mouth, which, due to their relatively small space scale, have not been recognized before, is clarified. Hydrological processess of specific importance to the distribution and transformation of antropogenic inputs are river plume dynamics, coastal upwelling and mixing and downwelling over the shelf break and slope in this part of the basin. A layer of low hydrological variability (“conservative layer”) appears to be a natural feature of the area, hypothesized to precondition specific biological and chemical processes there. The results suggest that the interplay between the Danube anthropogenic nutrient load with the natural hydrological fronts and gradients provides opportunities for enhanced biological activity thus contributing to the global environmental changes in the Black Sea NWS.

Numerical model and calculation of the water circulation in the north-western Black Sea

A multilevel model based on primitive equations and a monotonic finite-difference scheme is applied to study the fluid dynamics over the north-western Black Sea shelf. Wind-generated currents and currents induced by river discharge are simulated in terms of the barotropic version. The effects of the bottom topography, the rigid-lid approximation, and the interaction of wind and river discharge-induced flows are examined.