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The level of scientific knowledge about a gas hydrate deposit (GHD) in the northern deep-water part of the Bulgarian Exclusive Economic Zone (BEEZ), energy, climate and environmental problems determine the need of urgent creation and realization of a Bulgarian program for gas hydrate development. We present a review of this knowledge and define 3 preliminary steps for funds optimizations and fast creation and implementation of pilot and innovative economically profitable technologies for fuel production (CH4 and/or H2) with low geohazard and environmental risk and negative carbon footprint on the atmosphere.

The potentially toxic genus Pseudo-nitzschia is constantly present in phytoplankton community in the Black Sea often proliferating to bloom concentrations. Production of domoic acid (DA) has been confirmed by local P. calliantha strain and the presence of the neurotoxin has been detected in cultured molluscs and plankton samples from the Bulgarian Black Sea coast. This study aims to provide an overview of the long-term trends of Pseudo-nitzschia blooms in the Black Sea based on inventory of the available information for the period 1959-2019 and assess the relation with key environmental variables. Pseudo-nitzschia species diversity and identification constraints are critically analyzed along with data about the presence of DA in the basin. The results demonstrate that Pseudo-nitzschia spp. may bloom at any time of the year under different environmental regimes. Application of advanced identification techniques, technologically adequate regular monitoring, complemented by toxin analysis is essential to improve our understanding of Pseudo-nitzschia bloom dynamics in order to protect public and ecosystem health hazards.

Background The Black Sea is the largest brackish water body in the world, although it is connected to the Mediterranean Sea and presents an upper water layer similar to some regions of the former, albeit with lower salinity and temperature. Despite its well-known hydrology and physicochemical features, this enormous water mass remains poorly studied at the microbial genomics level. Results We have sampled its different water masses and analyzed the microbiome by shotgun and genome-resolved metagenomics, generating a large number of metagenome-assembled genomes (MAGs) from them. We found various similarities with previously described Black Sea metagenomic datasets, that show remarkable stability in its microbiome. Our datasets are also comparable to other marine anoxic water columns like the Cariaco Basin. The oxic zone resembles to standard marine (e.g. Mediterranean) photic zones, with Cyanobacteria (Synechococcus but a conspicuously absent Prochlorococcus), and photoheterotrophs domination (largely again with marine relatives). The chemocline presents very different characteristics from the oxic surface with many examples of chemolithotrophic metabolism (Thioglobus) and facultatively anaerobic microbes. The euxinic anaerobic zone presents, as expected, features in common with the bottom of meromictic lakes with a massive dominance of sulfate reduction as energy-generating metabolism, a few (but detectable) methanogenesis marker genes, and a large number of “dark matter” streamlined genomes of largely unpredictable ecology. Conclusions The Black Sea oxic zone presents many similarities to the global ocean while the redoxcline and euxinic water masses have similarities to other similar aquatic environments of marine (Cariaco Basin or other Black Sea regions) or freshwater (meromictic monimolimnion strata) origin. The MAG collection represents very well the different types of metabolisms expected in this kind of environment. We are adding critical information about this unique and important ecosystem and its microbiome.

One of the assets, assigned to the phytoplankton resting stages, is that of serving as the “memory” of the aquatic ecosystems and preserved biodiversity in the course of time. However, an accurate cyst identification proves to be a more difficult and extremely challenging process, even today. In order to gain a better taxonomic coverage of cyst assemblages in the Black Sea, an integrated approach of the classical morphological identification with metabarcoding methods (MySeq sequencing of V7-V9 regions of the 18S rDNA) was applied on thirteen surface sediment samples collected from different sites. A total number of 112 dinoflagellate taxa was detected at the species level and ascribed to 51 genera. In general, it is the molecular analysis that yields a higher number of taxa as compared to those obtained through the morphological taxonomy (66 taxa based on the DNA sequences versus 56 morphologically-identified taxa). Besides, it should be pointed out that the integrated dataset includes 14 potentially toxic dinoflagellate species. Discerned, subsequently, was a good dataset consistency for ten species, followed by some discrepancies as to a number of taxa, identified with one of the methods only, due to specific methodological biases. On the whole, it could be concluded that the combination of morphological and molecular methods is likely to increase the potential for a more reliable taxonomic assessment of phytoplankton diversity in marine sediments which, in turn, proves conclusively the utmost importance of the integrated approach.

The clear and reliable detection of effluent plumes using satellite data is especially challenging. The surface signature of such events is of a small scale; it shows a complex interaction with the local environment and depends greatly on the effluent and marine water constitution. In the context of remote sensing techniques for detecting treated wastewater discharges, we study the surface signature of small river plumes, as they share specific characteristics, such as higher turbidity levels and increased nutrient concentration, and are fresh compared to the salty marine water. The Bulgarian Black Sea zone proves to be a challenging study area, with its optically complex waters and positive freshwater balance. Additionally, the Bulgarian Black Sea coast is a known tourist destination with an increased seasonal load; thus, the problem of the identification of wastewater discharges is a topical issue. In this study, we analyze the absorption components of the Inherent Optical Properties (IOPs) for 84 study points that are located at outfall discharging areas, river estuaries and at different distances from the shoreline, reaching the open sea area at a bottom depth of more than 2000 m. The calculations of IOPs take into account all available Sentinel 2 cloudless acquisitions for three years from 2017 until 2019 and are performed using the Case-2 Regional CoastColour (C2RCC) processor, implemented in the Sentinel Application Platform (SNAP). The predominant absorber for each study area and its temporal variation is determined, deriving the specific characteristics of the different areas and tracking their seasonal and annual course. Optical data from the Galata AERONET-OC site are used for validating the absorption coefficient of phytoplankton pigment. A conclusion regarding the possibility of distinguishing riverine, marine and coastal water is derived. The study provides a sound basis for estimating the advantages and drawbacks of optical satellite data for tracking the extent of effluent and fluvial plumes with unknown concentrations of optically significant seawater constituents.

The Black Sea is the largest meromictic sea with a reservoir of anoxic water extending from 100 to 1000 m depth. These deeper layers are characterised by a poorly understood fluorescence signal called "deep red fluorescence", a chlorophyll a-(Chl a) like signal found in deep dark oceanic waters. In two cruises, we repeatedly found up to 10(3) cells ml(-1) of picocyanobacteria at 750 m depth in these waters and isolated two phycoerythrin-rich Synechococcus sp. strains (BS55D and BS56D). Tests on BS56D revealed its high adaptability, involving the accumulation of Chl a in anoxic/dark conditions and its capacity to photosynthesise when re-exposed to light. Whole-genome sequencing of the two strains showed the presence of genes that confirms the putative ability of our strains to survive in harsh mesopelagic environments. This discovery provides new evidence to support early speculations associating the "deep red fluorescence" signal to viable picocyanobacteria populations in the deep oxygen-depleted oceans, suggesting a reconsideration of the ecological role of a viable stock of Synechococcus in dark deep waters.

The quality of the Black Sea ecosystem is partly but importantly dependent on the survival and sustainability of the top predator populations. It is difficult to foresee all consequences for the regional biodiversity if cetaceans disappear as it had happened with the Mediterranean monk seals in the past. During 7 days, between 30 September and 7 October, 2019, a joint oceanographical survey was made with a multipurpose R/V Mare Nigrum in offshore as well as deep sea locations, within the Romanian (RO), Bulgarian (BG) and western Turkish (TK) national waters of the Black Sea in the frame of ANEMONE project. The total track line was around 700 nautical miles and the sampled area covered 9754,58 km2. Observations were made of cetaceans and floating litter, following line transect sampling method, with a single platform (2 observers, on the left and right of the vessel bridge) over 380.44 km of transects. A total of 54 cetacean sightings and 81 floating litter items were recorded. All the three species, short-beaked common dolphin (Delphinus delphis ssp. ponticus), Black Sea bottlenose dolphin (Tursiops truncatus ssp. ponticus), and Black Sea harbour porpoise (Phocoena phocoena ssp. relicta), were registered with a similar density (individuals/km2), 0.012 for RO sector and 0.013 for BG-TK sector. The number of debris varied between 1 and 24 items, reaching 5.26± 5.93 items on average. Among the transects, 53% contained less than 5 items and only 13% were with more than 10 items. Based on these results, the average density of floating macro-litter in BG waters was found 2.43 ± 2.4 items/km2, 1.73 ± 1.24 items/km2 in the RO waters and 2.43±2.17 items/km2 in TR waters. This study was the first to make a joint and continuous survey effort for both cetaceans and litter simultaneously in the Black Sea.Key words: Black Sea, cetaceans, marine litter, joint cruise, ANEMONE project.

The Black Sea is an extraordinarily complex water body for ocean color remote sensing, as it belong to Case 2 waters, which are characterized by relatively high absorption by Colored Dissolved Organic Matter (CDOM) while the concentration of non-pigmented particulate matter does not co-vary in a predictable manner with chlorophyll a . The optical complexity of the Black Sea is the reason why the standard bio-optical algorithms developed for Case 1 waters, are the source of large uncertainties (of the order of hundreds of percent) of chlorophyll a concentration in the coastal and shelf regions. In the framework of ESA contract “BIO-OPTICS FOR OCEAN COLOR REMOTE SENSING OF THE BLACK SEA - Black Sea Color” we developed empirical ocean color algorithm for chlorophyll a retrieval from Sentinel 3A/OLCI primary ocean color products using the in situ reference bio-optical datasets collected in the Black Sea in the period 2012-2019. Results obtained from the assessment of operational S3A/OLCI chlorophyll products, highlighted and confirmed that the specific regional algorithm is essential for the Black Sea. The coefficients of the regional algorithm were derived from the regression of log-transformed pigment concentrations and remote sensing reflectance ratio at 490nm and 560 nm with determination coefficient R2 =0.88 and number of samples N=186. The algorithm predicts chlorophyll a values using a cubic polynomial formulation. The result of assessment of the regional chlorophyll a product against independent in situ measurements from the data utilized for algorithm development, showed relatively high accuracy (31.7%), fewer underestimations (MPD=-9.2%) and a good agreement (R2=0.66) between datasets indicating that the regional algorithm is more effective in reproducing the pigment concentration in the Black Sea waters in comparison to the standard Sentinel 3A/OLCI algorithms. Our analysis revealed the importance of providing regional algorithms strictly required to suit the peculiar bio-optical properties featuring this basin. However, this requires collection of accurate in situ measurements in the different parts of the Black Sea. The validity of the reported empirical algorithm obviously depends on the size of the dataset used for its development. The Black Sea waters vary at a basin level due to the sub-regional features, environmental factors and seasonal variability, consequently the presented regional algorithm might have a limited generalization capability. Clearly, more in situ data with improved spatial and temporal coverage are critically needed for further calibration and validation of the ocean color products in the Black Sea.

We propose a new possible earthquake precursor, a coastal water jet originating from shallow water gas seeps and colored by sediments, lifted from increased gas seeps emissions, preceding some earthquakes with offshore epicenters along the Bulgarian Black Sea coast and M ≥ 3. The new possible earthquake precursor is site specific and may be observed in shallow coastal water regions where active faults are accompanied by hydrocarbon gas seeps. We point out to a region where it can be easily detected by direct observation and satellite remote sensing, Zelenka methane seeps (ZMS), near the Bulgarian Black Sea coast. The ZMS activation is related to the tectonic stress and fracturing preceding and accompanying the earthquakes in the Shabla-Kaliakra-Balchik region along the northern part of the Bulgarian Black Sea coast. We also propose an earthquake forecasting experiment, based on the following four hypotheses: 1) The change of the methane emission of shallow horizons is related to crustal strain changes preceding earthquakes in the region; 2) extreme change of the activity of underwater methane seepages appears immediately before nearby earthquakes; 3) shallow water methane seepages activity can be monitored by remote sensing; 4) satellites can register effects from an extreme increase in their emissions. The proposed earthquake forecasting experiment is based on the monitoring of methane seepages activity in the ZMS area by direct observation and remote sensing which may provide indication for preparatory earthquake activity preceding offshore earthquakes in the region.

Background: The Black Sea is the largest brackish water body in the world, although it is connected to the Mediterranean Sea and presents an upper water layer similar to some regions of the former albeit with lower salinity and (mostly) temperature. In spite of its well-known hydrology and physico chemistry, this enormous water mass remains poorly studied at the microbial genomics level. Results: We have sampled its different water masses and analyzed the microbiome by classic and genome-resolved metagenomics generating a large number of metagenome-assembled genomes (MAGs) from them. The oxic zone presents many similarities to the global ocean while the euxinic water mass has similarities to other similar aquatic environments of marine or freshwater (meromictic monimolimnion strata) origin. The MAG collection represents very well the different types of metabolisms expected in this kind of environments and includes Cyanobacteria (Synechococcus), photoheterotrophs (largely with marine relatives), facultative/microaerophilic microbes again largely marine, chemolithotrophs (N and S oxidizers) and a large number of anaerobes, mostly sulfate reducers but also a few methanogens and a large number of “dark matter” streamlined genomes of largely unpredictable ecology. Conclusions: The Black Sea presents a mixture of similarities to other water bodies. The photic zone has many microbes in common with that of the Mediterranean with the relevant exception of the absence of Prochlorococcus. The chemocline already presents very different characteristics with many examples of chemolithotrophic metabolism (Thioglobus) and facultatively anaerobic microbes. Finally the euxinic anaerobic zone presents, as expected, features in common with the bottom of meromictic lakes with a massive dominance of sulfate reduction as energy generating metabolism and a small but detectable methanogenesis.We are adding critical information about this unique and important ecosystem and its microbiome.

BackgroundThe Black Sea is the largest brackish water body in the world, although it is connected to the Mediterranean Sea and presents an upper water layer similar to some regions of the former albeit with lower salinity and (mostly) temperature. In spite of its well-known hydrology and physico chemistry, this enormous water mass remains poorly studied at the microbial genomics level.ResultsWe have sampled its different water masses and analyzed the microbiome by classic and genome-resolved metagenomics generating a large number of metagenome-assembled genomes (MAGs) from them. The oxic zone presents many similarities to the global ocean while the euxinic water mass has similarities to other similar aquatic environments of marine or freshwater (meromictic monimolimnion strata) origin. The MAG collection represents very well the different types of metabolisms expected in this kind of environments and includes Cyanobacteria (Synechococcus), photoheterotrophs (largely with marine relatives), facultative/microaerophilic microbes again largely marine, chemolithotrophs (N and S oxidizers) and a large number of anaerobes, mostly sulfate reducers but also a few methanogens and a large number of “dark matter” streamlined genomes of largely unpredictable ecology.ConclusionsThe Black Sea presents a mixture of similarities to other water bodies. The photic zone has many microbes in common with that of the Mediterranean with the relevant exception of the absence of Prochlorococcus. The chemocline already presents very different characteristics with many examples of chemolithotrophic metabolism (Thioglobus) and facultatively anaerobic microbes. Finally the euxinic anaerobic zone presents, as expected, features in common with the bottom of meromictic lakes with a massive dominance of sulfate reduction as energy generating metabolism and a small but detectable methanogenesis.We are adding critical information about this unique and important ecosystem and its microbiome.

The National Geo-Information Center (NGIC) is a distributed research infrastructure funded by the National road map for scientific infrastructure (2017-2023) of Bulgaria. It operates in a variety of disciplines such as geophysics, geology, seismology, geodesy, oceanology, climatology, soil science, etc. providing data products and services. Created as a partnership between four institutes working in the field of Earth observation: the National Institute of Geophysics, Geodesy and Geography (NIGGG), the National Institute of Meteorology and Hydrology (NIMH), the Institute of Oceanology (IO), the Geological Institute (GI), and two institutes competent in ICT: the Institute of Mathematics and Informatics (IMI) and the Institute of Information and Communication Technologies (IICT), NGIC consortium serve as primary community of data collectors for national geoscience research. Besides the science, NGIC aims to support decision makers during the process of prevention and protection of the population from natural and anthropogenic risks and disasters.Individual NGIC partners originated independently and differ from one another in management and disciplinary scope. Thus, the conceptual model of the NGIC system architecture is based on a federated model structure in which the partners retain their independence and contribute to the development of the common infrastructure through the data and research they carry out. The basic conceptual model of architecture uses both service and microservice concepts and may be altered according to the specifics of the organization environment and development goals of the NGIC information system. It consists of three layers: “Sources” layer containing the providers of Data, Data products, Services and Soft-ware (DDSS), “Interoperability”- regulating the access, automation of discovery and selection of DDSS and data collection from the sources, and “Integration” layer which produces integrated data products.The diversity of NGIC’s data, data products, and services is a major strength and of high value to its users like governmental institutions and agencies, research organizations and universities, private sector enterprises, media and the public. NGIC will pursue collaboration with initiatives, projects and research infrastructures for Earth observation to enhance access to an integrated global data resource.

We measured the community-scale metabolism of seagrass meadows in Bulgaria (Byala [BY]) and Korea (Hoopo Bay [HP]) to understand their ecosystem function in coastal waters. A noninvasive in situ eddy covariance technique was applied to estimate net O2 flux in the seagrass meadows. From the high-quality and high-resolution time series O2 data acquired over > 24 h, the O2 flux driven by turbulence was extracted at 15-min intervals. The spectrum analysis of vertical flow velocity and O2 concentration clearly showed well-developed turbulence characteristics in the inertial subrange region. The hourly averaged net O2 fluxes per day ranged from -474 to 326 mmol O2 m-2 d-1 (-19 ± 41 mmol O2 m-2 d-1) at BY and from -74 to 482 mmol O2 m-2 d-1 (31 ± 17 mmol O2 m-2 d-1) at HP. The net O2 production rapidly responded to photosynthetically available radiation (PAR) and showed a good relationship between production and irradiance (P-I curve). The hysteresis pattern of P-I relationships during daytime also suggested increasing heterotrophic respiration in the afternoon. With the flow velocity between 3.30 and 6.70 cm s-1, the community metabolism during daytime and nighttime was significantly increased by 20 times and 5 times, respectively. The local hydrodynamic characteristics may be vital to determining the efficiency of community photosynthesis. The net ecosystem metabolism at BY was estimated to be -17 mmol O2 m-2 d-1, which was assessed as heterotrophy. However, that at HP was 36 mmol O2 m-2 d-1, which suggested an autotrophic state.

The ultimate goal of modern operational oceanography are end user oriented products with high scientific quality. Beneficiaries are the governmental services, coast and offshore based enterprises and research institutions that make use of the products generated by operational oceanography. Direct users are coastal managers, shipping, search and rescue, oil spill combat, offshore industry, ports, fishing, tourism, and recreation industry. Indirect beneficiaries, through climate forecasting based on ocean observations, are food, energy, water and medical suppliers. Availability of updated information on the actual state as well as forecast of marine environment is essential for the success and safety of maritime operations in the offshore industry. Various systems for the collection and presentation of marine data for the needs of different users have been developed and put in operation in the Black Sea. The systems are located both along the coast and in the open sea and the information they provide is used by both the maritime industry and the widest range of users. The Black Sea Monitoring and Forecasting Center in the frame of the Copernicus Marine Service is providing regular and systematic information about the physical state of the ocean, marine ecosystem and wave conditions in the Black Sea area, assimilating observations, keeping efficient operations, advanced technology and high quality modeling products. Combining and optimizing in situ, remote sensing, modeling and forecasting into a Black Sea observing system is a task that has to be solved, and that will allow to get a more complete and comprehensive picture of the state of the marine environment as well as to forecast future changes of physical and biogeochemical state of the Black Sea and the Black Sea ecosystem.

In this study the performance of Medium Resolution Imaging Spectrometer (MERIS) geophysical products were evaluated using in situ measurements in northwestern part of the Black Sea. The in situ chlorophyll a (Chl-a), total suspended matter (TSM) and Scechi disk depth (SDD) were collected from two Institute of Oceanology, BAS cruises during spring season of 2006 and 2009. A strict comparison method between two data sets was adopted resulting in 27 and 33 match ups for TSM and Chl a respectively. The method comprised the arithmetic average of valid MERIS values calculated over the 3 × 3 - pixels square found within time difference of ± 3 h from the in situ measurement. Additionally, classification of the in situ data was performed, in order to assess accuracy of MERIS algal_2 and TSM products in respect to the sea water with different optical properties. The in situ data were subdivided into three groups to represent clear, moderate turbid and turbid waters by applying K - mean clustering method on the measured concentrations of Chl-a, TSM and transparency. Statistical analysis of MERIS derived TSM and Chl-a and in situ data were carried out for the different water types. In the case of TSM concentrations, was found a reasonably good agreement between two data sets in clear and moderate turbid waters. The estimated R2 are greater than or equal to 0.66 and log_RMS differences for clear and moderate turbid waters ranging between 0.09 g/m3 and 0.19 g/m3. The similar correlations were estimated for Chl-a concentrations, but the value for log_RMS in turbid waters is higher to those obtained for TSM. For both variables, the best results of comparison were found for the moderate turbid waters, that corresponding to high coefficients of determination (R2>0.75) and small log_RMS differences of 0.1 mg/m3 for Chl-a and 0.09 g/m3 for TSM. The present study suggested that MERIS Case 2 products are reasonably accurate in moderate turbid shelf waters, but not yet reliable in turbid coastal waters of the northwestern Black Sea.

Winds over the ocean play an important role in meteorology, oceanography and climatology. They affect air-sea variations in heat, humidity, gases and particles, regulating the crucial relation between the ocean and the atmosphere that establishes and supports the climate on regional and global scale. Therefore, the knowledge of wind fields over the oceans is essential for global weather forecast purposes. Furthermore, the accurate forecasting of ocean surface winds contribute to good wave forecasts, which provide informativeness and safety in marine industry, navigation and other human activities in open and off-shore seas. The sources of surface observations that are generally used to make analyses of winds over the oceans not always can provide data with temporal and spatial regularity. These gaps can be filled in with wind data registered by satellite sensors like NASA's QuikSCAT satellite radar scatterometer. It provides on operational basis wind vector measurements over global oceans with considerable reliability and sufficient time frequency. The standard operational QuikSCAT wind vector product has a spatial resolution of 25km × 25km. However, the recent measurement methodology of QuikSCAT allows for wind vector retrievals at better spatial resolution of 12.5 km.