Deep Black Sea Research Articles

History of the geological development of the Ukrainian sector of the Black Sea from the middle Early Cretaceous to the beginning of the Late Miocene

Regional seismic investigations have made it possible to obtain new knowledge on the geological history of the Ukrainian sector of the Black Sea during rifting from Albian to Cenomanian, post-rift subsidence (Turonian¾Maastrichtian and Paleocene¾Middle Eocene), tectonic compression at the end of the middle Eocene and post-rift subsidence interrupted by a series of short-lived, compressional events (late Eocene ¾ the beginning of the Early Miocene). Rifting occurred simultaneously in the entire area of study and formed three long rift basins, each of which consisted of a system of (half)grabens, separated from each other and their margins by faults with amplitudes of up to3 km. The intensity of Cretaceous rifting was significantly less than would be required to produce continental lithosphere break-up and oceanic crust formation, or through-going «oceanisation» of continental lithosphere. Sedimentation during the pre-Late Eocene post-rift phase took place in relatively shallow marine conditions. Eocene compression caused a strong deformation of the sedimentary cover, partial and complete inversion of rift faults and the formation of three largely separate sea basins, between which a large landmass arose. The primary area of deposition of sedimentary sequences was significantly reduced due to strong deformations caused by compressional phases in the Late Miocene. That which is now the deep Black Sea was a relatively shallow basin until the beginning or even the end of the Pleistocene. Only thereafter did the water depth increase rapidly to more than 2 km. Research results indicate that modern tectonic reconstructions of the Western Black Sea and Eastern Black Sea basins, which are based on assumptions about the formation of the (sub)oceanic crust in these basins and/or different times of their formation, look unreliable. It also follows that any view of back-arc basins as small oceanic basins is not universally applicable.

Methane gas hydrates of the Black Sea – environmental problem or energy source?

Purpose. The purpose of this paper is to substantiate the technological solution of equilibrium conditions in the system “methane – water phase – hydrate – R-2M”; to reveal existing ecological problems of methane gas hydrate extraction from the Black Sea bottom; to determine whether gas hydrate deposits of Black Sea methane are an ecological problem or should be considered as an energy source, to explain the necessity of introduction of the effect of forced self-preservation of methane gas hydrates into development of gas hydrates from the sea bottom.
 Results. This article analyses current research on gas hydrates specifically in the Black Sea. It shows that the necessary conditions exist for the accumulation of gas hydrates in certain areas of the deep Black Sea (one of the most favourable regions among modern sea basins). This article discusses some ideas for the development of experimental studies of the metastable state of methane gas hydrates at negative temperatures: stability and mechanisms of decomposition. Despite the great variety of technological solutions and schemes of gas hydrates application proposed by the leading researchers in the world, they have been tested practically on a small number of laboratory and model installations, mainly for water desalination and concentration of water solutions, separation of two-component gas mixtures. In fact, there is no data to calculate the processes of formation and melting of ice-gas hydrate methane. The effect of self-preservation of methane gas hydrates deserves special attention.
 Scientific novelty. An attempt was made to substantiate the issue of whether gas hydrate deposits of methane in the Black Sea are an environmental problem or should they be considered as an additional source of energy and even as a “fuel of the future”. The authors for the first time introduced the concept of “forced preservation (activation) effect of methane gas hydrates”, which makes it possible to stabilize methane hydrate decomposition when the system is transferred from the area of hydrate stability to the area of thermodynamic parameters, thus significantly reducing the environmental problems of the Black Sea.
 Practical value. This article offers a technological solution for stabilization of equilibrium conditions by hydrophobic material “Ramsinks-2M” in the system “methane-water phase-hydrate-R-2M” to regulate the self-preservation effect of methane gas hydrates

The "Dark Side" of Picocyanobacteria: Life as We Do Not Know It (Yet).

Picocyanobacteria of the genus Synechococcus (together with Cyanobium and Prochlorococcus) have captured the attention of microbial ecologists since their description in the 1970s. These pico-sized microorganisms are ubiquitous in aquatic environments and are known to be some of the most ancient and adaptable primary producers. Yet, it was only recently, and thanks to developments in molecular biology and in the understanding of gene sequences and genomes, that we could shed light on the depth of the connection between their evolution and the history of life on the planet. Here, we briefly review the current understanding of these small prokaryotic cells, from their physiological features to their role and dynamics in different aquatic environments, focussing particularly on the still poorly understood ability of picocyanobacteria to adapt to dark conditions. While the recent discovery of Synechococcus strains able to survive in the deep Black Sea highlights how adaptable picocyanobacteria can be, it also raises more questions—showing how much we still do not know about microbial life. Using available information from brackish Black Sea strains able to perform and survive in dark (anoxic) conditions, we illustrate how adaptation to narrow ecological niches interacts with gene evolution and metabolic capacity.

Element enrichment and provenance of the detrital component in Holocene sediments from the western Black Sea

Summary Concentrations of a large set of major and trace elements, and Sr, Nd and Pb isotope ratios were measured in Holocene sediments cored in the western deep Black Sea in order to unravel: (1) the controls of element enrichment, and (2) sources of the detrital component. The transition of the basin from oxic to euxinic resulted in enrichment or depletion in a number of elements in the deep-sea sediments. Authigenic Fe enrichment appears to depend on the amount of Fe mobilized from the sediment through the benthic redox shuttle mechanism and free H2S in the water column (degree of “euxinization”). Manganese enrichment is controlled by diagenetic reactions within the sediment: the dissolution of Mn minerals, Mn2+ diffusion upward and reprecipitation. Barium enrichment is also controlled by diagenetic reactions, sulfate reduction and methanogenesis, that take place above and below the sulfate-methane transition, respectively. The major part of V, Co, Ni, Cu, Zn, Cr, Mo, Cd and Sb is inferred to have co-precipitated with Fe in the euxinic deep waters and to have been incorporated into authigenic Fe-sulfides. Basin reservoir effect additionally influences the Mo enrichment. The U enrichment is interpreted to have a different origin in the two organic-rich stratigraphic units (II and I). It is inferred to be: (i) at the expense of the U inventory of the deepwater pool and a result of inorganic reduction of U at euxinic conditions in the lower Unit II; and (ii) at the expense of the U inventory of the surface water pool and a result of biogenic uptake and transfer to the sediment by the plankton in the upper Unit I. The high field strength elements are closely linked to the detrital component and their depletion in the organic-rich sediments reflects a dilution of the detrital component by the biogenic one. The enrichments of REE, Sn and Th are likely controlled by adsorption on clay minerals. Sr-Nd-Pb isotope compositions of the alumino-silicate component of the studied sediments are relatively uniform. They are most likely controlled by riverine suspended matter supplied mainly in the NW Black Sea (Danube Delta) and transported southward by marine currents, and to a lesser degree by suspended matter from the small rivers draining SE Bulgaria and NW Turkey. Wind-blown dust from the Sahara Desert appears to have a minor contribution to the alumino-silicate component of the sediments. The slight shift in the Pb isotopes in Unit I upper layers is possibly caused by the addition of anthropogenic Pb.

Turbidite deposition and diagenesis in the southwestern Black Sea: Implications for biogeochemical cycling in an anoxic basin

The biogeochemical cycles of iron, phosphorus and sulfur are intimately linked and the fate of these elements is highly redox-dependent. Under anoxic conditions, iron is reduced to Fe(II), for an important part driven by reaction with sulfide. Reduction and sulfidation diminish the affinity of iron for phosphorus, thereby affecting sedimentary phosphorus retention. The coupled cycling of iron-phosphorus-sulfur as a function of redox conditions thereby helps control nutrient availability and primary productivity in marine systems. The Black Sea is the world's largest permanently stratified basin with a strong gradient from oxic surface waters to anoxic and strongly sulfidic deep waters, and is therefore well-suited to investigate redox-dependent changes in coupled iron-phosphorus-sulfur cycling. The presence of sulfide in the deep Black Sea alters the chemical speciation of iron (Fe) and phosphorus (P) in particulate matter in the water column and sediment. These alterations and their impact are poorly constrained for turbidites, which are deposits formed by mass transport from the continental slope into the deep basin of the Black Sea through turbidity currents. Here, we compare the geochemistry of sediments on the southwestern (SW) Black Sea slope overlain by oxygenated waters (234 m below sea surface, mbss) with that of a sediment record with turbidite intervals from the sulfidic SW deep basin (2169 mbss). The aims were to investigate the potential of SW slope sediment as source material for turbidites, and to assess the geochemical impact of reaction with sulfide. The bulk chemistry (Al, CaCO3, Fe) of the SW deep Black Sea turbidite intervals was similar to that of SW Black Sea slope sediments (234 m water depth), suggesting that the latter are source material for deep SW Black Sea turbidites. The source sediment is characterized by strong enrichments in highly reactive Fe(III) and Mn phases, high rates of sulfate reduction and the presence of methane. Similar total Fe contents in the slope and deep turbidite sediments suggest that Fe is efficiently retained in the sediment. In contrast, Mn is depleted during down-slope transport and P contents in the turbidite intervals are about 50% lower than in the slope sediment, indicating significant P release during and after turbidite deposition. Calculations using the obtained data and conservative estimates of the areal extent of turbidite deposition in the SW Black Sea indicate that turbidity currents have the potential to impact coupled Fe-P-S biogeochemical cycling by boosting Fe input, dissolved P accumulation, sulfide oxidation and FeS2 burial in the deep Black Sea.

Organic matter along longitudinal and vertical gradients in the Black Sea

We studied organic matter in the central Black Sea and its northeastern and northwestern shelf break within three weeks in November 2013 to test the hypothesis that in situ production could explain lateral and vertical variability in its composition and distribution. The wide spatial coverage over a short period of time achieved during this study revealed longitudinal variability in organic matter characteristics reflecting productivity at the Black Sea surface. Particulate organic matter was dominantly autochthonous in the central Black Sea. Allochthonous influence of river discharge was only traced on the northwestern shelf by high concentrations but low freshness of particulate organic matter. Compared to the NW shelf break and central Black Sea, primary production was high near the NE shelf break, likely fueled by input from the Azov Sea. Vertical patterns were similar throughout the deep Black Sea and appeared to also be governed by in situ processes rather than reflect variability in the surface water. As concentrations of organic matter decreased with depth, its elemental and isotopic composition indicated chemoautotrophic production at the oxic-anoxic interface and organic matter degradation in the benthic boundary layer. Though profiles of dissolved organic carbon indicated a minor source in anoxic deep water, likely linked to chemosynthesis and reflux from sediments, a negative deviation of concentrations from a conservative mixing line between two endmembers suggested net removal of labile dissolved organic carbon.

Phosphorus burial in sediments of the sulfidic deep Black Sea: Key roles for adsorption by calcium carbonate and apatite authigenesis

Sedimentary burial of the essential nutrient phosphorus (P) under anoxic and sulfidic conditions is incompletely understood. Here, we use chemical and micro-scale spectroscopic methods to characterize sedimentary P burial along a water column redox transect (six stations, 78–2107m water depth) in the Black Sea from the shelf with its oxygenated waters to the anoxic and sulfidic deep basin. Organic P is an important P pool under all redox regimes, accounting for up to 60% of P burial. We find a general down-core increase in the relative importance of organic P, especially on the shelf where P bound to iron (Fe) and manganese (Mn) (oxyhydr)oxides is abundant in the uppermost sediment but rapidly declines in concentration with sediment depth. Our chemical and spectroscopic data indicate that the carbonate-rich sediments (Unit I, ∼3000years, ∼0–30cm depth) of the sulfidic deep Black Sea contain three major P pools: calcium phosphate (apatite), organic P and P that is strongly associated with CaCO3 and possibly clay surfaces. Apatite concentrations increase from 5% to 25% of total P in the uppermost centimeters of the deep basin sediments, highlighting the importance of apatite formation for long-term P burial. Iron(II)-associated P (ludlamite) was detected with X-ray absorption spectroscopy but was shown to be a minor P pool (∼5%), indicating that lateral Fe–P transport from the shelf (“shuttling”) likely occurs but does not impact the P burial budget of the deep Black Sea. The CaCO3–P pool was relatively constant throughout the Unit I sediment interval and accounted for up to 55% of total P. Our results highlight that carbonate-bound P can be an important sink for P in CaCO3-rich sediments of anoxic, sulfidic basins and should also be considered as a potential P sink (and P source in case of CaCO3 dissolution) when reconstructing past ocean P dynamics from geological records.

Ecosystem status of the deep Black Sea, soft sediment, benthic community

The deep soft sediment Black Sea benthic community is dominated by cold seep habitats formed by the microbial breakdown of phytoplankton. The deep Black Sea benthic ecosystem is chemosynthetic with methanogenesis and the sulfate-driven anaerobic oxidation of methane acting as the primary metabolic pathways. Due to the depth and lack of metazoan life the deep Black Sea benthic ecosystem is generally regarded to be at low risk from anthropogenic impact and has little legislation pertaining directly to the preservation of the chemosynthetic habitats. The principal ecosystem services provided by the Black Sea include carbon sequestration and preservation of historical artefacts. Compared to other ecosystems, information on microbial biodiversity and ecosystem services in the deep Black Sea is lacking, and we highlight a need to plan and implement research programmes to address significant gaps and to enhance scientific understanding of this environment.

On Influence of Current Variability in the Deep Black Sea upon Water Dynamics of Narrow North Caucasian Continental Shelf

On Influence of Current Variability in the Deep Black Sea upon Water Dynamics of Narrow North Caucasian Continental Shelf

O vliyanii izmenchivosti techeniya v glubokovodnoy zone Chernogo morya na dinamiku vod uzkogo severokavkazskogo shel'fa

O vliyanii izmenchivosti techeniya v glubokovodnoy zone Chernogo morya na dinamiku vod uzkogo severokavkazskogo shel'fa

Net removal of dissolved organic carbon in the anoxic waters of the Black Sea

Dissolved organic carbon (DOC) concentrations in the deep Black Sea are ~2.5 times higher than found in the global ocean. The two major external sources of DOC are rivers and the Sea of Marmara, a transit point for waters from the Mediterranean Sea. In addition, expansive phytoplankton blooms contribute autochthonous carbon to the Black Sea's ~800 Tg C DOC reservoir. Here, a basin-wide zonal section of DOC is explored using data from the 2013 Dutch GEOTRACES GA04-N, cruise 64PE373. DOC distributions are interpreted with respect to well-described hydrographic and biogeochemical layers of the Black Sea. Observed DOC concentrations were >180μmolkg−1 at the surface, decreasing to ~125μmolkg−1 at the base of the oxic layer and reaching a minimum of ~113μmolkg−1 in the upper anoxic layer between ~150 and 500m. At greater depths the concentrations increased; maximum anoxic layer concentrations of 122μmolkg−1 were found in the homogeneous benthic bottom layer (>1775m). Concentrations are then predicted based on conservation with respect to salinity using linear end-member mixing models, and predictions are compared with observations to estimate net removal (i.e., deficits) and accumulation (i.e., surpluses). A maximum surplus of ~10μmolkg−1 was identified at the surface, likely due to local primary production. DOC exported to depth was non-conservative: up to ~34‐41μmolkg−1 was removed from the basin's oxic layer in <5years, and an additional 13±5μmolkg−1 was removed from the anoxic layer during its ~300 to 600‐year residence time, given steady state. These deficits represent a removal of ~19% in the oxic water and a further removal of ~10% under anoxia, for a net removal of 48μmolkg−1 (or ~29%) of allochthonous DOC, with respect to predicted concentrations. We find no evidence for DOC accumulation (i.e., net production) in the anoxic Black Sea, and suggest that concentrations are elevated relative to the ocean due to input of terrigenous DOC from rivers; we estimate that >50% of DOC in the deep Black Sea is terrigenous. The Black Sea's relatively elevated DOC pool may be analogous to a hypothesized anoxic Eocene ocean's elevated reservoir only if the Eocene ocean received a substantial amount of terrigenous DOC.

PELOIDS OF THE DEEP BLACK SEA – MATERIAL COMPOSITION, PROPERTIES AND POTENTIAL RESOURCES

The main purpose of this study is to prove that certain types of genetic materials of the deepwater Black Sea sediments correspond to the notion of “deepwater peloids”, and that their stocks in the upper layers of the bottom sediments are virtually inexhaustible. To achieve the main goal the number of problems is solved, namely the particle size, mineral and chemical composition of the solid phase of the deepwater silt deposits were defined, including the analysis of their carbonate and organic matter content, moisture content, mass, density, bulk density, plastic strength, stickiness and other properties of the bottom sediments. The preliminary estimates of reserves and the prospective resources estimation of deepwater Black Sea peloids were conducted. The object of the study is the main material and genetic types of the deepwater silt sediments of the Black Sea.As the material for this study the authors used the archival and published data of analytical processing with a wide range of involved methods and core samples of bottom sediments obtained in numerous expeditions in the deep Black Sea, including those obtained during the 30th voyage of the SRS “Vladimir Parshin” (2010), as well as 62nd and 75th voyages of the SRS “Professor Vodyanitsky” (2005, 2013) [1, 3, 6]. According to their research results the authors proved that for the last 7 – 10 thousand years the multiphase dispersed heterogeneous physic-chemical system was formed in the deep Black Sea that spatially occupied mainly the upper (0 – 3 m) layer of the bottom sediments. With the unique granule-metric, mineral, chemical and physic-chemical and physic-mechanical properties, this system may be defined as “peloids”.The results of geological and geologic-environmental studies of the deepwater area of the Black Sea confirmed the perspective of conducting within its Ukrainian sector of the specific geologic exploration operations in order to delineate the deposits of the Black Sea deepwater peloids. Preliminary calculations show that such deposit may be huge in size.The target area for immediate geologic exploration works for identification of the main types of industrial deepwater Black Sea peloids, their stocks and medicinal properties is defined. Given these results it could be predicted that production and widespread use of the Black Sea deep peloids shall be economically feasible with the application of sustainable technologies and ensuring compliance with both Ukrainian and international law.

Sources and downward fluxes of polycyclic aromatic hydrocarbons in the open southwestern Black Sea

The composition, abundance and fluxes of polycyclic aromatic hydrocarbons (PAHs) were investigated in time-series sediment traps set at 1000m and 2000m depth in the open southwestern Black Sea (October 2007–September 2008). Total PAH (TPAH22) concentrations ranged from 299–3540ngg−1, averaging 1190±698ngg−1, while TPAH22 flux varied from 17.7–310ngm−2d−1, averaging 128±86.6ngm−2d−1. Molecular profiles and diagnostic ratios of both low and high molecular weight compounds indicate the presence of PAHs derived from multiple pyrolytic/combustion sources (petroleum, grass, wood and coal combustion) and petrogenic sources (unburned fossil fuels). Temporal patterns of PAH loads/fluxes are linked to the variability in the magnitude of emissions and/or to the variability of mass flux, organic carbon flux and carbonate flux, the latter two being mostly controlled by marine productivity fluctuations. High biogenic fluxes observed in the Black Sea promote the vertical export of PAHs to deep Black Sea waters, enhancing also the transport of labile compounds at high flux seasons. Lateral transport/advection of PAHs seems also of importance at certain periods in deep Black Sea basins.

Intermediate sulfur oxidation state compounds in the euxinic surface sediments of the Dvurechenskii mud volcano (Black Sea)

The deep Black Sea is known to be depleted in electron-acceptors for sulfide oxidation. This study on depth distributions of sulfur species (S(II), S(0), Sn2-, S2O32-, SO32-, SO42-) in the Dvurechenskii mud volcano, a cold seep situated in the permanently anoxic eastern Black Sea basin (Sorokin Trough, 2060m water depth), showed remarkable concentrations of sulfide oxidation products. Sulfite concentrations of up to 11μmolL−1, thiosulfate concentrations of up to 22μmolL−1, zero-valent sulfur concentrations of up to 150μmolL−1 and up to five polysulfide species were measured in the upper 20cm of the sediment. Electron-acceptors found to be available in the Dvurechenskii mud volcano (DMV) for the oxidation of hydrogen sulfide to sulfide oxidation intermediates are iron-minerals, and probably also reactive manganese phases. Up to 60μmolg−1 of reactive iron-minerals and up to 170μmolL−1 dissolved iron was present in the central summit with the highest fluid upflow and fresh mud outflow. Thus, the source for the oxidative power in the DMV are reactive iron phases extruded with the mud from an ancient source in the deeply buried sediments, leading to the formation of various sulfur intermediates in comparably high concentrations. Another possible source of sulfide oxidation intermediates in DMV sediments could be the formation of zero-valent sulfur by sulfate dependent anaerobic microbial oxidation of methane followed by disproportionation of zero-valent sulfur. Sulfide oxidation intermediates, which are produced by these processes, do not reach thermodynamic equilibrium with rhombic sulfur, especially close to the active center of the DMV due to a short equilibration time. Thus, mud volcano sediments, such as in the DMV, can provide oxidizing niches even in a highly reduced environment like the abyssal part of the Black Sea.

A Calciosolenia brasiliensis (Coccolithophorida) find in neogene sediments of a deep Black Sea basin and its connection with the Mediterranean

A Calciosolenia brasiliensis (Coccolithophorida) find in neogene sediments of a deep Black Sea basin and its connection with the Mediterranean

Recent sedimentation in the Black Sea: New insights from radionuclide distributions and sulfur isotopes

The Black Sea is the world's largest anoxic–sulfidic marine basin and has unique sedimentation conditions. Recent studies suggested that mass accumulation rates (MAR) in this environment have increased in the past century when compared to the last 2000 years (Unit 1 period). In this paper we test this hypothesis with new MAR data and further explore the relationship between the depositional pattern and pyrite–sulfur isotopic signature. Based on 15 cores sampled in 2001 and 2003, our dataset comprises radioactive isotopes (210Pb, 226Ra, 137Cs) and sulfur stable isotopes (δ34SVCDT) along with organic, inorganic carbon and pyrite–sulfur. We calculated MARs using 210Pb profiles and/or Chernobyl-derived 137Cs horizon buried in the sediment column. Our turbidite-free deep basin sediment MARs (61 to 76gm−2yr−1) agreed with the previous results (50–100gm−2yr−1) and confirm the view that MARs of the deep Black Sea basin have been increasing. A unique feature of our dataset was the presence of Chernobyl-derived radionuclides below up to 20cm thick turbidite layers (deposited between 1986 and 2003), which enabled us to compute MARs for these coring locations. MARs were 1120±103 and 5230±125gm−2yr−1 for the last two decades in two turbidite-impacted western central basin cores, 20–100 times the long-term rates of the deep basin. This fast depositional pattern was reflected in the geochemical and isotopic data as well. Turbidites had isotopically heavier pyrite–sulfur compared to the Unit 1-type water column formed pyrite. This is probably because the turbidites originated from slope and transported slope pyrite isotopic signature to the deep basin. Diagenetic effects within the turbidite can make pyrite–sulfur even heavier. These tightly linked results demonstrate the importance of turbidites in recent sedimentation of the Black Sea.

New model for molybdenum behavior in euxinic waters

Rogoznica Lake, on the Adriatic coast of Croatia, undergoes vertical mixing in autumn, but quickly restratifies and becomes intensely sulfidic during the succeeding 11 months. Autumn's vertically homogeneous dissolved Mo concentrations quickly revert to a summer profile in which Mo concentrations are lower by an order of magnitude in the sulfidic layer than in the oxic layer. Other redox sensitive elements (As, U and V) are much less affected on this time scale. Below the depth where sulfidic waters become saturated with iron monosulfide, Mo concentrations become nearly constant. A similar pattern can be recognized in other euxinic basins and seems inconsistent with Mo removal by sorption on sinking particles. Precipitation of a previously unrecognized, probably nanoscale Fe(II)–Mo(VI) sulfide mineral is postulated to explain this phenomenon. By fitting the Rogoznica data, a provisional composition and solubility product constant for this material are derived. The mineral's formula approximates Fe 5Mo 3S 14. Its Mo content is similar to that of a synthetic precipitate previously shown by X-ray spectroscopy to resemble molybdenum's host phase in black shales. Assuming saturation with this mineral, dissolved Mo in the deep water column of a number of other euxinic basins can be predicted in most cases to within a factor of three. The model has important implications for Mo behavior in euxinic basins. For example, the model attributes the near-total Mo removal from deep Black Sea waters to a serendipitous combination of pH and H 2S concentration, implying that such removal would not be a general property of euxinic basins. This is a key point with regard to Mo isotope systematics. Contrary to previous views, the model assigns a critical role to pH in controlling the efficiency of Mo removal from euxinic basins.

Preservation, origin and genetic imprint of extracellular DNA in permanently anoxic deep-sea sediments

Molecular approaches that target the total DNA pool recovered from permanently anoxic marine ecosystems have revealed an extraordinary diversity of prokaryotes and unicellular eukaryotes. However, the presence of gene sequences contained within the extracellular DNA pool is still largely neglected. We have investigated the preservation, origin and genetic imprint of extracellular DNA recovered from permanently anoxic deep-sea sediments of the Black Sea. Despite high DNase activities, huge amounts of total extracellular DNA were found in both the surface and subsurface sediment layers, suggesting reduced availability of the extracellular DNA pool to nuclease degradation. The reduced degradation of the total extracellular DNA was confirmed by its low decay rate and the high accumulation in the deeper sediment layers. The copy numbers of 16S and 18S rDNA contained within the extracellular DNA pool in both the surface and subsurface sediment layers was very high, indicating that permanently anoxic sediments of the deep Black Sea are hot spots of preserved extracellular gene sequences. The extracellular DNA recovered from these sediment layers also contained highly diversified 18S rDNA sequences. These were not only representative of the major protistan lineages, but also of new very divergent lineages, branching as independent clades at the base of the tree. Our findings indicate that the extracellular DNA pool is a major archive of present/past eukaryotic gene sequences, and they highlight the importance of integrating molecular cell-oriented approaches with molecular analyses of the extracellular DNA pool, for a better assessment of microbial diversity and temporal changes in marine benthic ecosystems.

Long term trends in the sea surface temperature of the Black Sea

Abstract. There is growing understanding that recent deterioration of the Black Sea ecosystem was partly due to changes in the marine physical environment. This study uses high resolution 0.25° climatology to analyze sea surface temperature variability over the 20th century in two contrasting regions of the sea. Results show that the deep Black Sea was cooling during the first three quarters of the century and was warming in the last 15–20 years; on aggregate there was a statistically significant cooling trend. The SST variability over the Western shelf was more volatile and it does not show statistically significant trends. The cooling of the deep Black Sea is at variance with the general trend in the North Atlantic and may be related to the decrease of westerly winds over the Black Sea, and a greater influence of the Siberian anticyclone. The timing of the changeover from cooling to warming coincides with the regime shift in the Black Sea ecosystem.

Earthquake-induced turbidite deposition as a previously unrecognized sink for hydrogen sulfide in the Black Sea sediments

The depth profiles of excess 210Pb, 137Cs, elemental sulfur, reactive iron and porewater hydrogen sulfide of a western central basin sediment core in the Black Sea collectively point to the presence of a 20 cm thick reactive iron rich turbidite layer. This layer was most probably deposited there after the 1999 earthquakes in Northwestern Turkey, which caused oxidation of porewater hydrogen sulfide and anomalous accumulation of the product elemental sulfur in the solid phase. A time-variable mathematical model was constructed to explore the non-steady state diagenesis of Fe–S species in a turbidite mud emplaced on normal anoxic–sulfidic deep Black Sea sediments. The 20 cm thick turbidite layer initially contained 80 µmol (g dry wt.) − 1 of Fe(III) in the form of goethite, which led to the rapid (1 day) oxidation and depletion of porewater sulfide and formation of solid phase sulfur intermediates such as S(0) and FeS. S(0) accumulated faster than FeS and was present in the sediment at high concentrations after 5–8 years following the deposition of the turbidite. Reduced iron was in the solid phase long after the consumption of all Fe(III), enabling the coexistence of S(0) and solid phase reactive iron (which has not been sulfidized yet) for a long period of time. The porewaters had sub-micromolar concentrations of dissolved sulfide in the first 2 years after deposition with Fe(II) exceeding 1 mM. The turbidite layer should serve as a sink for the sulfide from the overlying waters for about 10 years after its deposition. Considering the ubiquity of the deep-basin turbidites found in the Black Sea and the dense tectonic activity on the Northern Anatolian Fault in Northern Turkey, an estimated 0.144 Tg sulfur/year could be buried as S 8 and FeS 2 due to the earthquake-induced turbidites. This value is about 14% of the annual sulfur burial (as pyrite) and 3–5% of the annual sulfide oxidation due to lateral injections of oxic Mediterranean waters to the anoxic–sulfidic Black Sea waters. It is highly likely that earthquake-induced turbidites and subsequent sulfide oxidation in the deep basin represent a previously unrecognized sink in the budget of hydrogen sulfide in the Black Sea.