Influx of Streaming Methane into Anoxic Waters of the Black Sea Basin

Oceanology - Based on long-term data on the spatial distribution and fluxes of streaming (bubbling) methane in the Black Sea, the study considers various types of streaming gas emissions...     

Methane in the Sevastopol coastal area, Black Sea

Concentrations of dissolved methane in seawater and bottom sediments, as well as of methane emanating from gas seeps were measured at 18 stations including several small bays in the Sevastopol coastal area (Black Sea) during 2007–2008. Methane concentrations in surface waters ranged from 10 to 2,970 nmol l^?1, and correlated well with values recorded for sediments. Methane concentrations in the water column were influenced by water depth, as well as by air and water temperatures. In the spring and summer of 2008, in situ CH₄ saturation relative to air was in the range of 970–71,900%. Maximum saturation was in summer. CH₄ fluxes to the atmosphere from the Sevastopol coastal area were estimated to vary from 190 to 1,550 μmol m^?2 day^?1. Gas bubbles escaping from the seepages contained about 57 vol% methane. Radiocarbon dating of the methane revealed an age not exceeding 150 years, implying a biogenic origin.     

Radionuclides and mercury in the salt lakes of the Crimea

90 Sr concentrations,resulting from the Chernobyl NPP accident,were determined in the salt lakes of the Crimea(Lakes Kiyatskoe,Kirleutskoe,Kizil-Yar,Bakalskoe and Donuzlav),together with the redistribution between the components of the ecosystems.The content of mercury in the waters of the studied reservoirs was also established.Vertical distributions of natural radionuclide activities( 238 U,232 Th,226 Ra,210 Pb,40 K) and anthropogenic 137 Cs concentrations(as radiotracers) were determined in the bottom sediments of the Koyashskoe salt lake(located in the south-eastern Crimea) to evaluate the longterm dynamics and biogeochemical processes.Radiochemical and chemical analysis was undertaken and radiotracer and statistical methods were applied to the analytical data.The highest concentrations of 90 Sr in the water of Lake Kiyatskoe(350.5 and 98.0 Bq/m 3) and Lake Kirleutskoe(121.3 Bq/m 3) were due to the discharge of the Dnieper water from the North-Crimean Canal.The high content of mercury in Lake Kiyatskoe(363.2 ng/L) and in seawater near Lake Kizil-Yar(364 ng/L) exceeded the maximum permissible concentration(3.5 times the maximum).Natural radionuclides provide the main contribution to the total radioactivity(artificial and natural combined) in the bottom sediments of Lake Koyashskoe.The significant concentration of 210 Pb in the upper layer of bottom sediments of the lake indicates an active inflow of its parent radionuclide—gaseous 222 Rn from the lower layers of the bottom sediment.The average sedimentation rates in Lake Koyashskoe,determined using 210 Pb and 137 Cs data,were 0.117 and 0.109 cm per year,respectively.     

The Dnepr Canyon: evidence for a continuous submarine channel link between the outer shelf and the deep-sea basin of the northwestern Black Sea

Multibeam bathymetric surveys and single-beam profiles were collected in 2003–2010 from aboard the Ukrainian RV Professor Vodyanitskiy (cruises PV-58 and PV-60, 2003 and 2004), and the German RV Meteor (cruise M-72, legs 1 and 4, 2007) and RV Maria S. Merian (cruise MSM-15, leg 2, 2010) along the continental margin of the NW Black Sea. Integrating published, reprocessed and novel data has revealed the existence of a major continuous channel extending from the Dnepr paleo-delta into greater water depths. It is more than 90 km long, 1.1 km wide and up to 125 m deep. On the upper slope (120–960 m water depth), a number of smaller channels merge into the large, Y-shaped Dnepr Canyon, which then continues obliquely downslope via this submarine channel to at least 1,815 m water depth off the Crimean continental margin, NW Black Sea. The channel could be an important, hitherto unknown link between the shallow oxic and deep anoxic environments of the Black Sea, along which sediment and organic matter could be funneled into the deep-sea basin. This would have far-reaching implications for investigations dealing with marine geology and biology, climate change, as well as oil and natural gas exploitation. The unusual alignment of the channel along the margin of the basin, as well as the location and mode of channel termination in deeper waters deserve future research.     

Geochronological reconstruction of Cs transport from the Coruh river to the SE Black Sea: comparative assessment of radionuclide retention in the mountainous catchment area

The deposition record of ¹³⁷Cs was traced in the SE Black Sea sediments adjacent to the Coruh river mouth in comparison with the earlier studied chronology of ¹³⁷Cs deposition in front of the Danube delta (NW Black Sea). In both cases, the ¹³⁷Cs profiles showed two subsurface peaks attributable to maximum fallout of ‘bomb’ and Chernobyl radionuclides. The Coruh profile revealed a larger contribution of ‘bomb’ ¹³⁷Cs in comparison with the Chernobyl input, suggesting different coverage of NW and SE Black Sea regions with the Chernobyl fallout. The ¹³⁷Cs-derived dating showed that maximum deposition of particulate bound ¹³⁷Cs in sediments adjacent to the Coruh river mouth was delayed for 14 yr relative to date of Chernobyl accident, reflecting a buffer effect of the watershed soils. This transit time is 3 times longer than in the Danube catchment area, indicating a difference in retention processes in these mountainous (Coruh) and lowland (Danube) river basins. The ¹³⁷Cs profile in Coruh sediments showed penetration of ¹³⁷Cs to much greater depth than would be expected from ¹³⁷Cs fallout chronology, suggesting the sediment mixing rate of 1.3 cm² yr⁻¹. This value was used to evaluate deposition chronology of ¹³⁷Cs, applying the model developed for pulse fallout case. Comparing the measured and modelled data has allowed differentiation of the flood-induced discharge of the ¹³⁷Cs-containing suspended matter and the slower transit of eroded soil particles from the contaminated catchment areas. The obtained results may be used for the prediction of period when the pollutants, deposited over the river basins, can reach the Black Sea.     

Meiobenthos from an active methane seepage area in the NW Black Sea

Meiobenthos densities and higher taxon composition were studied in an active gas seepage area at depths from 182 to 252 m in the submarine Dnieper Canyon located in the northwestern part of the Black Sea. The meiobenthos was represented by Ciliata, Foraminifera, Nematoda, Polychaeta, Bivalvia, Gastropoda, Amphipoda, and Acarina. Also present in the sediment samples were juvenile stages of Copepoda and Cladocera which may be of planktonic origin. Nematoda and Foraminifera were the dominant groups. The abundance of the meiobenthos varied between 2397 and 52,593 ind.·m⁻². Maximum densities of Nematoda and Foraminifera were recorded in the upper sediment layer of a permanent H₂S zone at depths from 220 to 250 m. This dense concentration of meiobenthos was found in an area where intense methane seeps were covered by methane‐oxidizing microbial mats. Results suggest that methane and its microbial oxidation products are the factors responsible for the presence of a highly sulfidic and biologically productive zone characterized by specially adapted benthic groups. At the same time, an inverse correlation was found between meiofauna densities and methane concentrations in the uppermost sediment layers. The hypothesis is that the concentration of Nematoda and Foraminifera within the areas enriched with methane is an ecological compromise between the food requirements of these organisms and their adaptations to the toxic H₂S.     

Chemical speciation of copper and zinc in surface waters of the western Black Sea

The chemical speciation of Cu and Zn was investigated by voltammetric titration methods in the surface waters (10 m) of the western Black Sea during an Istanbul–Sevastopol cruise conducted in November 1998. Supporting parameters (temperature (T), salinity (S), pH, alkalinity (Alk), suspended particulate matter (SPM) and dissolved and particulate ²³⁴Th) were obtained in order to distinguish hydrographic features against involvement of the metals in biogeochemical processes. In the Turkish continental slope region, the cruise track intersected a narrow vein of colder water originating on the western shelf. The core of this cold water vein was characterised by a relatively low salinity, higher specific alkalinity and higher metal (especially Cu) and metal-binding ligand concentrations.A very large portion of Cu (93–99.8%) and Zn (82–97%) was organically complexed. The degree of complexation was highest in shelf waters and lowest in the central gyre. Titration data for Cu were modelled by two classes of organic binding ligands characterised by (C_L1=3–12 nM, log K₁′=13.1–13.9) and (C_L2=20–70 nM, log K₂′=9.4–11.2). These ligands occurred mainly in the ‘dissolved’ phase, as defined by 0.4-μm filtration. The stronger Cu-binding ligand seemed to be produced in situ in response to Cu concentration, whereas the weaker Cu-binding ligand appeared to be derived from terrestrial sources and/or reducing shelf sediments. Titration results for Zn were generally represented by one class of ligands (C_L1=8–23 nM, log K₁′=9.4–10.2), which were almost uniformly distributed between the ‘dissolved’ (78±8%) and the particulate phase (22±8%). The concentration of these strong Zn-binding ligands showed a very good correlation with SPM (r²=0.64), which improved when the dissolved ligands alone were considered (r²=0.78). It is hypothesised that these ligands were produced in situ by the bacterial breakdown of particulate organic matter.     

Long-Term Dynamics of the Concentrations of Organochlorine Compounds and Mercury in the Bottom Sediments of the Chernorechenskoe Reservoir

Water Resources - The accumulation of organochlorine compounds (OCs) and mercury in the bottom sediments of the Chernorechenskoe Reservoir since the mid-1960s to 2008 has been studied....