Sources of fluids and gases expelled at cold seeps offshore Georgia, eastern Black Sea

Four seep sites located within an ∼20 km² area offshore Georgia (Batumi seep area, Pechori Mound, Iberia Mound, and Colkheti Seep) show characteristic differences with respect to element concentrations, and oxygen, hydrogen, strontium, and chlorine isotope signatures in pore waters, as well as impregnation of sediments with petroleum and hydrocarbon potential. All seep sites have active gas seepage, near surface authigenic carbonates and gas hydrates. Cokheti Seep, Iberia Mound, and Pechori Mound are characterized by oil-stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release. Pechori Mound is further characterized by deep fluid advection of lower salinity pore fluids. The Pechori Mound pore fluids are altered by mineral/water reactions at elevated temperatures (between 60 and 110 °C) indicated by heavier oxygen and lighter chlorine isotope values, distinct Li and B enrichment, and K depletion. Strontium isotope ratios indicate that fluids originate from late Oligocene strata. This finding is supported by the occurrence of hydrocarbon impregnations within the sediments. Furthermore, light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at Pechori Mound, Iberia Mound, and Colkheti Seep. C₁₅₊ hydrocarbons at the oil seeps are allochtonous, whereas those at the Batumi seep area are autochthonous. The presence of oleanane, an angiosperm biomarker, suggests that the hydrocarbon source rocks belong to the Maikopian Formation. In summary, all investigated seep sites show a high hydrocarbon potential and hydrocarbons of Iberia Mound, Colkheti Seep, and Pechori Mound are predominantly of thermogenic origin. However, only at the latter seep site advection of deep pore fluids is indicated.     

Vodyanitskii mud volcano,Sorokin trough,Black Sea: Geological characterization and quantification of gas bubble streams

Vodyanitskii mud volcano is located at a depth of about 2070 m in the Sorokin Trough, Black sea. It is a 500-m wide and 20-m high cone surrounded by a depression, which is typical of many mud volcanoes in the Black Sea. 75 kHz sidescan sonar show different generations of mud flows that include mud breccia, authigenic carbonates, and gas hydrates that were sampled by gravity coring. The fluids that flow through or erupt with the mud are enriched in chloride (up to ∼650 mmol L⁻¹ at ∼150-cm sediment depth) suggesting a deep source, which is similar to the fluids of the close-by Dvurechenskii mud volcano. Direct observation with the remotely operated vehicle Quest revealed gas bubbles emanating at two distinct sites at the crest of the mud volcano, which confirms earlier observations of bubble-induced hydroacoustic anomalies in echosounder records. The sediments at the main bubble emission site show a thermal anomaly with temperatures at ∼60 cm sediment depth that were 0.9 °C warmer than the bottom water. Chemical and isotopic analyses of the emanated gas revealed that it consisted primarily of methane (99.8%) and was of microbial origin (δD-CH₄ = −170.8‰ (SMOW), δ¹³C-CH₄ = −61.0‰ (V-PDB), δ¹³C-C₂H₆ = −44.0‰ (V-PDB)). The gas flux was estimated using the video observations of the ROV. Assuming that the flux is constant with time, about 0.9 ± 0.5 × 10⁶ mol of methane is released every year. This value is of the same order-of-magnitude as reported fluxes of dissolved methane released with pore water at other mud volcanoes. This suggests that bubble emanation is a significant pathway transporting methane from the sediments into the water column.     

Biogeography, Substrate Preference, and Feeding Types of North Adriatic Intertidal Collembola

Abstract. A survey of North Adriatic intertidal Collembola is given, including the first records of Friesea acuminata, Archisotoma interstitialis, Entomobrya dollfusi , and Pseudosinella hauseri. Granulometric and biococnological analyses of culittoral loose sediments allowed determination of the animals' substrate preference. The limitation to cuhaline habitats is tested by comparison with mixohaline shores nearby. Life-form typology is applied to elucidate the largely unknown relations of intertidal Collembola to the sediment surface or superficial strata. The different modes of nutrition are distinguished by mouthparts and by gut content analyses.     

Effects of ionizing radiation on the survival of bacterial spores in artificial martian regolith

Bacterial spores of Bacillus subtilis were used as a model system to study the effects of ionizing radiation on the survivability of spores uncovered and covered with artificial martian regolith. Spore survival after X-ray exposure was mainly depending on the role of non-homologous end-joining (NHEJ) as the major DNA double-strand break repair pathway during germination, the involvement of major small, acid-soluble spore proteins (SASP) as DNA radioprotectants and the coverage by martian regolith, whereas spores covered with martian regolith were significantly more sensitive to X-rays than uncovered spores, which is mainly due to the interaction of X-rays with artificial martian regolith resulting in the formation of secondary electrons and reactive oxygen species.     

Different Behavior of Iron(III) and Aluminum(III) Salts To Coagulate Silica Particle Suspension

The different coagulation‐flocculation behavior of iron(III) and aluminum(III) to coagulate silica particle suspension with four coagulants — FeCl₃, Fe₂(SO₄)₃, AlCl₃, and in our laboratory produced polyaluminum chloride PACl‐2.0 — was investigated through studying particle property changes and coagulation efficiency, for example, variations in zeta potential of particles, particle number, average particle diameter, particle size distribution, and residual turbidity of the supernatant water. Influences of flocculation intensity and pH value on the coagulation‐flocculation process were also studied. The results suggest that, under the test conditions, among these four coagulants FeCl₃ possesses an obviously stronger ability to form larger flocs and to remove turbidity, on the other hand, PACl‐2.0 obviously showed a better charge neutralization ability.     

Crust and upper mantle structure of the Bohemian Massif from the dispersion of seismic surface waves

Summary The phase velocity dispersion of Rayleigh waves for the Moxa-Vienna (MOX-VIE) and Moxa-Kaperské Hory (MOX-KHC) profiles, and of both Rayleigh and Love waves for the Kaperské Hory-Ksi (KHC-KSP) profile have been measured and inverted into models of shearwave velocity vs. depth. The three paths cross, respectively, the central part of the Bohemian Massif, its western margin, and the Bohemian Pluton and Cretaceous. For the MOX-VIE profile mean and lower crustal shear wave velocities of 3.7 and 3.9 km/s, respectively, a mean Moho depth of 34 km, and no existence of a low-velocity layer in the lower crust were found. The model obtained for the MOX-KHC profile is characterized by a slightly lower velocity in the lower crust (3.8 km/s), by a slightly lower Moho depth (32 km), and by the appearance of a weak low-velocity channel between 55 and 140 km. The crustal section of the final model for the KHC-KSP profile agrees well with the KHKS82 model derived by Novotný from results of DSS along international profile VII. Our final Rayleigh-wave model has significantly lower shear-wave velocities down to 215 km in the mantle. A systematic difference of 0.18 km/s between the average velocities of Rayleigh and Love waves has been revealed for the depth range from 30 to 215 km. Since almost no contamination of the fundamental Love mode with higher modes has been observed, and since the investigated structure hardly contains an unresolved system of thin, alternately low- and high-velocity layers, the cause of the difference is evidently polarization anisotropy of the upper mantle beneath the Bohemian Massif. It is recommended that the discussed investigations should be supplemented with data from the fan of KSP-GRF (Gräfenberg Array, Germany) paths and from the KHC-BRG (Berggiesshübel, Germany) profile.     

Editors' note

Pure and Applied Geophysics -