Seasonal Dynamics of Microbial Processes in Bottom Sediments of the Sevastopol Coastal Area

Oceanology - A seasonal study of microbial methane oxidation (MO) and sulfate reduction (SR) processes in bottom sediments was carried out at five stations in the estuarian Sevastopol coastal area,...     

Biogeochemical processes in the Chukchi Sea

Study of biogeochemical processes in water and sediments of the Chukchi Sea in August 2004 revealed atypical maximums of the concentration of biogenic elements (N, P, and Si) and the rate of microbial sulfate reduction in the surface layer (0–3 cm) of marine sediments. The C: N: P ratio in the organic matter (OM) of this layer does not fit the Redfield-Richards stoichiometric model. Specific features of biogeochemical processes in sea are likely related to the complex dynamics of water, high primary productivity (110–1400 mg C/(m² day)), low depth of basin (<50 m in 60% of the water area), reduced food chain due to low population of zooplankton, high density of zoobenthos (up to 4230 g m^?2), and high activity of microbial processes. Drastic decrease in the concentration of biogenic elements, iodine, total alkalinity (Alk), and population of microorganisms beneath the 0–3 cm layer testify to a large-scale OM decay at the water-seafloor barrier. Our original experimental data support the high annual rate of OM mineralization at the bottom of the Chukchi Sea.     

Microbial processes of carbon cycle as the base of food chain of Håkon Mosby Mud Volcano benthic community

Box and gravity cores recovered from the Håkon Mosby mud volcano (HMMV) during cruise 15 of the R/V Professor Logachev were analyzed for bacterial activity and benthic fauna distribution. The high bacterium number (up to 9.6×10⁹ cells cm^-3 of the sediment) and marked rates of sulfate reduction (up to 0.155?mg?S?dm^-3?day^-1) and methane oxidation (up to 9.9?μg?C?dm^-3?day^-1) were shown for the upper horizons of the sediments of the HMMV peripheral zone. The benthic community is characterized by the presence of two pogonophoran species, Oligobrachia sp. and Sclerolinum sp., harboring symbiotic methanotrophic bacteria.     

Methane fluxes in the southeastern Baltic Sea

New data from surveys of gas-bearing mud areas in the Gdansk Deep (southeastern Baltic Sea) were collected during four research cruises in 2009–2011. These revealed the presence of seven large pockmarks apart from the three already known, and enabled significant improvement of the existing digital map of gassy mud distribution. Based on geochemical sediment analyses, calculated diffusive methane fluxes from the upper (0–5?cm) seabed layer into near-bottom waters were highest—3.3?mmol/(m²?day)—in pockmark mud, contrasting strongly with the minimum value of 0.004?mmol/(m²?day) observed in typical, background mud. However, fluxes of less than 0.1?mmol/(m²?day) were observed in all sediment types, including pockmarks. In a newer attempt to roughly estimate budgets at a more regional scale, diffusive methane venting amounts to 280?×?10⁶?mmol/day for southeastern Baltic Sea muddy sediments. Elongated pockforms in the southern Gotland Deep, known since the end of the 1980s as pockmarks, had methane concentrations that were similar to those of gassy mud from the Gdansk Basin, and there was no geo-acoustic evidence of considerably increased gas levels.     

Authigenic carbonates in methane seeps from the Norwegian sea: Mineralogy, geochemistry, and genesis

Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active CH₄bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community consists of specific methane-producing bacteria, which act as methanetrophic ones in conditions of excess methane, and sulfate reducers developing on hydrogen, which is an intermediate product of microbial CH₄ oxidation. Isotopically light carbon (δ¹³C_av =−28.9%0) of carbon dioxide produced during CH₄ oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (δ¹⁸O_av = 5%0) in carbonates is inherited from seawater sulfate. A rapid sulfate reduction (up to 12 mg S dm⁻³ day⁻¹) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this, carbonates can only be formed in surface sediments near the water-bottom interface. Authigenic carbonates occurring within sediments occur do notin situ. Salinity, as well as CO ₃ ²⁻ /Ca and Mg/Ca ratios, correspond to the field of nonmagnesian calcium carbonate precipitation. Calcite is the dominant carbonate mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. The radiocarbon age of carbonates is about 10000 yr.     

Primary production and chlorophyll content in the Southeastern Baltic Sea in 2003–2007

The values and seasonal variations of the primary production and chlorophyll a content were investigated in the Russian sector of the Southeastern Baltic in 2003–2007. The annual average values of the primary production and chlorophyll content for this area were 231 gC m⁻² year⁻¹ and 2.9 mg/m³, respectively; i.e., they corresponded to the mesotrophic level according to the trophic classification. The spatial distribution of the primary production and the chlorophyll concentrations in the different seasons and the annual average increased values exhibited at the northern coast of the Sambian Peninsula and the Curonian Spit were determined. In these areas, the values of the primary production and the chlorophyll concentrations corresponded to the eutrophic level.     

Seasonal variations in methane concentrations and diffusive fluxes in the Curonian and Vistula lagoons,Baltic Sea

Expected seasonal variations in methane concentrations and diffusive fluxes from surficial sediments into near-bottom waters were investigated in autumn 2012 and winter 2013 in the Curonian and Vistula lagoons of the Baltic Sea, expanding on earlier findings for summer 2011. Methane concentrations in bottom sediments (upper ca. 2 cm) generally ranged from ca. 1 to 1,000 μmol/dm³, and in near-bottom waters from ca. 0 to 1 μmol/l. Highest concentrations were found in the Curonian Lagoon, plausibly explained by the influence of freshwater conditions and finer-grained, organic-rich sediments. Vistula Lagoon methane concentrations and fluxes are dampened by periodic saline water inflow from the open sea, intensifying sulphate reduction. Calculated diffusive methane fluxes from the upper sediment layer (usually 0–5 cm, i.e. excluding any fluffy layer) into near-bottom waters were highest—2.48 mmol/(m² day)—in clayey silts of the Curonian Lagoon in autumn (September) 2012, contrasting strongly with the minimum value of 0.002 mmol/(m² day) observed there in February 2013 under ice-covered conditions. Seasonal and even weekly variations in methane dynamics can be largely explained by two main drivers, i.e. wind and temperature, operating at various spatiotemporal scales via, for example, wind wave-induced resuspension of bottom sediments, and involving regional weather patterns including autumnal low-pressure zones over the Gulf of Gdansk.     

Paleomagnetic,petromagnetic, and terrigenous—Mineralogical studies of Upper Bathonian—Lower Callovian sediments in the Prosek section,Nizhni Novgorod region

The Bathonian—Callovian boundary section located near the Prosek Settlement (Nizhni Novgorod region) is described with the characteristic of its grain-size composition and terrigenous—mineralogical, petromagnetic, and paleomagnetic properties. Based on lithological—mineralogical and petromagnetic data, the section is subdivided into four members corresponding to the most significant sedimentation rhythms. No sharp changes in the composition of sediments are noted through the section, which indicates its relative continuity. Despite the significant re magnetization of these sediments during the Quaternary, the characteristic component (ChRM) is definable by the method of the intersection of large circles. The similarity between coordinates of the calculated virtual geomagnetic pole (VGMP) and the positions of standard virtual geomagnetic poles in the stable European continent during corresponding periods serves as an important argument in favor of the primary nature of the ChRM. The compiled magnetostratigraphic section is well consistent with the paleomagnetic zonation, established in the coeval sediments of “West Europe. As compared with the Bathonian—Callovian boundary section in the Albstadt—Pfeffingen of Germany, which claims to the GSSP role, the Prosek section represents a more favorable object for paleomagnetic studies. Combined with the lack of large-scale gaps in the sedimentary record and, with other conditions being equal, this makes this section a more preferable candidate for the Callovian GSSP standard.     

Structure and Production Potential of Summer Phytoplankton of Lake Baikal in the Present Period

Water Resources - A study of the structure and production parameters of phytoplankton (biomass, photosynthesis rate, chlorophyll a content, and assimilation numbers) in the coastal and pelagic...     

Microbially mediated methane and sulfur cycling in pockmark sediments of the Gdansk Basin, Baltic Sea

In the Russian sector of the Gdansk Basin (Baltic Sea), high organic matter influx fuels microbial processes resulting in the formation of reduced sediments with elevated methane concentrations. Investigated areas of geoacoustic anomalies (～245 km²) were found to contain three distinct geomorphologic structures (pockmarks), with a total area of ～1 km². Methane anomalies recorded in the water above one of these pockmarks were traced as high as 10 m above the bottom. In pockmark sediments, sulfate reduction and anaerobic oxidation of methane (AOM) occurred at high rates of 33 and 50 µmol dm^?3 day^?1, respectively. Integrated over 0–180 cm sediment depths, AOM exceeded methanogenesis almost tenfold. High AOM rates resulted from methane influx from deeper sediment layers. The δ¹³C signature of methane carbon (?78.1 to ?71.1‰) indicates the biogenic origin of pockmark methane. In pockmark sediments, up to 70% of reduced sulfur compounds was possibly produced via AOM.