A. Yu. Lein

Microbiological Processes of the Carbon and Sulfur Cycles at Cold Methane Seeps of the North Atlantic

Functioning of microbial communities in surface sediments of the Haakon Mosby underwater mud volcano (lat. 72°N) and in gas seepage fields of the Vestnesa Ridge was investigated using Mir-1 and Mir-2 deep-sea submersibles during the 40th voyage of the research vessel Academician Mstislav Keldysh. Large areas of sedimentary deposits of the Haakon Mosby mud volcano (HMMV) and pockmarks of the Vestnesa Ridge (VR) are covered with bacterial mats 0.1 to 0.5 cm thick. The microbial community making up bacterial mats of the HMMV was dominated by large filamentous bacteria with filaments measuring up to 100 μm in length and 2 to 8 μm in width. The occurrence of rosettes allowed the observed filamentous bacteria to be referred to the morphologically similar genera Leucothrix or Thiothrix. Three morphological types of filamentous bacteria were identified in bacterial mats covering VR pockmarks. Filaments of type one are morphologically similar with representatives of the genera Thioploca or Desmanthos. Type two filaments had numerous inclusions of sulfur and resembled representatives of the genus Thiothrix. The third morphological type was constituted by single filaments made up of tightly connected disk-like cells and can be assigned to the genus Beggiatoa. The rates of methane oxidation (up to 1570 μl C/(dm3 day)) and sulfate reduction (up to 17 mg S/(dm3day)) measured in the surface sediments of HMMV and VR were close to the maximum rates of these processes observed in heavily polluted regions of the northwestern shelf of the Black Sea. High rates of microbiological processes correlated with the high number of bacteria. The rate of methane production in sediments studied was notably lower and ranged from 0.1 to 3.5 μ CH4/(dm3 day). Large areas of the HMMV caldera were populated by pogonophoras, represented by the two species Sclerolinum sp. and Oligobrachia sp. The mass development of Sclerolinum sp. in the HMMV caldera was by the activity of aerobic methane-oxidizing bacteria localized inside the cells of these animals. Bacterial cells were also found in the trophosome tissue of Oligobrachia sp., but in cells of these bacteria, we did not observe the membrane structures typical of methanotrophs. The localization pattern of pogonophoras on the surface of reduced sediments suggests that the predominant bacteria in Oligobrachia tissues are sulfur-oxidizing endosymbionts.

Geochemical peculiarities of the carbonate constructions formed during microbial oxidation of methane under anaerobic conditions

The aragonite constructions of the Black Sea are formed in a stable anaerobic zone and are a perfect object to study the natural mechanism of anaerobic methane oxidation. The most probable pathway of methane oxidation is its methanogen-mediated reaction with bicarbonates, dissolved in seawater, with the formation of water and acetate, which is then consumed by other components of the anaerobic community. Comparison of the δ13C values of carbonate minerals and organic matter once more demonstrated that the formation of the organic matter of biomass is accompanied by intense fractionation of carbon isotopes, as a result of which the total organic matter of biomass acquires an extremely light isotopic composition, characterized by δ13C values as low as –83.8‰.

Microbial Processes of the Carbon and Sulfur Cycles in Lake Mogil'noe

In the beginning of the summer of 1999, complex microbiological and biogeochemical investigations of meromictic Lake Mogilnoe (Kildin Island, Barents Sea) were carried out. The analysis of the results shows a clearly pronounced vertical zonality of the microbial processes occurring in the water column of the lake. To a depth of 8 m, the total number and activity of microorganisms was limited by the relatively low content of organic matter (OM). In the upper part of the hydrogen-sulfide zone of the lake (beginning at a depth of 8.25 m), the content of particulate OM and the microbial number sharply increased. In this zone, the daily production of OM during anaerobic photosynthesis at the expense of massive development of colored sulfur bacteria reached 620 mg C/m2, which was twofold greater than the daily production of phytoplankton photosynthesis and led to a considerable change in the isotopic composition (δ13C) of the particulate OM. In the same intermediate layer, the highest rates of sulfate reduction were recorded, and fractionation of stable sulfur isotopes occurred. Below 10 m was the third hydrochemical zone, characterized by maximum concentrations of H2S and CH4and by a relatively high rate of autotrophic methanogenesis. The comparison of the results obtained with the results of investigations of previous years, performed in the end of summer, shows a decrease in the intensity of all microbial processes inspected. An exception was anoxygenic photosynthesis, which can utilize not only the de novo formed H2S but also the H2S accumulated in the lake during the winter period.

Microbial processes at the aerobic-anaerobic interface in the deep-water zone of the black sea

Chemical and key microbiological processes (assimilation of carbon dioxide, oxidation and formation of methane, and sulfate reduction) occurring at the aerobic-anaerobic interface in the deep-water zone of the Black Sea were investigated. Measurements were taken at depths from 90 to 300 m at intervals of 5–10 m. The integral rate of the dark assimilation of carbon dioxide varied from 120 to 207 mg C/(m2 day) with a maximum at the boundary of cyclonic currents. The organic matter (OM) formed from methane comprised less than 5% of the OM formed from carbon dioxide. A comparison between the rates of methane oxidation and methane production suggests that methane that is oxidized at depths from 100 to 300 m was formed in deeper water horizons. The maximum rate of sulfate reduction (1230 mg S/(m2 day)) was observed in the western halistatic region, and the minimum rate (490 mg S/(m2 day)), in the eastern halistatic region. The average rate of hydrogen sulfide production measured at three deep-sea stations amounted to 755 mg S/(m2 day), or 276 g S/(m2 year).

The Biogeochemical Cycle of Methane in the Coastal Zone and Littoral of the Kandalaksha Bay of the White Sea

Microbiological and biogeochemical investigations of the processes of methane production (MP) and methane oxidation (MO) in the coastal waters and littoral of the Kandalaksha Bay of the White Sea were carried out. The studies were conducted in the coastal zones and in the water areas of the Kandalaksha Preserve, Moscow State University White Sea Biological Station, and the Zoological Institute (RAS) biological station in August 1999, 2000, and 2001 and in March 2001. The rate of CO2 assimilation in the shallow and littoral sediments was 35–27u2009800 μg C/(dm3 day) in summer and 32.8–88.9 μg C/(dm3 day) in winter. The maximal rates of MP were observed in the littoral sediments in the zone of macrophyte decomposition, in local depressions, and in the estuary of a freshwater creek (up to 113 μl/(dm3 day)). The maximal level of MO was observed in the shallow estuarine sediments (up to 2450 μl/(dm3 day)). During the winter season, at the temperature of –0.5 to 0.5°C, the MP rate in the littoral sediments was 0.02–0.3 μl/(dm3 day), while the MO rate was 0.06–0.7 μl/(dm3 day). The isotopic data obtained indicate that the Corg of the mats and of the upper sediment layers is enriched with the heavy 13C isotope by 1–4‰ as compared to the Corg of the suspension. A striking difference was found between the levels of methane emission by the typical littoral microlandscapes. In fine sediments, the average emission was 675 μl CH4/(m2 day); in stormy discharge stretch sediments, it was 1670 μl CH4/(m2 day); and under stones and in silted pits, 1370 μl CH4/(m2day). The calculation, performed with consideration of the microlandscape areas with a high production, allowed the CH4 production of 1 km2 of the littoral to be estimated as 192–300 l CH4/(km2 day).

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.

Methane Content in the Bottom Sediments and Water Column of the Black Sea

The methane content in the bottom sediments and water column of the Black Sea was determined using various methods of desorption and analysis of gases and various methods of calculating their concentrations. The head-space method with the use of salting out and calculation by an internal standard proved to be the most accurate procedure for the analysis of methane concentration in bottom sediments. The methane content in bottom sediments increased downward along the sediment thickness. In the upper 50–70 cm of shelf sediments, two minimums of methane concentration were revealed; in deep-sea sediments, only one minimum was recorded (in the 20–50 cm horizons). In the water column, methane concentrations slowly grew from the surface to a depth of 150–200 m and abruptly increased to a depth of 700–1200 m, remaining virtually constant in underlying layers. In certain deep-sea regions, peaks of methane content in the 1000–1200 m horizons of the water column were revealed, which were most probably due to local influx of abyssal waters enriched with this gas.

The effect of microorganisms and seasonal factors on the isotopic composition of particulate organic carbon from the black sea

The isotopic composition of particulate organic carbon (POC) from the Black Sea deep-water zone was studied during a Russian-Swiss expedition in May 1998. POC from the upper part of the hydrogen sulfide zone (the C-layer) was found to be considerably enriched with the12C isotope, as compared to the POC of the oxycline and anaerobic zone. In the C-layer waters, the concurrent presence of dissolved oxygen and hydrogen sulfide and an increased rate of dark CO2 fixation were recorded, suggesting that the change in the POC isotopic composition occurs at the expense of newly formed isotopically light organic matter of the biomass of autotrophic bacteria involved in the sulfur cycle. In the anaerobic waters below the C-layer, the organic matter of the biomass of autotrophs is consumed by the community of heterotrophic microorganisms; this results in weighting of the POC isotopic composition. Analysis of the data obtained and data available in the literature allows an inference to be made about the considerable seasonable variability of the POC δ13C value, which depends on the ratio of terrigenic and planktonogenic components in the particulate organic matter.

Rates of Microbial Production and Oxidation of Methane in the Bottom Sediments and Water Column of the Black Sea

Rates of biogeochemical (microbial) processes of methane production and methane oxidation were determined in the bottom sediments and water column of the Black Sea. Aerobic bacterial oxidation of methane was confined to the upper 20–30 cm of Holocene bottom sediments of the shelf (0.7–259 ng C/(dm3 day)) and to oxygenated waters (0.2–45 ng C/(dm3 day)). In reduced sediments of the deep-sea zone and in the hydrogen sulfide–containing water column, considerable rates of anaerobic methane oxidation were recorded, comparable to or exceeding the rates of methane oxidation in oxygenated layers. From one-fourth to one-half of the methane formed in bottom sediments was oxidized immediately therein. The major part of the remaining methane was oxidized in the water column, and a smaller portion arrived in the atmosphere.

The Process of Microbial Sulfate Reduction in Sediments of the Coastal Zone and Littoral of the Kandalaksha Bay of the White Sea

Microbiological and biogeochemical investigations of the coastal zone and the littoral of the Kandalaksha Bay of the White Sea were carried out. The material for investigations was obtained in the series of expeditions of the Institute of Microbiology, Russian Academy of Sciences, in August 1999, 2000, 2001, and in March 2003. The studies were conducted on the littoral and in the water area of the Kandalaksha Preserve, the Moscow University Belomorsk Biological Station, and the Zoological Institute Biological Station, Russian Academy of Sciences. Sediment sampling on the littoral was carried out in the typical microlandscapes differing in the sediment properties and macrobenthos distribution. The maximal sulfate reduction rate (SRR) was shown for the shallow part of the Chernorechenskaya Bay (up to 2550 μg S/(dm3 day)) and in the Babye More Bay (up to 3191 μg S/(dm3 day)). During the winter season, at a temperature of –0.5 × 0.5°C, the SRR in the sediments of the Kartesh Bay was 7.9 × 13 μg S/(dm3 day). In the widest limits, the SRR values varied in the sediment cores sampled on the littoral. The minimal values (11 μg S/(dm3 day)) were obtained in the core samples on the silt–sandy littoral. The littoral finely dispersed sediments rich in organic matter were characterized by high SRR values (524–1413 μg S/(dm3 day)). The maximal SRR values were shown for the sediments present within the stretch of decomposing macrophytes, in local pits at the lower littoral waterline, and in the mouth of a freshwater stream (51–159 mg S/(dm3 day)). A sharp difference in the level of H2S production in the type microlandscapes was shown. The average hydrogen sulfide production in finely dispersed sediments constituted 125 mg S/(m2 day); in stormy discharge deposits, 1950 mg S/(m2 day); in depressions under stones and in silted pits, 4300 mg S/(m2 day). A calculation made with regard to the area of microlandscapes with increased productivity shows that the daily H2S production per 1 km2 of the littoral (August) is 60.8 to 202 kg S/(km2 day), while the organic carbon consumption for sulfate reduction per 1 km2 of the littoral is 46 to 152 kg Corg/(km2 day).