Search

During TTR11 Cruise (2001), three areas of active fluid venting and mud volcanism were investigated in the Black Sea below the oxic zone at depths varying between 800 and 2200 m. Authigenic carbonates often associated with microbial mats were recovered from the sea floor and the shallow subsurface. Structural and petrographic observations allowed the distinction of five different types of authigenic carbonates; three of these consist of carbonate-cemented layered hemipelagic sedimentary units, while the other two consist of carbonate-cemented mud breccia sediment and authigenic micrite slabs. The carbonate cements consist predominantly of micritic Mg calcite. Their d 13 CCaCO3 varies between 8.5x and 46.9x at the different sampling locations,indicatingthatauthigenic carbonatesincorporate variableproportions ofcarbonderivedfromthe anaerobicoxidationof methane (AOM), the oxidation of organic matter and from sea water. Methane is the dominant component among other hydrocarbon gases in these sediments. Its relative amount varies from 99.9% to 95.1% of total hydrocarbon gases and its d 13 C values range fromi40xtoi74x. Methane in sediments associated with the carbonate crusts shows carbon isotopic values 25–30x lighter than the authigenic carbonates at all the studied sites, indicating that methane present in the seeping fluids confers a distinct isotopic signature to the carbonate deposits at each location. Models proposed for the formation of carbonate slabs in the subsurface imply methane seepage impeded by homogenous clayey laminae or by pre-existing slabs, coupled with microbial activity oxidising methane and organic matter present in the sediment. Mud breccia crust pavements on the sea floor form by carbonate cementation of methane-charged sediment. Gas saturation of the sediment is confirmed by the presence of gas hydrates, whose shape indicates an association with authigenic carbonates, supporting the idea that sedimentary structures can control gas distribution.

Distributions and carbon isotopic compositions of microbial lipid biomarkers were investigated in sediment cores from the G11 and G12 pockmarks in the Nyegga sector of the Storegga Slide on the mid-Norwegian margin to explore differences in depth zonation, type and carbon assimilation mode of anaerobic methane-oxidizing archaea (ANMEs) and associated sulphate-reducing bacteria responsible for anaerobic oxidation of methane (AOM) in these cold seep environments. While the G11 site is characterised by black reduced sediments colonized by gastropods and Siboglinidae tubeworms, the G12 site has black reduced sediments devoid of fauna but surrounded by a peripheral occurrence of gastropods and white filamentous microbial mats. At both sites, bulk sediments contained abundant archaeal and bacterial lipid biomarkers substantially depleted in C-13, consisting mainly of isoprenoidal hydrocarbons and dialkyl glycerol diethers, fatty acids and non-isoprenoidal monoalkylglycerol ethers. At the G11 site, down-core profiles revealed that lipid biomarkers were in maximum abundance from 10 cm depth to the core bottom at 16 cm depth, associated with delta C-13 values of -57 to -136aEuro degrees. At the G12 site, by contrast, lipid biomarkers were in high abundance in the upper 5 cm sediment layer, associated with delta C-13 values of -43 to -133aEuro degrees. This suggests that, as expected from the benthic fauna characteristics of the sites, AOM takes place mainly at depth in the G11 pockmark but just below the seafloor in the G12 pockmark. These patterns can be explained largely by variable fluid flow rates. Furthermore, at both sites, a dominance of ANME-2 archaea accompanied by their bacterial partners is inferred based on lipid biomarker distributions and carbon isotope signatures, which is in agreement with recently published DNA analyses for the G11 pockmark. However, the present data reveal high discrepancies in the contents and delta C-13 values for both archaeal and bacterial lipid profiles, implying the possible involvement of at least two distinct AOM-related microbial consortia at the inferred AOM depth zonation of G11 and G12 pockmark sediments. In both sediment cores, the delta C-13 profiles for most archaeal lipids suggest a direct assimilation of dissolved inorganic carbon (DIC) in addition to methane by ANMEs (chemoautotrophy); constant and highly depleted delta C-13 profiles for PMI:3, an archaeal lipid biomarker presumably related to ANME-2, suggest a direct assimilation of C-13-depleted methane-derived carbon via AOM (methanotrophy). Evidently, the common approach of investigating lipid biomarker contents and delta C-13 signatures in cold seep sediments does not suffice to precisely discriminate between the carbon assimilation mode for each ANME archaeal group and associated bacteria. Rather, this needs to be combined with further specific labelling studies including different carbon sources (methane carbon, methane-derived organic intermediates and DIC) in order to unravel the metabolic pathways of each microbial consortium involved in AOM (ANME-1 vs. ANME-2 vs. ANME-3 archaeal group and associated bacteria).

A Siberian peat contains a high abundance of three unknown isomers of hexamethylated branched (br) GDGTs, of which two are present as a second peak eluting shortly after the known hexamethyl br GDGT containing two 5,13,16-trimethyloctacosanyl moieties. Tandem high performance liquid chromatography–mass spectrometry (HPLC–MS2) did not reveal substantial differences in the MS2 spectrum of the two peaks. HPLC isolation of the two peaks of the hexamethylated br GDGT followed by ether cleavage and GC–MS characterization of the hydrocarbons formed, using supersonic molecular beam (SMB) ionization, revealed the second peak to be composed mainly of a novel hexamethyl br GDGT, possessing two 6,13,16-trimethyloctacosanyl moieties. In addition, both chromatographically separated hexamethylated br GDGTs contained a smaller quantity (20–33%) of a non-symmetrical isomer, with one 13,16-dimethyloctacosanyl and one tetramethyloctacosanyl (either 5,13,16,24- or 6,13,16,23-) moiety. Hexamethylated br GDGTs thus consist of four structural isomers. Furthermore, the pentamethylated br GDGT was also isolated and shown to contain both 5,13,16- and 6,13,16-trimethyloctacosanyl moieties, so is composed of two structural isomers. The assignments reveal why environmental distributions of br GDGTs are sometimes complex, which may have implications for the use of br GDGTs in palaeoclimate reconstruction.

A novel proxy for continental mean annual air temperature (MAAT) and soil pH, the MBT/CBT-paleothermometer, is based on the temperature (T) and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs) in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a high Alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the past 11 000 yr. The distribution of bacterial GDGTs in the catchment soils is very similar to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record seems undisturbed, probably without any significant alteration of their distribution through in situ production in the lake itself or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C). Moreover, downcore MBT/CBT-derived MAAT estimates match in timing and magnitude other proxy-based T reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century) and the Medieval Warm Period (MWP, ~9th to 14th century). Together, our observations indicate the quantitative applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. In addition to the MWP, our lacustrine paleo T record indicates Holocene warm phases at about 3, 5, 7 and 11 kyr before present, which agrees in timing with other records from both the Alps and the sub-polar North-East Atlantic Ocean. The good temporal match of the warm periods determined for the central Alpine region with north-west European winter precipitation strength implies a strong and far-reaching influence of the North Atlantic Oscillation on continental European T variations during the Holocene.

A novel proxy for continental mean annual air temperature (MAAT) and soil-pH, the MBT/CBT-paleothermometer, is based on the temperature (T) and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs) in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a small high-alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the entire Holocene. The composition of bacterial GDGTs in soils are almost identical to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record is undisturbed, apparently without any significant alteration of their distribution through in situ production or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT-estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C). Moreover, downcore MBT/CBT-derived MAAT-estimates match in timing and magnitude other proxy-based T-reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century) and the Medieval Warm Period (~10th to 14th century). Together, our observations confirm the applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. Consistent with other T-records from both the Alps and from the subpolar NE-Atlantic, our lacustrine paleotemperature record indicates Holocene MAAT-variations with an apparent cyclicity of ~2 kyr. The good temporal match of the warm periods determined for the S-Alpine region with NW-European winter precipitation strength implies a strong and far-reaching influence of the North Atlantic Oscillation on continental European Holocene T-variations.

Publisher Summary This chapter discusses the benthic deep-seaa carbonates with reference to reefs and seeps. Extensive accumulations of deep-water carbonates across the global seafloor are dependent on pelagic carbonate productivity in the surfacial ocean waters. When the organisms die, their tests sink down to the seafloor, where they accumulate as calcareous oozes. The main contributors to calcareous oozes include the planktonic foraminifers, coccolithophores, and pteropods. Despite the extensive formation of pelagic calcareous oozes and their undeniable dominance as the global deep-water carbonates, higher rates of deep-water carbonate accumulation exist in limited areas because of the processes controlling the formation of benthic reefs and of authigenic carbonate. Reef-forming organisms are sessile and generate microhabitats that attract other organisms. In deep water, two carbonate reef contexts are significant: (1) those offered by cold-water corals and (2) those offered by deep-sea oysters. Aphotic reef deposits are also valuable as archives of environmental and climate change. Recently the deep-sea pycnodontine oyster Neopycnodonte zibrowii forms discovered and locally significant accumulation centres for deep-sea carbonates. In addition to deep-sea carbonates formed from the remains of calcareous organisms, carbonates can also form as a result of chemical reactions in sediments.

Tubular carbonate concretions of up to 1 m in length and perpendicular to bedding, occur abundantly in the Upper Pliensbachian (upper Amaltheus margaritatus Zone, Gibbosus Subzone) in outcrops (Fontaneilles section) in the vicinity of Rivière-sûr-Tarn, southern France. Stable isotope analyses of these concretions show negative &delta13C values that decrease from the rim to the center from −18.8‰ to −25.7‰ (V-PDB), but normal marine δ18O values (−1.8‰). Carbon isotope analyses of Late Pliensbachian bulk carbonate (matrix) samples from the Fontaneilles section show clearly decreasing C-isotope values across the A. margaritatus Zone, from +1‰ to −3‰ (V-PDB). Isotope analyses of coeval belemnite rostra do not document such a negative C-isotope trend with values remaining stable around +2‰ (V-PDB). Computer tomographic (CT) scanning of the tubular concretions show multiple canals that are lined or filled entirely with pyrite. Previously, the formation of these concretions with one, two, or more central tubes, has been ascribed to the activity of an enigmatic organism, possibly with annelid or arthropod affinities, known as Tisoa siphonalis. Our results suggest tisoan structures are abiogenic. Based on our geochemical analyses and sedimentological observations we suggest that these concretions formed as a combination of the anaerobic oxidation of methane (AOM) and sulfate reduction within the sediment. Fluids rich in methane and/or hydrocarbons likely altered local bulk rock carbon isotope records, but did not affect the global carbon cycle. Interestingly, Tisoa siphonalis has been described from many locations in the Grands Causses Basin in southern France, and from northern France and Luxemburg, always occurring at the same stratigraphic level. Upper Pliensbachian authigenic carbonates thus possibly cover an area of many thousand square kilometers. Greatly reduced sedimentation rates are needed to explain the stabilization of the sulfate-methane transition zone in the sedimentary column in order for the tubular concretions to form. Late Pliensbachian cooling, reducing run-off, and/or the influx of colder water and more vigorous circulation could be responsible for a halt in sedimentation. At the same time (thermogenic) methane may have destabilized during a major phase of Late Pliensbachian sea level fall. As such Tisoa siphonalis is more than a geological curiosity, and its further study could prove pivotal in understanding Early Jurassic paleoenvironmental change.

We report on a multidisciplinary study of cold seeps explored in the Central Nile deep-sea fan of the Egyptian margin. Our approach combines in situ seafloor observation, geophysics, sedimentological data, measurement of bottom-water methane anomalies, pore-water and sediment geochemistry, and Th-230/U dating of authigenic carbonates. Two areas were investigated, which correspond to different sedimentary provinces. The lower slope, at similar to 2100 m water depth, indicates deformation of sediments by gravitational processes, exhibiting slope-parallel elongated ridges and seafloor depressions. In contrast, the middle slope, at similar to 1650 m water depth, exhibits a series of debris-flow deposits not remobilized by post-depositional gravity processes. Significant differences exist between fluid-escape structures from the two studied areas. At the lower slope, methane anomalies were detected in bottom-waters above the depressions, whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities. Carbonate U/Th age dates (similar to 8 kyr BP), pore-water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past. In contrast, large (similar to 1 km(2)) carbonate-paved areas were discovered in the middle slope, with U/Th isotope evidence for ongoing carbonate precipitation during the Late Holocene (since similar to 5 kyr BP at least). Our results suggest that fluid venting is closely related to sediment deformation in the Central Nile margin. It is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of 'fossil' carbonate ridges, whereas pervasive diffuse flow prevails at the unfailed middle slope.

Marine Geology, v. 261, n. 1-4, p. 138-152, 2009. http://dx.doi.org/10.1016/j.margeo.2009.02.005; International audience; This paper reports the first "in situ" seafloor observations of fluid escape structures in a fault-controlled caldera-type depression of about 8 km diameter, named the Menes caldera, in the Eastern Mediterranean sea off Egypt (western province of the Nile Deep Sea Fan). A detailed analysis of seven Nautile dives, performed during the Nautinil cruise in 2003, focused on determining the nature, origin, importance, mechanisms and environmental impacts of the fluid escape processes from the geological observations. Seafloor maps, constructed from direct visual observations and video records made from the submersible, and sampling results, for three mud volcanoes of the caldera, Cheops, Chephren and Mykerinos show differences in activity but many common characteristics. The three volcanoes show a crater-like depression. The study reveals a strong contrast between Mykerinos, where no seepage activity was found, and the craters of Cheops and Chephren, where an intense activity of brine seepage was discovered. On Cheops, a dome of dark grey mud raises slightly above the brine surface in the central part of the brine lake, and shows numerous circular vents of 1-2 m diameter that become gradually colonized by microbial mats. Chephren hosts a deep (> 200 m) and warm (45 °C) brine lake. Alternations of areas void of or covered with microbial mats at the surface of the Chephren brine lake indicate large surface disturbances that may result from the occurrence of several active vents at the bottom of the lake. A special feature at Chephren is a brine overflow at the western edge of the crater, also indicative of the very high activity of brine seepage. The Nautinil observations indicate that the Menes caldera in the Eastern Mediterranean is a highly active site of brine seepage. Growth faults rooted in pre-Messinian sediment layers provide pathways for warm fluids to escape pressurized source levels below the Messinian salt.

The Eastern Mediterranean hosts a variety of active cold seep systems, such as gas chimneys, mud volcanoes and pockmarks, in water depths of 500 to 3200 m. As part of the NAUTINIL expedition in 2003, the sediments of cold seeps on the Nile Deep Sea Fan (NDSF) were sampled for the first time for biogeochemical and microbiological analyses. Here we compare rates of the anaerobic oxidation of methane (AOM) and sulfate reduction (SR) as well as the microbial community structure of a variety of cold seep systems including mud volcanoes, pockmarks and brine seeps. Our results revealed strong differences in microbial activity among the different seep systems of the Eastern, Central and Western provinces of the NDSF, as well as the Olimpi field (Central Mediterranean Ridge). Integrated over a sediment depth of 10 cm below the seafloor, SR rates ranged from 0.1–66 mmol m− 2 d− 1 and AOM rates from 0.1–3.6 mmol m− 2 d− 1. SR was often considerably higher than methane oxidation, indicating that electron donors other than methane were utilized. In general, the lowest rates were associated with pockmarks and carbonate pavements, and highest rates with bacterial mats above the gassy sediments of mud volcano centers. 16S rRNA gene analysis and fluorescence in situ hybridization (FISH), revealed the presence of all known groups of marine methane oxidizing Archaea (i.e. ANME-1, -2, -3) and also of methane oxidizing Bacteria (i.e. Methylobacter sp. and relatives) in some seep sediments. Presumably syntrophic sulfate-reducing bacterial partners of ANMEs were also detected in association with the ANMEs. Several ANMEs formed consortia with unknown bacterial partners. The microbial community structure reflected the presence of typical seep microorganisms at all sites investigated, but differed to varying extents between the different types of seeps. Despite the high availability of methane and sulfate, methanotrophic microbial activity and biomass were lower at the seeps of the Eastern Mediterranean compared to those of other continental margins for unknown reasons.

We investigated lipid biomarkers in three depth-intervals of a methane-derived carbonate crust collected from a pockmark in the Nile Deep-Sea fan sampled during the Nautinil cruise of the R/V l'Atalante . A diverse set of 13 C-depleted archaeal and bacterial lipids were detected along this crust with δ 13 C values as low as − 118‰. This provides evidence that anaerobic oxidation of methane was the main process that induced the formation of this carbonate crust. Archaeal lipid biomarker distributions revealed the presence of archaea belonging both to the ANME-1 and ANME-2 phylogenetic clusters, with the former predominating. The distribution and compound specific δ 13 C values of AOM-derived lipid biomarkers showed no significant variations with depth. These results infer that the archaeal community structure and thus the local seepage environment remained relatively stable during the 5000 kyr period of the carbonate crust precipitation.

In this study we determined the composition and biogeochemistry of novel, brightly colored, white and orange microbial mats at the surface of a brine seep at the outer rim of the Chefren mud volcano. These mats were interspersed with one another, but their underlying sediment biogeochemistries differed considerably. Microscopy revealed that the white mats were granules composed of elemental S filaments, similar to those produced by the sulfide-oxidizing epsilonproteobacterium “ Candidatus Arcobacter sulfidicus.” Fluorescence in situ hybridization indicated that microorganisms targeted by a “ Ca . Arcobacter sulfidicus”-specific oligonucleotide probe constituted up to 24% of the total the cells within these mats. Several 16S rRNA gene sequences from organisms closely related to “ Ca . Arcobacter sulfidicus” were identified. In contrast, the orange mat consisted mostly of bright orange flakes composed of empty Fe(III) (hydr)oxide-coated microbial sheaths, similar to those produced by the neutrophilic Fe(II)-oxidizing betaproteobacterium Leptothrix ochracea . None of the 16S rRNA gene sequences obtained from these samples were closely related to sequences of known neutrophilic aerobic Fe(II)-oxidizing bacteria. The sediments below both types of mats showed relatively high sulfate reduction rates (300 nmol·cm −3 ·day −1 ) partially fueled by the anaerobic oxidation of methane (10 to 20 nmol·cm −3 ·day −1 ). Free sulfide produced below the white mat was depleted by sulfide oxidation within the mat itself. Below the orange mat free Fe(II) reached the surface layer and was depleted in part by microbial Fe(II) oxidation. Both mats and the sediments underneath them hosted very diverse microbial communities and contained mineral precipitates, most likely due to differences in fluid flow patterns.

Four mud volcanoes of several kilometres diameter named Amon, Osiris, Isis, and North Alex and located above gas chimneys on the Central Nile Deep Sea Fan, were investigated for the first time with the submersible Nautile. One of the objectives was to characterize the seafloor morphology and the seepage activity across the mud volcanoes. The seepage activity was dominated by emissions of methane and heavier hydrocarbons associated with a major thermal contribution. The most active parts of the mud volcanoes were highly gas-saturated (methane concentrations in the water and in the sediments, respectively, of several hundreds of nmol/L and several mmol/L of wet sediment) and associated with significantly high thermal gradients (at 10 m below the seafloor, the recorded temperatures reached more than 40 °C). Patches of highly reduced blackish sediments, mats of sulphide-oxidizing bacteria, and precipitates of authigenic carbonate were detected, indicative of anaerobic methane consumption. The chemosynthetic fauna was, however, not very abundant, inhibited most likely by the high and vigorous fluxes, and was associated mainly with carbonate-crust-covered seafloor encountered on the southwestern flank of Amon. Mud expulsions are not very common at present and were found limited to the most active emission centres of two mud volcanoes, where slow extrusion of mud occurs. Each of the mud volcanoes is fed principally by a main narrow channel located below the most elevated areas, most commonly in the centres of the structures. The distribution, shape, and seafloor morphology of the mud volcanoes and associated seeps over the Central Nile Deep Sea Fan are clearly tectonically controlled.

The Sorokin Trough (NE Black Sea) and the Gulf of Cadiz (NE Atlantic) are both mud volcano (MV) provinces characterized by the presence of gas hydrates, methane-related carbonates, and chemosynthetic biota but possess differences in geological history, tectonics, composition of sedimentary cover, and water column conditions. This thesis compares the geological and biogeochemical processes taking place within these MV provinces. It attempted to elucidate the deep-fluid dynamics in both areas, to identify possible sources for ascending hydrocarbon gases, and to assess the source-strata for the erupted sediments. The environmental impact of expelled methane-rich fluids on the development of microbial communities involved in the anaerobic oxidation of methane (AOM), a process inducing carbonate precipitation, was also investigated. A significant contribution of non-microbial, mature hydrocarbons in the migrated fluid was apparent from the composition and the stable carbon isotope signatures of the gases. Comparison of the hydrocarbon gas and biomarker data revealed that the formation of the MV fluid starts with the discharge of over-pressurized hydrocarbons and is followed by dynamic entrainment of the surround sediments on its way up. The biomarker composition of the mud breccia matrix in the Sorokin Trough indicated different depths of de-fluidization related to the position of fracture zones or diapiric folds in the subsurface. The biomarker composition of various MVs from the Gulf of Cadiz designated similar source strata for the erupted material. The study of living microbial mats and related carbonates from the Sorokin Trough and an ancient methane-related carbonate crust from the Gulf of Cadiz revealed a substantial contribution of microbes involved in AOM to the microbial community and the dominant role of AOM in processes of carbonate formation. The lipid biomarker and 16S rRNA gene sequence data showed that AOM signals appear to be strongest within carbonates and are considerably weaker in the surrounding sediments, indicating that local oversaturation of pore waters with bicarbonate, (formed by AOM) induced carbonate precipitation. The data also revealed changes in the archaeal community structure during carbonate crust formation in the Gulf of Cadiz, which are interpreted as resulting from changes in the conditions (e.g. methane flux) during the crusts' accretion. Despite the presence of an anoxic water column in the Sorokin Trough and oxygenated waters in the Gulf of Cadiz, the lipid biomarker and 16S rDNA sequence data demonstrated AOM to be the dominant biogeochemical process for methane oxidation in both areas. The distribution of anaerobic methanotrophs is directly linked to the intensity of methane flux and to fluid chemistry. However, in comparison with the Sorokin Trough, the AOM signal in the Gulf of Cadiz is muted. This probably indicates the absence of active fluid transport in the Gulf although the ubiquitous presence of outcropping methane-related carbonates signifies episodes of fluid discharge in the past. Reduced AOM in the Gulf of Cadiz is likely the result of “fluid-flux-starvation” environments established after a period of MV eruptions followed by a consumption of allochthonous methane and other organic and inorganic constituents. In contrast, fluid inflow in the Sorokin Trough is still going on, resulting in development of chemosynthetic microbial communities and in carbonate precipitation.

The paper presents a procedure for spiral computed tomography that may be used if there are some difficulties in the diagnosis of impaction of different teeth. Examples art used to show the capacities of specified diagnosis in solving the problems and difficulties in surgical or orthodontic treatment.

A methane-derived carbonate crust was collected from the recently discovered NIOZ mud volcano in the Sorokin Trough, NE Black Sea during the 11th Training-through-Research cruise of the R/V Professor Logachev. Among several specific bacterial and archaeal membrane lipids present in this crust, two novel macrocyclic diphytanyl glycerol diethers, containing one or two cyclopentane rings, were detected. Their structures were tentatively identified based on the interpretation of mass spectra, comparison with previously reported mass spectral data, and a hydrogenation experiment. This macrocyclic type of archaeal core membrane diether lipid has so far been identified only in the deep-sea hydrothermal vent methanogen Methanococcus jannaschii. Here, we provide the first evidence that these macrocyclic diethers can also contain internal cyclopentane rings. The molecular structure of the novel diethers resembles that of dibiphytanyl tetraethers in which biphytane chains, containing one and two pentacyclic rings, also occur. Such tetraethers were abundant in the crust. Compound-specific isotope measurements revealed ä13C values of –104 to –111‰ for these new archaeal lipids, indicating that they are derived from methanotrophic archaea acting within anaerobic methane-oxidizing consortia, which subsequently induce authigenic carbonate formation.

A methane-derived carbonate crust was collected from the recently discovered NIOZ mud volcano in the Sorokin Trough, NE Black Sea during the 11th Training-through-Research cruise of the R/V Professor Logachev. Among several specific bacterial and archaeal membrane lipids present in this crust, two novel macrocyclic diphytanyl glycerol diethers, containing one or two cyclopentane rings, were detected. Their structures were tentatively identified based on the interpretation of mass spectra, comparison with previously reported mass spectral data, and a hydrogenation experiment. This macrocyclic type of archaeal core membrane diether lipid has so far been identified only in the deep-sea hydrothermal vent methanogen Methanococcus jannaschii. Here, we provide the first evidence that these macrocyclic diethers can also contain internal cyclopentane rings. The molecular structure of the novel diethers resembles that of dibiphytanyl tetraethers in which biphytane chains, containing one and two pentacyclic rings, also occur. Such tetraethers were abundant in the crust. Compound-specific isotope measurements revealed δ13C values of –104 to –111‰ for these new archaeal lipids, indicating that they are derived from methanotrophic archaea acting within anaerobic methane-oxidizing consortia, which subsequently induce authigenic carbonate formation.