anaerobic oxidation of methane in hypersaline messinian environments revealed by 13c depleted molecular fossils abstract the messinian sequence of evaporitic deposits in italy includes authigenic carbonates that have been suggested to derive from the microbial degradation of organic compounds but the biogeochemical mechanisms that led to their formation remained unknown to unravel these mechanisms 13 c depleted carbonate rocks including native sulphur bearing limestone calcare solfifero from two locations in sicily and bedded limestone from the northern apennines have been studied their 13 c values as low as 49 reflect incorporation of carbon derived from the oxidation of methane which was previously suggested to have been linked to bacterial sulphate reduction molecular fossils extracted from the limestones reveal that methane was indeed oxidized in an anaerobic process by archaea and sulphate reducing bacteria the observed biomarker patterns resemble those of methane seep carbonates which form as a consequence of the anaerobic oxidation of methane aom aom specific 13 c depleted archaeal biomarkers such as pmi 13 c 101 to 75 as well as compounds derived from sulphate reducing bacteria iso and anteiso fatty acids 13 c as low as 85 were identified in the messinian carbonates although the biomarker results clearly point to aom the compound inventory also revealed distinct differences to patterns found at marine methane seeps for example sn 3 hydroxyarchaeol is in some samples the only hydroxyarchaeol present something usually not found at seeps archaeol is less depleted in 13 c than pmi at most sites 13 c 55 to 30 pointing to the co occurrence of methanogenic or halophilic archaea with archaea involved in aom 1 the presence of calcite pseudomorphs after lenticular gypsum 2 18 o enrichment in carbonates and 3 the biomarkers o phytanyl o sesterterpanyl glycerolether extended archaeol tetrahymanol and possibly phytanylglycerol monoethers as well as non isoprenoidal macrocyclic glycerol diethers confirm that carbonate formation took place under evaporitic conditions aom has previously been shown to be inhibited in some brine pools on the modern seafloor our observations however demonstrate that aom functions in hypersaline environments as well

archaeal lipid biomarkers and isotopic evidence of anaerobic methane oxidation associated with gas hydrates in the gulf of mexico abstract anaerobic oxidation of methane aom occurs in the gulf of mexico gas hydrate systems here we show lipid biomarker and isotopic evidence that archaea are involved in aom the estimated abundance of total archaeal lipids ranges from 44 8 to 60 4 g g dry sediment in hydrate bearing samples but is below detection limit in the hydrate free sample the 13c values of archaeal lipids range from 69 to 99 in hydrate bearing samples these results suggest that biomass of archaea is significantly enhanced through aom at the gas hydrate deposits these data also support a currently acknowledged mechanism of aom mediated by a consortium of sulfate reducing bacteria and archaea observed in a variety of methane rich marine settings anaerobic oxidation of oil hydrocarbons also occurs in the gulf of mexico gas hydrate systems as shown by degradation of n alkanes c15 in the anoxic sediments these processes convert hydrocarbons to carbon dioxide and increase pore water alkalinity which promote the precipitation of enormous volumes of authigenic carbonate rock depleted in 13c this long term geologic sequestration of carbon may affect models of global climate change

a molecular organic carbon isotope record of miocene climate changes the difference in carbon 13 13c contents of hopane and sterane biomarkers in the monterey formation naples beach california parallels the miocene inorganic record of the change in 18o 18o reflecting the miocene evolution from a well mixed to a highly stratified photic zone upper 100 meters in the pacific steranes 13c 25 4 0 7 per mil versus the pee dee belemnite standard from shallow photic zone organisms do not change isotopically throughout the miocene in contrast sulfur bound c35 hopanes likely derived from bacterial plankton living at the base of the photic zone have systematically decreasing 13c concentrations in middle and late miocene samples 13c 29 5 to 31 5 per mil consistent with the middle miocene formation of a carbon dioxide rich cold water mass at the base of the photic zone

classification of sea floor features associated with methane seeps along the gulf of cadiz continental margin abstract based on recently gathered swath bathymetry high to ultra high resolution seismic and underwater camera data along with dredging and coring samples this paper examines the relationship between sea floor features and the nature of hydrocarbon enriched fluid and gas leaks from degassing of deeply buried sediments along the continental margin of the gulf of cadiz eastern central atlantic a classification into three main groups is proposed on the basis of the morphology and nature of deposits 1 mud volcanoes 2 methane derived authigenic carbonates mdac mounds and 3 crater like pockmarks mud volcanoes are topographically cone shaped sea floor edifices built up from catastrophic mud and fluid degassing intercalated with periods of inactivity so far more than 25 mud volcanoes have been discovered in the gulf of cadiz named in memory of deceased colleagues e g ginsburg and baraza or researchers birth places e g faro cibeles almazan san petersburgh yuma rabat bonjardim coruna gades these structures range from 800 to 2500 m in diameter and tower 150 300 m above the seabed the volcanoes consistently feature a well defined outer ring or circular terrace and an inner dome all mud volcanoes are built up of episodes of mud breccia flows intercalated with deep current deposits with evident indications of gas saturation degassing structures a strong h2s smell and chemosynthetic fauna such as pogonophora sp tube worms and calyptogena sp commonly observed carbonate crusts and slabs overlying some mud volcanoes are thought to have been formed by slow diffuse venting during periods of inactivity or slower rates of fluid venting following the ejection of mud a fermentation process the result of microbial mediated oxidation of hydrocarbon enriched fluids seems to play an important role in the growth of large deep water carbonate mounds and chimneys during periods of low methane seep fluid pressure more than 400 crater like pockmarks a common sea floor feature in the tasyo field have been observed their seabed diameter ranges from 500 to 3000 m with steep slopes ranging from 12 to 35 according to their internal structure pockmarks can be grouped into 1 pockmarks with low central mounds and 2 crater like pockmarks apparently collapse structures lacking central mounds with a flat to slightly undulating sea bottom surrounded by steep slopes up to 25

ch 4 consuming microorganisms and the formation of carbonate crusts at cold seeps to understand the role played by microorganisms in the formation of cold seep carbonates we conducted an integrated microbial mineralogical and organic geochemical study of methane related authigenic carbonate crusts formed on eastern mediterranean mud volcanoes we show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane combined lipid biomarker analysis and 16s rrna gene surveys identified a highly diversified methane consuming archaeal community possibly comprising novel species implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation moreover pore water sulphate gradients produced by co occurring methane based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation we propose that this may be the dominant mode of carbonate crust formation at cold seeps world wide in agreement with aquatic chemistry predictions and explaining carbonate mineralogy

highly isotopically depleted isoprenoids molecular markers for ancient methane venting abstract we propose that organic compounds found in a miocene limestone from marmorito northern italy are source markers for organic matter present in ancient methane vent systems cold seeps the limestone contains high concentrations of the tail to tail linked acyclic c20 isoprenoid 2 6 11 15 tetramethylhexadecane crocetane a c25 homolog 2 6 10 15 19 pentamethylicosane pme and a distinctive glycerol ether lipid containing 3 7 11 15 tetramethylhexadecyl phytanyl moieties the chemical structures of these biomarkers indicate a common origin from archaea their extremely 13c depleted isotope compositions 13c 108 to 115 6 pdb suggest that the respective archaea have directly or indirectly introduced isotopically depleted methane derived carbon into their biomass we postulate that a second major cluster of biomarkers showing heavier isotope values 13c 88 is derived from sulfate reducing bacteria srb the observed biomarkers sustain the idea that methanogenic bacteria in a syntrophic community with srb are responsible for the anaerobic oxidation of methane in marine sediments marmorito may thus represent a conceivable ancient scenario for methane consumption performed by a defined two membered bacterial consortium 1 archaea that perform reversed methanogenesis by oxidizing methane and producing co2 and h2 and 2 srb that consume the resulting h2 furthermore the respective organic molecules are unlike other compounds tightly bound to the crystalline carbonate phase the marmorito carbonates can thus be regarded as cold seep microbialites rather than mere authigenic carbonates

archaea mediate anaerobic oxidation of methane in deep euxinic waters of the black sea we evaluate anaerobic oxidation of methane aom in the black sea water column by determining distributions of archaea specific glyceryl dialkyl glyceryl tetraethers gdgts and 13c isotopic compositions of their constituent biphytanes in suspended particulate matter spm sinking particulate matter collected in sediment traps and surface sediments we also determined isotopic compositions of fatty acids specific to sulfate reducing bacteria to test for biomarker and isotopic evidence of a syntrophic relationship between archaea and sulfate reducing bacteria in carrying out aom bicyclic and tricyclic gdgts and their constituent 13c depleted monocyclic and bicyclic biphytanes down to 67 indicative of archaea involved in aom were present in spm in the anoxic zone below 700 m depth in contrast gdgt 0 and crenarchaeol derived from planktonic crenarchaeota dominated the gdgt distributions in the oxic surface and shallow anoxic waters fatty acids indicative of sulfate reducing bacteria i e iso and anteiso c15 were not strongly isotopically depleted e g 32 to 25 although anteiso c15 was 5 more depleted in 13c than iso c15 our results suggest that either aom is carried out by archaea independent of sulfate reducing bacteria or those sulfate reducing bacteria involved in a syntrophy with methane oxidizing archaea constitute a small enough fraction of the total sulfate reducing bacterial community that an isotope depletion in their fatty acids is not readily detected sinking particulate material collected in sediment traps and the underlying sediments in the anoxic zone contained the biomarker and isotope signature of upper water column archaea aom specific gdgts and 13c depleted biphytanes characteristic of the spm in the deep anoxic zone are not incorporated into sinking particles and are not efficiently transported to the sediments this observation suggests that sediments may not always record aom in overlying euxinic water columns and helps explain the absence of aom derived biomarkers in sediments deposited during past periods of elevated levels of methane in the ocean

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

microbial methane turnover at mud volcanoes of the gulf of cadiz the gulf of cadiz is a tectonically active area of the european continental margin and characterised by a high abundance of mud volcanoes diapirs pockmarks and carbonate chimneys during the r v sonne expedition gap gibraltar arc processes so 175 in december 2003 several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes captain arutyunov bonjardim ginsburg gemini and a newly discovered mud volcano like structure called no name show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed the presence of a distinct sulphate methane transition zone smt overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor anaerobic oxidation of methane aom and sulphate reduction sr rates show maxima at the smt which was found between 20 and 200 cm below seafloor at the different mud volcanoes in comparison to other methane seeps aom activity 383 mmol m 2 year 1 and diffusive methane fluxes 321 mmol m 2 year 1 in mud volcano sediments of the gulf of cadiz are low to mid range corresponding lipid biomarker and 16s rdna clone library analysis give evidence that aom is mediated by a mixed community of anaerobic methanotrophic archaea and associated sulphate reducing bacteria srb in the studied mud volcanoes little is known about the variability of methane fluxes in this environment carbonate crusts littering the seafloor of mud volcanoes in the northern part of the gulf of cadiz had strongly 13c depleted lipid signatures indicative of higher seepage activities in the past however actual seafloor video observations showed only scarce traces of methane seepage and associated biological processes at the seafloor no active fluid or free gas escape to the hydrosphere was observed visually at any of the surveyed mud volcanoes and biogeochemical measurements indicate a complete methane consumption in the seafloor our observations suggest that the emission of methane to the hydrosphere from the mud volcano structures studied here may be insignificant at present

evolution of the methane cycle in ace lake antarctica during the holocene response of methanogens and methanotrophs to environmental change abstract post glacial ace lake vestfold hills antarctica which was initially a freshwater lake and then an open marine system is currently a meromictic basin with anoxic sulfidic and methane saturated bottom waters lipid and 16s ribosomal rna gene stratigraphy of up to 10 400 year old sediment core samples from the lake revealed that these environmentally induced chemical and physical changes caused clear shifts in the species composition of archaea and aerobic methanotrophic bacteria the combined presence of lipids specific for methanogenic archaea and molecular remains of aerobic methanotrophic bacteria 13c depleted 8 14 sterols and 16s rrna genes revealed that an active methane cycle occurred in ace lake during the last 3000 calendar years and that the extant methanotrophs were most likely introduced when it became a marine inlet 9400 y bp rdna sequences of known methanogens were only recovered from the oldest sediments deposited during the freshwater phase the latter sequences showed 100 sequence similarity with methanosarcinales species from freshwater environments and were the source of sn 2 and sn3 hydroxyarchaeols archaeal phylotypes related to uncultivated archaea associated with various marine environments were recovered from the present day anoxic water column and sediments deposited during the meromictic and marine period

methane related carbonate cements in pockmarks of the north sea abstract some pockmarks on the norwegian continental shelf contain patches of cemented sediment that can provide hardgrounds attractive to a variety of benthonic organisms detailed examination of a sandstone sample from a pockmark in norwegian block 25 7 in the north sea has revealed the presence of mg calcite and aragonite cements some of the latter forming botryoids all cement types are characterized by extremely light carbon isotopic compositions with a mean 13c value of 56 1 pdb which shows that the cements contain carbonate produced by oxidation of biogenic methane oxidation occurred in both the oxic and anoxic diagenetic zones trace amounts of interstitial methane mean 13c 40 8 and higher hydrocarbon gases up to c5 with a c1 cn ratio of 0 855 0 874 in the pockmark sediments indicate that some thermogenic methane may be mixed with the biogenic gas

fabric and formation of grapestone concretions within an unusual ancient methane seep system eocene bulgaria terra nova 23 56 61 2011 abstract authigenic carbonates at methane seeps provide valuable information on the evolution of seepage dynamics in this study we report on an unusual type of 13c depleted 13c 44 8 to 8 3 v pdb vienna peedee belemnite calcite cemented grapestone concretion composed of small spheroidal nodules 0 1 15 cm across associated with an ancient seep setting in eocene marine sediments pobiti kamani area ne bulgaria field observations suggest that the nodules started to grow close to the ancient sea floor and apparently were agitated by fluid flow promoting their spheroidal shape the precipitation of calcite between sand grains started at multiple closely spaced nucleation sites induced by locally elevated calcite supersaturation in response to anaerobic microbial consumption of ascending methane consecutive nodule growth continued deeper in the sediment with the formation of dark and light concentric bands surrounding one or more nodule cores the occurrence of similar grapestone concretions at seeps might indicate changing redox conditions at the seep site

scratching the surface estimating dimensions of large igneous provinces a study of five major basaltic provinces including oceanic plateaus volcanic passive margins and continental flood basalts shows that they are voluminous constructions of extrusive igneous rock underlain by intrusive rock crustal thickness ranges from 20 to 40 km and lower crust is characterized by high 7 0 7 6 km s seismic velocities volumes and emplacement rates derived for two oceanic plateaus the ontong java and kerguelen broken ridge reveal short lived pulses of increased global crustal production and suggest an origin involving the lower mantle the ontong java rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid ocean ridge system despite the importance off large igneous provinces in studies of mantle dynamics and the global environment scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features

time integrated variation of sources of fluids and seepage dynamics archived in authigenic carbonates from gulf of mexico gas hydrate seafloor observatory article i nfo authigenic carbonate rocks recovered from the gulf of mexico gas hydrate seafloor observatory in mississippi canyon block 118 mc118 at approximately 900 m water depth were studied using mineralogical bulk geochemical and lipid biomarker analyses carbonate rocks occurred as fractured blocks and nodular masses incorporated in carbonate breccias the carbonates were comprised mainly of high mg calcite and aragonite the stable carbon isotope composition

patterns of carbonate authigenesis at the kouilou pockmarks on the congo deep sea fan abstract different types of seep carbonates were recovered from the kouilou pockmarks on the congo deep sea fan in approximately 3100 m water depth the carbonate aggregates are represented by pyritiferous nodules crusts and slabs tubes and filled molds the latter are interpreted to represent casts of former burrows of bivalves and holothurians the nodules consisting of high mg calcite apparently formed deeper within the sediments than the predominantly aragonitic crusts and slabs nodule formation was caused by anaerobic oxidation of methane dominantly involving archaea of the phylogenetic anme 1 group whereas aragonitic crusts resulted from the activity of archaea of the anme 2 cluster evidence for this correlation is based on the distribution of specific biomarkers in the two types of carbonate aggregates showing higher hydroxyarchaeol to archaeol ratios in the crusts as opposed to nodules formation of crusts closer to the seafloor than nodules is indicated by higher carbonate contents of crusts probably reflecting higher porosities of the host sediment during carbonate formation this finding is supported by lower 18 o values of crusts agreeing with precipitation from pore waters similar in composition to seawater the aragonitic mineralogy of the crusts is also in accord with precipitation from sulfate rich pore waters similar to seawater moreover the interpretation regarding the relative depth of formation of crusts and nodules agrees with the commonly observed pattern that anme 1 archaea tend to occur deeper in the sediment than members of the anme 2 group methane represents the predominant carbon source of all carbonates 13 c values as low as 58 9 v pdb and the encrusted archaeal biomarkers 13 c values as low as 140 v pdb oxygen isotope values of some nodular carbonates ranging from 3 9 to 5 1 v pdb are too high for precipitation in equilibrium with seawater probably reflecting the destabilization of gas hydrates which are particularly abundant at the kouilou pockmarks

authigenic carbonates at cold seeps in the marmara sea turkey a lipid biomarker and stable carbon and oxygen isotope investigation abstract cold seeps along the north anatolian fault in the marmara sea turkey have been recently explored during international expeditions through submersible surveys seafloor mapping and extensive sampling of sediments biota carbonates and pore waters in this study we investigated the main mineralogy carbon and oxygen isotopic compositions and lipid biomarkers in authigenic carbonates retrieved from active seepage areas in the marmara sea abundant microbial lipid biomarkers with light 13 c values as low as 113 as well as light 13 c caco 3 values of bulk carbonate 34 to 21 provided evidence that anaerobic oxidation of methane aom mediated by methanotrophic archaea anme and their bacterial partners is the major process leading to sequestration of methane derived carbon diagnostic lipid distributions indicated that anme 2 archaea and associated sulphate reducing bacteria srb as the prevalent aom mediating microbes diverse non isoprenoid dialkyl glycerol ethers dages including tentatively identified novel compounds were identified with similar 13 c values as lipid biomarkers of srb 105 to 68 though dages are often assigned to srb other unknown bacteria closely involved in aom are likely as source organisms as well despite dominant aom related lipid biomarker patterns the stable carbon isotopic composition of bulk carbonates in two samples from south cinarcik basin and central high in combination with higher hydrocarbon signatures and environmental parameters suggested that oxidation of non methane hydrocarbons including oil may be a contributor to the dissolved inorganic carbon pool and may also be involved in carbonate authigenesis at hydrocarbon seepage settings as previously proposed in the gulf of mexico

algal and bacterial hydrocarbons in particulate matter and interfacial sediment of the cariaco trench particulate matter samples 53 m size fractions and sediment from the sediment water interface were collected in the cariaco trench an anoxic marine basin on the continental shelf of venezuela and analyzed for hydrocarbons concentrations of hydrocarbons were highest 10 20 ng 1 in oxic surface waters 0 150 m and at the top of the anoxic zone 350 600 m and were low 3 4 ng l in the low oxygen zone above the oxic anoxic interface 150 250 m and anoxic bottom waters 600 1150 m branched c25 trienes and tetraenes dominated the hydrocarbon distributions in 53 m particles particle size and depth distributions of the hydrocarbons demonstrate the importance of algal hydrocarbons in surface waters coupled with increased abundances of bacterial hydrocarbons especially in the 53 m particles in the anoxic zone these observations illustrate the importance of oxic anoxic interfaces even in the oceanic water column as zones of intense microbial alteration of organic matter and as sources of some of the organic compounds found in sediments

pseudofossils in relict methane seep carbonates resemble endemic microbial consortia pleistocene age methane seep carbonates from the eel river basin california contain aggregate like structures composed of tightly packed hollow spheres that morphologically resemble syntrophic archaeal bacterial consortia known to catalyze the anaerobic oxidation of methane aom tetragonal microstructures also present in the carbonates resemble seep endemic methanosarcinales cell clusters despite morphological similarities to the seep endemic microbes that likely mediated the authigenesis of eel river basin carbonates and sulfides detailed petrographic sem and magnetic microscopic imaging remanence rock magnetism laser raman and energy dispersive x ray spectroscopy suggest that these microstructures are not microfossils but rather mineral structures that result from the diagenetic alteration of euhedral fe sulfide framboids electron microscopy shows that during diagenesis reaction rims composed of fe oxide form around framboid microcrystalites subsequent dissolution of greigite or pyrite crystals leaves behind hollow cell like casings external molds a transformation that occurs on timescales of 100 kyr or less despite their superficial resemblance to morphologically distinctive extant microbes in local sediments the presence of acellular precursor grains as well as of partially altered transitional forms complicate the interpretation of these and other framboidal microstructures that have been reported from the rock record

1300 m high rising bubbles from mud volcanoes at 2080m in the black sea hydroacoustic characteristics and temporal variability a mud volcano area in the deep waters 2000 m of the black sea was studied by hydroacoustic measurements during several cruises between january 2002 and june 2004 gas bubbles in the water column give strong backscatter signals and thus can be detected even in great water depths by echosounders as the 38 khz ek500 scientific split beam system that was used during the surveys because of their shape in echograms and to differentiate against geochemical plumes and real upwelling bubble water plumes we call these hydroacoustic manifestations of bubbles in the water column flares digital recording and processing of the data allows a 3d visualization and data comparison over the entire observation period without artefacts caused by changing system settings during our surveys we discovered bubble release from three separate mud volcanoes dvurechenskiy dmv vodianitskiy vmv and the nameless seep site nss in about 2080 m water depth simultaneously bubble release was observed between 9 june 2003 and 5 june 2004 the most frequently surveyed dmv was found to be inactive during very intensive studies in january 2002 the first activity was observed on 27 june 2002 which finally ceased between 5 and 15 june 2004 after a period of continuously decreasing activity this observed 2 yr bubble release period at a mud volcano may give an indication for the duration of active periods the absence of short term variations within days or hours may indicate that the bubble release from the observed mud volcanoes does not undergo rapid changes the recorded echograms show that bubbles rise about 1300 m high through the water column to a final water depth of about 770 m which is 75 m below the phase boundary of pure methane hydrate in the black sea with a release depth from 2068 m and a detected rise height of 1300 m the flare at vmv is among the deepest and highest reported so far and gives evidence of highly extended bubble life times up to 108 min in deep marine environments to better understand how a methane bubble gas analyses of the pore water and gas hydrate gave 99 4 methane can rise so high without dissolving we applied a recently developed bubble dissolution model that takes into account a decreased mass transfer due to an immediately formed gas hydrate rim using the hydroacoustically determined bubble rising speeds 19 22 cm s at the bottom 12 14 cm s at the flare top and the relation between the rising speed of dirty gas hydrate rimmed bubbles and the bubble size we could validate that a gas hydrate rimmed bubble with a diameter of 9 mm could survive the 1300 m rise through the water column before it is finally dissolved a diameter of about 9 mm is reasonable for bubbles released at seep sites and the coincidence between the observed bubble rising speed and the model approach of a 9 mm bubble supports the assumption of gas hydrate rimmed bubbles

evidence for archaeal methanogenesis within veins at the onshore serpentinite hosted chimaera seeps turkey abstract serpentinite hosted ecosystems are potential sites where life may first have evolved on earth serpentinization reactions produce strongly reducing and highly alkaline fluids that are typified by high concentrations of molecular hydrogen h2 and methane ch4 which can be used as an energy source by chemosynthetic life low temperature serpentinization at slow spreading mid ocean ridges provides an ideal environment for rich microbial communities similar environments have also been discovered on land where present day low temperature serpentinization occurs during the circulation of groundwater through exposed ophiolites triggering the production of ch4 and h2 as well as the precipitation of secondary carbonate minerals the rock samples analyzed here are from the chimaera seeps in turkey representing serpentinized peridotites that are cross cut by veins composed of brucite and hydromagnesite hydromagnesite features a mean 13c value of 19 8 caused by kinetic isotope fractionation during air groundwater exchange of co2 followed by co2 hydroxylation to bicarbonate within the groundwater geochemical modeling revealed that mixing of mg and ca rich groundwaters is required for hydromagnesite formation at the expense of brucite within the carbonate hydroxide veins the lipid biomarkers pentamethylicosane pmi and squalane with 13c values of 10 and 14 respectively and unsaturated derivatives thereof were identified archaeol sn2 hydroxyarchaeol and sn3 hydroxyarchaeol are other prominent archaeal biomarkers in the veins also revealing high 13c values from 6 to 13 these isotope patterns combined with the absence of crocetane a biomarker for methanotrophic archaea reveal that the microbial communities of the chimaera seeps performed methanogenesis from a co2 limited pool rather than methanotrophy moreover bacterial dialkyl glycerol diethers dages with unusually high 13c values 9 to 2 and minor monoalkyl glycerol monoethers mages were identified suggesting that bacterial sulfate reduction is also active at the chimaera site this study reveals that archaeal methanogenesis and bacterial sulfate reduction may be prominent at onshore peridotite hosted sites and that biogenic ch4 may contribute to abiotic ch4 emissions from terrestrial seeps

a detailed study of the active crustal deformation in the aegean and surrounding area abstract a detailed study of the active crustal deformation in the aegean sea and surrounding area is presented the estimation of the deformation velocities is not performed in broad seismic zones but in seismogenic sources of limited spatial extent where the seismic energy is practically released in order to describe the spatial variations of the components of the strain rate tensor the deformation analysis is based on previous work where the seismicity and the available focal mechanisms are used separately for estimating the rate and shape of the deformation respectively the calculations were performed for 63 seismogenic sources identified in the aegean sea and surrounding area which belong to eight belts with an almost uniform orientation of the stress field along the coasts of albania and northwestern greece up to leukada island the collision of the adria plate with eurasia results in a compressional velocity of about 4 mm yr in a direction n49 e almost normal to the coast line the dextral movement with almost 3 cm yr along the cephalonia transform fault with strike n45 e is expressed as an almost equal extension and compression in n s and e w direction respectively along the convex outer part of the hellenic arc a crustal shortening of 1 3 cm yr is observed in a mean direction n34 e the direction of this shortening is almost constant from the southern ionian islands zakynthos up to rodos while the shortening rate does not significantly change from the outer sources to the inner ones the aegean sea and surrounding area is characterised by an extensional deformation the direction of the maximum extension in the northern part of this area shows an anticlockwise rotation from east to west thus this extension has a nne direction in northwestern turkey n11 e a nnw direction in central and northern greece as well as along the southern aegean volcanic arc and its extension to southwestern turkey n12 w and a wnw direction in the westernmost part of this extensional area n72 w the mean value of the extensional velocities in this area is 5 mm yr the northern part of asia minor and of the aegean sea is characterised by the dextral strike slip movement of about 2 cm yr of the north anatolian fault and its continuation in the northern aegean where this movement gradually decreases to about 6 mm yr the vertical crustal upper 10 km of the crust thickening is about 2 mm yr along the convex side of the hellenic arc and the vertical crustal thinning is about 1 mm yr in the aegean sea these values were obtained from the component u 33 of the velocity tensor

biogeochemical controls on glycerol dialkyl glycerol tetraether lipid distributions in sediments characterized by diffusive methane flux the tex86 tetraether index of tetraethers consisting of 86 carbon atoms is a proxy for sea surface temperature sst based on the distribution of isoprenoidal glycerol dialkyl glycerol tetraether gdgt membrane lipids synthesized by marine pelagic thaumarchaeota one of the caveats of this proxy is the production of additional gdgts by sedimentary euryarchaeota involved in anaerobic oxidation of methane aom that occurs at deep sea methane seeps but is also widespread in many continental shelf settings here gdgt distributions are investigated through the sulfate methane transition zone smtz in aarhus bay denmark to examine the extent the tex86 proxy is compromised in such a continental shelf setting where aom is characterized by a diffusive rather than rapid advective methane flux both free extractable and non extractable lipid fractions were analyzed as it was expected that pelagic derived and sediment derived gdgts could become incorporated into the molecular and sedimentary matrix to a different extent the results show a large change of tex86 values mainly due to the relative high amounts of gdgt 2 produced by aom related archaea both in the free and non extractable lipid fractions this additional gdgt input renders calculation of ssts based on tex86 inappropriate at the smtz the aom related gdgt signature however did not persist into deeper sediments perhaps reflecting rapid remineralization of the gdgts at the smtz although the process of aom at aarhus bay might not be representative for all continental margin settings it illustrates that aom in a variety of settings not just cold seeps can influence sedimentary gdgt distributions

cold seeps and authigenic carbonate formation in monterey bay california abstract authigenic carbonate associated with modern cold seep biological communities and their extinct analogues exhibit a broad range in stable isotope and mineral composition within the limited geographic area of monterey bay although such variations in ancient samples have been used to infer differing tectonic settings these carbonates all formed within a faulted continental margin environment and chemical variations reflect local differences in the sources and flux of carbon to sediment pore fluids the slow seepage of fluid and with it dissolved carbon along the transform faulted continental margin results in discrete areas of enhanced microbial sulfate reduction oxidation of methane from both biogenic and thermogenic origins as well as the active precipitation of both high mg calcite hmc and dolomite the authigenic carbonates include semicontinuous pavements of shallow cemented sediments surrounding benthic communities circular or pipe like chimneys interpreted as cemented conduits formed as a result of methane gas expulsion centimeter to meter scale rings doughnuts or slabs winnowed from variable depths within sediments and carbonate veins ankerite or calcite or cements in faulted basement rocks draped with bacterial mat abundant pyrite framboids preferentially filling the tests of the benthic foraminifer uvigerina peregrina and characteristic of the hmc bearing samples are products of a zone of shallow microbial sulfate reduction a process fundamental to the nourishment of the chemosynthetic cold seep communities sites on a sedimented ridge west of the san gregorio fault zone have carbon isotopic values between 35 and 56 that are strongly influenced by carbon derived from methane the higher values of 18 o more enriched in 18 o are found closer to the active fault zone carbonates from sites within the san gregorio fault zone or from monterey canyon floor exposures of miocene sediments have carbon isotope values between 7 and 26 that are mixtures of sedimentary organic carbon and microbially oxidized hydrocarbons from organic rich petroleum source rocks dolomite bearing samples are more enriched in both 18 o and 13 c bulk carbonate samples with heavier 18 o 18 o 3 5 result from the abundance of authigenic dolomite and low temperatures of formation local destabilization of clathrates might also create pore fluids that are more enriched in both 13 c and 18 o

the archaeal lipid composition of partially lithified cold seep mats the anaerobic oxidation of methane aom by converting methane to bicarbonate which is then precipitated as extensive carbonate crusts is an important methane sink in the earth s ocean systems here we employ a multidisciplinary approach to investigate the role of microorganisms in carbonate precipitation using biomarker analysis scanning electron microscopy sem and x ray diffraction we examined two microbial mats from the black sea and found that one comprised carbonate in both aragonite and mg calcite forms and most likely anme 1 archaea whereas the other contained only mg calcite and most likely anme 2 archaea we conclude as have others that the different microbial communities could impart different influences on carbonate mineralogy and morphology although further research is needed this is a contribution to our understanding of those relationships which could prove critical in the interpretation of ancient sedimentary deposits

comparative characteristics of the black sea and mediterranean ridge mud volcanoes morphological and structural characteristics of the black sea and mediterranean ridge mud volcanoes studied during several unesco esf cruises of the r v gelendzhik 1991 1994 are compared on the basis of single and multi channel seismic and sidescan sonar observations morphologically three types of mud volcanoes were distinguished in the black sea and six types in the mediterranean they differ in size shape and presence of the mud flows some types from both localities are very similar to each other but in any case their deep structure is very distinctive this difference in deep structure is explained by their development in different geological conditions under an extensional regime with high terrigenous input in the black sea and under strong lateral compression on the mediterranean ridge

differential aerobic and anaerobic oxidation of hydrocarbon gases discharged at mud volcanoes in the nile deep sea fan abstract the present study investigates hydrocarbon oxidation processes at isis and amon mud volcanoes mv s in the eastern nile deep sea fan in the water column molecular and carbon isotopic signatures of light hydrocarbons indicate that gases rapidly dissolve in seawater and are partially oxidized in the upper sediments anaerobic oxidation of the light hydrocarbons takes place as clearly shown by their molecular and isotopic composition these processes lead to the presence of a distinct sulfate hydrocarbon interface at 120 145 cm and 20 50 cm below the seafloor for isis and amon mv s respectively in contrast to processes occurring in the water column a clear preferential oxidation of methane propane and n butane over ethane and i butane is observed in the anoxic sediments furthermore for the first time fractionation factors have been determined for the anaerobic oxidation of propane and butane being respectively 4 80 and 0 7 for 13 c and 43 3 for 2 h of propane

mass spectra of sn 2 hydroxyarchaeol a polar lipid biomarker for anaerobic methanotrophy 1 extremely 13c depleted sn 2 hydroxyarchaeol is widely observed at marine methane seep sites it is the first biosynthetic product that provides information about a previously unknown microorganism involved in anaerobic methanotrophy a process that occurs widely in marine sediments the mono and di tms derivatives of this compound yield sharply differing and distinctive mass spectra depending on reaction conditions either of these products can be formed in the course of conventional analyses

biomarker indicators for anaerobic oxidizers of methane in brackish marine sediments with diffusive methane fluxes the anaerobic oxidation of methane aom is a major methane sink in marine sediments and plays a crucial role in mitigating methane fluxes to the overlying water column we investigated biomarker distributions and compound specific isotopic signatures in sediments from sites on the northern european continental margin that are characterized by a diffusive flux of methane at all sites the organic matter om is predominantly derived from terrestrial higher plants with subordinate abundances of algal biomarkers but biomarkers for archaea and bacteria are also present the co occurrence of the archaeal lipids archaeol sn 2 hydroxyarchaeol and 2 6 10 15 19 pentamethylicosane pmi with non isoprenoidal glycerol diethers inferred to derive from sulfate reducing bacteria srb is similar to microbial biomarker assemblages observed at cold seeps the archaeal and inferred srb biomarker concentrations typically reach maxima close to the sulfate methane transition zone smtz where archaeal biomarkers are depleted in 13c the 16s rrna gene sequences from the smtz of the aarhus bay sediment core indicate the occurrence of anme 1 archaea consistent with inferences derived from biomarker distributions the observations suggest that aom in these diffusive settings is mediated by consortia of archaea and bacteria similar to those found at many seep and methane hydrate sites around the world

sources of hydrocarbon gases in mud volcanoes from the sorokin trough ne black sea based on molecular and carbon isotopic compositions abstract molecular and stable carbon isotope properties of hydrocarbon gases methane through pentanes and sometimes hexanes from seven sediment cores collected from five mud volcanoes mvs in the sorokin trough ne black sea suggest that these gases are initially derived from the comparable hydrocarbon pools and are likely initial products of non microbial oil cracking processes our results state that dry characteristics of gas and 13 c depleted signatures of methane are result of a high admixture of secondary microbial gas formed due to subsequent microbial anaerobic degradation of redeposited hydrocarbons in the shallow reservoirs the wet gas components in all mvs and gas hydrates are related to each other the compositional variations in c 2 content appear to result from a complex of secondary processes such oil cracking in the deep subsurface migration and mixing of resulted gaseous and liquid hydrocarbons biodegradation of possibly redeposited hydrocarbons forming shallow reservoirs and additional alterations of hydrocarbon gases in the surface sediments due to currently active microbial processes such as aom c 2 consumption etc our data show that the most unaltered gas is in the mud breccia from the kazakov mv the gas mixture possibly represents the original properties of the hydrocarbons trapped in the deep subsurface of the sorokin trough analysis of the hydrocarbon gas data complemented with published maturity characteristics of organic matter from maycopian rock clasts and mud breccia matrix implies that the original source of gases is likely to be located below the maycopian shale formation

formation of tubular carbonate conduits at athina mud volcano eastern mediterranean sea abstract tubular carbonate conduits tcc represent the termination of fluid plumbing systems in environments of hydrocarbon seepage and play a relevant role in the discharge of methane from sub seafloor sediments to the water column however the biogeochemical reactions and biological activities involved in their formation are not fully understood to address this tcc samples were collected with a remotely operated vehicle from the seabed on the sw flank of the athina mud volcano in the eastern mediterranean sea petrographic mineralogical stable carbon and oxygen isotope and lipid biomarker analyses were performed to elucidate the formation processes of the tubular carbonates clotted and fibrous aragonite form the internal lining of the cavities while the outer portion of the tubes is formed by micritic mg calcite cementing hemipelagic sediment 13c depleted mg calcite and aragonite as low as 14 4 v pdb and lipid biomarkers archaeol 89 8 v pdb indicate that carbonate precipitation was influenced by sulfate dependent anaerobic oxidation of methane aom aom locally enhances aragonite precipitation thereby facilitating early lithification of the conduits within the mud volcano sediments the size and morphology of the tcc comparable with the buried portion of tubeworm colonies found in the proximity of the sampling site however our results suggest that tcc likely formed by the action of burrowing organism rather than being mineralizations of the tubeworm colonies this study provides new insights into the interpretation and understanding of tcc highlighting the role of macrofaunal activity in the formation of migration pathways for hydrocarbon rich fluids on the flank of a mud volcano

authigenic carbonate precipitates from the ne black sea a mineralogical geochemical and lipid biomarker study carbonate precipitates recovered from 2 000 m water depth at the dolgovskoy mound shatsky ridge north eastern black sea were studied using mineralogical geochemical and lipid biomarker analyses the carbonates differ in shape from simple pavements to cavernous structures with thick microbial mats attached to their lower side and within cavities low 13c values measured on carbonates 41 to 32 v pdb and extracted lipid biomarkers indicate that anaerobic oxidation of methane aom played a crucial role in precipitating these carbonates the internal structure of the carbonates is dominated by finely laminated coccolith ooze and homogeneous clay layers both cemented by micritic high magnesium calcite hmc and pure botryoidal yellowish low magnesium calcite lmc grown in direct contact to microbial mats 18o measurements suggest that the authigenic hmc precipitated in equilibrium with the black sea bottom water while the yellowish lmc rims have been growing in slightly 18o depleted interstitial water although precipitated under significantly different environmental conditions especially with respect to methane availability all analysed carbonate samples show lipid patterns that are typical for anme 1 dominated aom consortia in the case of the hmc samples with significant contributions of allochthonous components of marine and terrestrial origin reflecting the hemipelagic nature of the primary sediment

lipid and carbon isotopic evidence of methane oxidizing and sulfate reducing bacteria in association with gas hydrates from the gulf of mexico an integrated lipid biomarker carbon isotope approach reveals new insight to microbial methane oxidation in the gulf of mexico gas hydrate system hydrate bearing and hydrate free sediments were collected from the gulf of mexico slope using a research submersible phospholipid fatty acids consist mainly of c16 c18 compounds which are largely derived from bacteria the phospholipid fatty acids suggest that total biomass is enhanced 11 30 fold in gas hydrate bearing sediment compared to hydrate free sediment lipid biomarkers indicative of sulfate reducing bacteria are strongly depleted in 13c 13c 48 to 70 in the hydrate bearing samples suggesting that they are involved in the oxidation of methane 13c 47 for thermogenic methane and 70 for biogenic methane isotopic properties of other biomarkers suggest that sulfur oxidizing bacteria beggiatoa may also contribute to the lipid pool in hydrate bearing samples which are characterized by less negative 13c values to 11 2 in the hydrate free sample fatty acid biomarkers have 13c values of 27 6 to 39 6 indicating that crude oil average 27 or terrestrial organic carbon average 20 are the likely carbon sources our results provide the first lipid biomarker stable isotope evidence that sulfate reducing bacteria play an important role in anaerobic methane oxidation in the gulf of mexico gas hydrates the coupled activities of methane oxidizing and sulfate reducing organisms contribute to the development of ecosystems in deep sea environments and result in sequestration of carbon as buried organic carbon and authigenic carbonates these have implications for studying climate change based on carbon budgets

lipid biomarker patterns reflect different formation environments of mussel and tubeworm dominated seep carbonates from the gulf of mexico atwater valley and green canyon abstract mussels and tubeworms thriving at many methane seeps typically live in symbiosis with chemosynthetic chiefly methanotrophic or thiotrophic bacteria it has been shown that the activities of chemosymbiotic animals can result in large differences in the sedimentary environments of their habitats here we put forward the concept that such environmental variability can be archived in the lipid biomarker inventories of authigenic carbonates forming in different locally confined environments at seeps mussel beds and tubeworm bushes in this case to test this hypothesis lipid biomarker patterns of carbonates from mussel and tubeworm environments from two seep sites atwater valley 340 and green canyon 852 of the gulf of mexico were analyzed previous work revealed stronger carbon isotope fractionation between the methane source and biomarkers of anaerobic methane oxidizing archaea 2 anme 2 sulfate reducing desulfosarcina desulfococcus dss consortia than for anme 1 dss consortia both performing anaerobic oxidation of methane aom similar 13cmethane values were found at the mussel and tubeworm sites from the same seeps and the local microbial consortia also appear to be largely similar based on the observed aom biomarker inventories yet a large average offset of 32 between the 13c values of molecular fossils of sulfate reducing bacteria srb involved in aom was observed with lower values typifying tubeworm carbonates than mussel carbonates this pattern is interpreted to reflect local effects on isotope fractionation caused by the chemosymbiotic metazoans at mussel and tubeworm dominated sites at tubeworm dominated sites the excess sulfate produced by thiotrophic symbionts of tubeworms and pumped down into the sediment results in persistent production of aom derived bicarbonate and the enrichment of 12c in sub surface sediments interestingly tubeworm carbonates also contain high amounts of non isoprenoidal dialkyl glycerol diethers dages with extreme 13c depletions representing compounds that derived from non dss cluster srb most likely 13c depleted aom derived organic intermediates were used as carbon sources by the dage producing non dss cluster srb possibly performing organoclastic sulfate reduction our study identifies significant variation in biomarker patterns between mussel and tubeworm carbonates at two seep sites in the gulf of mexico such variation allows to characterize different habitats at seeps which are shaped by the interaction of chemosymbiotic seep metazoans and their symbionts with the local environment metazoan community composition apparently controls geobiological interaction in seep ecosystems to a large degree which may allow tracing of the effects of chemosymbiosis into the rock record

continental margin brine seeps their geological consequences local dissolution observed at the base of the florida escarpment appears to result from acid generated by sea floor oxidation of dissolved sulfide species carried in brines that seep from the base of the escarpment the extent of seep corrosion depends upon the amount of sulfide that has exited the platform and the efficiency with which the acid attacks the limestones of the escarpment calculations suggest that brine seepage influences the shape of these escarpments by undercutting and steepening the carbonate continental margin edges other processes competing for the dissolved sulfides are bacterial chemosynthesis and sulfide mineralization which produces organic carbon and sulfide mineral rich deposits along the unconformity that separates the buried escarpment from onlapping abyssal sediments

recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach study of organic matter in immature sediments from a messinian evaporitic basin shows that consideration of structures modes of occurrence and carbon isotopic compositions of free and sulfur bound carbon skeletons allow identification of biochemical precursors detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way moreover unprecedented biochemicals were recognized these extend the horizon of biomarker geochemistry

archaeal lipid biomarker as a tool to constrain the origin of methane at ancient methane seeps insight into subsurface fluid flow in the geological past abstract the origin of methane discharged at ancient methane seeps is a key to understand subsurface fluid flow processes in sedimentary basins the carbon isotopic composition of methane seep carbonates can be used to estimate the origin of methane but mixing of multiple carbon sources results in ambiguous interpretation we here constrained the origin of methane at ancient seeps by using the carbon isotopic composition and the isotope fractionation of lipid biomarkers of anaerobic methane oxidizing archaea we estimated the carbon isotope fractionation between methane and biomarkers as the offset between their 13c values at modern seep sites in the japan sea and other regions of the world the biomarker pentamethylicosane pmi extracted from a modern seep carbonate of the japan sea shows a 44 offset from the seep methane on the basis of literature data we calculated the carbon isotope offset as mostly 20 60 for pmi at modern seeps across the world we also assessed the relationship of the 13c values between methane and biomarkers by regression analysis on the data taken at the modern seeps obtaining regression formulas to estimate the 13c values of methane from those of biomarkers for ancient seeps we examined miocene to pleistocene methane seep carbonate rocks collected from japan sea sediments pmi extracted from these ancient carbonates have 13c values ranging from 137 to 93 using the 13c values of pmi and the carbon isotope offset and regression formulas we estimated that the methane at the ancient seeps was mainly of biogenic origin and migrated from the shallow subsurface

a comprehensive approach to the study of methane seep deposits from the lincoln creek formation western washington state usa a comprehensive approach using palaeontology petrography stable isotope geochemistry and biomarker analyses was applied to the study of seven small methane seep carbonate deposits these deposits are in the oligocene part of the lincoln creek formation exposed along the canyon and satsop rivers in western washington each deposit preserves invertebrate fossils many representing typical seep biota authigenic carbonates with 1 3 c values as low as 51 pdb reveal that the carbon is predominately methane derived carbonates contain the irregular isoprenoid hydrocarbons 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi lipid biomarkers diagnostic for archaea these lipids are strongly depleted in 1 3 c 1 3 c values as low as 120 pdb indicating that archaea were involved in the anaerobic oxidation of methane small filaments preserved in the carbonate may represent methanotrophic archaea archaeal methanogenesis induced the formation of a late diagenetic phase brownish calcite consisting of dumbbell shaped crystal aggregates that exhibit 1 3 c values as high as 7 pdb clotted microfabrics of primary origin point to microbial mediation of carbonate precipitation downward directed carbonate aggregation in the seeps produced inverted stromatactoid cavities large filaments interpreted as green algae based on their size shape arrangement and biomarkers imply that deposition occurred in places in water no deeper than 210 m

lipid biomarker patterns of authigenic carbonates reveal fluid composition and seepage intensity at haima cold seeps south china sea abstract authigenic carbonates retrieved from sites rov1 and rov2 of the haima hydrocarbon seeps of the south china sea at approximately 1390 m water depth were studied using lipid biomarker analyses abundant molecular fossils of anaerobic methane oxidizing archaea anme and sulfate reducing bacteria srb with strong 13c depletions 13c values as low as 126 in combination with low 13ccarbonate values 42 7 to 36 8 provide evidence that anaerobic oxidation of methane aom was the major process driving the precipitation of the studied seep carbonates the extremely low 13c values of archaeal biomarkers confirm that biogenic methane was the main carbon source but the seepage of accessory crude oil is also suggested by the presence of unresolved complex mixtures in the hydrocarbon fractions a suite of 13c depleted biomarkers indicate the predominance of anme 1 dss consortia at both sites which indicates that the studied carbonates formed during low to medium methane flux somewhat higher contents of archaeal biomarkers and their stronger 13c depletion at site rov2 probably reflect at least temporarily higher seepage intensities than at site rov1 abundant bacterial dialkyl glycerol diethers dages revealing a large offset of their 13c values compared to srb derived terminally branched fatty acids were possibly produced by distinct srb species other than members of the dss cluster the encountered hopanoids are attributed to aerobic methanotrophic bacteria based on their moderate 13c depletion the application of molecular fossils in combination with their compound specific isotope signatures is an efficient tool to reconstruct the composition of seepage fluids and seepage intensities

archaeal and bacterial lipids in authigenic carbonate crusts from eastern mediterranean mud volcanoes abstract we investigated the distributions and 13 c values of lipid biomarkers in authigenic methane related carbonate crusts formed on eastern mediterranean mud volcanoes a highly diverse suite of microbial membrane lipids was detected strongly 13 c depleted lipids diagnostic for archaea include isoprenoid glycerol diethers isoprenoid glycerol dialkyl glycerol tetraethers and several c 20 c 35 isoprenoid hydrocarbons bacterial lipids mainly consist of dialkyl glycerol diethers branched fatty acids and hopanoids showing important 13 c depletions albeit less than archaeal lipids the data provide further evidence for the involvement of archaea and bacteria in the anaerobic oxidation of methane aom and in the sequestration of methane derived carbon in authigenic carbonate crusts varying distributions and isotopic compositions of 13 c depleted lipids argue for heterogeneous aom related microbial consortia expanding on existing work at cold seeps distinctive biomarker features and inferred microbial assemblages are observed in these crusts in agreement with available phylogenetic data for the samples our results support the potential of lipids for distinguishing methanotrophic communities despite the observed variances conservative features in the abundances and isotopic offsets of microbial biomarkers occur likely reflecting the overall relationships between archaea and bacteria and the nature of carbon flow between them

carbonate formation by anaerobic oxidation of methane evidence from lipid biomarker and fossil 16s rdna carbonate chimneys and other carbonate structures occur widespread in the gulf of cadiz and probably reflect the presence of cold seeps and associated release of methane in the geological past possibly in the early pleistocene but it is unclear under what conditions and by which processes these carbonates were formed we studied a fossil methane related carbonate crust collected from the kidd mud volcano in the gulf concentrations of microbial lipids their stable carbon isotope composition sequences of fossil 16s rrna genes of anaerobic methanotrophic archaea in combination with mineralogical and carbon and oxygen isotopic composition of carbonate were obtained for seven different horizons of the crust this combination of organic and inorganic geochemical techniques with molecular ecological methods gave a consistent view on processes resulting in the formation of the crust and indicated that it took place in two phases and in a downward direction archaeal lipid biomarkers and fossil 16s rrna gene sequence data revealed the dominance of archaeal anme 2 group and elevated methane partial pressures during the formation of the top part of the crust the lower part of the carbonate was likely formed in an environment with reduced methane fluxes as revealed by the dominance of fossil remains of anme 1 archaea the combination of these methods can be used as an effective tool to reconstruct in unprecedented detail the palaeo biogeochemical processes resulting in the formation of carbonate fabrics this interdisciplinary strategy may also be applied for other fossil methane derived carbonates generating new concepts and knowledge about past methane related carbonate systems

palaeo methane seepage history traced by biomarker patterns in a carbonate crust nile deep sea fan eastern mediterranean sea abstract 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 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 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

biogenic fabrics in seep carbonates from an active gas vent site in green canyon block 238 gulf of mexico abstract carbonate crusts collected from an active methane seep site in the offshore louisiana of gulf of mexico have c pdb 13 49 16 to 52 29 and a group of unsaturated 2 6 10 15 19 pentamethylicosane pmi compounds produced by methane oxidizing archaea moa with c pdb 13 of pmi compounds from 107 2 to 115 5 indicating that the crusts formed as the result of bacterially catalyzed methane oxidation and sulfate reduction the fabric of the two flat sides of the crust is distinctly different the top side is composed entirely of microcrystalline calcite while the bottom is composed entirely of wormy carbonate cement that could be a random low fidelity replacement of bacteria in the interior of the 1 cm thick crust microcrystalline calcite is coated by wormy carbonate cement and dispersed pyrite framboids appear to be collaborating colonies of moa and sulfate reducing bacteria srb we propose that the wormy carbonate texture particularly with microcrystalline calcite and pyrite framboids present may be a useful indicator of biologically controlled fabrics produced during methane oxidation and sulfate reduction by moa and srb

cold seep deposits of beauvoisin oxfordian southeastern france and marmorito miocene northern italy microbially induced authigenic carbonates the relation of two well known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study archaea are found to be associated with the formation of oxfordian seep carbonates from beauvoisin and with a miocene limestone from marmorito tube worm limestone carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative 13ccarbonate values respectively highly positive values 15 reflect the use of 13c enriched co2 produced by methanogenesis low 13c values of the marmorito carbonates 30 indicate the oxidation of seepage derived hydrocarbons likewise the 13c content of specific tail to tail linked isoprenoids biomarkers for archaea was found to be strikingly depleted in these samples as low as 115 the isotopic signatures corroborate that archaea were involved in the cycling of seepage derived organic carbon at the ancient localities another miocene limestone marmorito limestone shows a strong imprint of methanotrophic bacteria as indicated by 13c values of carbonate as low as 40 and biomarker evidence epifluorescence microscopy and field emission scanning electron microscopy revealed that bacterial biofilms were involved in carbonate aggregation in addition to lucinid bivalves previously reported from both localities we infer that sponges from beauvoisin and tube worms from marmorito depended on chemosynthesis as well low 13c values of nodules related to sponge taphonomy 27 indicate that sponges might have been linked to an enhanced hydrocarbon oxidation tube worm fossils from marmorito closely resemble chemosynthetic pogonophoran tube worms from recent cold seeps and are embedded in isotopically light carbonate 13c 30

archaea mediating anaerobic methane oxidation in deep sea sediments at cold seeps of the eastern aleutian subduction zone cold seeps in the aleutian deep sea trench support prolific benthic communities and generate carbonate precipitates which are dependent on carbon dioxide delivered from anaerobic methane oxidation this process is active in the anaerobic sediments at the sulfate reduction methane production boundary and is probably performed by archaea working in syntrophic co operation with sulfate reducing bacteria diagnostic lipid biomarkers of archaeal origin include irregular isoprenoids such as 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi as well as the glycerol ether lipid archaeol 2 3 di o phytanyl sn glycerol these biomarkers are prominent lipid constituents in the anaerobic sediments as well as in the carbonate precipitates carbon isotopic compositions of the biomarkers are strongly depleted in 13c with values of 13c as low as 130 3 pdb the process of anaerobic methane oxidation is also reflected in the carbon isotope composition of organic matter with 13c values of 39 2 and 41 8 and of the carbonate precipitates with values of 45 4 and 48 7 this suggests that methane oxidizing archaea have accumulated within the microbial community which is active at the cold seep sites the dominance of crocetane in sediments at one station indicates that probably due to decreased methane venting archaea might no longer be growing whereas high amounts of crocetenes found at other more active stations may indicate recent fluid venting and active archaea comparison with other biomarker studies suggests that various archaeal assemblages might be involved in the anaerobic consumption of methane the assemblages are apparently dependent on specific conditions found at each cold seep environment selective conditions probably include water depth temperature degree of anoxia and supply of free methane

authigenic carbonates derived from oxidized methane vented from the makran accretionary prism off pakistan we report the first discovery and sampling of a methane hydrogen sulfide rich cold seep from the makran accretionary prism off pakistan arabian sea a variety of cm to m scale pockmarks and gas seepage structures were identified from underwater tv photo sled profiles crossing the oxygen minimum zone omz related to highresolution seismic parasound records from the seeps isotopically light bacterially formed methane is emanating that is partly oxidized to hco3 in the bacterial sulfate reduction zone this results in the precipitation of irregular dark gray to black crusts of indurated authigenic carbonates mainly cryptocrystalline magnesian calcite and ca rich dolomite near the sediment seawater interface within the omz downcore the crusts grade into hemipelagic carbonate poor silty clays with transitional lithologies in between similar to the pockmark carbonates from the oregon margin and in the north sea the authigenic carbonates are extremely depleted in 13c 13ccarbonate 40 this suggests that they were derived from bacterial methane 13cmethane 77 8 that was oxidized under anaerobic conditions the authigenic carbonates are associated with white fluffy mats of chemoautotrophic h2s oxidizing bacteria small pockmarks appear to be concentrated at small scale escarpments suggesting focussed fault controlled pore fluid expulsion due to the tectonic dewatering and degassing of the accretionary prism whereas diffuse discharge of pore fluids is inferred from the widespread occurrence of tiny gas bubble tubes

distributions and carbon isotopic compositions of lipid biomarkers in authigenic carbonate crusts from the nordic margin norwegian sea abstract we investigated the distributions and 13c values of lipid biomarkers in authigenic carbonate crusts from the nordic margin norwegian sea abundant highly 13c depleted archaeal and bacterial biomarkers revealed that anaerobic oxidation of methane aom is associated with carbonate authigenesis at the hakon mosby mud volcano hmmv and the nyegga pockmark field no conclusive evidence for aom was found in the crust sample from the storegga slide anme 2 methanotrophic archaea and sulfate reducing bacteria from the desulfosarcina desulfococcus cluster were inferred from lipid fingerprints distinct patterns of 13c depleted non isoprenoid dialkyl glycerol diethers dages are possibly associated with unknown microbial partners in the aom

archaeal lipids in neogene dolomites monterey and sisquoc formations california planktic versus benthic archaeal sources abstract the distribution of archaeal lipids including archaeol and glycerol dibiphytanyl glycerol tetraethers gdgts in dolomite concretions and surrounding sediment from the monterey formation miocene and the sisquoc formation miocene pliocene were examined to distinguish planktic from benthic contributions for this purpose dolomites with positive 13 c values 7 to 13 were chosen such highly positive values point to pronounced methanogenesis of benthic archaea in the sedimentary column at first glance distributions and relative abundances of gdgts in both dolomites and background sediment were similar resembling patterns of marine planktic crenarchaea a contribution of benthic euryarchaea to the gdgt pool became evident only from variations in the 13 c values of different biphytanes obtained after ether cleavage of gdgts whereas bi and tricyclic biphytanes had an isotopic signal typical of planktic archaea 13 c 23 6 to 20 5 and 23 4 to 21 2 respectively for both dolomite and background sediment acyclic and monocyclic biphytanes showed lower values for dolomite samples 25 1 to 22 6 and 27 6 to 24 7 respectively indicating a contribution of lipids from benthic archaea the isoprenoid diether archaeol 13 c 23 9 to 22 9 assigned to euryarchaea was only detected in dolomite samples also reflecting additional input from sedimentary archaea probably autotrophic methanogens the occurrence of lipids derived from methanogenic archaea agrees with the strong 13 c enrichment of dolomites and with mineral formation taking place in the zone of archaeal methanogenesis this implies that the lipid biomarker inventory of sedimentary strata needs to be interpreted carefully as it is often not straightforward to discriminate between input from the water column and sedimentary microbial activity

authigenic carbonates from the eastern black sea as an archive for shallow gas hydrate dynamics results from the combination of ct imaging with mineralogical and stable isotope analyses authigenic carbonates associated with cold seeps provide valuable archives of changes in the long term seepage activity to investigate the role of shallow buried hydrates on the seepage strength and fluid composition we analysed methane derived carbonate precipitates from a high flux hydrocarbon seepage area batumi seep area located on the south eastern black sea slope in ca 850 m in a novel approach we combined computerized x ray tomography ct with mineralogical and isotope geochemical methods to get additional insights into the three dimensional internal structure of the carbonate build ups x ray diffractometry revealed the presence of two different authigenic carbonate phases i e pure aragonitic rims associated with vital microbial mats and high mg calcite cementing the hemipelagic sediment as indicated by the ct images the initial sediment has been strongly deformed first plastic then brittle leading to brecciation of the progressively cemented sediment the aragonitic rims on the other hand represent a presumably recent carbonate growth phase since they cover the already deformed sediment the stable oxygen isotope signature indicates that the high mg calcite cement incorporated pore water mixed with substantial hydrate water amounts this points at a dominant role of high gas fluid flux from decomposing gas hydrates leading to the deformation and cementation of the overlying sediment in contrast the aragonitic rims do not show an influence of 18o enriched hydrate water the differences in 18o between the presumably recent aragonite precipitates and the older high mg cements suggest that periods of hydrate dissociation and vigorous fluid discharge alternated with times of hydrate stability and moderate fluid flow these results indicate that shallow buried gas hydrates are prone to episodic decomposition with associated vigorous fluid flow this might have a profound impact on the seafloor morphology resulting e g in the formation of carbonate pavements and pockmark like structures but might also affect the local carbon cycle

biomarker and 16s rdna evidence for anaerobic oxidation of methane and related carbonate precipitation in deep sea mud volcanoes of the sorokin trough black sea many mud volcanoes were recently discovered in the euxinic bottom waters of the sorokin trough ne black sea three of them i e nioz odessa and kazakov were selected for a detailed biogeochemical investigation four methane related carbonate crusts covered with microbial mats and sediments dmud brecciat from these mud volcanoes were collected during the 11th training through research cruise ttr 11 in 2001 the first finding of methanotrophic microbial mats associated with authigenic carbonates in the deep black sea we measured the concentrations and 13c values of methane and specific archaeal and bacterial lipids and determined archaeal and bacterial 16s rrna gene sequences the 13c of the microbial lipids reflected the carbon isotopic values of the methane indicating that methane was the main carbon source for microorganisms inducing carbonate formation anaerobic oxidation of methane aom in these settings was performed by archaea affiliated with the so called anme 1 group none of the identified archaeal sequences were closely related to known methanogens the combined 16s rrna gene sequence and biomarker data revealed a distinct difference in archaeal assemblage between the carbonate crusts and mud breccias besides gene sequences of sulfate reducing bacteria dna analysis of bacterial communities revealed a diversity of bacteria with apparent contrasting metabolic properties the methane utilization via aom processes was detected in the uppermost sediments where it subsequently induces authigenic carbonate precipitation most probably below seafloor the results of integrated biomarker and 16s rrna gene study reveal a crucial role of aom processes in formation of authigenic carbonates in methane seep environments

first biomarker evidence for methane oxidation at cold seeps in the southeast atlantic regab pockmark abstract sediment cores from the regab pockmark an active cold seep area in the southeast atlantic were analysed for their lipid biomarker distribution and associated stable carbon isotopic composition substantial amounts of diagnostic archaeal lipids were found consisting mainly of archaeol sn 2 hydroxyarchaeol and crocetane all archaeal lipids were profoundly depleted in 13c with 13c values as low as 133 concurrently abundant monoalkylglycerolethers mage assigned to sulphate reducing bacteria were identified and showed strong 13c depletions 13c between 86 and 95 the structural and isotopic patterns of these microbial lipids provided compelling evidence for anaerobic oxidation of methane aom occurring in regab sediments mediated by archaea and sulphate reducing bacteria lipid fingerprints indicated that anaerobic methanotrophic archaea anme 2 and sulphate reducing bacteria from the desulfosarcina desulfococcus cluster are the dominant aom assemblages depth profiles implied that highest aom takes place below the upper 2 cm mainly in the 6 12 cm depth interval significant abundances of 13c depleted diploptene and 4 methylsterols were found as well inferring that aerobic methanotrophy occurs in the surface sediment interval this first biomarker study at the recently investigated cold seeps in the se atlantic expand on existing work on aom settings and add new evidence for aerobic and anaerobic methanotrophic communities occurring in close vicinity

the formation of giant tubular concretions triggered by anaerobic oxidation of methane as revealed by archaeal molecular fossils lower eocene varna bulgaria abstract impressive several meters high tubular concretions in shallow marine calcareous sands and sandstones represent part of the well exposed subsurface plumbing network of an early eocene methane seep system in the balkanides foreland pobiti kamani area varna ne bulgaria an integrated approach including petrography inorganic geochemistry and lipid biomarker analyses was used to reconstruct the evolution of pore fluids and cementation conditions during tube formation and particularly the role of methane related carbonate diagenesis host sediment lithification from marine pore waters was perturbed soon after deposition by oxidation of predominantly microbial methane causing pervasive cementation by a 13 c poor homogeneous calcite cement 13 c values as low as 44 5 v pdb the importance of microbially mediated anaerobic oxidation of methane aom is confirmed by extremely 13 c depleted archaeal biomarkers 13 c values as low as 123 v pdb a suite of macrocyclic dialkyl glycerol diethers mdgd 0 to 2 and sn 3 hydroxyarchaeol comprises a characteristic trait of the eocene tubular concretions and might represent molecular fossils of so far unknown methane oxidizing archaea anme subsurface calcite cementation surrounding the ascending methane plume resulted from the changing pore water chemistry in response to aom and could have on a local scale been encouraged by the concurrent alteration of detrital feldspar fluctuating 13 c up to 8 v pdb and 18 o 0 5 to 9 v pdb signatures within a single tubular sandstone concretion are at least partly the consequence of isotopic resetting during late meteoric water circulation

generation accumulation and resource potential of biogenic gas biogenic gas is generated at low temperatures by decomposition of organic matter by anaerobic microorganisms more than 20 of the world s discovered gas reserves are of biogenic origin a higher percentage of gases of predominantly biogenic origin will be discovered in the future biogenic gas is an important target for exploration because it occurs in geologically predictable circumstances and in areally widespread large quantities at shallow depths in rapidly accumulating marine sediments a succession of microbial ecosystems leads to the generation of biogenic gas after oxygen is consumed by aerobic respiration sulfate reduction becomes the dominant form of respiration methane generation and accumulation become dominant only after sulfate in sediment pore water is depleted the most important mechanism of methane generation in marine sediments is the reduction of co2 by hydrogen electrons produced by the anaerobic oxidation of organic matter co2 is the product of either metabolic decarboxylation or chemical decarboxylation at slightly higher temperatures the factors that control the level of methane production after sediment burial are anoxic environment sulfate deficient environment low temperatu e availability of organic matter and sufficient space the timing of these factors is such that most biogenic gas is generated prior to burial depths of 1 000 m in marine sediments most of the biogenic gas formed can be retained in solution in the interstitial pore waters because of higher methane solubility at the higher hydrostatic pressures due to the weight of the overlying water column under certain conditions of high pressures and or low temperatures biogenic methane combines with water to form gas hydrates biogenic gas usually can be distinguished from thermogenic gas by chemical and isotopic analyses the hydrocarbon fraction of biogenic gas consists predominantly of methane the presence of as much as 2 of heavier hydrocarbons can be attributed to admixture of minor thermogenic gas due to low temperature degradation of organic matter the amounts of hydrocarbon components other than methane generally are proportional to temperature age and organic matter content of the sediments biogenic methane is enriched in the light isotope 12c dgr13c1 lighter than 55 ppt owing to kinetic isotope fractionation by methanogens the variations in isotopic composition of biogenic methane are controlled primarily by dgr13c of the original co2 substrate which reflects the net isotopic effect of both addition and removal of co2 the methane isotopic composition also can be affected by mixing of isotopically heavier thermogenic gas the possible complicating factors require that geologic chemical and isotopic evidence be considered in attempts to interpret the origin of gas accumulations accumulations of biogenic gas have been discovered in canada germany italy japan trinidad the united states and ussr in cretaceous and younger rocks at less than 3 350 m of burial and in marine and nonmarine rocks other gas accumulations of biogenic origin have undoubtedly been discovered however data that permit their recognition are not available

methane derived carbonates and authigenic pyrite from the northwestern black sea abstract methane seeps in the northwestern black sea are accompanied by carbonate and pyrite precipitates sediments were sampled at locations on the romanian 120 m depth and ukrainian 180 200 m depth shelf and slope layered carbonate crusts are formed of i carbonate cemented siliciclastic sediment containing dreissenoid bivalves ii microcrystalline high mg calcite or aragonite and iii aragonitic cement the dreissena sediment is subrecent and was deposited during the freshwater phase of the black sea it has been affected by seepage of methane rich fluids which induced intergranular precipitation of authigenic carbonates the microcrystalline carbonates exhibit an intense autofluorescence high mg calcite contains 11 14 mol mgco3 the aragonitic cement 8300 9500 ppm sr forms either isopachous layers or botryoids microbial filaments about 10 20 m in diameter and up to 900 m in length are preserved within and on carbonate crusts the carbonates are depleted in 13c microcrystalline carbonate ranges from 27 to 41 pdb and botryoidal aragonite ranges from 26 to 38 pdb the 13c depletion indicates that the carbonates predominantly derive from the microbial oxidation of methane carbonate deposits do not project up into the oxic water column they are restricted to the anoxic water column and to anoxic sediments revealing the crucial role of anaerobic methane oxidation for carbonate precipitation 14c contents give apparent radiocarbon ages of 20 640 180 a bp for a sample of botryoidal aragonite and 19 110 180 a bp for a sample of microcrystalline carbonate compatible with minimum ages of carbon derived from a fossil hydrocarbon source the 18o values of methane derived carbonates show a narrow range from 1 2 to 0 2 pdb 87sr 86sr ratios of microcrystalline carbonate mean 0 70927 and aragonitic cement mean 0 70918 are indistinguishable from ambient seawater mean 0 70917 and thus indicate a shallow sr source higher 87sr 86sr ratios of the dreissena sediment mean 0 71005 are probably caused by sr derived from detrital mica carbonates are accompanied by blocks and crusts composed of pyrite the framboidal sulphide exhibits a palisade like fabric with framboids arranged to parallel pillars sulphur isotopic ratios 34s ranging from 16 8 to 19 7 cdt indicate that the sulphur derives not from the 34s depleted h2s of the water column or the uppermost sediment layers most likely pyrite formed in the lacustrine sediments after the first incursion of mediterranean seawater

molecular indicators of methane metabolisms at cold seeps along the united states atlantic margin abstract anaerobic oxidation of methane aom and the environmental conditions supporting aom on continental margins is an essential component to global methane budgets diagnostic lipid biomarkers and their compound specific isotope analysis preserved in authigenic carbonates at cold seeps can serve as fingerprints to archaeal bacterial consortia involved in aom however despite the discovery of several hundreds of seeps along the united states atlantic margin usam there are relatively few biomarker investigations of cold seep carbonates along this passive margin a lipid biomarker carbon isotope and dna marker gene study was therefore undertaken to determine the microbial origins of authigenic carbonates from two usam seeps norfolk and the baltimore canyon seep fields results from this study capture a distinct archaeal lipid signature from putative methanotrophic archaea including archaeol i sn 2 hydroxyarchaeol 2 6 10 15 19 pentamethylicosane pmi and crocetane the 13c depleted aom related archaeal lipid samples i e archaeol 91 6 sn 2 hydroxyarchaeol 129 2 pmi 92 8 and crocetane 70 9 confirm the dominance of methane assimilation and isotope fractionation during aom these results are consistent with the detection of archaeal anaerobic methanotrophs anmes based on 16s rrna gene sequencing the norfolk authigenic carbonate contained anme 1a 1b 2a 2b and 2c whereas only the anme 2 clade was detected at baltimore and present as the subclusters 2a 2b and 2b the anme 2d clade may also be present particularly at the baltimore seep site given the high abundance of candidatus methanoperedens nitroreducens detected in the mcra gene sequencing the presence of terminally branched fatty acids antesio and iso c15 0 components as well as c16 1 7 with 13c values as low as 107 6 are indicative of sulfate reducing bacteria srb at the norfolk seep site and supports syntrophy of srb with methane oxidizing archaea in contrast nitrate driven aom in syntrophy m nitroreducens at the baltimore seep site is consistent with elevated fatty acid 13c values and lack of deltaproteobacteria at the baltimore seep site taken together the range in lipid composition distribution and carbon isotopic composition observed at the norfolk and baltimore seep sites suggests aom is performed by multiple archaea instead of a single species and may be paired with either or both nitrate and sulfate reduction given the heterogeneous nature of cold seep ecosystems this study fills a critical spatial gap in our knowledge of aom activity at two seep sites along a passive margin

application of lipid biomarkers to detect sources of organic matter in mud volcano deposits and post eruptional methanotrophic processes in the gulf of cadiz ne atlantic abstract the gulf of cadiz is known as an active mud volcano mv and fluid venting region discovered during the training through research ttr expeditions in 1999 ttr 9 here we report a study of lipid biomarkers in the mud breccia matrix from three mvs in this region the lipid biomarker composition revealed strong compositional resemblance as well as similar thermal maturity properties for the studied mvs this indicates that the primary source of the erupted material for these mvs is located in similar litho stratigraphic units in both areas upward migrated fluid went through the sedimentary series of the allochthonous olistrostrome and through the upper cretaceous horizons the relatively immature characteristics of organic matter from both mud breccia rock clasts and matrix together with the more mature properties of hydrocarbon gases from the same sampling locations indicate that source strata for the initial fluid are located deeper in the subsurface than the source strata for the erupted sedimentary material the presence of microbial lipid biomarkers derived from archaea and sulfate reducing bacteria in the mud breccias revealed anaerobic oxidation of methane aom as a dominant microbial process in these habitats our data suggest that the aom derived lipids are at least in part fossil in origin i e they do not reflect active aom communities and thus reflect aom activity in these mvs integrated over time the low concentrations of aom related biomarkers in these mvs suggest relatively low intensities of aom in the studied mv deposits the distribution of biomarkers suggests an abrupt and brief cold seep activity in the past and the absence of a continuous methane influx in the studied locations

molecular and isotopic analysis of anaerobic methane oxidizing communities in marine sediments convergent lines of molecular carbon isotopic and phylogenetic evidence have previously indicated hinrichs k u hayes j m sylva s p brewer p g delong e f 1999 methane consuming archaebacteria in marine sediments nature 398 802 805 that archaea are involved in the anaerobic oxidation of methane in sediments from the eel river basin offshore northern california now further studies of those same sediments and of sediments from a methane seep in the santa barbara basin have confirmed and extended those results mass spectrometric and chromatographic analyses of an authentic standard of sn 2 hydroxyarchaeol hydroxylated at c 3 in the sn 2 phytanyl moiety have confirmed our previous tentative identification of this compound but shown that the previously examined product was the mono tms rather than di tms derivative further analyses of 13 c depleted lipids appreciably more abundant in samples from the santa barbara basin have shown that the archaeal lipids are accompanied by two sets of products that are only slightly less depleted in 13 c these are additional glycerol ethers and fatty acids the alkyl substituents in the ethers mostly monoethers with some diethers are non isoprenoidal the carbon number distributions and isotopic compositions of the alkyl substituents and of the fatty acids are similar suggesting strongly that they are produced by the same organisms their structures n alkyl and methyl branched n alkyl require a bacterial rather than archaeal source the non isoprenoidal glycerol ethers are novel constituents in marine sediments but have been previously reported in thermophilic sulfate and nitrate reducing organisms which lie near the base of the rrna based phylogenetic tree based on previous observations that the anaerobic oxidation of methane involves a net transfer of electrons from methane to sulfate it appears likely that the non archaeal 13 c depleted lipids are products of one or more previously unknown sulfate reducing bacteria which grow syntrophically with the methane utilizing archaea their products account for 50 of the fatty acids in the sample from the santa barbara basin at all methane seep sites examined the preservation of aquatic products is apparently enhanced because the methane oxidizing consortium utilizes much of the sulfate that would otherwise be available for remineralization of materials from the water column