dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

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

microbially mediated fossil bearing carbonate concretions and their significance for palaeoenvironmental reconstructions a multi proxy organic and inorganic geochemical appraisal carbonate concretions are widespread within the geological record however the lack of recent known analogues creates a need for novel approaches to unravel the major microbial players involved in concretion formation and establish their suitability as palaeoenvironmental recorders here we used a combination of geochemical and geological techniques to study two pyritiferous calcite concretions and compared the results with their host sediment toarcian posidonia shale 183 ma sw germany the c 13 depleted nature of the concretion bodies with average values of delta c 13 carb 14 8 delta c 13 org 32 4 and delta c 13 n alkanes 34 9 indicates that sulphate reducing bacteria srb played a major role in the concretion growth and preservation of the nucleus via the rapid decomposition of organic matter om however rock eval analyses from both concretions revealed elevated hydrogen indices hi in the body and low hi values at the rim these values suggest that most of the microbial activity did not occur in the concretion body but rather at the rim and at the surface of the nuclei which generally supports the exceptional preservation of om in carbonate concretions furthermore enrichment in euhedral pyrite in the concretion rims suggests they were formed through increased activities of iron reducing fer bacteria coupled to a decrease of srb activity leading towards conditions more favourable to the direct precipitation of pyrite despite low delta c 13 values the known lipid biomarkers such as acyclic extended isoprenoids or 3 beta methyl hopanes did not reveal evidence of an active methane cycling the present study emphasises the crucial role of carbonate concretion in om preservation and highlights their great potential as palaeoenvironmental recorders c 2016 elsevier b v all rights reserved

diagenesis of organic matter in suspended particles and sediments in the cariaco trench abstract suspended particulate materials and bottom sediments from the cariaco trench were analysed for lipid content to investigate the diagenesis of organic matter in an anoxic water column and sediment distributions of fatty acids sterols and the acyclic isoprenoid hydrocarbons lycopane and 2 6 10 15 19 pentamethyleicosane support the hypothesis that alteration of organic matter usually attributed to sedimentary diagenesis occurs in the water column typical indicators of diagenetic processes including preferential loss of unsaturated fatty acids increased abundances of branched fatty acids stenol to stanol conversion and abundant acyclic isoprenoids were observed in the water column across the oxic anoxic interface in the cariaco trench lipid distributions in the sediment were remarkably uniform with depth we conclude that organic material delivered to the sediment has been extensively altered in the water column but that which is buried is preserved without much additional alteration

models of stochastic spatially varying stress in the crust compatible with focal mechanism data and how stress inversions can be biased toward the stress rate evidence suggests that slip in earthquakes and the resultant stress changes are spatially heterogeneous if crustal stress from past earthquakes is spatially heterogeneous then earthquake focal mechanisms should also be spatially variable we describe the statistical attributes of simulated earthquake catalogs including hypocenters and focal mechanisms for a spatially 3d time varying model of the crustal stress tensor with stochastic spatial variations it is assumed that temporal variations in stress are spatially smooth and are primarily caused by plate tectonics spatial variations in stress are assumed to be the result of past earthquakes and are independent of time for periods between major earthquakes it is further assumed that heterogeneous stress can be modeled as a stochastic process that is specified by an autocorrelation function synthetic catalogs of earthquake hypocenters and their associated focal mechanisms are produced by identifying the locations and times at which the second deviatoric stress invariant exceeds a specified limit the model produces a seismicity catalog that is spatially biased the only points in the grid that exceed the failure stress are those where the heterogeneous stress is approximately aligned with the stress rate this bias results in a focal mechanism catalog that appears less heterogeneous than the underlying stress orientations comparison of synthetic focal mechanism catalogs with catalogs of real earthquakes suggests that stress in the crust is heterogeneous stochastic parameters are estimated which generate distance dependent spatial variations in focal mechanisms similar to those reported by hardebeck 2006 for southern california

a precise search for drastic temperature shifts of the past 40 000 years in southeastern europe 1 climatic models simulate abrupt oscillations that are associated in the north atlantic with dansgaard oeschger and heinrich events however the geographic extension of temperature anomalies is largely uncontrolled due to the scarcity of quantitative records of sufficient time resolution on the european continent here we propose based on a recently developed temperature proxy tex86 a reconstruction of millennial scale temperature variations in a black sea sediment archive for the last 40 000 years prior to any paleoclimatological interpretations the effects of potential bias such as seasonality and depth of maximum export production on temperature reconstructions are considered for the black sea based on previous work a tentative method for temperature corrections taking into account varying terrigenous inputs is further proposed reconstructed temperatures for black sea core md042790 were remarkably stable during the last glacial however significant shifts toward lower temperatures of 2 c occurred during heinrich events 2 and 3 the deglaciation displayed a temperature increase of 10 c consistent with neighboring european reconstructions a younger dryas cooling of approximately 5 6 c was clearly expressed in the reconstruction in notable contrast to observations from nearby archives heinrich events imprinted our glacial temperature record consistent with a strong reorganization of oceanic circulation and a large spreading of the temperature anomaly from the north atlantic toward the southeast furthermore in contrast to high latitude records our black sea record lacks the signatures of dansgaard oeschger interstadials suggesting a decreasing temperature gradient away from the north atlantic

distribution of intact and core gdgts in marine sediments abstract we conducted a survey of archaeal gdgt glycerol dibiphytanyl glycerol tetraether distributions in marine sediments deposited in a range of depositional settings the focus was comparison of two pools presumed to have distinct geobiological significance i e intact polar gdgts ip gdgts and core gdgts c gdgts the former pool has been suggested to be related to living communities of benthic archaea in marine sediments while the latter is commonly interpreted to consist of molecular fossils from past planktonic archaeal communities that inhabited the surface ocean understanding the link between these two pools is important for assessment of the validity of current molecular proxies for sedimentary archaeal biomass and past sea surface temperatures the relative distributions of gdgts in the two pools in a core at a ch4 rich site in the black sea provide evidence for in situ production of glycosidic ip gdgts and their subsequent degradation to corresponding c gdgts on timescales that are short in geological terms in addition we monitored the relationship between the ip gdgt and c gdgt pools in a sample set from various ocean basins with subseafloor depth from a few cm to 320 m and 0 to 4 myr in age notable differences between the two pools can be summarized as follows the gdgt with acyclic biphytanes gdgt 0 and its analogues with two and three cyclopentane moieties gdgt 2 and 3 are generally more abundant in the pool of ip gdgts while crenarchaeol tends to be more abundant in the c gdgt pool consequently the ring index is generally higher for the c gdgts while tex86 a molecular proxy ratio not considering the two major gdgts tends to be higher in the ip gdgt pool these differences in the proportion of individual gdgts in the two pools are probably due to in situ production of ip gdgts with distributions differing from those of c gdgts despite these differences we observed significant correlation of these two ratios between the two pools specifically in both pools tex86 is high in sediments from warm oceanic regimes and low in cold regimes we discuss these relationships and suggest that recycling of core gdgts by benthic archaea is an important mechanism linking both molecular pools

mineralogy and geochemistry of coal wastes from the starzykowiec coal waste dump upper silesia poland abstract coal wastes the products of coal processing deposited on dumps can undergo processes of self heating and self ignition causing endogenic fires burning coal waste dumps are dangerous for the environment the coal dump located at the chwalowice coal mine upper silesian coal basin poland represents a long term fire which affected the organic mineral and chemical composition of a huge amount of deposited wastes collected samples were divided into groups on the basis of kind on the amount or absence of organic matter content and on the basis of mineral phase composition chemical composition of examined samples reveals heating combustion processes in altered coal wastes the organic matter present in the coal wastes changes through the following processes all causing changes in c n o and h content 1 organic matter oxidation 2 organic matter devolatilization and 3 coke formation two processes alter the mineral phases and change the chemical composition of the combusting wastes 4 mineral phase oxidation e g pyrite and marcasite oxidation to fe 2 o 3 and 5 mineral dehydration h 2 o or oh groups are released from clay minerals and micas the latter are followed by isochemical processes 6 mineral structure rebuilding while heating enantiotropic transformations of e g sio 2 and 7 metastable phase formation processes 6 and 7 can change the chemistry of deposited wastes through 8 the formation of high temperature minerals in combustion process e g mullite and 9 mineral crystallization from melt e g indialite after dump quenching some minerals can become unstable because of 10 weathering processes the behavior of trace elements is also strictly connected with the behavior of mineral phases which have undergone the burning processes most of them appear to stay unchanged moreover organic matter content does not generally influence their concentration although the combustion processes are so spontaneous that their products cannot be predicted in all details some dependence between chemical composition of the sample and its location within the dump or after burning were found

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

temporal and spatial variation in tetraether membrane lipids of marine crenarchaeota in particulate organic matter implications for tex86 paleothermometry the tex86 is a new temperature proxy which is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraether gdgt lipids of the membranes of crenarchaeota that occur ubiquitously in oceans and shelf seas this proxy was calibrated by core top sediments but it is as yet not clear during which season and at which depth in the water column the gdgt signal used for tex86 paleothermometry is biosynthesized here we analyzed 200 particulate organic matter pom samples from 11 different marine settings for tex86 this revealed that the gdgts occur seasonally in surface waters and occur in higher abundances during the winter and spring months the depth distribution showed that gdgts generally appeared in higher amounts below 100 m depth in the water column however the tex86 values for waters below the photic zone 150 1500 m did not correlate with the in situ temperature but rather correlated linearly with surface temperature the tex86 for pom from the upper 100 m showed a linear correlation with in situ temperature which was nearly identical to the previously reported core top equation the correlation of all pom samples with surface temperature was also strikingly similar to the core top correlation these findings demonstrate that the gdgt signal which reaches the sediment is mainly derived from the upper 100 m of the water column this may be caused by the fact that gdgts from the photic zone are much more effectively transported to the sediment by grazing and repackaging in large particles than gdgts from deeper waters

evidence for self similar triangular slip distributions on earthquakes implications for earthquake and fault mechanics we characterize average slip distributions on earthquakes beyond their individual heterogeneity for that we analyze a large number of seismic slip distributions both measured at the surface after earthquakes 44 profiles and derived from slip inversion models 76 models investigating the overall shape of these slip profiles we find that they are roughly triangular both along strike and dip and most of them 70 80 are asymmetric long linear slopes and high slip gradients therefore are the key ingredients to describe earthquake slip profiles the scaling relations between maximum displacement and length or width suggest furthermore that the triangular slip profiles are self similar such slip patterns make earthquakes dominated by one major zone of maximum slip hence one major asperity analyzing the position of hypocenters with respect to these asperities we find that earthquakes nucleate at a distance from them that averages 20 30 of their total length compiling observations on 56 earthquakes we show that this distance i e the asperity size is structurally defined we then compare the earthquake slip profiles to cumulative slip profiles measured on long term faults of various ages and sizes and find that all profiles have a similar shape triangular and asymmetric hence combining data for a large number of earthquakes leads to point out average generic characteristics of the coseismic slip that are similar to those that emerge from the accumulation of events with time on a single fault this suggests that these characteristics result from robust physical properties

archaea in black sea water column particulate matter and sediments evidence from ether lipid derivatives abstract phytane and long chain c40 head to head acyclic c40 0cy and cyclic isoprenoids with 1 3 cyclopentyl rings c40 1cy c40 2cy and c40 3cy derived from archaeal core lipids are present in black sea particulate matter from both the oxic and anoxic zones and in sediment cores from the central basin and the western continental margin the occurrence of these ether linked isoprenoids throughout the water column and sediments suggests that archaea are widely distributed in the black sea methanogens are the probable source of ether linked phytane and some of the acyclic c40 compounds while psychrophilic archaea related to hyperthermophiles are the likely sources of the cyclic isoprenoids

stereochemical studies of acyclic isoprenoids xii lipids of methanogenic bacteria and possible contributions to sediments abstract abundant volatile lipids of methanobacterium thermoautotrophicum and methanosarcina barkeri include isoprenoid hydrocarbons c30 and c15 c20 and c25 isoprenoid alcohols m barkeri contains 2 6 10 15 19 pentamethyleicosane whose relative stereochemistry is the same as found in marine sediments indicating that it is a marker of methanogenic activity the c20 c30 and c25 alkenes in m thermoautotrophicum also have a preferred sterochemistry the latter have the 2 6 10 14 18 pentamethyleicosanyl skeleton suggesting that the alkane in marine sediments may derive from methanogens the stereochemistry of squalane in a marine sediment is also compatible with an origin in methanogens in contrast the stereochemistry of pristane in m thermoautotrophicum indicates a fossil fuel contaminant origin suggesting that this and certain other alkanes reported in archaebacteria might also be of contaminant origin there is therefore little evidence at present that the pristane in immature marine sediments originates in methanogens the c15 and c20 saturated alcohols in m thermoautotrophicum have mainly the all r configuration if this is generally true for methanogens the c20 alcohol in the messel shale may originate mainly from methanogens whereas that in the green river shale may originate mainly from photosynthetic organisms

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

biomarkers for aerobic methanotrophy in the water column of the stratified gotland deep baltic sea filter samples from the oxic zone and suboxic zone of the physically stratified water column and sediment samples of the gotland deep baltic sea were analyzed for bacteriohopanepolyol bhp and phospholipid fatty acid plfa concentrations in total eight bhps were identified with the greatest diversity in the suboxic zone there 35 aminobacteriohopane 31 32 33 34 tetrol aminotetrol and 35 aminobacteriohopane 30 31 32 33 34 pentol aminopentol whose concentrations decreased concurrently from the lower to the upper suboxic zone indicated type i methanotrophic bacteria and thus aerobic oxidation of methane the presence and activity of type i aerobic methanotrophic bacteria was further supported by the presence of 13c depleted plfas specifically 16 1 8c and 16 1 5c 13c as low as 41 2 however the relative amount of methanotroph specific compounds was low aminopentol 0 2 of total bhps 16 1 8c ca 0 5 of total plfas suggesting a minor contribution of aerobic methanotrophic bacteria to the particulate organic matter the distinctive bhp pattern in the suboxic zone including aerobic methanotroph biomarkers and a tentative marker for a pelagic redoxcline putative 22s isomer of the ubiquitous 22r bacteriohopanetetrol bht was mirrored in the sediment samples our data indicate that a major portion of the sedimentary hopanoids of the gotland deep is sourced from the suboxic part of the water column via an effective but unknown transport mechanism

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

archaeal lipids and anaerobic oxidation of methane in euxinic water columns a comparative study of the black sea and cariaco basin abstract the black sea and the cariaco basin are both large euxinic marine basins in which methane concentrations are high and where anaerobic oxidation of methane aom is an important part of the carbon cycle aom can be recognized by lipid biomarkers that are specific to methanotrophic archaea involved and by strongly 13c depleted isotope compositions consistent with uptake of 13c depleted methane derived carbon the working hypothesis for our investigation was that aom in both the black sea and cariaco basin would generate measurable diagnostic biomarkers and isotope depletions to test this hypothesis we analyzed particulate matter and surface sediments for intact glycerol dialkyl glycerol tetreaethers gdgts components of archaeal membrane lipids and measured stable carbon isotope compositions of their constituent biphytanes several gdgts and strongly 13c depleted biphytanes indicative of aom were present in the deep anoxic region of the black sea 700 m unexpectedly this biomarker signal was not detected in the upper anoxic zone of the black sea or in the entire water column of the cariaco basin even though previous studies had shown high rates of aom to occur in both basins it is possible that the aom derived biomarker signal is masked by archaeal lipids derived from non methanotrophic archaea which utilize 13c enriched carbon substrates alternately we speculate that the methanotrophic community may be highly diverse in euxinic basins possibly producing another suite of biomarkers that we did not measure this conclusion will require further testing by coordinated organic geochemical microbial ecology studies

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

the influence of oxic degradation on the sedimentary biomarker record ii evidence from arabian sea sediments abstract biomarker accumulation rates in nine different time slices in three cores on and at the foot of a submarine high in the northern arabian sea the murray ridge were measured to investigate the influence of oxygen exposure time on the preservation of biomarker signals in the sedimentary record all three sites experienced the same history of surface water productivity and sediment supply but had different bottom water redox conditions due to their different positions in just below well below relative to the present location of the intense oxygen minimum zone omz past variations in the intensity and position of the omz known from a wide variety of proxies toc content distribution and abundance of planktonic and benthic foraminifera and pteropods trace metals and 15 n enabled specific biomarker i e n alkanes steroids alkenones alkyldiols c 26 fatty acid loliolide biphytane diols and archaeal tetraether lipids accumulation rates at contrasting oxygen exposure times to be compared the results indicate that these accumulation rates can vary by more than an order of magnitude for marine biomarkers in addition there are significant differences in the degree of oxic degradation of different types of biomarkers terrestrial n alkanes are much more resistant than alkenones and n alkyl diols which are more refractory than steroids and biphytane diols these differences in degree of oxic degradation indicate that biomarker distributions will change on increasing exposure to oxygen these findings have a significant impact on the application of biomarkers to sedimentary settings in which oxygen exposure time is likely to change significantly

details of stress directions in the alaska subduction zone from fault plane solutions we used the cumulative misfit method to divide a data set with heterogeneous stress orientations into subsets with homogeneous stress directions we propose that slope changes of the cumulative misfit as a function of earthquake number pinpoint the boundaries of homogeneous stresses using a synthetic data set of 50 fault plane solutions composed of two halves corresponding to two incompatible stress tensors we tested the validity and efficacy of the cumulative misfit method our acceptance criteria for results of stress tensor inversions are 1 the directions must be well constrained that is the 95 confidence regions of the greatest and least principal stresses do not overlap and 2 there must be evidence for homogeneity in the sample that is the average misfit of the inversion is less than 6 we estimated stress directions in the alaska wadati benioff zone wbz using 470 fault plane solutions which we determined for earthquakes with ml 3 and 67 published fault plane solutions for earthquakes with ms 5 we succeeded in subdividing the data set of the small and large earthquakes into 25 and 3 subsets with the average misfit ranging from 3 2 to 5 5 the average misfits of the subsets we accept as satisfying the assumption of homogeneity are smaller than the average misfit of the overall data set f 10 by factors of 2 to 3 we estimated the stress fields at two scales along the alaska wbz the stress directions measured by the large earthquakes ms 5 were homogeneous over large volumes with extension downdip and the direction of greatest compression along strike this unusual orientation of the greatest principal stress is attributed to the bend of the slab under central alaska which generates compressive stresses along strike the stress orientations revealed by small earthquakes in contrast exhibited a great deal of heterogeneity as a function of space although their general trend confirms the overall stress directions obtained from the large events we propose that the ratio of the dimensions of the stress field sensed by earthquakes to the rupture dimensions is about 20 to 50 the estimated stress directions of the crustal earthquakes corresponded to the following mechanisms 1 strike slip faulting with the greatest principal stress oriented n s near fairbanks and 2 thrusting with the greatest principal stress oriented nw se near mount mckinley

constraining fault constitutive behavior with slip and stress heterogeneity 1 we study how enforcing self consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event we explore features of rupture dynamics that 1 lead to slip heterogeneity in earthquake ruptures and 2 maintain these conditions following rupture so that the stress field is compatible with the generation of aftershocks and facilitates heterogeneous slip in subsequent events our three dimensional finite element simulations of magnitude 7 events on a vertical planar strike slip fault show that the conditions that lead to slip heterogeneity remain in place after large events when the dynamic stress drop initial shear stress and breakdown work fracture energy are spatially heterogeneous in these models the breakdown work is on the order of mj m 2 which is comparable to the radiated energy these conditions producing slip heterogeneity also tend to produce narrower slip pulses independent of a slip rate dependence in the fault constitutive model an alternative mechanism for generating these confined slip pulses appears to be fault constitutive models that have a stronger rate dependence which also makes them difficult to implement in numerical models we hypothesize that self consistent ruptures could also be produced by very narrow slip pulses propagating in a self sustaining heterogeneous stress field with breakdown work comparable to fracture energy estimates of kj m 2

algal and archaeal polyisoprenoids in a recent marine sediment molecular isotopic evidence for anaerobic oxidation of methane 1 analyses of 13c contents of individual organic molecules in a marine sediment show that crocetane 2 6 11 15 tetramethylhexadecane an isomer of phytane is produced by microorganisms that use methane as their main source of carbon the sediments lie at a water depth of 68 m in the kattegat the strait between denmark and sweden crocetane appears first 185 cm below the sediment water interface in the zone marking the transition from sulfate reduction to methanogenesis its 13c value is 90 10 versus vienna pee dee belemnite vpdb its structure which includes four isoprene units arranged symmetrically around a tail to tail linkage suggests that it is produced by a member of the archaea growing at the intersection of the diffusion gradients for sulfate and methane in sedimentary pore waters the source organism apparently functions as a methane consuming member of the microbial consortium responsible for the anaerobic oxidation of methane hoehler et al 1994 in which as first demonstrated quantitatively in these sediments iversen and jorgensen 1985 electrons are transferred from methane to sulfate the presence of archaeal biomass throughout the sediment section is indicated by significant concentrations of 2 6 10 15 19 pentamethylicosane pmi and of ether bound phytane and biphytane the pmi reaches a minimum value of 47 well below the transition zone its isotopic depletion could reflect either methanogenic or methanotrophic sources the ether bound lipids are isotopically uniform throughout the section and are presumed to derive from archaea that utilize a carbon source unaffected by the oxidation of methane

distribution of intact and core tetraether lipids in water column profiles of suspended particulate matter off cape blanc nw africa in the reconstruction of sea surface temperature sst from sedimentary archives secondary sources lateral transport and selective preservation are considered to be mainly negligible in terms of influencing the primary signal this is also true for the archaeal glycerol dialkyl glycerol tetraethers gdgts that form the basis for the tex86 sst proxy our samples represent four years variability on a transect off cape blanc nw africa we studied the subsurface production vertical and lateral transport of intact polar lipids and core gdgts in the water column at high vertical resolution on the basis of suspended particulate matter spm samples from the photic zone the subsurface oxygen minimum zone omz nepheloid layers nl and the water column between these furthermore we compared the water column spm gdgt composition with that in underlying surface sediments this is the first study that reports tex86 values from the precursor intact polar lipids ipls associated with specific head groups ipl specific tex86 we show a clear deviation from the sea surface gdgt composition in the omz between 300 and 600 m since neither lateral transport nor selective degradation provides a satisfactory explanation for the observed tex derived temperature profiles with a bias towards higher temperatures for both core and ipl specific tex86 values we suggest that subsurface in situ production of archaea with a distinct relationship between lipid biosynthesis and temperature is the responsible mechanism however in the nw african upwelling system the gdgt contribution of the omz to the surface sediments does not seem to affect the sedimentary tex86 as it shows no bias and still reflects the signal of the surface waters between 0 and 60 m

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

attenuation of 1 6 s lg waves in eurasia we report our investigation of the lg attenuation characteristics in eurasia using digital recordings from the incorporated research institutions for seismology chinese digital seismic network broadband stations to maximize the utilization of the current station and source distribution in the region we have derived a new technique known as the source pair receiver pair sprp method for lg attenuation measurement the procedure eliminates seismic source and site effects leaving behind decontaminated amplitude data from which regional wave attenuation is estimated for lg attenuation studies the sprp method is more flexible and of greater general applicability than its predecessor the reversed two station method chun et al 1987 the application of the sprp method to our time domain analysis of 33 regional and far regional seismic events has provided stable regional average for lg attenuation in periods of 1 6 s our time domain analysis aided by a damped least squares inversion algorithm has led to robust measurements of lg attenuation q and its frequency dependence in nine subregions of tectonic significance regions of active tectonics and seismicity generally have lower q0 than that in the stable continental interior subregional q and are found compatible with the published results in areas of relatively uniform geology values are comparatively poorly determined suggesting that they are susceptible to the presence of crustal heterogeneities along the wave paths

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

lipid geochemistry of methane seep related black sea carbonates abstract carbonates recovered from anoxic waters between 235 and 1555 m depth in the northwestern black sea were analyzed for lipid biomarkers and stable carbon isotopic compositions in addition a methane seep related microbial mat and a sample of surface sediment recovered from a non seep site were studied for comparison high concentrations of strongly 13 c depleted lipids attributed to bacteria and archaea mediating the anaerobic oxidation of methane aom were found in all samples except for the sediment differences of the dominant aom performing communities between the carbonates indicated by specific lipid patterns appear to be caused by the respective biogeochemical settings high proportions of anme 2 consortia are found at sites of assumingly high partial pressures of methane while anme 1 associations dominate at locations of moderate methane supply in the sedimentary concretion a complex mixture of biomarkers for terrestrial and planktonic organisms was found different molecular structures along with strong variations in the stable carbon isotopic compositions 13 c 20 2 to 94 3 allow for an estimation of the proportions of tetraether bound biphytanes derived from planktonic crenarchaeota and methanotrophic euryarchaeota our data imply that the shape of aom derived carbonate precipitates in black sea environments is crucially influenced by the respective methane supply active aom driven chimney like bioherms similar to those previously observed on the ukrainian shelf might also develop in the deep euxinic zone at 1555 m water depths

origins of archaeal tetraether lipids in sediments insights from radiocarbon analysis abstract understanding the supply and preservation of glycerol dibiphytanyl glycerol tetraethers gdgts in marine sediments helps inform their use in paleoceanography compound specific radiocarbon measurements of sedimentary alkenones from multiple environments have been used to gain insight into processes that affect u 37 k paleotemperature reconstructions similar analyses are warranted to investigate how analogous processes affecting gdgts impact tex 86 paleotemperatures here we present radiocarbon measurements on individual gdgts from bermuda rise and santa monica basin sediments and discuss the results in the context of previous studies of co depositional alkenones and foraminifera the 14 c contents of gdgts and planktonic foraminifera in bermuda rise are very similar suggesting a local source and tex 86 derived temperatures agree more closely with foraminiferal temperatures than do u 37 k temperatures in contrast gdgts in santa monica basin are depleted in 14 c relative to both alkenones and foraminifera and tex 86 temperatures agree poorly with known surface water values we propose three possible factors that could explain these results i gdgts may be labile relative to alkenones during advective transport through oxic waters ii archaeal production deep in the water column may contribute 14 c depleted gdgts to sediments and iii some gdgts also may derive from sedimentary archaeal communities each of these three processes is likely to occur with varying relative importance depending on geographic location the latter two may help to explain why tex 86 temperature reconstructions from santa monica basin do not appear to reflect actual sea surface temperatures terrigenous gdgts are unlikely to be major contributors to bermuda rise or santa monica basin sediments based on values of the bit index the results also indicate that the crenarchaeol regioisomer is governed by processes different from other gdgts individual measurements of the crenarchaeol regioisomer are significantly depleted in 14 c relative to co occurring gdgts indicating an alternative origin for this compound that presently remains unknown re examination of the contribution of crenarchaeol regioisomer to the tex 86 index shows that it is a significant influence on the sensitivity of temperature reconstructions

distribution of glycerol dialkyl glycerol tetraether lipids in the water column of lake tanganyika abstract we studied the distribution of glycerol dialkyl glycerol tetraethers gdgts in suspended particulate matter from the water column of lake tanganyika east africa where sediment studies had shown the applicability of the tex 86 proxy for reconstructing surface lake water temperature gdgts in particular crenarchaeol showed maximum abundance within the suboxic zone 100 180 m suggesting that this is the preferred niche of ammonia oxidizing thaumarchaeota despite evidence for anaerobic methane oxidation in deep anoxic water 300 1200 m no unambiguous evidence for an imprint of methanotrophic archaea on gdgt distribution was found comparison of tex 86 and bit indices with those of surface sediments suggests that the sedimentary gdgts are derived predominantly from the oxic zone and suboxic zone of the lake

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

descent toward the icehouse eocene sea surface cooling inferred from gdgt distributions the tex86 proxy based on the distribution of marine isoprenoidal glycerol dialkyl glycerol tetraether lipids gdgts is increasingly used to reconstruct sea surface temperature sst during the eocene epoch 56 0 33 9 ma here we compile published tex86 records critically reevaluate them in light of new understandings in tex86 palaeothermometry and supplement them with new data in order to evaluate long term temperature trends in the eocene we investigate the effect of archaea other than marine thaumarchaeota upon tex86 values using the branched to isoprenoid tetraether index bit the abundance of gdgt 0 relative to crenarchaeol gdgt 0 and the methane index mi we also introduce a new ratio gdgtrs which may help identify red sea type gdgt distributions in the geological record using the offset between tex86h and tex86l h l and the ratio between gdgt 2 and gdgt 3 2 3 we evaluate different tex86 calibrations and present the first integrated sst compilation for the eocene 55 to 34 ma although the available data are still sparse some geographic trends can now be resolved in the high latitudes 55 there was substantial cooling during the eocene 6 c our compiled record also indicates tropical cooling of 2 5 c during the same interval using an ensemble of climate model simulations that span the eocene our results indicate that only a small percentage 10 of the reconstructed temperature change can be ascribed to ocean gateway reorganization or paleogeographic change collectively this indicates that atmospheric carbon dioxide pco2 was the likely driver of surface water cooling during the descent toward the icehouse

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

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

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

a multilayered water column in the ediacaran yangtze platform insights from carbonate and organic matter paired δ13c abstract large carbon isotope fluctuations have been systematically reported for ediacaran carbonate rocks the meaning of which remains controversial in order to better understand the mechanisms behind such variations we present new paired 13c data on carbonates 13ccarb and their associated organic matter 13corg from a shelf margin section yangjiaping of the doushantuo formation in this section the doushantuo formation starts with cap dolostones presenting 13ccarb values around 5 and 13corg values between 30 3 and 27 6 up section phased variations in 13ccarb and 13corg describe positive and negative excursions while their difference 13cdol org 13ccarb 13corg remains around 29 2 these new data allow the first reconstruction of lateral variations of 13ccarb 13corg and 13ccarb org for a shelf to basin cross section of the yangtze platform south china after integration with results reported previously for two other sections across the yangtze platform the isotope signals reveal strong lateral heterogeneities with complex variations of 13ccarb and 13cdol org in the inner shelf section phased variations in the shelf margin section with positive 13ccarb and 13cdol org close to 29 and dominantly negative 13ccarb with 13corg as low as 35 in the basin these variations are incompatible with the idea that the 13ccarb can systematically be used as a proxy of ocean surface waters assuming that 13ccarb are acquired in bottom waters and or upper sediments we show that the heterogeneous 13ccarb and 13cdol org are compatible with a stratified water column composed of up to three layers i an oxic surface layer where dissolved inorganic carbon dic is probably in isotope equilibrium with the atmosphere ii an intermediate euxinic layer with a lower 13cdic due to organic matter oxidation by ongoing sulphate reduction iii a bottom euxinic layer that seems to be restricted to the inner shelf lagoonal facies lacking sulphate containing methane and with a higher 13cdic due to dic production by methanogenesis if our model holds true it suggests that not only negative but also positive ediacaran carbon isotope excursions may reflect ocean stratification the positive excursion possibly recording a sulphate free methanogenic layer at the bottom of restricted basins

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

evolution of the zonal gradients across the equatorial pacific during the miocene pleistocene combining u k 37 0 and tex 86 derived temperatures and oxygen isotopic values of mixed layer and thermocline species from the iodp site u1338 east equatorial pacific and odp site 806 west equatorial pacific we assess the evolution of the zonal sea surface temperature gradients and thermocline depth across the equatorial pacific from the late miocene through the pleistocene data suggest a long term shoaling of the thermocline along the equator throughout the miocene pliocene that accelerated around 5 3 ma we identify a critical transition at about 3 8 ma from a el nino like dominated mean state during the late miocene and early pliocene to a la nina like dominated state during the late pliocene pleistocene this transition coincides with the restriction of the indonesian seaway and the onset of ice growth in the northern hemisphere and in antarctica that led to the long term strengthening of the walker circulation and affected low latitude zonal gradient

how earth s atmosphere evolved to an oxic state a status report the evolution of the earth s atmosphere is essentially the story of atmospheric oxygen virtually every realm of the earth sciences biology geology geochemistry oceanography and atmospheric science is needed to piece together an understanding of the history of oxygen over the past decade new data from these fields has shown that there were two significant increases in atmospheric o2 levels at around 2 4 2 3 and 0 8 0 6 billion years ago respectively throughout earth history oceanic sulfate concentrations appear to have increased in accord with greater o2 levels while levels of methane a strong greenhouse gas may have inversely mirrored o2 both oxic transitions occurred in eras characterized by bsnowball earthq events and significant disturbances in the carbon cycle perhaps associated with increases in o2 and losses of methane to understand what controlled the oxygenation of the atmosphere it is necessary to determine how o2 is consumed on geologic time scales through reaction with reductants released from the earth s crust and mantle there was apparently a long delay between the appearance of oxygenic photosynthesis and oxygenation of the atmosphere and a plausible explanation is that excess reductants scavenged photosynthetic o2 from the early atmosphere however a quantitative understanding of how and why o2 became abundant on our reducing planet is still lacking thus the study of the early atmosphere remains a frontier field with much to be discovered d 2005 elsevier b v all rights reserved

methane index a tetraether archaeal lipid biomarker indicator for detecting the instability of marine gas hydrates abstract gas hydrates represent one of the largest pools of readily exchangeable carbon on earth s surface releases of the greenhouse gas methane from hydrates are proposed to be responsible for climate change at numerous events in geological history many of these inferred events however were based on carbonate carbon isotopes which are susceptible to diagenetic alterations here we propose a molecular fossil proxy i e the methane index mi to detect and document the destabilization and dissociation of marine gas hydrates mi consists of the relative distribution of glycerol dibiphytanyl glycerol tetraethers gdgts the core membrane lipids of archaea the rational behind mi is that in hydrate impacted environments the pool of archaeal tetraether lipids is dominated by gdgt 1 2 and 3 due to the large contribution of signals from the methanotrophic archaeal community our study in the gulf of mexico cold seep sediments demonstrates a correlation between mi and the compound specific carbon isotope of gdgts which is strong evidence supporting the mi methane consumption relationship preliminary applications of mi in a number of hydrate impacted and or methane rich environments show diagnostic mi values corroborating the idea that mi may serve as a robust indicator for hydrate dissociation that is useful for studies of global carbon cycling and paleoclimate change

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

the effect of rising atmospheric oxygen on carbon and sulfur isotope anomalies in the neoproterozoic johnnie formation death valley usa abstract carbonates within the rainstorm member in the terminal neoproterozoic johnnie formation of death valley california record a remarkable negative carbon isotope anomaly to a nadir of near 11 that accompanies a dramatic rise in trace sulfate abundance and fall of carbonate associated sulfate 34 s values the carbonates including the laterally extensive johnnie oolite were deposited during marine flooding atop a sequence boundary best observed in cratonward sections the 12 c rich alkalinity delivered to the seawater pool was likely associated with a dramatic rise in atmospheric o 2 which resulted in 1 the oxidation of exposed continental shelf sediments rich in fossil organic matter and sulfides and 2 the ventilation of the oceans similar carbon isotope anomalies are recorded in broadly equivalent successions that post date known marinoan glacial deposits and pre date the precambrian cambrian boundary in oman india china australia and namibia supporting the view that the oxygenation event was global thus the biogeochemical anomaly post dates the last widely recognized neoproterozoic ice age but is nonetheless associated with sea level drawdown that is likely to be eustatic in origin the radiation of a high diversity microbiota and the first appearance of large metazoan fossils ediacaran animals follow this carbon isotope anomaly suggesting that a critical threshold with respect to atmospheric o 2 had been crossed by this time a negative excursion of similar magnitude occurs in overlying strata at the precambrian cambrian boundary which likely reflects similar processes