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

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

the influence of temperature ph and growth rate on the δ18o composition of inorganically precipitated calcite abstract the oxygen isotope composition of carbonate minerals varies with temperature as well as other environmental variables for carbonates that precipitate slowly under conditions that approach thermodynamic equilibrium the temperature dependence of 18 o uptake is the dominant signal and the measured 18 o content can be used as a paleotemperature proxy in the more common case where carbonate minerals grow in a regime where they are not in isotopic equilibrium with their host solution their oxygen isotope compositions are a convolution of multiple environmental variables here we present results from calcite growth experiments demonstrating the occurrence of large 2 non equilibrium oxygen isotope effects under conditions relevant to biogenic calcite growth and many natural inorganic systems we show that these non equilibrium effects vary systematically with ph and crystal growth rate an isotopic ion by ion crystal growth model quantifies the competing roles of temperature ph and growth rate and provides a general description of calcite water oxygen isotope fractionation under non equilibrium conditions the crystal growth model results show that 1 there are both equilibrium and kinetic contributions to calcite oxygen isotopes at biogenic growth rates 2 calcite does not directly inherit the oxygen isotope composition of dic even at fast growth rates 3 there is a kinetically controlled variation of about 1 per ph unit between ph 7 7 and 9 3 at constant growth rate for inorganic calcite as well as biogenic calcite and 4 extreme light isotope enrichments in calcite in alkaline environments are likely due to disequilibrium among dic species in aqueous solution the model can be extended to 13 c uptake into carbonates as well as clumped isotopes but additional data are needed to constrain the kinetic fractionation factors for carbon isotopes the experimental and model results constitute an important step in separating the relative influence of inorganic and biologic processes on isotopic fractionation and may aid the development of new paleoproxies based on non equilibrium effects

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

geochemical investigation of oils and source rocks from qianjiang depression of jianghan basin a terrigenous saline basin china abstract six oils and seven suspected source rocks from the jianghan saline basin in the central eastern part of china have been examined using a variety of geochemical techniques the results from this study show that oils from the third and fourth sections of the qianjiang formation eocene are derived from similar source materials but have a different source from the oils of xingouzui formation eocene in the same basin the oils of the xingouzui formation eocene are more mature and probably have a greater input of terrigenous source material and in all probability have migrated greater distances than the qianjiang oils oils from these sections are derived from an environment characterized as being extremely anoxic strongly reducing and highly saline the suspected source rocks examined in the study were from the qianjiang formation and were generally mature except for the shallowest sample the biomarker distributions in the suspected source rocks examined from the qianjiang formation were very different from those of the oils present in the same sections it is proposed that oils from the qianjiang formation have sources in addition to or exclusive of the suspected source rocks examined in this study

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

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

the influence of kinetics on the oxygen isotope composition of calcium carbonate paleotemperature reconstructions rely on knowledge of the equilibrium separation of oxygen isotopes between aqueous solution and calcium carbonate although oxygen isotope separation is expected on theoretical grounds the temperature dependence remains uncertain because other factors such as slow exchange of isotopes between dissolved co2 species and water can obscure the temperature signal this is problematic for crystal growth experiments on laboratory timescales and for interpreting the oxygen isotope composition of crystals formed in natural settings we present results from experiments in which inorganic calcite is precipitated in the presence of 0 25 m dissolved bovine carbonic anhydrase ca the presence of dissolved ca accelerates oxygen isotope equilibration between the dissolved carbon species co2 h2co3 hco3 co32 and water thereby eliminating this source of isotopic disequilibrium during calcite growth the experimental results allow us to isolate for the first time kinetic oxygen isotope effects occurring at the calcite water interface we present a framework of ion by ion growth of calcite that reconciles our new measurements with measurements of natural cave calcites that are the best candidate for having precipitated under near equilibrium conditions our findings suggest that isotopic equilibrium between calcite and water is unlikely to have been established in laboratory experiments or in many natural settings the use of ca in carbonate precipitation experiments offers new opportunities to refine oxygen isotope based geothermometers and to interrogate environmental variables other than temperature that influence calcite growth rates

hydrocarbon geochemistry of the puget sound region ii sedimentary diterpenoid steroid and triterpenoid hydrocarbons cyclic components of the aliphatic hydrocarbon mixtures extracted from puget sound sediment cores include a suite of c19 and c20 diterpenoid hydrocarbons of which fichtelite sandaracopimaradiene and isopimaradiene have been identified although apparently also derived from vascular plants these diterpenoid hydrocarbons have relative abundances distinctly different from the co existing plant wax n alkane suite five c27 c28 and c29 diasteranes and four c29 c30 and c31 17 h 21 h hopanes occur in relatively constant proportion as components of a highly weathered fossil hydrocarbon assemblage these chromatographically resolved cycloalkanes along with the strongly covarying unresolved complex mixture have been introduced to puget sound sediments from adjacent urban centres at increasing levels over the last 100 yr in the absence of any major oil spill naturally occurring triterpenoid hydrocarbons including hop 22 29 ene diploptene are also present a new group of c30 polyenes has been detected which contains compounds apparently structurally related to a co existing bicyclic c25 diene and to c20 and c25 acyclic multibranched hydrocarbons described in a previous paper barrick et al 1980

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

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

barium in deep sea bamboo corals phase associations barium stable isotopes prospects for paleoceanography abstract reconstruction of past seawater 138 134 banist barium isotopic compositions can augment existing proxies of water mass provenance and deep ocean circulation deep sea bamboo corals are uniquely poised to record ba isotopic variations given their widespread oceanographic distribution and incorporation of ambient ba in approximate proportion to that in surrounding seawater however the utility of such records requires knowing the phases hosting ba in deep sea coral skeletons that specimens faithfully capture modern ba isotopic chemistry and that internal skeletal variability relates principally to historical variations in the composition of ambient seawater we investigated each of these requirements using a stepped cleaning experiment a core top comparison of eight live collected specimens from the california margin 870 2 055 m against ambient seawater and through examination of historical variability in skeletal ba chemistry respectively first we report that non carbonate phases minimally contribute to bamboo coral ba ca obviating the need for chemical cleaning of live collected specimens second using newly obtained profiles of northeast pacific ba isotopic chemistry we observe that bamboo corals faithfully reflect ambient seawater with a taxonomically and environmentally invariant ba isotopic offset 138 134 bacoral sw of 0 37 0 03 2 sd n 8 the partition coefficient for ba k d ba is similarly insensitive to taxonomy but linearly decreases with depth the driving mechanism is unresolved third we find minimal ba ca and ba isotopic variability in historical growth representing the past century we interpret this invariance as evidencing the overall fidelity of deep sea bamboo corals for ambient ba chemistry over their long lifespans the insensitivity of 138 134 bacoral sw to environmental gradients indicates that the ba isotopic composition of bamboo corals can be solely interpreted in terms of seawater composition which should find myriad applications to the study of past ocean circulation over a range of timescales

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

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

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

steranes and triterpanes generated from kerogen pyrolysis in the absence and presence of minerals abstract steranes and triterpanes generated from pyrolysis of immature monterey formation kerogen in the presence and absence of calcite illite and montmorillonite reveal results that are both consistent and divergent with published data that reflect the use of these biological markers as maturation indicators the extent of isomerization of biomarkers generated from pyrolysis of kerogen at 300 c for 2 hours at c 20 in 14 h 17 h steranes at c 22 in 17 h 21 h hopanes and of 17 h 21 h hopanes correspond to early diagenetic stages in rock extracts from sedimentary basins isomerization increases with heating time and after 1000 hours attains values which correspond to the catagenetic stage in sedimentary basins or equivalent to that of mature oil stepwise pyrolysis of the kerogen indicates faster isomerization rates for steranes and triterpanes in the bitumen than for those retained in the kerogen structure confirming earlier studies presence of a mineral matrix can influence the isomerization of steranes and triterpanes considerably comparisons with results from kerogen heated alone for a given maturation stage show that calcite inhibits illite catalyzes slightly and montmorillonite has a pronounced catalytic effect on these reactions this effect results in early isomerization of steranes and hopanes corresponding to the catagenetic stage in the presence of montmorillonite while kerogen or kerogen with calcite held at the same temperature 300 c and time 10 hours only yield isomerized products which correspond to a diagenetic stage further illite and montmorillonite affect various isomerization reactions differently the fastest reaction is the isomerization at c 20 in 14 h 17 h steranes followed by that at c 22 in 17 h 21 h hopanes and the slowest is the formation of 14 h 17 h steranes these results show that maturation measurements of rock or oil samples from sedimentary basins which use biological markers have to take into account the mineral matrix effects which have been largely ignored until present

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

biodegradation of 25 norhopanes in a liaohe basin ne china oil reservoir a suite of reservoir cores in an oil column from the shuguang oil field liaohe basin ne china was characterized geochemically to investigate the behaviour of 25 norhopanes nhs during biodegradation the extracted bitumens show similar organofacies type and maturity levels with biodegradation as the primary control on compositional variation all bitumens suffered severe biodegradation influence which removed all regular steranes and most of the pentacyclic terpanes leaving nhs as dominant components in total ion chromatograms of the saturated hydrocarbon fraction however the nhs are not the endpoint of hopane destruction they are biodegraded as well biodegradation of nhs can be illustrated by significant depletion in their concentrations and systematic variation in ratios of resistant to vulnerable components throughout the oil column the biodegradation sequence is somewhat similar to normal pentacyclic terpanes among the nh series 18 25 30 bisnorneohopane is the most recalcitrant to biodegradation the 18 22 25 29 30 tetranorneohopane is more resistant to biodegradation than 17 22 25 29 30 tetranorhopane and 34nhs are more resistant than other nhs degradation of nhs provides a new angle to understanding the complicated inter relationships in subsurface biodegraded reservoirs

variations in seawater sr ca recorded in deep sea bamboo corals 1 a depth transect of deep sea bamboo corals along the california margin provides evidence that coral strontium to calcium ratios sr cacoral record seawater sr ca ratios sr casw a calibration was constructed utilizing sr cacoral ratios and previously published pacific sr casw data r2 0 53 n 12 p 0 01 sr cacoral mmol mol 4 62 sr casw mmol mol 36 64 sr casw is ultimately governed by the remineralization of sr containing shells of surface water derived marine organisms e g acantharia at intermediate water depths california margin sr cacoral records from 792 and 1295 m document fluctuations in sr casw that appear decadal scale these results suggest that sr casw may not be as stable as previously assumed and may be influenced by surface productivity on short timescales

a refined method for calculating paleotemperatures from linear correlations in bamboo coral carbon and oxygen isotopes bamboo corals represent an emerging paleoclimate archive with the potential to record variability at intermediate depths throughout much of the global ocean realizing this potential has been complicated by biologically mediated vital effects which are evident in linear correlations of skeletal carbon 13c and oxygen 18o isotope composition previous efforts to develop a bamboo coral 18o paleothermometer by accounting for such vital effects have not been completely successful as they still rely on empirical calibrations that are offset from the temperature dependence of abiogenic experiments here we describe an approach that better corrects for bamboo coral vital effects and allows paleotemperatures to be calculated directly from the abiogenic temperature dependence the success of the method lies in calculating apparent equilibrium carbon and oxygen isotope fractionation at the temperature ph and growth rate of each coral as well as in the use of model ii regressions rigorous propagation of uncertainty suggests typical errors of 2 3 c but in select cases errors as low as 0 98 c can be achieved for densely sampled and strongly correlated data sets this lower limit approaches the value attributed to uncertainty in ph and growth rate estimates alone as predicted by a series of pseudoproxy experiments the incorporation of isotopically light metabolic co2 appears to be negligible in most pacific corals but may be significant in atlantic specimens potentially requiring an additional correction the success of the method therefore hinges on how well complex environmental systems and biomineralization strategies are constrained with the most reliable temperatures occurring when calcifying fluid ph growth rate and incorporation of metabolic carbon into skeletal calcite are constrained using multiple geochemical proxies

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

effects of seawater ph and biomineralization on the boron isotopic composition of deep sea bamboo corals abstract the ocean is currently absorbing excess carbon from anthropogenic emissions leading to reduced seawater ph termed ocean acidification instrumental records of ocean acidification are unavailable from well ventilated areas of the deep ocean necessitating proxy records to improve spatio temporal understanding on the rate and magnitude of deep ocean acidification here we investigate boron carbon and oxygen isotopes on live collected deep sea bamboo corals genus keratoisis from a phtot range of 7 5 8 1 these analyses are used to explore the potential for using bamboo coral skeletons as archives of past deep sea ph and to trace anthropogenic acidification in the subsurface north atlantic ocean 850 2000 m water depth boron isotope ratios of the most recently secreted calcite of bamboo coral skeletons are close to the calculated isotopic composition of borate anion in seawater 11bborate for north atlantic corals and 1 2 higher than 11bborate for pacific corals within individual coral skeletons carbon and oxygen isotopes correlate positively and linearly a feature associated with vital effects during coral calcification 11b variability of 0 5 2 is observed within single specimens which exceeds the expected anthropogenic trend in modern north atlantic corals 11b values are generally elevated in pacific corals relative to 11bborate which may reflect ph driven physiological processes aiding coral calcification in environments unfavorable for calcite precipitation elevated 11b values are also observed proximal to the central axis in multiple atlantic and pacific specimens relative to 11bborate which might reflect ontogenetic variability in calcification rates although the observed boron isotope variability is too large to resolve the present anthropogenic ocean acidification signal at the studied depths in the north atlantic 0 03 0 07 ph units ph changes 0 1 units might still be reconstructed using 11b measurements in bamboo corals

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

organic geochemistry of the oils from the southern geological province of cuba abstract the aliphatic hydrocarbon composition acyclic isoprenoids hopanoids and steroids of oils from the most productive fields in the southern geological province of cuba have been studied this province is defined by its position with respect to the cretaceous overthrust belt generated during the formation of oceanic crust along the axis of the proto caribbean basin the relative abundances of 18 h 22 29 30 trisnorneohopane gammacerane and diasteranes suggest that pina oils are related to the carbonate oils from the placetas unit in the northern province low ts ts tm and c27 29 rr rr sd ratios the cristales and jatibonico oils exhibit some differentiating features such as higher ts ts tm and absence of gammacerane the oils from this province do not exhibit significant differences in either hopane c32 22s s r and c30 or sterane c29 20s s r maturity ratios however the relative content of 5 h 14 h 17 h cholestanes c29 ratio indicates that pina oils are more mature than cristales and jatibonico oils several of these oils cristales jatibonico and pina 26 are heavily biodegraded lacking n alkanes norpristane pristane and phytane the two former oils do not contain acyclic isoprenoid hydrocarbons other biodegradation products the 25 norhopanes are found in all the oils their occurrence is probably due to mixing of severely biodegraded oil residues with undegraded crude oils during accumulation in the reservoir

maturity mapping of northern gulf of mexico oils using biomarkers abstract the observed maturity trends determined from 481 northern gulf of mexico oils and offshore seeps follow the major geological trends of the basin in a manner consistent with published heatflow measurements onshore the luling mexia gilbertown pickens pollard fault zones appear to act as areas of enhanced heatflow as indicated by the high maturity of nearby oils near base of oil window to the north and south of these fault lines oils of reduced maturity are encountered offshore louisiana oils of lower maturity comparable to the middle to early oil window are found the low maturity of these oils appears to be linked to salt diapirism by contrast the mature condensates offshore texas appear to link in part with shale diapirism and growth faulting analyses of oils and seepage from the flexure trend area indicates that hydrocarbon maturity is reduced towards the south where the tertiary overburden thins

a process based model for non equilibrium clumped isotope effects in carbonates abstract the equilibrium clumped isotope composition of carbonate minerals is independent of the composition of the aqueous solution however many carbonate minerals grow at rates that place them in a non equilibrium regime with respect to carbon and oxygen isotopes with unknown consequences for clumped isotopes we develop a process based model that allows one to calculate the oxygen carbon and clumped isotope composition of calcite as a function of temperature crystal growth rate and solution ph in the model carbon and oxygen isotope fractionation occurs through the mass dependent attachment detachment kinetics of the isotopologues of hco 3 and co2 3 to and from the calcite surface which in turn influence the clumped isotope composition of calcite at experimental and biogenic growth rates the mineral is expected to inherit a clumped isotopic composition that is similar to that of the dic pool which helps to explain 1 why different organisms share the same clumped isotope versus temperature calibration curves 2 why many inorganic calibration curves are slightly different from one another and 3 why foraminifera coccoliths and deep sea corals can have near equilibrium clumped isotope compositions but far from equilibrium carbon and oxygen isotope compositions some aspects of the model can be generalized to other mineral systems and should serve as a useful reference in future efforts to quantify kinetic clumped isotope effects

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

classification of offshore gulf of mexico oils and gas condensates five groups of petroleums can be recognized in the offshore gulf of mexico on the basis of carbon isotope and sulfur isotope ratios sulfur content and relative abundances of nickel and vanadium of 355 oils analyzed 341 96 1 are evidently closely related and cannot be subdivided on the basis of carbon or sulfur isotopes we suggest that these oils represent a single broad superfamily however two subgroups within this set are distinguishable on the basis of sulfur content and relative abundances of nickel and vanadium group 1a sigma 13 c 26 5 0 4 parts per mil sigma 34 s 5 6 2 4 parts per mil s 0 25 0 15 v ni v 0 27 0 10 and group 1b sigma 13 c 26 5 0 3 parts per mil sigma 34 s 5 9 1 2 parts per mil s 0 73 0 43 v ni v 0 67 0 07 group 1a oils are broadly distributed across the louisiana and adjacent texas continental shelf whereas group 1b oils are found along the louisiana shelf edge and continental slope group 1b oils have substantial genetic affinities to those from the campeche shelf offshore mexico of mesozoic origin the remaining 14 analyzed petroleums include supermature condensates from offshore texas and oils from offshore southern florida believed to be cogenetic with those from the jurassic smackover formation a three dimensional appraisal of geohistory suggests that petroleum generation began in the eocene in the region of the rio grande delta progressed coastwise to the mississippi delta area by the miocene and then occurred in regions of progres ively deeper water during the pliocene pleistocene

saturated and olefinic hydrocarbons in recent sediments from the baltic sea abstract saturated and olefinic hydrocarbons in the top sections of contemporary sediments from four stations in the baltic sea teili 1 f 81 eb 1 and xv 1 were analysed by capillary gas chromatography and gc ms techniques the 0 2 2 4 4 5 and 10 11 cm sections showed a small unresolved complex mixture ucm however in all these sections a strong predominance of odd over even carbon numbered compounds exists indicating an insignificant petroleum hydrocarbon input in the areas studied the resolved hydrocarbons are of mixed marine autochthonous and terrigenous origin the 0 5 cm sections contained the highest proportions of short chain and branched chain hydrocarbons derived mostly from algae and bacteria in general an increase was observed in the ratios of saturated to unsaturated and of longer chain to short chain hydrocarbons with increasing depth because of the facile diagenesis of unsaturated components and faster biodegradation of short chain hydrocarbons in addition between one and seven hydrocarbons the exact structure of which could not be assigned were detected in the samples most of these components were cyclic and unsaturated and a number were triterpenes

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

biological markers in bitumens and pyrolyzates of upper cretaceous bituminous chalks from the ghareb formation israel abstract the sterane and triterpane distributions of three bituminous chalks from the upper cretaceous ghareb formation israel were investigated both in the original extractable bitumens and in extracts obtained after pyrolysis of whole rock and isolated kerogen samples at 450 c pyrolysis was performed in a closed system under hydrous whole rock and anhydrous conditions isolated kerogens the carbon number distributions of steranes and triterpanes differ significantly between original bitumen and pyrolyzates unlike the bitumens in which diasteranes were not detected the anhydrous pyrolyzates contain small amounts of diasteranes the presence of water during pyrolysis leads to an increase of sterane isomerization the abundant formation of diasteranes and an increase of the 18 h trisnorneohopane 17 h trisnorhopane ratio sterane isomerization maturation parameters show a closer match between original bitumen and pyrolyzates after pyrolysis in a closed system when compared with an open system

a novel microbial hydrocarbon degradation pathway revealed by hopane demethylation in a petroleum reservoir abstract the origin of 25 norhopanes is controversial despite their abundance in many biodegraded oils in a biodegraded oil reservoir we found concomitant and directionally opposite changes with depth in the concentrations of certain 17 hopanes and their 17 25 norhopane counterparts demonstrating microbially induced demethylation of hopanes these observations suggest a hitherto unknown biodegradation mechanism and provide insight into the poorly understood process of natural petroleum biodegradation

multiple oil families in the west siberian basin two major oil families are identified in the west siberian basin twenty six of 32 analyzed oils occur in jurassic and cretaceous reservoirs and are derived from anoxic marine upper jurassic bazhenov source rock based on geochemical comparison of oils and source rock extracts these oils are widely distributed both north and immediately south of the ob river and their biomarker ratios indicate a wide range of source rock thermal maturity from early to middle oil window van egan russkoye samotlor sovninsko sovyet olyenye ozynornoye and kogolym to peak oil window srednekhulym yem yegov vostochno surgut khokhryakov fedorov and urengoi to late oil window salym some of these oils have been mildly e g fedorov 75 to heavily e g russkoye biodegraded n the reservoir the bazhenov sourced oils show different compositions that support regional variations of organic facies in the source rock for example the anoxic marine bazhenov facies which generated the oils in the samotlor fedorov and nearby fields was particularly clay poor and sulfur rich six nonbiodegraded highly mature oils show geochemical characteristics that suggest they were derived from clastic rich lacustrine or nearshore marine source rocks dominated by terrigenous higher plant input like those in the lower to middle jurassic tyumen formation although no correlation was observed between the oils and a single rock sample yem yegov 15 from the formation the six oils occur in the tyumen taitym geologiche and cheremshan and fractured basement paleozoic gerasimov yagyl yakh and verchnekombar reservoirs in positions readily accessible to any oil migrating from the tyumen source rock for example at the gerasimov location the tyumen formation lies unconformably on weathered basement paleozoic reservoir rocks most of the probable tyumen sourced oils ar from south of the ob river but the occurrence of geologiche oil to the north suggests that related oils may be widespread in the basin

biomarker distributions in crude oils and source rocks from different sedimentary environments abstract the saturated and aromatic hydrocarbons from a significant number of oils and source rocks derived from terrestrial and marine organic matter have been analysed by gc and gc ms results show that certain classes of biomarkers including bicyclic sesquiterpanes tricyclic terpanes pregnanes methylsteranes rearranged steranes hopane sulfides benzohopanes long chain alkylbenzenes and pentacyclic triterpanes can be used to distinguish differences in source input and or depositional environments variations in the distributions of the naphthalenes phenanthrenes fluorenes dibenzofurans dibenzothiophenes naphthobenzothiophenes and triaromatic steroid hydrocarbons may also reflect disparities in source input or sedimentary environments

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

influence of temperature on the composition of magnesian calcite overgrowths precipitated from seawater a constant disequilibrium technique was used to determine the composition of magnesian calcite overgrowths precipitated on pure calcite seeds from artificial seawater at 5 25 and 40 c the amount of magnesium incorporated in the overgrowths at a given temperature is independent of the precipitation rate over a wide range of saturation states and is believed to correspond to a composition in true equilibrium with seawater the distribution coefficient of magnesium dmg2 c in the magnesian calcite overgrowths increases almost linearly with temperature being 0 0121 0 0013 at 5 c 0 0172 0 0022 at 25 c and 0 0271 0 0013 at 40 c these values apply only to magnesian calcites precipitated from standard composition seawater since a previous study has shown dmg2 c to be a function of the mg2 ca2 ratio in the parent solution results of this study are compared with values reported previously by other workers and with the compositional distribution of naturally occurring magnesian calcite cements and ooids found in seawater it appears that variations in temperature are not sufficient to account for the compositional variability of naturally occurring inorganic marine magnesian calcite cements

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

growth and composition of high mg calcite in the skeleton of a bermudian gorgonian plexaurella dichotoma potential for paleothermometry 1 we used a secondary ion mass spectrometry sims ion microprobe to analyze magnesium to calcium mg ca and strontium to calcium sr ca ratios of high mg calcite loculi within the skeleton of a shallow water gorgonian plexaurella dichotoma from bermuda a cross section of the gorgonian skeleton reveals loculi embedded within proteinaceous gorgonin arranged in concentric rings about the axial core viewed in cross section the loculi are fan shaped 10 140 m in diameter and composed of bundles of needle shaped crystals that appear to radiate out from a calcification center discrete sample spots each 20 m diameter were sputtered from successive loculi along a sample track 3 mm long over this distance 25 bands of high low density gorgonin couplets were encountered estimated to represent the period 1963 to 1988 mg ca ratios show an overall positive correlation with annual sea surface temperatures ssts that is strongest in the autumn months october december high resolution analyses along the growth axes of individual loculi reveal low variability and no trend consistent with our interpretation of seasonal growth of these calcite inclusions the sensitivity of mg ca to interannual changes in average autumn temperatures is 0 47 mmol mol per c conversely interannual variability in calcite sr ca does not follow the interannual variability in sst and may be influenced primarily by growth rate

petroleum geocghemistry of the tarragona basin spanish mediterranean off shore abstract nine oils obtained from the tarragona basin spanish mediterranean off shore have been characterized geochemically in order to asses their source and maturity histories miocene deposits constitute the only known rock with hydrocarbon source potential of the area the sterane distributions indicate a common marine source for all of them except for amposta crude the occurrence in this oil of a series of unique biological markers and distributions methylsteranes and hopanes gammacerane etc enables us to postulate that marginal hypersalline carbonate evaporite episodes may have occurred in the basin during highly restricted deposition in the miocene thus determining a different oil composition analysis of formation waters supports the restricted marine depositional environment of the tarragona basin as well as the observed biodegradation of the oils recovered on the tarragona platform the oils belong to a maturity sequence that has been defined by new indices based on the isomerization of methyl substituted aromatic hydrocarbons dibenzothiophenes and long chain alkyltoluenes furthermore a series of long chain isoalkylbenzenes have been tentatively identified and assigned as archaebacterial markers

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

long term behavior of hydrogeological structures associated with faulting an example from the deep crystalline rock in the mizunami url central japan abstract fracture zones around faults damage zones in crystalline rocks such as granite can act as significant transport pathways because the permeability of damage zones around active faults will likely be increased by the fracture network system understanding the characteristics and long term behavior of damage zones along smaller scale faults is important for the safety assessment of deep underground facilities in the plutons of an orogenic belt for example facilities for the disposal of high level radioactive waste therefore this paper describes the features of a damage zone and the long term behavior of its hydrogeological structures associated with faulting in an underground environment based on the results of geological and hydraulic investigations 300 and 500 m below ground level at the mizunami underground research laboratory central japan detailed borehole and gallery wall investigations show the distributions of fractures fracture fillings predominant fracture orientations groundwater inflow points and hydraulic transmissivity in and around a damage zone the results indicate that there are three stages in the development of hydrogeological structures the first stage is the formation of background fractures that formed after the temperature of granitic plutons decreased through the ductile brittle transition forming fractures under brittle deformation conditions the second stage is the formation of a damage zone and corresponding increase in hydraulic permeability as a result of the formation of relatively small fractures associated with faulting the third stage is the formation of fracture fillings because of the infiltration of groundwater through the damage zone decreasing the hydraulic permeability of the zone in the late third stage unconsolidated clayey fillings form in the large fractures associated with faulting resulting in decreased permeability of the fractures in the damage zone around the fault these results underline the importance of understanding the development stages to evaluate the effect of faulting in orogenic belt plutons

calibration of the calcite water oxygen isotope geothermometer at devils hole nevada a natural laboratory abstract the 18 o of ground water 13 54 0 05 and inorganically precipitated holocene vein calcite 14 56 0 03 from devils hole cave 2 in southcentral nevada yield an oxygen isotopic fractionation factor between calcite and water at 33 7 c of 1 02849 0 00013 1000 ln calcite water 28 09 0 13 using the commonly accepted value of calcite water t of 0 00020 k 1 this corresponds to a 1000 ln calcite water value at 25 c of 29 80 which differs substantially from the current accepted value of 28 3 use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in devils hole that is 8 c lower than the measured ground water temperature alternatively previously published fractionation factors would yield a 18 o of water from which the calcite precipitated that is too negative by 1 5 using a temperature of 33 7 c several lines of evidence indicate that the geochemical environment of devils hole has been remarkably constant for at least 10 ka accordingly a re evaluation of calcite water oxygen isotopic fractionation factor may be in order assuming the devils hole oxygen isotopic value of calcite water represents thermodynamic equilibrium many marine carbonates are precipitated with a 18 o value that is too low apparently due to a kinetic isotopic fractionation that preferentially enriches 16 o in the solid carbonate over 18 o feigning oxygen isotopic equilibrium

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

the geochemistry of deep sea coral skeletons a review of vital effects and applications for palaeoceanography deep sea corals were discovered over a century ago but it is only over recent years that focused efforts have been made to explore the history of the oceans using the geochemistry of their skeletal remains they offer a promising archive of past oceanic environments given their global distribution layered growth patterns longevity and preservation as well as our ability to date them using radiometric techniques this paper provides an overview of the current state of the art in terms of geochemical approaches to using deep sea coral skeletons to explore the history of the ocean deep sea coral skeletons have a wide array of morphologies e g solitary cup corals branching colonial corals and materials calcite aragonite and proteins as such their biomineralization strategies are diverse leading to complex geochemistry within coral skeletons notwithstanding these complications progress has been made on developing methods for reconstructing the oceanographic environment in the past using trace elements and isotopic methods promising approaches within certain coral groups include clumped isotopes and mg li for temperature reconstructions boron isotopes and radiocarbon for carbon cycling end and radiocarbon for circulation studies and 15 n p ca and ba ca for nutrient tracer studies likewise there is now a range of techniques for dating deep sea corals skeletons e g u series radiocarbon and determining their growth rates e g radiocarbon and 210 pb dating studies on historic coral populations in the atlantic southern ocean and pacific point to climate and environmental changes being dominant controls on coral populations over millennial and orbital timescales this paper provides a review of a range of successes and promising approaches it also highlights areas in which further research would likely provide new insights into biomineralization palaeoceanography and distribution of past coral populations

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

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

the origins of petroleum in the northern gulf of mexico abstract the distribution and chemistry of oils in the northern gulf of mexico and the adjacent onshore can be explained by multiple sources fades variations maturation and post generation alteration genetic families include jurassic smackover flexure trend upper cretaceous and paleogene oils smackover oils have high sulfur contents pristane phytane ratios c 35 c 34 hopane ratios 1 0 and c 30 c 29 hopane ratios usuall 1 0 flexure trend oils are similar and contain abundant extended hopanes high sulfur contents and v ni v 0 5 these oils are inferred to be sourced in upper jurassic lower cretaceous strata upper cretaceous oils contain a distinctive suite of tricyclic and nonhopanoid triterpanes oleanane is low or absent paleogene oils can be recognized by the presence of 18 h oleanane and a lack of extended hopanes these oils occur from south texas to southern and offshore louisiana two subfamilies can be recognized based on the relative abundance of triterpanes and steranes these oils have a presumed paleogene source mixing of oil types is quite prevalent at the geographic boundaries of oil types the initial control on the distribution of oil and gas in the northern gulf of mexico is provided by the areal extent of source rocks secondary control is due to cenozoic deposition which provides the thermal stress to generate as well as destroy oil salt tectonics provide conduits for migrating fluids to escape the zone of thermal destruction mesozoic source strata again become important in the deep gulf of mexico where cenozoic sediments thin

reproducibility of trace element profiles in a specimen of the deep water bamboo coral keratoisis sp abstract bamboo corals order gorgonacea family isididae are attractive prospects for deep sea paleoceanographic reconstruction capturing trace elements in their calcitic skeletons that may serve as environmental proxies with subdecadal resolution over multi century timescales we study the reproducibility and fidelity of trace element profiles ba mg sr mn u pb in a 420 year old specimen of the bamboo coral keratoisis sp from the se usa using laser ablation icp ms to obtain multiple replicate profiles we use spectral techniques to distinguish noise and irreproducible variations from fully reproducible geochemical fluctuations that are candidates for environmental signals by quantifying variability between profiles we assess the fidelity with which the corals potentially record environmental information barium is the most reproducible element in the skeleton with large fluctuations along different growth radii reproducing to within 4 both mg and sr have very uniform levels within the coral but display low amplitude irreproducible variations that might represent an internal biological process in the case of mg which has been proposed as a paleotemperature proxy this irreproducibility would represent an intrinsic uncertainty of 0 1 to 0 4 c both mn and pb contain some irreproducibility superimposed upon broad reproducible profiles that may be environmental signals some of the irreproducible pb fluctuations correlate with cracks and dark bands in the sample suggesting detrital or surface contamination uranium displays large amplitude variations which are not reproducible along different radii this suggests that uranium cannot be used for paleoenvironmental reconstruction and may show signs of early diagenesis a possibility that could complicate attempts to date young keratoisis sp samples by u series geochemistry the highly reproducible ba signal allows precise alignment of profiles and thus we can show that growth rate along one radius can vary by a factor of two relative to growth along a different radius there is no evidence that this large variation in relative growth rate affects either the mg or sr incorporation in addition geochemical anomalies in ba and mg indicate that the very central axis of the specimen may represent a different mode of growth this study suggests that keratoisis sp corals are imperfect recorders of geochemical information but do contain reproducible variations which are good candidates for environmental signals

linear correlations in bamboo coral δ 13 c and δ 18 o sampled by sims and micromill evaluating paleoceanographic potential and biomineralization mechanisms using δ 11 b and 47 composition abstract bamboo corals represent an intriguing paleoceanographic archive with the potential to reconstruct variations throughout the water column over multiple centuries realizing this potential partially depends on if and at what resolution timeseries of variability can be generated recent work demonstrates that bamboo coral growth temperature averaged over its entire lifespan can be derived from linear correlations in its carbon and oxygen isotope composition 13 c 18 o when the apparent equilibrium fractionations for a coral s growth rate and calcifying ph are used building on this method this study applies it to coeval coral skeleton to assess the possibility of extracting paleoceanographic timeseries from bamboo coral skeletons using boron isotope 11 b based ph estimates micromilled samples yield accurate paleotemperatures with uncertainties of 2 c this is attributed to the inability to measure 13 c and 18 o in exactly the same skeleton as is the case for micromilled samples a micromilled sampling strategy is therefore likely the most practical means of applying the method carbonate clumped isotopes 47 estimate temperatures slightly warmer than observed suggesting they may not accurately record the subtle variations of the latest holocene when interpreted in conjunction 18 o 11 b and 47 data suggest that ph up regulation plays a role in generating linear 13 c 18 o trends however oxygen isotope fractionation and 47 are lower than would be predicted by ph alone potential explanations for this discrepancy include biological processes that favor the incorporation of carbonate ion into coral skeleton uncertainties in the 11 b ph proxy the influence of magnesium on calcite fluid isotope fractionation or uncertainties in the fractionation factors used to calculate apparent equilibrium despite some remaining uncertainties the method can resolve many observed decadal scale thermocline temperature anomalies suggesting that appropriately located bamboo corals could help constrain the behavior of similar temporal variability prior to instrumental monitoring

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

the origin of 4 methyl steranes and pregnanes from tertiary strata in the qaidam basin china abstract a geochemical study of oils and source rocks in tertiary saline lake facies from the qaidam basin of china demonstrates that pregnanes are mainly derived from the thermal degradation of organic matter in source rocks synchronous with hydrocarbon genesis whereas 4 methyl steranes may principally be a product of microbial activity during diagenesis

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

controls on carbon isotope fractionation by diatoms in the peru upwelling region the fractionation of carbon isotopes during photosynthesis by phytoplankton is quantified for samples of suspended material collected along two transects across the peru continental margin in 1992 the magnitude of fractionation is estimated using the 13c of 24 methylcholesta 5 24 28 dien 3 ol diatoms and compared to that of c37 2 alkenone haptophytes isotopic fractionation by diatoms exhibits a wide range and large scatter when plotted against the reciprocal of the concentration of co2 aq while a strong correlation is observed for fractionation by alkenone bearing haptophytes diatom growth rates calculated from silicate concentrations and assuming monod growth kinetics normalized to co2 aq are well correlated to diatom fractionation factors these results support the concept that growth rates in addition to co2 concentrations impose a control on the fractionation of carbon isotopes by both taxonomic groups of algae in addition the very small fractionation factors for diatoms indicate that species in the peru upwelling region employed mechanisms which actively transport inorganic carbon into cells a size dependence is observed for the 13c of the diatom sterol 24 methylcholesta 5 24 28 dien 3 ol is enriched in 13c in samples of suspended material 20 m relative to the 20 m fraction this suggests that surface area to volume ratios also impose a control on the fractionation of carbon isotopes by diatoms a proposition that is supported by detailed cell geometry and isotopic data for two larger size fractions from one sample

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

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

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

oxygen isotope fractionation between calcite and fluid as a function of growth rate and temperature an in situ study the 18o content of carbonates expressed as 18o is widely used in paleothermometry yet it is clear from comparison of experimental results and natural carbonate samples that chemical isotopic equilibrium is not always achieved in nature this observation underscores the importance of exploring possible effects of growth rate on isotopic fractionation which is the focus of this study in situ secondary ion mass spectrometry sims analyses of 18o were performed on single crystals of experimentally grown calcite the change in growth rate v over time within each crystal was monitored by addition of multiple rare earth element ree spikes into the fluid from which the calcite grew the values of 18o in bulk calcites and experimental fluids were measured by stable isotope ratio mass spectrometers the average sims 18o overlaps with those determined by conventional mass spectrometry within analytical uncertainty the fractionation factor expressed as 18o approaches its equilibrium value in slowly grown calcites v 0 02 nm s and decreases by 1 5 with increasing growth rate from 10 3 to 0 34 nm s here 18o 103 ln 18o and 18o 18o 16o calcite 18o 16o fluid our results provide the first in situ evidence that under equilibrium conditions 18o may be depleted in the near surface region of calcite relative to the bulk crystal lattice and that this 18o depleted zone can be captured during rapid crystal growth crystal growth rate is therefore a potentially important consideration when using 18o in natural carbonates as a proxy for ocean and terrestrial temperature

bamboo coral ba ca calibration of a new deep ocean refractory nutrient proxy abstract it is poorly understood how intermediate water masses are affected by decadal scale climate via biogeochemical cycling export production and changes in circulation ventilation to this end a geochemical nutrient proxy from deep sea bamboo corals would provide decadal to centennial scale records of deep and intermediate water nutrient dynamics seawater barium basw has a nutrient like distribution in the water column similar to silicate so ba ca records in foraminifera shallow water surface corals and other deep sea corals have been used to trace refractory nutrients here we present the first calibration of a nutrient proxy from skeletal barium preserved in the calcitic internodes of deep sea bamboo corals collected from intermediate water depths a calibration was calculated from a broadly distributed suite of isidella and keratoisis corals spanning a silicate and basw gradient n 33 corals 300 2800 m ba ca b a m b o o c o r a l mol mol 0 079 0 008 ba sw nmol kg 4 205 0 870 r 2 0 77 n 33 the strong linear correlation between ba cabamboo coral and basw suggests that coral ba ca is a reliable recorder of seawater barium and therefore silicate we find a distribution coefficient dba for ba cabamboo coral of 1 3 0 2 similar to that of other corals surface and deep sea dwelling and inorganic calcium carbonate precipitation experiments dba 1 2 1 5 this suggests that ba incorporation is primarily driven by cationic substitution in bamboo corals and holds promise as a globally applicable refractory nutrient proxy we find interannual decadal scale variability in a ba cabamboo coral timeseries from a california margin coral san juan seamount 1295 m these data suggest that additional high resolution ba cabamboo coral records may reveal a connection between regional scale intermediate water biogeochemistry and low latitude surface ocean atmospheric climate

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

25 norhopanes formation during biodegradation of petroleum in the subsurface abstract quantitative data from petroleum systems in china liaohe basin and canada athabasca tar sands support the theory that 25 norhopanes are produced during biodegradation of petroleum in the subsurface within a single oil column both case histories showed increasing severity of degradation indicated by destruction of hopanes and production of 25 norhopanes downward to the oil water contact in the athabasca samples between the peters k e moldowan j m 1993 the biomarker guide interpreting molecular fossils in petroleum and ancient sediments prentice hall englewood cliffs new jersey p 363 scale of biodegradation levels 5 9 concentrations of c 28 20s triaromatic steroids and other biodegradation resistant compounds increased by 35 reflecting a concentration effect as a consequence of removal of more degradable compounds over the same interval the concentrations of c 28 17 25 norhopane and c 29 17 25 norhopane increased by an order of magnitude thus requiring that the balance be met by their net production during degradation a detailed molecular investigation of the athabasca bitumen revealed that c 30 17 hopane degrades faster than c 29 17 hopane whilst the rate of formation of both c 29 17 25 norhopane and c 28 17 25 norhopane are similar complicating a straightforward interpretation of demethylation of hopanes to form 25 norhopanes hopane degradation in the athabasca tar sand may also occur without the production of 25 norhopanes the results show that even within a single petroleum accumulation a number of mechanisms control changes in the abundance and composition of hopanes and 25 norhopanes

organic geochemistry of cuban oils i the northern geological province the isoprenoid hopanoid and steroid compositions of 15 oils from the most productive oil fields in cuba were studied to determine source rock depositional environments and organic matter sources the oils which are from the northern geological province of cuba and can be defined by the position with respect to the overthrust belt can be grouped into two families those from the remedios 1 and those from the placetas 2 tectonostratigraphic units remedios oils contain 17 h diahopane high relative amounts of 18 h 22 29 30 trisnorneohopane and diasteranes which is indicative of generation from clay rich source rocks the crude oils of the placetas unit exhibit a sterane hopane composition consistent with a carbonate origin nevertheless these polycyclic hydrocarbons exhibit significant changes in composition indicating that several organic matter sources e g a carbonate evaporitic origin of varadero and varadero sur oils have contributed to the oils from this unit the remedios oils are more mature evaluated from the c29 20s s r and c29 20r sterane indices than the placetas oils a wide range of biodegradation levels are encountered in these oils from 0 to 7 8 using the scale derived by volkman et al 1983 the high relative abundance of 25 norhopanes is a distinctive feature of remedios oils the presence of these compounds in lightly biodegraded or nondegraded oils corresponds to a mixing of paleobiodegraded oil with more recently sourced nondegraded oil in the reservoir the most biodegraded oil cantel exhibits c27rr rr sd and c29 20s s r sterane ratios c30 and ts ts tm hopane ratios that have been altered by microbial attack

reproducibility of ba ca variations recorded by northeast pacific bamboo corals trace elemental ratios preserved in the calcitic skeleton of bamboo corals have been shown to serve as archives of past ocean conditions the concentration of dissolved barium basw a bioactive nutrientlike element is linked to biogeochemical processes such as the cycling and export of nutrients recent work has calibrated bamboo coral ba ca a new basw proxy using corals spanning the oxygen minimum zone beneath the california current system however it was previously unclear whether ba cacoral records were internally reproducible here we investigate the accuracy of using laser ablation inductively coupled plasma mass spectrometry for ba cacoral analyses and test the internal reproducibility of ba ca among replicate radial transects in the calcite of nine bamboo corals collected from the gulf of alaska 643 720 m and the california margin 870 2054 m data from replicate ba ca transects were aligned using visible growth bands to account for nonconcentric growth smoothed data were reproducible within 4 for eight corals n 3 radii coral this intracoral reproducibility further validates using bamboo coral ba ca for basw reconstructions sections of the ba ca records that were potentially influenced by noncarbonate bound ba phases occurred in regions where elevated mg ca or pb ca and coincided with anomalous regions on photomicrographs after removing these regions of the records increased ba cacoral variability was evident in corals between 800 and 1500 m these findings support additional proxy validation to understand basw variability on interannual timescales which could lead to new insights into deep sea biogeochemistry over the past several centuries

multiple sources of alkanes in quaternary oceanic sediment of antarctica normal alkanes n c13n c36 isoprenoid hydrocarbons i c15 i c16 i c18 i c19 and i c20 triterpanes c27c32 and c27c29 are present in low concentrations offshore antarctica in near surface quaternary sediment of the wilkes land continental margin and of the western ross sea the distributions of these hydrocarbons are interpreted relative to possible sources and processes the hydrocarbons appear to be mixtures of primary and recycled material from marine and terrigenous sources the n alkanes are most abundant and are characterized by two distinct populations one of probable marine origin and the other likely from terrigenous vascular plant sources because the continent of antarctica today is devoid of higher plants the plant derived hydrocarbons in these offshore sediments probably came from wind blown material and recycled antarctic sediment that contains land plant remains from an earlier period of time isoprenoid hydrocarbons are partially recycled and mainly of marine origin the dominance of pristane over phytane suggests oxic paleoenvironmental conditions both modern and ancient triterpanes and steranes are present and the distribution of these indicates a mixture of primary and recycled bacterial algal and possible higher plant materials although the sampled sediments were deposited during the quaternary they apparently contain a significant component of hydrocarbons of pre quaternary age

sterane and triterpane patterns as diagnostic tools in the mapping of oils condensates and source rocks of the gulf of mexico region abstract four hundred and eighty one gulf of mexico oils and condensates can be subdivided into nine major families based on their sterane m z 217 218 and triterpane m z 191 177 biomarker mass chromatogram patterns these families are 1 carbonate sourced oils reservoired in jurassic cretaceous reservoirs onshore and plio pleistocene reservoirs offshore 2 austin chalk reservoired oils 3 tuscaloosa oils 4 wilcox reservoired oils la 5 south texas palaeogene reservoired oils 6 mississippi delta oils 7 post mature oils of uncertain affinities 8 migration contaminated oils showing attributes of a mixing of immature and post mature sources and 9 oils and condensates lacking biomarkers each oil family is concentrated in specific age defined producing trends ranging in age from jurassic to pleistocene for tertiary reservoirs these producing trends shift geographically with time in a manner analogous to the clockwise migrating cenozoic depocenter model for the northern gulf of mexico at least six ages of marine source rock deposition may be implicated in the genesis of these oils 1 the kimmeridgian oxfordian including smackover and norphlet formations 2 the aptian including pine island bexar and sunniland formations 3 the albian paluxy formation 4 the cenomanian turonian including eagle ford and tuscaloosa formations 5 the coniacian santonian eagle ford and austin chalk and 6 the palaeocene wilcox midway sparta formations the jurassic and cretaceous source rocks correspond to described oceanic anoxic events of probable global significance this paper will concentrate on describing the biomarker patterns of the oils and postulated source rocks but due to reasons of space isotopic elemental and other data will only be briefly discussed

polycyclic alkanes in a biodegraded oil from the kelamayi oilfield northwestern china abstract a comparison is made of the distributions of certain classes of saturated hydrocarbon biomarkers in an unaltered oil and a severely biodegraded oil from the kelamayi oilfield in the zhungeer basin of northwestern china both oils are thought to have the same source rock the n alkanes acyclic isoprenoids carotenoid derived alkanes and regular c27 c29 steranes which are present in the nondegraded oil were not detected in the biodegraded sample additionally the biodegraded oil shows an increase in the abundance oil and the presence of 17 h 25 norhopanes 17s h 25 norhopanes c 10 demethylated tricyclic terpanes and a c 10 demethylated c23 tetracyclic terpane which were not detected in the nondegraded oil c26 and c25 regular steranes appear to show a much greater resistance to microbial attack than the c27 c29 regular steranes as indicated by an isomer distribution for these low molecular weight steranes that is expected for nondegraded samples in the biodegraded oil unknown tricyclic compounds showing a base fragment ion of m z 219 and a similar carbon number abundance to the steranes in the nonbiodegraded sample are present in relatively high concentrations in the biodegraded oil these compounds are also present in very low abundance in some nondegraded oils from the kelamayi basin indicating that their much higher concentration in the microbialy altered oil is possibly due to their resistance to biodegradation however at present their derivation from the microbial alteration of steranes cannot be ruled out several series of bicyclic compounds are also present in higher concentrations in the biodegraded oil

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

the sources and deposition of organic matter in the late quaternary pigmy basin gulf of mexico abstract the concentration and carbon isotopic composition 13c of sedimentary organic carbon corg n c ratios and terrigenous and marine 13corg endmembers form a basis from which to address problems of late quaternary glacial interglacial climatic variability in a 208 7 m hydraulic piston core dsdp 619 from the pigmy basin in the northern gulf of mexico while interpretations of sedimentary 13corg time series records are often not unique paired analyses of 13corg and n c are consistent with the hypothesis that the corg in the pigmy basin is a climatically determined mixture of c3 photosynthetic terrigenous and marine organic matter confirming the earlier 13corg model of sackett 1964 a high resolution 1 4 2 9 ka sample 13corg record shows that sedimentary organic carbon in interglacial oxygen isotope sub stages 1 and 5a b are enriched in 13c average 1 values are 24 2 1 2 o and 22 9 0 7 o relative to pdb respectively while glacial isotope stage values 2 are relatively depleted 25 6 0 5 concentrations of terrigenous and marine sedimentary organic carbon are calculated for the first time using 13corg and corg measurements and empirically determined terrigenous and marine 13corg endmembers the net accumulation rate of terrigenous organic carbon is 4 3 2 6 times higher in isotope stages 2 4 than in sub stages 1 and 5a b recording higher erosion rates of terrigenous organic material in glacial times the concentration and net accumulation rates of marine and terrigenous corg suggest that the nutrient bearing plume of the mississippi river may have advanced and retreated across the pigmy basin as sea level fell and rose in response to glacial interglacial sea level change

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

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

temperature and vital effect controls on bamboo coral isididae isotope geochemistry a test of the lines method deep sea bamboo corals hold promise as long term climatic archives yet little information exists linking bamboo coral geochemistry to measured environmental parameters this study focuses on a suite of 10 bamboo corals collected from the pacific and atlantic basins 250 2136 m water depth to investigate coral longevity growth rates and isotopic signatures calcite samples for stable isotopes and radiocarbon were collected from the base the corals where the entire history of growth is recorded in three of the coral specimens samples were also taken from an upper branch for comparison radiocarbon and growth band width analyses indicate that the skeletal calcite precipitates from ambient dissolved inorganic carbon and that the corals live for 150 300 years with extension rates of 9 128 m yr a linear relationship between coral calcite 18o and 13c indicates that the isotopic composition is influenced by vital effects 18o 13c slope of 0 17 0 47 as with scleractinian deep sea corals the intercept from a linear regression of 18o versus 13c is a function of temperature such that a reliable paleotemperature proxy can be obtained using the lines method although the coral calcite 18o 13c slope is maintained throughout the coral base ontogeny the branches and central cores of the bases exhibit 18o 13c values that are shifted far from equilibrium we find that a reliable intercept value can be derived from the 18o 13c regression of multiple samples distributed throughout one specimen or from multiple samples within individual growth bands

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

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

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

oxygen and carbon isotope fractionation in calcitic deep sea corals implications for paleotemperature reconstruction abstract inhabiting areas of the ocean where paleoenvironmental records are sparse deep sea corals represent valuable yet largely untapped holocene records of intermediate and deep ocean variability 18o and 13c were analyzed in nine live collected deep sea gorgonian corals isididae and coralliidae in order to further develop the lines paleotemperature method least squares linear regression analysis for full lifespan 18o vs 13c corrected for 18owater and 13cdic was utilized to yield equations of the form y mx b 18o and intercept values were found to be a function of temperature and to approximate calcite 18o equilibrium the corals in this study extend the previously reported calibration hill et al 2011 over a broader range of temperatures from 5 c to 11 2 c when combined with the data from hill et al 2011 a new expression for the relationship between the 18ointercept value and temperature is proposed t c 4 12 0 38 18 o intercept 12 33 0 75 r 2 0 90 p value 0 0001 error estimates are 0 7 c for corals living at cold temperatures 2 c 1 4 c in warmer waters 11 c and 0 5 c at the mean water temperature of the data set 4 6 c the first multi specimen verification of the lines method was performed on three co located bamboo isididae corals and found to give nearly coincident 18o intercepts detailed intraspecimen sampling reveals 18o and 13c isotopic variability within coeval portions of the skeleton in one specimen lines method analysis was utilized on multiple samples taken from the same temporal increment of the skeleton yielding multiple 18o intercepts calculated temperatures using the calibration proposed here describe a temperature range of 7 9 to 10 3 c which approaches the temperature range of 11 1 0 7 c at the coral collection location