estimating eruption temperature from thermal emission spectra of lava fountain activity in the erta ale ethiopia volcano lava lake implications for observing io s volcanoes 1 we have analysed high spatial resolution and high temporal resolution temperature measurements of the active lava lake at erta ale volcano ethiopia to derive requirements for measuring eruption temperatures at io s volcanoes lava lakes are particularly attractive targets because they are persistent in activity and large often with ongoing lava fountain activity that exposes lava at near eruption temperature using infrared thermography we find that extracting useful temperature estimates from remote sensing data requires a high spatial resolution to isolate lava fountains from adjacent cooler lava and b rapid acquisition of multi color data because existing spacecraft data of io s volcanoes do not meet these criteria it is particularly important to design future instruments so that they will be able to collect such data near simultaneous data at more than two relatively short wavelengths shorter than 1 m are needed to constrain eruption temperatures resolving parts of the lava lake or fountains that are near the eruption temperature is also essential and we provide a rough estimate of the required image scale

a 5 million year comparison of mg ca and alkenone paleothermometers geochemical sea surface temperature sst proxies such as the magnesium to calcium ratio mg ca in foraminifera and the alkenone unsaturation index uk 37 are becoming widely used in pre pleistocene climate records this study quantitatively compares previously published mg ca and uk 37 data from ocean drilling program odp site 847 in the eastern equatorial pacific to assess the utility of these proxies to reconstruct tropical sst over the last 5 ma foraminiferal mg ca sst calibrations that include a dissolution correction are most appropriate at this location because they provide sst estimates for the youngest sample that are close to modern mean annual sst the long term trends in the two records are remarkably similar and confirm a 3 5 c cooling trend from the early pliocene warm period to the late pleistocene noted in previous work absolute temperature estimates are similar for both proxies when errors in the dissolution correction used to estimate sst from mg ca are taken into account comparing the two sst records at odp site 847 to other records in the region shows that the eastern equatorial pacific was 2 4 c warmer during the early pliocene compared to today

distribution and significance of novel low molecular weight sterenes in an immature evaporitic sediment from the jinxian sag north china abstract an unusual series of c 22 c 27 monounsaturated sterenes and c 24 c 30 tetracyclic terpanes 17 21 seco hopanes were detected in relatively high concentrations in an immature evaporitic marl sediment of the jinxian sag bohai bay basin north china the site of unsaturation in these novel sterenes is assigned tentatively to the d ring on the basis of mass spectral interpretation which also distinguishes them from reported unsaturated sterenes other hydrocarbon biomarker or stable isotope characteristics are indicative of microbial e g methyl hopanes phytoplankton or higher plant depleted 13 c values of isoprenoids and hopanes inputs and an anoxic carbonate depositional environment hexacyclic hopanes tetracyclic terpanes the hydrocarbon composition showed no obvious biodegradation and the relatively high concentration of unsaturated terpenoids e g gammacerene and low values of other established maturity parameters t s t m 0 23 r o 0 44 t max 417 c are consistent with sediments of low maturity the novel low molecular weight sterenes and the tetracyclic terpanes may be early diagenetic products of microbial sources in a carbonate environment

novel family of hexacyclic hopanoid alkanes c32c35 occurring in sediments and oils from anoxic paleoenvironments abstract four novel hexacyclic alkanes fairly common in crude oils and rock extracts from evaporitic series have been tentatively identified on the basis of gc ms data as c 32 c 33 c 34 and c 35 hexahydrobenzohopanes these structures only recorded in carbonate anhydrite sequences i e very anoxic paleoenvironments tend to concentrate when pristane to phytane ratios increase changes in their relative concentration to hopanes appear to be more related to variations in source and or environmental conditions than to maturity the ratio of the novel hexacylic c 35 hopane to c 35 hopane compared with other biomarker ratios suggests that hexacyclic alkanes and hopanes are byproducts of the same hopanoid precursors via different chemical reactions in addition the novel hexacyclic alkanes are bacterially resistant and may serve as a useful family to define the paleoenvironment viz very anoxic of the parent source rock of a drastically biodegraded oil

mid holocene el nino southern oscillation enso attenuation revealed by individual foraminifera in eastern tropical pacific sediments holocene reconstructions of the el nino southern oscillation enso provide valuable perspective on its recent evolution and can be important for assessing its future optimal assessment of past enso variability requires observations from its center of action in the eastern equatorial pacific but these are limited due to paucity of high resolution paleoceanographic archives e g corals here we use a new approach to quantify past enso variance based on the oxygen isotopic composition 18 o of individual foraminifera globigerinoides ruber from deep sea sediments in the enso source region individual g ruber foraminifera behave as monthly recorders of sea surface conditions including enso extremes circumventing the lack of annual resolution in the sediments intrapopulation 18 o distributions derived with this method from a core near the galapagos islands reveal mid holocene reductions in variance of 50 requiring drastic attenuation of the enso amplitude furthermore mg ca thermometry indicates that mid holocene background conditions were accompanied by a stronger zonal temperature gradient that coincided with a northward displaced intertropical convergence zone itcz the results suggest that the position of the itcz is an important factor in the low frequency modulation of enso and could influence its future evolution

petroleum geology of the puguang sour gas field in the sichuan basin sw china abstract the puguang sour gas field in northeastern sichuan basin is the largest gas discovery in the paleozoic marine strata in china with at least 9 trillion cubic feet tcf of proven gas reserves it is one of the many anticlinal structures formed during the indo sinian orogeny with gas being trapped in a composite structure lithology pool the presence of the upper permian coal measures lower silurian and lower cambrian marine shales provided excellent hydrocarbon source rocks the lower triassic and upper permian oolitic dolomites serve as high quality reservoir rocks with 10 25 porosity and 1 1000 md permeability largely due to diagenetically produced secondary porosity the lower and middle triassic evaporate beds have acted as the direct top seal for the large lower triassic upper permian gas accumulation the thick upper triassic and jurassic mudstone beds regionally cap the underlying marine carbonate strata the deep seated basement faults acted as vertical hydrocarbon migration conduits during faulting and became effective flow barriers when the faulting ceased the deep burial of a paleo oil accumulation in reservoirs rich in sulfate resulted in extensive thermochemical sulfate reduction tsr this together with the new gas injection and structural reconfiguration transformed a paleo oil pool to a large sour gas pool

early generation of 20s 5α h 14α h 17α h and 5α h 14β h 17β h steranes in low salinity lacustrine shales abstract a quantitative sterane biomarker study was conducted on a series of paralic freshwater lacustrine shale samples ranging in maturity from immature to near oil window maturity taken from section 3 of the shahejie formation es3 in the liaohe basin n e china concentrations of 5 h 14 h 17 h 20s and 5 h 14 h 17 h steranes remain nearly constant throughout the sample suite however the decrease in the absolute concentrations of the 20r 5 h 14 h 17 h c 29 steranes with increasing maturity results in an increase in the conventionally defined maturity parameters 20s 20 s 20r and sterane ratios in addition the data suggest that relatively early generation of 5 h 14 h 17 h 20s and 5 h 14 h 17 h steranes has occurred in lacustrine sediments with a vitrinate reflectance 0 3 r o the data provide strong support for the major importance of relative thermal stability of epimers but do not exclude the possibility of isomerization as a viable mechanism for production

the evolution of el nino past and future abstract we review forecasts of the future of el nino and the southern oscillation enso a coupled instability of the ocean atmosphere system in the tropical pacific with global impacts enso in the modern world is briefly described and the physics of the enso cycle is discussed particular attention is given to the bjerknes feedback the instability mechanism which figures prominently in enso past and future our knowledge of enso in the paleoclimate record has expanded rapidly within the last 5 yr the enso cycle is present in all relevant records going back 130 kyr it was systematically weaker during the early and middle holocene and model studies indicate that this results from reduced amplification in the late summer and early fall a consequence of the altered mean climate in response to boreal summer perihelion data from corals shows substantial decadal and longer variations in the strength of the enso cycle within the past 1000 yr it is suggested that this may be due to solar and volcanic variations in solar insolation amplified by the bjerknes feedback there is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future but it is very far from conclusive the comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of enso s future some predict more enso activity some less with the highly uncertain consensus forecast indicating little change

diversity of enso events unified by convective threshold sea surface temperature a nonlinear enso index author s williams in patricola cm abstract 2018 american geophysical union all rights reserved we show that the well known failure of any single index to capture the diversity and extremes of el nino southern oscillation enso results from the inability of existing indices to uniquely characterize the average longitude of deep convection in the walker circulation we present a simple sea surface temperature sst based index of this longitude that compactly characterizes the different spatial patterns or flavors of observed and projected enso events it recovers the familiar global responses of temperature precipitation and tropical cyclones to enso and identifies historical extreme el nino events despite its simplicity the new longitude index describes the nonlinear relationship between the first two principal components of sst and unlike previous indices accounts for background sst changes associated with the seasonal cycle and climate change the index reveals that extreme el nino el nino modoki and la nina events are projected to become more frequent in the future at the expense of neutral enso conditions

uncommon steranes in brazilian marginal crude oils dinoflagellate molecular fossils in the sergipe alagoas basin brazil comprehensive two dimensional gas chromatography with time of flight mass spectrometry gc gc tofms was used to identify unusual steranes in branched cyclic hydrocarbon fractions of crude oils from sergipe alagoas basin brazil and infer the geochemical settings of their cretaceous source rocks hopane sterane and sterane ratios and the presence of gammacerane and carotane in the oil samples indicates a saline source rock depositional environment and predominantly marine organic matter om input steroidal hydrocarbons were represented by alkyl steranes and several sterane series including abundant short chain steranes c21 and c22 regular steranes c27 c29 and diasteranes c21 c23 c27 c29 the ring a methyl sterane series contained 3 methyl steranes c22 and c23 c28 c30 abundant 3 methyldiginane c22 and 3 methyldiacholestanes c28 including 4 methyl steranes with abundant c30 4 23 24 trimethylcholestanes in the branched cyclic fraction of these crude oils the c29 sterane isomers 23 24 dimethylcholestane and 24 ethylcholestanes were resolved by gc gc tofms and a c29 dinosterane derivative was identified for the first time in brazilian crude oils the 23 24 dimethyl and 4 23 24 trimethyl steroids can be related to dinoflagellate om and abundant dinosteranes suggests dinoflagellate blooms during source rock deposition in this brazilian marginal basin additionally the detection of c28 c32 3 alkyl cholestanes c29 c33 3 alkyl 24 methylcholestanes and c30 c34 3 alkyl 24 ethylcholestane with ethyl to pentyl groups at c 3 resulted in a complex sterane fingerprint as expected for petroleum generated from source rocks deposited under predominantly marine saline conditions with high microalgal input these biomarker results provide additional insight into the character and geologic processes responsible for the source rocks of crude oils in the brazilian marginal basins this information will be a valuable exploration tool that can be used to constrain the distribution of different oil types in these basins

tropical ocean atmosphere controls on inter annual climate variability in the cretaceous arctic 1 the first annually resolved sedimentary record from the cretaceous is used to develop time series of inter annual and decadal scale climate variability from the arctic ocean analysis of records spanning 1000 years reveals strong periodicities in the quasi biennial oscillation and el nino southern oscillation enso band as well as a 14 year period which all closely match periodicities typical of modern high latitude climate variability this supports the view that an arctic ocean free of permanent sea ice would be driven by similar forcing to the present state implicating tropical ocean atmosphere interaction and demonstrating that stratosphere troposphere coupling likely played a prominent role in the transmission of cretaceous equatorial climate forcing to polar latitudes as has recently been established for the modern earth system on the other hand the prominent enso periodicities in our records argue against the hypothesized link between past warm climates and permanent el nino states

evaluating the sulfur isotopic composition of biodegraded petroleum the case of the western canada sedimentary basin abstract the sulfur isotopic composition 34s of petroleum is believed to be affected mainly by sulfur incorporation reactions into the sedimentary organic matter during the early diagenesis however secondary processes could affect the original 34s of oil under the effect of thermal maturity or of the microbial activity of biodegraded reservoirs in this study the different processes that may affect the 34s of in reservoir oils were assessed based on the sulfur content and isotopes of a series of oil and core samples coming from various reservoirs of the lower cretaceous mannville group western canada sedimentary basin wcsb based on the molecular study these samples appear to have reached various levels of maturity and biodegradation ranging from 0 to 6 5 on the biodegradation scale of peters and moldowan in addition mixing of organic matter coming from different source rocks was identified based on the comparison with extensive correlation studies performed in the wcsb investigation of the 34s shows a trend that seems a priori correlated to the level of biodegradation however a careful interpretation of molecular and sulfur isotope data leads to the conclusion that the observed 34s variations have rather to be ascribed to contributions of oils generated by various source rocks alternatively variations of 34s could neither be related to maturity differences nor to kinetic effects during organic sulfur compounds biodegradation in the case of some specific core samples showing a common origin based on biomarker study 34s variations might not be related to different sources but to secondary sulfur incorporation exchange processes occurring within the reservoir these processes would involve reduced sulfur species from bacterial sulfate reduction formed in situ or migrated into mannville reservoirs this hypothesis is supported by laboratory experiments showing sulfur exchange incorporation under plausible conditions for shallow reservoirs

ocean response to wind variations warm water volume and simple models of enso in the low frequency approximation abstract physical processes that control enso are relatively fast for instance it takes only several months for a kelvin wave to cross the pacific basin tk 2 months while rossby waves travel the same distance in about half a year compared to such short time scales the typical periodicity of el nino is much longer t 2 7 yr thus enso is fundamentally a low frequency phenomenon in the context of these faster processes here the author takes advantage of this fact and uses the smallness of the ratio ek tk t to expand solutions of the ocean shallow water equations into power series the actual parameter of expansion also includes the oceanic damping rate using such an expansion referred to here as the low frequency approximation the author relates thermocline depth anomalies to temperature variations in the eastern equatorial pacific via an explicit integral operator this allows a simplified formulation of enso dynamics based on an integro differential equation within this formulation

two dimensional gas chromatograms as fingerprints of sour gas associated oils abstract examining a well documented case history in western canada sedimentary basin using two dimensional gas chromatography gc gc has produced a useful tool for fingerprinting thermochemical sulfate reduction tsr affected petroleum fluids application of the approach and data interpretation strategies to the northeastern jinxian sag of bohai bay basin has provided molecular evidence for tsr as a plausible source for the h2s in the gases associated with the studied oils

comments by on organic geochemistry 36 1717 1730 abstract in this short communication we reply to the comments of worden and cai worden r h cai c f 2006 geochemical characteristics of the zhaolanzhuang sour gas accumulation and thermochemical sulfate reduction in the jinxian sag of bohai bay basin by zhang et al organic geochemistry 36 1717 1730 organic geochemistry 37 on the data and interpretation of zhang et al zhang s c zhu g y liang y b dai j x liang h b li m w 2005 geochemical characteristics of the zhaolanzhuang sour gas accumulation and thermochemical sulfate reduction in the jixian sag of bohai bay basin organic geochemistry 36 1717 1730 concerning the origin of an eocene sour gas and high sulfur oil accumulation from the jinxian sag bohai bay basin china we provide clarifications on the current temperature range of sour gas reservoirs and comment on the reliability of 34 s data of various sulfur species used by zhang et al 2005 and cai c f worden r h wolff g a bottrell s wang d l li x 2005 origin of sulfur rich oils and h 2 s in tertiary lacustrine sections of the jinxian sag bohai bay basin china applied geochemistry 20 1427 1444 we conclude that there is no verified evidence in support of bacteria sulfate reduction as the dominant geochemical process that contributed to the sour gases in the eocene reservoirs of the jinxian sag but more geological and sulfur isotope data are still needed to confirm the thermochemical sulfate reduction occurring in deeper parts of the petroleum reservoirs

short crested wave induced liquefaction in porous seabed to simplify a complicated problem most previous investigations of wave induced seabed response have been concerned with an isotropic seabed with uniform soil characteristics even though strong evidence of anisotropic soil behavior and variable soil characteristics has been reported in soil mechanics literature this paper proposes a finite element model to investigate the response of a cross anisotropic seabed with variable soil characteristics subjected to a three dimensional short crested wave system based on the present model together with the liquefaction criterion the wave induced liquefaction potential can be estimated the numerical results indicate that the influence of cross anisotropic soil behavior and variable soil characteristics on the wave induced seabed response including liquefaction potential cannot always be ignored without committing substantial errors

pacific variability under present day and middle miocene boundary conditions we use the coupled climate model mpi esm to show that for higher co2 levels the el nino southern oscillation enso and the pacific decadal oscillation pdo merge into a single mode of pacific variability regardless of present day or middle miocene 15 ma topographic boundary conditions hence topographic differences determining the landscape of past climates play a smaller role for pacific variability than previously thought we attribute the single variability mode to resonance between these two oscillation patterns in order to estimate the strength of the resonance we compute the spectral power of the enso and pdo time series and their coherence we find that for both middle miocene and present day topographic conditions higher co2 forcing leads to stronger resonance between enso and pdo our results show that 1 stronger co2 forcing enhances pacific variability resulting in stronger atmospheric bridge and that 2 past climates are likely to exhibit pacific variability corresponding either to enso pdo or our proposed single mode

simulating pliocene warmth and a permanent el nino like state the role of cloud albedo available evidence suggests that during the early pliocene 4 5 ma the mean east west sea surface temperature sst gradient in the equatorial pacific ocean was significantly smaller than today possibly reaching only 1 2 c the meridional sst gradients were also substantially weaker implying an expanded ocean warm pool in low latitudes subsequent global cooling led to the establishment of the stronger modern temperature gradients given our understanding of the physical processes that maintain the present day cold tongue in the east warm pool in the west and hence sharp temperature contrasts determining the key factors that maintained early pliocene climate still presents a challenge for climate theories and models this study demonstrates how different cloud properties could provide a solution we show that a reduction in the meridional gradient in cloud albedo can sustain reduced meridional and zonal sst gradients an expanded warm pool and warmer thermal stratification in the ocean and weaker hadley and walker circulations in the atmosphere having conducted a range of hypothetical modified cloud albedo experiments we arrive at our pliocene simulation which shows good agreement with proxy sst data from major equatorial and coastal upwelling regions the tropical warm pool middle and high latitudes and available subsurface temperature data as suggested by the observations the simulated pliocene like climate sustains a robust el nino southern oscillation despite the reduced mean east west sst gradient our results demonstrate that cloud albedo changes may be a critical element of pliocene climate and that simulating the meridional sst gradient correctly is central to replicating the geographical patterns of pliocene warmth

el nino like climate teleconnections in new england during the late pleistocene a glacial varve chronology from new england spanning the 4000 year period from 17 500 to 13 500 calendar years before the present was analyzed for evidence of climate variability during the late pleistocene the chronology shows a distinct interannual 3 to 5 years band of enhanced variability suggestive of el nino southern oscillation enso teleconnections into north america during the late pleistocene when the laurentide ice sheet was near its maximum extent and climatic boundary conditions were different than those of today this interannual variability largely disappears by the young end of the 4000 year chronology with only the highest frequency components roughly 3 year period persisting this record provides evidence of enso like climate variability during near peak glacial conditions

modulation of orbitally forced enso variation by tibetan plateau topography abstract the modulation of the orbitally induced variation in the el nino southern oscillation enso by tibetan plateau tp topography was investigated with four fully coupled ocean atmosphere model experiments under the modern boundary conditions the modeled orbitally induced enso change was strongly affected by the presence of the tp specifically in the experiments with orbital forcing at 6 ka in comparison to the counterpart experiments with modern orbital forcing it was shown that the orbitally forced enso variability was slightly weakened by 3 in the presence of the tp but increased significantly by 13 in the simulation of the absence of the tp this difference was primarily attributed to the anomalous zonal winds over the tropical central to eastern pacific in response to the increased summertime incoming insolation which was intrinsically related to the different changes in the asian monsoon and tropical pacific walker circulation under the absence of modulation by the tp the anomalous westerly winds dominated the equatorial pacific and favored the development of a stronger el nino event and in turn the further intensification of la nina due to the stronger heat discharge during the recession of the stronger el nino in contrast the simulation with the presence of the tp showed the enhanced easterly wind anomalies in the boreal summer over the tropical pacific which further reduced increased the magnitude of the el nino la nina event in the subsequent winter these results suggest that the tp is a potentially crucial boundary condition for evaluating the changes in the enso dynamics on orbital scales during the cenozoic

observations of warm water volume changes in the equatorial pacific and their relationship to el nino and la nina abstract this paper describes observed changes in surface winds sea surface temperature sst and the volume of water warmer than 20 c wwv in the equatorial pacific ocean for the period 1980 99 the purpose is to test recent hypotheses about the relationship between variations in wwv and the el nino southern oscillation enso cycle the results confirm inferences based on theory models and previous empirical analyses using proxy data namely sea level that enso involves a recharge and discharge of wwv along the equator and that the cyclic nature of enso results from a disequilibrium between zonal winds and zonal mean thermocline depth the authors also find that the magnitude of enso sst anomalies is directly related to the magnitude of zonal mean wwv anomalies furthermore for a given change in equatorial wwv the corresponding warm el nino sst anomalies are larger than the corresponding cold la nina anomalies this asymmetry between the warm and cold phases of the enso cycle implies differences

wave induced soil response in a nearly saturated sea bed of finite thickness consolidation and storage equations are used to develop a closed form solution for the wave induced pore pressure soil displacements and effective stresses in an elastic sea bed subject to a system of two intersecting waves a homogeneous soil matrix of finite thickness in isotropic and saturated conditions only is considered the three dimensional general solutions so developed are readily reducible to the conditions for soil of infinite thickness and also for the limiting cases of two dimensional progressive and standing waves for soil of finite thickness for which no explicit solutions have previously been available verification of this solution with results of two dimensional solutions available from a semi analytical method a boundary layer approximation and a numerical model is carried out validation is performed by comparison with experimental results the effects on wave induced pore pressure of sea bed thick ness shear modulus of soil and grain size are discussed les equations de stockag

complex patterns of steroidal biomarkers in tertiary lacustrine sediments of the biyang basin china gas chromatography gc gas chromatography mass spectrometry gc ms and gas chromatography mass spectrometry mass spectrometry gc ms ms with co injected synthetic standards were used to analyse the biomarker patterns of some tertiary lacustrine clayey dolomites from the biyang basin china the lithology low pr ph ratio and high gammacerane content of these sediments indicated that high salinity prevailed during their deposition the distributions of steroidal hydrocarbons were particularly unusual and several pseudohomologous series including regular steranes c27 c29 4 methyl steranes c28 c30 including dinosteranes 3b ethyl steranes c29 c31 lanostanes c30 c32 and a variety of other 3b alkylated steranes were identified 3b n propylcholestane 3b n propylstigmastane and 4 4 dimethylcholestane were identified using authentic standards and this is the first time these compounds have been unambiguously characterised in sediments crown copyright 2001 published by elsevier science ltd all rights reserved

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

pregnanes as molecular indicators for depositional environments of sediments and petroleum source rocks steroids with unconventional side chains have increasingly been applied as diagnostic markers for geological source and age assessments however one of the most distinctive characteristics the abnormal abundance of pregnane and homopregnane in ancient sediments and petroleum remains unresolved higher pregnane and homopregnane as well as c23 c26 20 n alkylpregnanes relative to the regular steranes were observed in samples collected from different petroleum basins in china these included precambrian marine carbonate derived petroleum nw sichuan basin lower paleozoic marine marl derived crude oils tarim basin and eocene hypersaline lacustrine carbonate source rocks and associated petroleum bohai bay basin however all of the samples have many common biomarker characteristics such as pristane phytane ratios 1 low amounts of diasteranes and high c29 c30 hopane 0 6 1 c35 c34 hopane mostly p 1 and dibenzothiophene phenanthrene dbt phen mostly 0 5 1 ratios revealing a contribution from anoxic carbonate marl source rocks deposited in restricted clastic starved settings we suggest that 5a l4b l7b pregnane and homopregnane as well as their higher c23 c26 homologues are geological products derived from steroids bound to the kerogen by a sulfurized side chain carbon or carbonate minerals are considered to be natural catalysts for this cracking reaction via preferential cleavage of the bond between c 20 and c 22 similar distributions occur in the short chain analogues of 4 methylsterane triaromatic steroid and methyltriaromatic steroid hydrocarbons providing circumstantial evidence for this proposal the ratio of pregnane and homopregnane to the total regular steranes and the ratio of c27 diasteranes to cholestanes can be sensitive indicators of sedimentary environments and facies in general high diasteranes and low pregnanes with homologues indicate an oxic water column or significant input of terrigenous organic matter in clay rich source rocks and some organic lean carbonate rocks low diasteranes with high pregnanes implies restricted sulfur rich conditions typical of anoxic carbonate source rocks furthermore the two ratios may be useful to assess the variation of mineralogy and openness of source rock depositional settings

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

what controls the mean east west sea surface temperature gradient in the equatorial pacific the role of cloud albedo abstractthe mean east west sea surface temperature gradient along the equator is a key feature of tropical climate tightly coupled to the atmospheric walker circulation and the oceanic east west thermocline tilt it effectively defines tropical climate conditions in the pacific its presence permits the el nino southern oscillation phenomenon what determines this temperature gradient within the fully coupled ocean atmosphere system is therefore a central question in climate dynamics critical for understanding past and future climates using a comprehensive coupled model community earth system model cesm the authors demonstrate how the meridional gradient in cloud albedo between the tropics and midlatitudes sets the mean east west sea surface temperature gradient in the equatorial pacific to change in the numerical experiments the authors change the optical properties of clouds by modifying the atmospheric water path but only in the shortwave radiation scheme of the model when is va

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

low temperature sulphate reduction biological versus abiological sulphate is considered to have been a major source of sulphide in strata bound and stratiform base metal sulphide deposits many of these deposits however appear to have been formed at moderate temperatures 200 c which poses the question by what mechanism s was sulphate reduced to sulphide two modes of reduction have been established experimentally 1 catalysis by sulphate reducing bacteria which at present is only known to occur below ca 100 c and 2 abiological reduction by ferrous iron or organic matter which has only been clearly shown above ca 250 c several attempts have been made to demonstrate abiological reduction below 200 c and some new data are presented here although the results do not exclude the possibility that such a reaction may be geochemically significant there has been no unequivocal demonstration of nett sulphide formation from sulphate at these temperatures recent studies of the microbiology of hydrothermal regions have opened up the prospect of bacterial sulp

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

numerical analysis of wave induced poro elastic seabed response around a hexagonal gravity based offshore foundation abstract in order to prevent the future risk of soil and structural failures for the offshore foundations it is essential to evaluate the seabed soil behaviors in the vicinity of the foundation under dynamic wave loadings the objective of this paper is to investigate the wave induced soil response and liquefaction risk around a hexagonal gravity based offshore foundation three dimensional 3d numerical analysis is performed by applying an integrated multiphysics model developed in the finite volume method fvm based openfoam framework the integrated model incorporates solvers of the nonlinear waves the linear elastic structure and the anisotropic poro elastic seabed soil the free surface model and soil model are verified by grid convergence studies the wave induced soil response model is validated by reproducing a laboratory experiment and a good agreement is obtained distributions of wave induced shear stress pore pressure vertical displacement and seepage flow structure in the seabed are investigated it is found that the presence of the foundation significantly amplifies the wave induced shearing effect and vertical displacement in the underlying seabed soil seabed consolidation state in the presence of the structure is evaluated since the foundation is embedded in the seabed at a depth the vertices of the hexagonal foundation cause the stress concentration in the nearby soil during the consolidation process therefore the momentary liquefaction at the vertices is not as significant as that at the edges due to the high initial effective stress a parametric study with different wave heights is conducted to examine the changes of soil response and momentary liquefaction depth around the hexagonal foundation effects of isotropic and anisotropic soil permeability on the pore pressure distribution are investigated it shows that the effect of anisotropic permeability should be considered for the medium sand that is modelled in the present study

the influence of thermochemical sulphate reduction on hydrocarbon composition in nisku reservoirs brazeau river area alberta canada abstract the upper devonian nisku formation reservoirs of the brazeau river area of west central alberta canada produce oil and sweet and sour gas condensate generally oil pools are located updip in the study area and sour 6 31 h2s gas condensate downdip h2s in the study area is formed by thermochemical sulphate reduction tsr all liquid hydrocarbons probably have one source with the duvernay formation being the most likely candidate assessing the relative maturity of the oils and condensates is difficult because of the wide variation in thermal maturity and the effects of tsr but the ratio of pristane n heptadecane does appear to decrease with increasing maturity for this sample set with increasing tsr the following changes were noted decrease in the saturate aromatic hydrocarbon ratio increase in the relative abundance of organo sulphur compounds e g benzothiophenes 34s values of liquid hydrocarbon samples approached the values for anhydrite of the nisku formation in the study area and an increase in 13c of the saturate fraction h2s concentrations in hydrodynamically isolated pools provide a good estimate of the extent of tsr in these reservoirs however other pools have anomalously high h2s concentrations for their depth suggesting that the h2s was generated at greater depths and migrated updip into these pools

robust enso across a wide range of climates abstractel nino southern oscillation enso is a pronounced mode of climate variability that originates in the tropical pacific and affects weather patterns worldwide growing evidence suggests that despite extensive changes in tropical climate enso was active over vast geological epochs stretching millions of years from the late cretaceous to the holocene in particular enso persisted during the pliocene when a dramatic reduction occurred in the mean east west temperature gradient in the equatorial pacific the mechanisms for sustained enso in such climates are poorly understood here a comprehensive climate model is used to simulate enso for a broad range of tropical pacific mean climates characterized by different climatological sst gradients it is found that the simulated enso remains surprisingly robust when the east west gradient is reduced from 6 to 1 c the amplitude of enso decreases only by 30 40 its dominant period remains close to 3 4 yr and the spectral peak stays above red noise t

two leading enso modes and el nino types in the zebiak cane model abstractmodern instrumental records reveal that el nino events differ in their spatial patterns and temporal evolutions attempts have been made to categorize them roughly into two main types eastern pacific ep or cold tongue and central pacific cp or warm pool el nino events in this study we use a modified version of zebiak cane mzc coupled model to examine the dynamics of these two types of el nino events we conducted linear eigen analysis of the model to show that there are two leading enso el nino southern oscillation modes with their sst patterns resembling those of two types of el nino thus we refer them as the ep and cp enso modes these two modes sensitively depend on the changes in the mean states the heat budget analyses demonstrate that the ep cp mode is dominated by thermocline zonal advective feedback therefore weak strong mean wind stress and deep shallow mean thermocline prefers the ep cp enso mode because of the relatively dominance of thermocline zonal advect

el nino southern oscillation variability from the late cretaceous marca shale of california changes in the possible behavior of el nino southern oscillation enso with global warming have provoked interest in records of enso from past greenhouse climate states the latest cretaceous laminated marca shale of california permits a seasonal scale reconstruction of water column flux events and hence interannual paleoclimate variability the annual flux cycle resembles that of the modern gulf of california with diatoms characteristic of spring upwelling blooms followed by silt and clay and is consistent with the existence of a paleo north american monsoon that brought input of terrigenous sediment during summer storms and precipitation runoff variation is also indicated in the extent of water column oxygenation by differences in lamina preservation time series analysis of interannual variability in terrigenous sediment and diatom flux and in the degree of bioturbation indicates strong periodicities in the quasi biennial 2 1 2 8 yr and low frequency 4 1 6 3 yr bands both characteristic of enso forcing as well as decadal frequencies this evidence for robust late cretaceous enso variability does not support the theory of a permanent el nino in the sense of a continual el nino like state in periods of warmer climate

the pliocene paradox mechanisms for a permanent el nino during the early pliocene 5 to 3 million years ago globally averaged temperatures were substantially higher than they are today even though the external factors that determine climate were essentially the same in the tropics el nino was continual or permanent rather than intermittent the appearance of northern continental glaciers and of cold surface waters in oceanic upwelling zones in low latitudes both coastal and equatorial signaled the termination of those warm climate conditions and the end of permanent el nino this led to the amplification of obliquity but not precession cycles in equatorial sea surface temperatures and in global ice volume with the former leading the latter by several thousand years a possible explanation is that the gradual shoaling of the oceanic thermocline reached a threshold around 3 million years ago when the winds started bringing cold waters to the surface in low latitudes this introduced feedbacks involving ocean atmosphere interactions that along with ice albedo feedbacks amplified obliquity cycles a future melting of glaciers changes in the hydrological cycle and a deepening of the thermocline could restore the warm conditions of the early pliocene

the occurrence of 19 28 bisnorlanostane derivatives in a plant fossil a novel geochemical degradation process of triterpenoids abstract four novel triterpene ketones bearing 24 methyl 28 nor and 24 methyl 19 28 bisnor 5 lanostane skeletons were identified in a fossil of a stem of a plant belonging to the lauraceae family the structures of these compounds have been determined by comparison of their spectral data with those of authentic specimens derived from lanosterol and 24 methylenecycloartanol this is the first finding of compounds bearing a 19 28 bisnorlanostane skeleton which implies a novel possible microbiological pathway of degradation of lanostanes in the sedimentary environment

a deep eastern equatorial pacific thermocline during the early pliocene warm period abstract during the early pliocene warm period 4 6 4 2 ma in the eastern equatorial pacific upwelling region sea surface temperatures were warm in comparison to modern conditions warm upwelling regions have global effects on the heat budget and atmospheric circulation and are argued to have contributed to pliocene warmth though warm upwelling regions could be explained by weak winds and or a deep thermocline the temporal and spatial evolution of the equatorial thermocline is poorly understood here we reconstruct temporal and spatial changes in subsurface temperature to monitor thermocline depth and show the thermocline was deeper during the early pliocene warm period than it is today we measured subsurface temperature records from eastern equatorial pacific odp transect sites 848 849 and 853 using mg ca records from globorotalia tumida which has a depth habitat of 50 100 m in the early pliocene subsurface temperatures were 4 5 c warmer than modern temperatures indicating the thermocline was relatively deep subsurface temperatures steeply cooled 2 3 c from 4 8 to 4 0 ma and continued to cool an additional 2 3 c from 4 0 ma to present compared to records from other regions the data suggests the pronounced subsurface cooling between 4 8 and 4 0 ma was a regional signal related to restriction of the isthmus of panama while continued cooling from 4 0 ma to present was likely related to global processes that changed global thermocline structure additionally the spatial evolution of the equatorial thermocline along a n s transect across odp sites 853 849 and 848 suggests an intensification of the southeast trades from the pliocene to present large scale atmospheric and oceanographic circulation processes link high and low latitude climate through their influence on equatorial thermocline source water regions and consequently the equatorial thermocline through these low latitude high latitude linkages changes in the equatorial thermocline and thermocline source water played an important role in the transition from the warm pliocene to the cold pleistocene

identification of c24 and c25 lanostanes in tertiary sulfur rich crude oils from the jinxian sag bohai bay basin northern china abstract unusual short chain lanostanes c 24 and c 25 and c 30 lanostane were identified in sulfur rich crude oils from the jinxian sag bohai bay basin northern china besides the regular steranes c 27 30 a series of 4 methyl steranes c 22 23 c 27 30 4 4 dimethyl steranes c 22 24 c 28 30 short chain steranes c 23 26 abundant pregnanes c 21 22 and androstanes c 19 20 together with sulfur containing steroids 20 thienylpregnanes and thienylandrostanes were detected in the aliphatic and branched cyclic hydrocarbon fraction of these crude oils a literature survey of some long chain sterane analogues e g a nor steranes norcholestanes c 30 steranes lanostanes and pregnanes seems to point to a sponge and or dinoflagellate source 4 methyl 4 4 dimethyl steroids and lanosterols 4 4 14 trimethyl steroids as the basic skeleton of lanostanes can be derived from methanotrophic bacteria thus a biological origin from a prokaryotic methylotroph can be used to explain the common source of abundant short chain steranes c 23 26 4 methyl c 22 23 and 4 4 dimethyl steranes c 22 24 as well as lanostanes c 24 25 and c 30 analogues in our oil samples generally the steroids appear to have been extensively sulfurized with sulfur substitution at the c 22 position in the side chain during the early stage of diagenesis which was readily subject to attack by bacterial degradation enzymatic cleavage and or abiotic oxidation as a consequence short chain sterane analogues e g abundant pregnanes and androstanes in this study and short chain lanostanes c 24 c 25 might later be released through cleavage of weak c s bonds at the c 22 carbon in the sulfurized steroids and lanostane sulfides finally the formation of the short chain c 24 c 25 lanostanes and distinctive occurrence of short chain steranes in this study can be well explained by microbial biodegradation of sulfurized lanostanoids and steroids in the reservoir

reduced el nino southern oscillation during the last glacial maximum el nino southern oscillation enso is a major source of global interannual variability but its response to climate change is uncertain paleoclimate records from the last glacial maximum lgm provide insight into enso behavior when global boundary conditions ice sheet extent atmospheric partial pressure of co2 were different from those today in this work we reconstruct lgm temperature variability at equatorial pacific sites using measurements of individual planktonic foraminifera shells a deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue resulting in reduced enso variability during the lgm compared to the late holocene these results suggest that enso was not tied directly to the east west temperature gradient as previously suggested rather the thermocline of the eastern equatorial pacific played a decisive role in the enso response to lgm climate

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

eocene el nino evidence for robust tropical dynamics in the hothouse much uncertainty surrounds the interactions between the el nino southern oscillation enso and long term global change past periods of extreme global warmth exemplified by the eocene 55 to 35 million years ago provide a good testing ground for theories for this interaction here we compare eocene coupled climate model simulations with annually resolved variability records preserved in lake sediments the simulations show pacific deep ocean and high latitude surface warming of approximately 10 degrees c but little change in the tropical thermocline structure atmosphere ocean dynamics and enso in agreement with proxies this result contrasts with theories linking past and future hothouse climates with a shift toward a permanent el nino like state

gas souring by thermochemical sulfate reduction at 140 c reply natural gas in the permian triassic khuff formation of abu dhabi contains variable amounts of h2s gas souring occurred through thermochemical sulfate reduction of anhydrite by hydrocarbon gases sour gas is observed only in reservoirs hotter than a critical reaction temperature 140 c petrographic examination of core from a wide depth range showed that the anhydrite reactant has been replaced by calcite reaction product only in samples deeper than 4300 m gas composition data show that only reservoirs deeper than 4300 m contain large quantities of h2s i e 10 at present day geothermal gradients 4300 m is equivalent to 140 c fluid inclusion analysis of calcite reaction product has shown that calcite growth only became significan at temperatures greater than 140 c thus three independent indicators all show that 140 c is the critical temperature above which gas souring by thermochemical sulfate reduction begins the previously suggested lower temperature thresholds for other sour gas provinces 80 130 c derive from gas composition data that may not allow adequately either for the reservoir temperature history or for the migration of gas generated at higher temperatures into present traps conversely published proposals for higher threshold temperature 180 200 c derive from short duration experimental data that are not easily extrapolated to geologically realistic temperatures and time scales therefore the temperature of 140 c derived from our study of the khuff formation may be th best estimate of temperature required for in situ thermochemical sulfate reduction to produce the high h2s concentrations encountered in deep carbonate gas reservoirs

the effect of subtropical cooling on the amplitude of enso a numerical study the effect of an enhanced subtropical surface cooling on el nino southern oscillation enso through the ocean tunnel is investigated using a coupled model here the term ocean tunnel refers to the water pathway that connects the equatorial upwelling water to the subtropical extratropical surface water the subtropical cooling is introduced through a reduction of the radiative convective equilibrium sst sstp in that region the sstp for the equatorial region is kept fixed it is found that an enhanced cooling in the subtropics results in a regime with stronger enso this is because an enhanced subtropical cooling reduces the temperature of the water feeding the equatorial undercurrent through the ocean tunnel the resulting larger difference between the warm pool sst and the temperature of the equatorial thermocline water the source water for the equatorial upwelling tends to increase the equatorial zonal sst contrast between the western and the eastern pacific in response to this destabilizing forcing to the coupled equatorial ocean atmosphere a stronger enso develops enso is found to regulate the time mean difference between the warm pool sst and the temperature of the equatorial undercurrent the findings provide further support for the heat pump hypothesis for enso which states that enso is an instability driven by the meridional differential heating over the pacific ocean and that enso regulates the long term stability of the coupled equatorial pacific climate the results also substantiate the notion that surface variability from higher latitudes may influence equatorial sst variability through the ocean tunnel

extended wind stress analyses for enso abstract surface wind stresses are fundamental to understanding el nino yet most observational stress products are too short to permit multidecadal enso studies two exceptions are the florida state university subjective analysis fsu1 and the ncep ncar reanalysis ncep1 which are widely used in climate research here the focus is on the aspects of the stress most relevant to enso namely the climatological background anomaly spectrum response to sst changes subannual noise forcing and seasonal phase locking and how these differ between fsu1 and ncep1 over the tropical pacific for 1961 99 the ncep1 stress climatology is distinguished from fsu1 by weaker equatorial easterlies stronger off equatorial cyclonic curl stronger southerlies along the peruvian coast and weaker convergence zones with weaker seasonality compared to fsu1 the ncep1 zonal stress anomalies x are weaker less noisy and show less persistent westerly peaks during el nino events ncep1 also shows a more stationary spec

wave induced stresses in unsaturated submarine sediments a simple method to solve the problem of pore pres sure and effective stresses induced by harmonic waves in a poroelastic sediment is presented by using biot s equation and a compatibility condition for elasticity the sediment is assumed to obey the effective stress principle in the normal definition for saturated sedi ments although it may contain gas bubbles occluded in the porewater the governing equation is a fourth order partial differential equation in terms of pore pressure or effective mean normal stress the solutions contain skempton s pore pressure coefficient b for unsaturated sediments with b 1 the pore pressure and effective stresses induced by wave action consist of two parts one part depends only on the wavelength and the other part depends on both the sediment and the wave characteristics the second part is out of phase with the wave when the submarine sediment is unsaturated the wave induced negative effective nor mal stresses become greater under the trough of waves a zone

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

natural gas constituent and carbon isotopic composition in petroliferous basins china abstract there are abundant gas resources in petroliferous basins of china large to midsize gas fields are found in eastern central and western of china however origin constituents and isotopic composition of natural gas in different gas fields are varied distinctly and some present strong chemical secondary alteration and show variation both in age and space based on the systematic analysis of constituents and carbon isotope of a large number of gas samples combined with the geological characteristics this paper classifies the origins of the gases explores the gas isotope characteristics and evolutionary regulation with the variation time and space and further discusses the distinctive geochemistry of the gases in china these gases are dominated by dry gas its methane carbon isotope values range from 10 to 70 ethane from 16 to 52 propane from 13 to 43 and butane from 18 to 34 the carbon isotopes of most gases show the characteristics of humic derived gas and crude oil cracked gas in addition large primary biogenic gas fields have been discovered in the qaidam basin inorganic derived alkane gases have been discovered in deep of the songliao basin half of these gas fields are characterized by the alkane carbon isotope reversal in different degrees research indicates there are several reasons can result in carbon isotope reversal firstly gas charge of different genetic types or different source in one gas reservoir may cause carbon isotope reversal besides high over mature evolution of gas can also lead to the carbon isotopic reversal of alkanes thirdly secondary alteration of hydrocarbons may also result in abnormal distribution of carbon isotope isotope transforms to unusual light and heavy

evidence for active el nino southern oscillation variability in the late miocene greenhouse climate an evaporite varve thickness record from the late miocene mediterranean reveals significant signals of interannual variability the frequency and persistence of which are compared with climatic oscillations affecting the region today sustained variability in the 2 7 yr band resembles the modern spectrum of the el nino southern oscillation enso and contrasts with that of the north atlantic oscillation nao the cyclicity of which is less stationary in frequency and less sustained in duration fully coupled climate model simulations demonstrate not only that enso variability persisted during the late miocene but also that its teleconnections may have extended further than today as high latitude climate modes weakened due to a reduced meridional temperature gradient enso appears to have exerted a stronger influence on the evaporative balance of the mediterranean in the late miocene than it does today this evidence suggests that the pacific prior to the northern hemisphere glaciation was characterized by ongoing interannual variability

a stability analysis of tropical ocean atmosphere interactions bridging measurements and theory for el nino abstract interactions between the tropical oceans and atmosphere permit a spectrum of natural modes of oscillation whose properties period intensity spatial structure and direction of propagation depend on the background climatic state i e the mean state this mean state can be described by parameters that include the following the time averaged intensity of the pacific trade winds the mean depth h of the thermocline and the temperature difference across the thermocline t a stability analysis by means of a simple coupled ocean atmosphere model indicates two distinct families of unstable modes one has long periods of several years involves sea surface temperature variations determined by vertical movements of the thermocline that are part of the adjustment of the ocean basin to the fluctuating winds requires a relatively deep thermocline and corresponds to the delayed oscillator the other family requires a shallow thermocline has short periods of a year or two has sea surface tempe

origin of sulfur rich oils and h2s in tertiary lacustrine sections of the jinxian sag bohai bay basin china abstract very high s oils up to 14 7 with h 2 s contents of up to 92 in the associated gas have been found in the tertiary in the jinxian sag bohai bay basin pr china several oil samples were analyzed for c and s stable isotopes and biomarkers to try to understand the origin of these unusual oil samples the high s oils occur in relatively shallow reservoirs in the northern part of the jinxian sag in anhydrite rich reservoirs and are characteristic of oils derived from s rich source rocks deposited in an enclosed and productive stratified hypersaline water body in contrast low s oils as low as 0 03 in the southern part of the jinxian sag occur in tertiary lacustrine reservoirs with minimal anhydrite these southern oils were probably derived from less s rich source rocks deposited under a relatively open and freshwater to brackish lake environment that had larger amounts of higher plant inputs the extremely high s oil samples 10 underwent biodegradation of normal alkanes resulting in a degree of concentration of s in the residual petroleum although isoprenoid alkanes remain showing that biodegradation was not extreme interestingly the high s oils occur in h 2 s rich reservoirs h 2 s up to 92 by volume where the h 2 s was derived from bacterial so 4 reduction most likely in the source rock prior to migration three oils in the jinxian sag have 34 s values from 0 3 to 16 2 and the oil with the highest s content shows the lightest 34 s value this 34 s value for that oil is close to the 34 s value for h 2 s 0 it is possible that h 2 s was incorporated into functionalized compounds within the residual petroleum during biodegradation at depth in the reservoir thus accounting for the very high concentrations of s in petroleum

geochemical characteristics of the zhaolanzhuang sour gas accumulation and thermochemical sulfate reduction in the jixian sag of bohai bay basin abstract natural gas from the zhaolanzhuang field of the jizhong superdepression bohai bay basin contains the highest proportions of h 2 s 40 92 among the sour gases encountered in china the gas payzones include the eocene oligocene kongdian formation ek and the es4 member of the shahejie formation the sedimentary sequence consists of halite anhydrite carbonate sandstone and shale interbeds deposited in the evaporative brackish water lacustrine salt lake setting in the deepest part of the jinxian sag the total thickness of evaporites is more than 1000 m of which halite accounts for over 40 various organic rich mudstones intercalated with the evaporites are currently within the conventional hydrocarbon window with a depth of 2500 3500 m and likely the source for the oil and sour gas in the zhaolanzhuang field the temperatures of the gas reservoirs range from 75 to 100 c too low for significant thermochemical sulfate reduction the co occurrence of abundant elemental sulfur with the sour gas and the 34 s values of the various sulfur containing compounds indicate that the h 2 s gases were most likely derived from much deeper source kitchens where significant thermochemical sulfate reduction has occurred

origin of deep strata gas of tazhong in tarim basin china abstract tazhong is located in the interior of the taklamakan desert in the tarim basin deep carbonates are targeted exploration areas with abundant gas and the largest ordovician gas condensate field has been discovered the hydrocarbon is mainly distributed in the reef shoal complex of the upper ordovician lianglitage formation and in the interbedded weathered reservoirs of the lower middle ordovician yingshan formation despite the deep burial depth of the reservoirs and strong heterogeneity the reservoir bodies are large multiple layered and enrichment in hydrocarbons indicates a great exploration potential the ordovician gas condensate reservoir in the tazhong consists mainly of methane with a gas dryness coefficient of 0 91 0 98 the ordovician gas in the tazhong belongs to secondary oil cracking gas the comprehensive analysis of natural gas composition stable carbon isotopes and adamantane content showed that the natural gas was from paleo reservoir cracking at depth basin geothermal history burial history fluid inclusion data and geological analysis show that the gas accumulation occurred 5 ma ago the sulfur isotope of sulfides the presence of 2 thia adamantane and existence of light co 2 carbon isotopes indicate that the h 2 s was formed via tsr the natural gas accumulated through migration along faults

sulfur isotope analysis of bitumen and pyrite associated with thermal sulfate reduction in reservoir carbonates at the big piney la barge production complex sulfur isotopes of solid bitumen and associated pyrite from the madison limestone in the big piney la barge production complex were measured using a secondary ion mass spectrometry sims method the solid bitumens a product of thermochemical sulfate reduction yielded 34s values of 18 9 3 9 that are consistent with inferred values for native mississippian sulfate in contrast coarse and fine grain pyrite grains were found to be 34s depleted with values similar to that of the produced h2s 34s 10 we interpret these results to indicate that two different sources of sulfate were involved with tsr within the madison limestone autochthonous anhydrite which is now completely replaced with calcite and permian age sulfate dissolved in the aquifer while checking for inclusions within the bitumen that could lead to erroneous measurement we found the bitumen possesses a 5 m rim and internal worm like features enriched in organic sulfur we hypothesize that the rim is the result of back reaction of the late forming h2s with the solid bitumen and that the 1 m diameter wormy features may result from liquid liquid immiscibility occurring at the high temperatures of formation

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

unprecedented occurrence of novel c26 c28 21 norcholestanes and related triaromatic series in evaporitic lacustrine sediments a novel series of c26 c28 21 norcholestanes and their triaromatic analogs have been tentatively identified as major components in eogene evaporitic sediments in jinxian sag of the bohai bay basin northern china these compounds may be viewed as representatives of a new class of molecules whose biological or diagenetic origin remains to be determined their unprecedented high abundance in the evaporitic lacustrine sediments and related oils show important source and or depositional environment controls in addition to thermal maturity

suppression of el nino during the mid holocene by changes in the earth s orbit a number of recent reports have interpreted paleoproxy data to describe the state of the tropical pacific especially changes in the behavior of the el nino southern oscillation enso over the holocene these interpretations are often contradictory especially for the eastern tropical pacific and adjacent areas of south america here we suggest a picture of the mid holocene tropical pacific region which reconciles the data enso variability was present throughout the holocene but underwent a steady increase from the mid holocene to the present in the mid holocene extreme warm el nino events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial pacific and largely arid coastal regions as in the present climate this picture emerges from an experiment in which a simple numerical model of the coupled ocean atmosphere system in the tropical pacific was driven by orbital forcing we suggest that the observed behavior of the tropical pacific climate over the mid to late holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics which dominates extratropical influences

soil response in cross anisotropic seabed due to standing waves the evaluation of wave induced seabed response is particularly useful for geotechnical and coastal engineers involved in the design of foundations for offshore structures however most previous theoretical investigations available considered only isotropic behavior in a porous seabed even though the behavior of anisotropic soil has been reported in the literature in this paper an analytical solution for the standing wave induced soil response in a cross anisotropic seabed is proposed based on the analytical solution presented the wave induced liquefaction potential can then be estimated the numerical results indicate that the soil response in a saturated cross anisotropic seabed of infinite thickness depends on both the wave condition and soil properties this result contradicts the conclusion obtained from the conventional isotropic models the effects of the anisotropic parameters on the wave induced liquefaction potential are also discussed in detail

origin of deep sour natural gas in the ordovician carbonate reservoir of the tazhong uplift tarim basin northwest china insights from gas geochemistry and formation water abstract deep sour gases are found in the ordovician carbonate reservoir of the tazhong uplift in the tarim basin northwest china all sour gases in this field are dominated by gas hydrocarbons c1 c4 with varying amounts of h2s most of the gases in the eastern tazhong are characterized by high gas dryness coefficients 0 95 13c enriched methane 13c1 ranging from 44 6 to 35 8 and small difference between values of the 13c2 and 13c1 13c2 1 in contrast the gases in the western tazhong are characterized by relatively low gas dryness coefficients mostly

predicting co2 occurrence on a regional scale southeast asia example abstract prediction of co 2 occurrence in natural gases is difficult owing to the interplay among basinal sources e g volcanic emanations carbonate hydrolysis and metamorphism organic diagenesis and maturation reservoir processes e g mineralogical transformations and poorly understood physicochemical phenomena e g differential solubility of gas components carbonate buffering phase segregation published approaches to assessing co 2 risk are based either on circumstantial evidence of basinal influences or statistical analysis of reservoir attributes the present study presents the results of empirical statistical and neural network analysis of co 2 abundance in natural gas and discusses potentially influential basinal and reservoir attributes to quantify risk factors for anomalous co 2 occurrences in southeast asia the results of this study indicate that tectonic setting including basement crustal age basement fault density reservoir temperature and reservoir pressure are key elements controlling co 2 abundance assignment of co 2 risk at the basin level can be roughly approximated using the results of this study more accurate assessments of co 2 risk at the basin play field and reservoir levels require more comprehensive geological and geochemical data as well as consideration of potentially influential physico chemical processes

response in seabed of finite depth with variable permeability conventional investigations of the wave seabed interaction have assumed that the seabed has an uniform permeability however the soil permeability in most marine sediments varies with burial depth due to consolidation under overburden pressure here an analytical solution describing the short crested wave induced soil response in a seabed with variable permeability is derived the soil matrix considered here is hydraulically anisotropic and of finite thickness the wave induced soil response is obtained from a set of governing equations incorporating a variable permeability the results indicate that the soil response is affected significantly by variable permeability the influences of soil characteristics on the relative differences in pore pressure between the solutions for variable and uniform permeability are detailed

seabed shear modulus profile inversion using surface gravity water wave induced bottom motion summary the motion of a layered seabed induced by propagating gravity water waves is modelled by the coupling matrix for a massless incompressible elastic bed according to yamamoto an amplitude inversion scheme is developed to extract the bottom shear modulus profile from the motion of the seabed at a point on the bed surface using the linear inverse theory combined with the yamamoto theory of wave seabed interaction numerical tests using synthetic data without noise confirmed that the inversion is unique and consistent the inversion technique is applied to a set of field data from the mississippi river delta a good agreement is obtained between the inverted profile and the direct measurements

sulfur isotope ratios in petroleum research and exploration williston basin the three major types of crude oil in the williston basin the type i oils of the winnipeg red river system the type ii oils of the bakken madison system and the type iii oils of the tyler pennsylvanian system can be distinguished by their sulfur isotope compositions they have characteristic dgr34s values of 5 8 1 2 parts per thousand ppt 2 8 0 8 ppt and 4 0 0 7 ppt respectively highly mature oils have less typical values type ii oils which have migrated over a distance of some 150 km beyond the region of generation have maintained their characteristic dgr34s values even though sulfur may have been lost this indicates little or no interaction with reservoir sulfates under normal circumstances on the periphery of the basin type ii oils altered by water washing and biodegradation have altered dgr34s values which increase from 2 9 to 9 4 ppt with the increasing degree of crude oil degradation the bakken shales source of the type ii oils have dgr34s distribution patterns in the reduced sulfur typical of marine sediments the dgr34s values for the type ii oils match most closely the dgr34s value of organic sulfur in the black bituminous shales of the lower bakken

aerobic methanotrophy at ancient marine methane seeps a synthesis abstract the molecular fingerprints of the chemosynthesis based microbial communities at methane seeps tend to be extremely well preserved in authigenic carbonates the key process at seeps is the anaerobic oxidation of methane aom which is performed by consortia of methanotrophic archaea and sulphate reducing bacteria besides the occurrence of 13 c depleted isoprenoids and n alkyl chains derived from methanotrophic archaea and sulphate reducing bacteria respectively 13 c depleted triterpenoids have been reported from a number of seep deposits in order to evaluate the significance of these apparently non aom related molecular fossils the biomarker inventories of one campanian and two miocene methane seep limestones are compared these examples provide strong evidence that methane was not solely oxidized by an anaerobic process structural and carbon isotope data reveal that aerobic methanotrophy was common at some ancient methane seeps as well the miocene marmorito limestone contains abundant 3 methylated hopanoids 13 c 100 most likely 3 methylated hopanepolyols prevailing in aerobic methanotrophs were the precursor lipids of these compounds a series of isotopically depleted 4 methylated steranes lanostanes 13 c 80 to 70 and similarly isotopically depleted 17 h 21 h 32 hopanoic acid in the miocene pietralunga seep limestone also are derived probably from aerobic methanotrophs lanosterol which is known to be produced by aerobic methanotrophs is the most likely precursor of 4 methylated steranes less obvious is the origin of 8 14 secohexahydrobenzohopanes 13 c 110 to 107 in late cretaceous seep limestones these hopanoids probably reflect early degradational products of precursor lipids locally produced by seep endemic aerobic methanotrophs

the south pacific meridional mode a mechanism for enso like variability in this study the authors investigate the connection between the south pacific atmospheric variability and the tropical pacific climate in models of different degrees of coupling between the atmosphere and ocean a robust mode of variability defined as the south pacific meridional mode spmm is identified in a multimodel ensemble of climate model experiments where the atmosphere is only thermodynamically coupled to a slab ocean mixed layer the physical interpretation of the spmm is nearly identical to the north pacific meridionalmode npmm withtheoff equatorialsoutheasttradewindvariabilityalteringthelatentheatflux and sea surface temperature sst and initiating a wind evaporation sst feedback that propagates signals into the tropics the authors also show that a positive cloud feedback plays a role in the development of this mode butthiseffectismodeldependent whilephysicallyanalogoustothenpmm thespmmhasastronger expression in the equatorial pacific and directly perturbs the zonal gradients of sst and sea level pressure slp on the equator thus leading to enso like variability despite the lack of ocean atmosphere dynamical coupling further analysis suggests that the spmm is also active in fully coupled climate models and observations this study highlights the important role of the southern hemisphere in tropical climate variability and suggests that including observations from the data poor south pacific could improve the enso predictability

geochemical characteristics of the zhaolanzhuang sour gas accumulation and thermochemical sulfate reduction in the jixian sag of bohai bay basin by zhang et al organic geochemistry 36 1717 1730 abstract in this discussion we compare the interpretation of data on an eocene sour gas and high sulfur oil accumulation from the jinxian sag bohai bay basin china provided by zhang s c zhu g y liang y b dai j x liang h b li m w 2005 geochemical characteristics of the zhaolanzhuang sour gas accumulation and thermochemical sulfate reduction in the jixian sag of bohai bay basin organic geochemistry 36 1717 1730 with our earlier published interpretation cai c f worden r h wolff g a bottrell s wang d l li x 2005 origin of sulfur rich oils and h 2 s in tertiary lacustrine sections of the jinxian sag bohai bay basin china applied geochemistry 20 1427 1444 while zhang s c zhu g y liang y b dai j x liang h b li m w 2005 geochemical characteristics of the zhaolanzhuang sour gas accumulation and thermochemical sulfate reduction in the jixian sag of bohai bay basin organic geochemistry 36 1717 1730 considered that tsr was the cause of the elevated h 2 s in contrast we concluded that bsr was the process responsible for the high concentrations of h 2 s this in turn led to the unusually high degree of sulfurization of the oil we here contend that there is no evidence in support of tsr in the eocene sediments of the jinxian sag bohai bay basin china

collective role of thermocline and zonal advective feedbacks in the enso mode the vertical advection of anomalous subsurface temperature by the mean upwelling and the zonal advection of mean sea surface temperature sst by anomalous current are known to be essential for the equatorial sst anomaly associated with the el nino southern oscillation enso in the coupled model these two processes are referred to as the thermocline feedback and the zonal advective feedback respectively using a version of a recharge oscillator model for enso obtained from the stripped down approximation of the cane zebiak type model it is demonstrated that these two feedbacks which are linked dynamically through the geostrophic approximation tend constructively to contribute to the growth and phase transition of enso however these two feedbacks control the leading coupled mode in different ways the thermocline feedback leads to a coupled mode through the merging of the damped sst mode and ocean adjustment mode whereas the zonal advective feedback tends to destabilize the gravest ocean basin mode with both of these feedbacks the leading modes of the coupled model still can be traced back to these different origins under moderate changes in the model setup the main consequence of these sensitivities is that the growth rate and frequency of the enso mode may be sensitive to slight changes in basic state parameters which control the strength of these feedbacks

a simplified finite element analysis of wave induced effective stresses and pore pressures in permeable sea beds the wave induced pore pressures and effective stresses in a saturated submarine sediment are treated by means of the finite element method by using the general theory of behaviour of the saturated poro elastic media presented by biot 1972 1973 field equations of motion are established by introducing a valid approximation for very slow phenomena the full formulation is simplified and the well known equations of consolidation are obtained stability conditions and accuracy of the process of solution are discussed a verification of the written finite element program is made by a comparative study with the infinite depth solution given by yamamoto 1978 and madsen 1978 the effects of bed thickness permeability and soil stiffness on the wave induced pore pressures effective normal stresses shear stresses horizontal and vertical displacement at the mud line and with depth are investigated by various examples the response of a heterogeneous sea bed to a harmonic wave loading is compared with a h

the origin and fate of 4 methyl steroid hydrocarbons i diagenesis of 4 methyl sterenes abstract treatment of 4 methylcholest 4 ene under mild acid conditions at low temperatures gives chemical evidence for certain features seen in the distributions of sedimentary 4 methyl steroid hydrocarbons and further indicates that many low temperature diagenetic reactions of steroids are explicable in terms of acid catalysed rearrangements specifically the results provide i indirect evidence that the 4 ene skeleton is a key intermediate in the dehydration of 4 methyl stanols in sediments ii an explanation for the distribution of 4 methyl sterenes and a nor sterenes in the lacustrine messel shale eocene iii an explanation for the presence of 4 methyl steranes in relatively immature sedimentary rocks despite the precursor stanols having the 4 methyl configuration with increasing maturity in the paris basin shales lower toarcian the less stable 4 methyl steranes decrease gradually in abundance relative to their 4 methyl counterparts at a rate fairly similar to the change in pristane stereochemistry