drift dynamics in a coupled model initialized for decadal forecasts drifts are always present in models when initialized from observed conditions because of intrinsic model errors those potentially affect any type of climate predictions based on numerical experiments model drifts are usually removed through more or less sophisticated techniques for skill assessment but they are rarely analysed in this study we provide a detailed physical and dynamical description of the drifts in the cnrm cm5 coupled model using a set of decadal retrospective forecasts produced within cmip5 the scope of the paper is to give some physical insights and lines of approach to on one hand implement more appropriate techniques of initialisation that minimize the drift in forecast mode and on the other hand eventually reduce the systematic biases of the models we first document a novel protocol for ocean initialization adopted by the cnrm cerfacs group for forecasting purpose in cmip5 initial states for starting dates of the predictions are obtained from a preliminary integration of the coupled model where full field ocean surface temperature and salinity are restored everywhere to observations through flux derivative terms and full field subsurface fields below the prognostic ocean mixed layer are nudged towards nemovar reanalyses nudging is applied only outside the 15 s 15 n band allowing for dynamical balance between the depth and tilt of the tropical thermocline and the model intrinsic biased wind a sensitivity experiment to the latitudinal extension of no nudging zone 1 s 1 n instead of 15 hereafter referred to as noeq has been carried out in this paper we concentrate our analyses on two specific regions the tropical pacific and the north atlantic basins in the pacific we show that the first year of the forecasts is characterized by a quasi systematic excitation of el nino southern oscillation enso warm events whatever the starting dates this through ocean to atmosphere heat transfer materialized by diabatic heating can be viewed for the coupled model as an efficient way to rapidly adjust to its own biased climate mean state weak cold enso events tend to occur the second year of the forecast due to the so called discharge recharge mechanism while the spurious oscillatory behavior is progressively damped the latter mechanism is much more pronounced in retrospective forecasts initialized from the noeq configuration for which the enso flip flop is still detectable at leadtime 4 year associated atmospheric teleconnections interfere worldwide with regional drifts especially in the north pacific and more remotely in the north atlantic in the latter basin the drift can be interpreted as the model response to intrinsic atmospheric circulation biases found in the stand alone atmosphere component of the model which project onto the negative phase of the north atlantic oscillation a fast adjustment up to 5 year leadtime occurs leading to a rapid slackening of both the vertical atlantic meridional overturning circulation and horizontal circulations especially in the subpolar gyre slower adjustment of the entire water masses distribution in the north atlantic then takes over involving several mechanisms we show that a weak feedback is locally present between the atmospheric circulation and the ocean drift that controls the timescale of the setting of the coupled model biases

application of thermochronology to hydrothermal ore deposits thermochronology finds many applications in economic geology utilizing temperature sensitive radiometric dating techniques to reveal low temperature upper crustal processes can elucidate many aspects of deposit genesis including timing and duration of mineralization processes rate of exhumation and erosion of intrusive ore deposits and comparative preservation potential the tools are utilized to best advantage when combined with other thermochronometry techniques that provide complementary information in addition when thermochronometers are combined with geochronometers e g zircon u pb over 800 c of thermal history is revealed from emplacement to erosion fig 1 with the advent of computational algorithms that provide more accurate and detailed models of thermochronology results the economic geologist has a powerful tool to use when assessing economic favorability of a region or prospect this chapter summarizes the various ways that low temperature thermochronometers have been utilized in studies of economic mineralization and primarily focuses on studies of porphyry ore deposits these deposits are well characterized and provide a good platform from which to demonstrate the extended understanding of ore formation processes that is provided by thermochronology studies in this section we review the fundamental application of u th he fission track and 40ar 39ar thermochronometry methods to mineralized systems we then present a synopsis of how these techniques can be used in thermal history analysis either alone or in combination with other chronometers in order to provide more information on deposit genesis the discussion is presented from low through to higher temperature thermochronometers corresponding to their presentation on figure 1 u th he thermochronology as documented earlier in the volume u th he thermochronology is based on measuring the accumulation of radiogenic 4he produced from u and th decay the daughter helium is retained until the mineral is heated to a temperature at which its structure and helium retentivity change this closure temperature varies from

recognition of 18β h oleanane in several crudes and tertiary upper cretaceous sediments definition of a new maturity parameter abstract ekweozor et al chem geol 27 11 28 and 29 37 first discovered an unknown compound with a gc retention time very close to that of the 18 h olenane peak in oils and tertiary sediments of the nigerian delta this compound was called j several authors wang et al advances in organic geochemistry 1981 pp 108 113 wiley chichester 1983 schoelle et al ibid pp 156 163 reported the occurrence of 18 h oleanane without underlying the presence of j because of their coelution in this study the presence of j has been confirmed in more than 150 rock extracts and 19 oils from different countries and is identified as the 18 h oleanane by comparison to retention time and mass spectrum and by its coelution with an authentic standard apart from tertiary sediments the 18 h and 18 h oleananes have also been found in upper cretaceous sediments which extends the occurrence of these compounds back in age a maturity correlation has been found between the relative concentration of 18 h oleanane and 18 h oleanane in fact an increase in the 18 h 18 h oleanane ratio has been observed with increasing depth in several wells the 18 h 18 h oleanane ratio has been correlated with other classical maturity parameters i e ts tm ro and tmax

tricyclic terpane maturity parameters response to heating by an igneous intrusion the effects of thermal maturation upon the abundance and composition of the tricyclic terpanes have been investigated within a single sedimentary horizon within the dun caan shale member isle of skye scotland intruded by a 0 9 m thick tertiary dolerite dyke heating by the igneous body caused the concentrations of all 13 h 14 h and 13 h 14 h tricyclic terpanes to increase towards or within the effective oil window recording generation from abundant non hydrocarbon precursors such as kerogen and asphaltene bound components progressive changes in tricyclic terpane composition accompany these concentration changes an increase in the c23 maturity parameter towards the dyke resulted from the relatively greater rate of generation of the isomer combined with the earlier decline in concentration by degradation or isomerisation of the component the tricyclics tricyclics hopanes parameter shows a dramatic increase within the latter part of the oil window due to the greater relative thermal stability of the tricyclic terpanes the quantitative data demonstrate the importance of the processes of generation from non hydrocarbon fractions of the sedimentary organic matter and thermal degradation in the operation of tricyclic terpane maturity parameters

decadal variability of subpolar gyre transport and its reverberation in the north atlantic overturning 1 analyses of sea surface height ssh records based on satellite altimeter data and hydrographic properties have suggested a considerable weakening of the north atlantic subpolar gyre during the 1990s here we report hindcast simulations with high resolution ocean circulation models that demonstrate a close correspondence of the ssh changes with the volume transport of the boundary current system in the labrador sea the 1990s decline of about 15 of the long term mean appears as part of a decadal variability of the gyre transport driven by changes in both heat flux and wind stress associated with the north atlantic oscillation nao the changes in the subpolar gyre as manifested in the deep western boundary current off labrador reverberate in the strength of the meridional overturning circulation moc in the subtropical north atlantic suggesting the potential of a subpolar transport index as an element of a moc monitoring system

novel tricyclic and tetracyclic terpanes in tertiary deltaic oils structural identification origin and application to petroleum correlation abstract tricyclic terpanes of the cheilanthane series in crude oils and sediments are routinely used for geochemical correlation the cheilanthanes are particularly useful to identify crude oils derived from marine clastic or carbonate source rock as well as input to the source rocks from marine algal or terrigenous organic matter however they sometimes have limitations for the correlation of oils expelled from different source rocks that received similar organic matter e g oils from source rocks dominated by terrigenous organic matter novel non cheilanthane tricyclic terpanes consisting of c21 and c25 compounds and a c27 tetracyclic terpane were identified in oils from the assam india beaufort mackenzie canada and the niger nigeria deltas nmr data reveal that all three compounds have an oleanane type structure with rings c d and e intact while rings a and b have been degraded leaving a side chain attached to ring c in the case of the tricyclics and only a degraded a ring in the tetracyclic on the basis of occurrence nmr structure and co variance with oleanane abundance these new tricyclic and tetracyclic compounds are believed to form from a ring functionalised oleanoid precursors in angiosperm flowering plants the distribution of these compounds in representative oils from the niger delta accumulations permits separation of the oils into at least three distinct source rock organofacies

early diagenesis of terrigenous triterpenoids and its implications for petroleum geochemistry abstract the distribution of triterpanes in sediments and crude oils is commonly used for oil oil and oil source rock correlation in petroleum geochemistry while isomer ratios of such compounds are applied as maturity parameters the triterpane pattern in terrestrially influenced geological samples is however remarkably less diverse than the triterpenoid skeletons occurring in the extant higher plant biosphere natural observations laboratory experiments and molecular mechanics calculations have revealed that acid catalysed double bond isomerization and skeletal rearrangement reactions of terrigenous triterpenoids during early diagenesis are the key to understanding the triterpane patterns in more matured geological materials examples studied in detail are the double bond isomerization of oleanenes and the subsequent hydrogenation of the products into oleanane and 18 oleanane and the transformation of taraxer 14 ene and lup 20 29 ene into oleanenes although the reactions are likely to be kinetically controlled the main products formed and ultimately preserved are the thermodynamically most stable ones the experimental results and natural observations have significant implications for the use of terrigenous triterpenoid compounds in petroleum geochemistry

biomarkers of oligocene lacustrine source rocks beibuwan song hong basin junction offshore northern vietnam abstract highly oil prone source rocks containing sapropelic type i and mixed types i and iii kerogen are found in 233 m of the 500 m deep fully cored enreca 3 well drilled on bach long vi island located at the junction between the beibuwan and the song hong basins offshore northern vietnam the cored succession is made up entirely by oligocene deep lacustrine deposits the origin of the organic matter om in 62 samples is evaluated on the basis of gas chromatography mass spectrometry gc ms and gc ms ms om in 55 samples is sourced primarily from lacustrine organisms and contains abundant 4 methylsteranes tetracyclic polyprenoids tpp and lycopane and no markers for marine organic matter the proportion of triterpanes derived from angiosperms is low in most saturated fractions and only traces of gymnosperm diterpanes are detected in contrast all aromatic fractions have a high proportion of compounds having an origin from both gymnosperms and angiosperms very high concentrations of hopanoids in both fractions suggest significant bacterial alteration of the original om most samples have a high concentration of rare c31 diaromatic 8 14 secohopanes with a fluorene moiety low pristane phytane pr ph ratios indicate that anoxic suboxic bottom water conditions existed during om accumulation the presence of carotane gammacerane and traces of arylisoprenoids could indicate a stratified water column om in a few samples with lower than average hydrogen index hi is mainly of terrestrial origin with a higher proportion of c29 steranes diterpanes and oleanoids and lower concentrations of both saturated and aromatic hopanes higher pr ph a higher c34 isohopane ratio ihr34 and a lower homohopane index hhi indicate that this low hi om was originally deposited under more oxic conditions and subsequently transported to deeper water low sterane and hopane isomerization ratios show that no samples have reached the oil window some novel maturity parameters for immature lacustrine samples are proposed

dynamics of decadal variability in the atlantic subpolar gyre a stochastically forced oscillator internal variability of the atlantic subpolar gyre is investigated in a 600 years control simulation of a comprehensive coupled climate model the subpolar gyre shows irregular oscillations of decadal time scale with most spectral power between 15 and 20 years positive and negative feedback mechanisms act successively on the circulation leading to an internal oscillation this involves periodically enhanced deep convection in the subpolar gyre center and intermittently enhanced air sea thermal coupling as a result anomalies of the large scale atmospheric circulation can be transferred to the ocean on the ocean s intrinsic time scale exciting the oscillator stochastically a detailed understanding of oscillatory mechanisms of the ocean and their sensitivity to atmospheric forcing holds considerable potential for decadal predictions as well as for the interpretation of proxy data records

salinity driven thermocline transients in a wind and thermohaline forced isopycnic coordinate model of the north atlantic abstract an isopycnic coordinate oceanic circulation model formulated with the aim of simulating thermodynamically and mechanically driven flow in realistic basins is presented special emphasis is placed on the handling of diabatic surface processes and on thermocline ventilation the model performance is illustrated by a 30 year spinup run with coarse horizontal resolution 2 mesh in a domain with north atlantic topography extending from 10 to 60 n latitude the vertical structure encompasses 10 isopycnic layers in steps of 0 2 units capped by a thermodynamically active mixed layer from an initially isohaline state with isopycnals prescribed by zonally averaged climatology the model is forced by seasonally varying wind stress radiative and freshwater fluxes and by a thermal relaxation process at the surface after a mechanical spinup time of about 15 years a quasi stationary pattern of mean circulation and annual variability ensues characterized by pronounced subtropical mode water formation

triterpanes and ring a degraded triterpanes as biomarkers characteristic of tertiary oils derived from predominantly higher plant sources abstract a number of oils previously proposed to be derived from terrigenous source materials have been obtained from the taranaki basin new zealand niger delta beaufort mackenzie region taiwan and indonesia and their c24 tetracyclic and c30 pentacyclic terpenoid distributions examined by gc ms and gc ms ms the c24 tetracyclic terpanes are thought to be derived from their corresponding c30 hopane oleanane ursane and lupane counterparts as previously reported a mixture of at least nine c30 pentacyclic terpanes are found to be present with remarkably uniform distributions in oils from these widely separated provinces whilst definitive structures have not been proposed for these compounds information has been obtained as to whether these pentacyclic terpanes are all six membered rings or contain one or two five membered rings the presence of this mixture of tetracyclic and pentacyclic terpanes provides a good indicator for oils derived from terrigenous source materials and in the case of these basins of tertiary age

a wind driven isopycnic coordinate model of the north and equatorial atlantic ocean 1 model development and supporting experiments numerical approximations to the dynamic equations are given which allow basin size ocean circulation models formulated in isopycnic coordinates to accommodate variable bottom topography and irregular coastlines emphasis is placed on computational economy through the use of a split explicit time integration scheme on the proper formulation of the advection and coriolis terms in the momentum equation in case of strongly varying layer thickness and on the correct estimation of the horizontal pressure gradient force in grid boxes truncated by steep bottom slopes the algorithms are tested in a series of two and three layer double gyre experiments in cases of steady forcing leading to a steady circulation we are able to reproduce the expected motionless final state in coordinate layers that are below the direct influence of the wind forcing this includes layers intersecting topographic obstacles a long term 25 30 year vacillation tentatively associated with the outcropping of isopycnals along the edge of the cyclonic gyre in a steadily forced model is documented the paper forms the basis for a subsequent study in which circulation features obtained in a realistic north atlantic setting will be discussed

the oleananes origin maturation and limits of occurence in southern nigeria sedimentary basins oleananes occur within well defined age and paleogeographic boundaries in the sedimentary province of southern nigeria thus signifying that the biomarkers may be analogous to index fossils in anambra syncline lower benue trough the biomarkers are found in rocks which are as old as late upper cretaceous in tertiary niger delta the concentration composition and distribution of the oleananes in rocks and oils are determined mainly by palaeodepositional environment and thermal history and are independent of age and geographical location of specific samples oleanane content varies with increasing burial depth with peak concentration coinciding within rm range 0 4 0 6 implying early generation of hydrocarbons from the basin s typically resin rich kerogens it is evident that the oleanane content parameter is superior to the hopane and sterane isomerisation indices for monitoring thermal maturation in the delta and for differentiating paralic from paralic marine source facies as well as early from late generated oils

mechanisms for variable north atlantic nordic seas exchanges 1 the variable oceanic exchanges between the nordic seas and the atlantic proper have been investigated using an isopycnic coordinate ocean model for the period 1948 2007 observed and simulated time series of volume transports in the denmark strait ds between iceland and the faroe islands and in the faroe shetland channel fsc are used to evaluate the model and the model captures much of the variability the inflow of atlantic water in the fsc and the outflow of light polar water in the ds and of dense overflow water in both fsc and ds are all found to covary with an atmospheric pattern resembling the north atlantic oscillation an increase in the fsc inflow is associated with a decrease in the fsc overflow and an increase in the ds overflow the exchanges response to the atmospheric forcing is mainly of a barotropic nature but they are also influenced by baroclinic processes the modeled antiphase between fsc inflow and overflow is connected to a vertical displacement of the isopycnal separating the two water masses in the channel and along the path of the norwegian atlantic slope current consistent with hydraulic control of the fsc exchanges

δ2 triterpenes early intermediates in the diagenesis of terrigenous triterpenoids a series of 2 triterpenoids oleana 2 12 diene oleana 2 13 18 diene oleana 2 18 diene ursa 2 12 diene and taraxera 2 14 diene has been identified in holocene buried mangrove sediments florida usa by comparison of the mass spectra of and by co injections with authentic standards in the oligocene brandon lignite vermont usa oleana 2 12 diene and oleana 2 13 18 diene were also identified along with two a ring contracted amyrin derivatives by comparison with the sedimentary occurrence of related analogues of oxyallobetulin and betulin and the demonstrated diagenetic formation of lup 2 ene from lupan 3 one these novel terrigenous biological markers are considered diagenetic products formed by dehydration of precursor molecules such as and amyrin and taraxerol the identification of these early intermediates brings us one step closer to the full understanding of the diagenetic fate of terrigenous triterpenoids

origin and mixing of crude oils in triassic reservoirs of mahu slope area in junggar basin nw china implication for control on oil distribution in basin having multiple source rocks abstract the origin of crude oils and their varied geochemical features along the western and northern slope of the mahu depression in the junggar basin has been controversial based on the molecular and isotopic geochemistry of hydrocarbons from 46 drill stem test crude oil samples and 36 core samples three oil groups i ii iii and five subgroups i 1 i 2 ii iii 1 and iii 2 have been recognized and oil source correlations have been established the subgroup i 1 oils originated mainly from lower permian fengcheng p 1 f carbonate source rocks subgroup i 2 from p 1 f mudstone source rock and group ii oils from middle permian wuerhe p 2 w mudstone source rock whose potential was underestimated in the past group iii consists of mixed oils i e subgroup iii 1 received contributions from p 1 f carbonates and p 2 w mudstones and subgroup iii 2 is a mixture of oils from p 1 f mudstones and p 2 w generated oils in order to determine the main source rocks the laboratory oil mixing experiments were carried out tricyclic terpane biomarker parameters tts were used to quantify the source contributions whole oil carbon isotope ratios were also used to verify the proportions of different oils in each mixture the results show that subgroup iii 1 oils have diverse mixing ratios in different reservoir subgroup iii 2 oils are mainly from p 1 f mudstones and p 2 w source rock contributes little finally the accumulation process of oil fields along the northern slope of the mahu depression was analyzed and the contributions from different sources were revealed this study provides an effective quantitative method to identify contributions from different lacustrine source rocks to mixed oils in the mahu depression which could be helpful in predicting location and composition of undiscovered oils

large bio geographical shifts in the north eastern atlantic ocean from the subpolar gyre via plankton to blue whiting and pilot whales pronounced changes in fauna extending from the english channel in the south to the barents sea in the north east and off greenland in the north west have occurred in the late 1920s the late 1960s and again in the late 1990s we attribute these events to exchanges of subarctic and subtropical water masses in the north eastern north atlantic ocean associated with changes in the strength and extent of the subpolar gyre these exchanges lead to variations in the influence exerted by the subarctic or lusitanian biomes on the intermediate faunistic zone in the north eastern atlantic this strong and persistent bottom up bio physical link is demonstrated using a numerical ocean general circulation model and data on four trophically connected levels in the food chain phytoplankton zooplankton blue whiting and pilot whales the plankton data give a unique basin scale depiction of these changes and a long pilot whale record from the faroe islands offers an exceptional temporal perspective over three centuries recent advances in simulating the dynamics of the subpolar gyre suggests a potential for predicting the distribution of the main faunistic zones in the north eastern atlantic a few years into the future which might facilitate a more rational management of the commercially important fisheries in this region

decline of subpolar north atlantic circulation during the 1990s observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid to high latitude north atlantic ocean topex poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation combining the data from earlier satellites we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s direct current meter observations in the boundary current of the labrador sea support the weakening circulation trend of the 1990s and together with hydrographic data show that the mid to late 1990s decline extends deep in the water column analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation

sunda strait and central sumatra fault sunda strait marks the limit between java trench frontal subduction and sumatra trench oblique subduction the right lateral central sumatra fault accommodates the oblique subduction it does not pass sunda strait but ends between sumatra and java in a complex pattern of dominantly normal faults associated with subsidence seismicity and volcanism we examine the implications of this phenomenon in sunda strait and in the adjacent fore arc basin and accretionary prism which underwent north south compression due to subduction as well as east west extension we propose that the strait is a consequence of the northwestward motion of the southwestern sumatra block along the central sumatra fault we also propose that the extensional zone in the sunda strait widens considerably to the southwest toward the trench and changes into a composite zone of deformation affected by strike slip as well as normal faulting

cenozoic thermotectonic history of the sunda asri basin southeast sumatra new insights from apatite fission track thermochronology abstract the tectonic and thermal history of cenozoic rocks from four wells asri 1 ne ria 1 hariet 1 and yani 2 in the sunda asri basin has been reconstructed using apatite fission track aft analysis combined with modelling of previously determined vitrinite reflectance vr measurements the wells all penetrate recent to middle eocene successions in which only the eocene to oligocene successions have been subjected to temperatures suitable for partial annealing due to rapid late miocene to recent burial with respect to organic thermal maturities the zone of minimum annealing coincides with undermature heating and records provenance aft ages whilst the zone of partial annealing agrees well with mature heating suitable for generation of hydrocarbons the integrated aft and vr data suggest that the sunda asri basin continues subsiding probably due to extension initiated in the late eocene and the successions near the base of the wells were recently exposed to the high present day temperatures the recent heating of rocks is consistent with up to 800 m of plio pleistocene burial both the aft and vr results indicate that geothermal gradients remained relatively constant through the cenozoic

global linkages originating from decadal oceanic variability in the subpolar north atlantic the anomalous decadal warming of the subpolar north atlantic ocean spna and the northward spreading of this warm water has been linked to rapid arctic sea ice loss and more frequent cold europe

characteristics and petroleum origin of the carboniferous volcanic rock reservoirs in the shixi bulge of junggar basin western china abstract shixi bulge of the central junggar basin in western china is a unique region that provides insight into the geological and geochemical characteristics of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks in the shixi bulge mainly consist of striped lava and agglomerate as well as breccia lava and tight tuff volcanic rocks differ in porosity and permeability striped lava exhibits the highest porosity average 14 2 but the lowest permeability average 0 67 10 15 m among the rock types primary gas pores are widely developed and mostly filled secondary dissolution pores and fractures are two major reservoir storage spaces capillary pressure curves suggest the existence of four pore structure types of reservoir rocks several factors namely lithology pore structure and various diagenesis govern the physical properties of volcanic rocks the oil is characterized by a high concentration of tricyclic terpane a terpane distribution of c 23 21 c 20 and sterane distributions of c 27 28 29 and c 27 c 28 29 oil and gas geochemistry revealed that the oil is a mixture derived primarily from p 2 w source rock and secondarily from p 1 j source rock in the sag west of pen 1 well the gases are likely gas mixtures of humic and sapropelic organic origins with the sapropelic gas type dominant in the mixture the gas mixture is most likely cracked from kerogen rather than oils the carboniferous volcanic reservoirs in shixi bulge share some unique characteristics that may provide useful insights into the various roles of different volcanic reservoir types in old volcanic provinces the presence of these reservoirs will undoubtedly encourage future petroleum exploration in volcanic rocks up to the deep parts of sedimentary basins

geochemical application of tricyclic and tetracyclic terpanes biomarkers in crude oils of nw china composition and distribution of tricyclic terpanes tetracyclic terpanes and hopane in crude oils from tarim turpan ordos and qaidam basins nw china were investigated and some new source dependent parameters were developed and evaluated c 19 and c 20 tricyclic terpanes are more abundant in terrigenous oils with c 24 tetracyclic terpane dominant relatively higher carbon number tricyclic terpanes especially c 23 tricyclic terpane are often the dominant homologues in crude oils from saline lacustrine and marine sources on the whole the relative content of c 23 tricyclic terpane of crude oils follow the order of saline lacustrine oils marine oils freshwater lacustrine oils terrigenous oils for c19 23 tricyclic terpane some new parameters based on the tricyclic hopane and tetracyclic tricyclic terpane as well as tetracyclic hopane ratios could be used to distinguish the oils and source rocks with similar maturity deposited in different sedimentary environments c 2015 elsevier ltd all rights reserved

heat flow distribution in southeast asia with consideration of volcanic heat abstract as of 1995 in southeast asia from 15 s to 25 n and from 90 to 160 e 2539 heat flow measurements are available despite a recent increase in the number of measurements still important data gaps exist in the region especially around the volcanic regions so far the contribution of heat flux from active volcanoes has largely been overlooked in regional heat flow maps because of uncertainties surrounding it we have tried to estimate the volcanic heat in this region with the assumption that these volcanoes emit a similar amount of heat as those in northeast honshu japan where heat flow studies and seismic tomography enable us to estimate that as a first approximation a volcano can be represented by 140 mw m 2 of heat flow a heat flow map including volcanic heat estimated in this way makes the heat flow in the sunda arc and the philippines where conventional heat flow data are scarce much higher than on a map without the volcanic heat

long term observations of north atlantic current transport at the gateway between western and eastern atlantic in the western north atlantic warm and saline water is brought by the north atlantic current nac from the subtropics into the subpolar gyre four inverted echo sounders with high precision pressure sensors pies were moored between 47 40 n and 52 30 n to study the main pathways of the nac from the western into the eastern basin the array configuration that forms three segments northern central and southern allows partitioning of the nac and some assessment of nac flow paths through the different mid atlantic ridge fracture zones we exploit the correlation between the nac transport measured between 2006 and 2010 and the geostrophic velocity from altimeter data to extend the time series of nac transports to the period from 1992 to 2013 the mean nac transport over the entire 21 years is 27 5 sv consisting of 60 warm water of subtropical origin and 40 subpolar water we did not find a significant trend in the total transport time series but individual segments had opposing trends leading to a more focused nac in the central subsection and decreasing transports in the southern and northern segments the spectral analysis exhibits several significant peaks the two most prominent are around 120 days identified as the time scale of meanders and eddies and at 4 9 years most likely related to the nao transport composites for the years of highest and lowest nao indices showed a significantly higher transport 2 9 sv during strong nao years mainly in the southern segment

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

stochastically forced multidecadal variability in the north atlantic a model study observations show a multidecadal signal in the north atlantic ocean but the underlying mechanism and cause of its timescale remain unknown previous studies have suggested that it may be driven by the north atlantic oscillation nao which is the dominant pattern of winter atmospheric variability to further address this issue the global ocean general circulation model nucleus for european modelling of the ocean nemo is driven using a 2 000 years long white noise forcing associated with the nao focusing on key ocean circulation patterns we show that the atlantic meridional overturning circulation amoc and sub polar gyre spg strength both have enhanced power at low frequencies but no dominant timescale and thus provide no evidence for a oscillatory ocean only mode of variability instead both indices respond linearly to the nao forcing but with different response times the variability of the amoc at 30 n is strongly enhanced on timescales longer than 90 years while that of the spg strength starts increasing at 15 years the different response characteristics are confirmed by constructing simple statistical models that show amoc and spg variability can be related to the nao variability of the previous 53 and 10 winters respectively alternatively the amoc and the spg strength can be reconstructed with auto regressive ar models of order seven and five respectively both statistical models reconstruct interannual and multidecadal amoc variability well while on the other hand the ar 5 reconstruction of the spg strength only captures multidecadal variability using these methods to reconstruct ocean variables can be useful for prediction and model intercomparision

information from low density expendable bathythermograph transects north atlantic mean temperature structure and quasi decadal variability the 1999 ocean observing system conference recommended that the low density ld expendable bathythermograph xbt network be discontinued contingent on the completion of studies showing that the global argo network and or satellite altimetry can provide equivalent information herein information content in north atlantic ld lines relative to quasi decadal variability in upper layer temperature structure is addressed as the first step in achieving this recommendation two ld lines are located in the subpolar gyre and support results from previous studies of shorter length that ocean advection and not only air sea fluxes plays an important role particularly in the eastern gyre in determining the characteristics of the water masses transported to the source regions of north atlantic deep water several sections cross the gulf stream and labrador current they provide evidence to support the hypothesis that changes in the intensity of labrador current properties cause meridional motions of the gulf stream decadal variability in the subtropical gyre of the north atlantic has been attributed to westward propagation of temperature anomalies by the mean currents and planetary waves modeling studies suggest that these signals are dominant in the thermocline at the northern latitudes order 30 of the subtropical gyre similar calculations from a line crossing the subtropical gyre at these same latitudes shows no indication of westward propagation quasi decadal signals in upper layer temperature are coincident across the entire gyre with some suggestion of eastward motion of temperature anomalies one line on the southern boundary of the subtropical gyre does include westward signal movement from the eastern boundary based on the information content of individual lines recommendations are made relative to the continuation of specific transects until it has been demonstrated that argo and satellite altimetry can provide equivalent results

multiple equilibria as a possible mechanism for decadal variability in the north atlantic ocean decadal climate variability in the north atlantic has received increased attention in recent years because modeling results suggest predictability of heat content and circulation indices several years ahead however determining the applicability of these results in the real world is challenging because of an incomplete understanding of the underlying mechanisms here the authors show that recent attempts to reconstruct the decadal variations in one of the dominant circulation systems of the region the subpolar gyre spg are not always consistent a coherent picture is partly recovered by a simple conceptual model solely forced by reanalyzed surface air temperatures this confirms that surface heat flux indeed plays a leading role for this typeofvariability ashasbeensuggestedinpreviousstudies theresultsfurthersuggestthatlargevariationsin the spg correspond to the crossing of a bifurcation point that is predicted from idealized experiments and an analytical solution of the model used herein performance of this conceptual model is tested against a statistical stochastic model hysteresis and the existence of two stable modes of the spg circulation shape its response to forcing by atmospheric temperatures the identification of the essential dynamics and the reduction to a minimal model of spg variability provide a quantifiable basis and a framework for future studies on decadal climate variability and predictability

variability of the simulated meridional heat transport in the north atlantic for the period 1951 1993 a 43 year ocean model simulation for the period 1951 1993 is analyzed with a focus on the meridional heat transport mht as a proxy for the strength of meridional overturning cell moc at 25 n the surface heat flux forcing associated with the north atlantic oscillation nao pattern is related to the variability in mht both on interannual and longer timescales the manifestation of the interannual and decadal oceanic response to nao is nonlocal as evidenced by the concentrated heat content and sea level variability at the gulf stream and north atlantic current regions and shown by the comparison of the model sea level variability to the altimeter data between low mht years in mid 1980s and high mht years in early 1990s the same area is singled out by empirical orthogonal function analysis in the leading mode of the sea level mht and time series of the leading sea level mode are highly correlated which reflects the importance of the moc in determining the variability of the heat content of the whole basin also the model suggests that the mht moc has entered a very strong phase since the mid 1980s and this trend has continued up to the end of 1993 this behavior follows the general trend in the nao index

the paleogene vegetation and petroleum system in the tropics a biomarker approach abstract the present study investigates the biomarker signatures of sediments and crude oils to infer the paleovegetation from the two petroleum systems of assam basin eastern india they are classified as the paleocene middle eocene and the middle eocene oligocene petroleum systems the sediments are oil and gas prone with an early catagenetic stage of thermal evolution here we report tricyclic diterpanes such as rimuane pimarane rosane and isopimarane along with tetracyclic diterpanes ent beyerane phyllocladane kaurane from paleocene eocene coal bearing sediments and crude oils these diterpane biomarkers attest dominant contribution from conifers possibly from podocarpaceae and araucariaceae however diterpanes are not detected in oligocene sediments and oils crude oils from both paleocene eocene and oligocene reservoirs and organic rich sediments contain angiosperm biomarkers such oleanane and related triterpanes along with bicadinane a biomarker specific for the dipterocarpaceae family of angiosperms the equatorial position of india during early paleogene along with the presence of angiosperm signatures including dipterocarpaceae and gymnosperms reflect the emergence of tropical rainforest elements in eastern india absence of diterpenoids in oligocene samples and difference in angiosperm parameters from paleocene eocene samples suggests a change in source vegetation and organofacies

a dipole pattern of the sea surface height anomaly in the north atlantic 1990s 2000s 1 despite a long term trend of sea level rise continuing into the 2000s in the subpolar north atlantic variations in the sea surface height have behaved differently in both spatial and temporal domains a dipole pattern centered between the northern atlantic subpolar region and the region near the gulf stream was observed in the linear trends of the sea surface height anomaly ssha by applying the ensemble empirical mode decomposition eemd we found that this dipole pattern is mainly associated with the interannual to decadal ssha oscillations of the two regions which are 180 out of phase with each other over the time span of this study the low frequency variations of the ssha in the subpolar region are strongly inversely correlated with the cumulative north atlantic oscillation nao index r 0 84 in contrast with the gulf stream region which is positively correlated r 0 22 this therefore reveals an asymmetric response of the regional ssha to the cumulative nao forcing in which the subpolar variability leads that of the gulf stream region by 29 months moreover there is a remarkable reversal of the ssha trends from the 1990s to the 2000s which is unexpected given a weak and fluctuating nao behavior since mid 1990s such ssha variations in the 2000s might be related to the lagged variations of the atlantic meridional overturning circulation amoc

geochemical application of sterane and triterpane biomarkers to a description of oils from the taranaki basin in new zealand abstract the distributions of sterane and terpane biomarkers in a suite of 25 oils from onshore and offshore regions of the taranaki basin of new zealand have been determined by gc ms features of these distributions include the presence of relatively high concentrations of a number of c 24 tetracyclic terpanes the virtual absence of tricyclic terpanes a predominance of c 29 normal iso and dia steranes and the presence of a number of non hopanoid triterpanes in one member of the suite urenui 18 h oleanane is the most abundant component m z 191 ion chromatogram of the terpane class of biomarkers based upon the distributions of 18 h oleanane the mckee and moturoa families of oils can be delineated these terpane distributions are qualitatively similar to those encountered in crude oils from a number of far eastern basins and from the handil field of the mahakam delta indonesia the taranaki oils are of approximately the same thermal maturity maturity parameters calculated from the distributions of c 29 steranes and of 17s h 21 h and 17 h 21s h hopanes confirm recent findings of incomplete nuclear isomerisation in oils derived from tertiary sediments an attempt has been made to correlate the mckee 1 and maui 4 crude oils with potential source rocks from depths of 3708 m and 3825 m respectively the rocks studied have attained insufficient maturity to have been the sources of these oils

heterocyclic aromatic hydrocarbon distributions in petroleum a source facies assessment tool abstract this study reports a novel source facies assessment application from distributions of heterocyclic aromatic hydrocarbons in petroleum i e dibenzothiophene dbt dibenzofuran dbf and fluorene f to illustrate the approach initially a large set of crude oils from global petroleum basins are geochemically characterized based on source facies organic matter type and environment of deposition variation petroleum bulk properties and molecular distributions of isoprenoids terpanes steranes and related parameters are applied to demonstrate the source facies and maturity of the entire oil suite and to delineate the oil suite into marine carbonate marine shale marine shale with terrigenous organic matter om coaly and lacustrine source facies families from within this interpretive context the relative percentages of hetercyclic aromatic hydrocarbons are reported and discussed from each of these source facies families a triplot drawn from the percentages of dbt dbf and f is shown to effectively differentiate the oils source facies classifications marine carbonate oils show highest dbt plotted in the dbt vertex freshwater lacustrine sourced oils positioned near to 100 f vertex coaly sourced oils revealed highest dbf the marine shale and marine shale with terrigenous om oil families plotted away from three vertices and represent a distinctive position with in the triplot these results establish an effective source facies assessment tool triplot based on heterocyclic aromatic hydrocarbon distributions these novel signatures which are derived from variations in the chemical composition of source rocks hence kerogen lead to the occurrence of kerogen catalysis in sedimentary reaction like carbon catalysis for the formation of heterocyclic aromatic hydrocarbons

response of the northern north atlantic and arctic oceans to a sudden change of the north atlantic oscillation 1 the influence of a switch from a long time high north atlantic oscillation nao state to an enduring nao situation is investigated with a coupled sea ice ocean model we compare the response to a sustained shift to nao conditions with that to a short lived transition to nao and back to nao forcing observed changes in sea ice and oceanic variables between high and low nao states are well captured in the model response the ocean circulation adjustment includes a fast barotropic anomaly accompanied by an enhancement of the meridional overturning and the northward heat transport at 48 n the slow response contains a substantial decrease of the northward heat transport which is caused by a reduction of the transport of subpolar and subtropical gyres after a delay of around 2 years the oceanic heat transport reacts to counteract the meridional temperature gradient imposed by the surface forcing the propagation time of baroclinic rossby waves is irrelevant for the delay between the forcing and the oceanic response rather the strength of the subpolar gyres is determined by the rapid spin up of a topographic sverdrup circulation and the subsequent slower changes through the jebar joint effect of baroclinicity and relief in an experiment where only the wind stress is changed to nao conditions the adjustment is dampened strongly by the nao thermohaline forcing the gyres decrease slower than in the nao case comparison with an experiment where only the wind stress is changed to nao conditions indicates that the thermohaline forcing is most important the heat fluxes counteract the wind stress forcing such that the meridional overturning and the northward heat transport decrease only slightly compared to the control run

an anatomy of the cooling of the north atlantic ocean in the 1960s and 1970s abstractin the 1960s and early 1970s sea surface temperatures in the north atlantic ocean cooled rapidly there is still considerable uncertainty about the causes of this event although various mechanisms have been proposed in this observational study it is demonstrated that the cooling proceeded in several distinct stages cool anomalies initially appeared in the mid 1960s in the nordic seas and gulf stream extension before spreading to cover most of the subpolar gyre subsequently cool anomalies spread into the tropical north atlantic before retreating in the late 1970s back to the subpolar gyre there is strong evidence that changes in atmospheric circulation linked to a southward shift of the atlantic itcz played an important role in the event particularly in the period 1972 76 theories for the cooling event must account for its distinctive space time evolution the authors analysis suggests that the most likely drivers were 1 the great salinity anomaly of the late 1960s 2 an earlier

on the currents and transports connected with the atlantic meridional overturning circulation in the subpolar north atlantic results from an interannually forced 0 08 degrees eddy resolving simulation based on the hybrid coordinate ocean model in conjunction with a small but well determined transport database are used to investigate the currents and transports associated with the atlantic meridional overturning circulation amoc in the subpolar north atlantic spna the model results yield a consistent warming in the western spna since the early 1990s along with mean transports similar to those observed for the trans basin amoc across the world ocean circulation experiment hydrographic section ar19 16 4 sv and boundary currents at the exit of the labrador sea near 53 degrees n 39 0 sv and east of the grand banks near 43 degrees n 15 9 sv over a 34 year integration the model determined amoc across the ar19 section and the western boundary current near 53 degrees n both exhibit no systematic trend but some long term interannual and longer variabilities including a decadal transport variation of 3 4 sv from relatively high in the 1990s to low in the 2000s the decadal variability of the model boundary current transport near 53 degrees n lags the observed winter time north atlantic oscillation index by about 2 years and leads the model amoc across the ar19 section by about 1 year the model results also show that the long term variabilities are low compared to those on shorter time scales thus rapid sampling of the current over long time intervals is required to filter out high frequency variabilities in order to determine the lower frequency variabilities of interest

tectonic features of the southern sumatra western java forearc of indonesia 1 multichannel reflection seismic profiles along the active sunda arc where the indo australian plate subducts under the overriding eurasian margin revealed two accretionary wedges the inner wedge i is of assumed paleogene age and the outer wedge ii is of neogene to recent age the inner wedge i is composed of tectonic flakes stretching from southeast sumatra across the sunda strait to northwest java implying a similar plate tectonic regime in these areas at the time of flake development during upper oligocene today wedge i forms the outer arc high and the backstop for the younger outer wedge ii the missing outer arc high of the southern sunda strait is explained by a combination of neogene transtension due to a clockwise rotation of sumatra with respect to java and by arc parallel strike slip movements the rotation created transtensional pull apart basins along the western sunda strait semangka graben as opposed to transpression and inversion on the eastern sunda strait within the new detected krakatau basin the arc parallel transpressional mentawai strike slip fault zone mfz was correlated from the sumatra forearc basin to the northwest java forearc basin off the sunda strait northward bending branches of the mfz are connected with the right lateral sumatra fault zone sfz along the volcanic arc segment on sumatra it is speculated that the sfz was attached to the cimandiri pelabuhan ratu strike slip fault of java prior to the presumed rotation of sumatra and that since the late lower miocene the main slip movement shifted from the volcanic arc position to the forearc basin area due to increasingly oblique plate convergence

thermal history reconstruction using apatite fission track analysis and vitrinite reflectance a case study from the uk east midlands and southern north sea apatite fission track analysis afta is a method of obtaining ther mal history information in sediments in sections that have been hotter in the past afta provides estimates of maximum palaeotemperatures and the time at which a sedimentary section began cooling from maximum palaeotempera tures it is useful for studying the thermal history of sequences containing source rocks and can provide information critical to the understanding of the timing of oil generation integration of afta and vitrinite reflectance vr data allows a coherent thermal history framework to be established and a formal method of analysing palaeogeothermal gradients has been developed by combining afta and vr data this approach allows definition of the major facets of thermal history based on directly measurable parameters rather than on assumed values of palaeo heatflow and provides rigorous estimates of the amount of uplift and erosion the case study demonstrates the application of this approach to the east midlands shelf region here afta data have revealed an episode of maximum palaeotemperatures prior to cooling commencing at around 60 ma combined afta and vr data show that this cooling was due to kilometre scale early ter tiary uplift and erosion under near normal geothermal gradients our estimates of uplift and erosion are significantly greater than those of pervious workers and show that uplift and erosion was not restricted to the recognized axes of inversion but was regional in extent this has implications for the evolution of source rock maturity in this region and in other basins in around the uk where afta has indicated early tertiary heating and where the extent and amount of tertiary uplift and erosion may have also been underestimated by previous workers apatite fission track analysis afta tm is a method of obtaining thermal history information in sediments and is particularly useful for studying the thermal history of sequences containing hydrocarbon source rocks as well as providing estimates of maximum palaeotemperatures afta provides a direct estimate of the time at which a sedimentary section began cooling from its maximum palaeotemperature a key advantage over traditional geochemical methods in many situations this knowledge is critical to the understanding of the timimg of oil generation and migration in relation to trap formation information on the timing of maximum palaeotempera ture can also be of significant value in the interpretation of vitrinite reflectance vr data and combination of afta and vr data allows a consistent integrated thermal history interpretation the afta technique is applied most usefully in sedimentary sections which have been hotter in the past than they are at the present day it is therefore applicable to large regions of britain and the uk continental shelf that have been subject to deeper burial in the past or affected by other sources of heating the basis of the technique has

a decadal prediction case study late twentieth century north atlantic ocean heat content an ensemble of initialized decadal prediction dp experiments using the community climate system model version 4 ccsm4 shows considerable skill at forecasting changes in north atlantic upper ocean heat content and surface temperature up to a decade in advance coupled model ensembles were integrated forward from each of 10 different start dates spanning from 1961 to 2006 with ocean and sea ice initial conditions obtained from a forced historical experiment a coordinated ocean ice reference experiment with interannual forcing core ia which exhibits good correspondence with late twentieth century ocean observations from the north atlantic subpolar gyre spg region north atlantic heat content anomalies from the dp ensemble correlate highly with those from the core ia simulation after correcting for a drift bias in particular theobservedlarge rapid rise in spgheatcontentin themid 1990sis successfullypredicted in the ensemble initialized in january of 1991 a budget of spg heat content from the core ia experiment sheds light on the origins of the 1990s regime shift and it demonstrates the extent to which low frequency changes in ocean heat advection related to the atlantic meridional overturning circulation dominate temperature tendencies in this region similar budgets from the dp ensembles reveal varying degrees of predictive skill in the individual heat budget terms with large advective heat flux anomalies from the south exhibiting the highest correlation with core ia the skill of the dp in this region is thus tied to correct initialization of ocean circulation anomalies while external forcing is found to contribute negligibly and for incorrect reasons to predictive skill in this region over this time period

a possible mechanism for the strong weakening of the north atlantic subpolar gyre in the mid 1990s 1 the extent and strength of the north atlantic subpolar gyre spg changed rapidly in the mid 1990s going from large and strong in 1995 to substantially weakened in the following years the abrupt change in the intensity of the spg is commonly linked to the reversal of the north atlantic oscillation nao index changing from strong positive to negative values in the winter 1995 96 in this study we investigate the impact of the initial spg state on the subsequent behavior of the spg by means of an ocean general circulation model driven by ncep ncar reanalysis fields our sensitivity integrations suggest that the weakening of the spg cannot be explained by the change in the atmospheric forcing alone rather for the time period around 1995 the spg was about to weaken irrespective of the actual atmospheric forcing due to the ocean state governed by the persistently strong positive nao during the preceding seven years 1989 1995 our analysis indicates that it was this preconditioning of the ocean in combination with the sudden drop in the nao in 1995 96 that lead to the strong and rapid weakening of the spg in the second half of the 1990s this hypothesis explains the diverging evolution of the strength of the spg and the atmospheric forcing winter nao after 1995 as has been suggested recently

hydrocarbon biomarkers thermal maturity and depositional setting of tasmanite oil shales from tasmania australia this study represents the first geological and organic geochemical investigation of samples of tasmanite oil shale representing different thermal maturities from three separate locations in tasmania australia the most abundant aliphatic hydrocarbon in the immature oil shale from latrobe is a c19 tricyclic alkane whereas in the more mature samples from oonah and douglas river low molecular weight n alkanes dominate the extractable hydrocarbon distribution the aromatic hydrocarbons are predominantly derivatives of tricyclic compounds with 1 2 8 trimethylphenanthrene increasing in relative abundance with increasing maturity geological and geochemical evidence suggests that the sediments were deposited in a marine environment of high latitude with associated cold waters and seasonal seaice it is proposed that the organism contributing the bulk of the kerogen tasmanites occupied an environmental niche similar to that of modern sea ice diatoms and that bloom conditions coupled with physical isolation from atmospheric co2 led to the distinctive isotopically heavy 13c values 13 5 to 11 7 for the kerogen 13c data from modern sea ice diatoms 7 supports this hypothesis isotopic analysis of n alkanes in the bitumen 13 5 to 31 suggest a multiple source from bacteria and algae on the other hand the n alkanes generated from closed system pyrolysis of the kerogen 15 are mainly derived from the preserved tasmanites biopolymer algaenan the tricyclic compounds mean 8 both in the bitumen and pyrolysate have a common precursor they are consistently enriched in 13c compared with the kerogen and probably have a different source from the n alkanes the identification of a location where the maturity of the tasmanite oil shale approaches the oil window raises the possibility that it may be a viable petroleum source rock

last interglacial mis5e hydrographic shifts linked to meltwater discharges from the east greenland margin abstract proximal evidence of the surface ocean response to size reduction of the greenland ice sheet gis during the last interglacial mis5e and preceding glacial termination t2 remains largely elusive using a new sediment record from the western iceland sea the behavior of the northeastern gis and its relation to the subpolar north atlantic surface hydrography is examined extremely light oxygen isotopic 18o values are found off central east greenland during early mis5e and point to enhanced meltwater release potentially from the northeastern sector of the gis data from downstream the cold east greenland current egc and its eastward branches suggest a far reaching effect of this meltwater not only in the nordic seas but also in the se labrador sea in particular whereas an early mis5e warming at 128 5 126 5 ka in the two regions coincided with the relative reduction of meltwater input into the egc the subsequent cooling noted at 126 5 ka followed a renewed major freshwater event off central east greenland our data further indicate persistent freshwater influence from the east greenland margin over the entire mis5e interval and in addition also reveal a late mis5e meltwater event the latter event occurred just prior to the last glacial inception and emphasizes the importance of greenland meltwater as forcing factor on interglacial climates

ocean effects of blocking variations in the circulations of the atlantic ocean and the atmosphere above it influence societies far beyond the ocean basin itself scientists have long tried to understand and predict the dramatic year to year variability of the north atlantic oscillation nao 1 but modeling the associated ocean atmosphere interaction remains a challenge 2 attention has turned to longer term warming and cooling episodes of the north atlantic ocean these variations often referred to as atlantic multidecadal variability amv are widely assumed to arise from variability in the ocean s overturning circulation 3 in which warm water flows northward near the ocean surface and returns southward at depth in contrast hakkinen et al argue on page 655 of this issue 4 that the amv owes its existence to atmospheric events with time scales as short as a week

biomarker evidence for intermittent photic zone euxinia in the aptian albian organic sedimentary record from the ionian zone epirus greece new biomarker evidence is presented that constrains the conditions of deposition and preservation of sediments rich in extractable organic matter from the aptian albian sedimentary record of the ionian zone in nw greece analyses were specifically carried out on total lipid extracts from 12 organic rich samples from the vigla shale member two of which represent the regional record for the early albian paquier event of oae1b in the aliphatic fractions compound groups such as n alkanes isoprenoid alkanes steroids hopanoids and terpenoids were recognized pointing to a mixed origin from algae and prokaryotes with an additional measurable contribution from terrigenous plant matter these compounds suggest deposition of the primary organic sediments under conditions of decreased bottom water oxygen concentrations mass spectral evidence from the aromatic fractions of most samples reveal the variable presence of diagenetic and catagenetic derivatives of carotenoid pigments including some with bound sulfur that are characteristic of photoautotrophic sulfur bacteria the presence of specific biomarkers originating from photosynthetic anaerobic microorganisms similar to those in ancient and contemporary euxinic basins such as the black sea suggest that photic zone euxinic conditions were intermittently operative in the aptian albian stages of the ionian basin but were not exclusively characteristic of the black shale representing the paquier event itself

first direct estimates of volume and water mass transports across the reykjanes ridge the reykjanes ridge is a major topographic feature located south of iceland in the north atlantic ocean that strongly influences the subpolar gyre spg circulation based on velocity and hydrographic measurements carried out along the crest of the reykjanes ridge from the icelandic continental shelf to 50 n during the rrex cruise in june july 2015 we derived the first direct estimates of volume and water mass transports over the reykjanes ridge north of 53 15 n circulation was mainly westward south of this latitude it was mainly eastward the westward transport was estimated at 21 9 2 5 sv sv 106 m3 s 1 and represents the spg intensity the westward flows followed two main pathways at 57 n near the bight fracture zone and at 59 62 n we argue that those pathways were connected to the northern branch of the north atlantic current and to the sub arctic front respectively which were both intersected by the southern part of the section in addition to this horizontal circulation mixing and bathymetry shaped the water mass distribution water mass transformations in the iceland basin lead to the formation of weakly stratified subpolar mode water spmw we explain why spmw the main water mass contributing to the westward flow was denser at 57 n than at 59 62 n at higher densities both intermediate water and icelandic slope water contributed more to the westward transport across the reykjanes ridge than the sum of labrador sea water and iceland scotland overflow water plain language summary the reykjanes ridge the northern section of the mid atlantic ridge strongly influences the cyclonic circulation of the north atlantic subpolar gyre a major component of the climate system up to now no dedicated dataset was available to describe the circulation across this ridge to fill this gap surface to bottom measurements of flow velocity and water mass properties were carried out along the crest of the ridge from iceland to 50 degree sign n in 2015

unusual carbon isotope compositions of biomarker hydrocarbons in a permian tasmanite abstract the permian oil shale sample of this study is from a deposit in tasmania in which the only recognizable structures are large thick walled unicellular specimens of the green alga tasmanites the fossils are so densely packed that this shale is termed tasmanite the carbon isotopic composition of bulk kerogen carbon c 13 c org 16 6 vs pdb is unusually enriched in 13 c compared to marine permian organic carbon 25 to 30 this 13 c enrichment suggests specific environmental conditions co 2 draw down and or physiological specialties cell size and growth rate of tasmanites which in modern environments are known to cause 13 c enrichment in marine phytoplankton isotope signatures of extractable organic species unlike in normal immature oil shales are considerably enriched in 13 c compared to the kerogen the bitumen 10 9 is composed predominantly of extended saturated c 18 c 25 tricyclic terpane hydrocarbons 9 9 to 12 2 total range with an average of 10 8 these tricyclics are not only found as free lipids in the extract but also in pyrolysates with similar isotopic signatures and are therefore likely biosynthesis products of tasmanites the monoaromatic and diaromatic tricyclic terpane hydrocarbons c 17 c 19 have similar isotopic signatures 9 3 to 12 8 total range with an average of 10 6 two monoaromatic tetracyclic hydrocarbons c 23 and c 24 a quantitatively minor but biogenetically interesting group average at 10 2 in contrast pristane and phytane as well as n alkanes 18 to 22 are depleted in 13 c compared to kerogen carbon the isotopic similarity of all the cyclic terpanes in this sample together with their occurrence in the free lipids and kerogen suggests that they have a common origin and are biosynthesis products of the marine unicellular green algae tasmanites the tetracyclic terpanes therefore are not des a oleananes derived from land plants but are possibly monoaromatic des a gammaceranes or other des a triterpenoids derived from marine sources the unusual enrichment in 13 c in the cyclic hydrocarbons is hypothesized to result from the special growth conditions of the algae isoprenoids and n alkanes are also likely biosynthesis products of tasmanites possibly during the spore formation stage when physiological and environmental conditions were different than during planktonic biosynthesis

organic geochemistry of the silurian tanezzuft formation and crude oils nc115 concession murzuq basin southwest libya abstract thirty six silurian core and cuttings samples and 10 crude oil samples from ordovician reservoirs in the nc115 concession murzuq basin southwest libya were studied by organic geochemical methods to determine source rock organic facies conditions of deposition thermal maturity and genetic relationships the lower silurian hot shale at the base of the tanezzuft formation is a high quality oil gas prone source rock that is currently within the early oil maturity window the overall average toc content of the hot shale is 7 2 wt with a maximum recorded value of 20 9 wt by contrast the overlying deposits of the tanezzuft formation have an average toc of 0 6 wt and a maximum value of 1 1 wt the organic matter in the hot shale consists predominantly of mixed algal and terrigenous type ii iii kerogen whereas the rest of the formation is dominated by terrigenous type iii organic matter with some type ii iii kerogen oils from the a b and h oil fields in the nc115 concession were almost certainly derived from marine shale source rocks that contained mixed algal and terrigenous organic input reflecting deposition under suboxic to anoxic conditions the oils are light and sweet and despite being similar were almost certainly derived from different facies and maturation levels within mature source rocks the b oils were generated from slightly less mature source rocks than the others based on hierarchical cluster analysis hca principal component analysis pca selected source related biomarkers and stable carbon isotope ratios the nc115 oils can be divided into two genetic families family i oils from ordovician mamuniyat reservoirs were probably derived from older palaeozoic source rocks whereas family ii oils from ordovician mamuniyat hawaz reservoirs were probably charged from a younger palaeozoic source of relatively high maturity a third family appears to be a mixture of the two but is most similar to family ii oils these oil families were derived from one proven mature source rock the early silurian rhuddanian hot shale there is a good correlation between the family ii and iii oils and the hot shale based on carbon isotope compositions saturated and aromatic maturity parameters indicate that these oils were generated from a source rock of considerably higher maturity than the examined rock samples the results imply that the oils originated from more mature source rocks outside the nc115 concession and migrated to their current positions after generation

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

prediction of source rock characteristics based on terpane biomarkers in crude oils a multivariate statistical approach abstract the distributions of eight tricyclic and eight pentacyclic terpanes were determined for 216 crude oils located worldwide with subsequent simultaneous rq mode factor analysis and stepwise discriminate analysis for the purpose of predicting source rock features or depositional environments five categories of source rocks are evident nearshore marine i e paralic deltaic deeper water marine lacustrine phosphaticrich source beds and ordovician age source rocks the first two factors of the rq mode factor analysis describe 45 percent of the variation in the data set the tricyclic terpanes appear to be twice as significant as pentacyclic terpanes in determining the variation among samples lacustrine oils are characterized by greater relative abundances of c 21 diterpane and gammacerane nearshore marine sources by c 19 and c 20 diterpanes and oleanane deeper water marine facies by c 24 and c 25 tricyclic and c 31 plus c 32 extended hopanes and ordovician age oils by c 27 and c 29 pentacyclic terpanes although thermal maturity trends can be observed in factor space the trends do not necessarily obscure the source rock interpretations also since bacterial degradation of crude oils rarely affects tricyclic terpanes biodegraded oils can be used in predicting source rock features the precision to which source rock depositional environments are determined might be increased with the addition of other biomarker e g steranes and stable isotope data using multivariate statistical techniques

oleananes in oils and sediments evidence of marine influence during early diagenesis abstract the oleananes as markers for the angiosperms provide valuable source and age information when present in an oil nevertheless they are not quantitatively related to the land plant input and indeed their presence reflects only a small leak in diagenetic processes leading primarily to aromatic oleanoids because they are minor products the abundance of oleananes in terrigenous oils and sediments may be highly sensitive to changes in early diagenetic conditions here we present evidence that contact of plant matter with seawater during early diagenesis enhances the expression of oleananes in a mature sediment or oil oleananes are absent or present at very low concentrations in samples from the base of an eocene coal seam affected by postdepositional seawater intrusion however their abundance increases toward the top of the seam in correlation with organic sulphur dibenzothiophene phenanthrene and the homohopane index similarly in deltaic sediments from the south sumatra basin oleanane hopane is strongly correlated with indicators of marine influence such as c 27 c 29 steranes and the homohopane index in each case increasing oleanane abundance is accompanied by a reduction in the extent of aromatisation and for the south sumatra basin the proportion of a ring contracted oleananes an angiosperm derived miocene coal from the philippines deposited under freshwater conditions shows abundant aromatic oleanoids but no oleananes these results show that oleananes need to be used with caution as age and source markers in fluvio deltaic and lacustrine petroleum systems on the other hand their sensitivity to early diagenetic conditions may make them useful in locating effective source rocks in such systems

on the linkage between labrador sea water volume and overturning circulation in the labrador sea a case study on proxies abstractalthough proxies have generally been used to study deep ocean convection and overturning circulation in the labrador sea their efficacy has not been explicitly evaluated because observations that directly measure those variables are scarce in this study the volume of newly formed labrador sea water lsw and the overturning circulation in the labrador sea are estimated using observational data and output from a high resolution ocean model and then compared to proxies used to represent those variables the comparisons reveal the limitations of proxies highlighting the desirability of robust estimates derived from direct monitoring in the region i e from argo and overturning in the subpolar north atlantic program osnap a linkage among lsw formation overturning circulation in the labrador sea and the export of lsw from the basin on interannual time scales is found in the model

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

impacts of source input and secondary alteration on the extended tricyclic terpane ratio a case study from palaeozoic sourced oils and condensates in the tarim basin nw china abstract a suite of oils and condensates from cambrian ordovician sources in the cratonic region of the tarim basin nw china has been characterized by gas chromatography mass spectrometry with a focus on factors affecting the extended tricyclic terpane ratio etr c28 c29 tt ts these oils and condensates show etr values ranging from 0 3 to 12 4 suggesting variable source contributions deposited under different environmental conditions coupled with tri and tetracyclic terpane distributions etr can be used as an organofacies discriminator most of the samples have high etr values 2 0 a low relative abundance of the c19 tricyclic terpane c19tt and the c24 tetracyclic terpane c24tet characteristic of a clastic marine depositional environment possibly with upwelling conditions a specific organofacies for a few samples is characterized by low etr values 0 8 and c24tet c26tt 1 0 ratios reflecting deposition under dysoxic conditions however various other alteration processes such as thermal maturity thermochemical sulfate reduction tsr biodegradation and in reservoir mixing probably have a significant impact on this parameter which makes understanding the meaning of the etr complicated the effect of thermal maturity on etr is minimal in the oil generation window but the etr values decrease dramatically at the post oil generation stage tsr seems to preferentially lead to the loss of the c28tt and c29tt before the 18 h 22 29 30 trisnorneohopane ts and thus the etr value decreases as tsr progresses while the dibenzothiophene phenanthrene ratio can help to differentiate tsr alteration from thermal cracking processes the etr is no longer a valid geochemical parameter when these two processes occur etr also increases with biodegradation the c28 and c29tt are more resistant to biodegradation than ts supporting evidence can be derived from a positive correlation between etr and c29 25 norhopane to c30 hopane ratio in reservoir mixing is another important alteration process which normally results in lower etr values after a fresh charge is mixed with a biodegraded charge in a reservoir evaporative fractionation may also have an impact on etr values some unusually high etr values might be attributed to evaporative fractionation the etr values from our case study suggests that the etr parameter is much more complicated than just being an age diagnostic parameter maturation and secondary alteration processes need to be fully accounted for before the etr can be properly applied to interpretations of depositional environment conditions such as upwelling

improved understanding of the petroleum systems of the niger delta basin nigeria biomarker and n alkane compound specific stable carbon isotope analyses csia were carried out on 58 crude oil samples from shallow water and deepwater fields of the niger delta in order to predict the depositional environment and organic matter characteristics of their potential source rocks using a source organofacies prediction approach from oil geochemistry the presence in the western deepwater oils relatively abundant c27 steranes c30 24 n propyl cholestane low oleanane index relatively low pr ph ratios gammacerane and positive to nearly flat c12 c30 n alkane compound specific stable carbon isotope profiles suggests that the source facies that expelled these oils contain significant marine derived organic matter deposited under sub oxic and stratified water column conditions this contrasts with the terrigenous organic matter dominated source rocks accepted for shallow water niger delta oils oils in the shallow water accumulations can be separated into terrigenous and mixed marine terrigenous families the terrigenous family indicates expulsion from source rock s containing overwhelmingly higher plant source organic matter average oleanane index 0 48 high c29 steranes as well as having negative sloping n alkane isotope profiles oxic source depositional conditions pr ph 2 5 and non stratified conditions absence to low gammacerane content are inferred for the terrigenous family the mixed marine terrigenous family has biomarker properties that are a combination of the deepwater and terrigenous shallow water oils bitumen extracts of the sub delta late cretaceous araromi formation shale in the dahomey basin are comparable both molecularly and isotopically to the studied western deepwater oil set but with an over all poor geochemical correlation this poor geochemical match between araromi shale and the western deepwater oils does not downgrade the potential of sub delta cretaceous source rock contribution to the regional oil charge in the deepwater niger delta

coherent surface subsurface fingerprint of the atlantic meridional overturning circulation 1 satellite altimeter data shows a weakening of the north atlantic subpolar gyre during the 1990s which is thought as an indicator of a slowdown of the atlantic meridional overturning circulation amoc however whether the recent slowing subpolar gyre is a decadal variation or a long term trend remains unclear here i show that altimeter data is highly correlated with instrumental subsurface ocean temperature data in the north atlantic and both show opposite signs between the subpolar gyre and the gulf stream path such a dipole pattern is a distinctive fingerprint of amoc variability as shown for the first time by a 1000 year coupled ocean atmosphere model simulation the results suggest that contrary to previous interpretations the recent slowdown of the subpolar gyre is a part of a multidecadal variation and suggests a strengthening of the amoc the ongoing satellite and subsurface temperature measurements could be used to monitor future amoc variations sensitively

oleanane parameter verification by quantitative study of the biomarker occurrence in sediments of the niger delta abstract the variation of the absolute concentration of oleananes in three selevted sedimentary columns of the tertiary niger delta is paralleled by the corresponding oleanane parameter op profile thereby confirming that the latter can be utilized for estimating the relative contribution of terrigenous organic matter it is shown that op features a dynamic range especially at the oil generative window ogw and can precisely delimit the top of the ogw which for the niger delta is shown to coincide approximately with the 80 c isotherm and ro 0 55 this study provides the first direct evidence of the inadequacy of vitrinite reflectance as a maturity parameter for type iii kerogen furthermore based on the new findings an alternative model for oleanene oleanane interconversions in the geosphere is proposed

two stable equilibria of the atlantic subpolar gyre the cyclonic circulation of the atlantic subpolar gyre is a key mechanism for north atlantic climate variability on a wide range of time scales it is generally accepted that it is driven by both cyclonic winds and buoyancy forcing yet the individual importance and dynamical interactions of the two contributions remain unclear the authors propose a simplified four box model representing the convective basin of the labrador sea and its shallow and deep boundary current system the western subpolar gyre convective heat loss drives a baroclinicflow of relatively light water around the dense center eddy salt flux from the boundary current to the center increases with a stronger circulation favors the formation of dense waters and thereby sustains a strong baroclinic flow approximately 10 25 of the total in contrast when the baroclinic flow is not active surface waters may be too fresh to convect and a buoyancy driven circulation cannot develop this situation corresponds to a second stable circulation mode a hysteresis is found for variations in surface freshwater flux and the salinity of the near surface boundary current an analytical solution is presented and analyzed

geochemical evidence of organic matter source input and depositional environments in the lower and upper eagle ford formation south texas abstract late cretaceous source rocks in the south texas eagle ford formation were characterized based on geochemical features of the iona 1 core which penetrates the lower and upper eagle ford formation this set of immature samples provides a detailed record of the variation of organic matter om sources across different depositional facies our results show that organic matter rich shales are dominated by marine type ii kerogen lower eagle ford lef contains high sulfur kerogen type ii s with s c 0 04 and a minor contribution of terrestrial om is evident in the upper eagle ford uef combined geochemical data from iona 1 core samples based on bulk geochemical rock properties residual oil chromatography and biomarker analyses reveal that the total organic carbon content and extractable bitumen content in the lef are higher than in the uef redox sensitive biomarkers demonstrate that sulfur rich photic zone anoxia euxinia developed in the lef and that persistent oxygenation occurs during deposition of the uef sulfur rich kerogen in the lef in turn generates medium high sulfur containing oils up to 2 6 as a consequence of the elevated sulfur contents in the lef oil bitumen generation initiated earlier and at lower maturity levels than in the uef high levels of anomalous 22s 22s 22r homohopane ratios and 20s 5 14 17 steranes have been observed in the lef interval which is controversial because of the low maturity level indicated by most bulk geochemical thermal maturity parameters including tmax calculated ro 0 45 and ts ts tm as well as c29ts c29ts c29 hopane and c29 sterane ratios these anomalously high thermal maturity parameters are more likely caused by enhanced isomerisations due to high organic sulfur content under reducing depositional environments in the lef rather than by thermal maturation hypothetical diagenetic pathways for the sulfurisation of homohopanoids and steroids are proposed to explain their abnormal isomerisations in the lef

the role of heating winds and topography on sea level changes in the north atlantic seasonal and interannual to decadal variations of large scale altimetric sea surface height ssh owing to surface heating and wind forcing in the presence of topography are investigated using simplified models the dominant forcing mechanisms are time scale dependent on the seasonal time scale locally forced thermosteric height explains most of the ssh variance north of 18 n first mode linear long baroclinic rossby waves forced by changes in the winds and eastern boundary conditions explain most of the variance between 10 n and 15 n and are also important east of greenland on interannual to decadal time scales local thermosteric height remains important at several locations in the middle and high latitudes a topographic sverdrup response explains interannual to decadal ssh between 53 n and 63 n east of greenland farther south the linear rossby wave model explains ssh variations on interannual to decadal time scales between 30 n and 50 n from mid basin to the eastern boundary propagation of the eastern boundary condition into the interior dominates the interannual to decadal ssh signals south of 30 n the effect from nao related heat flux on ssh is small but forcing the topographic sverdrup models with nao regressed winds gives slightly better agreement with the observed ssh in the subpolar gyre on interannual to decadal time scales than using the full winds

significance to hydrocarbon exploration of terrestrial organic matter introduced into deep marine systems insights from the lower cretaceous in the levant basin abstract oil shows from wells in the levant basin and egypt are suggestive of potential economic discoveries within unpenetrated mesozoic reservoirs in the eastern mediterranean analysis of some of these oils indicate a non marine source of mixed deltaic terrestrial or lacustrine origin for the organic matter data from barremian aptian sediments from the mnuph 1 core in northern israel opens a window on potential importance of terrestrial sourced kerogen deposited in source rocks in a marine depositional environment core analyses of the barremian nabi sa id fm demonstrate the occurrence of a gas prone immature source rock of 77 m gross thickness averaging 4 6 toc peaking at 37 toc rock eval pyrolysis biomarker n alkane sterane and tricyclic terpane indices atomic c n ratios and 13corg ranges indicate mixed terrestrial marine organic source rocks for the barremian while higher up the aptian hidra fm contains source rocks with organic matter derived dominantly from carbohydrate rich land plants the interval at mnuph 1 includes abundant evidence for off shelf mass transport of terrestrial and proximal marine sediments into the deep marine basin these features are used to explain the anomaly of a terrestrial source for organic matter in this setting mass transport and consequent mixing of distal marine proximal marine and land derived sediment is in fact the norm at the foot of continental slopes globally the dominantly type iii source rocks described here would be unlikely to expel oil but might produce thermogenic gas thermogenic gas identified in similar marine settings might wrongly be interpreted as having been generated from marine organic matter misleadingly indicative of a prospective oil source when prospecting for deep rooted hydrocarbon accumulations in offshore marine settings an alternative system dominated by basinward sediment transport of gas prone terrestrial source rocks into strategically positioned toe of slope marine settings is supported here and could well be producing gas in the levant basin

north atlantic interdecadal variability oceanic response to the north atlantic oscillation 1865 1997 abstract in contrast to the atmosphere knowledge about interdecadal variability of the north atlantic circulation is relatively restricted it is the objective of this study to contribute to understanding how the north atlantic circulation responds to a forcing by the north atlantic oscillation nao on interdecadal timescales for this purpose the authors analyze observed atmospheric and sea surface temperature sst data along with the response of an ocean general circulation model to a realistic monthly surface flux forcing that is solely associated with the nao for the period 1865 1997 in agreement with previous studies it is shown that the relationship between the local forcing by the nao and observed sst anomalies on interdecadal timescales points toward the importance of oceanic dynamics in generating sst anomalies a comparison between observed and modeled sst anomalies reveals that the model results can be used to assess interdecadal variability of the north atlantic circulation the observed

study on diagenesis of organic matter in immature rocks abstract since many immature oils have been found in a number of tertiary basins of china a series of cores oligocene and several immature rocks after thermal simulation have been investigated for their biomarker distributions by gc and gc ms the presence of biomarkers in the cores seem to follow a rule of less to greater stability of hopenes hopanes diasterenes with increasing the depth of cores and subsequently the 22r 22s configuration of hopanes reaches equilibrium the thermal simulation experiments with immature rocks demonstrated that it is possible to generate some immature oils from immature rocks during the diagenesis stage the tricyclic terpanes generated from source rocks during diagenesis stage tended to be enriched in the oils compared to their source rocks and the relative abundance of lower molecular weight tricyclic terpanes to their higher molecular weight homologues may be useful for the subdivision of diagenesis

on the mechanism of tectonic transport in zones of oblique subduction abstract many cases of oblique subduction are known throughout the world today and many more must have existed in the past in at least one modern case sumatra the over riding plate has responded to oblique subduction by forming a strike slip fault that traverses the magmatic arc and displaces its leading edge in the direction of the transverse component of oblique convergence conditions favoring this sort of tectonic response are shown to be 1 1 a high angle of oblique convergence 2 2 a low angle of subduction and 3 3 relative thermal softening of the magmatic arc this mechanism may have been responsible in part for northward transport of western cordilleran magmatic arc and subduction zone rocks in the late cretaceous and earliest tertiary it also may help to explain evidence of southward transport and left lateral shear in northern mexico and the caribbean region in pre jurassic time

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

response of the north atlantic subpolar gyre to persistent north atlantic oscillation like forcing the response of the north atlantic subpolar gyre spg to a persistent positive or negative phase of the north atlantic oscillation nao is investigated using an ocean general circulation model forced with idealized atmospheric reanalysis fields the integrations are analyzed with reference to a base line integration for which the model is forced with idealized fields representing a neutral state of the nao in the positive nao case the results suggest that the well known cooling and strengthening of the spg are after about 10 years replaced by a warming and subsequent weakening of the spg the latter changes are caused by the advection of warm water from the subtropical gyre stg region driven by a spin up of the atlantic meridional overturning circulation amoc and the effect of an anomalous wind stress curl in the northeastern north atlantic which counteracts the local buoyancy forcing of the spg in the negative nao case however the spg response does not involve a sign reversal but rather shows a gradual weakening throughout the integration the asymmetric spg response to the sign of persistent nao like forcing and the different time scales involved demonstrate strong non linearity in the north atlantic ocean circulation response to atmospheric forcing the latter finding indicates that analysis based on the arithmetic difference between the two nao states e g nao minus nao may hide important aspects of the ocean response to atmospheric forcing

geochemical composition and origin of tertiary oils in the yinggehai and qiongdongnan basins offshore south china sea abstract this study comprehensively characterizes the geochemical compositions of tertiary crude oils in the yinggehai and qiongdongnan basins offshore south china sea and differentiates their source properties using chemical and isotopic data the oils in the two basins have distinct source characteristics the majority of the oils from the yacheng yc field in the qiongdongnan basin are commonly marked by high pr ph ratios mostly from 4 5 to 7 0 unusually abundant angiosperm derived compounds and a domination of c29 in diasteranes suggesting a predominantly terrigenous organic source in contrast the oils from the dongfang df and ledong ld fields in the yinggehai basin have relatively lower pr ph values 2 5 5 5 and a low amount of bicadinanes moreover some oils in this basin contain abundant 4 methylsteranes and detectable c30 desmethyl steranes the difference in the molecular composition is also apparent with regard to the aromatic hydrocarbons the former oils contain more abundant biphenyls fluorenes and 2 phenylnaphthalene than the latter ones the oils from the qiongdongnan basin are relatively depleted in 13c and have 13c values of the whole oil in the range of 24 9 to 26 9 consistent with the great terrigenous input in contrast the yinggehai oils are isotopically heavier with 13c values from 21 6 to 23 6 typical of a marine isotope signature correspondingly their n alkane isotopes have different 13c ranges and exhibit distinct distribution profiles based on the oil source rock correlation the oils in the yc field were generated from the coastal plain swamp and shallow marine strata of the oligocene in the qiongdongnan basin while the yinggehai oils were sourced from the miocene shallow marine mudstones in the basin

distribution of aliphatic des a triterpenoids in the dajiuhu peat deposit southern china abstract aliphatic des a triterpenoids have been tentatively assigned in samples taken from a 260 cm thick peat sequence from the dajiuhu basin of southern china using gas chromatography mass spectrometry gc ms the compounds possessing the carbon skeletons of oleanane ursane or lupane are generally considered as the microbial degradation products of plant triterpenoids under anoxic conditions abundant aliphatic des a triterpenoids were observed only in peat samples during the transitional period from the last glaciation to the early holocene 9 5 11 6 cal 14 c ka bp among these des a lupane is the only saturated ring a degraded compound whilst mono and di unsaturated des a triterpenes are dominated by oleanane and ursane derivatives the mono and di unsaturated des a triterpenes show a strong correlation r 2 0 94 in abundance indicating that they may be derived from the same source or process des a lupane shows no correlation in abundance with the mono or di unsaturated des a triterpenes r 2 des a triterpenoids corresponds to the interval with relatively high sedimentation rate 0 3 mm per year these data indicate that the abundance of aliphatic des a triterpenoids in the dajiuhu peat deposit in the early holocene may result from the prevailing reducing conditions in the water table or surficial sediment and or rapid preservation of the early diagenetic products our study highlights the potential application of des a triterpenes in the reconstruction of palaeoenvironments based on peat sequences