twenty first century warming of a large antarctic ice shelf cavity by a redirected coastal current the redirection of warm water under the filchner ronne ice shelf during the second half of this century could cause the ice shelf base to melt at a rate 20 times higher than at present warm ocean currents are known to erode ice shelves from below but changes in currents can be forced by many different mechanisms leading to uncertain outcomes this study highlights the vulnerability to climate change of a small antarctic coastal region which has potentially severe consequences for the mass balance of a large antarctic ice shelf hellmer et al use climate modelling to show that the projected loss of sea ice in the weddell sea east of the antarctic peninsula leads to an increase in wind stress which in turn accelerates a warm ocean current far underneath the vast filchner ronne ice shelf the authors predict that the increased warmth could increase melt by a factor of 20 with possible consequences for ice stream dynamics in the east antarctic ice sheet the antarctic ice sheet loses mass at its fringes bordering the southern ocean at this boundary warm circumpolar water can override the continental slope front reaching the grounding line1 2 through submarine glacial troughs and causing high rates of melting at the deep ice shelf bases3 4 the interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice mass loss here we show that a redirection of the coastal current into the filchner trough and underneath the filchner ronne ice shelf during the second half of the twenty first century would lead to increased movement of warm waters into the deep southern ice shelf cavity water temperatures in the cavity would increase by more than 2 degrees celsius and boost average basal melting from 0 2 metres or 82 billion tonnes per year to almost 4 metres or 1 600 billion tonnes per year our results which are based on the output of a coupled ice ocean model forced by a range of atmospheric outputs from the hadcm35 climate model suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern weddell sea due to thinning of the formerly consolidated sea ice cover the projected ice loss at the base of the filchner ronne ice shelf represents 80 per cent of the present antarctic surface mass balance6 thus the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of antarctic ice streams and ice shelves and global sea level rise

horizontal circulation and volume transports in the weddell gyre derived from argo float data argo floats provide both hydrographic and trajectory data affording the opportunity to investigate surface to mid depth ocean dynamics here argo float data are used to determine the absolute geostrophic velocity field of the upper 50 2000 m of the weddell gyre from which the overall circulation pattern is investigated the weddell gyre plays a pivotal role in the modification of climate by advecting heat towards the antarctic ice shelves and by modifying the water masses that feed into the lowest limb of the global ocean overturning circulation warm deep water the source water mass that delivers heat to the weddell gyre is conveniently located within the upper 2000 m domain covered by the floats we investigate its volume transport as it circulates the gyre full depth volume transports are estimated by applying a quadratic function to extrapolate the relative dynamic height field component to the full ocean depth using ctd profiles from ship based surveys to determine an extrapolation error major new insights are provided by this study there is an established double gyre structure to the circulation with a strong eastern cell and a weaker western cell regional variation of the baroclinic component of the flow field is revealed indicating a northeast to southwest reduction in the baroclinic flow along with a strong meridional gradient of baroclinic flow along the northern limb of the gyre especially east of 25 w the zonal mean gyre strength away from the shelf edge is 32 5 sv 1 sv 1 106 m3 s 1 of which 13 3 sv are associated with the advection of warm deep water there is a considerable amount of recirculation within the gyre interior where water does not traverse the full zonal extent of the gyre the recirculation is stronger in the eastern cell of the observed double gyre structure the interior circulation cells partly explain the large variations in previous gyre strength estimates we provide an extensive review of previous estimates in context of the new results obtained

the antarctic slope current near 30 e the antarctic slope current flows westward above the continental slope of antarctica entering the weddell sea near 30 e and supplying dense water to the deep overturning cell there and contributing to global antarctic bottom water formation observations from the 2008 i6s hydrographic section are used to investigate the strength of the slope current near 30 e a prominent topographic feature the gunnerus bank diverts the slope current upstream of this longitude and has a large effect on the current s structure splitting it into a coastal and offshore component the bank also enhances water mass mixing and lateral exchange across the slope as part of the 2008 occupation an additional line was made along the crest of the bank forming a closed volume over the western side by combining hydrographic and lowered acoustic doppler current profiler measurements in this box using an inverse method the slope current transport is estimated to be 9 6 2 3 sv the transport associated with the antarctic slope front is 4 0 0 3 sv of which 1 8 0 3 sv enters the weddell gyre as recently formed dense water

primary migration by diffusion through kerogen i model experiments with organic coated rocks abstract laboratory experiments were performed to assess diffusion through kerogen as a mechanism of hydrocarbon transport through fine grained rocks such transport can be important in primary migration within source rocks and in leakage through seals to test the concept of diffusion through organic matter networks model experiments were performed in which hydrocarbon diffusion was measured through austin chalk cores that had been coated with a monolayer of fatty acids hydrocarbon fluxes through the coated cores were compared to hydrocarbon fluxes through uncoated austin chalk cores results showed that the organic coating enhanced transport through the core by a hundredfold over diffusion through its water filled pore space alone

magnetic and tectonostratigraphic correlation at a terrane boundary the tappins group of the southern uplands prominent aeromagnetic anomalies around ballantrae in southwest scotland have long been associated with extensive outcrops of basic ultrabasic igneous rocks in the midland valley terrane however recent reprocessing of data from a 1978 detailed aeromagnetic survey has demonstrated excellent correlation between discrete aeromagnetic features and certain magnetic greywacke formations within the early caradoc tappins group this heterogeneous unit forms the oldest and most northwesterly tectonostratigraphic tract in the southern uplands terrane and is characterized by relatively high detrital magnetite and serpentinite content and elevated values for cr and ni this suggests original close sedimentary links with an ophiolitic terrane not unlike the presently adjacent ballantrae complex or its extensive along strike correlatives a consideration which has important implications for terrane reconstructions in this region

kinetic modelling of petroleum formation and cracking implications from the high pressure high temperature elgin field uk north sea in this paper we use a case study to test the simulation of generation migration and cracking of petroleum fluids by a 2d compositional basin simulator using kinetic models based on chemical classes of compounds the selected area is the high pressure 1100 bar high temperature 190 c elgin field in the north sea this study is mainly focused on kinetic modelling of secondary cracking because in this zone paraffinic condensates with almost 50 c6 alkanes were recently discovered whereas only gas c5 was expected given the high temperature conditions the detailed hydrocarbon composition observed today in the fulmar sands reservoir of the elgin field is compared with the results of several simulations aimed at testing the influence of jurassic source rocks retention properties kinetic parameters and temperature variations on the predicted composition of fluids the influence of pressure was neglected in the modelling on the basis of results published in the literature results show that in this north sea area primary cracking of the kerogen into oil is completed whichever source rock is considered and that secondary cracking of accumulated petroleum compounds in the reservoir is presently in progress under these conditions source rock type and retention during primary and secondary migration have little influence on the present oil composition the occurrence of a monophasic paraffinic fluid in the elgin reservoir despite the high temperature is due to its very recent increase from 160 c to over 180 c in the last million years the fluid composition evolves rapidly and our compositional kinetic scheme accounts correctly for the presence of c6 hydrocarbons in these geological conditions first results using the compositional kinetic scheme of behar et al behar f kressman s rudkiewicz j l vandenbroucke m 1991 experimental simulation in a confined system and kinetic modelling of kerogen and oil cracking organic geochemistry 19 1 3 173 189 for secondary cracking showed a reasonably good fit between calculated and observed detailed fluid composition except for methylated aromatics which are overestimated and methane which is underestimated a recent comparison of kinetic parameters obtained from pyrolysis experiments on model compounds showed that it is not realistic to assume as done previously the same frequency factor for all chemical classes of compounds the higher stability of methylated aromatics relative to saturates observed under laboratory conditions would be extended to geological conditions a second set of simulations using frequency factors and activation energies obtained on these model compounds gave a better fit for methylated aromatics however methane is still strongly underestimated and reasons which could explain this discrepancy are discussed

on the structure and the transport of the eastern weddell gyre abstract the circulation pattern and volume transports in the eastern weddell gyre are estimated on the basis of hydrographic data collected by r v polarstern between 1989 and 1996 in the northeastern edge of the weddell gyre eastward flowing water masses from the antarctic circumpolar current and the weddell sea converge due to the strong effect of topographic constraints on ocean currents in the weakly stratified waters of high latitudes the wedge like structure of the southwest indian ridge can cause the convergence the increased shear leads to instabilities of the current at the eastern end of the ridge which produce an intense mesoscale eddy field between 15 and 30 e in the eddies water from the weddell cold regime and the antarctic circumpolar current waters mix and form the water masses of the weddell warm regime these waters are advected southward and flow towards the westward southern rim current which is driven by the antarctic eastwind band hence there is not a continous flow from the northern to the southern rim but a decay of the mean flow in the northeast and a reformation in the south volume transports across the greenwich meridian estimated on the basis of a combined ctd adcp data set result in an eastward flow of 61 sv in the northern rim current and a westward return flow of 66 sv in the southern part of the gyre the transport is about twice as high as previous estimates between kapp norvegia and the northern tip of the antarctic pensinsula indicating a significant gyre circulation north of 70 s

eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea 1 the eastern weddell sea is characterized by narrow continental shelves and warm deep water wdw is located in close proximity to the ice shelves in this region the exchange of wdw across the antarctic slope front asf determines the rate of basal ice shelf melting here we present a unique data set consisting of 2351 vertical profiles of temperature and salinity collected by southern elephant seals mirounga leonina and a profile beneath the fimbul ice shelf fis obtained via drilling through 395 m of ice this data set reveals variations in salinity and temperature through winter and using a conceptual model of the coastal salt budget we quantify the main exchange processes our data show that modified wdw with temperatures below 1 5 c is advected onto the shelf and into the ice shelf cavities by an eddy overturning of the asf the onshore ekman flux of surface waters during summer is the main source of freshwater that leads to the formation of low salinity shelf waters in the region the modified wdw that reaches beneath the ice shelves is too cold for basal ice shelf melting to create such low salinity water a high resolution model of an idealized asf continental shelf ice shelf system supports the conclusions from the data analysis the inflow of wdw onto the continental shelf and into the ice shelf cavity occurs within a bottom boundary layer where the eddy advection in the model is particularly strong in close agreement with the observed vertical profile of temperature beneath the fis citation nost o a m biuw v tverberg c lydersen t hattermann q zhou l h smedsrud and k m kovacs 2011 eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea j geophys res 116 c11014 doi 10 1029 2011jc006965

on the sources of weddell gyre antarctic bottom water in march april 1995 as part of the world ocean circulation experiment section a23 we completed 49 hydrographic stations across the weddell gyre and southern antarctic circumpolar current from the antarctic continental shelf 72 5 s 16 5 w to south georgia 55 s 34 5 w chlorofluorocarbon cfc 11 cfc 12 and cfc 113 data collected at these stations reveal that distinct sources renew the antarctic bottom water defined as waters with potential temperatures less than 0 c of the weddell gyre weddell sea bottom water defined as waters with potential temperatures less than 0 7 c formed in the western weddell sea has cfc concentrations about 5 to 6 times higher in the eastward flowing northern weddell gyre than in the westward flowing southern limb our cfc measurements suggest that distinct sources of weddell sea bottom water exist in the western weddell sea in agreement with previous descriptions based on potential temperature and salinity signals in the northern weddell gyre high cfc concentrations in weddell sea deep water potential temperatures between 0 c and 0 7 c confirm the long recognized sources for this water mass in the western and southwestern weddell sea in the southern weddell gyre at about 20 w and along the antarctic continental slope weddell sea deep water with potential temperatures around 0 45 c shows a deep cfc maximum about 1000 m above the seafloor cfc concentrations in this deep southern core are about 80 of those of new weddell sea deep water in the northern weddell gyre near 30 w the a23 cfc and hydrographic data are not consistent with the hypothesis that weddell sea deep waters are derived from a single source in the western weddell sea instead these tracers suggest that an important portion of the weddell sea deep water in the southern weddell gyre originates outside the western weddell sea probably near the amery basin and environs around 75 e these features of the circulation and renewal of the deep weddell gyre should be carefully considered in simulations dealing with fluxes pathways and formation rates of antarctic bottom water

magnetic susceptibility contrasts in ordovician greywackes of the southern uplands of scotland ordovician greywacke formations of the southern uplands are demonstrated to have consistent differences in magnetic susceptibility which parallel differences in petrography the observed susceptibilities range from a minimum of 0 16 x 10 3 si for the quartz rich feldspar poor glenwhargen formation to a maximum of 13 81 x 10 3 si for the quartz poor feldspar rich march bum formation and are considered to be directly related to variation in the amount of detrital magnetite in the greywackes rapid measurement of magnetic susceptibility is demonstrated to be a valuable field technique for distinguishing otherwise uniform sedimentary sequences on the basis of differing magnetite content detailed field observations illustrate considerable variation in suscep tibility within metre scale sections perpendicular to bedding through graded sedimentary units which may be caused by density and or grain size effects laboratory measurements of the intensity of natural remanent magnetisation in the petrographically contrasting kirkcolm and galdenoch forma tions show a similar variation to that observed in susceptibility thermally distributed scattered magnetization directions indicate that no primary remanence has survived the low grade burial metamorphic event in the southern uplands

synoptic gulf stream velocity profiles through simultaneous inversion of hydrographic and acoustic doppler data data from a shipborne acoustic profiling device have been combined with conductivity temperature depth o 2 sections across the gulf stream to form estimates of the absolute flow fields the procedure for the combination was a form of inverse method the results suggest that at the time of the observations june 1982 the net gulf stream transport off hatteras was 107 11 sv and that across a section near 72 5ow it had increased to 125 6 sv subject to further uncertainty from the definition of the stream the transport of the deep western boundary current was 9 3 sv these and other transport estimates are plausibly close to previous calculations but we do not claim that they represent the temporal mean for comparison purposes we have done an inversion using the hydrographic o 2 data alone as in previously published results and obtained qualitative agreement with the combined inversion inversion of the acoustic measurements alone when corrected for instrument biases leaves unacceptably large mass transport residuals in the deep water our conclusion is that the inversion of the combined data sets produces results much improved over those from using either acoustic or hydrographic chemical constraints in isolation the procedures are close analogues to those which can be used with satellite altimeters and are a procedure for obtaining very accurate geoid slope measurements

remotely induced warming of antarctic bottom water in the eastern weddell gyre 1 four repeat hydrographic sections across the eastern weddell gyre at 30 e reveal a warming by 0 1 c and lightening by 0 02 0 03 kg m 3 of the antarctic bottom water aabw entering the gyre from the indian sector of the southern ocean between the mid 1990s and late 2000s historical hydrographic and altimetric measurements in the region suggest that the most likely explanation for the change is increased entrainment of warmer mid depth circumpolar deep water by cascading shelf water plumes close to cape darnley where the indian sourced aabw entering the weddell gyre from the east is ventilated this change in entrainment is associated with a concurrent southward shift of the antarctic circumpolar current s acc southern boundary in the region this mechanism of aabw warming may affect wherever the acc flows close to antarctica

tidally driven vorticity diurnal shear and turbulence atop fieberling seamount abstract fine and microstructure profiles collected over fieberling seamount at 32 26 n in the eastern north pacific reveal a variety of intensified baroclinic motions driven by astronomical diurnal tides the forced response consists of three phenomena coexisting in a layer 200 m thick above the summit plain i an anticyclonic vortex cap of core relative vorticity 0 5f ii diurnal fluctuations of 15 cm s 1 amplitude and 200 m vertical wavelength and iii turbulence levels corresponding to an eddy diffusivity e 10 10 4 m2 s 1 the vortex cannot be explained by taylor proudman dynamics because of its 0 3fn2 negative potential vorticity anomaly the 0 3f fortnightly cycle in the vortex s strength suggests that it is at least partially maintained against dissipative erosion by tidal rectification the diurnal motions are slightly subinertial turning clockwise in time and counterclockwise with depth over the summit plain they also exhibit a fortnightly cycle in their amplitude pointing to

the transport of the weddell gyre across the prime meridian abstract current meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the weddell gyre on the greenwich meridian the record length mean volume transport is 45 sv to the east within the northern and 56 sv to the west within the southern limb of the weddell gyre thus 11 sv must leave the gyre circulation west of the greenwich meridian and enter it east of it the deficit occurs with 8 sv mainly in the circumpolar deep water cdw warm deep water wdw layer surface waters and weddell sea deep water wsdw contribute 2 and 3 sv respectively in contrast to this 3 sv more of weddell sea bottom water wsbw flow in the northern limb to the east than in the southern limb to the west which suggests a wsbw formation rate of about 3 sv in the western weddell sea in the southern boundary of the antarctic circumpolar current acc a volume transport of 35 16 sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity the large heat content of the northern limb points to an extensive heat exchange between the weddell sea and the world ocean west of the prime meridian hence the heat transport as well as the volume transport suggest that the water masses of the weddell gyre are not exclusively replaced in its eastern part but that there is a significant exchange of water masses to the west of the prime meridian

comment and reply on age and origin of ballantrae ophiolite and its significance to the caledonian orogeny and the ordovician time scale comment

primary migration behaviour of hydrocarbons from laboratory experiments to geological situations through fluid flow models abstract primary migration is a complex process involving coupled fluid generation and mass transfer in low permeable rocks joint experimental and modelling work have been performed in order to better understand this problem eventually experimental results have been modelled and extrapolated to geological conditions maturation and expulsion experiments have been carried out with water saturated immature type ii source rocks from the paris basin with sample weights up to 3 kg temperatures were stepwise increased from 20 c to 285 330 or 380 c at constant hydrostatic pressures of respectively 17 or 55 mpa during up to 5000 h during the experiments generated fluids expelled out of the heating cell and were sampled prior to a complete analysis mass balances were checked on hydrocarbon gases liquid hydrocarbons co 2 and water meanwhile closed system pyrolysis experiments were performed on isolated kerogen extracted from the same source rocks they allowed us to derive a compositional kinetic cracking reaction network it was then possible to tackle the expulsion of fluids out of the source rock the kinetic scheme provides a guideline to understand the generation of fluids from kerogen the expulsion experiments provide an insight into the expulsion mechanisms no axial stress has been applied to the samples in the experiments therefore the influence of rock compaction due to effective stress was not studied in these experiments a numerical model of expulsion has been set up based on volume and mass balance conservation equations in the source rock the volume is assumed to vary as solid kerogen transforms to liquid products and solid residue the mass of each compound is kept in balance as it is created or destroyed through primary and secondary cracking and expelled through multiphase fluid flow therefore depending on pressure temperature and composition fluids in the source rock are split into several phases following a thermodynamical equation of state all mobile phases flow according to darcy s law experiments were modelled the best fit being achieved with the following conditions all fluids including water co 2 and hydrocarbons are allowed to form a multiphase mixture the heavy compounds resins and asphaltenes are in a single very viscous phase and are less easily expelled as most of them are cracked inside the source rock extrapolations to geological pressure and temperature conditions were performed afterwards in order to check the phase behaviour and the expulsion efficiency

fronts transport and weddell gyre at 30 e between africa and antarctica a detailed description of the frontal structure of major currents and estimates of transport between africa and antarctica at 30 e were made on the basis of a finely resolved hydrographic section made during the 1996 civa 2 cruise particular emphasis was put on a refinement of the eastern boundary of the weddell gyre by analyzing also supplementary hydrographic data from the 1993 civa 1 cruise and the best available historical hydrographic data in the weddell and enderby basins contrary to the general belief our results show that the weddell gyre extends far beyond 30 e reaching at least as far east as the enderby land promontory 53 e from this point westward currents along the antarctic continental margin constitute the gyre s southern boundary thus closing the cyclonic circulation of the gyre at its easternmost end as the most convincing evidence for this refined circulation scheme significant westward transport south of 65 s has been identified from the civa 1 acoustic doppler current profiler data we have shown also using an inertial jet model that the blocked feature of the weddell cold regime 57 s to the west of 25 e is due to the topographic control of flow by local bathymetry during the civa 2 cruise 70 of the antarctic circumpolar current acc was concentrated near the polar front 51 s with surface speeds reaching up to 70 cm s 1 the baroclinic current field in the subpolar area south of the weddell front 58 s for civa 2 and 57 s for civa 1 is featureless 3 cm s 1 but yielding a nonnegligible eastward transport of 15 sv 1 sv 106 m3 s 1 this bottom referenced baroclinic transport is entirely compensated by a substantial westward barotropic transport south of 65 s the acc transport across the 30 e section during the civa 2 cruise is estimated to be 160 sv

observations of the antarctic slope undercurrent in the southeastern weddell sea 1 the antarctic slope front presents a dynamical barrier between the cold antarctic shelf waters in contact with ice shelves and the warmer subsurface waters offshore two hydrographic sections with full depth current measurements were undertaken in january and february 2009 across the slope and shelf in the southeastern weddell sea southwestward surface intensified currents of 30 cm s 1 and northeastward undercurrents of 6 9 cm s 1 were in thermal wind balance with the sloping isopycnals across the front which migrated offshore by 30 km in the time interval between the two sections a mid depth undercurrent on february 23 was associated with a 130 m uplift of the main pycnocline bringing warm deep water closer to the shelf break this vertical displacement comparable to that caused by seasonal variations in wind speed implies that undercurrents may affect the exchanges between coastal and deep waters near the antarctic continental margins

turbidite geochemistry and provenance studies in the southern uplands of scotland regional lithogeochemical data from the southern uplands have been used to characterize a distinctive stratigraphy across this region a suite of 840 point counted and petrographically classified greywacke samples were used to establish chemical fingerprints for a series of greywacke dominated lithostratigraphical units these fingerprints were then used to evaluate a further 1455 greywacke samples collected throughout the southern uplands and longford down and enabled a series of strike parallel geochemical tracts to be defined four principal geochemical groups are recognized relating to cratonic and volcanic derived greywacke provenances and both carbonate rich and hydrothermally altered greywackes volcanic derived units display higher ti fe mg ca na mn cr ga ni sr v and zn values than their cratonic counterparts which with the exception of the carbonate rich hawick group display higher si k la nb rb th and zr volcaniclastic greywackes display ree patterns dissimilar to typical post archean upper crust but similar to their andesitic components whereas cratonic groups have ree patterns close to that of upper crust systematic strike parallel geochemical variation in the southern uplands is controlled by petrographical differences which directly reflect provenance with individual lithostratigraphical units derived from variable mixtures of ophiolitic calc alkaline acid igneous low grade metamorphic and carbonate rich detritus

on the origin of the deep cfc maximum in the eastern weddell sea numerical model results cfc tracer observations indicate that prydz bay in the indian sector of the southern ocean is a region of deep and bottom water formation results of a circum polar ocean circulation model which includes cfc an age tracer and numerical floats indicate prydz bay as being a convection site which contributes to the reservoir of freshly ventilated waters in the weddell sea in contrast to the newly formed weddell sea bottom water captured near bottom water masses of prydz bay origin spread on hori zons which pass the ridges confining the weddell sea there fore contributing directly to the ventilation of the global abyss

the contribution of the weddell gyre to the lower limb of the global overturning circulation the horizontal and vertical circulation of the weddell gyre is diagnosed using a box inverse model constructed with recent hydrographic sections and including mobile sea ice and eddy transports the gyre is found to convey 42 8 sv 1 sv 106 m3 s 1 across the central weddell sea and to intensify to 54 15 sv further offshore this circulation injects 36 13 tw of heat from the antarctic circumpolar current to the gyre and exports 51 23 msv of freshwater including 13 1 msv as sea ice to the mid latitude southern ocean the gyre s overturning circulation has an asymmetric double cell structure in which 13 4 sv of circumpolar deep water cdw and relatively light antarctic bottom water aabw are transformed into upper ocean water masses by mid gyre upwelling at a rate of 2 2 sv and into denser aabw by downwelling focussed at the western boundary 8 2 sv the gyre circulation exhibits a substantial throughflow component by which cdw and aabw enter the gyre from the indian sector undergo ventilation and densification within the gyre and are exported to the south atlantic across the gyre s northern rim the relatively modest net production of aabw in the weddell gyre 6 2 sv suggests that the gyre s prominence in the closure of the lower limb of global oceanic overturning stems largely from the recycling and equatorward export of indian sourced aabw

differential fluid migration behaviour and tectonic movement in lower silurian and lower cambrian shale gas systems in china using isotope geochemistry abstract isotope geochemistry has been introduced as a means to trace origin of the hydrocarbon and characterize highly productive shale gas systems recently to assess the impact of tectonic movement and the sealing of shale gas systems isotope geochemistry pressure coefficients and the distribution of bitumens are analysed many samples yield isotope geochemical data with typical carbon isotopic reversals 13 c 1 13 c 2 and hydrogen isotopic reversals 13 d c2h6 13 d ch4 in the lower silurian shale gas isotopically reversed gases are considered to originate in sealed self contained petroleum systems besides isotope reversals order degree of shale gas has positive correlation with gas production isotopically normal gases from the lower cambrian indicate that this formation was a continued relatively open petroleum system when oil and gas generated the pressure coefficients of the lower silurian shale gas reservoir range from 1 45 to 2 03 indicating that the reservoir is overpressurized whereas the lower cambrian shale gas reservoir possesses a normal pressure system overpressurization of the lower silurian shale gas reservoir also indicates that it is a well sealed system the distribution and isotope geochemistry of bitumens in the sinian dolomite and cambrian shale suggests that the source rock of the sinian hydrocarbon is the cambrian shale an unconformity induced from tectonic movement during the tongwan period is interpreted to be the fluid migration tunnel and the cause of the differential shale gas content and production finally the isotopic reversals associated with maturity pressure coefficients and tectonic evolution can both assess the preservation conditions of the reservoir and explain the differential fluid migration behaviour

the antarctic slope current in a changing climate the antarctic slope current asc is a coherent circulation feature that rings the antarctic continental shelf and regulates the flow of water towards the antarctic coastline the structure and variability of the asc influences key processes near the antarctic coastline that have global implications such as the melting of antarctic ice shelves and water mass formation that determines the strength of the global overturning circulation recent theoretical modeling and observational advances have revealed new dynamical properties of the asc making it timely to review earlier reviews of the asc focused largely on local classifications of water properties of the asc s primary front here we instead provide a classification of the current s frontal structure based on the dynamical mechanisms that govern both the along slope and cross slope circulation these two modes of circulation are strongly coupled similar to the antarctic circumpolar current highly variable motions such as dense overflows tides and eddies are shown to be critical components of cross slope and cross shelf exchange but understanding of how the distribution and intensity of these processes will evolve in a changing climate remains poor due to observational and modeling limitations results linking the asc to larger modes of climate variability such as el nino show that the asc is an integral part of global climate an improved dynamical understanding of the asc is still needed to accurately model and predict future antarctic sea ice extent the stability of the antarctic ice sheets and the southern ocean s contribution to the global carbon cycle

study of petroleum generation by compaction pyrolysis i construction of a novel pyrolysis system with compaction and expulsion of pyrolyzate from source rock abstract a compaction pyrolysis system was developed to simulate changes of source rocks during the course of burial and subsidence in a sedimentary basin this system can reproduce a number of phenomena that previous methods could not achieve with programmed temperature and pressure controllers the system can simulate the following facets of sediment diagenesis in the natural system 1 a increase in temperature overburden pressure and fluid pressure during burial and subsidence of a formation 2 b petroleum generation from thermal degradation of kerogen 3 c expulsion of interstitial and bound water during compaction of sedimentary rocks 4 d expulsion of oil and gas generated 5 e phase changes of clay minerals zeolites and silica minerals due to increases in temperature and pressure in addition comparison of compaction pyrolysis with non compacting hydrous pyrolysis shows the following 1 1 the composition of gas from compaction pyrolysis was similar to that of natural gases containing only small proportions of unsaturated hydro carbons in contrast gas from hydrous pyrolysis contain 5 10 unsaturated hydrocarbons 2 2 both compaction and hydrous pyrolysis produced oils resembling crude oil in the natural system 3 3 while macerals after hydrous pyrolysis showed abundant holes by evaporation of volatile products by pyrolysis macerals after compaction pyrolysis showed fewer holes however in samples from compaction pyrolysis deformation from compaction was observed 4 4 during the compaction pyrolysis experiment expulsion of oil and gas from source rock compaction cell was observed with the increase in fluid pressure and fluid volume in summary compaction pyrolysis permits a more realistic reproduction of natural phenomena as a result of which a more detailed study of petroleum generation and migration is possible

tectonostratigraphy of the glen app area southern uplands scotland anatomy of an ordovician accretionary complex the stratigraphy and structure of the glen app coastal area northwestern southern uplands are characterized by structural repetition of both chaotic and coherent units of the middle ordovician caradocian tappins group the chaotic unit the currarie formation comprises blocks including basalt chert and terrigenous sedimentary rocks set in folded and in places sheared red to grey siliceous mudstone the coherent unit is turbiditic and is divided into the dalreoch formation in the north and the corsewall formation in the south the former is characterized by inclined isoclinal folds and thrusts whereas the latter shows a homoclinal dip although both are largely overturned northwards small scale duplexes are observed within the coherent turbidites of the dalreoch formation and chaotic units larger duplexes identified on the basis of mapping are oriented at an oblique angle to the general trend of regional structures the chemistry of basalt blocks within the currarie formation shows a within plate type suggesting an origin as seamounts the tectono stratigraphy of the area is interpreted as the result of accretion of a substantial seamount at a subduction zone during mid ordovician time thrust interleaving of chaotic and coherent units is inferred to have taken place in and above the decollement zone while thick turbidite beds without strong folding were probably preserved below the decollement and emplaced below a large scale nappe interpretation of the glen app area as part of an accretionary complex confirms that an ocean basin remained open in part of the iapetus system at least until caradocian times