interannual enso and interdecadal enso like variability in the southern hemisphere tropospheric circulation abstract recent work has identified variability in the pacific ocean sst with a structure qualitatively similar to enso but at lower frequencies than enso zhang et al have documented the atmospheric circulation anomalies in the tropics and northern hemisphere that are associated with decadal enso like variability and compared these anomalies to those associated with the interannual enso cycle here the authors extend the study of zhang et al to the southern hemisphere using the national centers for environmental prediction national center for atmospheric research reanalysis data for 1958 96 consistent with previous studies the southern hemisphere circulation anomalies associated with enso display a teleconnection pattern from the central tropical pacific into the far southeastern pacific ocean comparatively larger circulation anomalies are found in the southern hemisphere associated with the decadal enso like variability though aloft the structure of the anomalies emphasizes the polar vortex wit

characterization of seafloor pockmark seepage of hydrocarbons employing fractal a case study from the western continental margin of india here we apply quantitative technique to describe the seafloor seepages based on the multibeam backscatter and bathymetric investigations to characterize the pockmark morphology the variable seafloor backscatter strength for coarser seafloor sediments are related to the diagenesis derived from biodegraded seepages in this regard box counting method is used to estimate fractal dimension for backscatter imagery data of 398 blocks these blocks are further sub grouped into six classes depending on the spread of pockmark related seepages the study area lies 102 km west off marmagao along the central west coast of india which contains pre dominantly 70 gas charged sediments comparison between the estimated self similar fractals reveals that there is approximately 97 correlation between the box dbox and information dinfo dimensions box dimension derived fractal dimension values suggest that the seepages are more along the fault trace in deeper waters in comparison to sparsely distributed shallow water seepages besides this poor seepage is confined within the smooth to moderately rough seafloor it is established that the high backscatter strength along the upper slope of the pockmark region having higher fractal dimensions reflects multifractal behavior of seepage distribution entire area indicates patchy seepage patterns as supported by estimated fractal values showing intermittent fluctuations which emphasizes non linear behavior estimated self organizing criticality soc parameters for six representative blocks reveal that the nature of pockmark fault trace sediment nature coupled with slumping of pockmark s wall sediment movement due to bottom currents are controlling the dynamic balance in the area seepage system further our study emphasizing the multifractal behavior of seepage blocks clearly depicts the drift in the seepage pattern

gas hydrate reservoirs and gas migration mechanisms in the terrebonne basin gulf of mexico highlights identify new fine grained hydrate filled fracture units in the terrebonne basin identify new hydrate bearing thin sands mostly within fractured muds present detailed seismic amplitude maps of the new hydrate bearing units discuss methane migration mechanisms and hydrate formation in thin sands identify and discuss source reservoir relationships between thick muds and thin sands abstract the interactions of microbial methane generation in fine grained clay rich sediments methane migration and gas hydrate accumulation in coarse grained sand rich sediments are not yet fully understood the terrebonne basin in the northern gulf of mexico provides an ideal setting to investigate the migration of methane resulting in the formation of hydrate in thin sand units interbedded with fractured muds using 3d seismic and well log data we have identified several previously unidentified hydrate bearing units in the terrebonne basin two units are 100 m thick fine grained clay rich units where gas hydrate occurs in near vertical fractures in some locations these fine grained units lack fracture features and they contain 1 4 m thick hydrate bearing sands in addition several other thin sand units were identified that contain gas hydrate including one sand that was intersected by a well at the location of a discontinuous bottom simulating reflector using correlation of well log data to seismic data we have mapped and described these new units in detail across the extent of the available data allowing us to determine the variation of seismic amplitudes and investigate the distribution of free gas and or hydrate we present several potential source reservoir scenarios between the thick fractured mud units and thin hydrate bearing sands we observe that hydrate preferentially forms within thin sand layers rather than fractures when sands are present in larger marine mud units based on regional mapping showing the patchy lateral extent of the thin sand layers we propose that diffusive methane migration or short migration of microbially generated methane from the marine mud units led to the formation of hydrate in these thin sands as discontinuous sands would not be conducive to long range migration of methane from deeper reservoirs

correlation of reservoired gases using the carbon isotopic compositions of wet gas components the carbon isotopic compositions of the wet gas components particularly propane isobutane and normal butane have been found to be particularly valuable for correlating one reservoired gas with another the usefulness of these components for correlation results from their carbon isotopic compositions reflecting both the nature of their source and their maturity this source control is strongest for gases derived from the more highly structured types of kerogen i e woody coaly type iii although the wet gas components carbon isotopic compositions of most gases are at least partly controlled by their source for levels of maturity below the point at which thermal destruction of the wet components occurs as a result the wet gas components are found to provide more ositive correlations than is methane alone three exploration examples illustrate the use of the carbon isotopic compositions of the wet gas components for correlation the leduc reef trend of alberta canada the sleipner area in the north sea and the lena field offshore louisiana united states the three examples also illustrate the need to integrate geochemical interpretations with regional geology to obtain a good understanding of the hydrocarbon source

characteristic features of pockmarks on the north sea floor and scotian shelf this paper presents the results of a comparative study of pockmarks and associated features appearing on both sides of the north atlantic on the scotian shelf off nova scotia and in the northern north sea pockmarks are formed in seabed material consisting of soft silty clay the seismic sonar and lithologic characteristics of the sediments on the scotian shelf are remarkably similar to those found in the northern north sea sediment clouds suspended in the water column immediately over the seabed have previously been observed on side scan records associated with gas charged sediments on corresponding shallow seismic records these and similar observations strongly suggest that most pockmarks are caused by gas efflux through the seafloor however the detailed mechanism of formation and the origin of the gas in the sediments is still unknown

a possible enso signal in the ross sea an examination of the observational record in the ross sea over the period 1982 1994 indicates that there is a statistically significant relationship between the ross sea sea surface temperature sst and the enso signal in the tropical pacific during this period the ross sea ssts lag the enso signal by 2 4 months with the highest correlation coefficient occurring with a lag of 3 months observations of the sea ice concentration during 1982 1994 also indicate a relation between the sea ice concentration in the ross sea and the enso cycle with reduced sea ice concentrations in el nino years

geochemistry of shallow tropical marine sediments from the arafura sea australia abstract tropical shelves have not been the focus of many biogeochemical studies this study presents new data from sediments collected in the arafura sea including headspace gas and lipid contents this allows assessment of modern depositional environments and reconstruction of environmental changes that have affected this tropical carbonate shelf during the last glacial transgression biomarker compositions from surface sediment and core samples from the upper 2 5 m revealed that marine algal input dominated the recently deposited organic matter over the survey area in a region closest to the shore high taraxerol abundance indicated a strong input of mangrove material to samples below 2 5 m indicating strong mangrove development associated with rising sea level during the transgression following the last glacial maximum when sea level stabilized around 6000 bp biomarker data indicate that the terrigenous contribution decreased and that palaeo channels formed during erosion of the continental shelf were infilled with marine dominated material sediments within these palaeo channels contained elevated concentration of dissolved ch4 at the base of the cores the source of the gas was determined to be microbial in origin based on depleted 13c isotopic composition 96 and very low concentration of wet gas components

relationships between the interannual variability of antarctic sea ice and the southern oscillation abstract a climatology of antarctic sea ice extent based on 20 years of data 1973 1992 is presented including measures of interannual variability and extrema in the first half of the year the greatest variability is found in the western hemisphere particularly in the weddell and ross sea regions while in the second semester the variability displays a considerable degree of zonal symmetry we have used this dataset to explore the possible links between antarctic sea ice extent and the southern oscillation index soi to do this we have calculated their correlation for all pairings of calendar months as well as with the soi taken from the year before and subsequent to that of the time of the sea ice data most of the correlations assume their largest magnitude when the soi leads the anomalies in the sea ice but these differ considerably between the three ocean basins the extent of indian ocean sea ice in the months april through july is positively correlated with the soi during most of the previou

geostatistical analysis of seafloor depressions on the southeast margin of new zealand s south island investigating the impact of dynamic near seafloor processes on geomorphology abstract seafloor depressions are widespread on the present day continental slope along the southeast coast of new zealand s south island the depressions appear to be bathymetrically constrained to depths below 500 m correlating to the top of the gas hydrate stability zone and above 1100 m similar depressions observed on the chatham rise are interpreted to have formed as a result of gas hydrate dissociation leading to the hypothesis that a similar origin can be applied for the depressions investigated in this study our investigation however has found limited geophysical or geochemical evidence to support this hypothesis the objective of this paper is to examine whether a causal relationship can be established between potential mechanisms of depression formation and the present day seafloor geomorphology geostatistical analysis methods applied to multibeam bathymetry and interpretation of 3d seismic data have been used to empirically describe the geomorphology of the seafloor depressions and investigate potential correlations between geomorphology and other processes such as current flow along the shelf and slope in this region and underlying polygonal fault systems although the results of our analysis do not preclude that the seafloor depressions formed as a result of gas hydrate dissociation neither does our geophysical or geochemical evidence support the theory therefore we propose an alternative mechanism that may have been responsible for the formation of these structures based on the evidence presented in this study the most likely mechanism responsible for the formation of these seafloor depressions is groundwater flux related to the interaction of current systems and the complex geomorphology of submarine canyons on the southeast coast of the south island

morphology of pockmarks along the western continental margin of india employing multibeam bathymetry and backscatter data this study addresses the morphology of pockmarks along the western continental margin of india using multibeam bathymetry and backscatter data here for the first time we have utilized the application of arcgis geographical information system for understanding the morphology of pockmarks from the western continental margin of india the pockmarks observed in water depths of 145 330 m are circular elliptical or elongated in plan view with an average length and width of 157 72 m and 83 19 m respectively the average pockmark relief and perimeter are 1 9 0 9 m and 412 181 m respectively the pockmarks have average areas and volumes of 10 759 m and 15 315 m respectively spatial separation that coincides with 210 m isobath divides the pockmarks into two groups with differing distributions and morphologies these pockmarks originated from seepages of biogenic or thermogenic gas or from pore fluids from deeper sources migrated vertically along the faults besides a possible structural control the pockmark morphologies are also affected by bottom currents and or by submarine slumping the average acoustic backscatter strength from pockmark centre is higher 35 db than the average backscatter of the total area 40 db which suggests their possible linkage to the precipitation of diagenitic minerals from biodegradation of seepage material

the importance of changing oceanography in controlling late quaternary carbonate sedimentation on a high energy tropical oceanic ramp north western australia the north west shelf is an ocean facing carbonate ramp that lies in a warm water setting adjacent to an arid hinterland of moderate to low relief the sea floor is strongly affected by cyclonic storms long period swells and large internal tides resulting in preferentially accumulating coarse grained sediments circulation is dominated by the south flowing low salinity leeuwin current upwelling associated with the indian ocean gyre seaward flowing saline bottom waters generated by seasonal evaporation and flashy fluvial discharge sediments are palimpsest a variable mixture of relict stranded and holocene grains relict intraclasts both skeletal and lithic interpreted as having formed during sea level highstands of marine isotope stages mis 3 and 4 are now localized to the mid ramp the most conspicuous stranded particles are ooids and peloids which 14c dating shows formed at 15 4 12 7 ka in somewhat saline waters during initial stages of post last glacial maximum lgm sea level rise it appears that initiation of leeuwin current flow with its relatively less saline but oceanic waters arrested ooid formation such that subsequent benthic holocene sediment is principally biofragmental with sedimentation localized to the inner ramp and a ridge of planktic foraminifera offshore inner ramp deposits are a mixture of heterozoan and photozoan elements depositional facies reflect episodic environmental perturbation by riverine derived sediments and nutrients resulting in a mixed habitat of oligotrophic coral reefs and large benthic foraminifera and mesotrophic macroalgae and bryozoans indicators holocene mid ramp sediment is heterozoan in character but sparse most probably because of the periodic seaward flow of saline bottom waters generated by coastal evaporation holocene outer ramp sediment is mainly pelagic veneering shallow water sediments of marine isotope stage 2 including lgm deposits phosphate accumulations at 200 m water depth suggest periodic upwelling or fe redox pumping whereas enhanced near surface productivity probably associated with the interaction between the leeuwin current and indian ocean surface water results in a linear ridge of pelagic sediment at 140 m water depth this ramp depositional system in an arid climate has important applications for the geological record inner ramp sediments can contain important heterozoan elements mid ramp sediments with bedforms created by internal tides can form in water depths exceeding 50 m saline outflow can arrest or dramatically slow mid ramp sedimentation mimicking maximum flooding intervals and outer ramp planktic productivity can generate locally important fine grained carbonate sediment bodies changing oceanography during sea level rise can profoundly affect sediment composition sedimentation rate and packaging

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

australian offshore natural hydrocarbon seepage studies a review and re evaluation abstract surprisingly few natural hydrocarbon seeps have been identified in australia s offshore basins despite studies spanning thirty years early studies of natural hydrocarbon seepage around the australian margin were generally based on the geochemical analysis of stranded bitumens water column geochemical sniffer sampling synthetic aperture radar or airborne laser fluorosensor later studies involved the integration of these remote sensing and geochemical techniques with multi channel and shallow seismic a review of these earlier studies indicates that many seepage interpretations need to be re evaluated and that previous data sets when placed in a global context often represent normal background hydrocarbon levels low recent burial and subsidence rates are not favourable for high rates of seepage there are also difficulties in proving seepage on high energy shallow carbonate shelves where seabed features may be rapidly re worked and modern marine signatures are overprinted on authigenic seep carbonates thus the relatively few sites of proven natural hydrocarbon seepage in australia s offshore sedimentary basins can be reconciled relative to their geological occurrences and the dominantly passive margin setting active thermogenic methane seepage on the yampi shelf the only proven documented occurrence in australia is driven by deposition of a thick late tertiary carbonate succession and late miocene tectonic reactivation therefore to increase the success of detecting and correctly interpreting natural hydrocarbon seepage data need to be analysed and integrated within the context of the local geological setting and with an understanding of what is observed globally

gas migration pathways and slope failures in the danube fan black sea abstract a large geophysical dataset including bathymetry and 2d and 3d p cable seismic data revealed evidence of numerous gas flares near the s2 canyon in the danube fan northwestern black sea this dataset allows us to investigate potential relationships between gas migration pathways gas vents observed at the seafloor and submarine slope failures vertical gas migration structures as revealed in the seismics appear to be concentrated near submarine slope failure structures where these seismically defined features extend upwards to the seafloor they correlate with the location of gas flares however not all these structures reach the seafloor in some cases because they are capped by overlying sediments a strong correlation is inferred between gas migration pathways heterogeneous mass transport deposits and contacts between adjacent units of contrasting lithology although missing age constrains prevent a final judgement we discuss the potential relationship between submarine slope failures and gas migration in order to determine if gas migration is a precursor to failure or if the presence of slope failures and associated mass transport deposits facilitates the migration of gas our observations indicate that lithological heterogeneity mass transport deposits and minor sediment deformation control gas migration pathways and the formation of gas chimney like features gas migration is focused and gradual resulting in gas flares where the chimney like features extend to the seafloor with no evidence of erosive features such as pockmarks

comment on evidence for the biotic origin of seabed pockmarks on the australian continental shelf by r j mueller marine and petroleum geology 2015 doi 10 1016 j marpetgeo 2014 12 016 abstract the study of seabed depressions that may be related to fluid seepage requires a multi layer approach the application of a one hypothesis fits all approach to understanding seabed characteristics fails to critically assess information necessary to undertake a robust assessment here we contend that the broad brush approach assigning pockmark formation on the northwest shelf of australia to a single organism is insufficiently robust to assign a reliable interpretation of pockmark formation in this setting

maturity and petrography of bitumens in the carboniferous of ireland abstract a set of bitumen samples from the carboniferous of ireland shows a general trend of increasing maturity southwards across the island this trend is consistent with a similar southwards increase in maturity exhibited by the host rocks vitrinite reflectance reflecting proximity to the hercynian orogen to the south of ireland increasing maturity is reflected by decreasing h c ratio and increasing reflectance bireflectance and anisotropy and is accompanied by heavier carbon isotope composition for the most mature samples bitumen reflectance is the most sensitive parameter and ranges up to 3 6 most of the bitumens occur in hydrothermal mineral veins and were generated locally by the passage of hot fluids through carboniferous shales and limestones some bitumens contain inclusions of metalliferous and other inorganic minerals high sedimentation rates during the carboniferous caused hydrocarbon generation before the late carboniferous hercynian orogeny so that the bitumens experienced thermal overprinting by the orogeny and show the same maturity trend as the country rocks anisotropy is exhibited by all bitumen samples with reflectances of 2 0 or over mesophase textures occur in bitumens with reflectances over 3 0 including one case where fluid inclusion homogenization temperatures in coeval minerals calcite and fluorite are less than 200 c

the antarctic dipole and its predictability this study investigates the nature of interan nualvariability ofantarcticseaiceanditsrelationshipwith the tropical climate we nd that the dominant interan nual variance structure in the sea ice edge and surface air temperature elds is organized as a quasi stationary wave which we call the antarctic dipole adp it is charac terized by an out of phase relationship between the ice and temperature anomalies in the central eastern pacic and atlantic sectors of the antarctic the dipole consists of a strong standing mode and a weaker propagating motion within each basin s ice eld it has the same wavelength as the antarctic circumpolar wave acw and dominates the acw variance the dipole is clearly associated with tropical enso events it can be predicted with moderate skill using linear regression involving surface temperature two to four months ahead the prediction performs better in extreme warm cold years and best in la ni na years

rapid climate driven changes in outlet glaciers on the pacific coast of east antarctica multidecadal trends in the terminus position of outlet glaciers along the margin of the east antarctic ice sheet reveal three epochal patterns of glacier retreat or advance consistent with a rapid and coherent response to air temperature and sea ice trends it is widely known that glaciers in west antarctica and greenland have been discharging ice into the oceans in response to warming in recent years and that sea levels have risen as a result by contrast we hear little about the much larger east antarctic ice sheet which has been viewed as being less vulnerable to climate change owing to its location in an extremely cold climate chris stokes and colleagues have used satellite imagery to map a large sample of glaciers along the pacific coast of east antarctica and show that in fact they are responding to decadal climate variability in concert with climate glaciers retreated in the 1970s and 1980s advanced in the 1990s and approximately split between advance and retreat since the 2000s the authors conclude that parts of the world s largest ice sheet may be more responsive to external forcing than previously recognized observations of ocean terminating outlet glaciers in greenland and west antarctica1 2 3 4 5 6 indicate that their contribution to sea level is accelerating as a result of increased velocity thinning and retreat7 8 9 10 11 thinning has also been reported along the margin of the much larger east antarctic ice sheet1 but whether glaciers are advancing or retreating there is largely unknown and there has been no attempt to place such changes in the context of localized mass loss7 9 or climatic or oceanic forcing here we present multidecadal trends in the terminus position of 175 ocean terminating outlet glaciers along 5 400 kilometres of the margin of the east antarctic ice sheet and reveal widespread and synchronous changes despite large fluctuations between glaciers linked to their size three epochal patterns emerged 63 per cent of glaciers retreated from 1974 to 1990 72 per cent advanced from 1990 to 2000 and 58 per cent advanced from 2000 to 2010 these trends were most pronounced along the warmer western south pacific coast whereas glaciers along the cooler ross sea coast experienced no significant changes we find that glacier change along the pacific coast is consistent with a rapid and coherent response to air temperature and sea ice trends linked through the dominant mode of atmospheric variability the southern annular mode we conclude that parts of the world s largest ice sheet may be more vulnerable to external forcing than recognized previously

characterisation and correlation of active hydrocarbon seepage using geophysical data sets an example from the tropical carbonate yampi shelf northwest australia abstract for the first time in australia active present day hydrocarbon seepage has been imaged on the tropical carbonate yampi shelf in 50 and 90 m water depth seepage is evidenced by gas plumes in the water column that are associated with seabed features such as clusters of reflective blocks hard grounds pockmark fields and mounds seepage activity and intensity seems to vary with changes in pressure related to macro tidal cycles the seabed features coincide with sub surface features such as areas of seismic signal attenuation under high amplitude reflectors seismic discontinuities and bright spots hydrocarbon migration seepage pathways appear to be controlled by the reactivation of pre existing fractures and dykes within the basement the types of seabed features and their preservation on a tropical carbonate shelf are strongly influenced by the coarse bioclastic nature of sediments and the high energy of macro tidal currents and storm reworking

chemical changes of fluid inclusion oil trapped during the evolution of an oil reservoir jabiru 1a case study timor sea australia abstract this study of the jabiru oil field timor sea australia shows how the variability of visual properties of fluid inclusions in palaeo oil zones can be mapped to identify internal structures that result from fluid interactions in the reservoir variability in the attributes of oil inclusion assemblages oias is greater within an inferred palaeo gas cap zone 1 and current residual zone zone 3 and less within the current oil zone zone 2 in zone 3 where water imbibed a higher proportion of oias with visual white fluorescing oil inclusions correlates with less mono aromatic compounds and a higher abundance of polar compounds determined on a bulk extract of inclusion oil using high performance liquid chromatography hplc the ch 2 ch 3 ratios and water contents determined by fourier transform infrared spectroscopy ft ir are higher in zone 1 where gas drained there is a higher proportion of oias with visual yellow fluorescing oil inclusions and these correlate with low hplc mono aromatic and moderate polar contents and low ft ir ch 2 ch 3 ratios and water contents interpretation of the grains with oil inclusions goi and pressure volume temperature composition pvtx fluid inclusion data suggests that a gas saturated blue fluorescing palaeo oil was present in the three zones at the same pressure temperature fluid inclusion forming event pt 1 lighter gas saturated blue fluorescing oil was present in zone 2 but was rarer in zones 1 and 3 at the later fluid inclusion forming event pt 2 the yellow and white inclusion oils trapped in zones 1 and 3 respectively are gas depleted and interpreted to result from the interaction between non movable residual oil around grains with the surrounding gas and water respectively comparison between the pvtx data and the published burial curve suggests that most of the fluid inclusions were trapped during two different hot fluid flow events the full oil column is interpreted to have been present during early mid tertiary the palaeo oil column was reduced during the late miocene by imbibition of water in the present residual zone and drainage of gas at the top of the reservoir

organic facies of the asbian early carboniferous queensferry beds lower oil shale group south queensferry scotland and a brief comparison with other carboniferous north atlantic oil shale deposits abstract the 71 m foreshore exposure of the queensferry beds at south queensferry is currently the best accessible section of the oil shale group of the midland valley of scotland a combination of bulk organic geochemistry and kerogen microscopy palynofacies organic petrology is used to define four organic facies and one variant organic facies 1 occurs in silty mudstones has a mean toc of only 2 and type iii iv gas prone or inert kerogen hi 800 variant 3a is additionally characterised by an abundance of small 4 m spherical cells of possible cyanobacterial origin occurring in one sample adjacent to a stromatolitic limestone organic facies 2 is transitional between 1 and 3 organic facies 4 has atypically low c s ratios and corresponds to the pumpherston marine band these organic facies can also be distinguished using biomarker parameters pr ph oep c25 c15 predominant carbon number etc the hi is very strongly correlated with the relative fluorescence of the organic matter and strongly correlated with the aom phytoclast ratio and the botryococcus and total alginite contents it is inversely correlated with the diameter of black equant phytoclasts the organic rich shales thus correspond to distal lower energy anoxic conditions during periods of meromixis high preservation low dilution similar carboniferous lacustrine source rocks occur in eastern canada and east greenland all are characterised by large lateral extents 500 2 000 km2 a geographic and temporal association with strong syndepositional subsidence generally low botryococcus contents and a dominance of amorphous type ii kerogen

equatorial aridity and climatic oscillations during the early carboniferous southern britain evidence from palaeosols palaeokarsts and styles of meteoric diagenesis shows that the early carboniferous climate of southern britain was dominantly seasonally semi arid this semi aridity occurred while the region was in an equatorial palaeolatitudinal position the cause of the seasonal aridity was possibly the deflection of easterly winds into a major low pressure zone set up over gondwana during the southern hemisphere summer

breakup of land fast sea ice in lutzow holm bay east antarctica and its teleconnection to tropical pacific sea surface temperatures a large land fast sea ice breakup occurred in 2016 in lutzow holm bay east antarctica the breakup caused calving from the shirase glacier tongue although similar breakups and calving have been observed in the past the timing and magnitudes are not well constrained the ice s breakup latitude during 1997 2016 was analyzed to investigate the variables controlling breakup and examine correlation with local calving for a longer period the breakup latitude in april had a persistently high correlation with sea surface temperature sst in the tropical pacific which exceeds correlations with local atmospheric variables the years of five out of six observed calving events from the mid 20th century can correspond to those of warm sst episodes and calving front retreat in the 1980s to warmer sst shift our proposed teleconnection between tropical sst and antarctic sea ice could lead to better predictions of breakup and might impact the glacier flux for a wider region

evidence for fluid migration following pockmark formation examples from the nile deep sea fan a large number of pockmarks have been identified in the rosetta region of the western nile deep sea fan co located high resolution 2d and chirp datasets have been used to identify seabed and buried pockmarks which are interpreted to span the holocene to pleistocene period the pockmarks range in size and stratigraphic position from large buried pockmarks to small unit seabed pockmarks clusters of small unit pockmarks are stratigraphically positioned above the centre of large buried pleistocene pockmarks and are used to infer 1 rejuvenation of the larger pockmark conduit once burial has occurred and 2 a change in the frequency and magnitude of pockmark formation events

factors determining the spatial distribution of gas charged sediments in the continental shelf off southeastern korea abstract a high resolution seismic survey piston coring and water column measurements were conducted on the continental shelf off southeastern korea to examine the gas charged sediments and gas seepage in the water column we examined the factors controlling the spatial distribution of the acoustic blanking zone in recent korea strait shelf mud kssm deposits along the southeastern shelf the molecular composition methane hydrogen and carbon dioxide isotope values of headspace gases and the geochemical composition of core sediments were measured in 11 piston cores dissolved methane concentrations in the water column were observed at 6 of the 11 coring sites acoustic blanking of the recent kssm deposits was limited to areas with water depths between 30 and 105 m along the continental shelf except line l 13 133 m depth the flanks of the acoustic blanking zone can be classified as distinct disturbed and step types based on their configurations the highest methane concentration in the headspace gases was about 2 7 2 4 m below the seafloor which matched the top of the acoustic blanking zone no obvious methane was found in piston cores obtained from the gas free zone the 13 c ch4 ranged from 56 5 to 106 3 relative to vienna pee dee belemnite v pdb and the d ch4 ranged from 194 to 207 relative to vienna standard mean ocean water v smow these isotope values show that methane is produced by the microbial reduction of co 2 ch 4 oxidation results in a significantly heavier carbon isotope fraction from 91 2 to 56 5 in the 2 m below the seafloor with constant 13 c co2 isotope fractionation no obvious differences were seen in the total carbon tc 2 438 3 378 total nitrogen tn 0 159 0 548 total organic carbon toc 1 139 2 078 or caco 3 2 825 15 258 in the continental shelf whereas the toc was high and the caco 3 low distant from the nakdong river distinct dissolved methane anomalies 21 87 ppm were seen in the water column in the acoustic blanking and gas seepage zones this level was about 15 times higher than the dissolved methane level 1 5 ppm in the water column in the gas free zone these results indicate that the acoustic blanking zone accumulates biogenic methane methane seepage was observed in the water column throughout the acoustic blanking zone of the continental shelf off southeastern korea

sea level at the last glacial maximum evidence from northwestern australia to constrain ice volumes for oxygen isotope stage 2 new sea level information from the bonaparte gulf in northwestern australia is used to constrain the magnitude and rates of change of ice volumes during the last glacial maximum lgm the region is tectonically stable and far from the former ice covered regions the glacio hydro isostatic adjustment of the coast is therefore relatively small and the corrections for this evect are not sensitive to details of the rebound model microfossil analysis and ams radiocarbon dating of 11 gravity cores taken across the shelf and bonaparte gulf demonstrate that 1 the lgm sea levels were locally at 125 4 m 2 the lgm terminated abruptly at 19 000 cal yr bp with a rapid rise in sea level of about 15 m over the next 500 years and 3 the onset of the minimum sea levels occurred before 22 000 cal yr bp when corrected for the glacio hydro isostatic evects the increase of lgm ice volumes over the present day ice volume is 52 5 106 km3 the termination of the lgm is marked by a rapid ice discharge of 5 2 106 km3 2001 elsevier science b v all rights reserved

seasonal variations of the antarctic coastal ocean in the vicinity of lutzow holm bay during the period of 1990 1992 year round oceanographic observations were conducted in the vicinity of lutzow holm bay east antarctica it was found that the thickness of the winter water ww layer characterized by a cold fresh oxygen rich water exhibits its maximum in the austral fall typically 500 m and its minimum in the austral summer typically 350 400 m the associated density variation of the water column explains only about one third of the seasonal variations in sea level at the coast which suggests a large seasonal variation in barotropic coastal flow prominent freshening occurs in the ww layer during fall this appears to be caused by the accumulation of ww whose upper portion is freshened in the preceding summer these seasonal variations appear to occur every year we propose that the seasonal variation in the ww layer is mainly caused by the seasonal variation in the wind over the coastal ocean in fall the prevailing easterly wind intensifies which increases the ekman convergence of ww in the coastal ocean while in summer the opposite occurs

petrology of a suite of sedimentary rocks associated with some cole bearing basins in northwestern thailand abstract a number of basins in northwestern thailand contain thick sequences of cenozoic sedimentary rocks oil shales and coals are prominent lithologies within these sequences and occur together in some basins most of the sequences are however dominated by either oil shales or coals the major oil shale deposit is in the mae sot basin but oil shales also occur in the ban huay dua mae moh ban pa ka li mae teep ban na hong and jae hom basins drilling and detailed mapping in the mae sot basin indicate thick sequences of oil shales and organic petrological studies show that they contain abundant lamalginite trace amounts of telalginite liptodetrinite bitumen resinite and huminite inertinite are also present in some of the rocks the parts of the sequences rich in authigenic minerals are in general petrographically similar to green river formation lamosites where clay silt sized epiclastics are more abundant similarities exist to australian tertiary lamosites vitrinite reflectance date from the oil shales and associated coals indicate a low level of maturity oil shales from the other basins are petrographically similar to the mae sot lamosites however some differences do exist the mae sot and other lamosites were deposited in lacustrine environments that probably had highly variable water depths

antarctic sea ice relationships with indices of the atmospheric circulation of the southern hemisphere a link between the antarctic sea ice extent and low frequency atmospheric variations particularly enso has been suggested by recent modeling and empirical studies this question is examined here using a high resolution by week by region data base of antarctic sea ice extent for the 1973 1982 period although of relatively short duration by northern hemisphere standards such a data base offers an opportunity rare in southern hemisphere climate studies the seaice variations are examined in the context of longer term indices of the large scale atmospheric circulation these are a southern oscillation index soi and an index of sea level pressure slp wavenumber one in the southern hemisphere extratropics the indices are updated through 1982 and their associations with regional scale pressure indices in the australia new zealand sector are also examined the 1973 1982 period is anomalous when compared with the period 1951 1972 correlation analysis of the monthly sea ice and circulation index values reveals that much of the apparent link between the ice and the soi suggested in previous studies arises from autocorrelations present in both data sets and the strong annual cycle of sea ice extent removing these effects from the data and re running the correlations reveals that most of the resulting significant associations between the ice and one or other of the circulation indices can probably be explained on the basis of chance in order to reconcile these findings with previous studies that show some strong ice circulation interactions on regional scales only those months in which significant correlations occur between both largescale circulation indices and the sea ice are examined further these occur preferentially in the ross and weddell sectors which constitute the regions contributing most to the variability of antarctic sea ice the analysis suggests that the sea ice extent changes lag the soi by several months but may precede changes in extratropical slp wavenumber one confirmation of these tentative regional ice extent circulation teleconnections necessarily awaits the forward extension of the high resolution sea ice data base beyond the 10 years available here

fault associated seabed mounds carbonate knolls off western ireland and north west australia abstract groups of seabed mounds suspected to be modern carbonate knolls or bioherms have been located on reflection seismic data in the porcupine basin off western ireland and in the vulcan sub basin off north west australia the size of these mounds is impressive often being over 1 km across and over 100 m high in the porcupine basin they occur in water depths of 650 1000 m whereas in the vulcan sub basin they occur in water depths of 200 350 m shallow seabed coring in the porcupine basin has provided data on the age lithological composition and hydrocarbon concentrations in the upper 3 m layer of sediment both on and off the mounds in both basins the mounds occur close to faults which may provide conduits for upward migrating hydrocarbons the seepage of hydrocarbons is suspected to have caused local eutrophication or fertilization by providing nutrients to bacteria which in turn are part of the food chain for higher organisms the dominant organism in the porcupine basin examples appears to be the deep water coral lophelia sp whereas in the vulcan sub basin the mounds appear to be halimeda dominated

coupled ocean atmosphere ice response to variations in the southern annular mode abstract the coupled ocean atmosphere ice response to variations in the southern annular mode sam is examined in the national center for atmospheric research ncar community coupled climate model version 2 the model shows considerable skill in capturing the predominantly zonally symmetric sam while regional deviations between model and observation sam winds go a long way in explaining the generally small differences between simulated and observed sam responses in the ocean and sea ice systems vacillations in the position and strength of the circumpolar winds and the ensuing variations in advection of heat and moisture result in a dynamic and thermodynamic forcing of the ocean and sea ice both meridional and zonal components of ocean circulation are modified through ekman transport which in turn leads to anomalous surface convergences and divergences that strongly affect the meridional overturning circulation and potentially the pathways of intermediate water ventilation a heat budget analysis de

hydrocarbon compositions of bitumens from mineralized devonian lavas and carboniferous sedimentary rocks central scotland abstract solid bitumens occur in mineralized veins in the lower devonian ochil volcanic formation in the midland valley of scotland bitumens are also widespread in the carboniferous of the midland valley gas chromatography g c mass spectrometry m s studies undertaken on bitumens from the devonian rocks and on devonian and carboniferous mudrocks show that the bitumens contain biomarkers and that carboniferous rocks are the more likely source for the bitumens hydrocarbons may have migrated into the devonian rocks along the ochil fault zone from a downthrown carboniferous basin to the south of the fault the organic geochemistry of bitumen samples from the carboniferous rocks reflects varying degrees of biodegradation and heating by igneous intrusions

intermittent structural weakening and acceleration of the thwaites glacier tongue between 2000 and 2018 evolving conditions at the terminus of thwaites glacier will be important in determining the rate of its future sea level contribution over the coming decades here we use remote sensing observations to investigate recent changes 2000 2018 in the structure and velocity of thwaites glacier and its floating tongue we show that the main trunk of thwaites glacier has accelerated by 38 over this period while its previously intact floating tongue has transitioned to a weaker melange of fractured icebergs bounded by sea ice however the rate of structural weakening and acceleration was not uniform across the observational period and we identify two periods of rapid acceleration and structural weakening 2006 2012 2016 2018 separated by a period of deceleration and re advance of the structurally intact shear margin boundary 2012 2015 the timing of these accelerations decelerations strongly suggests a link to variable ocean forcing the weakened tongue now has some dependency on landfast sea ice for structural integrity and is vulnerable to changes in landfast ice persistency future reductions in landfast sea ice could manifest from changes in climate and or the imminent removal of the b 22a iceberg from the thwaites embayment such changes could have important implications for the integrity of the ice tongue and future glacier discharge

time and process rates over the past 100 m y a case for dramatically increased landscape denudation rates during the late quaternary in northern australia a central question in the earth sciences is how rates and styles of landscape evolution have varied over time in response to climate and sea level change tectonic and isostatic uplift and human disturbance the quaternary has been a period of major landscape evolution in many glaciated regions of the world but few data sets of sufficient length are available to assess its significance to the long term development of landscapes in nonglaciated regions analysis of denudation rates over the past 0 5 m y and 100 m y for upland and lowland surfaces in western arnhem land tropical northern australia shows that denudation rates have increased by at least an order of magnitude in the late quaternary compared to the previous 100 m y despite tectonic stability and the absence of glaciation in this region over the past 120 m y the lowlands have undergone denudation rates up to an order of magnitude higher than the uplands so that the landscape has increased in relief independently of the absolute rate of denudation this result is counter to several prominent theories of landscape development that postulate relief reduction over millions of years at least 3 7 of the post cretaceous denudation of this landscape occurred during the most recent 0 5 m y we suggest that the quaternary here was a period of greatly accelerated erosion resulting from changes in climate and sea level accompanying glacial interglacial cycles general sea level regression since the mid cretaceous also likely initiated substantial lowland erosion in this region it appears therefore that the past 100 m y have been punctuated by at least two episodes of accelerated landscape denudation

impact of the 1997 98 enso on upper ocean characteristics in marguerite bay western antarctic peninsula 1 a year round sequence of hydrographic casts is used to trace the evolution of the upper ocean waters in marguerite bay western antarctic peninsula wap between 1998 and 2002 winter 1998 was anomalous showing an unusually deep mixed layer that became progressively more saline until spring reaching salinities as high as 34 0 the remnant of this mixed layer the winter water ww was the deepest and most saline observed atmospheric and cryospheric conditions were anomalous during winter 1998 at both local and regional scales locally we observed low sea ice concentrations high air temperatures and a high frequency of northerly winds these are the local manifestations of the strong enso event of 1997 1998 that was then rapidly weakening at the regional scale this enso produced significant anomalies in the sea ice distribution throughout the amundsen bellingshausen sea area and a large scale low pressure anomaly over the southeast pacific was seen to be responsible for the warm northerly winds we use a coupled mixed layer ice production model to investigate the enso driven forcings for the anomalous ocean conditions observed in winter 1998 this reveals that ice production is the main control on upper ocean stratification and that the deep saline mixed layer in 1998 was forced by anomalous sea ice conditions on spatial scales larger than purely local we conclude that the near coastal hydrography along the peninsula shows a profound response to enso with atmospheric and cryospheric forcings both implicated

the spatial pattern and drainage cell characteristics of a pockmark field nile deep sea fan over 25 300 seabed pockmarks were mapped from the rosetta channel region of the western niledeepseafan ndsf using concurrent high resolution 2d chirp profiler and multibeam bathymetry data which spans the holocene pleistocene period within the region apockmarkfield containing 13 800 pockmarks was analysed using spatial statistics to determine the distribution of pockmarks within the field pockmarks within the field are small 16 m diameter shallow 0 5 m deep circular depressions which formed within the last 6500 years the fluid source for the field is identified as an accumulation generation of gas beneath a hemipelagic seal c 20 40 ms beneath the seabed the position of the pockmarks is shown to be unrelated to the depth to the fluid source and an irregular high amplitude acoustic anomaly which is tentatively interpreted as a possible carbonate precipitate of biogenic microbial activity statistical spatial analysis of the field confirms the distribution of pockmarks is not random an exclusion zone surrounding each individual pockmark is identified the exclusion zone is a unique minimum radius around each pockmark which is not penetrated by any other pockmark the exclusion zone works in unison with self organised criticality soc in determining the spatial distribution of pockmarks within the field the exclusion zone is interpreted as apockmark drainagecell a conceptual model for apockmarkdrainagecell is proposed whereby pockmark formation dissipates a radius area of fluid and overpressure thereby preventing the formation of another pockmark within that cell consequently pockmarks are observed to separate or produce anti clustering tendencies within the field

the spatio temporal patterns of landfast ice in antarctica during 2006 2011 and 2016 2017 using high resolution sar imagery abstract landfast ice is an important component of the antarctic sea ice regime it affects the antarctic climate and ecological system in this study the first high resolution long time series of the landfast ice edge from 2006 to 2011 and 2016 to 2017 is presented the dataset was produced based on the improved net gradient difference algorithm using 2470 sar scenes from envisat and sentinel 1a b as well as manual analysis of modis imagery to fill in sar data gaps the study results show that the landfast ice area in november for all studied years was approximately 49 49 3 25 104 km2 accounting for about 3 4 of the total antarctic sea ice area the maximum area was 55 70 104 km2 in november 2007 compared to the minimum area 44 01 104 km2 in 2011 the area in west antarctica was about 40 of that in east antarctica the distribution of landfast ice in antarctica has significant regional differences the extent in the indian ocean sector is the maximum with a mean value of 16 49 1 1 104 km2 however the ratio of the landfast ice area to the sea ice area in the pacific ocean sector is the highest twenty four landfast ice zones with groups of small grounded icebergs were identified most of which were located in east antarctica particularly along the wilkes land and oates land two cases are presented to illustrate how giant grounded icebergs affected landfast ice results from this study are well suited to underpin the antarctic climate or ecological system studies

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

response to comments by nicholas et al 2016 on evidence for the biotic origin of seabed pockmarks on the australian continental shelf abstract nicholas et al 2016 restate the results and conclusions of their own past work and that of colleagues on the north west shelf although they accept that fish may be involved in pockmark maintenance they do not accept that fish can initiate such features the fluid flow theory with which they have been working therefore remains intact however the restatement also provides no new information and no cause to revise the conclusions of mueller 2015 more field data is required

a depositional model for spherulitic carbonates associated with alkaline volcanic lakes the south atlantic aptian pre salt reservoirs are formed by a combination of spherulitic carbonates and mg rich clays accumulated in volcanic alkaline lake settings with exotic chemistries so far outcrop analogues characterised by metre thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates represents a major scientific challenge with business impact in particular the controls on spatial distribution and the environment of spherulitic facies formation remain poorly constrained little studied and hotly debated to shed light on this conundrum a spherulitic carbonate rich alkaline volcanic lacustrine succession has been analysed at outcrop scale the carboniferous east kirkton limestone scotland despite clays being very scarce and limited to layers of amorphous mg si minerals a diverse array of spherulitic calcitic components were formed including coated grains crusts and build ups this setting enables the mechanisms of spherulitic calcite development and the patterns of sediment accumulation to be explored in a geobiological and hydrochemical scenario similar to the pre salt subsurface occurrences but divorced from clay influence the integration of logs borehole data outcrop photomosaics and petrographic observations collectively allowed the reconstruction of a depositional model for the east kirkton lacustrine succession in this model calcite spherule nucleation took place at the sediment water interface in the littoral zone driven by the co occurrence of 1 high alkalinity 2 ca mg rich hydrochemistry and 3 microbial derived colloidal exopolymeric substances these environmental conditions permitted the coeval development of spherulitic cementstone build ups and spherulitic grainstone packstone within the wave agitated zone and the accumulation of floatstones and laminites of spherulitic grains in deeper lake regions by means of downslope reworking this model is consistent with the previously documented microbial bloom occurrences and highlights the need to better understand the complex microbe solution interactions before any reliable facies model is envisaged

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

slow oceanic teleconnections linking the antarctic circumpolar wave with the tropical el nino southern oscillation a case study for the period 1982 1994 shows that a major source for the antarctic circumpolar wave is in the western subtropical south pacific where interannual anomalies in sea surface temperature sst and precipitable water prwat form once established these interannual anomalies in tandem with anomalies in sea level pressure slp move south toward the southern ocean the system then migrates east around the globe through a combination of oceanic advection with the antarctic circumpolar current and ocean atmosphere coupling the coincidence of interannual anomalies in sst slp and prwat indicates the extratropical ocean and atmosphere are tightly linked on these timescales large portions of the interannual sst anomalies branch advectively northward into the south atlantic and indian oceans ultimately reaching the tropics in each basin some 6 8 years after appearing in the low latitude pacific this constitutes a slow oceanic teleconnection that is unique in climate dynamics made possible by the continuity of earth s oceans via the southern ocean in the tropical indian ocean these interannual anomalies move east and arrive at the indo pacific transition in advance of the trans pacific propagation of the respective el nino southern oscillation enso phases the interannual sst and prwat anomalies that appear in the subtropical south pacific are directly linked with the enso cycle on the equator through anomalous vertical convection and a regional overturning cell in the troposphere the same cell that initiates fast planetary waves in the atmosphere that carry enso signals around the southern hemisphere on much shorter timescales

effect of igneous intrusion on the organic geochemistry of a siltstone and an oil shale horizon in the midland valley of scotland abstract the effect of rapid thermal stress on the organic geochemistry of a siltstone intruded by a quartz dolerite dyke and an oil shale intruded by an alkali dolerite sill has been studied using optical petrography rock eval pyrolysis gas chromatrography and gas chromatography mass spectrometry maturity dependent ratios derived from both the aliphatic and aromatic hydrocarbon fractions corroborate the observation of raymond and murchison 1988b that the alkali dolerite sills which were intruded soon after sedimentation had a lesser effect than the later quartz dolerite intrusions the maturity parameters based on the alkylnaphthalene and alkylphenanthrene isomer ratios are more suitable for studying maturity variations in heat affected samples than those based on the commonly used aliphatic biological markers these aromatic compounds survive to higher ranks and the isomer ratios continue changing

shallow gas and fluid migration in the northern arafura sea offshore northern australia abstract a variety of shallow gas indicators and fluid migration pathways have been interpreted from new sub bottom profiler multibeam bathymetry side scan sonar and echo sounder data together with geochemical analyses of sampled sediments from the northern arafura sea offshore northern australia this study provides new geological data and a seismic stratigraphy of the youngest units in the money shoal basin in an area that has not been closely studied in over 30 years the shallow gas indicators include pockmarks low frequency enhanced reflectors and acoustic blanking these indicators are supported by gas within shallow cores geochemistry indicates that this gas has a microbial origin but deeper fluid movement is also suggested by the presence of interpreted hydrocarbon slicks based on synthetic aperture radar data a region of likely hydrocarbon seepage is indicated by the clear coincidence of shallow gas indicators with an area of increased faulting and a zone of poor quality seismic data recognised on conventional seismic data together with anomalies interpreted on remote sensing data aligned with mapped deep structures

carboniferous petroleum systems around the mid north sea high uk the existence of an extensive prospective visean namurian carboniferous petroleum system in and around the hitherto under explored mid north sea high is documented evidence is drawn from integrated analysis of over 50 000 line kilometres of seismic data and well data together with regional source rock screening reservoir analysis and basin modelling visean namurian marine and non marine mudstones and coal source rocks are interbedded within fluvial and marine reservoir sandstones within a stacked succession up to 5 km thick source rocks are dominantly gas prone with oil prone intervals and have reached oil to gas maturity levels dependent on location burial thermal history modelling indicates a kitchen area on the southern margin of the mid north sea high with northwest and northeastwards migration of gas and oil during mesozoic and cenozoic times a variety of structural and stratigraphic traps are possible including intraformational carboniferous traps with a regional seal at permian zechstein level synthesis of many previously unpublished datasets demonstrates the visean namurian play south of the mid north sea high as part of an extensive petroleum system from the east irish sea across onshore to offshore uk and into the netherlands sector of the north sea the purpose of this synthesis is to highlight future exploration opportunities beneath and northwards of the productive westphalian southern north sea gas basin and to begin to de risk the petroleum systems that are exemplified by the lower carboniferous breagh field in a frontier area of the mature north sea province

the role of algal blooms in the formation of lacustrine petroleum source rocks evidence from jiyang depression bohai gulf rift basin eastern china abstract algal blooms are responsible for the laminae in the lacustrine shahejie formation in the jiyang depression one of the sub basins of the bohai gulf rift basin in eastern china about 65 oil fields have been discovered in this depression during the past 40 years and the oil is mainly derived from three types of finely laminated lacustrine rocks of shahejie formation eocene oligocene these lacustrine petroleum source rocks are oil shales calcareous shales and calcareous laminated mudstones optical sem and bsei analyses of these source rocks reveal that there are algal coccoliths and dinoflagellates laminae in the rocks the individual algal lamina is generally composed almost wholly of one species such as reticulofenestra bohaiensis in coccolith laminae and fromea as well as bohaidina in dinoflagellate laminae this distribution suggests that the algal laminae formed from algal blooms in the ancient lake other components of source rocks included organic matter laminae carbonate laminae and clay rich laminae we also discuss the sedimentation of organic matter laminae and carbonate laminae which were related to algal blooms we conclude that the laminated lacustrine petroleum source sediment of jiyang depression formed during episodes of algal blooms alternating with chemical and detrital sedimentation and this represents the primary mechanism responsible for the formation of lacustrine petroleum source rocks

pinnacle features at the base of isolated carbonate buildups marking point sources of fluid offshore northwest australia we investigated pinnacle features at the base of late oligocene miocene isolated carbonate buildups using three dimensional seismic and borehole data from the browse basin northwest australia brightened seismic reflections dim spots and other evidence of fluid accumulation occur below most pinnacle features an important observation is that all pinnacles generated topography on successive late oligocene miocene paleoseafloors therefore forming preferential zones for the settlement of reef building organisms by raising the paleo seafloor into the photic zone their height ranges from 31 m to 174 m for a volume varying from 33 km3 to 11 105 km3 most of the pinnacles however are less than 2000 km3 in volume and present heights of 61 80 m as a result of this work pinnacles are explained as the first patch reefs formed in association with mud volcanoes or methanogenic carbonates and they are considered as precluding the growth of the larger isolated carbonate buildups we postulate that pinnacle features above fluidflow conduits demonstrate a valid seep reef relationship and we propose them to be refined diagnostic features for understanding fluid flow through geological time

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

the occurrence of isorenieratane and 24 n propylcholestanes in paleogene lacustrine source rocks from the dongying depression bohai bay basin implications for bacterial sulfate reduction photic zone euxinia and seawater incursions abstract lacustrine organic rich source rocks shales and mudstones were examined to assess the depositional environment and organic input sources of the third and fourth members of the eocene shahejie formation bohai bay basin china major organic contributions to the shahejie formation from dinoflagellates diatoms botryococcus and marine pelagophyte chrysophyte algae were determined using n alkane distributions gammacerane index and diagnostic steranes traces of higher plant biomarkers suggest that terrigenous organic inputs were limited the pervasive presence of carotane aryl isoprenoids paleorenieratane renieratane isorenieratane 2 methylhopanes and crocetane indicate significant organic contributions from bacterial communities including cyanobacteria purple sulfur bacteria chromatiaceae green sulfur bacteria chlorobiaceae and sulfate reducing bacteria the extent of h2s content bacterial sulfate reduction and photic zone euxinia pze were evaluated by determining the aryl isoprenoids ratio air 0 7 9 0 the presence of isorenieratene derivatives and the fate of sulfur in the water column there was a decrease of pze extent and duration from the northeast to the southwest of the palaeo lake and there was a decrease of water body salinity and bottom water anoxia from the fourth to the third member of the shahejie formation abrupt environmental perturbations in the third member of the shahejie formation are indicated not only by significant changes in parameters such as the pristane phytane and carotane n c20 alkane ratios the gammacerane index the isorenieratane c18 aryl isoprenoid and the air but also by the time lag in the expansion of cyanobacterial lineages after the expansion of purple green sulfur bacteria as well as seawater incursions the unexpected occurrence of intact c30 4 desmethylsteranes 24 n propylcholestanes in the shahejie formation is first reported here after very careful checking and provides unambiguous biological evidence for at least two marine transgression events reaching the eocene dongying palaeo lake the organic enrichment of the petroleum source rocks in the shahejie formation is a consequence of combined indigenous lacustrine algal production the constrained and favourable preservation conditions and significant bacterial contributions and marine organic matter inputs to the lake

understanding the sam influence on the south pacific enso teleconnection the relationship between the el nino southern oscillation enso and the southern hemisphere annular mode sam is examined with the goal of understanding how various strong sam events modulate the enso teleconnection to the south pacific 45 70 s 150 70 w the focus is on multi month multi event variations during the last 50 years a significant p 0 10 relationship is observed most marked during the austral summer and in the 1970s and 1990s in most cases the significant relationship is brought about by la nina el nino events occurring with positive negative phases of the sam more often than expected by chance the south pacific teleconnection magnitude is found to be strongly dependent on the sam phase only when enso events occur with a weak sam or when a la nina el nino occurs with a positive negative sam phase are significant south pacific teleconnections found this modulation in the south pacific enso teleconnection is directly tied to the interaction of the anomalous enso and sam transient eddy momentum fluxes during la nina sam and el nino sam combinations the anomalous transient momentum fluxes in the pacific act to reinforce the circulation anomalies in the midlatitudes altering the circulation in such a way to maintain the enso teleconnections in la nina sam and el nino sam cases the anomalous transient eddies oppose each other in the midlatitudes overall acting to reduce the magnitude of the high latitude enso teleconnection

high resolution ice cores from us itase west antarctica development and validation of chronologies and determination of precision and accuracy shallow ice cores were obtained from widely distributed sites across the west antarctic ice sheet as part of the united states portion of the international trans antarctic scientific expedition us itase program the us itase cores have been dated by annual layer counting primarily through the identification of summer peaks in non sea salt sulfate nssso4 2 concentration absolute dating accuracy of better than 2 years and relative dating accuracy better than 1 year is demonstrated by the identification of multiple volcanic marker horizons in each of the cores tambora indonesia 1815 being the most prominent independent validation is provided by the tracing of isochronal layers from site to site using high frequency ice penetrating radar observations and by the timing of mid winter warming events in stable isotope ratios which demonstrate significantly better than 1 year accuracy in the last 20 years dating precision to 1 month is demonstrated by the occurrence of summer nitrate peaks and stable isotope ratios in phase with nssso4 2 and winter time sea salt peaks out of phase with phase variation of 1 month dating precision and accuracy are uniform with depth for at least the last 100 years

sea level and environmental changes since the last interglacial in the gulf of carpentaria australia an overview abstract the gulf of carpentaria is an epicontinental sea maximum depth 70 m between australia and new guinea bordered to the east by torres strait currently 12 m deep and to the west by the arafura sill 53 m below present sea level throughout the quaternary during times of low sea level the gulf was separated from the open waters of the indian and pacific oceans forming lake carpentaria an isolation basin perched above contemporaneous sea level with outlet channels to the arafura sea a preliminary interpretation is presented of the palaeoenvironments recorded in six sediment cores collected by the images program in the gulf of carpentaria the longest core approx 15 m spans the past 130 ka and includes a record of sea level lake level changes with particular complexity between 80 and 40 ka when sea level repeatedly breached and withdrew from gulf lake carpentaria evidence from biotic remains foraminifers ostracods pollen sedimentology and geochemistry clearly identifies a final marine transgression at about 9 7 ka radiocarbon years before this transgression lake carpentaria was surrounded by grassland was near full and may have had a surface area approaching 600 km 300 km and a depth of about 15 m the earlier rise in sea level which accompanied the marine isotopic stage 6 5 transgression at about 130 ka is constrained by sedimentological and biotic evidence and dated by optical and thermoluminescence and amino acid racemisation methods

surface geochemical exploration for oil and gas new life for an old technology surface geochemical exploration for petroleum is the search for chemically identifiable surface or near surface occurrences of hydrocarbons or hydrocarbon induced changes as clues to the location of oil and gas accumulations it extends through a range of observations from clearly visible oil and gas seepage macroseepage at one extreme to identification of minute traces of hydrocarbons microseepage or hydrocarbon induced changes at the other