variability and forcing of the east australian current 1 the spatial and temporal variability of the east australian current eac is investigated using 6 years 1993 1998 of surface geostrophic stream function from an optimal interpolation of altimeter sea surface heights and velocities derived from tracking thermal features in satellite imagery variability appears as a series of cyclones and anticyclones propagating southwestward and westward with periods between 90 and 180 days the behavior of the variability changes over the 6 years energy in the mesoscale frequencies moves slowly south and diminishes with more westward propagation in the region where the current separates from the coast we find no evidence for a consistent forcing of the eac by mesoscale signals propagating westward from the south pacific basin we suggest that the observations are consistent with variability originating between 32 s and 35 s through intrinsic instabilities of the current

decadal sea level variability in the south pacific in a global eddy resolving ocean model hindcast sea level variability and related oceanic changes in the south pacific from 1970 to 2003 are investigated using a hindcast simulation of an eddy resolving ocean general circulation model ogcm for the earth simulator ofes along with sea level data from tide gauges since 1970 and a satellite altimeter since 1992 the first empirical orthogonal function mode of sea level anomalies slas of ofes exhibits broad positive slas over the central and western south pacific the corresponding principal component indicates roughly stable high low and high slas separated by a rapid sea level fall in the late 1970s and sea level rise in the late 1990s consistent with tide gauge and satellite observations these decadal changes are accompanied by circulation changes of the subtropical gyre at 1000 m depth and changes of upper ocean zonal current and eddy activity around the tasman front in general agreement with previous related studies it is found that sea level variations in the tasman sea can be explained by propagation of long baroclinic rossby waves forced by wind stress curl anomalies if the impact of new zealand is taken into account the corresponding atmospheric variations are associated with decadal variability of el nino southern oscillation enso thus decadal sea level variability in the western and central south pacific in the past three and half decades and decadal enso variability are likely to be connected the sea level rise in the 1990s which attracted much attention in relation to the global warming is likely associated with the decadal cooling in the tropical pacific

on the east australian current variability encroachment and upwelling 1 observations from an intensive oceanographic field program which took place in 1998 1999 about the separation point of the east australian current eac show significant spatial and temporal variability of the eac upstream of the separation point southward flowing currents are strong with subinertial velocities of up to 130 cm s 1 in the near surface waters whereas downstream currents are highly variable in both strength 1 70 cm s 1 and direction upwelling is observed to occur through both wind driven and current driven processes with wind effects playing a lesser role by contrast the encroachment of the eac upon the coast has a profound effect on the coastal waters accelerating the southward alongshore currents and decreasing the temperature in the bottom boundary layer bbl by up to 5 degreesc as the axis of the jet moves onshore negative vorticity increases in association with an increase in nonlinear acceleration during this time bottom friction is increased the burger number is reduced and the bbl shut down time lengthens the observed upwelling is attributed to enhanced onshore ekman pumping through the bbl resulting from increased bottom stress as the southerly flow accelerates when the eac encroaches across the continental shelf

organic geochemistry and petrography of lower cretaceous wealden black shales of the lower saxony basin the transition from lacustrine oil shales to gas shales abstract ninety seven wealden black shale samples from three wells in the lower saxony basin have been studied by organic geochemical and organic petrographical methods to determine their maturity organic facies and depositional environment the maturities of the three wells range from early mature ex a late to postmature ex c to overmature ex b as determined by vitrinite reflectance measurements diamondoid ratios and other geochemical maturity parameters ex c and ex b show distinct petrographic features related to oil generation and migration in particular the occurrence of dispersed solid bitumen replacing initial type i kerogen suggests a formerly active petroleum system structural and textural differences between early mature alginites and solid bitumen in postmature to overmature samples show an alteration of the pore system with increasing maturity a freshwater depositional environment is indicated by widespread occurrence of botryococcus algae and other small alginite particles predominating in the immature well these alginites are absent in the more mature gas shales of wells ex c and ex b geochemical evidence of algae and phytoplankton in general is provided by numerous biomarker parameters while the occurrence of carotane in some samples indicates events of increased salinity although no hypersaline conditions are inferred due to very low gammacerane indices increased amounts of vitrinite and inertinite in samples of ex b suggest locally significant terrigenous input of organic matter for some periods during wealden shale deposition high sulfur organic carbon ratios provide evidence for sulfate rich waters and partly anoxic bottom water conditions while the lower mature lacustrine source rocks generate paraffinic waxy oils gas and condensates are produced at post mature stages furthermore maturity distribution maps from 3d numerical petroleum systems modeling reveal substantial differences in respect to petroleum generation

analysis of secondary migration of hydrocarbons in the ordovician carbonate reservoirs in the tazhong uplift tarim basin china the process and mechanisms of secondary hydrocarbon migration in the tazhong uplift tarim basin were investigated based on the analysis of the regional structure and by integrating geologic hydrodynamic and geochemical parameters parameters successfully analyzed included the fluid potential fluid properties production outputs and diamantane index the results indicated that hydrocarbons migrated into the tazhong uplift from the northern part of the manjiaer depression through a series of injection points ips during four orogenies that is the early caledonian 510 ma the late caledonian 439 ma the late hercynian indosinian 290 ma and the yanshanian himalayan 208 ma a total of six ips were identified at the intersections of the northeast trending faults and the northwest trending flower strike faults the hydrocarbons migrated from the ips into traps along regional trends from northwest to southeast and from northeast to southwest the hydrocarbon migration process and patterns determined the distribution of hydrocarbon properties and production rates in the tazhong uplift with increasing distance from the ips daily hydrocarbon production decreases and the hydrocarbons become progressively heavier and display lower gas oil ratios

light hydrocarbons and diamondoids of light oils in deep reservoirs of shuntuoguole low uplift tarim basin implication for the evaluation on thermal maturity secondary alteration and source characteristics abstract the shuntuoguole low uplift in tarim basin is particular because it provides insights into geochemistry of light oils at ultra deep ordovician oil reservoirs 7200 8200 m the light hydrocarbons and diamondoids of 16 oil samples from shunbei no i fault zone f1 and v fault zone f5 were analyzed to investigate their thermal maturity source characteristics and secondary alteration the oils show high similarity in the characteristics of light hydrocarbons and diamondoids the light hydrocarbons are characterized by high contents of alkanes and low contents of cycloalkanes and aromatics and the diamondoids show a domination of adamantanes and their alkylated isomers compared diamantanes thermal maturity indicators derived from diamondoids and c5 c7 light hydrocarbons indicate that the oils are highly mature and the corresponding equivalent vitrinite reflectance rc determined by light hydrocarbons and methyldiadamantane index are in the ranges of 1 2 1 5 signatures of biodegradation and thermochemical sulfate reduction were not observed in the oils the geochemical information from the light hydrocarbons and distribution patterns of molar concentration of n alkanes indicate that the oils from f1 experienced noticeable evaporative fractionation and the oils from f5 did not this was supposed to be the primarily reason for the physical difference between oils from the both fault zones the parameters derived from the light hydrocarbons and diamondoids indicate the oils are from same source rocks which are associated with marine materials with type ii kerogen such as algae and bacteria and both of cambrian lower ordovician o1 and middle upper ordovician o2 3 source rocks in the deep lower palaeozoic strata contributed to the oils

application of diamondoids to distinguish source rock facies abstract diamondoid distributions in solvent extracts from marine siliciclastic shales marine carbonates and coals of a wide variety of maturities were determined by gc msd for this sample set published diamondoid maturity parameters did not change systematically throughout the oil window it was found that several novel diamondoid ratios were indicative of source it was possible to distinguish between terrigenous marine carbonate and marine siliciclastic facies the proposed dimethyl diamantane facies ratios are virtually unaffected by maturity while the ethyl adamantane ratio appears to be affected by maturity in the late gas window range

decadal variability of east australian current transport inferred from repeated high density xbt transects a ctd survey and satellite altimetry a time series of the net geostrophic transport through the tasman sea representing the flow of the east australian current eac extension is determined from a full depth ctd section 15 years of high density xbt transects and satellite altimetry data a section between sydney and wellington px34 has been occupied four times per year since 1991 with high resolution xbt sampling two methods to infer baroclinic transport from proxy data along the section are presented the first uses shallow xbt transects to derive geostrophic transport relative to a deep 2000 m reference level in the second approach synts the subsurface temperature and salinity structure are inferred from satellite surface height and temperature fields using a model developed from historical in situ observations the baroclinic transport is then computed in the usual manner the methods are validated using both a full depth ctd occupation of the px34 section and further transects crossing the eac in the northern tasman sea there is close agreement between the 49 xbt and synts px34 transport estimates obtained between 1992 and 2006 the time series of transport through the sydney wellington section shows a range of temporal signals from eddyscale seasonal interannnual to decadal in particular we note that the net eac flow ranges from 5 sv in 1995 to a maximum of 16 sv in 2000 2001 this decadal variation confirms the eac response to a spin up of the south pacific circulation forced by changes in the basin wide winds and matches the changes in oceanic properties observed in the tasman sea

east australian current volume transports at 30 s estimates from the world ocean circulation experiment hydrographic sections pr11 p6 and the pcm3 current meter array between september 1991 and march 1994 the oceanic region off the east coast of australia at 30 s was the subject of an intense observational program part of the world ocean circulation experiment the objective was to improve our understanding of the dynamics of the east australian current eac and to measure its volume and energy flux the two main components were the pacific current meter array 3 pcm3 with six moorings spanning a total distance of 120 km and repeat high resolution hydrographic surveys the long term average frompcm3 shows the eac as a narrow swift and highly variable current centered at 40 km from the coast with strong shear in the upper 1000 m and mean southward velocities of 0 6 m s 1 in the core the measurements also revealed a thick countercurrent underneath the poleward flow the mean volume transport for the entire section covered by the array between the coast and 154 4 e was 22 1 4 6 sv toward the south with an rms variability of 30 sv combining the data from the pcm3 array with the hydrographic sections generated nine detailed snapshots of the absolute geostrophic current field the snapshots were used to evaluate the reliability of the pcm3 data for determining volume transports the rms difference between transports derived from direct current observations and from hydrographie data was 3 8 sv indicating that the pcm3 array can be used to describe the current variability despite the sparse spatial distribution of velocity measurements transport variability was dominated by periods between 90 and 140 days which are attributed to eddy shedding in the region occasional intense northward flow events were observed where total transports reached up to 50 sv northward on those occasions the southward boundary current changed from being surface intensified and mainly baroclinic to northward and more barotropic related to the northward migration past the array of the eac coastal separation point

a numerical modeling study of the east australian current encircling and overwashing a warm core eddy 1 warm core eddies wces often form in the meanders of western boundary currents wbcs wces are frequently overwashed with less dense waters sourced from the wbc we use the regional ocean modelling system to investigate the ocean state during the overwashing of one such wce in october 2008 in the east australian current eac comparisons of model outputs with satellite sea surface temperature and vertical profiles show that the model provides a realistic simulation of the eddy during the period when the eac encircled and then overwashed the eddy during the encircling stage an eddy with closed circulation persisted at depth in the surface eac water entered from the north encircled the eddy and exited to the east the overwashing stage was initiated by the expulsion of cyclonic vorticity for the following 8 days after the expulsion waters from the eac washed over the top of the eddy transferring heat and anticyclonic vorticity radially inward after approximately one rotation period of overwashing the eddy separated the overwashing creates a two layer system that forms a subsurface maximum velocity at the interface of the two layers analysis of water mass properties eulerian tracer dynamics and lagrangian particle tracks show that the original eddy sinks 10 50 m during the overwashing period overwashing has been observed in many wbcs and occurs in most wces in the western tasman sea

the east australian current and property transport at 27 s from 2012 to 2013 abstractthe east australian current eac is the complex and highly energetic poleward western boundary current of the south pacific ocean a full depth current meter and property temperature and salinity mooring array was deployed from the continental shelf to the abyssal waters off brisbane australia 27 s for 18 months from april 2012 to august 2013 the eac mooring array is an essential component of the australian integrated marine observing system imos during this period the eac was coherent with an eddy kinetic to mean kinetic energy ratio of less than 1 the 18 month mean poleward only mass transport above 2000 m is 22 1 7 5 sverdrups sv 1 sv 106 m3 s 1 the mean poleward only heat transport and flow weighted temperature above 2000 m are 1 35 0 42 pw and 15 33 c respectively a difference in the poleward only and net poleward mass and heat transports above 2000 m of 6 3 sv and 0 24 pw reflects the presence of an equatorward eac retroflection at the eastern offshore end of the

storm tracks in the southern hemisphere subtropical oceans ocean storm tracks have previously been associated with the midlatitude western boundary currents wbcs and the antarctic circumpolar current acc here we identify and examine large scale baroclinically unstable waves occurring within waveguides associated with potential density gradients in the subtropical regions of the southern hemisphere sh oceans where the trade winds and westerlies meet and at depths associated with mode water formation in contrast to the northern hemisphere subtropics the sh pathways are more extensive allowing large scale coherent disturbances to communicate information westward from the midlatitudes to the subtropics south pacific ocean and from the subtropics to the tropics indian ocean particular consideration is given to the subtropical south pacific ocean as this is a region where resonant interactions between large scale rossby waves and significant topographic features have been reported to occur using an ocean general circulation model and a simple potential energy transfer diagnostic we identify the relevant nonlinearly modified structures comparing their propagation characteristics to planetary rossby waves calculated using a shallow water model although at first appearance baroclinic disturbances resemble planetary rossby waves we show they are inherently nonlinear multiscale and are amplified where topography occurs the location of the disturbances coincides with regions of high variability in sea surface height observed in satellite altimetry and their speeds closely match the large scale coherent westward propagating structures described in the observational literature our study provides evidence that in addition to the midlatitude wbcs and the acc significant ocean storm tracks are also manifest in the sh subtropics

do east australian current anticyclonic eddies leave the tasman sea using satellite altimetry and high resolution model output we analyze the pathway of large long lived anticyclonic eddies that originate near the east australian current eac separation point we show that 25 30 of these eddies propagate southward around tasmania leave the tasman sea and decay in the great australian bight this pathway has not been previously documented owing to poor satellite sampling off eastern tasmania as eddies propagate southward they often stall for several months at near constant latitude along the pathway eddies become increasingly barotropic eddy intensity is primarily influenced by merging with other eddies and a gradual decay otherwise surface temperature anomaly associated with anticyclonic eddies changes as they propagate while surface salinity anomaly tends to remain relatively unchanged as they propagate

the retroflection paradox abstract the classical question of what happens when a warm western boundary current such as the north brazil current nbc retroflects is addressed analytically using a reduced gravity nonlinear model the traditional view is that the northwestward flowing current separates from the wall turns to the right looking offshore and forms a zonal boundary current that flows eastward integration of the steady inviscid momentum equation along the boundary gives the longshore momentum flux or flow force and shows that such a scenario leads to a paradox to resolve the paradox the separated current must constantly shed anticyclones which propagate to the northwest due to and an interaction with the boundary this new eddy shedding mechanism which is not related to the traditional instability of a zonal jet may explain why the nbc must produce rings a nonlinear analytical solution to the problem is constructed with the aid of a powerful theoretical approach based on the idea that nonlinear periodic

a chironomid inferred summer temperature reconstruction from subtropical australia during the last glacial maximum lgm and the last deglaciation abstract a chironomid based mean february temperature reconstruction from welsby lagoon north stradbroke island australia covering the last glacial maximum lgm and deglaciation between c 23 2 and 15 5 cal ka bp is presented mean february temperature reconstructions show a maximum inferred cooling of c 6 5 c at c 18 5 cal ka bp followed by rapid warming to near holocene values immediately after the lgm the inferred timing magnitude and trend of maximum cooling and warming display strong similarities to marine records from areas affected by the east australian current eac the warming trend started at c 18 1 cal ka bp and is consistent with the start of deglaciation from antarctic records near holocene values are maintained through the deglaciation to 15 5 cal ka bp these records suggest that changes in the australian subtropics are linked to southern high latitudes

the abundance and distribution of diamondoids in biodegraded oils from the san joaquin valley implications for biodegradation of diamondoids in petroleum reservoirs abstract the biodegradability of diamondoids was investigated using a collection of crude oil samples from the san joaquin valley california that had been biodegraded to varying extent in the reservoir our results show that diamondoids are subjected to biodegradation which is selective as well as stepwise adamantanes are generally more susceptible to biodegradation than other diamondoids such as diamantanes and triamantanes we report a possible pathway for the microbial degradation of adamantane this cage hydrocarbon possibly breaks down to a metabolic intermediate through the action of microbes at higher levels of biodegradation in petroleum reservoirs microbial alteration has only a minor effect on diamondoid abundance in oil at low levels of biodegradation our results suggest that most diamondoids with the exception of adamantane are resistant to biodegradation like the polycyclic terpanes e g c19 c24 tricyclic terpanes hopanes gammacerane oleananes ts tm c29 ts steranes and diasteranes microbial alteration of diamondoids has a negligible impact on the quantification of oil cracking achieved using the diamondoid biomarker method

eddy train encounters with a continental boundary a south atlantic case study satellite altimetry suggests that large anticyclonic eddies rings originating from the agulhas current retroflection occasionally make their way across the entire south atlantic ocean what happens when these rings encounter a western boundary current in this work interactions between a train of nonlinear lenslike eddies and a southern hemisphere continental boundary are investigated analytically and numerically on a b plane the train of eddies is modeled as a steady double frontal zonal current with the same vorticity and transport as the eddies themselves the continental boundary is represented by a vertical wall which is purely meridional in one case and is tilted with respect to the north in another case it is demonstrated analytically that the eddy wall encounter produces an equatorward flow parallel to the continental wall thus suggesting a weakening of the transport of the associated poleward flowing western boundary current upstream of the encounter zone and unchanged transport downstream a large stationary eddy is established in thecontactzonebecauseitsb inducedforceisnecessarytobalancetheotherforcesalongthewall thesizeof this eddy is directly proportional to the transport of the eddy train and the meridional tilt of the wall these scenarios are in good agreement with results obtained numerically using an isopycnal bleck and boudra model

identifying multiple sources of petroleum fluids in browse basin accumulations using diamondoids and semi volatile aromatic compounds abstract hydrocarbon fluid correlation studies often rely on compounds that are source specific but only represent a minor fraction of the bulk fluid e g steranes the correlation in the present study utilises compounds that represent a significant proportion of the bulk fluid namely semi volatile aromatics sva and diamondoids comprehensive two dimensional gas chromatography coupled to time of flight mass spectrometry gc gc tofms was used to analyse diamondoids and sva in whole oil condensate samples from the browse basin north west shelf australia together with aromatic maturity ratios and the stable carbon isotopic composition for selected diamondoids and alkylbenzenes these analyses demonstrate that numerous accumulations within the browse basin contain hydrocarbons from mixed sources the diamondoid and sva data provides further information on the current hydrocarbon fluid discrimination which is primarily based on saturated biomarker compositions results of this study reveal a complex fill history by identifying the presence of a high maturity fluid s in the biodegraded accumulations on the yampi shelf i e in the greater cornea field and at gwydion 1 this high maturity fluid is most likely derived from the lower middle jurassic plover formation j10 j20 supersequences in the greater cornea area and in the case of gwydion 1 additional hydrocarbons may also be derived from the upper jurassic vulcan formation j30 k10 supersequences other accumulations that comprise mixtures include mimia 1 and concerto 1 st1 deep located to the north of the ichthys field and could represent charge from several jurassic source rocks the most mature fluids analysed in this basin are family ii plover sourced and reservoired condensates from kronos 1 dinichthys north 1 and gorgonichthys 1 as demonstrated by their elevated concentrations of the methyladamantanes and methyldiamantanes the dinichthys north 1 and gorgonichthys 1 condensates also show a significant enrichment in the 13c compound specific values of the di tri and tetra methylbenzenes whereas the kronos 1 condensate does not suggesting derivation from different source kitchens

circulation of the pacific ocean seen in a global ocean model ocean circulation and climate advanced modelling project occam this paper compares observations made in the pacific ocean and the 8 12 year climatology of a global numerical model meridional mass and heat transports and their divergences are calculated and zonal averages compared with the air sea exchange values of doney et al 1998 with mixed success the large scale distribution of sea surface height and near surface currents are shown to be well reproduced by the model but their variance is underestimated severely so in areas of weak variability synoptic wind forcing enhances the latter though only slightly while higher model resolution improves agreement in areas of strong variability model mean transports in the east australian current in the vitiaz strait and in the kuroshio exceed measurements by 10 0 18 sv respectively and variability is underestimated by factors between 2 and 4 near 1000 m and in strong currents the flow is overestimated but over most of the ocean model output does not match either the magnitude or the spatial variability of the observations in contrast the inflow of bottom water and its spreading path throughout both south and north pacific is well described good agreement is found with measured transport through the samoan passage but at 32 s east of the tonga kermadec ridge the model yields only 60 of the observed value the sverdrup balance is shown to hold widely in the model interior utilizing the complete depth integrated vorticity equation it is found that bottom pressure torques balance the advection of planetary vorticity in both surface and bottom intensified western boundary currents

gas geochemistry of the mobile bay jurassic norphlet formation thermal controls and implications for reservoir connectivity the mobile bay gas field is located offshore alabama in the northern gulf of mexico production is from eolian dunes of the jurassic norphlet sandstone at depths exceeding 6100 m 20 000 ft and temperatures greater than 200c reservoir connectivity and compositional variation including the distribution of nonhydrocarbon gases h2s and co2 are critical factors in production strategy to evaluate the controls on compositional variation and connectivity detailed molecular and isotopic analyses were conducted for 29 wells analysis of volatiles in fluid inclusions suggests that the field was originally filled with oil that subsequently cracked to gas in addition to the thermal destruction cracking of oil the process of thermochemical sulfate reduction tsr continues to destroy the remaining hydrocarbons through oxidation of gas and reduction of sulfate to form h2s and co2 the variable extent of the tsr process at mobile bay results in a wide range of hydrocarbon and h2s compositions condensates are almost exclusively composed of diamondoids whose composition appears controlled by h2s concentrations in contrast to hydrocarbon and h2s contents co2 concentrations are relatively constant throughout the field carbon isotopic ratios for co2 correlate positively with those for wet gas hydrocarbons but are heavier than expected for co2 originating from hydrocarbon oxidation via tsr the narrow range of co2 contents and heavy isotope ratios suggests that co2 is regulated by water rock equilibration and carbonate precipitation the destruction of the hydrocarbon gas and mineralization of the carbon dioxide product create a volume reduction and an associated drop in reservoir pressure this process creates several internal sinks or exits that may control the spill direction for gas in the field

modeling the east australian current in the western tasman sea the east australian current eac is a western boundary current flowing southward off the east coast of australia its eddy variability has been shown to be vigorous a typical feature being the formation of a large warm core eddy in the western tasman sea the dynamics controlling the development of such an eddy are the subject of this paper the princeton ocean model was tuned for conditions that prevail in the western tasman sea and initialized with features based on the royal australian navy weekly temperature charts a 70 day simulation initialized with summer conditions captures the formation of a large warm core eddy that matches fairly well the observations analyses of the results demonstrate that the formation of these eddies is associated with a wide range of dynamical aspects observed in the region such as oscillation and propagation of the tasman front eac separation from the coast formation of cold core frontal eddies and nutrient enrichment of coastal waters

the study on the source of the oil seeps and bitumens in the tianjingshan structure of the northern longmen mountain structure of sichuan basin china abstract the tianjingshan structure of the northern longmen mountain is located in the north of the sichuan province china two primary source rocks are present in this region the overmature infracambrian lower cambrian source rocks and the mature upper permian source rocks oil seeps and solid bitumens occur extensively in the mesozoic and paleozoic marine strata indicating good exploration prospects in this area however oil to source correlation in the tianjingshan structure is difficult due to both high maturity of the lower cambrian source rocks and severe biodegradation of oil seeps and bitumens in this work one oil seep from the permian qixia formation and two severely degraded bitumens from the cambrian strata in the tianjingshan structure were correlated with their potential source rocks hydropyrolysis was used to release biomarkers bound to kerogen of the overmature lower cambrian source rock the released biomarkers were used for the oil to source correlation together with those indexes resistant to thermal degradation and biodegradation based on the geochemical data and the petroleum geological settings of the area it can be inferred that the cambrian ordovician and silurian bitumens with light bulk isotopic values commonly 13 c

quantitative mapping of the east australian current encroachment using time series himawari 8 sea surface temperature data the east australian current eac is a highly dynamic western boundary current that exerts significant influences on the marine ecosystem off south east margin of australia for the first time a quantitative mapping of the eac system was conducted using himawari 8 sea surface temperature data and a topographic position index tpi based image processing technique the validation using bluelink reanalysis data suggested good reliability of our mapping results subsequent quantitative examination provides new insights into the eac s cross shelf movement which is a driving force of adjacent slope shelf circulations along the coast of new south wales nsw large scale and high frequency eac encroachment was observed being every 60 80 days upstream 30 32 s and every 90 100 days downstream 33 35 s which is associated with the eac s intrinsic oscillation and eddy shedding downstream the eac encroachment exhibits a 20 day longer period and a double amplitude such dephasing is most likely due to the abrupt change of regime at the eac separation point 32 33 s upstream the eac encroachment also exhibits seasonality being 10 15 km closer to the coast in austral summer which is due to the seasonal eac broadening higher frequency 16 32 days and smaller magnitude eac intrusion was observed along the entire nsw coast 28 37 s which is possibly associated with eac s meanders and frontal eddies in the extension zone 37 30 44 s we observed maximum eac encroachment in summer which is an expression of the seasonal boundary flow off eastern tasmania a dataset of eac encroachment 2015 2017 is available see data availability

diamondoid hydrocarbon ratios novel maturity indices for highly mature crude oils abstract diamondoid hydrocarbons have been identified in oil and source rock samples from the tarim yinggehai qiongdongnan and other chinese basins two diamondoid hydrocarbon ratios have been used as novel high maturity indices to evaluate the maturation and evolution of crude oils and condensates in these chinese basins the two ratios 1 ma 1 ma 2 ma mai methyl adamantane index and 4 md 1 md 3 md 4 md mdi methyl diamantane index were found to increase with increasing vitrinite reflectance the initial values for the ratios are ca 50 and 30 respectively diamondoid hydrocarbons are products of rearrangement of polycyclic hydrocarbons and their ratios are found to be affected by organic input to a minor extent based on this study crude oils from the tarim basin are generally believed to be very mature ro 1 1 the cambrian ordovician source beds are the major source rocks of crude oils and natural gases in this basin condensates from the tarim yinggehai and qiongdongnan basins have higher maturities equivalent to ro values of 1 6 2 0 gases and condensates from the yinggehai and qiongdongnan basins are generated mainly from tertiary source rocks below 4000 5000 m

eddy shedding and energy conversions in the east australian current 1 mesoscale variability and eddy shedding in the tasman sea particularly of the east australian current eac is studied through the analysis of remotely sensed observations and outputs from a global ocean model previous observations of the western boundary current separation from the coast showed strong variability at periods ranging between 90 and 140 days we show from satellite altimetric observations that rapid northward migration of the separation point of the eac follows the formation of large eddies at periods of 100 days after an eddy separation event the normally southward flowing current swiftly assumes a more zonal configuration near the separation latitude with a cyclonic circulation developing inshore the formation of large separation eddies is preceded by the southward propagation of sea level anomalies along the east australian continental slope from 25 s sea level anomalies grow as they travel south eventually being pinched off in the form of large anticyclones at 32 s in the current retroflection area energy conversion terms in a global ocean model and in altimetric data suggest both barotropic and baroclinic instability may account for the growth of these anomalies as they propagate south east of the main eac jet there is evidence that eddies may be feeding potential energy back to the mean flow

aliased tidal errors in topex poseidon sea surface height data alias periods and wavelengths for the m2 s2 n2 k1 o1 and p1 tidal constituents are calculated for topex poseidon alias wavelengths calculated in previous studies are shown to be in error and a correct method is presented with the exception of the k1 constituent all of these tidal aliases for topex poseidon have periods shorter than 90 days and are unlikely to be confounded with long period sea surface height signals associated with real ocean processes in particular the correspondence between the periods and wavelengths of the m2 alias and annual baroclinic rossby waves that plagued geosat sea surface height data is avoided the potential for aliasing residual tidal errors in smoothed estimates of sea surface height is calculated for the six tidal constituents the potential for aliasing the lunar tidal constituents m2 n2 and o1 fluctuates with latitude and is different for estimates made at the crossovers of ascending and descending ground tracks than for estimates at points midway between crossovers the potential for aliasing the solar tidal constituents s2 k1 and p1 varies smoothly with latitude s2 is strongly aliased for latitudes within 50 degrees of the equator while k1 and p1 are only weakly aliased in that range a weighted least squares method for estimating and removing residual tidal errors from topex poseidon sea surface height data is presented a clear understanding of the nature of aliased tidal error in topex poseidon data aids the unambiguous identification of real propagating sea surface height signals unequivocal evidence of annual period westward propagating waves in the north atlantic is presented

three dimensional structure of a swarm of the salp thalia democratica within a cold core eddy off southeast australia 1 swarms of the salp thalia democratica periodically occur off southeast australia following the austral spring bloom of phytoplankton in october 2008 a filament of upwelled water was advected south by the adjacent east australian current and formed a 30 km diameter cold core eddy cce the three dimensional structure of a subsurface swarm of t democratica within the eddy was examined using both oblique and vertical hauls and an optical plankton counter opc deployed on a towed body the cce displayed distinct uplift of the nutricline and elevated fluorescence net samples show the zooplankton community was dominated by t democratica comprising 73 88 of zooplankton abundance the size distribution of t democratica measured from net samples was 0 5 5 mm and was used to interpret the opc transects which showed the swarm formed a 15 km diameter disc located 20 40 m deep in the center of the eddy the maximum salp abundance was in the pycnocline and coincided with the subsurface fluorescence maximum the mean abundance of t democratica size particles within the disc was 5003 individuals m 3 ind m 3 contrasted with only 604 ind m 3 at the outer edge of the eddy the vertically concentrated and horizontally constrained disc shaped salp swarm occurred at the interface of salp bearing inner shelf water and nutrient rich upwelled water in a cce the physical processes that formed the cce on the inshore edge of the western boundary current led to the largest density of salps recorded

dynamics of separating western boundary currents abstract in this work pratt and stern s quasigeostrophic 1 layer infinite jet model is connected to a western boundary by a system of two converging boundary currents the model has a piecewise constant potential vorticity structure and the departing jet has a zonal cusplike profile in the ocean interior the relative strengths of the coastal jets can be varied and the coastline can be tilted relative to north the coastline tilt and the coastal current asymmetry cause an alongshore momentum imbalance that creates a spatially damped quasi stationary wave pattern the presence of the boundary favors the long waves in the model which behave fairly linearly in all study cases the effects of the coastline tilt and the coastal current asymmetry are varied to reinforce or cancel each other in the former case a retroflection type of boundary current separation like the one observed in most southern hemisphere western boundary currents is obtained in the latter case a much smoother separation results

energetics of eddy mean flow interactions in the brazil current between 20 s and 36 s the energetics of eddy mean flow interactions in the brazil current bc between 20 s and 36 s are investigated in nineteen transects perpendicular to the 200 m isobath ten years 2000 2009 of output data from the hybrid coordinate ocean model hycom ncoda reanalysis with a spatial resolution of 1 12 5 and five day averages are used the mean kinetic energy mke and eddy kinetic energy eke fields presented the same subsurface spatial pattern but with reduced values the eke increases southward with high values along the bc path and the offshore portion of the jet the values of the barotropic conversion term btc are highest in the surface layers and decreased with depth whereas the values of the baroclinic conversion term bcc and the vertical eddy heat flux vehf are highest in the subsurface despite the vertical thickening of the bc the highest energy conversion rates are confined to the upper 700 m of the water column the energetic analysis showed that the current features mixed instability processes the vertical weighted mean of the btc and bcc presented an oscillatory pattern related to the bathymetry the eddy field accelerates the time mean flow upstream and downstream of bathymetric features and drains energy from the time mean flow over the features the bc is baroclinically unstable south of 28 s and the highest energy conversion rates occur in cabo de sao tome cabo frio and the cone do rio grande

quantitative diamondoid analysis indicates oil cosourcing from a deep petroleum system onshore niger delta basin the niger delta basin is one of the most prolific hydrocarbon provinces in the world yet the origin of the vast amounts of oil and gas found in the numerous sub basins across the delta remains contested a total of 180 oil samples from more than 40 oil fields in the niger delta were analyzed by gas chromatography gc gc mass spectrometry gc ms and selected samples by gc tandem mass spectrometry gc msms the interpreted thermal maturity and source depositional environments of these hydrocarbons show significant variation depending on the components analyzed and allow no clear correlation to a single source rock but rather imply extensive mixed contributions diamondoid hydrocarbon parameters were used for the first time on these paleogene neogene reservoired oils to investigate source thermal maturity and mixing effects and to perform cross correlations of these oils the diamondoid abundances and distributions support the hypothesis of co sourcing of oil from a thermally cracked sub delta type ii marine source which was then mixed with oils of relatively lower maturities in the paleogene neogene reservoirs future geochemical interpretations should treat the niger delta oils as potential mixtures of oils of variable maturities from different sources often with the most important source biomarkers depleted because of the extent of thermal cracking

generation and evolution of diamondoids in source rock abstract thermal maturation related variations in the abundance and distribution of diamondoids in source rocks were investigated by thermal simulation experiments on extracts and kerogen obtained from a same marine shale and by quantitative analysis of diamondoids within pyrolysates using highly sensitive and selective gas chromatography triple quadrupole mass spectrometry gc ms ms the results indicate that diamondoids within the marine shale are generated mainly during 0 8 1 7 easyro generally deriving from extractable organic matter within source rocks and are destroyed after 1 7 easyro to be entirely removed by ca 3 0 easyro ternary plots of the relative distribution of diamondoids and bivariate diagrams for diamondoid parameters e g dma md vs dmai 1 and dma md vs tmai 1 show systematic changes in diamondoids with increasing thermal maturity expressed as easyro

crude oil families in the euphrates graben syria abstract the most petroliferous province in syria is the euphrates graben system in the eastern part of the country the source of the produced light and heavy oils has been a matter of debate from a petroleum geochemistry perspective as there are several possible source rock and just one proven source rock r mah formation based on gross composition and oil oil correlation of biomarker and non biomarker characteristics three oil families have here been identified in the study area crude oils of family 1 have been found to be generated from a marine and clay rich source rock that is older than jurassic in age based on age related biomarker parameters steranes and nordiacholestane ratios maturity related parameters aliphatic biomarkers and diamondoids signal that the source of this oil family had a high maturation level these features fit very well to the tanf formation abba group which is equivalent to lower silurian hot shales found elsewhere in the middle east and north africa however the upper cretaceous r mah formation and shiranish formation were found to be responsible for generating the majority of the crude oils studied family 2 compositional and molecular differences between families 2a and 2b were attributed to facies and subtle maturation variations geochemical oil source rock correlations indicate that family 2a was most likely sourced from the shiranish formation while family 2b was sourced from the r mah formation secondary alteration processes influenced bulk petroleum composition most notably the depletion of light ends and the lowering of api gravity particularly in the northwestern part of the graben

eddy momentum flux and its contribution to the southern ocean momentum balance a large amount of momentum is transferred to the southern ocean by strong westerly winds analytical and numerical models have suggested that transient eddies may be important in transporting this momentum away from the region of wind forcing either horizontally1or vertically downwards where it is balanced by bottom topographic drag2 5 there are however few long term in situ observations of horizontal eddy momentum flux6 8 and no large scale measurements of vertical eddy fluxes to test these models as a result the momentum balance of the antarctic circumpolar current acc remains uncertain and the role of eddies controversial here we use geosat satellite altimeter data to resolve directional eddy kinetic energy and horizontal eddy momentum flux in the acc on fine spatial and temporal scales the complex spatial distribution of surface eddy momentum flux is strongly influenced by bottom topography the horizontal eddy momentum flux tends generally to concentrate the mean flow although some regions of divergence are observed our results show that the zonally averaged horizontal eddy momentum flux from transient eddies is an order of magnitude too small and in the wrong direction to directly balance the eastward momentum input from wind1

on the cross shelf exchange driven by frontal eddies along a western boundary current during austral winter 2007 western boundary currents are characterized by high mesoscale eddy activity including that of cyclonic frontal eddies cfes these form frequently adjacent to the shelf break export coastal water and affect biological productivity here we study the physical properties of eddies identified within the intensification zone of the east australian current eac through the analysis of remotely sensed data the application of an ocean circulation model and the evaluation of lagrangian simulations during austral winter 2007 we examine the spatial and temporal evolution of identified eddies investigate their formation mechanism and quantify the contribution made to cross shelf exchanges the mesoscale eddies are tracked from generation to decay using an eddy detection and tracking method in this case study we identify two cfes referred to as c1 and c2 with lifetimes of 11 and 38 days and radii of 45 and 70 km respectively and one anticyclonic eddy ace with a lifetime of 62 days and a radius of 60 km both cfes interact with the ace leading to quasi stationary dipole eddies located in the vicinity of the shelf this is the first time dipole eddies are reported for the intensification zone of the eac the location of cfes characterised by negative sea surface height anomaly ssha and clockwise rotation coincides with remotely sensed sea surface temperature sst and chlorophyll a chl a anomalies cfes c1 and c2 appear to contribute in different ways to the cross shelf transport along the shelf break cfe c1 drives a stronger onshore transport while cfe c2 appears to enhance the offshore transport the estimated daily cross shelf export of shelf water associated with cfe c2 is estimated with about 1 23 sv 106 km3 day 1 it renews the regional shelf water in about 7 days the lifetime of cfe c2 is about 38 days thus the eddy had the potential to flush the shelf at least five times the transient cfes were found for the first time to intensify the cross shelf exchange that is due to the wind driven cyclonic circulation of the fraser gyre this seasonally occurring gyre dominates the local shelf during austral autumn and winter the results from this study demonstrate the importance of cfes in exporting cooler and chl a enriched shelf water into the warmer and oligotrophic waters of the southward flowing eac

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 2 maturity assessment abstract the thermal maturity of forty three crude oil samples collected from the cratonic portion of the tarim basin nw china has been assessed using a variety of parameters while compound ratios of diamondoids alkylated naphthalenes methyl phenanthrenes and methyl dibenzothiophenes showed consistent trends with increasing maturity a large discrepancy was observed for the maturity levels of the oils determined from these parameters equivalent vitrinite reflectance values calculated from methylphenanthrene index 1 mpi1 methyldibenzothiophene ratio mdr and methyldiamontane index mdi were in the range of 0 66 0 97 1 11 1 64 and 0 89 1 74 ro respectively while we caution that some of the discrepancy may be related to calibration problems the difference observed from different compound classes could be real reflecting the multiple charge to petroleum accumulations as the diamondoid hydrocarbons were possibly generated at later maturation stages than most aromatic hydrocarbons as diamondoids with methyl substitution on the bridgehead positions are more stable than those with substitution on other positions several compound ratios based on ethyl admantanes dimethyl admantanes trimethyl admantanes and dimethyl diamantanes also correlated with the established maturity indicators such as mdr and mdi while condensates with high maturity levels represent the late charge hydrocarbons some of them with relatively low maturity levels may be affected by evaporative fractionation processes the normal gravity oils cover a wide maturity range consistent with multiple charges and in reservoir mixing while the waxy oils with high apparent maturity levels may be the products of wax precipitation due to a later gas injection into an oil column heavy oils with low apparent maturity levels could be the residue of oil that has lost its light end

the fate of diamondoids in coals and sedimentary rocks diamondoids were detected in the extracts of a series of coals and rocks varying in maturity lithology source input and depositional environment at the same maturity level diamondoids are generally about a magnitude more abundant in source rocks than in coals the concentrations of diamondoids are maturity dependent however while diamondoids become more abundant with the increasing thermal maturity a diminution in diamondoid concentrations is observed at the maturity value of about r sub o 4 0 in both coals and rocks the occurrence of diamantane destruction at 550 sup o c during pyrolysis suggests that diamondoids may be eventually destroyed at high temperatures in the earth here we propose three main phases of diamondoid life in nature diamondoid generation phase i r sub o 4 0

a quantitative study of aromatic hydrocarbons in a natural maturity shale sequence the 3 methylphenanthrene retene ratio a pragmatic maturity parameter abstract the aim of this study is to illustrate the use of multivariate statistical methods in identifying potential maturity parameters a study of the quantitative aromatic hydrocarbon results from a natural maturity sequence through a thick 3000 m organic lean shale followed by multivariate statistical treatment of the data was performed the study series consists of low toc ca 0 5 wt and rock eval s2 generally below 1 mg hc g rock shales showing a continuous maturity increase from tmax values of 410 c to ca 490 c this trend is mirrored by a concomitant decrease in the hydrogen index from values of around 150 mg hc g toc to ca 40 mg hc g toc based on the production indices and gc ms analysis of the saturated hydrocarbon biomarkers no indications of migrated hydrocarbons or major facies variations were found in the studied samples in essence this shale sequence represents a near perfect natural maturity series the 3 methylphenanthrene retene ratio shows an exponential increase with maturity and is proposed as a very sensitive maturity indicator extending into the late oil window this maturity ratio has since been successfully applied to both source rock extract kerogen type iii ii iii and ii and oil studies

reservoir alteration of crude oils in the junggar basin northwest china insights from diamondoid indices abstract reservoir alteration of crude oils is ubiquitous in petroleum reservoirs alteration can change the composition and physicochemical properties of crude oils and complicate oil source correlations and origin studies of crude oils thus the identification and assessment of reservoir alteration could provide a better understanding of the formation and evolution of crude oils in this study the effects of reservoir alteration e g biodegradation gas washing water washing and mixing on oils in the junggar basin northwest china were identified and assessed by combining diamondoid indices with other commonly studied crude oil properties the results indicate that 1 diamondoid indices can be used to evaluate the intensity of reservoir alteration on oils e g slight biodegradation and water washing has no effect on diamondoids moderate biodegradation and water washing can result in a marked increase in diamondoid concentrations severe biodegradation and water washing significantly changes diamondoid concentration and isomerization ratios 2 diamondoid indices can assist in determining the type of reservoir alteration of oils e g condensate formed by gas washing has a lower diamondoid concentration than that generated by thermal cracking differing from biodegradation and water washing gas washing can affect diamondoid ratios mixing can be identified by a combination of diamondoid concentrations and other parameters such as api gravity and biomarker indices in oils therefore diamondoids provide specific information as to the reservoir alteration of oils which is useful in further understanding of the origin and evolution of crude oils in the junggar basin

structure and variability of the kuroshio current in tokara strait four years of mooring array measurements in tokara strait south of kyushu japan from 1992 to 1996 are used to analyze the structure and temporal variability of the kuroshio current the mean kuroshio current in tokara strait shows a nearly permanent subsurface double core structure possibly due to topographic blockage effects the dominant variations of the kuroshio in tokara strait are separated into long term variability typically 100 day period and short term variability 10 days to 1 month according to spectrum and wavelet analysis the long term variability has a large horizontal scale across the strait with a striking twofold banded structure in spatial correlations this is due to the north south kuroshio axis shift that advects the double core structure of the mean current the axis shift can be indexed with the northeastward current velocity at the northernmost station a composite analysis using this index shows well defined northward and southward axis shift structures of the kuroshio current from the composite of the topex poseidon sea level anomaly in terms of this index the kuroshio axis shift and the current structure change are associated with a dipole shape sea level anomaly east of tokara strait on the other hand the short term variability of high kinetic energy only has a small horizontal scale within the northern part of the current which is related to frontal variability there exists a deep southwestward undercurrent below 600 m in the northern part of tokara strait flowing along the isobaths the undercurrent becomes stronger during the northward shift of the kuroshio axis while it almost disappears during the southward shift

on the steadiness and instability of the intermediate western boundary current between 24 and 18 s abstractthe intermediate western boundary current iwbc transports antarctic intermediate water across the vitoria trindade ridge vtr a seamount chain at 20 s off brazil recent studies sugges

cross shelf dynamics in a western boundary current regime implications for upwelling abstractthe cross shelf dynamics up and downstream of the separation of the south pacific ocean s western boundary current wbc are studied using two years of high resolution velocity and temperature measurements from mooring arrays the shelf circulation is dominated by the east australian current eac and its eddy field with mean poleward depth integrated magnitudes on the shelf break of 0 35 and 0 15 m s 1 up and downstream of the separation point respectively the high cross shelf variability is analyzed though a momentum budget showing a dominant geostrophic balance at both locations among the secondary midshelf terms the bottom stress influence is higher upstream of the separation point while the wind stress is dominant downstream this study investigates the response of the velocity and temperature cross shelf structure to both wind and eac intrusions despite the deep water up to 140 m the response to a dominant along shelf wind stress forcing is a classic two layer ekman structure du

recent freshening of the east australian current and its eddies the east australian current eac has a relatively weak mean flow and an energetic eddy field that dominates the circulation the properties of the mean flow have been studied in detail but the changes in the eddy field have received little attention we analyze argo temperature and salinity profiles for 2005 2012 to construct a picture of the time mean and time varying properties of eac eddies we find that eddies and the surrounding waters of the western tasman sea are freshening at a rate of 0 017 0 025 practical salinity unit yr over the top 100 m with no significant temperature change consistent with the observations fields from an eddy resolving ocean model show freshening with no temperature trend moreover the model results indicate that observed changes are significant in the context of the variability over the last 20 years and may be part of a multiyear perhaps decadal cycle we attribute the freshening of the region to increased precipitation off eastern australia

patterns of vertical velocity induced by eddy distortion in an ocean model vertical motions within eddies play an important role in the exchange of properties and energy between the upper ocean and the ocean interior here we analyze alternating upward and downward cells in anticyclonic eddies in the east australian current region using a global eddy resolving model the cells explain over 50 of the variance of vertical velocity within these eddies we show that the upward and downward cells relate to eddy distortion defined as the change in eddy shape over time in anticyclonic eddies in the southern hemisphere an inward distortion is associated with upward motion and an outward distortion is associated with downward motion we discuss two mechanisms that link eddy distortion to vertical velocity one mechanism relates to changes in stratification and relative vorticity in the eddy interior the other mechanism relates to divergence of the horizontal flow in different quadrants of the eddy we show that mesoscale changes in sea level anomaly can be used to infer the vertical motion within eddies

source and thermal maturity of crude oils in the junggar basin in northwest china determined from the concentration and distribution of diamondoids abstract here we discuss three types of diamondoid parameters for oils from the junggar basin these are absolute concentrations concentration ratios and isomerization ratios according to the absolute diamondoid concentrations the oils collected from different areas of the basin were broadly divided into three maturity stages 1 low mature 1000 ppm adamantanes 50 ppm diamantanes the oils in the northwestern region of the junggar basin are in the low mature to mature stages based on a combination of diamondoid concentration ratios and biomarker indices these oils can be divided into three groups i e group i oils in the wuxia zone derived from the lower permian fengcheng formation p1f group ii oils in the kebai zone sourced from middle permian lower wuerhe formation p2w and group iii oils in the mahu depression generated from more mature source rocks of jiamuhe formation p1j or the p1f diamondoid concentrations and isomerization ratios were used to precisely evaluate the thermal maturity of mature oils and highly mature condensates respectively our results indicate that the oils in the central part of the basin have decreasing thermal maturity from south to north whereas the oils in the kelameili area display increasing thermal maturity from east to west in this study we found that different diamondoid indices are useful only in certain thermal maturity ranges therefore at least for the junggar basin it is crucial to know which thermal region one is in before using diamondoid ratios for maturity assessment

the effect of organic matter type on formation and evolution of diamondoids abstract a series of anhydrous pyrolysis experiments using sealed gold tubes were performed on three types of kerogen to investigate the effect organic matter type has on the generation and evolution of thermogenic diamondoids based on the compositional variation of pyrolysis products the cracking of kerogens can be divided into three stages oil generation 0 6 1 5 easyro wet gas generation 1 5 2 1 easyro and dry gas generation 2 1 easyro the experimental results indicate that diamondoids were mainly generated in the oil and wet gas generation stages and decomposed in the dry gas generation stage in addition to thermal maturity the formation of diamondoids is also influenced by the type of organic matter type i and iia kerogens produced more diamondoids than type iii kerogen and diamondoids generated from type iii kerogen were dominantly adamantanes therefore the concentration and concentration ratios of diamondoids can be used to assess the maturity of source rocks 1 0 1 5 easyro and determine the type of organic matter 1 0 2 0 easyro isomerization ratios of diamondoids depend mainly on thermal maturity and the type of organic matter has little effect the use of isomerization ratios to determine thermal maturity is best for source rocks at higher maturity levels 1 5 3 0 easyro therefore bivariate diagrams of concentration versus isomerization indices of diamondoids e g dmas mds vs dmai 1 and dmas mds vs tmai 1 can be used to evaluate the source rock maturity over a wider easyro range 1 0 3 0 easyro than single diamondoid parameters as there are differences in the concentration and distribution of diamondoids in the extracts of three source rocks the possibility exists to use diamondoid indices of immature rocks to determine the type of source rock

wind forced variability in eddy formation eddy shedding and the separation of the east australian current the east australian current eac like many other subtropical western boundary currents is believed to be penetrating further poleward in recent decades previous observational and model studies have used steady state dynamics to relate changes in the westerly winds to changes in the separation behavior of the eac as yet little work has been undertaken on the impact of forcing variability on the eac and tasman sea circulation here using an eddy permitting regional ocean model we present a suite of simulations forced by the same time mean fields but with different atmospheric and remote ocean variability these eddy permitting results demonstrate the nonlinear response of the eac to variable nonstationary inhomogeneous forcing these simulations show an eac with high intrinsic variability and stochastic eddy shedding we show that wind stress variability on time scales shorter than 56 days leads to increases in eddy shedding rates and southward eddy propagation producing an increased transport and southward reach of the mean eac extension we adopt an energetics framework that shows the eac extension changes to be coincident with an increase in offshore upstream eddy variance via increased barotropic instability and increase in subsurface mean kinetic energy along the length of the eac the response of eac separation to regional variable wind stress has important implications for both past and future climate change studies

oil source correlation for the paleo reservoir in the majiang area and remnant reservoir in the kaili area south china abstract there are different viewpoints on the oil source correlation of the majiang paleo reservoir and the neighbouring kaili remnant reservoir in the southern guizhou depression of china three potential source rocks in this depression could be inferred the lower cambrian marine mudstone lower silurian shale and lower permian mudstone most of the potential source rocks are of high maturity the solid bitumens and oil seepages in the southern guizhou depression suffered severe secondary alterations such as thermal degradation and biodegradation the solid bitumens of the majiang paleo reservoir are also of high maturity the oil seepages and soft bitumen of the kaili remnant reservoir were severely biodegraded all these secondary alterations may obscure oil source correlations by routine biomarkers thus it is very important to select appropriate biomarker parameters for the oil source correlation in this work biomarkers resistant to thermal degradation and biodegradation and the data of organic carbon isotopic compositions were used for the correlation the 13c values of n alkanes in asphaltene pyrolysates were also used to make oil oil and oil source correlations between severely biodegraded oils the results indicate that the lower cambrian marine mudstones are the main source for the ordovician silurian o s solid bitumens of the majiang area and the ordovician silurian oil seepages and soft bitumens of the kaili area remnant reservoir in the eastern kaili area might have been charged at least twice by the oil generated from the lower cambrian marine source rocks

berthierine formation in reservoir rocks from the siri oilfield danish north sea as result of fluid rock interactions part ii deciphering organic inorganic processes by hydrogeochemical modeling abstract berthierine formation reduces the permeability of the glauconitic reservoir sandstones in the siri oilfield danish north sea and is therefore a considerable production factor a new hydrogeochemical batch model that is based on thermodynamics of chemical equilibrium was developed to identify the processes which activated and controlled berthierine formation a good match has been achieved between the mineralogical alteration features observed in the siri field and the results of the batch modeling this match points to the validity of the modeling mechanisms for berthierine formation based on the identified mechanisms the modeling enables to quantify the mass conversion of hydrogeochemical processes in glauconite bearing and berthierine forming water rock gas systems the modeling results reveal that intense berthierine formation in the siri field resulted from in situ glauconite alteration within a more or less closed system due to hydrocarbon degradation driven water rock gas interactions this process is accompanied by formation of secondary sio2 s and potassium mica precipitation of iron bearing carbonates is prevented by berthierine formation although the glauconitic sandstones are rich in iron and carbonate species moreover such systems are brought to disequilibrium by the release of reducing and acidic agents originating from oil degradation and undergo long term diffusion dominated mass fluxes instead of advective mass fluxes

the effect of thermochemical sulfate reduction on formation and isomerization of thiadiamondoids and diamondoids in the lower paleozoic petroleum pools of the tarim basin nw china abstract we attempted to differentiate the effects of thermal chemical alteration tca from thermochemical sulfate reduction tsr on formation and isomeric distribution of thiadiamondoids and diamondoids in oils and condensate from deeply buried cambrian and ordovician carbonate reservoirs in the tarim basin china diamondoids and thiadiamondoids with 1 3 cages were detected in all the oils analyzed total thiadiamondoid concentrations reflect extent of tsr diamondoid concentrations and most of the diamondoid based maturity proxies and the source rock lithology proxy increase with increasing extent of tsr indicating that they are controlled by the extent of the tsr process or reaction with h 2 s to a greater degree than by tca tsr may have oxidized hydrocarbons to oxygenated species and finally to co 2 and newly generated and concentrated diamondoids and organic sulfur compounds the most extensive tsr altered zs1c condensate contains 3 2 wt total dibenzothiophenes 0 4 wt thiadiamondoids and 5 9 wt diamondoids together with higher polymantanes including tetramantanes and pentamantanes in association with polythiadiamondoids including dithiaadamantanes trithiaadamantanes and tetrathiaadamantanes these polythiadiamondoids have been detected only from heavily tsr altered petroleum in this study and north american samples and may be derived from the sulfurization of hydrocarbons including diamondoids under high temperature and highly reducing conditions during advanced stages of tsr the polymantanes may have been generated from alkylation of lower cage diamondoids and subsequent homologation or from free radical reactions this study indicates that tsr may have led to the generation and isomerization of thiadiamondoids and diamondoids and thus diamondoid based maturity and lithology proxies cannot be used to reflect maturity and lithology in the tsr active areas and that the occurrence of polythiadiamondoids can be used to indicate heavy tsr alteration

temperate shelf water dispersal by australian boundary currents implications for population connectivity boundary currents have been recognized as potential drivers of spatial heterogeneity in the ocean because of their role in physical transport and influence on large scale coastal processes in this study we used particle tracking methods in a data assimilating eddy resolving ocean circulation model to determine the effect of multiple boundary currents on connectivity around temperate australia during the austral winter results demonstrated that oceanographic connectivity was asymmetric around australia having greater eastward trajectories due to more favorable ocean boundary currents during this season we validated connectivity patterns with genetic data from an ecologically important species the kelp ecklonia radiata which has greater genetic similarity between the west and south coasts of australia compared with the east coast likely due to predominantly eastward propagule dispersal boundary current circulation was a coarse predictor of kelp genetic connectivity on multigeneration time scales and the nature of these relationships varied among the three boundary current systems according to mean current strength

methyl diamantane index mdi as a maturity parameter for lower palaeozoic carbonate rocks at high maturity and overmaturity diamantanes were identified in extracts from the lower ordovician majiagou formations o1m5 of the central gas field shanganning basin china at 3100 3800 m corresponding to ro 1 9 3 9 the mdi methyl diamantane index 4 md 1 md 3 md 4 md ranges from 40 to 65 for the source rock extracts changes in the mdi index in the very mature sections ro 2 0 are relatively small and no linear correlation between mdi and ro o r mdi and depth is noted as previously reported suggesting the possibility that the mdi may have limited applicability in maturity determinations 2000 elsevier science ltd all rights reserved

mesoscale structure of the mean east australian current system and its relationship with topography abstract we document the mean circulation of the east australian current eac system which is the major western boundary current in the southwest pacific ocean a new high resolution climatology of the region csiro atlas of regional seas cars is used to produce regional fields of steric height and sections of geostrophic velocity the realism of these fields has been enhanced by the high spatial resolution allowance for bathymetric control and the influence of land barriers the increased detail in the maps and sections reveal the major influence that the complex regional topography has on the circulation the results also provide the appropriate resolution for comparison with recent model studies of the region we have been able to both resolve well known features with greater detail and identify previously unrecognized aspects of the circulation important results include 1 the zonal inflow north of 30 s breaks into a series of individual jets after flowing through the island chains as suggested by recent model results 2 the interaction of the zonal inflow with the local topography as it undergoes bifurcation is documented 3 a detailed picture of the evolution of the eac at the western boundary is presented including surface currents and transports 4 separation and recirculation of the eac within the tasman abyssal basin are shown to occur as a double cell structure constrained by bathymetry 5 the eac outflow is resolved as a series of eastward and northeastward currents 6 the path of the tasman front is defined as it interacts with the tasman ridge systems 7 a quasi permanent eddy is identified for the first time adjacent to the norfolk ridge northwest of new zealand

rings in the ocean certain robust long lived eddy features in t he world s ocean have come to be k nown as rings the nomenclature stems from fuglister 1 1972 who c oined t he name based on the c ircle or ring of gulf stream waters t hat surrounded a class of eddies formed from t he g ulf stream through the pinch off of meanders here it s uffices to define rings as intense eddies or vortices that represent a wrapped up piece of a major ocean c urrent they t ranslate over space scales of hundreds to thousands of k ilometers and exist for periods lasting from months to years rings move t hrough the ocean carrying anomalies s imilar to the contrasts in physical biological and chemical properties observed across the major ocean c urrents while the term ring is t ied to fuglister t he existence ofthese features was evident at least as early as t he 1930s when iselin 2 1936 1940 encountered strong cold anomalies in the region south of the gulf stream that we would identify as c old corc cyclonic rings today iselin fully rec ognized these features as part of the highly time dependent eddy motion in the ocean later iselin fuglister 1948 were the first to survey what is now k nown as a warm core anticyc lonic ring there are tw o types of rings cold core rings are made up of w aters from the poleward s ide of c urrents like the gulf stream that are introduced to

the application of diamondoid indices in the tarim oils this study presents new data for the identification of the source and assessment of the thermal maturity of oils based on the diamondoid indices of oils from the tazhong and luntai uplifts in the tarim basin in northwest china the oil samples were divided into three groups according to biomarker characteristics and the abundance and distribution of diamondoids group i oils are located along the tazhong no 1 fault zone which contained abundant diamondoids and are of high thermal maturity suggesting they are late charged hydrocarbons that were derived from a middle upper ordovician source group ii oils are mainly located in blocks close to the tazhong no 1 fault zone and are dominated by early formed hydrocarbons from cambrian lower ordovician source rocks group iii lacustrine oils comprise relatively low concentrations of diamondoids compared with group i and group ii oils group iii oils were sourced from jurassic or possibly triassic units and are hosted by the low relief yingmaili section of the luntai uplift the thermal maturity of the oils in each group was evaluated using diamondoid parameters a few group i oils exhibit intense thermal cracking to estimate the extent of oil cracking using the concentrations of diamondoids in oils this study proposes a practical approach that facilitates the determination of baseline 4 and 3 methyldiamantane concentrations application of this method indicates that the tarim basin marine oils contain a baseline concentration of approximately 69 ppm

life history of a cyclonic ring detached from the kuroshio extension as seen by the geosat altimeter the sea surface dynamic topography ssdt sea surface height relative to the geoid is approximately estimated by combining the temporal fluctuation of ssdt determined from altimetry data with the climatological mean ssdt calculated from hydrographic data this approximated ssdt or composite ssdt is obtained in the area southeast of japan for the first year 1986 1987 of the geosat exact repeat mission variations in the kuroshio current system are well described by the composite ssdt in particular a complete life history of a cyclonic ring is observed for the first time in this region namely westward propagation of a southward meander of the kuroshio extension its pinching off to form a cyclonic ring the ring s westward movement its coalescence with the kuroshio and its eastward advection all available hydrographic data and cloud free satellite infrared images support the existence of this series of phenomena

seasonal modulations in the eddy field of the south pacific ocean abstract decade long satellite altimeter data from the ocean topography experiment topex poseidon and european remote sensing satellite 1 and 2 ers 1 2 missions are analyzed to investigate the eddy signals in the south pacific ocean high eddy kinetic energy eke bands with well defined annual cycles are detected along the eastward flowing surface currents of the south tropical countercurrent stcc between 21 29 s and the south equatorial countercurrent secc centered near 9 s overriding the westward flowing south equatorial current sec the stcc layer has the sign of its mean potential vorticity gradient opposite to that in the sec layer subjecting the vertically sheared stcc sec system to baroclinic instability in austral winter the stcc sec system is baroclinically more unstable than in other seasons because of the large vertical shear and weak stratification this seasonal variation in the intensity of baroclinic instability is responsible for the seasonal modulation of the stcc s eke fi

long term trends in the east australian current separation latitude and eddy driven transport an observed warming of the tasman sea in recent decades has been linked to a poleward shift of the maximum wind stress curl and a strengthening of the poleward flow along the coast of southeastern australia however changes in the east australian current eac separation latitude as well as in the contribution of the eac the eac extension and its eddy field to the total southward transport due to such a strengthening remain unknown this study uses 30 years 1980 2010 of the ocean forecast for the earth simulator ofes sea surface height and velocity outputs to obtain a three decade long time series of i the eac separation latitude ii the southward transport along the coast of southeastern australia 28 s 39 s and iii the southward transport across the eac separation latitude a lagrangian approach is implemented and the spin parameter is used to provide a quantitative distinction between the transports occurring outside and inside cyclonic and anticyclonic eddies significant positive trends of the low pass southward transports indicate that the intensification of the poleward flow has occurred both within the eac and in the eac extension in addition a significant increase in southward transport inside and outside eddies is found importantly the contribution of eddy driven transport has a large temporal variability and shows a sharp increase from 2005 onward finally our results show that the eac has not penetrated further south but it has separated more frequently at the southernmost latitudes within the region where it typically turns eastward

the cold core eddy and strong upwelling off the coast of new south wales in early 2007 abstract during the austral summer of 2006 07 a series of extreme oceanic events occurred in the tasman sea following a series of strong wind driven upwelling events an intense cold core eddy developed off sydney australia a data assimilating eddy resolving ocean model is used to create a three dimensional time varying reanalysis of these events the reanalysis indicates that the cold anomalies associated with the upwellings were in excess of 5 c near the coast where sea level decreased by as much as 0 2 m the reanalysed three dimensional structure of the cold core eddy shows the eddy leaning to the west north west in towards the continental shelf the diameter of the eddy is about 100 km and the sea level anomaly at the eddy centre peaks at around 1 m with an associated sub surface temperature anomaly in excess of 8 c at 200 m depth corresponding to an upward isotherm excursion of 600 m the circulation around the cyclonic eddy is ageostrophic with upwelling in the southern sector of the eddy where flow is onshore and climbing the continental slope and downwelling in the northern sector where flow is descending off the slope three dimensional trajectories of water parcels around the eddy involve 50 100 m vertical excursions based on the reanalysed circulation and composite satellite images of chlorophyll a we hypothesise that the circulation around the eddy led to significant nutrient enrichment in the euphotic zone around the perimeter of the eddy

a tale of two eddies the biophysical characteristics of two contrasting cyclonic eddies in the east australian current system mesoscale cyclonic eddies are known to be highly productive less well known are the dynamics and productivity of smaller cyclonic eddies known as frontal eddies that form on the landward side of western boundary currents in this study we investigate the physical and biogeochemical properties of two contrasting cyclonic eddies in the east australian current eac the first murphy a mesoscale cyclonic eddy that formed at 28 s with a diameter of 160 km and high surface chlorophyll a concentrations which lived 47 days the second freddy a smaller frontal eddy 35 km diameter that formed from a shelf water billow 7 days prior to sampling at 31 5 s and was advected off the shelf along the eac front from 200m to 4000m of water both eddies were at least 1000m deep with a similar steric height anomaly we introduce and employ the method of closest approach using shipboard adcp velocities to estimate the eddy centers which reveals significant tilting through the water column we estimate rotation rates of 4 10 days and 1 9 days and rossby numbers 0 25 0 1 and 0 6 0 1 from the surface to 600m for murphy and freddy respectively high resolution altimetry measurements from the saral altika satellite provide estimates of the ageostrophic component of rotation our results show that the frontal eddy is significantly more ageostrophic energetic and productive than the mesoscale cyclone despite its small size and short life 4 weeks we suggest that frontal eddies have potential to contribute significantly to the net productivity of the tasman sea region this article is protected by copyright all rights reserved

southern hemisphere western boundary current variability revealed by geos 3 altimeter geos 3 altimeter data are adjusted to minimize differences at the intersections or crossovers between ascending and descending orbits this procedure removes noise created by orbital uncertainty and permits study of sea level variations without knowledge of the geoid the root mean squares rms of the adjusted differences grouped within 2 latitude by 2 longitude boxes are mapped for the western boundary current regime and adjacent antarctic circumpolar current segment for each southern hemisphere ocean as well as for the eastern indian ocean where sufficient crossover data are available the rms crossover values are compared to surface based hydrographic data studies of ocean transients for verification of the altimeter results the altimeter data clearly reveal reasonable patterns of sea level transients associated with the western boundary currents and antarctic circumpolar current in addition the rms values reveal regions of locally amplified tidal features adjacent to the patagonian coast of argentina and in the region west of new zealand the altimeter data verify and expand on the results of limited surface based data sets particularly in the case of the circulation transients south of madagascar and southwest of new caledonia in the eastern indian ocean the altimeter data suggest variable sea level conditions near 10 20 s near 20 30 s and near 50 s the last is associated with the antarctic circumpolar current but the source of the northern variable regions is not clear

observed characteristics and vertical structure of mesoscale eddies in the southwest tropical pacific in the southwest pacific ocean waters transit from the subtropical gyre before being redistributed equatorward and poleward while the mean pathways are known the contribution to the mixing and transport of the water from mesoscale eddies has not been comprehensively investigated in this research satellite altimetry data combined with an eddy detection and tracking algorithm is used to investigate the distribution and surface characteristics of mesoscale eddies in this region of complex bathymetry 10 s 30 s 140 e 190 e detected eddies are then colocalized with in situ data from argo floats to determine their vertical structure and the effect of eddies on the water masses the numerous islands affect the eddy behavior as most eddies are formed in the lee of islands propagate westward and decay when encountering shallow bathymetry eddies are sparse and short lived in the tropical area north of fiji impacting only the top 200 meters of water they do not appear to be able to trap and transport waters in this region in the coral sea a region of lateral shear between currents transporting waters of different origins eddies are more numerous and energetic they affect the water properties down to at least 500 m depth and anticyclonic eddies trap water to 200 m contributing to the upper thermocline waters mixing and transport south of new caledonia mesoscale eddies are ubiquitous with typical lifetimes longer than 5 months they affect the temperature salinity and velocities down to 1 000 m depth and weakly contribute to the mixing of lower thermocline waters

verification of geosat sea surface topography in the gulf stream extension with surface drifting buoys and hydrographic measurements altimeter data from geosat have been analyzed in the gulf stream extension area horizontal maps of the sea surface height anomaly relative to an annual mean for various 17 day intervals were constructed using an objective mapping procedure the mean sea level was approximated by the dynamic topography from climatological hydrographic data geostrophic surface velocities derived from the composite maps mean plus anomaly are significantly correlated with surface drifter velocities observed during an oceanographie experiment in the spring of 1987 the drifter velocities contain much energy on scales less than 100 km which are not resolved in the altimetric maps it is shown that the composite sea surface height also agrees well with ground verification from hydrographic data along sections in a triangle between the azores newfoundland and bermuda except in regions of high mean gradients

variability in the south pacific deep western boundary current from current meter observations and a high resolution global model observations of the south pacific deep western boundary current from the world ocean circulation experiment pacific current meter array 9 woce pcm 9 current meter array are compared with the los alamos national laboratory high resolution global ocean model a simple integration of pcm 9 velocity yields a mean northward transport of water deeper than 3000 m that is some 5 times greater than the model mean transport of 3 35 106 m3 s 1 the low modeled abyssal transport suggests a poor simulation of the mean thermohaline circulation however model and observed transport variability correlate significantly space time spectral analysis shows planetary waves are responsible for most of the variability and are resolved well in the model the details of interaction of the long waves at the western boundary are different in model and data the model reflects these waves predominantly as planetary short waves which decay over the region 600 800 km east of the kermadec ridge pcm 9 has a higher proportion of energy as topographic waves along the kermadec ridge these two classes of waves are associated with the two observed zonal scales in the boundary current the model results can be separated into vertical modes baroclinic energy is found at all timescales including those too short for free baroclinic waves the baroclinic flow correlates with the barotropic so as to enhance surface and reduce abyssal kinetic energy this is the signature of planetary wave scattering at the submerged western boundary ridge and results in enhanced baroclinic wave energy in the tasman sea

diamondoid hydrocarbon ratios as indicators of biodegradation in australian crude oils the effect of biodegradation on diamondoid distributions in petroleum has been investigated on a series of crude oils reservoired in two australian sedimentary basins the gippsland basin and the carnarvon basin the ratio of methyladamantanes to adamantane rises with increasing biodegradation significant changes in the ratio occur at extreme levels indicating that diamondoids can be indicators of petroleum biodegradation especially when most other hydrocarbons have been removed the methyladamantane adamantane ratio can also be used to assess the composition of crude oils that are comprised of a mixture of severely biodegraded and non biodegraded oil

evaluation of globcurrent surface ocean current products a case study in australia abstract australia s marginal seas include a wide range of ocean current regimes ranging from tide dominated in the north west where the continental shelf is wide to boundary current and eddy dominated in the south east where the shelf is narrow here we take the opportunity to test the globcurrent surface ocean current products against in situ observations in these two contrasting regimes observations by acoustic doppler current profiler adcp instruments of australia s integrated marine observing system imos and drifting buoys of the global drifting programme gdp are used the monthly timescale variability of the globcurrent alongshore current component is in moderately good agreement with the observations on the continental shelf in the south east but neither the shorter period variability nor the long term mean are representative of the adcp observations while the observed tidal currents are negligibly small the wind driven signals are not but these are evidently too transient to be adequately sampled by altimetry the inclusion of an ekman component does not represent these signals because the interaction of the ekman transport with the coastal boundary condition is not included similarly the error of the time mean velocity which is the dominant error is because that product is not designed to represent the highly anisotropic nature of the sea level gradients over the continental shelf nor the constraints on the flow field that are imposed by the topography we thus conclude that the globcurrent product needs improvements before it can be described as very suitable for applications on this and probably other narrow continental shelf off the continental shelf in contrast the globcurrent products compare quite well with the trajectories of drifting buoys confirming that the products are quite suitable for blue water applications in contrast to the south east the tides are very strong in the north west region of australia the sub tidal variability is weak in both relative and absolute senses consequently the removal of the tidal signal from the sea level observations needs to be very complete for the residual error to be smaller than the true sub tidal signal transient wind forced signals are also occasionally large so this step of the de aliasing also needs to be very accurate unfortunately it appears that more work is required before accurate estimates of sub tidal variability are available from globcurrent the magnitude of the globcurrent estimates of sub tidal current variability far exceed the magnitude of and are uncorrelated with the detided adcp data

revisiting the circulation of the east australian current its path separation and eddy field abstract the traditional view of the east australian current eac as depicted in many schematics is of a continuous boundary current that flows along the shelf off eastern australia between approximately 18 s and about 32 5 s where it separates from the coast and continues either towards new zealand along the tasman front or towards tasmania as the eac extension additionally it is widely recognised that eddies are prevalent in the eac region particularly south of the eac separation we revisit this long standing paradigm and suggest that the eac is perhaps better viewed as a continuous meandering stream flowing adjacent to the coast that feeds a field of mesoscale eddies observations show that eac eddies are prevalent over a broad region of the western tasman sea as far north as 25 s typically with maximum intensity between 30 and 35 s at any instant in time the eac jet is usually evident as a poleward stream adjacent to the continental shelf edge other commonly accepted components of the eac system including the tasman front and eac extension are rarely seen as distinct identifiable features rather these features are evident only in time mean fields when the eddy variability is filtered out it is also common for the eac to be spatially discontinuous due to the presence of eddies often with multiple short streams that sometimes separate and re attach to the coast recognition of the eac as an eddy dominated current system has seen many recent studies focus on various aspects of eddies in the eac system providing new insights into mesoscale ocean dynamics recent studies of individual eddies have shown that the circulation within eddies including tilting and vertical motion is more complex than previously understood a summary of these studies along with a review of the eac system particularly its path separation and eddy field is presented here

mapping mesoscale variability of the azores current using topex poseidon and ers 1 altimetry together with hydrographic and lagrangian measurements the semaphore mesoscale air sea experiment was conducted in the azores madeira region from july to november 1993 topex poseidon tip and ers 1 were flying simultaneously at that time the main purposes of this paper are to evaluate the estimation of the oceanic mesoscale circulation from the two different sets of altimetric data tip and ers 1 and to compare the results with in situ measurements provided by the semaphore hydrographic surveys and smface drifters three expendable bathytermograph conductivity temperature depth surveys in a 500 km2 box and a set of 47 lagrangian surface drifters drogued at 150m comparisons are carried out through the maps obtained by objective analysis ti om the four data sets the mapping accuracy of tip ers i tip and ers 1 combined and in situ data is investigated as weii as the sensitivity of the mapping to the correlation functions used there is a good qualitative agreement between altimetric maps and corresponding drifter and hydrographic maps for the three hydrographic surveys correlations are about 0 8 and the regression fit is about 0 6 0 7 the lower values are clue to the smooth climatology used to reference the altimetric maps the correlation for time differences is better with regression lines not significantly different from i especiaily when ers 1 and tip are combined tip mapping is almost as good as ers 1 mapping which was rather unexpected since the ers 1 space time sampling is better suited for the mesoscale this may reflect the fact that the signal mapped by the hydrography and drifters does not contain the high frequency wavenumber components tip and ers 1 combined provide better results although the improvement is not as large as expected probaply for the same reason