sedimentary facies and diagenesis of the lower miocene rudeis formation southwestern offshore margin of the gulf of suez egypt and implications for its reservoir quality abstract studying sedimentary facies and diagenetic peculiarities are highly important for the understanding of carbonate reservoir quality including those of relatively poorly known areas of great economic importance the early miocene rudeis formation 60 191 m thick is composed mainly of fractured stylolitic vuggy moldic bioclastic coralline algal dolostone and biogenic limestone with common occurrences of pore filling anhydrite and pebble sized anhydrite nodules the diagenetic characteristics of the formation in the zeit bay field gulf of suez egypt affect its reservoir quality as can be deduced from the analysis of cores from six boreholes compaction anhydritization cementation and micritization decreased the reservoir quality whereas dissolution stylolitization and microfracturing enhanced the production potential

sandstone diagenesis and reservoir quality prediction models myths and reality models and concepts of sandstone diagenesis developed over the past two decades are currently employed with variable success to predict reservoir quality in hydrocarbon exploration not all of these are equally supported by quantitative data observations and rigorous hypothesis testing simple plots of sandstone porosity versus extrinsic parameters such as current subsurface depth or temperature are commonly extrapolated but rarely yield accurate predictions for lithified sandstones calibrated numerical models that simulate compaction and quartz cementation when linked to basin models have proven successful in predicting sandstone porosity and permeability where sufficient analog information regarding sandstone texture composition and quartz surface area is available analysis of global regional and local data sets indicates the following regarding contemporary diagenetic models used to predict reservoir quality 1 the effectiveness of grain coatings on quartz grains e g chlorite microquartz as an inhibitor of quartz cementation is supported by abundant empirical data and recent experimental results 2 vertical effective stress although a fundamental factor in compaction cannot be used alone as an accurate predictor of porosity for lithified sandstones 3 secondary porosity related to dissolution of framework grains and or cements is most commonly volumetrically minor 2 exceptions are rare and not easily predicted with current models 4 the hypothesis and widely held belief that hydrocarbon pore fluids suppress porosity loss due to quartz cementation is not supported by detailed data and does not represent a viable predictive model 5 heat flow perturbations associated with allochthonous salt bodies can result in suppressed thermal exposure thereby slowing the rate of quartz cementation in some subsalt sands

balanced ocean data assimilation near the equator the question is addressed whether using unbalanced updates in ocean data assimilation schemes for seasonal forecasting systems can result in a relatively poor simulation of zonal currents an assimilation scheme where temperature observations are used for updating only the density field is compared to a scheme where updates of density field and zonal velocities are related by geostrophic balance this is done for an equatorial linear shallow water model it is found that equatorial zonal velocities can be detoriated if velocity is not updated in the assimilation procedure adding balanced updates to the zonal velocity is shown to be a simple remedy for the shallow water model next optimal interpolation oi schemes with balanced updates of the zonal velocity are implemented in two ocean general circulation models first tests indicate a beneficial impact on equatorial upper ocean zonal currents

the pacific subsurface countercurrents and an inertial model abstract the tsuchiya jets or subsurface countercurrents extend across the pacific ocean carrying 7 2 106 m3 s 1 eastward on each side of the equator mean meridional sections of potential temperature salinity neutral density anomaly and the square of buoyancy frequency are presented for the western central and eastern tropical pacific ocean these sections are used together with maps of depth and salinity on isopycnals as well as thickness between isopycnals to describe the evolution of the tsuchiya jets as they flow from west to east an inertial jet model is formulated in which conservation of the bernoulli function and potential vorticity combine with the eastward shoaling of the tropical pycnocline to dictate the jet structure this model jet is consistent with a number of features of the tsuchiya jets their roughly constant volume transports their advection of properties such as salinity and oxygen over long zonal distances their rapidity and narrowness their poleward shift from we

eulerian and eddy induced meridional overturning circulations in the tropics abstract inspired by recent measurements of the eddy induced meridional overturning circulation in the tropical north pacific ocean by roemmich and gilson the authors analyze an oceanic general circulation model for its eulerian and eddy induced meridional overturning circulations throughout the tropics the model representation for the mesoscale eddy induced circulation is the parameterization by gent and mcwilliams and there are also rectified contributions to the time mean overturning circulation due to seasonal and interannual fluctuations the eddy induced circulation is similar in all tropical basins it has a strength of about 10 of the eulerian mainly ekman circulation and its contribution to the meridional heat flux is a similar fraction the pattern of the meridional streamfunction is one of double cells in the vertical and antisymmetry about the equator near the equator there is downwelling above the undercurrent and upwelling below with the return circulations closed within the upper 2

characteristics of interleaving in the western equatorial pacific 1 the characteristics of intrusive thermohaline features in the thermocline of the western equatorial pacific are examined during two different climatic states the vertical and meridional structure of the features is determined from a total of 12 high resolution meridional sections although there is considerable variability of the broader structure of the flow and temperature salinity fields the spatial scale of the interleaving is found to be persistent over all sections the turner angle and correlations between the spice anomaly and density anomaly suggest that double diffusive processes may be important in the vertical flux of properties the characteristics of the interleaving are compared with the results from the theories of double diffusive interleaving and inertial instability it is found that the observations are consistent with both it is difficult to differentiate between the two theories in explaining the presence of the layers indeed both mechanisms may be playing a role the magnitude of the cross equatorial fluxes of heat and salt due to the features is estimated and shown to be comparable with estimates due to other processes there is a strong potential for the interleaving to impinge on the large scale dynamics of the equatorial pacific ocean

surface ocean variability at galapagos from 1936 1982 calibration of geochemical tracers in corals a variety of geochemical tracers has been developed in reef corals as a means of reconstructing the natural variability of the tropical surface ocean over wide ranging time frames the purpose of this paper is to calibrate the performance of five of these tracers in a modern coral colony over an extended period a 47 year growth interval 1936 1982 in a colony of pavona clavus taken from san cristobal island galapagos islands was sectioned into 187 quarterly intervals and analyzed for 18o 13o ba ca cd ca and mn ca the resulting time series are compared with eastern pacific sea surface temperatures one of few instrumental data bases available for calibration over this time period linear least squares regressions of four of the tracers 18o 13o ba ca cd ca against peruvian sst show highly significant correlations p 0 0001 over the annual biennial and enso 3 8 years frequency bands cross spectral comparisons show even stronger coherency with sst frequently accounting for 70 80 of the variance in these tracers these results as well as the phase relationships determined from the spectral analyses suggest that the coupling between sst and 18o and the nutrientlike tracers ba and cd is controlled principally by seasonal upwelling cycles and interannual interruptions of these cycles brought about by el nino and anti el nino phenomena an inverse relationship between sst and 13c has its primary origins in the co occurrence of the warm sst phase with high light levels during the first half of the calendar year the association with sunlight derives from the photosynthetic response of algal symbionts which results in fractionation of light and heavy carbon isotopes between soft tissues and caco3 skeleton the fifth tracer the transition metal mn exhibits poorer correlations against both sst and the other tracers slight shifts in phasing of the historical mn ca annual cycle suggest that the general water column distribution of this tracer which is the reverse of a nutrient may not be stable the erratic behavior of mn illustrates how complex hydrography near galapagos may influence tracers with diverse source signatures

mid eocene alluvial lacustrine succession at gebel el goza el hamra shabrawet area ne eastern desert egypt facies analysis sequence stratigraphy and paleoclimatic implications abstract this study aims to provide the depositional facies sequence stratigraphic and paleoclimatic characteristics of the mid eocene bartonian continental succession exposed at gebel el goza el hamra shabrawet area ne eastern desert egypt the studied succession consists of siliciclastic rocks followed upward by carbonate rocks detailed field observation and petrographic investigation indicate accumulation in floodplain dominated alluvial and shallow lacustrine systems the floodplain dominated alluvial facies 45 m thick is composed mainly of carbonate nodules bearing mottled mudrock with subordinate sandstone and conglomerate beds the conglomerate and pebbly sandstone bodies interpreted as ephemeral braided channel deposits the massive laminated planner cross bedded fine to medium grained sandstone bodies interlayered within mudstone reflect sheet flood deposits the mudrocks associated with paleosols represent distal floodplain deposits the shallow lacustrine facies 15 m thick is made up of an alternation of marlstone micritic limestone dolostone and mudrock beds with charophytes and small gastropods both the alluvial and lacustrine facies show evidence of macro and micro pedogenic features pollen assemblages stable 18 o and 13 c isotopes and paleopedogenic features reflect prevalence of arid to semi arid climatic conditions during the bartonian the sequence stratigraphic framework shows an overall fining upward depositional sequence consisting of low and high accommodation systems tracts last hast and is bounded by two sequence boundaries sb 1 sb 2 conglomerate and pebbly sandstone deposits braided channel and sheet flood deposits of the lower part of the alluvial facies reflect a last mudrock and silty claystone facies distal floodplain deposits of the upper part of alluvial facies and its overlying lacustrine facies correspond to a hast the last hast and sb were formed during different accommodation to sediment supply a s ratio phases the variation in a s ratios was mainly controlled by sea level change as well as by local tectonic subsidence and uplift of the basin coincident with the reactivation of the syrian arc system during the bartonian

isopycnal and diapycnal circulation of the upper equatorial atlantic ocean in 1983 1984 isopycnal circulation and diapycnal processes in the equatorial atlantic ocean are investigated using eight cruises from november 1982 to july 1984 an eastward decrease of the transport of the equatorial undercurrent is observed averaging 18 2 106 m3 s 1 at 35 w to 10 2 106 m3 s 1 at 4 w there is also a meridional convergence at the undercurrent level and a larger meridional divergence in the surface layer of 15 106 m3 s 1 between 35 w and 4 w in the eastern equatorial atlantic the undercurrent core density as well as the salinity above the undercurrent experience a large seasonal cycle during the season where the eastern atlantic thermocline is closest to the surface and surface waters are coldest the current peaks in denser waters and subsurface salinity maximum are weaker an analysis of the salinity on isopycnal surfaces indicates that there is significant diapycnal mixing in the upper thermocline in the eastern atlantic the upper thermocline vertical heat diffusivity coefficient scaled over 1 of latitude varies between 3 cm2 s 1 during the upwelling season and nearly 0 early in the year this seasonal mixing is an important element of undercurrent dynamics the turbulent heat flux at the base of the surface layer averages 50 w m 2 between 1 5 n and 1 5 s the surface layer heat budget implies an average oceanic gain of 60 w m 2 between 1 5 n and 1 5 s which could result from exchanges with the atmosphere the heat flux and fresh water seasonal cycles needed to close the budgets are not realistic however the eastern equatorial atlantic thermocline seasonal upwelling is associated with a large inflow into the surface layer over the two years this flow averaging 11 12 106 m3 s 1 originates from the upper thermocline and diapycnal transports near the core of the undercurrent or below are found to be small below the core of the undercurrent we also find that mixing is not intense for instance at 26 5 in the upper part of the thermostad vertical heat diffusivity is only 0 6 cm2 s 1 assuming that mixing takes place over 1 of latitude the uncertainties on these budgets are however large and assumptions on the dynamics that were used could not be checked

observations of annual and el nino thermal and flow variations at 0 110 w and 0 95 w during 1980 1985 moored measurements of the surface wind and of the current and temperature fields within the uppermost 250 m were recorded from march 1980 to september 1985 at 0 110 w and from july 1981 to november 1983 at 0 95 w at these sites the annual mean thicknesses of the equatorial undercurrent euc and of the surface portion of the south equatorial current sec were about 200 m and 20 m respectively the annual mean euc core speed was 0 9 m s 1 annual cycles of temperature and zonal current at 110 w were most distinctive near the surface at nominal depths of 15 m and 47 5 m the average annual amplitudes were 1 5 c and 0 5 m s 1 at about 100 m the annual amplitudes were about 0 5 c and 0 10 m s 1 at 15 m the annual mean zonal current was 0 05 m s 1 which was not representative of the monthly mean zonal current in april the monthly mean direction was eastward and in october it was westward with speeds of about 0 5 m s 1 in both months warmer water occurred in april and colder water in october the direction of the zonal wind component was westward throughout the year and the annual amplitude of the zonal wind was only about 2 5 times larger than that of the zonal current the average amplitude of the annual cycle of the meridional current component was less than 0 05 m s 1 and not distinguishable from year to year monthly mean variations monthly mean anomalous or el nino currents at 110 w were defined as the difference between the observations and the annual cycle during the august december 1982 onset phase of el nino the strength of the normally westward flowing near surface sec was greatly reduced to near zero speed by an el nino eastward flowing zonal current of about 0 3 m s 1 the largest vertically averaged 15 250 m zonal current anomaly 0 5 m s 1 occurred in january and february 1983 and represented a substantial decrease in the eastward transport of the euc causing a disappearance of the undercurrent the duration of the euc disappearance was longer at 95 w than at 110 w a surface intensified eastward jet with a maximum daily speed of 1 75 m s 1 at 15 m occurred in may 1983 at 110 w but not at 95 w a massive redistribution of heat throughout the mixed layer and thermocline was associated with the 1982 1983 el nino beginning in august 1982 the thermocline at 110 w and 95 w sank 100 m reaching its maximum depth in december 1982 temperatures at 100 m and 150 m which normally were about 15 c and 14 c reached 27 5 c and 22 5 c the time rate of change of the 15 to 200 m heat content was 500 w m 2 during the august december 1982 warming phase and 460 w m 2 during the january february 1983 subsurface cooling phase the euc disappeared during the subsurface cooling phase a second less intensive mixed layer deepening occurred in may 1983 at 95 w but not at 110 w

fluid geochemistry of montserrat island west indies two geochemical surveys carried out in march 1991 and september 1992 revealed the existence of a hydrothermal system in the southern portion of montserrat island below soufriere hills volcano this conclusion is supported by the presence of a the thermal springs of plymouth which are fed by deep na cl waters cl concentration 25 000 mg kg temperature ca 250 c mixed with shallow steam heated waters b the four fumarolic fields of galway s soufriere gages upper soufriere gages lower soufriere and tar river soufriere where acid to neutral steam heated waters are present together with several fumarolic vents discharging vapors formed through boiling of hydrothermal aqueous solutions involvement of magmatic fluids in the recharge of the hydrothermal aquifers is suggested by a the high 3he 4he ratios of fumarolic fluids i e 8 2 ra at galway s soufriere and 5 9 ra at gages lower soufriere b the d and 18o values of na cl thermal springs and steam condensates indicating the involvement of arc type magmatic water in the formation of deep geothermal liquids and c the ch4 co2 ratios of fumarolic fluids which are lower than expected for equilibrium with the feo feo1 5 hydrothermal rock buffer but being shifted towards the so2 h2s magmatic gas buffer

internal waves and mixing in the upper equatorial pacific ocean microstructure measurements in the equatorial pacific at 140 w in late 1984 show a pronounced diurnal variation in both high frequency internal wave energy and kinetic energy dissipation rate observations indicated that after sunset internal waves presumably generated by convective overturns in the mixed layer propagate downward and increase turbulence levels in the pycnocline it is proposed that large mixed layer eddies in the south equatorial current interact with the large shear caused by the equatorial undercurrent to generate a westward going anisotropic wave field the momentum transport in the radiated wave field results in a drag force on the equatorial mean flow field the observed mean wind stress at 140 w during tropic heat i which is twice as large as the annual mean wind is closer to the estimated radiation stress 10 4 m2 s 2 at the base of the mixed layer 30 m than to the estimated turbulent stress 10 5 m2 s 2 a wave dissipation model based on the observed turbulent kinetic energy dissipation rate is introduced in order to estimate the wave momentum flux divergence in the stratified region above the undercurrent core the model predicts that most of the downward wave momentum flux penetrates through the undercurrent core it is hypothesized that when the wind stress is strong the equatorial pacific ocean responds by generating a westward traveling internal wave field which transports much of the surface wind stress below the actively mixing surface layer

climate variability of the equatorial thermocline inferred from a two moving layer model of the ventilated thermocline a two moving layer model is used to examine the structure of the equatorial thermocline and its connection with the extratropical thermocline it is found that cooling warming in extratropics generates a low high potential vorticity anomaly and induces downward upward movement of the thermocline and the perturbation propagates to the equatorial thermocline inducing a downward upward movement of the thermocline and intensification weakening of the undercurrent thus surface cooling in the extratropics can induce warming of the equatorial thermocline in addition the total mass flux in the subsurface layer in the extratropics and the equatorial undercurrent is enhanced although in the extratropics perturbations generated by localized cooling warming are confined within the characteristic cone defined by the unperturbed trajectories of the thermocline circulation when these perturbations propagate into the equatorial region they are no longer confined by the characteristic cone in the meridional direction

fission track evidence on the initial rifting of the red sea two pulses no propagation fission track analyses indicate that the red sea initially opened simultaneously along its entire length two distinct pulses of uplift and erosion characterized the early stages of rifting in the red sea throughout egypt and in southwestern saudi arabia the first pulse began at 34 million years ago ma the second pulse began in the early miocene 21 to 25 ma and marked the start of the main phase of extension these data support a rigid plate model for continental extension these results also indicate that the initiation of rift flank uplift and therefore rifting and volcanism occurred nearly simultaneously this conflicts with classical models of active and passive extension that predict sequential development of these features

diagnostic model of the three dimensional circulation in the upper equatorial pacific ocean abstract to investigate the processes that maintain the large scale annual average thermal structure of the equatorial pacific the three dimensional ocean circulation for a large area is determined from a diagnostic model applied to repeated meridional hydrographic sections along 150 w and 11o w from 5 n to 5 s geostrophic balances are used to determine velocity profiles from 0 to 500 db across the boundaries of the region zonal velocities across 150 w and 110 w at approximately 1 lattitude intervals from 5 n to 5 s and meridional velocities across 5 n and 5 s averaged over the zonal distance between 150 w and 110 w poleward wind driven flows across 5 n and 5 s based on climatological zonal wind stress are added to the geostrophic velocities in the mixed layers to achieve overall mass conservation the reference dynamic height field at 500 db is adjusted at four of the 21 stations by about 1 dyn cm horizontal nondivergence is used to determine meridional velocities between 0 75 and 5 latitudes

the role of the turbulent stress divergence in the equatorial pacific zonal momentum balance from a comprehensive set of upper ocean measurements made during a moderate e1 nifio in boreal spring 1987 we reassess the role of turbulence in transporting momentum vertically at the equator an examination of the terms in the vertically integrated zonal momentum equations indicates that on short time scales the zonal pressure gradient is not balanced by the surface wind stress despite an apparent balance of these terms on longer seasonal time scales the vertical redistribution of zonal momentum is complex the strength of the wind determines both the magnitude and likely the mechanisms of momentum transport between the surface and the core of the undercurrent during low wind

do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific 1 the paleoceanographic recording fidelity of pelagic sediments is limited by chemical diagenesis and physical mixing bioturbation and horizontal sediment transport diagenesis and bioturbation are relatively well studied but the effects of physical sedimentation have been largely ignored modeling u series isotopes e g 230th can potentially quantify horizontal sediment movement but model horizontal sediment focusing often equals or exceeds the vertical particle rain we find no evidence of this level of sediment focusing in the equatorial pacific from geophysical data or sediment core comparisons the overestimate of sediment focusing by 230th is probably caused by poor model assumptions that sediment does not fractionate does not sort according to size during transport and that 230th cannot leak from slowly accumulating sediments both assumptions are weak u series methods do hold promise to quantify sediment focusing if properly calibrated with calibration the trade offs between seeking high sedimentation rates for better time resolution and the blurring by horizontal sediment focusing can be better assessed

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

upwelling and productivity changes inferred from a temperature record in the central equatorial pacific a series of c37 39 alkenones synthesized by prymnesiophyte algae is commonly preserved in marine sediments and can be used for estimating past sea surface temperatures ssts 1 2 here we present an alkenone analysis of sediments taken from the central equatorial pacific ocean core w8402a 14gc 0 57 n 138 57 w which shows that sst varied slightly 2 c but coherently with milankovitch insolation cycles over the past 250 kyr the in phase response of the sst to the precessional component of insolation indicates that this part of the sst time series may be driven by changes in local trade wind strength and the longer 100 kyr eccentricity component indicates a response to basin wide south pacific winds using a simple heat balance model we use our palaeotemperature record to constrain the upwelling rates that have occurred in the past similar sst records from the eastern pacific could constrain the horizontal advection component of the sst record and allow for better estimates of upwelling upwelling and palaeoproductivity then could be compared to determine whether changes in equatorial nutrient levels actually cause equivalent changes in productivity

radiocarbon variability in the western equatorial pacific inferred from a high resolution coral record from nauru island we have generated a high resolution coral delta sup 14 c record spanning the last 50 years to document the seasonal and interannual redistribution of surface waters in the western tropical pacific prebomb 1947 endash 1956 delta sup 14 c values average minus 63 per thousand and have a total range of 30 per thousand values begin to increase in 1957 reaching a maximum of 137 per thousand in mid 1983 large interannual variability of up to 80 per thousand closely follows the el ni tilde n o southern oscillation enso during each enso warm phase delta sup 14 c values begin to increase reflecting the reduction of low sup 14 c water upwelling in the east and the invasion of subtropical water into the western equatorial tropical pacific maximum delta sup 14 c values are in phase or lag the corresponding sea surface temperature maxima in the eastern tropical pacific whereas the rapid return to more negative delta sup 14 c is in phase with eastern pacific enso indices the highest amplitude excursions occur during the 1965 1966 and 1972 1973 events when the sup 14 c contrast is highest between the eastern pacific and subtropics the 1982 1983 el ni tilde n o although a larger enso event has a lower delta sup 14 c amplitude reflecting the penetration of bomb radiocarbon into the equatorial undercurrent and the reduced contrast in delta sup 14 c betweenmore thermocline and subtropical surface waters at that time this coral record demonstrates the potential for using similar radiocarbon time series for documenting variability in pacific shallow circulation over interannual and decadal timescales copyright 1998 american geophysical union less

comparison of diagenetic characteristics and pore evolution in outcrops and cores of tight sandstone reservoirs in the triassic yanchang formation the ordos basin china the sedimentary and diagenetic control on tight sandstone reservoir quality is a key focus of hydrocarbon exploration this paper compares reservoir characteristics such as diagenetic processes pore types and porosity evolution of cores and outcrops of the yanchang formation the ordos basin northwestern china to identify diagenetic trends and processes responsible for improving reservoir quality and to develop a model for identifying reservoir sweet spots in tight sandstone formations samples of the yanchang formation sandstone are taken from wells and adjacent outcrops in the ordos basin no significant differences were found in porosity destructive diagenesis such as compaction and cementation between the core and outcrop samples however the effects of dissolution are far more pronounced in cores than in the outcrop resulting in a higher core sample porosity high density sampling of the outcrop revealed that the reservoir sweet spot model is controlled by sedimentation whereas three distinct vertical diagenetic zones were identified in adjacent wells a comprehensive analysis of cores and outcrop samples shows that both areas experienced similar sedimentation and early diagenetic patterns however the diagenetic processes experienced by core and outcrop sandstones diverged during the later part of burial and uplift with dissolution being responsible for the contrasting reservoir porosities between core and outcrop

do tropical cells ventilate the indo pacific equatorial thermocline source waters of the indo pacific equatorial thermocline are studied with a high resolution ocean model in the annual mean fields tropical and subtropical overturning cells are found that upwell at the equator and downwell at 5 degrees and 20 degrees poleward of the equator respectively tropical cells are common in ocean models but their role in ventilating the equatorial thermocline is obscure because the downwelled water is too warm to match the subsurface equatorial waters the tropical cells are much weaker when the overturning is considered in density coordinates when high frequency mass fluxes are included tropical cells are compensated by an eddy induced overturning seasonal variations and tropical instability waves are responsible for the compensation it follows that only subtropical cells transfer surface water to the equatorial thermocline strong tropical cells are shown to be an artefact

surface energy fluxes and coupled variability in the tropics of a coupled general circulation model abstract the effect of wind evaporative feedbacks upon enso and the coupling of pacific and indian ocean variability is considered based upon a 110 yr simulation from a coupled ocean and atmosphere general circulation model enso like modes which propagate westward are found in the model pacific ocean examination of the sst budget shows that the modes amplify and propagate as a result of changes in the surface energy flux and upwelling rates surface flux variability is dominated by the solar and evaporative components and wind evaporative feedbacks are shown to lead to growth and westward propagation of coupled anomalies in the model pacific a region of mean easterly winds eastward propagating coupled modes in the model indian ocean a region of mean equatorial westerlies are also found and are attributed to the same feedback interaction of the pacific and indian ocean modes through the evaporation field is demonstrated and their relevance to observed coupled ocean atmosphere variability is co

tectonic processes in papua new guinea and past productivity in the eastern equatorial pacific ocean phytoplankton growth in the eastern equatorial pacific ocean today accounts for about half of the new production the fraction of primary production fuelled by externally supplied nutrients in the global ocean the recent demonstration that an inadequate supply of iron limits primary production in this region1 supports earlier speculation that in the past fluctuations in the atmospheric deposition of iron bearing dust may have driven large changes in productivity2 but we argue here that only small 2 nm increases in the iron concentration in source waters of the upwelling equatorial undercurrent are needed to fuel intense diatom production across the entire eastern equatorial pacific ocean episodic increases in iron concentrations of this magnitude or larger were probably frequent in the past because a large component of the undercurrent originates in the convergent island arc region of papua new guinea which has experienced intensive volcanic erosional and seismic activity over the past 16 million years cycles of plankton productivity recorded in eastern equatorial pacific sediments may therefore reflect the influence of tectonic processes in the papua new guinea region superimposed on the effects of global climate forcing

the zonal momentum balance of the equatorial undercurrent in the central pacific abstract current velocity data from an array of subsurface moorings deployed during the tropical instability wave experiment from may 1990 to june 1991 are used to diagnose the upper ocean zonal momentum balance at 0 140 w the flow field and associated zonal momentum flux divergence are fully three dimensional over the upper 250 m consistent with the earliest descriptions and theoretical ideas of the equatorial undercurrent euc estimates of the vertical stress divergence show dynamical flow regimes that change between the surface and the base of the euc being essentially linear modified by nonlinearity near the surface weakly nonlinear at the euc core and fully nonlinear below the core the vertical stress divergence is much larger over the lower portion of the euc than previously reported but this is consistent with the observed downstream deceleration of the euc and the idea that vertical mixing is important in maintaining the thermostad nonlinearity becomes increasingly important with dec

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

mercury species concentrations and fluxes in the central tropical pacific ocean the formation of the toxic and bioaccumulating monomethylmercury mmhg in marine systems is poorly understood due in part to sparse data from many ocean regions we present dissolved mercury hg speciation data from 10 stations in the north and south equatorial pacific spanning large water mass differences and gradients in oxygen utilization we also compare the mercury content in suspended particles from six stations and sinking particles from three stations to constrain local hg sources and sinks concentrations of total hg thg and methylated hg in the surface and intermediate waters of the equatorial and south pacific suggest hg cycling distinct from that of the north pacific gyre maximum concentrations of 180 fm for both mmhg and dimethylmercury dmhg are observed in the equatorial pacific south of the equator concentrations of mmhg and dmhg are less than 100 fm sinking fluxes of particulate thg can reasonably explain the shape of dissolved thg profiles but those of mmhg are too low to account for dissolved mmhg profiles however methylated hg species are lower than predicted from remineralization rates based on north pacific data consistent with limitation of methylation in equatorial and south pacific waters full water column depth profiles were also measured for the first time in these regions concentrations of thg are elevated in deep waters of the north pacific compared to those in the intermediate and surface waters and taper off in the south pacific comparisons with previous measurements from nearby regions suggest little enrichment of thg or mmhg over the past 20 years

on the baroclinic response of the zonal pressure gradient in the equatorial atlantic ocean temperature time series obtained from surface moorings deployed along the equator in the atlantic ocean during the seasonal response of the equatorial atlantic experiment and the programme francais ocean et climat dans l atlantique equatorial were used to investigate the baroclinic response of the zonal pressure gradient due to the sloping isopycnals the zonal pressure gradient evolved as a complicated function of time depth and zonal position the most rapid and spatially inhomogeneous variations corresponded to periods of rapidly changing easterly wind stress following these periods the baroclinic response due to the sloping isopycnals was observed to overshoot its intended equilibrium before relaxing to it in so doing it tended to buffer pressure gradient variations at the depth of the equatorial undercurrent euc over much of the year the isopycnal slopes opposed the surface slope after the winds relaxed in winter however the isopycnal slopes reversed and acted in concert with the surface slope thereby enhancing the pressure gradient at the depth of the euc relative to that at the surface this reversal might be important in maintaining the euc during times of weak easterly wind stress the vertical structure of the zonal pressure gradient varied with the depth of the thermocline when the winds were weak and the thermocline was shallow the baroclinic response of the zonal pressure gradient due to the sloping isopycnals was primarily effected in the upper 50 m after the winds intensified and the thermocline deepened the baroclinic response extended down to at least 150 m

depositional cycles of the lower miocene rudeis formation southwestern offshore margin of the gulf of suez egypt implications for reservoir evaluation abstract the lower miocene rudeis formation in the zeit bay field gulf of suez egypt has been studied by analysis of cores from six boreholes the objective was to detail the sedimentary cycles in the formation and their implications for the reservoir characteristics as well as to obtain a more detailed insight into the precise age by establishing a foraminifer zonation the formation which was found to be some 60 191 m thick is composed almost exclusively of various types of carbonates these contain foraminifers that prove a burdigalian age and that also provide insight into the depositional environments which turned out to form three belts these belts represent an intertidal lagoon barrier shoals and a reef complex respectively indicating a down dip depositional profile of a shallow marine rimmed carbonate shelf analysis of the cyclicity pattern of the rudeis formation supported by facies analysis and cyclolog curves makes it possible to distinguish three superimposed 3rd order depositional cycles which are subdivided into several higher order cycles that are strongly controlled by eustatic sea level fluctuations a set of lithofacies isopach maps has been constructed for these cycles with the objective to facilitate interpretation of the spatial distribution of the reservoir quality for hydrocarbons the maps show that the reservoir quality of the rudeis formation is heterogeneous because of the highly variable characteristics of the various lithofacies types

degassing at the soufriere hills volcano montserrat recorded in matrix glass compositions compositions of matrix glasses from the current eruption of soufriere hills volcano indicate that decompression driven crystallization results in 20 70 wt groundmass crystallization during eruption and variable degassing variations in crystallinity and volatile contents water and chlorine of matrix glasses are attributed to variations in extrusion rates and residence times in the lava dome residual water contents in pumice clasts 0 2 0 6 wt indicate minimum pressures of 1 1 3 7 mpa in 1997 vulcanian explosions residual water contents of 1 6 wt in a ballistic block ejected in sub plinian explosive activity on 17 september 1996 imply larger pressure drops similar to20 mpa variable residual water contents in dome samples are consistent with pressure variations of up to 9 mpa in the lava dome interior large variation in chlorine contents between lava blocks compared with explosion pumice clasts indicates that shallow level processes dominate degassing low melt chlorine contents of dome samples cannot be explained by open or closed system degassing especially when crystallization is taken into account instead heterogeneous chlorine leaching by circulation of groundwater vapour in the dome is proposed variable and elevated matrix glass deltad values can also be attributed to interaction with isotopically heavy surface waters hcl emission during the current eruption can be accounted for by cl loss from the melt consistent with the melt being undersaturated in chlorine

intraseasonal vertical velocity variation caused by the equatorial wave in the central equatorial indian ocean intraseasonal vertical velocity variation in the central equatorial indian ocean was investigated using observations from the field experiment mirai indian ocean cruise for the study of the mjo convection onset mismo and from the research moored array for african asian australian monsoon analysis and prediction rama in october november 2006 using an array of four subsurface moored acoustic doppler current profilers adcps we estimated vertical velocity by applying the continuity equation results indicated alternating downwelling and upwelling episodes at around thermocline depth with maximum amplitudes larger than 8 0 10 5 m s 1 or about 7 m per day the vertical velocity variation was mainly produced by the divergence convergence of meridional currents with a quasi biweekly period of 11 16 days the temporal changes in temperature around thermocline depth were consistent with variations in vertical velocity whereas upwelling had less impact on the surface layer temperature intraseasonal variations in the ocean may be a part of biweekly fluctuations by remotely forced mixed rossby gravity waves which have a meridional current maximum at the equator accompanied by divergence convergence in the surface layer a few degrees from the equator

seasonal variability in the equatorial pacific abstract five to nine years of observations from the tropical atmosphere ocean array in the tropical pacific are used to document the seasonal cycle of surface winds zonal currents sst thermocline depth and dynamic height along the equator the normally westward surface zonal current reverses direction in late boreal spring and early summer this seasonal variation in the zonal surface current propagates westward as do seasonal variations in the equatorial undercurrent and zonal surface winds at the equator at 5 n and 5 s the seasonal variations in the 20 c isotherm and dynamic height also propagate westward conversely at the equator in the eastern and central pacific the variations in 20 c isotherm depth and dynamic height propagate eastward these seasonal variations are interpreted by means of a simple dynamical model based on linear equatorial wave theory model results indicate that seasonal variability between 5 n and 5 s is dominated by wind forced equatorial kelvin waves and first meridi

a convergent instability wave front in the central tropical pacific abstract a narrow front encountered at 2 1 n 140 w was characterized by high productivity and a 2 c temperature drop satellite sea surface temperature sst imagery showed this front to extend over 400 km from just north of the equator to 5 n along the western leading edge of a tropical instability wave cold cusp during 3 days of observations the front propagated westward at 64 cm s 1 while oriented sw ne water velocities and densities around the front were measured using a shipboard acoustic doppler current profiler and hydrographic stations these data showed warm fresh northern water moving southward at speeds of up to 50 cm s 1 to encounter cold salty equatorial water moving northward at up to 40 cm s 1 both slabs were embedded in the south equatorial current here a uniform 100 m deep westward flow of 90 cm s 1 at their meeting a net convergence of 30 cm s 1 across the 1 km wide front drove intense downselling of up to 0 9 cm s 1 both t s relations and velocity fields indicate that cold water subducted beneath the warmer water and continued northward to beyond 3 n deepening to 120 m for analysis the data were gridded in a co ordinate system centered on the front and moving with it the dynamics near the front consisted of a balance between pressure gradient and non linear advection the coriolis force was smaller and associated mostly with the broader scale flow thus the front itself was not geostrophic but rather the leading edge of a density driven flow that can be accurately modeled as a dissipative lock exchange the subduction released potential energy at the rate of 5290 230 w m 1 of front length comparable to previous estimates of large scale energy conversion nevertheless the kinetic energy gain by the larger scale instability was only 840 31 w m 1 implying that the rest of the energy was lost to the large scale flow turbulent dissination as derived from the rate of mixing accounted for only 500 300 w m 1 of this loss on the full 100 km scale of the layered flow the coriolis force became important the orientation of the surface front and the angle of the interface s northward deepening produced a pressure gradient that balanced the meridional flow geostrophically

variability in the eastern equatorial pacific ocean during 1986 1988 we examine variability in the eastern equatorial pacific during 1986 1988 using conductivity temperature depth data velocity and temperature data from equatorial moorings between 110 w and 140 w and wind data from a basin scale zonal array of islands and moorings between 110 w and 165 e the period studied coincides with the el nino southern oscillation enso event of 1986 1987 and a subsequent cold event in 1988 weak warm sea surface temperature anomalies first appeared in the eastern equatorial pacific in mid 1986 and increased to 1 c in september november 1986 in association with a 30 cm s 1 weakening of the south equatorial current and a 20 to 40 m depression of the thermocline these warm anomalies lasted until early 1988 after which a large scale shoaling of the thermocline led to sea surface temperatures more than 3 c colder than climatology year to year fluctuations in the eastern pacific were related primarily to zonal wind variations in the central and western pacific westerly wind stress anomalies of 0 02 0 05 n m 2 were observed between 140 w and 165 e from the latter half of 1986 until the end of 1987 these were replaced by easterly wind anomalies of similar magnitude between 157 w and 165 e in 1988 energetic intraseasonal fluctuations with periods of 2 3 months were also prominent in zonal current temperature and dynamic height time series these fluctuations propagate eastward at approximately first baroclinic mode kelvin wave phase speeds and are forced west of the date line by episodes of westerly winds extrema in several oceanic variables occurred in association with these waves though their precise dynamical link to the enso cycle is unclear from our data sea surface temperature and thermocline depth anomalies at 0 110 w were less pronounced during the 1986 87 enso than during the 1982 1983 enso the equatorial undercurrent though weaker than normal in early 1987 did not disappear as it did in early 1983

tracing papua new guinea imprint on the central equatorial pacific ocean using neodymium isotopic compositions and rare earth element patterns abstract the nd isotopic composition ic and rare earth patterns of hydrodynamic structures of the equatorial pacific ocean were characterized along 140 w the nd ic of antarctic intermediate water aaiw and of the lower layer of the equatorial undercurrent euc at 140 w 13 c water are much more radiogenic at the equator than at their origin in the south equatorial current 12 s revealing that these water masses have been in contact with the highly radiogenic papua new guinea png slope in both cases only a small fraction less than 9 of the sediment deposited on the png slope is required to be exchanged or dissolved to explain these nd ic variations whereas the hydrographic properties of the same water masses remain unchanged this confirms the usefulness of this tracer to identify pathways of water masses these results emphasize the importance of jets in transporting lithogenic material into the subsurface layers of remote areas where aeolian inputs are particularly weak and corroborate the previous results on fe and al maximum in this area m l wells g k vallis e a silver nature 398 1999 601 604 the nd ic of the upper layer of the euc contrasts strongly to that of the subpycnocline layer indicating that the equatorial upwelling only affects the surface waters and is not effective between 120 and 150 m we calculate that the nd imprint of the png input is likely to vanish from this surface layer as it traverses the basin due to the replacement of upwelled waters by non radiogenic ones

vertical velocity in the central tropical pacific a circulation model perspective for jgofs abstract results from a variety of experiments with a primitive equation ocean general circulation model are examined to provide insight about variations in vertical velocity w that may have occurred during the jgofs equatorial pacific field program measurements of w during this period are not available so a model offers the only plausible dynamically consistent way to obtain this information variability associated with four different aspects of the tropical pacific circulation is discussed the seasonal average the tropical instability waves tiw the interannual variability in strong and modest enso events and the kelvin response associated with remote forcing from westerly wind events in the western pacific results from 140 w are presented according to the model tiw provide the greatest source of w variability near and somewhat north of the equator w can range from about 1500 cm day 1 upward to 1000 cm day 1 downward over a typical 30 day period with significant structure in both the zonal and meridional directions remotely forced response can be very large on the day to day timescale but diminishes typically to at most a few hundred cm day 1 up or down when averaged over 10 days interannual variation associated with a major enso event can involve complete disruption of the seasonal cycle the disappearance of tiws and great diminution or disappearance of the normal equatorial upwelling the seasonal cycle variations are of the smallest amplitude the maximum variation is perhaps 100 cm day 1 near the equator and somewhat more just north of the equatorial waveguide in the downwelling part of the seasonal circulation the field program period was studied using the different available wind analyses to force the model over the 1991 1992 period because the wind analyses have substantial differences they force substantially different w fields in the ocean model unfortunately no wind analysis can be shown to be substantially superior to any other during this period thus estimates of the net vertical transport of any quantity of jgofs interest must take into account the wide range of possible w values

export production fluctuations in the eastern equatorial pacific during the pliocene pleistocene reconstruction using barite accumulation rates export production is an important component of the carbon cycle modulating the climate system by transferring co2 from the atmosphere to the deep ocean via the biological pump here we use barite accumulation rates to reconstruct export production in the eastern equatorial pacific over the past 4 3 ma we find that export production fluctuated considerably on multiple time scales export production was on average higher 51 g c m 2 yr 1 during the pliocene than the pleistocene 40 g c m 2 yr 1 decreasing between 3 and 1 ma from more than 60 to 20 g c m 2 yr 1 followed by an increase over the last million years these trends likely reflect basin scale changes in nutrient inventory and ocean circulation our record reveals decoupling between export production and temperatures on these long million years time scale on orbital time scales export production was generally higher during cold periods glacial maxima between 4 3 and 1 1 ma this could be due to stronger wind stress and higher upwelling rates during glacial periods a shift in the timing of maximum export production to deglaciations is seen in the last 1 1 million years results from this study suggest that in the eastern equatorial pacific mechanisms that affect nutrient supply and or ecosystem structure and in turn carbon export on orbital time scales differ from those operating on longer time scales and that processes linking export production and climate modulated oceanic conditions changed about 1 1 million years ago these observations should be accounted for in climate models to ensure better predictions of future climate change

satellite derived surface current divergence in relation to tropical atlantic sst and wind the relationships between tropical atlantic ocean surface currents and horizontal mass divergence sea surface temperature sst and winds on monthly to annual time scales are described for the time period from 1993 through 2003 surface horizontal mass divergence upwelling is calculated using surface currents estimated from satellite sea surface height surface vector wind and sst data with a quasi linear steadystate model geostrophic and ekman dynamical contributions are considered the satellite derived surface currents match climatological drifter and ship drift currents well and divergence patterns are consistent with the annual north south movement of the intertropical convergence zone itcz and equatorial cold tongue evolution while the zonal velocity component is strongest the meridional velocity component controls divergence along the equator and to the north beneath the itcz zonal velocity divergence is weaker but nonnegligible along the equator a strong divergence upwelling season in the central eastern equatorial atlantic peaks in may while equatorial sst is cooling within the cold tongue in addition a secondary weaker and shorter equatorial divergence occurs in november also coincident with a slight sst cooling the vertical transport at 30 m depth averaged across the equatorial atlantic ocean between 2 s and 2 n for the record length is 15 6 10 6 m 3 s 1 results are consistent with what is known about equatorial upwelling and cold tongue evolution and establish a new method for observing the tropical upper ocean relative to geostrophic and ekman dynamics at spatial and temporal coverage characteristic of satellite based observations

a zonal momentum balance on density layers for the central and eastern equatorial pacific abstract brown et al analyzed the kinematics of flow in the equatorial pacific ocean along time varying isopycnals in a three dimensional eddy permitting model here the dynamics of these flows is explored in the same model via the zonal momentum equation zme previous work has shown that the dominant terms of the zme on and near the equator are the pressure gradient wind stress and coriolis term in one model study the nonlinear and friction terms were significant but negated each other in this study with a higher resolution model and more realistic friction scheme it is shown that the nonlinear term is important along and north of the equator while the explicit friction term is negligible the part of the nonlinear term derived from high frequency eddy flows acts like a friction on the equatorial undercurrent while the remaining part of the nonlinear term from smooth flows enhances it in density coordinates meridional tropical cells lie on either side of the equator in the first half of t