osmotic generation of anomalous fluid pressures in geological environments osmotic pressures are generated by differences in chemical potential of a solution across a membrane but whether osmosis can have a significant effect on the pressure of fluids in geological environments has been controversial because the membrane properties of geological media are poorly understood anomalous pressures large departures from hydrostatic pressure that are not explicable in terms of topographic or fluid density effects are widely found in geological settings and are commonly considered to result from processes that alter the pore or fluid volume which in turn implies crustal changes happening at a rate too slow to observe directly yet if osmosis can explain some anomalies there is no need to invoke such dynamic geological processes in those cases here i report results of a nine year in situ measurement of fluid pressures and solute concentrations in shale that are consistent with the generation of large up to 20 mpa osmotic pressure anomalies which could persist for tens of millions of years osmotic pressures of this magnitude and duration can explain many of the pressure anomalies observed in geological settings they require however small shale porosity and large contrasts in the amount of dissolved solids in the pore waters criteria that may help to distinguish between osmotic and crustal dynamic origins of anomalous pressures

gas condensate migration and oil fractionation in deltaic systems abstract the term evaporative fractionation is proposed to describe several phenomena involved in the secondary alteration of reservoired oil firstly it is suggested that oil is frequently partially vaporized in the reservoir secondly that gas bearing substantial portions of the oil in solution is conducted along faults to form independent gas condensate accumulations thirdly that residual oils formed in this fashion bear internal evidence of fractionation in addition to the conspicuous loss of light ends there is an increase in the content of light aromatic and naphthenic hydrocarbons relative to paraffins in the residual oil evaporative fractionation effects are recognized for the first time in the distillation and physical property data of us bureau of mines routine method oil analyses fractionation effects are postulated to be the cause of sigmoid as opposed to normal curvilinear aromatic profiles the effects of evaporative fractionation are widespread in oils throughout the united states they are evident in approximately 75 of oils in the gulf coast region and in a large proportion of the gas condensate accumulations the process is a major and apparently unrecognized means of petroleum alteration and of generation of gas condensates experimental evidence shows that partial vaporization results in enhanced levels of light aromatic hydrocarbons in residual oils oil samples were partially vaporized in excess methane at elevated pressure and temperature followed by removal of the vapour the gas chromatographic features of many gulf coast oils were reproduced various levels of light end depletion and enhancement of aromaticity were brought about

assimilation of moored velocity data in a model of coastal wind driven circulation off oregon multivariate capabilities 1 horizontal current measurements from an array of moored acoustic doppler profilers are assimilated sequentially into a model of coastal wind driven circulation off oregon during the upwelling season of may august 2001 model results are compared against independent moored and ship survey data to document a positive effect of velocity data assimilation da on other oceanic variables of interest such as the sea surface height ssh temperature potential density surface salinity and near bottom turbulence parameters significant improvement is achieved for the nearshore ssh even when data are assimilated from only two moorings at an alongshore distance of 50 km from the ssh verification site at 45 n in an area of simple shelf bathymetry with relatively small alongshore variations the model even without da provides a good description of the isopycnal structure on a cross shore section at 44 2 n over complicated bathymetry velocity da may improve the slope of isopycnals but at the same time not necessarily the density values themselves data assimilation based on a time invariant representation of the forecast error covariance may inhibit spatial variability on horizontal scales smaller than the assumed forecast error decorrelation scale an experiment involving assimilation of both velocity and moored salinity measurements demonstrates that moored velocity da improves transport of buoyant surface water the level of improvement in the near bottom turbulent dissipation and bottom stress found with the da model indicates that it is suitable for future studies of spatial and temporal variability in the bottom boundary layer off oregon

a kalman filter analysis of sea level height in the tropical pacific abstract the kalman filter is implemented and tested for a simple model of sea level anomalies in the tropical pacific using tide gauge data from six selected island stations to update the model the kalman filter requires detailed statistical assumptions about the errors in the model and the data in this study it is assumed that the model errors are dominated by the errors in the wind stress analysis the error model is a simple covariance function with parameters fit from the observed differences between the tide gauge data and the model output the fitted parameters are consistent with independent estimates of the errors in the wind stress analysis the calibrated error model is used in a kalman filtering scheme to generate monthly sea level height anomaly maps for the tropical pacific the filtered maps i e those which result from data assimilation exhibit fine structure that is absent from the unfiltered model output even in regions removed from the data insertion points error estimates an

osmotic model to explain anomalous hydraulic heads laboratory experiments have shown that compacted clays act as osmotic membranes when they separate aqueous solutions of unequal ionic concentration theoretically osmotically induced differential hydraulic pressure in groundwater systems can be relatively high the magnitude depends primarily upon concentration differences across the membrane type of ions type of clay and pore size in experiments thin compacted clay membranes commonly exhibit varying degrees of osmotic efficiency due to ion leak age through the clay in natural systems the membrane and the solution containers are not as distinct and well defined as they are in the laboratory moreover the membrane is commonly thick inhomogeneous and composite in a buried triassic basin at the savannah river plant near aiken south carolina it is suspected that osmosis causes the saline water in the basin center to be slightly geopressurized in relation to freshwater in the overlying coastal plain aquifer two wells have heads of 7 88 and 12 98 bars 114 3 and 188 3 psi above the head in the coastal plain aquifer the head in each of these wells approximates the osmotic equilibrium head calculated from solution concentration of water produced by each well 12 000 and 18 500 mg l respectively other wells penetrating the top and edge of the triassic basin probably penetrate a zone where ion leakage gives rise to less saline water thus these wells are not geopressurized

active fluid flow in the eugene island area offshore louisiana a sedimentary basin is a thermochemical reactor i e a complex dynamically interrelated system that is deformed and faulted by tectonic forces modified by sedimentation and erosion influenced by geopressuring and chemical reaction and subjected to constantly changing temperature pressure and fluid composition and movement we understand little about the coupling among these processes that comprise basin thermochemical reactors despite many recent advances in basin science and technology however we are certain that these processes are coupled so strongly that changes in one can completely alter the operation of all the others in a basin

seasonal and interannual variability in along slope oceanic properties off the us west coast inferences from a high resolution regional model a 6 year 2009 2014 simulation using a 2 km horizontal resolution ocean circulation model of the northeast pacific coast is analyzed with focus on seasonal and interannual variability in along slope subsurface oceanic properties specifically the fields are sampled on the isopycnal surface 26 5 kg m 3 that is found between depths of 150 and 300 m below the ocean surface over the continental slope the fields analyzed include the depth z26 5 temperature t26 5 along slope currents 26 5 and the average potential vorticity pv between 26 5 and 26 25 kg m 3 each field is averaged in the cross shore direction over the continental slope and presented as a function of the alongshore coordinate and time the seasonal cycle in z26 5 shows a coherent upwelling downwelling pattern from mexico to canada propagating to the north with a speed of 0 5 m s 1 the anomalously deep 20 m z26 5 displacement in spring summer 2014 is forced by the southern boundary condition at 24 n as a manifestation of an emerging strong el nino the seasonal cycle in t26 5 is most pronounced between 36 53 n indicating that subarctic waters are replaced by warmer californian waters in summer with the speed close 0 15 m s 1 which is consistent with earlier estimates of the undercurrent speed and also present 26 5 analyses the seasonal patterns and anomalies in z26 5 and t26 5 find confirmation in available long term glider and ship borne observations the pv seasonality over the slope is qualitatively different to the south and north of the southern edge of heceta bank 43 9 n

a nested grid model of the oregon coastal transition zone simulations and comparisons with observations during the 2001 upwelling season 1 the oregon coastal transition zone octz extends several hundred kilometers offshore where shelf flows interact with the northern california current a primitive equation numerical ocean model is used to study the upwelling circulation in this region from 1 may to 1 november 2001 this octz model obtains initial and boundary conditions from a larger scale model of the california current system and forcing from a regional atmospheric model product the model results are compared with extensive in situ and remotely sensed data and the model is found to provide a realistic representation of flows both over the shelf and in the broader octz simulation of coastal sea level and shelf currents over the complex topography of the central oregon coast is improved quantitatively relative to previous regional models a particularly significant qualitative improvement is realistic representation of coastal jet separation and eddy formation offshore of cape blanco three dimensional lagrangian analysis of water parcel displacement shows that the surface waters inshore of the separated jet are upwelled from near the bottom along the shelf as far north as 45 5 n a large eddy which incorporates some of this upwelled water and carries it farther westward forms offshore in the late summer ensemble simulations show a distinction between the strongly deterministic response to wind forcing over the shelf and the more unstable less predictable jet separation and offshore eddy formation processes in the region near cape blanco

shallow magnetic inclinations in the cretaceous valle group baja california remagnetization compaction or terrane translation paleomagnetic data from albian to turonian sedimentary rocks on cedros island mexico 28 2 n 115 2 w support the interpretation that cretaceous rocks of western baja california have moved farther northward than the 3 of latitude assignable to neogene oblique rifting in the gulf of california averaged cretaceous paleomagnetic results from cedros island support 20 10 of northward displacement and 14 7 of clockwise rotation with respect to cratonic north america positive field stability tests from the vizcaino terrane substantiate a mid cretaceous age for the high temperature characteristic remanent magnetization in mid cretaceous strata therefore coincidence of characteristic magnetization directions and the expected quaternary axial dipole direction is not due to post mid cretaceous remagnetization a slump test performed on internally coherent intrabasinal slump blocks within a paleontologically dated olistostrome demonstrates a mid cretaceous age of magnetization in the valle group the in situ high temperature natural remanent magnetization directions markedly diverge from the expected quaternary axial dipole indicating that the characteristic high temperature magnetization was acquired prior to intrabasinal slumping early acquisition of the characteristic magnetization is also supported by a regional attitude test involving three localities in coherent mid cretaceous valle group strata paleomagnetic inclinations in mudstone are not different from those in sandstone indicating that burial compaction did not bias the results toward shallow inclinations in the vizcaino terrane

distant effect of assimilation of moored currents into a model of coastal wind driven circulation off oregon 1 an optimal interpolation oi sequential algorithm is implemented for a threedimensional primitive equation model to assimilate current measurements from acoustic doppler profilers moored on the oregon shelf as a part of the coastal ocean advances in shelf transport coast upwelling experiment may august 2001 a stationary estimate of the forecast error covariance required by the oi is computed based on the error covariance in the model solution not constrained by data assimilation lagged model error covariances are used to account for the effect of previously assimilated data the forecast error covariance has a shorter alongshore spatial scale than the model error covariance unconstrained by the data as an effect of propagating dynamical modes assimilation of currents from one or two of the moorings located on the path of the upwelling jet helps to improve the model data rms error and correlation at the mooring sites located at an alongshore distance of 90 km south or north from the assimilation sites the coastal jet is deflected offshore over heceta bank and assimilation of data from an inner shelf mooring in the jet separation zone does not help to improve prediction in the far field larger improvements are obtained for the first part of the study period yeardays 146 190 in the second part days 191 237 the geometry of our limited area model possibly limits prediction accuracy in numerical experiments involving assimilation of data from only one mooring the actual and expected rms error improvements are compared providing a consistency test for the forecast error covariance

ensemble based estimates of the predictability of wind driven coastal ocean flow over topography abstract the predictability of coastal ocean circulation over the central oregon shelf a region of strong wind driven currents and variable topography is studied using ensembles of 50 day primitive equation ocean model simulations with realistic topography simplified lateral boundary conditions and forcing from both idealized and observed wind time series representative of the summer upwelling season the main focus is on the balance relevant to practical predictability between deterministic response to known or well predicted forcing uncertainty in initial conditions and sensitivity to instabilities and topographic interactions large ensemble and single simulation variances are found downstream of topographic features associated with transitions between along isobath and cross isobath flow which are in turn related both to the time integrated amplitude of upwelling favorable wind forcing and to the formation of small scale eddies simulated predictability experiments are conducted and model fo

magma migration and magmatic solitary waves in 3 d numerical studies of fluid flow in the mantle sug gest that magma migration is an inherently time dependent process that produces magmatic solitary waves from obstruc tions in melt flux previous work has considered one and two dimensional problems here we present the results of three dimensional calculations that utilize a new efficient multi grid scheme we demonstrate that one and two dimensional solitary waves are unstable and break up into sets of 3 d solitary waves which are perfectly spherical when propagat ing through a uniform porosity medium while these waves are not solirons their non linear interactions are qualitatively similar the solitary waves are highly opportunistic and es tablish efficient pathways for migration by linking up with nearby waves when the initial condition is a random dis tribution of porosity the porosity structure can organize into elongate time dependent channels formed from chains of solitary waves these results are natural consequences of the assumptions that the matrix is permeable and viscously deformable we suggest that solitary waves are likely to exist in the mantle and may contribute to the episodicity of mantle magmatism

creep and time dependent damage in argillaceous rocks abstract this paper presents the results of laboratory tests on the time dependent behaviour of three rocks characterized by a high proportion of clay particles the viscosity of these sedimentary rocks was studied under different loading conditions in uniaxial compression static or cyclic creep tests and quasistatic tests low loading strain rate were performed across various orientations of fabric planes the quasistatic tests showed similarities in the mechanical response of these three argillaceous rocks a late phase of dilation and a linear development of volumetric deformation before the beginning of unstable crack propagation the development of secondary and tertiary creep phases during the creep tests highlighted the existence of a deviatoric stress threshold below which only primary creep is observed long term creep tests also showed that the volumetric variation is not constant during the development of viscoplastic deformations a microstructural analysis of thin sections extracted from specimens after the tests gave evidence of cataclastic and granular creep damage to the argillaceous matrix occurs and no cracks were observed in the quartz and carbonate grains this evidence was also demonstrated for tests with loading at a high strain rate finally this study highlights the significant viscoplasticity of argillaceous rocks the mechanical properties deteriorate rapidly when crack propagation becomes unstable and the viscoplastic strains seem to be due to clay particle slips known as granular creep

test for bias in paleomagnetically determined paleolatitudes from pacific plate deep sea drilling project sediments paleolatitudes determined from paleomagnetic study of azimuthally unoriented sediment cores recovered by deep sea drilling on the pacific plate have been previously used in determining reference poles for the pacific plate apparent polar wander apw path from discordant paleoinclinations and corresponding paleolatitudes determined from these data some workers have inferred tectonic tilting or large horizontal motion of some deep sea drilling sites relative to other parts of the pacific plate here the reliability of these paleolatitudes is evaluated by comparing them with paleolatitudes determined from a pacific plate reference apw path determined from seamount poles skewness and amplitudes of magnetic profiles across magnetically lineated seafloor and paleocolatitudes from azimuthally unoriented basalt cores and from equatorial sediment facies the reference apw path includes a new determination of the early cretaceous pole from several types of paleomagnetic data which agree well with one another sediment paleolatitudes are found to be systematically less southerly than those predicted from the reference apw path a discrepancy that corresponds to inclinations shallower than expected thus most deep sea drilling sediment paleomagnetic paleolatitudes are unreliable and should be omitted from the data used in determining reference apw paths inclination and paleolatitude discrepancies noted in prior studies may be due not to tectonic causes but to shallowly biased inclinations

geophysics a moving fluid pulse in a fault zone evidence from the south eugene island block 330 oil and gas field in the gulf of mexico off louisiana suggests that the fault zones there have acted as conduits for fluids rising from deep in the earth s crust and now one of these fault burps has been observed directly seismic reflection imaging revealed the rapid ascent of a pulse of fluid rising vertically up the fault by 1 km between 1985 and 1992 burps like this may be important factors in subsurface hydrocarbon migration in the gulf of mexico fault zones are linked with a complex and dynamic system of plumbing in the earth s subsurface here we use time lapse seismic reflection imaging to reveal a pulse of fluid ascending rapidly inside one of these fault zones such intermittent fault burping is likely to be an important factor in the migration of subsurface hydrocarbons

detrital remanent magnetization viscosity theory of the lock in zone post depositional remanent magnetization pdrm becomes permanent within a lock in zone whose apparent time delay depth and time span thickness are related to the characteristic time constants of compaction and magnetic grain rotation two simple models of the pdrm lock in zone are described using yaskawa s idea of effective sedimentary viscosity and mooney s empirical relation for the viscosity of a concentrated suspension of spheres the impulse response of the lock in zone determines the fidelity of the paleomagnetic recording

erratum to fluid transport by solitary waves along growing faults a field example from the south eugene island basin gulf of mexico earth planet sci lett 202 2002 321 335

modeling bottom mixed layer variability on the mid oregon shelf during summer upwelling abstract results from a model of wind driven circulation are analyzed to study spatial and temporal variability in the bottom mixed layer bml on the mid oregon shelf in summer 2001 the model assimilates acoustic doppler profiler velocities from two cross shore lines of moorings 90 km apart to provide improved accuracy of near bottom velocities and turbulence variables in the area between the mooring lines model results suggest that the response of the bml thickness to upwelling and downwelling favorable winds differs qualitatively between an area of simple bathymetric slope at 45 n and a wider shelf area east of stonewall bank 44 5 n at 45 n the bml grows in response to downwelling favorable conditions in agreement with known theories east of stonewall bank the bml thickness is increased following upwelling events in this area the southward upwelling jet detaches from the coast and flows over a wider part of the oregon shelf creating conditions for ekman pumping near the bottom based on

analytical and numerical solutions for alternative overpressuring processes application to the callovo oxfordian sedimentary sequence in the paris basin france 1 previous studies that made use of basin models have shown that the normal geological evolution of the paris basin does not generate the observed albeit weak excess pressures in some shale layers of the basin other processes that may have created the overpressures currently neglected in such models are investigated here terms accounting for osmotic effects and tectonic stress changes are successively added to the diffusivity equation the effect of changes in outcrop boundary conditions is also calculated with a pseudo two dimensional analytical solution these solutions are applied to the callovo oxfordian shale formation in the eastern part of the paris basin france it is shown that a long term transient osmotic effect starting in the tertiary could explain in part the observed excess pressures in the callovo oxfordian shale assuming effective diffusion coefficients of 1 5 10 12 m2 s 1 in line with the measurements and a pore radius b around 20 a for the shales however because of the uncertainty on the value of the shale pore radius additional head measurements and osmotic experiments on samples should be made to fully establish the possibility of an osmotic process our study also shows that recent changes in hydrodynamic boundary conditions could also explain excess pressure distribution in this shale layer it is plausible that a combination of the two processes could best explain the distribution and intensity of the overpressures tectonic stress changes do not appear to be important it is shown that for such processes to maintain high pressures strong and recent increase in tectonic compressive stress would be required

assimilation of surface velocity data into a primitive equation coastal ocean model summer of 1998 are 0 42 and 0 78 respectively demonstrating the effectiveness of the das our estimates of the error covariances are shown to be appropriate through a series of objective statistical tests analysis of the term balances of the model equations show that the dominant modeled dynamical balances are preserved by the das and that uncertainties in the spatial variability of the wind forcing are likely to be one source of model error by varying the relative magnitudes of the estimated forecast and observation error covariances the das is shown to be most effective when approximately 80 of the analysis is made up of the model solution index terms 4263 oceanography general ocean prediction 4219 oceanography general continental shelf processes 4255 oceanography general numerical modeling 3337 meteorology and atmospheric dynamics numerical modeling and data assimilation 4516 oceanography physical eastern boundary currents 4594 oceanography physical instruments and techniques keywords practical data assimilation numerical modeling upwelling highfrequency radar data

osmotic flow through a cretaceous clay in southern saskatchewan canada clays and shales can act as semipermeable membranes causing osmotic flow and or osmotically induced fluid pressures despite laboratory proof of the osmotic behaviour of clay rich geologic material the influence of this osmotic behaviour on in situ groundwater flow and solute transport is inconclusive this is due in part to the lack of laboratory experimental work involving undisturbed core samples and to the lack of field scale research the ability of undisturbed clay samples to conduct flow hydraulically and osmotically was investigated using dilute salt solutions undisturbed cretaceous clay samples from southern saskatchewan were used in a laboratory experimental program the experiments included constant head hydraulic conductivity kh tests and osmotic flow tests conducted over a range of pore fluid concentrations of 0 054 1 12 equiv l the clay samples exhibited semipermeable membrane behaviour by conducting flow osmotically the hydraulic conductivity of the clay increased by a factor of

modeling upwelling circulation off the oregon coast 1 time dependent three dimensional upwelling circulation on the continental shelf off the oregon coast is studied using a primitive equation numerical model a limited area domain with a high resolution curvilinear grid is utilized the response of the coastal ocean to forcing by observed wind stress and heat flux during the summer 2001 time period of the coastal ocean advances in shelf transport coast field experiment is investigated model results are compared to coast current and hydrographic measurements the shelf velocity and density fields are generally characterized by the presence of a southward alongshore coastal jet with an upwelling density front on the shoreward side of the jet the large variability in shelf topography associated with heceta bank exerts a major influence on the shelf velocity and density fields over the bank the alongshore coastal jet is displaced offshore and colder upwelled water extends farther from the coast northward mean flow and upward motion are found inshore of the jet three dimensional flow structures in response to variable shelf bottom topography are presented and an analysis of time and space dependent alongshore momentum balances is applied to clarify the associated dynamics in general northward pressure gradients set up over the bank during southward upwelling winds accelerate currents on the inshore side of the jet northward when the winds relax analysis of term balances in the depth averaged equation for potential temperature shows that during upwelling across shore advection makes the major contribution to cooling over most of the region except inshore over heceta bank where alongshore advection also plays a significant role

new paleomagnetic rock magnetic and petrographic results from the valle group baja california mexico exploring the causes of anomalously shallow paleomagnetic inclinations 1 a detailed paleomagnetic rock magnetic and sedimentologic study was conducted on cenomanian age strata of the valle group at el campito baja california to examine the burial compaction effects on the paleomagnetic inclination of marine sedimentary rocks alternating field and thermal demagnetization isolated a characteristic remanence at 16 of 18 sites with a mean of dec 342 6 inc 19 1 and 95 3 4 the inclination is 38 7 shallower than that predicted by the reference paleopole for north america laboratory experiments indicate that compaction could account for only 7 5 of the inclination shallowing fold tests at different scales yield both positive and negative results making a tight constraint on the remanence s age impossible a primary postdepositional remanence is supported by bedding parallel foliations in the anisotropy of anhysteretic remanence fabric although primary anomalously shallow inclinations could indicate significant southerly then northerly paleolatitudinal offset a more likely scenario is a late cenozoic low temperature remagnetization which is suggested by alteration along the edges of some detrital silicate grains and a bimodal magnetic grain size distribution revealed by isothermal remanence data the synthesis of the data indicates that the vizcaino terrane was contiguous with the cordillera margin during remagnetization and underwent a subsequent 13 5 5 4 clockwise rotation we tentatively interpret that the remagnetization resulted from burial and or miocene volcanism which caused an acquisition of thermochemical remanent magnetization tcrm this study reveals a complicated remanence that resists easy interpretation and suggests caution in studies of similar rocks

a dynamically consistent analysis of the mesoscale eddy field at the western north pacific subarctic front 1 in this study we analyze the energetics of the quasigeostrophic qg currents observed in the course of an extensive soviet field experiment in 1987 the analyzed data span over the period of 1 month and cover the region 37 5 42 5 n 151 5 158 e at an average horizontal resolution of 35 km the processed data set includes the results of measurements at 668 hydrographic stations 118 moorings geosat sea surface height anomalies ecmwf winds and etop05 bottom topography a variational data assimilation method is employed to interpolate observations onto a regular space time grid an ensemble average over optimized ocean states is utilized to estimate posterior error bars assimilation has shown that the observed mesoscale structures are well described by qg dynamics which can explain 80 85 of the variability in the velocity and density fields the model data misfits lie within the observational error bars for all the data types used in assimilation the standard laplacian type parameterization of the small scale processes was found to be inconsistent with observations as the least model data misfits were obtained with zero diffusivity coefficients analysis of the interpolated patterns revealed a pronounced mesoscale mixing event characterized by the development of a warm streamer swirling around the upper cold core of an old anticyclonic kuroshio extension eddy the process was accompanied by a fast northwestward displacement of the eddy and induced detachment of a warm elongated vortex from its eastern rim within a week the vortex penetrated northward into the subarctic zone and eventually split into several smaller scale eddies energy analysis of the optimal solution indicates that baroclinic instability is the likely source of their energy computation of energy exchanges between depth averaged and shear components of the observed currents reveals the vertical energy cascade barotropization of the shear flow at a rate of 29 4 10 7 cm2 s 3 and the weaker kinetic energy transfer of opposite sign due to topographic interaction mean currents in the region are baroclinically unstable with an estimate of the available potential energy flux from the mean current to the eddies 53 8 10 7 cm2 s 3 potential enstrophy is transferred to mesoscale at a rate of 33 7 10 19 s 3 these figures can be considered as experimental evidence of the properties of free geostrophic turbulence which were predicted by theory and observed in numerical experiments

episodic fluid expulsion from geopressured sediments numerical simulation of fluid explusion from geopressured sediments using a one dimensional finite difference model shows that large volumes of fluid can be transported through a fractured seal during short lived 100 year expulsion events in this model abnormal fluid pressures are maintained by an impermeable seal when the fluid pressure exceeds 85 of the lithostatic pressure a vertical fracture opens in the seal providing a permeable pathway from the geopressured sediments into the overlying section fluid pressure in the seal decreases as fluid flows through the fracture closing the fracture as sediments in the seal compact once the fracture closes the seal remains impermeable until fluid flowing from deeper in the section increases fluid pressure to the fracture criteria a process that takes 10 000 500 000 years fractures emplaced in relatively incompressible seals such as compacted and or cemented sediments remain open for 20 50 years fluid fluxes through the seal integrated over the life of these events are 1 5 107 kg m2 and temperatures in the overlying sediments are increased by 5 20 c these temperature anomalies decay to less than half their original value in 300 years suggesting that the thermal anomalies observed in wells that are attributed to fluid expulsion formed in response to a very recent or currently active event

on the theory of solitons of fluid pressure and solute density in geologic porous media with applications to shale clay and sandstone we here analyze a new model of transients of pore pressure p and solute density in geologic porous media this model is rooted in the nonlinear wave theory its focus is on advection and effect of large pressure jumps on strain it takes into account nonlinear and also time dependent versions of the hooke law about stress rate and strain the model solutions strictly relate p and evolving under the effect of a strong external stress as a result the presence of quick and sharp transients in low permeability rocks is unveiled i e the nonlinear burgers solitons we therefore show that the actual transport process in porous rocks for large signals is not only the linear diffusion but also a solitons presence could control the process a test of a presence of solitons is applied to pierre shale bearpaw shale boom clay and oznam mugu silt and clay an application about the presence of solitons for nuclear waste disposal and salt water intrusions is also discussed finally in a kind of theoretical experiment we show that solitons could also be present in higher permeability rocks jordan and st peter sandstones thus supporting the idea of a possible occurrence of osmosis also in sandstones

buoyancy driven propagation of isolated fluid filled fractures implications for fluid transport in gulf of mexico geopressured sediments a large portion of the sediments within the northern gulf of mexico contain pore fluid pressures in excess of hydrostatic development of geopressure is generally attributed to compaction disequilibrium caused by rapid deposition of low permeability sediments in the miocene and plio pleistocene numerous studies have examined the formation of overpressures and or expulsion of geopressured fluids into overlying hydropressured strata however very little attention has been given to fluid flow within the geopressured zone itself movement of oils from cretaceous or older source rocks into plio pleistocene reservoirs in the gulf basin requires as much as 10 km of vertical migration in a few million years precipitation of cements in some geopressured sediments also implies large scale fluid flow new evidence from a deep well in the eugene island area offshore louisiana indicates that geopressured sediments are mechanically very weak with a poisson s ratio greater than 0 4 and a shear modulus or rigidity less than 1 gpa in addition large scale fluid flow either through interconnected pores or fractures is not occurring in this location at least at present an alternative hypothesis is that upward fluid transport in geopressured sediments is caused by buoyancy driven propagation of isolated fluid filled fractures using linear fracture mechanics i show that vertical fractures with lengths of a few meters can propagate at velocities of 1000 m yr mass flux rates 100 kg m2 yr are significant assuming a mechanism for formation of fluid filled fractures exists such as hydrofracturing when fluid pressures exceeded the minimum confining stress fracture propagation velocity and mass flux rate are strongly dependent on the shear modulus of geopressured sediments

comment on shallow magnetic inclinations in the cretaceous valle group baja california remagnetization compaction or terrane translation by douglas p smith and cathy j busby

evaluation of solitary waves as a mechanism for oil transport in poroelastic media a case study of the south eugene island field gulf of mexico basin abstract hydrocarbons in shallow reservoirs of the eugene island 330 field in the gulf of mexico basin are thought to have migrated rapidly along low permeability sediments of the red fault zone as discrete pressure pulses from source rocks at depths of about 4 5 km the aim of this research was to evaluate the hypothesis that these pressure pulses represent solitary waves by investigating the mechanics of solitary wave formation and motion and wave oil transport capability a two dimensional numerical model of eugene island minibasin formation predicted overpressures at the hydrocarbon source depth to increase at an average rate of 30 pa yr reaching 52 mpa by the present day and oil velocities of 10 12 m yr far too low for kilometer scale oil transport to fill shallow plio pleistocene reservoirs within the 3 6 million year minibasin history calculations from a separate one dimensional model that used the pressure generation rate from the two dimensional model showed that solitary waves could only form and migrate within sediments that have very low permeabilities between 10 25 and 10 24 m 2 and that are highly overpressured to 91 93 of lithostatic pressure solitary waves were found to have a maximum pore volume of 10 5 m 3 to travel a maximum distance of 1 2 km and to have a maximum velocity of 10 3 m yr based on these results solitary waves are unlikely to have transported oil to the shallowest reservoirs in the eugene island field in a poroelastic fault gouge rheology at the pressure generation rates likely to have been caused by disequilibrium compaction and hydrocarbon generation however solitary waves could perhaps be important agents for oil transport in other locations where reservoirs are closer to the source rocks where the pore space is occupied by more than one fluid or where sudden fracturing of overpressured hydrocarbon source sediments would allow the solitary waves to propagate as shock waves

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

fluid flow in the south eugene island area offshore louisiana results of numerical simulations abstract numerical simulations of heat and fluid transport in the south eugene island sei area offshore louisiana suggest fluids migrate from deep abnormally pressured sediments along fault zones and into overlying oil and gas reservoirs in the simulations fluid flow along the fault produces a narrow thermal anomaly around the fault a negative thermal anomaly forms adjacent to the thermal maximum when permeable sediments dip away from the fault zone in the simulations this negative thermal anomaly dissipates 100 200 years after it forms the presence of a similar negative thermal anomaly in the sei area suggests that fluid movement in the area is a recent event the observation that the thermal maximum in the study area is not centered about the fault zone further suggests that the primary vertical conduit for fluid flow in the sei area is not a major fault but minor splay faults in the hanging wall

thermal evolution of the north central gulf coast the subsidence history of the north louisiana salt basin determined from well data indicates that the region underwent extension during rifting and has since passively subsided due to conductive cooling of the lithosphere timing of the rifting event is consistent with opening of the gulf of mexico during late triassic to early jurassic time crustal extension by a factor of 1 5 to 2 was computed from tectonic subsidence curves however data from the early subsidence history are insufficient to distinguish between uniform and nonuniform extension of the lithosphere the magnitude of extension is in good agreement with total sediment and crustal thicknesses from seismic refraction data in the adjacent central mississippi salt basin the temperature distribution within the sediments is calculated using a simple heat conduction model temperature and subsidence effects of thermal insulation by overlying sediments are included the computed temperature distribution is in good agreement with bottom hole temperatures measured in deep wells temperature histories predicted for selected stratigraphic horizons within the north louisiana salt basin suggest that thermal conditions have been favorable for hydrocarbon generation in the older stata results from a two dimensional heat conduction model suggest that a probable cause for the early formation of the adjacent uplifts is lateral heat conduction from the basin rapid extension of the lithosphere underneath areas with horizontal dimensions of 50 100 km produces extremely rapid early subsidence due to lateral heat conduction the moderate subsidence rate observed in the north louisiana salt basin during the jurassic and early cretaceous suggests slow extension over a long period of time

assimilation of drifter observations for the reconstruction of the eulerian circulation field 1 in light of the increasing number of drifting buoys in the ocean and recent advances in the realism of ocean general circulation models toward oceanic forecasting the problem of assimilation of lagrangian observations data in eulerian models is investigated a new and general rigorous approach is developed based on optimal interpolation oi methods which takes into account directly the lagrangian nature of the observations an idealized version of this general formulation is tested in the framework of identical twin experiments using a reduced gravity quasi geostrophic model an extensive study is conducted to quantify the effectiveness of lagrangian data assimilation as a function of the number of drifters the frequency of assimilation and the uncertainties associated with the forcing functions driving the ocean model the performance of the lagrangian assimilation technique is also compared to that of conventional methods of assimilating drifters as moving current meters and assimilation of eulerian data such as fixed point velocities overall the results are very favorable for the assimilation of lagrangian observations to improve the eulerian velocity field in ocean models the results of our assimilation twin experiments imply an optimal sampling frequency for oceanic lagrangian instruments in the range of 20 50 of the lagrangian integral timescale of the flow field index terms 4255 oceanography general numerical modeling 4263 oceanography general ocean prediction 3337 meteorology and atmospheric dynamics numerical modeling and data assimilation keywords lagrangian assimilation drifters lagrangian velocity eulerian velocity numerical model

importance of thermo osmosis for fluid flow and transport in clay formations hosting a nuclear waste repository abstract three osmotic processes have been identified in clay rich media electro and chemo osmosis flows of water caused by salinity and electrical potential gradients have so far attracted almost exclusive attention but despite the recurring concern about the importance of thermo osmosis a flow of water driven by a temperature gradient in argillaceous media it remains largely neglected here we propose a new formalism for estimating the thermo osmotic permeability based on a theoretical analysis at the molecular and pore scale then upscaled we show that the thermo osmotic permeability can be estimated only from surface charge density temperature pore size and salinity the possible prominent role of thermo osmosis in compacted shale layers with a temperature gradient is then exemplified this first general estimate of the thermo osmotic permeability can be used to improve our understanding of the influence on fluid flow and pressure fields of the natural geothermal gradient in sedimentary basins which is required e g for safety assessments of nuclear waste repositories in shale layers

constitutive equations for ionic transport in porous shales 1 the constitutive coupled equations describing ionic transport in a porous shale are obtained at the scale of a representative elementary volume by volume averaging the local nernst planck and stokes equations the final relationships check the onsager reciprocity to the first order of perturbation of the state variables with respect to the thermostatic state this state is characterized by a modified version of the donnan equilibrium model which accounts for the partition of the counterions between the stern and diffuse gouy chapman layers after upscaling the local equations the material properties entering the macroscopic constitutive equations are explicitly related to the porosity of the shale its cation exchange capacity and some textural properties such as the electrical cementation exponent entering archie s law this new model is then applied to predict the salt filtering and electrodiffusion efficiencies of a shale layer

kilometer scale upward migration of hydrocarbons in geopressured sediments by buoyancy driven propagation of methane filled fractures several lines of evidence support kilometer scale upward migration of fluids in the gulf of mexico basin discharge of hypersaline brines at the sea floor long term natural hydrocarbon seeps and microseeps gas chimneys lead zinc mineralization in salt dome cap rocks and allochthonous brines in cenozoic sediments we explore the hypothesis that upward fluid transport in geopressured sediments is caused by buoyancy driven propagation of isolated methane filled fractures in other words instead of fluid migrating along a fixed network of interconnected pores or fractures fluid enclosed within an isolated fracture is transported upward by hydrofracturing the mechanically weak geopressured sediments thus the fluid filled fracture propagates upward through the sediments hydrofracture is driven by the pressure difference buoyancy between the enclosed methane and the surrounding sediments our results show that methane filled fractures with half lengths of a few meters should propagate upward through geopressured sediments with velocities of hundreds of meters per year or higher as methane filled fractures increase in volume and decrease in density with decreasing confining pressure they develop the potential to entrain and transport more than 1000 kg m3 of oil or brine methane filled fractures should propagate to the surface unless they are trapped beneath a layer that has high fracture toughness such as salt or are absorbed when they intersect a permeable 10 md sand layer

assimilation of hf radar derived radials and total currents in the monterey bay area abstract impact of hf radar surface current assimilation on ocean circulation model predictions in the monterey bay area is studied and evaluated during the time frame of the autonomous ocean sampling network aosn ii experiment august september 2003 in the first instance a previously described method for assimilation of surface current data is applied to 33 h low pass filtered data and a non tidal version of the circulation model it is demonstrated that assimilation of surface velocity data significantly improves the surface and subsurface correlation of model currents with moored current observations these results from the aosn ii period illustrate that surface current assimilation is beneficial even in cases for which very high resolution 3 km atmospheric forcing is utilized the assimilation approach is also tested with hourly unfiltered codar type hf radar derived surface currents within a model configuration that includes tidal forcing it is shown that assimilation of unfiltered with tides surface current observations into the model with tides improves the sub tidal model predictions to the level comparable with the assimilation of filtered data into the non tidal model which is significant with respect to options for designing real time nowcast and forecast systems finally the approach is extended and evaluated for the direct assimilation of hf radar derived radial velocity components the model runs that included assimilation of radials from at least two hf radar sites show better correlations with observations than the non assimilative run especially those runs that included radials from the santa cruz site directions of radials for that site coincide with the directions of dominant southward flow during upwelling events and the northward flow during relaxation events direct assimilation of radial currents extends the range of influence of the data into regions covered by only one hf radar site

connectivity and larval dispersal along the oregon coast estimated by numerical simulations 1 connectivity and larval dispersal is explored off the oregon coast during the summer upwelling season of 2001 using numerical ocean circulation simulations the study region with strong wind driven currents and variable topography is modeled using the regional ocean modeling system roms forced by the coupled ocean atmosphere mesoscale prediction system a large number of passive particles as models of planktonic larvae are released daily for 120 days from 1 may to 28 august at depths of 1 7 15 20 50 and 75 m at every grid point shoreward of the 200 m isobath on average 32 km offshore the particles are transported by the three dimensional currents of the model simulation the competency time window for larval settlement is assumed to be in between days 15 and 35 after larvae are released larval settlement occurs at the shallowest location during the competency time window connectivity matrices reveal that some of the places of highest retention are similar to the proposed oregon marine reserve sites especially cape perpetua the heceta bank region has high probabilities as both a source and a destination for settled larvae larvae released in the heceta bank region often settle at higher latitudes than their release location there are strong correlations between the number of settled larvae shallower than the 50 m isobath and a 6 to 8 day running mean of the alongshore wind stress larvae are retained near the shore when the winds averaged over the previous 6 to 8 days are relaxed or downwelling favorable

vertical and lateral fluid flow related to a large growth fault south eugene island block 330 field offshore louisiana data from sediments in and near a large growth fault adjacent to the giant south eugene island block 330 field offshore louisiana indicate that the fault has acted as a conduit for fluids whose flux has varied in space and time core and cuttings samples from two wells that penetrated the same fault about 300 m apart show markedly different thermal histories and evidence for mass flux sediments within and adjacent to the fault zone in the u s department of energy pennzoil pathfinder well at about 2200 m sstvd subsea true vertical depth showed little paleothermal or geochemical evidence for throughgoing fluid flow the sediments were characterized by low vitrinite reflectances ro averaging 0 3 ro moderate to high d18o and d13c values and little difference in major or trace element composition between deformed and undeformed sediments in contrast faulted sediments from the a6st well which intersects the a fault at 1993 m sstvd show evidence for a paleothermal anomaly 0 55 ro and depleted d18o and d13c values sodium is depleted and calcium is enriched in a mudstone gouge zone at the top of the fault cut in the well this effect diminishes with distance from this gouge zone cuttings from other wells in south eugene island block 330 show slightly elevated vitrinite reflectance in fault intercepts relative to sediments outside the fault zone overall indicators of mass and heat flux indicate the main growth fault zone in south eugene island block 330 has acted as a conduit for ascending fluids although the cumulative fluxes vary along strike this conclusion is corroborated by oil and gas distribution in downthrown sands in blocks 330 and 331 which identify the fault system in northwestern block 330 as a major feeder simple modeling of coupled heat and mass flux indicates the paleothermal anomaly in the fault zone intersected by a6st well was short lived having a duration less than 150 yr the anomaly could have been produced by a 2 106 m3 pulse of fluid ascending the fault at an actual velocity of over 1 km yr darcy flux of 330 m yr from 3 km deeper in the basin simple darcy law computation indicates a transient fault permeability on the order of 110 md during this flow pulsing of fluid up the fault was probably the norm although most flow did not produce such strong thermal anomalies as the one detected in the a6st well analysis of fluid pressures shows that the main fault is a profound lateral permeability barrier having up to 1800 psi of water pressure differential across it the hydrocarbon sealing capacity of the fault depends on the pressure difference across the fault fault permeability is best understood in terms of effective stress under ambient conditions the fault is at high pressure relative to downthrown reservoirs a pulse of high pressure fluid ascending end page 244 the fault lowers effective stress in the fault zone sufficiently to produce a significant transient increase in permeability if the fluid is in an area of the fault adjacent to downthrown relatively low pressure reservoir sands the fluid will discharge into them permeability in and adjacent to the fault then decreases such that fluid cannot reenter the fault zone and escape from the reservoir

variational assimilation of satellite observations in a coastal ocean model off oregon 1 satellite along track sea surface height ssh and multisatellite sea surface temperature sst maps are assimilated in a coastal ocean circulation model off oregon the study period is june october 2005 featuring intensive separation of the coastal upwelling jets in the eddy dominated coastal transition zone ctz the data assimilation da system combines the nonlinear regional ocean modeling system roms and the advanced variational regional ocean representer analyzer avrora tangent linear and adjoint codes developed by our group the variational representer da method is implemented in a series of 6 day time windows with initial conditions corrected at the beginning of each window to avoid the problem of matching the model and observed ssh mean levels the observed ssh slope has been assimilated location timing and intensity of jets and eddies in the ctz are constrained to improve accuracy of nonlinear model analyses and forecasts in the case assimilating ssh alone the geometry of the sst front is improved ssh assimilation results in the cross shore transport more uniformly distributed along the coast than in the free run model an outer front is identified in the da analyses at a distance of 200 km from the coast a strong subsurface horizontal temperature gradient across this front influences the depth of the thermocline in an area between the front and the continental slope the da correction term is comparable in magnitude to dominant terms in the volume integrated heat equation the time averaged da correction term in the volume integrated heat balance is closer to 0 in the combined ssh sst assimilation case than in the case assimilating ssh alone

absolute inclination values from deep sea sediments a reexamination of the cretaceous pacific record new data are used to examine anomalously shallow paleomagnetic inclinations derived from previous analyses of cretaceous dsdp sediments of the central western pacific ocean while viscous remanent magnetizations vrms are shown to produce a similar effect the bias toward shallow values is still present with thoroughly demagnetized data superimposed upon this bias is a trend towards maximum flattening at an expected inclination of approximately 55 degree with the flattening falling to zero at the equator and pole flattening due to sediment compaction or inclination error is proposed to explain these observations

elastic wave velocity in marine sediments with gas hydrates effective medium modeling we offer a first principle based effective medium model for elastic wave velocity in unconsolidated high porosity ocean bottom sediments containing gas hydrate the dry sediment frame elastic constants depend on porosity elastic moduli of the solid phase and effective pressure elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation to model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions a hydrate modifies the pore fluid elastic properties without affecting the frame b hydrate becomes a component of the solid phase modifying the elasticity of the frame the goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data we apply the model to sonic and vsp data from odp hole 995 and obtain hydrate concentration estimates from assumption b consistent with estimates obtained from resistivity chlorinity and evolved gas data

finite amplitude evolution of instabilities associated with the coastal upwelling front abstract a primitive equation model is used to study the finite amplitude evolution of instabilities associated with the coastal upwelling front simulations of increasing complexity are examined that represent idealizations of summer conditions off the oregon coast including cases with steady and with time variable wind in a domain with alongshore uniform bathymetry and with time variable wind in a domain with realistic oregon coast bathymetry the numerical results indicate that the fastest growing mode in this system has approximately an 8 10 km alongshore wavelength but that once the disturbances grow to finite amplitude the predominant alongfront scale increases rapidly because of nonlinear effects separation of the total kinetic energy into contributions from the alongshore average flow and perturbation about that average shows that the initial growth of the perturbation kinetic energy is due to potential energy conversion but transfer of energy from the kinetic energy of the alongshore average

organic geochemical indicators of dynamic fluid flow processes in petroleum basins a variety of preliminary geophysical geochemical and geological observations anderson et al geophysics 12 17 april 1991a b anderson oil gas j 85 91 26 april 1993 along with well production data schumacher aapg ann conv abstr april 1993 have led to the hypothesis that fluid injection into eugene island block 330 ei 330 in the u s louisiana gulf coast may be a continuing episodic process with the most recent injections having occurred on short geologic time scales 10 000 yr or less organic geochemical evidence presented here suggests these processes may occur on very short time scales years a process called dynamic fluid injection was proposed to explain these observations and is envisioned as episodic pressure build up followed by rapid escape of gas and oil through geopressure and injection into overlying reservoirs

data assimilation model study of the santa barbara channel circulation the seasonal circulation in the santa barbara channel sbc consists of a cyclonic eddy in the western basin and a poleward current along the northern coast in this study the monthly mean circulation is simulated using a three dimensional primitive equation model with data assimilation included the data are derived from the santa barbara channel and santa maria basin coastal circulation study covering an 8 month period from january to august 1994 the 6 hourly moored temperature observations in the upper 100 m water column are continuously assimilated into the model using a local correction method although salinity and wind forcing are not explicitly included comparisons with the observations indicate that the model results generate realistic flow and temperature structures inside the sbc the assimilation model faithfully reproduces the cyclonic eddy but it fails to predict the currents at the exits of the channel the issue of the data need is addressed through a sensitivity study

remagnetization of cretaceous forearc strata on santa margarita and magdalena islands baja california sur implications for northward transport along the california margin paleomagnetic data for two sections of cretaceous forearc strata with different structural attitudes on santa margarita and magdalena islands in baja california sur mexico indicate that these rocks have been remagnetized probably during the late cenozoic the in situ paleomagnetic directions however are similar to data from other cretaceous rocks on peninsular california with unexpectedly shallow inclinations and easterly declinations these data have been interpreted as indicating either northward tectonic transport 10 15 of latitude and clockwise rotation 20 or compaction shallowing of magnetic inclinations in sedimentary rocks combined with southwestward tilting of plutonic rocks the available paleomagnetic data for cretaceous forearc strata in southern and baja california can be divided into three groups 1 sections with normal polarity magnetizations that fail fold tests and are remagnetized 2 sections with normal polarity magnetizations with no or inconclusive fold tests that may or may not be remagnetized and 3 sections with both normal and reversed polarity intervals where pervasive remagnetization has not occurred other rocks of the mesozoic great valley group coast range ophiolite and franciscan complex in california also have secondary magnetizations with directions similar to younger geomagnetic field directions although these widespread remagnetizations could have variable local causes we propose regional burial and uplift related to changes in subduction parameters as a possible explanation two episodes of remagnetization are apparent one in the late cretaceous and a second in the late cenozoic on the other hand the unremagnetized and apparently reliable data from sedimentary and plutonic rocks on the baja peninsula consistently indicate northward translation 14 3 and clockwise rotation 29 8 with respect to north america since the late cretaceous

continuity of the poleward undercurrent along the eastern boundary of the mid latitude north pacific abstract several recent data sets improve our view of the poleward undercurrent of the california current system as part of a triennial national marine fisheries service nmfs survey of pacific whiting a series of 105 shipboard acoustic doppler current profiler adcp velocity sections across the shelf break from 33 to 51 n at about 18 km meridional spacing were collected from july to august 1995 significant 0 05 m s 1 subsurface poleward flow occurred in 91 of the sections a mean cross shelf section using the entire data set has statistical significance revealing an undercurrent core 0 1 m s 1 from 200 275 m depth 20 25 km off the shelf break the mean poleward volume transport in a 125 325 m layer is 0 8 0 2 10 6 m 3 s 1 we focus particular attention on the cape blanco to cape mendocino region and the nmfs results are compared with shipboard adcp three weeks later from a study of coastal upwelling processes near cape blanco adcp streamfunction maps are derived and strongly suggest that one portion of flow is continuous over the 440 km meridional extent of the analysis region other portions of the flow show evidence of offshore turning separation and the formation of anti cyclonic eddies we also note that isopycnic potential vorticity from alongslope ctd stations during the nmfs survey appears to be a tracer for the poleward flow

a modeling study of the three dimensional continental shelf circulation off oregon part ii dynamical analysis abstract sixty day simulations of the subinertial continental shelf circulation off oregon are performed for a hindcast study of summer 1999 in part i the model results are shown to compare favorably with in situ currents and hydrographic measurements obtained from an array of moored instruments and field surveys and high frequency radar derived surface currents in this paper the modeled three dimensional time varying circulation and dynamical balances are analyzed providing a detailed synoptic description of the continental shelf circulation off oregon for summer 1999 the circulation is clearly wind driven and strongly influenced by alongshore variations in shelf topography in the region of the coast where the alongshore topographic variations are small the upwelling circulation is consistent with standard conceptual models for two dimensional across shore circulation in the regions where the alongshore topographic variations are greater the upwelling circulation is highly three dimensional ov