structural control on sweet spot distribution in a carbonate reservoir concepts and 3 d models cogollo group lower cretaceous venezuela numerous major hydrocarbon accumulations are related to burial diagenesis in carbonate reservoirs however three dimensional 3 d modeling of such reservoirs is a major challenge the geometries of diagenetic fronts are poorly understood and few quantitative data on field and outcrop examples for these diagenetic zones exist the early cretaceous cogollo carbonates urdaneta west field northwest venezuela are an example of deeply buried 5000 m 1600 ft diagenetically altered limestones producing from a few high porosity streaks and fracture corridors reservoir sweet spots formed because of the interplay of structural evolution and diagenesis structural deformation not only generated a fracture network but also influenced primary facies distribution circulation of diagenetic fluids and distribution of early charged paleohighs in the reservoir the prediction of reservoir sweet spots is of key importance for economic success in the cogollo carbonates but constitutes a major challenge this article outlines the genetic relationships between structural evolution and sweet spot distribution as well as the workflow developed to transfer these concepts into 3 d geocellular models these 3 d models include a novel approach to fracture permeability prediction based on a geomechanical approach the reservoir model predicts sweet spots along leached faults which are best preserved in early charged paleohighs the cogollo and other reservoirs suggest that favorable structural development can generate and retain significant matrix porosity even at great depth the workflow established and applied might help to maximize field potential in similar settings

genetic types of carbonate shoal reservoirs in the middle triassic of the sichuan basin sw china abstract carbonate shoal reservoirs of the middle triassic leikoupo formation in the sichuan basin were investigated for potential gas resources the carbonate shoal reservoirs can be divided on the basis of their formation mechanism into residual intergranular pore karst further divided into syndepositional burial and epigenetic karstification types dolomitized and composite reservoirs residual intergranular pores and dissolved pores are the main reservoir spaces in the residual intergranular pore reservoirs isolated intragranular corroded pores and moldic pores are the main reservoir spaces in syndepositional karstification reservoirs the main spaces in burial karstification reservoirs are dissolved pores and holes and pores and caves on various scales are the main reservoir spaces of epigenetic karstification reservoirs intercrystal pores and intercrystal solution pores are the main reservoir spaces of dolomitized reservoirs composite reservoirs are characterized by a variety of reservoir spaces with pores holes and fissures high quality shoal reservoirs were formed by superposition of carbonate shoals and constructive diagenetic modification preservation of residual intergranular pores was crucial for development of residual intergranular pore reservoirs platform interior micro highlands relative declines in sea level and rainfall controlled the development of syndepositional karstification reservoirs dissolution by unsaturated acidic fluids pre existing pores and pore throats and the direction of corrosive fluid flow were important for burial karstification reservoirs epigenetic karstification reservoirs formed as a result of significant sea level drops or tectonic movement dolomitized reservoirs formed in shoals affected by dolomitization caused by evaporation of seawater or that occurred during burial composite shoal reservoirs were formed by two or more processes

experimental investigation of the thermal time series method for surface water groundwater interactions 1 diel temperature fluctuations have been used to quantify vertical water flow through saturated sediments with 1 d analytical heat models the underlying transport equation relies on assumptions that could be violated using field temperature records to test the capability of this method a hydraulic laboratory experiment was designed a mass of fully water saturated homogeneous sand was exposed to 19 different uniform pressure gradients inducing steady state darcy velocities 0 q 25 m d 1 an areal heating grid generated steady sinusoidal thermal forcing multipoint sediment temperature responses demonstrated increasing spatial variability for increasing velocities this introduced horizontal temperature gradients velocities calculated from heat tracing were compared to velocities independently obtained from solute slugs heat and solute derived velocities agreed for q 3 m d 1 but heat derived velocities were consistently larger at higher velocities temperature amplitude and phase derived velocities revealed significant scatter when compared to solute velocities this scatter reduced when amplitude and phase derived velocities were compared for each sensor pair the variability in heat derived velocities therefore represents a spatially variable flow field in the sand however amplitude and phase derived velocities deviated from a 1 1 relationship at higher velocities this can partly be explained by longitudinal thermal dispersivity and partly by enhanced thermal spreading due to horizontal temperature gradients originating from nonuniform flow this is surprising given the homogeneous sand and transition zone transport conditions pet 0 7 these findings have implications for the quantification of velocities from field records because field conditions are likely more heterogeneous which would exacerbate the effects found in this study

flow simulation with reactive transport applied to carbonate rock diagenesis abstract significant volumes of the known hydrocarbon reserves are found in carbonate rocks many of these dolomitized the spatial distribution of diagenesis on these rocks is one of the main challenges in oil reservoir modeling reactive transport models can be a powerful tool to understand the active diagenetic processes and their effects on the quality of these reservoirs in this study it was used for the first time the cmg gem simulator to model diagenetic evolution of a carbonate sequence subjected to compaction driven and geothermal flow in a simulated period of 200 thousand years it was simulated carbonate cementation dolomitization and dissolution with and without presence of faults among the analyzed variables the volume of circulating fluid was the most important factor for both mechanisms flow simulated velocities obtained had magnitudes smaller than 10 6 m day diagenesis was insignificant for these low speeds at simulated time interval only dolomitized facies presented relevant diagenesis in form of calcite dissolution and dolomite precipitation simulations with flow rates of 1 m day revealed a considerable increase in observed diagenesis especially in carbonate cementation and in porosity enhancement diagenesis was more pronounced in more permeable sediments highlighting the role of fluid flow in diagenetic reactions relative dissolution was greatly reduced during simulations performed with absence of dolomite and dolomitization reactions the presence of faults strongly influences spatial distribution of diagenesis especially relatively to dissolution more permeable facies were more dissolved near fault decreasing with increasing distance low permeability facies as mudstones are not dissolved even near fault spatial distribution of diagenesis would then be dependent mainly on the quality of original pore structure of fault presence and mineral composition of rock

regional primitive equation studies of the gulf stream meander and ring formation region abstract primitive equation and quasi geostrophic eddy resolving open ocean models are used for hindcast studies in the gulf stream meander and ring formation region a feature model approach is used to initialize the models based on one month of observations during november to december 1984 flat bottom and topographic calculations are carried out using an initial gulf stream velocity profile based on the pegasus dataset all of the major events observed in the upper thermocline are reproduced by both numerical models the addition of bottom topography is shown to significantly alter the character of the deep velocity fields large basin scale circulations found near the bottom in both flat bottom calculations were replaced by energetic jets and eddies associated with the dominant spatial scales of the bottom topography use of the quasi geostrophic model to dynamically adjust the initial conditions for the primitive equation model is shown to reduce the growth of large scale meanders on time scales o

bed scale spatial patterns in dolomite abundance part ii effect of varied fluid chemistry flow rate precursor mineralogy temperature textural heterogeneity nucleation density and bed geometry

quantifying streambed deposition and scour from stream and hyporheic water temperature time series 1 we propose a new method based on temperature time series of surface and streambed pore waters to monitor local changes in streambed surface elevations at a nominally daily time scale the proposed method uses the naturally occurring daily temperature signal changes in amplitude and phase between stream water and the water flowing within the streambed sediment application of the method in a fine bedded stream predicts the timing and magnitude of a prescribed sequence of scour and deposition this provides a new effective easy to use and economic methodology to monitor the temporal evolution of erosion and depositional patterns in rivers

a census of eddy activities in the south china sea during 1993 2007 1 numerous mesoscale eddies occur each year in the south china sea scs but their statistical characteristics are still not well documented a pacific basin wide three dimensional physical biogeochemical model has been developed and the result in the scs subdomain is used to quantify the eddy activities during the period of 1993 2007 the modeled results are compared with a merged and gridded satellite product of sea level anomaly by using the same eddy identification and tracking method on average there are about 32 9 2 4 eddies predicted by the model and 32 8 3 4 eddies observed by satellite each year and about 52 of them are cyclonic eddies the radius of these eddies ranges from about 46 5 to 223 5 km with a mean value of 87 4 km more than 70 of the eddies have a radius smaller than 100 km the mean area covered by these eddies each year is around 160 170 km2 equivalent to 9 8 of the scs area with water depths greater than 1000 m linear relationships are found between eddy lifetime and eddy magnitude and between eddy vertical extent and eddy magnitude showing that strong eddies usually last longer and penetrate deeper than weak ones interannual variations in eddy numbers and the total eddy occupied area indicate that eddy activities in the scs do not directly correspond to the el nino southern oscillation events the wind stress curls are thought to be an important but not the only mechanism of eddy genesis in the scs

spatiotemporal variability of hyporheic exchange through a pool riffle pool sequence 1 stream water enters and exits the streambed sediment due to hyporheic fluxes which stem primarily from the interaction between surface water hydraulics and streambed morphology these fluxes sustain a rich ecotone whose habitat quality depends on their direction and magnitude the spatiotemporal variability of hyporheic fluxes is not well understood over several temporal scales and consequently we studied their spatial and temporal variation over a pool riffle pool sequence at multiple locations from winter to summer we instrumented a pool riffle pool sequence of bear valley creek an important salmonid spawning gravel bed stream in central idaho with temperature monitoring probes recording at high temporal resolution 12 minute intervals using the thermal time series weekly winter season seepage fluxes were calculated with a steady state analytical solution and spring summer fluxes with a new analytical solution that can also quantify the streambed thermal properties longitudinal pool riffle pool conceptualizations of downwelling and upwelling behavior were generally observed except during the winter season when seepage fluxes tended toward downwelling conditions seepage fluxes near the edges of the channel were typically greater than fluxes near the center of the channel and demonstrated greater seasonal variability results show that the interaction between streamflow and streambed topography has a primary control near the center of the channel whereas the interaction between stream water and groundwater table has a primary control on seepage fluxes near the banks of the stream

hyporheic exchange in gravel bed rivers with pool riffle morphology laboratory experiments and three dimensional modeling received 7 june 2005 revised 30 june 2006 accepted 25 august 2006 published 31 january 2007 1 we report the first laboratory simulations of hyporheic exchange in gravel pool riffle channels which are characterized by coarse sediment steep slopes and three dimensional bed forms that strongly influence surface flow these channels are particularly important habitat for salmonids many of which are currently at risk worldwide and which incubate their offspring within the hyporheic zone here we perform a set of laboratory experiments examining the effects of discharge and bed form amplitude on hyporheic exchange with surface subsurface mixing measured directly from the concentration decay of a conservative tracer fluorescein injected into the surface flow near bed pressure measurements were also used to predict hyporheic exchange from a three dimensional pumping transport model comparison of the predicted and observed hyporheic exchange shows good agreement indicating that the major mechanism for exchange is bed form induced advection however the effect of bed forms is modulated by discharge and the degree of topographic submergence we also tested the performance of the hydrostatic pressure as a proxy for the observed near bed pressure in driving hyporheic exchange which would facilitate field measurement and analysis of hyporheic flow in natural rivers we found agreement with measured hyporheic exchange only for low bed form amplitudes and high flows

influence of a gulf stream warm core ring on water mass and chlorophyll distributions along the southern flank of georges bank during late spring 1997 a gulf stream warm core ring wcr strongly in uenced water mass and chlorophyll distributions along the southern ank of georges bank entrainment of georges bank shelf water by the wcr centered at the central southern ank persisted through may by late may shelf water encircled nearly the entire wcr and horizontal convergence toward the central southern ank was evident scotian shelf water ssw extended across northeast channel onto georges bank near the northeast peak and along the southern ank between the 60 m isobath and the shelfbreak front ssw extended furthest southwest along the southern ank shelfbreak satellite imagery from the ocean color and temperature sensor octs showed that by late may in addition to the high chlorophyll concentrations within the entrained shelf water encircling the wcr pigment rich bands of chlorophyll developed along the 60 and 100 m isobaths where this biological enhancement developed along 100 km of the shelfbreak 100 m isobath shelf waters extended furthest seaward due to entrainment by the wcr the enhanced shelfbreak chlorophyll was sampled in situ along two transects separated by 40 km along shelf along both transects the enhanced chlorophyll coincided with divergent cross shelf ow maximum along shelf ow and minimum surface temperature coincidence of the highest surface chlorophyll and lowest surface temperature with divergent cross shelf ow is consistent with upwelling coincidence with along shelf jets and their associated vertical shear is consistent with turbulent vertical mixing the importance of turbulent vertical mixing was supported maximum velocity at the shelfbreak coincided with the subsurface temperature minimum of ssw near 30 m depth estimated gradient richardson numbers ri above the ssw were below critical 0 25 within the shelfbreak chlorophyll maximum along both transects and surface chlorophyll was signi cantly inversely correlated with ri along the southern ank wcr entrainment of shelf water continued into june as

reactive transport modeling of brine reflux dolomitization anhydrite precipitation and porosity evolution abstract both geothermal convection and brine reflux drive circulation of sea water derived fluids through carbonate platforms during early burial but dynamic interactions between heat and solute transport and resulting diagenesis are at present poorly understood this paper describes high resolution reactive transport model rtm simulations that suggest that reflux of 85 ppt brines rapidly restricts geothermal convection to the platform margin with flow focused in the more permeable shallow carbonates in a baseline simulation involving an elongate 25 km wide grain dominated packstone platform brine reflux resulted in complete dolomitization beneath the 5 km wide brine pool in 335 ky the dolomite body then extends downward at c 22 m 100 ky into an underlying broad area of partial dolomitization this process enhances porosity at shallow depth but beneath the dolomite body precipitation of anhydrite occludes porosity and limits the depth of reflux in contrast geothermal convection at the platform margin forms a smaller partially dolomitized body over a longer time 60 dolomite after 1 my with very minor associated anhydrite cementation reflux diagenesis is sensitive to platform geometry with higher rates of fluid flow increasing the depth of alteration beneath the brine pool for a circular platform compared to the linear baseline fluid flow across thermal gradients enhances reaction rates and ignoring heat transport by 85 ppt brine reflux underestimates the extent of reflux dolomite by 25 and associated anhydrite by 90 the depth and rate of anhydritization is sensitive to the geothermal heat flux whereas platform top temperatures affect dolomitization rate reflux diagenesis is also sensitive to brine density which affects both fluid flow and reaction rates sediment permeability and reactive surface area rsa are key intrinsic controls on diagenesis where the permeability structure permits sufficient fluid flow diagenesis preferentially affects more reactive fine grained sediments however as flow rates decline reactions become focused in the more permeable but less reactive sediments simulations thus shed light on why in some settings reflux preferentially dolomitizes muddy sediments but elsewhere favors grainstones once active reflux ceases brines continue to flow in the subsurface but this latent reflux causes only minor dolomitization due to prior mg2 consumption at shallow depth

observations of bedload transport in a gravel bed river during high flow using fiber optic dts methods the question how does a streambed change over a minor flood does not have a clear answer due to lack of measurement methods during high flows we investigate bedload transport and disentrainment during a 1 5 year flood by linking field measurements using fiber optic distributed temperature sensing dts cable with sediment transport theory and an existing explicit analytical solution to predict depth of sediment deposition from amplitude and phase changes of the diurnal near bed pore water temperature the method facilitates the study of gravel transport by using near bed temperature time series to estimate rates of sediment deposition continuously over the duration of a high flow event coinciding with bar formation the observations indicate that all gravel and cobble particles present were transported along the riffle at a relatively low shields number for the median particle size and were re deposited on the lee side of the bar at rates that varied over time during a constant flow approximately 1 6 of the bed was predicted to be mobile during the 1 5 year flood indicating that large inactive regions of the bed particularly between riffles persist between years despite field observations of narrow zones of local transport and bar growth on the order of 3 5 times the median particle size in contrast during a 7 year flood approximately 8 55 of the bed was predicted to become mobile indicating that the continuous along stream mobility required to mobilize coarse gravel through long pools and downstream the next riffle is infrequent

multi scale modeling of the north pacific ocean assessment and analysis of simulated basin scale variability 1996 2003 1 a primitive equation ocean general circulation model is used to investigate climate impacts in the north pacific ocean in the 1996 to 2003 period the objective is to assess the model ability to reproduce observed modes of variability and study their impact in the northeast pacific this work is done within the framework of the u s global ecosystem globec northeast pacific program studying the links between climate variability and ecosystem dynamics three large scale events are considered the 1997 1998 el nino the 1999 regime shift and the 2002 cold fresh subsurface anomalous water mass that was observed in the gulf of alaska and off the coast of oregon the circulation model is shown to generate the correct seasonal to interannual large scale variability and is able to represent the climatic signals of interest in the eastern pacific we show that the influence of the 1997 1998 el nino reached the coastal gulf of alaska and induced an increase in the upper ocean heat content along the coast of north america an analysis of the sea surface temperature for the model years shows agreement between model and data in the representation of the 1999 shift to a cold phase in the eastern and northern north pacific finally using the model results we speculate that the origin of the 2002 cold fresh anomaly in the northeast pacific was due to enhanced mixing during the preceding winter in the center of the alaska gyre owing to anomalous changes in the density structure of the upper ocean this water was able to move geostrophically toward the coast and it persisted in the northeast pacific below the mixed layer the following year

dolomitization anhydrite cementation and porosity evolution in a reflux system insights from reactive transport models significant volumes of world hydrocarbon reserves occur in dolostones and the majority of these reservoirs are interpreted to be of reflux origin we used a two dimensional numerical reactive transport model to investigate systematically the temporal and spatial distribution of replacement dolomitization dolomite cementation anhydrite cementation and porosity evolution in a reflux system we tested the sensitivity of reflux dolomitization to brine concentration mesohaline to near halite saturated brines near surface temperature flow rate porosity permeability feedback relationships reactive surface area and the effect of initial porosity permeability heterogeneity simulations support the contention that hypersaline reflux is capable of extensive pervasive dolomitization and that mesohaline reflux dolomitization is viable reflux generated a tabular dolomite body that is thickest close to the brine source and thins basinward incorporation of initial porosity and permeability heterogeneity resulted in a dolomite body with pronounced lateral fingers replacement dolomitization increased porosity up to 8 but postreplacement reflux resulted in the precipitation of minor dolomite cements overdolomitization anhydrite cements that were spatially and temporally associated with replacement dolomitization caused a significant porosity reduction of up to 25 simulated rates of replacement dolomitization by reflux are fast up to three orders of magnitude faster than seawater dolomitization the rate of dolomitization and anhydrite mineralization proved to be critically sensitive to the flow rate and the brine chemistry temperature and reactive surface area were important controls on the rate of dolomitization whereas the feedback relationship between porosity and permeability was a relatively moderate control our reactive transport models predict the general spatial and temporal trends in dolomite porosity and anhydrite observed in some major dolomite reservoirs

numerical modeling of an estuary a comprehensive skill assessment i numerical simulations of the hudson river estuary using a terrain following three dimensional model regional ocean modeling system roms are compared with an extensive set of time series and spatially resolved measurements over a 43 day period with large variations in tidal forcing and river discharge the model is particularly effective at reproducing the observed temporal variations in both the salinity and current structure including tidal spring neap and river discharge induced variability large observed variations in stratification between neap and spring tides are captured qualitatively and quantitatively by the model the observed structure and variations of the longitudinal salinity gradient are also well reproduced the most notable discrepancy between the model and the data is in the vertical salinity structure while the surface to bottom salinity difference is well reproduced the stratification in the model tends to extend all the way to the water surface whereas the observations indicate a distinct pycnocline and a surface mixed layer because the southern boundary condition is located near the mouth the estuary the salinity within the domain is particularly sensitive to the specification of salinity at the boundary a boundary condition for the horizontal salinity gradient based on the local value of salinity is developed to incorporate physical processes beyond the open boundary not resolved by the model model results are sensitive to the specification of the bottom roughness length and vertical stability functions insofar as they influence the intensity of vertical mixing the results only varied slightly between different turbulence closure methods of k e k and k kl

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

a model of the summer progression of the cold pool temperature in the middle atlantic bight abstract a simple one dimensional model in the alongshelf direction that incorporates spatially non uniform heating advection and initial temperature field is proposed to explain the summer progression of the cold pool temperature in the middle atlantic bight the observed local cooling is shown to require an upstream cold water source at the onset of the heating season the observed secondary temperature minimum that stagnates at the hudson shelf valley and the observed thermal front in the new york bight can be explained by the alongshelf variation of the heating rate which is attributed mainly to the varying shelf width and hence the heat capacity of the cold pool although the model is highly idealized a crude simulation using the input functions inferred from data has reproduced all the gross features observed in the thermal field

hydrographic observations and mixing processes in the new york bight 1975 1977 a series of 15 hydrographic cruises in the new york bight over 1975 1977 is described and analyzed the cruises cover all seasons but focus primarily on spring and summer temperature and salinity data show wide seasonal and interannual variability each of the three regions inner bight midshelf and outer shelf slope has distinctive properties and dynamics the inner bight properties are affected primarily by river flow and wind driven flows up the shelf valley which often splits the freshwater surface layer into two plumes one east and one west of the valley head the cold pool temperature structure on the midshelf is different each year the water with the lowest recorded temperature 2 58 was on the bottom after the thermocline formation in may 1977 mixing models of the inner bight confirmed previous estimates of residence time as 6 8 days and yielded k 5 x 106 cm2 es with an advective transport component of 1 cm s r to the southwest a model of the mixing of the lower layer cold pool on the midshelf with onshore offshore and upper layer waters yields k 7 x 106 and 0 1 cm2 s as the on offshore horizontal and vertical diffusion coefficients

geothermal convection in the tengiz carbonate platform kazakhstan reactive transport models of diagenesis and reservoir quality a fundamental challenge in carbonate reservoir characterization is predicting the spatial distribution of diagenesis we used a reactive transport model to investigate the viability of geothermal convection and associated patterns of diagenetic porosity modification in the tengiz isolated carbonate platform reservoir before burial forced convection generates significant calcite dissolution locally up to 45 toward the platform center minor calcite cementation up to 0 4 in the slope and moderate calcite dissolution and cementation up to 1 6 in serpukhovian boundstone convective cells the patterns and rates of diagenesis proved critically sensitive to specified vertical permeability after burial with 200 m 660 ft of salt modeled subsurface temperature contrasts drive platform scale free convection flow is hydraulically closed but significant dissolution up to 7 3 after 20 m y occurred in the serpukhovian and visean platform interior and minor cementation up to 0 7 occurred toward the margin a shale filled salt withdrawal basin 500 m 1640 ft deep significantly modifies the subsurface temperature distribution and free convective flow ascending groundwaters beneath the withdrawal basin created a zone of calcite dissolution up to 24 5 in 20 m y with a mushroom geometry and minor cementation up to 2 3 in 20 m y in the distal platform interior and margin rates of diagenesis are dramatically reduced with increasing overburden as compaction retards convective flow from a generic perspective free convection persists if the salt overburden is substituted with shale although flow is reversed resulting in a different distribution of diagenesis simulations of geothermal convection provide a physically viable model for the integration of direct diagenetic observations to augment predictions of reservoir quality in tengiz and other carbonate platform reservoirs

effects of stream discharge alluvial depth and bar amplitude on hyporheic flow in pool riffle channels 1 hyporheic flow results from the interaction between streamflow and channel morphology and is an important component of stream ecosystems because it enhances water and solute exchange between the river and its bed hyporheic flow in pool riffle channels is particularly complex because of three dimensional topography that spans a range of partially to fully submerged conditions inducing both static and dynamic head variations hence these channels exhibit transitional conditions of streambed pressure and hyporheic flow compared to previous studies of fully submerged two dimensional bed forms here we conduct a series of three dimensional simulations to investigate the effects of bed topography depth of alluvium and stream discharge on hyporheic flow in pool riffle reaches with variable bed form submergence and we propose three empirical formulae to predict the mean depth of hyporheic exchange and characteristic values of the residence time distribution mean and standard deviation hyporheic exchange is predicted with a three dimensional pumping model and hyporheic flow is modeled as a darcy flow we find that the hyporheic residence time is well approximated by a lognormal distribution for both partially and entirely submerged pool riffle topography with the parameters of the distribution defined by the mean and variance of the log transformed residence time depth of alluvium has a substantial effect on hyporheic flow when alluvial depth is less than a third of the bed form wavelength for the conditions examined

effects of stream morphodynamics on hyporheic zone thermal regime 1 we develop a heat transport model to study the impact of streambed morphology on temperature distribution within the hyporheic zone of gravel bed rivers the heat transport model which includes conduction diffusion and advection is solved by a lagrangian approach neglecting transverse dispersion and considering stream water temperature as boundary condition at the streambed first we show that the model accurately reproduces the temperature distribution measured within the hyporheic zone of a reach of the bear valley creek idaho usa our model reveals spatially complex patterns of hyporheic water temperatures that vary with time within the hyporheic zone and at the streambed surface the analysis shows that temperature distributions are primarily related to the hyporheic residence time and consequently to the bed morphology and in stream flow discharge results show that the hyporheic temperature amplitudes are smaller than the surface water temperature and they decrease with stream size leading hyporheic zones of large streams to be independent from in stream daily temperature fluctuations

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

meridional gulf stream shifts can influence wintertime variability in the north atlantic storm track and greenland blocking author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geophysical research letters 46 3 2019 1702 1708 doi 10 1029 2018gl081087

wind influence on the mesoscale activity along the gulf stream and the north atlantic currents two independent data sets are used to diagnose the wind effect on the mesoscale activity in the north atlantic ocean the oceanic surface variability is described with topex poseidon sea surface height measurements from october 1992 to september 1997 spatial extensions and temporal variations of high mesoscale activity are compared with the zonal and meridional components of the ers 1 wind stress the ekman pumping and the zonal sverdrupian velocity regions with high mesoscale surface variability seem to be correlated to regions with eastward sverdrupian velocities when the sverdrupian velocity is eastward and increases with time the mesoscale activity is intensified indicating a growth of instability rates theoretical and numerical results based on the interplay of barotropic eastward sverdrup flows and westward propagation of long rossby waves suggest that the wind controls western regions where baroclinic instability is favored interactions between the eddy field and the mean circulation are therefore analyzed to try to extract the instability mechanism responsible for the growth of the mesoscale activity along the gulf stream and the north atlantic current our results seem to suggest that the seasonal changes of mesoscale activity associated with eastward currents are linked to seasonal changes of the eastward sverdrupian velocity

seasonal and interannual changes in the north atlantic subpolar gyre from geosat and topex poseidon altimetry sea surface slopes from the altimetric satellites geosat and topex poseidon are used to calculate eddy kinetic energy of the north atlantic subpolar gyre 40 65 n 60 5 w using two years of data from each satellite december 1986 to december 1988 and october 1992 to september 1994 respectively interannual differences in the north atlantic current nac are revealed in regions of strong currents the eddies are driven by baroclinic instability of the mean flow are not seasonally varying and may therefore be used as a surrogate for the mean flow itself wind stress curl fields for the same periods show that the northward and southward shifts in the current branches across the mid atlantic ridge are related to interannual differences in the winter wind stress curl pattern when the zero in wind stress curl is well defined and wind stress is at a maximum outside the nac the eddies are driven primarily by wind stress indicated by a significant seasonality time series of eddy kinetic energy and wind stress are generated for the 4 years and the magnitude phase and significance of annual and semiannual signals are determined interannual changes in the timing of the maximum eddy kinetic energy are associated with that of the maximum wind stress with each being shifted by a month or two later or earlier throughout much of the northern north atlantic a significant annual signal in eddy kinetic energy is observed lagging the wind stress by on average 6 weeks a negligible lag is found in the region of the east greenland current and irminger sea whereas the greatest lag about 2 months is found in the labrador sea

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

gulf stream path analysis near the new england seamounts as part of the naval ocean research and development activity s regional energetics experiment 12 inverted echo sounders iess were deployed from june 1985 to july 1986 in two arrays across the historical mean path of the gulf stream near 67 w and 58 w slightly upstream and downstream of the new england seamount chain gulf stream positions and directions were computed at half day intervals for adjacent ies pairs levels of variability at the two array locations were similar but the characteristics of the meanders in terms of propagation and current direction were quite different evidence was found for a quasi stationary meander near 58 w features deduced from ies measurements are compared with concurrent infrared air dropped expendable bathythermograph and geosat altimetry observations

energetics of eddy mean flow interactions in the gulf stream region a detailed energetics analysis of the gulf stream gs and associated eddies is performed using a highresolution multidecadal regional ocean model simulation the energy equations for the time mean and timevaryingflowsarederivedasatheoreticalframeworkfortheanalysis theeddy meanflowenergycomponents and their conversions show complex spatial distributions in the along coast region the cross stream and cross bump variations are seen in the eddy mean flow energy conversions whereas in the off coast region a mixed positive negative conversion pattern is observed the local variations of the eddy mean flow interaction are influenced by the varying bottom topography when considering the domain averaged energetics theeddy meanflowinteractionshowssignificantalong streamvariability upstreamofcapehatteras the energy is mainly transferred from the mean flow to the eddy field through barotropic and baroclinic instabilities upon separating from the coast the gs becomes highly unstable and both energy conversions intensify when the gs flows into the off coast region an inverse conversion from the eddy field to the mean flow dominates the power transfer for the entire gs region the mean current is intrinsically unstable and transfers 28 26gw of kinetic energy and 26 80gw of available potential energy to the eddy field the mesoscaleeddykineticenergyisgeneratedbymixedbarotropicandbaroclinicinstabilities contributing28 26 and 9 15gw respectively beyond directly supplying the barotropic pathway mean kinetic energy also provides 11 55gw of power to mean available potential energy and subsequently facilitates the baroclinic instability pathway

reactive transport modeling an essential tool and a new research approach for the earth sciences abstract reactive transport modeling is an essential tool for the analysis of coupled physical chemical and biological processes in earth systems and has additional potential to better integrate the results from focused fundamental research on earth materials appropriately designed models can describe the interactions of competing processes at a range of spatial and time scales and hence are critical for connecting the advancing capabilities for materials characterization at the atomic scale with the macroscopic behavior of complex earth systems reactive transport modeling has had a significant impact on the treatment of contaminant retardation in the subsurface the description of elemental and nutrient fluxes between major earth reservoirs and in the treatment of deep earth processes such as metamorphism and magma transport active topics of research include the development of pore scale and hybrid or multiple continua models to capture the scale dependence of coupled reactive transport processes frontier research questions that are only now being addressed include the effects of chemical microenvironments coupled thermal mechanical chemical processes controls on mineral fluid reaction rates in natural media and scaling of reactive transport processes from the microscopic to pore to field scale

variability in the vertical hyporheic water exchange affected by hydraulic conductivity and river morphology at a natural confluent meander bend river confluences and their associated tributaries are key morphodynamic nodes that play important roles in controlling hydraulic geometry and hyporheic water exchange in fluvial networks however the existing knowledge regarding hyporheic water exchange associated with river confluence morphology is relatively scarce on the 14th and 15th of january 2016 the general hydraulic and morphological characteristics of the confluent meander bend cmb between the juehe river and the haohe river in the southern region of xi an city shaanxi province china were investigated the patterns and magnitudes of vertical hyporheic water exchange vhwe were estimated based on a one dimension heat steady state model while the sediment vertical hydraulic conductivity kv was calculated via in situ permeameter tests the results demonstrated that six hydrodynamic zones and their extensions were observed at the cmb during the test period these zones were likely controlled by the obtuse junction angle and low momentum flux ratio influencing the sediment grain size distribution of the cmb the vhwe patterns at the test site during the test period mostly showed upwelling flow dominated by regional groundwater discharging into the river the occurrence of longitudinal downwelling and upwelling patterns along the meander bend at the cmb was likely subjected to the comprehensive influences of the local sinuosity of the meander bend and regional groundwater discharge and finally formed regional and local flow paths additionally in dominated upwelling areas the change in vhwe magnitudes was nearly consistent with that in kv values and higher values of both variables generally occurred in erosional zones near the thalweg paths of the cmb which were mostly made up of sand and gravel this was potentially caused by the erosional and depositional processes subjected to confluence morphology furthermore lower kv values observed in downwelling areas at the cmb were attributed to sediment clogging caused by local downwelling flow the confluence morphology and sediment kv are thus likely the driving factors which cause local variations in the vhwe of fluvial systems

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

eddy characteristics in the eastern south pacific 1 the main eddy characteristics length scales rotation period swirl and translation velocities are determined in the eastern south pacific region 10 35 s and 70 100 w based on surface drifter measurements satellite altimetry and hydrographic data from the woce p19 section the chile peru current eddies have a typical diameter of order of 30 km smaller than the typical rossby radii observed in the region they are principally formed near the south american coast and propagate seaward with a translation velocity varying from 3 cm s 1 in the southern part of the study domain to 6 cm s 1 north of 15 s long lived anticyclonic eddies propagate northwestward with a mean angle of around 333 t whereas cyclonic vortices propagate westward consistent with the vortices propagation theory on a plane the radial distribution of the swirl velocity shows that the chile peru current eddies have a maximum diameter of order 200 km with a swirl velocity of around 14 cm s 1 and a rotation period of 50 days hydrographic data reveal a vertical extent down to around 2000 m for energetic eddies no significant difference is observed between the tangential velocities of cyclonic and anticyclonic eddies geostrophic balance can be considered for large radii whereas ageostrophic dynamics may play an important role near the eddy centers

gulf stream eddy characteristics in a high resolution ocean model 1 a detailed statistical study of the mesoscale eddy activity in the gulf stream gs region is performed based on a high resolution multidecadal regional ocean model hindcast an eddy detection and tracking method that can be used to capture eddy features from large datasets is presented this method is applied to the 50 year model hindcast within a domain with the most energetic eddy activity along the gs detection results are then analyzed to investigate the kinematic properties and temporal variability of gs mesoscale eddies the studied kinematic properties include the eddy size duration intensity propagation and spatial distribution on average cyclonic eddies are smaller in size but more energetic and remain coherent longer than anticyclonic ones cyclonic eddies generally travel further from the generation sites and have a strong tendency for westward propagation with a small equatorward deflection anticyclonic eddies remain near their generation locations and tend to propagate northward the temporal evolution of eddy properties for long lived eddies lifetime 90 days is also examined for both cyclonic and anticyclonic eddies the size increases rapidly to their maximum value within the first 20 days at which point they begin to slowly decay in terms of intensity cyclonic eddies show a quasi linear decay while the anticyclonic ones reach a quasi steady state after 3 4 months of a more rapid decay finally the seasonal variability of the gs mesoscale eddies is explored in autumn and winter both types of eddies are more numerous and larger but less intense while in spring they are more intense but less numerous and generally smaller several possible mechanisms including the wind stress thermal forcing and topographic influence are considered to explain the seasonal cycle of eddy variability

reactive transport modeling of early burial dolomitization of carbonate platforms by geothermal convection reactive transport models rtms permit quantitative investigation of diagenesis and its effects on reservoir quality the rtm toughreact is used to investigate diagenesis in an isolated platform driven by geothermal kohout convection of seawater which has been invoked to explain dolomitization during early burial previous short 0 1 m y rtm simulations suggested that convection can drive dolomitization mostly at greater than 50c and anhydritization but complete dolomitization requires greater than 30 60 m y our more extended rtm simulations 30 m y indicate significant nonlinearities in the system consistent with high temperature experiments with parts of the platform completely dolomitized within 10 15 m y as dolomitization proceeds the process becomes predominantly flux controlled with development of a wedge shaped dolomite body which thins from the margin to the interior at considerably shallower depth and cooler temperatures 20 30c than suggested by short simulations dolomitization is relatively insensitive to boundary conditions such as relative sea level and platform geometry but is significantly slower in circular than elongate platforms sediment permeability and reactive surface area commonly inversely related are key controls dolomitization is limited to the margin of low permeability muddy platforms despite a high reactive surface area dolomitization of more permeable grainy platforms is limited by a lower reactive surface area occurring only in the platform core due to widespread cooling sedimentary layering produces a complex diagenetic stratigraphy dolomitization favoring more reactive beds at shallow depth where permeability is not limiting but switching to more permeable beds at depth bank marginal fracturing limits dolomitization of the platform interior whether the fractures are baffles or conduits for flow

average circulation seasonal cycle and mesoscale dynamics of the peru current system a modeling approach h isolines the pccc appears to be directly forced by the cyclonic wind stress curl the model is able to produce the upwelling front the cold water tongue which extends toward the equator and the equatorial front as described in the literature model seasonal changes in sst and ssh are compared to measurements for the central pcs model eke is 10 to 30 lower than the observations the model eddy diameters follow a strong equatorward increase the injection length scales derived from the energy spectra strongly correlate to the rossby radius of deformation confirming the predominant role of baroclinic instability at 3 s the model solution appears to switch from a turbulent oceanic regime to an equatorial regime dominated by zonal currents

impacts of nonuniform flow on estimates of vertical streambed flux 1 the use of inverse one dimensional 1 d analytical methods for estimating vertical stream aquifer exchange flux is now commonplace however the application of such simple models can lead to significant errors in estimates of vertical exchange flux where the model assumptions are violated in real systems an idea that is gaining acceptance in the literature is that the presence of nonvertical flow is such a violation however it is shown here that nonvertical flow by itself will not necessarily lead to errors in vertical flux estimation but rather that significant errors can stem from nonuniform convergent divergent flow fields and or hydrodynamic dispersion even within uniform flow fields nonuniform flow may also be expected in some cases to create discrepancies between flux estimates made on the basis of vertical head gradient measurements and those made using 1 d analytical heat tracer methods significant differences are observed in the estimates of heat derived fluxes obtained by the amplitude ratio and phase shift time series methods when convergent and divergent flows are apparent such differences may potentially be used to infer that convergent or divergent flow is occurring and that a 1 d analysis is inappropriate

divergent pathways of cyclonic and anti cyclonic ocean eddies satellite altimetry is used to study the propagation pathways of warm and cold ocean eddies in different ocean basins we consider eddies that have a life span longer than 3 months and we present three regional studies in the southeast indian the southeast atlantic and the northeast pacific oceans the case studies show that simple theories for vortex propagation on a plane work in regions where energetic eddies propagate though a weak background flow under these conditions anticyclonic cyclonic eddies propagate westward and equatorward poleward this divergence in the eddy pathways implies a net equatorward eddy heat flux and has implications for the meridional transport of freshwater carbon nutrients etc

modelling of thermal convection in sedimentary basins and its relevance to diagenetic reactions abstract mathematical calculations of thermal convection have been carried out using a porous three player model to simulate pore water flow in a sedimentary basin with layers of different permeabilities the calculated flow lines demonstrate that even very thin layers eg around salt domes and igneous or hydrothermal intrusions analyses of formation waters from sedimentary basins like the north sea often show evidence of a crude stratification of the pore water with respect to salinity and isotopic composition this is evidence suggesting that large scale convection or other types of mixing does not take place and positive salinity depth gradient may help to physically stabilize the formation water the fact that many of the shallow reservoir rocks from the north sea have formation water with low salinity and negative 18 o values suggest that this is modified meteoric water and that migration of petroleum from deeper parts of the basin occurred as a separate phase along restricted migration pathways and was not associated with a high flux of pore water in the absence of thermal convection the total pore water flux through sandstones will be rather small except locally where we may have focused compactional flow through small cross sections diagenetic reactions will therefore normally be relatively isochemical during deeper burial