interplay between detrital and diagenetic processes since the last glacial maximum on the northwest iberian continental shelf abstract integrated analyses of magnetic geochemical and textural data on six cores from the northwestern iberian continental shelf allowed the reconstruction of the paleoenvironmental evolution of this area since the last glacial maximum lgm four sedimentary units were identified representing a succession from fluvial and subaerial settings to high and finally low energy marine deposits subsequent to the post lgm sea level rise the uppermost unit was deposited during the holocene and its magnetic properties were controlled by the interplay between detrital input and early diagenetic reductive dissolution of magnetic minerals identification of a primary steady state early diagenetic signal allowed the recognition of periods of increased detrital input bounded by intervals of lower detrital input and intensified reductive diagenesis related to intensified upwelling in the area these paleoenvironmental alternations are consistent with the climatic evolution of the late holocene during the roman warm period and medieval warm period the combined effect of greater humidity and intense agricultural and mining activities led to a greater erosion and transport of detrital sediments to the shelf in contrast enhanced diagenetic reduction intervals caused by upwelling intensification were roughly coincident with the colder dark ages and the little ice age

tidal mixing and trapping in mangrove swamps lateral trapping in mangrove swamps is a dominant process controlling longitudinal mixing in mangrove fringed tidal rivers in the dry season the effective value of the longitudinal diffusivity is increased by the trapping effect by typically two orders of magnitude from its value in the absence of swamps in the wet season freshwater is trapped within the swamp and the adjoining boundary in the tidal river for long periods following the passage of a short lived flood this may have important ecological implications a fluid mud layer appears to be created by strong tidal currents over colloidal mangrove mud

outwelling from tropical tidal salt flats abstract the norman river flows into the gulf of carpentaria north east australia the estuary is surrounded by 250 km2 of vegetation free saline supratidal mud flats which are only inundated by the tides at spring high tide in summer when the seasonal sea level is 0 5 1 m higher than in winter the first summer tidal inundation of the salt flats in november 1985 resulted in a readily measurable export from the salt flats of salt and nutrients outwelling values of 90 g salt m 2 per tidal cycle 1 0 mmol silicate m 2 and 3 10 2 mmol orthophosphate m 2 were measured about a quarter of the 4000 km2 of salt flats along the southern shore of the gulf of carpentaria outwell into the gulf the rest outwell into the estuaries where salt outwelling increases the strength of the salinity maximum zone of the estuaries further isolating the rivers from the gulf during the dry season

negative estuarine circulation in the ria of pontevedra nw spain an along estuary negative circulation was measured in the ria of pontevedra nw spain on may 13 1998 this two layered circulation pattern with near bed water moving seaward and near surface water landward was generated by the existence of two different water masses at intermediate depths water in the inner part of the estuary was a mixture of estuarine water and eastern north atlantic central water enacw which had entered the estuary some days before due to an intense upwelling event water in the middle part of the estuary was a mixture of estuarine water and fresh water coming from the river discharge which had been higher during the days previous to may 13 this water mass distribution gave rise to the existence of denser water in the inner part of the estuary than in the middle one generating the observed negative circulation pattern

dynamics of hypersaline coastal waters in the great barrier reef the coastal waters of the great barrier reef gbr are hypersaline salinity 37 during the dry season as a result of evaporation greatly exceeding rainfall of shallow waters and of the presence of numerous bays along the coast preventing rapid flushing these hypersaline waters are not flushed out by salinity driven baroclinic currents because these waters are vertically well mixed instead these waters are transported by a longshore residual current and thus form a coastal boundary layer of hypersaline waters as a result the hypersalinity distribution is 2 d with both cross shelf and longshore gradients of salinity the cross shelf gradients are largely controlled by turbulent diffusion while the longshore gradients are controlled by the residual currents that transport hypersaline waters longshore south ward in the central and southern regions of the gbr because every bay supplies hypersaline waters the width of the coastal hypersaline layer increases southwards steady state is reached in about 100 days which is the typical duration of the dry season the dynamics of the gbr hypersaline coastal boundary layer thus differ from the classical inverse hypersaline systems e g in saloum river estuary laguna san ignacio mission bay tomales bay san diego bay hervey bay shark bay coorong coast lagoon spencer gulf gulf of california and many others where the salinity gradient is mainly 1 d with a dominant along channel salinity gradient

a generalized biot gassmann model for the acoustic properties of shaley sandstones1 we obtain the wave velocities of clay bearing sandstones as a function of clay content porosity and frequency unlike previous theories based simply on slowness and or moduli averaging or two phase models we use a biot type three phase theory that considers the existence of two solids sand grains and clay particles and a fluid the theory which is consistent with the critical porosity concept uses three free parameters that determine the dependence of the dry rock moduli of the sand and clay matrices as a function of porosity and clay content testing of the model with laboratory data shows good agreement between predictions and measurements in addition to a rock physics model that can be useful for petrophysical interpretation of wave velocities obtained from well logs and surface seismic data the model provides the differential equation for computing synthetic seismograms in inhomogeneous media from the seismic to the ultrasonic frequency bands

transformation of a subtropical river into a hyperhaline estuary the casamance river senegal paleogeographical implications abstract located in the south of senegal in the transitional guineo congolian soudanian zone the casamance system is composed of a small river supplied by a narrow drainage basin and followed by a 250 km long estuary the continuous rainfall decrease experienced by the region since the beginning of the century drastically affected the casamance river this climatic change suddenly accelerated during 1968 1970 which led to a four stage succession before 1968 1970 stage 1 rainfall 1300 mm the casamance estuary showed the customary negative upstream salinity gradient between 1968 1970 and 1978 stage 2 rainfall 1000 mm under decreasing rainfall the casamance estuary shifted to a hyperline inverse estuary it showed well defined physical chemical and biological zonations fresh groundwater resources supplying the upper reaches of the river during the dry season were progressively depleted between 1978 and 1986 1987 stage 3 the salinity peak of the end of the dry season progressively rose and shifted upward the ecological zonation showed the increasing marine influence until 1986 between 1986 1987 and 1990 stage 4 the dry season fresh water input had weakened with the depletion of groundwater resources a slight increase in rainfall was insufficient to repulse the hyperhaline waters and the restricted area extended upstream and downstream the physical chemical and biological zonations strongly widened and flattened in the future the return to stage 1 conditions by an increase in average rainfall would take decades inevitably it will be much longer than the transformation into a hyperhaline estuary thus a slight decrease of the average rainfall in the region provoked a drastic change of the hydrological and biological patterns of the ria the result seems to be a major crisis in the region and might be recorded in the fossil records we discuss these observations in terms of possible misreadings of paleoenvironments and in relation with long term climate trends

wave velocities and attenuation of shaley sandstones as a function of pore pressure and partial saturation we obtain the wave velocities and quality factors of clay bearing sandstones as a function of pore pressure frequency and partial saturation the model is based on a biot type three phase theory that considers the coexistence of two solids sand grains and clay particles and a fluid mixture additional attenuation is described with the constant q model and viscodynamic functions to model the high frequency behaviour we apply a uniform gas fluid mixing law that satisfies the wood and voigt averages at low and high frequencies respectively pressure effects are accounted for by using an effective stress law by fitting a permeability model of the kozeny carman type to core data the model is able to predict wave velocity and attenuation from seismic to ultrasonic frequencies including the effects of partial saturation testing of the model with laboratory data shows good agreement between predictions and measurements

eddies in the northeastern north atlantic statistics from observations from a moving ship statistics of currents and hydrographic data collected from a moving ship in the northeastern north atlantic have been used to investigate the role of eddies in the circulation of the ocean the mean currents show besides a north atlantic current of about 12 cm s 1 a significant westward flow perhaps 4 cm s 1 just north of the azores eddy kinetic energies in the western basin reach about 1000 cm2 s 2 while there is indication of a weak secondary maximum of about 300 cm2 s 2 in the eastern basin both the eddy kinetic energy and the thermohaline variability show a strong asymmetry with greater variability on the south side of the main branch of the north atlantic current at about 51 n the momentum budget of the north atlantic current shows a dominant geostrophic balance with terms of order 10 cm s 1 the gradients of the reynolds stresses contribute about 0 1 cm s 1 and the nonlinear terms less than 0 01 cm s 1 the residual meridional velocity implied by the meridional heat transport is of order 3 cm s 1 the eddy scale was estimated by means of the average zero crossing length scale of the transverse velocity correlation function to be 46 km there is significant interannual variability of both mean conditions and mesoscale variability in the region of the north atlantic current the northward eddy heat transport appears to be zero in the mixed layer but may be a significant proportion of the total oceanic heat transport at the intergyre boundary in the thermocline estimates of the magnitudes of eddy diffusivities for both momentum and heat give values of about 104 m2 s 1

frontal surveys with a towed profiling conductivity temperature depth measurement package seasoar in april 1986 rv oceanus participated in the frontal air sea interaction experiment fasinex1 in the region 27 29 n 68 71 w the objective was to survey a pronounced oceanic front2 4 and its effect on the oceanic and atmospheric boundary layers although moorings have yet to be recovered and much of the data analysis is as yet only preliminary it is possible to report here the typical density structure of a front as derived from seasoar5 6 fig 1a observations which were analysed within a few hours of collection previously unreported detail is revealed including subducted pycnostads areas of weak vertical density gradient with anomalous temperature salinity signature splitting of the frontal jet and three dimensional structure not apparent in the surface temperature field

the knudsen theorem and the total exchange flow analysis framework applied to the baltic sea abstract the knudsen theorem for estuarine exchange flow based on mass conservation of water and salt and its generalization with resolution in salinity coordinates the total exchange flow tef analysis framework are reviewed here the former had been developed and applied to quantify exchange flow between the north sea and the baltic sea more than a century ago in this paper the underlying short research paper published in 1900 by martin knudsen originally written in german is translated into english reaching far beyond the knudsen relation in particular the extensive scientific achievements of martin knudsen on the salinity of seawater are reviewed using the knudsen theorem and the tef analysis framework validated multi decadal years 1949 2013 model simulations are analyzed in terms of exchange flow through straits of the western baltic sea when comparing the model results to the original findings of martin knudsen it is impressive to see how relevant his analysis of ratios of averaged inflowing and outflowing water masses still is today given that they were based on just a few salinity observations the model based long term knudsen and tef analyses of exchange flow in the western baltic sea reproduces the major baltic inflows mbis that have occurred since the 1950s for the complex inflow years 2002 2003 with two baroclinic summer inflows and one barotropic winter inflow in between the strong underestimation of the exchange flow by eulerian analysis as compared to tef analysis is demonstrated

an inversion of the estuarine circulation by sluice water discharge and its impact on suspended sediment transport abstract the wadden sea is characterized by a complex topography of branching channels and intertidal flats in which the interplay between fresh water discharges wind forcing and the tidal current causes sediment transport rates and direction to be highly variable in space and time during three field campaigns indications of a negative estuarine circulation have been found in a channel adjacent to the coast in the western dutch wadden sea contrary to the classical picture of estuarine circulation a periodic density stratification was observed that builds up during flood and breaks down during ebb this can be related to a large freshwater source at the mouth of the channel the sluice in kornwerderzand in this study observations of this phenomenon are presented and with the help of a numerical model the different drivers for residual suspended matter transport in this area namely tidal asymmetries in the current velocity and the above mentioned periodic stratification are investigated it is found that the residual current in the area of interest points in ebb direction caused by both the elongated ebb flow phase and the periodic stratification on the contrary the stronger flood currents cause a transport of suspended matter in flood direction this transport is counteracted and therefore diminished by the effects of the sluice discharge

a semi empirical velocity porosity clay model for petrophysical interpretation of p and s velocities we design a velocity porosity model for sand shale environments with the emphasis on its application to petrophysical interpretation of compressional and shear velocities in order to achieve this objective we extend the velocity porosity model proposed by krief et al to account for the effect of clay content in sandstones using the published laboratory experiments on rocks and well log data in a wide range of porosities and clay contents the model of krief et al works well for clean compacted rocks it assumes that compressional and shear velocities in a porous fluid saturated rock obey gassmann formulae with the biot compliance coefficient in order to use this model for clay rich rocks we assume that the bulk and shear moduli of the grain material and the dependence of the compliance on porosity are functions of the clay content statistical analysis of published laboratory data shows that the moduli of the matrix grain material are best defined by low hashin shtrikman bounds the parameters of the model include the bulk and shear moduli of the sand and clay mineral components as well as coefficients which define the dependence of the bulk and shear compliance on porosity and clay content the constants of the model are determined by a multivariate non linear regression fit for p and s velocities as functions of porosity and clay content using the data acquired in the area of interest in order to demonstrate the potential application of the proposed model to petrophysical interpretation we design an inversion procedure which allows us to estimate porosity saturation and or clay content from compressional and shear velocities testing of the model on laboratory data and a set of well logs from carnarvon basin australia shows good agreement between predictions and measurements this simple velocity porosity clay semi empirical model could be used for more reliable petrophysical interpretation of compressional and shear velocities obtained from well logs or surface seismic data

simulated degradation of lunar impact craters and a new method for age dating farside mare deposits with the advent of clementine data it is now possible to determine the lithology and extent of geologic materials on the moon particularly the farside mare deposits however traditional crater counting techniques do not provide reliable age estimates of these materials owing to their small surface areas to support such studies we present a model for estimating their age by analyzing the morphometry of degraded craters 1 3 km in diameter a photoclinometric model was adapted for use with monoscopic 0 750 m ultraviolet visible and high resolution images where we extracted the topography of fresh craters a two dimensional computer model simulating linear diffusional creep was applied to fresh craters at a variety of diameters the resulting profiles were then compared to photoclinometric profiles of degraded craters of known ages for calibration application of the resulting model to degraded craters in the mare deposit of the central apollo basin 36 5 latitude 208 0 longitude indicates that this material was emplaced during the early imbrian period 3 85 ga by calculating the amount of material eroded from each of the degraded craters observed in this unit the average erosion rate is estimated to be 2 0 0 1 10 7 mm yr on the moon since the imbrian the estimated amount of material eroded during any given period suggests that the erosion rate has decreased with time implying that the flux of larger impactors has as well

structural geology of impact craters abstract the formation of impact craters is a highly dynamic and complex process that subjects the impacted target rocks to numerous types of deformation mechanisms understanding and interpreting these styles of micro meso and macroscale deformation has proved itself challenging for the field of structural geology in this paper we give an overview of the structural inventory found in craters of all size ranges on earth and look into the structures of craters on other planetary bodies structural features are discussed here that are caused by i extremely high pressures and temperatures that occur during the initial passage of the shock wave through the target rock and projectile ii the resulting flow field in the target that excavates and ejects rock materials and iii the gravitationally induced modification of the crater cavity into the final crater form a special focus is put on the effects that low angle impacting bodies have on crater formation we hope that this review will help both planetary scientists and structural geologists understand the deformation processes and resulting structures generated by meteorite impact

water circulation and coastal trapping of brackish water in a tropical mangrove dominated bay in kenya water circulation patterns in a tropical mangrove fringed bay with seagrass and coral reef are driven by tides that generate strong reversing tidal currents the wind which has an onshore component generates a net clockwise rotating eddy the dominant tidally driven water circulation pattern coupled with the effects of onshore wind and alongshore current generated by wave breaking promotes the coastal trapping of turbid brackish water and its inherent nutrient content this brackish water inundates the mangrove swamp and seagrass beds but not the coral reef ecosystem weak stratification prevails during the wet season in the upper parts of kidogoweni creek as a result of freshwater influx from rivers in the dry season well mixed homogeneous water is found in most regions of the bay a small zone of hypersaline water salinity reaching 38 psu is found in the upper region of the mangrove dominated creeks during the dry season the connection between the mangrove swamp with its wide salinity variations and seagrass beds is apparently through river plumes and tidal effects the link between seagrass beds and coral reefs is mainly through tidal influences

labrador sea water in the eastern north atlantic part i a synoptic circulation inferred from a minimum in potential vorticity abstract a synoptic distribution of labrador sea water lsw in the eastern north atlantic is determined from a regularly sampled but sparse 3 resolution survey covering 39 to 54 n 11 to 34 w during spring 1991 the core of lsw can be defined by a minimum in potential vorticity pv using property values at this minimum the authors infer the circulation of lsw in addition using a known source function for salinities at the core of lsw estimates are able to be made of lsw vintages the authors then compared the synoptic circulation to historical data youngest 1986 vintage lsw crosses the mid atlantic ridge to the eastern basin between 48 and 51 n at 34 w this water then flows north to the iceland basin and eastward to the rockall trough where it was found to be of 1978 vintage tongues of low salinity low temperature and high oxygen extend southward on the eastern side of the mid atlantic ridge indicating that lsw also flows southward in the eastern basin at the southern edge of the s

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

dynamics of the turbidity maximum in king sound tropical western australia king sound is a 100 km long embayment located in tropical northwestern australia with a spring tidal range of 11 m this is the second largest tide in the world after the bay of fundy in canada intertidal areas cover about 800 km2 the upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m 3 field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998 the tide was a propagating wave shoaling and dissipating by friction as it entered the sound this mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb an evaporation driven salinity maximum zone was found in the upper reaches of the sound and this was also where the turbidity maximum occurred tidal pumping by the tidal asymmetry and possibly the biological filter formed by muddy marine snow trapped the fine sediment in the upper regions of king sound wind driven waves contributed significantly to entrainment of bottom fine sediment possibly through wave pumping of the sediment and not wave induced orbital velocities field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height

inverse estuarine features of the upper gulf of california the upper gulf of california is the shallow depth 30 m tidal area at the head of the gulf of california it is an inverse estuary due to the high evaporation rate e 1 1 m year 1 and almost nil freshwater input from rainfall and the colorado river historical and recent hydrographic data show that the area is almost vertically well mixed throughout the year that the horizontal distribution of properties follows the bathymetry and that the hydrography has a strong annual modulation as in other negative estuaries the year round salinity increase toward the head causes the density to do likewise despite the seasonally reversing temperature gradient the pressure gradient thus formed leads to water mass formation and gravity currents speed 0 1 ms 1 both in winter and in summer in winter the high salinity water sinks beyond 200 m while in summer it only reaches a depth of 20 30 m the gravity currents appear to be modulated by the fortnightly tidal cycle with events in neap tides this phenomenon causes the presence at least during neap tides of slight stratification t 0 2

field observations of hypersaline runoff through a shallow estuary abstract this study investigates a rare situation at the mond river estuary in the persian gulf in which the classical estuarine density gradient coincides with hypersaline runoff entering from saline soils upstream of the estuary after severe precipitation this builds a unique estuarine setting where two salt water masses one originating from the coastal ocean and the other being discharged from upstream confine a range of almost freshwater in the middle of estuary this freshwater lens estuary fle situation includes two saltwater sources with opposing senses of estuarine circulation therefore the tidal damping by the strong river flood can occur especially during neap tide when high unsteadiness number 0 04 signified ebb oriented condition which was induced by straining residual lateral circulation near the fle mouth transition from well mixed to weak strain induced periodic stratification regimes indicated the importance of the spring neap tidal variations close to the mouth a 13 66 day periodic tidal asymmetry from the triad k1 o1 m2 ebb dominance during spring tide and flood dominance in neap tide was overcome by higher harmonics

reconnaissance survey of the duolun ring structure in inner mongolia not an impact structure the duolun basin which is located in inner mongolia china has been proposed to be an impact structure with an apparent rim diameter of about 70 or even 170 km the designation as an impact structure was based on its nearly circular topography consisting of an annular moat that surrounds an inner hummocky region and the widespread occurrences of various igneous rocks polymict breccias and deformed crustal rocks critical shock metamorphic evidence is not available to support the impact hypothesis we conducted two independent reconnaissance field surveys to this area and studied the lithology both within and outside of the ring structure we collected samples from all lithologies that might contain evidence of shock metamorphism as suggested by their locations especially those sharing similar appearances with impact breccias suevites impact melt rocks and shatter cones field investigation together with thin section examination discovered that the suspected impact melt rocks are actually early cretaceous and late jurassic lava flows and pyroclastic deposits of rhyolitic to trachytic compositions and the interpreted impact glass is typical volcanic glass petrographic analyses of all the samples reveal no indications for shock metamorphic overprint all these lines of evidence suggest that the duolun basin was not formed through impact cratering the structural deformation and spatial distribution pattern of the igneous rocks suggest that the duolun basin is most likely a jurassic cretaceous complex rhyolite caldera system that has been partly filled with sediments forming an annular basin followed by resurgent doming of the central area

structure and circulation of the upper atlantic ocean northeast of the azores historical data primarily from the igy but spanning the years 1914 1983 have been re examined in an attempt to define the structure and circulation of the upper ocean 0 800 m in the eastern north atlantic 30 50 n 10 40 w the saline greater than 35 7 anticyclonic surface gyre shallows to the north like a wedge being 300 500 m deep at 36 n east of 30 w and outcropping at about 45 n it lies above the mediterranean water separated from it by a salinity minimum and by a pycnostad of subpolar mode water mccartney and talley 1982 eastward flow between 36 n and 46 n is primarily confined to the saline wedge with speeds of 2 4 cm s 1 the flow converges gradually towards the east resulting in fronts and strong meridional property gradients e g mixed layer depth robinson bauer and schroeder 1979 east of 15 w the majority of the supolar mode water is formed by deep winter convection north of the saline wedge and subducts to the south under it southward advection and ventilation rates in the northeast atlantic the main ventilation region for the north atlantic sarmiento rooth and roether 1982 are similar estimated to be 0 2 cm s 1 the freshening of the surface layer between 1967 and 1976 that has been found in widely separated regions of the north atlantic rockall trough sargasso sea labrador sea is also present northeast of the azores salinities down to 500 m have decreased by 0 1 equivalent to an addition of a 1 4 m column of fresh water at the surface the freshening on t 27 1 decreases to negligible values southwards of 40 n it is suggested that changes in the balance of evaporation and precipitation must have occured

wind and tidal influence on water circulation in a galician ria nw spain abstract the wind effect on water circulation was described by means of hydrodynamical and thermohaline measurements carried out in the ria of pontevedra nw spain from february to july 1998 the samples were measured both at an anchored station situated in the inner part of the ria and at other stations located in the main channel in this way temporal and spatial events were related thermohaline variables salinity and temperature were used to clarify the current patterns measured at the anchored station it has been observed that there is a clear predominance of wind in the main estuary axis direction the wind direction is strongly dependent on topography wind speeds higher than 4 ms 1 are able to dominate the current at surface layers even against tidal effect easterly winds force water to leave the estuary at surface layers while westerly winds force water to enter it diurnal breezes associated with westerly winds were rarely recorded bottom layers were controlled by tide except during an upwelling event

axial convergence in a well mixed estuary abstract transverse secondary circulations involving surface convergence observed in a well mixed estuary in north wales are made visible by the collection of surface material along an axial line which extends continuously for many kilometres through the estuary the circulation and axial convergence however are seen only during the flood phase of the tide and no similar behaviour has been observed during the ebb phase convergent circulations in the estuary are associated with small but steady transverse density gradients in the cross section produced by non uniform advection of the longitudinal gradient through the channel a diagnostic model using measured mean distributions of cross sectional density indicates surface transverse velocities 0 1 ms 1 similar to those observed in the estuary the model further predicts appreciable transverse divergent currents at a fractional depth of 0 75 a prediction which has been tested in the estuary using a vertical array of accurately resolving current direction indicators

foredunes and blowouts initiation geomorphology and dynamics this paper reviews the initiation dynamics geomorphology and evolution of incipient foredunes established foredunes and blowouts incipient foredunes may be initiated in a variety of ways leading to the formation of ramps terraces or ridges depending on progradation rates vegetation type and cover sediment transport rates and scale of erosional processes vegetation cover morphology growth rates and types combine with aerodynamic processes to determine dune and swale morphology established foredunes are classified into five morpho ecological types and the flow behaviour over two types is detailed a new model of foredune evolutionary paths at various possible time scales is presented blowout initiation dynamics and sediment transport and evolution is examined throughout the review the gaps in present understanding of dune processes and a range of ideas for new research possibilities are provided

pore pressure estimation in reservoir rocks from seismic reflection data a method is used to obtain pore pressure in shaly sandstones based upon an acoustic model for seismic velocity versus clay content and effective pressure calibration of the model requires log data porosity clay content and sonic velocities to obtain the dry rock moduli and the effective stress coefficients as a function of depth and pore pressure the seismic p wave velocity derived from reflection tomography is fitted to the theoretical velocity by using pore pressure as the fitting parameter this approach based on a rock physics model is an improvement over existing pore pressure prediction methods which mainly rely on empirical relations between velocity and pressure the method is applied to the tune field in the viking graben sedimentary basin of the north sea we have obtained a high resolution velocity map that reveals the sensitivity to pore pressure and fluid saturation in the tarbert reservoir the velocity map of the tarbert reservoir and the inverted pressure distribution agree with the structural features of the tarbert formation and its known pressure compartments

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

climate and anthropogenic factors influencing an estuarine ecosystem from nw iberia new high resolution multiproxy analyses from san simon bay ria de vigo abstract two sedimentary sequences coastal and subtidal were studied in san simon bay ria de vigo situated on the atlantic coast of nw iberia the coastal record is a shallowing upward sequence which evidences a locally developed low marsh situated below the current beach and dated at the second half of the 4th century during the following decades this low marsh was progressively replaced by an alder swamp which formed on it this suggests an apparent stabilisation or slow down of the relative sea level rsl in this site at the beginning of the dark ages da the subtidal sequence studied reflects the main changes in the landscape the hydrological conditions climate and rsl affecting this part of nw iberia during the last 1250 years evidence of changing dinocysts content in the sediment reveals that two centennial or decadal scale episodes existed of shelf marine waters more intensely penetrating inside the bay between the 15th 18th centuries and at ca 1800 1930 ad besides we related different proxies with the occurrence of four main climatic stages namely the previously described dark ages da ca 350 750 ad the mediaeval climatic anomaly mca ca 750 1100 ad and the little ice age lia ca 1500 1930 ad in addition we propose a regional mca lia transition ca 1100 1500 ad that it has not been previously described our environmental characterization indicates a persistent north atlantic oscillation nao negative mode domain in ria de vigo during the mca but this became weaker during the lia and probably also during the earlier da nao mode become more irregular during the mca lia transition generally persisting in dominant negative mode except for a phase of minor upwelling intensification at ca 1150 1350 ad which mainly affected the external parts of the ria we postulate that an almost simultaneous phase ca 1100 1350 ad of stronger continental contribution in the sediments may be related to increasing storm intensities probably linked to a reinforcement of the easter atlantic ea pattern and also that the intertidal supratidal ecosystems inside san simon bay may have extended further in the past at least towards the end of the 5th century and between ca 1050 1350 ad and ca 1450 1750 ad a number of local historical references are consistent with our palaeoecological data and so support the chronology proposed as well as many of the environmental changes reconstructed this good agreement will help in the interpretation of other analogous sequences extending back in time

wind driven upwelling in the vicinity of cape finisterre spain observations and numerical simulations of upwelling along the galician coast of spain during april 1982 are presented in situ measurements include shipboard determinations of hydrographic and biological parameters from a grid of stations covering the continental shelf from cape finisterre to ria de vigo sea level data from vigo and la coruna and wind stress estimates derived from the ship winds and from surface pressure charts sea surface temperature information and pigment concentration information have been obtained from a sequence of satellite images from the noaa 7 advanced very high resolution radiometer and the nimbus 7 coastal zone color scanner respectively since the cape finisterre sector of the iberian peninsula is characterized by an abrupt change in coastline orientation wind driven upwelling can occur in that region over a 270 range of wind direction these data document the evolution of upwelling and the resultant coastal circulation in response to two wind events that occurred over a 10 day period salient features of the circulation include a southward coastal jet and a northward flow further offshore along the western coast numerical simulations of the coastal currents the vertical excursion of a density interface from a static equilibrium position and coastal sea level are conducted using a wind patch characterized by constant direction and negative curl the simulations show that during these wind events the greatest upwelling will occur either at cape finisterre or along the northern coast as was observed in this case and as has been reported by others it is suggested on the basis of the analysis of the sea level records and on the numerical simulations that wave disturbances propagate northward along the coast at a speed of 120 160 km day finally it is speculated that much of the organic material formed during upwelling events north of the cape finisterre is advected out to sea northwest of the cape

a prominent colour front in false bay south africa cross frontal structure composition and origin abstract colour fronts are a frequent occurrence in false bay south africa and their occurrence has been the subject of previous study and anecdotal conjecture the opportunity arose to make a cross frontal study of this feature in november 2005 photographs were taken and subsequently satellite imagery was obtained measurements were made of temperature salinity turbidity dissolved oxygen suspended solids plant nutrients and chlorophyll a cross frontal comparisons were also made on particulate material using a scanning electron microscope sem and elemental dispersive x ray edx analysis frontal waters were milky white green in colour in stark contrast to the adjacent clearer green blue waters the milky white green water mw gw was found to be warmer apparently less saline more turbid richer in nitrate and silicate and had a higher chlorophyll a concentration the dissolved oxygen signal was less pronounced both water types being supersaturated paradoxically in spite of the higher turbidity in the mw gw both water types had similar weights of suspended solids although the mw gw material was found to be more abundant and fragmentary when compared with its green blue water g bw counterpart the mw gw was rich in calcium whereas the g bw was silicon enriched the central findings of this study are that the strong southerly onshore wind conditions prior to mw gw formation introduced calcium rich fine particulates into the waters of the surf zone the sources of these particulates are thought to be the sea bed sediments and the sea land interface the particulates are close to neutral buoyancy enabling the mw gw to persist over the time scale of days a mechanism reinforced by the warming of this water in the nearshore zone the water was then advected by wind forcing and subsequently its own inertia around the north west corner of false bay at which stage it was easily observed and sampled it is suggested that the eventual collapse of the front was due to the slowing down of inertial movement in combination with the passive sinking of fine particulates and evaporative cooling resulting in downward convection

the carancas meteorite impact crater peru geologic surveying and modeling of crater formation and atmospheric passage the recent carancas meteorite impact event caused a worldwide sensation an h4 5 chondrite struck the earth south of lake titicaca in peru on september 15 2007 and formed a crater 14 2 m across it is the smallest youngest and one of two eye witnessed impact crater events on earth the impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight the small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters the carancas cratering event however demonstrates that meter sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances we present results of a detailed geologic survey of the crater and its ejecta to constrain the possible range of impact parameters we carried out numerical models of crater formation with the isale hydrocode in two and three dimensions depending on the strength properties of the target the impact energies range between approximately 100 1000 mj 0 024 0 24 t tnt by modeling the atmospheric traverse we demonstrate that low cosmic velocities 12 1 4 kms 1 and shallow entry angles 20 are prerequisites to keep aerodynamic stresses low 10 mpa and thus to prevent fragmentation of stony meteoroids with standard strength properties this scenario results in a strong meteoroid deceleration a deflection of the trajectory to a steeper impact angle 40 60 and an impact velocity of 350 600 ms 1 which is insufficient to produce a shock wave and significant shock effects in target minerals aerodynamic and crater modeling are consistent with field data and our microscopic inspection however these data are in conflict with trajectories inferred from the analysis of infrasound signals

evolution of seismic interpretation during the last three decades the ingredients of seismic interpretation include the right mix of geological and geophysical knowledge together with a liberal dose of imagination tempered with a considerable amount of patience seismic interpretation is a skill that one acquires with experience but is constantly reinvigorated with new ideas and tools provided by younger university graduates the prime ingredients for seismic interpretation are seismic reflection data coupled with a geologic depositional and tectonic model which together provide the framework for integrating borehole microseismic and production data resulting in a good reservoir model although commonly used in both engineering and environmental applications most seismic reflection surveys are acquired for oil and gas exploration in both land and offshore areas around the world hydrocarbon accumulations are found at varying depths of a few thousand meters below the earth s surface which are ultimately confirmed by drilling because the cost of drilling closely sp

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

an isopycnic model study of the north atlantic part ii interdecadal variability of the subtropical gyre abstract in a companion paper a spinup integration of the north atlantic ocean with the miami isopycnic coordinate model was presented the wintertime mixed layer in the central north atlantic was subject to relatively little change in salinity or depth but cooled markedly most probably because of heat loss associated with a partial surface relaxation to climatological sea surface temperatures in a region in which the gulf stream was too far to the north this mixed layer cooling caused the isopycnic layers in the model ventilated subtropical gyre to rise and surprisingly to warm while the experiment was not an attempt to simulate changes in the real atlantic ocean it nevertheless appears from observations that in recent decades the mixed layer in nature has undergone a change similar to that exhibited by the model mixed layer since it is expected that changes in the ventilated subtropical gyre will be governed largely by changes in the mixed layer in the central north atlantic from where the ve

hailar crater a possible impact structure in inner mongolia china abstract hailar crater a probable impact structure is a circular depression about 300 m diameter in inner mongolia northeast china with broad elevated rims the present rim to floor depth is 8 20 m regional geological background and geomorphological comparison suggest that this feature is likely not formed by surface processes such as salt diapir karst aeolian glacial or volcanic activity its unique occurrence in this region and well preserved morphology are most consistent with it being a cenozoic impact crater two field expeditions in 2016 and 2017 investigated the origin of this structure recognizing that 1 no additional craters were identified around hailar crater in the centimeter scale digital topography models that were constructed using a drone imaging system and stereo photogrammetry 2 no bedrock exposures are visible within or adjacent to the crater because of thick regolith coverage and only small pieces of angular unconsolidated rocks are present on the crater wall and the gently sloped crater rim suggesting recent energetic formation of the crater 3 most samples collected from the crater have identical lithology and petrographic characteristics with the background terrain but some crater samples contain more abundant clasts and silicate hydrothermal veins indicating that rocks from depths have been exposed by the crater 4 no shock metamorphic features were found in the samples after thin section examinations and 5 a systematic sample survey and iron detector scan within and outside of the crater found no iron rich meteorites larger than 2 cm in size in a depth of 30 cm although no conclusive evidence for an impact origin is found yet hailar crater was most likely formed by an impact based on its unique occurrence and comparative geomorphologic study we suggest that drilling in the crater center is required to verify the impact origin where hypothesized melt bearing impactites may be encountered

a new velocity model for clay sand mixtu res1 none of the standard porosity velocity models e g the time average equation raymer s equations is satisfactory for interpreting well logging data over a broad depth range clays in the section are the usual source of the difficulty through the bias and scatter that they introduce into the relationship between porosity and p wave transit time because clays are composed of fine sheet like particles they normally form pores with much smaller aspect ratios than those associated with sand grains this difference in pore geometry provides the key to obtaining more consistent resistivity and sonic log interpretations a velocity model for clay sand mixtures has been developed in terms of the kuster and toksoz effective medium and gassmann theories in this model the total pore space is assumed to consist of two parts 1 pores associated with sand grains and 2 pores associated with clays including bound water the essential feature of the model is the assumption that the geometry of pores associated with sand grains is significantly different from that associated with clays because of this porosity in shales affects elastic compliance differently from porosity in sand stones the predictive power of the model is demonstrated by the agreement between its predictions and laboratory measurements and by its ability to predict sonic logs from other logs over large depth intervals where formations vary from unconsolidated to consolidated sandstones and shales

modulus decomposition of compressional and shear velocities in sand bodies the advent of borehole shear slowness measurements in sonically slow formations has lead to breakthroughs in the subsurface profiling of geological bodies in sand bodies compressional and shear velocities depend predictably on porosity mineralogy grain contacts and fluid saturation an interpretation is best performed by decomposing the velocities into moduli that are intrinsic measures of the rock frame and pore fluid compressibilities careful experiments on pure materials i e pure quartz sandstones demonstrate two simplifying constitutive relationships first the bulk and shear frame moduli are simple functions of the porosity a comparison of the measured shear frame modulus to the prediction for the pure material distinguishes sand from shale second the ratio of the bulk and shear frame moduli is a constant 0 9 independent of the porosity the measured velocities are directly inverted to yield the bulk modulus of the pore fluid the fluid saturation effects are so dramatic at high porosit

the number of impact craters on earth any room for further discoveries abstract only 128 impact craters exposed at earth s surface have been found so far while new craters are discovered occasionally taking into account the permanent consumption of craters by erosion we present the first estimate on the number of impact craters that should be present at earth s surface our study yields no evidence for any systematic incompleteness in the available inventory of the craters larger than about 6 km in diameter exposed at the surface in contrast more than 90 craters in the diameter range from 1 km to 6 km should still be waiting to be discovered and even more than 250 between 0 25 km and 1 km diameter the transition from a probably complete inventory above 6 km to a strongly incomplete record at smaller sizes may be related to the difference between simple and complex craters beyond these results on the terrestrial crater record our findings tentatively suggest that erosion rates on the 10 to 100 million year scale may be closer to present day erosion rates than previously assumed

oceanic ventilation in the eastern north atlantic abstract ventilation of the eastern north atlantic by subpolar mode water is illustrated by recent hydrographic section and analyzed using a large scale stationary thermocline model including a surface mixed layer the distributions of potential vorticity along the hydrographic lines and the geostrophic transports across them confirm the circulation pattern of the mode water that was previously deduced from older data that is arrival from the west at intergyre latitudes and southward subduction of the lightest part at about 42 n the model approach emphasizes the large scale advective thermodynarnic equilibrium which controls the shape of the thick 500 m winter mixed layer observed in the eastern basin following recent theories the process of ventilation is interpreted in terms of exchanges between the mixed layer and the stratified thermocline mode water is formed where thermocline water is entrained into a thick mixed layer and is subducted where mixed layer water is injected into the thermocli

wind influence on water exchange between the ria of ferrol nw spain and the shelf abstract the wind induced water exchange between the ria of ferrol nw spain and the adjacent shelf is analyzed by means of a three dimensional hydrodynamic model mohid2000 since thermohaline measurements indicate that the estuary can be considered vertically homogeneous a barotropic version of the model has been used real in situ wind measurements have been used for model calibration and further analysis the approach to study the wind effect on water exchange through the ria strait consisted in subtracting the signal calculated with only tidal forcing t s from the one with wind and tidal forcing wt s this shows the existence of a residual circulation with water flowing in wind direction along surfaces layers and a counter current flowing in the opposite direction at bottom layers the flux across the strait of ferrol has shown to increase linearly on wind strength with a correlation larger than 96 and reaching values close to 20 m 3 s 1 under real wind forcing

on a possible parent crater for australasian tektites geochemical isotopic geographical and other constraints abstract tektites are natural glasses formed by the melting of earth s surface materials during the impact of a large extraterrestrial body at present they are found in four main strewn fields associated with separate impacts central european moldavites australasian australites indochinites philippinites javaites etc north american georgiaites and bediasites and west african tektites from the ivory coast ivorites the location of the impact site and parent crater for australasian tektites aat has remained an unanswered question for decades the current review discusses possible locations of the aat parent crater on the basis of published geochemical mineralogical petrographic and isotopic data on both aat and potential source materials this was aided by new geochemical data for a representative set of aat covering the main morphological types and parts of the aat strewn field and also assumes some ballistic palaeogeographic palaeoclimatic and palaeoecological constraints the review focuses particularly on three parallel tasks 1 collecting comprehensive data geochemical composition sr nd rb li and b isotopes and cosmogenic 10 be for revisiting chinese loess or its precursors as the most suitable source materials for aat 2 criticisms of the generally accepted location of the impact in southeast asia indochina based mainly on a lack of suitable targets and a mismatch between the geochemical and isotopic compositions of aat and prevailing sedimentary targets in indochina 3 supporting evidence in addition to 1 for a hypothesis locating the aat parent crater to the arid area of northwest china which could provide a sufficient supply of suitable source materials as well as ideal conditions for burial of the crater under the tallest megadunes on earth

water and suspended sediment division at a stratified tidal junction 1 tidal junctions play a crucial role in the transport of water salt and sediment through a delta distributary network water salt and sediment are exchanged at tidal junctions thereby influencing the transports in the connecting branches and the overall dynamics of the system this paper presents observations of water salt and sediment transports in three channels that connect at a stratified tidal junction flow variation in one channel was found to lag behind flow variation in a connected channel by more than 1 h which is largely attributed to channel length differences from the junction to the sea the water columns in the three channels were periodically stratified during spring tide whereas the salinity structure represented a salt wedge during neap tide salinity differences between the three channels were substantial the channels contain water bodies of different salinity and act largely independently flow velocities in the upper and lower layers differed substantially flow in the lower layer was generally in the direction of acceleration produced by the baroclinic pressure gradient interestingly baroclinic pressure gradients were sometimes directed landward indicating the presence of saltier water at the land side of the estuary in sharp channel bends close to the junction secondary flow was strongest at the highest axial flow velocity during spring tide in one channel bend these circulations steered the suspended sediment toward the inner bend which affected the suspended sediment division

assessing preferential seepage and monitoring mortar injection through an earthen dam settled over a gypsiferous substrate using combined geophysical methods abstract for several decades the sant llorenc de montgai reservoir has experienced different problems that could affect the safety of the engineering structure for this reason several corrective actions have been taken over the years here we present a study involving complementary geophysical methods including electrical resistivity tomography seismic refraction tomography and frequency domain electromagnetic surveys the analysis of the inverted electrical resistivity tomography cross sections combined with the seismic refraction results and land subsidence monitoring data show the likely mechanism of abnormal seepage the areas where mortar injections were applied as a corrective measure are also clearly delineated in addition the evolution of the state of the embankment has been established from two successive electrical resistivity tomography surveys in the last two decades the results show areas where corrective mortar injections have been effective while in other areas new abnormal seepage has been detected the lithological heterogeneity of the bedrock especially the dissolution of gypsum rich rocks induced subsidence effects and caused abnormal seepage in different areas along the embankment our results indicate how corrective solutions can be optimized to reduce the cost of corrective engineering interventions

a finite difference injection approach to modeling seismic fluid flow monitoring a highly efficient and accurate tool for predicting the seismic response of reservoir fluid flow has been developed which integrates the finite difference injection method with a reservoir simulator and a petrophysical model finite difference methods allow for the full response to be synthesized as the wavefield interacts with a seismic model this includes wave propagation in arbitrary heterogeneous anisotropic and anelastic media scattering and mode conversions the finite difference injection method in turn can be used to efficiently synthesize the seismic response from models after local alterations to the model thus it is ideally suited for time lapse seismic studies the modeling methodology is demonstrated on a case study from the gullfaks field in the north sea six complete marine seismic surveys over the reservoir at different stages during waterflood oil production were synthesized a total of 180 shot gathers were synthesized with computational savings of a factor of 54 after one single

an unusual two layered tidal circulation induced by stratification and wind in the ria of pontevedra nw spain abstract a two layered tidal circulation pattern has been observed in the ria of pontevedra at an anchored station 24 m deep located at 42 3917 n and 8 7380 w during a tidal cycle water leaves the estuary continuously through surface layers till 8 12 m depth and enters the estuary through bottom layers this unusual pattern in a partially mixed estuary is observed to depend on the particular summer stratification conditions and on the presence of easterly winds inside the estuary the vertical stratification is generated by solar heating and favourable upwelling conditions on the adjacent shelf which reinforces the estuarine positive circulation and provokes the inflow of typical upwelling water enaw through bottom layers on the other hand the easterly winds inside the estuary are strong enough around 8 m s 1 to force the surface water to move even against tide this situation is compared to two typical patterns observed in the estuary a winter situation where wind drives the surface water against tidal forcing and a spring situation where the water column follows the tidal pattern in both cases bottom layers are hardly influenced by wind forcing

density driven secondary circulation in a tropical mangrove estuary abstract observations of suspended sediment concentration ssc salinity and current were made in the normanby river estuary cape york peninsula northern australia the estuarine reaches are approximately 80 km in length and are fringed by mangroves a well developed axial convergence was found to exist almost unbroken for a distance of at least 30 km on flood tides clearly delineated by an accumulation of mangrove leaves and seed pods on the water surface the convergence migrated to the inside of most bends suspended sediment concentration profiles were very well mixed both vertically and laterally salinity profiles showed a cross channel salinity gradient of 0 2 25 m sufficient to form density driven secondary cells the cells produce an effective transverse mixing coefficient of 0 25 m 2 s 1 of the same order of magnitude as the conventional transverse diffusion coefficients for natural meandering channels mangrove seeds were present in the channel centre during flood tides and were moved to the channel banks during ebb tides due to the lateral shear in longitudinal currents mangrove seeds are predicted to move landward up the estuary at a rate of 1 km per day when density driven circulation cells are active influencing mangrove seed dispersal

hypersalinity flushing and transient salt wedges in a tidal gulf an inverse estuary abstract because of high evaporation and low rainfall gulfs and embayments in the arid coastal regions of australia are endowed with highly saline water masses with salinities ranging from oceanic values at their mouths to values as high as 60 at their heads this presents the case of an inverse estuary in gulf st vincent of south australia an example of such an inverse estuary the salinity at the head ranges from 39 in winter to 42 in summer in sympathy with the seasonal changes of the local excess of evaporation over precipitation the salient characteristics of temperature salinity and density distributions in the gulf are here described despite a seasonal reversal of spatial temperature gradients the salinity gradient maintains the same sign and is strong enough to control a persistent density gradient from mouth to head in parallel with the case of estuaries a flushing time for salt is defined and estimated for the northern regions of the gulf although the water mass was initially assumed to be vertically well mixed because of tidally induced turbulence the present observations reveal the striking feature that at neap tides the horizontal density gradient forces a salt wedge from the north below the fresher water in the south

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

labrador sea water in the eastern north atlantic part ii mixing dynamics and the advective diffusive balance abstract deep wintertime convection in the labrador basin produces labrador sea water lsw which spreads throughout the north atlantic the lsw is not formed with constant characteristics but varies on decadal timescale these changes in the source of lsw propagate throughout the north atlantic having a dramatic impact on middepth properties in regions far removed from the labrador basin here by means of a property variance correlation analysis on isopycnal surfaces through the core of lsw the authors show that the boundary anomalies of lsw survive the effects of mixing over the length and timescales taken for lsw to reach the eastern north atlantic typically the anomaly amplitude is reduced by a factor of 5 during transit and from a simple estimate the integrated timescale for this reduction is seven years uncertainties in the oxygen anomaly analysis exclude specific interpretation but constrain the boundary condition variability to about 5 the lateral effect of unresolved processes resembl

an evaporation driven salinity maximum zone in australian tropical estuaries abstract the distribution of temperature and salinity in three tropical australian estuaries was measured in october 1983 in the hot dry season as a result of evaporation a salinity maximum zone exists near the mouth of the river where downwelling occurs and a classical and an inverse internal estuarine circulation prevail respectively upstream and downstream of the salinity maximum zone the zone of salinity maximum can be thought of as a high salinity plug inhibiting so much the mixing of estuarine and ocean waters that in some cases freshwater dose not reach the ocean

effects of pore aspect ratios on velocity prediction from well log data we develop a semi empirical model which combines the theoretical model of xu and white and the empirical formula of han nur and morgan in sand clay environments this new model may be used for petrophysical interpretation of p and s wave velocities in particular we are able to obtain an independent estimation of aspect ratios based on log data and seismic velocity and also the relationship between velocities and other reservoir parameters e g porosity and clay content thus providing a prediction of shear wave velocity to achieve this we first use kuster and toksoz s theory to derive bulk and shear moduli in a sand clay mixture secondly xu and white s model is combined with an artificial neural network to invert the depth dependent variation of pore aspect ratios finally these aspect ratio results are linked to the empirical formula of han nur and morgan using a multiple regression algorithm for petrophysical interpretation tests on field data from a north sea reservoir show that this semi empirical model provides simple but satisfactory results for the prediction of shear wave velocities and the estimation of reservoir parameters

vivaldi 1991 a study of the formation circulation and ventilation of eastern north atlantic central water abstract a synoptic hydrographic data set comprising 32 full depth ctd casts and 2500 ctd seasoar profiles to 500 m is used to describe the s properties and circulation of central water east of the mid atlantic ridge and between 39 n and 54 n eastward transport of 20 10 6 m 3 s 1 in the north atlantic current turns entirely northwards to the west of 54 n 20 w this transport consists in the upper layers of western north atlantic water freshened at temperatures below 10 c by mixing with subarctic intermediate water northern and southern branches of the north atlantic current are well defined and both turn northwards west of 20 w a further 10 10 6 m 3 s 1 of eastern north atlantic water forms and recirculates anticyclonically to the west of spain south of the north atlantic current and north of 40 n eastern north atlantic water is most weakly stratified east of 20 w and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to western north atlantic water thus eastern north atlantic water is a winter mode water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature near the southern entrance to the rockall trough there is evidence that salinities are also increased by mediterranean water influence circulation south of the north atlantic current is complex there is no evidence for direct ventilation southwards across 40 n where water properties s potential vorticity and cfc 113 and historical data all indicate westward ventilation east of 24 w with weak southward ventilation occurring further west in the vicinity of the azores the circulation pattern suggested is remarkably similar to that proposed by helland hansen and nansen in 1926 the eastern north atlantic geophysiske publicajoner 4 1 76 with anticyclonic circulation of colder eastern north atlantic water north of 40 n meeting warmer water from south of 40 n circulating cyclonically north of the azores current the distribution of pycnostads and s properties between 20 w and 35 w north of the azores indicates alternate bands of western and eastern north atlantic water moving eastward and westward respectively including evidence for westward motion immediately south of the southern branch of the north atlantic current possibly by westward propagation of anticyclonic eddies containing deep pycnostads

evidence of dynamics reversal in tropical estuaries geomorphological and sedimentological consequences salum and casamance rivers senegal south dakar senegambian estuaries are subject to an unusual hydrodynamical regime caused by weak or absent run off in the salum delta each distributary lacks fresh water during most of the year only the tidal flows arc responsible for geomorphological and sedimentological effects the current distribution shows a net discharge upstream due to the extensive evaporation and evapotranspiration in mangrove swamps and tidal flats consequently the salinity is always higher towards the river than near the sea a high salinity bottom layer suggests the occurrence of a supersaline wedge of reverse sense to the salt wedge of a normal estuary such an inverse pattern is similarly displayed by sedimentological features double upstream tumed spits and by the external location of the turbidity maximum a coherent reverse estuary model is suggested from our field observations

an inshore poleward current in the nw of the iberian peninsula detected from satellite images and its relation withg catenatum and d acuminata blooms in the galician rias abstract toxic gymnodinium catenatum blooms usually occur in the galician rias at the end of the upwelling season which necessitates a ban on harvesting shellfish extraction with subsequent economic losses for this sector one of the possible causes cited in the literature is the advection of populations from outside the area but no evidence was available to substantiate this oceanographic conditions at the end of the upwelling season in the nw coast of the iberian peninsula 39 43 n have been studied for the years 1986 1990 1995 and 1998 sea surface temperature data from satellite images wind data drifter tracks and in situ oceanic data from the galician rias have been combined to clarify the oceanographic structures in the area at the commencement of the blooms on the inner shelf an inshore poleward current advecting warm water has been identified after the cessation of upwelling on the middle and outer shelf a tongue of cold water as a remnant of the previous upwelling continued to move southward on the slope and offshore the poleward counter current reported by several authors was detected carrying warm oceanic water northwards it is suggested that the inshore poleward current not previously reported in the literature could advect initial populations of dinoflagellates to the rias from northern portuguese waters this would explain why blooms such as g catenatum have been found usually in portuguese waters several weeks before the galician rias showing an apparent northward movement but cells of this toxic dinoflagellate species have not been found in waters of the offshore poleward counter current

observational evidence of winter spice injection abstract temperature and salinity t s profiles from the global array of argo floats support the existence of spice formation regions in the subtropics of each ocean basin where large destabilizing vertical salinity gradients coincide with weak stratification in winter in these characteristic regions convective boundary layer mixing generates a strongly density compensated sdc layer at the base of the well mixed layer the degree of density compensation of the t s gradients of an upper ocean water column is quantified using a bulk vertical turner angle tub between the surface and upper pycnocline the winter generation of the sdc layer in spice formation zones is clearly seen in argo data as a large amplitude seasonal cycle of tub in regions of the subtropical oceans characterized by high mean tub in formation regions argo floats provide ample evidence of large abrupt spice injection t s increase on subducted isopycnals due to vertical mixing associated with the winter increase in tub a simp

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

fluid substitution in shaley sediment using effective porosity the traditional method of fluid substitution in porous rock requires the total porosity and the elastic modulus of the mineral phase as input and assumes that the fluid reaches instantaneous hydraulic equilibrium throughout the pore space this assumption may not be appropriate for shaley sediment because of the low permeability of shale and the resulting immobility of the water in it to address this problem we propose an alternative method that uses effective porosity instead of total porosity effective porosity is lower than total porosity if porous shale is present in the system a new composite mineral phase is introduced which includes the porous water saturated shale together with the nonporous minerals and whose elastic modulus is an average of those of its components including the porous shale this alternative method increases the sensitivity of the elastic properties of sediment to pore fluid changes and therefore may be used as a physics based theoretical tool to better explain and interpret seismic data during exploration as well as variations in seismic response as hydrocarbon production progresses

the werra cyclotheme upper permian fore sudetic monocline poland insights into fluctuations of the sedimentary environment from organic geochemical studies abstract a study of the extracts of samples recording a transgressive regressive succession of the werra cyclothem zechstein upper permian from the southern margin of the european permian basin the fore sudetic monocline poland provides an insight into major sources of organic matter and diagenetic processes the studied cross section comprises all lithologies representative for the european basin including transgressive sandstones weissliegend and organic rich shales kupferschiefer followed by carbonates as well as regressive anhydrites with intercalations of rock salt due to the variable influence of overlapping diagenetic processes that affected the organic matter i e maturation and late diagenetic oxidation related to base metal mineralisation a reliable comparison of the biomarker results is only possible for the major upper part of the section ca 38 m including carbonates and evaporites but not for the oxidised first 2 3 m from the base of the kupferschiefer the transition from carbonate to evaporate sedimentation is associated with a shift to predominant even c numbered n alkanes increased abundance of carotanes and high homohopane index reflecting enhanced reducing conditions the presence of the c25 regular isoprenoid squalane biphytane and the rapid decrease in the pristane phytane ratio in the evaporites are mainly controlled by the important contribution from both halophilic and methanogenic archaea the occurrence of gammacerane in the anhydrites suggests development of water column stratification at some stages of the sea regression this is associated with appearance of specific aryl isoprenoids with a lycopane carbon skeleton most likely related to botrycoccus braunii race l algae lycopane derivative occurrence suggests that such an algal race could have occurred since permian currently known recent eocene the presence of the abundant freshwater brackish algal biomarkers in evaporititic deposits can be envisaged in the costal part of the zechstein basin with temporary salt wedge estuary water stratification the algae bloomed in the top fertile fresh brackish water layer fed by rivers and the algal biomass was deposited on the sea floor covered with evaporitic brine the stratification periodically broke down during precipitation of the rock salt presumably due to a decrease in riverine water input as revealed by characteristic disappearance of gammacerane and hopane distributions similar to those observed for the carbonate rocks the methylphenanthrenes phenanthrene ratio was used together with methyldibenzothiophenes dibenzothiophene ratio to assess maturity these maturity estimations indicate that the peak of oil window has been reached which is confirmed by other biomarker maturity parameters based on sterane and hopane distributions the maturity stage of oil generation and expulsion was further confirmed by the presence of solid bitumen as cements in the sandstone underlying kupferschiefer and bitumen veins and lenses in the carbonates

hydrographic conditions associated with the relaxation of an upwelling event off the galician coast nw spain during the galicia xi cruise froin may 10 to may 14 1991 the relaxation of a previous strong tipwelling event took place along the galician coast caused by a shift in the position of the azores high the coldest tenperatures and highest nitrate levels were forrod near the coast corresponding to the advection of subsurface waters particularly of eastern north atlantic water enaw on the basis of thermohaline properties enaw of polar enawp and tropical enawt origin are distinguished the highest salinity values found correspond to a saline wedge of enaw t located off the west coast of galicia the relaxation of tipwelling produced a shoreward migration of surface water from oceanic stations which crone into contact with upwelled eastern north atlantic water ti mn the coastal stations to tbrm a convergence front 28 lan off the coast meanwhile the saline wedge displaced towards both the north and the shore which is thvored by the compression of the tipwelling system to a narrow coastal strip outwardly limited by the convergence zone

optimal trace selection for ava processing of shale sand reservoirs when processing data a principal aim is to maximize information inferred from a data set by minimizing the expected postprocessing uncertainties on parameters of interest nonlinearstatisticalexperimentaldesignsedmethodscan be used to find optimal trace profiles for processing amplitude variation with angle ava surveys that account for all prior petrophysical information about the target reservoir optimalselectionschangeaspriorknowledgeofrockparameters and reservoir fluid content changes and which of the prior parameters have the greatest effect on selected traces canbeassessed theresultsshowthatoptimalprofilesarefar more sensitive to prior information about reservoir porosity than to information about saturating fluid properties by applying ray tracing methods ava results can be used to design optimal processing profiles from seismic data sets for multiple targets each with different prior model uncertainties

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

the subpolar mode water of the north atlantic ocean abstract the warm waters of the subtropical and subpolar basins of the north atlantic have tight regional temperature salinity relationships and are conventionally called the regional central waters a volumetric census of the temperature salinity characteristics of the north atlantic by wright and worthington 1970 shows that waters characterized by certain segments of the t s relationships have large volumes compared to those of other segments volumetric mode waters such mode waters appear as layers with increased vertical separation between isopycnals pycnostads the present study reports on the existence of pycnostads in the central and eastern north atlantic these subpolar mode waters are formed by deep winter convection in the subpolar north atlantic and participate in the upper water circulation of the northern north atlantic the seasonal outcropping of the pycnostads occurs within and adjacent to the north atlantic current the irminger current the east and west greenland currents and

the water masses of the central north atlantic in 1983 84 abstract hydrographic surveys carried out in 1983 84 along both sides of the mid atlantic ridge between 24 and 53 n provide a detailed description of the well known north atlantic water masses with particular emphasis on their meridional distribution and zonal dissymetry in the upper layers the dense horizontal sampling resolves the several narrow gulf stream extensions into the ocean interior giving the image in the central water density range of a mosaic of mode waters separated by fronts at intermediate depths a vertical shear in the distributions of the mediterranean water and labrador sea water stands out both water masses having their lower part displaced southwards relative to their upper parts bottom waters containing nearly 20 percent of pure antarctic bottom water are observed at 50 n in the eastern basin in contrast with the western basin where proportions greater than 10 percent were found only south of 36 n along our section this water mass analysis also gives indications that stron

estimates of yet to find impact crater population on earth abstract one hundred and seventy six craters on earth are currently accepted as resulting from bolide impact this list is growing at a rate of approximately two craters per year because of new discoveries and revised interpretations here we take the subset of craters most relevant to sedimentary basin exploration and utilization phanerozoic kilometre scale craters and tackle the question of how many remain to be found in phanerozoic strata on earth a surprising range in predictions of crater numbers is obtained from published crater population functions reaching two orders of magnitude variation for craters in the range 1 5 km diameter this range in predictions is largely due to variations in treatment of impactor breakup in the atmosphere also required is quantification of the total area and timespan of phanerozoic sediment currently preserved on earth an estimate of 8 87 10 15 km 2 a is derived here together with a relatively conservative crater population function this yields a prediction of 845 craters subtracting the 131 known phanerozoic craters larger than 1 km leaves a predicted population yet to find of 714 of which 228 are larger than 2 5 km uncertainties subsets of this population and spatial distribution are also considered

ultrasonic velocities in sands revisited ultrasonic compressional and shear wave velocities of isotropic sands are shown to be dependent on their mineralogy their porosity their fluid content and their state of consolidation under fixed temperature and pressure conditions this leads to a distinction between two broad classes of sands those that are well consolidated and those that are loosely consolidated changes in elastic velocities reflect changes in the ratio of bulk and shear moduli to density in response to lithologic variations we decouple the two effects by examining changes in elastic moduli with respect to changes in lithology and we observe three main points 1 for consolidated sandstones the effects of mineralogy and porosity can be approximated both empirically and theoretically by a modified isostrain theory the dry bulk and shear moduli of the rock aggregate follow a mixing law being linear combinations of the respective moduli of the individual constituents the dry elastic moduli of families of clean sands and s

seabed drifter movement in san diego bay and adjacent waters the seabed drifter has been used successfully to provide valuable information in many estuarine and open sea environments it was therefore selected for use in the san diego area five hundred drifters were released in san diego bay and adjacent ocean waters to delineate bottom flow patterns four significant bottom drift regimes are differentiated off coastal main bay channel open and semi enclosed docking basins mean residual bottom drift ranged between 0 17km day 1 off the coast to essentially zero in the docking basins off coast drifter results 31 recovery showed a persistent northmoving bottom current with shallow near coast drift distances between 4 and 25 km this nearshore north moving bottom current appears to cause a net bottom water inflow into the main san diego bay channel 44 recovery in the open bay a reverse trend was observed from the 16 of the drifters recovered at the head of the estuary evaporative densification is believed to occur with the heavier water sinking and moving outward towards the estuary mouth resulting in an area of opposing bottom water currents in this area san diego gas and electric power plant takes in an average 150 million gallons of cooling water daily which discharged as warm surface water is suggested as the surface divergence mode required to reconcile the observed flow with the three san diego bay electric power plants utilizing more than 5 of the maximum tidal prism for cooling purposes this flow may play a major role in the overall bay circulation and requires quantitative investigation

hydrodynamic model study of the ria de pontevedra under estuarine conditions the ria de pontevedra is one of the galician rias baixas partially mixed estuaries on the north west coast of the iberian peninsula the hydrodynamics of the rias is far from being fully understood in this application the hydrodynamics of the ria de pontevedra is studied by means of a 3 d baroclinic model our aim was to establish the circulation pattern driven by tide and the horizontal density gradient between river and shelf waters under estuarine conditions the spatial variability of tidal velocities and salinities is studied the residual component of the flow related to transport is described and discussed as expected in a partially mixed estuary a double layered residual pattern is observed with water flowing seaward in a surface layer and upstream in a bottom layer a cross channel residual flow not described up to date is presented

hydro sedimentary processes of a shallow tropical estuary under amazon influence the mahury estuary french guiana along the guianas coast coastal dynamic is characterized by the migration of mud banks originating from the amazon this singular feature affects the dynamic and the morphology of local estuaries and can induce rapid bathymetric evolution in lower estuaries since 2012 the navigation channel of the mahury estuary french guiana is enduring a severe siltation whose origin comes from a mud bank crossing the estuary mouth this study aims to determine how the migration of a mud bank through an estuary mouth could influence the transport and fluxes in the estuary field measurements were performed over a year with the monitoring of the salt intrusion length mooring surveys during spring neap cycles and shipboard profiling surveys during semi diurnal cycles salt intrusion lengths underline a significant seasonal variation characterized by the transition from a steady state length during high river discharge and a wide range of lengths with the tidal range during low to moderate river discharge during the rainy season measurements indicate a fluvial dominated condition with low suspended sediment concentrations most of the semi diurnal cycle residual sediment fluxes are usually seaward excepted when river discharge is below seasonal average during the dry season maximum suspended sediment concentrations are higher in the middle part of the estuary residual sediment fluxes are landward along the estuary and stronger during neap tides in the estuary mouth and few kilometers upstream in this area a persistent density stratification traps sediments in the bottom layer and generates a gravitational circulation during neap tides which enhances landward transports up to 2 56 t m 1 over a semi diurnal cycle in the middle estuary landward fluxes are most significant during the dry season and also during the rainy season when the river discharge is below the seasonal average although this study includes temporal and spatial limitations it underlines significant mud inflows in the middle part of the estuary during low to moderate river discharges comparison with old data suggests higher sediment loads in the estuary during the migration of a mud bank but must be confirmed by further studies during the interbank period

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in

acoustic properties of sediments saturated with gas hydrate free gas and water we obtain the wave velocities and quality factors of gas hydrate bearing sediments as a function of pore pressure temperature frequency and partial saturation the model is based on a biot type three phase theory that considers the existence of two solids grains and gas hydrate and a fluid mixture attenuation is described with the constant q model and viscodynamic functions to model the high frequency behaviour we apply a uniform gas water mixing law that satisfies wood s and voigt s averages at low and high frequencies respectively the acoustic model is calibrated to agree with the patchy saturation theory at high frequencies white s model pressure effects are accounted by using an effective stress law for the dry rock moduli and permeabilities the dry rock moduli of the sediment are calibrated with data from the cascadia margin moreover we calculate the depth of the bottom simulating reflector bsr below the sea floor as a function of sea floor depth geothermal gradient below the sea floor and temperature at the sea floor