secondary circulation in a region of flow curvature relationship with tidal forcing and river discharge 1 on the basis of a 301 day acoustic doppler current profiler mooring in an estuarine tidal strait the strength and structure of secondary circulation in a region of flow curvature is related to variations in tidal forcing and river discharge during low flow conditions the structure of secondary flow is consistent with a centrifugally forced helical flow with bottom flow toward the inside of the bend and surface flow toward the outside of the bend the strength of secondary flow increases linearly with tidal range and is consistent with a vertical eddy viscosity that is linearly dependent on tidal current speed during times of high river discharge the strength of secondary flow is significantly reduced and its vertical structure undergoes a fundamental change over the spring neap cycle during spring tides the classic helical flow pattern is evident albeit weaker than during low flow conditions however during neap tides a more complex two cell structure is evident the change between these two states occurs with a spring neap transition in the subtidal flow indicating that it is also accompanied by changing stratification simple scaling analysis suggests that during weakly stratified conditions secondary circulation will influence stream wise dynamics and dispersion for channels with widths on order or less than 0 1 h cd where h is the water column depth and cd is a quadratic bottom drag coefficient in contrast during highly stratified conditions lateral excursions due to secondary flows are limited to approximately one tenth of the channel s width and are an ineffective lateral mixing agent

mixing and turbulence in a flooding coastal river abstractan experimental study of turbulence and vertical mixing was carried out in the lower east pearl river mississippi and louisiana during a high discharge period in february and march of 2010 direct estimates were made of the time varying profile of turbulent reynolds stresses x u w through the water column from this both the vertical eddy viscosity km and mean vertical mixing time were calculated and the water column was shown to be vertically well mixed at all times segmenting the stresses into stresses due to river discharge and stresses due to tidal flows shows the coequal nature of each component and highlights the ways they vary in importance during different flow regimes two simple turbulence models are examined and compared to the measured mixing parameters

lateral circulation in well mixed and stratified estuarine flows with curvature abstract a field experiment was conducted to examine stratified and unstratified curvature generated lateral circulation and momentum balances in an estuarine tidal channel conductivity temperature depth and current profiler data were collected vertically and laterally across the channel at a sharp bend over a fortnightly period to measure the terms of the lateral momentum budget well mixed conditions allow the development of classic two layer helical flow around a bend stratification strengthens curvature induced lateral circulation but the development of a lateral baroclinic pressure gradient opposes the resultant motions the spatial and temporal response of this baroclinic pressure gradient is different than centrifugal acceleration producing a three layer profile as the baroclinic term becomes stronger or as centrifugal acceleration disappears as the flow exits the bend two layer flow with the opposite direction from curvature occurs in both stratified and well mixed conditions downstre

on the nature of transverse variability in a coastal plain estuary even though estuarine processes are inherently three dimensional most of the previous studies have focused primarily on the axial longitudinal and vertical variabilities recent surveys in the lower delaware bay indicate the presence of significant transverse variability in the salinity distribution and residual circulation pattern conceptual models are developed to examine the mechanisms which might explain the observed transverse structure results indicate that both the gravitational effect and wind forcing are capable of generating substantial transverse structure in drowned river valley estuaries with triangular cross sections

observations of stratified turbulent mixing in an estuary neap to spring variations during high river flow abstract observations of turbulent mixing stratification and currents were made with a free falling microstructure profiler and a 600 khz adcp in the hudson river off manhattan in may 1994 the ship was anchored in a relatively straight and uniform channel about 15 m deep over 4 days of intense observations from 19 to 24 may 1994 the progression from neap tides to spring tides caused a severe reduction in stratification from an initial top to bottom salinity difference of 18 to 3 6 while low gradient richardson numbers ri occurred only in the weakly stratified bottom layer on flood during neap tides low ri spanned the water column on the second half of ebb during spring tides turbulent dissipation rates varied roughly inversely to ri during neap conditions turbulent mixing was intense only in the bottom layer on flood where eddy diffusivities k reached more than 10 2 m 2 s 1 while mixing was weak in the centre of the halocline near 5 m during spring tides strong mixing occurred throughout the water column during the latter part of ebb with typical k 5 10 3 m 2 s 1 and typical vertical salt flux of 0 0015 kg m 2 s 1 if it existed in isolation this flux would eliminate the haline stratification on a time scale of 4 h ebb time bands of low ri and intense mixing showed increasing phase lag with increasing distance from the bottom the spring tide ebb time internal turbulent stress was relatively uniform with depth with a typical magnitude of 0 4 pa 4 dyne cm 2 turbulent overturning thorpe scales ranged from below 1 cm in the neap tide halocline to a few metres in the weakly stratified bottom layer on flood the strong spring tide ebb time mixing had thorpe scales of typically 0 5 m throughout the water column ozmidov scales tracked thorpe scales except in the weakly stratified layer above the bottom

the effects of channels and shoals on exchange between the chesapeake bay and the adjacent ocean the role of bathymetric changes in determining the transport of water and salt in the lower chesapeake bay lcb was investigated using high resolution acoustic doppler current profiler adcp and conductivity temperature depth profiles a cross channel transect was repeated eight times during neap tides on october 6 7 1993 which illustrated the lateral structure of the longitudinal and transverse flow fields and the intratidal variations in the flow structure across the lcb amplitude and phase of the m2 tidal component as well as the mean flow velocity were calculated using least squares fitting at every point of a uniform grid obtained from the adcp data the results differ from the classical two layer pattern of estuarine circulation modified by coriolis effects but are consistent with recent hydrographic observations semidiurnal flow was highest over the navigational channels and lateral gradients were strongest in regions of sharp bathymetric changes the phase lag of the semidiurnal flow also showed lateral and vertical gradients that represented advances at the bottom with respect to the surface and over the shoals in relation to the channels the section of the water column measured indicated a mean outflow of 0 7 104 m3 s and a mean inflow of 1 3 104 m3 s the apparent gain of water by the estuary during the period of observation can be explained by meteorologically forced net barotropic inflow the depth averaged mean longitudinal flow consisted of inflow in the navigational channels and outflow over the shoals the mean transverse flow showed near surface convergence over the channels we propose a possible explanation for the observed flow and density structure as follows the barotropic and baroclinic forcing interact with the bathymetry to extend the inflow from the bottom to the surface thereby inducing a transverse circulation that yields near surface convergence over the channels

meteoric burial diagenesis of middle pennsylvanian limestones in the orogrande basin new mexico water rock interactions and basin geothermics abstract stable isotopic compositions of cyclic middle pennsylvanian gobbler formation limestones record two stages of alteration early open system meteoric diagenesis during episodic subaerial exposure stabilized cycle top carbonate in the presence of meteoric fluid at high water rock ratios 400 4000 subsequent closed system burial diagenesis stabilized meteoric and residual marine carbonate in the presence of connate pore fluids at elevated temperatures to 150 c and low water rock ratios 1 0 10 present 18o distributions record normal to high geothermal gradients 27 86 c km during burial stabilization high basin center geothermal gradients probably resulted from elevated heat flow due to rapid crustal extens on and subsidence of the orogrande basin during the late pennsylvanian a dike injection lithospheric extension model with 40 oceanization best accounts for subsidence and geothermal patterns of the orogrande basin

an enigmatic conchostracan fauna in the eastern dead sea region of jordan first records of rossolimnadiopsis novozhilov from the early triassic ma in formation abstract the late permian early triassic sedimentary succession in the eastern dead sea region of jordan was surveyed for conchostracans crustacea branchiopoda whereas their occurrence in the middle late permian umm irna formation could not be confirmed the overlying ma in formation contained a fauna comprising rossolimnadiopsis novozhilov and other thus far taxonomically undetermined conchostracans here a new species rossolimnadiopsis hanskerpi nov sp is described and figured it shows a very distinctive concavely curved dorsal margin and an elevated outwardly curved semi circular flange rossolimnadiopsis hanskerpi nov sp occurs in dark gray laminated lacustrine siltstones of the ma in formation nimra member which is considered to be of early triassic age based on literature data rossolimnadiopsis was previously recorded only from two localities in the moscow syncline in central russia in addition to jordan the genus has been identified in india and possibly in germany all these occurrences seem to be restricted to a narrow stratigraphic interval ranging from the late permian to the early triassic

resolving miss conceptions and misconceptions a geological approach to sedimentary surface textures generated by microbial and abiotic processes the rock record contains a rich variety of sedimentary surface textures on siliciclastic sandstone siltstone and mudstone bedding planes in recent years an increasing number of these textures have been attributed to surficial microbial mats at the time of deposition resulting in their classification as microbially induced sedimentary structures or miss research into miss has developed at a rapid rate resulting in a number of misconceptions in the literature here we attempt to rectify these miss misunderstandings the first part of this paper surveys the stratigraphic and environmental range of reported miss revealing that contrary to popular belief there are more reported miss bearing rock units of phanerozoic than precambrian age furthermore miss exhibit a pan environmental and almost continuous record since the archean claims for the stratigraphic restriction of miss to intervals prior to the evolution of grazing organisms or after mass extinction events as well as claims for the environmental restriction of miss appear to result from sampling bias in the second part of the paper we suggest that raised awareness of miss has come at the cost of a decreasing appreciation of abiotic processes that may create morphologically similar features by introducing the umbrella term sedimentary surface textures of which miss are one subset we suggest a practical methodology for classifying such structures in the geological record we illustrate how elucidating the formative mechanisms of ancient sedimentary surface textures usually requires consideration of a suite of sedimentological evidence from surrounding strata resultant interpretations microbial or non microbial should be couched within a reasonable degree of uncertainty this approach recognizes that morphological similarity alone does not constitute scientific proof of a common origin and reinstates a passive descriptive terminology for sedimentary surface textures that cannot be achieved with the current miss lexicon it is hoped that this new terminology will reduce the number of overly sensational and misleading claims of miss occurrence and permit the means to practically separate initial observation from interpretation furthermore this methodology offers a scientific approach that appreciates the low likelihood of conclusively identifying microbial structures from visual appearance alone informing the search for true miss in earth s geological record and potentially on other planetary bodies such as mars

three dimensional tidal flow in an elongated rotating basin the three dimensional tidal circulation in an elongated basin of arbitrary depth is described with a linear constant density model on the f plane rotation fundamentally alters the lateral flow introducing a lateral recirculation comparable in magnitude to the axial flow as long as friction is not too large this circulation is due to the imbalance between the cross channel sea level gradient which is in near geostrophic balance with the coriolis acceleration associated with the vertically averaged axial flow and the coriolis acceleration associated with the vertically sheared axial flow during flood condition for example the lateral coriolis acceleration near the surface exceeds the pressure gradient tending to accelerate the lateral flow while the converse is true near the bottom as a result with rotation fluid parcels tend to corkscrew into and out of the basin in a tidal period the axial flow is only weakly modified by rotation when friction is small the axial velocity is uniform in each section except in a narrow bottom boundary layer where it decreases to zero the boundary layer thickness increases with friction so that with moderate or large friction axial velocities are sheared from bottom to surface when friction is large the local and coriolis accelerations are both small and the dynamics are governed by a balance between friction and the pressure gradient

modeling influence of stratification on lateral circulation in a stratified estuary abstract the dynamics of lateral circulation in the passaic river estuary is examined in this modeling study the pattern of lateral circulation varies significantly over a tidal cycle as a result of the temporal variation of stratification induced by tidal straining during highly stratified ebb tides the lateral circulation exhibits a vertical two cell structure strong stratification suppresses vertical mixing in the deep channel whereas the shoal above the halocline remains relatively well mixed as a result in the upper layer the lateral asymmetry of vertical mixing produces denser water on the shoal and fresher water over the thalweg this density gradient drives a circulation with surface currents directed toward the shoal and the currents at the base of the pycnocline are directed toward the thalweg in the lower layer the lateral circulation tends to reduce the tilting of isopycnals and gradually diminishes at the end of the ebb tide a lateral baroclinic pressure gradient is a dominant dri

secondary circulation in a highly stratified estuary observations from the hudson river estuary are presented to discuss the interaction between secondary flows and stratification in the vicinity of a headland during highly stratified conditions analysis of the cross stream momentum balance suggests that centrifugal accelerations are in near balance with the cross stream baroclincity results emphasize that the interaction between stratification and secondary flows can set up a cross stream internal seiche this results in a reduction and subsequent reversal of the secondary flows downstream of a headland simple scaling arguments suggest that the spin down time for tidally driven eddies is related to stratification

wind driven lateral circulation in a stratified estuary and its effects on the along channel flow 1 in the stratified rotating estuary of chesapeake bay the ekman transport drives a counterclockwise lateral circulation under down estuary winds and a clockwise lateral circulation under up estuary winds looking into estuary the clockwise circulation is about twice as strong as the counterclockwise circulation analysis of the streamwise vorticity equation reveals a balance among three terms titling of the planetary vorticity by vertical shear in the along channel current baroclinic forcing due to sloping isopycnals at cross channel sections and turbulent diffusion the baroclinic forcing is highly asymmetric between the down and up estuary winds while the counter clockwise lateral circulation tilts isopycnals vertically and creates lateral barolinic pressure gradient to oppose the ekman transport under the down estuary wind the clockwise circulation initially flattens the isopycnals and the baroclinic forcing reinforces the ekman transport under the up estuary wind the coriolis acceleration associated with the lateral flows is of the first order importance in the along channel momentum balance it has a sign opposite to the stress divergence in the surface layer and the pressure gradient in the bottom layer thereby reducing the shear in the along channel current compared with the non rotating system the shear reduction is about 30 40 two summary diagrams are constructed to show how the averaged streamwise vorticity and along channel current shear vary with the wedderburn w and kelvin ke numbers

structure variability and salt flux in a strongly forced salt wedge estuary this researchwas funded by national science foundation grant oce 0452054 ralston also received partial support from the penzance endowed fund in support of assistant scientists and the john f and dorothy h magee fund in support of scientific staff at woods hole oceanographic institution

wrinkle structures a critical review abstract in this paper a variety of so called wrinkle structures is reviewed in an attempt to help distinguish between crinkly decorations arising from physical processes that acted on siliciclastic bedding surfaces and true microbially induced wrinkle structures two types of small scale microbially induced sedimentary structures are prominent due to their distinct geometry and mode of occurrence 1 elephant skin textures characterized by reticulate patterns of sharp crested ridges forming mm to cm scale polygons occurring on argillite or argillaceous veneers above fine grained sandstone and likely reflecting growth structures of microbial mats 2 kinneyia structures characterized by mm scale flat topped winding ridges and intervening troughs and pits sometimes resembling small scale interference ripples kinneyia structures usually occur on upper surfaces of siltstone sandstone beds themselves frequently event deposits and are thought to have formed beneath microbial mats additionally more linear variations of mat growth structures partly resembling small scale petees may be developed finally some wrinkly structures resulting from tractional mat deformation or mat slumping are occasionally preserved these may appear as arcuate belts of non penetrative small scale folds or as wrinkled bulges on otherwise flat surfaces wrinkle structures as indicators for the former presence of mats gain in importance if other mat related structures are additionally observed in the same clastic succession e g sand chips sandy intraclasts or spindle shaped or sinuously curved to circular sand cracks frequently combined in networks furthermore appropriate lithologies and facies are required for instance if compared with the distribution of modern cohesive microbial mats laminated siltstone argillite with intercalated siltstone sandstone beds representing event deposits in tidal flat successions would be compatible with microbial mat development within a variety of physically induced small scale wrinkly structures miniature load structures may above all be misinterpreted as microbially induced wrinkle structures due to their similar size and appearance and their comparatively frequent occurrence

physical properties of young 3 5 ma oceanic crust from the eastern flank of the juan de fuca ridge comparison of wireline and core measurements with global data 1 we compile and compare petrophysical data from the upper oceanic crust in hole u1301b on 3 5 ma seafloor on the eastern flank of the juan de fuca ridge measurements include core scale lab based and in situ wireline measurements of formation porosity electrical resistivity bulk density p wave velocity and gamma ray emission a comparison between hole u1301b data and those from other sites ranging in age from 5 9 to 167 ma demonstrates some important differences hole u1301b samples tend to have lower bulk density values for a given porosity than do other young crustal sites hole u1301b samples also tend to have higher values of formation factor the ratio of fluid conductivity to saturated rock conductivity which may indicate development of tortuous microporosity that is more consistent with samples from older seafloor evaluation of global trends of petrophysical properties versus crustal age indicates that hole u1301b in situ data is consistent with global trends but core scale p wave velocity and bulk density values fall below global trend values predicted for young crust this last observation is likely related to basement topography and the regional exposure until relatively recently of basement outcrops around site u1301 until most of the exposed basement in this area was buried hydrothermal circulation extracted much of the lithospheric heat kept basement fluid temperatures low and limited the rate and extent of alteration a subsequent period of higher temperature fluid circulation with more restricted and less oxidative conditions resulted in enhanced and pervasive alteration of crustal rocks

the dynamics of a partially mixed estuary measurements of velocity density and pressure gradient in the lower hudson river estuary were used to quantify the dominant terms in the momentum equation and to characterize their variations at tidal and spring neap timescales the vertical momentum flux assumed to be due mainly to turbulent shear stress was estimated indirectly based on the residual from the acceleration and pressure gradient terms the indirect estimates of stress compared favorably to bottom stress estimates using a quadratic drag law supporting the hypothesis that the tidal momentum equation involves a local balance between tidal acceleration pressure gradient and stress divergence estimates of eddy viscosity indicated that there was significant tidal asymmetry with flood tide values exceeding ebb values by a factor of 2 as a consequence of the asymmetry the vertical structure of the tidally averaged stress bore no resemblance to the tidally averaged shear in spite of the asymmetry of vertical mixing the tidally averaged estuarine circulation was found to depend simply on the intensity of bottom turbulence which could be parameterized by a rayleigh drag formulation based on the tidal velocity magnitude and the tidally averaged near bottom flow this seemingly paradoxical result indicates that the estuarine circulation can be modeled without detailed knowledge of the effective eddy viscosity only requiring an estimate of the bottom drag coefficient the tidal forcing conditions and the baroclinic pressure gradient a notable characteristic of this solution is an inverse dependence of the estuarine circulation on the amplitude of the tides

combined effects of wind tide and horizontal density gradients on stratification in estuaries and coastal seas abstract the aim of this one dimensional water column study is to combine modified versions of three characteristic parameters for periodic tidal flow under the influence of a longitudinal buoyancy gradient the horizontal richardson number the inverse strouhal number and the inverse ekman number into a parameter space study including constant wind forcing from various directions it is shown how the underlying dynamical equations can be cast into nondimensional form depending mainly on these three nondimensional parameters plus the relative wind speed and the wind direction idealized model simulations are carried out for the whole realistic range of horizontal richardson and inverse strouhal numbers for various latitudes showing the amplitude of the tidally induced stratification for a wide range of scenarios it is found that classical threshold values for the horizontal richardson number indicating the switch from periodic stratification to permanent stratification are valid only for special cas

coastal plain origin of trace fossil bearing red beds in the early permian of southern new mexico u s a abstract the early permian robledo mountains formation of the hueco group in the robledo mountains south central new mexico u s a is a world class ichnofossil lagerstatte of supposed peritidal origin abundant and diverse invertebrate and vertebrate trace fossils occur in several thin horizons of siliciclastic red beds that are intercalated with thick successions of shallow marine limestone and shale the depositional environment of the red beds has been discussed for decades but without any detailed sedimentary facies analysis a recently completed systematic excavation shows that the majority of trace fossils is related to mud draped surfaces within distal crevasse splay siltstone to fine grained sandstone interbedded mudstone with well preserved macrofloral remains and a lungfish aestivation burrow represents a hitherto disregarded facies in overbank fines both environmental subzones were at least loosely covered with low growing plants and experienced common periods of subaerial exposure none of the physical and biological structures recorded in the measured section indicates tidal influence but instead they support the reconstruction of a freshwater ecosystem dominated by arthropods and tetrapods given their proximity to carbonates of unambiguous subtidal origin we propose that the trace fossil bearing red beds of the robledo mountains formation formed in distal parts of an extensive coastal floodplain during alternating wet and dry conditions if this interpretation is correct it provides an impetus to continue ichnological and sedimentological field research in the study area because the true tidal flat ichnoguilds still await elucidation

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

lateral circulation generates flood tide stratification and estuarine exchange flow in a curved tidal inlet abstractcross channel transect measurements of microstructure and velocity in a well mixed and curved tidal inlet in the german wadden sea show the occurrence of significant late flood stratification this stratification is found to be a result of lateral straining this study observes a strong single cell lateral circulation which is strongly pronounced at late flood and absent during most of ebb this tidal asymmetry is caused by a systematic interplay between centrifugal forcing and the lateral baroclinic pressure gradient during flood a positive feedback between the terms generates strong lateral circulation whereas during ebb a negative feedback leads to a suppression of the cross channel exchange a theoretical framework based on vorticity is developed which allows lateral and longitudinal circulation to be studied in a consistent way with this framework it is possible to show that the tidal asymmetry of the lateral flow is a major driver of residual longitudinal estuarine circulation here ide

lateral circulation and suspended sediment transport in a curved estuarine channel winyah bay sc usa 1 shipborne vertical profiles of flow and suspended sediment concentration collected on a transect across a curved nonsymmetrical estuarine channel are presented analysis of the transient cross channel momentum balance equation shows that the lateral circulation pattern is controlled by the interaction between centrifugal and lateral baroclinic forcings although those two might not be necessarily in balance as suggested earlier by seim and gregg 1997 instead differential along channel advection and local acceleration appear to influence greatly lateral circulation dynamics during ebb when the water column is highly stratified the interaction between centrifugal acceleration and opposite directed lateral baroclinic forcing results in weak lateral flows during flood lateral flows are dominated by centrifugal acceleration which is directed toward the outside of the curvature at the mid depth because of the nonlogarithmic current profile and reinforced by lateral baroclinic forcing this results in strong two layer clockwise circulation looking up estuary during flood the eastward directed bottom currents during ebb deliver only a small amount of suspended sediment from the relatively narrow western shoal to the channel bed during flood the west directed near bed currents deliver a significant amount of sediments from the gentle broad eastern shoal which in conjunction with the locally resuspended sediment load promotes the development of the estuarine turbidity maximum increased lateral advection of sediments during flood reinforces a tidal asymmetry in the development of turbidity maximum decomposition analysis of lateral sediment fluxes averaged over a tidal cycle suggests convergence of sediment toward the center of the channel is driven mainly by the oscillatory tidal component

influence of sedimentation local and regional hydrothermal circulation and thermal rebound on measurements of seafloor heat flux 1 we quantify the influence of environmental processes on measurements of seafloor heat flux with a new one dimensional thermal model that includes time varying sedimentation and boundary conditions represents several scales of hydrothermal and transient conductive processes within basement and allows fluid seepage through accumulating sediments variations in basement thermal conductivity the extent of hydrothermal mixing in upper basement and fluid seepage through sediments each influence seafloor heat flux by 2 8 conductive thermal rebound following the cessation of advective heat loss from the crust may lower seafloor heat flux values by 5 10 even after several to several tens of million years the new models indicate that thermal rebound takes much longer than suggested by earlier analytical calculations mainly because earlier models did not account for the heat capacitance of the conductive lithosphere application of the new model to 3 5 3 6 ma seafloor on the eastern flank of the juan de fuca ridge suggests that anomalously low heat flux in this area is best explained by incomplete conductive thermal rebound in the last 100 200 ka following the burial of numerous basement outcrops application of the new model to the eastern flank of the east pacific rise and extrapolation out to the age of some of the oldest remaining seafloor indicate that sedimentation corrections may be important even where accumulation rates are typical of global values model results also suggest that conductive thermal rebound through thick sediments may bias measurements made on moderate to old seafloor even where there is little evidence at present for ridge flank hydrothermal circulation

numerical modelling of the sydney harbour estuary new south wales lateral circulation and asymmetric vertical mixing abstract a fully calibrated three dimensional hydrodynamic model of the sydney harbour estuary was used to determine the dominant forcing of regulating estuarine circulation in a sinuous channel under conditions of low river discharge during dry weather the system characterized by stratified flood and mixed ebb during spring tides and stratified flood and ebb during neap tides was analysed using model results of current profiles density field eddy viscosity and gradient richardson number at a mooring station and cross channel transect the magnitude and direction of lateral circulation was modulated in the flood ebb and spring neap cycles due to changes in the interactions between the tides and the complex geometry during spring tides a differential advection induced lateral baroclinic pressure gradient tends to drive the lateral circulation and stratifies the water column when the along estuary circulation is strong enough to break the stratification induced by the lateral baroclinic pressure gradient centrifugal force works in concert with nonlinear advection establishing a classical two layer helical flow across the channel channel bends also induce vertical mixing as a result of the overturning of the density fields the lateral circulation redistributes the differential advection induced lateral shear of the along estuary momentum and is transferred to either reinforce or cancel the along estuary circulation the lateral bathymetry variability in a channel is therefore the key factor causing the intratidal asymmetries in the along estuary circulations stratification suppresses lateral circulation during neap tides and generates a three layer lateral circulation structure in the water column during stratified ebb

reconstruction of tidal discharges in the st lawrence fluvial estuary the method of cubature revisited knowledge of tidal flows in rivers and estuaries is often scarce yet vital in determining flushing properties and sediment transport rates while many rivers still remain ungauged methodological difficulties often arise in gauged systems resulting in short flow records compared to historical water level data notwithstanding discharge reconstructions in estuaries are possible using indirect methods based on long term tidal data in this paper we revisit the method of cubature integrating the continuity equation for discharges at different sections the method consists in computing temporal changes in water volume from simultaneous tidal heights readings along the river and storage width estimations these water balance estimates remain challenging to produce because they require spatial interpolation of gappy tidal records and an accurate representation of inundated areas over time improvements on the method are made by using a 1d nonstationary tidal harmonic model that provides continuous tidal data along the estuary with no temporal or spatial gaps secondly a 2d finite element discretization is used to compute the time varying wetted surface area relying on detailed topographic data over intertidal flats the method is applied to the st lawrence fluvial estuary slfe and validated against discharge data collected along 9 cross sections of the river reaching relative rmse below 4 of the diurnal tidal discharge range at downstream locations and below 9 upstream one year reconstructions conducted in the slfe also show the potential of the method to reproduce the tidal discharge variability along the tidal river continuum for a wide range of temporal scales

three dimensional residual tidal circulation in an elongated rotating basin abstract the three dimensional residual circulation driven by tides in an elongated basin of arbitrary depth is described with a small amplitude constant density model on the f plane the inclusion of rotation fundamentally alters the residual flow with rotation fluid is drawn into the basin on the right side of an observer looking toward the closed end in the northern hemisphere and the return flow is on the opposite side a lateral circulation is superposed on the axial flow with upwelling over the deeper part of each section and downwelling near the sides the residual flow is driven by a combination of advective terms including the lateral advection of axial momentum associated with the coriolis acceleration and stokes forcing tidally averaged fluid parcel trajectories are determined by integrating the lagrangian mean velocities with or without rotation these trajectories vary considerably depending on small differences in initial position as well as on basin shape and other parameters of the

paleoclimatic controls on stable oxygen and carbon isotopes in caliche of the abo formation permian south central new mexico u s a abstract the stable oxygen and carbon isotopic composition of caliche in fluvial and supratidal rocks of the abo formation permian south central new mexico is controlled by paleoclimate and depositional environment fluvial caliche consists of low mg calcite nodules and vertically oriented tubules that display stage ii texture micrite matrix support brecciation ooids pisoliths aveolar septal texture and peloids are common in the fluvial caliche and along with red color and slickensides in the host shale indicate pedogenesis in a well oxidized vadose zone in contrast periodic waterlogging of the supratidal paleosols probably due to high water table is indicated by drab colors carbonaceous flecks horizontal rhizoliths and the paucity of vadose textures in the stage ii caliche n dules stable oxygen isotopes are similar in the fluvial and supratidal caliches and range from 21 6 to 30 5 smow the data exhibit a crude bimodality and 18o enrichment with a decrease in age higher in the section consideration of these data in the context or temperature relations suggests that 1 surface waters responsible for caliche formation increased in 18o from roughly 8 to 1 over the 18 m y time interval that separated the lowest stratigraphic nodule horizon from the highest 2 the inc easing 18o values also reflect a warming trend approximately 15 to nearly 3 c in the mean monthly temperature over this same time period with perhaps an associated increase in permian ocean temperatures and 3 the significant variation in 18o from oldest to youngest caliche was probably enhanced by the amount effect such that as the temperature increased the amount of precipitation decreased resulting in high 18o values caliches in the abo are enriched in heavy carbon 7 2 to 1 5 pdb compared to that of soil carbonate derived exclusively from c plants 12 pdb and the supratidal caliches contain somewhat heavier carbon compared to the fluvial caliche the 13c values for both environments increase with a decrease in caliche age these results indicate that as the temperature increased and rainfall decreased with time the level of c3 plant productivity apparently declined allowing a greater influx of atmospheric co2 into the soil this can only occur when soil respiration rates are quite low or at very sha low depths less than 10 cm or both atmospheric co2 seems to have invaded the supratidal soils to a somewhat greater extent than the fluvial soils

quantifying the contributions of tidal straining and gravitational circulation to residual circulation in periodically stratified tidal estuaries abstract this numerical modeling study quantifies for the first time the contribution of various processes to estuarine circulation in periodically stratified tidal flow under the impact of a constant horizontal buoyancy gradient the one dimensional water column equations with periodic forcing are first cast into nondimensional form resulting in a multidimensional parameter space spanned by the modified inverse strouhal number and the modified horizontal richardson number as well as relative wind speed and wind direction and the residual runoff the along tide momentum equation is then solved for the tidal mean velocity profile in such a way that it is equated to the sum of the contributions of tidal straining resulting from the temporal correlation between eddy viscosity and vertical shear gravitational circulation resulting from the depth varying forcing by a constant horizontal buoyancy gradient wind straining and depth mean residual flow resulting from net freshwater runoff this definitio

near bottom turbulence measurements in a partially mixed estuary turbulent energy balance velocity structure and along channel momentum balance abstract a set of moored bottom mounted and shipboard measurements obtained in a straight section of the lower hudson estuary during late summer and early fall of 1995 determine velocity density and along channel pressure gradient throughout the 15 m water column as well as providing direct eddy correlation estimates of reynolds stress and indirect inertial range estimates of dissipation within 3 m of the bottom the analysis focuses on testing 1 a simplified turbulent kinetic energy equation in which production balances dissipation 2 the prandtl karman law of the wall which is a relationship between bottom stress and near bottom velocity gradient and 3 a simplified depth integrated along channel momentum balance involving local acceleration pressure gradient and bottom stress estimates of production and dissipation agree well throughout the entire record the relationship between bottom stress and velocity gradient is consistent with the law of the wall within approximately 1 m of the sea

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

an observational study of salt fluxes in delaware bay an observational study was conducted in delaware bay during the summer of 2011 aiming to quantify the different mechanisms driving the salt flux in this system seven moorings equipped with bottom mounted adcps and ct sensors at difference depths were deployed across a section of the estuary the total area averaged and tidal averaged salt flux was decomposed in three different contributions the advective salt flux that represents the flux caused by river input and meteorological induced flows the steady shear dispersion that is the salt flux driven by the estuarine exchange flow and the tidal oscillatory salt flux that is induced by the tidal currents the advective salt flux dominated over the steady shear dispersion and tidal oscillatory salt flux because it was driven mainly by changes in sea surface height associated with wind driven setup and setdown the steady shear dispersion was always positive and presented a spring neap variability that was consistent with a two layer exchange flow on the other hand the tidal oscillatory salt flux fluctuated between positive and negative values but increased around a strong neap tide and decreased on the following spring tide this variability is contrary to previous parameterizations whereby the tidal salt flux is proportional to the amplitude of the tidal currents the observational estimate was compared to a parameterization that relates tidal salt flux as proportional to tidal current amplitude and stratification the observational estimate agreed with this new parameterization when the river discharge was relatively constant

turbulent stresses and secondary currents in a tidal forced channel with significant curvature and asymmetric bed forms acoustic doppler current profilers are deployed to measure both the mean flow and turbulent properties in a channel with significant curvature direct measurements of the reynolds stress show a significant asymmetry over the tidal cycle where stresses are enhanced during the flood tide and less prominent over the ebb tide this asymmetry is corroborated by logarithmic fits using 10 min averaged velocity data a smaller yet similar tendency asymmetry in drag coefficient is inferred by fitting the velocity and estimated large scale pressure gradient to a one dimensional along channel momentum balance this smaller asymmetry is consistent with recent modeling work simulating regional flows in the vicinity of the study site the asymmetry in drag suggests the importance of previously reported bed forms for this channel and demonstrates spatial and temporarily variations in bed stress secondary circulation patterns observed in a relatively straight section of channel appear driven by local curvature rather th

three dimensional tidal flow around headlands field measurements of tidal flow around a headland indicate secondary circulation induced by flow curvature the secondary flow defined to be the flow in the plane normal to the direction of the vertically averaged current is directed toward the headland near the bottom and seaward near the surface consistent with theoretical predictions the strength of the secondary flow varies from 5 to 15 of the streamwise flow it is strongest when the water column is stratified because of both the enhanced shear of the streamwise flow and the reduced frictional damping of the secondary flow the transverse exchange accomplished by the secondary flow significantly influences the structure of the streamwise flow causing a broadening of the transverse shear and changing the horizontal and vertical distributions of momentum it may also have a significant influence on horizontal dispersion in the vicinity of headlands

the importance of aspiration and channel curvature in producing strong vertical mixing over a sill on the basis of observations of the time dependent tidally forced flow over a long sill we find that aspiration and channel curvature set the flow structure and condition the flow to allow intense vertical mixing aspiration reduces the potential energy of the water column by thinning it while maintaining its density contrast channel curvature induces a cross channel circulation that can rapidly overturn a stratified flow eighteen along channel sections of density velocity and dissipation rate of turbulent kinetic energy were collected in and around the tacoma narrows of puget sound a site suspected of driving a strong vertical circulation in adjoining main basin rapid inflow to the narrows on flood from one channel of a triple junction reduces dynamic pressure allowing dense water from below sill depth to be uplifted or aspirated into the narrows we estimate water from below 150 m 3 times the sill depth is drawn into the narrows on a 3 m flood tide once in the narrows the flow remains stratified until it passes a 50 bend where a strong secondary circulation overturns the 50 m deep water column and generates intense turbulent mixing cross channel velocities of up to 0 4 m s 1 are observed and maximum values of exceed 10 3 w kg 1 upon leaving the sill stratification is reestablished and turbulence decays a similar set of sequences occurs on ebb except that the outflow bypasses the flood inflow channel and instead discharges into colvos passage the third branch of the triple junction colvos passage ultimately discharges the ebb effluent back into main basin enhancing the impact of mixing at the narrows by discharging the mixed product far from the source scaling of the cross channel momentum equation suggests that below a threshold value of along channel velocity stratification should suppress secondary circulation for a given vertical shear radius of curvature and channel width above the threshold velocity the magnitude of the cross channel velocity is roughly consistent with predictions for unstratified flow we estimate the maximum effective eddy diffusivity that aspiration and mixing in the narrows can produce in main basin to be 10 3 m2 s 1

cyclic sedimentation in the mixed siliciclastic carbonate abo hueco transitional zone lower permian southwestern new mexico abstract in southwestern new mexico lower permian wolfcampian rocks grade southward from nonmarine siliciclastics abo and earp formations to marine carbonates hueco and horquilla formations a transitional zone between siliciclastic and carbonate facies trends east northeast across southwestern new mexico and consists of 64 to 186 m of cyclically interbedded siliciclastic and carbonate rocks which were deposited in tidal flat and shallow marine environments shallow marine facies include fossiliferous limestone and olive gray shale tidal flat facies consist of 1 ripple laminated sandstone which was deposited on intertidal sandflats near mean low tide 2 mixed sandstone shale which was deposited on an intertidal flat shoreward of the ripple laminated sandstone facies and 3 nodula shale which is characterized by pedogenic calcareous nodules and was deposited in a supratidal setting the intertidal facies are truncated by or grade laterally into rare channel sandstones which represent tidal creek or estuarine facies in addition to siliciclastic tidal flat deposits a few beds of laminated carbonate also were deposited in the intertidal zone vertical sequence analysis aids in delineating three types of depositional cycles asymmetrical cycles display the vertical sequence basal fossiliferous limestone olive gray shale ripple laminated sandstone mixed sandstone shale nodular shale and record shoreline progradation the asymmetrical cycle is always overlain by fossiliferous limestone which indicates a major transgression that inhibited siliciclastic sedimentation a common symmetrical cycle consists of fossiliferous limestone olive gray shale ripple laminated sandstone olive gray shale fossiliferous limestone and indicates systematic seaward and landward migration of facies zones associated with small scale sea level changes a less common symmetrical cycle involves laminated carbonate fossiliferous limestone aminated carbonate cyclic sedimentation in abo hueco transitional strata is most likely the result of glacial eustatic sea level fluctuations

modeling the lateral circulation in straight stratified estuaries the dynamics of lateral circulation in an idealized straight estuary under varying stratification conditions is investigated using a three dimensional hydrostatic primitive equation model in order to determine the importance of lateral circulation to the momentum budget within the estuary for all model runs lateral circulation is about 4 times as strong during flood tides as during ebbs this flood ebb asymmetry is due to a feedback between the lateral circulation and the along channel tidal currents as well as to time varying stratification over a tidal cycle as the stratification is increased the lateral circulation is significantly reduced because of the adverse pressure gradient set up by isopycnals being tilted by the lateral flow itself when rotation is included a timedependent cross channel ekman circulation is driven and the tidally averaged bottom lateral circulation is enhanced toward the right bank when looking toward the ocean in the northern hemisphere this asymmetry in the tidally averaged bottom lateral circulation may lead to asymmetric sediment transport leading to asymmetric channel profiles in straight estuaries for the weakly stratified model run advection due to lateral currents is a dominant term in both the along channel and cross channel momentum equations over a tidal cycle and for the tidally averaged momentum equations in the tidally averaged along channel momentum equation lateral advection acts as a driving term for the estuarine exchange flow and can be larger than the along channel pressure gradient therefore it should not be ignored when estimating momentum budgets in estuaries

age variation in the physical properties of oceanic basalts implications for crustal formation and evolution the time dependent variability of the physical properties of upper oceanic crustal rocks have been characterized by compiling acoustic velocity density porosity iron oxidation state and h2o data from the upper 50 m of all deep sea drilling project and ocean drilling program drill holes which recovered basalt samples from normal oceanic basement this data compilation is interpreted in terms of the geological processes responsible for these changes as the seafloor ages drill site averages of both acoustic velocity and bulk density show a decrease with increasing age for crustal ages less than 100 ma similarly chemical data from the same drill cores indicate the presence of two distinct alteration processes oxidation of ferrous to ferric ions within the rock forming minerals proceeds rapidly within the first 5 ma after formation slows in the subsequent 5 to 20 m y period and then appears to stop hydration of the silicate minerals also appears to generally increase with age over the full 150 m y age range of the samples although at a slower rate than oxidation the observed distribution of the physical properties of the upper crustal rocks for the first 100 ma can be explained by three processes 1 a large initial variability of vp and density caused by the range of original porosity of the rocks 2 an age progressive alteration associated with oxidation that systematically reduces both vp and density with increasing age for the first 5 m y and 3 an additional nonoxidative alteration that increases the hydration of the silicate minerals with a resulting major impact on the physical properties still unexplained however is the lack of an expected trend of decreasing porosity with increasing age and alteration and the large nonsystematic scatter in the physical property data for samples older than 100 ma

early permian asselian vegetation from a seasonally dry coast in western equatorial pangea paleoecology and evolutionary significance abstract the pennsylvanian permian transition has been inferred to be a time of significant glaciation in the southern hemisphere the effects of which were manifested throughout the world in the equatorial regions of pangea the response of terrestrial ecosystems was highly variable geographically reflecting the interactions of polar ice and geographic patterns on atmospheric circulation in general however there was a drying trend throughout most of the western and central equatorial belt in western pangea the climate proved to be considerably more seasonally dry and with much lower mean annual rainfall than in areas in the more central and easterly portions of the supercontinent here we describe lower permian upper asselian fossil plant assemblages from the community pit formation in prehistoric trackways national monument near las cruces south central new mexico u s a the fossils occur in sediments within a 140 m wide channel that was incised into indurated marine carbonates the channel filling can be divided into three phases a basal channel limestone conglomerate facies contains allochthonous trunks of walchian conifers a middle channel fill is composed of micritic limestone beds containing a brackish to marine fauna with carbon oxygen and strontium isotopic composition that provide independent support for salinity inferences the middle limestone also contains a par autochthonous adpressed megaflora co dominated by voltzian conifers and the callipterid lodevia oxydata the upper portions of the channel are filled with muddy gypsiferous limestone that lacks plant fossils this is the geologically oldest occurrence of voltzian conifers it also is the westernmost occurrence of l oxydata a rare callipterid known only from the pennsylvanian permian transition in poland the appalachian basin and new mexico the presence of in situ fine roots within these channel fill limestone beds and the taphonomic constraints on the incorporation of aerial plant remains into a lime mudstone indicate that the channel sediments were periodically colonized by plants which suggests that these species were tolerant of salinity making these plants one of if not the earliest unambiguous mangroves

amphibian burrows and ephemeral ponds of the lower permian speiser shale kansas evidence for seasonality in the midcontinent abstract burrows attributed to the lysorophid brachydectes elongatus occur within a green mudstone lens in the lower permian wolfcampian speiser shale council grove group of eastern kansas the burrow bearing unit consists of a 100 m long lens of massive calcareous silty mudstone with a maximum thickness of 35 cm the lens also contains the fossils of fish amphibians reptiles charophytes stomachara and ostracodes carbonita the mudstone lens pinches out laterally into red pedogenically modified mudstone the burrows occur in three layers at the top of each layer is a subaerial exposure surface indicated by rhizoliths mudcracks and coarse grained lags the mudstone lens is interpreted as the deposit of a shallow ephemeral pond the burrows occur in three vertically and temporally separated clusters with concentrations up to 20 m2 the burrows show two types of architecture type i burrows are elongate elliptical tubes 4 32 cm long and 2 7 cm in width type ii burrows are short elliptical tubes 1 5 3 5 cm in length and 2 5 5 cm in width the burrow fill consists of a mudstone capped by sandy siltstone each burrow layer contains a varying number of articulated and disarticulated lysorophid skeletons within the burrows and surrounding matrix while similar to permian lungfish burrows the architecture and surficial morphology of the lysorophid burrows permits their distinction even in the absence of body fossils the occurrence of burrow layers capped by subaerial exposure surfaces and separated by layers of non burrowed massive mudstone indicates that burrowing occurred in response to episodic perhaps seasonal droughts on the permian coastal plain the lysorophid burrowing behavior is analogous to that of the extant amphibians amphiuma sp and siren intermedia which inhabit rivers and ponds in the southeastern usa

frictional estuarine flow in juan de fuca strait with implications for secondary circulation estuarine flow in juan de fuca strait is highly seasonal in nature and an appreciable along channel surface pressure gradient is coincident with the peak fraser river discharge an upper layer momentum balance requires the vertical eddy viscosity av to be of the order of 0 02 m2 s 1 slightly larger than implied by conventional empirical formulae and used in current models mixing in an estuarine channel and a large vertical eddy viscosity should lead to significant cross channel flows this secondary circulation which may resemble internal ekman layers and intrusions of water mixed at the sloping sides of the strait is much less understood than the basic along channel estuarine exchange unfortunately historical current meter data in juan de fuca strait are of insufficient spatial resolution to show the predicted patterns

vegetation induced sedimentary structures from fossil forests in the pennsylvanian joggins formation nova scotia vegetation induced sedimentary structures viss are primary structures formed by the interaction of detrital sediment with in situ plants viss provide physical evidence of vegetation s fundamental role in mediating sediment accumulation and erosion in clastic depositional systems despite the abundance of modern viss descriptions from the ancient record are surprisingly rare analysis of fossil forests in floodplain strata of the pennsylvanian joggins formation has identified seven types of viss five hydrodynamic types comprise simple forms developed around a single plant centroclinal cross strata scratch circles upturned beds and complex forms where structures have amalgamated between several plants coalesced scour fills scour and mound beds two types mudstone filled hollows downturned beds form by the decay of an entombed plant and represent infilling of an empty hollow and or soft sediment deformation hydrodynamic types are present in both dryland and wetland settings whereas decay related types occur only in dryland settings where the water table was perennially or periodically low viss represent significant accumulations of sediment and are present in a high proportion of joggins formation strata the paucity of descriptions from the ancient record suggests that these structures have been overlooked or misinterpreted as strictly hydrodynamic recognition of viss in early to middle palaeozoic strata may provide an important insight into the distribution of early land plants in oxidizing environments where organic material was not preserved

holocene coastal carbonates and evaporites of the southern arabian gulf and their ancient analogues abstract the holocene sediments of the coast of the united arab emirates in the southeastern arabian gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates evaporites and siliciclastics throughout the geologic record this paper is intended as a convenient single source for the description of sediments of this region providing information on how to reach the classic localities and some of the analogs the holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide the sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud with these latter fine sediments increasing as the water deepens the pelecypod rich sediments also collect east of abu dhabi island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons west of abu dhabi island the shallow water margin is the site of coral reefs and coralgal sands whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common they are particularly common on the less protected shallow water margins of the lagoons west of abu dhabi island pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern abu dhabi lining the inner shores of the protected lagoons of abu dhabi and on other islands to the west are cyano bacterial mats and mangrove swamps landward of these a prograding north facing shoreline is formed by supratidal salt flats sabkhas in which evaporite minerals are accumulating this paper describes the localities associated with 1 the mangrove swamps of the west side of the al dhabaiya peninsula 2 the indurated cemented carbonate crusts cyanobacterial flats and sabkha evaporites on the shore of the khor al bazam south of qanatir island 3 the reef and oolitic sand flats on the coast just east of jebel dhana and 4 the marine travertine and aragonite coats associated with the beach sediments in a small bay south of jebel dhana and 5 the sabkha mutti between jebel barakah and al sila similar sedimentological associations of carbonate and evaporites to those of the holocene of the united arab emirates are to be found in the tertiary and mesozoic sedimentary rocks of the immediate subsurface in the arabian gulf other analogs to this setting include the paleozoic carbonates of the western usa europe and asia mesozoic carbonates of the gulf of mexico europe and middle east and tertiary sedimentary rocks in the middle east

the maastrichtian danian maimara tracksite yacoraite formation salta group quebrada de humahuaca argentina environments and ichnofacies implications fil console gonella carlos alfredo consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet tucuman instituto superior de correlacion geologica universidad nacional de tucuman facultad de ciencias naturales e instituto miguel lillo departamento de geologia catedra geologia estructural instituto superior de correlacion geologica argentina

intermittently closed open lakes and lagoons their global distribution and boundary conditions abstract intermittently closed open lakes and lagoons icolls are a particularly dynamic form of estuary characterised by periodic entrance closure to the ocean closure occurs when a subaerial sand berm stabilises across the entrance channel during times of low fluvial discharge icolls are of global importance as they provide valuable ecological habitats for many species and are associated with a wide range of management issues due to their cycle of entrance closure and opening icolls are found to be more widespread globally than previously described with 1477 of these estuaries being identified in this study this constitutes an estimated 3 of the world s estuaries and 15 of all estuaries along microtidal coastlines icolls are concentrated along microtidal to low mesotidal coastlines in the mid latitudes and predominantly on coasts with temperate climates this distribution is related to greater wave heights as driven by high intensity winds and a longer fetch distance the highest proportion of icolls are present in australia 21 all global icolls south africa 16 and mexico 16 in australia a comparison with fluvial input found that it is less important than marine processes in determining icoll formation and that icolls are associated with a relative tidal range of

cycle of vertical and horizontal mixing in a shallow tidal creek 1 an experimental study of vertical mixing and along channel dispersion parameterized in terms of horizontal mixing near the mouth of the duplin river a tidal creek bordered by extensive intertidal salt marshes on sapelo island georgia was carried out over several spring neap cycles in the fall of 2005 vertical mixing is modulated on both m4 and fortnightly frequencies with maximum turbulent stresses being generated near the bed on periods of maximum flood and ebb and propagating into the water column showing a linear dependence with depth values are significantly greater on spring tide than on neap horizontal mixing evaluated by salt fluxes is driven and dominated by tidal dispersion which is also modulated by the fortnightly spring neap cycle net export of salt from the lower duplin is shown to be due to residual advection modified by upstream tidal pumping the tidal dispersion coefficient exhibits a pulsating character with greater values on spring tide followed by smaller values on neap tide