combined flow processes and sedimentary structures on the shoreface of the wave dominated grande riviere de la baleine delta abstract shoreface sediments exposed in raised deltaic deposits along the hudson bay coast are characterized by a thick succession of predominantly parallel laminated and small scale cross laminated fine sand ripple forms where preserved include both combined flow and wave ripple geometries hummocky cross stratification is present in lower parts of the section similar facies have been found in cores from the present day shoreface measurements of waves currents and suspended sediment concentrations in 10 m water depth conducted over a 15 day period in the fall of 1999 captured four different meteorological periods these included an intense four day storm which sustained significant wave heights over 3 m for 15 hours and a storm surge of over 1 m height fair weather conditions produce weak alongshore tidal flows but oscillatory motions generated by small local waves predominate during storms orbital motions dominate the flow but a strong inertial flow generated by wind forcing is also present comparison with a published combined flow bedform stability diagram suggests that the predominant bedforms at 10 m depth would be small 2 d wave dominated ripples and small weakly asymmetrical 3 d ripples under fair weather conditions and large 3 d ripples and upper plane bed under storm wave conditions the predominantly interbedded parallel laminated and small scale cross laminated facies is therefore interpreted to be characteristic of the upper shoreface where the seabed experiences intense oscillatory motions under all storms and even some fair weather conditions combined flow ripples would form during storm events because of the stronger wind driven mean residual current hummocky cross stratification forms in deeper water during storms where the ratio of maximum orbital velocity to mean residual current velocity remains for longer periods in the large 3 d ripple field during the waning phase of storms a numerical bed predictor model using the 15 day data set as input also suggests bimodal conditions fluctuating between wave ripples and upper plane bed at 10 m water depth this model further indicates that combined flow ripples would form rarely but tends to underestimate the threshold of sediment suspension

sediment transport processes in an ancient mud dominated succession a comparison of processes operating in marine offshore settings and anoxic basinal environments abstract few studies describe and compare the transport mechanisms operating to disperse mud in different parts of basins instead the physical processes operating to disperse mud in offshore environments where storm and tidal processes are interpreted to dominate are generally considered in isolation from those occurring in basinal settings where changes in bottom water anoxia and suspension settling from buoyant plumes are mostly interpreted to dominate using microtextural mineralogical and geochemical data derived from the analyses of 151 thin sections obtained from the lower jurassic mudstone dominated succession exposed on the coast of ne england we investigate how varying sediment dispersal mechanisms bioturbation and early diagenesis operated to produce the lithofacies variability observed in particular we consider the processes of sediment delivery while bottom waters were interpreted to be euxinic analyses of these samples reveal that the succession is highly variable at millimetre to centimetre scales six main lithofacies were observed 1 sand and clay bearing silt rich mudstones 2 silt bearing clay rich mudstones 3 clay rich mudstones 4 clay calcareous nannoplankton and organic carbon bearing mudstones 5 fine grained muddy sandstones 6 cement rich mudstones these units are organized typically into stacked successions of sharp based normally graded thin

postglacial relative sea level histories along the eastern canadian coastline abstract we have assembled a database of relative sea level rsl data points from the eastern coast of canada from hudson bay to the border with the usa in compiling this database we have critically reviewed 1092 radiocarbon dated samples from raised beaches isolation basins intertidal and marine deposits and archaeological indicators to produce 405 sea level index points and 687 sea level limiting points our comprehensive systematic and quality controlled rsl database allowed for the reconstruction of the postglacial evolution of 34 regions of eastern canada providing new basin scale insights into the processes driving rsl changes in the last 16 ka the combination of a database of sea level index points with an innovative empirical bayesian spatio temporal statistical model provided new insights into rates and magnitude of the spatially variable glacial isostatic adjustment gia which dominated the postglacial rsl evolution in this sector of north america a continuous postglacial rsl fall is observed at latitudes 50 n with higher rates up to 35 mm a 1 recorded in southeastern hudson bay at lower latitudes the evolution is non monotonic with rsl that dropped to a spatially variable early holocene lowstand followed by a mid holocene highstand and eventually a gradual drop to present rsl this pattern is particularly evident in the st lawrence corridor along the majority of the newfoundland new brunswick and western nova scotia coasts a late pleistocene early holocene rsl lowstand was followed by a continuous rise through the holocene at the margin of the former ice sheet i e eastern nova scotia our data identify a continuous rsl rise through the holocene these records are characterized by decreasing rates of rsl rise through time commencing with a rapid rise during the early holocene up to 17 mm a 1 a slowdown in the mid holocene average rates 9 mm a 1 and a further reduction in the late holocene average rates

mg rich ferric illite in marine transgressive and highstand systems tracts examples from the paleoproterozoic semri group central india this paper focusses upon two glauconitic sandstones in the paleoproterozoic deoland formation and chorhat sandstone both belonging to the semri group central india in both the cases glauconitic minerals occur in sandstones deposited in the marine realm within a transgressive systems tract tst for the former unit and within a highstand systems tract hst for the latter the proportion of glauconitic minerals increases in the paleo offshore direction petrography reveals selective early glauconitization of detrital k feldspars along their fringes cleavages and the fractures created by volume expansion during progressive alteration leading to the generation of peloids with small relics of the precursors xrd and mineral chemistry reveal a structure typical of glauconite and more akin to mg rich ferric illite the mineral chemistry of the glauconitic mineral phases remains the same whether the glauconitization process was incipient or at an advanced

variability of an under ice river plume in hudson bay observations of the great whale river plume in the coastal waters of hudson bay canada during late winter and early spring during four different years showed its area to vary as a power of the discharge the under ice plume area was much larger than plume area in open water for comparable discharges differences in plume geometry were related to elapsed time since ice formation and low frequency variability of the coastal circulation the strength and orientation of the coastal motion was weakly correlated with the cross hudson bay atmospheric pressure gradient the passage of low pressure systems over hudson bay is thought to generate a progressive edge wave in the absence of direct wind forcing the amplitude of the low frequency variations in coastal circulation decreased with the increasing spatial extent of the landfast ice in the study area

double celled subtropical gyre in the south atlantic ocean means trends and interannual changes 1 we present here a study of the mean upper layer structure of the south atlantic subtropical gyre sasg and its modes of variability based on archiving validation and interpretation of satellite oceanographic data sea level anomaly data gravity recovery and climate experiment based mean dynamic topography mdt models reynolds sea surface temperatures and two tide gauge time series from permanent service for mean sea level analysis of the mdts shows that the sasg mean structure is represented by a double cell circulation the southern cell being a narrow quasi zonal strip centered around 33 s its southern limb is limited by the recently discovered saint helena current tristan da cunha current sthc tcc and the north subtropical front around 35 s this system is shown to be well separated from the south atlantic current south subtropical front around 42 45 s a method based on singular spectrum analysis was used to determine the principal modes of variability through the decomposition of the data into band passed data sets the altimeter sea level trend analysis suggests that the sasg pattern is slowly migrating southward and has been growing in amplitude between 1994 and 2006 with local growth rates of 5 10 mm yr occurring in the southern cell flow intensifications in this period 2 3 cm s in the south equatorial current and north brazil undercurrent 3 5 cm s in the benguela current and weakening by 4 5 cm s in the sthc tcc are recorded the altimeter derived sea level trend is coherent with the growing phase of a bidecadal oscillation found from both tide gauges

the jackass mountain group of south central british columbia depositional setting and evolution of an early cretaceous deltaic complex121this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia 2earth science sector ess contribution 20100280 the lower cretaceous jackass mountain group of southwestern british columbia records a complex history of deltaic and proximal marine sedimentation in a tectonically active area of the canadian cor

estimating the mean diapycnal mixing using a finescale strain parameterization abstractfinescale methods are currently being applied to estimate the mean turbulent dissipation rate and diffusivity on regional and global scales this study evaluates finescale estimates derived from isopycnal strain by comparing them with average microstructure profiles from six diverse environments including the equator above ridges near seamounts and in strong currents the finescale strain estimates are derived from at least 10 nearby argo profiles generally 60 km distant with no temporal restrictions including measurements separated by seasons or decades the absence of temporal limits is reasonable in these cases since the authors find the dissipation rate is steady over seasonal time scales at the latitudes being considered 0 30 and 40 50 in contrast a seasonal cycle of a factor of 2 5 in the upper 1000 m is found under storm tracks 30 40 in both hemispheres agreement between the mean dissipation rate calculated using argo profiles and mean from microstructure profiles is wi

field observations of bedforms and sediment transport thresholds of fine sand under combined waves and currents abstract seabed video images and s4 wave current meter data collected during the build up of a moderate storm on the scotian shelf are analysed for bedform development and sediment transport threshold of fine sand under combined waves and currents as the storm built up the following sequence of bedforms was observed 1 relict wave dominant ripples with worm tubes and animal tracks during the preceding fairweather period 2 irregular sinuous asymmetrical current dominant and intermediate wave current ripples under bedload transport 3 regular nearly straight or sinuous asymmetrical to slightly asymmetrical wave dominant ripples under saltation suspension 4 upper plane bed under sheet flow conditions 5 small crest reversing transitory ripples at the peak of the storm and 6 large scale lunate megaripples which developed when the storm decayed these data also show that only single sets of asymmetrical intermediate wave current ripples will form when waves and currents are co linear the development of the crest reversing transitory ripples indicates a high energy transition stage under quasi sheet flow conditions a direct comparison of the skin friction combined shear velocity and the critical shear velocities for bedload suspension and sheet flow transport under estimated the onset of these sediment transport modes as the presence of ripples causes the shear stress to increase from ripple trough to ripple crest the ripple enhanced skin friction shear velocity must be used to determine properly the initiation of bedload transport at high transport stages the boundary layer dynamics is controlled mainly by the thickness of the bedload transport layer thus a transport related bedload shear velocity predicted based upon the sum of the grain roughness and bedload roughness has to be compared against the conventional threshold criterion to properly define the onset of suspension and sheet flow transport modes

weak mixing in the eastern north atlantic an application of the tracer contour inverse method abstract the tracer contour inverse method is used to infer mixing and circulation in the eastern north atlantic solutions for the vertical mixing coefficient d the along isopycnal mixing coefficient k and a geostrophic streamfunction are all direct outputs of the method the method predicts a vertical mixing coefficient o 10 5 m2 s 1 in the upper 1000 m of the water column consistent with in situ observations the method predicts a depth dependent along isopycnal mixing coefficient that decreases from o 1000 m2 s 1 close to the mixed layer to o 100 m2 s 1 in the interior which is also consistent with observations and previous hypotheses the robustness of the result is tested with a rigorous sensitivity analysis including the use of two independently constructed datasets this study confirms the utility of the tracer contour inverse method the results presented support the hypothesis that vertical mixing is small in the thermocline of the subtropical atlantic ocean a strong depth dependence o

quasi planar laminated sandstone beds of the lower cretaceous bootlegger member north central montana evidence of combined flow sedimentation abstract lower shoreface to shallow shelf strata of the bootlegger member of the lower cretaceous blackleaf formation are characterized by interbedded sandstone and mudstone sandstone beds are characterized by a peculiar planar lamination showing a subtle although perceptible undulation spacing to height ratios of the undulation are generally 100 or more typically the undulation shows no evidence of lateral accretion but only vertical aggradation and as a result most beds consist of a single laminaset aspects of quasi planar laminated beds indicate single event storm sedimentation and paleocurrent data indicate offshore sediment transport by its sedimentary characteristics and its similarity with a bed configuration generated in un experimental wave duct quasi planar lamination is produced by high energy combined flows this style of stratification should be common in the shallow marine stratigraphic record and its recognition should aid in interpreting high energy combined flow depositional events

marine and nonmarine deposition in a long term low accommodation setting an example from the middle pleistocene qm2 unit eastern central italy abstract facies anatomy and large scale stratigraphic organization of mid pleistocene strata qm2 unit exposed near the town of ortona eastern central italy have been defined through an integrated outcrop and subsurface dataset and record sedimentation within a long term low accommodation setting the studied interval can be subdivided into nine facies associations reflecting a range of continental marginal marine nearshore and innermost shelf environments and contains a well preserved record of high frequency relative sea level changes in the form of a stack of three unconformity bounded sequences each of the three sequences designated qm23 qm22 and qm21 from oldest to youngest consists of a specific subset of the nine identified facies associations as a function of preserved depositional systems and systems tracts typically the following architectural elements occur in ascending stratigraphic order i a basal unconformity molded by fluvial incision and subaerial exposure during sea level fall and shoreface erosion during subsequent rise ii a maximum regressive surface which is coincident with the sequence boundary iii a transgressive systems tract including braided river conglomerates and floodplain fines within the confines of an incised valley palustrine carbonates and back barrier lagoon mudstones and a deepening and fining upward shoreface to offshore transition facies succession bounded at the base by a wave ravinement surface iv a sharp regressive surface of marine erosion produced by shoreface incision during relative sea level fall and v a prograding downstepping and offlapping sharp based lithofacies assemblage of either beach conglomerates or sandstones ascribed to the falling stage systems tract overlain by a rooted paleosol marking subaerial exposure sequences were deposited on the uplifting palaeo adriatic shelf in response to repeated high frequency and high amplitude eustatic changes in sea level that would promote the creation of accommodation space by subtracting space to deposition the contemporaneous regional uplift of the basin margin may be accounted for the shingled downstepping configuration of individual sequences to form a falling stage sequence set of a larger composite sequence in dip view the erosional contact at the base of the qm2 falling stage sequence set is a composite regressive surface resulting from the downdip convergence and amalgamation of multiple erosional surfaces produced by the progressive basinward translation of successive sequences results from this study have direct implications for the oil and gas field development and exploration when making predictions of reservoir and seal geometries within shallow marine marginal marine and nonmarine sediments emplaced in similar long term limited accommodation settings

experiments on bed configurations in fine sands under bidirectional purely oscillatory flow and the origin of hummocky cross stratification abstract we made experiments on bed configurations in bidirectional purely oscillatory flows at a wide range of oscillation periods t and maximum orbital velocities um in two closed flow ducts 0 1 m and 0 4 m wide the motivation was that understanding of bed configurations in oscillatory flows with long periods and high velocities during storm induced deposition in the shallow ocean is needed for interpreting the stratification in such deposits the ripples produced were classified geometrically as two dimensional 2d or three dimensional 3d in plan view geometry and dynamically as oscillatory current ripples dependent upon the patterns of flow and sediment transport specific to the existence of the oscillation itself and reversing current ripples dependent on he existence of the current in one direction or the other during the oscillation runs in the small duct with effectively 0 19 mm and 0 30 mm sand showed the familiar small 2d oscillatory current ripples at short t and low um passing into much larger ripples with spacing up to 2 m at periods of 6 20 s and velocities up to 1 m s with no apparent limit on size with increasing t and um even in such a narrow duct there was some evidence of 3d geometry of the large ripples runs in the large duct with effectively 0 11 mm sand at a single period of about 9 5 s showed a progression from small 2d oscillatory current ripples through small 3d reversing current ripples to large round crested 3d oscillatory current ripples with prominent superimposed 3d to 2d reversing current ripples the large 3d ripples which increased in spacing to 1 3 m at the h ghest attainable um of 1 m s shifted in position and changed in size with time seemingly at random causing substantial local and temporary erosion and deposition at a given point on the bed there was no net aggradation during the runs but a deposit was synthesized by taking a time series of sidewall bed profiles during a run in which large 3d ripples developed from an initially plane bed and changed irregularly in size and position as they grew toward equilibrium and then plotting the profiles one above the previous with a constant upward increment the resulting stratification is strikingly similar to much hummocky cross stratification in ancient sandstones this suggests that some hummocky cross stratification is generated during sediment fallout from strong purely oscillatory flows at moderate to long oscillation periods as large 3d oscillatory current bed forms develop from a planar bed during strong but waning flow

global surface eddy diffusivities derived from satellite altimetry 1 velocities derived from aviso sea surface height observations adjusted to be nondivergent are used to simulate the evolution of passive tracers at the ocean surface eddy mixing rates are derived from the tracer fields in two ways first the method of nakamura is applied to a sector in the east pacific second the osborn cox diffusivity is calculated globally to yield estimates of diffusivity in two dimensions the results from the east pacific show weak meridional mixing at the surface in the southern ocean 1000 m2 s 1 consistent with previous results but higher mixing rates 3000 5000 m2 s 1 in the tropical ocean the osborn cox diagnostic provides a global picture of mixing rates and agrees reasonably well with the results from the east pacific it also shows extremely high mixing rates 104 m2 s 1 in western boundary current regions the osborn cox diffusivity is sensitive to the tracer initialization which we attribute to the presence of anisotropic mixing processes the mixing rates are strongly influenced by the presence of a mean flow nearly everywhere as shown by comparison with an eddy only calculation with the mean flow absent finally results are compared with other recent estimates of mixing rates using lagrangian and inverse methods

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

exploratory flow duct experiments on combined flow bed configurations and some implications for interpreting storm event stratification abstract experiments were conducted to define equilibrium combined flow bed configurations developed under a wide range of oscillatory uo and unidirectional uu velocity components with a constant oscillation period of 8 5 sec and median grain size of 0 09 mm in the range of flows studied uo 0 0 80 m sec uu 0 0 25 m sec the bed phases are no movement small 2d ripples small 3d ripples large 3d ripples and plane bed small 2d ripples are stable at low uo and uu by increasing either velocity component the plan view bed configuration becomes progressively less regular as small 3d ripples develop small 3d ripples are stable at low to moderate uo and a wide r nge of uu under purely oscillatory flow as uo increases beyond about 0 40 m sec large scale hummocky bed forms become stable when a unidirectional component is applied these bed forms quickly develop a downstream asymmetry and generally move in the direction of uu the dip angles of the lee flanks increase with increasing uu although they remain less than the angle of repose at high oscillatory velocities uo 0 70 0 80 m sec plane bed is the stable bed phase when uu 0 05 m sec much hummocky cross stratification shows a preferred dip direction of the coset laminae our experiments support the idea that such cross stratification is produced by combined flow the large 3d ripples produced at high oscillatory velocities and small to moderate unidirectional velocities would presumably generate what might be called anisotropic hummocky cross stratification if we had been able to aggrade the bed during the runs this would be the case even in dominantly oscillatory flow the experiments show that even a weak unidirectional current of several centimeters per second superimposed upon a strong oscillatory flow results in bed forms that move predominantly in a single direction and that leave sets of laminae that dip predominantly in that direction in runs at large uo the purely oscillatory large scale bed forms were quickly planed off as uu was increased from zero but a series of almost stationary gentle undulations on the bed surface persisted for indefinitely long times where the original topographic highs were situated even at the highest unidirectional flow investigated 0 25 m sec this suggests a possible origin for the gentle undulation observed in cretaceous parallel laminated shallow marine sandstones described by arnott 1987 1988 with spacings up to a few meters and heights not much more than a centimeter

neoproterozoic substrate condition vis a vis microbial mat structure and its implications sonia sandstone rajasthan india dst fast track project young scientist scheme no sr ftp es 03 2011 cas phase v upe ii programme of jadavpur university national research foundation and university of pretoria south africa

transport of north pacific intermediate water in the kuroshio oyashio interfrontal zone abstract we have estimated the volume transports of the subarctic and subtropical waters in the intermediate layer in the potential density range of 26 6 27 5 in the kuroshio oyashio interfrontal zone using hydrographic data and directly measured velocity data with a ladcp from the r v soyo maru cruise performed in may june 1998 the subarctic water flowing into this area along the oyashio near hokkaido 5 2 sv and from the subarctic front 2 0 sv merged with the subtropical water 13 5 sv along the kuroshio near japan and formed 20 7 sv of north pacific intermediate water npiw npiw mainly flowed eastward along the kuroshio extension and the transport across 158 e was about 18 8 sv 7 2 sv of subarctic water and 11 6 sv of subtropical water another 2 3 sv of the subtropical water were transported farther northward across 39 n these results support the hypothesis that npiw is mainly formed along the kuroshio extension

distribution and modification of north pacific intermediate water in the kuroshio oyashio interfrontal zone abstract a multiship ctd survey was conducted in the kuroshio oyash interfrontal zone in the area of 30 41 n 140 e 180 from may to june 1992 to examine the distribution modification process and formation site of north pacific intermediate water npiw low salinity oyashio water and high salinity kuroshio water merge along the kuroshio extension just off the east coast of japan and together flow eastward eastward geostrophic transport and salinity across the kuroshio strong current indicate that the mixture of the kuroshio and oyashia waters along the kuroshio extension can produce new npiw transport estimate suggests that the new npiw bifurcates into the interfrontal zone and into the recirculation of the subtropical gyre a salinity minimum structure can he also created due to the isopycnal mixing along the kuroshio extension between the oyashio and kuroshio waters which have different salinity and vertical velocity structures the low salinity oyashio water seen along the oyashio branches and t

maintenance of the shoreface by wave orbital currents and mean flow observations from the long island coast waves and currents were observed for a total of 36 days in august 1976 and 1977 calculations of wave transport of sediment using a bagnold equation for transport and second order stokes theory show that wave orbital current asymmetry results in landward sediment transport in 10 m or less water depth but does not significantly effect transport at greater depths calculations of sand transport using the madsen grant formulation show that during a 36 day observation period sediment in less than 10 m of water generally moved landward into the breaker and then along coast with the wave driven littoral flow the calculations show that below 10 m the generally upwelling coast parallel mean flow did not move sediment however during two days of a mild summer northeaster storm a downwelling coastal jet developed with 60 cm sec sup 1 maximum current the calculations show that if this flow had been combined with the intense wave regime of the succeeding several days sediment would have been entrained across the lower as well as the upper shoreface movement would have been offshore and alongshore such storm transport is believed to be typical of the more intense winter storms and to be responsible for the erosionalmore shoreface retreat that has caused up to a kilometer of shoreline retreat on the long island coast in the last century less

high resolution seismo stratigraphy and sedimentological properties of late and postglacial sediments in lac guillaume delisle estuary and nastapoka sound eastern hudson bay lac guillaume delisle estuary and nastapoka sound are two sedimentary basins that recorded the late quaternary deglaciation on the eastern coast of hudson bay acoustic profiles reveal an average sediments thickness of 15 m in the estuary and 6 m in the sound these sediments reach 70 m thick in deep glacial troughs within the studied basins four seismo stratigraphic units overlying the acoustic basement were recognized unit 1 subaqueous ice contact and draped glaciomarine deposits associated with the quebec labrador ice sector qlis of the laurentide ice sheet lis and the tyrrell sea records the presence of a short ice marginal stillstand during glacial retreat unit 2 paraglacial and postglacial fluvial deltaic deposits and unit 3 postglacial silty deposits result from erosion of emerged sediments and redeposition in response to changes in relative sea level rsl finally unit 4 is composed of deformed deposits associated with a mass wasting event the stratigraphic sequence and the spatia

observations of sand waves megaripples and hummocks in the dutch coastal area and their relation to currents and combined flow conditions 1 this paper aims to investigate the distribution and stability of large scale bed forms in response to storm and fair weather conditions in a shallow marine environment multibeam and side scan sonar data off the dutch coast median grain size 0 25 0 35 mm were collected to monitor sand waves 100 800 m and superimposed megaripples 1 40 m through multiple storm and fair weather events box cores were used to observe the vertical bed structure and grain size in the dutch coastal area two dimensional 2 d megaripples x 1 15 m are the dominant bed forms in current dominated 0 4 m s tidal flow regimes with oscillatory flows 0 4 m s undulating bed topography of mound like 3 d bed forms 20 40 m is observed immediately after storms these bed forms are covered by smaller 3 d megaripples which are related to sets of low angle converging laminae in box cores interpreted as hummocky cross stratification hcs the sand waves form compound bed forms of sets of 2 d and 3 d megaripples the morphology of the sand waves is a function of the general wind wave climate of the marine environmental setting with flat topped 3 d sand waves occurring in shallow wave dominated settings and 2 d sand waves occurring in the tide dominated environment farther offshore copyright 2005 by the american geophysical union

combined flow model for vertical stratification sequences in shallow marine storm deposited beds abstract we develop a model to help explain the wide variety of vertical stratification sequences in shallow marine sandstones this model embodied in a set of vertical sequence cartoons predicts or accounts for vertical stratification sequences in beds of free sandstone deposited from a full range of decelerating combined flows as well as from purely unidirectional and oscillatory flows according to the model vertical stratification sequences in storm deposited sandstone beds are the outcome of the time history of the bed configuration as deposition proceeds the idealized sequences are based on the initial velocities and subsequent deceleration histories of the unidirectional and oscillatory flow components twenty qualitatively different sequences starting with plane bed are generated and an additional 26 sequences result from omitting one or more of the lowermost intervals in succession the model thus accounts for 46 distinct kinds of sequences five major simplifying assumptions are built into the model bidirectional flows linear deceleration of both unidirectional and oscillatory flow components time independent deposition rate time independent sediment size and equilibrium bed configurations owing to these assumptions the model is likely to be applicable to only a small subset of vertical stratification sequences observed in shallow marine sandstones as more information on combined flow bed configurations becomes available these assumptions could be relaxed to provide a more refined and complete representation of vertical stratification sequences since the model generates vertical sequences formed from any kind of decelerating flow the bouma sequence for deposits from purely unidirectional turbidity currents and also sequences resulting from decelerating purely oscillatory flows similar in appearance to many proposed generalized tempestite sequences are end member cases in the model the model is also extended slightly to explain the geometry of the uppermost bedding surfaces of storm generated sandstones by consideration of disequilibrium effects

microbial mat structures in profile the neoproterozoic sonia sandstone rajasthan india abstract ubiquitous microorganisms especially cyanobacteria preferably grow on the sediment surface thereby producing microbial mats in the absence of grazers and bioturbators microbial mat is a unique feature of the proterozoic most of the papers so far published described a wide variety of bed surface microbial mat structures with rare illustrations from sections perpendicular to bedding nonetheless bed surface exposures are relatively rare in rock records this limitation of bed surface exposures in rock records suggest that a study of microbial mats in bed across sections is needed the 60 m thick coastal marine interval of the sonia sandstone formation is bounded between two terrestrial intervals a transgressive lag at the base and an unconformity at the top and has been chosen for exploration of microbial mat structures in bed across sections a wide variety of microbial mat induced structures in bed across sections are preserved within the coastal interval of the sonia sandstone though many of these structures are similar in some aspects with bed surface structures some of those presented here are new the palaeogeographic range of these microbial structures extends from supralittoral to neritic diagenetic alterations of microbial mats produce pyrite and those zones are suitable for the preservation of microbial remains sem and edax analyses show fossil preservation of filamentous microbial remains that confirm the presence of microbial mats within the coastal interval of the sonia sandstone effects of proliferation of microbial mats in the siliciclastic depositional setting are numerous the mat cover on sediment surfaces hinders reworking and or erosion of the sediments thereby increases the net sedimentation rate successive deposition and preservation of thick microbial mat layer under reducing environments should have a great potential for hydrocarbon production and preservation and therefore these proterozoic formations could be a target for exploration

eifelian givetian middle devonian high paleolatitude storm and wave dominated shallow marine depositional systems from the bidouw subgroup bokkeveld group of south africa abstract the sedimentology of the eifelian givetian middle devonian bidouw subgroup in the clanwilliam sub basin of south africa has been reassessed four distinct lithofacies associations are recognized a d and are representative of the deposits of offshore os offshore transition zone to distal lower shoreface otz dlsf proximal lower shoreface plsf and upper shoreface beach usf beach paleoenvironments these paleoenvironments are arranged as several t r controlled storm and wave dominated shallow marine depositional systems the presence of storm and wave dominated shallow marine depositional systems in the bidouw subgroup as well as the preceding emsian eifelian early middle devonian ceres subgroup provides an alternative explanation to storm and wave dominated delta and mixed wave and tide dominated delta models that have previously been proposed for the bokkeveld group sequence stratigraphic analysis of the bidouw subgroup suggests that although sedimentation occurred during two large scale second order transgressive events the succession was predominantly regressive third order and fourth order transgressive regressive t r sequences are more numerous with respect to the preceding ceres subgroup suggesting that the driver for t r cyclicity and relative sea level change was more active during the eifelian givetian than in the emsian eifelian of south africa these data are important since relative sea level change and its effects on paleoenvironmental change at high paleolatitudes during the devonian period are poorly known

observation of frontal waves and associated salinity minimum formation along the kuroshio extension 1 high resolution observations with a towed conductivity temperature depth system were conducted along the kuroshio extension where the kuroshio and the oyashio merge and new north pacific intermediate water npiw is formed large amplitude frontal waves at an intermediate depth corresponding to a density range of npiw 26 6 26 9 were discovered here along the main stream of the kuroshio extension a remarkable salinity minimum due to the intense intrusions of oyashio water was observed near the trough of the frontal wave with an apparent wavelength of 100 km around the troughs crests of the frontal waves the horizontal velocity in the intermediate layer was directed to the southern kuroshio water side northern oyashio water side relative to the upper layer horizontal velocity fields converged diverged around the wave trough crest indicating downwelling upwelling the amplitude of the frontal waves was observed to grow in the downstream direction where isolated eddies were observed this suggests that the development of frontal waves and wave breaking enhance isopycnal mixing and cross frontal exchange across the main stream of the kuroshio extension

a 210pb sediment budget and granulometric record of sediment fluxes in a subarctic deltaic system the great whale river canada abstract to elucidate how modern river discharge conditions of the great whale river gwr are represented in the marine sedimentary record eight box and gravity cores were examined in terms of 210 pb and 137 cs radiochemistry granulometry and physical sedimentary structures these data were analyzed to provide insights into sedimentary processes and patterns at the study site sediment accumulation in the study area appears to be a relatively steady process over time scales of 50 100 yr allowing biological activity to overprint the primary depositional fabric subtle differences between 137 cs and 210 pb sediment accumulation rates sars suggest an offshore shift in the locus of fine sediment deposition during the past 150 yr which may be a result of ongoing climatic warming leading to decreasing sea ice coverage and a more energetic marine environment under present day conditions 23 40 000 t yr of the discharged sediment appear to accumulate in a 25 km 2 area off the river mouth the remaining 77 136 000 t yr are either deposited further offshore possibly along the northeastern shore as a result of hudson bay s counterclockwise circulation or dispersed into the hudson bay system grain diameter frequency analyses suggest that environmental processes controlling sediment transport and deposition vary over decadal time scales although we cannot define an exact cause for this pattern these shifts may be related to variations in river discharge wave climate possibly due to windier conditions or less sea ice dampening bioturbation or a combination of all this suggests that also longer term river discharge signals are preserved in the marine sedimentary record offshore the great whale river in summary no major change in sediment discharge over the past 150 yr was observed however the offshore shift in the locus of sediment deposition suggests that a warming climate will lead to more energetic marine conditions less sea ice coverage and an increased offshore transport of terrestrial matter

southward eddy heat transport occurring along southern flanks of the kuroshio extension and the gulf stream in a 1 10 global ocean general circulation model abstractthe present study investigates meridional heat transport induced by oceanic mesoscale variability in the world ocean using a global ocean general circulation model ogcm running on the earth simulator the results indicate prominent poleward eddy heat transport around the western boundary currents and the antarctic circumpolar current and equatorward eddy heat transport in the equatorial region consistent with the previous studies using coarse resolution ogcms such poleward eddy heat transport in midlatitude oceans suggests that the eddies act to reduce meridional background temperature gradients across the currents as would be expected based on baroclinic instability interestingly however along the southern flanks of the eastward jets of the kuroshio extension and the gulf stream southward eddy heat transport occurs in subsurface layers this is likely due to the southward migration of warm water cores originating from southern areas adjacent to these currents southward movement of th

experiments on oscillatory flow and combined flow bed forms implications for interpreting parts of the shallow marine sedimentary record abstract analog laboratory experiments were conducted to investigate subaqueous bed forms generated under storm like oscillatory and combined flow experiments were carried out in a large wave tunnel and used a range of sand sizes fine and very fine wave periods 10 5 and 8 s oscillatory velocities 0 to 125 cm s and unidirectional velocities 0 to 25 cm s at low unidirectional velocities 10 cm s addition of an increasing collinear oscillatory flow caused the bed to evolve from small scale wavelength 100 cm symmetric orbital ripples to plane bed at higher unidirectional velocities 10 cm s a similar trend was noted but ripples were more asymmetric three phase diagrams are presented to summarize the observed relationships of bed configurations to flow conditions these diagrams are intended to assist in the interpretation of shallow marine sedimentary environments where oscillatory and combined flow are thought to be omnipresent distinctive features of small scale asymmetric combined flow ripples generated are a 3d planform round crest and convex up sigmoidal profile with local pronounced scour at the toe of the stoss side giving the ripple profile a boxy appearance similarly large scale asymmetric combined flow ripples had broad and round crests convex up stoss sides and compressed profiles due to scouring at the toe of the stoss side hummocky bed forms were generated under moderate to high oscillatory velocities and low unidirectional velocities hummocks were not observed as a distinct bed state but rather appeared to mark transitions in bed form scale and symmetry hummocks were more prevalent at longer oscillatory periods and in finer grained sediment stratification produced by synthetically aggrading hummocky bed profiles closely resembles hummocky cross stratification with the introduction of only a small unidirectional flow component hummocks evolve into downstream migrating large scale asymmetric ripples and the resultant cross stratification becomes similar to that produced by unidirectional flow dunes accordingly these experiments suggest that much of the hummocky cross stratification observed in the stratigraphic record is produced by storm generated long period oscillatory dominant combined flows inasmuch as long period high energy waves require deep wide basins to form hummocky cross stratification may therefore serve as a useful indicator of deposition in unrestricted open water conditions

stratigraphic controls of soft bodied fossil occurrences in the cambrian chengjiang biota lagerstatte maotianshan shale yunnan province china abstract the early cambrian maotianshan shale exposed near kunming china is one of the oldest and best preserved konservat lagerstatten containing the chengjiang biota although the fossils have been well studied the depositional processes and stratigraphic relationships amongst the fossil bearing localities are poorly understood largely due to limited continuous exposures and structural complexity in this area in this study we use a detailed facies and stacking pattern analysis to delineate the depositional history and stratigraphic relationship of the maotianshan sedimentologic observations from five prolific fossil localities of the chengjiang biota have yielded six distinct facies within the maotianshan shale the three coarse grained facies composed of siltstones and very fine sandstones f1 f3 contain sedimentary structures including hummocky cross stratification and combined flow ripples that are consistent with deposition within storm wave base the fine grained facies composed of interbedded silty mudstones and clay rich mudstones f4 f6 were deposited below the wave base and represent episodes of lower storm frequency and pelagic sedimentation these six facies have specific stacking patterns indicating the presence of five distinct depositional units each of those depositional units is bound on its upper and lower contact by a flooding surface fining upward successions near the base of each stratigraphic unit are interpreted as short lived marine transgressions these are overlain by coarsening upward stacked facies interpreted as a period of shoreline progradation the fossils of the chengjiang fauna are exclusively found in the coarsening upward part of the depositional units the oldest fossil bearing intervals are associated with the most westerns sections in the study area in contrast the youngest fossil bearing intervals are found in the most eastern sections this time transgressive relationship is interpreted to reflect a genetic relation between distinct sedimentary processes and environments and the burial and preservation of the chengjiang biota

high frequency eustatic sea level changes during the middle to early late ordovician of southern jordan indirect evidence for a darriwilian ice age in gondwana abstract the middle to early late ordovician hiswah and dubaydib formations in southern jordan provide a well constrained sedimentary record of 4th and 3rd order relative sea level change along the northern tectonically quiescent subpolar gondwana continental margin cyclic deposition occurred on a wave and storm dominated microtidal shelf dominated by shoreface and offshore transition zone facies cycles are commonly bounded by amalgamated bounding surfaces sb ts or sb mfs and are characterised by stacked transgressive systems tracts tsts the small facies dislocation across key sequence bounding surfaces indicates a 15 50 m change in relative sea level fourth order sequences are hypothesized to be paced by the long eccentricity 405 kyr cycle and consequently 3rd order sequences are calculated to be 1 2 m y and 2 4 m y long these correlate with the global eustatic sea level curve in comparison with mesozoic and cenozoic sequence stratigraphical data we conclude that the 1 2 m y cycles correspond with long obliquity cycles predominant in icehouse conditions and the 2 4 m y cycles with the long eccentricity cycle predominant during greenhouse conditions we propose a darriwilian ice age during which orbitally induced cold snaps caused the expansion and amalgamation of small medium scale ice sheets the reduced size of the correlative positive carbon isotope excursion compared to that in the hirnantian may indicate that the darriwilian ice sheets only reached the sea in a few places the absence of glacio terrestrial deposits of middle ordovician age is most likely due to subsequent glacial erosion during repeated ice advances up to and including those in the hirnantian the existence of darriwilian ice sheets is consistent with zooplankton province distributions that indicate a polar front at 40 s during the ice age it is likely that polar ice existed throughout the ordovician

tectonostratigraphy of the chazyan late middle early late ordovician mixed siliciclastic carbonate platform quebec embayment abstract the middle to lower upper ordovician chazyan platform succession of eastern north america extends landward of the ancient quebec embayment along the laurentian margin part of a foreland basin peripheral to an arc collisional plate boundary the platform grades from seaward reefal carbonate chazy group champlain valley into platform and foreland interior tide and wave dominated siliciclastics rockcliffe formation and restricted peritidal muddy carbonate hog s back formation the latter two formations occur in the sedimentary ottawa embayment which overlies the trace of a neoproterozoic rift prominent tectonostratigraphic surfaces bound and subdivide the chazyan platform interior succession and are characterized by abrupt marine transgressions local synsedimentary faults and seismogenic beds the depositional history includes 1 accumulation of shallow marine siliciclastics rockcliffe fm across a differentially faulted paleoplatform 2 abrupt regional retrogradation 100 km of this siliciclastic system replaced by an intraplatform shale basin lower hog s back formation 3 basin fill and development of a low energy muddy carbonate platform interior upper hog s back formation coincident with regional fall in sea level and change in subsidence along the laurentian margin and 4 abrupt high frequency base level changes preceding regional onlap of mohawkian turinian shale contemporary with local synsedimentary deformation and rapid subsidence along the distal arc collisional plate boundary structurally controlled sedimentation patterns in the platform and foreland interior document episodic tectonism coincident with relatively sustained deposition along the outer platform the chazy group this difference is interpreted to be a response to foreland interior flexuring modified by local reactivation of the precambrian rift that was coincident with preferential subsidence at seaward sites more proximal to structural loading along the arc collision plate boundary

morphology and facies architecture of a falling sea level strandplain umiujaq hudson bay canada coastal strandplain deposits near umiujaq eastern hudson bay canada were formed under falling relative sea level conditions resulting from postglacial isostatic uplift ground probing radar profiles across the strandplain reveal a lower progradational unit lpu discordantly overlain by an upper progradational unit upu which were correlated with stratigraphic sections exposed in incised valley walls the discordance is a wave erosion surface wes that separates fine shoreface sands of the lpu from coarse sand and gravel of the upu major basal downlap surfaces can be traced updip into marine terraces and define downstepping wedges the downstepping is interpreted as representing autocyclic morphological reconfiguration rather than a response to changes in the rate of sea level fall the internal architecture is strongly dependent on the accommodation and thus on antecedent topography a conceptual model for strandplain deposition under falling sea level incorporates a bipartite shallowing upward sandy succession when sufficient accommodation is available where accommodation space is limited a sharp based bar and beach sandbody directly overlies muddy deeper water deposits and the wes resembles a regressive surface of erosion

eddy stirring and horizontal diffusivity from argo float observations geographic and depth variability stirring along isopycnals is a significant factor in determining the distribution of tracers within the ocean salinity anomalies on density surfaces from argo float profiles are used to investigate horizontal stirring and estimate eddy mixing lengths eddy mixing length and velocity fluctuations from the ecco2 global state estimate are used to estimate horizontal diffusivity at a 300 km scale in the upper 2000 m with near global coverage diffusivity varies by over two orders of magnitude with latitude longitude and depth in all basins diffusivity is elevated in zonal bands corresponding to strong current regions including western boundary current extension regions the antarctic circumpolar current and equatorial current systems the estimated mixing lengths and diffusivities provide an observationally based data set that can be used to test and constrain predictions and parameterizations of eddy stirring

deglaciation landforms and c 14 chronology of the lac guillaume delisle area eastern hudson bay a report on field evidence abstract this paper presents new field data pertaining to the deglaciation of the lac guillaume delisle area aiming to establish its emplacement in time and space between the breaching of the laurentide ice sheet lis over hudson bay and the final ice disintegration over northern quebec and labrador the deglaciation of the east coast of hudson bay started at 8200 cal bp in the south western sector of the lac guillaume delisle estuary when the marine limit was at 271 m above sea level asl by 8000 cal bp frontal moraines and proximal glacio marine sediments were deposited in the transverse valleys along the coastal cuesta ridges at a mean elevation of 250 m asl they are associated with a regional topographic pinning event of the western margin of the quebec labrador ice sheet qlis on the high coastal relief at that time the coastal relief encouraged a change in deglaciation mode from fast calving in the open and deep tyrrell sea to a tidewater ice sheet controlled by the topography the ice front thereafter retreated eastward under very large and fast crustal unloading where ice contact deltas fed by short sandar and eskers were deposited between 7900 and 7400 cal bp between 240 and 195 m asl as the ice front was receding inland and lost contact with tyrrell sea a series of deposits and landforms characterize this modification in the sedimentation regime when the ice sheet margin changed from tidewater to terrestrial dating shows that the deglaciation of the western margin of qlis on land was very fast i e faster than when the front of the ice sheet was in contact with the tyrrell sea as the fall of the relative sea level continued a large volume of paraglacial sediments was deposited in the river valleys making up vast fluvial terraces and deltas between 6500 and 5800 cal bp between 125 and 100 m asl since then land emergence has continued at a rate of about 1 3 m century downcutting by rivers post glacial deltaic sedimentation and shoreline changes still continue today

damping and phase advance of the tide in western hudson bay by the annual ice cover abstract admittance analysts of yearlong current meter records and tidal height data shows that the annual ice cover affects the tidal currents and heights in hudson bay along the west coast of the bay the semidiurnal tidal current and height are reduced by 10 and arrive twenty minutes earlier in winter than in summer the diurnal tide shows similar characteristics but its weaker signal does not produce as reliable and consistent results a simple theory of a rejecting kelvin wave in a rectangular bay predicts that the extra damping by the ice cover causes the amphidromic points to move towards the shore along which the reflecting wave travels thus during the winter one sees relatively more of the incident wave than the reflected wave which causes a phase advance while the sum of their amplitudes decreases although further numerical modeling is required to determine the exact increase in linear damping coefficient caused by the ice cover the simple analytical theory estimates it to be of the same or

spatial and temporal variability of global ocean mixing inferred from argo profiles 1 the influence of turbulent ocean mixing transcends its inherently small scales to affect large scale ocean processes including water mass transformation stratification maintenance and the overturning circulation however the distribution of ocean mixing is not well described by sparse ship based observations since this mixing is both spatially patchy and temporally intermittent we use strain information from argo float profiles in the upper 2 000 m of the ocean to generate over 400 000 estimates of the energy dissipation rate indicative of ocean mixing these estimates rely on numerous assumptions and do not take the place of direct measurement methods temporally averaged estimates reveal clear spatial patterns in the parameterized dissipation rate and diffusivity distribution across all the oceans they corroborate previous observations linking elevated dissipation rates to regions of rough topography we also observe heightened estimated dissipation rates in areas of high eddy kinetic energy as well as heightened diffusivity in high latitudes where stratification is weak the seasonal dependence of mixing is observed in the northwest pacific suggesting a wind forced response in the upper ocean

backset lamination produced by supercritical backwash flows at the beachface shoreface transition of a storm dominated gravelly beach middle pleistocene central italy abstract bedforms and resulting sedimentary structures of interpreted upper flow regime origin are fairly common in various ancient and modern depositional settings yet outcrop examples of shallow water strata dominated by sedimentary structures arising from such flow conditions are rarely documented this outcrop based study presents the first detailed analysis of mid pleistocene beachface shoreface strata containing sedimentary structures interpreted to have been formed by storm generated backwash flows during the transition in flow regime from supercritical to subcritical here we propose that moving down the steep beachface backwash flows rapidly accelerated and became thinner experienced abrupt deceleration and flow thickening passing through an erosional hydraulic jump in the trough at the toe of the beachface and then waned to thicker and subcritical conditions just downflow of the hydraulic jump in this frame landward dipping backset laminae deposited on the downflow side of the trough evolved into thinner upper stage plane parallel laminae further downstream the transition from the proximal to the distal upper shoreface records a significant increase of preserved wave ripples and burrowed intervals in concert with a progressive decrease in thickness and grain size of individual sets of plane parallel laminae and increase of gravel filled gutter casts

foredune development along a subarctic emerging coastline eastern hudson bay canada abstract a study of sedimentary processes and evolution of subarctic foredunes along a rapidly emerging coastline in southeastern hudson bay showed that niveo eolian sedimentation is a significant process contributing to the formation of these foredunes the fall storm berm and the sand laden ice foot are the prime sedimentary sources for the niveoeolian deposits which are generally coarser grained than the eolian sand deposited during summer the annual sedimentation in the backshore zone is less than in typical mid latitude regions the development of established foredunes in this subarctic environment seems to require a longer period of time than in other climatic zones the short term backshore evolution 1954 1990 shows that sediment supply appears to be a major factor controlling foredune morphology and dynamics phases of sediment surplus seem to correspond to rapid seaward progradation and formation of low foredune terraces or low foredune ridges with a beach ridge like morphology conversely high foredunes probably develop during periods of lower sediment supply and slower beach progradation on a longer time scale the relative sea level fall controls coastline progradation and results in the formation of raised coast parallel relict foredune ridges

pathways of the north pacific intermediate water identified through the tangent linear and adjoint models of an ocean general circulation model 1 this study develops a strategy for tracing a target water mass and applies it to analyzing the pathway of the north pacific intermediate water npiw from the subarctic gyre to the northwestern part of the subtropical gyre south of japan in a simulation of an ocean general circulation model this strategy estimates the pathway of the water mass that travels from an origin to a destination area during a specific period using a conservation property concerning tangent linear and adjoint models in our analysis a large fraction of the low salinity origin water mass of npiw initially comes from the okhotsk or bering sea flows through the southeastern side of the kuril islands and is advected to the mixed water region mwr by the oyashio current it then enters the kuroshio extension ke at the first ke ridge and is advected eastward by the ke current however it deviates southward from the ke axis around 158 e over the shatsky rise or around 170 e on the western side of the emperor seamount chain and enters the subtropical gyre it is finally transported westward by the recirculation flow this pathway corresponds well to the shortcut route of npiw from mwr to the region south of japan inferred from analysis of the long term freshening trend of npiw observation copyright 2013 john wiley sons ltd

predicting ripple roughness and sand resuspension under combined flows in a shoreface environment ripple measurements and flow and sediment dynamical data obtained from the shoreface of the middle atlantic bight using instrumented tripods were analyzed to evaluate various predictors of ripple geometry and roughness ripple roughness controls on sand resuspension and suspended sediment concentration profiles under combined waves and currents were also evaluated the limited observation of sand ripples in the field indicates that the grant and madsen 1982 method overestimates ripple roughness while the nielsen 1981 method tends to under predict ripple roughness a modified ripple predictor is thus proposed based on the grant and madsen method and it is shown to give reasonable predictions under the present experiment conditions this modified ripple prediction along with wave current and suspended sediment concentration data recorded by the tripods were then brought into the combined flow bottom boundary layer model of grant and madsen 1986 and the modified rouse equation of glenn and grant 1987 to calculate sand resuspension coefficient 0 and to predict suspended sediment concentration profiles it was found that under low energy fair weather conditions sand ripples are in the equilibrium range and ripple roughness increases with the bed shear stress this causes strong vortex activity close to seabed and thus higher resuspension coefficient reference concentrations are moderate due to this high resuspension coefficient even though bed shear stresses are low under moderate storm conditions ripple break off occurs and ripple roughness will decrease with bed shear stress this reduces the vortex activity and hence sand resuspension coefficient 0 the combination of this moderately high bed shear stress and reduced but still moderate ripple roughness favours sand suspension and produces the highest reference concentration for the encountered experimental conditions as bed shear stress is further increased ripples are nearly washed out and sand resuspension coefficient is further decreased approaching the previously suggested constant value of 1 3 10 4 this corresponds with the lowest reference concentration despite the high bed shear stress suspended sediment concentrations predicted by the modified rouse equation using this time variable resuspension coefficient and properly calculated bottom boundary layer parameters are reasonable compared to the field measured concentration profiles