controlling factors of rhythmic sedimentation processes on an intertidal estuarine mudflat role of the turbidity maximum in the macrotidal seine estuary france the aim of this study is to analyse and to quantify the fine particles transfer i e 7 1 m then deposition of spm from the turbidity maximum becomes important allowing fine particles to settle on the mudflat where the current velocities are low 0 4 m s 1 on tides of lower range 7 1 m bed elevation levels suggest that erosion of the mudflat surface dominates however dewatering processes also occur in the soft mud deposits resulting in compaction during periods of wave activity and periods of increasing river discharge the mudflat surface experiences rapid erosion these periods of erosion sudden or progressive imply a transfer of fine grained material from the mudflat surface back into the tm the long term 22 months high frequency 1 measurement every 10 min and high resolution 0 6 mm dataset obtained from the altimeter allows quantification of the volume of material exchanged between the intertidal area and the estuarine standing stock of spm the maximum of deposition on the studied mudflat during the study was of 27 cm with highest deposition occurring after the periods of highest river flow and implying that between 25 and 40 of the maximum estimated mass of spm held within the estuarine tm 300 000 500 000 t had been temporarily deposited on the mudflat likewise following periods of resuspension by wave activity bed elevations reduced by an order of 1 cm suggesting a release of between 1 1 5 of the tm load from the mudflat back into suspension the study shows that lateral exchanges of sediment between the intertidal reaches of the estuary and the water column are an important part of the sediment budget and that the supply of sediment available for deposition i e the tm has a causal relationship with sedimentation rates experienced by intertidal mudflats

holocene and modern sediments in the seine estuary france a synthesis this synthesis of numerous studies on the holocene and modern sediments in the macrotidal setting of the seine estuary demonstrates their overall evolution in common with a number of estuaries the lower seine was an incised valley during the weichselian glacio eustatic sea level fall and infilling occurred during the subsequent lowstand the holocene sea level rise and the late holocene stillstand in the upper estuary above the basal gravel bed fluvial freshwater deposits filled the valley next fine sand and silts invaded the estuary upstream to rouen the sequence ends in loam resulting from an increase in the supply of sediment to the fluvial system in the upper estuary anthropogenic deepening of the modern channel results in erosion of the holocene sediments the only bedforms are thin and narrow sand sheets and some rare megaripples in the lower estuary above the weichselian basal gravel the holocene wedge records the change from a transgressed fluvial setting i e gravel beds to an open estuarine environment i e tidal delta the modern seine estuary has been progressively infilled by marine sands and silts now silts and clays supplied during high river flows accumulate at the outlet and offshore sands and gravel of the eastern bay of the seine are temporarily covered with veneers of mud these freshly deposited muds i e mud patches are periodically partly reworked by waves and strong tidal currents but silting of the inner shelf is noticeable copyright 2003 john wiley sons ltd

on the dimensions of passive ripple marks in the nearshore zone abstract it has been proven on the basis of field observations that the length and height of passive ripple marks in the nearshore zone depend primarily on the sediment grain size d as it turns out the relationships d and d may be approximated with a high degree of accuracy by the equation 17 3 d 1 22 83 5 d 1 08 in which and are expressed in centimeters and d in millimeters it follows that passive ripple dimensions together with grain size distribution of bedload can present only a minimum shear stress at a moment preceding storm damping they will never indicate the storm strength in its maximal development and it is therefore impossible to completely reconstruct the ancient conditions of wave generation by passive ripple mark parameters

sea surface temperature records in the northern south china sea from mid holocene coral sr ca ratios 1 three mid holocene sea surface temperature sst records spanning more than 30 years were reconstructed for the northern south china sea using sr ca ratios in porites corals the results indicate warmer than present climates between circa 6100 yr b p and circa 6500 yr b p with the mid holocene average minimum monthly winter ssts the average maximum monthly summer ssts and the average annual ssts being about 0 5 degrees 1 4 degrees c 0 degrees 2 0 degrees c and 0 2 degrees 1 5 degrees c higher respectively than they were during 1970 1994 summer ssts decrease from circa 6500 yr b p to circa 6100 yr b p with a minimum centered at circa 6300 yr b p the higher average summer ssts are consistent with a stronger summer monsoon during the mid holocene and the decreasing trend indicates a secular decrease of summer monsoon strength which reflects the change in summer insolation in the northern hemisphere el nino southern oscillation enso cycles were apparent in both the mid holocene coral and modern instrumental records however the enso variability in the mid holocene ssts was weaker than that in the modern record and the sst record with the highest summer temperatures from circa 6460 yr b p to 6496 yr b p shows no robust enso cycle this agrees with other studies that indicate that stronger summer monsoon circulation may have been associated with suppressed enso variability during the mid holocene

source discrimination of fine grained deposits occurring on marine beaches the calvados beaches eastern bay of the seine france in tide dominated systems fine grained deposits occur in intertidal areas of inner estuaries as loci of convergence of fluvial and marine material even in the vicinity of estuaries mud deposits are rare on open sandy beaches this study focuses on temporary occurrences of muddy sediments on marine beaches along the calvados coastline in normandy adjacent to the macrotidal seine estuary france clay mineralogy major minor trace elements and radionuclides were used as particulate markers to determine the provenance of the mud deposits the fine fraction defined here as particles 50 m was analysed in surficial muddy sediments on seven beaches between the seine estuary and the orne river mouth sampled between february 2002 and june 2003 the deposits were compared to earlier holocene relict deposits which crop out on some beaches and on the shoreface and to mesozoic marls and limestones which have detached from the coastal cliffs the use of the three types of particulate markers revealed no significant seasonal or geographical variations between the beaches the muddy deposits were made up of the same sedimentary pool of particles the clay mineralogical and geochemical characteristics of these mud deposits enabled modern i e present day and earlier holocene fine silts and clays to be distinguished from ancient i e mesozoic sediments the use of radionuclides 60co and 137cs confirmed the marine influence in the modern deposits with a decreasing gradient along the calvados beaches towards the east the presence of several specific major minor trace elements e g ti p revealed that some of the fine material originated in the seine estuary despite the occurrence of easily erodable rocks i e clays marls and limestones in the coastal cliffs this source represented a limited supply which is only of local significance small rivers such as the orne dives and touques which discharge in the study area act as secondary suppliers of fine grained material to this system in spite of the exposed coastal setting where strong tidal currents and waves occur the beaches have become a distal part of the seine estuarine system and form a temporary sink for strongly mixed fine material mainly of riverine seine river and open marine bay of the seine and the central english channel origins this is consistent with the infilling of the estuary the reduction in accommodation space in its inner part and the offshore shifting of the depocentre of the mud

the last millennia history of detrital sedimentation in the lower seine valley normandy nw france review post glacial climate changes and sea level fluctuations have strongly influenced n w european environments and sedimentation to these natural events increasing anthropogenic pressure has to be added forest clearance and agricultural development are the main factors responsible for the erosional processes in northwest europe this article analyses holocene sequences of the lower seine valley lsv paris basin to understand better the origin of detrital and terrigenous input and how much humans have contributed to it three main sectors of the lsv are analysed estuarine fluvial and tributaries since neolithic times there are seven erosional phases that can be identified and essentially linked to human pressure terra nova 00 000 000 2010

holocene to modern fine grained sedimentation on a macrotidal shoreface to inner shelf setting eastern bay of the seine france abstract this paper presents the results of an investigation on different timescales of the main mechanisms governing fine grained sedimentation on a macrotidal sandy shoreface to inner shelf setting with a supply of terrigenous sediment the subtidal area of the southeastern bay of the seine calvados coast france interpretation and calibration of side scan sonar imagery clearly shows that compact clays crop out in water depths of 3 6 m radiocarbon dating and palynological studies of the material sampled using long cores from this subtidal area show that these relict sediments constitute the infilling of lateral valleys of the palaeo seine during the last 10 000 years the lower parts of these deposits consist of compact clays that accumulated in a floodplain setting later a salt marsh environment and are succeeded by sediment with sand mud couplets which formed in a tidal estuarine system the top of this sequence has been truncated by a wave erosion surface formed during the holocene transgression today the sediment accumulating is composed of fine sand mixed with fine grained sediment and sometimes temporarily covered by fresh mud the more recent sedimentological data compared with surveys in the 1960s 1970s demonstrate both an increase in the erosion of the submerged earlier holocene clays and an increase in the mud silt clay content of the superficial sediments on a seasonal timescale the seafloor is affected by high frequency variations in the nature of the contemporary sedimentary cover spatial and temporal observations of the seafloor composition have been undertaken during different seasons for four years 1998 2001 to study these sedimentation events the sedimentation on the inner shelf is at its maximum when veneers of fresh mud occur after some particular hydrological periods i e sustained high river outputs following several dry years i e prolonged weak river flows when significant volumes of mud have been stored within the seine estuary such mud veneers result from 1 the direct supply of river born material 2 the seaward shifting of the turbidity maximum and 3 the resuspension of mud from the lower estuary i e fluid mud and intertidal flats under wind waves and have been termed estuarine flood deposits on a longer timescale of at least the last decades the southeastern bay of the seine is an area of erosion but it is subjected to ephemeral fine grained sedimentation on a seasonal timescale

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

middle to late holocene landscape changes and geoarchaeological implications in the marshes of the dives estuary nw france abstract holocene palaeogeographic changes in the lower dives valley a small estuarine system in normandy france have been investigated using a combination of facies interpretation from borehole cores 14c dating and pollen analysis the palaeoenvironmental record is broadly similar to that of other coastal and estuarine systems along the english channel but exhibits specific features in comparison with large estuarine and coastal systems especially as regards the narrow lower valley and its margins the identified environments included uniform tidal 6800 5500 2200 2000 cal bp freshwater fen 5500 3300 cal bp and drained floodplain 300 0 cal bp in contrast landscape variability was high during the periods 3300 2300 and 1900 300 cal bp in relation to gradients in environmental conditions from downstream to the upper reaches of the valley a significant palaeogeographic change between ca 3000 and 2200 cal bp indicates that episodes of strong coastal hydrodynamic forcing notably storm events may have had dramatic consequences with significant implications for human activities the pollen diagrams show evidence of the opening up of woodland in order to develop pastures and agriculture on the edges of the freshwater marsh during the bronze age 4500 2800 cal bp although the settlement patterns remain unknown because of the sparse archaeological discoveries related to this period during the iron age increased land use in the valley bottom had a significant impact on the environment from the iron age to the late roman period 2800 1500 cal bp the dramatic change caused by marine flooding and the large size of the tidal environment favoured the development of salt extraction sites from the coast to the inner estuary from the early middle ages restricted tidal influences and the progressive silting of the valley bottom by overbank deposits enabled a lasting change with the development of pastureland and the miscellaneous exploitation of the various environments finally after the 17th century the systematic reclamation and drainage of the wetland produced marked changes inducing in particular a significant loss of landscape and ecological diversity in this regard the pattern of land use in the middle ages probably represents an example of sustainable landscape exploitation

measurement and prediction of wave generated suborbital ripples 1 experiments in a large scale wave flume using regular and irregular waves with periods between 4 s and 6 s and heights between 0 2 m and 1 55 m have examined the formation of wave generated ripples using sediment beds composed of four grain sizes d50 0 349 mm 0 329 mm 0 220 mm and 0 162 mm in a water depth of approximately 4 m estimates of wave generated ripple height and wavelength were obtained using zero down crossing analyses of bed profiles measured by acoustic means along a 4 m transect normal to the ripple crests further information pertaining to was obtained from bed images obtained using scanning sonar the analyses reported here focus on the sequence bedforms that evolved in response to stepwise increases and decreases in wave height results show that ripples for the most part are suborbital in nature and do not conform well to empirical equations used frequently to predict and values in the field on the basis of the present data two new equations for prediction of and are obtained and their use in field situations where hydrodynamic and sedimentary conditions favor development of suborbital bedforms is recommended

infilling stratigraphy of macrotidal tide dominated estuaries controlling mechanisms sea level fluctuations bedrock morphology sediment supply and climate changes the examples of the seine estuary and the mont saint michel bay english channel nw france this article presents a synthesis of recent works performed on two macrotidal tide dominated estuaries located along the southern coast of the english channel the seine estuary and the mont saint michel bay nw france on the basis of very high resolution seismic data combined with sediment cores and ams dating these works allow reconstructing the holocene in ll of such singular estuaries yet rarely documented in the literature rate in sea level rise bedrock morphology sediment supply are the main controlling factors of the general in ll pattern both in lls are composed of two units the transgressive systems tract tst and highstand systems tract hst the maximum ooding surface mfs is dated around 6500 cal bp when the holocene sea level rise slowed down and corresponds to the main architectural change the tst is poorly preserved compared with the hst that constitutes the main depositional unit making this incised valley ll deviating from the classical models the hst is composed above the axis of the incised valley of a highly wandering estuarine channel belt characterized by deep tidal reworking throughout its building on the margin of this high energy estuarine system the hst is made of wave dominated barriers tidal ats and offshore tidal banks they constitute dominantly aggradational systems the aggradation rate of which is in accordance with the rate of sea level rise from 6500 cal bp onwards consequently the impacts of the rapid climate changesthat characterized mid to late holocene times can be preserved in these marginal successions various sedimentary and geometrical signatures indicate that periodic enhanced storminess episodes probably related to the bond cold events 1500 years periodicity are responsible for the most drastic environmental changes in these macrotidal tide dominated settings the role of long term tidal cycles as well as the impact of human activities are also considered

tidal asymmetry in sediment resuspension on a macrotidal beach in northwestern australia abstract a field experiment was conducted on a macrotidal beach in northwestern australia to investigate the relation between sediment resuspension and sea bed morphology continuous measurements of waves currents and suspended sediment concentrations were carried out over a period of several hours around high tide concurrent with half hourly visual observations of the sea bed morphology the incident waves had a significant wave height of 0 35 m and period 11 s most of the data were collected outside the surf zone where sediment resuspension was mainly by wave groups and suspended sediment transport was primarily accomplished by mean longshore and cross shore currents the sediment resuspension process was further characterised by a pronounced tidal asymmetry with suspended sediment concentrations and transport rates during the falling tide significantly larger than during the rising tide the asymmetry is attributed to the combined effects of a larger bed roughness and stronger mean nearshore flows during the falling tide the increase in bed roughness occurred during the rising tide under the influence of decreasing bed shear stresses when post vortex ripple morphology developed on a previously plane bed around high tide the ripples were fully developed and had attained a ripple height of approximately 0 005 m and a ripple length of 0 06 0 08 m application of the van rijn van rijn l c 1989 handbook sediment transport by currents and waves delft hydraulics report h461 sediment transport model further confirmed that enhanced sediment resuspension during the falling tide was primarily the result of the development of ripple morphology with increased mean current strengths playing a secondary role the results have major implications for modelling suspended sediment transport on macrotidal beaches

geometry prediction for wave generated bedforms published data on wave generated bedform geometry from field and laboratory measurements are re evaluated in terms of relative fluid orbit diameter at the bed and a wave period parameter d 8t2 laboratory bedform data shows a strong dependence on these parameters however for very small values of the period parameter typically field data there is evidence that bedform length depends only on sediment grain size the disappearance of sediment bedforms at high fluid velocities apparently occurs through a decrease in bedform height improved methods for the prediction of bedform geometry under waves are provided in graphical form and computer code

reconstruction of paleo wave conditions during the late pleistocene from marine terrace deposits monterey bay california the santa cruz coastal terrace fringes much of the northern monterey bay region california it consists mainly of a regressive sequence of high energy barred nearshore marine sediments deposited during the last sangamonian highstand of sea level this sequence can be sub divided into several depth dependent facies on the basis of paleo current data and vertical sequence of sedimentary structures these include a lower shoreface facies deposited in 10 16 m water depth an upper shoreface facies including both a storm dominated assemblage and a surf zone assemblage deposited in 0 10 m water depth and a foreshore facies deposited in the swash zone up to 3 5 m above high tide the magnitudes of the storm events responsible for depositing these sediments were estimated by calculating paleo wave heights using a variety of criteria e g critical threshold equations breaker depths berm heights in addition the climate and paleogeography during the deposition of these sediments were essentially the same as today allowing the use of present day wave statistics to estimate the frequency of these storm events the largest storms formed offshore flowing currents e g rip wind forced and possibly storm surge ebb currents that resulted in the deposition of approximately 30 of the sediments seaward of the surf zone however the magnitude and frequency of these events are unknown the remaining 70 of the sediment beyond the surf zone was deposited in response to smaller storm waves which were on the average at least 1 6 m high such waves presently occur no more than 15 of the time sediments deposited during fairweather conditions i e the remaining 85 of the time have a low preservation potential and are generally not preserved in this facies in contrast surf zone sediments were deposited by a variety of processes associated with waves whose maximum offshore heights were probably 2 2 m such waves presently occur up to 92 of the time sediments within the swash zone were deposited by waves up to 3 m high the largest of which presently occur approximately 2 of the time most of the sediments were deposited by storms of intermediate magnitude and frequency different facies however appear to preferentially record events of different recurrence intervals in particular surf zone sediments were deposited under relatively small storm and post storm conditions whereas sediments deposited farther offshore record increasingly larger less frequent storm events relatively rare events e g the 100 or 1000 yr events do not appear to have significantly affected sedimentation in these nearshore environments

evaluating the use of the massive coral diploastrea heliopora for paleoclimate reconstruction 1 to date coral based paleoclimate research in the pacific has primarily utilized core samples from the genus porites and has been most successful reconstructing past variability on interannual timescales particularly the el nino southern oscillation enso the indo pacific coral genus diploastrea however owing to its slower extension rate denser structure and longer lifespan can potentially preserve geochemical proxy records 2 3 times longer than porites cores of the same length before its potential can be realized diploastrea must first be calibrated and its climate signal assessed we present oxygen isotope 18o and sr ca results from two diploastrea cores collected in fiji 16 49 s 179 14 e that allow for simultaneous evaluation of this coral s paleoclimatic utility and the reproducibility of each tracer at this site comparison to a porites record from the same location allows for further evaluation of diploastrea as a paleoclimatic archive we demonstrate that diploastrea s septal and columellar material yield similar 18o sst relationships and that despite some sacrifice of the seasonal 18o amplitude bulk sampling of either region is satisfactory for resolving interannual and lower frequency modes of climatic variability therefore paleoclimate reconstructions employing either a septal or columellar sampling regime of this genus may be useful at filling in spatial and temporal sampling gaps which currently hinder the reconstruction of long term changes in major climate fields in the western pacific

variations in shoreface progradation and ravinement along the texas coast gulf of mexico shoreface architecture evolution mid holocene to present and depths of transgressive ravinement were examined from sabine pass at the texas louisiana border to south padre island near the texas mexico border using 30 shoreface transects shoreface transects extend out to 16 m water depth each created from an echo sounding profile and on average seven sediment cores the shoreface is composed of three broad sedimentological facies the upper shoreface composed almost entirely of sand the proximal lower shoreface composed of sand with thickly to medium bedded 50 10 cm mud and the distal lower shoreface composed dominantly of mud with medium to thinly bedded 20 3 cm sand shoreface architecture and evolution is extremely variable along the texas coast shoreface gradients increase from 2 25 m km 1 in east texas to 3 50 m km 1 in south texas shoreface sands coarsen towards south texas east and south texas shoreface deposits are thin and retrograding whereas central texas shoreface deposits are thicker and prograding central texas is characterized by stacked shoreface successions whereas in east texas lower shoreface sands are preserved only in offshore banks preservation of shoreface deposits is low in south texas although eustatic fluctuations and accommodation space have a strong impact on overall mid holocene to present shoreface evolution and preservation potential along strike variations in sediment supply and wave energy are the main factors controlling shoreface architecture the transgressive ravinement surface varies from 6 to 15 m along the texas coast

sedimentary characterization of bed types along the guadiana estuary sw europe before the construction of the alqueva dam abstract the guadiana river estuary is one of the most important mesotidal fluvio marine systems of the south western iberian peninsula the river mouth was formed as a narrow channel that was excavated by fluvial incision during the pleistocene lowstand and was then flooded 6500 years ago the estuary is in an advanced state of sediment infilling in its proximal part due to its narrow morphology which prevents passage of sediment through to the open coast consequently sediment is accumulating in the river mouth which causes progradation the analysis of the sediments into the estuarine channel grain size organic carbon content and bedform distribution side scan sonar allows a distinction between two types of sedimentation to be made a fluvial marine sedimentation favoured by tidal action and an autochthonous sedimentation that is related to water mixing the net transport of sediments is towards the sea because of the tidal current asymmetry the autochthonous deposits and the sediments from the extreme fluvial floods that tides are unable to rework are preserved on the meandering convex margins under low tidal velocities these areas acquire a lateral tidal bar morphology with cohesive beds because the narrow geometry of the estuary inhibits the presence of longitudinal tidal bars as may be expected in tide dominated systems the higher energy zones deeper zones of the channel become bypassing channels where the flocculated material cannot be settled on the bottom this part of the channel then develops sandy beds with mesoforms as ebb oriented two dimensional and three dimensional dunes sand waves and megaripples

reconstruction of ancient sea conditions with an example from the swiss molasse ancient sea conditions can be estimated from the grain size spacing and steepness of preserved ripple marks the element of greatest uncertainty in such reconstructions is the relationship between near bed orbital diameter of water particles and the ripple spacing this relationship is simple for vortex ripples of high steepness but is problematical for the low steepness forms known as post vortex rolling grain or anorbital ripples the existence field for wave ripples is between the threshold velocity for sediment movement and the onset of sheet flow most low steepness forms occurring close to the bed planation threshold a range of maximum period of formative waves can be obtained using combinations of orbital diameter and orbital velocity assuming linear wave theory to be a reasonable approximation probable wave heights wave lengths and water depths can be investigated using the transformation of wave parameters in shallowing waters and the constraints on wave dimensions provided by the wave breaking condition given reasonable estimates of wave height crude estimates of wave power allow a comparison of ancient wave influenced sequences with modern counterparts wave ripple marks preserved in the upper marine molasse of western switzerland have been investigated results which are in agreement with regional geology suggest deposition in a seaway of approximately 100 km width where moderate period waves t 3 6 s were generated the depositional facies belts were adjusted to the prevailing waves tides and fluvial outflows

rapid human induced siltation of the macro tidal ord river estuary western australia field studies on the sediment dynamics of the two arms of cambridge gulf tropical western australia were undertaken the system is macro tidal with 8 m tides the west arm is the estuary of the durack and pentecost rivers which are largely untouched by human activities the east arm is the estuary of the ord river affected by land clearing which started 100 years ago and by two river dams constructed 30 years ago prior to damming of the ord river the natural flow in all rivers was highly seasonal characterized by small at times negligible flow during the dry season which lasts eight months and occasional river floods during the wet season which lasts four months the river flow has been regulated in the east arm as a result of damming this resulted in suppressing large river floods the salinity intrusion length has decreased by about 50 in the east arm following river damming the east arm has silted measurably over the last 30 years with the stream cross sectional area decreasing by about 50 field and numerical studies suggest that this is due to the dam induced suppression of large river floods which has in turn allowed a greater amount of tidal pumping of sediment into the east arm from cambridge gulf since tidal pumping is increasing as the system is silting the east arm appears to now be geomorphologically unstable as a result of human activities numerical studies suggest it may take as little as 100 years for the ord river to reach a new equilibrium modelling suggests that this equilibrium may be characterized by a salinity intrusion length half that before damming a channel width and depth reduced by 70 and a much stronger tidal asymmetry characterized by an increasing size of the tidal bore the west arm appears to be at equilibrium since there has been no net loss or gain of sediment for the last 111 years tidal dynamics and river floods appear responsible for self scouring this channel

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

suspended sediment transport in the seine estuary france effect of man made modifications on estuary shelf sedimentology abstract man made modifications of the seine estuary have produced large geometric changes with important hydrographic and sedimentological consequences affecting estuary shelf interrelationships the estuary once had shallow meandering ebb and flood tidal channels and broad tidal flats today after 130 years of landfill marsh reclamation jettying and dredging there is only a narrow deep jettied channel extending to the sea most of the tidal flats and marshes have been filled these modifications have concentrated river discharge and ebb flow into a narrow jettied channel which in turn has produced a seaward migration of the salt intrusion and the turbidity maximum as the estuary volume was reduced river flow dilution was also reduced and its mean residence time in the estuary was shortened at the same time sedimentation and landfill have reduced the area available for sedimentation of fluvial sediments this change has amplified seaward transport of fluvial suspended sediment and increased the size of shelf mud zones off the estuary mouth man has thus changed the geologic role of the estuary from a sink for fluvial and marine sediment to a source of fluvial sediment for the shelf

rippled scour depressions on the inner continental shelf off central california abstract side scan sonar records taken during the recent coastal ocean dynamics experiment code show elongate shore normal rippled depressions of low relief on the inner continental shelf off central california between bodega bay and point arena these features extend up to 2 km from the coast into water depths of up to 65 m the proposed mechanism for their generation is storm generated bottom currents associated with coastal downwelling during the late fall and winter which scour the surficial fine sand sediment and expose the coarser sand substrate in the depressions the zones of most intense erosion and the irregular spacing of the features may be controlled by submerged rock ledges and other prominent coastal features the large straight crested ripples within the depressions heights to 40 cm wavelengths to 1 7 m are probably formed by large amplitude long period surface waves generated by winter storms

hydrodynamics and sedimentation in wave dominated coastal environmentsreconstruction of ancient sea conditions with an example from the swiss molasse ancient sea conditions can be estimated from the grain size spacing and steepness of preserved ripple marks the element of greatest uncertainty in such reconstructions is the relationship between near bed orbital diameter of water particles and the ripple spacing this relationship is simple for vortex ripples of high steepness but is problematical for the low steepness forms known as post vortex rolling grain or anorbital ripples the existence field for wave ripples is between the threshold velocity for sediment movement and the onset of sheet flow most low steepness forms occurring close to the bed planation threshold a range of maximum period of formative waves can be obtained using combinations of orbital diameter and orbital velocity assuming linear wave theory to be a reasonable approximation probable wave heights wave lengths and water depths can be investigated using the transformation of wave parameters in shallowing waters and the constraints on wave dimensions provided by the wave breaking condition given reasonable estimates of wave height crude estimates of wave power allow a comparison of ancient wave influenced sequences with modern counterparts wave ripple marks preserved in the upper marine molasse of western switzerland have been investigated results which are in agreement with regional geology suggest deposition in a seaway of approximately 100 km width where moderate period waves t 3 6 s were generated the depositional facies belts were adjusted to the prevailing waves tides and fluvial outflows

the superficial sediments of the english channel and its western approaches the english channel and its western approaches constitute a 700 km long epicontinental sea located in a temperate environment and in a tectonic setting where subsidence is minimal a sedimentological survey of this region reveals quite distinct provinces a central sector western channel where predominantly bioclastic sediments are widely represented bounded by two mainly terrigenous rich zones the outer terrace of the celtic sea and the eastern channel lateral sedimentary variations of decreasing grain size are interpreted in terms of current velocity patterns the various types of such sequences may relate to the degree of mixing of older lithoclastic sediments with the holocene bioclastic supply a scenario for the evolution of the recent sedimentation of this epicontinental sea is presented starting from a permanent marine zone at least since the wurm period that bounds the bay of biscay the holocene transgression progressed over the english channel in the western channel earlier terrigenous deposits were gradually overlapped by bioclastic sediments that originated on the pre mesozoic rocky substratum and which were particularly extensive off the armorican massif in the subsequently submerged eastern channel the pre holocene clastic source has undergone comparatively less modification and still crops out in most of the area with the opening of the straits of dover at about 9000 yr bp submersion was complete and new hydrodynamic conditions developed as the eustatic level stabilized the present sediment distribution is in harmony with the hydrodynamic setting except on the southern rise of the celtic sea where both morphology and sedimentary patterns still largely reflect pre holocene conditions resume la mer de la manche et ses approches occidentales constituent une plateforme epicontinentale qui s etend suivant un axe ne sw d environ 700 km depuis le pas de calais jusqu au rebord continental c est un milieu sedimentaire de climat tempere a subsidence negligeable et a faible taux de sedimentation la couverture de depots meubles est mince quelques metres en general sauf au niveau des bancs sableux et des paleovallees souvent comblees s alluvions anciennes la repartition des sediments superficiels est essentiellement controlee par les courants de maree particulierement forts le long des cotes armoricaines et en manche centrale en manche occidentale un important gradient de vitesses decroissantes se developpe du sud est au nord ouest les houles s exercent principalement sur la frange cotiere ou leur action devient dominante dans l ensemble les depbts fins sont rares et concentres dans les baies et les estuaires ou les suspensions se decantent par contre les sediments graveleux a caillouteux sont largement repartis une opposition nette se dessine entre une province orientale surtout terrigene et une province occidentale au materiel bioclastique abondant presentant un gradient de dispersion en direction du sud ouest ces caracteres morphologiques et sedimentaires du milieu sont fortement marques par son histoire quaternaire notamment par la derniere oscillation marine un schema de mise en place et d evolution du modele sedimentaire au cours du quatenaire recent est propose partant de la zone en permanence submergee durant le wurm la transgression holocene progressa sur la manche le pas de calais s ouvrit vers 9000 bp et peu a peu les conditions hydrodynamiques actuelles se mirent en place sous un climat devenu tempere progressivement les depots terrigenes anciens furent contamines par du materiel bioclastique holocene

unified view of sediment transport by currents and waves i initiation of motion bed roughness and bed load transport attention is given to the properties of sediment beds over the full range of conditions silts to gravel in particular the effect of fine silt on the bed composition and on initiation of motion critical conditions is discussed high quality bed load transport data sets are identified and analyzed showing that the bed load transport in the sand range is related to velocity to power 2 5 the bed load transport is not much affected by particle size the prediction of bed roughness is addressed and the prediction of bed load transport in steady river flow is extended to coastal flow applying an intrawave approach simplified bed load transport formulas are presented which can be used to obtain a quick estimate of bed load transport in river and coastal flows it is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions the proposed model is fully predictive in the sense that only the basic hydrodynamic parameters dep

sediment exchanges between the seine estuary and its adjacent shelf the study of sediment dynamics within the seine estuary and its adjacent shelf permits some conclusions regarding sediment exchanges in this coastal zone on the shelf sediment transport is directed toward the seine estuary and contributes to the infilling of the estuary by marine sands and muds these were originally derived from land carried to the shelf at times of lower sea level and subsequently transported shoreward by dominant tidal and wave induced currents in the estuarine section tidal processes form a turbidity maximum both by inducing strong bed resuspension and by trapping fluvial and marine sediments due to flood current predominance occasionally this turbid zone extends seaward during periods of river floods and sediment is redispersed onto the shelf this phenomenon has been amplified by man made modifications of the estuarine morphology however currents patterns tend to retard the natural seaward escape of fluvial material mainly due to dredging operations at the present time thus man has changed the natural role of the estuary from a sink to a source of fluvial sediments for the shelf a tentative sedimentary budget is proposed taking into account the various sources of material and the complexity of sediment dynamics

sr ca sea surface temperature calibration in the coral porites lutea from subtropical northern south china sea strontium to calcium sr ca ratios in annual bands of porites corals are commonly used as past sea surface temperature proxy in tropical oceans whereas studies that refer to sr ca sst calibration in high latitude corals are rather rare in general here we present a 50 year 1961 2010 near fortnightly sr ca record in two porites lutea corals living near the northern limit of reef building corals in the subtropical northern south china sea where winter temperatures are extreme for hermatypic corals the sr ca time series shows a clear annual cyclicity with marked sharp narrow winter peaks comparison with an instrumental sst record since 1961 indicates that this sr ca record is chiefly modulated by sst two different methods are discussed for calibrating sr ca with sst the correlation between interpolated sr ca and sst is significant but the coefficient is relatively low mainly attributed to extreme cold winter ssts similar to 16 degrees c which cause a significant decrease or even cessation of coral skeletal extension another modified method using only annual low sr ca values which could clearly be matched with the same features in the instrumental sst record is more reliable the modified regression equation does not encompass ssts below 24 degrees c the fidelity of the coral based sr ca sst calibration was assessed and the precision of the method is estimated to be 031 0 62 degrees c based on the calibration verification exercise the modified method is suggested in marginal coral areas with extreme intra annual sst variation e g from 13 to 30 degrees c c 2013 elsevier b v all rights reserved