comparison of mesozooplankton communities at three shallow seamounts in the south west indian ocean abstract seamounts are recognised as hotspots of biodiversity attracting large numbers of top predators but the underlying mechanisms are still unclear we studied mesozooplankton abundance and size distribution at three shallow seamounts 60 m 240 m and 18 m deep in the south west indian ocean along a latitudinal gradient 19 s 27 s and 33 s samples were analysed using a zooscan allowing the use of a size based approach differences were observed between seamount areas but overall zooplankton communities did not seem to be affected by the changes in topography only in the lee of la perouse seamount was the zooplankton community slightly more concentrated than upstream suggesting that zooplankton were flushed downstream of the seamount the southernmost and shallowest seamount walters shoal had low abundance and its size spectrum differed greatly from the two other seamounts further north these differences were attributed to seasonality and mesozooplankton population dynamics whereas the other two seamounts exhibited a more typical oligotrophic pelagic ecosystem at equilibrium and dominated by small organisms at the time of sampling the unnamed seamount south of madagascar was influenced by a mesoscale dipole that impacted the zooplankton distribution potentially masking any seamount effect the normalised biomass size spectrum approach contributed to a better understanding of the ecosystem dynamics i e equilibrium vs non steady state but revealed little variability within a stable oligotrophic environment

fine sediment and its sources severn estuary and inner bristol channel southwest britain abstract a comparison of the clay mineral assemblages of 22 samples from the estuary with 22 samples from river floodplains strongly suggests that the fine sediment present in the contemporary severn estuary and inner bristol channel come almost exclusively from the river catchments that feed the system the catchments are geologically diverse and the clay minerals particularly expandable clays kaolinite and chlorite seem to come from preferred parts of the drainage area although the estuary is flood dominated and some fine sediment is supplied from seaward the amount appears negligible in comparison with the fluvial supply the sands however seem largely to have an immediate western origin

micronekton distributions and assemblages at two shallow seamounts of the south western indian ocean insights from acoustics and mesopelagic trawl data micronekton distributions and assemblages were investigated at two shallow seamounts of the south western indian ocean using a combination of trawl data and multi frequency acoustic visualisation techniques la perouse 60 m seamount is located on the outskirts of the oligotrophic indian south subtropical gyre province with weak mesoscale activities and low primary productivity all year round the mad ridge seamount thus termed in this study 240 m is located in the productive east african coastal eafr province with high mesoscale activities to the south of madagascar this resulted in higher micronekton species richness at mad ridge compared to la perouse resulting productivity at mad ridge seamount was likely due to the action of mesoscale eddies advecting larvae and productivity from the madagascar shelf rather than local dynamic processes such as taylor column formation mean micronekton abundance biomass as estimated from mesopelagic trawl catches were lower over the summit compared to the vicinity of the seamounts due to net selectivity and catchability and depth gradient on micronekton assemblages mean acoustic densities in the night shallow scattering layer ssl 10 200 m over the summit were not significantly different compared to the vicinity within 14 nautical miles of mad ridge at la perouse and mad ridge the night and day ssl were dominated by common diel vertical migrant and non migrant micronekton species respectively while seamount associated mesopelagic fishes such as diaphus suborbitalis la perouse and mad ridge and benthosema fibulatum performed diel vertical migrations dvm along the seamounts flanks seamount resident benthopelagic fishes including cookeolus japonicus mad ridge were aggregated over mad ridge summit both during the day and night before sunrise mid water migrants initiated the first vertical migration event from the intermediate to the deep scattering layer dsl la perouse 500 650m mad ridge 400 700 m or deeper during sunrise the other taxa contributing to the night ssl exhibited a successive series of vertical migration events from the surface to the dsl or deeper some scatterers were blocked in their upward and downward migrations due to the seamount topography more commonly known as the sound scattering layer interception topographic blockage hypothesis possible mechanisms leading to the observed patterns in micronekton vertical and horizontal distributions are discussed this study contributes to a better understanding of how seamounts influence the diel vertical migration horizontal distribution and community composition of micronekton and seamount associated resident species at two poorly studied shallow topographic features in the south western indian ocean

estuary schematisation in behaviour oriented modelling asmita aggregated scale morphological interaction between tidal basin and the adjacent coast is a behaviour oriented modelling approach which represents estuarine systems schematically it was originally developed for classic tidal inlets such as those found in the dutch wadden sea and venice lagoons where schematisations of two or three interacting elements e g flat channel and possibly an ebb tidal delta are appropriate however estuaries show a much wider range of form and human interference than these cases this paper presents results for two uk estuaries with differing morphologies and management histories the ribble estuary and southampton water are poorly represented by standard two and three element schematisations and required novel schematisations which considered the dominant processes shaping the two estuaries the new schematisations gave model predictions that 1 are better than the baseline assumption of no change through time 2 are better than standard schematisations and 3 are physically reasonably whilst retaining simplicity these results demonstrate a possible generic methodology to test different schematisations using simple models to characterise estuarine morphodynamics as a preliminary stage of estuary assessment

effects of navigational works on morphological changes in the bar area of the yangtze estuary abstract to improve navigability of the major access channel into shanghai harbor a large scale deep waterway project was carried out in the north passage np of the yangtze estuary in this paper we investigate how the navigational works affected morphological changes of this channel as well as those of the adjacent north channel nc hengsha east shoal hes jiuduansha shoal jds and the south passage sp morphological changes were assessed by analyzing digitized bathymetric data of this area prior to and after execution of the engineering works the qualitative relations between these changes along with the hydrodynamic changes as a result of the construction of engineering works were subsequently investigated the results reveal that the construction of training walls groins and jetties resulted in decreased ebb transport in the upper reach of the np and increased ebb transport in the upper reach of the sp in turn this led to intensive upstream erosion with large amounts of sediment transported seaward in the sp and associated sedimentation in the downstream area at the same time intense siltation occurred in the upper reach of the np while the main channel of the np mainly experienced erosion caused by the construction of training walls and groins that concentrated ebb flow in the main channel the waterway deepened significantly in previously shallow areas small tidal channels in the hes which used to connect the np and the nc were cut off by the northern training wall consequently residual flow in the middle reach of the nc flowed directly toward the northern bank of the hes leading to local erosion flow obstruction by the southern training wall reduced the upstream propagation of the flood tide in the sp as a result a collection of small flood channels evolved under the flushing action of flood currents in the jds preventing the natural trend of horizontal extension of the jds however the flow obstruction enhanced the vertical accretion of the jds

distribution of magnetic properties of surface sediment and its implications on sediment provenance and transport in pearl river estuary abstract this study examines the magnetic properties of surface sediments and their implications on sediment provenance and transport in the lingding bay ldb which is the largest bay of pearl river estuary in china the concentration of magnetic and high coercivity minerals exhibits a low high low distribution pattern in the north middle south direction the western ldb is mainly covered by finer magnetic mineral particles whereas the eastern ldb is dominated by coarser particles three surface sediment provenances i e three groups are identified according to magnetic properties and particle size groups i and iii have terrestrial sources from the east river and west north river respectively whereas group ii is from a marine source in the adjacent sea the distribution of these three sediment provenances and their magnetic properties indicate that surface sediments are transported towards the southern direction with a sediment sink that occurs in the outer ldb as further confirmed by the grain size trend analysis results the main sediment depocenter moves southward because of human interventions the results further suggest that the ratio of saturation isothermal remanent magnetization to magnetic susceptibility sirm may be used as an indicator for distinguishing marine and terrestrial provenances and the s ratio s 100 may be employed as an indicator of sediment transport our findings demonstrate that sediment magnetic diagnosis provides an efficient approach to trace sediment provenance and transport and thereafter monitors the sediment process impacted by human intervention in estuaries worldwide

linking the infilling of the north branch in the changjiang yangtze estuary to anthropogenic activities from 1958 to 2013 abstract many tidally dominated estuaries of the world are experiencing variations in bottom topography due to changes in natural forcings and intensive human activities here we focus on the morphological evolution of the north branch nb a tidally dominated distributary of the changjiang estuary our analysis is based on long term bathymetric and hydrological data collected between 1950 and 2010 the results show that mean water depth channel volume below 0 m and channel volume below 5 m have respectively decreased by 43 53 and 92 in the last 50 years a reduction of the whole estuarine surface with aggradation in elongated tidal sand bars and erosion at the mouth are the main morphological variations of the nb while a decrease in channel volume below 5 m due to infilling is the second mode of morphological change while the drastic decrease in sediment load from upstream is likely unrelated to the silting of the nb local land reclamation along the banks is directly responsible for the reduction of estuarine surface area and related tidal prism between 1958 and 2013 enhanced flood tide currents resulted in a large import of sediments from offshore into the nb triggering a sustained decrease in channel volume below 0 m it is argued that the recovery of the funnel shaped configuration of the estuary by restoring mud flats over 0 m dredging the southern part of the estuary bend and forbidding land reclamation could prevent the silting of the nb otherwise the nb will likely vanish in few decades

plankton distribution within a young cyclonic eddy off south western madagascar abstract mesoscale eddies are major features in ocean dynamics that significantly influence ocean production depending on their polarity life stage location and time of formation eddies in the south west indian ocean have been the focus of many studies especially in the mozambique channel where southward moving cyclonic and anticyclonic eddies feed into the agulhas current however eddies formed south of madagascar that move westwards towards the coast of south africa have been much less studied despite their significant contribution to the agulhas current this study aims to understand how the plankton communities i e pico nano phyto microzoo and mesozooplankton are distributed in a cyclonic eddy generated off southern madagascar we also investigate a possible link between the madagascar shelf and the eddy temperature salinity fluorescence and plankton abundance were measured at 25 stations spaced at 18 5 km intervals across a young 1 month old cyclonic eddy and at three locations on the madagascar shelf in july 2013 a patch of enhanced chlorophyll a concentration was found at four stations in the eddy homogeneously distributed vertically in the upper mixed layer and characterised by a higher proportion of diatoms compared to the other stations abundances of picoplankton nanoplankton ciliates and dinoflagellates were very similar within and outside the eddy zooplankton followed a contrasting pattern with higher biomass at four stations just to the west of this high diatom patch the mesozooplankton composition at these four stations revealed greater species similarities with the madagascar shelf than with the other stations suggesting a link between the shelf and the western side of the eddy the periphery of the eddy seems to have been primarily influenced by a strong geostrophic current propagating from the southern shelf of madagascar which then wrapped itself around the eddy this filament may be the source of the high zooplankton biomass in the eddy periphery which would account for the similarities in zooplankton community composition between the eddy periphery and the shelf

historical changes in the columbia river estuary historical changes in the hydrology sedimentology and physical oceanography of the columbia river estuary have been evaluated with a combination of statistical cartographic and numerical modelling techniques comparison of data digitized from us coast and geodetic survey bathymetric surveys conducted in the periods 1867 1875 1926 1937 and 1949 1958 reveals that large changes in the morphology of the estuary have been caused by navigational improvements jetties dredged channels and pile dikes and by the diking and filling of much of the wetland area lesser changes are attributable to natural shoaling and erosion there has been roughly a 15 decrease in tidal prism and a net accumulation of about 68 106m3 of sediment in the estuary large volumes of sediment have been eroded from the entrance region and deposited on the continental shelf and in the balance of the estuary contributing to formation of new land the bathymetric data indicate that ignoring erosion at the entrance 370 to 485 106m3 of sediment has been deposited in the estuary since 1868 at an average rate of about 0 5 cm y 1 roughly 5 times the rate at which sea level has fallen locally since the turn of the century riverflow data indicate that the seasonal flow cycle of the columbia river has been significantly altered by regulation and diversion of water for irrigation the greatest changes have occurred in the last thirty years flow variability over periods greater than a month has been significantly damped and the net discharge has been slightly reduced these changes in riverflow are too recent to be reflected in the available in the available bathymetric data results from a laterally averaged multiple channel two dimensional numerical flow model described in hamilton 1990 suggest that the changes in morphology and riverflow have reduced mixing increased stratification altered the response to fortnightly neap spring changes in tidal forcing and decreased the salinity intrusion length and the transport of salt into the estuary the overall effects of human intervention in the physical processes of the columbia river estuary i e decrease in freshwater inflow tidal prism and mixing increase in flushing time and fine sediment deposition and net accumulation of sediment are qualitatively similar to those observed in less energetic and more obviously altered estuarine systems a concurrent reduction in wetland habitats has resulted in an estimated 82 reduction in emergent plant production and a 15 reduction in benthic macroalgae production a combined production loss of 51 675 metric tons of organic carbon per year this has been at least partially compensated by a large increase in the supply of riverine detritus derived from freshwater phytoplankton primary production comparison of modern and estimated preregulation organic carbon budgets for the estuary indicates a shift from a food web based on comparatively refractory macrodetritus derived from emergent vegetation to one involving more labile microdetritus derived from allochthonous phytoplankton the shift has been driven by human induced changes to the physical environment of the estuary while this is a relatively comprehensive study of historical physical changes it is incomplete in that the sediment budget is still uncertain more precise quantification of the modern estuarine sediment budget will require both a better understanding of the fluvial input and dredging export terms and a sediment tranport model designed to explain historical changes in the sediment budget oceanographic studies to better determine the mechanisms leading to the formation of the turbidity maximum are also needed the combination of cartography and modelling used in this study should be applicable in other systems where large changes in morphology have occurred in historical time

late stage estuary infilling controlled by limited accommodation space in the hudson river high resolution seismic data and sediment cores reveal the late holocene subsurface stratigraphy of the broad tappan zee piermont region of the hudson river estuary we identify a series of distinct extensive horizons beneath the marginal flats channel banks and main channel in this area physical properties and lithology from sediment cores suggest that these horizons are surfaces of erosion or nondeposition radiocarbon dates indicate that they correspond with three distinct time horizons with maximum ages of 3400 2200 and 1600 yr bp we also distinguish two sedimentary facies that occupy the marginal flats and channel banks the deeper facies forms a deposit 2 km wide and 7 km long that accumulated at rates of 2 4 mm yr in the vicinity of the sparkill creek prior to 1700 yr bp overlying and onlapping the 2200 yr bp seismic surface based on its internal geometry morphology and proximity to a tributary we interpret this facies as a delta deposit the shallower facies accumulated more slowly 1 2 mm yr overlying the delta deposit to the south and dominating the marginal flats to the north surface sediment samples and geophysical data reveal that the modern marginal flats are no longer actively depositional but dominated by nondeposition or erosion limited accommodation space in the hudson river estuary may be the critical factor contributing to the observed sedimentary pattern characterized by intervals of deposition punctuated by episodes of erosion an estuarine system that has reached a state of morphological equilibrium will be sensitive to even small fluctuations in sea level and climate conditions which may account for the intervals of deposition and erosion we observe limited accommodation space and intermittent sediment deposition in the hudson river estuary may be due to its evolution from a fjord filled with glacial lake sediments which distinguishes its infilling behavior from the classic drowned river valley estuary

process based morphodynamic modeling of the yangtze estuary at a decadal timescale controls on estuarine evolution and future trends abstract understanding the decadal morphodynamic evolution of estuaries and deltas and their controls is of vital importance regarding management for estuarine function and sustainable development this work addresses this issue by applying a process based model system delft3d to hindcast and then forecast the morphodynamic evolution of the yangtze estuary at a decadal timescale forced by the river and tides the model considers sand mud mixture and the variations of river water discharge and sediment discharge the morphodynamic model is validated against three periods i e an accretion period 1958 1978 an erosion period 1986 1997 and a recent accretion period with human activities 2002 2010 model results show good performance with respect to spatial erosion and deposition patterns sediment volume changes and hypsometry curves the model reveals quite different behaviors for mud transport between the dry and wet seasons which is subject to the prescription of river boundary conditions and bed composition we define six scenarios to project evolution to the year 2030 under decreased river inputs and increased relative sea level the simulations reveal that overwhelming amount of erosion will likely occur in the inner and mouth bar area of the estuary particularly the mouth zone will shift from net deposition before 2010 to net erosion by 2030 mainly because of decreasing sediment supply changes in water discharge have minor effects on the projected trend net erosion will be considerable when the sediment supply is extremely low 100 mt yr 1 due to the abundance of erodible modern sediment in the yangtze estuary erosion within the mouth bar area may be unexpected including the deepening of the tidal inlet at east chongming mudflat and the formation of a flood channel on the seaward side of jiuduansha shoal overall the model results provide valuable information for sustainable delta management under changing conditions for both the yangtze system and other similar estuaries and deltas with diminishing sediment supplies

a simulation of estuary response to training wall construction using a regime approach a method based on regime theory for the long term prediction of the effects of civil engineering works on estuaries with muddy sediment conditions is described the method involves the use of a hybrid model consisting of a 1d flow model to describe the estuary geometry coupled with a discharge area algorithm to simulate the changes in estuary morphology the flow model and the morphological algorithm are used in an iterative mode to model the changes in estuary hydraulic conditions and bathymetry over time the application of the model to simulate the effects of training wall construction in the estuary of the river lune uk is described and the results compared with historical observations these observations showed that there was considerable siltation as a result of the construction of the training walls it is acknowledged that the application of the method to this scenario involving a 2d problem presents a difficult test however although the model generally underestimates the accretion in the case of the river lune it is still a potentially useful tool for the long term prediction of the effects of engineering works

the multi decadal morphodynamic changes of the mouth bar in a mixed fluvial tidal estuarine channel abstract inner channel mouth bars imb are common and vital geomorphological structures in estuaries that can efficiently promote the progradation of a fluvial delta however these significant structures face serious interferences by natural and human forces this study mainly focuses on imb deposited in the mixed fluvial tidal dominated south passage sp of the changjiang estuary between 1959 and 2018 to reveal how multidecadal morphodynamic variability in a mouth bar responds to natural forcing and human interferences the results show that the volume of the imb in the sp increased from 1128 106 m3 in 1959 to 1636 106 m3 in 1989 and then decreased to 462 106 m3 in 2018 meanwhile the evolution of the imb could be divided into five stages the growing phase 1959 to 1979 which showed a v shape the partial adjustment phase 1999 2003 which showed a crest dent shape the stable phase which showed a flat shape 2004 2010 the partial adjustment phase 2011 2017 when jiangyanan shola inserted into the sp and finally evolved into a flat shape in 2018 fluvial water discharge and suspended sediment discharge ssd did not control the variation in the mouth bar enso events were normally responsible for not only the periodic variations in the landward slope and the water depth of the crest of the imb but also occasional extreme changes in the imb moreover local sandbar insertion sediment from the seaside induced by strong tidal power and intensified engineering projects resulted in the continual shrinkage of the mouth bar by depositing more sediment at the mouth bar our work implies that understanding and governing this imb will bring additional economic benefits to this fast developing society but the protection of this delicate estuarine geomorphology system should still receive great attention

numerical modelling of hydrodynamics and sand transport in the tide dominated coastal to estuarine region abstract in order to understand the influences of tide waves and sediment sizes on the sand exchange between an estuary and the adjacent coastal region three estuaries around north west england were chosen for detailed study using a numerical morphological model system telemac hervouet and bates 2000 the numerical model was calibrated against available field measurements for both hydrodynamics and sediment transport simulations on sediment transport under a representative combined waves and tidal condition were carried out comparisons of the model results across the three different estuaries concentrate on effects from seabed bathymetry hydrodynamics and sediment sizes under the complex tide and wave interactions it is clear that the dominant hydrodynamic processes of an estuary are influenced by the tidal asymmetry wave driven currents and wave induced stirring effects which are all affected by the local seabed bathymetry given the same input tide and waves generally it is found that the net sediment transport direction at the estuary mouth depends on the relative strength of landwards transport in the shallow water depths due to tidal asymmetry and seawards transport within the estuary s deep channels in addition the overall sediment flux direction is largely dictated by local and surrounding sediment sizes

trophodynamic studies on the condor seamount azores portugal north atlantic abstract compared to the surrounding ocean waters seamounts are commonly considered habitats where biological productivity is higher and consumers proliferate despite their high productivity studies of seamount trophic webs are still scarce and fragmentary and little is known about the connections between the different compartments what are the trophic interactions of seamount fauna how do the pelagic and benthic environment couple in order to answer these questions stable isotopes 15n and 13c were measured in the organisms collected during the course of numerous campaigns at the condor seamount in the north atlantic the condor seamount food chain is composed of five trophic levels mesopelagic organisms are the link between the epipelagic environment and the benthic and benthopelagic organisms bridging the gap between primary consumers and the 4th and 5th trophic chain levels our results demonstrate through stable isotope analysis the important role of mesopelagic organisms in the transfer of energy within the seamount food web as modeling theoretical studies have previously suggested

morphological responses of an estuarine intertidal mudflat to constructions since 1978 to 2005 the seine estuary france abstract since 1834 the seine estuary france has been the site of numerous construction projects with the aim to accommodate and secure boat traffic since 1978 the increasing of the activities of le havre port located at the mouth of the estuary has accelerated the construction work rate several dykes a bridge and new port facilities have been constructed in rapid succession modifying considerably the hydrodynamic conditions which sustain a partially vegetated sandy muddy tidal flat located in the north bank of the estuary between the new port of le havre and the normandy bridge achieved in 1995 the present study deals with the morphological evolution of this zone from 1978 to 2005 the use of a low altitude remote sensing technique combined with traditional methods of ground survey and probes allow to demonstrate the impact of human activities on sedimentary and vegetation dynamics the northern mudflat of the estuary is the most affected by these human activities which surface have reduced of 62 during the last 27 years with an intensified local erosion during the last 27 months corresponding to a loss 1 250 000 m 3 of fine grained sediment at the same time the general sanding up in the channel of the zone has caused a loss of more than 31 of the tidal prism more than three quarters of which occurred during the last three years results also establish that the response times of the sedimentary or topographic readjustment to an installation depend on the extent and the nature of the construction in fact the sedimentary readjustments to an installation can be delayed by up to 10 years in the case of the seine estuary this delay is explained by a rapid succession of construction works which may occult the effect of a single installation except in the case of a dyke built perpendicular to ebb and flood currents the impacts of these installations reach a hydro sedimentary equilibrium on the level between 1 and 7 years after their completion

anthropogenic influence on sedimentation during the last 100 years inferred from magnetic properties in the changjiang estuary china a 100 year sedimentary record in the changjiang estuary was examined to elucidate natural and anthropogenic influences on the morphodynamic evolution of the estuary two gravity cores were acquired and their magnetic properties sediment size chemical elements and 210pb geochronology were analyzed to infer the sedimentation the results indicate that these sedimentological indexes especially magnetic properties and trace elements changed significantly during the last 100 years with an abrupt change occurring at around 1960 this abrupt change is likely the result of a reduction in hydrodynamic energy caused by the narrowing of an upstream estuary reach due to reclamation an increase of terrigenous input due to soil erosion in the upper and middle reaches of the changjiang and increases in steel production may have also had a significant influence as indicated by studies of other locations in the changjiang drainage basin

siltation on a highly regulated estuarine system the magdalena river mouth case northwestern south america abstracts comparison of geo referred bathymetric datasets from 2000 to 2017 at different timescales allowed to analyze changes in the sedimentary balance and to determine patterns of morphological adjustment in the magdalena river south america the magdalena river has one of the highest sediment yields among the major rivers of the world in addition it is a laterally constrained river mouth due to a series of man made structures inhibiting its morphological response thus it provides an illustrative example to study siltation processes in a river mouth system where a low capacity of morphological response interacts with a high magnitude sediment transport regime the river mouth exhibited an overall slow pace deepening trend between 2000 and 2017 however it experienced cyclic shifts between erosive and siltation states both at interannual and intra annual scales the rates of erosion were 310 mm yr 1 on average during the erosional stages whereas sedimentation rates were 293 mm yr 1 on average during the sedimentation stages maximum rates of erosion and sedimentation were 1450 mm yr 1 and 2625 mm yr 1 respectively however intra annual rates of sedimentation erosion were of the same magnitude or larger compared with the interannual rates such high rates and the rapid changes in the sedimentary balance is the result of the cumulative effect of its limited morphological response capacity and its large suspended sediment load these rapid processes generate constraints and threats to navigation particularly at intra annual scales consequently innovative intervention proposals recognizing the rapid transitions and geomorphological adaptations are required for managing this type of river mouths

seasonal and annual variations in the volumetric sediment balance of a macro tidal salt marsh abstract this paper examines the spatial and temporal variability in the volumetric sediment balance of allen creek marsh a macro tidal salt marsh in the bay of fundy the volumetric balance was determined as the balance of inputs of sediments and organic matter via accretion on the marsh surface and outputs of sedimentary material primarily due to erosion of the marsh margin changes in marsh surface elevation were measured at 20 buried plates and 3 modified sediment elevation tables from 1996 2002 and detailed margin surveys were conducted in 1997 1999 and 2001 using a differential global positioning system changes in surface area were calculated using gis overlay analysis and used in conjunction with accretion and erosion data to derive volumetric estimates of gains and losses of sedimentary material in the marsh system currently the volumetric sediment balance at allen creek marsh is positive however the processes of erosion and accretion demonstrate seasonal annual and spatial variability inputs to the system include deposition on the marsh surface from sediment laden waters and from ice rafting of sediments sediment is deposited onto the marsh surface year round even during the winter when vegetation cover is sparse and the amount of deposition in general is not significantly correlated with the frequency of tidal inundations based on the data from 1996 to 2002 the mid and high marsh zones experience mean accretion rates of approximately 1 4 cm year 1 whereas accretion rates in the low marsh region are statistically significantly lower 0 8 cm year 1 the absolute amount of accretion varies between seasons and from year to year the main loss to the marsh is through erosion of the marsh margin cliffs which can remove a comparatively large volume of sedimentary material in one mass wasting event and which also decreases the vegetated surface area available for deposition from sediment laden waters the volume of material removed from the marsh margin almost tripled between 1997 169 m3 and 2001 502 m3 following breaching of the side of a tidal creek channel altering the patterns of margin erosion and deposition in the marsh system during this time however other sheltered areas of the marsh system such as along the tidal creek banks showed evidence of new vegetation growth increasing the amount of vegetated surface area available for deposition the processes of erosion and deposition on the marsh surface exhibit considerable spatial variability with different regions of the marsh being more or less sensitive to seasonal variability in the dominant controls influencing sediment deposition and erosion in this system namely wave activity vegetation ice and water depths a key factor in predicting how a marsh will evolve and respond to a number of different controls e g sea level rise or reduced sediment supply is to quantify both accretion of the marsh surface and erosion of the marsh margin evaluating the marsh system as a volumetric whole this study demonstrates that a marsh system should be assessed in three dimensions rather than simply as a surface of accumulation this is particularly important for open coastal marshes exposed to the erosive action of waves

encounter of a deep western boundary current with the equator a numerical spin up experiment the encounter of a deep western boundary current with the equator is studied using an ultra high resolution numerical model of the equatorial ocean in a study of the origin of the deep equatorial current system the integration was carried out from a state of rest to 3500 days the spin up experiment shows that the deep western boundary current upon encountering the equator first turns along the equator the time scale of spin up is fast along the equator and the boundaries about 250 days but is considerably slower off the equator after this initial response the western boundary current slowly begins to penetrate into the opposite hemisphere as expected from the linear theory the eastward equatorial current gradually slows down the total water mass transport in the equatorial branch decreases steadily until by day 3000 it has dwindled to zero and all the mass transport in the western boundary current crosses into the other hemisphere however a vestige of the equatorial branch remains until the end of the integration with the speed of less than 3 cm s and with intermittent meandering an analysis of the momentum balance indicates that this meander may be a free equatorial inertial oscillation we postulate that a permanent steady bifurcation of the mid depth western boundary current that carries substantial mass does not occur and eventually all of the mass transport will continue into the opposite hemisphere the asymptotic flow field seems incompatible with the tracer field observed in the atlantic which clearly shows a splitting at the equator of the tracer signal associated with the upper north atlantic deep water we speculate that an inherently time dependent explanation of the tracer tongue is called for

quantifying 20th century deposition in complex estuarine environment an example from the hudson river sediment processes in estuaries are controlled by the interaction of factors that include tides fresh water inputs bed morphology sediment supply and hydrodynamics the interaction of these factors strongly influences the pattern of sediment deposition the ability to quantify sediment deposition on a regional scale will improve the understanding of the underlying processes and provide valuable information for managing estuarine systems this paper describes our approach for obtaining the deposition pattern and quantifying the amount of 20th century impacted sediments in the haverstraw bay section of the hudson river estuary through the combination of high resolution seismic data and rapidly acquired geochemical information from numerous sediment cores we estimate that our study site experiences an average sediment accumulation rate of 3 mm y and that 75 000 t y or 10 of the annual total sediment input measured at the poughkeepsie ny gauging station usgs is stored in this reach of the hudson river on 100 y timescales a detailed analysis of the depositional pattern indicates that the accumulation rate varies considerably throughout the study area ranging from non depositional to 8 mm y our data also clearly indicate that the dredged channel in haverstraw bay is currently the main focus of deposition in this area

inertial trajectories on a rotating earth abstract the trajectories of inertial flows on a rotating earth are calculated in an attempt to reconcile the differing heuristic suggestions in the literature on the subject it is shown that westward propagating nearly closed orbits are possible away from the equator for orbits crossing the equator we find a stationary figure eight like orbit together with eastward and westward propagating modes near the pole the convergence of longitudes causes the trajectories to be deflected cyclonically in contrast to the deflection of the coriolis force giving rise to a westward propagating mode that meanders about a central latitude

runoff and tidal influences on the estuarine turbidity maximum of a highly turbid system the upper humber and ouse estuary uk abstract results are presented from longitudinal and vertical measurements of salinity and turbidity made at spring and neap tides throughout the length of the upper humber and ouse estuary uk during a 1 year period that experienced strong freshwater runoff during winter and a long period of very low runoff during summer these data were complemented by tidal cycle profiling measurements at a site in the lower ouse despite the strong suspended particulate matter spm stratification salinity was fairly well mixed vertically except in the presence of high concentration near bed muddy layers the data consistently exhibited a strong estuarine turbidity maximum etm in the low salinity reaches of the estuary the geographical positions of the freshwater saltwater interface fsi x s and the up estuary intrusion of the etm the etm nose x p measured from the tidal limit exhibited a pronounced seasonal cycle a multiple regression for x p in terms of the monthly averaged runoff q 31 averaged over 31 days preceding the survey and the tidal range for the surveyed tide tr explained 97 of the variance in x p the etm nose was located in the lower estuary during high runoff winter conditions more than 50 km from the tidal limit and in the upper estuary during very low runoff summer conditions within 2 km of the tidal limit according to the regression the etm nose was shifted up estuary by 15 km between mean neap tides and mean spring tides the location of the fsi also depended strongly on runoff the regression for x s in terms of tr and q 31 explained 88 of the variance the fsi was located in the lower estuary during winter conditions and in the upper estuary during summer conditions and according to the regression there was an up estuary displacement of 6 km between mean neap tides and mean spring tides the separation between the etm nose and fsi x p x s tended to be positive etm nose down estuary of the fsi when the nose was located more than about 55 km down estuary from the tidal limit but was otherwise negative etm nose up estuary of the fsi when the nose was located within about 30 km of the tidal limit it tended also to be about 10 30 km up estuary of the fsi a multiple regression of x p x s in terms of x p and tr explained 78 of the variance the magnitude of the maximum depth averaged spm concentration within the etm p was most closely related to the location of the etm nose the logarithm of p decreased approximately linearly with x p and p was reduced from 35 g l 1 during summer when x p was less than 2 km to 3 5 g l 1 when x p was 58 km a regression explained 94 of the variance tidal cycle profiling illustrated the seasonal etm movements via the presence of very high turbidity waters in the lower estuary at high water during winter and spring at low water during summer and early autumn and at mid ebb through to mid flood in the late autumn this seasonal movement of the etm also was accompanied by a seasonal variability in sand sized subtidal and intertidal bed sediment distributions within the upper humber and ouse estuary in which very fine sand was transported down estuary over the high runoff winter period

a review of the trends observed in british isles mean sea level data measured by tide gauges summary this report presents an up to date review of the british isles bi mean sea level msl data set obtained from tide gauges and of the long term secular trends in bi msl the data are of mixed quality and not as copious as one would like for scientific analysis given the complexity of long term sea and land level changes around bi coasts nevertheless the small number of very long records can be studied evectively and indicate that twentieth century secular trends in bi msl are consistent with those obtained from nw europe as a whole and with the bottom range of estimates for global average msl change during the past 100 years century timescale low frequency accelerations in msl of the order of 0 4 0 8 mm yr 1 century 1 are obtained from the three longest records which are also similar to estimates from mainland europe sea level indices for the bi are constructed which can provide responsible agencies with a guide to the average state of bi sea level combined ocean tide and storm surge tide surge numerical modelling is demonstrated to be a valuable tool in understanding part of the variability of msl around the bi although modelling of long term changes is limited at present by the lack of adequate meteorological data sets from before 1955 nevertheless it is shown that even if a complete meteorological modelling data set were available it would not be able to account for all of the msl variability finally recommendations are made for the development of tide gauge and global positioning system gps recording in the bi for the purpose of long term msl monitoring in the next century

the mechanics of eddy transport from one hemisphere to the other summary the trajectory of a dense eddy propagating along the bottom of a meridional channel of parabolic crosssection from the southern to the northern hemisphere is described by a hamiltonian system with two degrees of freedom two simplie ed types of motion exist in which the meridional acceleration vanishes in midlatitudes the motion is geostrophic poleward equatorward directed along the western eastern e ank of the channel while on the equator the motion consists of zonal oscillations along the potential well generated by the bottom parabolic cross section of the channel the eddy s propagation along the equator is much faster than that in midlatitudes which enhances its dissipation via mixing with the overlying ocean water for motions that occur slightly off the equator the eastward segment isstable while the westward segment isunstable so an expulsion from the equatorial regime takes place during the latter a dense eddy that arrives near the equator along the west eank of the channel has to cross the channel to its east eank where it can either oscillate back westward to the other side or move poleward from the equator along the channel s east e ank the eddy s dissipation during the equatorial part of its trajectory is very large and the probability of the dissipated eddy leaving the equator to either hemisphere is identical the non integrability of the system is manifested in the sensitive combination of the equatorial and the midlatitude regimes that renders the dynamics of the transport of dense eddies across the equator chaotic this description explains both the sharp decrease in the amount of antarctic bottom water mass in the immediate vicinity of the equator in the western atlantic ocean and the splitter effect of the equator this effect encountered in earlier e uid dynamical numerical simulations causes a current and a cloud of particles to chaotically split into two parts eowing in different hemispheres

decadal changes in bathymetry of the yangtze river estuary human impacts and potential saltwater intrusion abstract this study analyzed bathymetric changes of the 77 km yangtze river estuary in china over the past ten years in order to understand the impacts of recent human activities on the estuary of a large alluvial river morphological changes were assessed by analyzing digitized bathymetric data of the estuarine channels from 2002 to 2013 additionally multi beam bathymetric measurements made in 2012 2014 and 2015 were utilized to investigate microtophographic bedforms of the lower reach of the estuary our results showed that the middle and upper reaches of the yangtze river estuary experienced substantial channel bed erosion in the past 10 years and that the recent human activities have contributed to the change these included the construction of a 70 km2 reservoir along the yangtze river estuary the qingcaosha reservoir for drinking water supply for the city of shanghai which has caused progressive bed erosion in the north channel the net volume of channel erosion in the hengsha passage from 2002 to 2013 was 0 86 108 m3 a large amount of the eroded sediment was trapped downstream causing overall accretion in the upper reach of the north passage the middle and upper reaches of the south passage also experienced intense erosion 0 45 108 m3 in the past ten years while high accretion occurred in the lower reach because of the deepening waterway project the channel dredging left a large range of dredging marks and hollows in the north passage the increasing saltwater intrusion found in the yangtze river estuary may have been a consequence of either dredging or erosion or both combined

secular bathymetric variations of the north channel in the changjiang yangtze estuary china 1880 2013 causes and effects abstract as the interface between the fluvial upland system and the open coast global estuaries are facing serious challenges owing to various anthropogenic activities especially to the changjiang estuary since the establishment of the three gorges dam tgd currently the world s largest hydraulic structure and certain other local hydraulic engineering structures the changjiang estuary has experienced severe bathymetric variations it is urgent to analyze the estuarine morphological response to the basin wide disturbance to enable a better management of estuarine environments north channel nc the largest anabranched estuary in the changjiang estuary is the focus of this study based on the analysis of bathymetric data between 1880 and 2013 and related hydrological data we developed the first study on the centennial bathymetric variations of the nc it is found that the bathymetric changes of nc include two main modes with the first mode representing 64 of the nc variability which indicates observable deposition in the mouth bar and its outer side area lower reach the second mode representing 11 of the nc variability which further demonstrates channel deepening along the inner side of the mouth bar upper reach during 1970 2013 further recent erosion observed along the inner side of the mouth bar is caused by riverine sediment decrease especially in relation to tgd induced sediment trapping since 2003 while the deposition along the lower reach since 2003 can be explained by the landward sediment transport because of flood tide force strengthen under the joint action of tgd induced seasonal flood discharge decrease and land reclamation induced lower reach narrowing generally the upper and lower nc reach are respectively dominated by fluvial and tidal discharge however episodic extreme floods can completely alter the channel morphology by smoothing the entire channel the results presented herein for the nc enrich our understanding of bathymetric variations of the changjiang estuary in response to human activities which can be well applied to other estuaries subject to similar interferences

morphological evolution of the south passage in the changjiang yangtze river estuary china abstract estuarine morphology of the world s major large rivers have experienced great changes due to intensive anthropogenic activities and natural forcings especially in the changjiang estuary located at the end of the longest river in asia this study focuses on morphological changes of the south passage sp which is one of the 4 channels in the branching estuary at the mouth of the changjiang yangtze river china a multivariate analysis technique of empirical orthogonal eigen function eof method was used to examine the major modes of change in the long term over 26 years water depth data the results show that the morphological changes at the sp could be divided into two stages between 1987 and 1997 the sp had a single stable channel with closure of a cross channel between 1997 and 2012 sp displayed southeastward elongation of a spit into the main channel and westward shoal incision by a cross channel the opening of the sp developed a two channel morphology which stabilized and showed infilling during 2003 2012 the average deposition rate was 10 cm yr in the past 30 years the most dominant morphological changes of sp included the deposition around the upstream opening of the channel the second most important pattern of morphological change was related to the downstream elongation retreat and lateral migration of the spit of the jiangyanan shoal which resulted in the two channel configuration of the sp additionally these morphological changes were not triggered by the decline of the distal sediment source from the upstream but due to the input of proximal sources of the shoal at the upstream opening of the sp and spill over sediment from the north passage via a short cut channel

a new view of near shore dynamics based on observations from hf radar abstract since 1984 the oscr hf radar system has been used in over 50 deployments to measure near shore surface currents for both scientific and engineering applications the enhanced scope resolution and accuracy of these measurements have yielded new insights into the tidal wind and density driven dynamics of the near shore zone tidal current ellipses obtained from these radar measurements have been shown to be in good aggrement with values calculated by numerical models both for the predominant constituents and also for higher harmonics coherent patterns of wind forced currents ahve been determined with strong evidence of a slab like surface response in one deployment with offshore winds blowing over relatively deep water this slab rotated clockwise at near inertial frequency strong up to 20cm s 1 persistent surface residual currents are commonly observed these are almost certainly generated by small horizontal density gradients these observed surface residuals provide ideal data for rigorous testing of 3 d numerical models with a threatened rise in sea level hf radar is well suited for observing the expected changes in the dynamics of near shore regions continuing development of these radar systems offers exciting prospects of remote sensing of both surface waves and currents future applications may extend beyond the near shore region to measurements along the shelf edge in oceanic gyres and for beach processes

a note on tidal asymmetry in the severn estuary a one dimensional non linear numerical model is used to investigate the tidally averaged frictional stress and set up of water level due to tidal asymmetry in the severn estuary these quantities depend on the overtides in the region a linearized model of the overtides is applied to calculations of the m4 currents in order to delineate the mechanisms responsible for their generation the relative importance of individual non linear mechanisms to the tidally averaged stress and set up is determined these mechanisms are interactions between tidal flow and changes in depth or breadth over a cross section frictional interaction between the tidal flow and stokes drift interaction between the tidal fluctuations in water depth and frictional retardation and non linear advection

shoal morphodynamics of the changjiang yangtze estuary influences from river damming estuarine hydraulic engineering and reclamation projects abstract concerns regarding estuarine shoal morphodynamics have increased worldwide because of intensive anthropogenic activities to explore response of estuarine shoals to possible couplings of multiple artificial interferences in river basins and within estuaries the link between the morphodynamic processes of the nanhui shoal nhs which is located along the southern margin of the changjiang estuary the largest estuary in asia and river damming estuarine hydraulic engineering and reclamation projects is discerned in this study the results reveal that the nhs exhibited secular polarization during 1998 2013 with a significant accretion of 1 8 10 8 m 3 landward from the tidal ridge and an erosion of 0 3 10 8 m 3 on the seaward edge respectively forming a steep slope with an elevation between 2 and 3 m meanwhile the nhs morphodynamics could be divided into 3 stages mild accretion with an undisturbed tidal channel during 1998 2002 strong sedimentation with a disrupted tidal channel during 2003 2008 and large scale landward accretion with an infilled tidal channel after 2009 moreover the nhs s volume variations exhibited an 18 month cycle even though an increased area of 35 km 2 above 2 m and a decreased area of 45 km 2 between 2 and 5 m were observed the primary causes of theses periodic changes in the nhs s volume are determined as the fluctuating changjiang water discharge and cyclically altered hydrodynamics of the south passage the deep waterway project dwp and reclamation projects were responsible for the polarization of seaward erosion and landward accretion respectively moreover these reclamation projects dominated the staggered changes in nhs morphodynamics by inducing continuous accretion within the tidal channel compared to estuarine engineering river damming induced dramatic declines in distal sediment may have played a minor role in flat changes of nhs

origin abundance and storage of organic carbon and sulphur in the holocene humber estuary emphasizing human impact on storage changes an organic carbon corg and sulphur s storage inventory for holocene sediments in the humber estuary is established sources of organic matter and their variation over time are identified and with chronological control the importance of estuarine sediments as corg and s stores is demonstrated humber holocene sediments are grouped into seven widespread environmental facies with statistically significant geochemical data sets 1 oak hazel fenwood ohf 2 alder carr ac appearing as peats in core 3 river channel muds or sands rcm s 4 high saltmarsh hsm 5 low saltmarsh lsm 6 intertidal mudflat itmf and 7 a sandy facies s carbon nitrogen and sulphur cns abundances show that these facies have diagnostic geochemical signatures and 13c values for bulk organic matter exhibit a range of average values 28 terrestrial peats 27 hsm and 24 5 itmf reflecting the up core transition from terrestrial peats through saltmarshes to more open marine mudflat environments as regional sea level rose chronology and average sedimentation rates are partly constrained by radiocarbon dates palaeomagnetic techniques helped define discrete sediment packages and discontinuities time gaps although the humber holocene sediment record is not continuous long term sedimentation rates about 1 mm a 1 show that sediment accretion kept pace with regional sea level rise between 6 and 2 cal ka bp this sedimentation rate combined with core evidence to allow a geographic reconstruction of the palaeo humber 3 2cal ka bp is used to calculate storage values for corg and s in the various environments of the palaeo humber comparison of the corg and s sedimentation and storage terms for the palaeo humber with modern values highlights the impacts of reclamation and commercial urban development in the estuary in the last 300 years ohf and ac peats which were the largest corg and s stores in the palaeo estuary are now absent reclaimed while saltmarshes are no longer widespread conservative calculations show a net decrease in corg deposition from about 3 2 105 tonne in the palaeo estuary to no more than 2 5 103 tonne today a 99 reduction in potential corg storage capacity the total modern yearly s deposition is approximately 2 of its value 2ka ago removal of saltmarsh and associated brackish freshwater wetland suggests that suspended sediment and associated corg and s are currently bypassing former holocene storage areas and may be impacting north sea biogeochemical cycling

freshwater tidal and wave influences on a small estuary observations are presented of water levels currents salinity turbidity sediment grain sizes and sediment transport in the devonshire avon estuary uk in order to improve knowledge of freshwater wave and tidal influences on small strongly tidal ria estuaries a large reduction in tidal range occurred progressing from the coastal zone to the upper estuary that was mainly a consequence of rising bed and river water levels the spring neap cycle also had an influence on the reduction in tidal range along the length of the estuary surface gravity waves were completely dissipated propagating into the estuarine channel from the coastal zone and despite strong wave induced resuspension suspended sediment was not transported into the lower estuary in observable amounts during the ensuing flood tide indicating that the wave suspended material was too coarse to remain in suspension once transported away from the surf zone turbidity in the lower estuary was relatively low during low runoff summer conditions and had largest values over low water when turbid waters from farther up estuary had been transported there strong resuspension events occurred at peak currents in the upper estuary during summer reflecting the presence of finer grained sediment sources turbidity was similar but greater in the lower estuary during high runoff winter conditions and strong resuspension occurred at peak currents indicating an easily erodible nearby sediment source due to down estuary movement and relocation of finer sediment over the winter a large shoal in the lower estuary exhibited a consistent pattern of accretion erosion during the high runoff months of late autumn and winter to spring that also was qualitatively consistent with sediment transport modelling and implied a erosion from the up estuary limit of the shoal with b down estuary bed load and suspended load transport that accreted the centre and down estuary limit of the shoal until c a diminished supply led to erosion via continued down estuary transport from the shoal centre

long term morphological change and its causes in the mersey estuary nw england changes in the morphology of the mersey estuary and their possible causes have been investigated using historical trend analysis and expert geomorphological assessment historical bathymetric charts were digitised and analysed within a gis to provide quantitative estimates of changes in areas and sediment volumes above and below selected elevation planes the results show that the estuary experienced major changes over the last 150 years notably between the late 19th century and ca 1950 an analysis of data relating to possible natural and human factors which could have influenced these changes suggests that training wall construction and dredging in the outer estuary and liverpool bay was the most significant factor contributing to change during this period these activities modified the hydrodynamic and sediment transport regime in a way which enhanced an existing natural tendency for movement of sediment from liverpool bay and the outer estuary into the inner estuary changes in other factors including sea level tidal range wind wave climate freshwater flow and embanking land reclamation were of relatively minor importance between 1950 and 1977 the rate of sediment accumulation in the inner estuary declined as the estuary approached a new condition of dynamic equilibrium and since 1977 there has been a slight net loss of sediment under these conditions the changes in natural forcing factors such as sea level and storminess are likely to have a relatively greater effect on the estuary than in the past

reconstructing balloon trajectories in the tropical stratosphere with a hybrid model using analysed fields a hybrid lagrangian eulerian model of particle motion is employed to reproduce the observed trajectories of three constant level balloon flights along the 0 0987 kg m 3 and 0 110 kg m 3 isopycnic surfaces during the equateur experiment conducted by centre nationale d etudes spatiales in the summer of 1998 the hybrid model employs velocity temperature and geopotential fields as provided by the european centre for medium range weather forecasts analysed data for several three week periods of the flights the balloon in the model is advected primarily by the ambient air velocity to which a correctional velocity calculated on the basis of a lagrangian dynamical model is added the latter is driven by the montgomery stream function gradient interpolated to the relevant isopycnic surface from the geopotential and temperature standard fields and coriolis and drag forces this correctional velocity is free from the continuity constraint satisfied by the air flow altogether the model employs two physical parameters the rayleigh friction coefficient and the fraction weight of correctional velocity in the advection to quantify the difference between the calculated and observed trajectories we compute the temporal mean of the separation between the two trajectories on time scales on the order of three weeks the best calculated trajectories are obtained when the correctional velocity fraction in the advection is between 5 and 25 and these best fitting trajectories have a mean separation that is down to 20 of that of the advection by the ambient air velocity only the implication of our results is that although a balloon is advected primarily 75 to 95 by the ambient air velocity the small deviations from this velocity result in a significantly more accurate calculated trajectory over periods of three weeks when a trajectory remains in one hemisphere for the entire three week period the best fitting fraction of the correctional velocity is smaller and the rayleigh friction coefficient is larger than in the case when the trajectory straddles the equator but the improvement factor does not differ significantly

long term morphological change in the ribble estuary northwest england morphological change in the ribble estuary northwest england has been studied using bathymetric charts topographical surveys and remote sensing data a sediment budget has been prepared from the analysis of these data the results reveal a net accretional trend over the last 150 years the main channels experienced major infilling sediment also accumulated in higher parts of the intertidal zone salt marshes and sand banks while the sediment volume in the lower intertidal zone remained essentially the same there were both zones of net erosion and deposition in the outer estuary with a small net gain in subtidal sediment volume infilling associated with major morphological change was accelerated in the nineteenth century and early twentieth century principally as a result of human activities the triggering factors for increased sedimentation were embankment construction and reclamation after 1810 which progressively reduced the intertidal area tidal prism and current velocities within the estuary additionally construction of a trained channel between 1847 and 1910 to secure navigation and maintenance of this channel by dredging concentrated the ebb flow in this overdeepened channel and reduced periodic scour over the sand banks on both sides enhancing sedimentation thus the effects of human activities have outstripped those of changes in natural forcing factors on the morphological development in the area

river flow control on intertidal mudflat sedimentation in the mouth of a macrotidal estuary abstract the objective of this study is to analyze the impact of hydrological variability influenced by climatic phenomena upon the sedimentary exchange between the turbidity maximum tm and a river mouth intertidal mudflat this study carried out over a period of 10 years 1997 2006 in the seine estuary france is specifically focused on two extreme periods a wet one from 2001 to 2002 and a drier one from 2005 to 2006 this study is based on an original approach combining data gathered via low altitude remote sensing with altimeter readings and ground level measurements during this 10 year period we observed a link between climate change and the sedimentary processes on the mudflat surface the modifications of sedimentary processes are mainly connected to the multiannual variability of hydrological flow rates that control the positioning of the turbidity maximum the source of the sedimentary material deposited in this intertidal zone the tm at the mouth of the seine estuary is well developed its maximum mass is estimated to be between 300 000 tons and 500 000 tons avoine et al 1981 with maximum concentrations in the surface waters ranging from 1 to 2 g l 1 le hir et al 2001 most of the fine particles stored within the tm have been found to originate from within the catchment area dupont et al 1994 in the seine estuary the dynamics of the estuarine tm in response to hydrodynamic forcings have been previously described avoine et al 1981 and modeled e g brenon and le hir 1999 le hir et al 2001 the tm is upstream of the northern mudflat when the river flow is low

coastal dune erosion at formby point north merseyside england causes and mechanisms abstract following a period of coastal progradation during the nineteenth century since ca 1900 a 5 km length of dune fronted shoreline at formby point located between the ribble and mersey estuaries in northwest england has been eroding at an average rate of up to 3 m yr although several factors probably contributed to the onset of erosion meteorological records suggest that a high frequency of strong westerly winds and by inference storm waves around the turn of the century played an important role the erosional trend was reinforced by the effects of training wall construction and dredge spoil dumping which changed the bathymetry in liverpool bay and led to greater focussing of wave energy onto the north central part of formby point sand eroded from this part of the shore has been transported by longshore drift northwards and southwards away from the point leading to beach and foredune accretion between ainsdale and southport and at altcar foredune erosion at formby point was also accelerated between 1900 and the mid 1970s by the abandonment of dune and foreshore management which had been extensively practised during the late 19th century and by a significant increase in recreational pressure sand mining and military activities since the instigation of a coastal management scheme in 1977 damage to the dunes from these causes has been greatly reduced but the dune protection and restoration works employed have had little effect on the underlying problem of beach and foredune erosion by waves especially during storm surges

computational modelling of morphodynamic response of a macro tidal beach to future climate variabilities abstract global climate variabilities have the potential to impact many coastlines around the world and can have detrimental effects on the stability of coastlines and their function as natural coastal defenses this paper investigates the impacts of future extreme storms and sea level rise on morphodynamics of the macro tidal sefton coast uk taking a process based model as a tool to simulate a snap shot of future beach change during storms sefton coast represents one of the largest dune systems in the uk where frontal dunes function as a natural barrier against extreme conditions future storm conditions were determined from global predictions of future waves at the end of the twenty first century future sea levels were determined based on climate change allowances set by the uk environment agency ea while future surge conditions were determined based on the guidelines also provided by ea a nested numerical modelling approach that combined a regional scale model with a local scale model with high resolution is used the modelling suite was first validated against measured waves water levels and beach change before using it to simulate morphodynamic change from numerous statistically significant future storm conditions future storm induced morphodynamic change of the sefton coast was then compared with that from the present storms the results reveal that this beach will experience significant climate change driven impacts where dune retreat during storms will be considerably higher in future the results also reveal that due to the shape of the beach and its orientation to predominant wave approach direction there will be a strong longshore variability of morphodynamic response to storms it was also found that the water level in front of the dune and hence surge and future sea level rise is the most critical factor that determines beach erosion during a storm

midlatitude equatorial dynamics of a grounded deep western boundary current part ii cross equatorial dynamics abstractthis is part ii of a two part theoretical study into the midlatitude cross equatorial dynamics of a deep western boundary current dwbc in an idealized meridionally aligned differentially rotating ocean basin with zonally varying parabolic bottom topography part i determined the midlatitude flow across the planetary vorticity gradient and the dynamics of the dwbc as it begins to enter the equatorial region in the intermediate equatorial region part ii determines the nonlinear dynamics of the dwbc as it flows across the basin along the equator in the inner equatorial region the large scale structure of the flow within the inner equatorial region corresponds to a zonally aligned nonlinear stationary planetary wave pattern that meanders about the equator in which the flow exits the equatorial region on the eastern side of the basin in addition to numerically determining the pathlines for the large scale equatorial flow an approximate nonlinear model is introduced for which an analytical so

the detailed dynamics of the june august hadley cell the seminal theory for the hadley cells has demonstrated that their existence is necessary for the reduction of tropical temperature gradients to a value such that the implied zonal winds are realisable at the heart of the theory is the notion of angular momentum conservation in the upper branch of the hadley cells eddy mixing associated with extra tropical systems is invoked to give continuity at the edge of the hadley cell and to reduce the subtropical jet by a factor of 3 or more to those observed in this paper a detailed view is presented of the dynamics of the june august hadley cell as given by era data for the period 1981 2010 with an emphasis on the dynamics of the upper branch the steady and transient northward fluxes of angular momentum have a very similar structure both having a maximum on the equator and a reversal in sign near 12 s with the transient flux merging into that associated with eddies on the winter sub tropical jet in the northward absolute vorticity flux the coriolis torque is balanced by both the steady and transient fluxes the overturning circulations that average to give the hadley cell are confined to specific longitudinal regions as are the steady and transient momentum fluxes in these regions both intra seasonal and synoptic variations are important the dominant contributor to the hadley cell is from the indian ocean and w pacific regions and the maxima in olr variability and meridional wind in these regions have a characteristic structure associated with the westward moving mixed rossby gravity wave much of the upper tropospheric motion into the winter hemisphere occurs in filaments of air from the summer equatorial region these filaments can reach the winter sub tropical jet leading to the strengthening of it and of the eddies on it implying strong tropical extratropical interaction

short and long term changes in estuary capacity changes in capacity have been examined in the lune ribble mersey and humber estuaries to assess the role played by land derived sediments in coastal accretion the engineering concept of dynamic equilibrium is introduced and shown to imply that land derived sediments should contribute exclusively to coastal accretion the various factors responsible for changing estuary capacity are also introduced capacity changes over the last 100 years show that all the estuaries considered have suffered large scale siltation with the majority of the sediment being derived from coastal and offshore sources in the case of the lune ribble and mersey estuaries engineering works have been responsible for large permanent changes in capacity the situation in the humber is less clear and siltation is probably a result of natural infilling the estuary having been over deepened by glacial and fluvial action in the past a detailed study of the mersey suggests that the estuary was also over deepened and over widened and has only been tidal for the last 9000 years or so calculations suggest that a new equilibrium will be achieved in about 250 years time and that the estuary may then be in a state of dynamic equilibrium the much smaller lune estuary may already have achieved this state although detailed evidence is scarce

stable isotope patterns of mesopelagic communities over two shallow seamounts of the south western indian ocean abstract the stable carbon 13c and nitrogen 15n isotope values of soft tissues of micronekton crustaceans squid mesopelagic fish and zooplankton were measured from organisms collected on the rv antea at two seamounts located in the south western indian ocean la perouse summit depth 60 m and mad ridge thus named in this study summit depth 240 m surface particulate organic matter pom surf showed higher 13c at the more productive mad ridge than at the oligotrophic la perouse seamount particulate organic matter and zooplankton were depleted in 15n at la perouse pinnacle compared with mad ridge gelatinous organisms and crustaceans occupied the lowest and intermediate trophic levels tl 2 and 3 respectively at both seamounts mesopelagic fish and smaller sized squid sampled at both seamounts occupied tl 3 to 4 whereas the large nektonic squid ommastrephes bartramii collected at mad ridge only exhibited a tl of 5 the 15n values of common open water mesopelagic taxa were strongly influenced by specimen size and feeding habits at both seamounts with an increase in 15n values with increasing size carnivorous fish species sampled exclusively over the seamounts flanks and summits exhibited tl values of 4 irrespective of their wide size ranges the work could not demonstrate any differences in 13c values of mesopelagic fish between the seamounts and the surrounding oceanic areas the study segregated clusters of mesopelagic organisms according to their 13c and 15n values with variations in stable isotope values reflecting a complex range of processes possibly linked to productivity as well as biological and ecological traits of the species size and feeding mode

a thirteen year record of bathymetric changes in the north passage changjiang yangtze estuary article i nfo the mouths of major rivers in the world have always been important waterways and as a result subject to significant human intervention therefore it is necessary to understand the coupling of natural processes and human intervention in the sediment movement and deposition to determine long term morphodynamic evolution in the mouth regions of major rivers a multivariate technique was used to analyze high resolution bathymetric data from the north passage of changjiang yangtze river which is the vital shipping channel in the mouth region and for the entire changjiang waterway our findings show that there are two modes of bathymetric changes the first mode represents 85 of the variability which includes the deposition in the peripheral groin fields along the shipping channel and deepening of the shipping channel which is primarily due to the channel maintenance the second mode represents 6 of the variability of the river mouth shoal seaward migration and size reduction attributable to the declining sediment discharge of the changjiang

seamount effect on circulation and distribution of ocean taxa in the vicinity of la perouse a shallow seamount in the southwestern indian ocean abstract the la perouse seamount 60 m depth has so far been poorly studied despite it being a short distance 160 km from reunion island as part of the madridge project a multidisciplinary cruise was conducted to evaluate the effect of this shallow seamount on the local hydrology and ecology current measurements temperature and chlorophyll a profiles and mesozooplankton and micronekton samples were collected between the summit and 35 km away micronekton data were supplemented with stomach content of pelagic top predators as well as fisheries statistics from the domestic longline fleet operating from reunion vertical current profiles revealed distinct patterns between the offshore and seamount flanked stations giving evidence of topographical induced flow instabilities notably on its leeward side west relative to the east flank distinct patterns in temperature and chlorophyll a vertical profiles suggest the formation of convergent and divergent circulation cells as a result of the irregular and crescent like summit topography spatial differences in zooplankton abundance were detected with higher biovolumes on the leeward flank the overall acoustic backscatter for micronekton over the summit was weaker than offshore but highly concentrated in the upper layer albacore tuna and swordfish dominate the longline catch west of reunion seemingly in association with a deep 900 m topographic feature yet the largest catch is not directly associated with la perouse which would be too shallow for top predators to aggregate around in the long term enhanced levels of phytoplankton or zooplankton enrichment at la perouse were not demonstrated in this study nor was there notable diversity of micronekton species this might explain the relatively limited importance of this seamount to the tuna fisheries in this region

observation of a mesoscale eddy dipole on the northern madagascar ridge consequences for the circulation and hydrography in the vicinity of a seamount abstract based on satellite and in situ data the dynamic characteristics and vertical structure of a surface intensified mesoscale eddy dipole recently expelled from the south east madagascar current semc is described for the first time the dipole was surveyed 250 nautical miles south of madagascar between 14 and 23 november 2016 during west east and south north transects carried out over the northern madagascar ridge the dipole consisted of two counter rotating vortices of similar size 100 km and intensity 0 7 f and an intense southwestward jet 150 cm s 1 in the frontal region between the two eddies the cyclonic eddy was lying on the western side of the anticyclonic eddy with azimuthal velocities reaching 100 cm s 1 at the surface and decreasing slowly with depth 40 cm s 1 at 600 m this dipole was defined as a highly non linear ro 0 7 isolated eddy type structure c 11 cm s 1 and u c 0 7 capable of trapping and advecting water masses over large distances the enhanced concentration of chlorophyll a found in the cyclone relative to the anticyclone could be tracked back to the spin up phase of the two eddies and attributed to eddy pumping the eddy cores were located above the pycnocline 1026 4 kg m 3 within the upper 600 m and consisted of varieties of subtropical underwater stuw found within the semc the stuw found in the anticyclone was more saline and oxygenated than in the cyclone highlighting mixing with the inshore shelf waters from the southeastern coastal upwelling cell off madagascar observations suggest that the dipole interacted strongly with the chaotic bathymetry of the region characterized by a group of five seamounts lying between 240 m and 1200 m the bathymetry blocked its westward advection trapping it in the vicinity of one shallow seamount for more than 4 weeks so enhancing the role of the eddy induced velocities in stirring the surrounding water masses squeezed between the southern madagascan shelf and the northern flank of the anticyclone two filament like dynamic features with very different water mass properties could be observed on the south north transect i one filament highly concentrated in chlorophyll a demonstrating the capacity of the eddy to export shelf water offshore ii intrusions of southern type stuw generally found south of the south indian counter current sicc recirculating on the external flanks of the anticyclone although the observed circulation and hydrography were largely constrained by the presence of the mesoscale eddy dipole unmistakable fine scale dynamics were also observed in the vicinity of the mad ridge seamount superimposed onto the mesoscale eddy flow

buried sandbodies within present day estuaries atlantic coast of france revealed by very high resolution seismic surveys abstract studies of sandbanks within estuaries and macrotidal bays are critical for management of those coastal environments where human activity concentrates they are also excellent analogues of reservoirs new very high resolution vhr seismic profilers are now available for studying at the outcrop resolution scale sandbodies in very shallow water we present here a vhr seismic study constrained by vibrocores repetitive bathymetric surveys and radiocarbon dating which provide evidence of buried sandbodies in mixed tide and wave influenced estuaries of the french atlantic coast the three selected buried sandbodies are chosen because they are located at various water depths and have different internal architecture and outer shape they include 1 a very shallow water around 2 m under low tide elongated nearshore sandbody emplaced during the last centuries 2 a 6 to 7 m deep elongated nearshore sandbody dated to 2965 30 bp and 3 sandwaves lying around 17 m of water depth over the top of a large rounded shape sandbody dated to 5260 30 bp deepest 6 and 17 m sandbodies are interpreted as remnants of lower sea levels and thus transgressive sandbodies all those sandbodies are buried under estuarine mud which have been mainly emplaced during the last millenium such major sedimentary transition from basal sand to upper mud is assumed to record a major environmental change in relation to both natural infilling of estuaries climate change and increasing human activities anthropogenic perturbations are however believed to be the most important factor they have mainly consisted of land reclamation and are responsible for 1 rapid infilling of tidal bays 2 tidal prism and tidal current energy decreases and 3 deposition of muddy sediments upon sandbodies

picoplankton and nanoplankton composition on and around a seamount affected by an eddy dipole south of madagascar abstract picoplankton and nanoplankton community abundances were sampled on and around a seamount located on the madagascar ridge in november 2016 prochlorococcus synechococcus picoeukaryote and nanoplankton community abundances both on the seamount and in the immediate vicinity approximately 100 km surrounding it were analysed using flow cytometry the original aim of the study was to estimate whether or not the seamount had an effect on the picoplankton and nanoplankton community distribution however coupled altimetry and in situ ship data indicated that a dipole eddy was also sampled during this time which had a substantial effect on the results results reveal that picoeukaryotes contributed the most to carbon biomass within the anticyclone showing higher abundances in the stations situated within the southern slopes of the seamount which also fell within the anticyclone the southern slope of the seamount contained higher synechococcus prochlorococcus and picoeukaryote abundances whereas nanoplankton dominated in the cyclonic eddy species composition and abundance was significantly different on versus off the seamount driven by nanoplankton biomass these results indicate significantly high abundance above the slopes of the seamount driven by picoeukaryotes which seem to be amplified by the dipole presence the resulting variability in microbial abundance both on the southern slopes of the seamount as well as within the dipole has far reaching implications with regard to larger organism proliferation and carbon export during such events in this region

micronekton distribution as influenced by mesoscale eddies madagascar shelf and shallow seamounts in the south western indian ocean an acoustic approach abstract an investigation of the vertical and horizontal distributions of micronekton as influenced by mesoscale eddies the madagascar shelf and shallow seamounts was undertaken using acoustic data collected during two research cruises at an unnamed pinnacle summit depth 240 m thereafter named mad ridge and at la perouse seamount 60 m in the south western indian ocean mad ridge is located to the south of madagascar in an eddy corridor known both for its high mesoscale activity and high primary productivity in contrast la perouse is located on the outskirts of the indian south subtropical gyre issg province characterised by low mesoscale activity and low primary productivity during the mad ridge cruise a dipole was located in the vicinity of the seamount with the anticyclone being almost stationary on the pinnacle total micronekton acoustic densities were greater at mad ridge than at la perouse micronekton acoustic densities of the total water column were lower within the anticyclone than within the cyclone during mad ridge micronekton followed the usual diel vertical migration dvm pattern except within the cyclone during mad ridge where greater acoustic densities were recorded in the daytime surface layer the backscatter intensities were stronger at the 38 khz than at the 70 and 120 khz frequencies in the daytime surface layer at mad ridge cyclonic stations these backscatter intensities likely correspond to gas filled swimbladders of epi and mesopelagic fish actively swimming and feeding within the cyclone or gelatinous organisms with gas inclusions our findings evidenced that the distributions of micronekton and dvm patterns are complex and are influenced significantly by physical processes within mesoscale eddies the mesoscale eddies effects were dominant over any potential seamount effects at the highly dynamic environment prevailing at mad ridge during the cruise no significant increase in total micronekton acoustic densities was observed over either seamount but dense aggregations of biological scatterers were observed on their summits during both day and night

particle size evidence of estuary evolution a rapid and diagnostic tool for determining the nature of recent saltmarsh accretion abstract a conceptual model of saltmarsh sedimentation based on high resolution particle size analysis has been tested on short cores c 0 5 m of known age from the dee estuary nw england uk here two components of the particle size distribution psd are interpreted as the traction load deposited by the faster tidal flow velocities fast tide and the suspension load that settles during the turn of the tide slow tide the feasibility of this model for diagnosing the driving mechanism of estuary evolution in both time and space is tested with reference to historical evidence of saltmarsh accretion up core trends in dated saltmarsh cores and the psds of present day saltmarsh surface sediments cores that show an up core progression from very fine skewed to near symmetrical psds are interpreted in the context of estuary infilling due to a positive sediment budget sediment surplus whilst those that show a persistence of near symmetrical very poorly sorted mesokurtic particle size distributions in the fine to very fine silts size range are considered to be the result of slow tide sedimentation the influences of the two end member styles of saltmarsh accretion i e i infilling due to sediment surplus and ii slow tide settling linked to sea level exhibit spatial and temporal trends as predicted particularly in cores from mid and lower saltmarsh locations the upper saltmarsh cores also show evidence of estuary infilling due to slow tide sedimentation at rates in excess of sea level rise the results confirm that the diagnostic approach can be applied as a pre filtering method for assessing the suitability of saltmarsh sediments for reconstructing sea level trends and for providing input data for improved estuary morphological modelling

seafloor environmental changes resulting from nineteenth century reclamation in mishou bay bungo channel southwest japan this study reconstructed environmental changes to the seafloor associated with reclamation in mishou bay bungo channel japan based on measurements of sediment grain size organic matter and sulfur contents of surface sediments and data from sediment cores grain size within sediment cores from the middle of mishou bay decreased from the beginning of the 1800s to the 1900s in contrast a grain size profile from the river mouth shows a gradual increase in grain size up through the sediment core these changes in grain size indicate a decrease in tidal current velocity within the middle of the bay and that the delta system is gradually prograding from the river mouth records of organic matter composition and sulfur contents indicate that the effect of the river on seafloor sedimentation became stronger during the nineteenth century these changes are related to reclamation during the late 1700s and 1800s the decrease in sea area resulting from reclamation probably led to a decrease in tidal prism and current velocity it is likely that the increasing effect of river water on sedimentation is associated with reclamation related progradation of the river delta system

intertidal morphology change following spartina anglica introduction tamar estuary tasmania the surface morphology and sediment characteristics of introduced spartina anglica marshes of the tamar estuary were analysed using a combination of spatial mapping land based topographical surveys sediment coring and identification of the pre introduction surface such a morphological investigation of estuarine change following spartina introduction has not been attempted elsewhere before a difference was found between marshes in upper and lower estuary surface topography of type 1 marshes of the upper estuary was found to be independent of the pre spartina surface morphology with deeper vertical development and exhibiting a flat to slightly concave upper marsh a convex ridge in the outer mid marsh and a relatively steeply graded convex lower marsh type 2 marshes of the lower estuary were thinner in vertical development and with surface topography dictated by the underlying pre spartina surface the difference was found to be due to variations in environmental conditions in sediment supply and wave current exposure between the two regions rather being an indication of relative maturity the seaward edge of marshes was found to be 0 5 m lower at the seaward end of the tamar relative to the landward reflecting tidal amplification up this confined estuary while spartina marshes are accretionary surveys demonstrated retreat of the seaward margins throughout the estuary over the past 17 years and the development of erosional scarps in type 1 marshes spatial mapping identified 374 ha of s anglica infestation within the tamar estuary with type 1 marshes occupying 240 ha and type 2 marshes occupying 134 ha topographic profiles and stratigraphic data were used to estimate total sediment volumes trapped by spartina in the tamar estuary finding approximately 1 193 441 m3 of material to have been trapped beneath spartina since its introduction in 1947 of which between 14 and 28 has been spartina derived organic matter

mapping intertidal estuarine sediment grain size distributions through airborne remote sensing abstract the intertidal environments of estuaries represent critical exchange environments of sediment and sediment bound contaminants ecological and sedimentological related investigations of these environments require monitoring methods that provide rapid spatially representative data on sediment grain size distribution remote sensing has the potential to provide synoptic information of intertidal environments previous in situ and laboratory based reflectance investigations have demonstrated that for effective quantification of sediment grain size distributions remote sensing platforms must include measurements within the short wave infrared swir in addition the timing of image acquisition in relation to tidal cycles and sediment moisture content is critical in optimising the spectral differences between the coarser sand and finer mud fraction of sediments daedalus 1268 airborne thematic mapper atm has been identified as an appropriate platform and sensor for providing accurate synoptic maps of estuarine sediment distributions this paper presents the results from the application of atm 1 75 m resolution data to the mapping of surface sediment grain size distributions across intertidal areas of ribble estuary lancashire uk atm imagery was acquired after the intertidal area was exposed to strong summer drying conditions pre processing and linear unmixing of the imagery collected of the intertidal zone following a period of drying allowed accurate sub pixel determinations 1 75 m resolution of sediment clay r2 0 79 but less accurate for sand r2 0 60 the results also demonstrate deterioration in the image calibration with increasing sediment moisture content and microphytobenthos cover however recombining the subpixel end member abundances through multivariate regression analysis improved the image calibration significantly for both sediment clay and sand content r2 0 8 for imagery collected in both dryer and wetter conditions these results demonstrate that atm data or similar can be used to gain quantitative information on intertidal sediment distributions and such data has application to a wide variety of estuarine research