wave induced advective transport below a rippled water sediment interface the exchange between the water column and the sediment bed and the transport inside the permeable sediment layer are important processes in the cycles of chemical elements in this paper we examine quantitatively the effects of modulations in the profile of the water sediment interface on this exchange and on the advective transport inside the sediment bed the flow field inside a sediment layer bounded between spatially periodic ripples on top and an impermeable bottom surface is modeled using darcy s law the forcing is due to progressive gravity waves in the water above the results of two different models for the pressure variation imposed on the upper boundary are compared the two pressure profiles are derived from potential flow theory and from a numerical solution to the navier stokes equations for the oscillatory flow over a rippled bed from an analytic solution to the two dimensional model the trajectories of pore water particles immediately below the ripple profile are found to be quite different from the simple elliptical pattern found below a flat bed the shapes of these trajectories can be quite complicated and vary considerably both along the length of the ripple and over the depth of the sediment layer close to its surface the total exchange across the water sediment interface averaged over one wave period is significantly higher across a rippled interface than across a flat bed this difference increases with increasing ripple slope and the strength of the wave motion and it decreases with increasing thickness of the sediment layer relative to the length of the gravity wave since rippled bed forms are commonly found in coastal waters the increase in the total exchange across a rippled water sediment boundary can enhance the exchange of solutes due to wave pumping immediately below the water sediment interface circulation cells with net advective transport over a wave period are found such net advection patterns can lead to spatial in the horizontal direction inhomogeneities of the vertical concentration or temperature profiles if the overlying water column and or the sediment bed act s as source or sink this gives a plausible physical mechanism to explain the spatial variations in vertical concentration profiles found in field measurements

balancing rare earth element distributions in the northwestern mediterranean sea abstract elemental concentrations of rare earth elements ree and isotopic compositions of neodymium end have been measured in three water column profiles in the north western mediterranean sea clear enrichments of ree are observed when comparing to adjacent atlantic waters suggesting ree inputs along the circulation in this area for the first time relative proportions of external sources including submarine groundwater discharges sgd have been quantified for the studied area atmospheric deposition is estimated to be the most important external source for all the ree with an average contribution of 44 followed by diffusion from porewaters which provide a 30 dissolved riverine fluxes account for 11 sgd for 10 and dissolution of remobilized surface sediments the remaining 6 mass balances accounting for seawater transport and identified external sources have been delineated for the three main water masses modified atlantic waters levantine intermediate waters and western mediterranean deep waters they show that the balances of ree in this area are dominated by seawater mass mixing superimposed on this hydrography ree vertical profiles are affected by external sources and biogeochemical cycling dissolved ree are correctly balanced in deep waters whereas substantial missing fluxes are identified in the surface and intermediate water masses additional net lree outputs and hree inputs are required in the surface waters while net output fluxes for all the ree are missing at intermediate waters the most likely process suggested here is an active reversible scavenging consistent with a stronger adsorption of lree compared to hree in the particular case of the redox sensitive cerium the most plausible mechanism to explain the net output missing fluxes is ce 3 removal by particle scavenging via oxidation to insoluble ce 4 estimated ce oxidation rates of 0 33 d 1 in surface waters agree well with previously published values exchange fluxes derived from the isotopic nd mass balance indicate higher nd scavenging in surface compared to intermediate waters

origin and characteristics of brackish groundwater in abu madi coastal area northern nile delta egypt abstract hydrogeochemical and geoelectrical resistivity investigations were carried out to assess the origin and characteristics of a brackish groundwater in abu madi coastal area twenty six surface water shallow and deep groundwater samples were collected and analyzed for various ionic concentrations as well as oxygen and hydrogen stable isotopic contents in addition a total of 20 vertical electrical sounding sites were conducted to investigate layers thicknesses resistivities and to detect the water bearing layers then 2 d electrical resistivity tomography ert along two profiles in the study area was conducted to get information about the surface water effect on recharge the stable isotopic composition and the chloride concentrations strongly suggest that the deep groundwater in abu madi area is dominated by inland freshwater with a minor seawater component this groundwater was recharged during the first and the third holocene humid climatic cycles where the sea surface was about 125 and 25 m below the current sea level respectively the brackish nature and higher piezometric surface of the groundwater as well as the occurrence of vertical low salinity seawater zone in front of the study area support the possibility of submarine groundwater discharge the geoelectrical resistivity surveying on the other hand revealed a number of geoelectrical groundwater bearing layers the main water bearing layer in the study area is represented by the sixth geoelectrical layer which has relatively high resistivity and a considerable thickness being consistent with the hydrogeochemical observations ert results point to the presence of shallow water bearing layers recharged from the surface water drains with low resistivity and surface rain water of moderate resistivity results from the hydrogeochemical analyses and the different hydrogeological data are consistent with the high resistivity values of this geoelectrical layer however the overall high specific conductance and high sodium hazards indicate that the groundwater in the study area should be carefully treated before irrigation and domestic uses through mixing it with surface irrigation water

influence of porewater advection on denitrification in carbonate sands evidence from repacked sediment column experiments abstract porewater flow enhances mineralization rates in organic poor permeable sands here a series of sediment column experiments were undertaken to assess the potential effect of advective porewater transport on denitrification in permeable carbonate sands collected from heron island great barrier reef experimental conditions flow path length advection rate and temperature were manipulated to represent conditions similar to near shore tropical environments hgcl2 poisoned controls were used to assess whether reactions were microbially mediated overall significant correlations were found between oxygen consumption and n2 production the n o2 slope of 0 114 implied that about 75 of all the nitrogen mineralized was denitrified a 4 fold increase in sediment column length from 10 to 40 cm resulted in an overall increase in oxygen consumption 1 6 fold tco2 production 1 8 fold and denitrification 1 9 fold oxic respiration increased quickly until advection reached 80 l m 2 h 1 and then plateaued at higher advection rates interestingly denitrification peaked up to 336 mol n2 m 2 h 1 at intermediate advection rates 30 80 l m 2 h 1 we speculate that intermediate advection rates enhance the development of microniches i e steep oxygen gradients within porous carbonate sands perhaps providing optimum conditions for denitrification the denitrification peak fell within the broad range of advection rates often on scales of 1 100 l m 2 h 1 typically found on continental shelves implying that carbonate sands may play a major but as yet unquantified role in oceanic nitrogen budgets

investigation of submarine groundwater discharge to tidal rivers evidence for regional and local scale seepage fluxes of submarine groundwater discharge sgd were investigated into two tidal rivers on the north and south shore of long island ny during july 2015 ground based handheld thermal infrared tir imagery combined with direct push point piezometer sampling documented spatially heterogeneous small scale intertidal seepage zones pore waters were relatively fresh and enriched in nitrogen n within these small scale seeps pore waters sampled just 20 cm away outside the boundary of the ground based tir located seepage zone were more saline and lower in n these ground based tir identified seeps geochemically represented the terrestrial fresh groundwater endmember whereas n in pore waters sampled outside of the tir identified seeps was derived from the remineralization of organic matter introduced into the sediment by tidal seawater infiltration a 222rn radon 222 time series was used to quantify fresh sgd associated n fluxes using the n endmembers sampled from the ground based tir pore water profiles n fluxes were up scaled to groundwater seepage zones identified from high resolution airborne tir imagery using the two dimensional size of the airborne tir surface water anomalies relative to the n flux from the time series sampling location results suggest that the n load from the north shore tidal river to long island sound is underrepresented by at least 1 6 3 6 whereas the n load from sgd to a south shore tidal river may be up to 9 higher than previous estimates these results demonstrate the importance of sgd in supplying nutrients to the lower reaches of tidal rivers and suggest that n loads in other tidal river environments may be underestimated if sgd is not accounted for

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

dynamic response of surface water groundwater exchange to currents tides and waves in a shallow estuary 1 in shallow fetch limited estuaries variations in current and wave energy promote heterogeneous surface water groundwater mixing benthic exchange which influences biogeochemical activity here we characterize heterogeneity in benthic exchange within the subtidal zone of the delaware inland bays by linking hydrodynamic circulation models with mathematical solutions for benthic exchange forced by current bedform interactions tides and waves benthic fluxes oscillate over tidal cycles as fluctuating water depths alter fluid interactions with the bed maximum current driven fluxes 1 10 cm d occur in channels with strong tidal currents maximum wave driven fluxes 1 10 cm d occur in downwind shoals during high energy storms simulated wave pumping rates increase by orders of magnitude demonstrating the importance of storms in solute transfer through the benthic layer under moderate wind conditions 5 m s integrated benthic exchange rates due to wave current and tidal pumping are each 1 10 m3 s on the order of fluid contributions from runoff and fresh groundwater discharge to the estuary benthic exchange is thus a significant and dynamic component of an estuary s fluid budget that may influence estuarine geochemistry and ecology

mean mixed depth of sediments the wherefore and the why the activities and consequently the bioturbational effects of deposit feeding organisms are largely restricted to a narrow surficial zone of marine sediments with a worldwide environmentally invariant mean of 9 8 cm with a standard deviation of 4 5 cm currently available theories of infaunal behavior cannot predict quantitatively this observation a new simple model that accounts for the feedback between resource food abundance its reactivity and the intensity of bioturbation leads to a quantitative estimate of 9 7 cm this model constitutes a fundamental advance in our understanding bioturbation

nonlinear interactions of waves and tides in a subterranean estuary previous studies have revealed hysteretic behavior in subterranean estuaries in response to intensified wave conditions caused by offshore storm events showing dependence of submarine groundwater discharge sgd and subsurface salt distribution on historic wave conditions although most shorelines worldwide are also exposed to tidal fluctuations it is unclear how tides moderate wave induced sgd and salinity distribution in subterranean estuaries this study presents numerical simulations that explore the combined influence of intensified wave conditions and tides on groundwater flow and salt transport in a subterranean estuary the results show that tides weaken the hysteretic wave effect on sgd suggesting that a tidally influenced subterranean estuary is less sensitive to intensified wave conditions with respect to the water fluxes across the aquifer sea interface however due to enhancement of salt freshwater mixing tides strengthen the hysteretic wave effect on the salt fluxes across the aquifer sea interface prolonging the recovery of salt distribution in the subterranean estuary to the prestorm state these findings reveal the nonlinear coupling nature of processes driven by oceanic oscillations at different time scales in subterranean estuaries

water filtration through reflective microtidal beaches and shallow sublittoral sands and its implications for an inshore ecosystem in western australia abstract volumes of seawater filtered through the intertidal zone were measured on three modally reflective microtidal beaches in western australia the filtered volumes were large 19 m 3 m 1 day 1 and 73 m 3 m 1 day 1 on two clean beaches but only 0 4 m 3 m 1 per tidal cycle on a beach covered in kelp and seagrass wrack the mean residence times of this water in the interstitial system and its percolation paths were both short 1 7 h and 2 5 m respectively water input was greater across a beach cusp horn than across a cusp embayment most input occurred in the upper swash zone where the water table was less than 20 cm deep tidal variations in input volumes were evident even with tide ranges of only 20 cm the inshore zone off these beaches filters on average 0 07 m 3 m 2 day 1 at an average depth of 5 5 m under 0 4 m waves of 6 5 s duration the importance of these procedures in the mineralization of organic materials and the regeneration of nutrients for an inshore lagoon ecosystem is estimated and discused

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

fresh and saline groundwater discharge to the ocean a regional perspective 1 studies of groundwater flow in coastal aquifers often focus strongly on freshwater and investigate flow in a narrow 5 km zone surrounding the coastline this work was designed to place coastal flow in a regional context and to compare fresh and saline submarine groundwater discharge sgd for regional flow systems numerical flow and transport models were developed to estimate sgd associated with topography driven flow seawater recirculation and geothermal convection in a passive margin setting simulations were based on two cross sections of north carolina and sensitivity studies were used to explore the impact of varying hydraulic and transport parameters results suggest that saline flow associated with seawater recirculation and geothermal convection should be considered in studies of sgd studies limited to shallow topography driven flow may be justified in using small study areas but flow systems contributing to sgd may span at least 20 km surrounding the coast and continental slope

clay coated sand grains in petroleum reservoirs understanding their distribution via a modern analogue abstract clay coated grains can inhibit ubiquitous porosity occluding quartz cement in deeply buried sandstones and thus lead to anomalously high porosity a moderate amount of clay that is distributed as grain coats is good for reservoir quality in deeply buried sandstones being able to predict the distribution of clay coated sand grains in petroleum reservoirs is thus important to help find and exploit anomalously good reservoir quality here we have adopted a high resolution analogue approach using the ravenglass estuary marginal shallow marine system in nw england u k extensive geomorphic mapping grain size analysis and bioturbation intensity counts were linked to a range of scanning electron microscopy techniques to characterize the distribution and origin of clay coated sand grains in surface sediment our work shows that grain coats are common in this marginal shallow marine system but they are heterogeneously distributed as a function of grain size clay fraction and depositional facies the distribution and characteristics of detrital clay coated grains can be predicted with knowledge of specific depositional environment clay fraction percentage and grain size the most extensive detrital clay coated grains are found in sediment composed of fine grained sand containing 3 5 to 13 0 clay fraction associated with inner estuary tidal flat facies thus against common convention the work presented here suggests that in deeply buried prospects the best porosity might be found in fine grained clay bearing inner tidal flat facies sands and not in coarse clean channel fill and bar facies

quantification of point source groundwater discharges to the ocean from the shoreline of the big island hawaii aerial thermal infrared imaging has revealed that submarine groundwater discharge sgd along the western coast of the big island of hawaii is often focused as point source discharges that create buoyant groundwater plumes that mix into the coastal ocean we quantified the sgd fluxes associated with several plumes using natural geochemical tracers offshore transects of 222rn and 224ra show elevated activities and corresponding low salinities in the nearshore waters within the plumes indicating that these naturally occurring radionuclides can be useful tracers of groundwater inputs in this area using a series of simultaneous mass balance equations for water salt and radon we determined the groundwater fluxes of six plumes near kona hawaii the average sgd fluxes ranged from 1100 m3 d21 to 12 000 m3 d21 of total fresh saline sgd the fresh meteoric groundwater equivalents for the same flows modeled by adjusting the groundwater end member to reflect freshwater rather than brackish groundwater composition ranged from 630 m3 d21 to 8600 m3 d21 these fluxes are in general agreement with earlier results obtained by hydrological water budgets and physical oceanographic analyses of fresh sgd rates in this region

advective flow through the upper continental shelf driven by storms buoyancy and submarine groundwater discharge data from monitoring wells on the carolina usa continental shelf require a reevaluation of pore water exchange across the seafloor temperature salinity and 226ra data from 3 offshore wells require rapid and frequent pore water exchange to depths of several meters through sands and other permeable sediments the exchange is driven by tidal pumping storms buoyancy and submarine groundwater discharge tidal pumping causes semidiurnal temperature cycles in one well that can only be explained by rapid fluid flow the effect of large storms is evident in sudden temperature changes 2 4 m below the seabed in two wells these changes require considerable pore water exchange sudden cooling of the ocean may cause pore waters to become buoyant with respect to the ocean and trigger pore water convection to several meters depth as observed in one well the wells also display frequent large factor of ten changes in 226ra activity this requires a substantial input of 226ra enriched fluids to replace 226ra that is lost during exchange events these data support a fourth flow process which is groundwater seeping from the underlying limestone the pore spaces in the overlying sand provide a temporary reservoir for these fluids we conclude that pore water residence times in 2 4 m thick sands on this continental margin are on the order of a few months or less

hydrothermalism in the mediterranean sea abstract hydrothermalism in the mediterranean sea results from the collision of the african and european plates with the subduction of the oceanic part of the african plate below europe high heat flows in the resulting volcanic arcs and back arc extensional areas have set up hydrothermal convection systems most of the known hydrothermal sites are in shallow coastal waters

tidal dynamics of the water table in beaches tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations only the movements forced by the tide are considered so a beach with negligible wave activity was chosen for the field measurements the data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide this latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter the observed behavior of the water table is explained in terms of perturbation extensions to the classical deep aquifer solution one extension deals with the nonlinearity in the interior the other with the boundary condition at the sloping beach face

geologic influence on groundwater salinity drives large seawater circulation through the continental shelf observations of offshore freshened groundwater and saline groundwater discharge along continental shelves have important implications for water resources ecosystem function and the composition of the ocean but they cannot be explained by basic theory we show that these independent observations are linked and result from processes that drive variable density groundwater flow through the spatial heterogeneity that is ubiquitous in geologic formations we use lithologic data to develop geostatistical models that mimic the architecture of coastal aquifers simulation of groundwater flow and salt transport through these random realizations shows that heterogeneity produces spatially complex subsurface salinity distributions that extend tens of kilometers offshore even at steady state the associated density gradients drive high saline groundwater circulation rates that cannot be predicted by equivalent homogeneous models results suggest that these phenomena may be common along continental shelves potentially altering estimates of ocean chemical budgets and impacting coastal water management for future generations

sediment nutrient dynamics on the south atlantic bight continental shelf continental shelf sediments on the south atlantic bight sab consist of relict sands that at depths ranging from 14 45 m fall within the photic zone and are sites in which significant rates of benthic primary production are observed thus sab seafloor sediments are a source of organic matter to the shelf system and are possibly a sink for nutrients regenerated within the sediments we have investigated the nutrient dynamics in sab shelf sediments along two transects off the coasts of georgia and florida as part of a study that addresses the significance of benthic primary production in terms of overall shelf biogeochemistry sandy sediments were sampled with a newly designed corer that permits retention of pore water in highly permeable sands and thus avoids commonly encountered washout problems nutrient ammonium silicate nitrate nitrite and phosphate distributions from sediments along both transects show substantial variation in concentration magnitudes and profile shapes over short horizontal spatial scales meters laboratory experiments and numerical models of diagenetic processes in these sediments suggest that 1 pore water advection driven by current flows over wave ripples and bioturbational features is likely an important transport process in promoting nutrient exchange in these porous sands more so than irrigation and 2 reaction rates in sab sediments are rapid and are comparable to those in nearshore muddy habitats in spite of this variation and the apparently high rates of advective transport time series measurements show a gradual increase in depth integrated nutrient concentrations at one station along the georgia transect from the spring through the fall this increase is probably related to elevations in temperature and metabolic rates in sediments during the warmer summer months measured oxygen and nutrient fluxes across the sediment water interface in paired transparent light chambers and opaque dark chambers did not conform to trends observed in shallow water systems where oxygen is typically evolved and nutrients are consumed in the light versus oxygen that is consumed and nutrients that are evolved in the dark the absence of measurable or consistent fluxes on the sab shelf is likely the result of low concentrations of nutrients in both the water column and the upper sediment layers however rapid regeneration rates in sediments and generally higher nutrient concentrations in deeper sediment layers suggest that sediments are an important source of the nutrients that fuel benthic primary production although ammonium is rapidly produced in these oxic sands nitrate concentrations are uniformly low and measurable nitrate generally appears in the oxic sedimentary layers the absence of high nitrate concentrations in the suboxic or anoxic zone suggests that denitrification may not be an important process in sab shelf sediments

seasonal temperature salinity changes and thermocline development in the mid atlantic bight as recorded by the isotopic composition of bivalves stable isotope records across annual growth increments in specimens of the surf clam spisula solidissima from the mid atlantic bight shelf from 10 m and 45 m depths reflect the changes in temperature and nutrient concentrations on the shelf over the year the 18 o and 13 c records from clams at the two depths record well mixed conditions in the water column during the winter months and the development of a thermocline during the summer spring high productivity and a transient salinity excursion in surface waters are also recorded reconstructing the paleoceanography of late cenozoic temperate continental shelves may be possible using stable isotope records from fossil spisula solidissima and other bivalves

geological controls and tidal forcing of submarine groundwater discharge from a confined aquifer in a coastal sand dune system submarine groundwater discharge sgd into the ocean is increasingly recognized as an important component of land ocean interaction numerous geological settings may be the source of terrestrially derived sgd including spatially extensive sand dune systems which are a common coastal setting in tropical subtropical and temperate regions throughout the world within the catchment of the great barrier reef lagoon numerous large scale sand dune systems exist creeks and rivers draining these systems are largely absent however terrestrially derived groundwater discharges from discrete springs in the intertidal zone the geological and hydrological controls of the discharge were investigated using a combination of geological geophysical and hydrological methods from sedimentary and geoelectric data it is inferred that a unit of sandy clay provides a confinement of the shallow aquifer system in the dune complex with groundwater discharging where this layer is breached groundwater discharge flux was inversely correlated with tidal water level but remained positive throughout the tidal cycle a simple hydrological model indicates that the continuous discharge is the result of a change in hydraulic pressure of the confined aquifer in response to tidal forcing at the seaward limit of the aquitard which is a previously undescribed effect of tidal modulation of sgd the observed groundwater discharge is likely to have a significant effect on the biogeochemistry of the coastal environment particularly in the absence of surface water drainage

hydraulic control of pore water geochemistry within the oxic suboxic zone of a permeable sediment the geochemical behavior of the top 70 cm of permeable reef flat sediments on checker reef oahu hawai i was examined using spatial and temporal changes in pore water o2 no no nh and n2o concentrations 221 324 the shallow depth of the sediment water interface relative to the height of waves propagating across the reef creates an environment in which pore water mixing and transport are dominated by wave induced mechanisms dissolved oxygen penetrated 15 50 cm in the four sites studied the depth integrated concentration of dissolved oxygen was greater under larger wave conditions and in more permeable sediments which suggests that dissolved oxygen may be a good indicator of the relationship between sediment metabolism and the physical nature of the sediment environment the absence of any subsurface n2o maxima limited temporal variability in pore water n2o concentrations and vertically coherent profiles of o2 no no and n2o suggest that suboxic processes are typically 22 32 restricted to spatial scales that are smaller than for oxic processes in these sediments the geochemical response of the sediments to a natural perturbation was monitored by examining the composition of pore waters immediately following a large wave event and for several weeks thereafter significant changes in the depth integrated concentrations of o2 no no and nh were observed following the perturbation however only changes in no 22 1

pore water advection and solute fluxes in permeable marine sediments i calibration and performance of the novel benthic chamber system sandy this contribution introduces the benthic chamber system sandy that was developed for studying in situ solute fluxes in permeable sandy sediments where advective pore water transport can dominate solute exchange across the sediment water interface the sandy system can be deployed at the seafloor where it autonomously performs measurements of sediment water solute fluxes the innovative features include an insertion mechanism that permits gentle and deep penetration of the chamber into hard consolidated sands with minimum disturbance and an adjustable stirrer that generates a rotationally symmetric pressure gradient between the center and the circumference of the enclosed sediment surface in contrast to similar systems sandy takes advective pore water exchange into account through adjustment of the stirring rate defined pressure gradients can be established that are similar in shape and magnitude to natural pressure gradients that develop at topographical structures of current exposed sediment surfaces solute fluxes measured in the chamber at a specific advective stirrer setting can be compared with those obtained at reduced stirring where pressure gradients are absent and solute exchange therefore is restricted to diffusion and bioirrigation rates of pore water exchange that were determined by means of tracer experiments at different stirrer settings in natural coarse grained north sea deposits demonstrate the feasibility of this approach this permits for the first time an evaluation of the contribution of advective exchange to the total interfacial solute flux in situ and makes sandy a valuable tool to study advection related processes in permeable shelf sediments

aerial infrared imaging reveals large nutrient rich groundwater inputs to the ocean 1 regional high resolution 0 1 c 0 5 m low altitude thermal infrared imagery tir reveals the exact input locations and fine scale mixing structure of massive cool groundwaters that discharge into the coastal zone as both diffuse flows and as 30 large point sourced nutrient rich plumes along the dry western half of the large volcanic island of hawaii these inputs are the sole source of new nutrient delivery to coastal waters in this oligotrophic setting water column profiling and nutrient sampling show that the plumes are cold buoyant nutrient rich brackish mixtures of groundwater and seawater by way of example we illustrate in detail one of the larger plumes which discharges ca 12 000 m3 d 1 ca 8 600 m3 d 1 freshwater rates comparable in volume to high flux groundwater outputs in better known tropical karst terrains we further show how nutrient mixing trends may be integrated into tir sea surface temperatures to produce surface water nutrient maps of regional extent

assessing the effects of regional tectonic activity on groundwater flow in a coastal aquifer in india the hydrodynamics of a coastal aquifer system was investigated in the kendrapara district odisha india the analysis of 248 groundwater samples collected across one monsoonal season indicates that the anisotropic coastal aquifer is affected by salinity taking into account the hydrodynamic variables of hydraulic head transmissivity saturated thickness and the effective porosity of the aquifer a darcy flow analysis of groundwater was carried out to determine the flow volume residual flow direction and flow rate of the aquifer system in the region these modelled outputs display significant disturbed nature of groundwater flow regimes which in turn is suggestive of major structural changes to the depositional basin geospatial and geostatistical cluster analysis carried out for the modelled parameters in relation to the tectonic elements of the region indicated that faults have a significant influence on aquifer hydrodynamics and in turn on the hydrogeochemistry of the system this inference is further justified from the spatial analysis of earthquake epicentres for the last 50 years which shows a close interrelationship with the north odisha boundary fault the investigation also draws inference from the sudden directional change of river brahmani which seems to be affected by the mahakalapara rajnagar strike slip fault on the basis of these findings it is suggested that the subsurface non granular clayey horizons have been extensively deformed by the tectonic disturbances this has led to the juxtaposition or detachment of aquifer domains which in turn has led to the intermixing of varied groundwater types giving rise to the observed salinity of the study region

tide induced recirculation across the aquifer ocean interface a parametric analysis is conducted to examine the influence of tides inland hydraulic conditions and aquifer properties on the rate of tide induced seawater recirculation through the nearshore aquifer understanding such influence is crucial for accurate prediction of subsurface chemical fluxes to coastal waters via groundwater discharge the analysis is based on numerical simulations of density dependent groundwater flow in a coastal aquifer subject to tidal oscillations across a sloping beach face the results reveal that the amplitude of tidal oscillations and the inland hydraulic gradient are the primary parameters controlling the tide induced recirculation rates significant tidal exchange is expected when the ratio of tidal to inland forcing is large the horizontal tidal shoreline excursion and aquifer depth both display asymptotic behavior influencing recirculation rates for only small values where the exchange process is limited by the potential for infiltration and shallowness of the aquifer respectively the analysis also indicates that tidal effects increase density driven recirculation rates due to enhanced convective flow within the saltwater wedge

tidally driven pore water exchange within offshore intertidal sandbanks part ii numerical simulations field measurements presented by gibbes b robinson c li l lockington d a carey h 2008 tidally driven pore water exchange within offshore intertidal sandbanks part i field measurements estuarine coastal and shelf science 79 pp 121 132 revealed a tidally driven pore water flow system within an offshore intertidal sandbank in moreton bay australia the field data suggested that this flow system might be capable of delivering nutrients and in particular bio available iron across the sediment water interface bio available iron has been implicated as a key nutrient in the growth of the toxic marine cyanobacteria lyngbya majuscula and therefore this pore water exchange process is of interest at sites where l majuscula blooms have been observed in this study two dimensional numerical simulations were used in conjunction with hydraulic data from field measurements to further investigate the tidally induced pore water flow patterns simulation results generally showed good agreement with the field data and revealed a more complex residual pore water flow system in the sandbank than shown by the field data the flow system strongly influenced by the geometry of the sandbank was characterized by two circulation cells which resulted in pore water discharge at the bank edge and also to a permanently ponded area within the sandbank interior simulated discharge volumes in these two zones were in the order of 0 813 m 3 and 0 143 m 3 per meter width along shore of sandbank per tidal cycle at the bank edge and sandbank interior respectively transit times of pore water circulating through these cells were found to range from approximate to 17 days to 60 years with an average time of 780 days the results suggest that the tidally driven flow systems might provide a mechanism for transport of bio available iron across the sediment water interface this flow could constitute a previously unrecognized source of bio available iron for l majuscula blooms in the bay c 2008 elsevier ltd all rights reserved

a model for interpreting continental shelf hydrographic processes from the stable isotope and cadmium calcium profiles of scallop shells abstract stable oxygen and carbon isotope and cadmium calcium profiles from the shells of scallops collected from the outer continental shelf of the south atlantic bight and the virginia bight appear to trace the hydrographic processes of the two regions a model is developed to distinguish two principal modes of nutrient and trace metal input to the outer shelf from the biogeochemical profiles of the shell the oxygen isotope profiles record bottom water temperature changes caused by seasonal temperature cycles and water mass movements nutrient input and subsequent phytoplankton blooms are recorded in the carbon isotope and cd ca profiles the shell profiles from the south atlantic bight record the dominant effect of upwelling caused by gulf stream meandering the shell profiles from the virginia bight show the influence of spring river runoff and summer water column stratification biogeochemical profiles in mollusk shells are potentially important tools for studying the dynamics of both modern and ancient continental shelf upwelling systems

wave driven porewater and solute circulation through rippled elastic sediment under highly transient forcing waves induce porewater flow and solute transport through permeable marine sediment however past studies have ignored high frequency pressure pulses under the assumption that the porewater flow field is adequately represented by a time averaged one or that the saturated sediment is incompressible we modeled porewater flow and solute transport inside ripples forced by instantaneous pressure profiles along the sediment water interface swi with 0 1 s temporal resolution the transient pressure profiles were taken from a field data driven large eddy simulation model of wave driven oscillatory flow the simulations suggest that in elastic permeable and saturated sediment a time averaged representation of the flow field may be inadequate and that this also leads to shortcomings in how transport is modeled bursts in fluid flushing occur when high frequency pressure fluctuations were considered leading to larger long term average fluid fluxes compared to a steady flow field driven by a time averaged pressure profile the pressure perturbations along the swi propagate within a few milliseconds to meter depths within the sediment leading to strongly transient porewater velocity fields this leads to enhanced dispersion of solutes and larger time averaged solute fluxes however enhanced solute flux across the swi diminished through time with increasing permeability the high frequency transient pressures and sediment elastic properties we considered have been largely ignored and unrecognized future observational and modeling studies should consider these processes especially since they mediate timing sensitive biogeochemical reactions

using multiple geochemical tracers to characterize the hydrogeology of the submarine spring off crescent beach florida abstract a spectacular submarine spring is located about 4 km east of crescent beach fl in the atlantic ocean the single vent feature of crescent beach spring provides a unique opportunity to examine onshore offshore hydrogeologic processes as well as point source submarine ground water discharge the floridan aquifer system in northeastern florida consists of tertiary interspersed limestone and dolomite strata impermeable beds confine the water bearing zones under artesian pressure miocene and younger confining strata have been eroded away at the vent feature enabling direct hydrologic communication of eocene ground water with coastal bottom waters the spring water had a salinity of 6 02 which was immediately diluted by ambient seawater during advection mixing the concentration of major solutes in spring water and onshore well waters confirm a generalized easterly flow direction of artesian ground water nutrient concentrations were generally low in the reducing vent samples and the majority of the total nitrogen species existed as nh 3 the submarine ground water tracers rn 222 1174 dpm l 1 dpm methane 232 nm and barium 294 5 nm were all highly enriched in the spring water relative to ambient seawater the concentrations of the reverse redox elements u v and mo were expectedly low in the submarine waters the strontium isotope ratio of the vent water 87 sr 86 sr 0 70798 suggests that the spring water contain an integrated signature indicative of floridan aquifer system ground water additional sr isotopic ratios from a series of surficial and lower floridan well samples suggest dynamic ground water mixing and do not provide clear evidence for a single hydrogeologic water source at the spring vent in this karst dominated aquifer such energetic mixing at the vent feature is expected and would be facilitated by conduit and fractured flow radium isotope activities were utilized to estimate flow path trajectories and to provide information on potential travel times between an onshore well and the spring using either 223 ra and 224 ra or 228 ra and qualifying this approach with several key assumptions estimates of water mass travel times from an upper floridan well in crescent beach to the submarine vent feature distance 4050 m are in the order of 0 01 0 1 m min 1

a fully coupled depth integrated model for surface water and groundwater flows abstract this paper presents the development of a fully coupled surface water and groundwater flow model the governing equations of the model are derived based on a control volume approach with the velocity profiles of the two types of flows being both taken into consideration the surface water and groundwater flows are both modelled based on the unified equations and the water exchange and interaction between the two types of flows can be taken into account the model can be used to simulate the surface water and groundwater flows simultaneously with the same numerical scheme without other effort being needed to link them the model is not only suitable for the porous medium consisting of fine sediments but also for coarse sediments and crushed rocks by adding a quadratic friction term benchmark tests are conducted to validate the model the model predictions agree well with the data

advective transport affecting metal and nutrient distributions and interfacial fluxes in permeable sediments abstract our laboratory flume experiments demonstrate that advective porewater flows produce biogeochemical reaction zones in permeable sediments leading to specific and reproducible complex patterns of fe mn and nutrients oxygenated water forced into the sediment when boundary flows were deflected by protruding sediment structures generated distinct zones of nitrification and ferric iron precipitation this inflow was balanced by ammonium rich porewater ascending from deeper sediment layers thereby creating an anoxic channel where dissolved fe2 and mn2 could reach the surface between the zones of ferric iron precipitation and fe2 upwelling a layer with increased manganese oxide and solid phase fe ii concentrations formed indicating redox reaction between these components the establishment of topography on the previously smooth sediment surface reversed the net interfacial flux of solutes while the smooth control core was found to be a sink for metals and nutrients the sediment with mounds acted as a source for these substances our experiments show that in sandy sediment with an oxidised surface layer reduced metal species can be released to the water column by flow topography interactions we conclude that advective transport processes constitute an important process controlling biogeochemical zonations and fluxes in permeable sea beds

dynamics of large and small scale bedforms on a macrotidal shoreface under shoaling and breaking waves abstract bedform dimensions bed position changes near bed velocities and suspended sand concentrations are analyzed from measurements at a single location on a macro tidal beach in the south west of england the study was conducted in 0 5 2 25 m water depth under both swell and wind generated storm waves with both weak and strong currents present bed positions and suspended sand concentrations were measured using the 3 transducers of a multi frequency acoustic backscatter sensor with 5 mm vertical resolution two distinct bed types based on wavelength were observed each with two or more subtypes possible i small scale bedforms 20 cm which include two dimensional 5 forms and three dimensional vortex 6 forms small scale forms were dominant under non breaking conditions while the large scale forms occurred under both non breaking and breaking waves the large scale forms dominate under breaking conditions both types but particularly low steepness forms were highly mobile with maximum horizontal migration rates of 5 cm min 1 large upto 15 cm and rapid upto 3 0 cm min 1 changes in vertical bed elevation were also observed in association with the development and migration of large scale forms large scale bedforms were also highly variable spatially often being interspersed with smaller scale forms under decaying flow regimes and with areas of flat bed under increasing regimes observations suggest these forms are present even under high energy surf zone conditions wave shields 1 models for predicting ripple dimensions did not perform well in this environment this lack of agreement reflects the complex hydrodynamic regimes associated with random grouped shoaling and breaking waves together with the presence of currents often at large angles to the waves as well as the rapid rates of change in the wave forcing associated with tidal cycle oscillations in this macrotidal environment suspended sediment concentrations and transport rates are particularly sensitive to the bedforms present and also to bed position changes associated with ripple migration estimates of transport rates are subject to potentially large errors upto 30 without compensation for bed elevation changes relative to sensor position

hydraulic exchange between a coral reef and surface sea water hydraulic exchange between overlying sea water and the internal structure of a patch reef in kaneohe bay oahu hawaii was studied with an array of wells 1 2 and 4 m deep two natural chemical tracers radon and salinity were used to calculate the exchange rate between surface sea water and reef interstitial waters dissolved radon concentrations are substantially higher in interstitial waters than is surface water the degree of radon enrichment is quantitatively related to the time elapsed since interstitial water had equilibrated with the atmosphere residence time estimates are 1 40 days with deeper wells having slower exchange the average residence time for 1 m deep wells was 2 1 days a rainstorm induced dilution of the salinity of kaneohe bay provides the second tracer samples of surface and reef interstitial waters following this salinity perturbation are used to calculate an average residence time of 2 6 days at a depth of 1 m and 42 days at a depth of 2 m three types of physical forces thought to cause exchange between surface and interstitial water are considered by measurement of the forcing functions and reef permeability hydraulic conductivities are about 50 m d with lower values near the seaward side of the reef more most exchange seems to be caused by high frequency wave driven oscillatory pumping and by unidirectional hydraulic head gradients of uncertain origin that are stable for at least 3 4 days wave driven mixing is probably more important shallower in the reef whereas head driven flow may dominate deeper in the reef tidal pumping does not seem to contribute to exchange all methods indicate that exchange in the upper part of checker reef is primarily through vertical exchange the best estimate for the residence time of water at a depth of 1 m is 2 days water at depths of 204 m probably has a residence time of weeks to months 49 refs 8 figs 6 tabs less

carbon cycling hysteresis in permeable carbonate sands over a diel cycle implications for ocean acidification dissolved inorganic carbon dissolved oxygen h and alkalinity fluxes from permeable carbonate sediments at heron island great barrier reef were measured over one diel cycle using benthic chambers designed to induce advective pore water exchange a complex hysteretic pattern between carbonate precipitation and dissolution in sands and the aragonite saturation state var of the overlying chamber water was observed throughout the incubations during the day precipitation followed a hysteretic pattern based on the incidence of photosynthetically active radiation with lower precipitation rates in the morning than in the afternoon the observed diel hysteresis seems to reflect a complex interaction between photosynthesis and respiration rather than var of the overlying water as the main driver of carbonate precipitation and dissolution within these permeable sediments changes in flux rates over a diel cycle demonstrate the importance of taking into account the shortterm variability of benthic metabolism when calculating net daily flux rates based on one diel cycle the sediments were a net daily source of alkalinity to the water column 5 13 to 8 84 mmol m22 d21 depending on advection rates and advection had a net stimulatory effect on carbonate dissolution the enhanced alkalinity release associated with benthic metabolism and pore water advection may partially buffer shallow coral reef ecosystems against ocean acidification on a local scale

holocene mean uplift rates across an active plate collision boundary in taiwan samples of holocene fossil coral from uplifted reefs of three tectonically distinct yet geographically proximal regions of taiwan have been dated by uranium series and 14c isotopes applying corrections for altitude change caused by sea level fluctuations enables evaluation of long term average holocene uplift rates for three areas across an active convergent margin i the hengchun peninsula of the eurasian tectonic plate ii the eastern coastal range of taiwan a plate boundary and iii two offshore islands lanyu and lutao both situated on the leading edge of the adjoining philippine plate the data indicate that while all three areas have experienced uplift through the holocene plate collision has caused significantly higher uplift rates in the region directly along the plate boundary

mixed convection and density dependent seawater circulation in coastal aquifers 1 density dependent circulation of seawater in coastal aquifers results in submarine groundwater discharge sgd across the seabed that is a mixture of terrestrial groundwater and former marine water in this study the controls of the relative amount of seawater to freshwater in sgd were investigated numerically using the feflow and sutra codes it was found that the key controls could be expressed in the form of a single nondimensional recirculation number that incorporates the combined effects of free convection forced convection and hydrodynamic dispersion on convective overturn within the coastal salt wedge anisotropy effects were incorporated into the recirculation number with limited success based on the principle of equivalent isotropic hydraulic conductivity the type of boundary condition employed along the seabed was shown to be important convective overturn was substantially increased if backward dispersion of salt into the aquifer from along the outflowing portion of the seabed boundary was prevented overall the results demonstrated a strong dependence of convective overturn on the aquifer dispersivities suggesting that results from numerical simulations are problematic to apply to real aquifer systems that typically exhibit uncertain scale dependent dispersion properties

coastal groundwater dynamics off santa barbara california combining geochemical tracers electromagnetic seepmeters and electrical resistivity this paper presents repeat field measurements of 222 rn and 223 224 226 228 ra electromagnetic seepage meter derived advective fluxes and multi electrode stationary and continuous marine resistivity surveys collected between november 2005 and april 2007 to study coastal groundwater dynamics within a marine beach in santa barbara california the study provides insight into magnitude and dynamics of submarine groundwater discharge sgd and associated nutrient loadings into near shore coastal waters where the predominant sgd drivers can be both spatially and temporally separated rn 222 and 223 224 226 228 ra were utilized to quantify the total and saline contribution respectively of sgd the two short lived 224 223 ra isotopes provided an estimate of apparent near shore water mass age as well as an estimate of the ra derived eddy diffusion coefficient kh 224 ra 2 86 0 7 m 2 s 1 223 ra 1 32 0 5 m 2 s 1 because 222 rn t 3 8 day and 224 ra t

estimating global shelf sediment mobility due to swell waves global climate models gcms such as those produced at the european centre for medium range weather forecasts ecmwf generate data that are relevant to the study of marine sedimentary processes we used estimates of significant wave height and period derived from an ecmwf gcm to predict for the first time the area of continental shelves over which sediment is mobilised the wave climatology was such that 0 1 mm diameter quartz sand had the potential to be mobilised on at least one occasion between july 1992 and july 1995 over 41 6 of the earth s continental shelves the north atlantic region has the most energetic global wave climate strong enough to mobilise 0 1 mm diameter quartz sand to water depths of up to 234 m at least once over a 3 year period

groundwater transport and the freshwater saltwater interface below sandy beaches summary current conceptual models for groundwater flow in beaches highlight an upper saline plume which is separated from the lower salt wedge by a zone of brackish to fresh groundwater discharge there is currently limited knowledge of what conditions allow an upper saline plume to exist and what factors control its formation we used variable density saturated unsaturated transient groundwater flow models to investigate the configuration of the freshwater saltwater interface in beaches with slopes varying from 0 1 to 0 01 in the absence of waves we also varied hydraulic conductivity dispersivity tidal amplitude and inflow of fresh groundwater the simulated salinity configuration of the freshwater saltwater interfaces varied significantly no upper saline plumes formed in any beach with hydraulic conductivities less than 10 m d the slope of the beach was also a significant control steeper beach faces allowed stronger upper saline plumes to develop median sediment grain size of the beach is strongly correlated to both beach slope and permeability and therefore the development of an upper saline plume prior studies of groundwater flow and salinity in beaches have used a range of theoretical dispersivities and the appropriate values of dispersivity to be used to represent real beaches remains unclear we found the upper saline plume to weaken with the use of larger values of dispersivity our results suggest that upper saline plumes do not form in all beaches and may be less common than previously considered

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

transfer of nonsorbing solutes to a streambed with bed forms theory a theoretical analysis of the exchange of nonsorbing solutes between a permeable streambed and the overlying water of a stream or river is presented in this paper in a companion paper elliott and brooks this issue the results of experimental studies of such exchange are presented the analysis focuses on water movements into within and out of the bed which result from the presence of bed forms ripples and dunes and highlights the mechanisms of pumping and turnover pumping is the movement of fluid through the bed induced by steady dynamic pressure variations over bed forms turnover occurs as moving bed forms trap and release interstitial fluid the detailed analysis was used to generate the distribution of the residence time of solute within the bed which can be used to calculate the net mass exchange due to pumping and turnover

flow induced uptake of particulate matter in permeable sediments we demonstrate the fast transfer of suspended particles from the boundary layer into the upper strata z 2 x 10 l l m2 incubated in a laboratory flume increased pressure up and downstream of small mounds z 2 5 cm drove water 5 5 cm into the core carrying suspended particles 1 pm to 2 2 cm sediment depth within 10 h simultaneously decreased pressure at the downstream slope of the protrusions drew pore fluid from deeper layers z 5 10 cm to the surface in the sediment friction reduced the velocity of the particulate tracers resulting in size fractionation and layers of increased particle concentration ripple topography 0 8 2 8 cm high enhanced interfacial particle 1 pm flux by a factor 2 3 when compared to a level control core the pathways of the particle and solute tracers below a sediment ripple are explained with a source sink model that describes the pore flow velocity field our results suggest that bedform induced interfacial flows are important for the uptake of particulate organic matter into permeable shelf sediments

convective transport within stable river sediments local pressure variations of the order of 100 1000 n m2 can be observed between the upstream and downstream faces of the typically triangular shaped dunelike sediment structures that form at the sediment water interface of rivers laboratory experiments were conducted examining the influence of this localized pressure variation on contaminant transport processes within the sediment numerical modeling of the in bed flow via boundary element methods was also undertaken in order to predict convective transport under typical field conditions the laboratory experiments and numerical simulation of the in bed flow in several rivers verified that the pressure distribution observed on the sediment surface and the resulting interstitial fluid convection can control transport of chemically inert nonsorbed contaminants in stable sediments in bed peclet numbers were of the order of 100 1000 indicating the negligible influence of diffusion under the conditions examined

estimation of submarine groundwater discharge from bulk ground electrical conductivity measurements the utility of bulk ground conductivity bgc measurements in the estimation of submarine groundwater discharge sgd was investigated at four sites covering a range of hydrogeological settings namely cockburn sound australia shelter island usa ubatuba bay brazil and flic en flac bay mauritius at each of the sites bgc was surveyed in the intertidal zone and seepage meters were used for direct measurements of sgd flow rates in the presence of detectable salinity gradients in the sediment a negative correlation between sgd and bgc was recorded the correlation is site specific and is dependent on both the type of sediment and the mixing processes for example at shelter island the maximum mean flow rates were 65 cm d 1 at a bgc of 0 ms cm 1 while at mauritius maximum mean flow rates were 364 cm d 1 at a bgc of 0 ms cm 1 bgc measurements are used to estimate sgd over a large scale and to separate its fresh and saline components extrapolating bgc measurements throughout the study sites yields a total discharge of 2 91 1 59 7 16 and 25 4 103 m3 d 1 km 1 of shoreline with a freshwater fraction of 41 24 29 and 63 at cockburn sound shelter island ubatuba bay and flic en flac bay respectively the results demonstrate that ground conductivity is a useful tracer to survey and separate freshwater and recirculated seawater component of sgd the presented investigation is a subset within a series of experiments designed to compare different methods to investigate sgd co organized and carried out by scor loicz ioc and iaea

combined time series resistivity and geochemical tracer techniques to examine submarine groundwater discharge at dor beach israel 1 a high resolution stationary geophysical and geochemical survey was conducted at dor beach israel to examine the shallow coastal hydrogeology and its control on the exchange of submarine groundwater with the shallow mediterranean sea time series resistivity profiles using a new 56 electrode 112 m long marine cable produced detailed profiles of the fresh water salt water interface and the subtle response of this interface to tidal excursions and other forcing factors such information when ground truthed with representative pore water salinities and formation resistivity values can provide unique information of the extent and rates of submarine groundwater discharge sgd time series 222rn measurements of the adjacent coastal water column complemented these geophysical techniques and were modeled to yield integrated advective flow rates across the sediment water interface which at dor beach ranged from about 0 to 30 cm day 1 mean 7 1 cm d 1 depending on the tidal range such results suggest that the underlying hydrogeologic framework at dor is favorable for substantial sgd extrapolating these sgd estimates across a 100 m wide coastal zone implies that the rn derived sgd rate would equal 7 1 m3 d 1 per m of shoreline and that the source of this discharging groundwater is a complex mixture of fresh groundwater derived from the upland kurkar deposits as well as locally recycled seawater

solute exchange by convection within estuarine sediments the rates of material transport through sediments are central to determining the biochemical status of sediments transport within sediments can occur by molecular diffusion through porewaters and by the activities of burrowing biological organisms but a number of physical processes can enhance transport within porewaters here convection is investigated as a mechanism for solute transport within sediments convection will occur as the gravitational adjustment to the occurrence of porewater which is of lower salinity and density than the water at the sediment surface this process could be important for exchange between sediments and the water column in regions subject to significant temporal variations in salinity such as estuaries

effects of bioturbation and bioirrigation by lugworms arenicola marina on physical and chemical sediment properties and implications for intertidal habitat succession sediment destabilization by sediment reworking organisms is common in coastal aquatic environments but the potential of bioturbation to inhibit shoreline succession has not been suggested previously the lugworm arenicola marina is a widespread and dominant large burrower at european atlantic shores and a major source of bioturbation and bioirrigation on the extensive intertidal flats in the wadden sea eastern north sea the hypothesis that lugworm activities inhibit the successive development from sandy to muddy sediments in depositional embayments has been tested by a large scale exclusion field experiment changes in sediment properties indicate a progressive clogging of interstices with fine particles and organic matter resulting in lower sediment permeability in exclusion areas compared to lugworm inhabited control areas chlorophyll content in the surface layer was consistently higher in the absence of lugworms lack of sub surface irrigation in the absence of lugworms combined with reduced sediment permeability resulted in increased concentrations of ammonium phosphate silicate and sulphide in the pore water concentrations 100 mm of sulphide gave rise to toxic conditions for macrofauna the effects of lugworms on sediment characteristics were more conspicuous in fine than in medium sand it is concluded that a marina contributes to the maintenance of permeable sand and thereby sustaining suitable conditions for the lugworm population itself without this ecosystem engineer mud flats would greatly expand at the expense of sand flats in the wadden sea 2007 published by elsevier ltd

tracing submarine hydrothermal inputs into a coastal bay in baja california using radon abstract hydrothermal fluid fluxes into deep ocean environments can be obtained from heat balance approaches however in shallow systems hydrothermal heat fluxes can be masked by solar heating in this paper we use radon 222rn as a naturally occurring geochemical tracer to map the location of hydrothermal fluid inputs as well as low temperature groundwater discharges and quantify fluxes into concepcion bay baja california mexico this fault bound bay contains intertidal seeps with salinities ranging from 5 3 to 25 6 temperatures reaching 64 c and nitrate reaching 900 m the bay is subject to natural eutrophication and frequent red tide events a detailed 222rn survey around the 100 km perimeter of concepcion bay allowed us to map the location of enhanced submarine groundwater inputs moorings at three contrasting coastal sites indicated that radon concentrations were higher at low tide and during the winter modeled hydrothermal fluid inputs ranged between 0 4 cm day in the middle of the bay and 43 9 cm day at the largest hydrothermal coastal seep site apparently faults allow meteoric water to be heated and serve as conduits for its subsequent discharge through permeable marine sediments when conservatively extrapolated to the entire bay using weighted distributions these fluxes are estimated at 17 5 m3 s a flow much higher than local ephemeral rivers about 42 of the fluxes described consisted of fresh groundwater with the remaining made up of recirculated seawater new nitrogen inputs associated with groundwater pathways are estimated to directly account for at least 15 of the local primary productivity our combined spatial survey time series strategy can be very useful to quantify hydrothermal fluid inputs in particular at vent sites where a temperature signal in shallow surface waters is difficult to be observed

rhenium 187 osmium 187 in iron meteorites and the strange origin of the kodaikanal meteorite a set of iron meteorites was investigated for re os isotopes and provides a well defined isochron age of 4 624 0 017 ba and an initial 187os 188os ratio of 0 095636 0 00009 actual ages may be a few percent lower due to uncertainty on the 187re decay constant within the small sample number presented here there is no evidence for age differences between classes a more detailed study of the meteorite kodaikanal shows that the metal reservoir of this meteorite formed approximately at the same time as the other iron meteorites in contrast with the silicate inclusions which display a formation age of 3 67 ba with all other chronometers a collisional origin is in agreement with the data on this meteorite major secondary events do not affect the re os system at the bulk rock scale in metal as it is the sole significant reservoir of these two elements a re os and rb sr investigation of meteoritic troilite exhibits disturbed chronometric systems which we attribute to the terrestrial history of the meteorite

a wave induced transport process in marine sediments we show how surface wave action can increase the rate of transport of solutes into a sandy seabed by orders of magnitude via a mechanism known as mechanical dispersion it is most effective for large sediment permeability and thickness high surface wave amplitude and shallow water a method for setting up the appropriate transport equation valid when dispersion is well developed is given its dispersion term contains two mechanical dispersion parameters that can be estimated roughly from existing data when the sediments are well sorted the dispersion can be inhomogeneous and anisotropic in homogeneous isotropic sediments the effect of surface wave action on transport into sediments on the eastern u s shelf is shown to be significant under certain conditions the effect on thawing of subsea permafrost beneath prudhoe bay alaska seems negligible

breathing of a coral cay tracing tidally driven seawater recirculation in permeable coral reef sediments 1 coral reefs are characterized by high gross productivity in spite of low nutrient concentrations this apparent paradox may be partially reconciled if seawater recirculation in permeable sediments over large meters and long hours to days scales is an important source of recycled nitrogen and phosphorus to coral reefs in this paper we use radon 222rn a natural tracer to quantify tidally driven pore water or groundwater exchange between 1 an offshore coral cay island and its fringing reef lagoon and 2 a reef lagoon and the surrounding ocean as seawater infiltrates heron island at high tide it acquires a radon signal that can be detected when pore waters emerge from carbonate sands at low tide a nonsteady state model indicated that vertical pore water upwelling rates or saline submarine groundwater discharge were 40 cm d within the reef lagoon and 100 cm d outside the lagoon at low tide within the lagoon tidal pumping and temperature driven convection were the main driving forces of pore water advection at low tide the reef lagoon level is about 1 m higher than the surrounding ocean as a result a steep hydraulic gradient develops at the reef edge driving unidirectional filtration through the reef framework groundwaters were highly enriched in nitrate average of 530 mol likely influenced by bird guano relative to lagoon waters 1 9 mol rough but conservative estimates indicated that groundwater derived nitrate fluxes 7 9 mmol m2 d can replace the entire lagoon nitrate inventory every 19 days we speculate that as offshore coral islands breath inhale seawater at high tide and exhale groundwater at low tide they release nutrients that lead to sustained productivity within coral reefs

palaeoclimates at lake turkana kenya from oxygen isotope ratios of gastropod shells climatic changes in the plio pleistocene of east africa during the evolutionary development of early man have been identified only in their broadest outlines a variety of palaeontological1 3 and geochemical4 techniques have already been applied to the study of palaeoclimates in this area but the use of stable oxygen isotope ratios so helpful in marine palaeoclimatology has not been fully exploited5 6 the frequent occurrence of well preserved mollusc shells in the sedimentary column at lake turkana provides a sensitive oxygen isotope record varying over a range of 7 which can be interpreted in terms of evaporative concentration of the heavier oxygen isotope in waters of the closed lake alternating with isotopically lighter freshwater when the lake has been open i report here the results of a study of the 18o 16o ratios of three species of gastropods from the sediments of the koobi fora region of lake turkana and evaluate how the technique might be applied to the study of the palaeoclimates of other tropical lakes

enhancement of denitrification in permeable carbonate sediment due to intra granular porosity a multi scale modelling analysis abstract it has recently been hypothesized that bulk denitrification rates in carbonate sands may be enhanced by reactions occurring in the intra granular pores cracks and crevices we tested this hypothesis using a series of flow and reactive transport models spanning from the pore scale mm to the continuum scales 10 cm bedforms pore scale simulations solved the coupled navier stokes and brinkman equations and represented flow through reactor experiments previously performed on coral reef sands the results revealed that intra granular transport and reactions can explain over all denitrification enhancement a sensitivity study with a single grain diffusive transport model showed that in the majority of cases the resultant increase in denitrification was not coupled to nitrification within a single grain only for large grain diameters of 2 and 4 mm was coupled nitrification denitrification important in most cases coupled nitrification denitrification instead arose as conditions became more reducing along a flow path as is the case in quartz sands without intragranular pores an intra granular reaction rate based on a single grain model was incorporated into a continuum scale darcy flow and reactive transport model for a rippled sand bed where porewater flow is driven by the turbulent current over the ripple the results of the darcy scale model suggest that intra granular pores increase the amount of slow flowing areas within which coupled nitrification denitrification can occur we conclude that the complex advective flow field does not strongly inhibit denitrification enhancement by carbonate sand grains as it does in silica sands thus intra granular reactions may enhance bulk denitrification in carbonate sediment with porous grains under natural advective conditions

transport and degradation of phytoplankton in permeable sediment in flume and field experiments we demonstrate that interfacial water flows generated when bottom currents interact with sea bed topography provide a fast and efficient pathway for the transport of suspended phytoplankton into subsurface layers of permeable sandy sediments the advective transport associated with small mounds and ripples as commonly found on shelf sediments increased penetration depth of unicellular algae dunaliella spec into sandy sediment permeability k 5 4 3 10 211 m 2 up to a factor of 7 and flux up to a factor of 9 relative to a smooth control sediment the pore water flow field produced a distinct distribution pattern of particulate organic matter in the sediment with subsurface concentration maxima and zones depleted of algae flux chamber simulations of advective transport of algae into sands of different grain sizes revealed increasing fluxes algal penetration depths and degradation rates with increasing permeability of the sediment two experiments conducted in intertidal sand flats confirmed the importance of the advective interfacial transport of phytoplankton for natural settings showing permeability dependent penetration of planktonic algae into embedded sand cores of different grain sizes the significance of our results is discussed with respect to particulate organic matter flux and mineralization in shelf sands and we suggest the concept of a decomposition layer in contrast to muddy sea beds with low permeabilities where transport of solutes is mainly driven by diffusion water can flow through marine sands providing a fast carrier for the exchange of substances between the water column and the upper sediment layers surface gravity waves cause pressure oscillations that increase fluid exchange at the sediment water interface and dispersion of solutes within the

changes in the oceanic 13c 12c ratio during the last 140 000 years high latitude surface water records detailed records of the carbon and oxygen isotopic ratios of neogloboquadrina pachyderma are compared between nine high latitude sediment cores from the northern and southern hemispheres covering the last 140 000 yrs the strong analogies between the 13c records permit to define a 13c stratigraphic scale with three clear cut transitions simultaneous with the oxygen isotopic transitions 65 125 kyrs 54 65 kyrs and 21 13 kyrs the 13c records of n pachyderma in the high latitude cores which follow the changes in 13c of the surface water tco2 near areas of deep water formation present trends similar to the benthic foraminifera 13c records in cores v19 30 and m12 392 although amplitudes of the isotopic shifts are different this implies that a large part of the observed variations represents global changes in the carbon distribution between biosphere and ocean the 13c12c ratios of n pachyderma in the north atlantic cores display larger regional variations at 18 kyrs b p than at present to explain these differences we have plotted the 18 kyrs b p 13c values of n pachyderma from 17 cores distributed n of 40 n comparison with published surface water temperature distribution at 18 kyrs b p indicates that a strong divergent cyclonic cell centered approximatively 55 n and 15 w was active during most of the last ice age maximum this hydrology analogous to the present weddell sea explains the published evidences of bottom water formation if located on the northern flank of the gyre and the strong polar front on the southern flank probable location of intermediate water formation

the tidal flushing of multiple loop animal burrows tidal flushing of animal burrows in mangrove swamps provides an effective and important mechanism for transport of salt and other soluble substances the burrows have complex morphologies consisting of multiple loops using established computational modelling techniques burrow geometries were simulated from characteristic burrow dimensions and the effect of multiple loops on flushing is studied the computational models show that flushing is enhanced in multiple loop burrows as upper loops can be completely evacuated increasing the volume of burrow water removed the models indicate that there may be a depth limit to which flushing occurs in complex burrow structures periscope loops extend further than one characteristic loop depth and are shown to affect the flushing of burrows if the surface water plume penetrates to their lower depth periscope loops with surface openings on the downstream side of the burrow relative to the tidal inundation most frequently experience this condition and thus have a great impact on burrow flushing field measurements of salinity agree with the hypothesis that there is a depth limit of flushing for complex burrows that is independent of burrow salinity and suggest a value of 30 35 cm the measurements also support the suggestion that significant flushing of burrows occurs within a single tidal event an experiment considered the movement of animals across the interface created by low salinity surface water and high salinity burrow water after a partial flushing event the motion enhances the effective diffusion coefficient of salt by a factor of at least 102 as compared with free diffusion of salt in water resulting in a more even distribution of dissolved salt in the burrow water between tidal inundations this distribution may lead to an increase in the depth to which flushing occurs during subsequent inundations

effects of wave forcing on a subterranean estuary wave and tide are important forcing factors that typically co exist in coastal environments a numerical study was conducted to investigate individual and combined effects of these forces on flow and mixing processes in a near shore subterranean estuary a hydrodynamic model based on the shallow water equations was used to simulate dynamic sea level oscillations driven by wave and tide the oscillating sea levels determined the seaward boundary condition of the coastal aquifer where variably saturated variable density flow was modeled the simulation results showed that waves induced an onshore upward tilt in the phase averaged sea level wave set up the resulting hydraulic gradient generated pore water circulations in the near shore zone of the coastal aquifer which led to formation of an upper saline plume usp similar to that due to tides however mixing of recirculating seawater in the usp with underlying fresh groundwater was less intensive under the high frequency wave oscillations in the case of combined forcing wave induced circulations coupled with the intra tidal flows strengthened the averaged circulating pore water flows in the near shore zone over the tidal period the circulating flows increased exchange between the subterranean estuary and ocean contributing 61 of the total submarine groundwater discharge for the simulated condition in comparison with the 40 and 49 proportions caused by the same but separate tidal and wave forcing respectively the combined forces also created a more extensive usp with the freshwater discharge zone shifted further seaward the freshwater flow paths in the intertidal subterranean estuary were altered with a significant increase of associated transit times the interplay of wave and tide led to increased mixing between discharging fresh groundwater and recirculating seawater these results demonstrated the complexity of near shore groundwater systems and have implications for future investigations on the fate of land sourced chemicals in the subterranean estuary prior to discharge to the ocean

ecological and paleoenvironmental information using stable isotope profiles from living and fossil molluscs stable oxygen and carbon isotopic profiles from recent specimens of spisula solidissima and placopecten magellanicus collected off the virginia coast are used to calibrate annual temperature controlled cycles in the 18o profile and shell growth characteristics the amplitude of the annual 18o cycles decreases with increasing water depth and may be used as a relative depth indicator the isotopic of profiles of two fossil specimens of pleistocene spisula are very similar in amplitude and character to modern analogues and verify the formation of annual growth increments in these fossil specimens offsets between the 18o profiles of the fossil and modern specimens are related to known temperature and ice volume effects during the late pleistocene and support the utility of mollusc isotope records as a stratigraphic tool carbon isotopic profiles from all specimens show light values in the spring and or fall associated with seasonal phytoplankton productivity offsets in the carbon isotopic composition between infaunal and epifaunal species may be related to sediment porewater geochemistry and oxidation of organic matter trends toward lighter 13c values through ontogeny suggest the effects of metabolic changes from a fast growing juvenile into a slower growing sexually mature adult anomalies in both the oxygen and carbon isotopic profiles identify the formation of minor shell growth increments as corresponding to hydrographic perturbations and to winter cold temperatures

grain size and depositional environment as predictors of permeability in coastal marine sands more than half of the surface sediments covering the continental shelves are sandy which may permit substantial sub seafloor pore water advection knowledge of sediment permeability is required for quantifying advection and associated solute transport but studies of marine sediments typically report grain size analyses rather than permeability here data from 23 studies were examined to determine the range in permeabilities reported for sublittoral marine sands and to assess the utility of permeability grain size relationships in this setting in the resulting database the permeability of small w30 cm undisturbed cores collected from the sea floor all fell between 2 10 12 and 4 10 10 m 2 a range where advective transport induced by wave and current action should be pervasive the range in grain size was very similar for near shore 10 m water depth but the permeability of the continental shelf samples was consistently lower for the same median grain size empirical permeability grain size relationships generated a poor fit r 2 0 35 for the aggregate data but separate relationships for near shore and continental shelf samples were significantly better r 2 0 66 and 0 77 respectively permeability grain size relationships thus may be useful for sublittoral sands but a larger database needs to be accumulated before reliable fit parameters and variability can be predicted thus it is recommended that permeability be routinely determined when characterizing sedimentological properties of marine sand deposits concurrent determinations of sediment bulk density and porosity may further improve estimates of permeability 2008 published by elsevier ltd

saltwater freshwater mixing dynamics in a sandy beach aquifer over tidal spring neap and seasonal cycles the biogeochemical reactivity of sandy beach aquifers is closely linked to physical flow and solute transport processes thus a clearer understanding of the hydrodynamics in the intertidal zone is needed to accurately estimate chemical fluxes to the marine environment a field and numerical modeling study was conducted over a 1 year timeframe to investigate the combined effects of tidal stage spring neap variability in tidal amplitude and seasonal inland water table oscillations on intertidal salinity and flow dynamics within a tide dominated microtidal sandy beach aquifer measured and simulated salinities revealed an intertidal saline circulation cell with a structure and cross sectional mixing zone area that varied over tidal spring neap and seasonal time scales the size of the circulation cell and area of the mixing zone were shown for the first time to be most affected by seasonal water table oscillations followed by tidal amplitude and tidal stage the intertidal circulation cell expanded horizontally and vertically as the inland water table declined displacing the fresh discharge zone and lower interface seaward over monthly spring neap cycles the center of the circulation cell shifted from beneath the backshore and upper beachface to the base of the beach salinity variations in the intertidal zone over semidiurnal tidal cycles were minimal the dynamics of the circulation cell were similar in simulations with and without a berm the highly transient nature of intertidal salinity over multiple time scales may have important implications for the types and rates of chemical transformations that occur in groundwater prior to discharge to the ocean

pleistocene marine calcareous macro and microfossils of navarino island chile as environmental proxies during the last interglacial in southern south america macro and microfossils including molluscs cirripeds echinoids foraminifers and ostracods are a significant component of a pleistocene marine unit located along the southern coast of the beagle channel on navarino island chile this paleontological record represents the richest and most diverse macro and micro assemblage recovered from pleistocene southern south america in total 97 taxa were identified 34 molluscs 57 foraminifers and 6 ostracods they comprise a mixture of specimens inhabiting shallow marine environments characterized by strong bottom currents and belonging to different local communities associated with the spatial heterogeneity in this basin the taxonomic composition of this paleofauna shows remarkable similarities with present day fauna indicating that both groups developed under similar environmental conditions however slight different climatic conditions at the age of deposition cannot be ruled out as well an ecosystem transition towards a truly marine environment with high number of taxa was recognized finally a hiatella cirriped assemblage deserves special attention since the polymorphic shell of fossil and living hiatella is used as a paleoenvironmental tool in this regard the small size of hiatella in the studied marine unit is best related to its mode of life as a nestler within empty tests of barnacles which apparently served as microenvironments for this species nevertheless more geochemical data on living and fossil hiatella shells from the beagle channel will be necessary to test the suitability of using this species to evaluate paleotemperatures and other sea water variations during the quaternary

diel coral reef acidification driven by porewater advection in permeable carbonate sands heron island great barrier reef can play a major role in proton h cycling in a coral reef lagoon the diel ph range up to 0 75 units in the heron island lagoon was the broadest ever reported for reef waters and the night time ph 7 69 was comparable to worst case scenario predictions for seawater ph in 2100 the net contribution of coarse carbonate sands to the whole system h fluxes was only 9 during the day but approached 100 at night when small scale i e flow and topography induced pressure gradients and large scale i e tidal pumping as traced by radon seawater recirculation processes were synergistic reef lagoon sands were a net sink for h a nd the sink strength was a function of porewater flushing rate our observations suggest that the metabolism of advection dominatedcarbonatesandsmayprovideacurrently unknown feedbackto ocean acidification citation santos i r r n glud d maher d erler and b d eyre 2011 diel coral reef acidification driven by porewater advection in permeable carbonate sands heron island great barrier reef geophys res lett 38 l03604 doi 10 1029 2010gl046053

heat transport dynamics at a sandy intertidal zone 1 intertidal zones are spatially complex and temporally dynamic environments coastal groundwater discharge including submarine groundwater discharge may provide stabilizing conditions for intertidal zone permeable sediments in this study we integrated detailed time series temperature observations porewater pressure measurements and two dimensional electrical resistivity tomography profiles to understand the coupled hydraulic thermal regime of a tropical sandy intertidal zone in a fringing coral reef lagoon rarotonga cook islands we found three heating patterns across the 15 m study transect over tidal and diel periods 1 a highly variable thermal regime dominated by swash infiltration and changes in saturation state in the upper foreshore with net heat import into the sediment 2 a groundwater supported underground stable cool region just seaward of the intertidal slope break also importing heat into the subsurface and 3 a zone of seawater recirculation that sustained consistently warm subsurface temperatures that exported heat across the sediment water interface simple calculations suggested thermal conduction as the main heat transport mechanism for the shallow intertidal sediment but deeper and or multidimensional groundwater flow was required to explain temperature patterns beyond 20 cm depth temperature differences between the distinct hydrodynamic zones of the foreshore site resulted in significant thermal gradients that persisted beyond tidal and diel periods the thermal buffering of intertidal zones by coastal groundwater systems both at surface seeps and in the shallow subsurface can be responsible for thermal refugia for some coastal organisms and hotspots for biogeochemical reactions

wave climate sediment supply and the depth of the sand mud transition a global survey abstract the influences of wave climate and sediment supply on the depths of sand mud transitions hsmt are investigated depths of sand mud transitions smt are based on published granulometric data from surface samples gathered from 14 sites in different wave dominated coastal environments with fluvial input including high energy columbia eel russian san lorenzo copper and nepean rivers moderate energy ebro nile santa clara tseng wen and kao ping rivers and low energy po pescara and tronto rivers regimes geometric mean diameter gmd and mud percent are compiled from samples along shore normal transects and significant correlation is found between these two textural descriptors nominally the smt is defined as the transition from gmd 63 m to 25 mud this dual definition is applied to the 14 systems and hsmt is tabulated for each system correlation is found between hsmt and the depth at which wave induced bottom shear stress equals the critical erosion shear stress of the largest mud particles and also between hsmt and significant wave height lack of correlation between hsmt and sediment load of nearby rivers indicates either that the influence of sediment supply on depth of the sand mud transition is small or is not adequately represented in this study shelf width and slope do not correlate with residuals from a formalized linear relationship between hsmt and significant wave height the relationship between hsmt and wave climate is useful for calibration of numerical models of erosion and deposition in wave dominated coastal environments for prediction of seabed properties in remote or inaccessible areas and for reconstruction of paleodepth based on facies changes from sand to mud in ancient rocks

time sequence observations of wave formed sand ripples on an ocean shoreface analysis of an 18 day time lapse film record of shoreface ripple development with concurrent measurements of near bottom flow and surface waves provides new insight on equilibrium bedform conditions adjustment of ripple planform to variable hydrodynamics and ripple migration behaviour the study was conducted in approximately 10 m water depth 1 km off martinique beach on the atlantic coast of nova scotia canada under low energy summer wave conditions significant wave height and peak period during the study averaged 0 7 m and 8 s respectively with extremes up to 1 7 m and 11 s during passage of three weak weather disturbances six mutually exclusive ripple types have been defined 1 short wavelength regular ripples 2 variable bifurcated ripples 3 variable terminated ripples 4 short crested ripples 5 long wavelength regular ripples and 6 chaotic ripples ripple wavelength ranged from 0 07 m to 0 24 m and displayed a strong reynolds number dependence together with other published field data the results suggest a lower limit of 0 06 m for the wavelength of wave ripples in ocean shoreface environments ripple orientation ranged through 38 and responded rapidly to changes in wave approach direction but did not conform to the orientation of the adjacent shoreline ripples were observed to migrate both on and off shore with and against the wave advance direction at rates up to 0 1 m h 1 associated with net flows other than wave induced onshore asymmetry and mass transport migration mainly of ripple types 1 and 2 occurred during the peak of storm events but showed no obvious correlation with measured near bottom flow magnitude or direction ripple behaviour demonstrates equilibrium with prevailing dynamic conditions when straight crested rippie types 1 and 5 are present disequilibrium in orientation or dimensions is expressed by increasing sinuosity bifurcation and crest termination in types 2 3 4 and 6

calibration and use of continuous heat type automated seepage meters for submarine groundwater discharge measurements abstract submarine groundwater discharge sgd assessments were conducted both in the laboratory and at a field site in the northeastern gulf of mexico using a continuous heat type automated seepage meter seepmeter the functioning of the seepmeter is based on measurements of a temperature gradient in the water between downstream and upstream positions in its flow pipe the device has the potential of providing long term high resolution measurements of sgd using a simple inexpensive laboratory set up we have shown that connecting an extension cable to the seepmeter has a negligible effect on its measuring capability similarly the observed influence of very low temperature 3 c on seepmeter measurements can be accounted for by conducting calibrations at such temperatures prior to field deployments compared to manual volumetric measurements calibration experiments showed that at higher water flow rates 28 cm day 1 or cm 3 cm 2 day 1 an analog flowmeter overestimated flow rates by 7 this was apparently due to flow resistance turbulence and formation of air bubbles in the seepmeter water flow tubes salinity had no significant effect on the performance of the seepmeter calibration results from fresh water and sea water showed close agreement at a 95 confidence level significance between the data sets from the two media r 2 0 98 comparatively the seepmeter sgd measurements provided data that are comparable to manually operated seepage meters the radon geochemical tracer approach and an electromagnetic em seepage meter

permeable coral reef sediment dissolution driven by elevated pco2 and pore water advection 1 ocean acidification oa is expected to drive the transition of coral reef ecosystems from net calcium carbonate caco3 precipitating to net dissolving within the next century although permeable sediments represent the largest reservoir of caco3 in coral reefs the dissolution of shallow caco3 sands under future pco2 levels has not been measured under natural conditions in situ advective chamber incubations under elevated pco2 800 atm shifted the sediments from net precipitating to net dissolving pore water advection more than doubled dissolution rates 1 10 g caco3 m 2 d 1 when compared to diffusive conditions 0 42 g caco3 m 2 d 1 sediment dissolution could reduce net ecosystem calcification rates of the heron island lagoon by 8 within the next century which is equivalent to a 25 reduction in the global average calcification rate of coral lagoons the dissolution of caco3 sediments needs to be taken into account in order to address how oa will impact the net accretion of coral reefs under future predicted increases in co2

gas venting and subsurface charge in the green canyon area gulf of mexico continental slope evidence of a deep bacterial methane source abstract questions as to the role of modern carbon in methanogenesis and the maximum depth of methane sources in the gulf of mexico continental slope remain unanswered a research submersible was used to sample mixed bacterial and thermal gas 13 c of methane 62 8 d 176 venting to the water column from the gulf slope in green canyon gc 286 the 14 c value of the methane 998 is consistent with fossil carbon another gas vent on gc 185 is 100 methane 13 c 62 9 d 155 and may be from a bacterial source the 14 c 997 of this bacterial methane is also consistent with fossil carbon fossil bacterial methane and thermal hydrocarbons are present in pliocene to pleistocene reservoirs 3509 4184 m of genesis field gc 205 161 160 oil in these reservoirs is biodegraded but gas is not suggesting that gas charge to reservoirs continues presently at 3 4 km depth mixed thermal and bacterial methane may charge the deep reservoirs and fossil methane from depth may ultimately vent on the sea floor at gc 286 and gc 185 results of this study of green canyon suggest that bacterial methane in gas vents and in reservoirs is from deep fossil sources

sedimentary controls on modern sand grain coat formation abstract coated sand grains can influence reservoir quality evolution during sandstone diagenesis porosity can be reduced and fluid flow restricted where grain coats encroach into pore space conversely pore lining grain coats can restrict the growth of pore filling quartz cement in deeply buried sandstones and thus can result in unusually high porosity in deeply buried sandstones being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality here we report a modern analogue study of 12 sediment cores from the anllons estuary galicia nw spain collected from a range of sub environments to help develop an understanding of the occurrence and distribution of coated grains the cores were described for grain size bioturbation and sedimentary structures and then sub sampled for electron and light microscopy laser granulometry and x ray diffraction analysis the anllons estuary is sand dominated with intertidal sand flats and saltmarsh environments at the margins there is a shallowing fining upwards trend in the estuary fill succession grain coats are present in nearly every sample analysed they are between 1 m and 100 m thick and typically lack internal organisation the extent of grain coat coverage can exceed 25 in some samples with coverage highest in the top 20 cm of cores samples from muddy intertidal flat and the muddy saltmarsh environments close to the margins of the estuary have the highest coat coverage mean coat coverage of 20 2 and 21 3 respectively the lowest mean coat coverage occurs in the sandy saltmarsh 10 4 beyond the upper tidal limit and sandy intertidal flat environments 8 4 close to the main estuary channel mean coat coverage correlates with the concentration of clay fraction the primary controls on the distribution of fine grained sediment and therefore grain coat distribution are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary bioturbation and clay illuviation mechanical infiltration are secondary processes that may redistribute fine grained sediment and produce grain coats here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary fills which are typically found in the fining upward part of progradational successions

stereo video observation of nearshore bedforms on a low energy beach abstract a new technique utilising underwater stereo video was tested for its ability to measure nearshore bed morphology at high frequency and high resolution a stereo video system was used to monitor small scale ripple morphology wavelengths 0 05 0 10 m heights 5 mm in the nearshore of a low energy beach in southwestern australia waves currents and suspended sediment concentrations were also monitored bed morphology could be measured with a mean accuracy of 2 mm with the stereo video system measurements in the field were limited to ripple crest positions since targets over the entire ripple profiles could not be identified in both the left and right stereo images this limitation could be overcome in the future by use of laser stripes to illuminate the profiles and the generation of epipolar lines within the analysis software to match corresponding targets in each of the images ripple crest positions were measured at 1 hz and the relationship between ripple movement and near bed hydrodynamics was investigated to test the applicability of the stereo video system to make high frequency bedform observations ripple crests were found to oscillate at the same frequency as the swell waves the magnitude of the ripple movement at swell wave frequencies was an order of magnitude greater than ripple movement at wind wave frequencies net onshore migration of the ripples corresponded to onshore wave asymmetry very weak mean cross shore currents and net onshore suspended sediment flux measured at an elevation of 0 05 m

oxygen and carbon isotopic records of mollusks in the kuokang shell bed taiwan implications and applications abstract oxygen and carbon isotopic compositions have been determined in fossil molluscan shells from the kuokang shell bed and in modern shells from coastal areas around taiwan fossil mollusks have been well preserved based on x ray diffraction stable isotopic data and their occurrence in the field the stable isotopic data of fossil shells indicate that they lived in an open sea environment heavier oxygen and lighter carbon isotopic ratios of these fossils relative to modern counterparts around taiwan indicate that these fossil mollusks grew in a glacial period as supported by the 14c dating results the calculated mean uplift rate for the kuokang shell bed shows a lower rate compared to the eastern and southern parts of taiwan and reflects a more stable away from collision nature for western taiwan

generalized analytical model for benthic water flux forced by surface gravity waves 1 a generalized analytical model for benthic water flux forced by linear surface gravity waves over a series of layered hydrogeologic units is developed by adapting a previous solution for a hydrogeologic unit with an infinite thickness case i to a unit with a finite thickness case ii and to a dual unit system case iii the model compares favorably with laboratory observations the amplitude of wave forced benthic water flux is shown to be directly proportional to the amplitude of the wave the permeability of the hydrogeologic unit and the wave number and inversely proportional to the kinematic viscosity of water a dimensionless amplitude parameter is introduced and shown to reach a maximum where the product of water depth and the wave number is 1 2 submarine groundwater discharge sgd is a benthic water discharge flux to a marine water body the case i model estimates an 11 5 cm d sgd forced by a wave with a 1 s period and 5 cm amplitude in water that is 0 5 m deep as this wave propagates into a region with a 0 3 m thick hydrogeologic unit with a no flow bottom boundary the case ii model estimates a 9 7 cm d wave forced sgd as this wave propagates into a region with a 0 2 m thick hydrogeologic unit over an infinitely thick more permeable unit the case iii quasi confined model estimates a 15 7 cm d wave forced sgd the quasi confined model has benthic constituent flux implications in coral reef karst and clastic regions waves may undermine tracer and seepage meter estimates of sgd at some locations

the driving forces of porewater and groundwater flow in permeable coastal sediments a review abstract advective flows rapidly transport water solutes and particles into and out of permeable sand beds and significantly affects the biogeochemistry of coastal environments in this paper we reviewed the drivers of porewater and groundwater advection in permeable shelf sediments in an attempt to bridge gaps among different disciplines studying similar problems we identified the following driving forces 1 terrestrial hydraulic gradients 2 seasonal changes in the aquifer level on land moving the location of the subterranean estuary 3 wave setup and tidal pumping 4 water level differences across permeable barriers 5 flow and topography induced pressure gradients 6 wave pumping 7 ripple and other bed form migration 8 fluid shear 9 density driven convection 10 bioirrigation and bioturbation 11 gas bubble upwelling and 12 sediment compaction while these drivers occur over spatial scales ranging from mm to km and temporal scales ranging from seconds to years their ultimate biogeochemical implications are very similar i e they are often a source of new or recycled nutrients to seawater and transform organic carbon into inorganic carbon drivers 2 12 result in no net water input into the ocean taking all these mechanisms into account we conservatively estimate that a volume equivalent to that of the entire ocean is filtered by permeable sediments at time scales of about 3000 years quantifying the relative contribution of these drivers is essential to understand the contribution of sediments to the global cycles of matter

submarine groundwater discharge revealed by 228 ra distribution in the upper atlantic ocean submarine groundwater discharge estimated from a 228ra inventory across the upper atlantic ocean provides a flux of 2 4 1013 m3 yr 1 equivalent to 80 160 of the influx from rivers into the atlantic ocean