controls on turbulent mixing in a strongly stratified and sheared tidal river plume abstractconsiderable effort has been made to parameterize turbulent kinetic energy tke dissipation rate e and mixing in buoyant plumes and stratified shear flows here a parameterization based on kunze et al is examined which estimates e as the amount of energy contained in an unstable shear layer ri ric that must be dissipated to increase the richardson number ri n2 s2 to a critical value ric within a turbulent decay time scale observations from the tidal columbia river plume are used to quantitatively assess the relevant parameters controlling e over a range of tidal and river discharge forcings observed e is found to be characterized by kunze et al s form within a factor of 2 while exhibiting slightly decreased skill near ri ric observed dissipation rates are compared to estimates from a constant interfacial drag formulation that neglects the direct effects of stratification this is found to be appropriate in energetic regimes when the bulk averaged richardson number rib is less than

observations of currents and water properties in the amazon frontal zone measurements of currents and water properties were obtained at various locations in the frontal zone of the amazon river outflow plume during four cruises in 1989 1991 as part of a multidisciplinary amazon shelf sediment study a salinity front resembling a salt wedge is found approximately 150 km seaward of the river mouth it continues northwestward more than 400 km along the shelf between the 10 and 20 m isobaths tidal currents which are oriented principally in the cross shelf direction reach 200 cm s 1 during spring tides and drop to less than 80 cm s 1 during neaps in the vicinity of the river mouth the nontidal flow is strongly sheared with near surface speeds of up to 100 cm s 1 and weak near bottom velocities the direction of the near surface flow is generally northwestward except near the river mouth where river discharge leads to a significant offshore component of flow the strong velocity shears are stabilized by strong stratification by salinity and by highly concentrated suspended sediment or fluid mud near the seabed variations in stratification and frontal position are due principally to spring neap variations in tidal mixing and seasonal variations in runoff

entrainment and flushing time in the fraser river estuary and plume from a steady salt balance analysis 1 a passenger ferry equipped with oceanographic instrumentation made eight transects across the fraser river plume in the strait of georgia british columbia each day for 4 years estimates of average plume salinity and volume were made from the observations and used in a quasi steady budget to estimate the net upward flux of ambient salt water into the plume this entrainment flux increases from a minimum of 17 000 m3s 1 at low river flow to a maximum of about 27 000 m3s 1 at intermediate flow the entrainment flux then becomes essentially independent of river flow although we argue on physical grounds it must eventually decrease entrainment velocities of a few mm s 1 were estimated from the entrainment flux when assuming that mixing primarily occurs along the salt wedge estuary or in the near field plume these values are consistent with previous estimates this in turn suggests that entrainment is not important over most of the plume s full extent and that bulk plume properties are set in the near field finally the observations are used to estimate a plume freshwater flushing time of 2 2 days with essentially no dependence on river discharge even though discharge varies seasonally by almost an order of magnitude this value lies in between the expected time scales for near field and far field plumes and is long enough for rotation to play an important role there is no evidence however of a coherent bulge as observed in other systems

hydraulic control of a highly stratified estuarine front abstract observations at the mouth of the fraser river british columbia canada indicate an abrupt frontal transition between unstratified river outflow and a highly stratified river plume with differences in salinity greater than 25 psu across a few meters in the vertical direction and several hundred meters in the horizontal direction the front roughly follows a natural break in the bathymetry crossing the channel at an angle of approximately 45 and is essentially stationary for a period of approximately 3 5 h centered on the low tide following the larger of two daily ebbs the location of the front is coincident with observations of significantly supercritical internal froude numbers at the front based on velocities in the along flow direction this observation contradicts the one dimensional theory which indicates that the froude number should be 1 however because the front is oriented obliquely to the outflow a coordinate system can be selected that is normal to the front and for which a c

dissolved redox sensitive elements re u and mo in intense denitrification zone of the arabian sea the concentrations of redox sensitive elements rhenium uranium and molybdenum have been measured in the suboxic water column of the arabian sea to determine their response behavior to intense oxygen minima and denitrifying conditions in the water column north of 12 n within the core of the intense oxygen minimum zone omz of the arabian sea the dissolved oxygen levels drop to values as low as 5 m accompanied by the presence of secondary nitrite maxima snm indicating the occurrence of denitrification in the water column the distributions of re u and mo in the arabian sea show that their dissolved concentrations in the suboxic layer are indistinguishable from those in the overlying and underlying oxic waters suggesting that there is no discernible removal of these elements from the suboxic denitrifying layers in contrast the lateral and vertical distribution of dissolved re u and mo concentrations vary as a function of salinity suggesting their conservative behavior the salinity normalized 35 re u and mo concentrations in the arabian sea are 40 pmol kg 13 8 nmol kg and 114 nmol kg respectively these concentrations are nearly identical to their abundances in the bay of bengal a basin adjacent to the arabian sea characterized by high freshwater influx and fluvial sediments the similarity in concentration suggests that the large variability in the biogenic and detrital particulate fluxes and the suboxic denitrifying conditions between these two oceanic regions do not affect the concentrations of re u and mo and that the prevailing biogeochemical conditions in these regions are inadequate for their removal from the water column

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

sediment trapping in the changjiang estuary observations in the north passage over a spring neap tidal cycle abstract water current salinity and suspended sediment concentration ssc were measured at three anchored boat sites along the north passage np of the changjiang estuary over a spring neap tidal cycle in order to study sediment trapping and siltation in the estuary pronounced stratification was observed during the late flood tide and the following early ebb tide along with an advancing and retreating salt wedge whereas strong vertical mixing occurred during the late ebb when the effect of the salt wedge faded therefore the ssc in the flood ebb tidal cycle tended to be asymmetric in the upper reach of the np the seaward advective near bed sediment transport dominated the total near bed sediment transport whereas in the middle reach of the np the landward tidal pumping component dominated accordingly a notable convergent near bed residual sediment transport was generated near the middle reach because the convergence of residual sediment transport in the region of a salt wedge is generally recognized as sediment trapping convergent near bed residual sediment transport is the cause of the high sedimentation rate in the np

the influence of dunes on mixing in a migrating salt wedge fraser river estuary canada dune bedforms and salt wedge intrusions are common features in many estuaries with sand beds and yet little is known about the interactions between the two flow visualization with an echosounder and velocity measurements with an acoustic doppler current profiler over areas of flat bed and sand dunes in the highly stratified fraser river estuary canada were used to examine the effect of dunes on interfacial mixing as the salt wedge migrates upstream over the flat bed mixing is restricted to the lower portion of the water column however as the salt wedge migrates into the dune field from the flat bed there is a dramatic change in the flow and large internal in phase waves develop over each of the larger dunes with water from the salt wedge reaching the surface of the estuary the friction richardson number shows that bed friction is more important in interfacial mixing over the dunes than over the flat bed and a plot of internal froude number versus obstacle dune height shows that the salt wedge flow over the dunes is mainly supercritical such bedforms can be expected to cause similar effects in interfacial mixing in other estuaries and sediment laden density currents and may thus be influential in fluid mixing and sediment transport copyright 2010 john wiley sons ltd

advection of the salt wedge and evolution of the internal flow structure in the rotterdam waterway an analysis of field measurements recorded over a tidal cycle in the rotterdam waterway is presented these measurements are the first to elucidate the processes influencing the along channel current structure and the excursion of the salt wedge in this estuary the salt wedge structure remained stable throughout the measuring period the velocity measurements indicate decoupling effects between the layers and that bed generated turbulence is confined below the pycnocline the barotropic m4 overtide structure is imposed at the mouth of the estuary and the generation of m4 overtides within the estuary is found to be relatively small internal tidal asymmetry does not make a significant contribution to the m4 velocity frequency band instead the combination of barotropic and baroclinic forcing in conjunction with the suppression of turbulence at the interface provides the main explanation for the time dependence and mean structure of the flow in the rotterdam waterway this gives rise to the observed differences in the length of the flood and ebb in the magnitudes of the flood and ebb velocities in the length of the slack water periods and in the timing of the onset of slack water at the surface and near the bed it results in the formation of distinct exchange flow profiles at the head of the salt wedge around slack water and the creation of maximal velocities at the pycnocline during flood advection governs the displacement and structure of the salt wedge since turbulent mixing is suppressed the tidal displacement of the salt wedge controls the height of the pycnocline above the bed at a particular site hence it controls the height to which bed generated turbulence can protrude into the water column consequently the authors find asymmetries in the structure of the internal flow turbulent mixing and bed stresses that are not related to classical internal tidal asymmetry

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

major factors influencing boron adsorption in sediments a case study of modern sediments in qinghai lake because the boron b concentration in water has an apparent positive correlation with salinity the b content adsorbed in sediments is often regarded as an important indicator to reconstruct the water salinity in a sedimentary environment the premise of the quantitative reconstruction of paleosalinity is that the b uptake in sediments is proportional to the b concentration in water however the study showed that there is no direct relationship the b absorption in sediments can be affected by both the content of the clay minerals and the total organic carbon content the data from testing modern sediments and water samples in the qinghai lake show that a higher content in clay minerals is beneficial for b adsorption furthermore the organic carbon from halophiles has a strong effect on the enrichment of b therefore the organic carbon content in sediments should be considered when the paleosalinity of water is reconstructed using its b content it is also thought that the adams and couch formulas are not suitable for reconstructing the salinity of water with a high organic carbon content in sediments because they consider only the effect of clay minerals on the adsorbed b without the contribution of organic carbon

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

modulation of the semidiurnal cycle of turbulent dissipation by wind driven upwelling in a coastal embayment with two 25 hour series of turbulent microstructure and currents observations carried out in august 2013 during spring chaos 1 and neap tides chaos 2 we investigated the semidiurnal cycle of turbulent dissipation in an embayment affected by coastal upwelling ria de vigo nw iberia at the time of sampling the bay hosted a net wind driven bi directional positive exchange flow and thermal stratification turbulent kinetic energy tke dissipation e at the interface between upwelled and surface waters was enhanced by two orders of magnitude during the ebbs 10 6 w kg 1 with respect to the floods 10 8 w kg 1 this pattern was caused by the constructive interference of the shear associated with the upwelling and tidal currents the vertical structure of the tidal currents was consistent with a deformation of tidal ellipses by stratification which was tightly coupled to the intensity of upwelling this two pronged interaction resulted in a modulation of the semidiurnal cycle of turbulent dissipation by coastal upwelling thus as a result of the upwelling relaxation conditions experienced during chaos 1 depth integrated interior tke dissipation rates were higher by a factor of 2 compared to chaos 2 by using a simple model we determined that observed variations in turbulent mixing had a limited influence on the tidal variations of stratification which were dominated by straining and advection the mixing mechanism described here is potentially relevant for the ecology of upwelling bays as it can stimulate the transport of nutrients from deep upwelled waters to the sun lit surface layers where primary production takes place

molybdenum and uranium geochemistry in continental margin sediments paleoproxy potential abstract we measured solid phase mo and u concentrations in marine sediments from the california mexico peru and chile margins to ascertain the behavior of mo and u during early diagenesis in continental margin settings at sites along the california mexico and peru margins where there are estimates of mass accumulation rates authigenic u accumulation rates range from 0 50 nmol m 2 day 1 at the california and mexico margin sites mo accumulation rates range from 0 to 134 nmol m 2 day 1 whereas at the peru margin site rates may be as high as 550 nmol m 2 day 1 we observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon corg in the case of mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial for most of the data presented in this manuscript continental margin sediments have a mo corg accumulation rate ratio of 20 mol mol 1 this value is significantly lower however than those reported for anoxic basins 100 mol mol 1 but is consistent with reported mo corg rain ratios from mexico margin sediment traps in contrast to mo there appears to be a single u corg burial ratio of 5 mol mol 1 which includes a range of environments from anoxic basins and open ocean sites we interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings however we note that any relationship between metal accumulation and organic carbon could be indirect in the particular case of mo based on what is known about mo geochemistry from the literature it is possible that mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study and that the observed association between mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial using the observed relationships between mo and corg burial as well as constraints from the mo isotope budget we estimate that continental margin sediments are an important sink for mo the magnitude of this sink 0 4 108 mol y 1 or larger may be as much as one quarter of the oceanic removal term and is likely to be larger than the modern anoxic basin sink

paleosalinity confidence limits and future applications error propagation is investigated through the only commonly applied technique for reconstruction of paleosalinity based on oxygen isotope residuals although this technique is known to be fairly inaccurate there remained a need for thorough assessment of confidence limits in a variety of global settings here it is found that a theoretical minimum error bar of between 0 3 and 0 7 applies to paleosalinity estimates and that real life practical limits are rarely better than 0 6 best results are expected in the latitudinal ranges 50 n and 70 s taking care to avoid the sea ice margin confidence intervals at low and mid latitudes including marginal seas are very wide at least 1 8 for the mediterranean and 2 2 for the equatorial atlantic it appears that oxygen isotope distributions are best used in their own right to investigate circulation and advective processes in coupled ocean atmosphere cryosphere models instead of calibrating them to paleosalinity to define restoring boundary conditions however isotope residual based paleosalinity maps from large numbers of regionally averaged studies in the above mentioned latitudinal bands may help in defining initial conditions and first order validation arguments for models

two layer hydraulics at the river ocean interface liftoff is the hydraulically forced detachment of buoyant freshwater from the channel bottom or seabed that occurs as river water discharges into the coastal ocean it is a key feature of strongly stratified systems occurring well upstream in the channel or seaward of the river mouth under sufficiently strong forcing we present a two layer hydraulic solution for the river ocean interface that considers the river estuary and near field river plume as a single interlinked system extending previous work that considered them separately this unified approach provides a prediction of the liftoff location and free surface profile for a wide range of forcing conditions which are characterized in terms of the freshwater froude number f f equiv q b 0 sqrt g 0 prime h 0 3 here q is the river discharge b 0 is the channel width g 0 prime equiv unicode stix x0394 unicode stix x1d70c 0 unicode stix x1d70c 2 g is the reduced gravitational acceleration unicode stix x0394 unicode stix x1d70c 0 is the density contrast between fresh and ocean water and h 0 is the total water depth at the river mouth the solution is validated with laboratory experiments using an experimental apparatus consisting of a long sloping river channel that discharges into a deep wide saltwater basin the experiments simulate the full range of hydraulic behaviours predicted by the model from saltwater intrusion to offshore liftoff for f f 1 liftoff occurs in the estuary channel and our results show that the relationship between intrusion length and f f depends on the channel slope for f f 1 corresponding to flood conditions in many natural systems liftoff is forced outside the river mouth and the hydraulic coupling between the channel and shelf becomes more important for these conditions and for intermediate to steeply sloped shelves the offshore liftoff distance varies linearly with f f 1 a particularly simple scaling given the nonlinearity and relative complexity of the governing equations the model and experimental results support a conceptual description of the river ocean interface that relates the liftoff location free surface elevation and the spreading rate of the buoyant river plume

salt wedge propagation in a mediterranean micro tidal river mouth abstract the dynamics of a seasonally formed salt wedge propagating along the micro tidal channel of strymon river estuary northern greece and its consequences on river water quality are thoroughly studied through intensive sampling campaigns the wedge is developed at the downstream river part under the summer limited freshwater discharge conditions q 3 s the geometric features of the wedge length and thickness appeared directly related to strymon river discharge a maximum intrusion length of 4 7 km along strymon river estuary was observed under minimum river discharge of almost 6 m 3 s relations produced from in situ data illustrate that limited river flow expands the wedge horizontally reducing its vertical dimension while higher flows lead to increased wedge thickness estuarine flushing time ranges between 0 2 and 1 5 days exponentially dependent on strymon river discharge wedge velocities depicted tidal asymmetry between tidal phases with consistent inward motion even under the ebb tidal stage strong vertical stratification prevails throughout the tidal cycle proving the limited vertical mixing between the two layers although higher interfacial stresses are produced in ebb bottom topography plays an interesting role in wedge propagation as the presence of an underwater sill either prevents saline intrusion during flood or isolates the front of the wedge from its core at the ebb ecological consequences of salt wedge propagation in strymon river estuary are the frequent evidence of bottom hypoxic conditions and the increased tss levels leading to the occurrence of a turbidity maximum at the tip of the salt wedge higher bod and ammonium levels were mostly observed at the river end associated to point and non point pollution sources nitrates and silicates were found associated with freshwater fluxes while ammonia levels were related to saline intrusions the reduced phosphorus freshwater fluxes resulting from phosphorus uptake at the upstream reservoir kerkini lake and the increased bottom turbidity induced by the salt wedge seem responsible for the limited chlorophyll a levels along strymon river estuary

influence of variable salinity conditions in a tidal creek on riparian groundwater flow and salinity dynamics while recent studies have revealed that tidal fluctuations in an estuary significantly affect groundwater flows and salt transport in the riparian zone only seawater salinity in the estuary has been considered a numerical study is conducted to investigate the influence of estuarine salinity variations on the groundwater flow and salt dynamics in the adjacent aquifer to extend our understanding of these complex and dynamic systems tidal salinity fluctuations synchronous with estuary stage were found to alter the magnitude and distribution of groundwater discharge to the estuary which subsequently impacted on groundwater salinity patterns and residence times especially in the riparian zone the effects of salinity fluctuations were not fully captured by adopting a constant time averaged estuarine salinity the modelling analysis also included an assessment of the impact of a seasonal freshwater flush in the estuary similar to that expected in tropical climates e g mean estuary level during flood significantly greater than average on adjacent groundwater flow and salinity conditions the three month freshwater flushing event temporarily disrupted the salt distribution and re circulation patterns predicted to occur under conditions of constant salinity and tidal water level fluctuations in the estuary the results indicate that the salinity variations in tidal estuaries impact significantly on estuary aquifer interaction and need to be accounted for to properly assess salinity and flow dynamics and groundwater residence times of riparian zones

trace metal evidence for changes in the redox environment associated with the transition from terrigenous clay to diatomaceous sediment saanich inlet bc abstract we measured the concentrations of redox sensitive trace metals mn v mo u cd and re in sediments from odp leg 169s hole 1033b in saanich inlet british columbia to determine changes in redox conditions associated with the onset of laminated sediments at 12 5 kyr the most striking result is a large peak in authigenic re along with detrital levels of mo at the glacial terrigenous clay diatomaceous sediment transition in contrast the underlying glacial terrigenous clay which extends throughout the bottom section of the core is chemically similar to detrital concentrations either cowichan river particulates or average shale values these data suggest a period of oxic bottom waters but reducing pore waters this could be due to the dramatic transformation of saanich inlet during the late deglaciation from an open bay to an inlet which restricted circulation and slowed bottom water oxygen renewal a peak and gradual increase in authigenic mn in younger sediments subsequent to the re peak suggests that increasingly oxic conditions followed the authigenic enrichment in re these conditions could be connected to the younger dryas cooling period which was coincident with an increase in well oxygenated upwelled waters on the west coast of north america that form the bottom waters of saanich inlet metal concentrations in a gray clay bed 11 kyr are similar to their concentrations in the glacial terrigenous clay implying that they have a common source authigenic enrichments of re with little authigenic mo and cd suggest that before the deposition of this bed bottom waters were oxic and pore water oxygen was consumed in the top centimeter or less laminations above the clay layer suggest anoxic conditions which are also indicated by higher authigenic mo and cd and slightly lower re mo ratios in these sediments the basin remained mostly anoxic after the gray clay was emplaced as seen by continuous authigenic enrichment of the redox sensitive trace metals these results are consistent with increased stratification of the water column brought about by an influx of fresh water to the basin by a large flood

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

temporal and spatial variability of vertical salt flux in a highly stratified estuary 1 the temporal and spatial variability of vertical salt flux in the fraser river estuary british columbia was investigated observationally using several different direct and indirect indicators of buoyancy flux data were collected from the estuary using shipboard instrumentation primarily an acoustic doppler current profiler and a towed conductivity temperature depth unit direct estimates of buoyancy flux were made from along channel control volume analyses and from measurements of overturn scales the spatial and temporal evolution of the salt wedge structure through a tidal cycle was evaluated using the results of these buoyancy flux calculations as well as gradient richardson number froude number and stratification profiles observations indicate that buoyancy flux is driven primarily by interfacial stress and not bottom stress as is common in many estuaries vertical salt flux as opposed to seaward advection of high salinity fluid was found to be the dominant mechanism responsible for removal of salt from the estuarine channel during each daily tidal cycle buoyancy flux was highly variable in time and space however with vertical salt flux during ebb tides on the order of 2 to 3 times greater than that estimated during floods this is due to an increase in the vertical shear of horizontal velocity and a sharp increase in stratification which was observed during early ebb enhanced mixing was observed spatially within a region dominated by a channel constriction in which the channel narrows by approximately 25

flow and sediment suspension events over low angle dunes fraser estuary canada 1 the morphodynamics of large sand bedded rivers and estuaries are ultimately controlled by the way bed material is moved and the development of large subaqueous sand dunes that control hydraulic flow resistance it is widely thought that the primary mechanism for moving sandy bed material in these channels is large scale coherent flow structures that cause suspension events whose properties vary with flow especially in tidally influenced environments here we examine mean flow and sediment suspension events over low angle dunes lee face angle 30 in the unsteady flow of the fraser estuary canada at high tide flow nearly ceased and a salt wedge entered the channel forcing salt water under the downstream moving fresh water the salt wedge persisted in the channel until late in the falling tide causing stratification in the water column and instabilities along the saline fresh water interface at low tide mean velocities peaked and forced the saline water out of the channel flow over the low angle dunes displayed topographically induced patterns previously observed over high angle dunes but permanent flow separation was not observed large scale sediment suspension events dominated sediment flux during low tide and became larger scale yet less frequent as the tide began to rise the suspension events appeared to form over the lower stoss of the dunes and grew up over the bed forms and less commonly emerged downstream of the crest suspension events move 69 of the total sediment in the flow above low angle dunes when they are present

diagenesis of oxyanions v u re and mo in pore waters and sediments from a continental margin this research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way we describe pore water and sediment measurements of iron fe manganese mn vanadium v uranium u rhenium re and molybdenum mo along a transect off washington state usa sediments become less reducing away from the continent and the stations have a range of oxygen penetration depths depth to unmeasurable o2 concentration varying from a few millimeters to five centi meters when oxygen penetrates 1 cm or less fe is reduced in the pore waters but reoxidized near the sediment water interface preventing a flux of fe 2 to overlying waters whereas mn oxides are reduced and mn 2 diffuses to overlying waters both re and u authigenically accumulate in sediments only at the most reducing location where the oxygen penetrates 0 3 cm below the sediment water interface does the surface 30 cm of sediments become reducing enough to authigenically accumulate mo stations in close proximity to the juan de fuca ridge crest are enriched in mn and fe from hydrothermal plume processes both v and mo clearly associate with mn cycling whereas u may be associating with either mn oxides and or fe oxyhydroxides rhenium is uncomplicated by adsorption to mn oxides and or fe oxyhydroxides and re accumulation in sediments appears to be due solely to the extent of reducing conditions therefore authigenic sediment re enrichment appears to be the best indicator for intermediate reducing conditions where oxygen penetrates less than 1 cm below the sediment water interface when coupled with negligible authigenic mo enrichment copyright 2005 elsevier ltd 1 introduction oceanic and atmospheric carbon cycles are strongly coupled with the ocean reservoir of dissolved inorganic carbon being 60 times larger than that of the atmosphere broecker and peng 1987 models that couple both ocean and atmosphere have been used to investigate why atmospheric carbon dioxide pco2 atm was reduced during the last glacial age and thus may be useful in predicting the environmental impact of future changes in pco2 atm some of these models require a large increase in organic carbon export through the more efficient use of nutrients to predict the lower pco2 atm observed during

the hydrology of the upper swan river estuary with focus on an artificial destratification trial a trial to artificially destratify part of the water column of the swan canning estuary took place over four weeks in 1997 destratification was attempted with bubble plumes created by pumping compressed air through a porous pipe near the bed at a location in the upper estuary the purpose of the trial was to determine whether the resultant bubble curtain could mix the water column thereby altering the extent of upstream and downstream mixing and the vertical structures of salinity temperature dissolved oxygen and turbidity the destratification trial was monitored using three techniques vertical profiles taken on several days at selected stations along the estuary fine scale profiles in the vicinity of the bubble curtain on one day and continuous water column profiles taken 1 km upstream of the curtain the seasonal upstream propagation of brackish water underneath a residual freshwater discharge was affected by the magnitude of freshwater discharge and tidal elevations superimposed upon diurnal and semi diurnal tides were non tidal water level changes induced mostly by variations in barometric pressure these caused large changes in the salt wedge position destratification by the bubble curtain was compromised by these large oscillations which limited the exposure of the salt wedge region to the mixing action of the bubble curtain complete vertical mixing of the water column was observed up to 30 m either side of the curtain on 30 october disruptions to the density stratification were not evident beyond 350 m of the curtain in the immediate vicinity 30 m of the curtain deficits of dissolved oxygen in bottom waters were generally reduced or obliterated and a naturally turbid plume of water near the bottom of the estuary was mixed through the water column the effects of the bubble curtain on dissolved oxygen turbidity and temperature were however similar to those for salinity with mixing confined to around 30 m from the curtain and no effect observed further than 350 m away the upper swan river estuary although relatively narrow and strongly vertically stratified is unsuited to destratification using bubble plumes cycling of spring and neap tides and non tidal water level changes together with freshwater inflows to the estuary strongly limit the longitudinal extent of mixing by bubble curtains copyright 2001 john wiley sons ltd

manganese and iron in indian ocean waters abstract the first vertical profiles of dissolved mn and fe for the nw indian ocean are reported the area is characterized by seasonal upwelling and a broad oxygen minimum zone in intermediate waters the dissolved fe profile exhibits a maximum 5 1 nm in the oxygen minimum zone with low values both in surface waters 0 3 nm and deep waters around 1 nm mn concentrations in the surface waters are elevated 2 0 4 3 nm and decrease rapidly in an offshore direction below the first 25 m concentrations decrease dramatically 0 5 1 3 nm indicating removal by oxidation and particle scavenging further down various mn maxima are observed which can be related to hydrographic features sigma 1 1 intermediate water originating from the red sea lost its dissolved o2 while flowing northward along the omani coast and exhibits a strong mn maximum 4 6 6 5 nm coincident with the deep o2 minimum 2 2 at the two inshore stations in the gulf of oman this is overlain by relatively modest mn maxima 2 7 nm related to arabian gulf overflow water 3 3 finally the strong mn maxima 4 4 5 6 nm in the oxygen minimum zone at the two offshore stations are related to yet another watermass below these various maxima concentrations decrease gradually to values as low as 90 pm at 2000 meters depth towards the seafloor concentrations increase again leading to a modest bottom water maximum 0 7 1 5 nm the overall vertical distributions of mn and fe are strikingly similar also in actual concentrations to those previously reported for the eastern equatorial pacific an area also characterized by an extensive o2 minimum zone

molybdenum in the northeast pacific ocean1 the concentration of dissolved molybdenum has been determined in several profiles from the northeast pacific ocean the salinity normalized concentration is essentially constant in all open ocean samples 107 nm 1 2 5 nm the dissolved distribution is not significantly affected by biological cycling

the dynamics of a subglacial salt wedge marine terminating glaciers such as those along the coastline of greenland often release meltwater into the ocean in the form of subglacial discharge plumes though these plumes can dramatically alter the mass loss along the front of a glacier the conditions surrounding their genesis remain poorly constrained in particular little is known about the geometry of subglacial outlets and the extent to which seawater may intrude into them here the latter is addressed by exploring the dynamics of an arrested salt wedge a steady state two layer flow system where salty water partially intrudes a channel carrying fresh water building on existing theory we formulate a model that predicts the length of a non entraining salt wedge as a function of the froude number the slope of the channel and coefficients for interfacial and wall drag in conjunction a series of laboratory experiments were conducted to observe a salt wedge within a rectangular channel for experiments conducted with laminar flow reynolds number re 800 good agreement with theoretical predictions are obtained when the drag coefficients are modelled as being inversely proportional to re however for fully turbulent flows on geophysical scales these drag coefficients are expected to asymptote toward finite values adopting reasonable drag coefficient estimates for this flow regime our theoretical model suggests that typical subglacial channels may permit seawater intrusions of the order of several kilometres while crude these results indicate that the ocean has a strong tendency to penetrate subglacial channels and potentially undercut the face of marine terminating glaciers

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

characterization of the ebre and rhone estuaries a basis for defining and classifying salt wedge estuaries river discharge is the main factor controlling the hydrologic dynamics of the ebre and rhone estuaries the topography of the estuary bed also influences the extent advance and retreat of the salt wedge tides have little influence because of the low tidal range mean annual river discharge is close to the critical value determining the formation and breakup of the salt wedge this is related to the fact that river flow controls the sedimentary dynamics of the estuary including the sandbar at the mouth when discharge is lower than the mean annual river flow the salt wedge is established and the estuary becomes a depositional environment with higher flows the salt wedge is washed away and erosive conditions prevail on the basis of the conditions in which the salt wedge is formed two types of highly stratified estuaries can be identified in the first one a salt wedge regime is established during low river flows whereas during high flows the wedge is washed away and the estuary becomes a river this circulation pattern corresponds to the salt wedge estuary or type 4 of the hansen rattray classification typical of riverdominated estuaries in microtidal seas in the second one a salt wedge is established during high river flows whereas a partially mixed estuary occurs during low flows this pattern corresponds to types 3b and 2b of the hansen rakray classification

numerical modeling of an estuary a comprehensive skill assessment i numerical simulations of the hudson river estuary using a terrain following three dimensional model regional ocean modeling system roms are compared with an extensive set of time series and spatially resolved measurements over a 43 day period with large variations in tidal forcing and river discharge the model is particularly effective at reproducing the observed temporal variations in both the salinity and current structure including tidal spring neap and river discharge induced variability large observed variations in stratification between neap and spring tides are captured qualitatively and quantitatively by the model the observed structure and variations of the longitudinal salinity gradient are also well reproduced the most notable discrepancy between the model and the data is in the vertical salinity structure while the surface to bottom salinity difference is well reproduced the stratification in the model tends to extend all the way to the water surface whereas the observations indicate a distinct pycnocline and a surface mixed layer because the southern boundary condition is located near the mouth the estuary the salinity within the domain is particularly sensitive to the specification of salinity at the boundary a boundary condition for the horizontal salinity gradient based on the local value of salinity is developed to incorporate physical processes beyond the open boundary not resolved by the model model results are sensitive to the specification of the bottom roughness length and vertical stability functions insofar as they influence the intensity of vertical mixing the results only varied slightly between different turbulence closure methods of k e k and k kl

the sensitivity of salt wedge estuaries to channel geometry abstractthe authors develop a two layer hydraulic model to determine the saline intrusion length in sloped and converging salt wedge estuaries they find that the nondimensional intrusion length cil hs depends significantly on the channel bottom slope and the rate and magnitude of landward width convergence in addition to the freshwater froude number in the definition of ci is a quadratic interfacial drag coefficient l is the salt wedge intrusion length and hs is the depth at the mouth of the estuary bottom slope is found to limit the saline intrusion length and this limitation accounts for the deviation of the observed exponent n in a scaling relationship with the river discharge of the form l q n from the canonical value of 2 to 2 5 predicted by the theory of schijf and schonfeld for a flat prismatic estuary the authors find that estuary convergence is important only when the ratio of the slope limited intrusion length to the convergence length is greater than one and that the effects of

a modeling study of tidally driven estuarine exchange through a narrow inlet onto a sloping shelf the circulation and particle transport through a narrow inlet kelvin number 0 5 and onto a sloping shelf are numerically examined using a three dimensional hydrodynamic model the model domain consists of an estuarine basin with vertical density stratification separated from a well mixed sloping shelf by a narrow inlet forcing is supplied by semidiurnal tides and buoyancy differential strong ebb flows resulting from this combined forcing transport estuarine water seaward through the inlet to form a radially spreading buoyant surface plume over the shelf a series of radial density fronts corresponding with the ebbing tidal outflow are found on the seaward side of the inlet mouth and are convergence zones for floating particles strong anticyclonic frontal flow advects particles around the boundary of the outflow plume particles released nearest the seaward side of the inlet mouth are able to enter the inlet at depth and remain while those particles released farther offshore rarely enter the inlet this result has clear implications for the shelf to estuary transport of pollutants or the larval phase of marine species asymmetric tidally induced eddies which appear on both sides of the inlet also contribute to the near field circulation calculations of gradient richardson number in the inlet show that regions susceptible to enhanced mixing occur during periods of maximum tidal velocities due to increased shear

controls on boron and germanium distribution in the low sulfur amos coal bed western kentucky coalfield usa abstract the duckmantian aged amos coal bed is a thin geochemical analysis of the amos coal bed shows higher concentrations of b and ge than other western kentucky coal beds high total b concentrations as well as high b be both considered to be indicators of marine environments increase toward the top of the coal bed most of the b values for the amos samples range from 66 to 103 ppm whole coal basis indicating deposition in a brackish environment high ge concentrations in coals have been considered to be a function of seam thickness and proximity to the top and bottom of the coal bed thin coals such as the amos are dominated by the coal bed margins and therefore have a tendency to have relatively high ge concentrations in the case of the amos coal bed the lower bench has a higher ge content suggesting that the substrate was a more important source of ge than the roof rock

geochemical evidence for anoxic deep water in the arabian sea during the last glaciation various paleoceanographic studies have indicated that the deep ocean was probably depleted in dissolved oxygen during the last glacial period approximately 18 kyr b p delta sup 18 o stage 2 compared to present time however direct evidence of low oxygen content in the deep waters has been lacking here the authors report geochemical evidence of near anoxic conditions in the deep arabian sea during the entire last glacial cycle delta sup 18 o stages 2 3 and 4 anoxia is inferred from the concomitant enrichment of organic carbon and authigenic uranium in the glacial sections of a core from the deep eastern arabian sea the anoxic conditions during the last glacial period probably caused by a change in deep water circulation evidently enhanced preservation of organic matter and simultaneous removal of uranium from seawater 57 refs 3 figs 2 tabs

molybdenum isotopes in two indian estuaries mixing characteristics and input to oceans abstract the distributions of dissolved and particulate mo and their isotope composition 98 mo have been measured in the narmada and the tapi estuaries draining into the arabian sea during monsoon the 98 mo of dissolved mo in the narmada estuary ranges from 0 49 to 2 19 in the salinity range 0 17 2 practical salinity unit psu quite similar to that in the tapi estuary 0 99 2 36 in the salinity range 0 20 3 psu mo concentration in suspended sediments of the narmada estuary collected during monsoon average 512 44 ng g range 459 602 ng g similar to that measured in one sample from the tapi estuary 560 ng g mo 98 mo of particulate mo in the narmada ranges from 0 21 to 0 48 with an average 0 03 0 2 dissolved mo in the narmada and the tapi rivers display isotopically heavier m compared to that in basalts the major lithology of their drainage this could result from a variety of processes preferential weathering of mo rich sulphide minerals dispersed in the basalts preferential removal of isotopically lighter mo during transport or contribution from marine cyclic salts supplied via rain or chemical weathering of organic rich shales in the basins the distribution of 98 mo in the narmada and the tapi estuaries with salinity does not follow the theoretical mixing line between river and seawater endmembers suggesting its non conservative behavior particulate mo and 98 mo show concomitant increase with salinity in the narmada estuary indicating loss of dissolved mo by adsorption onto fe mn oxyhydroxide balancing the mo budget along the course of these estuaries using inverse model suggests that in the narmada estuary there could be loss up to 8 of the dissolved mo and that in the tapi supply from anthropogenic sources could be up to 27 the results obtained in this study bring out the processes modifying riverine input of mo and its 98 mo in the estuaries oxic sink in the narmada and anthropogenic input in the tapi repetitive adsorption and desorption of mo in the narmada estuary can modify the supply of dissolved mo and its 98 mo relative to riverine supply by up to 40 this can significantly impact the mo isotope budget of the oceans in contrast in the tapi estuary there is enhancement in the dissolved supply of mo relative to that from river due to anthropogenic input of mo the investigations in these two estuaries underscore the importance of solute particle interactions and anthropogenic input in determining the mo flux and its 98 mo to the open arabian sea

observation and analysis of shear instability in the fraser river estuary 1 we investigate the occurrence of shear instability in the fraser river estuary instabilities observed with an echo sounder are compared with a linear stability analysis based on observed velocity and density profiles we find that each set of observed instabilities coincides with an unstable mode predicted by the taylor goldstein equation each of these instabilities occurs in a region where the gradient richardson number is less than the critical value of 1 4 both the taylor goldstein predictions and the echo soundings indicate the instabilities are concentrated either above or below the density interface this one sidedness is in contrast to the archetypal kelvin helmholtz instability although the dominant source of mixing in the estuary appears to be caused by shear instability when the tide produces strong near bed velocities small scale overturning due to boundary layer turbulence is apparent throughout the depth

paleoenvironmental implications of uranium concentrations in lacustrine calcareous clastic evaporite deposits in the western qaidam basin abstract uranium u provides especially useful information for reconstructing paleoredox conditions due to its unique geochemical properties and behavior in supergene environments its proxy potential under suboxic oxic conditions associated with salinization of surface water in closed hydrologic systems however has not been adequately explored this study examined the abundance and distribution of u in a sedimentary sequence of calcareous lacustrine clastics and salt layers from a high quality 938 5 m long core drilled in the western qaidam basin ne tibetan plateau this study examined u concentrations in calcareous clastic sediments including carbonates acid insoluble fractions as well as the amounts of iron and manganese oxides oxyhydroxides and salt layers in the calcareous clastic sediments variations in u concentrations within the acid insoluble fraction follow the fluctuations of reconstructed lake levels based on lithologic investigations providing a tool for tracing redox conditions in paleolake bottom water correlations between the variations in carbonate content with u and sr concentrations in the carbonate fractions demonstrate that the types and abundance of carbonate minerals control the u distribution in carbonates in the salt layers u and al concentrations correlate closely implying that both derived mainly from the detrital fraction in the salt layers however enrichments of u and mg are systematically higher in salt minerals formed in more concentrated brine and lower in those formed in less concentrated brine these results indicate that during the process of carbonate precipitation carbonate might effectively remove u from lake water during the subsequent stage of salt mineral precipitation u behavior is conservative and u resides for a long period in dissolved forms within the saline water giving rise to enhanced u enrichment in the more concentrated brines and the associated precipitated salt minerals our study suggests however that u related redox proxies should be interpreted with caution in suboxic oxic environments during the long term paleolake evolution

evaluation of oxygen isotopes in carbonate as an indicator of lake evolution in arid areas the modern qinghai lake qinghai tibet plateau abstract the oxygen isotopic composition of carbonate in lakes has been used as a useful indicator in palaeolimnological research and has made some important contributions to our understanding of lacustrine systems for modern lakes in arid or cold areas however there are few data available to test the effect of lake salinity and temperature on the oxygen isotopic composition of various carbonate sources such as ostracod bulk carbonate and fine grained carbonate for arid high altitude lake qinghai our results suggest that variations in the 18o values of carbonate in lake qinghai are mainly controlled by the oxygen isotope ratio of the lake water changing with water salinity as a secondary effect increasing water depth leads to cooler bottom and surface water which may result in more positive 18o values of ostracod and bulk carbonate

concentration oxidation state and particulate flux of uranium in the black sea abstract in contrast to its unreactive behavior in the open ocean uranium is removed from seawater to sediments of anoxic marine basins four biogeochemical processes have been proposed to account for this removal active uptake by organisms whose remains are preserved by the anoxic conditions of the sediments complexation of u vi by particulate organic matter chemical reduction of soluble u vi to insoluble u iv which is scavenged to the sediments by settling particles and precipitation of uranium within the sediments themselves the black sea is the largest anoxic marine basin in the world today waters below 150 200 m are anoxic and h2s levels build up to about 400 mol 1 1 in the bottom water maximum depth 2200 m concentrations of total u and the oxidation state of dissolved u were measured throughout the water column while particulate u fluxes were determined from time series sediment trap samples collected in the deep anoxic zone bottom waters were depleted in u by 40 relative to the initial u content of the water two independent methods gave residence times of dissolved u in the deep water column of about 103 years uranium occurred throughout the water column as soluble chemically labile reducible u vi rather than the thermodynamically favored u iv uranium is neither reduced to u iv by the high levels of h2s nor is it rapidly scavenged from the water column as would be expected for strongly hydrolyzed tetravalent actinides like u iv fluxes of particulate authigenic u measured with sediment traps are at least two orders of magnitude less than the rate of authigenic u burial in black sea sediments therefore the first three processes listed above contribute negligibly to the deposition of u in the sediments of anoxic marine basins such as the black sea the dominant removal process must involve precipitation of u in the sediments rather than scavenging from the water column

tidal asymmetry in an estuarine pycnocline 2 transport flood currents in shallow estuaries are driven by an along channel barotropic and baroclinic pressure gradient that increases monotonically toward the bottom while friction retards near bottom currents therefore in many estuaries there is a middepth maximum in flood currents we explore this phenomenon using a simple three layer model in which each layer has vertically uniform currents and constant density in this model the middle layer is of intermediate density and grows by shear induced entrainment from the other two layers this very simple model produces a middepth maximum in flood currents and simulates observed currents in the columbia river entrance channel within about 10 there is good qualitative agreement between model salinity transport and observed transport the model pycnocline rises and falls tidally in phase with the observed pycnocline although pycnocline depth and thickness are better simulated using results from a two layer model cudaback and jay 2000

a model to determine the advective circulation in a three layer salt wedge estuary application to the ebre river estuary a model to determine advective fluxes of water and salt in three layer salt wedge estuaries under steady river discharge is presented this model is a generalization of the knudsen s two layer model when applied to highly stratified estuaries the reason for this is that knudsen s model neglects the interface and produces biased estimates of the salt fluxes at this layer a basic assumption of the model is that velocity and salinity have linear profiles across the interface which is appropriate for such types of estuaries a physical description of the ebre estuary is given in terms of river discharge mean salinity in upper and lower layers and cross sectional area of all three layers these data are introduced into the model in order to obtain estimates of horizontal and vertical fluxes the equations for horizontal fluxes are the steady salt and water transport conditions at any cross section and a flow relation between the three layers solving the three mentioned equations explicit expressions for horizontal fluxes are obtained introducing the latter in the salt and water continuity equations of upper and lower layers vertical fluxes of water and salt at any given compartment along the estuary are obtained these vertical fluxes among the three layers allow more precise information to be obtained about mixing processes within the estuary a comparison of the results with those corresponding to the knudsen s two layer model shows that the model gives a more accurate estimate of advective fluxes in highly stratified estuaries

uranium isotopes in rivers estuaries and adjacent coastal sediments of western india their weathering transport and oceanic budget the two major river systems on the west coast of india narbada and tapti their estuaries and the coastal arabian sea sediments have been extensively studied for their uranium concentrations and 238u238u activity ratios the 238u concentrations in the aqueous phase of these river systems exhibit a strong positive correlation with the sum of the major cations na k mg ca and with the hco3 ion contents the abundance ratio of dissolved u to the sum of the major cations in these waters is similar to their ratio in typical crustal rocks these findings lead us to conclude that 238u is brought into the aqueous phase along with major cations and bicarbonate the strong positive correlation between 238u and total dissolved salts for selected rivers of the world yield an annual dissolved 238u flux of 0 88 1010g yr to the oceans a value very similar to its removal rate from the oceans 1 05 1010g yr estimated based on its correlation with hco3 contents of rivers in the estuaries both 238u and its great grand daughter 234u behave conservatively beyond chlorosities 0 14 g l these data confirm our earlier findings in other indian estuaries the behavior of uranium isotopes in the chlorosity zone 0 02 0 14 g l was studied in the narbada estuary in some detail the results though not conclusive seem to indicate a minor removal of these isotopes in this region reexamination of the results for the gironde and zaire estuaries martin et al 1978a and b also appear to confirm the conservative behavior of u isotopes in unpolluted estuaries it is borne out from all the available data that estuaries beyond 0 14 g l chlorosities act neither as a sink nor as a source for uranium isotopes the behavior in the low chlorosity zones warrants further detailed investigation a review of the uranium isotope measurements in river waters yield a discharge weighted average 238u concentration of 0 22 g l with a 234u238u activity ratio of 1 20 0 06ismissing the residence time of uranium isotopes in the oceans estimated from the 238u concentration and the 234u238u a r of the rivers yield conflicting results the material balance of uranium isotopes in the marine environment still remains a paradox if the disparity between the results is real then an additional 234u flux of about 0 25 dpm cm2 103 yr into the oceans about 20 of its river supply is necessitated

tidal asymmetry in an estuarine pycnocline depth and thickness tidal variations in estuarine stratification are revealed by the depth and thickness of the density interface the depth of the interface may be predicted using an inviscid two layer model that combines baroclinic estuarine circulation with barotropic tidal currents helfrich 1995 here we present results from a two layer model modified to include the effects of bottom friction and interfacial mixing modeled layer thickness and speed compare favorably with prior analytic studies farmer and armi 1986 pratt 1986 we use a bulk richardson number criterion to estimate the thickness of the pycnocline from two layer model results the predicted pycnocline depth and thickness compare remarkably well with observations we also investigate the effects of changing bottom friction and barotropic currents on the pycnocline thickness

suboxic trace metal geochemistry in the eastern tropical north pacific abstract we analyzed al ti fe mn cu ba cd u mo v and re in water column settling particulate and sediment 0 to 22 cm samples from the intense oxygen minimum zone omz of the eastern tropical north pacific near mazatlan mexico the goal was to determine how the geochemistry of these elements was influenced by suboxic water column conditions and whether the sediments have a unique suboxic geochemical signature the water column was characterized by a mn maximum reaching 8 nmol kg 1 at 400 m concentrations of cu ba cd mo re u and v were unaffected by the low o2 conditions and were comparable to those of the open ocean sinking particles were composed of lithogenic particles of detrital origin and nonlithogenic particles of biogenic origin al ti and fe were mostly at least 79 lithogenic about 75 of the mn was nonlithogenic significant amounts at least 58 of cu ba cd and mo were nonlithogenic sediment geochemistry varied across the continental shelf and slope cadmium u and re have prominent maxima centered at 310 m with 12 3 ppm 10 9 ppm and 68 3 ppb respectively at the core top high values of mo averaging 6 8 ppm and v averaging 90 ppm are seen in omz surface sediment additional down core enrichment occurs for all redox sensitive elements in the top 10 cm for u mo v and re surface sediments are a poor indicator of metal enrichment comparison of the nonlithogenic composition of sediments with sinking particles suggests that direct input of plankton material enriched in metals makes a significant contribution to the total composition especially for cd u and mo we evaluated re mo and cd u ratios as tracers for redox environments rhenium and mo concentrations and re mo ratios do not lead to consistent conclusions concurrent enrichments of re and mo are an indicator of an anoxic depositional environment in contrast high re mo ratios are an indicator of suboxic conditions cadmium is enriched in surface sediments while u has considerable down core enrichment the concentrations of cd and u and the cd u ratio do not follow patterns predicted from thermodynamics though the water column is suboxic these four redox sensitive elements indicate that the sediments are anoxic the implication for paleostudies is that a trace metal sediment signature that indicates anoxic conditions is not necessarily attributable to an anoxic water column

the influence of geological factors on the concentration of boron in australian and canadian coals abstract the concentration of boron in australian and canadian coals determined using atomic emission spectrometry aes inductively coupled plasma spectrometry icp aes and prompt gamma ray spectrometry is summarized in order to assess the variation of b content in coal with respect to rank age geological setting in seam and stratigraphic and the degree of paleosalinity of the coal forming environment this study indicates that no or very complex relations exist between boron and rank subbituminous to anthracite variations of b with ash content for canadian coals of different age devonian to oligocene eocene indicate that the b content of coals is not governed by the age of the coal there is some evidence of variation of b with maceral content in canadian coals particularly as related to the inertinite and vitrinite content of coals the b content of coal seams is sensitive to the environment of deposition with b contents remaining relatively stable and within the range of values designated for each depositional setting however b values may show variation in the same seam laterally due to changes of the environment of deposition and or the enrichment of b by a secondary source the vertical variation of b in a coal bearing section or strata is related to depositional environment and lithology of rock there is often little variation in b content for coal layers as compared to the partings dirt bands the b content of partings in a coal bearing strata may vary greatly as compared to the coal seams after reappraising earlier work and on the basis of more recent studies on australian and canadian coals it is proposed that the following ranges of values for b in coal indicate the degree of marine influence during the early stages of coalification up to 50 ppm b freshwater influenced coals 50 110 ppm b mildly brackish water influenced coals 110 ppm b brackish water influenced coals using these criteria assessments are given for the degree of marine influence on canadian and australian coals

processes controlling the distribution and cycling of manganese in the oxygen minimum zone of the arabian sea abstract vertical and horizontal distributions of dissolved and particulate manganese were investigated in the arabian sea northwestern indian ocean during the 1995 spring intermonsoon period march april us jgofs process cruise 2 tn045 the region is characterized by an intense basin wide oxygen minimum zone omz that strongly influences the manganese distribution in the omz two distinct dissolved mn d mn maxima were observed at depths of 200 300 m and 600 m respectively the latter peak displayed concentration maxima of approximately 6 nanomolar and was largely confined to stations north of 19 n latitude stations n2 n7 this mid depth maximum was associated with the low oxygen core of the omz o 2 saager et al 1989 geochimica et cosmochimica acta 53 2259 2267 this signal was largely absent at stations along the southern transect likely due to oxidative scavenging of d mn to the suspended particulate phase mid depth particulate mn maxima at some southern stations stations s4 s11 appear to be remnants of this feature the upper d mn maximum 200 300 m depth was more widely distributed than the 600 m peak with d mn concentrations of 3 to as high as 8 nm at most stations east of about 62 e longitude the signal was everywhere correlated with the secondary nitrite maximum at stations within the main denitrification zone delineated by naqvi 1991 nepheloid layers presumably bacterial also were associated with this depth interval particulate mn profiles displayed corresponding concentration minima and low mn al and reactive refractory mn ratios for this same depth interval suggesting reductive dissolution of mn oxyhydroxides these observations imply that in situ microbially mediated processes may be the predominant source of d mn in the upper omz while horizontal advection is more important deeper in the water column

glacial interglacial variability in the eastern tropical north pacific oxygen minimum zone recorded by redox sensitive trace metals 1 changes in the intensity of the oxygen minimum zone omz in the eastern tropical north pacific over the past 140 kyr are recorded as enrichments and depletions of redox sensitive metals in sediments of two piston cores one within and one below the modern omz from the continental margin off mazatlan mexico 22 41 n 106 28 w concentrations of al 7 7 0 6 ti 0 37 0 03 fe 3 1 0 25 mn 320 31 ppm and ba 560 82 ppm in core nh15p within the omz at 420 m water depth were relatively constant over the last 110 kyr in contrast concentrations of cd 4 8 2 ppm cu 29 8 9 1 ppm u 9 1 3 7 ppm mo 12 1 5 0 ppm v 138 2 51 9 ppm and re 45 8 25 5 ppb were all at least 30 higher in interglacial stages compared to glacial stages concentrations of al 7 4 0 3 ti 0 35 0 03 fe 3 5 0 4 and mn 385 77 ppm in core nh22p below the omz at 2025 m water depth were comparable to those in core nh15p while concentrations of ba 1662 292 ppm were about a factor of three higher in contrast concentrations of cd 0 9 0 3 ppm u 6 6 0 9 ppm mo 3 2 1 2 ppm v 81 8 10 1 ppm and re 25 4 12 ppb were lower in sediments of comparable age than the concentrations of these same metals in the omz core and the differences in their concentrations over glacial interglacial cycles were less pronounced than those in shallower core comparison of the nonlithogenic fraction of metals in the sediments with their estimated contribution from plankton suggests that organic matter is probably the major source of cu ba and perhaps cd to the sediment whereas the indirect effects of organic carbon and low bottom water oxygen concentrations on sediment redox state appear to be more important controls on the distributions u re mo and v changes in the depth at which re and mo precipitated in the sediments and in the re mo ratio suggest that the redox state of the surface sediment and overlying water at both core depths varied over time re and mo removal depths were shallower and re mo ratios were lower at the omz site than in deeper water suggesting that a more reducing environment prevailed over time at the shallower site although the redox state of the waters and sediment at both sites varied over glacial interglacial cycles the omz likely was never anoxic in the last 140 kyr this variability in redox state could be attributed to changes in regional export productivity changes in ocean circulation or a combination of both processes a paleoproductivity reconstruction from biogenic ba data suggests that glacial productivity was considerable lower than it was during interglacial stages model results suggest that the oxygen penetration depth an indicator of sediment redox state changed less than 1 cm as a result of the change in productivity changes in oxygen penetration depth estimated from re and u removal depths are significantly larger suggesting that changes in ventilation are a more important control on sediment redox state overall trace metal results confirm the tight coupling between ocean circulation marine productivity and global change

molybdenum vanadium and uranium weathering in small mountainous rivers and rivers draining high standing islands abstract rivers draining high standing islands hsis and small mountainous rivers smrs are known to have extremely high sediment fluxes and can also have high chemical weathering yields which makes them potentially important contributors to the global riverine elemental flux to the ocean this work reports on the riverine concentrations ocean flux and weathering yields of molybdenum mo vanadium v and uranium u in a large number of small but geochemically important rivers using 338 river samples from ten lithologically diverse regions these redox sensitive elements are used extensively to infer paleo redox conditions in the ocean and mo and v are also important rock derived micronutrients used by microorganisms in nitrogen fixation unlike in large river systems in which dissolved mo has been attributed predominately to pyrite dissolution mo concentrations in these rivers did not correlate with sulfate concentrations v was found to correlate strongly with si in terrains dominated by silicate rocks but this trend was not observed in primarily sedimentary regions many rivers exhibited much higher v si ratios than larger rivers and rivers draining young quaternary volcanic rocks in nicaragua had much higher dissolved v concentrations mean 1306 nm than previously studied rivers u concentrations were generally well below the global average with the exception of rivers draining primarily sedimentary lithologies containing carbonates and shales fluxes of u and mo from igneous terrains of intermediate composition are lower than the global average while fluxes of v from these regions are higher and up to two orders of magnitude higher in the nicaragua rivers weathering yields of mo and v in most regions are above the global mean despite lower than average concentrations measured in some of those systems indicating that the chemical weathering of these elements are higher in these smr watersheds than larger drainages in regions of active boundaries with andesite dacite lithologies rivers draining young pleistocene rocks had higher concentrations than did older miocene pliocene rocks of a similar composition this work shows that weathering yields of mo v and u from smrs are slightly higher than from large rivers and the age of igneous lithologies in these regions exhibits a measurable control on riverine concentrations of these elements

bottom water oxygenation history in southeastern arabian sea during the past 140 ka results from redox sensitive elements the concentrations of multiple redox sensitive elements such as re u mo cd v sb and tl were determined in sediments from the southeastern arabian sea 9 o 21 n 71 o 59 e to understand the bottom water oxygenation history throughout the past 140 ka the enrichment of redox sensitive elements re u cd and sb above average crustal abundances suggests that the last glacial maxima 17 48 ka stadials of marine isotope stage mis 5 5b and 5d and glacial termination gt ii 133 ka were associated with suboxic bottom water conditions sediments deposited during these suboxic conditions show the highest re content up to 54 ppb normalized to a carbonate free basis which is highly enriched over average continental crust 0 4ppb and these sediments appear to be the major sink for the global mass balance estimation marine isotope stages 1 3 4 and interstadials of mis 5 5a 5c 5e were all associated with near oxic conditions overall the lack of enrichment of mo and v above crustal abundance and a high re mo ppm ppm ratio avg 18 2x10 3 suggest that sediments of the southeastern arabian sea never contained free h2s during the last 140 ka these changes in the bottom water oxygen content can be related to the oceanic circulation pattern during this time and in part are reflected in relationships between the timing of redox changes and paleoproductivity proxies

rhenium in the black sea comparison with molybdenum and uranium rhenium concentrations were measured in the black sea to determine the behavior of this redox sensitive element in an anoxic basin under reducing conditions re is removed from solution leading to its depletion from black sea deep waters compared with uranium water column re and mo profiles show evidence of removal from mid depths suggesting that these elements are scavenged either in the water column or slope sediments to a greater degree than u black sea surface waters are enriched in re reflecting re in rivers draining into the northern black sea that are enhanced up to 80 fold over other large world rivers this enrichment is most likely anthropogenic and may be due to coal burning in the region a simple two box model is used to demonstrate that re concentrations in the black sea are not in steady state with respect to current riverine inputs and authigenic fluxes riverine inputs of u and mo are not as significant perhaps reflecting the fractionation of re from the other elements during a high temperature combustion process re2o7 is volatile above 270 c

turbulent mixing in a strongly forced salt wedge estuary up to about 400 m 3 s 1 above which a majority of the mixing occurs offshore observed buoyancy fluxes were more consistent with the k turbulence closure than the mellor yamada closure and more total mixing occurred in the estuary with k calculated buoyancy fluxes were sensitive to horizontal grid resolution as a lower resolution grid yielded less integrated buoyancy flux in the estuary and exported lower salinity water but likely had greater numerical mixing

modeling and understanding turbulent mixing in a macrotidal salt wedge estuary 1 a high resolution three dimensional numerical simulation is performed with the parallel unstructured grid suntans model to study the spatiotemporal dynamics of turbulent mixing in a shallow macrotidal salt wedge estuary that experiences periodic mixing and strong stratification unresolved vertical mixing is parameterized with the k kl closure scheme with the canuto a stability functions based on a careful comparison of multiple two equation closure schemes and stability functions via the generic length scale approach the predictions of velocity salinity richardson number and reynolds stress are in good agreement with field observations and the top and bottom salinity predictions achieve skill scores of 0 86 and 0 91 respectively the model shows that the salt wedge starts to strengthen upstream at the beginning of weak ebb and gradually expands downstream during the weak tide mixing is most active along a density interface during the weak ebb while it is most active in a bottom mixed layer during weak flood consistent with the findings inferred from the observations stratification decays during the strong ebb in a mixing event along the horizontal extent of the salt wedge while it is also being advected offshore local mixing is shown to account for roughly half of the decay rate of the stratification in this process numerical experiments are performed to investigate the response of stratification and mixing to changes in the magnitude of the buoyancy high sensitivity is shown under intermediate levels of stratification that occur in the real system which becomes considerably weaker under more extreme conditions

petrology of indus river sands a key to interpret erosion history of the western himalayan syntaxis the indus river has been progressively transformed in the last decades into a tightly regulated system of dams and channels to produce food and energy for the rapidly growing population of pakistan nevertheless indus river sands as far as the delta largely retain their distinct feldspar and amphibole rich composition which is unique with respect to all other major rivers draining the alpine himalayan belt except for the brahmaputra both the indus and brahmaputra rivers flow for half of their course along the india asia suture zone and receive major contributions from both asian active margin batholiths and upper amphibolite facies domes rapidly exhumed at the western and eastern himalayan syntaxes compositionofindussandschangesrepeatedlyandmarkedlyinladakhandbaltistan indicatingoverwhelmingsedimentflux from each successive tributary as the syntaxis is approached provenance estimates based on our integrated petrographic mineralogical data set indicate that active margin units karakorum and transhimalayan arcs provide 81 of the 250f50 10 6 t ofsedimentsreachingthetarbelareservoireachyear partitioningofsuchfluxamongtributariesandamongsourceunitsallowsus to tentatively assess sediment yields from major subcatchments extreme yields and erosion rates are calculated for both the karakorum belt up to 12 500f4700 t km 2 year and 4 5f1 7 mm year for the braldu catchment and nanga parbat massif 8100f3500t km 2 yearand3 0f1 3mm year thesevaluesapproachdenudationratescurrentlyestimatedforsouthkarakorum and nanga parbat crustal scale antiforms and highlight the major influence that rapid tectonic uplift and focused glacial and fluvial erosion of young metamorphic massifs around the western himalayan syntaxis have on sediment budgets of the indus system detailed information on bulk petrography and heavy minerals of modern indus sands not only represents an effective independent method to constrain denudation rates obtained from temperature time histories of exposed bedrock but also

dissolved rhenium in the yamuna river system and the ganga in the himalaya role of black shale weathering on the budgets of re os and u in rivers and co 2 in the atmosphere extensive measurements of dissolved re and major ion abundances in the yamuna river system yrs a major tributary of the ganga have been performed along its entire stretch in the himalaya from its source near the yamunotri glacier to its outflow at the foothills of the himalaya at saharanpur in addition re analysis has been made in granites and precambrian carbonates some of the major lithologies of the drainage basin these data coupled with those available for black shales in the lesser himalaya allow an assessment of these lithologies contributions to the re budget of the yrs the re concentrations in the yrs range from 0 5 to 35 7 pm with a mean of 9 4 pm a factor of 4 higher than that reported for its global average concentration in rivers dissolved re and cations na k ca mg are strongly correlated in the yrs indicating that they are released to these waters in roughly the same proportion throughout their course the re cations in most of these rivers are one to two orders of magnitude higher than the re na k mg ca measured in granites of the yamuna basin this leads to the conclusion that on average granites crystallines make only minor contributions to the dissolved re budget of the yrs on a basin wide scale though they may be important for rivers with low dissolved re similarly precambrian carbonates of the lesser himalaya do not seem to be a major contributor to dissolved re in these rivers as their re ca mg is much less than those in the rivers the observation that re concentrations in rivers flowing through black shales and in groundwaters percolating through phosphorite black shale carbonate layers in phosphorite mines are high and that re and so4 are significantly correlated in yrs seems to suggest that the bulk of the dissolved re is derived from black shale carbonaceous sediments material balance considerations based on average re of 30 ng g 1 in black shales from the lesser himalaya require that its abundance in the drainage basin of the yrs needs to be a few percent to yield average re of 9 4 pm furthermore the positive correlation between re and cations would require that these re rich sediments e g black shales and re poor lithologies e g crystallines precambrian carbonates contribute re and cations in roughly the same proportion throughout the drainage basin the available data on the abundance and distribution of black shales in the basin are not adequate to test if these requirements can be met the annual fluxes of dissolved re at the base of the himalaya from the yamuna are 150 mol at batamandi and 100 mol at saharanpur compared to 120 mol from the ganga at rishikesh the total flux from the yamuna and the ganga account for 0 4 of the global riverine re flux much higher than their contribution to global water discharge this is also borne out from the mobilization rate of re 1 to 3 g km 2 y 1 in the ganga and yamuna basins in the himalaya compared to the global average of 0 1 g km 2 y 1 black shale weathering can also significantly influence the budgets of os and u in rivers and co2 in rivers and the atmosphere using dissolved re in rivers as a proxy it is estimated that 6 9 108 kg y 1 of black shales are being weathered in the ganga and yamuna basins in the himalaya weathering of such amounts of black shales can account for the reported concentrations of os and u in these rivers furthermore if the weathering results in the conversion of organic carbon in the black shales to co2 it would release 2 105 mol of co2 km 2 y 1 in the yamuna and ganga basins in the himalaya comparable to the co2 consumption from silicate weathering

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

reconstructing paleosalinity from δ18o coupled model simulations of the last glacial maximum last interglacial and late holocene reconstructions of salinity are used to diagnose changes in the hydrological cycle and ocean circulation a widely used method of determining past salinity uses oxygen isotope ow residuals after the extraction of the global ice volume and temperature components this method relies on a constant relationship between ow and salinity throughout time here we use the isotope enabled fully coupled general circulation model gcm hadcm3 to test the application of spatially and time independent relationships in the reconstruction of past ocean salinity simulations of the late holocene lh last glacial maximum lgm and last interglacial lig climates are performed and benchmarked against existing compilations of stable oxygen isotopes in carbonates oc which primarily reflect ow and temperature we find that hadcm3 produces an accurate representation of the surface ocean oc distribution for the lh and lgm our simulations show considerable variability in spatial and temporal ow salinity relationships spatial gradients are generally shallower but within 50 of the actual simulated lh to lgm and lh to lig temporal gradients and temporal gradients calculated from multi decadal variability are generally shallower than both spatial and actual simulated gradients the largest sources of uncertainty in salinity reconstructions are found to be caused by changes in regional freshwater budgets ocean circulation and sea ice regimes these can cause errors in salinity estimates exceeding 4 psu our results suggest that paleosalinity reconstructions in the south atlantic indian and tropical pacific oceans should be most robust since these regions exhibit relatively constant ow salinity relationships across spatial and temporal scales largest uncertainties will affect north atlantic and high latitude paleosalinity reconstructions finally the results show that it is difficult to generate reliable salinity estimates for regions of dynamic oceanography such as the north atlantic without additional constraints

paleosalinity in a brackish lake during the holocene based on stable oxygen and carbon isotopes of shell carbonate in nakaumi lagoon southwest japan abstract based on the relationship between salinity and 18 o and 13 c of modern shells in the lake nakaumi shinji lagoon system southwestern japan where the salinity changes regularly from ca 1 psu to 34 psu a paleosalinity record for nakaumi lagoon during the holocene has been derived from bulk mollusk shell 18 o and 13 c data the robust relationships between the salinity and modern shell 18 o ar and 13 c ar aragonite were used to calibrate the paleosalinity reconstruction the salinity relationships are expressed by the regressions salinity psu 3 86 18 o ar vpdb 33 9 n 18 r 0 978 salinity psu 4 05 13 c ar vpdb 31 8 n 18 r 0 977 applying these equations to bulk shell 18 o ar and 13 c ar in the 20 m sediment core very similar salinity histories were reconstructed from either oxygen or carbon isotope ratio data at the beginning of lacustrine sediment deposition 8000 7500 14 c yr b p paleosalinity of the bottom water in the central portion of nakaumi lagoon increased from 22 to 32 psu during the 7500 5500 yr b p interval which approximately corresponds to the holocene climatic optimum and high sea level stand salinity ranged from 27 to 37 psu after 5500 yr b p salinity lessened under the cooling climate with a minimum value of 24 27 psu at 3000 1000 yr b p the results show a consistent relationship between climate change sea level and salinity in the lagoon during the holocene

a 36 kyr geochemical record from the sea of japan of organic matter flux variations and changes in intermediate water oxygen concentrations intervals of organic c and carbonate rich laminated sediments occur in the sea of japan with roughly the same frequency as temperature changes observed in greenland ice cores providing clear evidence of rapid oceanographic change during the past 36 kyr planktonic foraminiferal 18o data suggest that only the laminated sediments deposited during the last glacial maximum lgm and perhaps one other interval formed during a period of increased water column stratification sedimentary re and mo data are consistent with bottom waters that were sulfidic during the lgm and suboxic during other laminated intervals results of a numerical model of corg and re burial are consistent with a mechanism whereby an increased corg flux to the seafloor drove oxygen concentrations toward depletion during times of deposition of the suboxic laminated intervals such a process could have resulted from increased upwelling driven either by increased deep water formation due to colder and or more saline surface waters or by stronger northeasterly monsoonal winds

impact of water mass mixing and dust deposition on nd concentration and e nd of the arabian sea water column abstract the concentration and isotopic composition e nd of dissolved nd have been measured in the sub oxic denitrifying water column of the eastern arabian sea to explore the impact of water mass mixing and release from particles dissolved nd in the north eastern arabian sea is more radiogenic e nd 7 to 10 compared to its south eastern part e nd 11 to 15 suggesting contribution of nd from the bay of bengal bob the vertical profile of nd typically show higher values in surface waters 15 8 27 8 pmol kg followed by minima 12 18 pmol kg in the subsurface waters 200 300 m and a gradual increase with depth thereafter the nd concentration does not seem to show any changes in the sub oxic layers suggesting no impact of the sub oxic denitrifying conditions in this oceanic region on the biogeochemistry of nd the enrichment of nd in surface waters can be explained either by supply from high nd low salinity waters from the bob to the arabian sea via the east india coastal current eicc or alternatively the nd surface excess can be result of release from aeolian dust depositing over the sea surface inverse modeling computations suggest that in addition to nd contributed from water mass mixing some additional excess nd nd xs is required to balance the nd inventory in the water column there is significant nd xs in the surface waters of the north eastern arabian sea with e nd 6 similar to that of dust depositing over the arabian sea the fractional solubility of nd released from the aeolian dust was estimated to be varying from 3 to 17 for excess nd inventory per unit area nd xs of 20 g m 2 with nd ranging from 1 to 3 years this study highlights the significance of aeolian dust deposition in controlling the abundance and distribution of nd in the arabian sea the western arm of the northern indian ocean lying in the proximity to the arid landmass and characterized by high lithogenic aeolian dust deposition

why terrestrial coals cannot be dated using the re os geochronometer evidence from the finnmark platform southern barents sea and the fire clay coal horizon central appalachian basin abstract coal horizons in terrestrial sedimentary sections are key to understanding the structural and thermal evolution of sedimentary basins precise and accurate age information for coal horizons can define correlations and the temporal evolution of sedimentary successions while the biostratigraphy for coal horizons yields relative ages tied to radiometric ages through the continuously refined geological time scale direct radiometric ages of coal horizons have been derived only from tonsteins lithified ash beds the re os geochronometer has been proven to record accurate and precise depositional ages for sedimentary rocks rich in organic matter however the reliability of the re os geochronometer has not yet been assessed for coals deposited in strictly terrestrial environments here in order to test the re os geochronometer we measure the re os concentrations and isotopic composition of terrestrial coals from two distinct environments the finnmark platform southern barents sea and the central appalachian basin cab samples from the finnmark platform soldogg formation also include an adjacent organic rich shale horizon the shale and two coal horizons were also analysed for total organic carbon toc and rock eval data results show that the soldogg coals and shale reached the oil generation widow tmax 448 2 c with type iii or mixed type ii iii organic matter supporting the model for deposition in overbank deposits in a fluvial setting in contrast the fire clay coals in the cab were deposited in a broad expanse of mires average re 0 5 0 4 ng g and os 23 26 pg g concentrations of terrestrial soldogg and fire clay coals are similar to those of terrestrial maghara coal and a few orders of magnitude lower than the marine influenced matewan coal elevated re os ratio os common os os corrected for ingrowth of 187os since deposition of the sample for the fire clay coals suggests highly reducing and or euxinic conditions prevailing in the water column of the extensive carboniferous peat forming mire in which these coals were deposited in contrast lower re os for soldogg coals highlight less reducing conditions likely in a short lived mire in a dynamic braided stream system re and os concentrations of terrestrial coals are on the order of re and os of plant materials and river sediments suggesting that debris from plant materials and weathered continental crust are significant contributors of re and os to terrestrial coals with some contribution from water column of the coal mire this study is the first attempt to apply the re os geochronometer on terrestrial coals in case of the soldogg coals and shale the 187re 188os vs 187os 188os relationship displays scatter with no discernible linear trend the scatter is ascribed to heterogeneity in the initial 187os 188os ratios osi and lack of post depositional isotopic equilibration during subsequent diagenesis for the fire clay coals 187os 188os and 187re 188os are well correlated linear regression of the data however does not yield a geologically reasonable age rather the linear relationship results from binary mixing between two end members the fire clay coal and tonstein suggesting that re os systematics of terrestrial coals depositing very close to tonstein beds can be significantly disturbed we conclude that the post depositional equilibration with a large re os reservoir as with a marine incursion is necessary to record a meaningful re os radiometric age for the coals

geochemistry of boron in bulgarian coals a set of 466 individual full channel samples coals coaly shales and partings of thirteen bulgarian coal deposits as well as vitrain lenses gagatite and coalified woods embedded in sedimentary rocks have been analyzed by atomic emission spectroscopy the deposits consist of lignites subbituminous and bituminous coals the average boron content ranges from 15 to 164 ppm in the coals the boron content of the individual coal samples ranges from 2 to 164 ppm about 86 of the samples have a b content from 2 to 110 ppm which corresponds to the most probable interval of concentration for coals worldwide the boron content is not related to rank the lignites have the lowest boron content some of the vitrain and xylain samples studied are enriched in boron in comparison with the whole coal samples boron occurs in both organic borg and inorganic binorg forms excluding one deposit the boron content in the ash correlates negatively with the ash content whereas in coals it usually slightly increases with increasing ash content organically associated b dominates in the low ash coals and in the deposits enriched in boron the coals of the burgas deposit have the highest b content which is in agreement with the geological evidence for marine influence during the early stages of coalification the distribution of b is also independent of other geological factors

contrasting behavior of tungsten and molybdenum in the okinawa trough the east china sea and the yellow sea by using catalytic current polarography and high resolution inductively coupled plasma mass spectrometry w and mo in seawater were determined in the okinawa trough a backarc rift and in the east china sea and the yellow sea mo was distributed conservatively throughout the study area and its salinity normalized concentration was 104 6 nm n 105 w was also uniformly distributed south of the kuroshio current 56 7 pm n 51 anomalous high concentrations of w maximum 254 pm were found in the iheya graben in the middle okinawa trough gt 1 000 m depth which were probably supplied by hydrothermal activity the concentrations of mo and w in the east china sea and the yellow sea showed linear correlation with salinity 26 lt s lt 35 the mo data can be explained by mixing of seawater and river water of the changjiang mo 10 nm qu et al 1993 however the values of w extrapolated to s 0 were largely different between two cruises 1 200 pm in may june 1987 and 540 pm in june 1994 and much higher than the reported concentrations of 160 pm for world rivers by turekian 1969 and 30 pm for unpolluted japanesemore rivers by sohrin et al 1989 moreover significantly high w was observed in the bottom water at stations near the changjiang river estuary and the western yellow sea while these data may suggest that w is released from the anoxic sediments of the continental shelf more data are needed to elucidate the mechanism controlling the distribution of w less

internal hydraulics and mixing in a highly stratified estuary shipboard acoustic doppler current profiler and conductivity temperature depth data obtained during highly stratified conditions in the hudson river estuary along a section of variable width and breadth are presented the observations emphasize tidal period asymmetries in the vertical structure of current and salinity however these asymmetries exhibit significant along channel structure which is determined by channel morphology during the ebb the flow is linearly sheared and steep halocline slopes in the vicinity of channel contractions are maintained by momentum advection a minimum in vertical shear across the pycnocline occurs in channel contractions during food the pycnocline sharpens and flattens with a middepth velocity maximum embedded in the pycnocline which separates a stratified surface layer from a bottom mixed layer the along channel structure in vertical shear is consistent with a lateral vorticity equation estimates of richardson numbers suggest that vertical mixing across the pycnocline is enhanced downstream of channel contractions

u th dating of carbonate platform and slope sediments absolute chronology of marine sediment beyond the 14c age range provides a test for models of climate change and has many other applications u th techniques have been used for such chronology by dating corals but extending these techniques to marine sediment is complicated by the presence of significant initial 230th both in detrital material and scavenged from seawater in this study we investigate four methods of solving the initial 230th problem for a particular type of marine sediment the aragonite rich sediments of carbonate platforms and slopes bulk sediment u th analyses can be corrected for initial th to yield ages with 2 to 3 kyr precision for highstand periods when sediment aragonite contents are particularly high uncertainty on the corrections causes inadequate precision for sediment from other periods however removal of scavenged th before analysis would enable a dramatic increase in this precision but has not proved successful despite a range of chemical leach approaches using heavy liquids to separate the various carbonate minerals found in bahamas sediment enables an isochron approach to correct for initial th but the presence of initial th from two sources requires correction or removal of one source of initial th before the other is deconvolved by the isochron quantitative removal of detrital material before isochron analysis proves a successful approach such isochron data demonstrate that although sediment remains closed to u th on a centimetre scale nuclides are moved from grain to grain by recoil such intergrain exchange is expected to be observed in all sediments containing mineral grains with different u concentrations measured 234u 238u allows the recoil movement to be corrected and results in isochron ages with precision sometimes as low as 3 kyr the accuracy of this approach has been proved by dating samples within the 14c age range sediments spanning the penultimate deglaciation have also been dated after a small correction for bioturbation the age for this event is found to be 135 2 3 5 ka this date is 8 kyr before the peak in northern hemisphere insolation and suggests that deglaciation is initiated by a mechanism in the southern hemisphere or tropics this isochron approach shows considerable promise for dating of sediments older than this event which will provide further information about the timing and mechanisms of global climate change

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

tide induced variation of the dynamics of a salt wedge estuary abstract the time variations of the salt wedge intrusion in the fraser estuary british columbia were monitored during a variety of tidal and run off conditions using instruments and sampling methods that provided high resolution of the velocity and water properties in space and time the salt wedge was found to vary considerably in position and vertical structure through the tidal cycle due to the interaction of the tidal flow with the density driven motion of the salt wedge during the flood the salt wedge progressed up the estuary as a gravity current while during the ebb the salinity structure was eroded by shear instability the difference in character of the flow between flood and ebb is attributed to the transition between a subcritical and supercritical internal froude number during flood tide the internal state is subcritical and the estuarine shear flow is maintained with a small amount of vertical mixing while in the supercritical ebb flow vertical shears become so large that the pycnoc

hydraulics and mixing in a laterally divergent channel of a highly stratified estuary author posting american geophysical union 2017 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 122 2017 4743 4760 doi 10 1002 2016jc012455

role of straining and advection in the intratidal evolution of stratification vertical mixing and longitudinal dispersion of a shallow macrotidal salt wedge estuary 1 a month of flow observations in the snohomish river estuary reveals the complex intratidal and fortnightly stratification mixing and dispersion dynamics in this macrotidal shallow salt wedge estuary system both salt wedge propagation and concomitant straining of the density field dominate temporal and spatial variations in stratification leading to intratidal variability of shear and mixing that differs in important ways from observations in partially mixed estuaries bottom generated turbulent kinetic energy production is enhanced during spring tides and acts in concert with straining to counteract advection and minimize vertical stratification during the spring flood tides this bottom generated mixing contributes to a buoyancy flux near the top of a well mixed layer during strong flood tides during strong ebb tides interfacial shear production and buoyancy flux occur along the sharp straining enhanced interface just before the system becomes well mixed longitudinal dispersion is less sensitive to the spring neap cycle yet exhibits strong intratidal variability reduced longitudinal dispersion is observed during the large floods relative to the rest of the tidal cycle behavior we attribute to a lack of vertical shear overall ebb tide advection and straining enhance stratification and longitudinal dispersion and allow for interfacial mixing intratidal variability which varies on the spring neap scale is a dominant feature of this estuary suggesting the importance of intratidal processes and tidally varying mixing coefficients in similar strongly stratified strongly forced estuaries

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