fresh water seepage and pore water recycling on the seafloor sagami trough subduction zone japan we collected 19 samples of bottom sea water including 8 samples of shimmering fluid using the japanese submersible shinkai 2000 in the bathyal calyptogena community area the hatsushima area along sagami trough at the northern end of the philippine sea plate in order to clarify the source of fluid seepage shimmering fluid samples showed a maximum temperature of 11 6 c which is about 9 c higher than the ambient sea water the fluid chemistry of these samples is summarized as follows 1 alkalinity h2s sio2 nh4 co2 and ch4 show enrichment and cl so4 k na mg and ca show depletion compared with ambient sea water 2 cl depletion is about 20 and 3 the content and 3he4he ratio of dissolved helium show little anomaly compared with ambient sea water the observed chemical composition and temperature of the fluid is well explained by mixing of sea water pore water and land derived groundwater with a temperature of about 40 c and a seeping flux of about 400 m3 per day a preliminary estimation of the global chemical flux implies that groundwater discharge to the ocean including pore water recycling is an important factor in controlling ocean chemistry

coral oxygen isotope evidence for recent groundwater fluxes to the australian great barrier reef 1 high resolution measurements of sr ca and 18o 16o in mid holocene and modern porites corals were used to derive a history of freshwater fluxes to the australian great barrier reef gbr interannual variations in dry season seawater 18o 16o evident in the coral record for the late 20th century but not 6200 years ago correlate with variations in groundwater recharge of coastal aquifers the results suggest that a delay in groundwater recharge following the post glacial sea level rise and recent deforestation for agriculture may have lead to higher land sea hydraulic gradients and greater groundwater discharge to the gbr today oxygen isotope mass balance calculations show that 3 in mixing of co2 enriched groundwater could raise the partial pressure of co2 in coastal seawater by 90 atm following strong summer monsoons consequently modern nearshore corals in the gbr may now be subjected to lower aragonite saturation states which could reduce coral calcification and contribute to recent reef degradation

techniques for precise mapping of 226ra and 228ra in the ocean improvements in the analyses of sup 226 ra and sup 228 ra in seawater made possible by better extraction and processing techniques reduce significantly the errors associated with these measurements these improvements and the extensive sampling for ra isotopes conducted on the tto north atlantic study should enable us to use the distribution of sup 228 ra to study mixing processes on a 3 15 year time scale in both the upper and deep north atlantic the sup 228 ra profiles already analyzed show a closer resemblance to geosecs tritium data than to tto tritium data in the upper ocean this is because the transient tracer tritium was responding on a 10 year time scale during geosecs and a 20 year time scale during tto the steady state tracer sup 228 ra should always respond on a time scale of 8 years thus the sup 228 ra data obtained on tto should provide a means to extend the features of the geosecs tritium field to the regions of the tto study the sup 226 ra data are of high enough quality to identify features associated with different water masses changes in the positions of the deep water masses since the geosecs cruise are revealed by the sup 226 radata

the influence of ambient groundwater discharge on exchange zones induced by current bedform interactions summary we use numerical modeling to investigate the interactions between laminar flow in a water column current bedform induced flow in underlying permeable sediments and discharge of deep groundwater to the water column groundwater discharge reduces the spatial extent of current induced exchange zones within the sediments and may completely prevent the development of current bedform induced flow at high groundwater discharge although exchange zone size is reduced by groundwater discharge the reduction in exchange flux is not significant suggesting reduced residence times of materials cycled through these smaller zones fluid exchange zones tend to be centered around the reattachment points of eddies that also mark the location of flow divides within the sediments while deep groundwater is discharged preferentially along troughs exchange zone depth and the water column reynolds number are functionally related through a morgan mercer flodin model the relationship between the current induced flux through the sediments and the reynolds number is described by low order monotonic polynomial functions

spatial distribution and budget for submarine groundwater discharge in eckernforde bay western baltic sea submarine groundwater discharge sgd from subseafloor aquifers through muddy sediments was studied in eckernforde bay western baltic sea the fluid discharge was clearly traced by 222 rn enrichment in the water column and by the chloride profiles in pore water at several sites a considerable decrease in chloride to levels less than 10 of bottom water concentrations was observed within the upper few centimeters of sediment studies at 196 sites revealed that 22 of the seafloor of the bay area was affected by freshwater admixture and active fluid venting a maximal discharge rate of 9lm 22 d 21 was computed by modeling pore water profiles based on pore water data the freshwater flow from subseafloor aquifers to eckernforde bay was estimated to range from 4 3 10 6 to 57 3 10 6 m 3 yr 21 therefore 0 3 4 1 of the water volume of the bay is replaced each year owing to negligible surface runoff by rivers sgd is a significant pathway within the hydrological cycle of this coastal zone high resolution bathymetric data and side scan sonar surveys of pockmarks depressions up to 300 m long were obtained by using an autonomous underwater vehicle steep edges with depths increasing by more than 2 m within 8 10 m in lateral directions equivalent to slopes with an angle of as much as 118 were observed the formation of pockmarks within muddy sediments is suggested to be caused by the interaction between sediment fluidization and bottom currents fluid discharge from glacial coastal sediments covered by mud deposits is probably a widespread but easily overlooked pathway affecting the cycle of methane and dissolved constituents to coastal waters of the baltic sea

florida straits deglacial temperature and salinity change implications for tropical hydrologic cycle variability during the younger dryas temperature and d 18 osw a proxy for surface salinity records based on mg ca ratios and oxygen isotope measurements in the planktonic foraminifera globigerinoides ruber from a sediment core located on the western margin of the florida straits as a proxy for meltwater discharge influence on florida straits surface water salinity we also measured ba ca ratios in g ruber from the same core results show that riverine influence on florida straits surface water started by 17 2 ka bp and ended by 13 6 ka bp 600 years before the start of the younger dryas yd cold interval the initiation of the yd is marked by an abrupt increase in florida straits d 18 osw values indicating a shift to elevated sea surface salinity occurring in 130 years most likely resulting from increased regional aridity and or reduced precipitation in order to resolve the timing of tropical atmospheric circulation change relative to amoc variability across this transition we compare the timing of surface water changes to a recently published record of florida current variability in the same core reconstructed from benthic oxygen isotope measurements we find synchronous changes in atmospheric and ocean circulation on the transition into the yd consistent with an abrupt reduction in amoc as the driver of tropical atlantic atmospheric circulation change at this time

identification of rain freshened plumes in the coastal ocean using ra isotopes and si office of global programs noaa silver spring maryland abstract two transient plumes of freshened water in the south atlantic bight off the coast of south carolina were measured and mapped during a continental shelf cruise in july 1994 salinity in the plumes was depressed 1 2 parts per thousand compared to surrounding shelf waters one plume was at least 160 kin long 20 kin wide and 5 7 m deep the other was 75 km long 25 kin wide and 5 7 m deep both plumes disintegrated almost completely in 6 days due to mixing or advection away from the sampling area measurement and analysis of short lived ra isotopes and si indicated that the plumes were not caused by river discharge but were rather due to an intense rain event a few days prior to the sampling cruise with only salinity measurements we would have incorrectly concluded that the freshened water was a result of river plumes having entered the shelf the rain was associated with the system that spawned tropical storm alberto we estimate that 220 330 mm of rain fell on the coastal ocean immediately before the cruise accompanying the rain were pesticides and nutrients we estimate that the flux of nitrate from the rain was twice the riverine flux of nitrate to the study area in the month preceding the cruise plumes of freshened water in the coastal ocean may be derived from river runoff or heavy offshore rain events large rivers may cause ocean freshening at scales of over 1000 km atkinson and wallace 1975 ortner et ai 1995 moore et ai 1986 distinguishing the source of the fresh water after the fact is difficult here we employ si and ra tracers previously used to distinguish between amazon derived water and rainfall in the tropical atlantic to identify rainfall as the agent of a freshened plume off the coast of south carolina the estuary shelf ocean exchange experiment esoe was conducted to establish techniques to determine the rate of cross shelf exchange of estuarine and nearshore waters with waters of the middle and outer continental shelf the experiment was conducted in the south atlantic bight sab a misnamed region off the southeast u s coast between cape hatteras and cape canaveral july 6 17 1994 during a prolonged period of vertical shelf stratification esoe was designed to use the distributions of 223ra t 112 11 4d and 224ra t 112 3 66d as an index of the exchange time five shore perpendicular transects between the cape fear river cf and the savannah river sv were sampled from the coastline to the edge of the shelf two transects myrtle beach mb and charleston ch were resampled two more times and the winyah bay transect wb was sampled three more times to determine if the tracer distributions were stable on a 2 week timescale figure 1 illustrates these transects and gives the station locations for the first pass no single river dominates freshwater input to the south atlantic bight sab the savannah santee and pee dee are the largest rivers each discharged 100 500 m3 s i during the

ba ca in neogloboquadrina pachyderma as an indicator of deglacial meltwater discharge into the western arctic ocean 1 down core samples of the planktonic foraminifer neogloboquadrina pachyderma sinistral from the mendeleyev ridge in the western arctic ocean have been analyzed for ba ca and 18o the apparent distribution coefficient for n pachyderma sin is estimated at dba 0 22 0 02 a meltwater event is identified at around 11 8 14c kyr bp and is coincident with elevated ba ca ratios the barium enrichment is believed to be the result of enhanced weathering and erosion following glaciation additionally barium may have desorbed from shelf sediments as sea level rose changes in ba ca correlate with the retreat of the laurentide ice sheet and the evolution of the mackenzie river drainage basin therefore maximum ba ca in arctic surface waters at 11 8 ka may be indicative of an increase in the export of freshwater from the arctic to the north atlantic potentially contributing to the onset of the younger dryas this work suggests that ba ca in planktonic foraminifera may be a useful indicator of the timing and processes associated with deglaciation

geophysical evidence for karst formation associated with offshore groundwater transport an example from north carolina 1 marine geophysical data from long bay north carolina involving a novel combination of electromagnetic and high resolution chirp seismics show evidence of submarine karst formation associated with what has been inferred to be a site of high flux submarine groundwater discharge sgd a substantial distance offshore recently observed temperature and chemical signals from wells in this area provide the basis for the interpretation of the high flux sgd here and they also suggest a terrestrial source for the groundwater and thus a potentially important route for nutrient transport to the oceans our data indicate that karstification is localized to the high flux zone and we suggest that mixing of the chemically distinct but saline groundwater with seawater has resulted in the karstification as karstification increases permeability and flux a positive feedback would tend to progressively enhance submarine groundwater discharge our data reveal a significant local anomaly in apparent porosity a dense block that may have initiated the local focusing of groundwater flow conditions favorable to the formation of similar locally punctuated sites of high flux sgd are likely to exist along the mid to inner shelf of the southeastern united states where carbonate aquifers are prevalent

the behavior of u and th series nuclides in the estuarine environment rivers carry the products of continental weathering and continuously supply the oceans with a broad range of chemical constituents this erosional signature is however uniquely moderated by biogeochemical processing within estuaries estuaries are commonly described as complex filters at land sea margins where significant transformations can occur due to strong physico chemical gradients these changes differ for different classes of elements and can vary widely depending on the geographic location u and th series nuclides include a range of elements with vastly different characteristics and behaviors within such environments and the isotopic systematics provide methods for investigating the transport of these nuclides and other analog species across estuaries and into the coastal ocean there are numerous types and definitions of estuaries see dyer 1973 in this paper it is simply considered to be a region where freshwater and seawater mix to emphasize the chemical focus of the issues involved here this region can either be contained within a river channel or extend onto the shelf with effects often extending well into an adjoining ocean basin fairbridge 1980 these are complex ecological biogeochemical and hydrodynamic systems with strong gradients in the concentrations and composition of micro and macro particulate matter as well as dissolved organic and inorganic species particle reactive radionuclides and trace elements being transported across estuaries are subject to partitioning between the dissolved colloidal and particulate phases the variable chemical nature of the u and th series radionuclides is evident in their distributions in an estuarine environment such radionuclides can effectively serve as tracers to identify the sources fate and transport of particles and colloids as well as other pollutants that behave similarly to these nuclides these nuclides also have a wide range of half lives that can be used to examine processes over various time scales for example th and ra daughter isotopes have

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

tidal variations in groundwater storage and associated discharge from an intertidal coastal aquifer 1 we applied a hydrogeological numerical simulation to investigate spatial and temporal variations in groundwater flow and discharge at a well studied tidal flat margin in the german wadden sea the simulation was forced by high resolution sea level boundary conditions accuracy of the simulation was checked by comparing simulated with measured pressure heads obtained from direct burial pressure sensor measurements overall discharge calculated from the simulation for a time period of almost 12 month averages 0 97 m3 per meter of margin length per tide but may vary significantly most pronounced with the spring neap tide cycle the simulation predicts that the maximum hydraulic gradient at ebb tide controls the magnitude of discharge whereas duration of ebb tide is less important additionally simulated and measured pressure gradients can be used to investigate the influence of varying lithology on the groundwater flow regime the presence of a low permeable holocene silt layer ubiquitous in the study area creates a layered unconfined semiconfined aquifer system both parts of the aquifer are hydraulically connected to the deeply incising tidal creek but show a different response to the tidal forcing groundwater flow in the upper unconfined margin sediments can be described as a circulation of seawater where inflow and outflow are coupled to changes in saturation sediments below the confining layer release groundwater from storage during falling and ebb tide and recharge during rising and high tide we can show that tidally driven water exchange between semiconfined aquifers and coastal waters may have a major impact on total groundwater discharge

chemical signals from submarine fluid advection onto the continental shelf we report unambiguous signals of subsurface fluid input on the continental shelf 40 80 km from shore in water depths of 20 45 m the site of this input is near the continental shelf break off the south carolina coast between 32 33 n and 78 5 79 5 w repeated transects over this area reveal enrichments of 226ra 228ra and ba by factors of 3 4 above ambient ocean concentrations the short lived 223ra and 224ra are enriched by over an order of magnitude the ra and ba enrichments are not caused by up welling of deep water as no such 226ra or ba concentrations occur in the upper 2000 m of the atlantic ocean sediments in the region are largely relic sand and do not offer a viable source for 226ra 228ra and ba enrichments we conclude that the source is the discharge of submarine fluids enriched in 226ra 228ra and ba the salinity of water in the ra ba enriched zone is diluted by 0 2 0 6 relative to water at the same depth farther offshore pronounced salinity and density anomalies characterize one site of active discharge estimates of 226ra and ba concentrations in the fluids and the replacement time of water in the enriched zone suggest the fluid flux is similar to the summertime flow of major rivers in the area the region of ra ba enrichment is also characterized by a strong fluorescence signal indicating high concentrations of chlorophyll in the water it is probable that the leaking fluids supply nutrients that stimulate productivity in the bottom waters which are within the photic zone because the fluorescence signal is restricted to depths greater than 20 m it is unlikely that the signal could be recognized by satellite or aircraft sensors

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

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

solute transport into the jiulong river estuary via pore water exchange and submarine groundwater discharge new insights from 224ra 228th disequilibrium abstract pore water exchange pex and submarine groundwater discharge sgd represent two mechanisms for solute transport from the seabed into the coastal ocean however their relative importance remains to be assessed in this study we pursued the recently developed 224ra 228th disequilibrium approach to quantify pex fluxes of 224ra into the jiulong river estuary china by constructing a full mass balance of water column 224ra we were allowed to put various source terms i e sgd diffusive and advective pore water flow pex and river input in a single context this led to the first quantitative assessment of the relative importance of pex vs sgd in the delivery of solutes into an estuary we carried out two surveys in the jiulong river estuary one in january 2014 winter survey the other in august 2014 summer survey by virtue of a 1 d mass balance model of 224ra in the sediment column we demonstrated that pex fluxes of 224ra were highly variable both temporally and spatially and can change by 1 2 orders of magnitude in our study area moreover we identified a strong correlation between 224ra based irrigation rate and 234th based sediment mixing rate our results highlighted irrigation as the predominant pex process for solute transfer across the sediment water interface total pex flux of 224ra in 1010 dpm d 1 into the jiulong river estuary was estimated to be 22 3 3 0 and 33 7 5 5 during the winter and summer surveys respectively in comparison total sgd flux of 224ra in 1010 dpm d 1 was 11 3 8 6 and 49 5 16 3 in the respective seasons by multiplying the pex fluxes of 224ra by the ratio of the concentration gradients of component 224ra at the sediment water interface we quantified the total pex fluxes of dissolved inorganic carbon dic and nutrients nh4 no3 and h4sio4 into the jiulong river estuary in the meantime net export of dic and nutrients via sgd were estimated by multiplying the sgd fluxes of 224ra by the dic nutrients 224ra ratios in the sgd end members around this area our results revealed that pex driven fluxes of solutes rival net sgd input and river input in an estuary an additional new finding is that water column no3 in the surface estuary was effectively sequestered due to sgd probably as a result of intense denitrification occurring in the anoxic subterranean estuary

thermal regime of dune covered sediments under gaining and losing water bodies 1 we investigate the effects of current bed form induced flow and heat transport through permeable bottom sediments overlain by a marine or terrestrial water column that is gaining or losing deep groundwater heat transport is forced by the diel variation of temperature in the water column the investigation utilizes sequentially coupled simulations of turbulent flow in the water column and darcy flow and heat transport in the sediments the simulations address the question when where and by how much are diel water column temperature variations transmitted into sediments subjected to ambient groundwater discharge this is crucial information for detecting observing and predicting temperature sensitive biogeochemical and ecological processes in the bottom sediments when the groundwater gain or loss is small it has no appreciable effect on temperatures in the sediments which are controlled by heat conduction and current bed form induced heat advection as losing discharge increases the temperature signal from the water column penetrates deeper into the sediments with the largest temperature variations found under a downwelling zone along the stoss side of the bed form and damped temperature variations found near a narrow upwelling zone below the crest similar patterns are observed under gaining conditions but with temperature variations penetrating to shallower depths the interfacial exchange zone is diminished by upward movement of deep groundwater large gains or losses of deep groundwater prevent the formation of an interfacial exchange zone making heat transport almost vertically one dimensional the sensitivity of the sediment thermal regime to hydrodynamic conditions increases with increasing water column current reynolds number and with sediment permeability

estimating groundwater discharge into the northeastern gulf of mexico using radon 222 abstract submarine groundwater discharge sgd may provide important chemical constituents to the ocean but the dispersed nature of this process makes locating and quantifying its input extremely difficult since groundwater contains 3 4 orders of magnitude greater radon than seawater 222rn may be a useful tracer of this process if all other sources of radon to bottom waters can be evaluated we report development of a sgd tracing tool based on radon inventories in a coastal area of the northeastern gulf of mexico we evaluated factors that influence the concentration of radon in the water column i e production decay horizontal transport and loss across the pycnocline using a linked benthic exchange horizontal transport model total 222rn benthic fluxes 2420 dpm m 2 day 1 measured with in situ chambers are of the magnitude required to support measured sub pycnocline 222rn inventories while estimates of molecular diffusion show that this input is relatively small 230 dpm m 2 day 1 using this model approach together with measurements of the radon inventory we estimated a regional subsurface fluid flow ranging from 180 to 710 m3 sec 1 into the 620 km2 study area this discharge equivalent to an upward advective velocity of approximately 2 10 cm day 1 dispersed over this entire study area is equivalent to approximately 20 first magnitude springs

large submarine groundwater discharge and benthic eutrophication in bangdu bay on volcanic jeju island korea we estimated the submarine discharge of groundwater sgd and associated nutrients into the semienclosed bangdu bay on a volcanic island jeju korea by analyzing 222 rn ra isotopes 224 ra and 226 ra and nutrients in seawater pore water and coastal groundwater the submarine inputs of groundwater into bangdu bay of 120 180 m 3 m 22 yr 21 on the basis of 222 rn 224 ra 226 ra and si mass balances were much higher than those reported from typical continental margins the nutrient fluxes from sgd were about 90 20 and 80 of the total input except from open ocean waters for dissolved inorganic nitrogen din dissolved inorganic phosphorus dip and dissolved inorganic silicate dsi respectively these excess nutrient inputs from sgd are the major sources of new nutrients in this bay on the basis of photosynthetic pigments and benthic algal distributions we suggest that the large fluxes of excess nutrients from sgd can cause benthic eutrophication in a semienclosed bay on this highly permeable volcanic island

trace element cycling in a subterranean estuary part 1 geochemistry of the permeable sediments abstract subterranean estuaries are characterized by the mixing of terrestrially derived groundwater and seawater in a coastal aquifer subterranean estuaries like their river water seawater counterparts on the surface of the earth represent a major but less visible hydrological and geochemical interface between the continents and the ocean this article is the first in a two part series on the biogeochemistry of the subterranean estuary at the head of waquoit bay cape cod ma usa the pore water distributions of salinity fe and mn establish the salt and redox framework of this subterranean estuary the biogeochemistry of fe mn p ba u and th will be addressed from the perspective of the sediment composition a second article will focus on the groundwater and pore water chemistries of fe mn u and ba three sediment cores were collected from the head of waquoit bay where the coastal aquifer consists of permeable sandy sediment a selective dissolution method was used to measure the concentrations of p ba u and th that are associated with amorphous hydr oxides of iron and manganese and crystalline fe and mn hydr oxides the deeper sections of the cores are characterized by large amounts of iron hydr oxides that are precipitated onto organic c poor quartz sand from high salinity pore waters rich in dissolved ferrous iron unlike fe hydr oxides which increase with depth the mn hydr oxides display midcore maxima this type of vertical stratification is consistent with redox controlled diagenesis in which mn hydr oxides are formed at shallower depths than iron hydr oxides p and th are enriched in the deep sections of the cores consistent with their well documented affinity for fe hydr oxides in contrast the downcore distribution of ba especially in core 3 more closely tracks the concentration of mn hydr oxides even though mn hydr oxides are 200 300 times less abundant than fe hydr oxides in the cores mn hydr oxides are known to have an affinity for ba which is many orders of magnitude greater than iron hydr oxides hence the downcore distribution of ba in fe hydr oxide rich sediments is most probably controlled by the presence of mn hydr oxides u is enriched in the upper zones of the cores consistent with the formation of highly reducing near surface sediments in the intertidal zone at the head of the bay hence the recirculation of seawater through this type of subterranean estuary coupled with the abiotic and or biotic reduction of soluble u vi to insoluble u iv leads to the sediments acting as a oceanic net sink of u these results highlight the importance of permeable sediments as hosts to a wide range of biogeochemical reactions which may be impacting geochemical budgets on scales ranging from coastal aquifers to the continental shelf

ba ra th and u in marine mollusc shells and the potential of 226ra ba dating of holocene marine carbonate shells the geochemistry of ba ra th and u and the potential of using 226 ra ba ratios as an alternative dating method are explored in modern and holocene marine mollusc shells five modern shells of the antarctic scallop adamussium colbecki collected from the present day beach and six radiocarbon dated specimens from holocene beach terraces of the ross sea region antarctic between 700 and 6100 calibrated yr bp old have been analysed by mass spectrometry in clean shells 226 ra concentrations and 226 ra ba ratios show a clear decrease with increasing age suggesting the possibility of 226 ra dating limiting factors for such dating are ba and 226 ra present in surface contaminants and ingrowth of 226 ra from u present within the shell surface contamination is difficult to clean off entirely but moderate levels of residual contamination can be corrected using 232 th sub samples from the same shell with different proportions of contamination form a mixing line in a 226 ra ba 232 th ba graph and the 226 ra ba of the pure shell can be derived from the intercept on the 226 ra ba axis contaminant corrected 226 ra ba ratios of late holocene 14 c dated samples fall close to that expected from simple 226 ra excess decay from seawater 226 ra ba values 226 ra ingrowth from u incorporated into the shell during the lifetime of the mollusc can be corrected for however the unknown timing of post mortem u uptake into the shell makes a correction for 226 ra ingrowth from secondary u difficult to achieve in the a colbecki shells 226 ra ingrowth from such secondary u becomes significant only when ages exceed 2500 yr in younger shells 226 ra ba ratios corrected for surface contamination provide chronological information if evidence for a constant oceanic relationship between 226 ra and ba in the ocean can be confirmed for that time scale the 226 ra ba chronometer may enable the reconstruction of variability in sea surface 14 c reservoir ages from mollusc shells and allow its use as a paleoceanographic

radium isotopes reveal seasonal groundwater inputs to cockburn sound a marine embayment in western australia summary the mass balance and activity ratios of naturally occurring radium ra iso topes 223 ra 224 ra 226 ra 228 ra were investigated in cockburn sound western australia to further understand submarine groundwater discharge sgd into these coastal waters water samples from 11 marine stations and 20 groundwater sites encompassing threeaquifer layers were analysed for ra at four times at the end of winter september2003 early summer december 2003 late summer march 2004 and mid winter july2004 variable isotopic signatures of groundwater suggested that vertical mixing mayoccur between different aquifer layers and two isotopically different water sources wereidenti ed in marine waters both inside and outside of cockburn sound a mass balance ofthe long lived radium isotopes 228 ra and 226 ra produced a range of discharge estimatesfrom 0 8 10 7 l day 1 in late summer to 2 7 10 7 l day 1 at the end of winter signaturesof radium isotopes in the coastal waters suggested that groundwater discharge was notcon ned to the shoreline and may have occurred from a number of aquifer sources at atemporally variable scale a 2007 elsevier b v all rights reserved

the behavior of u and th series nuclides in groundwater groundwater has long been an active area of research driven by its importance both as a societal resource and as a component in the global hydrological cycle key issues in groundwater research include inferring rates of transport of chemical constituents determining the ages of groundwater and tracing water masses using chemical fingerprints while information on the trace elements pertinent to these topics can be obtained from aquifer tests using experimentally introduced tracers and from laboratory experiments on aquifer materials these studies are necessarily limited in time and space regional studies of aquifers can focus on greater scales and time periods but must contend with greater complexities and variations in this regard the isotopic systematics of the naturally occurring radionuclides in the u and th decay series have been invaluable in investigating aquifer behavior of u th and ra these nuclides are present in all groundwaters and are each represented by several isotopes with very different half lives so that processes occurring over a range of time scales can be studied table 1 within the host aquifer minerals the radionuclides in each decay series are generally expected to be in secular equilibrium and so have equal activities see bourdon et al 2003 in contrast these nuclides exhibit strong relative fractionations within the surrounding groundwaters that reflect contrasting behavior during release into the water and during interaction with the surrounding host aquifer rocks radionuclide data can be used within the framework of models of the processes involved to obtain quantitative assessments of radionuclide release from aquifer rocks and groundwater migration rates the isotopic variations that are generated also have the potential for providing fingerprints for groundwaters from specific aquifer environments and have even been explored as a means for calculating groundwater ages view this table table 1 radionuclides important in groundwater studies the highly fractionated nature of the

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

using the radium quartet for evaluating groundwater input and water exchange in salt marshes the fluxes of 226ra half life 1600 years and 228ra half life 5 7 years from the north inlet salt marsh to the sea are much larger than can be supported by decay of their th parents in the surface marsh sediments these fluxes are sustained almost entirely by groundwater flow through the marsh an average groundwater flow of approximately 10 cm3 cm 2 day 1 is indicated if the groundwater activities we have measured are representative the fluxes of 223ra half life 11 4 day and 224ra half life 3 6 day are factors of 22 and ten more than those expected from the flux of 226ra groundwater also sustains most of the flux of the short lived isotopes the measured ra activity ratio pattern in the marsh creeks matches the groundwater signature but is distinct from the pattern of the parent thorium isotopes in the sediment we present a model to explain the anomalous distribution pattern of these isotopes despite their large throughput the inventories of desorbable 226ra and 228ra in the top 15 cm sediment layer are very low nevertheless the activities of 226ra and 228ra in the porewaters are large indicating a low distribution coefficient 10 for radium and a short retention time 10 days in the surface sediment layer we surmise that groundwater flow may be a significant source of radium isotopes in the waters of shallow estuaries and coastal margins this source must be recognized while considering mass balance of any tracer be it radium nutrients other metals or 18o

seawater groundwater mixing in and fluxes from coastal sediment overlying discrete fresh seepage zones a modeling study submarine fresh groundwater discharging from discrete zones such as conduits overlain by thick sediment remains poorly documented and understood despite common anecdotal accounts of it we analyzed this phenomenon by a suite of variable density variably saturated groundwater flow simulations guided by field studies the field observations included point flux and salinity measurements using seepage meters spread across the intertidal and the subtidal zones the discretely measured seepage fluxes in the subtidal region were as high and the salinity was as fresh as those from the intertidal zone both fluxes and salinities varied with tides two dimensional simulations of the idealized beach ocean vertical section with discrete freshwater springs at the base showed the development of seawater recirculation cells along the edge of freshwater discharge plumes emanating from the outlets causing mixing brackish water discharges at the sediment water interface above where the plume mixes with the recirculating seawater sensitivity analyses showed that stronger terrestrial fresh groundwater flow increases the freshwater plume size but does not affect the mixing zone width tidal oscillations and a dynamic fresh groundwater flow widened the mixing zones and increased porewater flux across the sediment water interface sediment thickness had a minor effect on the width of both the freshwater plume and its surrounding mixing zone the subtidal freshwater plume and mixing zone likely represent a unique but potentially ubiquitous setting which hosts dramatic ecological and chemical gradients their local biogeochemical niche and coastal scale ecosystem impacts will need to be considered in investigations of coastlines

trace element cycling in a subterranean estuary part 2 geochemistry of the pore water abstract submarine groundwater discharge sgd is an important source of dissolved elements to the ocean yet little is known regarding the chemical reactions that control their flux from sandy coastal aquifers the net flux of elements from sgd to the coastal ocean is dependent on biogeochemical reactions in the groundwater seawater mixing zone recently termed the subterranean estuary this paper is the second in a two part series on the biogeochemistry of the waquoit bay coastal aquifer subterranean estuary the first paper addressed the biogeochemistry of fe mn p ba u and th from the perspective of the sediment composition of cores charette et al charette m a sholkovitz e r hansell c m 2005 trace element cycling in a subterranean estuary part 1 geochemistry of the permeable sediments geochim cosmochim acta 69 2095 2109 this paper uses pore water data from the subterranean estuary along with bay surface water data to establish a more detailed view into the estuarine chemistry and the chemical diagenesis of fe mn u ba and sr in coastal aquifers nine high resolution pore water groundwater profiles were collected from the head of the bay during july 2002 there were non conservative additions of both ba and sr in the salinity transition zone of the subterranean estuary however the extent of sr release was significantly less than that of its alkaline earth neighbor ba pore water ba concentrations approached 3000 nm compared with 25 50 nm in the surface waters of the bay the pore water sr salinity distribution suggests a 26 elevation in the amount of sr added to the subterranean estuary the release of dissolved ba to the mixing zone of surface estuaries is frequently attributed to an ion exchange process whereby seawater cations react with ba from river suspended clay mineral particles at low to intermediate salinity results presented here suggest that reductive dissolution of mn oxides in conjunction with changes in salinity may also be an important process in maintaining high concentrations of ba in the pore water of subterranean estuaries in contrast pore water u was significantly depleted in the subterranean estuary a result of sgd driven circulation of seawater through reducing permeable sediments this finding is supported by surface water concentrations of u in the bay which were significantly depleted in u compared with adjacent coastal waters using a global estimate of sgd we calculate u removal in subterranean estuaries at 20 106 mol u y 1 which is the same order of magnitude as the other major u sinks for the ocean our results suggest a need to revisit and reevaluate the oceanic budgets for elements that are likely influenced by sgd associated processes

impact of low salinity porewater on seafloor electromagnetic data a means of detecting submarine groundwater discharge submarine groundwater discharge has been recognized as an important process in coastal and shelf environments but due to the diffuse nature of the process methods to identify and map zones of discharge still need development vertical profiles of subseafloor salinity from two locations off the east coast of the u s and from a coastal embayment in cape cod ma have been used to model seafloor electromagnetic em responses to changes in porewater salinity ordinarily porewaters of salinity close to that of seawater will be electrically conductive replacement of this conductive porewater by a body of fresh groundwater will reduce the electrical conductivity of the porewater and hence that of the seafloor based on in situ measurements of porewater salinity and reasonable estimates of sediment porosity our modelling quantifies the changes in em apparent porosity measurements that might be expected over coastal and nearshore regions of fresh water discharge given the results obtained we demonstrate that existing em technology might be used to map zones of fresh water in conjunction with other methods

estimating submarine discharge of fresh groundwater from a volcanic island using a freshwater budget of the coastal water column 1 the magnitude of submarine fresh groundwater discharge sfgd was estimated using a freshwater budget of the coastal water which was calculated from salinity anomalies off a volcanic island jeju korea we obtained high resolution profiles of salinity from the entire coastal area of jeju island using accurate ctd sensors lower salinity anomalies relative to the pristine offshore seawaters were observed and assumed to be a result of sfgd on the basis of negligible surface runoffs from the island and the relatively high levels of 222rn in the low salinity waters the sfgd flux during the study period calculated from a freshwater budget of the water column was 2 5 3 8 106 m3 d 1 which is close to the long term average based on the inland water balance our study shows that sfgd can be accurately and easily measured using a freshwater budget of the coastal waters off a highly permeable coastal zone with little surface runoff

seasonal cycles in radium and barium within a subterranean estuary implications for groundwater derived chemical fluxes to surface waters abstract there is increasing evidence that submarine groundwater discharge sgd is an important source of water and dissolved materials to the ocean one of the primary tracers of this process is the quartet of radium isotopes 223 ra 224 ra 226 ra and 228 ra whereby excess activities in surface waters can often be attributed to an input supplied via sgd this approach requires the radium end member activity to be well constrained however natural variability in groundwater radium may span several orders of magnitude therefore this variability is usually the main driver of uncertainties in volumetric sgd estimates to investigate the physical and biogeochemical controls on groundwater radium activities we conducted a three year time series of radium and barium a chemical analogue for radium within the subterranean estuary of a coastal aquifer waquoit bay ma usa gonneea et al 2013 demonstrated that movement of the salinity interface within the subterranean estuary is driven by changes in the hydraulic gradient between groundwater level and sea level height for waquoit bay seasonal scale sea level change not groundwater level was the main driver in hydraulic gradient fluctuations seasonal changes in groundwater chemistry can be attributed to the resulting movement of the salinity transition zone between terrestrial and marine groundwater landward movement of the interface results in a large release of radium isotopes 226 ra 1400 dpm 100 l 1 and barium 3000 nmol kg 1 associated with an increase in groundwater salinity the magnitude of these releases cannot be explained by in situ production or weathering alone but is likely due to salinity driven desorption from surface bound sediment inventory the timing of these peak concentrations is not always in phase with model derived estimates of sgd as a result the groundwater concentration rather than the water flux is the main driver of ra and ba inputs to waquoit bay surface waters the behavior of the subterranean estuary as an ion exchange reservoir has important implications for the timing and flux of various nutrients and pollutants that transit this region prior to discharge in addition to modulating chemical fluxes via submarine groundwater discharge on seasonal time scales transgression of the subterranean estuary may alter the input of chemicals to the ocean on decadal and longer time scales during this study the observed excess flux of 226 ra and ba from the subterranean estuary can be accounted for with sorbed sediment pools and accelerating rates of sea level rise in this region

using radon 222 and radium 226 isotopes to deduce the functioning of a coastal aquifer adjacent to a hypersaline lake in nw iran abstract this study aims to assess the hydrogeochemistry of coastal groundwater the occurrence of 222rn and 226ra and their isotopic response to salinity and associated chemical compositions of groundwater in the coastal urmia aquifer ua at the western side of urmia lake ul the results of the pca show that 87 3 of groundwater chemistry changes are controlled by six principal components the interaction between groundwater and coastal igneous and metamorphic rocks in eastern areas next to the ul results in complex hydrogeochemical conditions than western areas based on correlation of u and salinity some coastal samples display conservative and the others non conservative behaviors differed from most previous studies 226ra and 222rn concentrations in coastal groundwater samples of ua do not show a good correlation with salinity given 10 of groundwater 222rn is originated from host rocks the radon concentrations recorded in the coastal groundwater samples are relatively in range that can effectively be supplied by the local rocks 5 49 bq l results of different chemical and isotopic parameters in this area indicate that there is no direct connection between fresh groundwater and ul saltwater this is because that the hard and thick salty layer in the lakebed acts as an impermeable barrier to prevent the underground hydraulic connection results show that removing the salty layer of ul as an option to progress in rehabilitation program of this lake may result in more hydraulic connection between the lake and groundwater resources in some areas