the fate and accumulation of bromide during playa salt deposition an example from lake frome south australia an advectivn diffusion model describing the distribution of br in porewaters underlying an accumulating deposit of halite on a playa lake can be used to predict the evolving composition of the accumulating salt growing as a result of evaporation the br cl ratio of the accumulating halite is proportional to the concentration or br at the surface of the brine body from which it is growing the evolution of interstitial br and therefore the composition of the accumulating salt is a function of 1 the diffusion coefficient of br in the brine saturated sediment 2 the advective velocity of the interstitial water 3 the initial concentration of br and cl at the onset of evaporation and 4 the distribution coefficient of br into the accumulating salt all of which can be estimated for the sediments and brines of lake frome south australia at lake frome the model is used to estimate mean evaporation rates for the salt covered surfaces which are found to be between 0 5 and 3 0 cm y these rates are lower than the rates estimated for the salt free surfaces of the lake by allison and barnes 1985 but are consistent with the expectation that groundwater input and therefore evaporation rates will be focused at the salt free lake margins rather than at the salt covered central regions of the playa and that the surface albedo of the salt covered zones will reduce energy penetration to the sediment and thus evaporation

determining vertical leakage from the great artesian basin australia through up scaling field estimates of phreatic evapotranspiration summary understanding the water balance of large groundwater systems is fundamental for the sustainable management of the resource the vertical leakage i e discharge to upper aquifers or the unconfined water table component of the great artesian basin gab is an example of a poorly constrained but large component of the water balance of australia s largest groundwater resource field estimates of phreatic evapotranspiration et were made at discharge zones along the southwestern margin of the gab using eddy covariance station and micro lysimeter measurements and inversion of chloride isotope soil profile measurements the field estimates were assigned to three major landforms associated with areas of increasingly higher evaporative discharge and progressively decreasing depths to the water table these landforms were mapped using remote sensing and digital elevation data with characteristically higher soil moisture salt precipitation and lower surface temperature compared to areas distal to discharge zones based on the field measurements broad ranges of phreatic et 0 5 10 10 100 and 100 300 mm y 1 were assigned to the major land types the higher phreatic et discharge zones mapped by supervised classification of satellite data are 8 28 of the total regional vertical leakage component estimated by numerical modelling of the gab in comparison the higher discharge zones estimated by landform mapping are 73 251 of the total vertical leakage component estimated by modelling the mapped distribution of the high discharge areas has important implications for modelling of the gab in the western sub basin most of the estimated recharge can be accounted for by phreatic et in the high discharge zones located around the basin margins implying that vertical leakage rates distal to the margins are very low and that discharge may exceed current recharge in contrast the results for the eastern sub basin suggest that vertical leakage rates around the south australian portion of the basin margin are low and that more of the vertical leakage component in the eastern sub basin is occurring distal to the basin margins consequently the pathways for vertical leakage in the eastern sub basin are likely to be more complex than for the western sub basin

oxygen isotope signatures from land snail helix melanostoma shells and body fluid proxies for reconstructing mediterranean and north african rainfall abstract in this paper we show that oxygen isotope ratios from the shell carbonate of the land snail helix melanostoma reflect local rainfall parameters stable oxygen isotopes were measured in the body fluid 18 o body and shells 18 o shell of live collected h melanostoma along a north south transect across the gebel akhdar in northeast libya 18 o body ranged between 8 1 and 13 0 whilst 18 o shell ranged between 1 0 and 2 8 to investigate the relationship between snail oxygen isotope composition and climate these measurements were correlated with ambient air temperature relative humidity rainfall amount and the 18 o composition of rainwater 18 o rain strong and significant correlations were found between 18 o shell and 18 o rain and between 18 o shell and rainfall amount r 2 0 79 and 0 85 respectively suggesting that h melanostoma shells can be used as a proxy for past rainfall conditions when combined in multiple linear regressions 18 o rain and rainfall amount explained 90 of the variance in 18 o shell r 2 0 90 simple and multiple linear regressions were used to develop predictive models for these climate parameters as h melanostoma shells are commonly found in mediterranean and north african archaeological and geological deposits the predictive equations developed in this study hold great potential for reconstructing pleistocene to holocene rainfall and aridity patterns in the gebel akhdar and for assessing the relationship between environmental changes and human behavioural changes

estimation of evaporation from the normally dry lake frome in south australia depth profiles of deuterium composition expressed as delta values have been used to make point estimates of evaporation from the floor of the normally dry lake frome a salt lake in northern south australia values from five sites varying between 90 and 230 mm yr 1 have been used to obtain a relatively crude approximation for mean evaporation rate from the lake of 170 mm yr 1 under the assumption that this represents discharge of water from the regional groundwater system the groundwater inflow into the lake is calculated as 5 108 m3 yr 1 two possible models which describe groundwater inflow into the lake are discussed

a study of soil water movement combining soil water potential with stable isotopes at two sites of shallow groundwater areas in the north china plain in the shallow groundwater areas of the north china plain ncp precipitation infiltration and evapotranspiration in the vertical direction are the main processes of the water cycle in which the unsaturated zone plays an important role in the transformation process between precipitation and groundwater in this paper two typical sites in cangzhou cz and hengshui hs of hebei province with shallow water tables were selected to analyse the relationship among precipitation soil water and groundwater at each site precipitation soil water at depths 10 20 30 50 70 100 150 200 300 cm and groundwater were sampled to analyse the stable isotope compositions of hydrogen and oxygen the soil water potentials at the corresponding depths were observed although the climates at the two sites are similar there are some differences in the infiltration process soil water movement and groundwater recharge sources evaporation occurred at the upper depths which led to the decrease of soil potential and the enrichment of heavy isotopes at the cz site precipitation infiltrated with piston mode and an obvious mixture effect existed during the infiltration process preferential flow may exist in the soil above 100 cm depth however at the hs site soil water moved in piston mode and groundwater was mainly recharged by precipitation when precipitation recharged the groundwater it experienced a strong evaporation effect the results of the soil water movement mechanism provides the transformation relationship among precipitation soil water and groundwater in the middle and eastern ncp copyright 2009 john wiley sons ltd

self induced fracture generation in zircon the mineral zircon has particular geological significance because of its use in the age determination of rocks and as a structural analogue phase for radioactive waste forms despite its widespread utility however radiation damage of the crystal structure metamictization causes a volume expansion of the crystal lattice and the generation of internal stresses which can induce fractures in the crystal a model has been developed which describes the state of stress in n concentric spherical shells each of which may have different material properties the case of a three shelled composite sphere has been examined explicitly in combination with fracture mechanics theory the model predicts that spatially distinct radial and or concentric fracture sets can be produced and such fracture patterns accurately describe the distribution and types of self induced fractures observed in natural zircons in general the formation of such microfractures in zircon is a function of the degree of metamictization shell thickness and the confining pressure the model predicts that the maximum depths in the earth s crust at which radial versus concentric fractures can form in a crystal are different suggesting that the types of fractures found in a suite of zircons from a particular rock might be potential indicators of the depth of burial because metamictization induced fractures may serve as potential pathways for the rapid leaching of various elements from the zircon crystal this may also have important implications in interpreting the u pb ages of fractured zircons or in evaluating the suitability of related crystalline phases as hosts for nuclear waste

groundwater recharge and discharge dynamics in an arid zone ephemeral lake system australia the coongie lakes are a series of ephemeral freshwater lakes on the lower reaches of cooper creek a large intermittent river of the arid lake eyre basin australia hydrogeological chemical and isotopic observations in conjunction with numerical modeling of groundwater responses to lake inundation events have been used to identify the dominant processes linking shallow unconfined groundwater with the hydrology of the lakes during wet and dry periods the lakes are predominantly zones of net groundwater recharge during inundation events however soil profile data suggests that drying of some of these lakes allows evaporative groundwater discharge to occur through the soil profile of the dry lake beds resulting in salinization of the soil profile of the more ephemeral lakes the occurrence of young high salinity groundwater is best explained by variations in soil profile flushing in response to wet and dry interannual periods of river discharge during interannual drier phases when filling of previously dry lakes is more common recharge is mostly via macropore flow during the rising stage of the inundation increased salinization of the lake bed sediments occurs during longer dry periods due to transport of solutes to the near surface from lake bed evaporation and limited flushing of the soil profile because of the macropore dominated flow during recharge during wet periods recharge is more likely dominated by matrix flow that results in leaching of the soil profile and increased export of solutes into the alluvial aquifer

impacts of evaporation on subsurface flow and salt accumulation in a tidally influenced beach we coupled a mass transfer formulation of evaporation to the density dependent variably saturated finite element model marun to predict the salinity under realistic conditions in a beach in the gulf of mexico the results showed that evaporation almost doubled the pore water salt concentration in the intertidal zone in comparison to the case with no evaporation the results also showed that for the relatively wet atmospheric conditions the maximum evaporation did not occur from the supratidal zone rather from the intertidal zone and it was due to the difference in moisture between pore water and atmosphere the highest salinity occurred during the spring tide period and extended into the neap tide period when the atmospheric condition was assumed to be constant and conducive to large evaporation high temperature and low air humidity the maximum salinity region shifted to the supratidal zone and persisted there due to low mixing the maximum salinity value in the intertidal zone for this case was not larger than that of the variable atmospheric condition case however the maximum was more landward than the more realistic variable atmospheric condition case which suggests that accurate characterization of pore water salinity in tidally influenced beaches requires accurate knowledge of atmospheric conditions in addition to beach and hydraulic properties the constant atmospheric condition simulations suggest that antecedent extreme conditions greatly affect the salinity in the supratidal zone but they are dampened in the intertidal zone

the accumulation of non formula elements in zircons during weathering ancient zircons from the jack hills western australia abstract in this contribution we describe the influx of non formula elements fe ca al y u and th into fractures and selected zone lamellae in zircons from jack hills during recent weathering and discuss the effects of this on overlapping sims u th pb and oxygen isotope analyses previous research has recognised the importance of fractures in the generation of anomalous u th pb and oxygen isotope systems in this report we show that besides fractures specific zones in euhedrally zoned zircon can act as pathways for the influx of weathering solutions and contain a similar range of trace element materials as do the fractures whereas zero age discordant u pb systems of jack hills zircons have been explained by many authors in terms of pb loss present results confirm conclusions of our previous study that the main discordance mechanism of jack hills zircons is u th gain due to overlap of sims analyses with mineralized fractures and zone lamellae with excess weathering fluid deposited u and th we explain the anomalously light and heavy oxygen isotopes and significant oh in sims analyses that overlap fractures and mineralized zones as due to the presence in the fractures of ca fe al oxides and hydroxides with complexly fractionated oxygen isotopic systems there is a suggestion in some of the elemental maps that there has been minor dispersion of trace elements away from fractures but sims u th pb and oxygen isotope analyses on parts of the zircon away from fractures and mineralized zones show no evidence of interaction with weathering fluid indicating that penetration of weathering fluids into the body of the zircon at the location of the sims spots has not occurred results of this study have implications for other sims u th pb and oxygen isotope studies of zircons from rocks that have been subjected to weathering and also for early tims u pb measurements of bulk zircon samples that show zero ma u pb discordance

estimation of bottom scattering characteristics from acoustic reverberation special research program bistatic data for many years sonar practitioners have used lambert s law on a flat bottom to describe clutter due to bottom reverberation this examination of a subset of the bistatic data from the b site of the arsrp natural laboratory examines the validity of this approximation eight pings transmitted by the cory chouest and received by the alliance were chosen to cover the bistatic angular range of 90 to 90 deg with respect to b transmission loss and area corrections to a flat bottom of representative depth were calculated using the artist ray tracing program these corrections were applied to the data to compute scattering strength in each beam time bin this scattering strength was averaged over areas with similar grazing angle to transmitter grazing angle to receiver and bistatic angle again these are angles to a flat bottom scenario the scattering strength plotted versus these three angles shows that neither lambert s law nor the generalized version by nayar et al describe bistatic scattering resea

estimation of long term diffuse groundwater discharge in the northern sahara using stable isotope profiles in soil water stable isotope profiles in soil water in the sahara have been interpreted in terms of the hydrologic processes taking place at one site where the water table is at about 10 m depth the isotope data are interpreted using the model of barnes and allison to show that the water loss by evaporation from the water table is about 2mm a 1 at another site nearby there is a net evaporative loss from the water table but the evaporation is interrupted by occasional infiltration events it is suggested that accumulation of chloride in soil water can give information about the onset of aridity in the sahara

numerical modeling of water flow below dry salt lakes effect of capillarity and viscosity abstract we investigate numerically the effects of capillarity and viscosity on density dependent flows below dry salt lakes the numerical model marun boufadel m c suidan m t venosa a d 1999a a numerical model for density and viscosity dependent flows in two dimensional variably saturated media j contam hydrol 37 1 20 is used to assess the combined and separate effects of capillarity and concentration engendered viscosity on the groundwater dynamics of a two dimensional system simulating a dry lake we found that accounting for concentration engendered viscosity effects under saturated water flow conditions gives totally different groundwater dynamics from the case where these effects are neglected however concentration dependent viscosity effects were minor when unsaturated water flow conditions were present under variably saturated flow conditions capillarity effects gave totally different hydraulics in the porous domain from the saturated flow case upwelling regions observed under saturated flow conditions were downwelling when capillarity effects were present a mesh orientation study revealed that density dependent flows were susceptible to the orientation of the diagonals of the triangular elements a discussion on the accuracy and the efficiency of the marun model in the context of density and viscosity dependent flows in two dimensional variably saturated media is also provided

dolomitization and sulfate reduction in the mixing zone between brine and meteoric water in the newly exposed shores of the dead sea pleistocene dolomites are associated either with evaporative processes such as in sabkhas and playas or with a mixing zone where mixing between two different solutions e g seawater and groundwater takes place we report here on the very recent formation of dolomite at shallow depths 6 12 cm in newly exposed gypsum rich sediments on the western shores of the dead sea sem and eds analysis as well as x ray diffraction analysis indicate that this dolomite is euhedral and close to ideal dolomite in composition these dolomite crystals differ from anhedral detrital ca rich dolomites from the cretaceous section of the watershed found in the whole section taking into account the sedimentation rate at the shore vicinity the maximal age of the euhedral dolomite was estimated as less than 60 years in the three profiles analysed euhedral dolomite was most abundant at a single layer where the gypsum content was locally lowered due to bacterial reduction of sulfate the sediments solution at the dead sea shore localities represent a mixing zone between dead sea residual solution and subsurface freshwater springs under such conditions formation of dolomite occurs at highly saline environment where very high mg ca ratios are attained

salt crust development in paddy fields owing to soil evaporation and drainage contribution of chloride and deuterium profile analysis summary in northeast thailand lowlands with shallow saline watertable rainfed paddy fields often present high salt concentration in the dry season forming patches or spots of salt crusts on the soil surface in this context the mechanisms implied in salt concentration during dry season were studied by establishing salt budget with evaporation and drainage estimates inside and outside a saline patch drainage was estimated by hydrus 1d modelling constrained by an hydrodynamic characterization and the profile of water contents at the end of dry season evaporation rates at the end of the dry season were computed by interpreting natural detailed profiles of deuterium d and chloride cl contents because of the drastic diminution of hydraulic conductivity at saturation with depth and the decrease of groundwater level at the end of the cropping season simulated hydrological balance with hydrus 1d pointed out zero cumulated fluxes for depths of 39 5 cm outside the saline patch and 37 5 cm inside the saline patch therefore all the chloride accumulated in the very upper layers during dry season comes from the chloride that was present in the 0 39 5 cm layers before the beginning of the drying inside the saline patch the tentative cl budget is coherent with the hypothesis of saturation of the profile by aquifer saline water during the flooding evaporation rates computed from the diffusion of chloride and deuterium at the end of the drying season when the aquifer level was 1 4 m deep range between 0 121 and 0 378 mm d 1 this does not sustain the assumption of a considerable salinity contribution from the aquifer during the dry season moreover evaporation estimates based on cl and d diffusion equilibrium showed depleted rates 38 63 inside the saline patch due to salt accumulation in the first 12 cm of the soil in the vapour transfer layer estimated evaporation rate based on the vapour movement of d was in the same order of magnitude than computed rate assuming liquid cl diffusion this coincidence is attributed to the liquid fluxes that occurred during the expansion of the vapour transfer layer during the progression of the evaporation front

processes affecting interstitial water in the unsaturated zone at the newly exposed shore of the dead sea israel abstract a main process affecting interstitial water and solutes at shallow depths on the newly formed shores of the dead sea ds is evaporation the evaporation rate from the unsaturated zone as calculated based on stable isotope profiles ranges from 0 5 to 36 mm yr 1 the high tritium concentrations 20 40 tu as compared with the main implication of the present study is that the evaporitic sediments can undergo rapid chemical and isotopic changes which later can be found preserved in the sequence thus the isotopic and chemical record of some of the phases found in saline ancient evaporitic sequences may have a freshwater signature

convection in groundwater below an evaporating salt lake 1 onset of instability convective groundwater motion can be generated in aquifers beneath and adjacent to saline lakes such motions strongly control the subsurface distribution of salts the formation of saline minerals and the distribution of contaminants that may be disposed of in the saline lake in particular schemes to use saline lakes as evaporation basins for irrigation waste waters must consider the groundwater dynamics associated with convection the convection is driven by the evaporative concentration of salts at the land surface leading to an unstable distribution of density however the evaporative groundwater discharge can dynamically stabilize this saline boundary layer and inhibit convection in this work we investigate the nature and onset of convection for a range of boundary conditions typically found in saline lakes processes involved in the accumulation of salt at the surface of a groundwater discharge zone and in the gravitational instability of the near surface groundwater are considered results of theoretical stability analysis are applied through laboratory and numerical experimentation to the more complex geometries typically found in the field these comparisons indicate that for large saline lakes the stability of the saline boundary layer can be parameterized by traditional rayleigh criteria in which the aquifer permeability and the evaporation rate from the lake bed are principal controlling factors for typical saline lake environments convection will dominate in sediments whose permeability exceeds approximately 10 14 m2 below this threshold permeability the boundary layer should be stabilized by the evaporative flux resulting in the accumulation of salts and evaporites at the land surface these results provide insight into the predictive behavior of groundwater dynamics and solute distributions in many natural systems

oxygen isotopic signature of 4 4 3 9 ga zircons as a monitor of differentiation processes on the moon abstract we report oxygen isotopic compositions for 14 zircon grains from a sample of sawdust from lunar breccia 14321 the zircons range in age from 4 4 to 3 9 ga and in u and th content from a few to several hundred ppm as such these grains represent a range of possible source rocks from granophyric to mafic composition and cover the total age range of the major initial lunar bombardment nevertheless results show that the oxygen isotopic compositions of the zircons fall within a narrow range of 18 o of about 1 per mil and have 18 o values indistinguishable from those observed for terrestrial mid ocean ridge basalts confirming the coincidence of lunar and earth oxygen isotopic compositions in the 17 o vs 18 o coordinates data form a tight group with a limited trend on the terrestrial fractionation line the zircon oxygen isotopes show minimal evidence of the extreme and variable mineral differentiation and element fractionation that have contributed to the formation of their parent rocks

evaporation and land surface energy budget at the salar de atacama northern chile playa systems are driven by evaporation processes yet the mechanisms by which evaporation occurs through playa salt crusts are still poorly understood in this study we examine playa evaporation as it relates to land surface energy fluxes salt crust characteristics groundwater and climate at the salar de atacama a 3000 km 2 playa in northern chile containing a uniquely broad range of salt crust types land surface energy budget measurements were taken at eight representative sites on this playa during winter august 2001 and summer january 2002 seasons measured values of net all wave radiation were highest at vegetated and rough halite crust sites and lowest over smooth highly reflective salt crusts over most of the salar de atacama net radiation was dissipated by means of soil and sensible heat fluxes dry salt crusts tended to heat and cool very quickly whereas soil heating and cooling occurred more gradually at wetter vegetated sites sensible heating was strongly linked to wind patterns with highest sensible heat fluxes occurring on summer days with strong afternoon winds very little energy available at the land surface was used to evaporate water eddy covariance measurements could only constrain evaporation rates to within 0 1 mm d k1 and some measured evaporation rates were less than this margin of uncertainty evaporation rates ranged from 0 1 to 1 1 mm d k1 in smooth salt crusts around the margin of the salar and from 0 4 to 2 8 mm d k1 in vegetated areas no evaporation was detected from the rugged halite salt crust that covers the interior of the salar though the depth to groundwater is less than 1 m in this area these crusts therefore represent a previously unrecorded end member condition in which the salt crusts form a practically impermeable barrier to evaporation q 2005 elsevier b v all rights reserved

reverberation at the mid atlantic ridge during the 1993 arsrp experiment seen by r v alliance from 200 1400 hz and some modeling inferences in july 1993 saclantcen participated in an experiment for the acoustic reverberation special research program arsrp the primary objective was to take high resolution measurements to shed light on the detailed physical processes dominating the low frequency scattering from rough topographic features and from deep sediment pond areas a very detailed set of monostatic and bistatic scattering experiments were conducted just west of the mid atlantic ridge near 26 degrees n 47 degrees w results from saclantcen s r v alliance are presented which show monostatic and bistatic scattering from selected bathymetric features using pulsed sources from 200 1400 hz and sus charges area water depths ranged from 3300 to greater than 5200 m the receivers were a horizontal array of 128 elements spaced at 0 5 1 and 2 m source depths varied from 120 to 1200 m and receiver depths ranged from 400 to 500 m received reverberation levels are presented as functions of the estimated scatterer position on area bathymetry maps results show the same high scattering areas from one seamount were observed in three distinct frequency bands centered at 227 350 and 700 hz even at 1350 hz the correlation of scattering highlights with nearby bathymetric features is quite good comparisons of measured reverberation and modeled reverberation are presented which suggest that the dominant longer range scattering from the large features is driven by the steep slopes present above the critical depth but that small scale roughness is also essential for strong backscatter

transport of uranium thorium and lead in metamict zircon under low temperature hydrothermal conditions abstract understanding the stability of radiation damaged zircon under low temperature hydrothermal conditions is crucial to the application of zircon for u pb geochronology and as a host phase for the disposal of plutonium waste we report the results of an investigation of the stability of partially metamict zircon by leaching experiments at 175 c with a 2 m alcl 3 and a 1 m hcl cacl 2 solution as hydrothermal fluids for 1340 h cathodoluminescence cl and backscattered electron bse images show that the zircon grains have developed a reaction rim several micrometers thick or deeply penetrating reticulated alteration zones with sharp boundaries to unaltered metamict zircon these zones have experienced severe loss of si u th and pb and gain of al or ca and a water species as revealed by electron microprobe sensitive high resolution ion microprobe shrimp analyses and infrared spectroscopy micro raman and infrared measurements on the altered areas show that disordered crystalline remnants of the partially metamict zircon structure were partially recovered whereas recrystallization of the embedding amorphous phase was not observed no detectable structural or chemical changes were detected inside the unaltered areas intensive fracturing which was most intense in the hcl cacl 2 experiment occurred inside the altered areas due to the volume reduction associated with the recovery of the disordered crystalline material and probably with the leaching reactions we explain the formation of deep penetrating alteration zones by a percolation type diffusion model which is based on the assumption that percolating interfaces or areas of low atomic density between crystalline and amorphous regions as well as between amorphous domains exist along which fast chemical transport is possible the idea of the existence of fast diffusion interfaces is supported by the sharp chemical gradients at the margin to unreacted zircon the model was used to estimate for the first time diffusion coefficients for u th and pb diffusion in amorphous zircon at 175 c by assuming that volume diffusion inside the amorphous domains is the loss rate limiting process these estimates show that volume diffusion in metamict zircon can cause significant loss of u th and especially loss of radiogenic pb over geological time scales even at temperatures as low as 175 c our results show that recent pb loss discordias can be generated 1 by predominate pb loss from metamict zircon through volume diffusion at low temperatures where thermal healing of the structure is insignificant and 2 by leaching of pb and u and th from metamict zircon through an external fluid

interaction of weathering solutions with oxygen and u pb isotopic systems of radiation damaged zircon from an archean granite darling range batholith western australia zircons from archean granites from the darling range batholith in the yilgarn craton of western australia have been shown to have complexly discordant u pb systems with a strong component of zero age disturbance the only geological event that has affected the granites in recent times is the pervasive regional weathering our aim in this study was to investigate the effects of weathering on the u pb and oxygen systems of the zircons and to this end we report secondary ion mass spectrometry sims results of oh oxygen and u pb isotope systems of six typical zircons from a sample of the granite these results confirmed the presence of oh in highly radiation damaged parts of the zircons demonstrating fluid interaction within grains the presence of oh was accompanied by significant changes in the 18o 16o ratios the data suggest trends where 18o values in individual grains both increase and decrease with increasing oh sims measurements showed the u pb systems are variably and unsystematically discordant in radiation damaged parts of the zircons particularly those with elevated oh contents the complex u pb systems are interpreted in terms of multiple disturbance events between 450 and 0 ma involving low temperature fluid induced movement of radiogenic pb decoupled from parent u and th within the radiation damaged zircons together with some pb loss

evaporation and concentration gradients created by episodic river recharge in a semi arid zone aquifer insights from cl δ 18 o δ 2 h and 3 h summary this study has significantly advanced our understanding of the origin of groundwater recharge in a semi arid zone region of the darling river catchment australia the generally accepted hypothesis in arid zone environments in australia that river water forms the primary groundwater recharge source has proven difficult to monitor this is due to the time lags between large floods the remoteness and expense of studying these hydrologically complex systems in detail in addition the highly episodic nature of dryland rivers complicates the interpretation of the groundwater signal a range of hydrochemical tracers chloride oxygen 18 deuterium and tritium measured in rain river water soil water and groundwater were used in this multi year study to trace the pathways of groundwater recharge under wet and dry climatic conditions the evaporation and cl concentrations observed in the unsaturated zone confirmed that small volumetric inputs from periodic rainfall were not the major recharge mechanism sampling which included an overbank flooding event in march 2012 provided firm evidence for groundwater originating from high flow episodic river recharge the use of long term environmental data to understand how economically important water resources respond to climate change with increasing temperatures is considered essential for future sustainability

the late quarternary salinity record of lake frome south australia evidence from na in stratigraphically preserved gypsum abstract traces of foreign ions are incorporated into the structure of gypsum during precipitation the amount of foreign material included in the crystal is dependent on its concentration in the precipitating solution and therefore the trace element composition of the gypsum can be related to the composition of brines from which it precipitated a late quaternary salinity record for lake frome south australia derived from the analysis of na in gypsum is consistent with much of the previously inferred climatic history of southeast australia the record indicates three periods of lake filling at 17 000 yr b p from 15 000 to 13 500 yr b p and from 13 000 to 11 000 yr b p lake frome was dry prior to 17 000 yr b p between 16 500 and 15 000 yr b p at 13 000 yr b p and between 6000 and 4000 yr b p

uncertainties around modelling of steady state phreatic evaporation with field soil profiles of δ18o and chloride summary the application of the general advection diffusion equation to model phreatic evaporation flux rates from solute concentration soil profiles has been applied to a variety of arid zone locations but the effects of heterogeneous and uncertain field data on modelling performance are rarely described we revisit and extend the model by accounting for the effects of variable water content and sediment type on the impedance factor and in turn effective diffusion coefficient we explore the local sensitivity of the extended model to its major assumptions and parameter values the mean diffusion coefficient of the soil profile data is most sensitive to the volumetric water content close to the evaporation front and so modelled evaporation results can be very sensitive to uncertainty around the position of the evaporation front the uncertainty in the position of the groundwater reservoir and its concentration has little effect where the lower part of the profile shows an asymptotic trend towards a representative value of groundwater concentration but can vary substantially with different values of groundwater depth and concentration if this is not the case field data from the southern margin of the great artesian basin are shown to exhibit considerable uncertainty around the boundary conditions of the advection diffusion model e g position of evaporation front depth and concentration of lower groundwater boundary condition resulting phreatic evaporation flux estimates show a wide range that needs to be considered when using these data in water balance studies of groundwater systems

the origin of high δ18o zircons marbles megacrysts and metamorphism the oxygen isotope ratios 18o of most igneous zircons range from 5 to 8 with 99 of published values from 1345 rocks below 10 metamorphic zircons from quartzite metapelite metabasite and eclogite record 18o values from 5 to 17 with 99 below 15 however zircons with anomalously high 18o up to 23 have been reported in detrital suites source rocks for these unusual zircons have not been identified we report data for zircons from sri lanka and myanmar that constrain a metamorphic petrogenesis for anomalously high 18o in zircon a suite of 28 large detrital zircon megacrysts from mogok myanmar analyzed by laser fluorination yields 18o from 9 4 to 25 5 the u pb standard cz3 a large detrital zircon megacryst from sri lanka yields 18o 15 4 0 1 2 se by ion microprobe a euhedral unzoned zircon in a thin section of sri lanka granulite facies calcite marble yields 18o 19 4 by ion microprobe and confirms a metamorphic petrogenesis of zircon in marble small oxygen isotope fractionations between zircon and most minerals require a high 18o source for the high 18o zircons predicted equilibrium values of 18o calcite zircon 2 3 from 800 to 600 c show that metamorphic zircon crystallizing in a high 18o marble will have high 18o the high 18o zircons 15 from both sri lanka and mogok overlap the values of primary marine carbonates and marbles are known detrital gemstone sources in both localities the high 18o zircons are thus metamorphic the 15 25 zircon values are consistent with a marble origin in a rock dominated system i e low fluid external rock the lower 18o zircon values 9 15 are consistent with an origin in an external fluid dominated system such as skarn derived from marble although many non metasomatized marbles also fall in this range of 18o high 18o 15 and the absence of zoning can thus be used as a tracer to identify a marble source for high 18o detrital zircons this recognition can aid provenance studies in complex metamorphic terranes where age determinations alone may not allow discrimination of coeval source rocks metamorphic zircon megacrysts have not been reported previously and appear to be associated with high grade marble identification of high 18o zircons can also aid geochronology studies that seek to date high grade metamorphic events due to the ability to distinguish metamorphic from detrital zircons in marble

secondary magnetic inclusions in detrital zircons from the jack hills western australia and implications for the origin of the geodynamo the time of origin of earth s dynamo is unknown detrital zircon crystals containing ferromagnetic inclusions from the jack hills of western australia have the potential to contain the oldest records of the geodynamo it has recently been argued that magnetization in these zircons indicates that an active dynamo existed as far back as 4 2 ga however the ages of ferromagnetic inclusions in the zircons are unknown here we present the first detailed characterization of the mineralogy and spatial distribution of ferromagnetic minerals in jack hills detrital zircons we demonstrate that ferromagnetic minerals in most jack hills zircons are commonly located in cracks and on the zircons exteriors hematite is observed to dominate the magnetization of many zircons while other zircons also contain significant quantities of magnetite and goethite this indicates that the magnetization of most zircons is likely to be dominantly carried by secondary minerals that could be hundreds of millions to billions of years younger than the zircons crystallization ages we conclude that the existence of the geodynamo prior to 3 5 ga has yet to be established

numerical investigation of coupled density driven flow and hydrogeochemical processes below playas numerical modeling approaches with varying complexity were explored to investigate coupled groundwater flow and geochemical processes in saline basins long term model simulations of a playa system gain insights into the complex feedback mechanisms between density driven flow and the spatio temporal patterns of precipitating evaporites and evolving brines using a reactive multicomponent transport model approach the simulations reproduced for the first time in a numerical study the evaporite precipitation sequences frequently observed in saline basins bull s eyes playa specific flow evapo concentration and chemical divides were found to be the primary controls for the location of evaporites formed and the resulting brine chemistry comparative simulations with the computationally far less demanding surrogate single species transport models showed that these were still able to replicate the major flow patterns obtained by the more complex reactive transport simulations however the simulated degree of salinization was clearly lower than in reactive multicomponent transport simulations for example in the late stages of the simulations when the brine becomes halite saturated the non reactive simulation overestimated the solute mass by almost 20 the simulations highlight the importance of the consideration of reactive transport processes for understanding and quantifying geochemical patterns concentrations of individual dissolved solutes and evaporite evolution this article is protected by copyright all rights reserved

hydrogeologic processes in saline systems playas sabkhas and saline lakes abstract pans playas sabkhas salinas saline lakes and salt flats are hydrologically similar varying only in their boundary conditions thus in evaluating geochemical processes in these systems a generic water and solute mass balance approach can be utilized a conceptual model of a coastal sabkha near the arabian gulf is used as an example to illustrate the various water and solute fluxes analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha but contribute only a small volume of the water local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge to rainfall ratio of more than 50 the contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha because of a short residence time of water steady state flow is expected within a short time 50 000 years the solute composition of the brine in a closed saline system depends largely on the original composition of the input water the high total ion content in the brine limits the efficiency of water rock interaction and absorption because most natural systems are hydrologically open the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation thus during the hot dry season months minerals exhibit retrograde solubility so that gypsum anhydrite and calcite precipitate evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone e g halite and carnallite provided that the relative humidity of the atmosphere is less than the activity of water the slope of the fresh brine water interface in saline lake systems is shallower than in fresh seawater interface because of the greater density difference between the fresh brine water bodies the interface between sabkha brines and seawater slopes seaward unlike normal marine fresh water systems that slope landward moreover the brine seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha s brine

dissolution of radiation damaged zircon in lateritic soils zircon crystals from lateritic soils at nsimi cameroon were investigated using electron microprobe analysis empa transmission electron microscopy tem scanning electron microscopy sem and raman spectroscopy to determine the extent of radiation damage from alpha decay events the soils belong to a small watershed developed on granitic rocks of the congo craton 2 9 ga interactions with fluids are evidenced by significant cao up to 1 5 wt al2o3 up to 2 9 wt and fe2o3 up to 2 9 wt concentrations in uo2 rich regions 0 05 to 1 wt of the zircon regional heating up to 500 c related to the pan african orogeny about 0 6 ga ago has lead to the recrystallization of the radiation damaged grains and the formation of a nanoporous microstructure the correlation observed between the presence of dissolution features and the actual damage state of zircon shows that zircon dissolution occurs under tropical weathering conditions and with preferential dissolution of the highly radiation damaged regions congruent dissolution of zircon and the limited mobility of zr are supported by the absence of zirconium oxide precipitates in the fractures of weathered grains of zircon

modelling density dependent flow and solute transport at the lake tutchewop saline disposal complex victoria abstract intercepted saline groundwaters and drainage effluent from irrigation are commonly stored in both natural and artificial saline disposal basins throughout the murray darling basin of australia their continued use as wastewater evaporation sites requires an understanding of existing groundwater dynamics the useful of individual basins their sustainability and possible environmental impacts remain largely unknown in this work the movement of salt to the underlying groundwater system from lake tutchewop a saline disposal complex in north central victoria was modelled in cross section due to the salinity contrast between the hypersaline basin waters and the regional groundwater it was necessary to simulate density dependent flow behaviour under certain conditions these density stratified systems may become unstable leading to the onset of convective behaviour which greatly increases the movement of salt from the basin to the groundwater system modelled concentration profiles in the aquifer system and calculated seepage rates from the basin show that lake tutchewop is stable under its present operating regime the downward movement of salt is mainly controlled by diffusion and dispersion the calibrated model was used to assess the impact of several management scenarios using time dependent boundary conditions for lake salinity and water levels the influence of heterogeneous basin linings on ensuing salt flux rates is examined and results show that increased solute transport will occur under such conditions a sensitivity analysis performed on governing variables showed that salt fluxes were most sensitive to lake salinity levels a solute rayleigh number defined in terms of basin salinity and hydrogeologic parameters is seen to be an effective tool for predicting the long term behaviour of such saline disposal basins the models and concepts developed in this work may find application in the design and management of saline disposal complexes

evidence of free convection in groundwater field based measurements beneath wind tidal flats free convection caused by salinity differences had not been conclusively detected or measured in the field a field experiment at wind tidal flats on padre island national seashore texas documents salinity driven free convection with both direct head and salinity data and indirect time lapse 3 d resistivity methods evaporative concentration of groundwater near the water table created unstable inverted density gradients reduced groundwater levels and reversed hydraulic gradients these factors allowed plumes or fingers of more saline denser fluid to flow downward into less dense fluid as observed in monitoring wells and 3 d surveys the development of density inversions can overcome the dissipating forces of dispersion and diffusion to create a sufficiently large unstable gradient to induce free convection the development of free convective flow of variable density fluids in groundwater can be detected and monitored through field techniques

monostatic and bistatic reverberation statistics west of the mid atlantic ridge monostatic and bistatic reverberation of highly resolved signals from very rough bottoms at one site is statistically analyzed scattering at a mean frequency of about 230 hz from a large number of bottom footprints is considered the reverberation envelope is found to be non rayleigh with the degree of departure from rayleigh dependent upon the bottom grazing angle for two cases considered g 5 and 40 and upon the bistatic angle in the entire range 0 to 180 these rough bottom observations can be explained by adopting a continuous scattering model having a rayleigh envelope added to a discrete scattering model arising from a small number of individual features within the sonar footprint having a distinctly non rayleigh envelope these models plus a heuristic mechanism of self selection within the discrete scattering model arguably explain the observed angle dependence of the reverberation statistics

floating brine crusts reduction of evaporation and possible replacement of fresh water to control dust from owens lake bed california summary owens lake california a saline terminal lake desiccated after diversion of its water source was formerly the single largest anthropogenic source of fugitive dust in north america over 100 billion m 3 yr 1 of fresh water are projected to be used for mandated dust control in over 100 km2 of constructed basins required to be wetted to curtail emissions an extensive evaporite deposit is located at the lake s topographic low and adjacent to the dust control basins because this deposit is non dust emissive it was investigated as a potential replacement for the fresh water used in dust control the deposit consists of precipitated layers of sodium carbonate and sulfate bathed by and covered with brine dominated by sodium chloride perennially covered with floating salt crust evaporation e rates through this crust were measured using a static chamber during the period of highest evaporative demand late june and early july 2009 annualized total e from these measurements was significantly below average annual precipitation thus ensuring that such salt deposits naturally remain wet throughout the year despite the arid climate because it remains wetted the evaporite deposit may therefore have the potential to replace fresh water to achieve dust control at near zero water use

evidence for a mesoscale thermal circulation over dry salt lakes abstract because of albedo and thermal conductivity effects dry salt lakes in central australia exhibit a characteristics thermal signature within the overall landscape having much cooler daytime surface temperatures and warmer nocturnal temperatures than the surrounding environment various aspects of a possible mesoscale thermal circulation arising from such a thermal differentiation have been investigated for the salt lake a moderately sized 70 km 2 dry salt lake in northwestern new south wales 30 05 s 142 08 e surface temperatures across the salt lake and surrounding landscape determined by field and polar orbiting noaa 9 satellite observations show marked variation with the salt crust remaining up to 16 k cooler than the surrounding sand country during the day and up to 8 k warmer at night that this thermal forcing can provide a horizontal pressure gradient sufficiently strong to induce air motion is confirmed by analysis of hourly output from a network of anemographs which were established around the perimeter of the salt lake during a five month autumn and winter period an extremely regular pattern of nocturnal near surface convergence lake warm and daytime divergence lake cool is shown a pattern which is enhanced when data are stratified for anticyclonic conditions with a weak pressure gradient 24 of total observations wind roses produced for a number of sites around the lake show a distinct diurnal reversal in near surface airflow with generally onshore flow by day and offshore flow at night confirmation that a diurnally reversing thermal circulation does operate under certain conditions at the salt lake is provided by pilot balloon analysis of winds aloft and by preliminary mesoscale modelling of airflow this circulation which has not previously been described in the literature may have important environmental and climatic implications in the australian context

environmental character and history of the lake eyre basin one seventh of the australian continent abstract one of the world s largest internally drained endorheic basins the 1 14 million km 2 lake eyre hydrological basin leb covers nearly 15 of the australian continent palaeoclimatic and associated flow regime variations are recorded in an archive of fluvial aeolian and lacustrine sediments that are particularly accessible for deposits from the past 300 ka and are especially relevant for the past 50 ka during which humans have inhabited australia due to its great size economic resources and diverse latitudinal extent it has for over six decades been the focus of environmental scientific and resource based studies across numerous disciplines with an emphasis on assessing the scientific and environmental research over this period this paper is divided into four parts part a provides an introduction and background part b provides the geological history including evidence of substantial tertiary and quaternary climate change part c covers the contemporary environmental conditions and part d presents a conclusion and summary this not only represents the first comprehensive review of current knowledge of any of the world s truly large dryland drainage basins but also highlights how more multi disciplinary research is required key remaining questions revolve around the impact of global weather systems on the leb the lake level story in relation to a more precise picture of late quaternary climate change the role of humans and climate in the demise of the megafauna modern hydrological changes the role of vegetation in altering channel morphology and flow efficiencies and nature of flood transmissions

evaporation rate from a salt pan estimates from chemical profiles in near surface groundwaters evaporation of water from saturated saline soils or sediments induces gradients of the solutes in the remaining interstitial solution these gradients lead to a systematic and predictable solute distribution in the soil solution which may be used in some cases to estimate the rate of evaporation simple one dimensional transport models for the distribution of cl and br indicate net evaporation rates from the salt covered surface of lake eyre south australia of between 0 9 and 2 8 cm yr 1 the former is a minimum estimate averaged over 20 yrs which includes the major 1974 filling event while the latter reflects the most recent summer evaporation period