relative contribution of ionospheric conductivity and electric field to the auroral electrojets data from continuous scans of the chatanika radar beam along the magnetic meridian plane are used to determine the latitudinal profile of height integrated ionospheric conductivities and horizontal electric fields from which the latitudinal distribution of ionospheric currents is deduced the observations cover invariant latitudes between 62 and 68 where the ims alaska meridian chain of magnetometers was also in operation although the conductivities and the electric fields are interrelated the relative importance of the two in driving the eastward and westward auroral electrojet currents can be assessed it is found that for moderate and large current densities i e 0 2 a m the northward electric field strength increases as the magnitude of the eastward electrojet in the evening sector increases the height integrated hall conductivity stays generally at the level of 10 mhos even when the current density becomes as large as 1 a m however when the eastward electrojet is small substantial electric fields of 10 20 mv m may still exist as if the magnetosphere has a persistent voltage source there appear to be two distinct components to the westward electrojet in the midnight and early morning sestors 0300 mlt is dominated by a strong southward electric field

twenty years of groundwater evolution in the triassic sandstone aquifer of lorraine impacts on baseline water quality abstract the lorraine triassic sandstone aquifer ltsa which has already been the subject of a chemical and radioisotopic study 1979 is used to investigate the impacts of 20 a of large scale pumping on baseline water quality in parallel new sampling of the aquifer 2001 provides new inorganic geochemical data including trace elements that allow improving the knowledge of baseline conditions and hydrochemical functioning of a major sandstone aquifer the good correlation between 14 c activities temperature and depth along the main flow line indicate regular downgradient trends and possible water stratification unreactive tracers mainly stable isotope ratios 18 o and 2 h as well as c isotopes are used to define a timescale for the aquifer showing two groups of groundwater namely of modern and holocene age and late pleistocene age with a mixing zone baseline quality is then represented by a wide range of concentrations mainly the result of time dependent water rock interaction as already observed elsewhere in triassic sandstone aquifers some trace elements such as li rb cs which are not limited by solubility constraints show linear trends during saturated flow downgradient the chemistry is also specifically characterised by a regular increase in na and cl and locally so 4 as a result of evaporite dissolution related to overlying or basement limits the aquifer is mostly oxidising with a redox boundary marked by u decrease some 40 km from outcrop groundwater abstraction since the 1970s has created a strong lowering 10 150 m of the water table especially from 1970 to 1980 based on nine boreholes previously sampled in 1979 a decreasing evolution in radiocarbon content of the tdic together with significant evolution of 18 o content indicate that old groundwater has moved upgradient the major difference in terms of baseline evolution is observed using cl and na concentration and locally so 4 indicating an increasing influence of water circulation involving overlying or basement formations or of mixing with permian waters from the point of view of aquifer management the perceptible no 3 increase could provide information on the progress of any contamination under the aerobic conditions in addition the few key elements indicators of disequilibrium related to overlying or deep waters should be included in regular monitoring programmes

identifying the origin of groundwater samples in a multi layer aquifer system with random forest classification summary accurate identification of the origin of groundwater samples is not always possible in complex multilayered aquifers this poses a major difficulty for a reliable interpretation of geochemical results the problem is especially severe when the information on the tubewells design is hard to obtain this paper shows a supervised classification method based on the random forest rf machine learning technique to identify the layer from where groundwater samples were extracted the classification rules were based on the major ion composition of the samples we applied this method to the campo de cartagena multi layer aquifer system in southeastern spain a large amount of hydrogeochemical data was available but only a limited fraction of the sampled tubewells included a reliable determination of the borehole design and consequently of the aquifer layer being exploited added difficulty was the very similar compositions of water samples extracted from different aquifer layers moreover not all groundwater samples included the same geochemical variables despite of the difficulty of such a background the random forest classification reached accuracies over 90 these results were much better than the linear discriminant analysis lda and decision trees cart supervised classification methods from a total of 1549 samples 805 proceeded from one unique identified aquifer 409 proceeded from a possible blend of waters from several aquifers and 335 were of unknown origin only 468 of the 805 unique aquifer samples included all the chemical variables needed to calibrate and validate the models finally 107 of the groundwater samples of unknown origin could be classified most unclassified samples did not feature a complete dataset the uncertainty on the identification of training samples was taken in account to enhance the model most of the samples that could not be identified had an incomplete dataset

groundwater recharge and evolution in the dunhuang basin northwestern china groundwater recharge and evolution in the quaternary aquifer beneath the dunhuang basin was investigated using chemical indicators stable isotopes and radiocarbon data to provide guidance for regional water management the quality of groundwater and surface water is generally good with low salinity and it is unpolluted the dissolution of halite and sylvite from fine grained sediments controls concentrations of na and k in the groundwater but na cl molar ratios 1 in all samples are also indicative of weathering of feldspar contributing to excess na the dissolution of carbonate minerals yields ca2 to the groundwater thereby exerting a strong influence on groundwater salinity the delta o 18 and delta h 2 values in unconfined groundwater are enriched along the groundwater flow path from sw to ne in contrast confined groundwater was depleted in heavy isotopes with mean values of 10 4 parts per thousand delta o 18 and 74 4 parts per thousand delta h 2 compared with the precipitation values all of the groundwater samples were strongly depleted in heavy isotopes indicating that modern direct recharge to the groundwater aquifers in the plains area is quite limited the unconfined water is generally young with radiocarbon values of 64 9 79 6 pmc in the northern basin radiocarbon content in the confined groundwater is less than 15 pmc and an uncorrected age of similar to 15 ka indicates that this groundwater was recharged during a humid climatic phases of the late pleistocence or early holocene the results have important implications for inter basin water allocation programmes and groundwater management in the dunhuang basin c 2012 elsevier ltd all rights reserved

hydrogeochemical and isotopic characterization of the groundwater in the chari baguirmi depression republic of chad the chari baguirmi groundwater in the republic of chad is undergoing a steady deterioration both qualitative and quantitative due to climatic severe droughts and anthropogenic overexploitation constraints however this major water resource has not been to date the object of any comprehensive scientific investigation to fill this gap and consider a sustainable exploitation a hydrodynamic and hydrochemical study was undertaken this aquifer is located south of lake chad and displays a significant natural piezometric depression piezometric campaign on an area of 70 000 km2 bounded by lake chad the chari river the mountains of guera and the dunes of harr was conducted to understand the hydrodynamics of the groundwater water samples were collected on 124 points scattered over the study area hydrochemical and isotopic analyses 18o and 2h were achieved on all samples the interpretation of hydrochemical data was done using the piper diagram the multivariate analysis hierarchical ascending classification the index of base exchanges and ratios of na cl na so4 cl so4 br cl sr ca the hydrochemical results coupled with groundwater isotopes data allowed to understand the processes that govern the mineralization and the origin of groundwater salinity these investigations allowed on the one hand to differentiate between two poles of water mixing and second to demonstrate that the mineralization process and origin of salinity in the center of depression are both related to the lithology of the geological formations crossed by groundwater flow and climatic events causing evaporation of water from the aquifer

hydrological factors in the interpretation of stable isotopic proxy data present and past a european perspective in the context of this paper stable isotopic proxies are those preserving directly or via known or calculable fractionation factors a record of 18o 16o and or 2h 1h in the water which contributed to their growth suitable proxies include amongst others tree ring cellulose bone phosphate lake sediment minerals and speleothem fluid inclusions a principal aim of studying isotopic proxies is to gain more information about past climates through a knowledge of how rainfall isotope compositions have changed over time however converting back from proxy to rainfall is not necessarily straightforward because however well the isotopic fractionation due to proxy growth or formation is understood a variety of modifying processes may have intervened between this and the actual rainfall events three main reservoirs of environmental water may contribute to the isotopic compositions of terrestrial proxy indicators surface waters soil moisture and groundwater each of these can in principle be isotopically modified compared to rainfall in the locality this review examines these effects and how they may change under different european climate types at the present day it is concluded that while groundwater isotopic compositions typically represent closely the bulk composition of rainfall under a variety of climatic regimes soil and particularly lake waters require detailed study if their isotope systematics are to be adequately understood the review also finds that to a large extent the present is the key to the past in terms of recharge processes during the late pleistocene though glaciation may have had profound isotopic consequences in certain areas while a more general aridity led to the apparent absence of recharge in most areas for much of the late devensian

late pleistocene precipitation δ18o interpolated across the global landmass global water cycles ecosystem assemblages and weathering rates were impacted by the 4 c of global warming that took place over the course of the last glacial termination fossil groundwaters can be useful indicators of late pleistocene precipitation isotope compositions which in turn can help to test hypotheses about the drivers and impacts of glacial interglacial climate changes here a global catalog of 126 fossil groundwater records is used to interpolate late pleistocene precipitation 18o across the global landmass the interpolated data show that extratropical late pleistocene terrestrial precipitation was near uniformly depleted in 18o relative to the late holocene by contrast tropical 18o responses to deglacial warming diverged late pleistocene 18o was higher than modern across india and south china but lower than modern throughout much of northern and southern africa groundwaters that recharged beneath large northern hemisphere ice sheets have different holocene pleistocene 18o relationships than paleowaters that recharged subaerially potentially aiding reconstructions of englacial transport in paleo ice sheets global terrestrial late pleistocene precipitation 18o maps may help to determine 3 d groundwater age distributions constrain pleistocene mammal movements and better understand glacial climate dynamics

carbon isotopes to constrain the origin and circulation pattern of groundwater in the north western part of the bohemian cretaceous basin czech republic abstract the bohemian cretaceous basin represents a complex hydrogeological system composed of several aquifers with very favourable hydrogeological properties these aquifers have been exploited for many years the sustainability of such resources might be guaranteed by well organised water management which requires a detailed knowledge about the functioning of the hydrogeological system although many efforts have previously been made to evaluate groundwater residence time the many intricate geochemical processes complicate groundwater dating the current study clarifies the functioning of this complex hydrogeological basin using hydrogeochemical and isotopic investigations chemical data and a combination of 13 c and 14 c isotopes within the cenomanian and the turonian layers indicate groundwater interactions with deep seated co 2 rock matrix surface waters and fossil organic matter very depleted 13 c values average 13 c 13 4 suggest interactions with fossil organic matter whereas enriched values account for the interaction with deep co 2 gas ascending from the upper mantle via the numerous faults and fractures and also to a lesser extent from calcite dissolution geochemical processes that take place in the system cause a clear depletion in 14 c that greatly complicates groundwater residence time evaluation different dilution correction models have been applied considering the different c origins the stable isotope content mainly 18 o values indicates both the contribution of modern precipitation and the partial infiltration of palaeowaters during colder climatic conditions from the end of the pleistocene the apparent 14 c groundwater ages range from modern to 11 1 ka bp which suggests some post glacial infiltration from melting ice sheets finally all the acquired information was used to propose a conceptual model of c origin within the basin

radiocarbon dating of groundwater of the aquifer confined in the lower triassic sandstones of the lorraine region france abstract blavoux b and olive ph 1981 radiocarbon dating of groundwater of the aquifer confined in the lower triassic sandstones of the lorraine region france in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 167ndash 183 stable isotope and groundwater chemistry analyses on samples from about 40 boreholes in the lorraine region eastern france are used to evaluate the paleohydrological regime of the lower triassic sandstone aquifer in the study of the mechanisms of the general water dynamics of the aquifer at present in this sandstone aquifer the estimation of the 14 c activity a 14 in the total dissolved carbon tdc to 100 of modern carbon is justified by the absence of carbonates in the reservoir and by the 13 c contents in the tdc a significant relation could be determined between the 14 c activity in the tdc and 13 c a 14 7 7 13 59 6 this gradual enrichment of the tdc with 13 c results from the escape of the dissolved co 2 the meaning of the radiometric age is discussed as a function of piston and exponential type flows the study of the stable isotopes 18 o and 2 h revealed two water families the most recent waters have 18 o values higher by 1 0 than the more than 10 4 yr old waters this 1 0 discontinuity corresponds to the improvement of weather conditions during the holocene which amounts to 2 5 c the isochrons of the aquifer reveal the existence of hydrogeological sections bounded by faults where the rates of circulation are different

palaeorecharge conditions of the deep aquifers of the northern aquitaine region france summary the study was carried out in the northern part of the aquitaine basin extending in southwest france the basin has been intensively exploited for various purposes for many years although the geological context is well known there are still some gaps in the knowledge about the hydrogeochemical regime groundwater average residence time and the palaeohydrological conditions prevailing during the recharge period which would help to secure sustainable exploitation of the resources environmental isotopes 18 o 2 h 3 h 13 c together with radiocarbon were used to evaluate hydrochemical evolution residence time and palaeorecharge conditions for jurassic cretaceous and eocene aquifers radiocarbon activity in the aquifers varies widely between 0 and 94 pmc after radiocarbon corrections the ages indicate both modern and old waters sometimes exceeding the limit for 14 c dating the fontes and garnier model is best adapted to the specificity of the carbonate system the content in stable isotopes of water is varying between 7 7 and 4 9 for 18 o and 52 3 to 29 6 for 2 h the wide ranges of stable isotopic values imply variable climatic conditions a group of isotopically depleted samples was detected indicating colder climatic conditions during the recharge radiocarbon ages calculation together with isotopic signature point out that the depletion in stable isotopic values fits the period between 20 and 15 ka b p and therefore indicate the last glacial maximum lgm according to the correction model the transition from pleistocene to holocene would occur between 15 and 12 ka b p palaeohydrological data from the northern aquitaine basin does not confirm a significant hiatus in the recharge history the recharge conditions in south europe seem to have occurred under discontinuous permafrost conditions as documented by many palaeoclimatological archives this is in favour of an uninterrupted recharge of the confined aquifers of northern aquitaine basin such information should be considered by modellers in their attempts to simulate the hydrogeological functioning of large confined aquifers on the very long time range

spatial evolution of frictional heating and the predicted thermospheric wind effects in the vicinity of an auroral arc measured with the sondrestrom incoherent scatter radar and the reimei satellite 1 simultaneous observation with the sondrestrom incoherent scatter is radar and the reimei satellite was conducted on 3 october 2007 the objective was to measure horizontal patterns of the ionospheric structure in the vicinity of an auroral arc the is radar was scanned azimuthally with a fixed elevation angle and the satellite narrow view camera 557 7 nm was directed downward taking pictures every 0 12 s a stationary auroral arc was captured at 05 17 ut 02 54 mlt with both instruments simultaneously gross ionospheric features measured with the is radar around the arc were in good agreement with the expected magnetosphere ionosphere current system of particular interest was the horizontal pattern in the ion speed and temperature in the f region the ion speed within the arc was close to zero by contrast the larger ion speed 350 400 m s 1 on the poleward side was parallel to the arc and almost no horizontal shear within about 20 km width perpendicular to the arc this area was separated into two parts by the ion temperature one was associated with clear enhancements in excess of 1200 k and another was with more moderate enhancements less than 1000 k the widths of the two areas were approximately 10 km each the horizontal shear seen in the ion temperature suggested the presence of a narrow thermospheric wind shear of about 10 km width this paper suggests that the possible cause for the thermospheric wind shear was ion drag associated with localized soft particle precipitation or f region ionization

residence time indicators in groundwater the east midlands triassic sandstone aquifer the east midlands triassic sherwood sandstone aquifer which has been the subject of detailed radiometric age studies is used to investigate both inert and reactive constituents of groundwater as indicators of residence time detailed resampling of the aquifer in 1992 has provided a considerable body of new inorganic geochemistry data though without radiocarbon several inert indicators are defined including the isotopic ratios 18o 2h 36cl noble gas ratios as well as the halogen elements cl br f i and their element ratios these form a group of essentially unreactive tracers primarily reflecting changing rainfall inputs and palaeoclimatic conditions except at outcrop where human impacts are also seen clearly the concentrations of cl mainly from atmospheric sources remain below 25 mg l 1 cl over a distance of some 30 km from outcrop reactive indicators the result of time dependent water rock interactions include 13c mg ca sr ca na cl and show diagnostic trends along the flow lines however the concentrations of certain trace elements li rb cs mn and mo which are not limited by solubility constraints show linear trends along the present day flow gradient this water rock interaction is taking place in groundwaters with low total mineralisation and it can be demonstrated that reactions involving these elements and isotopes are occurring entirely within the aquifer since high salinity groundwaters are found below the sherwood sandstone there is good correlation between some of the elements and 14c activities in the 1977 data set and this has been used to derive a concentration age relationship for the 1992 set of data a chemical timescale for the aquifer is then established using a li and b a combination of five trace elements the age of the fresh groundwater is thus shown to be up to 100 ka bp indicating the likelihood of semi continuous recharge during the devensian glacial period preceding the glacial maximum when no recharge occurred 10 20 ka bp this approach may be of value in extending groundwater dating beyond the radiocarbon timescale as well as interpreting sites where no radiocarbon data are available the scatter from the mean age line indicates those groundwaters which are derived from either rapid or slower than average flow zones within the aquifer as well as age stratification this stratification is borne out by a depth profile of groundwater from a new borehole near to outcrop which is shown by a combination of chemical and isotopic tracers to contain holocene overlying late pleistocene water

constraining the groundwater flow system and aquifer properties using major ions environmental traces and a simple physical model in china s jilantai basin this study uses major ions and environment isotopes 87sr 86sr 13c and 14c together with a proposed physical model to constrain hydrogeochemical processes groundwater ages recharge rates and physical parameters in china s jilantai basin the major processes are identified using major ions which include calcite dissolution and the exchange of na for ca in upstream areas and gypsum dissolution carbonate incongruent dissolution and silicate weathering in downstream areas sr and major ions indicate the dissolution of carbonate minerals or gypsum and silicate weathering 87sr 86sr variations indicate that shallow groundwater in discharge areas consists of more than 90 groundwater from rainfall in the ulan buh desert ubd and middle groundwater comes entirely from the helan mountains the major ions 87sr 86sr ratio and physical model reflect that inter aquifer mixing has occurred between shallow unconfined and upper confined aquifers but not in middle confined formations the 14c ages range from the present to 15 ka and the distribution of 14c residence times indicate that inter aquifer flow occurs on a regional scale and over the long term between shallow unconfined and upper confined aquifers the travel times using the physical model proposed in this paper are comparable to the 14c ages indicating that this model is suitable for calculating travel times for the middle confined aquifers that have effective aquitards the vertical leakage rates are 0 01 0 03 m day and the long term recharge rates are 15 mm year approximately 5 of annual rainfall the groundwater from this region is a locally valuable resource and the correct understanding of groundwater flow systems inter aquifer mixing and recharge rates is critical to managing these groundwater resources

high cesium concentrations in groundwater in the upper 1 2 km of fractured crystalline rock influence of groundwater origin and secondary minerals abstract dissolved and solid phase cesium cs was studied in the upper 1 2 km of a coastal granitoid fracture network on the baltic shield aspo hard rock laboratory and laxemar area se sweden there unusually high cs concentrations up to 5 6 g l 1 occur in the low temperature 1 median laxemar 3 7 g l 1 and groundwater with marine origin aspo hrl 4 2 g l 1 overall lower but variable cs concentrations were found in other types of groundwater the similar concentrations of cs in the saline groundwater which had a residence time in the order of millions of years and in the marine groundwater which had residence times in the order of years shows that duration of water rock interactions is not the single and primary control of dissolved cs in these systems the high cs concentrations in the saline groundwater is ascribed to long term weathering of minerals primarily cs enriched fracture coatings dominated by illite and mixed layer clays and possibly wall rock micaceous minerals the high cs concentrations in the groundwater of marine origin are in contrast explained by relatively fast cation exchange reactions as indicated by the field data and predicted by 1d solute transport modeling alkali cations with low energy hydration carried by intruding marine water are capable of nh 4 in particular and k to some extent replacing cs on frayed edge fes sites on illite in the fracture coatings the result is a rapid and persistent at least in the order of decades buildup of dissolved cs concentrations in fractures where marine water flows downward the identification of high cs concentrations in young groundwater of marine origin and the predicted capacity of nh 4 to displace cs from fracture solids are of particular relevance in the disposal of radioactive nuclear waste deep underground in crystalline rock

using groundwater geochemistry and environmental isotopes to assess the correction of 14c ages in a silicate dominated aquifer system summary the use of 14c to constrain groundwater residence times requires careful correction of 14c activities a14c and an assessment of the degree of inter aquifer mixing in groundwater of the campaspe valley in the southern murray basin australia 13c values of dissolved inorganic carbon dic range from 18 to 2 using these 13c values to correct 14c ages assuming that dissolution of or exchange with matrix calcite had occurred implies that locally 90 of the dic is derived from carbonates in turn this suggests that low salinity groundwater in the deeper confined calivil renmark formation up to 50 60 km from the basin margins in the campaspe valley has a component of modern recharge which would require that widespread leakage from the overlying shepparton formation had occurred however 87sr 86sr ratios and major ion geochemistry of groundwater imply that negligible inter aquifer mixing has occurred and that calcite dissolution is a very minor process the variable 13c values are most probably due to methanogenesis via reduction of co2 in the groundwater that results in the residual dic being enriched in 13c as methanogenesis by this mechanism has only a minor impact on a14c uncorrected 14c ages are a better estimate of groundwater residence times groundwater in the north of the campaspe valley has a residence time of 9 13 ka which agrees with ages calculated from head gradients and hydraulic conductivities calivil renmark groundwater from the adjacent pyramid hill region in an area where the aquifers contain lower hydraulic conductivity sediments is substantially older up to 20 25 ka the age of groundwater from the shepparton formation increases irregularly with depth with ages of in excess of 25 ka recorded at its base this study illustrates the need to fully understand hydrogeological processes in order to correct 14c ages especially in silicate dominated aquifers where dissolution of carbonates may not be the major process controlling 13c values

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

delineation of temporal variability and governing factors influencing the spatial variability of shallow groundwater chemistry in a tropical sedimentary island summary an attempt has been made to delineate the temporal variability and factors governing the shallow groundwater chemistry using analysis of variance anova and multivariate analysis notably r mode factor fa and hierarchical cluster analysis hca subsequently geostatistical isoplethic maps were applied to convey better understanding on the distribution of selected groundwater parameters the manukan island s shallow aquifer with sedimentary setting that constantly abstracted for freshwater supply has been selected for this study one way anova suggested that neither changes of tide level nor rainfall volume appeared to exert significant influence on the groundwater chemistry of the small island rather the groundwater chemistry was greatly governed by influence from seawater intrusion which characterized by considerable amount of ca na and cl such condition was well explained by a piper diagram where most plots were situated at the middle diamond shaped diagram indicating mixing condition fa likewise revealed that the shallow groundwater receives marked influence from carbonate dissolution and silicate weathering processes especially boreholes located in the inland area this can be clearly noted from the distinct groupings of relationships among different factors hca classified boreholes into three groups according to their locations in the coastal area suggesting significant chemical variations between boreholes with distance from coast such distribution pattern was particularly evident in the isoplethic map overall it appears that the shallow groundwater in the tropical island is not an appropriate source for drinking water in concern to its exceptionally high salinity and several elevated minor elements mn pb and se for this it is suggested that efforts in exploring other alternative sources should be performed outright

isotopic evidence for palaeowaters in the british isles before the 20th century groundwater circulation in the aquifers of the british isles had largely adjusted to the temperate maritime climate and sea levels established over the past 10 ka since the end of the pleistocene however in the last 100 a this natural regime has been disturbed by abstraction of water for public supply and industrial use and palaeowaters from earlier recharge episodes are now becoming a factor to be considered in water balance estimates this paper presents a synthesis of the existing palaeowater distribution in the british isles based on isotopic evidence 18o 2h and and14c as such it has relevance to palaeoclimatic studies in addition to the water resource implications the triassic basins of england and northern ireland contain saline waters beyond the range14c dating 40 ka stable isotopic ratios show enrichment in some basins and depletion in others without an overall pattern that would explain all the observed compositions the results for the wessex basin suggest recharge in pre quaternary times but for the other basins some flushing by pleistocene or holocene meteoric waters is indicated isolated occurrences of apparently long residence waters are found elsewhere throughout the british isles for example from carboniferous and lower palaeozoic strata in such cases environmental isotopes are more useful as constraints on hydrogeological models than as indicators of palaeoconditions major water supply aquifers are restricted almost entirely to england the two sandstone formations triassic sherwood sandstone and cretaceous lower greensand have a greater range of stable isotopic values between phreatic and confined conditions than the two carbonate formations jurassic lincolnshire limestone and cretaceous chalk this indicates that the sandstone aquifers are better archives of information on palaeoconditions than the carbonate aquifers they show that atmospheric circulation patterns over britain have probably remained the same since the late pleistocene however 14c data from all four of the major aquifers emphasise the hiatus in recharge during periglacial conditions which occurred between the late pleistocene and early holocene

flow pattern and residence time of groundwater within the south eastern taoudeni sedimentary basin burkina faso mali the knowledge about groundwater flow conditions within the southeastern taoudeni basin aquifer shared by burkina faso and mali is relatively limited with very little information on potentiometric heads recharge processes residence time and water quality a better evaluation of groundwater resources in this area is a strategic point for water resources management in the entire soudano sahelian region which endures since the beginning of the twentieth century a continuous decrease in precipitation amount this paper provides a transboundary synthesis using water 18o 2h and 3h and carbon isotopes 13c and 14c in conjunction with hydrogeological and hydrochemical data the objectives are to improve the conceptual model of groundwater recharge and flow within this sandstone reservoir and to assess the changes in the aquifer due to water abstraction and recent climate changes including an insight into sahelian aquifers palaeorecharge processes the local meteoric water line for the bobo dioulasso station is proposed 2h 8 0 0 5 18o 10 2 2 1 two main tendencies can be derived from groundwater chemistry first a slight evolution from the ca mg hco3 type towards a na k hco3 type that indicates developed interactions between groundwater and clay minerals related to the residence time of groundwater a second tendency towards cl no3 so4 hco3 water types indicates the anthropogenic influence on groundwater related to the poor sanitary conditions observed around wells the carbon 14 activity measured on the tdic varies between 0 3 and 122 pmc so our record contains samples covering a wide period from actual to pleistocene suggesting a continuous recharge of the system through time even if the sahel region has endured many different climate phases which have influenced the infiltration and recharge processes all groundwater samples have stable isotope compositions in the range of the present day regional and global meteoric water line which suggests that the sampled groundwater was not significantly affected by evaporation during recharge evolved waters are depleted relative to unevolved samples by 1 5 2 in 18o and 10 15 in 2h the whole dataset support the hypothesis of a largely unified homogeneous aquifer system with a multilayered structure but it also points out the very low renewability of the resource and a strong anthropogenic contamination of the shallowest horizons

residence time of chalk groundwaters in the paris basin and the north german basin a geochemical approach the comparative geochemical and isotopic study of confined and unconfined chalk groundwaters of the paris basin and the n german basin proves a significant chemical evolution during groundwater flow from the recharge zones to the deep confined aquifer different time dependent geochemical parameters have been tested as dating tools cation ratios sr2 ca2 mg2 ca2 n no 3 noble gas contents as paleotemperature indicators ne ar kr xe radiogenic he 13c 14c 18o 2h 3h cation ratios and 13c show the importance of incongruent dissolution processes in the chalk aquifer water rock interactions were taken into account in a multi step dissolution model to determine radiocarbon groundwater ages the oldest waters in the confined part of the paris basin chalk with maximum 14c ages of 14 000 a b p contain pleistocene recharge components as can be shown by a stable isotope depletion and noble gas temperatures significantly lower than in recent groundwaters chalk waters at the lagerdorf site in northern germany show a distinct stratification with respect to residence times and hydrochemistry

diagenetic alterations related to marine transgression and regression in fluvial and shallow marine sandstones of the triassic buntsandstein and keuper sequence the paris basin france abstract the distribution of diagenetic alterations in triassic fluvio deltaic quartzarenitic to sublitharenitic lowstand systems tract lst sandstones of the gres a voltzia formation anastomosing fluvial quartzarenitic transgressive systems tract tst sandstones of the gres a roseaux formation and shallow marine quartzarenitic to sublitharenitic tst sandstones of the gres coquiller formation the paris basin france can be linked to transgression and regression events and thus to the sequence stratigraphic context near surface eogenetic alterations which display a fairly systematic link to the depositional facies and sequence stratigraphic framework include i cementation by meteoric water calcite 18 o 8 9 and 13 c 9 1 in the fluvio deltaic lst sandstones ii cementation by mixed marine meteoric calcite 18 o 5 3 to 2 6 and 13 c 3 9 to 1 3 and dolomite 18 o 4 6 to 2 6 and 13 c 2 9 to 2 3 in the foreshore tst sandstones and below parasequence boundaries pb and transgressive surface ts and in the shoreface tst sandstones below maximum flooding surfaces mfs being facilitated by the presence of carbonate bioclasts iii dissolution of detrital silicates and precipitation of k feldspar overgrowths and kaolinite particularly in the fluvio deltaic lst sandstones owing to effective meteoric water circulation and vi formation of autochthonous glauconite which is increases in abundance towards the top of the fluvio deltaic lst sandstones and along ts and in the shoreface tst sandstones by alteration of micas owing to the flux of seawaters into the sandstones during transgression whereas parautochthonous glauconite is restricted to the ts sandstones owing to marine reworking mesogenetic alterations which include cementation by quartz overgrowths and illite display fairly systematic link to fluvio deltaic lst sandstones this study has revealed that linking of diagenesis to transgression and regression events enables a better understanding of the parameters that control the spatial and temporal distribution of diagenetic alterations in sandstones and of their impact on reservoir quality evolution

constraining groundwater flow residence times inter aquifer mixing and aquifer properties using environmental isotopes in the southeast murray basin australia environmental isotopes particularly d 18 o d 2 h and d 13 c values 87 sr 86 sr ratios and a 14 c constrain geochemical processes recharge distribution and rates and inter aquifer mixing in the riverine province of the southern murray basin due to methanogenesis and the variable d 13 c values of matrix calcite d 13 c

joint two dimensional observations of ground magnetic and ionospheric electric fields associated with auroral zone currents 32 auroral zone currents during the passage of a westward travelling surge

establishing constraints on groundwater ages with 36cl 14c 3h and noble gases a case study in the eastern paris basin france abstract groundwaters from the tithonian kimmeridgian oxfordian and upper dogger aquifers within the eastern part of the paris basin france were characterised using 3 h 14 c and 36 cl and noble gases tracers to evaluate their residence times and determine their recharge period this information is an important prerequisite to evaluating the confinement properties of the callovo oxfordian clay formation sandwiched between the oxfordian aquifer and the dogger aquifer currently being investigated by the french nuclear waste management agency andra for radioactive waste disposal data presented in this paper are used to test 4 hypotheses 1 the oxfordian limestone is isolated from the overlying tithonian kimmeridgian surface aquifer this first hypothesis is supported by the presence of measurable 3 h activities in groundwaters from the surface aquifer 6 11 tu and by its absence in groundwaters derived from deeper aquifers 2 the callovo oxfordian clay sequence in the vicinity of the url serves as an effective barrier to advective flow and transport between the underlying upper dogger aquifer and the overlying oxfordian limestone aquifer this second hypothesis is supported by relatively low concentrations of cl 3 5 78 mg l 1 na 15 145 mg l 1 br 0 08 0 4 mg l 1 and 4 he rad 0 2 2 3 ccstp g 1 and slightly higher 36 cl cl ratios 2 7 59 10 15 at at 1 in groundwaters from the oxfordian aquifer compared to those from the upper dogger aquifer 345 4027 mgcl l 1 402 2390 mgna l 1 1 8 22 2 mgbr l 1 1 6 37 2 ccstp he g 1 1 5 10 15 at 36 cl at 1 cl 3 groundwaters from the oxfordian aquifer in the vicinity of url are pre holocene with residence times exceeding 10 ka geochemical and isotopic lines of evidence for this hypothesis include a 13 c values measured on oxfordian aquifer waters that are close to 13 c of the aquifer matrix reflecting strong isotopic exchange over several thousand years b noble gas temperatures that indicate recharge temperatures between 3 and 8 6 c lower by 2 7 c than the modern average temperature in this area c radiogenic 4 he concentrations between 0 16 10 5 and 2 3 10 5 ccstp g 1 of water about 2 3 orders of magnitude greater than the 4 he concentration of air equilibrated water 4 groundwater residence time for the upper dogger aquifer in the vicinity of the url probably exceed several hundred thousand years such long residence times are indicated by the accumulation of radiogenic he up to 37 10 5 ccstp g 1 assuming a closed system primary contributors to uncertainties in interpretation of the data presented in this paper are the lack of well defined 36 cl cl input ratio knowledge about the 4 he rad sources for oxfordian and dogger aquifers knowledge about transport processes occurring through the dogger aquifer and the extensive dilution of initial 14 c activities by dissolution exchange with aquifer matrix overall however although the data presented in this paper remain semi quantitative due to inevitable intrinsic limitations of the methods none contradict the hypotheses of long residence times and aquifer isolation in the vicinity of the url

groundwater evolution in the continental intercalaire aquifer of southern algeria and tunisia trace element and isotopic indicators abstract the geochemical processes taking place along an 800 km flow line in the non carbonate continental intercalaire aquifer ci aquifer in north africa are described using chemical major and trace element and isotopic indicators the aquifer is hydraulically continuous from the atlas mountains in algeria to the chotts of tunisia and the geochemical evidence corroborates this the highest discharge temperature is 73 c but silica geothermometry indicates a maximum temperature of 94 c at depth chloride concentrations increase from 200 to 800 mg l 1 and the br cl ratios confirm the dissolution of non marine evaporites or interstitial waters as the main source of salinity fluoride concentrations are low and are likely to be derived from rainfall recording oscillations in source radiocarbon ages except near outcrop are at or near detection limits and the 18o and 2h values indicate a cooler recharge regime with rainfall having lower primary evaporation than today this is shown by the fact that mean isotope ratios of ci waters are around 3 lighter than the present day weighted mean value for rain major ion ratios and most trace elements indicate that despite the complex structure and stratigraphy uniform evolution with continuous water rock interaction takes place along the flow lines which are only disturbed near the tunisian chotts by groundwater converging from additional flow lines the ageing of the water can also be followed by the smooth increase in several indicator elements such as li k and mn which are least affected by solubility controls similarly the influence of marine facies in the tunisian sector may be recognised by the changing mg ca and higher br cl as well as trace element indicators the groundwaters are oxidising up to 300 km from outcrop dissolved o2 has persisted for at least 20 ka and within this zone the concentrations of several elements forming oxy anions such as u and cr increase and no3 remains conservative beyond 300 km from outcrop the groundwaters are reducing and contain high fe concentrations the basin contains huge reserves of fresh brackish waters but these need careful development due to the limiting high salinity and scaling tendency resulting from the high temperatures and mineral super saturation caused during abstraction as well as high concentrations of some harmful elements such as cr in the oxidising section

the hydrogeology and groundwater resources development of the cambro ordovician sandstone aquifer in saudi arabia and jordan abstract the saq cambro ordovician sandstones form the major national aquifer in saudi arabia and jordan significant abstraction of groundwater has taken place since the early 1950s and monitoring of the aquifer responses indicates a moderate transmissivity but high specific yield the groundwater quality is excellent for irrigation which is the present major use and is also good for potable purposes although large drawdowns are being experienced locally in confined areas of the aquifer the unconfined area responses show the aquifer to have an excellent potential for development under groundwater mining principles that may be considered for use outside the areas of occurrence

comparison of height integrated current densities derived from ground based magnetometer and rocket borne observations during the porcupine f3 and f4 flights on march 19 1979 the porcupine f3 rocket was launched from esrange sweden during a period of low magnetospheric activity while the porcupine f4 rocket launched on march 31 1979 flew during a rather disturbed interval besides other experiments the rockets took measurements of ionospheric electric fields and energetic particle spectra the electron spectra measured by the rocket were used to calculate height integrated ionospheric conductivities by using rees method together with the electric field measurements height integrated current densities could be calculated from the rocket measurements during both flights the magnetic perturbations recorded on the ground by the scandinavian magnetometer array indicated a westward electrojet since during both flights the electric field was nearly southward directed and parallel to the ground magnetic disturbance vectors the westward electrojet could be attributed to a nearly pure hall current in both cases from the magnetic data height integrated ionospheric current densities have been computed at the magnetic footprints of the rockets in the ionosphere by means of field separation and upward continuation a comparison of the current densities derived from ground based magnetometer and rocket borne observations shows a very good agreement in the quiet period during the porcupine f3 flight while there are differences during stronger magnetospheric activity porcupine f4 flight due to the different spatial and temporal resolution of rocket and ground observations

geochemical evidence for efficient aquifer isolation over geological timeframes aquitards layers of rock having low permeability have been suggested as potential long term reservoirs for toxic materials such as nuclear or chemical waste but information about the isolation properties of aquitard layers is essential to evaluate whether they can indeed be used safely as reservoirs here we investigate the long term mobility of groundwaters between two aquifers surrounding an aquitard layer in the eastern recharge area of the paris basin france using helium isotopes as a geochemical tracer the deeper trias sandstone aquifer which lies above the crystalline basement accumulates radiogenic 4he and primordial 3he from large regions of the crust and mantle at rates comparable to the degassing of the whole crust1 and of mid ocean ridges2 we show that the overlying carbonate dogger aquifer which is separated from the trias aquifer by an aquitard layer consisting of a 600 m succession of shales and clays is stagnant and has been extremely well isolated from the trias over the past several million years this finding together with previous studies at the centre of the paris basin3 4 shows that diffusive mass transfer across aquitards is negligible and that cross formational flow in basins takes place preferentially in faulted areas

hydrochemical evolution of the east midlands triassic sandstone aquifer england a detailed hydrogeochemical interpretation has been made of the red bed sherwood sandstone triassic aquifer of the east midlands of england on which a radiocarbon model has been used to establish a chronology of groundwaters along the flow line groundwater evolution is dominated by carbonate and sulphate mineral solution and precipitation and by redox reactions cation exchange reactions are negligible and the hydrogeochemistry has evolved in the absence of residual saline water three distinct zones are recognised 1 i recent groundwater mainly 100 y oxidising dominated by congruent dissolution of dolomite and by inputs from atmospheric and anthropogenic sources 2 ii groundwater age 103 104 y predominantly reducing dominated by incongruent dissolution of dolomite 3 iii groundwater age 104 y reducing conditions approach to isotopic and chemical equilibrium in the carbonate system dominance of gypsum dissolution the minor and trace element variation can be interpreted in relation to the principal geochemical reactions and recharge history na cl f and b are controlled by atmospheric inputs sr2 and mn2 trends can be explained by carbonate and sulphate mineral dissolution ba2 is derived from carbonates but controlled by barite equilibrium fe so42 no3 and u are strongly influenced by redox reactions the concentrations of transition metals and other elements remain very low only li and k are considered to represent additions by reaction of silicate minerals the extent of direct anthropogenic influence is probably limited to enhanced so4 no32 and possibly cu zn and pb in zone i

hydrochemical trends palaeorecharge and groundwater ages in the fissured chalk aquifer of the london and berkshire basins uk the hydrochemical radiochemical stable isotope 14c and dissolved noble gas composition of groundwaters has been determined along two profiles across the confined fissured chalk aquifer of the london basin of southern england and for selected sites in the adjacent berkshire basin during downgradient flow in the london basin aquifer the groundwater chemistry is modified by water rock interactions congruent and incongruent reaction of the carbonate lithology resulting in enhanced mg ca and sr ca ratios and 13c contents with increased residence times redox and ion exchange reactions and towards the centre of the basin mixing with a residual saline connate water stored in the chalk matrix there is evidence from anomalous water chemistries for a component of vertical leakage from overlying tertiary beds into the confined aquifer as a result of historical dewatering of the aquifer dissolved noble gas contents indicate the climate was up to 4 5 c cooler than at present during recharge of the waters now found in the centres of both basins stable isotope 2h and 18o depletions correspond to this recharge temperature change for evolved waters having 13c 8 pdb a negative linear correlation is demonstrated between derived recharge temperatures and 13c values which is interpreted as mixing between relatively warm light isotopic fracture borne waters and cooler stored waters of the matrix having a 13c signature more or less equilibrated with the chalk from geochemical 14c 4he age estimates the abstracted water is interpreted as being either of wholly holocene post devensian glacial origin or an admixture of holocene and late pleistocene pre glacial cold stage interstadial recharge devensian pleniglacial stage waters of the last glacial maximum are not represented

characteristics of the field aligned current system in the nighttime sector during auroral substorms fujii et al 1994 obtained characteristics of the electrodynamic parameters that is field aligned currents electric fields and electron precipitation which are associated with auroral substorm events in the nighttime sector through a unique analysis that places the ionospheric measurements of these parameters into the context of a generic substorm determined from global auroral images in this paper we investigate in considerably more detail the characteristics of the field aligned currents using data from the same set of passes as the previous study we show for the first time that the net upward field aligned currents throughout the surge and surge horn are sufficient to account for most if not all of the converging currents of the auroral electrojets current densities are largest in the surge and surge horn current region continuity does not appear to exist across the substorm bulge region much of the auroral substorm field aligned current is composed of filamentary currents and finite current segments at large angles to each other the westward electrojet may contain large gradients in intensity both in local time and latitude due to sets of localized field aligned currents the net downward current for several hours to the west of the surge is insufficient to account for the eastward electrojet consistent with the concept that this electrojet originates primarily on the dayside our pattern of field aligned currents associated with the surge has common features and also differs significantly from the patterns previously derived from data from radars and ground based magnetometer arrays our pattern is considerably more complex probably due to the much higher resolution in latitude of the satellite data it is also larger in area since our average substorm is much larger than those pertaining to the previous patterns giving a substorm wedge considerably wider than that obtained from the radar and array data

using 3h and 14c to constrain the degree of closed system dissolution of calcite in groundwater abstract this study uses 3h concentrations 14c activities a14c 87sr 86sr ratios and 13c values to constrain calcite dissolution in groundwater from the ovens catchment se australia taken in isolation the 13c values of dissolved organic c dic and 87sr 86sr ratios in the ovens groundwater imply that there has been significant calcite dissolution however the covariance of 3h and 14c and the calculated initial 14c activities a014c imply that most groundwater cannot have dissolved more than 20 of 14c free calcite under closed system conditions rather calcite dissolution must have been partially an open system process allowing 13c and 14c to re equilibrate with co2 in the unsaturated zone recognising that open system calcite dissolution has occurred is important for dating deeper groundwater that is removed from its recharge area in this and other basins the study is one of the first to use 14c and 3h to constrain the degree of calcite dissolution and illustrates that it is a valuable tool for assessing geochemical processes in recharge areas