chemical and physical denudation in the amazon river basin we present major and trace element data on the suspended and dissolved phases of the amazon river and its main tributaries the sr isotopic composition of the dissolved load is also reported special attention is paid to the abundances of ree and to their fractionation between the dissolved and suspended phase the rivers of the amazon basin are among the richest in dissolved ree and are similar to the rivers of the congo system however a greater range of fractionation between lree and hree is reported here at a global scale the rivers have intermediate patterns between those of the congo system and those of high ph rivers such as the indus and mississippi rivers only few elements rb u ba k na sr and ca are mobilized by silicate weathering these elements are strongly depleted in the suspended phase with respect to upper continental crust in the dissolved load these elements are controlled by atmospheric inputs and the weathering of the main lithologies we propose a model based on mass budget equations that allow the proportions derived from the different sources to be calculated as a consequence silicate carbonate and evaporite weathering rates can be estimated as well as the consumption of co2 by weathering of each of these lithologies physical weathering rates can be estimated by two complementary approaches on the one hand the multi year average of suspended sediments yields can be used to estimate physical denudation on the other hand we have developed a steady state model of erosion that allows us to calculate physical erosion rates on the basis of the dissolved load of rivers a mean crustal composition is assumed in this model for the rock sources of the drainage basins comparison of the rates predicted by the model to the observed rates shows good agreement for the lowland rivers but a strong discrepancy for the rivers derived from the andes andean rivers solimoes madeira and amazon have observed sediment yields much greater than those predicted according to the steady state model of chemical and physical weathering two interpretations can account for this inconsistency the first is that these rivers are not in steady state and hence that the soils are being destroyed the second requires that the local continental crust is different from the average continental crust of taylor and mclennan and contains a large proportion of sedimentary rocks using the measured sediment yields and assuming a steady state we can estimate the amount of sediment recycling for each drainage basin for the amazon at santarem we find that at least 25 of the mass of the upper continental crust of the amazon drainage basin is constituted of recycled material

boron isotope signatures in the coastal groundwaters of french guiana 1 drinking water used by the population of french guiana comes mostly from rivers and can induce major health impacts consequently groundwaters are being studied in terms of an alternative drinking water supply in this context boron isotopes were applied to the coastal aquifers to better constrain the water rock interactions we found that the 1 1 b signatures vary between 2 98 and 49 35 o in the groundwaters and between 36 35 and 42 41 o in the river waters and that the local seawater gave a value of 40 76 o we also noted an inverse correlation between groundwater ph and 1 1 b this relationship previously demonstrated experimentally is particularly well defined in the french guiana coastal aquifer because of the wide ph range 4 18 to 7 64 naturally present in the groundwaters it would appear that the variations in 1 1 b values are linked to water rock interaction processes e g dissolution precipitation of silicates

bottom temperatures in drake passage abstractlong time series of bottom temperatures in the southern ocean are rare the cdrake array with over 40 current and pressure recording inverted echo sounders moored across drake passage to monitor the antarctic circumpolar current acc variability and transport measured temperature at 1 and 50 m above the seafloor at depths 3500 m and at the southern continental margin the 4 yr dataset provided an opportunity to examine the temporal and spatial scales of bottom temperature variability high variability was observed ranges were 0 5 0 9 c in the northern passage and 0 3 0 6 c in the southern passage standard deviations in the two regions were 0 1 0 15 c and 0 05 c respectively meandering of the acc with its deep reaching thermocline accounted for up to 50 of the observed bottom temperature variance northern passage temperatures spaced less than 40 km apart were correlated with each other while those in the southern portion separated by 60 70 km were not a gap in the west scotia

the effect of ph and temperature on the isotopic fractionation of boron between saline brine and sediments the effects of ph and temperature on the adsorption distribution of boron in sediment and the boron isotopic fractionation factor between saline brine and sediment were studied the results show that the adsorption and isotopic fractionation of boron between saline brine and sediment are similar to that between seawater and marine or pure sediments in a certain ph range the adsorption distribution factor kd and isotopic fractionation factor of boron are controlled by the ph of the saline brine kd increases with ph while decreases an unusual aspect of this study was that 11b enrichment in the solid was seen during boron adsorption by clay at high ph these results have been used to study the distribution of boron isotopes in salt lakes of qaidam basin

interpretation of resistivity measurements over 2d structures1 resistivity measurements were carried out in a survey area in the south of germany this area is characterized by complicated subsurface geology schlumberger full arrays and their respective half arrays were recorded simultaneously the results obtained by the one dimensional 1d interpretation of the full array measurements were incorrect because of a resistivity discontinuity this discontinuity under a relatively thick overburden could only be located by the half array soundings its exact location and the resistivity distribution in the subsurface were ascertained by comparing the sounding curves with 2d model curves which are calculated by a finite difference method

the geochemistry of boron and its isotopes in groundwaters from marine and non marine sandstone aquifers abstract the geological evolution of b in two uk sandstone aquifers is followed from precipitation chemistry through to groundwaters in both the unconfined and confined zones measurements have been made of major element geochemistry b concentrations and b isotopic ratios the isotopic measurements were carried out using icp ms following a simple preconcentration step isotopic measurements of rainfall show a bimodal distribution and it is suggested that enriched signatures are characteristic of atlantic air over britain and depleted signatures representative of continental air in the marine lower greensand aquifer dissolution of glauconite results in the mobilisation of b and a correlation with so 4 suggests that this dissolution is related to the oxidation of pyrite which appears to be the so 4 forming reaction in the aquifer in the non marine hastings beds isotopic ratios and a correlation with hco 3 suggest that b is associated with the dissolution of ferroan carbonates in both aquifers the geochemical evolution of b is complex and more information is needed on the behaviour of b isotopes during evapotranspiration and groundwater recharge

boron isotopic compositions of brine sediments and source water in da qaidam lake qinghai china abstract the isotopic compositions of boron in da qaidam lake quinghai have been determined by using the technique of thermal ionization mass spectrometry of cesium tetraborate the brines are enriched in 11b with an average 11b of 5 49 2 34 compared with those of lake sediments and boron minerals produced by the lake the apparent isotopic fractionation factors between brine and lake sediments as well as boron minerals are 0 988 0 001 and 0 986 0 001 respectively source water 11b values range from 11 72 to 16 69 depending on their origin

geochemical mass balance and weathering rates of ultramafic schists in amazonia the hydrochemical balance of the yaou catchment in french guiana was determined over a period of 1 year combined with a detailed characterization of the primary minerals and their weathering products in order to estimate ultramafic rock weathering rates in a rainforest environment the time required to develop the main horizons of the laterite profile was obtained from estimations of the weathering rates and dissolution kinetics of some major parent minerals chlorite serpentine biotite calcite the specific transport of solute matter in the catchment is 205 kg ha a the cl and no3 net outputs shows that the system is in dynamic equilibrium notably with respect to the biomass reservoir the output flux of mg in solution is mainly supplied from the weathering of primary minerals whereas that of ca comes both from atmospheric contributions and from the dissolution of carbonates the fluxes of k and more particularly na derive essentially from the atmosphere knowing the weathering rate of primary minerals the total co2 consumption rate by silicate weathering is estimated at 1430 mol ha a the weathering rates of chlorite serpentine and biotite range from 18 to 65 mol ha a and those of talc and calcite are respectively 51 and 153 mol ha a weathering rates normalized to mineral modal proportions give a decreasing order of stability resistance to weathering calcite biotite chlorite serpentine talc that agrees with their vertical distribution in the weathering profile the dissolution kinetics of chlorite biotite and serpentine expressed in relation to the si release rate were calculated using estimations of the mineral exchange surface by a optical microscope image processing of crystal outlines and b bet specific surface measurements the release rate of si computed for biotite chlorite and serpentine ranges around 10 13 and 10 14 mol m2 s using microscope images on particle sizes the estimated dissolution kinetics is two orders of magnitude lower when using the bet measured exchange surface which is 100 times larger the saprolitization rate calculated from the weathering rates of calcite chlorite and biotite is on average 7 5 m ma the rate of latosol development calculated from the weathering rate of serpentine at the saprolite latosol interface is estimated at 4 5 m ma that means that the profile is chemically thickening at a rate of 3 m ma

geoelectrical model calculations for two dimensional resistivity distributions for the calculation of geoelectrical model curves for a two dimensional resistivity distribution the potential equation is transformed by means of a fourier cosine transform into a two dimensional helmholtz equation containing the separation parameter the numerical solution of this equation for different values of for an irregular grid is obtained using the method of finite differences combined with the method of overrelaxation the method by which derivatives are replaced by finite differences turned out to be very important especially for high resistivity contrasts after testing several methods designed to deal with any type of resistivity distribution a method of discretization similar to that used by brewitt taylor and weaver 1976 for magnetotelluric modeling for h polarization was found the best examples are given of model curves for schlumberger soundings over a vertical fault covered by overburden the incorrect use of horizontal layer models leads to erroneous interpretations that are more complex than the real subsurface situations

heterogeneities and interconnections in groundwaters coupled b li and stable isotope variations in a large aquifer system eocene sand aquifer southwestern france abstract the study of stable isotope of the water molecule and elemental data for groundwater in the large eocene sand aquifer system of sw france showed that the 18 o values of groundwater fall in the range 5 6 to 10 6 vs smow with 2 h values varying between and 34 3 to 72 3 vs smow there is no relationship between 18 o and 2 h values and the salinity but the stable isotopes data plot on or near the global meteoric water line taken as a whole the enriched samples clearly correlate with present day recharge while the most depleted samples reflect an old recharge groundwaters in the present study display large ranges of both boron concentrations 7 to 2550 g l 1 and boron isotopic compositions the lowest 11 b value being close to 18 0 and the highest one near 36 2 the scatter of b concentrations and 11 b values reflects the different rock types contributing to the supply of dissolved boron carbonates evaporites and silicates as well as an input from rainwater and fractionation during water rock interaction with clay minerals lithium concentrations in groundwater also span a wide range 0 6 to 253 g l 1 as do the lithium isotopic signatures that range between 6 5 and 28 6 we can evidence there that the b isotopic compositions are controlled by water rock interactions while li and 7 li variations are also controlled by water rock interaction processes dissolution and formation of alteration minerals that can occur at different temperatures within the groundwater system

fractionation of boron isotopes during erosion processes the example of himalayan rivers abstract the boron isotopic composition of 5 rain waters and 35 river waters running from the high himalayas 5050 m down to the bay of bengal were measured by ion microprobe to make a first survey of the boron isotopic fractionations present in a major erosion system the rains have rather homogeneous b concentrations and isotopic compositions 0 09 0 09 mol l and 5 4 1 7 at the exception of the two kathmandu samples which probably reflect a significant anthropic contamination the river waters show a large range of b concentrations from 0 09 to 28 68 mol l and of b isotopic compositions 11b values ranging from 7 0 to 29 4 no systematic correlation between the 11b values and the major ion chemistry of the river waters is present at the exception of the most b and cl rich rivers which have systematically the highest 11b values likely controlled by evaporite dissolution after correction for the evaporite contribution from 9 4 to 64 4 of dissolved b with a systematic decrease southwards the riverine b concentrations and 11b values are still highly variable from 0 10 to 5 83 mol l and from 5 8 to 24 1 respectively this variation reflects mostly different conditions of silicate weathering congruent and incongruent silicate dissolution the contribution from the dissolution of carbonates being quite negligible 5 of the dissolved b on the river b budget at variance with congruent silicate dissolution incongruent dissolution occurs with a large b isotope fractionation which depends on ph clay water 31 2 at acidic ph and 5 8 at higher ph the b systematic suggests strongly that these fractionations are produced over a wide range of ph from 7 to 9 5 in soils and don t result from reactions between the dissolved and suspended load in rivers the net result of himalayan erosion for the global b cycle is the input to the sea of waters with highly variable b concentrations and isotopic compositions 0 67 and 0 29 mol l 5 0 and 21 0 for the ganga and the brahmaputra during the monsoon period respectively

dense bottom layers in the scotia sea southern ocean creation lifespan and destruction the lower limb of the atlantic overturning circulation is renewed by dense waters from the southern ocean a substantial portion of which flow through the scotia sea we report dense bottom layers here with gradients in temperature and salinity comparable to those seen near the surface of the southern ocean these are overlain by layers with much weaker stratification and are caused by episodic overflows of dense waters across the south scotia ridge and topographic trapping within deep trenches one such layer was found to be at least 3 4 years older than the water immediately above the estimated vertical diffusivity to which this layer was subject is substantially less than the strong basin average deep mixing reported previously we conjecture that a vertical mixing in the scotia sea is strongly spatially inhomogeneous and b the flushing of these layers like their formation is related to overflow events and hence also strongly episodic

combined sounding profiling resistivity measurements with the three electrode arrays a combination of dc resistivity sounding and profiling measurements can be used to obtain the maximum information about distribution of resistivities in the earth combined sounding profiling measurements with the amn mnb arrays are considered the resistivity data from such measurements can be presented as a normal sounding curves b combined sounding profiling curves c profiling curves d pseudo sections or as transformations obtained by the so called gradient processing to emphasize the influence of the target objects the examples chosen from numerical modeling and field tests show the efficiency of measurements with three electrode arrays to accurately locate thin conductors and contacts of lithological units of different resistivities an interpreted cross section is compared with the results of other geophysical measurements vlf r dipole em ip showing good correlation

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

detecting small scale targets by the 2d inversion of two sided three electrode data application to an archaeological survey abstractthe detecting capabilities of some electrical arrays for the estimation of position sizeand depth of small scale targets were examined in view of the results obtained from2d inversions of apparent resistivity data the two sided three electrode apparent resistivity data are obtained by the application of left and right hand pole dipolearrays that also permit the computation of four electrode and dipole dipoleapparent resistivity values without actually measuring them synthetic apparent resistivity data sets of the dipole dipole four electrode and two sided three electrodearrays are calculated for models that simulate buried tombs the results of two dimensional inversions are compared with regard to the resolution in detecting theexact location size and depth of the target showing some advantage for the two sided three electrode array a field application was carried out in the archaeologicalsite known as alaca hoyuk a religious temple area of the hittite period the two dimensional inversion of the two sided three electrode apparent resistivity data hasled to locating a part of the city wall and a buried small room the validity of theinterpretation has been checked against the results of subsequent archaeologicalexcavations introductionthe two dimensional 2d inversion of direct current dc sounding data has become a standard tool for the investiga tion of targets buried at shallow and intermediate depths theapplications include archaeology environmental and hydro geological works mining exploration and engineeringstudies when using the traditional electrode arrays thedata acquisition is usually carried out by expanding electro des along a measurement profile the apparent resistivitydata obtained from all soundings are then used as the input ofa 2d inversion algorithm pelton rijo and swift 1978 andsasaki 1981 first introduced inversion algorithms applied tothe dipole dipole and schlumberger arrays respectively later loke and barker 1996 introduced a fast 2d inversionmethod for the wenner and dipole dipole electrode arrays this algorithm is based on a quasi newton method whichcalculates an approximate value of partial derivatives of theapparent resistivity data with respect to model parameters the finite difference technique is used for the computation ofthe model response one of the remarkable developments in dc methods is theuse of modern measuring systems with multicore cableswhich allows automatic switching between electrodes forpractical field operations the electrodes are located at equallyspaced measurement stations for example morris ronningand lile 1997 described a data acquisition system thatsimultaneously collects schlumberger and two dipole dipoledata however they did not indicate a quantitative inter pretation tool acworth and griffiths 1985 and griffithsand turnbull 1985 described wenner tripotential apparent resistivity measurements to reduce the number of ambiguitiesarising in the qualitative interpretation of apparent resistivitypseudosections the tripotential method produces threeapparent resistivity measurements for each position of acollinear equispaced quadripole of electrodes they used the

deep resistivity structure of the dikili bergama region west anatolia revealed by two dimensional inversion of vertical electrical sounding data within the framework of the national marine geological and geophysical program we re examined deep vertical electrical sounding ves data the data measured in 1968 by the general directorate of mineral research and exploration mta of turkey with the aim of exploring the deep resistivity structure of the dikili bergama region focus on the geothermal potential the geoelectrical resistivity survey was conducted using a schlumberger array with a maximum electrode half spacing of 4 5 km the two dimensional 2d inversion was utilized to interpret the ves data that were collected along 15 to 30 km profiles the 2d resistivity depth cross sections obtained show very low resistivity values near the dikili and kaynarca hot springs the 2d inversion results also indicate the presence of fault zones striking nearly n s and e w and fault bounded graben horst structures that show promising potential for geothermal field resources the 2d gravity model which is in good agreement with the density variation of the region supports the resistivity structure revealed by 2d inversion the lithology information obtained from the borehole near kaynarca also confirms the results of the resistivity interpretation and the density model

boron isotopic compositions of corals seawater or diagenesis record abstract the first analyses of modern and fossil corals calcite free using a positive ion cs2bo2 tims technique and a chemical procedure for b extraction are reported the 11b for modern corals fluctuates between 23 3 and 25 5 the range of variation of fossil corals from the last interglacial period is greater from 23 5 to 27 3 and the lowest 11b corresponds to the corals close to last glacial maximum boron concentrations show a variation from 49 to 58 ppm in the recent corals and from 39 to 52 ppm in ancient corals for the ancient corals linear correlations are observed in both 11b vs b concentration and 11b vs 1 b plots but these correlations are not observed for modern corals two interpretations are presented to account for these observations and to test the potential of 11b for reconstructing paleo ocean ph the first interpretation assumes a thermodynamic partitioning of b between seawater and carbonates and shows that both boron isotopic compositions and concentrations can be used to calculate the ph of seawater in which corals grow for our data such a model requires that both the ph and the co2 of the deglacial ocean was lower than present day values the second interpretation is based on the correlation observed for ancient corals between boron isotopic compositions and 1 b we suggest that the measured boron isotopic compositions of ancient corals are caused by the mixing of a primary aragonite the coral skeleton and secondary aragonite precipitated from 10b enriched reef pore fluids the characteristics 11b and b concentrations of the diagenetic aragonite and the fluids from which it precipitates can be constrained if this proves correct only the non recrystallised parts of ancient corals can be used for paleo ph reconstructions these recrystallisation processes did not affect the 234u 238u ratios of the corals

geochemical and boron oxygen and hydrogen isotopic constraints on the origin of salinity in groundwaters from the crystalline basement of the alpine foreland abstract the b isotopic composition in combination with o and h isotopes and hydrochemical tracers is utilized to constrain the evolution of basement hosted groundwaters via water rock interactions and fluid infiltration from external sedimentary reservoirs two distinct groundwater types have been identified in the central european crystalline basement n switzerland sw germany 1 fresh groundwaters characterized by low values of 11b 3 5 to 0 6 18o 12 0 to 10 0 and d 86 8 to 71 9 and 2 brackish groundwaters with distinctly heavier b o and h isotopic compositions 11b 6 4 to 17 6 18o 9 4 to 5 6 d 67 6 to 60 8 fresh groundwaters show a systematic decrease in 11b related to an increase in b concentrations and degree of total mineralization along the pathway of groundwater migration which can only be interpreted in terms of leaching of crystalline host rocks a 11b value of 3 3 is inferred for the crustal b source mainly hercynian granites involved in the leaching process in agreement with the known 11b range of granitic rocks the evolution of brackish groundwaters derived from crystalline basement reservoirs with little water circulation is more complex as indicated by b o h stable isotope and hydrochemical e g b cl na cl and br cl constraints brackish groundwaters from the study area are influenced by admixture of sediment derived fluids which infiltrated from late paleozoic permo carboniferous and early mesozoic lower triassic sedimentary strata the data presented show that b isotopes are sensitive to mixing processes of fluids derived from different crustal reservoirs and hence may be utilized as a tracer for constraining the internal autochthonous vs external allochthonous origin of salinity in basement hosted groundwaters

geochemistry of the maroni river french guiana during the low water stage implications for water rock interaction and groundwater characteristics abstract the maroni river draining a basin of 60 000 km 2 and flowing down to the atlantic ocean between french guiana and surinam was studied during a low flow period using the chemical and isotopic composition of its dissolved load the dissolved concentrations of major ions cl so 4 no 3 hco 3 ca na mg k trace elements rb and sr stable isotopes o and d and strontium isotopes 87 sr 86 sr were determined on samples from the main stream of the river and its tributaries and from groundwaters collected in wells and two boreholes the total dissolved solid tds and the sum of cations agree with those summarised for the major guyanan rivers the orinoco and amazon on a tds vs na na ca diagram all the data from the maroni catchment plot in the precipitation dominance field close to the plots of the tefe and negro rivers the groundwaters collected from wells largely mimic the surface waters and may represent alluvial groundwater along the maroni terraces whereas the groundwaters collected from the boreholes show clearly higher values and reflect an increase in water rock interaction the river and groundwaters of the maroni catchment have been isotopically enriched 18 o vs 2 h through evaporation and the 18 o and 2 h can be used as mixing tracers of river waters within the catchment after corrections for rainwater addition were computed for selected elements and for 87 sr 86 sr ratios using chloride as an atmospheric input reference the water rock interaction along the maroni catchment was investigated for cations and sr isotopes

cyclic variations of sulfate and boron concentrations and isotopes in deep groundwaters in the aquitaine basin france abstract concentrations and isotope contents of major and trace elements are principal factors in determining the origin of the chemical composition of groundwater this paper focuses specifically on the use of sulfur and boron isotopes to characterize the origin of cyclic variations in the deep eocene aquifer in the aquitaine sedimentary basin southwest of france it is part of a multi layer system mainly composed of sands and sandstone deposits groundwater contained in this deep reservoir is known to present stable chemical compositions allowing its use for various purposes like drinking water geothermal energy thermal activity and agricultural irrigation however among the dozens of wells exploiting this aquifer and despite the reservoir s substantial depth variations in sulfate concentration have been identified in a limited area of the reservoir these fluctuations are cyclic and they seem to be correlated with water level variations due to gas storage activities nearby in the same aquifer regular water samplings and analyses of major and trace elements and their isotopes have identified that bore concentration variations are correlated with sulfate variations a geochemical modelling approach based on water mixes elucidates the causes of these variations in chemical composition especially the boron and sulfate concentrations and their respective 11b and 34sso4 values from these numerical results we identify that different sources explain the variations of boron concentration one part coming from the silicates alteration present in sub layers of the exploited aquifer and the other part coming from the evaporites alteration present in the underlying molasse unit these results also confirm the existence of mass and potentially water transfers between the different sub layers of the reservoir and with the underlying molasse aquitard implying new constraints for the future hydrogeologic modelling

the boron isotope systematics of icelandic geothermal waters 1 meteoric water charged systems we have measured the boron isotope composition and boron and chloride concentrations of 27 icelandic geothermal fluids from both high and low temperature systems the 11b values range from 6 7 in the krafla system to 25 0 in a warm spring from the southern lowlands in addition we have also determined the 11b values of basaltic glass from nesjavellir 5 3 1 4 and travertine from snaefellsnes 22 0 5 the b isotope and cl b systematics of the high temperature systems are dominated by the composition of the local basalts the lower temperature systems show evidence for mixing with b and cl of a marine origin together with some uptake of b into secondary mineral phases the data from the snaefellsnes geothermal system indicate that the fluids have undergone interaction with basalts that have undergone significant low temperature alteration by seawater