boron isotope ratios of surface waters in guadeloupe lesser antilles abstract large variations are reported in the b concentrations and isotopic ratios of river and thermal spring waters in guadeloupe lesser antilles rivers have 11b values around 40 and b concentrations lower than 30 g l while thermal springs have 11b of 8 15 and b concentrations of 250 1000 g l river samples strongly impacted by hydrothermal inputs have intermediate 11b and b contents none of these surface water samples have 11b comparable to the local unweathered volcanic rocks around 0 implying that a huge isotopic fractionation of 40 takes place during rock weathering which could be explained by preferential incorporation of 10b during secondary mineral formation and adsorption on clays during rock weathering or in the soils the soil vegetation b cycle could also be a cause for such a fractionation atmospheric b with 11b of 45 represents 25 95 of the river b content the variety of the thermal spring chemical composition renders the understanding of b behavior in guadeloupe hydrothermal system quite difficult complementary geochemical tracers would be helpful

effusive history of the grande decouverte volcanic complex southern basse terre guadeloupe french west indies from new k ar cassignol gillot ages abstract the grande decouverte volcanic complex gdvc active since at least 0 2 ma is the most recent volcanic complex of the basse terre island guadeloupe lesser antilles arc a detailed geochronological study using the k ar cassignol gillot technique has been undertaken in order to reconstruct the history of effusive activity of this long lived volcanic system twenty new ages permit to suggest that the gdvc experienced at least six main effusive stages from 200 ka to present time to the north of the gdvc the gds grande decouverte soufriere volcano has been active since at least 200 ka and to the south the trmf trois rivieres madeleine field started to be emplaced 100 ka morphological investigations suggest that the whole trmf volcanism was emitted from vents distinct from the gds most probably a large e w fissure network linked to the marie galante rift the mean age of 62 5 ka obtained for the e w madeleine le palmiste alignment suggests that a fissure opening event occurred at that time however whole rock major and trace element signatures are similar for both systems suggesting that a common complex magma plumbing system has fed the overall gdvc we report very young ages for lava flows from the trmf which implies that

chemical weathering river geochemistry and atmospheric carbon fluxes from volcanic and ultramafic regions on luzon island the philippines abstract we investigated rates of chemical weathering of volcanic and ophiolitic rocks on luzon island the philippines luzon has a tropical climate and is volcanically and tectonically very active all factors that should enhance chemical weathering seventy five rivers and streams 10 draining ophiolites 65 draining volcanic bedrock and two volcanic hot springs were sampled and analyzed for major elements alkalinity and 87sr 86sr cationic fluxes from the volcanic basins are dominated by ca2 and mg2 and dissolved silica concentrations are high 500 1900 m silica concentrations in streams draining ophiolites are lower 400 900 m and the cationic charge is mostly mg2 the areally weighted average co2 export flux from our study area is 3 89 0 21 106 mol km2 yr or 5 99 0 64 106 mol km2 yr from ophiolites and 3 58 0 23 106 mol km2 yr from volcanic areas uncertainty given as 1 standard error s e this is 6 10 times higher than the current best estimate of areally averaged global co2 export by basalt chemical weathering and 2 3 times higher than the current best estimate of co2 export by basalt chemical weathering in the tropics extrapolating our findings to all tropical arcs we estimate that around one tenth of all atmospheric carbon exported via silicate weathering to the oceans annually is processed in these environments which amount to 1 of the global exorheic drainage area chemical weathering of volcanic terranes in the tropics appears to make a disproportionately large impact on the long term carbon cycle

accuracy of stable mg and ca isotope data obtained by mc icp ms using the standard addition method the standard addition method is evaluated to verify the accuracy and precision of mg and ca isotope data with complex matrices using the standard sample bracketing technique and analysis by mc icp ms the 44ca 42ca ratio of seawater expressed as 44 42ca relative to srm915a was determined as 0 93 0 03 95 confidence in agreement with estimates obtained by the double spike method using standard addition the seawater 26mg 24mg ratio expressed as 26mg relative to the dsm3 standard was determined as 0 80 0 06 95 confidence in agreement with previous estimates four terrestrial silicate rocks morb flood basalt glacial flour and granodiorite and olivine mineral separates from an island basalt are shown to exhibit no scatter within the error of the method averaging a 26mg of 0 20 0 05 95 confidence although a number of silicate rock data for mg isotope ratios have already been reported this is the first detailed effort to validate the accuracy of such data and test for residual analytical artifact after chemical purification of samples data regressions were evaluated statistically using the mean square weighted deviate mswd demonstrating that the uncertainty on individual data points are generally over estimated the external two standard deviation uncertainty on individual data points is estimated by monte carlo simulation as b0 075 about a factor of two improvement on early publications of mg isotope data the consistency of the standard addition estimates of 26mg in silicate rocks imply that if any residual matrix effects are present then they must be less than the spread of the data 0 11 given the diverse range of matrices in each of the samples the 26mg values of the silicate rocks suggest that mg isotope ratios in silicate material may only have a very restricted range the 26mg values of silicate material in the present study falls between the average values reported by teng et al teng f z wadhwa m helz r t 2007 investigation of magnesium isotope fractionation during basalt differentiation implications for a chondritic composition of the terrestrial mantle earth and planetary science letters 261 84 92 doi 10 1016 j epsl 2007 06 004 and wiechert and halliday wiechert u halliday a n 2006 non chondritic magnesium and the origins of the inner terrestrial planets earth and planetary science letters 256 360 371 doi 10 1016 j epsl 2007 01 007 and given the spread of published 26mg values for chondritic material a chondritic composition for terrestrial mg cannot be ruled out we suggest that some of the small discrepancies between our data and analysis of the same samples in earlier studies may have arisen because the chemical purification of mg prior to analysis can easily induce analytical artifact this method could be expanded to the isotope ratios of other elements which also rely on correcting for mass bias using the standard sample bracketing method where similar analytical discrepancies may also exist

the response of li and mg isotopes to rain events in a highly weathered catchment abstract storms are responsible for up to 50 of total annual rainfall on tropical islands and result in rapid increases in discharge from rivers storm events are however notoriously under sampled and their effects on weathering rates and processes are poorly constrained to address this we have undertaken high frequency sampling of quiock creek catchment a critical zone observatory located in guadeloupe over a period of 21 days encompassing several storm events chemical and isotopic li and mg analyses of different critical zone reservoirs throughfall soil pore water groundwater and river water were used to assess the interactions between rock water and secondary minerals the li concentrations and 7li values of these different reservoirs range from 14 to 95 nmol kg and 1 8 to 16 8 respectively after several rain events the average 7li value 13 3 of soil solutions from the lower part of the soil profile 150 cm below the surface was unchanged whereas in the upper part of the profile 7li values increased by 2 4 due to increased contribution from throughfall by contrast the 26mg value of soil waters in the upper part of the soil profile were not significantly affected by the rain events with an average value of 0 90 the 26mg values of the different fluid reservoirs were generally close to the value of throughfall 0 90 but higher 26mg values up to 0 58 were measured in the deeper parts of the soil profile whereas groundwaters that have a long residence time had lower 26mg values down to 1 48 these higher and lower values are attributed to respectively adsorption desorption of light mg isotopes on from the surface of clay minerals the 7li value of the river waters was 9 3 with a li concentration of 60 mol kg but during a storm these values decreased to respectively 7 8 and 40 mol kg this change in 7li is consistent with an increased contribution of li from the soil solution thus even in highly weathered catchments changes in hydrological conditions can have a significant impact on weathering processes and therefore the composition of river waters delivered to the ocean

chemical weathering of mafic rocks in boreal subarctic environment northwest russia under influence of glacial moraine deposits abstract chemical weathering of mafic rocks represents substantial sink of atmospheric co2 yet the mechanismes of this process in high latitude regions are poorly understood this work addresses geochemical migration and partitioning of major and trace elements between rock soil and surface waters during chemical weathering of mafic rocks and soil formation under the influence of a glacial moraine in the northwestern russian subarctic we used multidisciplinary approach which included major and trace element chemical analysis sr isotopic measurements and mineralogical structural and microscopic investigations quaternary pleistocene deposits were observed even in the deepest horizons of soil profiles and confirm a strong moraine influence as most soils showed podzolic features chemical and sr isotopic analyses revealed a strong impact of the moraine on soil chemistry and mineralogy mineralogical studies showed the presence of non aeolian quartz and zircon in soils which were not linked to the nature of the parental rocks i e mafic and felsic at the same time we observed the presence of etch pit corrosion on the surface of zircons and feldspars and a newly formed matter adjacent to the surface of primary phases the chemical index of alteration cia showed weak or no weathering of rocks within the soil profile and the weathering intensity scale confirmed the felsic chemical composition of soils developed over mafic and ultramafic rocks analysis of sr radiogenic isotopes demonstrated preferential removal of easily weatherable and less radiogenic minerals over the full depth of soil profile and a more radiogenic signature of the granitic moraine compared to mafic and felsic bedrocks the composition of most surface waters reflected the weathering of silicate rocks but did not allow for distinguishing purely mafic source the chemical weathering rates of ultramafic rocks were calculated to be higher than those for the granitic till but the moraine depositions which dominate this region hide evidence of the real weathering process this could be due to retention of mg and ca in soil due to precipitation of secondary phases such as mg vermiculite or divalent cation adsorption on mineral organic or organo mineral phases as a result weathering rates estimated for the olivinite rock appear to be lower than the weathering rates of mafic rocks reported in other boreal and subarctic regions overall the felsic moraine deposits are capable to sizably decrease the weathering intensity of mafic rocks which should be taken into account for chemical weathering modelling of high latitude regions subjected to glaciation in the past

from unweathered core to regolith in a single weathering andesitic clast rates and trends of in situ chemical weathering on a tropical volcanic island basse terre island french guadeloupe abstract we conduct x ray microprobe chemical and u series isotope analyses on an oriented weathering clast collected from the regolith of a weathered quaternary volcanoclastic debris flow on basse terre island french guadeloupe the sample consists of an unweathered basaltic andesite core surrounded by a weathering rind and an indurated crust that separates the rind from the overlying soil matrix u th disequilibria dating indicates that rind age increases away from the core rind boundary to a maximum of 66 ka this translates to a rind advance rate of 0 2 mm kyr 1 broadly consistent with rind advance rates calculated elsewhere on basse terre island the overlying indurated crust is 72 ka indicating a possible minimum duration of the rind formation elemental variations are constrained by a bulk chemical analysis along a vertical transects from the core to the overlying soil matrix and parallel electron microprobe analyses the hierarchy of elemental loss across the core rind boundary varies in the order ca na mg k mn si al ti 0 p fe consistent with the relative loss of phases in the clast from plagioclase glass pyroxene apatite ilmenite the abrupt

evidence for a new shallow magma intrusion at la soufriere of guadeloupe lesser antilles insights from long term geochemical monitoring of halogen rich hydrothermal fluids more than three decades of geochemical monitoring of hot springs and fumaroles of la soufriere of guadeloupe allows the construction of a working model of the shallow hydrothermal system this system is delimited by the nested caldera structures inherited from the repeated flank collapse events and the present dome built during the last magmatic eruption 1530 ad and which has been highly fractured by the subsequent phreatic or phreatomagmatic eruptions because it is confined into the low volume highly compartmented and partially sealed upper edifice structure the hydrothermal system is highly reactive to perturbations in the volcanic activity input of deep magmatic fluids the edifice structure sealing and fracturing and meteorology wet tropical regime the current unrest which began with a mild reactivation of fumarolic activity in 1990 increased markedly in 1992 with seismic swarms and an increase of degassing from the summit of the dome in 1997 seismic activity increased further and was accompanied by a sudden high flux hcl rich gas from summit fumaroles we focus on the interpretation of the time series of the chemistry and temperature of fumarolic gases and hot springs as well as the relative behaviours of halogens f cl br and i this extensive geochemical time series shows that the deep magmatic fluids have undergone large changes in composition due to condensation and chemical interaction with shallow groundwater scrubbing it is possible to trace back these processes and the potential contribution of a deep magmatic source using a limited set of geochemical time series t co2 and total s content in fumaroles t and cl in hot springs and the relative fractionations between f cl br and i in both fluids coupling 35 years of geochemical data with meteorological rainfall data and models of ion transport in the hydrothermal aquifers has allowed us to identify a series of magmatic gas pulses into the hydrothermal system since the 1976 1977 crisis the contrasting behaviours of s and cl bearing species in fumarolic gas and in thermal springs suggests that the current activity is the result of a new magma intrusion which was progressively emplaced at shallow depth since 1992 although it might still be evolving the characteristics of this new intrusion indicate that it hasalready reached a magnitude similar to the intrusion that was emplaced during the 1976 1977 eruptive crisis the assessment of potential hazards associated with evolution of the current unrest must consider the implications of recurrent intrusion and further pressurization of the hydrothermal system on the likelihood of renewed phreatic explosive activity moreover the role of hydrothermal pressurization on the basal friction along low strength layers within the upper part of the edifice must be evaluated with regards to partial flank collapse at this stage enhanced monitoring research and data analysis is required to quantify the uncertainties related to future scenarios of renewed eruptive activity and magmatic evolution

the influence of weathering processes on riverine magnesium isotopes in a basaltic terrain this study presents major trace element and mg isotope data for the dissolved load and suspended particulates of icelandic rivers draining dominantly basaltic catchments including both glacier fed and direct runoff rivers these samples provide the opportunity to understand the behaviour of mg isotopes during chemical weathering where variations due to lithology are not extant given the significant role of mg in the carbon cycle such variations may provide important information on the regulation of earth s climate hydrothermal waters groundwater precipitation glacial ice basalt glass olivine and representative soils have also been analysed the dissolved load shows a wide range of 26mg compositions compared to the parent basaltic glass 26mg 0 29 ranging from 0 96 to 0 64 while precipitation and hydrothermal waters possess 26mg values of 0 83 and 0 85 respectively with lower mg concentrations than the dissolved load biomass activity in vegetation and organic material in soils and rivers colloids appear to have little effect on the mg isotope compositions rather the data suggest that mg elemental and isotopic variations are largely controlled by the formation and stability of secondary phases in response to differing hydrological conditions in some samples seawater in the form of direct precipitation or glacial runoff also appears to be an important source of mg glacier fed rivers groundwaters and some direct runoff rivers with a high ph have higher 26mg than basalt which is most likely due to the incorporation of light mg isotopes in secondary minerals in contrast those direct runoff rivers which have a relatively low ph have low 26mg relative to basalt consistent with preferential incorporation of heavy mg isotopes into secondary phases although it is not possible to rule out some contribution from precipitation riverine suspended particulates are depleted in mobile elements and have 26mg compositions values both higher and lower than unweathered basalt in the glacier fed and direct runoff rivers where the 26mg of the dissolved phase is heavy due to the formation of secondary phases the suspended load is light because it contains more of those phases the opposite is true for the remainder of the direct runoff rivers which have low ph this could be due to dissolution of secondary minerals enriched in light mg which are unstable at low ph or the formation of new secondary phases

archean upper crust transition from mafic to felsic marks the onset of plate tectonics the archean eon witnessed the production of early continental crust the emergence of life and fundamental changes to the atmosphere the nature of the first continental crust which was the interface between the surface and deep earth has been obscured by the weathering erosion and tectonism that followed its formation we used ni co and cr zn ratios in archean terrigenous sedimentary rocks and archean igneous metaigneous rocks to track the bulk mgo composition of the archean upper continental crust this crust evolved from a highly mafic bulk composition before 3 0 billion years ago to a felsic bulk composition by 2 5 billion years ago this compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks suggesting the onset of global plate tectonics at 3 0 billion years ago

atmospheric contribution to cations cycling in highly weathered catchment guadeloupe lesser antilles abstract the important fertilizing role of atmospheric dust and particularly african dust in tropical rainforests is increasingly recognized but still poorly quantified to better evaluate dust input into the caribbean basin we sampled critical zone compartments of a small forested volcanic catchment in guadeloupe soils parent rock atmospheric dust plants soil solutions stream and rain waters the aims of this study are to track sources of cation nutrients ca mg k sr developed on highly weathered soil in the rainforest of guadeloupe to quantify plant recycling of these nutrients and to identify constraints on regolith development and its associated nutrient pool in the quiock creek catchment a large isotopic range of 87sr 86sr and end values was observed despite the small scale of observation sr isotopic composition of the dissolved load varied from 0 7084 in rainfall to 0 7110 in soil solution whereas it ranges between 0 7068 and 0 7153 for soil samples and between 0 7096 and 0 7102 for plants the nd isotopic composition varied between 8 39 in near surface soil samples to 2 71 in deeper soil all samples had an intermediate signature between that of the bedrock endmember 87sr 86sr 0 7038 end 4 8 and the atmospheric endmember sea salt 87sr 86sr 0 7092 and saharan dust 87sr 86sr 0 7187 end 11 5 the regolith was built on pyroclastic deposits but because of extreme leaching the regolith has lost its original bedrock signature and inherited an exogenous atmospheric signature our results show that only the chemical weathering of the fresh near surface minerals can provide nutrients to the ecosystem first 30 cm however this dust weathering is too low to sustain the tropical forest ecosystem on its own the cationic mass balance at the catchment scale as well as the sr isotopic signature show that cation and sr fluxes are of atmospheric origin only and that original bedrock no longer participates in nutrient cycles the vegetation reflects the 87sr 86sr of the dissolved pool of atmospheric sr at the soil plant scale the cation nutrient fluxes provided by vegetation litter fall leaf excretion are major compared to input and output fluxes the annual ca k sr and mg fluxes within the vegetation are respectively 31 28 20 and 3 times greater than the exported fluxes at the outlet of the basin the residence time of nutrients in the vegetation is 16 years for k and close to 45 years for sr ca and mg these results emphasize the highly efficient vegetative turnover that dominates the nutrient cycle in the quiock creek catchment this first characterization of biogeochemical cycles in the guadeloupean rainforest suggests that the forest community of quiock creek is sustained by a small near surface nutrient pool disconnected from the deep volcanic bedrock we also demonstrated that even with efficient nutrient recycling saharan dust plays a significant role in maintaining ecosystem productivity in guadeloupe over long time scales

carbon river fluxes and weathering co2 consumption in the congo and amazon river basins data on carbon river fluxes recently obtained by the authors for the congo basin within the framework of the pirat program insu cnrs orstom are compared with results previously obtained for the amazon basin a special interest is devoted to the bicarbonate river fluxes and to their relationships with river discharges the flux of atmospheric and soil co2 consumed by rock weathering is estimated to be 3 1 105 and 0 5 105 moles a km2 respectively for the amazon and the congo basin these co2 fluxes represent respectively 67 4 and 74 7 of the total bicarbonate river fluxes a comparison to other large river basins shows that this contribution is directly related to the proportion of carbonate rock areas a transfer function between the weathering co2 flux and the river discharge is calculated for each basin and allows the reconstitution of the variations of this flux using the river discharge fluctuations during the last century these interannual co2 fluctuations present average increasing trends of 10 for amazon basin and only 0 7 for the congo basin during the last century

erosive effects of the storm helena 1963 on basse terre island guadeloupe lesser antilles arc erosive effects of the tropical storm helena that hit the volcanic island of basse terre guadeloupe lesser antilles arc on 24 october 1963 has been measured using 80 aerial images acquired by the french geographic institute ign institut geographique national at the approximate scale of 1 8000 less than three months after the storm helena on these images 253 landslides triggered during the storm were identified and mapped these landslides were located in the central region of the island where catchments exhibit the highest relief even though the average thickness of the landslides was only 1 m i e less than the thickness of the weathered layer the total volume of displaced sediments corresponded to an average denudation of 2800 t km 2 i e 1 4 mm on the watersheds affected by landsliding to assess the erosional significance of this single climatic event we compare the volume of sediment mobilized by the storm helena to the long term denudation rate the latter estimated from a calculation of the total volume of material eroded since the emplacement of lavas using a digital elevation model is found to be 0 14 mm y assuming that helena is representative of the storms that hit basse terre island during the quaternary we find that a return period of about 10 to 15 years is enough to account for the long term denudation rate recorded for this island such a period is comparable with the actual return period of the tropical cyclones of the order of 4 to 5 years suggesting that the erosion of basse terre island is entirely controlled by tropical hurricanes

influence of atmospheric deposits and secondary minerals on li isotopes budget in a highly weathered catchment guadeloupe lesser antilles abstract to better constrain li dynamics in the tropics we sampled critical zone compartments of a small forested andesitic catchment in guadeloupe soils parent rock atmospheric dust plants soil solutions stream and rain waters the aims of this study are to identify the origin of li in the different compartments and to better characterize the behavior of li and its isotopes during water rock interaction in a highly cation depleted soil the li isotope signature 7li of throughfall samples varies between 11 2 and 26 4 as this is lower than the seawater signature 31 and vegetation does not fractionate li isotopes our data indicate that saharan dust 0 7 significantly contributes to the throughfall signature li isotope composition measured in a 12 5 m deep soil profile varies from 3 9 near the surface to 13 5 at 11 m depth compared to unweathered andesite 5 the deep soil signature is in agreement with preferential incorporation of light li into secondary minerals in the top soil however our results also emphasized that atmospheric deposition wet and dry is a main source of li to the soil the decreasing 7li with increasing depth is consistent with a vertical gradient of incorporation of heavy atmospheric li this input being maximal near the surface at the catchment scale throughfall and total atmospheric inputs sea salts saharan dust provide 12 1 and 23 9 g li yr 1 respectively to the quiock creek catchment these fluxes represent 34 and 67 respectively of li exported at the outlet indicating that atmospheric deposition is one of the main li inputs to the critical zone li concentration and isotopic mass balance at the catchment scale indicate that in addition to atmospheric deposition secondary mineral phase dissolution is a major solute source and that andesite no longer participates in significant production of li

topography and grounding in a simple bottom layer model a reduced gravity model for a dense bottom layer under a motionless deep layer is used to investigate bottom layer flow with topography the two competing effects in the model are topography which introduces a topographic beta effect and strong layer thickness variation which allows for the possibility of zero layer thickness or grounding the goal is to arrive at a simple observationally relevant characterization of the model which can help to distinguish different dynamical mechanisms operating in the ocean several regimes are identified including situations for which the layer depth goes to zero with and without topography ways of distinguishing observationally between competing effects are suggested the study is motivated by the observed shift of antarctic bottom water in the western north atlantic ocean from the west to the east this phenomenon is used to discriminate key elements of the model

selective sorption of potassium in a weathering sequence of volcanic ash soils from guadeloupe french west indies volcanic ash soils are usually associated within the weathering sequence glass allophane 4 halloysite on the eastern slopes of the volcano la soufriere guadeloupe this sequence occurs in a toposequence molli silicic andosol humic andosol haplic andosol haplic nitisol where the average annual rainfall decreases from 4000 mm at 420 m a s l to 2500 mrn at 30 m a s l of this sequence we selected four profiles and examined the relationships between weathering stage clay mineralogy and exchangeable k ca2 selectivity with increasing weathering the total content of alkaline and alkaline earth cations of the b horizon steadily decreased from 185 cmol c kg 1 soil in the molli silicic andosol to 24 cmol c kg 1 soil in the nitisol k selectivity was small in the molli silicie andosol but significantly increased with increasing weathering stage and increasing content of halloysite in the haplic andosol and nitisol the very strong selectivity for k ions may be linked with the presence of a 2 1 clay mineral but could not be attributed unequivocally to this mineral or to halloysite the 2 1 mineral occurred as a discrete phase mixed with halloysite and exhibited x ray diffraction features suggesting its vermiculitic nature c 2003 elsevier b v all rights reserved

lithologic and climatologic controls of river chemistry abstract the chemistries of rivers draining a variety of lithologic and climatic regions have been surveyed for the purpose of quantifying the fluxes of bicarbonate and silica from rivers with respect to bedrock lithology and runoff in all 101 different rivers each draining a primary lithology were examined across the united states puerto rico and iceland to minimize seasonal effects only rivers with at least two years of data were used basaltic catchments were examined in the greatest detail in a survey of hawaiian island watersheds the average river chemistries could be related to the distribution of soil associations within each catchment an analysis of cation activity relationships among rivers draining basaltic catchments shows that the river compositions define slopes which are consistent with an equilibrium ion exchange control on cation ratios among different lithologies unique weathering rate relationships were developed with yields at typical present day runoff rates 1 100 cm y increasing in the order sandstones granites basalts shales and carbonates the bicarbonate and silica fluxes for each of these lithologies have been quantified for use in global studies of chemical denudation our study confirms that the dissolved yield of a given drainage basin is determined by a balance between physical and chemical weathering thus a warm wet climate or the presence of abundant vegetation cannot guarantee high rates of chemical denudation unless accompanied by high rates of physical removal

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

controls on rind thickness on basaltic andesite clasts weathering in guadeloupe abstract a clast of low porosity basaltic andesite collected from the b horizon of a soil developed on a late quaternary volcaniclastic debris flow in the bras david watershed on basse terre island guadeloupe exhibits weathering like that observed in many weathered clasts of similar composition in other tropical locations specifically elemental profiles measured across the core rind interface document that primary minerals and glass weather to fe oxyhydroxides gibbsite and minor kaolinite in the rind the earliest reaction identified in the core is oxidation of fe in pyroxene but the earliest reaction that creates significant porosity is plagioclase dissolution elemental loss varies in the order ca na k mg si al fe p ti consistent with the relative reactivity of phases in the clast from plagioclase pyroxene glass apatite ilmenite the rind surrounds a core of unaltered material that is more spherical than the original clast the distance from the core rind boundary to a visually prominent rind layer l was measured as a proxy for the rind thickness at 36 locations on a slab cut vertically through the nominal center of the clast this distance averaged 24 4 3 1 mm maximum and minimum values for l 35 8 and 20 6 mm were observed where curvature of the core rind boundary is greatest 0 12 mm 1 and smallest 0 018 mm 1 respectively extrapolating from other rinds in other locations the rate of rind formation is estimated to vary by a factor of about 2 from 4 to 7 10 14 m s 1 from low to high curvature the observation of a higher rate of rind formation for a higher curvature interface is consistent with a diffusion limited model for weathering rind formation the diffusion limited model predicts that like rind thickness values of the thickness of the reaction front h for a given reaction defined as the zone over which a parent mineral such as plagioclase completely weathers to rind material should also increase with curvature values of h were quantified as a function of interface curvature using bulk chemical analysis 500

seasonal sensitivity of weathering processes hints from magnesium isotopes in a glacial stream seasonal changes in river chemistry offer the potential to assess how weathering processes respond to changing meteorological parameters and ultimately how chemical weathering might respond to climatic parameters systematic seasonal variations in magnesium isotope ratios the 26mg 24mg ratio expressed as 26mg in per mil units are reported in stream waters from a mono lithological granitic weathering limited first order catchment from the swiss alps damma glacier rain ground and pore waters in addition to plants rocks mineral separates and soil are also reported the concentration response of the river waters is attenuated compared to the large changes in discharge however the systematic trends in the isotope data imply that either the source of the mg changes in a systematic manner or that the process by which mg is released into solution changes as a function of discharge the two first order observations in the data that need to be explained are 1 the systematic enrichment in 24mg in the stream waters compared to the granitic rocks they drain and 2 a systematic increase in 26mg in the waters during the summer melt season both observations which are similar to many other rivers draining silicate rock can either be accounted for by 1 conservative mixing between at least two different sources of mg in addition to precipitation inputs or 2 process related fractionation if the stream water compositions can be rationalised by multi component mixing there is at least one unidentified component with a 26mg 1 2 this is considered unlikely multiple physicochemical processes could fractionate mg isotope ratios such as 1 preferential leaching of 24mg 2 exchange of mg onto or from mineral surfaces and into interlayer sites of clays 3 uptake by plants and 4 26mg could be preferentially retained during the formation of secondary phases such as clays amorphous phases or oxides these processes are not mutually exclusive and distinguishing between them at a field scale is not trivial but significant biological uptake is improbable at this site unless there is a non identified external input of mg 26mg must be accumulating in solid phase residues in the catchment because of at least one physicochemical process such processes are likely well described at least in the first order by a rayleigh distillation model simple calculations illustrate how much 26mg would accumulate in the catchment per unit time in the first order the isotopic enrichments in the solids are so small that they would not be detectable for the time scales that are relevant to this field site in spite of the marked impact on the water chemistry the seasonal signal detected by mg isotope ratios is promising for using them with a better understanding of fractionation mechanisms to quantify how specific weathering processes impact upon both export fluxes and retention of elements within catchments

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

reconciling chemical weathering rates across scales application of uranium series isotope systematics in volcanic weathering clasts from basse terre island french guadeloupe abstract to elucidate the factors that contribute to the orders of magnitude difference generally observed in apparent weathering rates across scales we utilized a u series isotopic technique to directly determine the duration and rates of chemical weathering recorded in weathering clasts in this study we systematically compiled 15 individual volcanic weathering clasts collected from eight andesitic watersheds along a gradient of mean annual precipitation ranging from 1600 mm to 6400 mm on the tropical volcanic basse terre island of french guadeloupe we measured u series isotope compositions to quantify weathering advance rates along the core rind transects in these weathering clasts total rind formation ages the length of time it took for these weathering clasts to form from andesitic rock fragments or volcanic clasts in the soil zones range from 60 kyr to 300 kyr as expected for each individual core rind weathering transect the rind ages generally increase almost linearly with distance away from the core rind boundary the derived clast weathering rates range from 0 08 0 04 to 0 34 0 01 mm kyr 1 and the rates exhibit a strong positive correlation r 2 0 74 with the annual runoff values of these watersheds this correlation documents the first direct evidence that weathering over geological timescales on the island is controlled by the amount of precipitation and corroborates the relationship that was previously reported for the riverine weathering fluxes at basse terre island in guadeloupe but measured with much shorter time scales the clast scale rates inferred for the characteristic length scale of mm are compared to the watershed scale rates of basse terre island length scale of km constantly higher rates are observed at the watershed scales than the clast scale and the discrepancy equals 1800 400 times despite changes in watershed characteristics such as watershed size relief and runoff values the discrepancy is attributed to the fractal nature of the roughness and surface area across scales for example the presence of undulations and fractures e g roughness at the bedrock saprolite contact of the watershed which is generally not assessed in the watershed surface area estimates is most likely the main contributor to the constant rate difference of 1800 times

remote and in situ plume measurements of acid gas release from la soufriere volcano guadeloupe this paper presents the first remote measurements of la soufriere gas emissions since the fumarolic and seismic reactivation in 1992 the chemical composition of the plumes has been measured from may 2003 to september 2004 using an open path fourier transform infrared op ftir spectrometer up to 15 m downwind the south crater hcl is clearly detected concentration between 2 4 and 12 ppmv whereas so2 and h2s generally remain below the detection limit of the op ftir direct measurements of so2 and h2s near the south crater with a lancom iii analyzer show a fast decrease of their concentrations with the distance calculated cl s mass ratios are high from 9 4 1 7 at 15 m from the vent to 2 8 0 6 at 140 m the enrichment in hcl of the gas emitted at la soufriere observed since 1998 corresponds to the degassing of a magma enriched in cl and depleted in s this result agrees with isotopic measurements which suggest a magmatic origin of the gases readjustments inside the volcanic system may have taken place during the seismic activity beginning in 1992 and enhance the transfer of magmatic gases to the summit

chemical and isotopic o h c composition of surface waters in the catchment of lake donggi cona nw china and implications for paleoenvironmental reconstructions abstract the oxygen hydrogen and carbon isotope ratios and major and trace element concentrations of surface waters are reported for the catchment of lake donggi cona qinghai province china the chemistry of the surface waters in the southeastern catchment is reflecting the dissolution of carbonate rocks whereas thermal waters add sodium and chlorine to the waters in the northern catchment the dongqu river draining the southeast catchment contributes 87 to 94 to the water budget of the lake thermal waters and waters from the northern catchment add 6 to 13 the combination of hydrogen and oxygen isotopes provides evidence that only small amounts of recycled lake water contribute to the precipitation in the catchment most of the moisture may be transported by the east asian summer monsoon or an eastern branch of the south asian monsoon into the donggi cona region from oxygen isotope ratios it is calculated that about 45 of the lake water input is evaporated and 55 leaves the lake through a channeled outflow the carbon isotope ratios identifies microbial respiration of organic matter probably in soils and sediments of the catchment as the major source of dissolved inorganic carbon in most surface waters and the lake an isotope effect from biological processes in the lake is minor and can be neglected in order to explain isotope ratios of inorganic carbon in lake water the results imply that oxygen isotope ratios in the lake sediment archives mainly mirror the relation between precipitation and evaporation p e which may be controlled by changes in the global water cycle like monsoon intensity or by tectonically driven local changes affecting the outflow flux a comparison between lake archives based on ostracod shells and the modern system indicates similar 18o values for the lake water since 4 3 ka but different 13cdic values this discrepancy between carbon isotope ratios in ostracod shells and modern lake water samples may be due to thermal waters with high 13cdic emerging near the coring site it is suggested that carbon isotopes of ostracods from a sediment drill core reflect the activity of a local thermal spring at the lake bottom whereas oxygen isotopes provide evidence for an open lake system since about 11 ka and that the climate and environment of the donggi cona region changed very little over the last 4300 years

mediterranean outflow mixing and dynamics the mediterranean sea produces a salty dense outflow that is strongly modified by entrainment as it first begins to descend the continental slope in the eastern gulf of cadiz the current accelerates to 1 3 meters per second which raises the internal froude number above 1 and is intensely turbulent through its full thickness the outflow loses about half of its density anomaly and roughly doubles its volume transport as it entrains less saline north atlantic central water within 100 kilometers downstream the current is turned by the coriolis force until it flows nearly parallel to topography in a damped geostrophic balance the mixed mediterranean outflow continues westward slowly descending the continental slope until it becomes neutrally buoyant in the thermocline where it becomes an important water mass

application of a transient reduced gravity plume model to the denmark strait overflow a hydrostatic reduced gravity two dimensional primitive equation numerical model for the simulation of transient bottom arrested gravity plumes was developed by adopting an algorithm from a wadden sea model a model that simulates the wetting and drying of mud flats sand banks etc with a movable lateral boundary the vertically integrated nonlinear rotational model accounts for the dissipation of momentum due to bottom friction and for the entrainment of water mass properties from a spatially structured but stagnant ambient water body it predicts the temporal and spatial evolution of the flow field and the water mass modification within a gravity plume that descends on an arbitrary topography previous model investigations considered a laterally integrated streamtube whereas our model resolves the plume horizontally in the streamtube approach it was assumed that the plume descends in a stationary almost geostrophic balance modified only by bottom drag and entrainment the results of this model demonstrate that this balance may be disturbed whenever the plume encounters topographic disturbances which for the initial intruding phase in particular accounts for its highly transient character the model results are in good agreement with theoretical and laboratory investigations and with observations as is demonstrated by some basic test experiments an application to the overflow of dense water through the denmark strait is presented

the magnesium isotope budget of the modern ocean constraints from riverine magnesium isotope ratios we have measured the magnesium mg isotope ratios in 45 rivers including 16 of the largest rivers in the world covering a range of geologic tectonic and climatic drainage basin environments the range in riverine 26mg is 2 5 half the variation in terrestrial rock although the mg isotopic composition of the source rock is important for small rivers at a global scale lithology is of limited significance for mg isotope ratios in rivers part of the variability at a global scale may be attributed to fractionation in the weathering environment the rivers analysed constitute 30 of the global mg riverine flux to the oceans and a flux weighted mg isotope composition of global runoff has been estimated at 1 09 even taking into account uncertainty this is distinct from seawater at 0 82 this difference arises either from the fractionation of mg isotope ratios in the ocean and or a mg budget which is not at steady state the difference is consistent with fractionation by carbonate precipitation in the simplest steady state scenario where the oceanic mass balance is maintained by riverine input and hydrothermal and dolomite output mg isotope ratios imply a minimum dolomite mg flux of 9 of the total output mg flux the implications of the distinct isotopic composition of the riverine flux from modern seawater is that the mg isotope ratio of seawater has probably varied outside of current analytical uncertainty mg isotope ratios may therefore provide a valuable new tracer in palaeo oceanography

chlorine isotopes of thermal springs in arc volcanoes for tracing shallow magmatic activity the evaluation of the status of shallow magma body i e from the final intrusion stage to quiescence and back to activity one of the key parameters that trigger and sustain volcanic eruptions has been challenging in modern volcanology among volatile tracers chlorine cl uniquely exsolves at shallow depths and is highly hydrophilic consequently cl enrichment in volcanic gases and thermal springs has been proposed as a sign for shallow magmatic activities however such enrichment could also result from numerous other processes e g water evaporation dissolution of old chloride mineral deposits seawater contamination that are unrelated to magmatic activity here based on stable isotope compositions of chloride and dissolved inorganic carbon as well as previous published 3he 4he data obtained in thermal springs from two recently erupted volcanoes la soufriere in guadeloupe and montagne pelee in martinique in the lesser antilles arc we show that the magmatic cl efficiently trapped in thermal springs displays negative 37cl values 0 65 0 65 consistent with a slab derived origin but distinct from the isotope compositions of chloride in surface reservoirs e g seawater local meteoric waters rivers and cold springs displaying common 37cl values of around 0 using this 37cl difference as an index of magmatic cl we further examined thermal spring samples including a 30 year archive from two thermal springs in guadeloupe covering samples from its last eruption in 1976 1977 to 2008 and an island wide sampling event in martinique in 2008 to trace the evolution of magmatic cl in the volcanic hydrothermal systems over time the results show that magmatic cl can be rapidly flushed out of the hydrothermal systems within 30 to 80 years after the eruption much quicker than other volatile tracers such as co2 and noble gases which can exsolve at greater depths and constantly migrate to the surface because arc volcanoes often have well developed hydrothermal systems where magmatic cl is easily transferred to the surface following its exsolution from shallow magma body we suggest that 37cl has great potential to be a unique proxy to monitor the cessation and revival of infrequent arc volcanoes particularly at centennial time scales

nutrient cycling in a tropical montane rainforest under a supply limited weathering regime traced by elemental mass balances and mg stable isotopes abstract forest ecosystem nutrition and rock weathering are intimately linked through the supply of mineral nutrients and recycling re utilisation of nutrients released from plant litter during mineralisation here we report on novel applications of mg stable isotopes in combination with mass balance calculations to quantify nutrient supply from bedrock atmospheric wet and dry deposition and recycling in a tropical ecosystem characterised by a supply limited weathering regime in the central highlands of sri lanka we measured mg stable isotopes radiogenic sr isotope ratios and element concentrations in the different compartments of the earth s critical zone bedrock saprolite soil soil pore water stream water and vegetation as tracers for element mass fluxes and pathways we find that in the clay rich saprolite mg isotopes are fractionated towards isotopically heavy mg during secondary mineral formation soil pore water and stream water are the complementary isotopically light reservoirs the mg isotope composition of above ground vegetation is on average identical to soil pore water based on these observations we suggest that a tight near surface mineral nutrient loop between plants and soil sustains the tropical forest ecosystem this loop is disconnected from the rock weathering nutrient source in the saprolite beneath soil external atmospheric wet and dry inputs mainly mg and ca strongly contribute to the plant available nutrient budget that the nutrient depleted regolith does not supply these findings based on mg stable isotopes agree with independently obtained information on bio element p k ca mg si recycling this nutrient supply setting contrasts with that reported for the southern sierra nevada usa where a kinetically limited weathering regime prevails our study illustrates the application of new flux estimators based on elemental and metal stable isotope measurements across a range of climate and weathering regimes

magnesium isotope systematics of the lithologically varied moselle river basin france abstract magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the moselle basin northeastern france this small basin is remarkable for its well constrained and varied lithology on a small distance scale and this is reflected in river water sr isotope compositions upstream where the moselle river drains silicate rocks of the vosges mountains waters are characterized by relatively high 87sr 86sr ratios 0 7128 0 7174 in contrast downstream of the city of epinal where the moselle river flows through carbonates and evaporites of the lorraine plateau 87sr 86sr ratios are lower down to 0 70824 magnesium in river waters draining silicates is systematically depleted in heavy isotopes 26mg values range from 1 2 to 0 7 relative to the value presently estimated for the continental crust and a local diorite 0 5 in comparison 26mg values measured in soil samples are higher 0 0 this suggests that mg isotope fractionation occurs during mineral leaching and or formation of secondary clay minerals on the lorraine plateau tributaries draining marls carbonates and evaporites are characterized by low ca mg 1 5 3 2 and low ca sr 80 400 when compared to local carbonate rocks ca mg 29 59 ca sr 370 2200 similar to other rivers draining carbonates the most likely cause of the mg and sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer 26mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year from 1 4 to 1 6 and from 1 2 to 1 4 respectively within the range defined for the underlying rocks downstream of epinal the compositions of the moselle river samples in a 26mg vs 87sr 86sr diagram can be explained by mixing curves between silicate carbonate and evaporite waters with a significant contribution from the vosgian silicate lithologies 70 temporal co variation between 26mg and 87sr 86sr for the moselle river throughout year is also observed and is consistent with a higher contribution from the vosges mountains in winter in terms of runoff and dissolved element flux overall this study shows that mg isotopes measured in waters rocks and soils coupled with other tracers such as sr isotopes could be used to better constrain riverine mg sources particularly if analytical uncertainties in mg isotope measurements can be improved in order to perform more precise quantifications

effects of biogeochemical processes on magnesium isotope variations in a forested catchment in the vosges mountains france abstract this study investigates the potential of mg isotopes as tracers of biogeochemical processes in a small forested catchment located on sandstones extremely poor in mg bearing minerals the average 26 mg is 0 63 0 12 and 0 0 14 for local rainwater and bedrock respectively from the c horizon to the upper eluvial e horizon soil 26 mg from 0 0 0 14 to 0 25 0 14 is close to the bedrock value while more than 70 of mg is lost suggesting a small isotopic shift during illite dissolution the surface soil horizon a h 26 mg is close to plant 26 mg and especially to the grass 26 mg value 0 49 the bulk 26 mg of trees and grass 0 32 and 0 41 respectively are higher than the average 26 mg values of the soil exchangeable fraction 0 92 to 0 42 and of rainwater 0 65 within plants roots are enriched in heavy isotopes whereas light isotopes are preferentially translocated and stored in the above ground parts in norway spruce the older needles forming the annual litterfall are isotopically lighter and strongly depleted in mg compared to more recent needles soil solution 26 mg shifts seasonally from low values lower than rainwater and close to litterfall during a high rainfall period in spring to higher values close to soil 26 mg in dryer periods of winter or summer at the watershed scale streamwater 26 mg varies between 0 85 0 14 and 0 08 0 14 and 26 mg values decrease linearly with discharge the high streamwater 26 mg at low flow close to bedrock 26 mg most likely reflects dissolution processes in the deep saprolite in relation to the very long water residence time conversely we suggest that low stream level 26 mg values are at least partly related to the contribution of surface flows from wet areas using a simple mass and isotopic balance approach we compute that mineral dissolution rates in the soil 0 35 kg mg ha 1 year 1 presently compensate for mg losses from the soil

tracking physicochemical conditions of evaporite deposition by stable magnesium isotopes a case study of late permian langbeinites magnesium isotopic compositions of evaporite deposits may record information concerning brine evolution during deposition we report mg isotopic values delta mg 26 dsm3 measured from an evaporite deposit of langbeinite k2mg2 so4 3 found in the permian salado formation we used these data to model mg isotope fractionation between langbeinite and its parent brine in addition both measured and theoretical results are used to estimate precipitation temperature and interpret depositional environment the salado langbeinite delta mg 26 values are relatively low and fall within a relatively narrow range 4 12 0 03 parts per thousand to 3 81 0 07 parts per thousand equilibrium fractionation factors between langbeinite and aqueous mg2 solutions were calculated using quantum chemical density functional theory all computations were performed at the b3lyp 6 31 g d p level solvation effects were addressed using a solvent model water droplet approach and mineral structures were investigated using volume variable cluster models vvcm the equilibrium mg isotopic fractionation factors a between langbeinite and model brine solution we obtained are 1 0005 1 0004 and 1 0003 delta mg 26 langb water approximate to 10 3 ln alpha 0 473 parts per thousand 0 390 parts per thousand and 0 322 parts per thousand at 10 degrees c 25 degrees c and 40 degrees c respectively these relatively large equilibrium fractionation factors indicate significant mg isotope fractionation between langbeinite and its parent brine during precipitation as langbeinite preferentially incorporates the heavier mg 26 and mg 25 isotopes rayleigh distillation modeling of the salado langbeinite s relatively light mg isotopic composition requires delta mg 26 dsm3 values of 4 parts per thousand for the parent brine models favor a precipitation temperature as high as 40 degrees c under equilibrium conditions potential disequilibrium precipitation conditions suggested by mg isotopic data also imply rapid deposition in a hot arid sedimentary environment prevailing in the southwestern u s during the late permian

controls on chemical weathering on a mountainous volcanic tropical island guadeloupe french west indies abstract guadeloupe island is a natural laboratory ideally suited to the study of biogeochemical processes in tropical and mountainous volcanic environments the island s east west rainfall gradient 1200 8000 mm yr is superimposed on a north south age gradient 2 7 ma to present providing a unique opportunity to investigate the influence of rainfall and rock age on the chemical weathering of volcanic terrains taking advantage of this configuration we present the first temporal survey 2007 2013 of the geochemical composition of the dissolved load of rain and river waters in guadeloupe our data demonstrate that the chemical composition of river water is influenced by rainfall abundance hydrothermal alteration from active or fossilized volcanic systems and interactions between water and minerals during chemical weathering processes the contribution of rain to the overall chemical balance is especially significant in the older northern part of the island where the ferralitic soils are base cation depleted between 15 and 65 of the ca or mg riverine budgets comes from atmospheric deposits highlighting the major role of rainfall in the geochemical budgets of small tropical and mountainous watersheds the river water dataset indicates that different chemical weathering processes dominate the budget depending on the age of the local bedrock in the younger southern part of the island a pool of easily weatherable andesitic minerals from the bedrock dominates the contribution from this pool decreases significantly to 5 15 wt of the bulk soil towards the older terrains in the north the northern rivers are characterized by low ca mg ratios 0 5 1 0 intermediate between those of fresh rocks 1 7 3 3 and soil 0 1 weathering in the northern part of the island is therefore dominated by the dissolution of depleted secondary minerals into soils the ca mg ratio of the river water increases from north to south eventually reaching values similar to those of the bedrocks arguing for congruent dissolution of the youngest volcanic rocks the magnesium isotopic composition of river water 26mg reflects inputs from both rain and weathering processes in southern and central rivers the mg isotopic value of waters after correction for rain inputs 26mgwea is systematically depleted in heavy isotopes mean value of 0 34 relative to that of the bedrock 0 24 to 0 15 in the north the 26mgwea of the river water 0 09 is heavier than that of the andesitic bedrock possibly reflecting the dissolution of 26mg rich secondary minerals ferralitic soil measured around 0 13 the robustness of 26mg and ca mg as proxies of the degree of soil weathering should be investigated further via more detailed sampling campaigns in the future by combining high frequency monitoring of river discharge with measurements of concentration discharge relationships for a wide range of chemical elements we estimate the mean annual chemical weathering fluxes for three rivers that belong to the obsera critical zone observatory fluxes vary from 51 7 to 91 8 t km2 yr north to south along the bedrock age gradient and are among the highest recorded in volcanic tropical regions flash floods can explain 21 31 of the annual chemical weathering fluxes the results highlight the importance of monitoring rivers over periods of several years in order to obtain accurate estimates of chemical exports in tropical and mountainous environments

fluxes of high versus low temperature water rock interactions in aerial volcanic areas example from the kamchatka peninsula russia abstract volcanic areas play a key role in the input of elements into the ocean and in the regulation of the geological carbon cycle the aim of this study is to investigate the budget of silicate weathering in an active volcanic area we compared the fluxes of the two major weathering regimes occurring at low temperature in soils and at high temperature in the active volcanic arc of kamchatka respectively the volcanic activity by inducing geothermal circulation and releasing gases to the surface produces extreme conditions in which intense water rock interactions occur and may have a strong impact on the weathering budgets our results show that the chemical composition of the kamchatka river water is controlled by surface low temperature weathering atmospheric input and in some limited cases strongly imprinted by high temperature water rock reactions we have determined the contribution of each source and calculated the rates of co 2 consumption and chemical weathering resulting from low and high temperature water rock interactions the weathering rates between 7 and 13 7 t km 2 yr for cations only and atmospheric co 2 consumption rates 0 33 0 46 10 6 mol km 2 yr for kamchatka river due to rock weathering in soils low temperature are entirely consistent with the previously published global weathering laws relating weathering rates of basalts with runoff and temperature in the kamchatka river co 2 consumption derived from hydrothermal activity represents about 11 of the total hco 3 flux exported by the river the high temperature weathering process explains 25 of the total cationic weathering rate in the kamchatka river although in the rivers non affected by hydrothermal activity the main weathering agent is carbonic acid reflected in the abundance of hco 3 in rivers in the region most impacted by hydrothermalism the protons responsible for minerals dissolution are provided not only by carbonic acid but also by sulphuric and hydrochloric acid a clear increase of weathering rates in rivers impacted by sulphuric acid can be observed in the kamchatka river 19 of cations are released by hydrothermal acids or the oxidative weathering of sulphur minerals our results emphasise the important impact of both low and high temperature weathering of volcanic rocks on global weathering fluxes to the ocean our results also show that besides carbonic acid derived from atmospheric co 2 hydrochloric acid and especially sulphuric acid are important weathering agents clearly sulphuric acid with hydrothermal activity are key parameters that cause first order increases of the chemical weathering rates in volcanic areas in these areas accurate determination of weathering budgets in volcanic area will require to better quantify sulphuric acid impact

adsorption and desorption controlled magnesium isotope fractionation during extreme weathering of basalt in hainan island china magnesium isotopic compositions of a set of clay rich saprolites developed on the neogene tholeiitic basalt from hainan island in southern china have been measured in order to document the behavior of mg isotopes during continental weathering compared with unaltered basalts 26mg 0 36 the overlying saprolites are strongly depleted in mg i e th mg 99 1 to 92 9 and display highly variable 26mg ranging from 0 49 to 0 40 magnesium concentration and 26mg value of the saprolites display a general increasing trend upwards in the lower part of the profile but a decreasing trend towards the surface in the upper part the variations of mg concentration and isotopic composition in this weathering profile can be explained through adsorption and desorption processes 1 adsorption of mg to kaolin minerals kaolinite and halloysite with preferential uptake of heavy mg isotopes onto kaolin minerals and 2 desorption of mg through cation exchange of mg with the relatively lower hydration energy cations in the upper profile evidence for adsorption is supported by the positive correlation between 26mg and the modal abundance of kaolin minerals in saprolite of the lower profile while negative correlations between 26mg and concentrations of lower hydration energy cations e g sr and cs in the upper profile support the desorption process our results highlight that adsorption and desorption of mg on clay minerals play an important role in behavior of mg isotopes during extreme weathering which may help to explain the large variation in mg isotopic composition of river waters

dynamic of particulate and dissolved organic carbon in small volcanic mountainous tropical watersheds abstract in the tropical zone small watersheds are affected by intense meteorological events these events play an important role in the erosion of soils and therefore on the associated organic carbon fluxes to the ocean we studied the geochemistry of three small watersheds around the basse terre volcanic island french west indies fwi during a four years period by measuring dissolved organic carbon doc particulate organic carbon poc and dissolved inorganic carbon dic concentrations the mean annual yields ranged between 8 1 15 8 tc km 2 yr 1 1 9 8 6 tc km 2 yr 1 and 8 1 25 5 tc km 2 yr 1 for dic doc and poc respectively floods and extreme floods i e extremely high discharge associated to extreme meteorological events such as cyclones or tropical storms account for 42 6 of the yearly water flux and represent 54 5 of the annual doc flux and more than 85 of the annual poc flux the dic flux occurs essentially during low water levels with 75 of the annual flux during low water levels and floods the dissolved carbon is exported in majority under the inorganic form dic doc 2 6 2 1 while during extreme floods the dissolved carbon transported is mostly organic dic doc 0 7 0 2 the partial residence time taking into account only the physical processes erosion and transport in guadeloupean soils has been estimated between 381 and 1000 years these relatively short times could be linked to the intensity of meteorological events rather than the frequency of meteorological events the total export of organic carbon coming from small tropical and volcanic mountainous rivers is estimated at 2 4 0 6 mtc yr 1 for doc and at 5 9 2 4 mtc yr 1 for poc emphasizing that these carbon fluxes are significant and should be included in global carbon budgets in addition the quality of terrestrial organic matter poc doc and c n ratios arriving to the ocean is different from the one of large river origin these inputs are responsible for a fast transport of terrestrial organic matter to the ocean but their effect on regional and global carbon budget is still a matter of debate

carbon and helium isotopes in thermal springs of la soufriere volcano guadeloupe lesser antilles implications for volcanological monitoring abstract la soufriere guadeloupe lesser antilles is one of the most active and dangerous volcanoes of the lesser antilles arc the renewal of the volcanic activity at la soufriere requires replenishment of the volatile poor andesitic stored magma with more primitive volatile rich basaltic magma this event will trigger early release of large quantities of highly volatile species like co 2 and helium in the hydrothermal system to use these precursors first their baseline abundances and their behaviour in the hydrothermal system must be known during the current phase of dormancy in this study we have combined a previous systematic investigation of noble gases with carbon data of hydrothermal fluids flowing out of la soufriere the results for dissolved gases reveal that an intense interaction between rising magmatic volatiles and groundwaters currently takes place at la soufriere we show that the pristine magmatic composition with a 13 c co2 value of 3 19 0 03 a 3 he 4 he ratio of 8 1 0 2 r a and a co 2 3 he ratio of 1 03 0 18 10 10 may vary during the ascent of magmatic fluids due to either fractionation or mixing processes with meteoric water and or an organic component here we provide a baseline for co 2 and helium isotopes at each monitored spring and describe the superficial processes affecting both elemental and isotopic ratios

a new scenario for the last magmatic eruption of la soufriere of guadeloupe lesser antilles in 1530 a d evidence from stratigraphy radiocarbon dating and magmatic evolution of erupted products la soufriere of guadeloupe is a dangerous volcano characterized over the last decade by moderate seismic and fumarolic unrest in the last 15 000 years it has experienced phreatic and magmatic eruptions and unusually numerous flank collapse events sometimes associated with a magmatic eruption we propose a new age of 1530 a d and a new eruptive scenario for the last magmatic eruption on the basis of a novel statistical analysis of radiocarbon age dates and new field and geochemical data this eruption is the only magmatic eruption likely to have occurred in guadeloupe during the last 1400 years the eruption mainly involved an andesitic magma which in the first phase of the eruption partially mixed with a slightly more differentiated magma stored in a small and shallow magma chamber ascent of magma to the surface generated a partial collapse of the hydrothermally altered edifice that increased the magma discharge and led to a sub plinian phase with scoria fallout and column collapse pyroclastic flows followed by near vent pyroclastic scoria fountains the eruption ended with growth of a lava dome our revised interpretation of the last magmatic eruption of la soufriere constitutes the most likely key to a future magmatic eruption scenario for this volcano which displays strong evidence of unrest since 1992

global reconstructions of cenozoic seafloor ages implications for bathymetry and sea level abstract although accurate estimates of cenozoic seafloor ages will serve to further our understanding of the relationship between mantle dynamics plate tectonics and a variety of surficial geological processes it is difficult to estimate ages of subducted seafloor however given the near constancy of surface velocities within a tectonic stage we can estimate cenozoic plate ages even for subducted lithosphere we reconstruct seafloor ages based on the cenozoic plate reconstructions and absolute rotation poles of gordon and jurdy r g gordon and d m jurdy cenozoic global plate motions j geophys res 91 1986 12389 12406 for the western pacific we explore alternative models based on the reconstructions of hall r hall cenozoic geological and plate tectonic evolution of se asia and the sw pacific computer based reconstructions model and animations j asian earth sci 20 2002 353 434 both reconstructions indicate an increase in average seafloor age since the early cenozoic resulting in an increase in the volume of ocean basins and a decreased sea level since the early cenozoic these trends are more pronounced for the gordon and jurdy r g gordon and d m jurdy cenozoic global plate motions j geophys res 91 1986 12 389 12 406 reconstruction because the hall r hall cenozoic geological and plate tectonic evolution of se asia and the sw pacific computer based reconstructions model and animations j asian earth sci 20 2002 353 434 reconstruction retains older seafloor in the western pacific which approximately halves the predicted sea level decrease since the early cenozoic 250 vs 125 m compared to geologic estimates of 150 m these changes in sea level occur despite decreases in oceanic lithosphere production rates of only about 20 in both models thus the changing distribution of seafloor age has a larger effect on sea level than changes in spreading rates or ridge lengths these reconstructions can also be used to estimate past heat flow the volume of subducted buoyancy and changes in the bathymetry of the cenozoic ocean basins

magnesium retention on the soil exchange complex controlling mg isotope variations in soils soil solutions and vegetation in volcanic soils iceland understanding the biogeochemical cycle of magnesium mg is not only crucial for terrestrial ecology as this element is a key nutrient for plants but also for quantifying chemical weathering fluxes of mg and associated atmospheric co2 consumption requiring distinction of biotic from abiotic contributions to mg fluxes exported to the hydrosphere here mg isotope compositions are reported for parent basalt bulk soils clay fractions exchangeable mg seasonal soil solutions and vegetation for five types of volcanic soils in iceland in order to improve the understanding of sources and processes controlling mg supply to vegetation and export to the hydrosphere bulk soils 26mg 0 40 0 11 are isotopically similar to the parent basalt 26mg 0 31 whereas clay fractions 26mg 0 62 0 12 exchangeable mg 26mg 0 75 0 14 and soil solutions 26mg 0 89 0 16 are all isotopically lighter than the basalt these compositions can be explained by a combination of mixing and isotope fractionation processes on the soil exchange complex successive adsorption desorption of heavy mg isotopes leads to the preferential loss of heavy mg from the soil profile leaving soils with light mg isotope compositions relative to the parent basalt additionally external contributions from sea spray and organic matter decomposition result in a mixture of mg sources on the soil exchange complex vegetation preferentially takes up heavy mg from the soil exchange complex 26mgplant exch 0 50 0 09 and changes in 26mg in vegetation reflect changes in bioavailable mg sources in soils this study highlights the major role of mg retention on the soil exchange complex amongst the factors controlling mg isotope variations in soils and soil solutions and demonstrates that mg isotopes provide a valuable tool for monitoring biotic and abiotic contributions of mg that is bioavailable for plants and is exported to the hydrosphere

quantifying chemical weathering rates along a precipitation gradient on basse terre island french guadeloupe new insight from u series isotopes in weathering rinds abstract inside soil and saprolite rock fragments can form weathering clasts alteration rinds surrounding an unweathered core and these weathering rinds provide an excellent field system for investigating the initiation of weathering and long term weathering rates recently uranium series u series disequilibria have shown great potential for determining rind formation rates and quantifying factors controlling weathering advance rates in weathering rinds to further investigate whether the u series isotope technique can document differences in long term weathering rates as a function of precipitation we conducted a new weathering rind study on tropical volcanic basse terre island in the lesser antilles archipelago in this study for the first time we characterized weathering reactions and quantified weathering advance rates in multiple weathering rinds across a steep precipitation gradient electron microprobe emp point measurements bulk major element contents and u series isotope compositions were determined in two weathering clasts from the deshaies watershed with mean annual precipitation map 1800 mm and temperature mat 23 c on these clasts five core rind transects were measured for locations with different curvature high medium and low of the rind core boundary results reveal that during rind formation the fraction of elemental loss decreases in the order ca na k mg si al zr ti fe such observations are consistent with the sequence of reactions after the initiation of weathering specifically glass matrix and primary minerals plagioclase pyroxene weather to produce fe oxyhydroxides gibbsite and minor kaolinite uranium shows addition profiles in the rind due to the infiltration of u containing soil pore water into the rind as dissolved u phases u is then incorporated into the rind as fe al oxides precipitate such processes lead to significant u series isotope disequilibria in the rinds this is the first time that multiple weathering clasts from the same watershed were analyzed for u series isotope disequlibrian and show consistent results the u series disequilibria allowed for the determination of rind formation ages and weathering advance rates with a u series mass balance model the weathering advance rates generally decreased with decreasing curvature 0 17 0 10 mm kyr for high curvature 0 12 0 05 mm kyr for medium curvature and 0 11 0 04 0 08 0 03 0 06 0 03 mm kyr for low curvature locations the observed positive correlation between the curvature and the weathering rates is well supported by predictions of weathering models i e that the curvature of the rind core boundary controls the porosity creation and weathering advance rates at the clast scale at the watershed scale the new weathering advance rates derived on the low curvature transects for the relatively dry deshaies watershed average rate of 0 08 mm kyr map 1800 mm and mat 23 c are 60 slower than the rind formation rates previously determined in the much wetter bras david watershed 0 18 mm kyr low curvature transect map 3400 mm and mat 23 c also on basse terre island thus a doubling of map roughly correlates with a doubling of weathering advance rate the new rind study highlights the effect of precipitation on weathering rates over a time scale of 100 kyr weathering rinds are thus a suitable system for investigating long term chemical weathering across environmental gradients complementing short term riverine solute fluxes

dynamics of dense water cascades at the shelf edge abstract plumes of dense shelf water cascade down continental slopes in many parts of the world s oceans and provide a mechanism for shelf ocean exchange in this paper a nonlinear process orientated theory is developed and used to examine the dynamics of cascading the theory is formulated in terms of a 1 layer model and incorporates bottom topography earth rotation internal and bottom friction and entrainment as well as externally imposed pressure gradients the theory occupies a niche between the stream tube class of model which considers only bulk properties of a plume and the full three dimensional primitive equation approach the model provides useful insights into the complex interplay between the controlling forces and it allows one to recover the shape and trajectory of dense plumes as well as the three dimensional flow field inside the bottom layer asymptotic limits are investigated and lead to several basic results a typical thickness of a fully developed plume is found to be twice t

basalt weathering in central siberia under permafrost conditions chemical weathering of basalts in the putorana plateau central siberia has been studied by combining chemical and mineralogical analysis of solids rocks soils river sediments and suspended matter and fluid solution chemistry altogether 70 large and small rivers 30 soil pore waters and groundwaters and over 30 solids were sampled during july to august 2001 analysis of multiannual data on discharge and chemical composition of several rivers of the region available from the russian hydrological survey allowed rigorous estimation of mean annual major element concentrations and dissolved and suspended fluxes associated with basalt weathering for the rivers tembenchi and taimura that drain monolithologic basic volcanic rocks the mean multiannual flux of total dissolved cations tds c ca mg na k corrected for atmospheric input is 5 7 0 5 t km 2 yr for the largest river nizhniya tunguska draining essentially basic rocks the tds c is 6 1 1 5 t km 2 yr the overall co2 consumption flux associated with basalt weathering in the studied region 700 000 km 2 achieves 0 08 10 12 mol yr which represents only 2 6 of the total co2 consumption associated with basalt weathering at the earth s surface the fluxes of suspended matter were estimated as 3 1 0 5 9 0 0 8 and 6 5 2 0 t km 2 yr for rivers taimura eratchimo and nizhniya tunguska respectively based on chemical analyses of river solutes and suspended matter the relative dissolved versus particulate annual transport of major components is cinorg corg na k ca mg si fe mn ti al which reflects the usual order of element mobility during weathering according to chemical and mineralogical soil and sediment analyses alteration of basalt consists of 1 replacement of the original basaltic glass by si al fe rich amorphous material 2 mechanical desegregation and grinding of parent rocks leading to accumulation of primary hydrothermal trioctahedral smectite and 3 transformation of these trioctahedral oxy smectites and mixed layer chlorite smectite into secondary dioctahedral smectite accompanied by removal of ca mg and fe and enrichment in al no vertical chemical differentiation of fluid and solid phases within the soil profile was identified all sampled soil pore waters and groundwaters were found to be close to equilibrium with respect to chalcedony gibbsite halloysite and allophanes but strongly supersaturated with respect to goethite nontronite and montmorillonite over the annual cycle the contribution of atmospheric precipitation permafrost melting underground reservoirs litter degradation and rock and soil mineral weathering for the overall tds c transport in the largest river of the region nizhniya tunguska is 9 3 3 10 5 10 5 5 25 20 and 45 30 respectively in the summertime direct contribution of rocks and soil mineral weathering via solid fluid interaction does not exceed 20 the main unknown factors of element mobilization from basalt to the river is litter degradation in the upper soil horizon and parameters of element turnover in the vegetation copyright 2005 elsevier ltd

changing sources of base cations during ecosystem development hawaiian islands 87 sr 86 sr evidence from a soil chronosequence in the hawaiian islands demonstrates that the atmosphere supplies 85 of putatively rock derived sr in older sites initially bedrock is the dominant source for sr and other lithophile elements such as ca but high rates of weathering and leaching of the substrate by 20 ka lead to a shift to atmospheric sources the loss of weathering inputs coincides with other physio chemical changes in the soil and results in a steep decline of base cations in the soil pool while these patterns imply the potential for limitation of biological productivity by low base cation supply the atmosphere provides a supply of base cations in excess of nutritional needs even after nearly all rock derived base cations have been leached from the soil this raises the possibility that p limitation in terrestrial ecosystems may develop at least as much because of low rates of atmospheric deposition of p relative to ca k and other rock derived elements as because of its chemical interaction in soil

magnesium isotope fractionation between brucite mg oh 2 and mg aqueous species implications for silicate weathering and biogeochemical processes article history brucite with its octahedral structure has a lattice configuration that is similar to the mg bearing octahedral layers in phyllosilicates understanding stable mg isotope fractionation between brucite and aqueous solution therefore bears on interpretation of mg isotope data in natural weathering systems in this study we experimentally determined mg isotope fractionation between brucite and two mg aqueous species the free mg aquo ion mg oh2 6 2 and edta bonded mg mg edta 2 results from recrystallization and brucite synthesis experiments suggest mild preferential partitioning of light mg isotopes into brucite compared to mg aquo ions at low temperatures where measured 26 mg brucite mg 2

the cenozoic evolution of the strontium and carbon cycles relative importance of continental erosion and mantle exchanges the past variations of the seawater 87sr86sr isotopic ratio are related to changes in the relative contribution of the mantle sr input to the ocean and the sr supply from continental weathering recently it has been postulated that the cenozoic increase in the seawater 87sr86sr isotopic ratio was associated with the uplift of the himalayan and andean mountains at that time these orogenies may have changed the sr isotopic ratio of the continental rocks undergoing weathering as a result of extensive metamorphism increased the river flux of sr through enhanced weathering in these regions and possibly caused the global climatic cooling trend of the cenozoic a model of the major geochemical cycles coupled to an energy balance climate model is used to explore the possible causes of the mesozoic cenozoic fluctuations in the seawater 87sr86sr isotopic ratio the contribution of the mantle exchanges at mid ocean ridges of the recycling of seafloor carbonates through plate margin volcanism and of the alteration of seafloor basalts to the fluctuations of the seawater 87sr86sr isotopic ratio are studied finally this model tentatively describes the impact of the himalayan orogeny on the geochemical cycles of sr and c some possible effects of the extensive metamorphism associated with the india asia collision and of the himalayan uplift are modelled the model reproduces the cenozoic increase of the seawater 87sr86sr isotopic ratio however the impact of the himalayan orogeny on the c cycle appears to be limited and insufficient to generate the global climatic cooling of the cenozoic rather in the model the cenozoic cooling is mostly due to the reduction of the co2 emission from mid ocean ridge volcanism and to changes in the chemical weathering rates in the rest of the world excluding the himalayas

mechanisms of magnesium isotope fractionation in volcanic soil weathering sequences guadeloupe magnesium mg stable isotopes are increasingly used as a weathering proxy in soils and rivers but the impact of the mineralogy of secondary phases on isotopefractionation remains obscure a better understanding of the behaviour of mg isotopes during weathering processes is a mandatory step toward deployment of this new tracer for understanding chemical fluxes exported from the critical zone here we investigate isotopic variations in 26mg in bulk soils and clay fractions relative to their parent andesite in three soilweatheringsequences from guadeloupe formed under contrasting climatic conditions soils formed in drier conditions low precipitation contain smectite whereas soils formed under wet conditions high rainfall are characterized by halloysite and fe oxides or kaolinite all clay fractions have mg isotopic compositions 26mg 0 41 to 0 10 similar to or heavier than their parent andesite 26mg 0 47 supporting the preferential incorporation of heavy mg isotopes in secondary mg bearing clay minerals with the first direct measurements on clay fractions soils with lighter mg isotope compositions have greater quantities of exchangeable mg the data support a contribution from sea spray to the exchangeable mg pool correlated to the soilweathering degree this study highlights for the first time that the soil 26mg not only depend on 26mg of the parent rock and on any fractionation that might occur but also on the mg retention on the exchange complex which could in turn be controlled by external inputs such as sea spray

modelling the phanerozoic carbon cycle and climate constraints from the 87sr 86sr isotopic ratio of seawater a numerical model describing the coupled evolution of the biogeochemical cycles of carbon sulfur calcium magnesium phosphorus and strontium has been developed to describe the long term changes of atmospheric carbon dioxide and climate during the phanerozoic the emphasis is on the effects of coupling the cycles of carbon and strontium various interpretations of the observed phanerozoic history of the seawater 87sr 86sr ratio are investigated with the model more specifically the abilities of continental weathering volcanism and surface lithology in generating that signal are tested and compared it is suggested that the observed fluctuations are mostly due to a changing weatherability over time it is shown that such a conclusion is very important for the modelling of the carbon cycle indeed it implies that the conventional belief that the evolution of atmospheric carbon dioxide and climate on a long time scale is governed by the balance between the volcanic input of co2 and the rate of silicate weathering is not true rather carbon exchanges between the mantle and the exogenic system are likely to have played a key role too further the increase of the global weathering rates with increasing surface temperature and or atmospheric co2 pressure usually postulated in long term carbon cycle and climate modelling is also inconsistent with the new model other factors appear to have modulated the weatherability of the continents through time such as mountain building and the existence of glaciers and ice sheets based on these observations a history of atmospheric carbon dioxide and climate during phanerozoic time consistent with the strontium isotopic data is reconstructed with the model and is shown to be compatible with paleoclimatic indicators such as the timing of glaciation and the estimates of cretaceous paleotemperatures