modeling of water rock interaction in the mackenzie basin competition between sulfuric and carbonic acids the chemical weathering of continental surfaces depends on many factors including lithology climate tectonics erosion soil or vegetation and also on the availability of acidity in the weathering zone in addition to atmospheric soil co2 sulfide oxidation may represent a significant source of protons for weathering reactions as shown previously for the rivers draining the mackenzie basin canada here a numerical model describing continental weathering reactions based on laboratory kinetic laws is coupled to a dynamic global vegetation model the b witch model in order to estimate the impact of sulfide oxidation on chemical weathering and associated atmospheric co2 consumption fluxes throughout the mackenzie river basin the model is first calibrated with available field data for the various sub basin of the mackenzie watershed and then a simulation is performed removing the contribution of sulfuric acid to the weathering system the main outcomes of the present study are that 1 the dissolved silica export is controlled by secondary minerals reactivity in soils and the calcium and magnesium fluxes are driven by the dissolution of calcite and dolomite 2 the atmospheric co2 consumption by weathering processes in the mackenzie river is limited accounting for only 24 of the total bicarbonate flux to the ocean confirming a previous study and suggesting that weathering processes in the mackenzie watershed acts as a source of carbon to the atmosphere at the geological timescale and 3 the presence of sulfide minerals within a river basin decreases the apparent net consumption of atmospheric co2 through chemical weathering we show that the actual production of sulfuric acid in the weathering zone of the mackenzie basin reduces the net atmospheric co2 consumption by about two compared to what the atmospheric co2 consumption should be in the absence of sulfide minerals sulfuric acid driven chemical weathering has thus to be considered at both short and long timescales when looking at the link between chemical weathering and the global carbon cycle

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

a sequence of events across the cretaceous tertiary boundary the lithological and biological sequence of events across the cretaceous tertiary k t as developed in thick and complete landbased sections and termed the standard k t event sequence is also found in many i sdp cores from all over the globe microtektite like spherules have been found in almost every core or outcrop with an iridium anomaly forming a worldwide strewnfield these microtektites are an excellent indicator of the k t boundary level the basal paleocene globigerina eugubma zone is nov established in all major ocean basins the difference in faunas between the pacific and tethys atlantic oceans may point to different recovery of the oldest paleocene planktonic foraminiferal assemblages in different ocean basins planktonic foraminifera and nannoplankton apparently show a different extinction recovery pattern at the k t boundary which suggests that the nannoplankton underwent final extinction later and recover later than planktonic foraminifera these patterns may be important for the evaluation of the type and range of environmental stress resulting from the hypothesized impact s at the k t boundary blocking of sunlight by the dust cloud still can account for the clear mass mortality at the k t boundary but seems less likely as explanation for the final nannoplankton extinction as photosynthetic nannoplankton appear to survive 1000 10 000 years into the tertiary

oceanic primary productivity and dissolved oxygen levels at the cretaceous tertiary boundary their decrease subsequent warming and recovery thirty six different geochemical and foraminiferal analyses were conducted on samples collected at closely spaced intervals across the cretaceous tertiary k t boundary exposed at caravaca spain a rapid reduction in the gradient between 13c values in fine fraction carbonate and benthic foraminiferal calcite and a decrease in the abundance of phosphorus a proxy for organic carbon and calcium were recorded in sediments 0 0 5 cm above the k t boundary these trends imply that an abrupt mass mortality occurred among pelagic organisms leading to a significant reduction in the flux of organic carbon to the seafloor in addition variations in sulfur isotope ratios the hydrocarbon generating potential of kerogen measured as the hydrogen index and foraminiferal indices of dissolved oxygen level all imply that a rapid decrease in dissolved oxygen was coincident with the 13c event evidence of the low oxygen event has also been recognized in japan and new zealand suggesting that intermediate water oxygen minima were widely developed during earliest danian time a threefold increase in the kaolinite illite ratio and a 1 2 decrease in 18o carbonate fine fraction were recorded in the basal 0 1 2 cm of danian age sediments these trends suggest that atmospheric warming and an increase in surface water temperature occurred 0 3 kyr after the 13c event recovery in the difference between 13c values in the carbonate fine fraction and in benthic foraminiferal calcite as well as increases in phosphorus and calcium contents occur at the base of planktonic foraminiferal zone pla implying that an increase in primary productivity commenced some 13 kyr after the k t boundary tables a1 a3 are available on diskette or via anonymous ftp from kosmos agu org directory apeno username anonymous password guest diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 or by phone at 800 966 2481 15 00 payment must accompany order

geochemical and isotopic signatures of surficial sediments from the western continental shelf of india inferring provenance weathering and the nature of organic matter abstract bottom sediments from thirteen transects sampled mainly at depth contours of 30 100 and 200 m along the western continental margin of india falling in two offshore sectors from dwaraka to goa and cape comorin to goa were analyzed for calcium carbonate major elements in silicate fraction trace and rare earth elements in the bulk fraction and carbon and nitrogen isotopes in organic matter to understand the provenance of sediments weathering patterns in the source areas and nature of organic matter major elements such as si ti mg and discrimination plots involving alkalies and silica have shown a distinct north south provinciality with the source signatures pointing at deccan basalt for sediments in the north from dwaraka to goa and gneisses and granulites of south india in the south shale normalized ree patterns and ree content suggest additional local sources mainly in the southwest coast of india degree of alteration determined using chemical index of alteration cia plagioclase index of alteration pia and a cn k plots have suggested that the sediments are moderately weathered despite the intense orographic rainfall in the source area variability in degree of chemical weathering is seen with the change in provenance in general the sediments north of goa with a provenance of deccan basalts show a higher chemical weathering index corg n molar ratios are mostly between 10 and 12 minimum and maximum being 6 9 and 14 respectively which are closer to values for marine organic matter this is corroborated by marine 13c values 18 2 to 21 6 while they broadly fall within the marine values heavier values are seen in northern transects off porbandar and dwaraka where the sediments have a provenance different from those in the south this could be due to a higher contribution from c4 type vegetation in the north consistent with heavier 13c values in terrestrial plants in source regions heavier 15n values are observed for the northern transects north of ratnagiri which is supported by the intense denitrification in the northern arabian sea

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

geochemistry and solute sources of surface waters of the tarim river basin in the extreme arid region nw tibetan plateau abstract major ion concentrations of river lake and snow waters were measured to better understand the water quality hydrochemical processes and solute sources of surface waters within the tarim river basin in the extreme arid region surface waters are slightly alkaline and are characterized by high total dissolved solids tds tds values varies over two orders of magnitude from fresh 76 to brackish 24 with a mean value of 1000 mg l higher than the global river average and river waters draining the himalayas and the southeastern tibetan plateau most of the samples were ca2 mg2 hco 3 type and suited for drinking and irrigation water quality of aksu river ak hotan river ht and northern rivers nr is better than the others rock weathering ion exchange and precipitation are the major hydrogeochemical processes responsible for the solutes in rivers waters anthropogenic input to the water chemistry is minor and human activities accelerate increase of river tds the quantitative solute sources are first calculated using a forward model in this area the results show that evaporite dissolution carbonate weathering atmospheric input and silicate weathering contributed 58 3 25 7 8 7 and 8 2 of the total dissolved cations for the whole basin evaporite dissolution dominated in lake waters lw ht yarkant river yk tarim river tr and southern rivers sr contributing 73 5 53 4 56 7 77 and 74 2 of the total dissolved cations respectively carbonate weathering dominated in ak and nr contributing 48 and 44 4 of the total dissolved cations respectively the tds flux of ht tr ak yk was 66 0 118 6 134 9 and 170 4 t km2 yr respectively higher than most of the rivers in the world knowledge of our research can promote effective management of water resources in this desert environment and add new data to global river database

effect of friction fatigue on pile capacity in dense sand the paper presents the results of a series of field tests performed to study the causes of friction fatigue experienced by displacement piles four instrumented model piles were installed at a dense sand test bed site the test series was designed to impose different levels of cyclic loading during pile installation static and cyclic load tests were subsequently performed to study the differences in the axial capacities developed for ostensibly monotonic and cyclic installations the test results indicated that the mobilized horizontal effective stress regime that controls pile side friction primarily depends on the in situ sand state as reflected by the cone penetration test cpt qc resistance a zone of highly stressed sand that produced a concentration of high shear resistance was mobilized in the vicinity of the pile base the horizontal effective stress that acted on the pile shaft reduced in response to cyclic loading with the largest reductions occurring for high intensity cyclic loading or when the pile had experienced only a few load cycles during installation although cyclic loading caused a reduction in the horizontal effective stress that acted on the pile shaft the elevated stress built up in the vicinity of the pile base during installation remained higher than that remote from the base the elevated stress in the vicinity of the pile base only dissipated after cyclic tension loading had been applied

a global geochemical mass budget applied to the congo basin rivers erosion rates and continental crust composition rivers carry the products of continental denudation either in a dissolved form chemical erosion or in a solid form physical erosion we focus in this paper on the relationship between physical erosion and chemical erosion we establish the mass budget of the congo basin rivers using chemical complementarities between river suspended sediments sandy bedload and dissolved load of the congo basin rivers reported in a previous paper dupre et al 1995 a series of equations are presented assuming that the physical and chemical erosion processes are in a steady state during one year the total mass of river borne material dissolved and particulate transported in the river over a given period of time should balance the mass of upper continental crust eroded during this time we show that the local continental crust on each drainage basin can be estimated and solve our steady state weathering model using an inversion procedure the very good agreement between modelled and measured values of the river suspended sediment concentrations validates the steady state hypothesis in this wet tropical area consequently in this area the sediment yield provide a good estimate of the rates of mechanical denudation this result also validates the calculation of the chemical and isotopic composition of the local continental upper crust using the bulk river load erosion rates for the silicate upper crust and thus independent of the lithological variability silicates evaporites and carbonates of the drainage basins are calculated mechanical erosion rates and chemical erosion rates for the congo basin at brazzaville are 8 t km2 y and 5 t km2 y the corresponding consumption of atmospheric co2 by weathering process is estimated to 51 103 mol km2 an these weathering and consumption rates are low in spite of the severity of the weathering conditions of the high soil temperature and of the intensity of precipitations these conclusions indicate the limiting influence the dynamic equilibrium of soils for silicate weathering finally by estimating the local continental crust chemical composition before the onset of erosion processes especially for the most soluble elements we can test the model of taylor and mclennan

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

close mass balance of long term carbon fluxes from ice core co 2 and ocean chemistry records on geological timescales carbon dioxide enters the atmosphere through volcanism and organic matter oxidation and is removed through mineral weathering and carbonate burial an analysis of ice core co2 records and marine carbonate chemistry indicates a tight coupling between these processes during the past 610 000 years which suggests that a weathering feedback driven by atmospheric co2 leads to a mass balance between co2 sources and sinks on long timescales feedbacks controlling long term fluxes in the carbon cycle and in particular atmospheric carbon dioxide are critical in stabilizing the earth s long term climate it has been hypothesized that atmospheric co2 concentrations over millions of years are controlled by a co2 driven weathering feedback that maintains a mass balance between the co2 input to the atmosphere from volcanism metamorphism and net organic matter oxidation and its removal by silicate rock weathering and subsequent carbonate mineral burial1 2 3 4 however this hypothesis is frequently challenged by alternative suggestions many involving continental uplift and either avoiding the need for a mass balance or invoking fortuitously balanced fluxes in the organic carbon cycle5 6 7 8 9 here we present observational evidence for a close mass balance of carbon cycle fluxes during the late pleistocene epoch using atmospheric co2 concentrations from ice cores10 11 12 we show that the mean long term trend of atmospheric co2 levels is no more than 22 p p m v over the past 610 000 years when these data are used in combination with indicators of ocean carbonate mineral saturation to force carbon cycle models the maximum imbalance between the supply and uptake of co2 is 1 2 during the late pleistocene this long term balance holds despite glacial interglacial variations on shorter timescales our results provide support for a weathering feedback driven by atmospheric co2 concentrations that maintains the observed fine mass balance

was the antarctic glaciation delayed by a high degassing rate during the early cenozoic abstract the cenozoic is a period of major climatic changes marked by the formation of the antarctic ice sheet at the eocene oligocene e o boundary the opening of the southern ocean seaways and the decrease in atmospheric co2 are two processes generally evoked to explain this e o cooling the debate is still ongoing but modeling studies tend to demonstrate that the decrease in atmospheric co2 is the main driver of the cooling however uncertainties persist on what drove the decrease in atmospheric co2 during the cenozoic in this study we investigate the impact of continental drift lithology distribution and volcanic degassing rates on the atmospheric carbon dioxide concentration over the cenozoic within a coupled climate carbon model geoclim in the model the continental drift results in driving low atmospheric co2 levels during the eocene and the oligocene the dispersed configuration and the location of a large continental area north africa northern south america within the inter tropical convergence zone itcz promote co2 consumption by weathering forcing co2 to remain low icehouse conditions are also promoted by the drifting of india and the weathering of the deccan basalts in the itcz during the eocene and by the weathering of the ethiopian traps during the oligocene to prevent the building up of the antarctic ice sheet at the eocene the model needs enhanced solid earth degassing flux by 50 so that atmospheric co2 levels stay above the glacial threshold 750 ppm we find that the decrease in atmospheric co2 from the eocene to the oligocene is probably due to a reduction in the source of volcanic co2 rather than an increase in silicate weathering the model results furthermore suggest that during the miocene period the northward drifting of both the african plate and india including the deccan traps might have decreased the continental surface exposed to chemical weathering therefore generating higher co2 values finally the uplift of the tibetan plateau from the miocene to the present day induces in the model an increase in silicate weathering through the intensification of the south eastern asian monsoon causing atmospheric co2 to come back to a pre industrial value

volatile fluxes during flood basalt eruptions and potential effects on the global environment a deccan perspective abstract we examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time characteristically a few million years within this period a short lived climactic phase that lasts about 1 ma typically emplaces a large proportion of the lava volume this phase consists of a series of huge eruptions each yielding 10 3 10 4 km 3 of magma each eruption lasted on the order of a decade or more and built an immense p hoehoe dominated lava flow field by eruptive activity along fissures tens to hundreds of km long high fire fountains emanating from vents along the fissures at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas the combination of large eruption magnitudes maintained high effusion rates during eruptions and the repeated nature of the characteristic large scale eruptive activity occurs in earth history only during periods of flood basalt volcanism based on recent analogs and determination of volatile contents of ancient flood basalt lavas we estimate that individual eruptions were capable of releasing 10 000 tg of so 2 resulting in atmospheric loadings of 1000 tg a 1 during a sustained decade long eruptive event we apply this model of flood basalt volcanism to estimate the potential mass of co 2 and so 2 released during formation of the 65 ma deccan province the deccan lava pile contains the record of hundreds of enormous p hoehoe flow fields erupted within a period of about 1 ma consequently atmospheric perturbations associated with so 2 emissions from just one of these long lasting eruptions were likely to have been severe and constantly augmented over a decade or longer by contrast the amounts of co 2 released would have been small compared with the mass already present in the atmosphere and thus much more limited in effect individual eruptions were followed by hiatuses of hundreds to thousands of years during which the gas contributions to the atmosphere would be recycled it is clear that the nature and potential atmospheric impact of a series of huge volume repeated long term degassing events requires further investigation in conjunction with appropriate climate models

seawater sr isotopes at the cretaceous tertiary boundary abstract seawater 87 sr 86 sr values increase abruptly by 28 10 6 across the cretaceous tertiary boundary ktb this small but rapid shift is superimposed on the larger scale structure of the seawater sr isotope curve the time scale of radiogenic sr addition appears to be too rapid to reconcile with sources associated with volcanism and we show that the amount of sr required to produce even this small increase is too large to be derived from 1 a kt bolide of the size constrained by the ir anomaly 2 continental crust ejecta from the impact of such a bolide 3 soot from global wildfires initiated by an impact or 4 any combination of these sources the probable source of the radiogenic sr is enhanced continental weathering but the high rate of increase appears to rule out processes such as sea level regression glaciation or tectonism a plausible mechanism for rapid addition of radiogenic sr to the oceans is enhanced weathering associated with globally distributed acid rain ph 1 which is a proposed by product of a bolide impact 51 epsl vol 83

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

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

modelling basalt weathering at elevated co2 concentrations implications for terminal to post magmatic rifting in the deccan traps kachchh india

chemical weathering in luzon philippines from clay mineralogy and major element geochemistry of river sediments clay mineralogy and major element geochemistry of 35 surface sediment samples collected in 21 major to moderate rivers of luzon philippines are used to evaluate the present chemical weathering process the clay mineral assemblage consists mainly of smectite average 86 with minor kaolinite 9 and chlorite 5 and very scarce illite 1 and does not show strong island wide differences the major element results of both bulk and clay fraction sediments indicate that the formation of clay minerals is accompanied by leaching of ca and na first and of fe and mn thereafter during the chemical weathering process a low moderate chemical weathering degree of bulk sediments and a moderate intensive degree of clay fraction sediments are obtained in luzon rivers based on proxies of chemical index of alteration cia and smectite crystallinity it is suggested that the majority of andesitic basaltic volcanic and sedimentary rocks along with the tectonically active geological setting and sub tropical east asian monsoon climate are responsible for the predominance of smectite in the clay mineral assemblage

chemical denudation rates of the western canadian orogenic belt the stikine terrane we report in this paper major element and sr isotopic ratio analyses for 19 rivers draining the stikine province in the western canadian cordillera dissolved solutes suspended sediments and river sands were analyzed the aim of the paper is to calculate chemical denudation rates for this uplifted accretionary prism mainly dominated by volcanics and volcanic derived sedimentary rocks the major chemical features of the stikine rivers are their dilute character and the excess of ca mg and sr in the dissolved load with regards to na molar ca na ratios from 2 to 14 mean value of 5 4 are observed although the region is dominated by silicate rocks suspended sediments show ca na ratios close to 0 4 isotopically most of the rivers investigated display lower sr isotopic ratios in the dissolved load compared to the suspended load which is very unusual to account for the excess of cations three different hypotheses are tested by an inversion method allowing us to determine the origin of each major solute the first scenario assumes that the excess of ca and mg is due to the dissolution of unradiogenic carbonates the second scenario supposes that the excess of base cations is derived from the preferential dissolution of ca and mg rich minerals such as amphiboles in the third scenario all solutes are assumed to derived from silicate weathering the cationic weathering rates of silicates although imprecise are in the order of 2 5 tons km2 year for the two first hypotheses if all solutes are taken into account denudation rates are between 9 and 15 tons km2 year on a global scale these numbers are among the lowest found for rivers draining basaltic rocks they are however found to be consistent with the global law for chemical weathering rates established for basaltic rocks showing that chemical denudation rate are linearly correlated to runoff and depend on temperature according to an arrhenius law the rivers draining the complex assemblage of volcanic and volcanic derived rocks in the subduction collision geological context of the stikine province thus respond similarly to the other volcanic provinces of the world this does not seem to be true for associated co2 consumption rates the abundance of sulfate ions in the dissolved load possibly derived from oxidative weathering of sulfides may indeed provide a non negligible part of the protons necessary for chemical weathering within canada the stikine geologic province is one whose silicates weather at a high rate the order of chemical weatherabilty of canadian geological province from the lowest to the highest is established as follows granites shales of the rockies volcanics of the western cordillera shales of the interior platform carbonates

estimating porosity of partially saturated sediments abstract the electrical resistivity of an unconsolidated sediment depends among other factors on the fraction of the pore space that is filled with fluid an empirical relation can be formed that relates measured resistivity and fluid content to the percent saturation the formula is applied to a core taken from a freshwater lake and the volume of gas in the sediment is estimated to a depth of 6 m into the lake bottom the procedures described can lead to improved estimates of porosity and bulk density

modeling the early paleozoic long term climatic trend the early paleozoic climate has been described as warm and equable however recent data based on conodont oxygen isotopic composition reveal a large long cooling trend through the ordovician followed by an abrupt cooling during the late ordovician glaciation this long term climate change is associated with a major radiation in the earth life history nonetheless the driving mechanisms for this cooling trend remain unknown carbon dioxide consumption by the weathering of fresh rocks from volcanic arcs has recently been suggested as a possible driver for this climate change however the impact of the plate motion context has not been explored yet although it might have a major impact on atmospheric co 2 levels simulations with a climate model coupled to a biogeochemical model geoclim show that the atmospheric co 2 decreased from more than 20 pal 5600 ppmv in the furongian down to approximately 10 pal 2800 ppmv in the llandovery before rising again in the early devonian we suggest that changes in geography and exposure of fresh volcanic rocks on continents are required to explain the large co 2 drawdown that led to the onset of cooler to glacial conditions from the middle ordovician to the llandovery the weathering of fresh volcanic rocks is itself responsible for 33 of the late ordovician atmospheric co 2 decrease the rest being related to the continent motion through the intertropical convergence zone itcz mean annual continental temperature falls by 3 c in the early ordovician reaching 13 5 c during the glacial interval and rises to 16 c in the early devonian

chemical weathering rates and atmospheric soil co2 consumption of igneous and metamorphic rocks under tropical climate in southeastern brazil abstract chemical weathering rates and atmosphere soil co 2 consumption of igneous and metamorphic rocks under tropical climate in southeastern brazil were evaluated using the chemical composition of surface waters and fresh rocks and soil horizon c in the upper sorocaba river basin surface water samples were collected between june 2009 and june 2010 and analyses were performed to assess ph electrical conductivity ec temperature and total dissolved solids tds including na k ca 2 mg 2 cl so 4 2 po 4 3 no 3 and sio 2 fresh rocks and c horizon samples were also collected taking into account their geological context abundance and spatial density to analyze major elements and mineralogy the concentration of tds and dissolved cations anions and silica increased during the dry period in relation to the wet period and the same behavior was observed for ph ec and temperature after corrections of anthropogenic contributions ca 21 t km 2 yr and atmospheric inputs ca 19 t km 2 yr the annual flux due to chemical weathering involving the igneous and metamorphic rocks was ca 29 t km 2 yr the co 2 atmospheric soil consumption in the upper sorocaba river basin was ca 0 2 10 6 mol km 2 yr and when extrapolated to the entire mantiqueira orogenic belt accounted an estimated consumption of 0 07 10 12 mol yr representing 0 6 of the total co 2 consumption flux derived from global average silicate weathering the chemical weathering rates of igneous and metamorphic rocks in the upper sorocaba river basin were estimated at 15 m my respectively the main weathering process in this watershed was the monossialitization with partial hydrolyses of bedrock minerals except quartz which was not weathered and remained in the soil profile the annual specific flux derived from igneous and metamorphic rocks at upper sorocaba river basin could be compared with watersheds in tropical climates however this value is higher than in other north american european asian and african granitoid watersheds and lower than in montane watersheds

chemical weathering in high sediment yielding watersheds new zealand 1 we have determined the chemical erosion yields for fifteen watersheds in new zealand ranging in size from 12 2 to 2928 km2 these rates coupled with previously measured physical erosion yields allow us to compare these two modes of landscape denudation the physical erosion yields are some of the highest measured in the world although in most instances the chemical erosion yields are only a small fraction of the total erosion yields the absolute values are very high our data strongly support the notion that chemical erosion rates are greatly influenced by the yield of physical erosion and that the rapid production of fresh surfaces as a result of high physical erosion rates and subsequent denudation is critical to the high chemical erosion yields observed

spatial distribution of dissolved constituents in icelandic river waters summary in this study we map the spatial distribution of selected dissolved constituents in icelandic river waters using gis methods to study and interpret the connection between river chemistry bedrock hydrology vegetation and aquatic ecology five parameters were selected alkalinity sio2 mo f and the dissolved inorganic nitrogen and dissolved inorganic phosphorus mole ratio din dip the highest concentrations were found in rivers draining young rocks within the volcanic rift zone and especially those draining active central volcanoes however several catchments on the margins of the rift zone also had high values for these parameters due to geothermal influence or wetlands within their catchment area the din dip mole ratio was higher than 16 in rivers draining old rocks but lowest in rivers within the volcanic rift zone thus primary production in the rivers is limited by fixed dissolved nitrogen within the rift zone but dissolved phosphorus in the old tertiary catchments nitrogen fixation within the rift zone can be enhanced by high dissolved molybdenum concentrations in the vicinity of volcanoes the river catchments in this study were subdivided into several hydrological categories importantly the variation in the hydrology of the catchments cannot alone explain the variation in dissolved constituents the presence or absence of central volcanoes young reactive rocks geothermal systems and wetlands is important for the chemistry of the river waters we used too many categories within several of the river catchments to be able to determine a statistically significant connection between the chemistry of the river waters and the hydrological categories more data are needed from rivers draining one single hydrological category the spatial dissolved constituent distribution clearly revealed the difference between the two extremes the young rocks of the volcanic rift zone and the old tertiary terrain

carbon isotope ratio of dissolved inorganic carbon dic in rivers draining the deccan traps india sources of dic and their magnitudes abstract chemical weathering of silicate and carbonate rocks by carbonic acid is important in the context of atmospheric co 2 sequestration and its delivery to the oceans via rivers as dissolved inorganic carbon dic in this work silicate weathering contribution to dic in the krishna river system draining the deccan basalts in south western india has been determined using a new approach based on 13 c si hco 3 systematics of the waters 13 c in the samples ranges from 8 5 to 20 7 and shows a strong linear inverse trend with si hco 3 r 2 0 80 the si hco 3 ratios in rivers vary from 0 55 to 0 10 the higher value matches the expected ratio for chemical weathering of deccan basalts based on their composition the 13 c si hco 3 trend suggests the mixing of two end members a carbonate derived endmember with low si hco 3 and enriched in 13 c and a silicate derived endmember with higher si hco 3 and depleted in 13 c small rivers of the western ghats are depleted in 13 c 13 c 18 7 2 and have high si hco 3 these properties are interpreted as signatures of basalt silicate weathering with co 2 from c 3 vegetation three samples from the krishna mainstream and two of its larger tributaries the bhima and the ghod are enriched in 13 c 13 c 8 5 to 15 with higher hco 3 and lower si hco 3 ratios indicating that a significant fraction of dic in these samples is derived from carbonate weathering carbonate dispersed in river sediments can be a likely source of dic

evolution of carbon cycle over the past 100 million years it is generally accepted that progressive cooling of global climate since the late cretaceous results from decreasing partial pressure of atmospheric co2 pco2 however details on how and why the carbon cycle evolved and how it would affect pco2 have not been fully resolved while the long term decline of pco2 might be caused by the decrease of volcanic degassing through the negative feedback between pco2 and silicate weathering seafloor spreading the major control of co2 degassing seems to have remained relatively constant alternative explanation known as uplift driven climate change hypothesis proposes that tectonic uplift may have enhanced the sink of atmospheric co2 by silicate weathering and thus produced the decline of pco2 however increasing weathering sink of co2 could deplete atmosphere all of its co2 within several million years while holding volcanic outgassing constant in this work major fluxes of long term carbon cycle are calculated based on a reverse model constrained by marine c sr and os isotopic records and the spreading rate of sea floor weathering of island basalt and continental silicate rocks are separated in the new model the results indicate a long term decline of island basalt weathering in consistent with the global cooling trend over the past 100 million years dramatic changes of the co2 fluxes associated continental silicate weathering reverse weathering volcanic degassing and the growth of organic carbon reservoir have been observed disturbance of atmospheric co2 cycle by these fluxes seems to be maintained by the concomitant adjustments of island basalt weathering that were sensitive to the pco2 controlled environment factors such as temperature and runoff the negative feedbacks between pco2 and weathering of island basalt might have played a significant role in stabilizing the long term carbon cycle

effect of aging on the penetration resistance of sands the main objective of this study was to understand the effect of aging on the penetration resistance of freshly deposited sands two types of sand locally available river sand used as masonry sand and beaufort sea sand were selected for the study the sands were allowed to age under a constant stress of 100 kpa in a specially designed apparatus in a dry state as well as submerged in distilled water and in simulated sea water penetration resistance of the sand beds was measured periodically by pushing 4 probes into the sand bed mineralogical and fabric studies on freshly deposited and aged sand samples were conducted to detect the effect of aging if any on sand grains the results indicate that aging significantly increases the penetration resistance of sands the rate of increase in penetration resistance was higher for the submerged sand as compared with the dry sand the increase in penetration resistance of the sand in a dry state was attributed to rearrangement of sand grains in the submerged

runoff control of soil degassing at an active volcano the case of piton de la fournaise reunion island abstract airborne atmospheric and in situ soil gas analyses demonstrate that distal gas leaks are non existent at piton de la fournaise pf despite frequent eruptions airborne traverses made at a constant altitude indicated that no detectable large scale co 2 degassing occurs from the volcano in situ soil gas traverses co 2 4 he 222 rn across the active rift zones the summit crater and the caldera rims show both a lack of positive anomalies and evidence of strong depleted concentrations for he and co 2 with respect to air depletions in soil he is explained by intense rain water infiltration a more unexpected result lies in the very low co 2 concentrations down to 92 ppm in bare soils in the summit region such a depletion was not previously reported and is attributed to considerable basalt weathering operating as the result of huge runoff a model has enabled both the runoff and the co 2 consumption occurring within the basaltic layers to be calculated data obtained are consistent with values expected from large scale erosion models and with the local calculated diffusive flux of co 2 in soils the huge runoff together with the basaltic lithology of the volcano are found to be the main factor controlling the soil gas signatures at pf

hydrochemistry of the narmada and tapti rivers india the chemistry of major ions and elements in narmada and tapti river water was studied based on the monitoring of the drainage basins for monsoon and post monsoon seasons in 2004 the results show the influence of rock weathering on the concentration of major ions in the surface water there is a significant contribution from the catchment geologies in the major constituents of water the total dissolved solids tds concentrations are reflecting the signature of weathering of rocks in the catchment areas in the narmada river hco 3 ca and mg are dominant ions whereas in the tapti river the ions dominating major compositions are hco 3 na and mg the high concentration of cl and so 4 2 is a signature of anthropogenic inputs in addition to the contribution of discharge from springs and or groundwater the high concentration of no 3 can exclusively be attributed to the anthropogenic activities the average concentration of dissolved silica being higher than the indian and world average is reflecting the contribution of silicate weathering the present study gives the silicate and carbonate weathering rates and the corresponding co consumption rates considering the contribution of carbonate rocks present in the selected river basins of the deccan basaltic province the mean silicate weathering rates during the investigation period for the narmada and tapti rivers show lower values but the corresponding mean co consumption rates give higher values compared with earlier estimated rates by dessert et al 2001 earth and planetary science letters 188 459 for the study period the mean carbonate weathering rates and the associated co consumption rates for the narmada and tapti rivers are 12 67 t km year and 7 32 t km year and 0 36 x 10 mol km year and 0 22 x 10 mol km year respectively

holocene and modern sediment storage in the subtropical macrotidal fitzroy river estuary southeast queensland australia the fitzroy river estuary is a macrotidal tide dominated estuary located in the dry tropics of central queensland and represents the major source of terrestrial sediment to the southern great barrier reef gbr lagoon the estuary currently receives most of its sediment during large episodic floods that are typically associated with cyclones mean annual sediment budgets for such systems are difficult to estimate due to the sporadic nature of flood discharge events which are highly seasonal and vary greatly in magnitude between years we have estimated the quantity and long term rate of accumulation of catchment derived sediment in the estuarine floodplain using the holocene stratigraphic sequence determined from a series of sediment cores dated with radiocarbon and optically stimulated luminescence osl methods approximately 13 760 million tonnes mt of fluvial sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 over the past 100 years sediment accumulation has been focused around mangrove and tidal creek environments which cover an area of 13 0 km 2 cores from the tidal creeks dated using cs c 137 pb 210 and osl provide sedimentation rates of approximately 15 mm yr 1 for the past 45 120 years or sediment mass accumulation of 1700 kt yr 1 which includes a component that is reworked into the estuary by tidal currents combined with the small amount of sediment that accumulates on the floodplain during floods similar to 1 mm yr 1 640 kt yr 1 we estimate that approximately 2350 kt yr 1 of sediment is trapped in the modem lower floodplain and estuary this estimate of sediment storage suggests that greater than 50 of the modem mean annual sediment discharge of the fitzroy river 4162 kt yr 1 may be retained in the lower floodplain and estuary these results provide useful insights into the spatial pattern of sedimentation long term rates of accumulation and estimates of sediment trapping in a tropical macrotidal sedimentary system crown copyright c 2007 published by elsevier b v all rights reserved

major and trace elements of river borne material the congo basin the congo river basin is the second largest drainage basin in the world after the amazon the materials carried by its main rivers provide the opportunity to study the products of denudation of a large fraction of the upper continental crust of the african continent this paper presents the chemical composition of the different phases carried in the congo rivers and is followed by a companion paper devoted to the modelling of major and trace elements the congo river between bangui and brazzaville as well as its main tributaries including a few organic rich rivers also called black rivers were sampled during the 1989 high water stage the three main phases suspended load dissolved load and bedload were analysed for twenty five major and trace elements concentrations normalized to the upper continental crust show that in each river suspended sediments and dissolved load are chemical complements for the most soluble elements ca na sr k ba rb and u while these elements are enriched in the dissolved loads they are considerably depleted in the corresponding suspended sediments this is consistent with their high mobility during weathering another type of complementarity is observed for zr and hf between suspended sediments and bedload related to the differential velocity of suspended sediments and zircons which are concentrated in bedloads compared to other rivers absolute dissolved concentrations of ca na sr k ba rb and u are remarkably low surprisingly high dissolved concentrations are found in the congo waters for other trace elements e g rees especially in the black rivers on a world scale these concentrations are among the highest measured in rivers and are shown to be ph dependent for a number of dissolved trace elements the dissolved loads are systematically normalized to the suspended loads for each river in order to remove the variations of the element abundances owing to source rock variations normalized diagrams for rees are presented and extended to the other elements they strongly support the argument that the apparent higher solubility of trace elements in the congo waters is due to the presence in the dissolved load of a colloidal phase as a result of 0 2 m filtration an important result is that these colloids are strongly depleted in fe and al with respect to the other elements finally the comparison of the dissolved suspended and sandy transport fluxes of each element in the congo basin rivers shows that although the proportions of for example the rees in the dissolved loads of the majority of the congo basin rivers is close to 10 of the total transport flux up to 80 of the rees are transported by the so called dissolved load in the black rivers

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

modeling climatic effects of carbon dioxide emissions from deccan traps volcanic eruptions around the cretaceous paleogene boundary abstract warming events observed in paleotemperature proxy records within 500 kyr of the cretaceous paleogene k pg boundary have often been attributed to atmospheric co 2 increases due to deccan traps flood volcanism currently there is uncertainty in the size nature and timing of the deccan eruptions all of which lead to uncertainty in the likely climatic effects modeling the impact of deccan traps eruption on climate is complicated by the discrepancy between the lifetimes of emitted gasses and the length of the total eruptive sequence though so 2 emissions can have important climatic effects the short atmospheric lifetimes of so 2 and resulting aerosols mean these effects are unlikely to be recognized in the proxy record here we focus on the co 2 emissions and attempt to match paleotemperature proxy records with plausible emissions scenarios we also test the relevance for climate of the number length and arrangement e g increasing or decreasing size of individual eruptions as well as the total duration and size of the overall eruptive sequence we find that the number and length of individual eruptions are largely unimportant to co 2 based based climate effects but that the pattern and duration of eruption have measureable effects unsurprisingly the total emitted co 2 from the deccan traps exerts a strong control on climatic effects and better constraints on the volume of emitted gas are necessary at the high end of the uncertainty range the deccan traps eruptions are capable of generating warming events recorded in the proxy record but rates of silicate weathering above modern rates are necessary to draw down co 2 in accordance with those records

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

multiple causes of earth s earliest global glaciation in the context of earth system evolution the causal factors driving the palaeoproterozoic huronian global glaciations occupy a central position the rise of o2 at 2320 ma which eliminated most of the methane was not apparently a single cause triggering the glaciation at c 2450 ma mantle plume driven continental uplifts led to the emplacement of voluminous continental flood basalts in low latitudes that were subsequently dissected by rifting major topographical features and continental drainage patterns were most likely similar to those in younger continental flood basalt provinces and would have enabled deep weathering and erosion of extensive basalt covered continental areas intense consumption of atmospheric co2 by silicate weathering of fresh basaltic surfaces would have been further amplified by a constant organic carbon burial rate these factors similar to those of younger glacial periods in combination with the diminished ch4 greenhouse led to an onset of global cooling at the million year timescale

frequency effects in the dynamic lateral stiffness of monopiles in sand insight from field tests and 3d fe modelling with the offshore wind industry rapidly expanding worldwide geotechnical research is being devoted to foundation optimisation most intensively for large diameter monopiles the analysis and desi

chemical weathering in the krishna basin and western ghats of the deccan traps india rates of basalt weathering and their controls rates of chemical and silicate weathering of the deccan trap basalts india have been determined through major ion measurements in the headwaters of the krishna and the bhima rivers their tributaries and the west flowing streams of the western ghats all of which flow almost entirely through the deccan basalts samples n 63 for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002 the total dissolved solid tds in the samples range from 27 to 640 mg l 1 the rivers draining the western ghats that flow through patches of cation deficient lateritic soils have lower tds average 74 mg l 1 whereas the bhima except at origin and its tributaries that seem to receive na cl and so4 from saline soils and anthropogenic inputs have values in excess of 170 mg l 1 many of the rivers sampled are supersaturated with respect to calcite the chemical weathering rates cwr of selected basins which exclude rivers supersaturated in calcite and which have high cl and so4 are in range of 3 to 60 t km 2 y 1 this yields an area weighted average cwr of 16 t km 2 y 1 for the deccan traps this is a factor of 2 lower than that reported for the narmada tapti wainganga ntw systems draining the more northern regions of the deccan the difference can be because of i natural variations in cwr among the different basins of the deccan ii selection of river basin for cwr calculation in this study and iii possible contribution of major ions from sources in addition to basalts to rivers of the northern deccan traps silicate weathering rates swr in the selected basins calculated using dissolved mg as an index varies between 3 to 60 t km 2 y 1 nearly identical to their cwr the ca mg and na mg in these rivers after correcting for rain input are quite similar to those in average basalts of the region suggesting near congruent release of ca mg and na from basalts to rivers comparison of calculated and measured silicate ca in these rivers indicates that at most 30 of ca can be of nonsilicate origin a likely source being carbonates in basalts and sediments the chemical and silicate weathering rates of the west flowing rivers of the deccan are 4 times higher than the east flowing rivers this difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates the silicon weathering rate swr in the krishna basin is 15 t km 2 y 1 within a factor of 2 to those in the yamuna bhagirathi and alaknanda basins of the himalaya suggesting that under favourable conditions intense physical weathering high runoff granites and the other silicates in the himalaya weather at rates similar to those of deccan basalts the co2 consumption rate for the deccan is deduced to be 3 6 105 moles km 2 y 1 based on the swr the rate though is two to three times lower than reported for the ntw rivers system it still reinforces the earlier findings that in general basalts weather more rapidly than other silicates and that they significantly influence the atmospheric co2 budget on long term scales

origin of deccan trap lavas evidence from combined trace element and sr nd and pb isotope studies abstract geochemical and isotope results are presented from a new study of the most southern basalts in the deccan trap india three chemical formations are recognised two of which can be correlated with the established stratigraphy in mahabaleshwar and imply a regional southerly dip of 0 06 over a distance of 250 km in detail sr isotope variations within the ambenali and mahabaleshwar formations can be shown to reflect three distinct end members which provide new constraints for petrogenetic models pb isotope data for selected basalts exhibit a wide range with 206 pb 204 pb 16 87 22 45 and a linear correlation on a pb pb diagram the least contaminated ambenali basalts plot within the pb array and interaction with mantle lithosphere involves a shift to less radiogenic pb whereas contamination with crust is characterised by more radiogenic pb unlike the karoo and parana continental flood basalt provinces only four flow units within the southern deccan appear to contain a significant contribution from mantle lithosphere the mahabaleshwar and ambenali formation basalts exhibit a striking negative pb sr isotope trend which is presently regarded as one of the features of interaction with shallow level lithospheric mantle it further suggests that basalts from the walvis ridge kerguelen and ninetyeast ridge all remobilised such shallow level material and that the deccan basalts which were not affected by crustal contamination reflect interaction between asthenospheric material similar to t type morb but related to the reunion hotspot and continental mantle lithosphere of the indian plate

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

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

did a katian large igneous province trigger the late ordovician glaciation a hypothesis tested with a carbon cycle model abstract the ordovician is known as a period with high temperatures and high sea levels and a cooling event at the end of the period leading to the hirnantian glaciation and the first of the big five mass extinctions of marine life the cause of this cooling event remains unclear several authors correlate it with a drop in atmospheric p co 2 to a threshold permitting the ice accumulation on the gondwana supercontinent however what are the reasons of the atmospheric p co 2 decrease here we follow the hypothesis initiated by barnes 2004 that an ordovician superplume event occurred during the middle to late ordovician such an event would not only have a large impact on the ordovician biodiversification barnes 2004 but it would also be responsible for the climatic upheaval during the late ordovician by the emplacement of a low latitudinal continental basaltic province that had an impact on the atmospheric p co 2 there is no direct evidence of a superplume event or of basaltic traps and the present study is therefore a hypothetical modelling approach where we demonstrate with a numerical box model including carbon alkalinity and phosphorus cycles coupled with a 1d climate model energy balance model ebm francois and walker 1992 that such a scenario allows to explain both the mid ashgill katian global warming event known as the boda event fortey and cocks 2005 and the subsequent late ordovician hirnantian glaciation because silicate weathering is enhanced upon warm and wet climate we try to constrain the size and the latitudinal emplacement of the basaltic province leading to a sufficient consumption of atmospheric p co 2 to the threshold proposed by herrmann et al 2004 a b to initiate a glaciation on gondwana

evidence for a rapid release of carbon at the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm and associated carbon isotope excursion cie are often touted as the best geologic analog for the current anthropogenic rise in pco2 however a causal mechanism for the petm cie remains unidentified because of large uncertainties in the duration of the cie s onset here we report on a sequence of rhythmic sedimentary couplets comprising the paleocene eocene marlboro clay salisbury embayment these couplets have corresponding 18o cycles that imply a climatic origin seasonal insolation is the only regular climate cycle that can plausibly account for 18o amplitudes and layer counts high resolution stable isotope records show 3 5 13c decrease over 13 couplets defining the cie onset which requires a large instantaneous release of 13c depleted carbon during the cie a clear 13c gradient developed on the shelf with the largest excursions in shallowest waters indicating atmospheric 13c decreased by 20 our observations and revised release rate are consistent with an atmospheric perturbation of 3 000 gigatons of carbon gtc

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

estimating silicate weathering timescales from geochemical modeling and spring water residence time in the kirishima volcanic area southern japan abstract kyushu island in southern japan is located within an area subjected to one of the highest rates of chemical weathering in the world this area is purported to have the highest discharge rate of dissolved silica and other cations within the japanese island arc to understand the timescale of chemical weathering in such a weathering hot spot details of water rock interaction are characterized using a conventional geochemical model for the kirishima volcanic area the model is focused on source water spring water with different residence times previously estimated by chlorofluorocarbons cfcs concentration analysis the geochemical and geological features of the spring water samples suggest that the primary reactant minerals are pyroxenes and plagioclase it was also found from activity diagram analysis that kaolinite and ca smectite are the major precipitable secondary minerals from the system the occurrence of these reactions was quantitatively confirmed by stoichiometric calculations of measured dissolved ions in combination with previous estimates of spring water residence ages it is concluded that saturation of dissolved silica and simultaneous transition of phase precipitation from kaolinite to ca smectite starts in ca 20 years after aqueous recharge our findings imply the usefulness of geochemical data as a function of water rock interaction timescale in certain field in future work these findings can be compared to data from other areas to improve understanding of global heterogeneity in chemical weathering rates

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

weathering and the global carbon cycle geomorphological perspectives abstract the links between the weathering of silicate minerals the global carbon cycle and climate change are complex and involve a whole range of often inter related tectonic climatic geomorphological and biological factors silicate weathering rates are known to have varied through geological time and increasingly sophisticated models now link such variation to the long term carbon cycle and climate change in order to improve the modelling further one key research need is for more and better datasets on weathering and the factors that control it as a contribution to this we review the nature of the weathering carbon cycle system the sources of evidence used to understand it and the challenges that remain in quantifying the feedbacks between weathering and the global carbon cycle we propose that increased understanding of geomorphological diversity of landscapes and processes and especially the dynamic relationships between weathering and erosion will aid clearer portrayal of the links between weathering and the long term carbon cycle

the impact of the central atlantic magmatic province on climate and on the sr and os isotope evolution of seawater abstract there is a wide range of geochemical sedimentological and palaeontological evidence suggesting that the interval at the end of the triassic and the beginning of the jurassic some 200 ma ago was a time of major environmental change the supercontinent pangaea began to rift eustatic sea level rose and there was a mass extinction in marine and terrestrial biota the eruption of at least 3 10 6 km 3 of basaltic lavas that comprise the central atlantic magmatic province camp also took place at that time and was intimately associated with the onset of rifting of pangaea emplacement of this large igneous province occurred within a relatively very short period of perhaps no more than 1 ma although relatively little of camp now remains the original province was extremely large extending from present day nova scotia to bolivia and from central southern usa to morocco of major relevance to the environmental impact of the camp was its relatively rapid emplacement and its original location across the equator recent advances in our understanding of the weathering of silicate rocks and in particular of fresh basaltic rocks have highlighted the importance of the weathering process in influencing environmental change in this contribution we examine the details of the seawater sr and os isotope records that span the triassic jurassic boundary in order to understand the nature and course of environmental change at that time correlation of sr isotope data from mainland europe and the uk shows that the rapid rate of decrease in the 87 sr 86 sr ratio of seawater which had started in the early rhaetian late triassic came to an end in the late rhaetian close to the triassic jurassic boundary at that time the 187 os 188 os ratio of seawater had also decreased to particularly low values in the late rhaetian the seawater 87 sr 86 sr ratio rapidly increased from 0 70765 to 0 70775 and then it and the seawater 187 os 188 os ratio both remained approximately constant for the duration of the hettangian the first 3 ma of the jurassic apart from a transient excursion to radiogenic os isotope values i e high 187 os 188 os ratios near the triassic jurassic boundary the unradiogenic 187 os 188 os ratio of seawater during the hettangian is interpreted as reflecting a major perturbation to global weathering patterns that was caused by the rapid weathering and erosion of the camp immediately after its emplacement we suggest that the rapid increase of seawater 87 sr 86 sr ratios in the late rhaetian and the approximately constant 87 sr 86 sr ratios throughout the hettangian were caused by the input of a large amount of additional radiogenic sr to the oceans which was likely to have been derived from a readily weathered lithology such as carbonate or evaporite at the start of the sinemurian the 87 sr 86 sr ratio of seawater began to decrease while at the same time the 187 os 188 os ratio of seawater increased to more radiogenic values we interpret the trends in the seawater sr and os isotope compositions at the start of the sinemurian as evidence that much of the camp had been removed by chemical weathering by which time the camp had ceased to have a major influence on earth s environment the patterns of change in the seawater sr and os isotope records that occurred in the latest triassic and earliest jurassic show many similarities with those that took place in the pliensbachian toarcian 183 ma ago overlapping the eruption of the karoo ferrar igneous province in both cases the seawater sr and os isotope records indicate that there was a relatively very brief interval during which rates of continental weathering increased greatly the similarities in the responses of the seawater sr and os isotope records at those times strongly suggest that the eruption and subsequent erosion of basaltic large igneous provinces have played a major role in defining the course of environmental change in the past

evaluation of installation effects on set up of field displacement piles in sand the paper presents results from a new series of tests on displacement piles in sand involving different installation modes and combines these with results from previous tests at the same site as

comments on deccan flood basalts at the cretaceous tertiary boundary by v courtillot j besse d vandamme r montigny j j jaeger and h cappetta the age of the flood basalts of the deccan area and the length of the interval during which the outpourings took place are not known precisely the authors have tried to date those basalts and estimate how long the volcanic activity lasted on the basis of new paleomagnetic paleontological and geochronological data of the deccan effusives they came to the preliminary conclusion that the volcanic activity may have lasted less than 1 ma and that the majority of the lavas poured out during chron 29r unfortunately the authors were not familiar with our paper on paleomagnetism and radiomettic age determinations of deccan trap lavas 2 in our paper we presented the paleomagnetic data derived from 223 individual lava flows from 16 sections all over the deccan area and gave the k ar age determinations for 13 selected unaltered lava flows we agree that the enormous volume of deccan extrusives poured out in a relatively short interval and that the volcanic activity was probably concerned with the spreading in the central indian ocean in late cretaceous and early tertiary time

stable isotope records across the cretaceous paleogene transition stevns klint denmark new insights from the chromium isotope system abstract late cretaceous to early paleogene time represents a critical transitional period in earth history global events include short term instability in climate and ocean circulation large igneous province emplacement and catastrophic extinction of marine and terrestrial fauna due at least in part to a bolide impact event the response of the ocean system to cretaceous paleogene k pg global events has been the subject of much research yet fundamental questions remain regarding carbon cycling climate ocean mixing and redox conditions to help elucidate paleoceanographic changes across the k pg transition we revisit the classic maastrichtian to danian chalk limestone succession at stevns klint denmark with a suite of new geochemical data including insights from the redox sensitive chromium isotope system we use carbon and oxygen isotope trends to form a well constrained framework for the succession before presenting strontium isotope chromium isotope and rare earth element data for the units deposited both before and after the k pg event carbon isotopes show only minor perturbation across the k pg boundary and oxygen isotopes record a prominent positive excursion with both of these trends standing in contrast to many k pg boundary sections worldwide strontium isotopes record a spike towards more radiogenic values which is consistent with a globally observed short term weathering pulse the chromium isotope profile of maastrichtian chalk begins with strongly positive values followed by a sharp negative excursion associated with a facies shift and initiation of bottom currents in the chalk sea 53 cr values then recover before falling steadily across the k pg boundary and into the danian limestone chromium isotope trends do not correspond to changes in hydrothermal input or basin redox conditions instead we propose that mixing of water masses with distinct chromium isotope signatures controlled temporal chromium isotope variability the local mixing event inferred from our maastrichtian chromium isotope data could be related to a temporary inflow of tethyan bottom waters or the shift from end maastrichtian greenhouse warming associated with deccan volcanism to the worldwide cooling phase that immediately preceded the k pg boundary no immediate change in chromium isotopes is recorded across the k pg boundary indicating that the bolide impactor did not substantially perturb the marine chromium cycle at least at the scale resolvable by our data instead chromium isotope trends continued to be controlled by local oceanographic processes highlighting the potential of the chromium isotope system to record isotopic heterogeneity and mixing events in ancient oceans

two sides to every range orographic influences on co2 consumption by silicate weathering abstract the effect of an orographic rain shadow on co 2 consumption by silicate weathering oco 2 si was examined in the sierra de las minas a mountain range in eastern guatemala this range is tall enough to intercept prevailing winds leading to greater rainfall on the windward or north compared to the leeward or south side of the range water was collected from and discharge was measured for streams draining both the north and south sides of the sierra de las minas water samples were analyzed for major ions and silica and this chemistry was used to interpret weathering inputs and calculate oco 2 si the median oco 2 si in north side streams 260 10 3 mol co 2 km 2 yr 1 was roughly 3 fold greater than the median oco 2 si in south side streams 78 10 3 mol co 2 km 2 yr 1 this difference is similar to the 3 fold greater discharge measured for north side streams compared to south side streams of the same area a positive linear relationship was observed between volumetric water yield l s 1 km 2 and oco 2 si supporting transport i e precipitation as the main factor controlling the differences observed between north and south side oco 2 si lithology and basin morphology differences had a negligible influence on oco 2 si patterns across the aspects of the range these orographically induced differences in oco 2 si may increase with changing precipitation regimes in a warming climate

the himalayas organic carbon burial and climate in the miocene cooling ages of rock in the himalayas imply that rapid exhumation between the main central thrust system and the south tibetan detachment system occurred between 21 and 17 ma the generation of relief and enhanced weathering which followed this event may have resulted in a pronounced increase in the delivery of dissolved strontium carbon phosphorus and other chemical weathering products to the ocean richter et al 1992 the increased supply of nutrients stimulated productivity in oceanic upwelling zones and expansion of the oxygen minimum zone leading to enhanced burial and preservation of organic matter in the monterey formation and other deposits from this interval a downdraw of atmospheric co2 associated with enhanced chemical weathering rates and organic matter burial may have led to global cooling and the expansion of the antarctic ice sheet by 15 ma the above scenario differs from the monterey hypothesis of vincent and berger in that co2 downdraw is primarily via silicate weathering rather than organic carbon burial and that organic carbon burial is driven by increased delivery of nutrients to the ocean rather than by stronger upwelling a carbon mass balance calculation which assumes that river fluxes have been increasing over the last 40 ma predicts that absolute organic carbon burial increased over this interval while at the same time the fraction of carbon buried as organic matter versus carbonate decreased this implies that the organic carbon cycle has acted as a net source of co2 to the atmosphere over the late cenozoic

silicate rock weathering and atmospheric soil co2 uptake in the amazon basin estimated from river water geochemistry seasonal and spatial variations abstract using the data of the camrex project 1982 1984 on the water geochemistry of the amazon river and its main tributaries it was possible to assess the silicate rock weathering processes and the associated consumption of atmospheric soil co2 taking into account seasonal and spatial variations this study confirms the important role of the andes in the fluvial transport of dissolved and particulate material by the amazon and it shows for the first time that the silicate weathering rate and atmospheric soil co2 consumption are higher in the andes than in the rest of the amazon basin the seasonal variations exhibit the significant role of runoff as a major factor controlling silicate weathering processes and show that the chemical erosion rates vary greatly from low discharge to high discharge the average weathering rate estimated for the whole amazon basin 15 m my is comparable to other estimations made for other tropical equatorial environments a comparison between physical and chemical weathering rates of silicate rocks for the amazon basin and for each tributary basin show that in the andes and in the amazon trough the soil thicknesses are decreasing whereas in the shield the soil profiles are deepening

low temperature alteration of the upper oceanic crust and the alkalinity budget of seawater abstract while the input of river alkalinity into seawater is relatively well known the complementary acidity production is poorly understood using the major element budget of seafloor alteration of the upper 500 m of 120 ma old oceanic crust at dsdp odp sites 417a 417d and 418a in the central western atlantic we estimate the acidity flux associated with the low temperature weathering of the upper oceanic crust the acidity flux is calculated based on major element fluxes and charge balance considerations the relevant chemical fluxes from seawater to the upper crust are 4 1 0 1 1 4 1 4 2 2 0 6 and 12 2 1011 mol yr 1 for k mg na and silicate ca respectively the associated acidity flux is 3 5 3 1011 eq yr 1 relative to continental weathering these fluxes are significant for k and silicate ca but are minor for na mg and acidity thus riverine fluxes of alkalinity are not significantly balanced by acidity fluxes from low temperature upper ocean crust alteration

paleoproductivity during the middle miocene carbon isotope events a data model approach 1 to what extent are individual middle miocene eccentricity scale benthic foraminiferal carbon isotope maxima the so called cm events related to changes in marine export productivity here we use benthic foraminiferal accumulation rates from three sites in the pacific and southern oceans and a geochemical box model to assess relationships between benthic foraminiferal 13c records export productivity and the global carbon cycle results from deep sea drilling project hole 588 and ocean drilling program site 747 show a distinct productivity maximum during cm 6 at 13 8 ma the time of major expansion of ice on antarctica productivity maxima during other cm events are only recorded at high latitude site 747 a set of numerical experiments tests whether changes in foraminiferal 13c records cm events and export productivity can be simulated solely by sea level fluctuations and the associated changes in global weathering deposition cycles by sea level fluctuations plus global climatic cooling and by sea level fluctuations plus invigorated ocean circulation consistent with data the periodic forcing of sea level and albedo and associated weathering cycles produces 13c variations of the correct temporal spacing albeit with a reduced amplitude a productivity response of the correct magnitude is achieved by enhancing ocean circulation during cold periods we suggest that the pacing of middle miocene 13c fluctuations is associated with cyclical sea level variations the amplitude however is muted perhaps due to the competing effects of a time lagged response to sea level lowstands but an immediate response to invigorated ocean circulation during cold phases

enhanced dissolution of basaltic glass in brackish waters impact on biogeochemical cycles in order to better constrain the geochemical budget of si in the ocean and potentially other elements released by the dissolution of silicates the alteration of riverine particulate material in estuaries and seawater needs to be estimated for this a series of alteration experiments of basaltic glass were performed at various degrees of salinity from 0 to 3 5 g l 1 in far from equilibrium conditions the solution used is a filtered natural seawater standard from the atlantic ocean the forward dissolution rates increase from 2 1 10 7 molsim 2s 1 s 0 gl 1 to 7 7 10 7 molsim 2s 1 s 3 5 gl 1 at 90 c and were extrapolated at 16 c from 2 9 10 10 molsim 2s 1 at s 0 gl 1 to 1 1 10 9 molsim 2s 1 at s 3 5 gl 1 this positive relationship between glass dissolution rate and salinity degree is consistent with published investigations concerning the role of specific cations and ligands present in seawater which can promote dissolution at the glass surface these results illustrate the potential of river basaltic glass particles to dissolve quickly in the water column after entering into the brackish waters of estuaries and before sinking on continental margins based on these dissolution rates and on assumptions on the particulate solid flux of fresh basaltic glass exported by rivers towards the ocean the corresponding flux of dissolved si is estimated to range between 2 and 8 1012 molsiyr 1 this is of the same order of magnitude as the estimated river dissolved si flux which represents therefore a significant input of si into the ocean additionally if the glass dissolution process remains congruent during the residence time of suspended particles into the water column the k flux to the ocean could also be significantly affected

basalt weathering across scales abstract weathering of silicate minerals impacts many geological and ecological processes for example the weathering of basalt contributes significantly to consumption of atmospheric carbon dioxide co2 and must be included in global calculations of such consumption over geological timeframes here we compare weathering advance rates for basalt wd where d and indicate the scale at which the rate is determined and surface area measured respectively from the laboratory to the watershed scales data collected at the laboratory weathering rind soil profile and watershed scales show that weathering advance rate of basalt is a fractal property that can be described by a fractal dimension dr 2 3 by combining the fractal description of rates with an arrhenius relationship for basalt weathering we derive the following equation to predict weathering advance rates at any spatial scale from weathering advance rates measured at the bet scale w d k 0 a d r 2 e e a r t here k0 is the pre exponential factor 1 29 107 mm3 mm 2 yr 1 ea is the activation energy 70 kj mol 1 and a is a spatial constant related to the scale of measurement of bet surface area 10 7 mm the term a d r 2 is the roughness the roughness fractal dimension can be conceptualized as a factor related to both the thickness of the reaction front and the specific surface area within the reaction front however the above equation can also be written in terms of a surface fractal dimension and the hypothetical average grain radius these fractal dimensions provide insight into reaction front geometry and should vary with lithology once the surface area discrepancy has been accounted for using this method we find a one to two order of magnitude range in weathering advance rates measured at any scale or temperature that can be attributed to factors such as changes in erosional regime parent lithology mechanism climate composition of reacting fluid and biological activity our scaled equation when used to predict global basalt co2 consumption based upon global lithologic maps yields an uptake flux 1 75 1013 mol co2 yr 1 within the predicted error of fluxes estimated based upon riverine measurements

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

seasonal variation of sediment deposition in the hudson river estuary abstract during and following the spring freshet rapid rates of sediment deposition were observed in the hudson river estuary side scan sonar surveys and sediment coring studies revealed a large amount of spatial variability in sedimentation within the estuary and a distinct seasonal progression during the freshet sediment was deposited in the seaward reaches of the estuary in the two month period after the freshet this sediment was eroded and sedimentation occurred 10 30 km further landward at the estuarine turbidity maximum etm zone the thickness of the new freshet deposit was as great as 40 cm in the etm indicating intense trapping and rapid deposition the location of this depocenter corresponded to a frontal zone where water column observations and modeling studies have indicated enhanced sediment trapping the mass of the new deposits was estimated at 300 000 metric tons during both 1998 and 1999 with similar spatial distributions in 1998 the estimated fluvial input was 560 000 metric tons significantly greater than the 120 000 metric tons estimated for 1999 thus the mass of the observed deposits appear to be more influenced by the redistribution of sediment within the estuary due to seasonal variations in erosion deposition conditions rather than by the direct input of sediment from the watershed

enrichment of ion exchangeable rare earth elements by felsic volcanic rock weathering in south china genetic mechanism and formation preference abstract felsic volcanic rocks are an important source for generating ion adsorption type rare earth element ree resources to better understand the supergene enrichment of rees related to felsic volcanic rock weathering this study conducted an investigation of indosinian felsic volcanic rocks from guangxi southwest china which have been subjected to deep weathering the weathering has formed large areas of thick regolith with the potential to host ion adsorption type ree mineralization the felsic volcanic rocks belong to the dacite rhyolite series and are peraluminous high k calc alkaline and ree rich 325 376 ppm abundant ree bearing accessory minerals are present in the felsic volcanic rocks including titanite average ree 15 1 wt allanite average ree 14 9 wt and apatite average ree 1510 ppm and these three minerals contain an estimated 88 7 of the whole rock rees content significant ree enrichment is present in the felsic volcanic rock derived regolith a typical rhyolite derived regolith profile has ree contents that increase from 376 ppm in the rhyolite to 1737 ppm in the regolith representing an almost five fold enrichment due to weathering the rees in the regolith are present in an ion exchangeable form irees which accounts for 52 87 of the total rees present trees the occurrence of irees is closely linked to clay minerals showing an affinity in the order halloysite kaolinite illite continuous operations of rees by an eluviation illuviation process from the source minerals titanite allanite apatite to sink minerals kaolinite halloysite illite results in an iree enriched zone in the middle and lower parts of the rhyolitic regolith notably besides the studied indosinian felsic volcanic rocks there are multi epochs of such lithology outcropped in south china their related irees mineralizations however are preferentially developed in the weathered terrains of early yanshanian and indosinian felsic volcanic rocks and not in those of the yanshanian and late yanshanian felsic volcanic rocks a comparison of the mineralized and barren units indicates that the irees mineralization hosted in felsic volcanic rocks regolith is controlled by some key endogenic and exogenic ore forming factors high initial ree concentrations in the unaltered felsic volcanic rocks a suitable climate and a relatively quiescent tectonic setting are favorable for the formation and preservation of irees mineralization

orbital scale evolution of the indian summer monsoon since 1 2 ma evidence from clay mineral records at iodp expedition 355 site u1456 in the eastern arabian sea abstract clay mineral assemblages at international ocean discovery program expedition 355 site u1456 drilled in the eastern arabian sea have been investigated to reveal the sediment provenances and reconstruct the erosion weathering patterns in the western himalaya and indian subcontinent thus constraining the evolution of the indian summer monsoon and its forcing mechanism since 1 2 ma the clay mineral assemblages at site u1456 mainly comprise smectite with an average value of 59 and illite with an average value of 33 with chlorite with an average value of 5 and kaolinite with an average value of 3 as minor constituents in terms of sediment provenance our results indicate that illite and chlorite are predominantly derived from the indus river which originates from the western himalaya and karakoram while smectite is primarily sourced from the narmada river and tapti river in the deccan traps with a non negligible contribution from the indus river in some cases variations in smectite illite chlorite ratio are ultimately controlled by the indian summer monsoon which is characterized by approximate glacial interglacial cyclicity showing higher values i e enhanced chemical weathering during interglacial periods in addition a major shift in smectite illite chlorite ratio at 0 9 ma is correlated to the mid pleistocene transition 1 2 0 9 ma both the marine isotope stage 13 event 533 478 ka and the mid brunhes event 430 ka are also recorded in the clay mineral proxies based on the spectral analysis smectite illite chlorite ratio displays a transition from nonprimary periodicity 29 kyr to strong eccentricity 100 kyr and precession 22 kyr periodicities at approximately 0 9 ma which corresponds to the mid pleistocene transition our study indicates that the variability of the indian summer monsoon at orbital timescales is controlled by high latitude i e ice volume and low latitude i e summer insolation processes

uplift and erosional history of the deccan traps india evidence from laterites and drainage patterns of the western ghats and konkan coast abstract the western ghats escarpment in the western coastal region of peninsular india is locally capped by plateau remnants on which a regional high level laterite carapace is preserved geochemical fingerprinting studies show that the laterite has been developed from a protolith of panhala formation basalts the youngest known formation of the deccan sequence the high level laterite is in detail structurally concordant with its underlying basalts and hence it is concluded that it represents the original top of the lava pile a younger low level laterite carapace is developed on the konkan plain below the escarpment where it lies discordantly on basalts of the ambenali and poladpur formations from which it developed in situ the low level laterite rises topographically northwards in response to differential uplift probably at a maximum in the nasik region the main structures of the ghats region excluding the coastal monocline are the nasik dome and the mahabaleshwar anticline these have no effect on regional drainage patterns and it is argued that they are largely secondary features developing in response to post volcanic uplift

global trends of pco2 across the cretaceous paleogene boundary supported by the first southern hemisphere stomatal proxy based pco2 reconstruction reliable reconstructions of atmospheric carbon dioxide concentrations pco2 are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo pco2 levels such reconstructions are needed 1 at a high temporal resolution for constraining the pre and post extinction atmospheres and 2 at a sufficient spatial resolution to constrain potential inter hemispheric differences here we estimate pco2 based on fossil lauraceae leaf cuticle specimens derived from three localities with strata spanning the latest cretaceous to the mid paleocene including a new cretaceous paleogene boundary k pg locality in new zealand we use two independent methods of stomatal density based pco2 reconstructions a transfer function calibrated using herbarium material and the stomatal ratio method producing three calibration sets our results based on the mean values of each of the three calibration methods indicate pco2 ranging between ca 460 and 650 ppm during the latest cretaceous falling precipitously to average values between ca 360 and 430 ppm across the k pg boundary and further to ca 305 320 ppm in the mid paleocene a spike of extremely high pco2 at the k pg could not be confirmed but our results are nonetheless consistent with previously published pco2 records from the northern hemisphere and show that stomatal density worldwide was responding to significant changes in pco2 across the k pg

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

variations in the strontium isotope composition of seawater during the paleocene and early eocene from odp leg 208 walvis ridge we refined the strontium isotope seawater curve for the paleocene and early eocene by analysis of samples recovered from the walvis ridge during ocean drilling project odp leg 208 the highest sr 87 sr 86 values occurred in the earliest paleocene at similar to 65 ma and generally decreased throughout the paleocene reaching minimum values between 53 and 51 ma in the early eocene before beginning to increase again at similar to 50 ma a plausible explanation for the sr 87 sr 86 decrease between 65 and 51 ma is increased rates of hydrothermal activity and or the eruption and weathering of large igneous provinces e g deccan traps and north atlantic strontium isotope variations closely parallel sea level and benthic delta o 18 changes during the late paleocene and early eocene supporting previous studies linking tectonic reorganization and increased volcanism to high sea level high co2 and warm global temperatures

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

addendum to inclusion of the weathering of volcanic rocks in the geocarbsulf model r a berner 2006 v 306 p 295 302 in the paper by berner 2006a 1 the compiled data presented by dessert and others 2001 2 for different values of the relative weathering rates of basalts versus granites was missed the term granite is used here to refer to all granitoid rocks including gneisses it is the primary

uranium isotopes in rivers estuaries and adjacent coastal sediments of western india their weathering transport and oceanic budget the two major river systems on the west coast of india narbada and tapti their estuaries and the coastal arabian sea sediments have been extensively studied for their uranium concentrations and 238u238u activity ratios the 238u concentrations in the aqueous phase of these river systems exhibit a strong positive correlation with the sum of the major cations na k mg ca and with the hco3 ion contents the abundance ratio of dissolved u to the sum of the major cations in these waters is similar to their ratio in typical crustal rocks these findings lead us to conclude that 238u is brought into the aqueous phase along with major cations and bicarbonate the strong positive correlation between 238u and total dissolved salts for selected rivers of the world yield an annual dissolved 238u flux of 0 88 1010g yr to the oceans a value very similar to its removal rate from the oceans 1 05 1010g yr estimated based on its correlation with hco3 contents of rivers in the estuaries both 238u and its great grand daughter 234u behave conservatively beyond chlorosities 0 14 g l these data confirm our earlier findings in other indian estuaries the behavior of uranium isotopes in the chlorosity zone 0 02 0 14 g l was studied in the narbada estuary in some detail the results though not conclusive seem to indicate a minor removal of these isotopes in this region reexamination of the results for the gironde and zaire estuaries martin et al 1978a and b also appear to confirm the conservative behavior of u isotopes in unpolluted estuaries it is borne out from all the available data that estuaries beyond 0 14 g l chlorosities act neither as a sink nor as a source for uranium isotopes the behavior in the low chlorosity zones warrants further detailed investigation a review of the uranium isotope measurements in river waters yield a discharge weighted average 238u concentration of 0 22 g l with a 234u238u activity ratio of 1 20 0 06ismissing the residence time of uranium isotopes in the oceans estimated from the 238u concentration and the 234u238u a r of the rivers yield conflicting results the material balance of uranium isotopes in the marine environment still remains a paradox if the disparity between the results is real then an additional 234u flux of about 0 25 dpm cm2 103 yr into the oceans about 20 of its river supply is necessitated

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

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

modeling the carbon and sulfur isotope compositions of marine sediments climate evolution during the devonian abstract a model of global biogeochemical cycles coupled to an energy balance climatic model modified after the combine model godderis y joachimski m m 2004 global change in the late devonian modeling the frasnian famennian short term carbon isotope excursions palaeogeogr palaeoclimatol palaeoecol 202 309 329 is used to calculate the short term evolution of atmospheric p co 2 during the devonian the geochemical cycles for carbon alkalinity phosphorus sulfur and oxygen are included in this model with also 13 c and 34 s cycles high resolution records of 13 c of marine carbonates and 34 s of marine sulfates are used as forcing parameters of the geochemical cycles in an inverse modeling atmospheric p co 2 and p o 2 at the end of the silurian are calculated to have been 3000 ppmv and 0 165 bar 0 75 pal respectively a long term decrease in p co 2 is modeled for almost the entire devonian short term lowering of p co 2 to concentrations around 2000 ppmv is calculated for the silurian devonian transition and the pragian contents around 900 ppmv are modeled for the eifelian givetian givetian frasnian and frasnian famennian boundaries as a consequence of enhanced organic carbon burial during deposition of lochkovian eifelian and frasnian grey and black shales organic carbon burial is enhanced by the increase of phosphorus delivery to the ocean triggered by short term sea level falls the corresponding short term global climatic cooling at the silurian devonian boundary at the end of the pragian and the givetian frasnian as well as frasnian famennian boundaries reached 2 c at the equator the rapid colonization of continental surface by land plants during the middle and late devonian increasing chemical alteration of the continents and co 2 consumption by silicate weathering is assumed to have caused cooling of surface seawater as suggested by the 18 o values of biogenic apatites

processes controlling δ7li in rivers illuminated by study of streams and groundwaters draining basalts we evaluate the factors influencing the abundance li and isotopic composition of riverine li delivered to the oceans through analyses and modeling of li and 7 li in streams and groundwaters draining a single continental lithology the columbia river basalts crbs the streams were sampled in different climate zones that lie east dry and west wet of the cascades mountains and during two different seasons summer and late winter in order to evaluate climatic and seasonal influences on li isotopes in rivers dissolved li 7 lidis 9 3t o 30 4 is systematically heavier than that of fresh or weathered crbs 4 7 to 6 0 liu et al 2013 suspended loads 5 9 to 0 3 and shallow groundwaters 6 7t o 9 4 consistent with previous studies showing that li isotope fractionation is affected by equilibration between stream water and secondary minerals however the lack of correlation between 7lidis and climate zone the uniform secondary minerals and bedrock coupled with the highly variable 20 7 lidis indicate that other factors exert a strong control on

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

sr and 87sr 86sr in estuaries of western india impact of submarine groundwater discharge abstract dissolved sr and 87sr 86sr are measured in the narmada tapi and the mandovi estuaries linked to the eastern arabian sea the concentration of dissolved sr and 87sr 86sr in the river water endmembers show significant differences reflecting the lithologies they drain the distribution of sr in all these estuaries shows a near perfect two endmember mixing between river water and seawater suggesting that there is no discernible net addition removal of sr from the estuarine waters in contrast 87sr 86sr shows non conservative behaviour in all these estuaries its distribution exhibits significant departure from the theoretical mixing lines a likely mechanism for this difference in the behaviour between dissolved sr and its 87sr 86sr is the discharge of submarine groundwater sgd which can modify the 87sr 86sr of the estuarine waters by exchange with sediments without causing measurable changes in sr concentration the impact of such an exchange process on the 87sr 86sr of the estuaries and therefore on the sr isotope composition of dissolved sr entering the arabian sea differs among the three estuaries and also between seasons in the narmada the non conservative behaviour of 87sr 86sr provides a handle to estimate the quantum of sgd to these estuaries the sr concentration 87sr 86sr ratio and salinity of the submarine groundwater and estimate of its fluxes to the narmada estuary have been made using inverse model calculations the model derived sgd flow rates are 5 and 280 cm day during pre monsoon and monsoon respectively the more radiogenic sr isotope composition of sgd relative to the seawater suggests that sgd acts as an additional source of 87sr to the arabian sea

chemical and physical weathering in south patagonian rivers a combined sr u be isotope approach abstract we investigated physical and chemical weathering in south patagonia encompassing both the tectonically active andes with alpine glaciers and the quiescent seaboard plain with arid climate chemical denudation rates determined from riverine dissolved major elements were 0 07 5 10 5 tons year 1 and the long term rates of co 2 consumption by alkaline earth silicates were 0 03 0 5 10 5 mol km 2 year 1 commensurate with the average global co 2 consumption rate 0 25 10 5 mol km 2 year 1 unradiogenic strontium isotope ratios indicated that the source of silicate weathering was volcanic sedimentary cover basin average total denudation rates based on 10 be measured in active streambed sediments ranged from 0 009 to 0 6 mm year 1 uranium series disequilibria suggested that there is significant redistribution of nuclides between the dissolved and suspended material when applying the simultaneous gain and loss model to the u series data of the suspended load sediment residence times of 10 150 ky were obtained comparison of the dissolved load based chemical denudation rate and 10 be based total denudation rate revealed that some basins are dominated by chemical and some by physical denudation

chemical indices cia and wip as proxies for integrated chemical weathering in china inferences from analysis of fluvial sediments abstract rivers play a key role in earth surface processes by weathering and eroding the upper continental crust under variable climate regimes how to quantitatively determine the chemical weathering intensity in the drainage basins using geochemistry of fluvial sediments remains unclear the chemical index of alteration cia and the weathering index of parker wip have been used worldwide as proxies to evaluate the chemical weathering intensity in large watersheds and in specific weathering profiles in this study concentrations of major oxides in the suspended particulate matter spm and fine grained floodplain sediments from 13 major rivers in china from north to south were analysed and compiled for the estimation of chemical weathering in china the gradual increase in cia and decrease in wip values with decreasing latitude of the catchments suggest enhanced weathering intensity in these river basins a combined monsoon climate effect of temperature runoff and precipitation primarily controls the chemical weathering in china the provenance rock types and relief play minor roles in weathering whereas an active tectonic setting and typhoon events play key roles in the weathering process in taiwan the cia values of the finer spm samples within a given river are overall greater than those in the corresponding coarser floodplain sediments underscoring the effect of sediment grain size on cia values the irregular seasonal variation of the cia within a specific river further confirms the notion that the cia does not reflect the instantaneous chemical weathering on continents although it is impossible to build a general model for regulating the chemical weathering of continents this study reveals that the integrated chemical weathering intensity in large latitudinal watersheds can with careful application be quantitatively estimated using the proper geochemical proxies of river sediments

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