li and δ7li in himalayan rivers proxies for silicate weathering this paper presents the first systematic survey of lithium and its isotopes in the dissolved load and suspended and bed sediments of tributaries of the ganges both before and after the monsoon locations were chosen in order to cover catchments draining both silicates and carbonates at high 2000 4000 m and low 550 1300 m altitudes modelling of the dissolved composition shows that the li ca ratio of the silicate endmember in himalayan rivers is at least an order of magnitude higher than that of the carbonate endmember most of the dissolved li 90 is derived from silicates even in carbonate dominated catchments while the sr isotope composition of the dissolved load reflects that of the bedrock the main control on its li isotope composition is fractionation during weathering fractionation between the dissolved and suspended load in silicate dominated catchments is greatest at high altitude and lower at low altitude where weathering is more intense tributaries draining silicates have lower dissolved 7li values by 2 3 to 4 2 following the monsoon when weathering is more intense because of higher runoff and elevated temperatures our data suggest that riverine li fluxes largely reflect silicate weathering rates while riverine 7li varies with weathering intensity as rivers presently contribute 50 of the li input to the oceans seawater li concentrations and 7li show potential as proxies for global silicate weathering processes

hydrothermal source of radiogenic sr to himalayan rivers 1 k 1 and cl 2 all of which are high in the hydrothermal waters cation concentrations decrease along the lesser himalayan reach of the river hot spring dissolved co2 has a d 13 c value to 15 9 indicating that metamorphic decarbonation reactions contribute co2 to the fluids hydrothermal co2 is partially neutralized in high temperature weathering reactions which generate alkalinity and yield abundant radiogenic sr radiogenic hydrothermal carbonate can form from these solutions and later weather releasing silicate sr but imparting carbonate characteristics to the overall water chemistry

silicate weathering rates decoupled from the 87sr 86sr ratio of the dissolved load during himalayan erosion this study establishes that carbonate weathering dominates the supply of sr with elevated 87sr 86sr ratios in the bhote kosi sun kosi river system central nepal a major himalayan tributary to the ganges the dissolved load of the bhote kosi sun kosi displays a rapid increase in the 87sr 86sr ratio in its lower section downstream of the main central thrust a feature common to other himalayan tributaries of the ganges mass balance analysis of the contributing sources to the dissolved load identifies the weathering of palaeoproterozoic impure carbonates comprised largely of dolomite and mica from the lesser himalaya as the most significant lithological control upon elevated 87sr 86sr ratios in situ laser ablation analysis of the dolomite component yields 87sr 86sr ratios of 0 93 to 1 11 indistinguishable from bulk rock this confirms the presence of a highly soluble source of radiogenic strontium and suggests that diffusive exchange during a protracted metamorphic history has homogenised sr isotopes between silicate and carbonate phases within the assemblage weathering of the carbonate component of such rocks has yielded unusually high 87sr 86sr at significant sr fluxes in the dissolved load approximately 60 of the impact of the bhote kosi sun kosi on the marine 87sr 86sr ratio can be traced to weathering of this carbonate since similar lithologies outcrop within the catchments of most himalayan tributaries that feed the ganges and brahmaputra rivers the presence of such radiogenic carbonates undermines the inference that the impact of these rivers on sr isotopes in seawater is indicative of high silicate weathering rates that result from the uplift of tibet and the himalaya

reconsideration of case histories for estimating undrained shear strength in sandy soils when sandy soils respond in a strain softening manner to undrained loading an estimation of the resulting undrained shear strength su is required to determine the potential for flow liquefaction

li ca in multiple species of benthic and planktonic foraminifera thermocline latitudinal and glacial interglacial variation li ca ratios were measured in planktonic and benthic foraminifera from a variety of hydrographic settings to investigate the factors influencing lithium incorporation into foraminiferal tests including temperature dissolution pressure and interspecies differences down core measurements of planktonic orbulina universa globigerinoides ruber and globigerinoides sacculifer and benthic foraminifera calcitic cibicides wuellerstorfi and aragonitic hoeglandina elegans show a systematic variation in li ca with 18o through the last glacial interglacial transition all species examined exhibit an increase in li ca between 14 to 50 from the holocene to the last glacial maximum li ca generally increases with decreasing temperature as seen in a latitudinal transect of planktonic o universa and down slope benthic species along the bahama bank margins postdepositional dissolution possibly causes a decrease in planktonic foraminiferal li ca along the sierra leone rise and increased water depth causes a decrease in benthic foraminiferal li ca in the deep caribbean however none of these effects are sufficient to account for the observed glacial interglacial changes physiological factors such as calcification rate may affect the li ca content of foraminiferal calcite the calcification rate in turn may be a function of carbonate ion concentration of ambient ocean water this work shows that incorporation of lithium by foraminifera appears to be influenced by factors other than seawater composition and does not appear to be dominated by changes in temperature dissolution or pressure we hypothesize that the consistent increase in foraminiferal li ca during the last glacial maximum may be linked to changes in seawater carbonate ion concentration important parameters to be tested include calcification rate and foraminiferal test size and weight if foraminiferal li ca is dominantly controlled by calcification rate as a function of seawater carbonate ion concentration then li ca may act as a proxy of past atmospheric co2

silicate versus carbonate weathering in the himalaya a comparison of the arun and seti river watersheds abstract we studied the water chemistry of two large and geologically differing himalayan watersheds in order to maximize the contrast between silicate versus carbonate weathering effects on river chemistry our previous research involved the seti river of westernmost nepal geologically typical of many rivers in nepal in draining mixed carbonate silicate lithologies including abundant carbonate rocks of the lesser himalayan sequence for comparison the arun river was chosen for study because south of the himalayan front it drains almost exclusively greater and lesser himalayan silicate rocks despite this dominance of silicate rocks carbonate weathering probably of metamorphic calcite in great himalayan paragneisses is clearly in evidence in many arun watersheds weathering of silicate rocks exposed all along the arun south of the range front has a small impact on mainstem river chemistry the mainstems of both the seti and arun systems are dominated by weathering of carbonate rocks although the contribution of silicate weathering is more visible in arun mainstem chemistry the carbonate weathering source to the arun mainstem is probably both limestone in the tethyan sequence widely exposed in northern headwaters of the system and metamorphic calcite within the greater himalayan sequence a number of small watersheds along the arun and seti appear to be carbonate free they probably provide the best constraints to date on the ca na and mg na ratios of waters draining himalayan silicate rocks two critical parameters for calculation of co 2 consumption by silicate weathering in the himalaya the observed ca na and mg na ratios would produce slightly higher estimates of silicate weathering fluxes than previous studies the geologic contrasts between the seti and the arun produce large differences in the 87 sr 86 sr ratio of each mainstem unlike the major element chemistry the seti mainstem displays much higher 87 sr 86 sr ratios than the arun mainstem the opposite of the expected relationship since radiogenic silicate rocks of the greater and lesser himalaya are so widely exposed along the arun 87 sr 86 sr ratios of the arun mainstem never exceed 0 734 and show little downstream change as the mainstem passes through silicate rocks of the greater and lesser himalaya 87 sr 86 sr ratios of the seti mainstem increase sharply from 0 725 to 0 785 when the river enters the belt of metacarbonate rocks of the northern lesser himalayan sequence a pattern also displayed by other himalayan rivers such as the kali gandaki and bhotse khola metacarbonate rocks including those of the lesser himalaya are a major source of radiogenic sr in modern himalayan rivers and probably have been key players in elevating marine 87 sr 86 sr ratios since the early miocene

lithium in foraminiferal shells implications for high temperature hydrothermal circulation fluxes and oceanic crustal generation rates the lithium content of planktonic foraminiferal calcite has been determined to evaluate temporal variability of seawater li concentrations over the past 116 m y mean foraminiferal calcite lithium calcium in each time interval is no more than 16 greater nor 25 less than the mean li ca of all samples li ca minima are observed for samples from 50 60 m y and 80 90 m y with li ca about 25 lower than in adjacent time intervals at no time during the past 40 m y does mean li ca appear to be higher than that at present subject to the limitations imposed by sample coverage and diagenesis a similar conclusion holds for the past 116 m y coupled with an oceanic mass balance model for li these data suggest that 1 oceanic li concentrations and therefore high temperature hydrothermal circulation fluxes during the past 40 m y and perhaps the past 100 m y have not been more than perhaps 30 40 greater than at present for intervals any longer than a million years at most and 2 these fluxes werenot a factor of two higher 100 m y ago by inference variations in oceanic crustal generation rates over these time periods are similarly limited decreases in hydrothermal circulation fluxes and crustal generation rates or fluctuations up to 20 in these rates of a few million years duration arenot necessarily ruled out by the li ca data the lack of variability in li ca over time is not unequivocal evidence that hydrothermal fluxes have not varied because the rates of removal processes may be linked to changes in input fluxes

the strontium isotopic budget of himalayan rivers in nepal and bangladesh abstract himalayan rivers have very unusual sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic we present sr o and c isotopic data from river and rain water bedload and bedrock samples for the western and central nepal himalaya and bangladesh including the monsoon season central himalayan rivers receive sr from several sources carbonate and clastic tethyan sediments high himalayan crystalline hhc gneisses and granitoids with minor marbles carbonates and metasediments of the lesser himalaya lh and miocene recent foreland basin sediment from the siwaliks group and the modern flood plain in the tethyan himalaya rivers have dissolved sr 6 mol l and 87sr 86sr 0 717 with a large contribution from moderately radiogenic carbonate rivers draining hhc gneisses are very dilute with sr 0 2 mol l and 87sr 86sr 0 74 lesser himalayan streams also have low sr 0 4 mol l and are highly radiogenic 87sr 86sr 0 78 highly radiogenic carbonates of the lh do not contribute significantly to the sr budget because they are sparse and have very low sr in large rivers exiting the himalaya sr systematics can be modeled as a mixture between tethyan rivers where slightly radiogenic carbonates mean 87sr 86sr 0 715 are the main source of sr and lesser himalaya waters where extremely radiogenic silicates 0 8 are the main source of sr hhc waters are less important because of their low sr rivers draining the siwaliks foreland basin sediments have sr 4 mol l and 87sr 86sr 0 725 weathering of silicates in the siwaliks and the flood plain results in a probably significant radiogenic 0 72 0 74 input to the ganges and brahmaputra g b but quantification of this flux is limited by uncertainties in the hydrologic budget the g b in bangladesh show strong seasonal variability with low sr and high 87sr 86sr during the monsoon sr in the brahmaputra ranges from 0 9 mol l and 0 722 in march to 0 3 mol l and 0 741 in august we estimate the seasonally weighted flux from the g b to be 6 5 108 mol yr with 87sr 86sr 0 7295

lithium isotope geochemistry of pore waters from ocean drilling program sites 918 and 919 irminger basin the distribution of li isotopes in pore waters to a depth of 1157 m below seafloor is presented for odp sites 918 and 919 in the irminger basin offshore greenland lithium isotope data are accompanied by strontium isotope ratios to decipher diagenetic reactions in the sediments which are characterized by the pervasive presence of volcanic material as well as by very high accumulation rates in the upper section the lowering of the 87sr 86sr ratio below contemporaneous seawater values indicates several zones of volcanic material alteration the li isotope profiles are complex suggesting a variety of exchange reactions with the solid phases these include cation exchange with nh4 and mobilization from sediments at depth in addition to the alteration of volcanic matter lithium isotopes are therefore a sensitive indicator of sediment water interaction 6li values of pore waters at these two sites vary between 42 and 25 at shallow depths 100 mbsf rapid decreases in the li concentration accompanied by a shift to heavier isotopic compositions indicate uptake of li into alteration products a positive anomaly of 6li observed at both sites is coincident with the nh4 maximum produced by organic matter decomposition and may be related to ion exchange of li from the sediments by nh4 in the lower sediment column at site 918 dissolved li increases with depth and is characterized by enrichment of 6li the li isotopic compositions of both the waters and the solid phase suggest that the enrichment of li in deep interstitial waters is a result of release from pelagic sediments the significance of sediment diagenesis and adsorption as sinks of oceanic li is evaluated the maximum diffusive flux into the sediment due to volcanic matter alteration can be no more than 5 of the combined inputs from rivers and submarine hydrothermal solutions adsorption on to sediments can only account for 5 10 of the total inputs from rivers and submarine hot springs

developments in the understanding and application of lithium isotopes in the earth and planetary sciences the significant relative mass difference c 16 between the two stable isotopes of li approximately 6li 7 5 7li 92 5 coupled with broad elemental dispersion in earth and planetary materials makes this a system of considerable interest in fingerprinting geochemical processes determining mass balances and in thermometry natural mass fractionation in this system is responsible for c 6 variation among materials examined to date fig 1 although the modern era of li isotope quantification has begun there are still many questions about the li isotopic compositions of fundamental materials and the nature of fractionation by important mechanisms that are unanswered e g hoefs 1997 figure 1 summary of lithium isotopic compositions of earth and planetary materials filled bars are solid samples open bars are liquids see text for references and details the purpose of this chapter is to summarize the current understanding of li isotopes in geo and cosmochemical systems and to indicate 1 where li isotopes have a high probability of adding new understanding of these systems 2 where some of the more significant deficits in knowledge exist the small but burgeoning li isotope community has not yet compiled the volume of peer reviewed literature needed to adequately assess even that which has been studied to date as a result significant portions of this chapter are based on data reported in abstracts and as such are more than normally subject to revisions over time this chapter is anticipated to serve as a starting point for those interested in research incorporating li isotope geochemistry or in understanding the state of extant research experiments in li isotope fractionation knowledge of significant li isotopic fractionation during basic chemical processes is long standing the early experiments by taylor and urey 1938 in which li isotopes were fractionated by incomplete extraction of an aqueous solution from a zeolite exchange

behavior of li rb and cs during basalt glass and olivine dissolution and chlorite smectite and zeolite precipitation from seawater experimental investigations and modelization between 50 and 300 c abstract this study investigates experimentally the behavior of li rb and cs during the hydrothermal alteration of a basalt glass and of forsterite the behavior of trace alkalis during the dissolution of a basalt glass and forsterite has been followed between 150 and 300 c rb and cs are preferentially leached from the glass while li exhibits a stoichiometric release with respect to silica on the other hand incongruent loss of li relative to si during forsterite dissolution reflects a crystallographic site energy control of the release of trace elements from crystalline silicates the partitioning of li rb and cs between hydrothermal solutions and chlorites smectites and zeolites has been experimentally investigated between 50 and 260 c the alteration phases were synthesized by altering silicate glasses in solutions containing the trace alkalis the lower the temperature the higher the exchange capacity of the mineral or the lower the ionic hydration energy then the more the element is incorporated into the solid phases computer simulations generated with the eq3 6 software package and our experimental data on distribution coefficients account for the behavior of alkali trace elements during the alteration of basalt glasses by seawater at mid ocean ridges

lithium isotopes as a probe of weathering processes orinoco river abstract lithium isotopes have the potential to be effective tracers of weathering processes due to their large relative mass difference and therefore fractionation in this study an attempt is made to fill a major gap in the knowledge of li isotope fractionation during continental weathering and of the mechanisms involved finally the relationship between the suspended and dissolved material is made on a basin wide scale the orinoco basin provides a clear contrast in reaction limited and transport limited weathering regimes that has already been documented by a comprehensive study on its fluvial geochemistry edmond et al geochim cosmochim acta 60 1996 2949 2976 edmond et al geochim cosmochim acta 59 1995 3301 3325 conspicuous in our new results is the difference in 6li of the dissolved load between the andean 30 to 22 and shield 22 to 7 tributaries while the 6li of the suspended load is similar between the two to a first approximation during superficial weathering in high relief tectonically active terrains the dissolved load is high in li and isotopically heavy more negative 6li whereas in stable shield regions the concentrations are low and isotopically light in proportion to the increasing degree of weathering

relative contributions of silicate and carbonate rocks to riverine sr fluxes in the headwaters of the ganges abstract exhumation of the himalayan tibetan orogen is implicated in the marked rise in seawater 87sr 86sr ratios since 40 ma however both silicate and carbonate rocks in the himalaya have elevated 87sr 86sr ratios and there is disagreement as to how much of the 87sr flux is derived from silicate weathering most previous studies have used element ratios from bedrock to constrain the proportions of silicate and carbonate derived sr in river waters here we use arrays of water compositions sampled from the head waters of the ganges in the indian and nepalese himalaya to constrain the end member element ratios the compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two component mixing of silicate and carbonate derived components and lie on a plane in multicomponent composition space key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes na 0 for carbonate and constant ca na for silicate the fractions of sr derived from silicate and carbonate sources are then calculated by mass balance in sr ca mg na composition space comparison of end member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low mg trace calcite in silicate rocks may explain discrepancies in sr ca na mg covariation alternatively composition dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation ratio diagrams however the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained silicates are calculated to provide 50 of the dissolved sr flux from the head waters of the ganges assuming that discrepancies between ca mg na covariation and the silicate rock compositions arise from addition of trace calcite if the ca mg na mixing plane is rotated by composition dependent secondary calcite deposition this estimate would be increased moreover when 87sr 86sr ratios of the sr inputs are considered silicate sr is responsible for 70 16 1 of the 87sr flux forcing changes in seawater sr isotopic composition since earlier studies predict that silicate weathering generates as little as 20 of the total sr flux in himalayan river systems this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated

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

lithium and lithium isotope profiles through the upper oceanic crust a study of seawater basalt exchange at odp sites 504b and 896a abstract ocean drilling program odp hole 504b near the costa rica rift is the deepest hole drilled in the ocean crust penetrating a volcanic section a transition zone and a sheeted dike complex the distribution of li and its isotopes through this 1 8 km section of oceanic crust reflects the varying conditions of seawater alteration with depth the upper volcanic rocks altered at low temperatures are enriched in li 5 6 27 3 ppm and have heavier isotopic compositions 7li 6 6 20 8 relative to fresh mid ocean ridge basalt morb due to uptake of seawater li into alteration clays the li content and isotopic compositions of the deeper volcanic rocks are similar to morb reflecting restricted seawater circulation in this section the transition zone is a region of mixing of seawater with upwelling hydrothermal fluids and sulfide mineralization li enrichment in this zone is accompanied by relatively light isotopic compositions 0 8 2 1 which signify influence of basalt derived li during mineralization and alteration li decreases with depth to 0 6 ppm in the sheeted dike complex as a result of increasing hydrothermal extraction in the high temperature reaction zone rocks in the dike complex have variable isotopic values that range from 1 7 to 7 9 depending on the extent of hydrothermal recrystallization and off axis low temperature alteration hydrothermally altered rocks are isotopically light because 6li is preferentially retained in greenschist and amphibolite facies minerals the 7li values of the highly altered rocks of the dike complex are complementary to those of high temperature mid ocean ridge vent fluids and compatible to equilibrium control by the alteration mineral assemblage the inventory of li in basement rocks permits a reevaluation of the role of oceanic crust in the budget of li in the ocean on balance the upper 1 8 km of oceanic crusts remains a sink for oceanic li the observations at 504b and an estimated flux from the underlying 0 5 km of gabbro suggest that the global hydrothermal flux is at most 8 109 mol yr compatible with geophysical thermal models this work defines the distribution of li and its isotopes in the upper ocean crust and provides a basis to interpret the contribution of subducted lithosphere to arc magmas and cycling of crustal material in the deep mantle

ostracod biodiversity from shelf to slope oceanic conditions off central bay of bengal india abstract thirty seven surface sediment samples collected through a multi corer in seven transects of orv sagar kanya sk 308 leg 1 from off central bay of bengal shelf to slope environment were analysed for living and dead ostracoda the samples which ranged in water depth from 29 m to 2540 m yielded a total of 46 species belonging to 32 genera the ostracod fauna of the bay of bengal exhibit a depth related distribution that is controlled by substrate and hydrographic conditions sandy substrates of shallow water depth 28 m are characterized by propontocypris sp and cytherelloidea malaccaensis these species are replaced by neonesidea cracenticlavula and bairdoppilata paraalcyonicola in high population which shows positive linear correlation with salinity temperature and total calcium carbonate tcc in the outer shelf 55 73 m paijenborchella sp dominates at 763 m in the bathypelagic zone giving way to parakrithella sp at greater depths of 2540 m on soft bottom substrates the fauna represents an interesting mixture of displaced species and others known from bathyal and abyssal depths in the bay of bengal including some pandemic deep sea species the ostracod faunal diversity is higher in shallower water than in the deeper water which may be due to the optimum temperature ph salinity and substrate the fauna are comprised of three associations shelf upper slope slope lower slope abyss a marked faunal turnover occurs at the outer shelf factor analysis was performed to determine the correlation of water and sediment parameters with the ostracod species this study provides a detailed account of bathymetry and ostracod biodiversity recorded in the study area

lithium and its isotopes in major world rivers implications for weathering and the oceanic budget abstract the outstanding problem in the lithium geochemical cycle is the lack of an isotopic mass balance in the ocean the 6li compositions of fresh basalts 4 the hydrothermal fluids derived from them average 9 and seawater significantly heavier at 32 are well understood but only very sparse river input data are available for li mass balance calculations in an attempt to rectify the situation we have measured the lithium concentrations and isotopic compositions of major world rivers draining representative geological terrains this helps both to constrain the river endmember and to understand the behavior of lithium isotopes in the continental weathering environment fluvial isotopic compositions display a very large range 6 0 to 32 2 there is no definitive relationship between 6li and lithology but in general rivers draining marine evaporites are 20 to 22 carbonates 26 to 32 black shales 26 shields 6 6 to 19 and mixed siliceous terrains 6 to 28 the flow weighted mean concentration of the measured rivers is 215 nm at 23 this updated riverine 6li value responsible for 30 of the global riverine discharge does not solve the isotopic imbalance if the measured li concentrations and isotopic compositions are representative of all rivers the presence of a yet unidentified sink with a higher fractionation factor 1 023 than determined for low temperature basalt alteration 1 019 is required for an isotopic steady state of li in the ocean authigenic clays are a possible candidate as clays are known to be enriched in both lithium and in the light isotope preferentially alternatively the hydrothermal flux must be much less than half of that estimated by the 3he inventory and the oceanic budgets for 87sr 86sr and mg the relationship of 6li to the major ions and 87sr 86sr suggests that the important processes affecting river dissolved lithium isotopic compositions are fractionation between solution and secondary minerals and thus the intensity of weathering

reconciling the elemental and sr isotope composition of himalayan weathering fluxes insights from the carbonate geochemistry of stream waters determining the relative proportions of silicate vs carbonate weathering in the himalaya is important for understanding atmospheric co2 consumption rates and the temporal evolution of seawater sr however recent studies have shown that major element mass balance equations attribute less co2 consumption to silicate weathering than methods utilizing ca sr and 87sr 86sr mixing equations to investigate this problem we compiled literature data providing elemental and 87sr 86sr analyses for stream waters and bedrock from tributary watersheds throughout the himalaya mountains in addition carbonate system parameters pco2 mineral saturation states were evaluated for a selected suite of stream waters the apparent discrepancy between the dominant weathering source of dissolved major elements vs sr can be reconciled in terms of carbonate mineral equilibria himalayan streams are predominantly ca2 mg2 hco3 waters derived from calcite and dolomite dissolution and mass balance calculations demonstrate that carbonate weathering contributes 87 and 76 of the dissolved ca2 and sr2 respectively however calculated ca sr ratios for the carbonate weathering flux are much lower than values observed in carbonate bedrock suggesting that these divalent cations do not behave conservatively during stream mixing over large temperature and pco2 gradients in the himalaya the state of calcite and dolomite saturation was evaluated across these gradients and the data show that upon descending through the himalaya 50 of the streams evaluated become highly supersaturated with respect to calcite as waters warm and degas co2 stream water ca mg and ca sr ratios decrease as the degree of supersaturation with respect to calcite increases and mg2 ca2 and hco3 mass balances support interpretations of preferential ca2 removal by calcite precipitation on the basis of patterns of saturation state and pco2 changes calcite precipitation was estimated to remove up to 70 of the ca2 originally derived from carbonate weathering accounting for the nonconservative behavior of ca2 during riverine transport brings the ca sr and 87sr 86sr composition of the carbonate weathering flux into agreement with the composition of carbonate bedrock thereby permitting consistency between elemental and sr isotope approaches to partitioning stream water solute sources these results resolve the dissolved sr2 budget and suggest that the conventional application of two component ca sr and 87sr 86sr mixing equations has overestimated silicate derived sr2 and hco3 fluxes from the himalaya in addition these findings demonstrate that integrating stream water carbonate mineral equilibria divalent cation compositional trends and sr isotope inventories provides a powerful approach for examining weathering fluxes

lithium isotopic composition of submarine basalts implications for the lithium cycle in the oceans abstract we have measured the li isotope composition of young pristine basalts from active ocean ridge crests of progressively older basalts along a dredging transect and a limited number of hydrothermally altered basalts the data significantly extend our limited knowledge of the isotopic abundance ratio of li in geological material fresh mid ocean ridge basalts have 6li values of between 3 4 and 4 7 relative to isotope standard l svec during low temperature weathering on the seafloor the isotopic composition of the rock becomes increasingly heavier due to addition of seawater li 6li 32 3 the oldest 46 m y and most altered rock studied has an isotopic composition of 14 a linear relationship exists between 6li and the inverse of li concentration suggesting that li in weathered basalts can be regarded as a two component mixture of basaltic li and seawater derived li that has been incorporated in alteration minerals most likely secondary clays such as smectite and phillipsite the inferred li isotopic composition of the alteration endmember indicates an apparent isotopic fractionation factor of 1 019 relative to the seawater source thus li uptake by secondary minerals from the low temperature weathering process and by analogy incorporation in similar authigenic minerals in marine sediments provides a mechanism for preferential removal of the lighter li isotope from ocean water however isotopic fractionation due to authigenic clay formation alone cannot account for the isotopic difference between seawater and its principal sources unless the hydrothermal flux is comparable to the river flux alternatively more important sinks of6li must exist if the steady state isotopic composition of li in ocean water is to be maintained

the significance of himalayan rivers for silicate weathering rates evidence from the bhote kosi tributary the significance of weathering by himalayan runoff for both the sr isotope marine record and the removal of atmospheric co2 through silicate dissolution has been examined by systematic sampling of dissolved loads and bedloads from the bhote kosi a tributary of the ganges that rises in tibet from tethyan sediment bedrock and traverses the major himalayan lithologies of eastern nepal before debouching onto the gangetic plains throughout the section the cation geochemistry of water samples is dominated by ca and mg ions suggesting that carbonates are the predominant lithology undergoing dissolution particularly within the lesser himalayas as the river transects the metasedimentary and granitic lithologies of the high himalayas the sr isotope ratio of the bedload rises rapidly closely reflecting the isotope geochemistry of the bedrock in contrast the 87sr 86sr ratio of the dissolved load remains roughly constant 0 719 0 723 downstream of the main central thrust where the river transects the carbonate bearing lithologies of the lesser himalayas the 87sr 86sr ratio of the dissolved load rises sharply 0 768 the relative contributions of silicate and carbonate weathering from each of the main himalayan units has been estimated from major cation sr concentration and sr isotope mass balance equations these calculations suggest that the high sr and high 87sr 86sr characteristics of riverine analyses arise initially from a component dissolved from the tibetan sedimentary series which is substantially enhanced by input weathering fluxes particularly as the river traverses the lesser himalayas whilst mechanical erosion is maximised within the high himalayan crystalline series as confirmed by 143nd 144nd ratios from the bedload at least 63 of the dissolved load is acquired by chemical weathering of bedrock lithologies and or of transported particulates within the lesser himalayas enhanced by higher ambient temperatures and slower discharge rates this may involve continued dissolution of the high himalayan crystalline series particulates in addition to lesser himalayan lithologies although himalayan rivers collectively have a major influence on the sr isotope marine record the high 87sr 86sr ratios of their dissolved load results from the mixing of a small component 90 of carbonate derived material some of which is characterised by a high 87sr 86sr ratio up to 0 8 elevated 87sr 86sr ratios in rivers are therefore not necessarily indicative of anomalously high dissolution rates of silicates

behaviour of li isotopes during continental weathering the bidar laterite profile india weathering of large basaltic provinces is a major sink of atmospheric carbon dioxide and is also an important part of the geochemical cycle of many other elements this study aims to improve our understanding of basaltic weathering by analysis of trace elements and li isotopes in a lateritic profile developed upon the deccan traps flood basalt at its base the profile consists of unaltered basalt that has a li concentration and 7li value of 5 ppm and 2 5 respectively which is upwards progressively altered to a highly weathered laterite iron rich residuum at the surface high concentrations of fe2o3 85 wt at 11 m depth indicate the presence of a palaeowatertable the transition metals the rare earth elements rees and u are also strongly enriched in this horizon whereas fluid mobile elements such as li and rb are depleted relative to the precursor basalt and the bulk 7li value is very low 5 5 a high proportion of leachable li is found in this horizon and this is enriched in 6li relative to the bulk we suggest that leaching extracts the labile weathering products and these have high 6li as 7li has been preferentially mobilised during basalt weathering throughout the rest of the profile li concentrations and li isotope values are best explained by two component mixing between the precursor basalt and aeolian material with high li and low 7li mass balance calculations show that at least 50 of the li present in the profile could have been supplied by a mineral aerosol that has a 7li value between 0 and 1 3 the depth integrated 7li value of the profile is 0 6 which suggests that 7li has been preferentially leached from the aerosol after its deposition the source of this aeolian material is most likely to be ancient continental crust it is possibly derived from archaen proterozoic terrain to the south and southeast of the deccan and or material from central asia similar to that which forms chinese loess and which is supplied to the north pacific basin

lithium isotope fractionation during continental weathering processes a comprehensive understanding of lithium isotope fractionation during terrestrial weathering is necessary in order to use lithium isotopes to trace chemical cycles climatic changes and igneous processes this study investigates lithium isotope fractionation in two laboratory experiments and by analyses of natural basalt weathering products partial dissolution of basalts in the laboratory does not result in fractionation of lithium isotopes but similar dissolution of a granite sample causes significant fractionation this may reflect dissolution of secondary minerals from the granite or differences in the li isotope composition of primary minerals in this more evolved igneous rock significant li isotope fractionation was also observed during sorption onto mineral surfaces in the laboratory although this was highly dependent on sample mineralogy no fractionation accompanies the outer sphere physisorption of li to smectite surfaces some fractionation accompanies sorption onto ferrihydrite and significant fractionation with 0 986 is seen during inner sphere chemisorption to gibbsite surfaces repeat experiments with varying amounts of sorption demonstrate that li remains in an exchangeable site on the gibbsite surface the extent of fractionation onto gibbsite observed in this study 13 is about half that required in order for clay surface removal to balance the ocean li isotope budget isotopic fractionation of li was found to occur on a 300 yr timescale in both cold and warm natural environments a minimally altered rock surface from iceland was found to be two lighter in 7li than the sample interior probably due to the preferential incorporation of 6li in clay or oxide rich alteration products on the sample surface soil samples from hawaii also demonstrate li fractionation during weathering in this environment rainwater 7li 10 contributes a significant flux of isotopically heavy li to the developing soil despite this soils have similar li isotope compositions to the primary basalt 7li 4 indicating that 6li is preferentially retained during weathering this conclusion is supported by isotopically heavy river water on hawaii 7li 22 and by the correlation between li concentration and 7li in the soil the lab and field based measurements of this study clearly demonstrate that lithium fractionates during weathering potentially providing information about the weathering environment now and in the past