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

lithium isotope evidence for enhanced silicate weathering during oae 1a early aptian selli event an abrupt rise in temperature forced by a massive input of co2 into the atmosphere is commonly invoked as the main trigger for oceanic anoxic events oaes global warming initiated a cascade of palaeoenvironmental perturbations starting with increased continental weathering and an accelerated hydrological cycle that delivered higher loads of nutrients to coastal areas stimulating biological productivity the end result was widespread anoxia and deposition of black shales the hallmarks of oaes in order to assess the role of weathering as both an oae initiator and terminator via co2 sequestration during the early aptian oae 1a selli event 120 ma the isotopic ratio of lithium isotopes was analysed in three sections of shallow marine carbonates from the pacific and tethyan realms and one basinal pelagic section from the tethyan domain because the isotopic composition of lithium in seawater is largely controlled by continental silicate weathering and high and low temperature alteration of basaltic material a shift to lighter 7li values is expected to characterize oaes the studied sections illustrate this phenomenon 7li values decrease to a minimum coincident with the negative carbon isotope excursion that effectively records the onset of oae 1a a second negative 7li excursion occurs coeval with the minimum in strontium isotopes after the event the striking similarity to the strontium isotope record argues for a common driver the formation and destruction weathering of an oceanic lip could account for the parallel trend in both isotope systems the double spike in lithium isotopes is probably related to a change in weathering congruencies such a chemostratigraphy is consistent with the hypothesis that an increase in silicate weathering in conjunction with organic carbon burial led to drawdown of atmospheric co2 during the early aptian oae 1a

the krafla geothermal field iceland 2 the natural state of the system a model of the natural state of the krafla reservoir system in iceland has been developed the model consists of a vertical cross section which includes reservoirs in both old and new well fields the physical processes considered include mass transport conductive and convective heat transfer and boiling and condensation natural heat losses to surface manifestations springs are also included the model matches very well all relevant data from the krafla field the natural flow of hot fluids through the reservoirs is estimated as approximately 20 kg s steam escaping to surface springs constitutes the bulk of the heat losses in the area modeled conductive heat losses through the caprock are approximately 1 w m2 and heat recharge from below is about 2 w m2

the relationship between riverine lithium isotope composition and silicate weathering rates in iceland abstract this study presents lithium isotope and elemental data for the dissolved phase and suspended and bedload sediments of the major icelandic rivers for the dissolved phase 7li values range between 10 1 and 23 8 while river sediments display lower and much more homogeneous values 7li 3 1 4 8 close to the composition of unweathered mid ocean ridge basalt morb high 7li values are associated with high k li na li and mg li ratios in waters draining mainly old and weathered basalt catchments whereas low 7li rivers are located in younger parts of the island simple mixing between precipitation li rich hydrothermal springs and basalt weathering is unable to explain the entire range of 7li values instead a simple model of li uptake by secondary minerals associated with clay water li isotope fractionation 7li ranging from 1 to 7 5 can explain both water and sediment 7li values a negative correlation is observed between basalt chemical erosion rates and 7li measured in icelandic rivers and an empirical law is inferred comparison with literature data suggests that this relationship may be applicable at a more global scale and if confirmed could be of particular use for estimating the evolution of continental weathering preserved in marine sedimentary records however more data are now needed for rivers draining silicates typical of the continental crust in order to refine large scale modelling

mechanisms controlling the silicon isotopic compositions of river waters it has been proposed that silicon si isotopes are fractionated during weathering and biological activity leading to heavy dissolved riverine compositions in this study the first seasonal variations of stable isotope compositions of dissolved riverine si are reported and compared with concomitant changes in water chemistry four different rivers in switzerland were sampled between march 2004 and july 2005 the unique high resolution multi collector icp ms nu1700 has been used to provide simultaneous interference free measurements of 28si 29si and 30si abundances with an average limiting precision of 0 04 on 30si this precision facilitates the clarification of small temporal variations in isotope composition the average of all the data for the 40 samples is 30si 0 84 0 19 1 sd despite significant differences in catchment lithologies biomass climate total dissolved solids and weathering fluxes the averaged isotopic composition of dissolved si in each river is strikingly similar with means of 0 70 0 12 for the birs 0 95 0 22 for the saane 0 93 0 12 for the ticino and 0 79 0 19 for the verzasca however the 30si undergoes seasonal variations of up to 0 6 comparisons between 30si and physico chemical parameters such as the concentration of dissolved si and other cations the discharge of the rivers and the resulting weathering fluxes permits an understanding of the processes that control the si budget and the fate of dissolved si within these rivers the main mechanism controlling the si isotope composition of the mountainous verzasca river appears to be a two component mixing between the seepage of soil ground waters with heavier si produced by clay formation and superficial runoff associated with lighter si during high discharge events a biologically mediated fractionation can be excluded in this particular river system the other rivers display increasing complexity with increases in the proportion of forested and cultivated landscapes as well as carbonate rocks in the catchment in these instances it is impossible to resolve the extent of the isotopic fractionation and contributed flux of si contributed by biological processes as opposed to abiotic weathering the presence of seasonal variations in si isotope composition in mountainous rivers provides evidence that extreme changes in climate affect the overall composition of dissolved si delivered to the oceans the oceanic si isotope composition is very sensitive to even small changes in the riverine si isotope composition and this parameter appears to be more critical than plausible changes in the si flux therefore concurrent changes in weathering style may need to be considered when using the si isotopic compositions of diatoms sponges and radiolaria as paleoproductivity proxies

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

sea level sediments and the composition of seawater the composition of seawater changed significantly during the course of the phanerozoic in concert with long term changes in sea level which were largely the result of changes in the volume of mid ocean ridges these reflect changes in the rate of seafloor spreading and determine the rate of seawater cycling through mid ocean ridges spencer and hardie 1990 and hardie 1996 proposed that the changes in the cycling rate of seawater through mid ocean ridges have been responsible for the changes in the composition of seawater during the phanerozoic this explanation cannot account for the major changes in the composition of seawater during the cenozoic which was a time of nearly constant seafloor spreading rate however changes in the rate of deposition of shallow water carbonates and their penecontemporaneous dolomitization can explain the cenozoic changes in seawater composition this indicates that sedimentologic parameters have played a major role in the chemical evolution of seawater the more rapid cycling of seawater through mors during the mesozoic can explain semiquantitatively the fairly minor differences between the composition of seawater in the eocene and in the jurassic changes in the composition of seawater during the paleozoic were probably determined both by changes in the rate of dolomite and gypsum anhydrite deposition and by changes in the rate of seawater cycling through mid ocean ridges if the causes of these compositional changes are the same as those during the cenozoic and mesozoic then sedimentologic factors have been significantly more important than the rate of cycling of seawater through mors in shaping the chemical evolution of seawater during the phanerozoic

glacial effects on weathering processes new insights from the elemental and lithium isotopic composition of west greenland rivers greenland is by far the dominant source of glacial runoff to the oceans but the controls on the chemical and isotopic composition of this runoff are poorly known to better constrain glacial effects on weathering processes we have conducted elemental and lithium isotope analyses of glacial and non glacial rivers in gneiss catchments in west greenland the glacial rivers have high total suspended solids 0 5 g l 1 and low total dissolved solids 12 scm 1 relative to the non glacial rivers and they contain a higher proportion of dissolved ca2 and k because of subglacial preferential weathering of trace carbonates and biotite the glacial rivers also have high so42 because of the oxidation of trace sulphides under the ice both glacial and non glacial rivers have high 7li respectively not vert similar 26 and not vert similar 30 relative to the rocks from which the li is derived not vert similar 8 saturation state modelling suggests that this is due to the formation of fe oxyhydroxides in the non glacial rivers with preferential uptake of 6li during inner sphere sorption of li on the fe oxyhydroxide surface glacial rivers however are undersaturated with respect to clay minerals and fe oxyhydroxides nevertheless leaching of suspended sediments indicates that not vert similar 65 of the li in these sediments is associated with fe oxyhydroxide phases and the 7li value of this li is low not vert similar 5 these results suggest that these fe oxyhydroxides formed under the ice as a product of sulphide oxidation with preferential uptake of 6li onto the mineral surface solubilisation of li from these fe oxyhydroxide phases is unlikely to represent a significant flux of li to the oceans moreover because the difference between the 7li values of glacial vs non glacial rivers is small glaciation has not had a significant impact on the li isotopic composition of the riverine flux delivered to the oceans in the past even at the height of the last deglaciation

assessing the role of climate on uranium and lithium isotope behaviour in rivers draining a basaltic terrain this study presents uranium u and lithium li isotope and major and trace element data for the dissolved load suspended particles and bedload from rivers draining dominantly basaltic catchments on the island of sao miguel in the azores archipelago uranium activity ratios are at secular equilibrium in the bedload but are higher for suspended material suggesting sorption of uranium from the solution onto particle surfaces the 234u 238u of the riverine dissolved phase varies between 1 02 and 1 86 and lies on a mixing trend between the values expected from chemical weathering of basalt high u 234u 238u at secular equilibrium and an endmember with low u and high 234u 238u which probably reflects recoil effects associated with physical weathering and or soil formation lithium isotope ratios are consistently lighter in suspended material than the corresponding bedload suggesting preferential retention of 6li in the suspended load in turn the 7li of the dissolved load is always isotopically heavier ranging from 5 9 to 36 2 although the lightest values are affected by hydrothermal input the lithium isotopic composition of the dissolved load reflects the balance of primary mineral dissolution to secondary mineral formation comparison of the behaviour of u and li isotopes between sao miguel iceland and other basaltic terrains suggests that whilst u isotopes are dominated by weathering regimes dependent on factors such as weathering rates temperature runoff and climate neither weathering intensity nor climate exerts a direct influence on li isotope behaviour rather the formation of secondary minerals which is indirectly controlled by climate weathering primary mineralogy and biology appears to play the dominant role

lithium isotopic composition of the mcmurdo dry valleys aquatic systems the mcmurdo dry valleys are the largest ice free area in antarctica and include several terminal lake basins these include lakes hoare fryxell bonney and vanda the hydrology of the lakes is controlled by the inputs of glacial meltwater and loss by sublimation of ice covers despite the extremely dilute inflow waters the lakes range in salinity from hypersaline to fresh due in large part to their landscape position and climatic history although the aqueous geochemistry of the region has been studied extensively over the past four decades the ultimate source of solutes to the lakes is still in question atmospheric input precipitation dissolution of salts in sediments chemical weathering remnant seawater and groundwater inputs have been suggested as the most likely sources of solutes to dry valley waters we have examined the lithium isotopic composition of glacial snow stream water and lake water to better understand the role of these sources in determining the overall chemistry of the lakes the data suggest that the dominant sources of lithium to the lakes are the dissolution of aeolian dust of crustal origin on the glacial surface marine aerosols dissolution of salts and chemical weathering in the stream channels and ancient seawater the streams in the valleys show mixing of seawater and or marine aerosol with an isotopically lighter silicate dust end member as seen in glacial snow our data reveal the following sources of lithium to the lakes streamwater in lake hoare seawater in the monimolimnia i e the dense bottom water in a permanently stratified lake of lakes bonney and fryxell a diffusional mixture of onyx river water and a deep water brine hypersaline groundwater discharge in don juan pond this work confirms yet provides a more conclusive link than previous findings between various salt sources and the role they play in solute accumulation in this extreme environment

new perspectives on the li isotopic composition of the upper continental crust and its weathering signature abstract lithium isotopes are increasingly used to trace both present day and past weathering processes at the surface of the earth and could potentially be used to evaluate the average degree of past weathering recorded by the upper continental crust ucc yet the previous estimate of average 7li of the ucc has a rather large uncertainty hindering the use of li isotopes for this purpose new 7li for desert and periglacial loess deposits windblown dust from several parts of the world europe argentina china and tajikistan demonstrate that the former are more homogeneous than the latter and may therefore serve as excellent proxies of the average composition of large tracts of the ucc the li isotopic compositions and concentrations of desert loess samples are controlled by eolian sorting that can be quantified by a binary mixing between a weathered fine grained end member dominated by phyllosilicates and having low 7li and an unweathered coarse grained end member that is a mixture of quartz and plagioclase having higher 7li we use correlations between insoluble elements ree nd hf and fe2o3 sio2 li concentrations henceforth referred as li and 7li to estimate a new more precise average li isotopic composition and concentration for the ucc li 30 5 3 6 2 ppm and li 7 0 6 0 6 2 the 7li for desert loess deposits is anti correlated with the chemical index of alteration cia using this relationship along with our average 7li we infer that 1 the present day cia of the average ucc is 61 2 4 2 higher than the common reference value of 53 and 2 the average proportion of chemically weathered components is as high as 37 10 17 2 at the surface of the earth

lithium isotopes in global mid ocean ridge basalts abstract the lithium isotope compositions of 30 well characterized samples of glassy lavas from the three major mid ocean ridge segments of the world spanning a wide range in radiogenic isotope and elemental content and sea floor physical parameters have been measured the overall data set shows a significant range in 7li 1 6 to 5 6 with no global correlation between li isotopes and other geochemical or tectonic parameters the samples with the greatest lithophile element depletion n morb k2o tio2

natural variations of δ30si ratios during progressive basalt weathering hawaiian islands abstract silicon stable isotopes can be used to trace the biogeochemical pathways of si as it moves from its continental sources to its sink in ocean sediments along the way si is incorporated into clay minerals taken up by plants where it forms plant opal and leached into rivers the major land to ocean conduit compared to igneous rocks the waters that drain continents are enriched in heavy si isotopes but the mechanisms that control fractionation have not been elucidated we studied si isotope fractionation along a 4 million yr basaltic soil chronosequence on the hawaiian islands using the natural context of these samples in combination with laboratory experiments we demonstrate that the isotopic composition of dissolved si in weathering systems is determined by the combined effects of rock disintegration clay mineral neosynthesis and si biocycling weathering preferentially releases 28si into solution whereas secondary mineral formation preferentially removes 28si from solution in humid environments leached soils have lost large amounts of this soluble si thus creating a net loss of 30si from the entire soil system as soils develop and greater fractions of si reside in neoformed clay minerals 30sibulk soil values change progressively toward more negative values basalt 30si values are about 0 5 but older soils have 30si values up to 2 5 the difference between the solid and solution 30si values remains more or less constant with progressive weathering and therefore soil water from older soils has a more negative 30si composition in the upper horizons of the hawaiian soils this weathering driven 30si shift is modified by the addition of unweathered primary minerals via dust carrying 30si values of about 0 5 and by biocycling of si via plants producing negative 30si values in phytoliths and positive 30si values in soil solutions derived from upper horizons due to the high concentrations of dissolved si in these near surface layers rivers have more positive 30si values than predicted based on the weathering status of the lower horizons when combined with published 30si values from large rivers worldwide we find that the results from hawaii point to weathering control of si isotopes delivered to the oceans and thus to an important continent ocean linkage that warrants further investigation

riverine silicon isotope variations in glaciated basaltic terrains implications for the si delivery to the ocean over glacial interglacial intervals marine primary production is dominated by diatoms and these are dependent upon the riverine delivery of silicon si to the ocean in paleoreconstruction of silicic acid utilisation by diatoms it is assumed that the isotopic composition of the si that is delivered from the continent to the oceans remains constant in this study it is shown that glacier fed icelandic rivers differ from those directly draining basaltic catchments in their dissolved si isotope compositions lighter values 30si 0 17 0 18 are associated with the high physical erosion rates in glacial rivers and heavier values 30si 0 97 0 31 are associated with lower physical erosion rates and enhanced formation of secondary minerals in direct runoff rivers the si isotopic compositions correlate with those of li and provide evidence of a climatic dependence that is likely to have led to glacial interglacial differences based on existing 30si measurements from diatoms in a sediment record from the southern ocean the interpretation of changes in si utilisation between the last glacial maximum lgm and the early holocene is revisited taking into account changing isotopic compositions of the river water delivered to the ocean over glacial interglacial intervals during the lgm si utilisation values are higher when allowing for changing si isotope input to the ocean 59 5 than when a constant si isotope input is assumed 42 47 5 this reduces but does not eliminate the difference relative to the holocene 88 5 therefore changes in si isotope delivery to the ocean need to be taken into account in the precise reconstruction of ocean si utilisation and primary productivity over glacial interglacial timescales

a lithium isotope study of hot springs and metabasalts from mid ocean ridge hydrothermal systems the li isotopic compositions of seawater and of fresh and altered basalts are distinct and therefore applicable to the study of the hydrothermal processes in the oceanic crust and the li balance in the ocean high temperature fluids from seven vents on the east pacific rise epr at 21 n and 11 13 n have 6li values ranging between 6 and 11 i e 3 7 heavier than fresh basalt values the intervent variations in li concentration and isotopic composition correlate well with water rock ratios no temporal change in the isotopic value was observed between 1981 and 1985 metabasalts show both li depletion and enrichment relative to fresh basalt they display light li isotopic values which reflect incorporation of li mobilized from fresh basalt from these observations we conclude that the li isotopic composition of submarine hot springs is controlled by a path dependent process involving dissolution of primary minerals and precipitation of li with alteration phases 6li values of fluids from the mid atlantic ridge 6 to 8 fall in the range of the epr indicating similar reaction controls at the two ridge systems the lack of 7li enrichment in the fluids from slower spreading ridges indicates that li is not recycled from older weathered crust thus the difference between the 3he and 87sr 86sr based hydrothermal flux and the crustal transfer rate of li cannot be reconciled by the inclusion of secondary li from older crust

lithium magnesium and uranium isotope behaviour in the estuarine environment of basaltic islands this study presents major and trace elements and uranium u lithium li and magnesium mg isotope data for dissolved and suspended particulate material from estuaries draining dominantly basaltic terrains in iceland borgarfjor ur and sao miguel povoacao in the azores archipelago the concentrations of dissolved sodium na calcium ca potassium k sulphate so4 mg and li and 7li 6li and 26mg 24mg isotope ratios vary directly as a function of the dissolved chloride concentration cl indicating that these species are non reactive in these estuaries however u appears to be affected either by colloid flocculation or the formation of fe oxyhydroxides in borgarfjor ur the major element composition of suspended particulate material in the estuary at borgarfjor ur shows that the detrital silicates delivered to the estuarine mixing zone are relatively unweathered accordingly the 26mg isotope composition of the suspended material is indistinguishable from that of the parent basalts however the 234u 238u activity ratios of the suspended material are significantly different from the parent basalt indicating rapid equilibration of the u isotopes between particles and seawater the li concentration and 7li isotope composition of the suspended load are also observed to increase with increasing cl consistent with ongoing weathering of detrital material and the formation of secondary minerals in seawater depending on the particle residence time in the estuary this process could remove as much as 15 25 of the global riverine input of li to the ocean

lithium isotopes in hydrothermally altered basalts from hengill sw iceland abstract the li isotope signatures of hydrothermal fluids are remarkably constant li 7 8 0 1 9 irrespective of the water rock ratio w r permeability temperature or fluid involved seawater or meteoric high temperature hydrothermal fluids represent the second most significant source of li to the ocean yet the homogeneity of the li isotopic signatures of this source remains to be explained and in this context the lack of data for the corresponding altered phases is problematic we measured li contents and li isotope signatures as well as mineralogy composition and local fluid temperature in hyaloclastites collected from a borehole in the hellisheidi geothermal system iceland which have been altered by high temperature aqueous fluids from 170 to 300 c li is more enriched in the solid phases than the other alkali metals highlighting its greater ability to be incorporated into secondary phases especially at high temperatures 250 c mass balance calculations show that the low li concentrations in hydrothermal fluids are best explained by a high water rock ratio and a high permeability of this system the li isotopic signature of the altered hyaloclastites li 7 between 1 9 and 4 0 remains close to the fresh basalt at deep levels and high temperatures 290 300 c as measured li 7 range between 3 7 and 4 0 and decreases at shallower depths and lower temperatures 150 270 c li 7 between 1 9 and 3 1 a mass balance model involving basalt dissolution secondary phase formation and successive isotope equilibrium during the migration and the cooling of the percolating fluid was developed the corresponding apparent mineral fluid li isotope fractionation factors resulting from precipitation of secondary phases li minerals fluid 7 range between 0 at 300 c and 8 5 at 170 c and highlight a key role of chlorite applying the same approach to mid ridge oceanic hydrothermal systems allows the relatively homogeneous isotope signatures of high temperature fluids of various locations to be explained

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

chemical weathering processes in the great artesian basin evidence from lithium and silicon isotopes variations in lithium and silicon isotope ratios in groundwaters of the great artesian basin in australia and the causes of these variations have been explored the chemistries of li and si in groundwater are influenced by the dissolution of primary phases the formation of secondary minerals and the reaction of solid phases with dissolved constituents while isotopic variations are generated by uptake into clays which preferentially incorporate the light isotopes the lithium isotopic composition expressed as view the mathml source li7 of the groundwaters ranges from 9 to 16 16 and clearly reflects changes in aquifer conditions reaction transport modelling indicates that changes in li concentrations are principally controlled by the ratio of the weathering rate of primary minerals to the precipitation rate of secondary minerals whereas view the mathml source li7 is affected by the extent of isotope fractionation during secondary mineral formation which is dependent on mineralogy the patterns of groundwater si concentrations and view the mathml source si30 values versus flow distance suggest that si is at steady state in the aquifer the view the mathml source si30 value of most of the groundwater samples is close to 1 1 which is significantly lower than the view the mathml source si30 value of the reservoir rocks 0 0 since precipitation of clays preferentially removes the light si isotopes from solution the most plausible explanation for these low groundwater view the mathml source si30 values is addition of si by dissolution of isotopically light secondary minerals these data together with model calculations show that li isotopes are extremely sensitive to changes in the chemical and physical conditions in the aquifer whereas si is not importantly the model suggests that even in large aquifers with long fluid residence times where steady state would be expected to be reached the concentrations and isotopic fractionation of trace elements are not controlled by li adsorption the model developed here provides a basis for using li isotopes measured in groundwaters and surface waters to constrain weathering processes

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

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

temporal record of lithium in seawater a tracer for silicate weathering abstract this paper presents multi species records of the li ca ratio and li isotopic composition 7 li of planktonic foraminifera from the pacific and atlantic oceans for the past 18 ma the li ca record is corrected for interspecific offsets determined from recent holocene foraminifera interspecific offsets in 7 li are not significant despite different diagenetic histories the records produced from both oceans are remarkably consistent corrected planktonic foraminiferal li ca ratios range from 6 3 to 10 9 mol mol while planktonic foraminiferal 7 li ranges from 25 to 31 both records are interpreted in terms of long term changes in seawater li ca and 7 li enabling issues related to higher resolution variability in li ca and 7 li to be ignored by assuming that the hydrothermal flux of li into the oceans and the flux of li removed from the oceans during low temperature uptake by marine basalts and sediments have not changed significantly since 18 ma and using published records for the seawater calcium concentration the seawater li ca and 7 li records can be used to estimate global average river 7 li and li fluxes our records indicate that the river flux of dissolved li decreased between 16 and 8 ma while the 7 li value of the river input increased these data imply that both silicate weathering rates and weathering intensity decreased over this interval which may have been responsible for putative increases in levels of atmospheric co 2 in contrast the riverine flux of li has increased since 8 ma while its 7 li value has increased this implies that the silicate weathering rate has increased while weathering intensity has decreased since that time

behavior of lithium isotopes in the changjiang river system sources effects and response to weathering and erosion abstract lithium li concentrations and li isotopic compositions of the main channel of the changjiang river and its main tributaries were measured to better understand the geochemical behavior of li and its isotopic fractionation during weathering and erosion the li concentrations of the dissolved loads of the main channel range from 475 to 4570 nmol l and decrease from the upper reaches to the lower reaches values are clearly higher than those reported for many of the world s largest rivers samples with very high li concentrations are affected by the dissolution of evaporites in the headwater region the 7 li values of the particulate material has a narrow range 4 7 to 0 7 whereas the dissolved load has very variable 7 li 7 6 to 42 1 with values increasing from the upper reaches to the lower reaches after correction for contributions other than silicate weathering we show that the li isotopic compositions of the dissolved load reflect the balance between dissolution of primary minerals and preferential incorporation of the light isotope into secondary products of erosion which enrich the solution in 7 li the evolution of the isotopic composition from the upper reaches to the lower reaches is mainly controlled by the fraction of li incorporated adsorbed in onto secondary minerals and in fine by probably the difference in weathering regimes i e kinetic limited vs transport limited we also show that the magnitude of the apparent isotopic fractionation between the bedrock and dissolved li for example are not always only due to variation of the isotopic fractionation factor but might also be due to composition li content of the bedrock and mineralogical controls the composition of the eroded silicate crust estimated by a steady state mass balance reveals the important contribution of sedimentary rocks shales and highlights the effects of sedimentary recycling on the composition of the continental crust

behaviour of lithium and its isotopes during weathering in the mackenzie basin canada we report li isotopic compositions for river waters and suspended sediments of about 40 rivers sampled within the mackenzie river basin in northwestern canada the aim of this study is to characterize the behaviour of li and its isotopes during weathering at the scale of a large mixed lithology basin the mackenzie river waters display systematically heavier li isotopic compositions relative to source rocks and suspended sediments the range in delta li 7 is larger in dissolved load from 9 3 parts per thousand to 29 0 parts per thousand compared to suspended sediments from 1 7 parts per thousand to 3 2 parts per thousand which are not significantly different from delta li 7 values in bedrocks our study shows that dissolved li is essentially derived from the weathering of silicates and that its isotopic composition in the dissolved load is inversely correlated with its relative mobility when compared to na the highest enrichment of li 7 in the dissolved load is reported when li is not or poorly incorporated in secondary phases after its release into solution by mineral dissolution this counterintuitive observation is interpreted by the mixing of water types derived from two different weathering regimes producing different li isotopic compositions within the mackenzie river basin the incipient weathering regime characterizing the rocky mountains and the shield areas produces li 7 enrichment in the fluid phase that is most simply explained by the precipitation of oxyhydroxide phases fractionating li isotopes the second weathering regime is found in the lowland area and produces the lower delta li 7 waters but still enriched in li 7 compared to bedrocks and the most li depleted waters compared to na fractionation factors suggest that the incorporation of li in clay minerals is the mechanism that explains the isotopic composition of the lowland rivers the correlation of boron and lithium concentrations found in the dissolved load of the mackenzie rivers suggests that precipitation of clay minerals is favoured by the relatively high residence time of water in groundwater in the shield and rocky mountains li isotopes suggest that clay minerals are not forming and that secondary minerals with stronger affinity for li 7 appear although the weathering mechanisms operating in the mackenzie basin need to be characterized more precisely the li isotope data reported here clearly show the control of li isotopes by the weathering intensity the spatial diversity of weathering regimes resulting from a complex combination of factors such as topography geology climate and hydrology explains in fine the spatial distribution of li isotopic ratios in the large drainage basin of the mackenzie river there is no simple relationship between li isotopic composition and chemical denudation fluxes in the mackenzie river basin

the lithium isotopic composition of waters of the mono basin california mono lake a major closed basin alkaline salt lake in eastern california derives its water from a mixture of creeks and springs with the former providing in excess of 75 of the total the li isotopic composition of lake water has not varied significantly over a 4 year meromictic period 7li 19 5 springs are isotopically distinct groundwater springs and seeps carry water enriched in isotopically heavy li whereas thermal springs supply isotopically light 7li 50 of the li to the lake 2 the li budget is sensitively balanced on small thermal spring contributions 3 of the total spring inflow and 3 the residence time of li in the lake is 28 ka other great basin closed lakes have variable li isotopic compositions 7li from 16 7 to 23 7 all of which differ significantly from those of several major lakes and seawater homogeneously 32

temperature dependent isotopic fractionation of lithium between clinopyroxene and high pressure hydrous fluids the fractionation of lithium isotopes between synthetic spodumene as representative of li bearing clinopyroxene and cl and oh bearing aqueous fluids was experimentally determined between 500 and 900 c at 2 0 gpa in all the experiments 7li was preferentially partitioned into the fluid the fractionation is temperature dependent and approximated by the equation 7li clinopyroxene fluid 4 61 1 000 t k 2 48 r 2 0 86 significant li isotopic fractionation of about 1 0 exists even at high temperatures of 900 c using neutral and weakly basic fluids revealed that the amount of fractionation is not different the li isotopic fractionation between altered basalt and hot spring water 350 c in natural samples is in good agreement with our experimentally determined fractionation curve the data confirm earlier speculations drawn from the li isotopic record of dehydrated metamorphic rocks that fluids expelled from a dehydrating slab carry heavier li into the mantle wedge and that a light li component is introduced into the deeper mantle li and li isotopes are redistributed among wedge minerals as fluids travel across the wedge into hotter regions of arc magma production this modifies the li isotopic characteristics of slab derived fluids erasing their source memory and explains the absence of cross arc variations of li isotopes in arc basalts

lithium isotope evidence for enhanced weathering during oceanic anoxic event 2 the ocean anoxic event 2 oae2 about 93 5 million years ago was marked by high atmospheric co2 concentration rapid global warming and marine anoxia and euxinia the event lasted for about 440 000 years and led to habitat loss and mass extinction the marine anoxia is thought to be linked to enhanced biological productivity but it is unclear what triggered the increased production and what allowed the subsequent rapid climate recovery here we use lithium isotope measurements from carbonates spanning the interval including oae2 to assess the role of silicate weathering we find the lightest values of the li isotope ratio 7li during oae2 indicating high levels of weathering and therefore atmospheric co2 removal which we attribute to an enhanced hydrological cycle we use a geochemical model to simulate the evolution of 7li and the ca sr and os isotope tracers our simulations suggest a scenario in which the eruption of a large igneous province led to high atmospheric co2 concentrations and rapid global warming which initiated oae2 the simulated warming was accompanied by a roughly 200 000 year pulse of accelerated weathering of mafic silicate rocks which removed co2 from the atmosphere the weathering also delivered nutrients to the oceans that stimulated primary productivity we suggest that this process together with the burial of organic carbon allowed the rapid recovery and stabilization from the greenhouse state

the stable calcium isotopic composition of rivers draining basaltic catchments in iceland calcium isotopic compositions 44 42ca were measured in icelandic rivers draining a range of catchment types the 44 42ca values of the rivers ranged from 0 45 to 0 67 which in all cases was higher than the 44 42ca value of basaltic rock standards 0 42 0 03 a single explanation was unable to satisfactorily explain the 44 42ca values of all rivers rather it was found that the rivers formed three distinct groups based on the extent of glacial coverage in each catchment the ca isotopic composition of rivers draining catchments with less than 10 glacial cover could be explained by the mixing of water sources basalt derived solutes meltwater taken to represent meteorological precipitation inputs and hydrothermal water however fractionation of 44 42ca in these catchments cannot unequivocally be ruled out in catchments with greater than 22 glacial cover ca isotopic compositions could not be explained by a mixture of water sources and instead reflected a fractionation process most likely the precipitation of ca bearing secondary minerals or the adsorption ion exchange of ca onto mineral surfaces the fractionation factor for this process was calculated to be 0 9999 the third group of rivers with partially glaciated 10 21 catchments grouped with glaciated catchments with respect to their sr geochemistry and with non glaciated catchments with respect to their ca geochemistry the difference in the controls of ca isotope fractionation between glaciated and unglaciated catchments was attributed to different weathering regimes

boron and lithium isotopes as groundwater tracers a study at the fresh kills landfill staten island new york usa abstract a study was conducted at the fresh kills landfill staten island new york to investigate the use of b and li isotopes as tracers of mixing and flow in the groundwater environment four end member waters are present at the fresh kills freshwater seawater a geochemically distinct transitional groundwater that occurs in the zone of mixing between seawater and freshwater and landfill leachate the 11b and 6li values of end member waters are distinct and have isotopic compositions that reflect the solute sources freshwater 11b 30 6li 22 transition zone groundwaters 11b 20 6li 27 seawater 11b 40 to 75 6li 37 to 44 leachate 11b 10 6li not determined those wells influenced by seawater exhibited a clear chemical mixing trend with seawater contributions ranging from 3 to 85 well waters with a high percentage of seawater 30 had 11b values that were within 1 of the seawater value 40 whereas a trend of increasing 11b values 55 to 75 was observed for wells with a lower percentage of seawater

seismic attenuation tomography using the frequency shift method we present a method for estimating seismic attenuation based on frequency shift data in most natural materials seismic attenuation increases with frequency the high frequency components of the seismic signal are attenuated more rapidly than the low frequency components as waves propagate as a result the centroid of the signal s spectrum experiences a downshift during propagation under the assumption of a frequency independent q model this downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically the frequency shift method is applicable in any seismic survey geometry where the signal bandwidth is broad enough and the attenuation is high enough to cause noticeable losses of high frequencies during propagation in comparison to some other methods of estimating attenuation our frequency shift method is relatively insensitive to geometric spreading reflection and transmission effects source and receiver coupling and radiation patterns and instrument responses tests of crosswell attenuation tomography on 1 d and 2 d geological structures are presented

lithium isotope systematics in a forested granitic catchment strengbach vosges mountains france abstract over the last decade it has become apparent that li isotopes may be a good proxy to trace silicate weathering however the exact mechanisms which drive the behaviour of li isotopes in surface environments are not totally understood and there is a need to better calibrate and characterize this proxy in this study we analysed the li concentrations and isotopic compositions in the various surface reservoirs soils rocks waters and plants of a small forested granitic catchment located in the vosges mountains strengbach catchment france ohge http ohge u strasbg fr li fluxes were calculated in both soil profiles and at the basin scale and it was found that even in this forested basin atmospheric inputs and litter fall represented a minor flux compared to input derived from the weathering of rocks and soil minerals which together represent a minimum of 70 of dissolved li li isotope ratios in soil pore waters show large depth dependent variations average dissolved 7 li decreases from 1 1 to 14 4 between 0 and 30 cm but is 30 7 at 60 cm this range of li isotopic compositions is very large and it encompasses almost the entire range of terrestrial li isotope compositions that have been previously reported we interpret these variations to result from both the dissolution and precipitation of secondary phases large isotopic variations were also measured in the springs and stream waters with 7 li varying from 5 3 to 19 6 7 li increases from the top to the bottom of the basin and also covaries with discharge at the outlet these variations are interpreted to reflect isotopic fractionations occurring during secondary phase precipitation along the water pathway through the rocks we suggest that the dissolved 7 li increases with increasing residence time of waters through the rocks and so with increasing time of interaction between waters and solids a dissolution precipitation model was used to fit the dissolved li isotopic compositions it was found that the isotopic compositions of springs and stream waters are explicable by an isotopic fractionation of 5 to 14 best fit 10 8 in agreement with li incorporation into clay in soil solutions it was found that isotopic fractionation during secondary precipitation is larger at least 23 suggesting a major role for different secondary phases such as iron oxides that maybe incorporate li with a higher isotope fractionation

the effect of hydrothermal spring weathering processes and primary productivity on lithium isotopes lake myvatn iceland lithium isotopes are rapidly becoming one of the most useful tracers of silicate weathering processes but little is known on their behaviour in groundwaters and hydrothermal springs and how these sources might influence the weathering signal in surface waters this study presents lithium isotope compositions 7li for cold groundwaters 3 7 c and hydrothermal springs that were at geothermal temperatures 200 300 c but have cooled during transport 17 44 c both represent an important source of water and nutrients for lake myvatn iceland we also present a time series from the laxa river which is the single outflow from the lake the 7li values in the input springs to lake myvatn are highly variable 5 27 and correlate inversely with temperature and total dissolved solids these co variations imply that even in such waters the processes controlling 7li variations during weathering still operate that is the ratio of primary rock dissolution to secondary mineral formation where the latter preferentially incorporates 6li with a temperature dependent fractionation factor in high temperature geothermal waters 300 c secondary mineral formation is inhibited and has a low fractionation factor leading to little 7li fractionation even in waters that have cooled considerably over several months from their geothermal temperatures fractionation is still low and 7li values are similar to those reported from waters measured at 350 c in contrast cooler groundwaters promote relatively high proportions of clay formation which scavenge dissolved solids including 6li the time series on the laxa river the single outflow from lake myvatn shows little 7li variation with time over the 12 month sampling period 17 21 demonstrating that in contrast to tracers such as si isotopes li isotopes are unaffected by the significant seasonal phytoplankton blooms that occur in the lake thus these results clearly illustrate that li isotopes are ideally suited to constrain silicate weathering processes because fractionation by secondary mineral formation operates even when groundwater and hydrothermal inputs are significant and because li isotopes are demonstrably unaffected by phytoplankton or plant growth

lithium isotope fractionation in the ganges brahmaputra floodplain and implications for groundwater impact on seawater isotopic composition abstract lithium isotopes are a promising proxy for reconstructing past weathering processes but unraveling the seawater record requires a comprehensive understanding of the magnitude and isotopic composition of li fluxes to the oceans and of how these change over time little information is available on the role of floodplain sediments and groundwater systems in setting the li isotope signature of the dissolved flux delivered from the continents to the oceans here we investigate the li dissolved fluxes of river waters and groundwaters in the ganges brahmaputra floodplain the data suggest that a maximum of 3 1 10 8 and 1 5 10 8 moles li yr are carried to the bay of bengal by ganges brahmaputra rivers and groundwaters respectively the riverine flux has a significantly heavier li isotope composition average 7li 26 than the groundwater flux average 7li 16 and increases downstream across the floodplain 7li in both river waters and shallow groundwater can be explained by li scavenging by quaternary floodplain sediments following a rayleigh fractionation process with preferential removal of 6li on the other hand deep groundwaters 40 m contributing to submarine groundwater discharge to the bay of bengal are enriched in 6li at depth likely due to the dissolution of floodplain sediments releasing li with a light isotope composition similarly low 7li has been reported in other large sedimentary aquifers the deep groundwater values are close to the average isotope composition of the global li inputs to the ocean 15 so groundwater submarine discharge has only a minor influence on the assessment of the modern li isotope budget of the ocean our analysis further suggests that groundwater discharge of li has probably played at most a small and secondary role in past changes in the isotope composition of the total continental flux of li to the ocean

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

partial diagenetic overprint of late jurassic belemnites from new zealand implications for the preservation potential of δ7li values in calcite fossils the preservation potential and trends of alteration of many isotopic systems e g li mg ca that are measured in fossil carbonates are little explored yet extensive paleoenvironmental interpretations have been made on the basis of these records here we present a geochemical dataset for a late jurassic 153 ma belemnite belemnopsis sp from new zealand that has been partially overprinted by alteration we report the physical pathways and settings of alteration the resulting elemental and isotopic trends including 7li values and li ca ratios and assess whether remnants of the primary shell composition have been preserved or can be extrapolated from the measured values the 18o and 13c values as well as sr ca and mn ca ratios were analysed along two profiles in addition 6 samples were analysed for 87sr 86sr sr ca and mn ca ratios five samples from the same specimen and 2 from the surrounding sediment were analysed for 7li values li ca sr ca and mn ca ratios and are compared to results for 6 other late jurassic belemnite rostra belemnopsis sp andhibolithes sp from the same region the 87sr 86sr ratios are lower less radiogenic in the most altered part of the rostrum whereas 7li values become more positive with progressive alteration the direction and magnitude of the trends in the geochemical record indicate that one main phase of alteration that occurred in the late cretaceous caused most of the diagenetic signature in the calcite despite relatively deep burial down to 4 km and thus elevated temperatures this diagenetic signature has subsequently been preserved even for the highly mobile element lithium suggesting that primary lithium isotope values can be maintained over geological timescales at least in thick macrofossil shells our best 7li estimate for pristine late jurassic 155 148 ma belemnites is 27 1 which points to a late jurassic seawater 7li of 29 32 compatible with the modern value of 31

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

riverine li isotope fractionation in the amazon river basin controlled by the weathering regimes we report li isotope composition 7li 7li of river borne dissolved and solid material in the largest river system on earth the amazon river basin to characterize li isotope fractionation arl a continental scale the 7li 7li in the dissolved load 1 2 to 32 is fractionated toward heavy values compared to the inferred bedrock 1 to 5 and the suspended sediments 6 8 to 0 5 as a result of the preferential incorporation of 66li into secondary minerals during weathering despite having very contrasted weathering and erosion regimes both andean headwaters and lowland rivers share similar ranges of dissolved 7li 7li 1 2 to 18 correlations between dissolved 7li 7li and li na and li mg ratios suggest that the proportion of li incorporated in secondary minerals during weathering act as the main control on the 7lidiss 7lidiss across the entire amazon basin a batch steady state fractionation model for andean and lowland rivers satisfactorily reproduces these variations with a fractionation factor between weathering products and dissolved load sec dis sec dis of 0 983 two types of supply limited weathering regimes can be identified for the lowlands clearwaters with dominant incorporation of li in secondary minerals and black waters e g rio negro where dissolution of secondary minerals enhanced by organic matter produces low 7li 7li apart from the black waters the 7li 7li of andean and lowland rivers is negatively correlated to the denudation rates with the lowest 7li 7li corresponding to the rivers having the highest denudation rates in contrast the main tributaries draining both the andes and the lowlands have higher 7li 7li compared to other rivers we propose that part of the dissolved li derived from weathering in the andes is re incorporated in sediments during transfer of water and sediments in floodplains and that this results in an increase of the dissolved 7li 7li along the course of these rivers unlike other rivers the dissolved 7li 7li in the main tributaries is best described by a rayleigh fractionation model with a fractionation factor sec dis sec dis of 0 991 altogether the control imposed by residence time in the weathering zone and floodplain processes results in i a non linear correlation between dissolved 7li 7li and the weathering intensity defined as w d and ii a positive relationship between the dissolved li flux and the denudation rate these results have important implications for the understanding of past ocean 7li 7li and its use as a paleo weathering proxy

precise magnesium isotope measurements in core top planktic and benthic foraminifera 1 this study presents a new methodology to obtain highly precise measurements 0 1 of magnesium isotope ratios in very small samples of foraminiferal carbonate 40 50 g here this technique is used to examine mg isotopic variation among different species of core top foraminifera over a range of different ambient conditions despite the high degree of temperature control on the abundance of elemental mg incorporated into foraminiferal tests analyses of surface dwelling globigerinoides ruber and g sacculifer from five cores with associated sea surface temperatures ranging from 20 to 31 c show no significant temperature dependent variations in their mg isotope ratios analyses of different size fractions of g sacculifer show an increase in mg ca with test size but no variation of mg isotope ratio in all nine planktic and benthic species were analyzed all show identical mg isotope ratios with a mean of 26mg 4 72 apart from small differences in three species namely o universa g sacculifer which are both 0 4 lighter than the average and p obliquiloculata which is 0 4 heavier these results highlight the constancy of foraminiferal mg isotope ratios despite changing environmental conditions which dominate mg ca variation and arguably affect ca isotope fractionation this is an important observation which needs to be included in any model of foraminiferal calcification the insusceptibility of 26mg values to external parameters makes mg isotopes ideally suited to constraining past variations in the mg isotope budget of the oceans and the information this carries about the history of oceanic dolomitization continental weathering and hydrothermal behavior

introduction to the 1997 8 el nino atlas of oceanographic conditions along the west coast of north america 23 n 50 n abstract hydrographic data collected along the west coast of north america between january 1997 and january 1999 have been compiled into a web based atlas of the 1997 8 el nino event this paper discusses the organization of the atlas describes the data that were incorporated into the atlas and explains how vertical and horizontal distributions for the different properties were constructed examples of figures from the atlas are shown

the lithium boron and strontium isotopic systematics of groundwaters from an arid aquifer system implications for recharge and weathering processes abstract saline groundwaters are common to inland australia but their hydrochemical evolution and origin remain largely unknown the saline groundwaters in the alluvial aquifers of the darling river have previously been found to exhibit broad similarity in traditional hydrochemical and isotopic tracers by contrast in this study the trace element isotopes 7li 11b and 87sr 86sr have illuminated more complex hydrogeochemical processes in the same aquifer system this paper reports the first ever set of 7li values in any groundwater system in australia they varied from 5 8 to 16 2 with an average value of 9 7 n 19 in the alluvial aquifers of the darling river catchment the 11b values were all higher than seawater and close to some of the highest 11b values ever reported in the literature for a groundwater system 44 4 to 53 9 average 48 8 n 17 the 87sr 86sr ratios ranged from 0 708 to 0 713 with an average value of 0 709 n 19 the differing signatures in these trace element isotope values highlighted by discovery of the deeper older groundwater system with heavier li isotope values and higher 87sr 86sr is an important finding of this research simple mixing models between river water and saline groundwater cannot explain the observed variation in trace element isotopes hydrochemical evolution was found to be dependent on proximity to the darling river and depth varying degrees of li and b isotopic fractionation during water sediment interaction were interpreted to account for the evolution of the saline groundwaters the measurement of these trace element isotopes has permitted delineation of groundwater end members that would have otherwise not been identified in their absence an inaccurate interpretation of the hydrochemical evolution of these saline groundwaters would have been made this study highlights the importance of a multi tracer approach which includes trace element isotopes in resolving complex geochemical processes in groundwater in semi arid to arid zone environments

isotope fractionation by chemical diffusion between molten basalt and rhyolite abstract experimental diffusion couples were used to study chemical diffusion between molten rhyolite and basalt with special emphasis on the associated fractionation of calcium and lithium isotopes diffusion couples were made by juxtaposing firmly packed powders of a natural basalt suny morb and a natural rhyolite lake county obsidian and then annealing them in a piston cylinder apparatus for times ranging from 0 1 to 15 7 h temperatures of 1350 1450 c and pressures of 1 2 1 3 gpa profiles of the major elements and many trace elements were measured on the recovered quenched glasses the diffusivities of all elements except lithium were found to be remarkably similar while the diffusivity of lithium was two to three orders of magnitude larger than that of any of the other elements measured chemical diffusion of calcium from molten basalt into rhyolite was driven by a concentration ratio of 18 and produced a fractionation of 44ca from 40ca of about 6 because of the relatively low concentration of lithium in the natural starting materials a small amount of spodumene lialsi2o6 was added to the basalt in order to increase the concentration difference between basalt and rhyolite which was expected to increase the magnitude of diffusive isotopic fractionation of lithium the concentration ratio between li doped basalt and natural rhyolite was 15 and the resulting diffusion of lithium into the rhyolite fractionated 7li from 6li by about 40 we anticipate that several other major rock forming elements such as magnesium iron and potassium will also exhibit similarly larger isotopic fractionation whenever they diffuse between natural melts with sufficiently large differences in the abundance of these elements

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

lithium magnesium and silicon isotope behaviour accompanying weathering in a basaltic soil and pore water profile in iceland this study presents lithium magnesium and silicon isotope ratios from pore waters and soils from a well characterised histic andosol in south west iceland the soil 7li composition ranges between values slightly lighter than basalt to those that are much heavier 1 1 to 26 8 and are possibly influenced by sea salt in contrast precipitation corrected dissolved pore water 7li values 1 8 10 0 appear to reflect preferential adsorption of 6li onto secondary minerals where allophane supersaturation results in high 7li values conversely low 7li together with high li are probably due to destabilisation of allophane at low ph and thus desorption of li when compared to icelandic river values it would appear that soil pore waters reflect an intermediate isotope composition between basalts and river waters precipitation corrected pore water mg isotope ratios 26mg range between 0 46 and 0 12 and correlate with the amount of heavy mg adsorbed onto the soil exchange complex silicon isotopes in the soils are isotopically lighter 30si 0 91 to 0 53 than basalt 0 29 whereas pore waters are heavier 0 13 to 1 03 soil 30si values show a clear evolution between unweathered basalt and a hypothetical isotopically light endmember representing secondary minerals dissolved si isotopes also respond to chemical weathering processes and show that isotopically heavy 30si corresponds to high cation fluxes and high secondary mineral formation however comparison of all these proposed isotopic weathering tracers suggests that they respond differently to the same chemical weathering conditions this indicates a differing behaviour during secondary mineral neoformation or adsorption depending on whether the incorporated element is a major or trace constituent in turn this behaviour can potentially yield important information on secondary mineral behaviour and destabilisation and thus on the chemical weathering processes

lithium isotope geochemistry of sediments and hydrothermal fluids of the guaymas basin gulf of california abstract lithium isotopic compositions of hydrothermally altered sediments of deep sea drilling project dsdp site 477 477a as well as high temperature vent fluids of the guaymas basin have been determined to gain an understanding of lithium exchange during fluid sediment interaction at this sediment covered spreading center unaltered turbidite of the basin has a 6 li value of 10 5 7 heavier than fresh oceanic basalts contact metamorphism induced by a shallow sill intrusion results in a decrease of the lithium content of the adjacent sediments and a lighter isotopic value 8 below the sill sediments altered by a deep seated hydrothermal system show strong depletions in lithium while lithium isotopic compositions vary greatly ranging from 11 to 1 the shift to lighter composition is the result of preferential retention of the lighter isotope in recrystallized phases after destruction of the primary minerals the complexity of the isotope profile is attributed to inhomogeneity in mineral composition the tortuous pathway of fluids and the temperature effect on isotopic fractionation the range of lithium concentration and 6 li values for the vent fluids sampled in 1982 and 1985 overlaps with that of the sediment free mid ocean ridge systems the lack of a distinct expression of sediment input is explained in terms of a flow through system with continuous water recharge the observations on the natural system agree well with the results of laboratory hydrothermal experiments the experimental study demonstrates the importance of temperature pressure water rock ratio substrate composition and reaction time on the lithium isotopic composition of the reacted fluid high temperature authigenic phases do not seem to constitute an important sink for lithium and sediments of a hydrothermal system such as guaymas are a source of lithium to the ocean the ready mobility of lithium in the sediment under elevated temperature and pressure conditions also has important implications for lithium cycling in subduction zones

direct evidence of the feedback between climate and weathering long term climate moderation is commonly attributed to chemical weathering the higher the temperature and precipitation the faster the weathering rate weathering releases divalent cations to the

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

quantifying the impact of freshwater diatom productivity on silicon isotopes and silicon fluxes lake myvatn iceland diatom productivity in the oceans plays a crucial role in the carbon cycle but is strongly dependent upon the continental silicon supply however the relative influence of weathering and biological processes on continental si fluxes remains poorly constrained this study aims to quantify the impact of terrestrial diatom productivity on si fluxes to the ocean lake myvatn in north iceland is one of the most productive lakes in the northern hemisphere with nutrient rich waters almost uniquely sourced by groundwater the primary production is mainly controlled by diatom growth but also by cyanobacteria and the lake output is via a single river thereby providing a relatively simple natural laboratory to quantify the impact of diatom growth on the chemistry and si budget of lake waters silicon stable isotopes o 30si provide a tracer of this biocycling and have been measured in groundwater inputs to the lake and in time series monitoring of waters at the lake outlet the o 30si values at the outlet range from 0 70 0 08 to 1 42 0 06 which is significantly heavier than the groundwater input average cold and hot springs 0 50 0 17 2sd and consistent with the preferential uptake of light si isotopes by diatoms the o 30si value at the outlet increases by up to 0 9 in spring and autumn relative to the si isotope composition of the inflow these seasonal diatom blooms can be modeled by an open system of si uptake and affect si fluxes at the outlet of the lake by up to 79 or 53 integrated over the year in the summer a shift to lighter o 30si values is correlated with a higher ph which results in dissolution of diatoms releasing light si isotopes from mass balance this seasonal diatom dissolution affects si fluxes by up to 33 but is limited to 3 7 integrated over the year these results clearly illustrate that biological activity can have a significant impact on both isotope composition and elemental abundance of continental derived si they also demonstrate the ph dependency of diatom dissolution and or preservation which is likely to affect not only the continental si fluxes to the ocean but also the si recycling in the oceans themselves

dissolution of primary minerals in natural waters abstract the saturation state of olivine plagioclase clinopyroxene orthopyroxene fe ti oxides and apatite of variable composition has been assessed in natural waters in iceland with temperature ranging from 0 c to 300 c and in situ ph from below 5 to above 10 cold waters are undersaturated with respect to olivine orthopyroxene clinopyroxene and plagioclases indicating that all these minerals tend to dissolve under weathering conditions with increasing ph and temperature the waters approach saturation with pyroxene olivine and plagioclases also the degree of undersaturation of olivine and orthopyroxene decreases with increasing fe content of the minerals and fe rich olivine and orthopyroxene are stable between 50 c and 150 c whereas mg rich ones tend to dissolve natural waters in iceland are saturated with respect to pure albite when above 50 c they are on the other hand undersaturated with ca rich plagioclase up to 250 c where the waters reach saturation pure magnetite and hematite are stable at all temperatures with increasing titanium content the minerals become unstable and the waters are undersaturated with respect to pure ulvospinel at temperatures up to 300 c pure ilmenite is however close to saturation under weathering conditions but undersaturated above 200 c f apatite is close to saturation at all temperatures on the other hand undersaturation with respect to oh apatite is observed at all temperatures the weathering susceptibilities of primary minerals of basalt in icelandic waters in increasing order are mg olivine fe olivine ti rich magnetite ca plagioclase mg orthopyroxene fe orthopyroxene clinopyroxene na plagioclase f apatite ti rich ilmenite ti poor magnetite ti poor hematite

riverine behaviour of uranium and lithium isotopes in an actively glaciated basaltic terrain this study presents u and li isotope and major and trace element data for the dissolved load suspended particulates and bedload for icelandic rivers draining predominantly basaltic catchments physical erosion rates range from 920 to 2084 t km2 yr with the higher values associated with glacier fed rivers chemical erosion rates range from 45 to 91 t km2 yr with lower rates being associated with glacier fed rivers uranium activity ratios 234u 238u are close to secular equilibrium in the suspended and bedloads but all dissolved load samples show values greater than unity ranging from 1 13 to 2 41 the highest 234u 238u values are found in glacier fed rivers and can be attributed to recoil effects as grinding by glaciers locally enhances rates of physical weathering activity ratios in glacial rivers decrease with distance from the glacial source due to input from non glacial tributaries which have high levels of dissolved uranium and lower activity ratios in contrast in non glacial rivers uranium activity ratios increase with distance downstream due to continued weathering in soils and of bedrock the 7li value of the suspended load is always lower than that of the bedload due to preferential retention of 6li in secondary minerals during weathering in turn the 7li value of the dissolved load is always greater than that of the bedload ranging from 17 0 to 43 7 7li for the dissolved load decreases with increasing levels of dissolved silicon and the saturation index of secondary minerals which suggests that 7li decreases with increasing chemical weathering there is no correlation between 7li values and uranium activity ratios for the dissolved load for non glacial rivers but for glacier fed rivers there is an increase in 7li with increasing 234u 238u suggesting that where physical comminution of mineral grains by glaciers is high chemical weathering is suppressed and vice versa

calcium isotopes in the global biogeochemical ca cycle implications for development of a ca isotope proxy abstract at the earth s surface calcium ca is a critical element at a variety of scales it is soluble in natural waters a biological nutrient and a major constituent of the dominant mineral sink for carbon in the ocean caco3 there is a 4 variation in the ca isotopic composition 44ca 40ca expressed as 44ca of various ca reservoirs on earth suggesting ca isotopes as a promising tracer of ca cycling in both the present and the past fifteen years of high precision ca isotope measurements has revealed much about the behavior of ca isotopes in the earth surface environment but there remain fundamental questions concerning how ca isotopes are used to elucidate the marine and terrestrial ca cycles the current work presents a data compilation of over 70 published ca isotope studies totaling over 2600 measurements presented on a common delta scale that includes data on rivers and groundwater dust soils and soil pore fluids vegetation rainwater silicate minerals rocks and authigenic marine minerals carbonates sulfates and phosphates both modern and ancient the data compilation suggests that 1 there is a significant difference between carbonate 0 60 and silicate 44ca 0 94 2 riverine 44ca 0 88 does not simply reflect the compiled carbonate 44ca and 3 terrestrial vegetation exhibits the largest range of ca isotopic compositions 3 5 in the terrestrial setting we discuss these observations in the context of the global ca cycle exploring the extent to which seawater 44ca variability is feasible and how we can achieve accurate reconstructions of seawater 44ca over geologic time scales the current study presents simple mass balance models that quantify the leverage of inputs to change the ca isotopic composition of the ocean as this directly impacts the manner in which ca isotopes are interpreted although ca fractionates isotopically in the modern system during continental cycling the 44ca range of riverine inputs to the ocean is considerably smaller than the variability observed in putative seawater proxies such as nannofossil ooze and marine barite in the terrestrial realm plants exhibit a wide 44ca range and there is evidence that ca fluxes via biomass degradation are significant at the catchment scale we therefore assess the ability of the continental biosphere to influence riverine and consequently seawater 44ca a steady state biosphere has little leverage to alter riverine 44ca except in cases where the 44ca of the recycling flux is isotopically distinct from the 44ca of the uptake flux a non steady state biosphere can substantially impact both soil and riverine 44ca driving exchangeable ca either heavier or lighter depending on the magnitude of the recycling flux relative to the uptake flux based on estimates of the size of the global biosphere 1 5 1015 mol ca we suggest a decaying biosphere has the potential to impact riverine 44ca by tenths of a permil over time scales in the marine realm we evaluate the effect of a variable fractionation factor accompanying global removal of ca from the ocean on seawater 44ca and suggest methods by which such a mechanism can be recognized in the rock record experimental data suggest that there is considerable leverage