transient features of the erosion of shales in the mackenzie basin canada evidences from boron isotopes abstract in order to refine our knowledge of the mechanisms that drive the weathering reactions and the rate at which elements are exported out of a shale basin we have analyzed the boron concentrations and isotopic compositions of 24 rivers contributing to the mackenzie basin canada boron has been chosen to conduct this study because of the relatively high sensitivity of its isotopic system to water rock interactions after examination of the chemical composition of the mackenzie river samples boron appears to be regulated in the largest part by reactions involving silicate rocks the other contributions of rainwaters and the dissolution of carbonate and evaporite rocks can locally control the b budget but they remain of second importance at the regional to continental scales it also appears that dissolved b in rivers is regulated by input of groundwaters the comparison between the isotopic composition of the b being exported by rivers soluble and particulates and of its bulk source indicates that it is behaving out of steady state in most of the mackenzie tributaries and particularly in rivers draining the plain a model of transport reaction is proposed in this study which demonstrates that b is controlled by rapid ion exchanges at the mineral water interface and by long term dissolution of shales the responses of the model to tested conditions reveal that the b isotopic ratio of river waters is highly sensitive to hydrological conditions and to changes of the weathering rate of shales of its partition coefficient with adsorbing surface and of the water velocity the departure of the b geochemical cycle from a steady state is interpreted as the record of changes in the weathering regime in the mackenzie basin the temporal evolution of the b cycle modeled here implies an increase of the weathering rate of shales in the mackenzie basin and or an increase of the partition coefficient between soluble b and adsorbing surfaces it also appears that these changes are consistent with timescales of the recent deglaciation of the basin this study demonstrates that the present b fluxes are actually responding to past changes of the water rock interactions and that the weathering history is a key parameter to interpret the modern geochemical fluxes this conclusion is valid for any other element that has similar chemical properties with solid surfaces

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

environmental versus biomineralization controls on the intratest variation in the trace element composition of the planktonic foraminifera g inflata and g scitula the intratest variation in the chemical composition of globorotalia scitula and g inflata recovered from a sediment trap sample collected at 3000 m in the north atlantic in early spring has been investigated using laser ablation inductively coupled plasma mass spectrometry and electron microprobe mg ca li ca b ca mn ca and ba ca vary by up to a factor of 10 through the test walls water column properties including temperature and salinity are well documented at the trap site and the observed variations are too large to be explained by vertical migration of the foraminifera however changes in calcite precipitation rate crystal structure or the chemical composition of the internal calcification reservoir also cannot by themselves fully account for the pattern of intratest variability nevertheless the average mg ca for each chamber generally produces a mg ca temperature that matches that measured in the water column the exception is small morphologically distinct g inflata tests that have anomalously high mg ca

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

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

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

lithium isotopic systematics of a type granites and their mafic enclaves further constraints on the li isotopic composition of the continental crust article i nfo lithium concentrations and isotopic compositions of 39 a type granites and mafic enclaves from 11 plutons in northeast china and the north china craton are used to constrain their genesis and to characterize further the average composition of the continental crust lithium concentrations 2 8 to 80 ppm in 29 a type granites are slightly higher than those of average i type granites and lower than those of average s type granites reflecting source differences lithium isotopic compositions 7 li 1 8 to 6 9 of a type granites fall within the range of worldwide i type and s type granites by contrast 10 mafic enclaves have significantly higher li concentrations 32 to 179 ppm and less variation in li isotopic compositions 7 li

silicon isotope variations accompanying basalt weathering in iceland abstract this study presents the si isotope compositions of the dissolved phase of twenty rivers from across iceland the high resolution nu plasma 1700 mc icp ms was used to provide interference free 30 si 28 si ratios with an average limiting precision of 0 04 30 si the si isotope composition ranges from 0 08 to 1 46 30 si averaging 0 63 0 38 1 sd this is only slightly lighter than the recently reported mean of 0 84 0 19 for high precision measurements of swiss rivers but is significantly lighter than compositions reported for some other rivers the si isotope composition varies slightly with the amount of glacial cover which provides evidence that the continental si input to the oceans may be climatically controlled and thus likely to vary over glacial interglacial cycles after correction for the dissolution of trace amounts of calcite in one region a correlation is found between 30 si and ca si this is consistent with the measured basaltic composition and indicates isotopic fractionation during si removal from the dissolved phase by calculating the fraction of si that is removed from the dissolved phase into secondary phases it is possible to use the riverine si flux si denudation rate to calculate the initial dissolution rate of si within these catchments from this study we estimate that the total amount of si being dissolved by primary weathering of iceland is 3 million tons per yr however only 50 of this si is released into the rivers and contributes to denudation using the si isotope composition and the si fraction removed it is possible to model the si isotope fractionation as either a rayleigh type fractionation or a steady state system both yield similar fractionation factors of about 1 5 30 si implying only one underlying fractionation process that is controlled by external parameters such as runoff furthermore rivers that follow a steady state fractionation model are associated with higher si dissolution rates and lower 30 si values indicating an inverse relationship between weathering rates and dissolved riverine si isotope composition

northern latitude chemical weathering rates clues from the mackenzie river basin canada abstract the main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate more than 110 river water samples from the mackenzie river system northern canada have been sampled and analyzed for major and trace elements and sr isotopic ratios in the dissolved phase the three main morphological units are reflected in water chemistry rivers from the canadian shield are very dilute dominated by silicate weathering millot et al 2002 whereas the rivers of the rocky and mackenzie mountains as well as the rivers of the sedimentary interior platform are dominated by carbonate weathering and are so 4 rich compared to the rivers of the mackenzie and rocky mountains the rivers of the interior plains are organic silica and na rich and constitute the dominant input term to the mackenzie river mainstream rivers of the canadian shield area do not significantly contribute to the mackenzie river system using elemental ratios and sr isotopic ratios a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering carbonate weathering rates are mostly controlled by runoff which is higher in the mountainous part of the mackenzie basin these rates are comparable to the carbonate weathering rates of warmer areas of the world it is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering but its extent remains difficult to assess conversely to what was stated by edmond and huh 1997 overall silicate weathering rates in the mackenzie basin are low ranging from 0 13 to 4 3 tons km 2 yr na k ca mg and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates in contrast to what has been observed in other large river systems such as the amazon and ganges rivers silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters this contradicts the raymo hypothesis raymo and ruddiman 1992 isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains e g by glaciers and deposited in the plains rather the relatively high chemical denudation rates in the plains are attributed to lithology uncompacted shales high mechanical denudation and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation the three to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by moulton et al 2000 between unvegetated and vegetated watershed this study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors such as organic matter associated with northern watersheds are able to counteract the effect of temperature this acceleration by a factor of 4 in the plains is equivalent to a 6 c increase in temperature

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

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

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

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

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

lithium sorption to yucca mountain tuffs the li ion has been used as a reactive tracer in field tests performed in the saturated and unsaturated zone in volcanic tuffs at yucca mountain nevada lithium sorbs weakly by cation exchange and permits field scale testing of laboratory based predictions of reactive solute transport a series of laboratory studies show that li sorption is nonlinear and varies with lithology in the different horizons of the tuff in particular both li sorption and li specific cation exchange capacity vary as functions of tuff mineralogy and can be predicted given quantitative x ray diffraction data these results indicate that li sorption is dominated by clay and zeolite minerals and that sorption coefficients can be predicted given mineralogic analysis results

benthic foraminiferal li ca insights into cenozoic seawater carbonate saturation state benthic foraminiferal li ca decreases down a norwegian sea holothermal depth transect suggesting that the saturation state of seawater with respect to calcium carbonate influences foraminiferal li ca benthic foraminiferal li ca increases by 17 across the glaciation event in the early oligocene which likely reflects the increase in seawater saturation state evidenced by the concomitant deepening of the calcite compensation depth following the establishment of the antarctic ice sheet benthic foraminiferal li ca bears a remarkable resemblance to the estimated oxygen isotopic composition of seawater suggesting that during this time seawater saturation was largely controlled by glacioeustatically driven changes in shallow water carbonate accumulation rates

extreme lithium isotopic fractionation during continental weathering revealed in saprolites from south carolina the lithium concentration and isotopic composition of two saprolites developed on a granite and diabase dike from south carolina have been measured in order to document the behavior of lithium isotopes during continental weathering both saprolites show a general trend of decreasing d 7 li with increasing weathering intensity as measured by both bulk density and the chemical index of alteration cia the saprolite developed on the granite is isotopically lighter than the fresh igneous rock d 7 li 6 8x to 1 4x vs 2 3x respectively and is generally depleted in lithium these observations are consistent with leaching of lithium via rayleigh distillation during progressive weathering most saprolites fall on a rayleigh distillation curve corresponding to an apparent fractionation factor a of 0 997 however two samples have higher lithium contents than the fresh granite and thus point to additional processes affecting lithium in the saprolite e g sorption of lithium on to clay minerals the saprolite profile developed on the diabase dike shows highly variable d 7 li values ranging down to extremely light compositions 20x previous work has identified a chemical and mineralogical discontinuity at a depth of 2 m but our lithium data show a marked discontinuity at 6 m depth saprolite samples at or above 6 m depth are highly weathered cia 88 95 depleted in lithium having b50 of the original diabase lithium and isotopically light 10x to 20x vs 4 3x for the unweathered diabase most of the data are consistent with leaching of lithium via rayleigh distillation during intense weathering with apparent a values of 0 995 to 0 980 samples experiencing lower apparent a values tend to have higher kaolinite smectite ratios suggesting a mineralogical control on isotopic fractionation however the lightest sample at 20x is only slightly depleted in lithium and would require extremely low a values to explain via rayleigh distilliation this extreme composition remains enigmatic saprolite samples below 6 m have highly variable d 7 li 5x to 14x and importantly lithium concentrations that are higher than that of the unweathered diabase up to 2 4 times the concentration of the fresh diabase these deeper saprolites thus cannot be explained by rayleigh distillation a positive correlation between d 7 li and li

diffusion driven extreme lithium isotopic fractionation in country rocks of the tin mountain pegmatite abstract lithium concentrations and isotopic compositions in the country rocks amphibolites and schists of the tin mountain pegmatite show systematic changes with distance to the contact both li and 7 li decrease dramatically along a 10 m traverse from the pegmatite into amphibolite with li concentration decreasing from 471 to 68 ppm and 7 li decreasing from 7 6 to 19 9 rubidium and cs also decrease from the pegmatite contact into the country rock but only within the first 2 m of the contact after which their concentrations remain constant neither mixing between pegmatite fluids and amphibolite nor li isotope fractionation by rayleigh distillation during fluid infiltration is a likely explanation of these observations due to the extremely light isotopic composition required for the amphibolite end member in the mixing model 7 li 20 and the similarly extreme isotopic fractionation required in a rayleigh distillation model rather these variations are likely due to isotopic fractionation accompanying li diffusion from the li rich pegmatite li 450 to 730 ppm into amphibolites li 20 ppm the fact that other alkali element concentrations vary only within 2 m of the contact reflects the orders of magnitude faster diffusion of li relative to heavier elements quartz mica schists in contact with the pegmatite also show large variations in both li and 7 li as a function of distance from contact 1 wt to 70 ppm and 10 8 to 18 6 respectively but over a longer distance of 30 m lithium concentrations of the schist decrease from 1 wt adjacent to the contact to 70 ppm 300 m from the contact the latter is a typical concentration in metapelites the nature of the 7 li variations in the schists is different than in the amphibolites schists within the first 2 m of the contact have nearly identical 7 li of 10 which mimics that of the estimated bulk pegmatite 8 to 11 at a distance of 30 m the 7 li reaches the lowest value in the schists of 18 6 similar to the lowest amphibolite measured at a distance of 300 m the 7 li climbs back to 2 5 which is within the range of 7 li of other schists in the region and metapelites worldwide the behavior of li in the schists can also be modeled by li diffusion with the effective diffusion coefficient in the schist being 10 times greater than that in the amphibolite the effective diffusion coefficients of li in the amphibolite and schist are 2 orders of magnitude greater that those in minerals which implicates the importance of fluid assisted grain boundary diffusion over solid state diffusion in transporting li through these rocks

the formation of eastern mediterranean sapropels abstract sapropel formation in the eastern mediterranean is explained by an oceanographic approach it is suggested that sapropels are not only a consequence of eustatic sea level changes as earlier proposed by olausson a model which is widely accepted but rather a result of a very sensitive reaction of the eastern mediterranean to any small climatic amelioration present day aeration of the deep eastern mediterranean basin results from circulation of oxygen rich deep water originating mainly in the adriatic assuming present day conditions a climatic amelioration towards more humid and warmer conditions leading to an increase of the water temperature in the adriatic basin by 0 7 c or to a decrease of its salinity by only 0 2 will cause stratification of water masses and enhance sapropel formation

erosion timescales derived from u decay series measurements in rivers the relative importance of the factors influencing weathering of continental rocks has been a topic of debate for the last few decades the principal reasons are the lack of reliable proxies for chemical weathering and the difficulty in constraining actual physical denudation rates in this study 234u 238u 230th 238u and 226ra 238u were measured by tims and by mc icp ms in the dissolved and suspended loads of rivers from the mackenzie basin northwest territories canada the data show a complementary nature between 234u 238u 230th 238u in the dissolved and suspended loads while 226ra is characterized by a more complex behavior modeling of fractionation of u series nuclides in the particulate matter and the corresponding dissolved phase permits us to constrain the duration of chemical erosion for the suspended load currently sampled in the watershed 9 28 10 ka as well as the rates of release of u series nuclides the results also imply significant recent changes of chemical erosion rates and underline the impact of the last glaciation on current continental fluxes of northern latitude rivers such as the mackenzie river

in situ measurements of li isotopes in foraminifera in situ measurement of li isotope ratios in foraminifera has been developed using a cameca ims 1270 ion microprobe in situ 7li analyses have been performed in biogenic calcite of planktonic foraminifera from various locations results show that for west pacific mixed globigerinoides and globorotalia 22 s161 e the isotopic variability between tests and within a single test respectively is not significantly greater than estimated analytical uncertainty 1 5 mean 7li for several planktonic foraminifera tests corresponds to the seawater value strongly suggesting negligible li isotope fractionation relative to seawater as previously inferred by hall et al 2005 using thermo ionization mass spectrometer and multicollector inductively coupled plasma mass spectrometry techniques combined with scanning electron microscopy and ion microprobe imaging micron sized grains enriched in lithium silica and aluminum have been found in the foraminifera calcite matrix a simple mixing model shows that 0 3 2 wt of marine clays incorporated within the analyzed calcite would lower the foraminifera 7li value by 3 to 10 relative to the isotopic composition of the pure calcite by comparison no such grains have been detected in corals the presence of micron sized silicate grains embedded within the foraminifera calcite is consistent with the erez 2003 biomineralization model involving calcite precipitation from seawater vacuoles by contrast coral calcium carbonate is instead precipitated from ions which have been pumped or diffused through several membranes impermeable to micrometric grains ion microprobe in situ 7li measurements in biogenic calcite present new methods for investigating both biomineralization processes and the past record of the ocean composition by exploring geochemical variations at a scale that is smaller in space and in time

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

determination of the lithium isotopic composition of planktic foraminifera and its application as a paleo seawater proxy to investigate the potential use of li isotopes in foraminifera as a paleo lithium seawater proxy the li isotopic compositions of planktic foraminifera orbulina universa globigerinoides sacculifer globorotalia menardii a ndgloborotalia truncatulinoides were determined by thermal ionization mass spectrometry tims using phosphate as an ion source and multi collector inductively coupled plasma mass spectrometer mc icp ms rigorous cleaning procedures were employed to purify foraminiferal tests of detrital metal oxide and organic phases in single species analyses data generated using both methods reveal that d 7 li in planktic foraminifera resemble seawater such that the isotopic fractionation from the precipitation of foraminiferal calcite appears to be minimal down core measurements indicate that the d 7 li of o universa has remained constant over the last 44 ka in the north atlantic suggesting little change of li isotopic composition of ocean water during the last glaciation consistent with the long mean residence time of li results suggest that planktic foraminifera may provide a reliable record of the lithium isotopic composition of ocean water in the past the first measurements of seawater d 7 li from the indian ocean average 33 0f1 2x 2r throughout the water column this value is within error of values previously reported for the atlantic and pacific oceans as is expected based on the long mean residence time of li in the ocean there is no evidence for a significant decrease in li cl ratios as reported by some workers with indian ocean waters averaging 9 10f0 11 ag g d 2005 elsevier b v all rights reserved

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

parallel magnetic fabrics in metamorphic granitoid and sedimentary rocks of the branisko and cierna hora mountains e slovakia and their tectonometamorphic control abstract the magnetic anisotropy of rocks from the branisko and cierna hora mountains west carpathians was investigated and the ferromagnetic and paramagnetic components were separated and found to be roughly coaxial the magnetic fabrics in metamorphic granitoid and sedimentary rocks display very similar patterns of principal susceptibilities metamorphites underwent a polyphase prograde and retrograde metamorphis granitoids were metamorphosed retrogressively and sedimentary rocks suffered a very weak prograde metamorphism retrogressive and progressive alpine metamorphism and the formation of magnetic anisotropy took place simultaneously before during and after the emplacement of the central west carpathian nappes

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

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

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

downstream and seasonal changes of lithium isotope ratios in the ganges brahmaputra river system the li isotope ratio 7li is expected to be a useful tracer of silicate weathering in river and groundwater systems which is an important contributor to the seawater compositional changes that accompany the evolution of the earth s surface environment to obtain accurate estimates of continental li fluxes to the ocean we determined 7li values of dissolved li in the lower ganges brahmaputra river system in both the dry and rainy seasons and in deep groundwater in the bengal basin dissolved li and 7li values in the lower reaches of the rivers 0 04 0 66 mol kg 1 and 19 1 to 34 2 respectively were predominantly derived from silicate weathering as is the case in the upper parts of these rivers we observed large changes in 7li over a distance of more than 1000 km downstream that were due mainly to rayleigh type removal of li from river water extremely high li concentrations 1 15 1 67 mol kg 1 and low 7li values 5 1 to 11 6 in groundwater samples indicate congruent isotope leaching and dissolution of silicate minerals in the deep aquifer where the water residence time is long in the rainy season li concentrations and 7li values were lower than in the dry season owing to the shorter residence time of river water and the substantial input of local subsurface flow through lowland alluvium these results suggest that accurate estimation of continental li fluxes to the ocean should take account of downstream and seasonal changes as well as aquifer depth variations in 7li values

behavior of lithium and its isotopes during weathering of hawaiian basalt 1 we examined the pedogenic behavior of lithium li and its isotopes in hawaii by sampling same age lava flows under mean annual rainfall ranging from 18 to 300 cm lithium concentrations in these soils vary from 1 to 29 ppm whereas na k and ca are completely leached from the soil at the most humid and severely weathered site li mg si and al show significant retention due to their association with secondary clay minerals in these soils allochthonous li delivered in marine and mineral aerosol mixes with basalt derived li modifying the isotopic composition of the li pool the ability of soil to retain li is related to its effective cation exchange capacity which in turn is governed by rainfall and leaching intensity and their resulting effect on mineralogy lithium isotope ratios have a large range 7li of 0 4 to 14 well beyond the intershield or temporal variation of the lavas of hawaiian volcanoes 2 5 to 5 7 the most unweathered samples have 7li 5 6 comparable to that of mauna kea and mauna loa lavas the li concentrations and isotope ratios together suggest that in arid to subhumid sites there is a net addition of isotopically heavier lithium from marine aerosol but that under greater rainfall there is a net loss of li and isotopically light li is preferentially retained thus during incongruent weathering of primary minerals li especially 6li is adsorbed and sequestered by the clay mineral fraction of high cation exchange capacity soils in drier regions but lost from highly weathered low cation exchange capacity acidic soils in the wetter regions

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 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