in situ measurements of calcium isotopes by ion microprobe in carbonates and application to foraminifera abstract an analytical procedure has been developed for the in situ measurement of calcium isotope composition of carbonates with a spatial resolution of 15 20 m on a cameca ims 1270 ion microprobe by using two faraday cup detectors the 40 ca and 44 ca can be measured simultaneously improving the internal reproducibility instrumental mass fractionation imf of calcium isotopes was observed to be independent of primary ion beam intensity and of the mg content of the carbonate but can depend on vacuum conditions three calcite reference materials were used in this study ens 0 mex and bret 105e and their 44 ca values relative to nist915a were reproducible within a typical 1 standard deviation of 0 15 this analytical procedure was applied to planktonic foraminifera globorotalia inflata dated at 2 8 ma from shatsky rise odp leg 198 the range of measured 44 ca within a single test is 1 7 this intratest variation can be attributed to several processes such as temperature variation ontogenic effects or differences between primary and secondary calcite i e calcite precipitated by different biomineralization processes despite this intratest variation the averages 44 ca for each foraminifer are similar and are in agreement with published 44 ca values measured for this age this study shows that in situ 44 ca measurements in tests of foraminifera are an appropriate tool for investigating biomineralization processes

environmental and biological controls on mg and li in deep sea scleractinian corals abstract deep sea scleractinian corals precipitate aragonite skeletons that provide valuable archives of past ocean conditions during calcification biological mediation causes variability in trace metal incorporation and isotopic ratios of the aragonite such that signals caused by environmental controls can be overwhelmed this complicates the interpretation of geochemical proxies used for paleo reconstructions in this study we examine the environmental controls on the mg li ratio of 34 individuals from seven genera of deep sea scleractinian corals desmophyllum balanophyllia caryophyllia enallopsammia flabellum trochocyanthus and lophelia in addition we examine the microscale distributions of mg and li in desmophyllum and balanophyllia using laser ablation inductively coupled plasma mass spectrometry la icp ms both mg ca and li ca ratios increased by more than a factor of two in the center of calcification regions compared to the outer fibrous regions of the coral skeleton as a result replicate 10 mg subsamples of coral show less variability in the mg li ratio than mg ca microscale mg and li results are consistent with rayleigh type incorporation of trace metals with additional processes dominating the composition within centers of calcification comparison of mg li to seawater properties near the site of collection shows that the ratio is not controlled by either carbonate ion or salinity it appears that temperature is the major control on the mg li ratio for all 34 samples the temperature correlation r2 0 62 is significantly better than for mg ca r2 0 06 for corals of the family caryophyllidae the r2 value increases to 0 82 with the exclusion of one sample that was observed to have an altered chalky texture despite this excellent correlation the scatter in the data suggests that the mg li ratio of deep sea corals cannot be used to reconstruct temperature to better than approximately 1 6 c without better temperature control and additional calibration points on modern coral samples

controlling factors of ca isotope fractionation in scleractinian corals evaluated by temperature ph and light controlled culture experiments abstract in this study the 44ca 40ca ratios of porites australiensis grown under three different culture experiments composed of temperature ph and light controlled culture experiments are measured the temperature dependent isotope fractionation of 0 02 c deduced from this study is similar to inorganic aragonite but the degree of isotope fractionation is about 0 4 offset in corals these observations agree with earlier results on different coral species suggesting ca isotope fractionation during ca transmembrane transport in corals while in cultured corals a significant temperature dependence of 44ca is observed the relationships between calcium isotope fractionation and ph as well as light intensity are negligible therefore variation of 44ca in porites corals is mainly controlled by temperature a combination of 44ca and sr ca of corals in temperature controlled experiments cannot be explained by rayleigh type fractionation directly from a fluid which is seawater like in terms of 44ca and sr ca through coral specific biomineralization processes overall mean 44ca of scleractinian corals including previous studies are different from biogenic aragonites secreted by sclerosponges and pteropods but are comparable with those of bivalves as well as calcitic coccolithophores and foraminifers these findings are important for better understanding biomineralization in corals and in order to constrain the ca isotopic composition of oceanic ca sinks in response to climate changes and associated with shifts of calcite and aragonite seas

origin of strontium and calcium in pedogenic needle fibre calcite nfc abstract strontium sr and calcium ca isotopic compositions and sr ca ratios have been analysed in different fractions of pedogenic needle fibre calcite nfc from the swiss jura mountains villiers neuch tel switzerland in order to determine their ca sources and to investigate the potential role of fungi in the origin of nfc 87sr 86sr ratios have been measured to trace the ca trapped within different pedogenic carbonate this ratio was compared for previously identified microscopic morphological groups of nfc the bulk soil fine earth

constraining the cause of the end guadalupian extinction with coupled records of carbon and calcium isotopes abstract a negative c 13 excursion in carbonate sediments near the guadalupian lopingian middle late permian boundary has been interpreted to have resulted from a large carbon cycle disturbance during the end guadalupian extinction event ca 260 ma however the carbon isotope data alone are insufficient to uniquely determine the type and magnitude of perturbation to the global carbon cycle calcium isotopes can be used to further constrain the cause of a carbon isotope excursion because the carbon and calcium cycles are coupled via caco3 burial in this study we present coupled carbon and calcium isotope records from three guadalupian lopingian g l sections in china penglaitan and chaotian and turkey koserelik tepe the c 13 and ca 44 40 records differ among our studied sections and do not co vary in the same manner no section shows c 13 and ca 44 40 changes consistent with massive rapid volcanic co2 emissions or methane clathrate destabilization additionally many sections with large 3 changes in c 13 exhibit o 18 evidence for diagenetic alteration only one section exhibits a large excursion in the ca 44 40 of limestone but the absence of a similar excursion in the ca 44 40 of conodont apatite suggests that the limestone excursion reflects a mineralogical control rather than a perturbation to the global calcium cycle hence we interpret the large isotopic changes observed in some sections to have resulted from local burial conditions or diagenetic effects rather than from a large carbon and calcium cycle disturbance perturbations to the global carbon and calcium cycles across the g l transition were much less intense than the disturbances that occurred across the subsequent permian triassic boundary this finding is consistent with the much smaller magnitude of the end guadalupian extinction relative to the end permian

a simple biomineralization model to explain li mg and sr incorporation into aragonitic foraminifera and corals abstract in contrast to li ca and mg ca li mg is strongly anticorrelated with temperature in aragonites precipitated by the benthic foraminifer hoeglundina elegans and a wide range of scleractinian coral taxa we propose a simple conceptual model of biomineralization that explains this pattern and is consistent with available abiotic aragonite partition coefficients under this model the organism actively modifies seawater within its calcification pool by raising its ca2 using a pump that strongly discriminates against both li and mg2 rayleigh fractionation during calcification effectively reverses this process removing ca2 while leaving most li and mg2 behind in the calcifying fluid the net effect of these two processes is that li mg in the calcifying fluid remains very close to the seawater value and temperature dependent abiotic partition coefficients are expressed in the biogenic aragonite li mg ratio we further show that coral sr ca is consistent with this model if the ca2 pump barely discriminates against sr2 in h elegans the covariation of sr ca and mg ca requires either that the pump more strongly discriminates against sr2 or that cation incorporation is affected by aragonite precipitation rate via the mechanism of surface entrapment in either case li mg is minimally affected by such vital effects which plague other elemental ratio paleotemperature proxies

biomineralization in perforate foraminifera in this paper we review the current understanding of biomineralization in perforate foraminifera ideas on the mechanisms responsible for the flux of ca2 and inorganic carbon from seawater into the test were originally based on light and electron microscopic observations of calcifying foraminifera from the 1980s onward tracer experiments fluorescent microscopy and high resolution test geochemical analysis have added to existing calcification models despite recent insights no general consensus on the physiological basis of foraminiferal biomineralization exists current models include seawater vacuolization transmembrane ion transport involvement of organic matrices and or ph regulation although the magnitude of these controls remain to be quantified disagreement between currently available models may be caused by the use of different foraminiferal species as subject for biomineralization experiments and or lack of a more systematic approach to study dis similarities between taxa in order to understand foraminiferal controls on element incorporation and isotope fractionation and thereby improve the value of foraminifera as paleoceanographic proxies it is necessary to identify key processes in foraminiferal biomineralization and formulate hypotheses regarding the involved physiological pathways to provide directions for future research

calcium isotope ratios in calcitic tests of benthic foraminifers abstract we analysed ca isotope ratios of the infaunal foraminiferal species cassidulina laevigata elphidium spp gyroidinoides spp and uvigerina peregrina as well as the epifaunal cibicidoides wuellerstorfi over a depth temperature gradient the calcium isotope ratios of the benthic foraminifers tests show a distinct anomaly around 4 c this anomaly is observed in both epi and infaunal species but there are also characteristic differences between both the 44 40 ca characteristics of benthic foraminifers may be explained by the interference of temperature and carbonate chemistry of the fluid on ca isotope fractionation we suggest that ca isotope composition of benthic foraminifer tests is dominantly controlled by temperature at temperatures higher than 5 c while in the temperature range below 5 c calcite saturation cc becomes an increasingly important controlling factor due to the non linear shape of the cc 44 40 ca relation of actively transported calcium the potential applicability of ca isotope ratios in benthic foraminifers for reconstruction of either temperatures or 44 40 ca sw is limited by the complex fractionation pattern below 5 c however due to the minor temperature dependence in the temperature range above 5 c benthic foraminifers might provide a possible alternative archive for 44 ca sw avoiding some uncertainties associated with planktic records relocation habitat calcification depth short time climate variability as long as a defined bottom water temperature above 5 c can be secured

temperature dependence of δ 7 li δ 44 ca and li ca during growth of calcium carbonate abstract lithium and calcium isotope ratios together with the li ca element ratio have been measured in calcites precipitated inorganically at temperatures ranging from 5 to 30 c and on seasonal growth bands from a coral these measurements indicate the potential uses of these three environmental proxies carbonate li isotopes are lighter than the solution from which they grow probably due to equilibrium fractionation this fractionation is not significantly influenced by temperature and because li is not involved in any known biological process this suggests that carbonates will provide a recorder for the past li isotope composition of natural waters and hence for past weathering conditions as has been observed previously for inorganic aragonite the ca isotopes in inorganic calcite are lighter than the growth solution and are only weakly dependent on temperature this confirms that the temperature dependence observed in some species of foraminifera geochem geophys geosyst 1 2001 reflects additional isotope fractionation due to biological processes during mineralization ca isotopes may therefore provide a powerful tool with which to investigate the processes of biomineralization finally li ca ratios in inorganic and biogenic carbonates increase as temperatures decrease with a sensitivity of 4 per c this temperature dependence of li ca may prove useful to assess past temperatures in cold environments such as the deep ocean

significant increases in global weathering during oceanic anoxic events 1a and 2 indicated by calcium isotopes abstract calcium isotope ratios 44 42ca were measured in carbonate rich sedimentary sections deposited during oceanic anoxic events 1a early aptian and 2 cenomanian turonian in sections from resolution guyot mid pacific mountains coppitella italy and the english chalk at eastbourne and south ferriby uk a negative excursion in 44 42ca of 0 20 and 0 10 is observed for the two events these 44 42ca excursions occur at the same stratigraphic level as the carbon isotope excursions that define the events but do not correlate with evidence for carbonate dissolution or lithological changes diagenetic and temperature effects on the calcium isotope ratios can be discounted leaving changes in global seawater composition as the most probable explanation for 44 42ca changes in four different carbonate sections an oceanic box model with coupled strontium and calcium isotope systems indicates that a global weathering increase is likely to be the dominant driver of transient excursions in calcium isotope ratios the model suggests that contributions from hydrothermal activity and carbonate dissolution are too small and short lived to affect the oceanic calcium reservoir measurably a modelled increase in weathering flux on the order of three times the modern flux combined with increased hydrothermal activity due to formation of the ontong java plateau oae1a and caribbean plateau oae2 can produce trends in both calcium and strontium isotopes that match the signals recorded in the carbonate sections this study presents the first major element record of a weathering response to oceanic anoxic events

assessing the biomineralization processes in the shell layers of modern brachiopods from oxygen isotopic composition and elemental ratios implications for their use as paleoenvironmental proxies abstract fossil brachiopod shells are often used as valuable archives to reconstruct paleoenvironmental conditions in deep time however biomineralization processes can impact their fidelity as geochemical proxies brachiopod shells comprise an outer primary layer a secondary fibrous layer and sometimes a tertiary columnar layer therefore it is essential to assess the potential effects of the biomineralization processes in each of the different shell microstructures of modern brachiopods this study analyses the oxygen isotopic composition together with li ca na ca mg ca and sr ca data at high spatial 20 50 m resolution in seven modern brachiopod species focusing on differences between the primary secondary and tertiary layers in all studied species 18o values of the outer primary layer are consistently out of equilibrium with seawater also this shell layer is enriched in li na mg and sr contrary to the primary layer the innermost secondary layer is near or at oxygen isotopic and elemental equilibrium with ambient seawater the columnar tertiary shell layer if present has the least variable and the heaviest oxygen isotopic composition within the range of equilibrium values with seawater this tertiary layer however is depleted in minor and trace elements relative to the other shell layers thus the tertiary layer is more suitable for oxygen isotopic studies whereas the innermost secondary layer of the most mature parts of the shell is the best target in two layered shells while we do not observe any clear interspecific relationships between mg ca and sr ca ratios on one hand and environmental parameters such as temperature salinity and ph on the other hand there is a positive interspecific relationship between na ca and salinity and a negative interspecific relationship between li ca and temperature suggesting their potential use as proxies of physicochemical parameters of seawater

controls on calcium isotope fractionation in sedimentary porewaters abstract the calcium isotopic composition of porewaters and authigenic carbonates in the anoxic sediments of a convergent continental margin drilled during ocean drilling program odp provides first insight into the different processes that control ca geochemistry in clastic marine organic rich sedimentary environments in 4 sites drilled during leg 204 at hydrate ridge cascadia margin offshore oregon usa sulfate is consumed during anaerobic oxidation of methane and of organic matter via sulfate reduction within the upper meters of the sedimentary section these reactions promote the precipitation of authigenic carbonates through the generation of bicarbonate which is reflected in a pronounced decrease in calcium concentration although ca isotope fractionation is observed during carbonate precipitation ca concentration in the pore fluids from odp leg 204 is decoupled from ca isotopy which seems to be mainly controlled by the release of light ca isotopes that completely overprint the carbonate formation effect different processes such as the release of organically bound ca ion exchange and ion pair formation may be responsible for the released light ca deeper within the sedimentary section additional processes such as ash alteration influence the ca isotopic composition of the porewater two sites drilled into the deeper core of the accretionary prism reveal the nature of fluids which have reacted with the oceanic basement these deep fluids are characterized by relatively high ca concentrations and low 44 40ca ratios

the influence of seawater carbonate chemistry mineralogy and diagenesis on calcium isotope variations in lower middle triassic carbonate rocks abstract the geological calcium cycle is linked to the geological carbon cycle through the weathering and burial of carbonate rocks as a result calcium ca isotope ratios 44ca 40ca expressed as 44 40ca can help to constrain ancient carbon cycle dynamics if ca cycle behavior can be reconstructed however the 44 40ca of carbonate rocks is influenced not only by the 44 40ca of seawater but also by diagenetic processes and fractionation associated with carbonate precipitation in this study we investigate the dominant controls on carbonate 44 40ca in upper permian to middle triassic limestones ca 253 to 244 ma from south china and turkey this time interval is ideal for assessing controls on ca isotope ratios in carbonate rocks because fluctuations in seawater 44 40ca may be expected based on several large carbon isotope 13c excursions ranging from 2 to 8 parallel negative 13c and 44 40ca excursions were previously identified across the end permian extinction horizon here we find a second negative excursion in 44 40ca of 0 2 within lower triassic strata in both south china and turkey however this excursion is not synchronous between regions and thus cannot be interpreted to reflect secular change in the 44 40ca of global seawater additionally 44 40ca values from turkey are consistently 0 3 lower than contemporaneous samples from south china providing further support for local or regional influences by measuring 44 40ca and sr concentrations sr in two stratigraphic sections located at opposite margins of the paleo tethys ocean we can determine whether the data represent global conditions e g secular variations in the 44 40ca of seawater versus local controls e g original mineralogy or diagenetic alteration the sr and 44 40ca data from this study are best described statistically by a log linear correlation that also exists in many previously published datasets of various geological ages using a model of early marine diagenetic water rock interaction we illustrate that this general correlation can be explained by the chemical evolution of bulk carbonate sediment samples with different initial mineralogical compositions that subsequently underwent recrystallization although early diagenetic resetting and carbonate mineralogy strongly influence the carbonate 44 40ca values the relationship between sr and 44 40ca holds potential for reconstructing first order secular changes in seawater 44 40ca composition

paired li ca and δ18o peaks in bivalve shells from the gulf of panama mark seasonal coastal upwelling abstract paired lithium to calcium li cashell and oxygen isotope 18oshell ratios were measured in four aragonitic megapitaria aurantiaca bivalve shells from the tropical eastern pacific and evaluated with respect to their linkage to seasonal coastal upwelling the li cashell and 18oshell of two specimens from the upwelling dominated gulf of panama are positively correlated and consistently reveal large seasonal variations of up to 300 mol mol and 3 respectively the li cashell and 18oshell of two shells from the adjacent non upwelling gulf of chiriqui are not correlated and show a reduced seasonal variability rarely exceeding 20 mol mol and 1 0 respectively in some m aurantiaca specimens the li cashell shows a weak positive correlation with growth increment width indicating that physiological growth rate effects might in part control the background li cashell unambiguous seasonal 18oshell signals used for a precise chronology for a live collected specimen from the gulf of panama imply that distinct parallel peaks in li cashell and 18oshell mark the cold and highly productive coastal upwelling season during february to april a comparison with environmental data reveals a negative correlation between li cashell and water temperature and a strong positive correlation between li cashell and chlorophyll a in the gulf of panama while a causal link between li cashell and temperature remains uncertain we argue that li cashell peaks in m aurantiaca are consistent with the concept of an incorporation of additional li provided by diatom dominated phytoplankton blooms during coastal upwelling our findings suggest that li cashell in m aurantiaca may serve as a new proxy for seasonal coastal upwelling the potential of which should be tested for other mollusk species and upwelling regions

evolution of the oceanic calcium cycle during the late mesozoic evidence from δ44 40ca of marine skeletal carbonates abstract the ca isotope compositions of 37 late mesozoic skeletal carbonates belemnites and brachiopods from the tethyan realm were analyzed by thermal tims and plasma mc icp ms ionization mass spectrometry a poor correlation between 44 40 ca and 18 o values of belemnites suggests only a weak temperature dependency for the ca isotope composition of belemnites likely less than 0 02 c the 44 40 ca record of belemnites was therefore used to reconstruct the ca isotope composition of paleo seawater 44 40 ca sw based on an experimentally determined fractionation factor between seawater ca and belemnite calcite cc sw of 0 9986 the inferred 44 40 ca sw record with an average stratigraphic resolution of 1 ma shows systematic temporal variation of 0 5 with the middle late jurassic 154 ma minimum of 1 4 and a subsequent general increase to the early cretaceous 124 ma maximum of 1 9 the global nature of the 44 40 ca sw record is supported by identical ca isotope compositions of coeval kimmeridgian belemnites collected from two distinct paleogeographic regions the southern new zealand and northern germany margin of the tethys ocean the observed late mesozoic 44 40 ca sw record was simulated using a simple ca isotope mass balance model and the results indicate that the variation in 44 40 ca sw record can be explained by changes in oceanic input fluxes of ca that were independent of the carbonate ion fluxes such as the hydrothermal ca flux or the release of ca to the oceans via dolomitization of marine carbonates

otolith microchemistry of modern versus well dated ancient naked carp gymnocypris przewalskii implication for water evolution of lake qinghai there is ongoing debate over how the water level and composition of the water in lake qinghai changed in the past and might change in future this study of the microchemistry of otoliths from ancient naked carp explores the chemistry of a relict lake isolated from lake qinghai during the little ice age lia a close correlation between the ages measured on fish bone and otoliths by ams 14c and by optically stimulated luminescence on overlying sediments confirms a high water level in lake qinghai before 680 300 years ago the contrasting compositions of the ancient otoliths relative to modern otoliths and waters indicate that the relict lake became enriched in 18o mg li b and to a lesser extent ba but depleted in 13c owing to strong evaporation authigenic carbonates precipitation micro organism activity and less fresh water input after it was isolated if there were long term fresh water input however a reverse trend might occur the most important observation is that because the waters have been supersaturated with respect to carbonates authigenic carbonate precipitation would result in low but consistent sr ca ratios in the lakes as recorded by both the ancient and modern otoliths the geochemical records of ancient versus modern biogenic carbonates provide insights into the long term hydroclimatic evolution processes of an inland water body

influences on the fractionation of calcium isotopes in planktonic foraminifera for paleoceanographic studies it is important to understand the processes that influence the calcium ca isotopic composition of foraminiferal calcite tests preserved in the sediment record seven species of planktonic foraminifera from coretop sediments collectively exhibited a ca temperature dependent fractionation of 0 013 per c thisisin agreement with previously published estimatesformostspecies ofplanktonic foraminifera as well asbiogenicandinorganiccalciteandaragonite fourspeciesofplanktonicforaminiferacollectedfromasedimenttrapshowedaconsiderableamountof scatterandnoconsistenttemperaturedependentfractionation analyzedsizefractionsofcoretopsamplesshownosignificantrelationshipwith 44 40 ca however preliminary results suggest that the symbiotic and spinose foraminifera globigerinoides sacculifer might exhibit a relationship between test size and 44 40 ca a one box model in which ca isotopes are allowed to fractionate by rayleigh distillation from a biomineralization reservoir internal pool was used to constrain the isotopic composition of the original biomineralization ca reservoir assuming around 85 of the ca reservoir is precipitatedandthefractionationfactorduringprecipitationis0 9985 0 00002 t c toexplaintheforaminiferalcaisotopedata thismodelindicates

the absence of lithium isotope fractionation during basalt differentiation new measurements by multicollector sector icp ms we report measurements of the isotopic composition of lithium in basalts using a multicollector magnetic sector plasma source mass spectrometer mc icp ms this is the first application of this analytical technique to li isotope determination external precision of multiple replicate and duplicate measurements for a variety of sample types averages 1 1 2 population the method allows for the rapid 8 min sample analysis of small samples 40 ng li relative to commonly used thermal ionization methods the technique has been applied to a suite of samples from kilauea iki lava lake hawaii the samples range from olivine rich cumulitic lava to sio2 and k2o enriched differentiated liquids and have 7li per mil deviation of sample 7li 6li relative to the l svec standard of 3 0 to 4 8 the data indicate a lack of per mil level li isotope fractionation as a result of crystal liquid fractionation at temperatures greater than 1050 c this conclusion has been tacitly assumed but never demonstrated and is important to the interpretation of li isotope results from such geochemically complex environments as island arcs

anomalous marine calcium cycle linked to carbonate factory change after the smithian thermal maximum early triassic abstract extreme greenhouse warming in the latest permian played a key role in the largest animal extinction event ever recorded in earth history the extinction was likely triggered by volcanic eruptions that dramatically increased atmospheric co2 levels and pushed the earth system into a lethally hot greenhouse state with stratified anoxic and more acidic oceans these conditions intensified a few million years later during the middle late smithian thermal maximum stm and a further biodiversity loss occurred during the subsequent cooling across the smithian spathian boundary ssb the marine carbonate factory is expected to have changed during this period but relevant studies are still lacking here we report calcium isotopic data of bulk carbonate rocks 44 40cacarb from two marine carbonate sections jiarong and shitouzhai in south china showing 0 5 0 7 positive shift of 44 40cacarb coupled to a 4 6 positive shift of 13ccarb from the middle smithian to the early spathian box modeling of the marine ca cycle yielded two scenarios i e constant and variable 44 40caseawater that can produce a 0 5 positive shift of 44 40cacarb 1 a local mineralogical shift in primary carbonate mineralogy at both sites from 80 aragonite to 80 calcite or 2 a 10 increase of global carbonate burial flux the former is consistent with a 20 50 fold rise of ca mg ratios and 10 50 fold decrease of sr ca ratios in the study sections and the latter fits well with massive carbonate deposition globally during the early spathian oceanic overturn and upwelling of alkaline deep waters during ssb climatic cooling is proposed as the main reason for the increase in carbonate burial flux thus the ssb transition marks an important step in the recovery of the marine fauna after the end permian mass extinction triggered by climatic cooling ocean ventilation and a pronounced rise in marine carbonate deposition on continental shelves

lithium isotope evidence for light element decoupling in the panama subarc mantle the systematics of fluid mobile trace elements in arc lavas from panama relative to their li isotopic compositions provide unique evidence for the fertilization and subsequent differential extraction of mobile species from the subarc mantle calc alkaline lavas that crystallized between 20 and 5 ma old group that possess 7 li as high as 11 2 have low b be otherwise identical and similarly old calcalkaline lavas with high b be to 23 have mid ocean ridge basalt morb like 7 li 4 7 to 5 6 adakite lavas 3 ma young group possess 7 li from 1 4 to 4 2 and have consistently lower b be than old group lavas consistent with derivation from melting of a devolatilized morb slab if li and b had comparable fluid mobility in the subarc mantle then slab fluids would carry both high b concentrations and elevated 7 li signatures into arc sources and samples with the highest 7 li would also have the highest b be our data suggest that although both li and b are initially derived from the slab older 7 li signatures may be preserved in the mantle beneath arcs as a result regions of the lithospheric mantle will develop li isotope signatures that are heavier than typical morb mantle

non biological fractionation of stable ca isotopes in soils of the atacama desert chile abstract we measured ca stable isotope ratios 44 40 ca in an ancient 2 my hyperarid soil where the primary source of mobile ca is atmospheric deposition most of the ca in the upper meter of this soil 3 5 kmol m 2 is present as sulfates 2 5 kmol m 2 and to a lesser extent carbonates 0 4 kmol m 2 in aqueous extracts of variably hydrated calcium sulfate minerals 44 40 ca e values vs bulk earth increase with depth 1 4 m from a minimum of 1 91 to a maximum of 0 59 the trend in carbonate 44 40 ca in the top six horizons resembles that of sulfate 44 40 ca but with values 0 1 0 6 higher the range of observed ca isotope values in this soil is about half that of 44 40 ca values observed on earth linear correlation among 44 40 ca 34 s and 18 o values indicates either a a simultaneous change in atmospheric input values for all three elements over time or b isotopic fractionation of all three elements during downward transport we present evidence that the latter is the primary cause of the isotopic variation that we observe sulfate 34 s values are positively correlated with sulfate 18 o values r 2 0 78 and negatively correlated with sulfate 44 40 ca e values r 2 0 70 if constant fractionation and conservation of mass with downward transport are assumed these relationships indicate a 44 40 ca fractionation factor of 0 4 in caso 4 the overall depth trend in ca isotopes is reproduced by a model of isotopic fractionation during downward ca transport that considers small and infrequent but regularly recurring rainfall events near surface low ca isotope values are reproduced by a rayleigh model derived from measured ca concentrations and the ca fractionation factor predicted by the relationship with s isotopes this indicates that the primary mechanism of stable isotope fractionation in caso 4 is incremental and effectively irreversible removal of an isotopically enriched dissolved phase by downward transport during small rainfall events

minor element and ca isotope composition of calcareous dinoflagellate cysts of cultured thoracosphaera heimii abstract we investigated the influences of temperature salinity and ph on the calcium isotope as well as trace and minor element uranium strontium magnesium to ca ratios on calcium carbonate cysts of the calcareous dinoflagellate species thoracosphaera heimii grown in laboratory cultures the natural habitat of this species is the photic zone preferentially at the chlorophyll maximum depth of temperate to tropical oceans and it is abundant in deep sea sediments over the entire cenozoic in our experiments temperatures ranged from 12 to 30 c salinity from 36 5 to 38 8 and ph from 7 9 to 8 4 the 44 40ca of t heimii cysts resembles that of other marine calcifiers including coccolithophores foraminifers and corals however its temperature sensitivity is considerably smaller and statistically insignificant and t heimii might serve as a recorder of changes in seawater 44 40ca over geologic time the sr ca ratios of t heimii cysts show a pronounced temperature sensitivity 0 016 mmol mol c 1 and have the potential to serve as a palaeo sea surface temperature proxy no clear temperature and ph dependences were observed for mg ca u ca seems to be influenced by temperature and ph but the correlations change sign at 23 c and ph 8 2 respectively

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

li ca enrichments in great scallop shells pecten maximus and their relationship with phytoplankton blooms article i nfo phytoplankton dynamics in coastal oceans is a major component of the global biogeochemical carbon cycle and is currently affected by global change through modifications in levels of primary productivity and com position of phytoplankton communities despite many attempts no straightforward geochemical proxy has been found yet in marine biogenic carbonates for reconstruction of past phytoplankton dynamics with high temporal resolution here we report on sub weekly variations of lithium to calcium ratios li cashell along the axis of maximum growth of great scallop shells pecten maximus collected alive between 1999 and 2007 in the bay of brest northwest france inter individual variability of li cashell time series was very low suggesting an environmental control on the incorporation of li within shells conversely inter annual variability of li cashell was high with limited seasonal li cashell variations in 2001 and 2007 and the presence of li enrichments from may to july in 1999 and 2004 comparison of these results with shell growth measure ments increment width and environmental parameters suggests i that shell calcification rate is likely the main factor controlling incorporation of li in pecten maximus shell calcite ii that seawater temperature has only a weak positive influence on li cashell of this species over the range 8 18 c and iii that during diatom blooms additional amounts of li may be trapped in the shell following dissolution of li rich frustules of ed ible species in the digestive tract of scallops being responsible for li cashell peaks therefore we suggest that li cashell ratio may be a novel proxy for timing and magnitude of diatom blooms in coastal ecosystems anal ysis of ancient shells may thus provide useful information on past phytoplankton dynamics and on the im portance of recent shifts observed from diatoms to non siliceous phytoplankton in coastal areas affected by anthropogenic activities

the δ44ca temperature calibration on fossil and cultured globigerinoides sacculifer new tool for reconstruction of past sea surface temperatures we report direct 44ca temperature calibration on cultured and fossil calcite foraminifera showing that ca isotopes are potentially a new proxy for past sea surface temperatures sst samples have been analyzed using a 43ca 48ca double spike and thermal ionization mass spectrometry tims in order to avoid species dependent isotope fractionation we focused our investigations on a single foraminifera species globigerinoides sacculifer which is known to inhabit shallow euphotic waters in tropical and subtropical oceans ca isotope measurements were performed on cultured g sacculifer that grew in seawater kept at temperatures of 19 5 26 5 and 29 5 c a 44ca change of 0 24 0 02 per 1 c is defined by the weighted linear regression through reproduced 44ca data of the three temperatures 95 confidence level application of this new method to fossil g sacculifer of an equatorial east atlantic sediment core geob1112 5 46 7 s 10 45 0 w 3125 m indicates that the 44ca difference between marine isotope stage 1 mis 1 and mis 2 is 0 71 0 24 according to the current 44ca temperature calibration this value corresponds to a temperature difference between mis 1 and mis 2 of 3 0 1 0 c

exploring the importance of authigenic clay formation in the global li cycle abstract lithium isotopic 7li and elemental concentrations of pore fluids and carbonates from iodp site u1338 hole a eastern equatorial pacific ocean suggest that clay authigenesis i e in situ precipitation is a significant sink for li in carbonate rich sedimentary sections systematic variations in pore fluid 7li with depth in the section suggest that clay authigenesis can i strongly decrease pore fluid li concentrations with depth and ii fractionate li isotopically to a considerable degree 5 21 relative to seawater we hypothesize that clay authigenesis in carbonate rich sections occurs due to the presence of reactive biogenic silica and reactive transport modeling supports the contention that the pore fluid 7li depth profile at site u1338 is best explained by faster authigenesis at depth the significance of clay authigenesis in carbonate rich sediments is two fold if global in scale i it can generate sizeable output fluxes in the global li cycle and ii the evolution of the sedimentary system over time can markedly impact the isotopic composition of the global li output flux we compile odp and iodp pore fluid li data from 267 sites of these 207 have li pore fluid concentration gradients in the upper 50 100 meters that indicate the sites as diffusive sinks of li we then estimate that clay authigenesis in carbonate rich sediments could reasonably generate a li output flux on the order of 1 2 1010 moles year which is comparable to the gross input fluxes in the modern li cycle a series of reactive transport simulations illustrate how clay authigenesis might impact the isotopic composition of the output flux of li from the global ocean the suggestion is that applying a constant fractionation factor from the global ocean over time is likely incorrect and that secular changes in the 7li of the output flux will be driven by rates of authigenesis burial rates and the depth extent of authigenesis in the sedimentary section utilizing a time dependent depositional diagenetic model the 7li values of bulk carbonate are shown to be a consequence not of recrystallization alone but recrystallization in the presence of clay authigenesis further our model results are used to illustrate how carbonate 7li may be used to constrain the temporal evolution of clay authigenesis in the sedimentary section ultimately this work suggests that the li isotopic composition of bulk carbonates can be altered diagenetically however such alteration is not a detriment but provides useful information on those diagenetic processes in the sedimentary column that impact the global li cycle thus li isotopes in bulk carbonates have the potential to elucidate diagenetic controls on the global li cycle over long time scales

lithium to calcium ratios in modern cenozoic and paleozoic articulate brachiopod shells li ca ratios in modern brachiopod shells generally correlate inversely with growth temperature ranging from 20 mol mol at 30 c to 50 mol mol at 0 c with no apparent interspecific offsets causes of the temperature effect on li ca ratios are not yet understood cenozoic brachiopod li ca ratios average 30 mol mol similar to the average observed in modern brachiopods relatively constant li ca ratios for eocene to pleistocene nonluminescent brachiopod shells consistent with previous observations of cenozoic planktonic foraminifera support the conclusion of little variation in cenozoic seawater li ca nonluminescent portions of permian and carboniferous brachiopods have li ca ratios substantially lower generally 10 mol mol than modern cenozoic or devonian samples mass balance considerations constrained by 18o of brachiopods suggest that low li concentrations in permo carboniferous seawater could be the result of a lower flux of dissolved li from the continents and or a higher flux of li from seawater to clastic marine sediments nonluminescent devonian brachiopods from a single hand specimen have li ca ratios around 70 of the modern average these li ca ratios can be explained by either somewhat higher temperature with constant seawater li ca somewhat lower seawater li ca at constant temperature or a combination of slightly elevated temperature and slightly lower seawater li ca

marine sedimentation of nano quartz forming flint in north sea danian chalk abstract a new theory for formation of flint in the north sea danian ekofisk formation chalk has been formulated according to which the flint formed by sedimentation of nano size quartz particles these quartz particles have crystallized in the sea from silicon supplied from dissolution of radiolarians in the present work this model has been tested by sedimentological and mineralogical investigation of sedimentary features in chalk containing silica methods applied are x ray diffraction xrd atomic force microscopy afm scanning electron microscopy sem and thermal analysis dta ega in the ekofisk formation silica was present in flint in quartz beds and as quartz particles dispersed in the chalk the quartz in the flint in the quartz intervals and the quartz particles in the chalk are one and the same kind of quartz it is composed of 0 1 0 3 m spheres of quartz having perfect three dimensional order but with slightly larger cell dimensions compared to standard quartz the quartz in the flint in the quartz horizons and dispersed in the chalk must accordingly have formed by one and the same mechanism which is crystallization in the water phase prior to sedimentation it is proposed that the difference in proportion of calcite in the flint and the quartz horizons on one side and the chalk with quartz particles on the other is due to different degrees of dissolution of the pelagic skeletal debris of coccolithophorids in the seawater during sedimentation this variation is attributed to differences in concentration of co2 in the seawater and the high amounts of co2 dissolving the calcite during sedimentation of the pure quartz are proposed to come from volcanic activity this implies that the quartz rich horizons consisting of dispersed quartz quartz horizons or flint are regional features and may as such be present as regional sheets in the pelagic danian ekofisk chalk reservoir

lithium in the aragonite skeletons of massive porites corals a new tool to reconstruct tropical sea surface temperatures previous studies have demonstrated the potential for the li content of coral aragonite to record information about environmental conditions but no detailed study of tropical corals exists here we present the li and mg to ca ratios at a bimonthly to monthly resolution over 25 years in two modern porites corals the genus most often used for paleoclimate reconstructions in the tropical indo pacific a strong relationship exists between coral li ca and locally measured sst indicating that coral li ca can be used to reconstruct tropical sst variations however li ca ratios of the skeleton deposited during 1979 1980 do not track local sst well and are anomalously high in places the mg ca ratios of this interval are also anomalously high and we suggest li ca can be used to reconstruct tropical sst only when mg ca data are used to carefully screen for relatively rare biological effects mg li or li mg ratios provide little advantage over li ca ratios except that the slope of the li mg temperature relationship is more similar between the two corals the mg li temperature relationship for the coral that experienced a large temperature range is similar to that found for cold water corals and aragonitic benthic foraminifera in previous studies the comparison with data from other biogenic aragonites suggests the relationship between li mg and water temperature can be described by a single exponential relationship despite this hint at an overarching control it is clear that biological processes strongly influence coral li ca and more calibration work is required before widely applying the proxy

modeling novel stable isotope ratios in the weathering zone when rock is converted to weathering products the involved processes can be fingerprinted using the stable isotope ratios of metals for example li mg ca fe sr and metalloids b si here we construct a framework for interpreting these novel stable isotope ratios quantitatively in the compartments of the weathering zone in a geomorphic context the approach is applicable to any novel stable isotope system and is based on a simple steady state mass balance model that represents the weathering zone from the scale of a soil column to that of entire continents our model is based on the assumption that the two main processes associated with isotope fractionation are formation of secondary precipitates such as clays and uptake of nutrients by plants the model results show that the isotope composition of a given element in the weathering zone compartments depends on 1 the ratio between the release flux to water through primary mineral dissolution and the erosion flux of isotopically fractionated solid material consisting of secondary precipitates and organic matter 2 the isotope fractionation factors associated with secondary mineral precipitation and uptake by plants a relationship is established between isotope ratios isotope fractionation factors and indexes for chemical weathering such as chemical depletion fractions cdf and elemental mass transfer coefficients derived from simple elemental concentration measurements from this relationship isotope fractionation factors can be calibrated from chemical and isotope data measured on field material furthermore we show how the ratio of solid export to dissolved export of a given element from the weathering system can be estimated from the comparison of the isotope composition between bedrock water and sediment this calculation can be applied to samples from soils from rivers and from the sedimentary record and does not require knowing the isotope fractionation factors involved in the reactions finally we apply the model to the oceanic li isotope record reconstructed from marine carbonate sediments in order to discuss changes in global geomorphic regimes through the cenozoic

li sr mg and na in foraminiferal calcite shells from laboratory culture sediment traps and sediment cores abstract constant temperature laboratory culture experiments of the planktonic foraminiferal species globigerinoides sacculifer brady suggest that the ratios of li and sr to ca in the shells are a function of these ratios in the culture solutions mg ca and na ca in the shells did not vary with changes of these ratios in the culture solution these are the first direct determinations of the relationship between foraminiferal shell chemistry and solution composition the possibility of temperature dependence for the minor elemental composition of foraminiferal shells was also investigated in the laboratory and by analysis of several planktonic and one benthic foraminiferal species from sediment trap and sediment core samples the sr ca mg ca and na ca ratios in the natural samples roughly correlate with calcification temperature whereas differences in the li ca ratios are small and not systematically related to temperature however laboratory culture experiments at 20 c and 30 c showed no variation in the li ca sr ca mg ca and na ca ratios with calcification temperature for the planktonic foraminifera g sacculifer and orbulina universa therefore observed differences in the sr ca mg ca and na ca ratios for the sediment trap and core foraminiferal samples cannot be ascribed to direct effects of calcification temperature but may be due to some other environmental factor which is correlated with temperature

new type of compositional zoning in calcite insights into crystal growth mechanisms compositional zoning of trace elements is observed in time equivalent regions within 10 overline 1 4 growth sectors of natural and synthetic calcite single crystals and has been called intrasectoral zoning to distinguish it from conventional sectoral zoning differential interference contrast microscopy shows that 101 overline 1 4 faces grow by the spiral mechanism cathodoluminescence microscopy and electron probe microanalyses reveal that trace element partitioning differences on 101 overline 1 4 faces correspond exactly to crystallographically controlled orientations of growth steps effective partitioning of mg and mn varies up to a factor of four between time correlative growth steps spreading in different directions effective sr partitioning varies by approximately 20 and is inversely correlated with enrichment trends of mg and mn preferential incorporation of different aqueous species at different growth steps may provide an explanation for morphological and chemical variation in natural calcites

negligible temperature dependence of calcium isotope fractionation in 12 species of planktonic foraminifera the influence of temperature on calcium ca isotope fractionation during biomineralization was investigated through the paired analyses of d44 42ca via mc icp ms and d18o on the calcite tests of 12 species of planktonic foraminifera from coretop sediments samples were collected from a suite of box cores from sites between 608n and 308s in the north atlantic and west indian oceans spanning a range in sea surface temperature of 9 27 8c the d44 42casrm915a of the samples ranged from 0 21x to 0 81x over a range in the d18ovpdb of the foraminiferal calcite of between 2 3x and 2 1x the bulk of the species investigated produced calcite with an average calcite seawater ca enrichment factor e of 0 65f0 08x n 45 the globorotaliid species and a single globigerina bulloides sample were confined to the upper 0 4x of the observed range in d44 42ca values with the globorotaliids displaying a lesser degree of fractionation of 0 56f0 23x n 15 possibly as a result of physiological or metabolic processes such as the production of calcite crusts at depth leading to the depletion of internal stores of ca no significant correlation between temperature and ca enrichment factor was observed in any of the 12 species of foraminifera investigated the influence of temperature on e was close to zero for the combined non globorotaliid species 0 07f0 10 k e versus 1000 k 0 0008f0 0012x 8c1 the results suggest that the theoretically expected relationship between the ca enrichment factor and temperature can be obscured by as yet unquantified metabolic and physiological processes in nature these processes are particularly relevant to the globorotaliid species and g bulloides in this core top study consequently their effects must be better understood before laboratory determined temperature calibrations can be applied to downcore material with confidence provided that the effects of metabolic and physiological processes on e remain constant through time orbulina universa globigerinoides sacculifer neogloboquadrina pachyderma and globigerinella aequilateralis are suitable for the investigation of temporal changes in the calcium isotopic composition of seawater

stable isotope profiles ca o c through modern brachiopod shells of t septentrionalis and g vitreus implications for calcium isotope paleo ocean chemistry brachiopod shells are widely used as an archive to reconstruct elemental and isotopic composition of seawater studies focused on oxygen and carbon isotopes over the last decades are increasingly extending to the emerging calcium isotope system to date only little attention has been paid to test the reliability of fossil brachiopods on their modern counterparts in this context the present study investigates two modern brachiopods terebratulina septentrionalis eastern canada 5 30 m depth 7 1 c seasonal temperature variation two layer shell and gryphus vitreus northern mediterranean 200 m depth constant all year round temperature three layer shell both species were sampled along the ontogenetic growth direction and calcium oxygen and carbon isotopes as well as elemental concentration were measured calcium isotopes were analyzed on tims the elemental composition was analyzed by la icp ms and icp aes the results indicate an intra specimen 44 40ca variation ranging from 0 16 to 0 33 pointing to a fairly homogenous distribution of calcium isotopes in brachiopod shells however in the light of the suggested 0 7 increase in calcium isotopes over the phanerozoic such intra specimen variations constrain ocean reconstruction 44 40ca values of t septentrionalis do not seem to be affected by growth rate calcium isotopic values of g vitreus are heavy in the central part of the shell and trend towards lighter values in peripheral areas approaching the maximum isotopic composition of t septentrionalis the maximum inter species 44 40ca difference of 0 62 between t septentrionalis and g vitreus indicates that care should be taken when using different taxa species with different strontium content or brachiopods with specialized shell structure such as g vitreus for ocean water reconstruction in terms of ca isotopic composition t septentrionalis may record ca isotopic fractionation related to seasonal seawater temperature variations in its shell but this is difficult to resolve at the current analytical precision average 18o derived temperatures of the two investigated species are close to on site measured temperatures

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

emplacement of foreland thrust systems emplacement driving mechanisms for thrust systems have been briefly reviewed and compared with distinctive structural styles in thrust belts a b type mode which implies a push from the rear and an elastic brittle behavior of the rock mass appears to be suitable as a general model for the emplacement of thrust sheets in thin skinned fold and thrust belts where stratal shortening of sedimentary covers and imbrication of upper level crustal rocks occur in such an environment that the mechanical behavior of the crustal section involved the mode and timing of deformation and the geometry of thrust systems are all strongly dependent upon the coupling between induced tectonic strain and transient close to lithostatic pore fluid pressure buildup over a critical areal extent the model presented here does not require a weak basal horizon for the detachment of thrust sheets and pore pressure pp does not need to be high at once under the entire length of the thrust wedge rather the transient buildup of pp and hence the spatial and temporal progressive weakening of the rock mass are directly coupled with deformation

silicate weathering and carbon cycle controls on the oligocene miocene transition glaciation changes in both silicate weathering rates and organic carbon burial have been proposed as drivers of the transient mi 1 glaciation event at the oligocene miocene transition omt 23 ma however detailed geochemical proxy data are required to test these hypotheses here we present records of li ca mg ca cd ca u ca 18o 13c and shell weight in planktonic foraminifera from marine sediments spanning the omt in the equatorial atlantic ocean li ca values increase by 1 mol mol across this interval we interpret this to indicate a 20 increase in silicate weathering rates which would have lowered atmospheric co2 potentially forcing the antarctic glaciation circa 23 ma 13c of thermocline dwelling planktonic foraminifera track the global increase in seawater 13c across the omt and during the mi 1 event hence supporting a hypothesized global increase in organic carbon burial rates high 13c previously measured in epipelagic planktonic foraminifera and high cd ca ratios during mi 1 are interpreted to represent locally enhanced primary productivity stimulated by increased nutrients supply to surface waters the fingerprint of high export production and associated organic carbon burial at this site is found in reduced bottom water oxygenation inferred from high foraminiferal u ca and enhanced respiratory dissolution of carbonates characterised by reduced foraminiferal shell weight replication of our results elsewhere would strengthen the case that weathering induced co2 sequestration preconditioned climate for antarctic ice sheet growth across the omt and increased burial of organic carbon acted as a feedback that intensified cooling at this time

calcium isotopes in igneous rocks and the origin of granite abstract the k ca radioactive parent daughter system provides a tool for tracing the origins of igneous rocks it is complementary to other isotopic systems because as stoichiometric constituents of major minerals the concentrations of k and ca and the k ca ratio in rocks are simply related to mineralogy in this paper we report the first high precision calcium isotopic analyses of continental granitic rocks island arc rocks and mid ocean ridge basalts these data show that mid ocean ridge basalts have the low 40 ca 42 ca ratios expected for the earth s mantle but that island arc rocks have slightly higher 40 ca 42 ca ratios indicative of crustal calcium in their magma sources many granitic rocks have high initial 40 ca 42 ca ratios and in conjunction with independent evidence for the age of the crustal sources these ratios provide constraints on the k ca ratios and in turn on the silica contents and residual mineralogy of the deep crustal magma sources

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