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

site specific equilibrium isotopic fractionation of oxygen carbon and calcium in apatite the stable isotope composition of biogenic apatite is an important geochemical marker that can record environmental parameters and is widely used to infer past climates biomineralization processes dietary preferences and habitat of vertebrates in this study theoretical equilibrium isotopic fractionation of oxygen carbon and calcium in hydroxyapatite and carbonate bearing hydroxyapatite is investigated using first principles methods based on density functional theory and compared to the theoretical isotopic fractionation properties of calcite co 2 and h 2 o considering the variability of apatite crystal chemistry special attention is given to specific contributions of crystal sites to isotopic fractionation significant internal fractionation is calculated for oxygen and carbon isotopes in co 3 between the different structural sites occupied by carbonate groups in apatite typically 7 for both 18 o 16 o and 13 c 12 c fractionation at 37 c compared with calcite water oxygen isotope fractionation occurrence of a type substitution in apatite structure in addition to the main b type substitution could explain the larger temperature dependence of oxygen isotope fractionation measured at low temperature between carbonate in apatite and water theoretical internal fractionation of oxygen isotopes between carbonate and phosphate in b type carbonated apatite 8 at 37 c is consistent with experimental values obtained from modern and well preserved fossil bio apatites concerning calcium theoretical results suggest a small fractionation between apatite and calcite a0 17 at 37 c internal fractionation reaching 0 8 at 37 c occurs between the two ca sites in hydroxyapatite furthermore the ca isotopic fractionation properties of apatite are affected by the occurrence of carbonate groups which could contribute to the variability observed on natural samples owing to the complexity of apatite crystal chemistry and in light of the theoretical results measurements of site specific isotopic fractionation properties could improve our understanding and the interpretation of isotopic records in apatites

incorporation of ca isotopes in carapaxes of marine ostracods abstract we studied mg ca sr ca and ca isotope ratios of ostracod carapaxes from surface sediments retrieved during research cruises to the southern and equatorial eastern atlantic collected specimens originate from water depth between 30 and about 5000 mbsl and cover bottom water temperatures between 0 and 23 c analysed taxa include buntonia sp cytherella sp henryhowella sp krithe sp poseidonamicus sp and ruggieria sp calcium isotope ratios of the studied specimens are in the overall range of other marine calcifiers and show a variability of about 0 75 over a temperature range of 20 c there is no overall linear relation between temperature and ca isotope fractionation but some species show a maximum 44 40ca at intermediate temperatures mg ca and sr ca agree well with values of previously published carapaxes demonstrating large inter and intra species variability and different responses to bottom water temperatures magnesium is highly variably distributed within the carapax with mg enrichment in the inner part of the shell of most taxa this enrichment is independent from the incorporation of sr which shows less variability within the carapax the ca isotope vs sr ca systematic in the ostracods deviates from inorganic calcite and foraminifers the ostracod array is most likely controlled by either mixing of material originating from a precursor phase and newly grown calcite or rayleigh type fractionation during precipitation from a restricted fluid reservoir indicating varying degrees of ca and sr consumption during calcite precipitation the different slope of the ca isotope vs sr ca relation shown by the ostracods compared to those of inorganic calcite and foraminifers opens a new approach for the determination of ca isotope and sr ca ratios of past ocean water

calcium isotopes in enamel of modern and plio pleistocene east african mammals abstract calcium isotope analyses show a depletion of heavy calcium isotopes in vertebrates compared to food sources along each trophic step recent studies show considerable variability of the calcium isotopic composition of bone and teeth in modern mammals leading to inconclusive interpretations regarding the utility of ca isotopes for trophic inference in mammal dominated terrestrial ecosystems here we analyzed modern enamel samples from the tsavo national park kenya and fossil enamel samples dated from ca 4 ma to 1 6 ma from the turkana basin kenya we found a constancy of taxa ordering between the modern and fossil datasets suggesting that the diagenesis of calcium isotopes is minimal in fossils in modern herbivore samples using similar digestive physiologies browsers are enriched in 44ca compared to grazers both grazer and browser herbivore tooth enamel is enriched in 44ca relative to carnivores by about 0 30 used together carbon and calcium isotope compositions may help refine the structure of the c3 and c4 trophic chains in the fossil record due to their high preservation potential combining both carbon and calcium isotope systems represent a reliable approach to the reconstruction of the structure of past ecosystems

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

isotopic approaches for quantifying the rates of marine burial diagenesis 1 diagenetic reactions in marine sediments have the potential to alter geochemical proxy records and affect the global carbon cycle over tens of thousands to millions of years this article describes advances in the use of ca sr and u series isotopes in constraining carbonate recrystallization and silicate dissolution rates in marine systems we specifically focus on recent efforts that interpret isotope variability in marine pore fluids using reactive transport models of varying complexity such studies suggest that calcite recrystallization rates are significant over time scales 1 myr approaching exchange rates of 0 4 1 myr 1 over longer time scales isotopic data point to continued exchange between calcite and coexisting pore fluid though at lower rates than in young sediments extrapolating these recrystallization rates over tens of millions of years we quantify the extent to which geochemical climate proxies such as mg ca in calcite can be altered diagenetically in some cases such diagenetic effects significantly affect the interpretation of long term climatic trends as well as determinations of absolute paleotemperatures silicate dissolution rates in siliclastic marine sediments appear to be similar in magnitude to dissolution rates in terrestrial environments 10 7 10 6 yr 1 such estimates suggest that silicate weathering in marine sediments may play an important role in the carbon cycle at least over time scales approaching 400 500 kyr

effects of diagenesis on strontium carbon nitrogen and oxygen concentration and isotopic composition of bone abstract paleodietary analysis based on variations in the trace element and stable isotopic composition of inorganic and organic phases in fossil bone depends on the assumption that measured values reflect in vivo values to test for postmortem alteration we measured 87 sr 86 sr 13 c 12 c 18 o 16 o and 15 n 14 n ratios and sr concentrations in modern and prehistoric 610 to 5470 yr old bones of animals with marine or terrestrial diets from greenland bones from modern terrestrial feeders have substantially lower sr concentrations and more radiogenic 87 sr 86 sr ratios than those from modern marine feeders this contrast was not preserved in the prehistoric samples which showed almost complete overlap for both sr concentration and isotopic composition in bones from the two types of animals leaching experiments x ray diffraction analysis and infrared spectroscopy indicate that alteration of the sr concentration and isotopic composition in prehistoric bone probably results from nearly complete exchange with groundwater oxygen isotope ratios in fossil apatite carbonate also failed to preserve the original discrimination between modern terrestrial and marine feeders the c isotope ratio of apatite carbonate did not discriminate between animals with marine or terrestrial diets in the modern samples even so the ranges of apatite 13 c values in prehistoric bone are more scattered than in modern samples for both groups suggesting alteration had occurred 13 c and 15 n values of collagen in modern bone are distinctly different for the two feeding types and this distinction is preserved in most of the prehistoric samples our results suggest that postmortem alteration of dietary tracers in the inorganic phases of bone may be a problem at all archaeological sites and must be evaluated in each case while collagen analyzed in this study was resistant to alteration evaluation of the possibility of diagenetic alteration of its isotopic composition in bones from other contexts is also warranted

calcium isotope evidence for suppression of carbonate dissolution in carbonate bearing organic rich sediments pore fluid calcium isotope calcium concentration and strontium concentration data are used to measure the rates of diagenetic dissolution and precipitation of calcite in deep sea sediments containing abundant clay and organic material this type of study of deep sea sediment diagenesis provides unique information about the ultra slow chemical reactions that occur in natural marine sediments that affect global geochemical cycles and the preservation of paleo environmental information in carbonate fossils for this study calcium isotope ratios 44 40ca of pore fluid calcium from ocean drilling program odp sites 984 north atlantic and 1082 off the coast of west africa were measured to augment available pore fluid measurements of calcium and strontium concentration both study sites have high sedimentation rates and support quantitative sulfate reduction methanogenesis and anaerobic methane oxidation the pattern of change of 44 40ca of pore fluid calcium versus depth at sites 984 and 1082 differs markedly from that of previously studied deep sea sites like 590b and 807 which are composed of nearly pure carbonate sediment in the 984 and 1082 pore fluids 44 40ca remains elevated near seawater values deep in the sediments rather than shifting rapidly toward the 44 40ca of carbonate solids this observation indicates that the rate of calcite dissolution is far lower than at previously studied carbonate rich sites the data are fit using a numerical model as well as more approximate analytical models to estimate the rates of carbonate dissolution and precipitation and the relationship of these rates to the abundance of clay and organic material our models give mutually consistent results and indicate that calcite dissolution rates at sites 984 and 1082 are roughly two orders of magnitude lower than at previously studied carbonate rich sites and the rate correlates with the abundance of clay our calculated rates are conservative for these sites the actual rates could be significantly slower because other processes that impact the calcium isotope composition of sedimentary pore fluid have not been included the results provide direct geochemical evidence for the anecdotal observation that the best preserved carbonate fossils are often found in clay or organic rich sedimentary horizons the results also suggest that the presence of clay minerals has a strong passivating effect on the surfaces of biogenic carbonate minerals slowing dissolution dramatically even in relation to the already slow rates typical of carbonate rich sediments

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

a critical assessment of mollusk 18 o 16 o mg ca and 44 ca 40 ca ratios as proxies for cretaceous seawater temperature seasonality seasonal temperature fluctuations of tethyan coastal water are recorded in a pristine 80 my old rudist shell from turkey in order to critically assess factors other than seawater temperature that might have influenced the shell geochemical record three different paleo temperature proxies 18o mg ca and 44ca were applied in a qualitative manner all three proxies reflect the same cyclical trends and thus yield robust evidence for seasonal fluctuations in late cretaceous surficial seawater temperature this suggests the successful application of the new 44ca temperature proxy to fossil mollusk calcite the direct comparison of the three data sets however demonstrates that all proxies are fraught with problems similar to other studies 18o 16o ratios point to warmer summer temperature maxima than those in comparable costal settings today nevertheless the 18o 16o proxy is subject to environmental factors that might lead to an overestimation of peak temperatures moreover mg ca molar ratios are less sensitive to environmental factors but were strongly affected by the ion regulating capability of the rudist bivalve that responded to the low mg ca ratio of cretaceous seawater similarly uncertainties of the 44ca composition of cretaceous seawater and the complex bio calcification of mollusks presently limit the interpretation of 44ca values in terms of absolute seawater temperature the multiproxy approach applied here however documents that these limitations do not obscure the dominant patterns of seasonal sea surface temperature variations recorded in the biogeochemical rudist archive

calcium isotopic fractionation in microbially mediated gypsum precipitates abstract gypsum caso4 2h2o precipitation experiments were carried out at low ph in the presence of the sulfur oxidizing bacterium acidithiobacillus thiooxidans the observed ca isotopic fractionation expressed as 44 40cas f 44 40casolid 44 40cafluid at the end of each experimental time period 50 to 60 days was 1 41 to 1 09 in the biotic experiments 1 09 in the killed control and 1 01 to 0 88 in the abiotic controls as there were no strong differences in the solution chemistry and the rate at which gypsum precipitated in the biotic and abiotic controls we deduce a biological ca isotope effect on the order of 0 3 the isotope effect correlates with a difference in crystal aspect ratios between the biotic experiments 8 05 3 99 and abiotic controls 31 9 8 40 we hypothesize that soluble and or insoluble organic compounds selectively inhibit crystal growth at specific crystal faces and that the growth inhibition affects the fractionation factor associated with gypsum precipitation the experimental results help explain ca isotopic variability in gypsum sampled from a sulfidic cave system in which gypsum crystals exhibiting a diversity of morphologies microcrystalline to cm scale needles have a broad range of 44 40ca values 1 2 0 4 relative to the limestone wall 44 40ca 1 3 in light of the laboratory experiments the variation in ca isotope values in the caves can be interpreted as a consequence of gypsum precipitation in the presence of microbial organic matter and subsequent isotopic re equilibration with the ca source

introduction to calcium isotope geochemistry past lessons and future directions abstract calcium ca isotopes have been utilized as geochemical tools since the 1970s increasing in popularity and scope since the mid to late 1990s research conducted over the past thirty years has revealed a range of applications for ca isotopes that are highlighted in this introduction and special issue as well as a series of interesting and fundamental problems that have yet to be resolved for such a chemically simple system in comparison to redox active elements for instance the level of complexity is both surprising and intellectually attractive while the advent of multiple collector inductively coupled plasma mass spectrometers made metals such as fe mg and zn considerably more accessible analytically the precision and ease of ca isotopic analysis did not radically improve in a comparable manner for a variety of reasons one of which may be perceived analytical difficulty the application of ca isotopes to geological questions remains in the shadows to some extent in the geosciences in this introduction we identify i areas that we think are most fertile for the application of ca isotopes as tools and ii outstanding questions and future directions that can move the field towards increased utility and broader acceptance by the geosciences community

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

ca isotope study of ordovician dolomite limestone and anhydrite in the williston basin implications for subsurface dolomitization and local ca cycling abstract a difference of 0 61 is reported between dolomite 1 66 and its precursor limestone 1 05 in the yeoman formation red river equivalent of the williston basin southeastern saskatchewan the significance of the large difference found and the preference for light isotope enrichment in the dolomite is evaluated with assistance from 87 sr 86 sr ratios and dolomitization models previously proposed for the studied rocks in particular i explore the possibility that 44 ca values in dolomite reflect the 44 ca values of the dolomitizing fluids without any correction for mineral fluid fractionation this hypothesis is based on recent studies showing negligible isotopic fractionation between carbonates and ca 2 bearing waters at very low precipitation rates fantle and depaolo 2007 jacobson and holmden 2008 if correct calcium isotopes hold promise as a tool for discriminating among numerous hydrological models of dolomite formation as a case in point the 44 ca value of the yeoman dolomite 1 66 is too low to reflect ca derived from the following sources 1 the original limestone 1 05 2 overlying beds of anhydrite 1 28 or 3 evaporated seawater 0 25 paleozoic carbonates ranging as low as 1 7 appear to be the lightest source of ca in the basin succession suggesting that the mg containing dolomitizing fluid was a connate water with a previous history of water rock interactions with paleozoic carbonates possibly involving earlier episodes of dolomitization and light ca release into migrating basinal fluids the relatively high seawater 44 ca values inferred from measurements of yeoman limestone and lake alma anhydrite suggest that seawater in the williston basin 450 ma was 0 22 0 46 higher in 44 ca than the contemporaneous ocean based on globally distributed brachiopods farkas et al 2007 this finding suggests that 44 ca values preserved in the deposits of epeiric seas may bias the 44 ca reconstruction of the ocean secular record if local ca cycling effects are not taken into account equations describing the isotope balance of ca in an epeiric sea indicate that seawater 44 ca values may be higher lower or equal to the 44 ca value of the ocean depending on the sizes of local scale ca deposition and weathering fluxes in relation to seawater ca exchange fluxes

alteration of volcanic matter in deep sea sediments evidence from the chemical composition of interstitial waters from deep sea drilling cores six deep sea drilling project dsdp sites 252 285 315 317 336 386 were examined for the chemical composition of the dissolved salts in interstitial waters the oxygen isotopic composition of the interstitial waters and the major ion composition of the bulk solid sediments an examination of the concentration depth profiles of dissolved calcium magnesium potassium and h218o in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in dsdp pelagic drill sites concentration gradients in ca mg k and h218o are largely due to alteration reactions occurring in the basalts of layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column oxygen isotope mass balance calculations require substantial alteration of layer 2 up to 25 of the upper 1000 m but only minor exchange of ca mg and k occurs with the overlying ocean this implies that alteration reactions in layer 2 are almost isochemical

the umiak field discovery northwest territories canada this paper examines the discovery process in terms of changing exploration paradigms and describes a field discovered because of this change in mindset prior to the umiak discovery all wells in the mackenzie delta had been drilled on structural highs reevaluation of two 30 yr old dry holes along with existing two dimensional 2 d seismic data resulted in discovery of the umiak gas field this reappraisal led to recognition that a stratigraphic trap might exist between these two wells drilled in the early 1970s the kilagmiotak m 16 well contained 290 m 951 ft of porous sandstone in the eocene taglu formation whereas the umiak j 37 well up dip and 11 km 6 8 mi to the west had no sandstone in the same interval examination of 2 d seismic lines found evidence of an updip sandstone pinchout beneath an angular unconformity on a tilted fault block strata in the tilted fault block below the unconformity contain strong amplitudes and flat spots interpretation of a subsequent three dimensional 3 d survey supported the play a partnership of alberta energy company operator now encana anadarko and gulf canada now conocophillips canada drilled the umiak n 16 discovery well during 2004 gas and some oil was found in gently dipping eocene taglu shoreface and delta front sandstones and within gently folded foreset beds of the eocene richards formation above a mid eocene unconformity the umiak n 05 appraisal well drilled a year later confirmed the discovery together these two wells delineate the fourth largest onshore gas accumulation on the mackenzie delta

calcium isotope fractionation during coccolith formation in emiliania huxleyi independence of growth and calcification rate 1 recently calcium isotope fractionation in the coccolithophore emiliania huxleyi was shown to exhibit a significant temperature dependency an important subsequent question in this context is whether the observed fractionation patterns are caused by temperature itself or related growth rate changes in order to separate growth and calcification rate effects from direct temperature effects batch culture experiments with the coccolithophore e huxleyi were conducted under varying light intensities despite large changes in cellular growth and calcification rates calcium isotope fractionation remained constant independence of calcium isotope fractionation on growth and calcification was also obtained in two additional sets of experiments in which growth rates changed in response to varying calcium concentration and seawater salinity these experiments also showed no direct effects of calcium concentration and salinity on calcium isotope fractionation values for calcium isotope fractionation of e huxleyi coccoliths fell within a range of 1 0 to 1 6 1000 ln confirming earlier results this range is similar to that observed in several foraminiferal species and coccolith oozes suggesting a rather homogeneous calcium isotopic composition in marine biogenic calcite our data further show that the calcium isotope fractionation does not change with changing isotopic composition of seawater this is a basic requirement for reconstructing the calcium isotopic composition of the ocean over time

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

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

calcium isotope fractionation in coccoliths of cultured calcidiscus leptoporus helicosphaera carteri syracosphaera pulchra and umbilicosphaera foliosa four species of marine calcifying algae the coccolithophores calcidiscus leptoporus helicosphaera carteri syracosphaera pulchra and umbilicosphaera foliosa were grown in laboratory cultures under temperatures varying between 14 and 23 c and one species c leptoporus under varying co32 ranging from 105 to 219 mol kg calcium isotope compositions of the coccoliths resemble in both absolute fractionation and temperature sensitivity previous calibrations of marine calcifying species e g emiliania huxleyi coccolithophores and orbulina universa planktonic foraminifera as well as inorganically precipitated caco3 but also reveal small species specific differences in contrast to inorganically precipitated calcite but similar to e huxleyi and o universa the carbonate ion concentration of the medium has no statistically significant influence on the ca isotope fractionation of c leptoporus coccoliths however combined data of e huxleyi and c leptoporus indicate that the observed trends might be related to changes of the calcite saturation state of the medium since coccoliths constitute a significant portion of the global oceanic caco3 export production the ca isotope fractionation in these biogenic structures is important for defining the isotopic composition of the ca sink of the ocean one of the key parameters for modelling changes to the marine ca budget over time for the present ocean our results are in general agreement with the previously postulated and applied mean value of the oceanic ca sink sed of about 1 3 but the observed inter and intra species differences point to possible changes in sed through earth history due to changing physico chemical conditions of the ocean and shifts in floral and faunal assemblages

biological and ecological insights into ca isotopes in planktic foraminifers as a palaeotemperature proxy sea surface temperature sst is a critical variable in the earth s climate system since it influences atmospheric circulation the hydrological cycle and via ocean surface density drives ocean circulation a detailed reconstruction of past sst s is therefore a central goal of palaeoceanographic studies although calcium isotopes in foraminiferal carbonate have been introduced as a new proxy for sst reconstruction there is considerable debate about their robustness and general applicability to resolve some of these questions we have investigated the extent to which other environmental parameters e g the calcification temperature depth stratification growth rates and or environmental adaptation may influence the 44ca values of planktic foraminifers in modern and eocene samples geographically distributed data sets are affected by the exchange of cryptic species i e morphologically similar but genetically distinct species and by a mixing of optimal versus less optimal adaptation thus we have compared species within individual samples to evaluate whether the well documented depth stratification of foraminifers is reflected in their calcium isotopes the eocene data set shows a general agreement between 44ca and 18o derived calcification temperatures which supports a temperature effect on ca isotope incorporation the vertical temperature gradient using the different depth habitats of several foraminiferal species indicates a 44ca temperature dependence of 0 034 c 1 similar to inorganic calcite 0 015 c 1 and cultured o universa 0 019 c 1 the gradient resembles the global sediment 44ca compilation but it is significantly smaller than the temperature calibration of 0 22 0 02 c 1 for cultured g sacculifer the modern data set shows a general correlation between 44ca and depth habitat reflecting a similar temperature gradient to the eocene sample set in contrast the lower absolute 44ca values for the eocene foraminifers suggest a lower seawater isotope composition in situ analyses of individual calcite layers reveal large isotopic differences between the different calcite layers of the foraminifers highlighting the strong biological control on 44ca in foraminiferal calcite that may overprint a potential t relationship

oxygen isotope analyses of co existing carbonate and phosphate in biogenic apatite a way to monitor diagenetic alteration of bone phosphate abstract the oxygen isotopic composition of phosphate 18 op and structural carbonate 18 oc of hydroxylapatite was determined in 31 bone and tooth samples of modern mammals from different countries these two variables are highly correlate r 2 0 98 and the calculated best fit of linear regression is very similar to the equation calculated from the phosphate and carbonate palaeotemperature equations 1 2 according to previous measurements 3 6 on fossils of different ages from different areas it seems quite improbable to find isotopically altered skeletal remains showing a good correlation between 18 op and 18 oc as is the case with modern samples it therefore seems possible at least in some cases to use these measurements for monitoring fossil bone and tooth diagenetic alteration when a set of points lie on the equilibrium line or close to it the 18 o values could be considered close to the original values in contrast when the points lie to the left or to the right of this line this probably means that the values are diagenetically modified due to interaction with meteoric water or 18 o enriched water respectively

determination of sr and ca sources in small tropical catchments la selva costa rica a comparison of sr and ca isotopes summary a comparative study of sr and ca isotopes was conducted to assess solute sources and effects of biogeochemical processes on surface water and groundwater in four small tropical catchments located at la selva biological station costa rica variable concentrations of dissolved sr 2 and ca 2 in the catchments are related to mixing of waters from different origin three catchments are influenced by high solute bedrock groundwater while another catchment is primarily supplied by local recharge 87 sr 86 sr ratios were employed to discriminate contributions from mineral weathering and atmospheric sources solutes in bedrock groundwater have a predominant geogenic origin whereas local recharge is characterized by low solute inputs from rainwater and minor in situ weathering releases from nutrient depleted soils bedrock groundwater contributes more than 60 of dissolved sr 2 to surface discharge in the salto saltito and arboleda catchments whereas the taconazo catchment receives more than 95 of dissolved sr 2 from rainwater 44 40 ca values of dissolved ca 2 vary greatly in the catchments mainly as a result of heterogeneous ca isotope compositions of the contributing sources based on differences in 44 40 ca values two distinct bedrock groundwaters discharging at the salto and the arboleda catchments are suggested effects of biological processes in the plant soil system on solute generation in the catchments are indicated by variable ca sr ratios however these effects cannot clearly be assessed by ca isotopes due to the strong heterogeneity of 44 40 ca values of ca 2 sources and high ca 2 concentrations in bedrock groundwater

testing urey s carbonate silicate cycle using the calcium isotopic composition of sedimentary carbonates abstract carbonate minerals constitute a major component of the sedimentary geological record and an archive of a fraction of the carbon and calcium cycled through the earth s surface reservoirs for over three billion years for calcium carbonate minerals constitute the ultimate sink for almost all calcium liberated during continental and submarine weathering of silicate minerals this study presents 500 stable isotope ratios of calcium in precambrian carbonate sediments both limestones and dolomites in an attempt to characterize the isotope mass balance of the sedimentary carbonate reservoir through time the mean of the dataset is indistinguishable from estimates of the calcium isotope ratio of bulk silicate earth consistent with the urey cycle being the dominant mechanism exchanging calcium among surface reservoirs the variability in bulk sediment calcium isotope ratios within each geological unit does not reflect changes in the global calcium cycle but rather highlights the importance of local mineralogical and or diagenetic effects in the carbonate record this dataset demonstrates the potential for calcium isotope ratios to help assess these local effects such as the former presence of aragonite even in rocks with a history of neomorphism and recrystallization additionally 29 calcium isotope measurements are presented from odp ocean drilling program site 801 that contribute to the characterization of altered oceanic crust as an additional sink for calcium and whose distinct isotopic signature places a limit on the importance of this subduction flux over earth history

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

ca isotope cycling in a forested ecosystem reports of large ca isotope fractionations between trees and soils prompted this study of a boreal forest ecosystem near la ronge saskatchewan to improve understanding of this phenomenon the results on five tree species black spruce trembling aspen white spruce jack pine balsam poplar confirm that nutrient ca uptake by plants favors the light isotopes thus driving residual ca in plant available soil pools towards enrichment in the heavy isotopes substantial within tree fraction occurs in tissues formed along the transpiration stream with low 44ca values in fine roots 2 mm intermediate values in stemwood and high values in foliage separation factors between different plant tissues are similar between species but the initial fractionation step in the tips of the fine roots is species specific and or sensitive to the local soil environment soil water 44ca values appear to increase with depth to at least 35 cm below the top of the forest floor which is close to the deepest level of fine roots the heavy plant fractionated signature of ca in the finely rooted upper soils filters downward where it is retained on ion exchange sites leached into groundwater and discharged into surface waters the relationship between ca uptake by tree fine roots and the pattern of 44ca enrichment with soil depth was modeled for two ca pools the forest floor litter and the underlying upper b mineral soil six study plots were investigated along two hillside toposequences trending upwards from a first order stream we used allometric equations describing the ca distribution in boreal tree species to calculate weighted average 44ca values for the stands in each plot and estimate ca uptake rates the 44ca value of precipitation was measured and soil weathering signatures deduced by acid leaching of lower b mineral soils steady state equations were used to derive a set of model ca fluxes and fractionation factors for each plot the model reproduces the increase in 44ca with depth found in forest floor and upper b soil waters transient model runs show that the forest ca cycle is sensitive to changes in plant ca uptake rate such as would occur during ontogeny or disturbance accordingly secular records of 44ca in tree ring cellulose have the potential to monitor changes in the forest ca cycle through time thus providing a new tool for evaluating natural and anthropogenic impacts on forest health another model run shows that by changing the size of the isotope fractionation factor and adjusting for differences in forest productivity that the range in ca isotope fractionation in forested ecosystems reported in the literature thus far is reproduced as a quantitative tool the ca cycling model produces a reasonable set of relative ca fluxes for the la ronge site consistent with environment canada s measurements for wet deposition in the region and simulated ca release from soil mineral weathering using the profile model but the sensitivity of the model is limited by the small range of fractionation observed in this boreal shield setting of 1 which limits accuracy if the model were applied to a site with a greater range in 44ca values among the principal ca fluxes it is capable of producing robust and reliable estimations of ca fluxes that are otherwise difficult to measure in forested ecosystems

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

ca isotopes in carbonate sediment and pore fluid from odp site 807a the ca2 aq calcite equilibrium fractionation factor and calcite recrystallization rates in pleistocene sediments abstract the calcium isotopic compositions 44ca of 30 high purity nannofossil ooze and chalk and 7 pore fluid samples from odp site 807a ontong java plateau are used in conjunction with numerical models to determine the equilibrium calcium isotope fractionation factor s f between calcite and dissolved ca2 and the rates of post depositional recrystallization in deep sea carbonate ooze the value of s f at equilibrium in the marine sedimentary section is 1 0000 0 0001 which is significantly different from the value 0 9987 0 0002 found in laboratory experiments of calcite precipitation and in the formation of biogenic calcite in the surface ocean we hypothesize that this fractionation factor is relevant to calcite precipitation in any system at equilibrium and that this equilibrium fractionation factor has implications for the mechanisms responsible for ca isotope fractionation during calcite precipitation we describe a steady state model that offers a unified framework for explaining ca isotope fractionation across the observed precipitation rate range of 14 orders of magnitude the model attributes ca isotope fractionation to the relative balance between the attachment and detachment fluxes at the calcite crystal surface this model represents our hypothesis for the mechanism responsible for isotope fractionation during calcite precipitation the ca isotope data provide evidence that the bulk rate of calcite recrystallization in freshly deposited carbonate ooze is 30 40 myr and decreases with age to about 2 myr in 2 3 million year old sediment the recrystallization rates determined from ca isotopes for pleistocene sediments are higher than those previously inferred from pore fluid sr concentration and are consistent with rates derived for late pleistocene siliciclastic sediments using uranium isotopes combining our results for the equilibrium fractionation factor and recrystallization rates we evaluate the effect of diagenesis on the ca isotopic composition of marine carbonates at site 807a since calcite precipitation rates in the sedimentary column are many orders of magnitude slower than laboratory experiments and the pore fluids are only slightly oversaturated with respect to calcite the isotopic composition of diagenetic calcite is likely to reflect equilibrium precipitation accordingly diagenesis produces a maximum shift in 44ca of 0 15 for site 807a sediments but will have a larger impact where sedimentation rates are low seawater circulates through the sediment pile or there are prolonged depositional hiatuses

characterization of calcium isotopes in natural and synthetic barite abstract the mineral barite baso4 accommodates calcium in its crystal lattice providing an archive of ca isotopes in the highly stable sulfate mineral holocene marine pelagic barite samples from the major ocean basins are isotopically indistinguishable from each other 44 40ca 2 01 0 15 but are different from hydrothermal and cold seep barite samples 44 40ca 4 13 to 2 72 laboratory precipitated synthetic barite samples are more depleted in the heavy ca isotopes than pelagic marine barite and span a range of ca isotope compositions 44 40ca 3 42 to 2 40 temperature saturation state a ba 2 a so 4 2 and aca2 aba2 each influence the fractionation of ca isotopes in synthetic barite however the fractionation in marine barite samples is not strongly related to any measured environmental parameter first principles lattice dynamical modeling predicts that at equilibrium ca substituted barite will have much lower 44ca 40ca than calcite by 9 at 0 c and 8 at 25 c based on this model none of the measured barite samples appear to be in isotopic equilibrium with their parent solutions although as predicted they do record lower 44 40ca values than seawater and calcite kinetic fractionation processes therefore most likely control the extent of isotopic fractionation exhibited in barite potential fractionation mechanisms include factors influencing ca2 substitution for ba2 in barite e g ionic strength and trace element concentration of the solution competing complexation reactions precipitation or growth rate temperature pressure and saturation state as well as nucleation and crystal growth rates these factors should be considered when investigating controls on isotopic fractionation of ca2 and other elements in inorganic and biogenic minerals

ca cycling and isotopic fluxes in forested ecosystems in hawaii 1 biogeochemical processes fractionate ca isotopes in plants and soils along a 4 million year developmental sequence in the hawaiian islands we observed that plants preferentially take up 40ca relative to 44ca and that biological fractionation and changes in the relative contributions from volcanic and marine sources produce a significant increase in 44ca in soil exchangeable pools our results imply moderate fluxes enriched in 44ca from strongly nutrient depleted old soils in contrast with high 40ca fluxes in young and little weathered environments in addition biological fractionation controls divergent geochemical pathways of ca and sr in the plant soil system while ca depletes progressively with increasing soil age sr ca ratios increase systematically sr isotope ratios provide a valuable tracer for provenance studies of alkaline earth elements in forested ecosystems but its usefulness is limited when deciphering biogeochemical processes involved in the terrestrial ca cycle ca isotopes in combination with sr ca ratios reveal more complex processes involved in the biogeochemistry of ca and sr

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

evidence for end permian ocean acidification from calcium isotopes in biogenic apatite c record of carbonate rocks 13 c carb for the selective extinction of heavily calcifi ed marine animals and for the abrupt transition in carbonate facies across the extinction horizon an additional proxy is necessary to distinguish among these options calcium isotopes hold promise for differentiating between suggested scenarios for change in seawater carbonate chemistry linked with the end permian extinction the calcium cycle is linked to the carbon cycle through the weathering of limestone and the deposition of calcium carbonate sediments calcium isotopes fractionate by 0 6 and 1 3 in calcite and aragonite respectively during the precipitation of modern carbonate minerals meaning carbonate sediments are enriched in the lighter isotope relative to the seawater from which they precipitated skulan et al 1997 tang et al 2008 imbalances between calcium delivery and burial fl uxes and changes in the magnitude of fractionation during carbonate deposition will result in changes in the 44 40 ca of seawater and will be recorded in marine sediments depaolo 2004 farkao et al 2007 therefore variation in the

high precision iron isotope measurements of terrestrial and lunar materials we present the analytical methods that have been developed for the first high precision fe isotope analyses that clearly identify naturally occurring mass dependent isotope fractionation a double spike approach is used which allows rigorous correction of instrumental mass fractionation based on 21 analyses of an ultra pure fe standard the external precision 1 sd for measuring the isotopic composition of fe is 0 14 mass for demonstrated reproducibility on samples this precision exceeds by at least an order of magnitude that of previous attempts to empirically control instrumentally produced mass fractionation dixon et al 1993 using the double spike method 15 terrestrial igneous rocks that range in composition from peridotite to rhyolite 5 high ti lunar basalts 5 fe mn nodules and a banded iron formation have been analyzed for their iron isotopic composition the terrestrial and lunar igneous rocks have the same isotopic compositions as the ultra pure fe standard providing a reference fe isotope composition for the earth and moon in contrast fe mn nodules and a sample of a banded iron formation have iron isotope compositions that vary over a relatively wide range from 56fe 0 9 to 1 2 this range is 15 times the analytical errors of our technique these natural isotopic fractionations are interpreted to reflect biological vital effects and illustrate the great potential fe isotope studies have for studying modern and ancient biological processes

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

a model of fossil tooth and bone diagenesis implications for paleodiet reconstruction from stable isotopes abstract diagenesis of structural carbonate in biogenic apatite in the postmortem environment is modeled as a process of water mineral interaction both closed and open system model calculations suggest that 13 c of structural carbonate in biogenic apatite is much more resistant to diagenetic modification than 18 o apatite structural carbonate retains an original 13 c signal in closed system diagenesis for open systems 13 c of biogenic apatite with very low porosity such as tooth enamel can survive most diagenesis and retain a primary isotopic signature on the hand 18 o of structural carbonate in biogenic apatite may not be a reliable indicator of the original isotopic ratios except in a diagenetic system with low temperature and very low water biomineral ratio application of the model to teeth and carbonate cement in sediments from the badlands south dakota illustrates that 13 c values of enamel samples preserve the original signal whereas 13 c values of dentine represent varying extents of diagenesis 18 o values of fossil teeth may record an early or late part of their water biomineral interaction history during diagenesis

precise age determinations and petrogenetic studies using the kca method high precision mass spectrometric determination of calcium isotope ratios allows the 40k 40ca radioactive decay to be used for dating a much broader range of geologic materials than is suggested by previous work 40ca42ca is used to monitor enrichments in 40ca and can be measured to 0 01 2 using an exponential mass discrimination correction russell et al 1978 and large ion currents the earth s mantle has such a low kca 0 01 that it has retained primordial 40ca42ca 151 016 0 011 normalized to 42ca44ca 0 31221 as determined by measurements on two meteorites pyroxene from an ultramafic nodule metabasalt and carbonatite 40ca42ca ratios can be conveniently expressed relative to this value as ca in units of 10 4 to test the method for age dating a mineral isochron has been obtained on a sample of pikes peak granite which has been shown to have concordant k ar rb sr and u pb ages plagioclase k feldspar biotite and whole rock yield an age of 1041 32 m y 2 in agreement with previous age determinations k 0 5543 b y 1 k 0 8952 40k 0 01167 the initial 40ca42ca of 151 024 0 016 ca 0 5 1 0 indicates that assimilation of high k ca crust was insufficient to affect calcium isotopes measurements on two mica granite from eastern nevada indicate that the magma sources had k ca 1 similar to intermediate composition crustal rocks these results show that the k ca system can be used as a precise geochromometer for common felsic igneous and metamorphic rocks and may prove applicable to sedimentary rocks containing authigenic k minerals the relatively short half life of 40k the non volatile daughter and the fact that potassium and calcium are stoichiometric constituents of many minerals make the k ca system complementary to other dating methods and potentially applicable to a variety of geologic problems

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

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

tracking chemical alteration in magmatic zircon using rare earth element abundances abstract trace elements in magmatic zircon provide a wealth of petrogenetic information about host magmas however they are susceptible to alteration through post magmatic interaction with hydrothermal fluids trace element analyses can also be biased by the inadvertent inclusion of exotic materials such as mineral or glass inclusions in analyzed volumes of zircon in order to screen out samples with altered chemical signatures zircons with high flat light rare earth element lree patterns are typically considered to be altered however visual selection of such patterns is qualitative and does not address ambiguous cases the light rare earth element index lree i dy nd dy sm provides an approach for quantitative screening for aqueous alteration and contamination of zircon by exotic materials and was used to assess secondary processes in the greenschist facies jack hills detrital zircon suite however in addition to aqueous alteration the lree i is also sensitive to melt compositional evolution and its applicability to alteration in settings other than the jack hills quartzite is thus far undetermined we investigate igneous zircon populations from a variety of geologic settings that show evidence for alteration by contact metamorphism during magma intrusion and deuteric fluid interactions during pluton crystallization in suites with a high proportion of texturally altered zircons low lree i values are common and this parameter correlates well with other contamination indicators based on the observed secondary phases deposited in the zircons during fluid flow filtering zircon trace element compositions based on the lree i appears to remove the majority of chemically altered zircon in many cases revealing previously obscured magmatic signals

calcium and calcium isotope changes during carbon cycle perturbations at the end permian negative carbon and calcium isotope excursions as well as climate shifts took place during the most severe mass extinction event in earth s history the end permian 252 ma investigating the connection between carbon and calcium cycles during transient carbon cycle perturbation events such as the end permian may help resolve the intricacies between the coupled calcium carbon cycles as well as provide a tool for constraining the causes of mass extinction here we identify the deficiencies of a simplified calcium model employed in several previous studies and we demonstrate the importance of a fully coupled carbon cycle model when investigating the dynamics of carbon and calcium cycling simulations with a modified version of the long term ocean atmosphere sediment carbon cycle reservoir model which includes a fully coupled carbon calcium cycle indicate that increased weathering rates and ocean acidification potentially caused by siberian trap volcanism are not capable of producing trends observed in the record as previously claimed our model results suggest that combined effects of carbon input via siberian trap volcanism 12 000 pg c the cessation of biological carbon export and variable calcium isotope fractionation due to a change in the seawater carbonate ion concentration represents a more plausible scenario this scenario successfully reconciles 13c and 44ca trends observed in the sediment record as well as the proposed warming of 6 c

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

evidence for mass dependent isotopic fractionation of strontium in a glaciated granitic watershed abstract the stable isotope composition of strontium expressed as 88 86sr may provide important constraints on the global exogenic strontium cycle here we present 88 86sr values and 87sr 86sr ratios for granitoid rocks a 150 yr soil chronosequence formed from these rocks surface waters and plants in a small glaciated watershed in the central swiss alps incipient chemical weathering in this young system whether of inorganic or biological origin has no resolvable effect on the 87sr 86sr ratios and 88 86sr values of bulk soils which remain indistinguishable from bedrock in terms of sr isotopic composition although due in part to the chemical heterogeneity of the forefield the lack of a resolvable difference between soil and bedrock isotopic composition indicates that these soils have thus far witnessed minimal net loss of sr a low degree of chemical weathering is also implied by bulk soil chemistry the isotopic composition of sr in streamwater is more radiogenic than median soil reflecting the preferential weathering of biotite in the catchment streamwater 88 86sr values however are indistinguishable from bulk soil 88 86sr values implying that no resolvable fractionation of sr isotopes takes place during release to the weathering flux in the damma forefield analyses of plant tissue reveal that plants rhododendron and vaccinium preferentially assimilate the lighter isotopes of sr such that their 88 86sr values are significantly lower than those of the soils in which they grow additionally 88 86sr values of foliar and floral tissues are lower than those of roots contrary to observations for ca for which sr is often used as an analogue in weathering studies we suggest that processes that discriminate against sr in favour of ca due to the different nutritional requirement of plants for these two elements are responsible for the observed contrast

biological control of calcium isotopic abundances in the global calcium cycle measurements of 44ca 40ca expressed as 44ca were made on igneous rocks and on shell and bone material from modern organisms to investigate the magnitude and origins of calcium isotopic fractionation in nature the results document a span of 4 in 44ca measured with the double spike technique to a precision of 0 15 volcanic rocks including basalt and rhyolite show little variability and cluster near 44ca 0 0 2 systematic analysis of biological samples indicates that biological processing of calcium discriminates against heavy isotopes and that biological fractionation is the primary generator of calcium isotopic fractionation in nature preliminary data suggest that calcium becomes isotopically lighter as it moves through food chains calcium carbonate shells of marine microorganisms and deep sea carbonate ooze have 44ca about 1 0 lower than seawater this fractionation causes seawater to be enriched in heavy calcium 44ca 0 9 relative to igneous rocks marine organisms consequently are isotopically heavier than their terrestrial counterparts at similar trophic level the calcium isotopic composition of living and fossil organisms may record information on diet and environment

on the utility of quantitative modeling to the interpretation of ca isotopes abstract though the utility of calcium isotopes is broad examples of applications are still relatively sparse some of this paucity as with many metal isotope systems may derive from a perception that the analytical tool is difficult to access alternatively potential users may be deterred by a sense that calcium isotopes are ambiguous difficult to interpret and or complicated by too many interrelated processes here we provide an overview of the quantitative modeling approaches available to facilitate interpretation of calcium isotopes in earth systems in particular their ability to push interpretations beyond the qualitative while no method is perfect the variety of approaches described here offer an accessible toolset that is incredibly valuable we suggest that the calcium isotope community should be expanding the use of such techniques noting their limitations and striving to improve upon current methods over time