glacial interglacial temperature change in the tropical west pacific a comparison of stalagmite based paleo thermometers in the tropics geochemical records from stalagmites have so far mainly been used to qualitatively reconstruct changes in precipitation but several new methods to reconstruct past temperatures from stalagmite material have emerged recently i liquid vapor homogenization of fluid inclusion water ii noble gas concentrations in fluid inclusion water iii the partitioning of oxygen isotopes between fluid inclusion water and calcite and iv the abundance of the 13 c 18 o 16 o clumped isotopologue in calcite we present for the first time a direct comparison of these four paleo thermometers by applying them to a fossil stalagmite covering nearly two glacial interglacial cycles marine isotope stages mis 12 9 and to two modern stalagmites all from northern borneo the temperature estimates from the different methods agree in most cases within errors for both the old and recent samples reconstructed formation temperatures of the recent samples match within 2 sigma errors with measured cave temperatures however slight but systematic deviations are observed between noble gas and liquid vapor homogenization temperatures whereas the temperature sensitivity of fluid inclusion 18 o and clumped isotopes is currently debated we find that the calibration of tremaine et al 2011 for fluid inclusion 18 o and a synthetic calcite based clumped isotope calibration ziegler et al in prep yield temperature estimates consistent with the other methods all methods with the potential exception of clumped isotopes show excellent agreement on the amplitude of glacial interglacial temperature change indicating temperature shifts of 4 5 c this amplitude is similar to the amplitude of mg ca based regional sea surface temperature records when correcting for sea level driven changes in cave elevation our reconstruction of tropical temperature evolution over the time period from 440 to 320 thousand years ago ka adds support to the view that climate sensitivity to varying greenhouse forcing is substantial also in the deep tropics

meteoric sphaerosiderite lines and their use for paleohydrology and paleoclimatology sphaerosiderite a morphologically distinct millimeter scale spherulitic siderite feco 3 forms predominantly in wetland soils and sediments and is common in the geologic record ancient sphaerosiderites are found in paleosol horizons within coal bearing stratigraphic intervals and like their modern counterparts are interpreted as having formed in water saturated environments here we report on sphaerosiderites from four different stratigraphic units each of which has highly variable 13 c and relatively stable 18 o compositions the unique isotopic trends are analogous to well documented meteoric calcite lines which we define here as meteoric sphaerosiderite lines meteoric sphaerosiderite lines provide a new means of constraining ground water 18 o and thus allow evaluation of paleohydrology and paleoclimate in humid

quantitative estimates of tropical temperature change in lowland central america during the last 42 ka determining the magnitude of tropical temperature change during the last glacial period is a fundamental problem in paleoclimate research large discrepancies exist in estimates of tropical cooling inferred from marine and terrestrial archives here we present a reconstruction of temperature for the last 42 ka from a lake sediment core from lake peten itza guatemala located at 17 n in lowland central america we compared three independent methods of glacial temperature reconstruction pollen based temperature estimates tandem measurements of 18o in biogenic carbonate and gypsum hydration water and clumped isotope thermometry pollen provides a near continuous record of temperature change for most of the glacial period but the occurrence of a no analog pollen assemblage during cold dry stadials renders temperature estimates unreliable for these intervals in contrast the gypsum hydration and clumped isotope methods are limited mainly to the stadial periods when gypsum and biogenic carbonate co occur the combination of palynological and geochemical methods leads to a continuous record of tropical temperature change in lowland central america over the last 42 ka furthermore the gypsum hydration water method and clumped isotope thermometry provide independent estimates of not only temperature but also the 18o of lake water that is dependent on the hydrologic balance between evaporation and precipitation over the lake surface and its catchment the results show that average glacial temperature was cooler in lowland central america by 5 10 c relative to the holocene the coldest and driest times occurred during north atlantic stadial events particularly heinrich stadials hss when temperature decreased by up to 6 to 10 c relative to today this magnitude of cooling is much greater than estimates derived from caribbean marine records and model simulations the extreme dry and cold conditions during hss in the lowland central america were associated with fresh water forcing in the north atlantic which led to reduced atlantic meridional overturning circulation cooling of the north atlantic southern advance of sea ice and southward shift of the intertropical convergence zone although some models correctly predict the sign of temperature and precipitation changes they consistently underestimate the degree of observed cooling and decreased precipitation over land in lowland central america

evaluating formation fluid models and calibrations using clumped isotope paleothermometry on bahamian dolomites abstract the use of stable oxygen isotopes to understand the mechanisms of dolomite formation has been hampered by the inability to precipitate well ordered dolomite under normal earth surface conditions several studies have attempted to address this problem either by precipitating high temperature ordered dolomites and extrapolating the data to low temperatures or by using more disordered very high mg calcites as a proxy for low temperature dolomites the result is eight equations that disagree significantly from each other by as much as 3 6 in the 18o value of the precipitating fluid at 25 c and produce differences which can greatly affect the interpretation of the formation mechanisms for low temperature dolomites however by combining the recently developed clumped isotope paleothermometer an independent isotopic measurement 47 that directly relates to the temperature of formation to late miocene to pleistocene aged dolomites from the bahamas with a well constrained thermal and fluid history we have attempted to narrow down the viable equations used to interpret the 18o values of dolomites the clumped isotope temperatures measured on the bahamian dolomites 16 37 c agrees with the range of temperatures expected in the bahamas pairing these temperatures with geological and mineralogical arguments we favor the equation suggested by matthews and katz 1977 as it is the only one that produces realistic 18o fluid values across the range of clumped isotope temperatures both the clumped isotope temperatures and 18o values of the precipitating fluid show a strong positive covariance that we have interpreted as reflecting the mixing of surface brines that have undergone varying amounts of evaporation and normal seawater the different mechanisms driving these fluids included formation by normal marine seawater driven by the compensatory flow of the mixing zone bank wide kohout convection and evaporative brine reflux

siderite clumped isotope thermometry a new paleoclimate proxy for humid continental environments abstract clumped isotope measurements can be used to exploit the paleoclimatic potential of pedogenic siderite feco3 however the applicability of this method is held back by the lack of clumped isotope calibrations of mineralogies other than calcite and aragonite here we present an inorganic calibration of siderites grown in the laboratory between 21 and 51 c linear regression of 47 values and temperature 106 t2 k yields the following relationship r2 0 997 47 rf 0 0356 0 0018 10 6 t 2 0 172 0 019 we demonstrate that this calibration is indistinguishable from calcite at current levels of analytical precision our observations suggest that there is likely no large systematic bias in the clumped isotope acid fractionation factors between the two different carbonate minerals we also present clumped isotope measurements of a natural siderite collected from holocene sediments of the mississippi river delta we find that siderites record warm season marsh water temperatures instead of mean annual temperatures as it has long been presumed this finding has important implications for the accuracy of siderite stable isotope and clumped isotope based climate reconstructions

combining soil water balance and clumped isotopes to understand the nature and timing of pedogenic carbonate formation abstract pedogenic carbonate is an important archive for paleoclimate paleoecology and paleoelevation studies however it can form under seasonal environmental conditions that differ significantly from the mean growing season environment or mean annual conditions potentially complicating its use for proxy reconstructions the observed seasonal temperature is typically but not always biased high relative to mean annual air temperature mat to evaluate the annual timing of pedogenic carbonate formation ten different soils were sampled across the western united states sites were selected to span a variety of precipitation regimes and soil orders precipitation regimes ranged from arid sites mean annual precipitation map 50 cm dominated by summer precipitation pedogenic carbonate formation temperatures derived from clumped isotope measurements ranged between 6 and 22 c with most samples falling at or below mat clumped isotope temperatures were compared to monthly precipitation normals and modeled monthly values of evapotranspiration and soil water content results show that carbonate formation temperatures agree with the annual timing of soil water depletion suggesting soil moisture content is a primary control on the timing of pedogenic carbonate formation although the seasonal bias is a function of environmental factors that are difficult to reconstruct in paleo studies the use of other paleosol proxies can help to assess if changes in clumped isotope temperatures are a function of changes in air temperature or hydrology these results have important implications for the production of accurate paleoclimate and paleoelevation estimates

the mid cretaceous water bearer isotope mass balance quantification of the albian hydrologic cycle a latitudinal gradient in meteoric n 18 o compositions compiled from paleosol sphaerosiderites throughout the cretaceous western interior basin kwib 34 75 n paleolatitude exhibits a steeper more depleted trend than modern predicted values 3 0x 34 n latitude to 9 7x 75 n lighter furthermore the sphaerosiderite meteoric n 18 o latitudinal gradient is significantly steeper and more depleted 5 8x 34 n to 13 8x 75 n lighter than a predicted gradient for the warm mid cretaceous using modern empirical temperature n 18 o precipitation relationships we have suggested that the steeper and more depleted relative to the modern theoretical gradient meteoric sphaerosiderite n 18 o latitudinal gradient resulted from increased air mass rainout effects in coastal areas of the kwib during the mid cretaceous the sphaerosiderite isotopic data have been used to constrain a mass balance model of the hydrologic cycle in the northern hemisphere and to quantify precipitation rates of the equable greenhouse albian stage in the kwib the mass balance model tracks the evolving isotopic composition of an air mass and its precipitation and is driven by latitudinal temperature gradients our simulations indicate that significant increases in albian precipitation 34 52 and evaporation fluxes 76 96 are required to reproduce the difference between modern and albian meteoric siderite n 18 o latitudinal gradients calculations of precipitation rates from model outputs suggest mid high latitude precipitation rates greatly exceeded modern rates 156 220 greater in mid latitudes 2600 3300 mm yr 99 greater at high latitudes 550 mm yr the calculated precipitation rates are significantly different from the precipitation rates predicted by some recent general circulation models gcms for the warm cretaceous particularly in the mid to high latitudes our mass balance model by no means replaces gcms however it is a simple and effective means of obtaining quantitative data regarding the mid cretaceous hydrologic cycle in the kwib our goal is to encourage the incorporation of isotopic tracers into gcm simulations of the midcretaceous and to show how our empirical data and mass balance model estimates help constrain the boundary conditions

diagenetic overprinting of the sphaerosiderite palaeoclimate proxy are records of pedogenic groundwater delta18o values preserved meteoric sphaerosiderite lines msls defined by invariant d 18 o and variable d 13 c values are obtained from ancient wetland palaeosol sphaerosiderites millimetre scale feco3 nodules and are a stable isotope proxy record of terrestrial meteoric isotopic compositions the palaeoclimatic utility of sphaerosiderite has been well tested however diagenetically altered horizons that do not yield simple msls have been encountered well preserved sphaerosiderites typically exhibit smooth exteriors spherulitic crystalline microstructures and relatively pure 95 mol feco3 compositions diagenetically altered sphaerosiderites typically exhibit corroded margins replacement textures and increased crystal lattice substitution of ca 2 m g 2 and mn 2 for fe 2 examples of diagenetically altered cretaceous sphaerosideritebearing palaeosols from the dakota formation kansas the swan river formation saskatchewan and the success s2 formation saskatchewan were examined in this study to determine the extent to which original early diagenetic d 18 o and d 13 c values are preserved all three units contain poikilotopic calcite cements with significantly different d 18 o and d 13 c values from the co occurring sphaerosiderites the complete isolation of all carbonate phases is necessary to ensure that inadvertent physical mixing does not affect the isotopic analyses the dakota and swan river samples ultimately yield distinct msls for the sphaerosiderites and mcls meteoric calcite lines for the calcite cements the success s2 sample yields a covariant d 18 o vs d 13 c trend resulting from precipitation in pore fluids that were mixtures between meteoric and modified marine phreatic waters the calcite cements in the success s2 formation yield meteoric d 18 o and d 13 c values a stable isotope mass balance model was used to produce hyperbolic fluid mixing trends between meteoric and modified marine end member compositions modelled hyperbolic fluid mixing curves for the success s2 formation suggest precipitation from fluids that were 25 sea water

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

13c 18o isotope signatures and clumped isotope thermometry in foraminifera and coccoliths accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes most proxies for temperature are not thermodynamically based appear to be subject to biological processes require regional calibrations and or are influenced by fluid composition as a result their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated independent proxies for past temperature could provide an important means of testing and or expanding on existing reconstructions here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths relate those abundances to independently estimated growth temperatures and discuss the possible scope of equilibrium and kinetic isotope effects the proportions of 13c 18o bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonate containing minerals apatite from fish reptile and mammal teeth calcitic brachiopods and molluscs aragonitic coral and mollusks most species that exhibit non equilibrium 18o 16o 18o and 13c 12c 13c ratios are characterized by 13c 18o bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium with possible exceptions among benthic foraminiferal samples from the arctic ocean where temperatures are near freezing observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species

quantification of a greenhouse hydrologic cycle from equatorial to polar latitudes the mid cretaceous water bearer revisited article this study aims to investigate the global hydrologic cycle during the mid cretaceous greenhouse by utilizing the oxygen isotopic composition of pedogenic carbonates calcite and siderite as proxies for the oxygen isotopic composition of precipitation the data set builds on the aptian albian sphaerosiderite 18 o data set presented by ufnar et al 2002 by incorporating additional low latitude data including pedogenic and early meteoric diagenetic calcite 18 o ufnar et al 2002 used the proxy data derived from the north american cretaceous western interior basin kwib in a mass balance model to estimate precipitation evaporation fluxes we have revised this mass balance model to handle sphaerosiderite and calcite proxies and to account for longitudinal travel by tropical air masses we use empirical and general circulation model gcm temperature gradients for the mid cretaceous and the empirically derived 18 o composition of groundwater as constraints in our mass balance model precipitation flux evaporation flux relative humidity seawater composition and continental feedback are adjusted to generate model calculated groundwater 18 o

a reassessment of the precision of carbonate clumped isotope measurements implications for calibrations and paleoclimate reconstructions carbonate clumped isotopes offer a potentially transformational tool to interpret earth s history but the proxy is still limited by poor interlaboratory reproducibility here we focus on the uncertainties that result from the analysis of only a few replicate measurements to understand the extent to which unconstrained errors affect calibration relationships and paleoclimate reconstructions we find that highly precise data can be routinely obtained with multiple replicate analyses but this is not always done in many laboratories for instance using published estimates of external reproducibilities we find that typical clumped isotope measurements three replicate analyses have margins of error at the 95 confidence level cl that are too large for many applications these errors however can be systematically reduced with more replicate measurements second using a monte carlo type simulation we demonstrate that the degree of disagreement on published calibration slopes is about what we should expect considering the precision of 47 data the number of samples and replicate analyses and the temperature range covered in published calibrations finally we show that the way errors are typically reported in clumped isotope data can be problematic and lead to the impression that data are more precise than warranted we recommend that uncertainties in 47 data should no longer be reported as the standard error of a few replicate measurements instead uncertainties should be reported as margins of error at a specified confidence level e g 68 or 95 cl these error bars are a more realistic indication of the reliability of a measurement

clumped isotopic signatures in land snail shells revisited possible palaeoenvironmental implications abstract it is crucial to understand the clumped isotope compositions 47 of modern land snail shells and their relationship with environmental parameters for palaeoenvironmental studies previous studies have shown significant variations in relationships between snail shell 47 and ambient air temperature and the reliability of shell 47 in indicating air temperature remains uncertain this study examined the shell 47 from china with mean annual temperatures ranging from 5 to 23 c and the snail body fluid 18o estimated from shell 18o and 47 derived temperatures for all snails studied in this study site averaged 47 values yield snail calcification temperatures ranging from 25 to 36 c which are higher than expected in either environmental temperatures or estimated snail activity temperatures we suggest that snails up regulate their body temperatures towards their preferred living conditions likely through behaviour or and physiology adaptation especially at low temperature environments which is likely significant than observed previously 47 disequilibrium associated with co2 degassing during snail calcification is potential but it could possibly be corrected by using an empirical calibration based on natural land snails varying degrees of 18o enrichment 8 relative to rainwater are observed in snail body fluids possibly due to variable evaporation during shell calcification coupled with model calculations the relationship between snail body fluid 18o and rainwater 18o could be improved by using 47 based temperature and 18o thermometry if snails prefer to be active at 90 relative humidity this study highlights the importance of land snail shell 47 coupled with shell 18o to indicate temperature and rainwater 18o at micro environments scales

clumped isotope fractionation during phosphoric acid digestion of carbonates at 70 c the application of clumped isotopes 47 in carbonate minerals as a sensitive temperature proxy in paleo environments depends on a well constrained clumped isotope fractionation for the necessary step of phosphoric acid digestion of the carbonate mineral to produce co2 published estimates for clumped isotope fractionations vary and the effect of different carbonate mineralogies is still under debate differences in the sample preparation design and sample digestion temperatures are potential sources for varying acid fractionations and could be a source for discrepant 47 temperature calibrations observed in different laboratories to evaluate the clumped isotope acid fractionation at 70 c and simultaneously account for a potential cation effect we analyzed a set of eight carbonate minerals calcite aragonite dolomite and magnesite that were driven to a stochastic isotope distribution by heating them to temperatures of 1000 c our study reveals significant cation and mineral specific differences for the 47 acid fractionation of carbonate minerals digested at 70 c or 100 c the 47 acid fractionation at 70 c for calcite is 0 197 0 002 for aragonite 0 172 0 003 whereas dolomite has a significantly larger acid fractionation of 0 226 0 002 for magnesite digested at 100 c we observed a 47 acid fractionation of 0 218 0 020 projected to an acid digestion at 25 c our acid fractionation for calcite of 0 260 is statistically indistinguishable from existing studies we further show that the 47 of the calcite standards eth 1 and eth 2 of 0 265 and 0 267 respectively are in the range of the determined acid fractionation projected to 25 c suggesting that they have an identical and near stochastic isotope distribution the observed differences in the 47 acid fractionation between calcite and aragonite 47 0 025 and between calcite and dolomite 47 0 029 does not correlate with the phosphoric acid fractionation of oxygen isotopes but rather depends on the radius of the cation as well as on the mineral structure our results reveal that the acid fractionation of dolomite at 70 c is significantly distinct from the one of calcite but at 90 c the two are within error of each other due to the different acid fractionation temperature dependence of calcite and dolomite thus it is necessary to use a mineral specific 47 acid fractionation factor for dolomite to avoid differences in the final 47 signal from dolomites digested at 90 c and dolomites digested at lower temperatures similar effects may apply also to other carbonates such as magnesite and siderite however their mineral specific 47 acid fractionation at digestion temperatures around 90 c might be also similar to the one of calcite so that potential differences could be within the range of the analytical error

carbonate clumped isotope bond reordering and geospeedometry carbonate clumped isotope thermometry is based on the preference of 13c and 18o to form bonds with each other at elevated temperatures such bond ordering is susceptible to resetting by diffusion of c and o through the solid mineral lattice this type of bond reordering has the potential to obscure primary paleoclimate information but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates we determined arrhenius parameters for solid state reordering of c o bonds in two different calcites through a series of laboratory heating experiments we find that the calcites have different susceptibilities to solid state reordering reaction progress follows a first order rate law in both calcites but only after an initial period of non first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature we show that the apparent equilibrium temperature equations or closure temperature equations for carbonate clumped isotope reordering are analogous dodson s equations for first order loss of daughter isotopes for each calcite the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of 5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years however because the calcites have different susceptibilities to reordering each calcite defines its own cooling rate apparent equilibrium temperature relationship the cooling rates of carrara marble inferred from carbonate clumped isotope geospeedometry are 10 6 10 3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods cooling rates for 13c depleted calcites from the late neoproterozoic doushantou cap carbonates in south china are on the order of 102 104 degrees per annum consistent with rapid cooling following formation of these calcites by a short lived hydrothermal event bristow et al 2011 nature v 474 p 68 71 most of the uncertainty in these estimates relates to uncertainty in arrhenius parameters for different calcites thus while the carbonate clumped isotope geospeedometer shows promise for recording cooling rates in settings and lithologies where other geospeedometers may not be applicable the uncertainty in cooling rate will be large without independent knowledge of the reordering kinetics of each study material thus the full potential of the method will only be realized if reordering kinetics can be accurately determined for each study material or predicted on the basis of mineral composition texture or other observable parameters

the clumped isotope geothermometer in soil and paleosol carbonate we studied both modern soils and buried paleosols in order to understand the relationship of temperature t c 47 estimated from clumped isotope compositions 47 of soil carbonates to actual surface and burial temperatures carbonates from modern soils with differing rainfall seasonality were sampled from arizona nevada tibet pakistan and india t c 47 obtained from these soils shows that soil carbonate forms in the warmest months of the year in the late morning to afternoon and probably in response to intense soil dewatering t c 47 obtained from modern soil carbonate ranges from 10 8 to 39 5 c on average t c 47 exceeds mean annual temperature by 10 15 c due to summertime bias in soil carbonate formation and to summertime ground heating by incident solar radiation secondary controls on t c 47 are soil depth and shading site mean annual air temperature maat across a broad range 0 30 c of site temperatures is highly correlated with t c 47 from soils following the equation maat c 1 20 t c 47 0 21 72 r 2 0 92 where t c 47 0 is the effective air temperature at the site estimated from t c 47 the effective air temperature represents the air temperature required to account for the t c 47 at each site after consideration of variations in t c 47 with soil depth and ground heating the highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from t c 47 in paleosol carbonate assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites t c 47 0 decreases systematically with elevation gain in the himalaya following the equation elevation m 229 t c 47 0 9300 r 2 0 95 assuming that temperature varied similarly with elevation in the past this equation can be used to reconstruct paleoelevation from clumped isotope analysis of ancient soil carbonates we also measured t c 47 from long sequences of deeply buried 5 km paleosol carbonate in the himalayan foreland in order to evaluate potential diagenetic resetting of clumped isotope composition we found that paleosol carbonate faithfully records plausible soil t c 47 down to 2 5 4 km burial depth or 90 125 c deeper than this and above this temperature t c 47 in paleosol carbonate is reset to temperatures 40 c we observe 40 c as the upper limit for t c 47 in modern soils from soil depths 25 cm and therefore that t c 47 40 c obtained from ancient soil carbonate indicates substantially warmer climate regimes compared to the present or non primary temperatures produced by resetting during diagenesis if representative this limits the use of t c 47 to reconstruct ancient surface temperature to modestly buried 3 4 km paleosol carbonates despite diagenetic resetting of 47 values 18 o and 13 c values of the same deeply buried paleosol carbonate appear unaltered we conclude that solid state reordering or recrystallization of clumping of carbon and oxygen isotopes can occur in the absence of open system exchange of paleosol carbonate with significant quantities of water or other phases

determining the δ47 acid fractionation in dolomites abstract this paper reports the fractionation of 47 during the digestion of dolomite in phosphoric acid between 25 c and 90 c using five different samples including three of pliocene age from the bahamas one from the jurassic in the middle east and one obtained from the national institute of standards nist 88b the composition of the dolomites analyzed varied from ca0 56mg0 44co3 to ca0 50mg0 50co3 fractionation values were also compared between the common acid bath and sealed vessel techniques at various temperatures no statistically significant differences were observed either between these two methods or as a function of the dolomite s stoichiometry these data produce a difference in fractionation of 0 153 0 011 for dolomite samples digested at 90 c compared to those reacted at 25 c a value higher and statistically different to previously published values utilization of this value in a study of dolomites from a core drilled on the island of san salvador in the bahamas yielded temperatures and 18ofluid values which agree with previous interpretations on the formation of these dolomites application of this value to other published studies produces lower estimates of temperature and 18ofluid values for the dolomitization process that are more consistent with the geologic models suggested for these studies

experimental determination of fe isotope fractionation between aqueous fe ii siderite and green rust in abiotic systems abstract iron isotope fractionation between aqueous iron and siderite has been measured using abiotic synthesis experiments at 20 c applying a rayleigh distillation model to three experiments in which siderite feco3 was continuously precipitated from solutions over the course of tens of hours the derived fractionation factor is 103ln fe ii siderite 0 48 0 22 2 this experimentally determined fractionation factor is significantly smaller by 1 5 than that calculated from vibrational frequencies and mossbauer shifts geochim cosmochim acta 64 2000 849 865 geochim cosmochim acta 65 2001 2487 2497 and lies on the high end of that inferred from natural mineral assemblages where the fe ii aq siderite fractionation factor was inferred to lie between 1 7 and 0 3 contrib mineral petrol 144 2003 523 547 the measured fe ii aq siderite fractionation from this study suggests that siderite from archean and proterozoic rocks which have moderately negative 56fe values 1 5 to 0 5 may reflect precipitation from fe ii aq whose origin was hydrothermal in contrast natural siderites that have higher 56fe values apparently require non hydrothermal sources of fe and or different pathways of formation or may reflect the effects of cation substitution on the fe ii aq carbonate fractionation factor

shallow burial alteration of dolomite and limestone clumped isotope geochemistry carbonate clumped isotope paleothermometry is a promising method for paleoclimate reconstructions and understanding diagenetic processes although clumped isotope compositions measured as 47 values can be altered by recrystallization and thermal resetting several studies have investigated the effects of deep burial and exhumation on 47 values we present 47 values of samples from an 4500 m long drill core from andros island bahamas which represent the spectrum from shallow to deep burial conditions these limestones and dolomites originally formed under near surface temperature conditions which are reflected by 27 c 47 temperatures in samples buried to 1 3 km depth below this depth calculated 47 temperatures increase by 10 c indicating a shift from preserved near surface temperatures to diagenetically modified values importantly this shift is not accompanied by a change in 18o and 13c values or cathodoluminescence and non uniform micrometer scale crystallization is observed in both 47 altered and unaltered rocks similar 47 temperatures recorded by each carbonate phase suggest that mineral specific differences are minor fine grained dolomites and calcites are viable materials for recording surface temperature conditions and both are susceptible to alteration of their primary clumped isotope abundances during burial diagenesis our results demonstrate that original 47 values of fine grained carbonates can be altered under mild diagenetic conditions

high latitude meteoric δ 18 o compositions from the cenomanian bastion ridge formation axel heiberg island canadian arctic archipelago a palaeoclimate proxy from the sverdrup basin

a data driven spline model designed to predict paleoclimate using paleosol geochemistry paleosols fossil soils are abundant in the sedimentary record and reflect at least in part regional paleoclimate paleopedology thus offers a great potential for elucidating high resolution deep time paleoclimate records however many fossil soils did not equilibrate with climate prior to burial and instead dominantly express physical and chemical features reflective of other soil forming factors current models that use elemental oxides for climate reconstruction bypass the issue of soil climate equilibration by restricting datasets to narrow ranges of soil properties soil forming environments and mean annual precipitation map and mean annual temperature mat here we evaluate a data driven paleosol paleoclimate model ppm1 0 that uses subsoil geochemistry to test the ability of soils from wide ranging environments to predict map and mat as a joint response with few initial assumptions the ppm1 0 was developed using a combined partial least squares regression plsr and a nonlinear spline on 685 mineral soil b horizons currently forming under map ranging from 130 to 6900 mm and mat ranging from 0 to 27 c the plsr results on 11 major and minor oxides show that four linear combinations of these oxides regressors 1 4 akin to classic oxide ratios have potential for predicting climate regressor 1 correlates with increasing map and mat through fe oxidation desilication base loss and residual enrichment regressor 2 correlates with mat through temperature dependent dissolution of na and k bearing minerals regressor 3 correlates with increasing map through decalcification and retention of si regressor 4 correlates with increasing map through mg retention in mafic rich parent material the nonlinear spline model fit on regressors 1 to 4 results in a root mean squared error rmsemap of 228 mm and rmsemat of 2 46 c ppm1 0 model simulations result in root mean squared predictive error rmspemap of 512 mm and rmspemat of 3 98 c the rmse values are lower than some preexisting mat models and show that subsoil weathering processes operating under a wide range of soil forming factors possess climate prediction potential which agrees with the state factor model of soil formation the nonlinear multivariate model space of ppm1 0 more accurately reflects the complex and nonlinear nature of many weathering processes as climate varies this approach is still limited as it was built using data primarily from the conterminous usa and does not account for effects of diagenesis yet because it is calibrated over a broader range of climatic variable space than previous work it should have the widest array of potential applications furthermore because it is not dependent on properties that may be poorly preserved in buried paleosols the ppm1 0 model is preferable for reconstructing deep time climate transitions in fact previous studies may have grossly underestimated paleo map for some paleosols

calibration of dolomite clumped isotope thermometry abstract use of the clumped isotope thermometer to decipher environments of dolomite formation has been inhibited by a lack of empirical data from dolomites formed at known temperatures calibrations for aragonite calcite siderite and apatite indicate that a universal 47 temperature relationship may exist across all carbonate bearing mineral phases however theoretical modeling and proposed acid fractionation differences have suggested that dolomites may have different 47 values relative to calcites precipitated at the same temperature to resolve this question we analyzed five synthetic and four natural dolomites formed at known temperatures these included synthetic dolomites grown in mg ca cl solutions at temperatures of 200 250 c and natural samples constrained by fluid inclusion analyses 70 c climate 28 and 27 c and deep ocean borehole temperature 21 c when using calcite 47 acid fractionation values these data result in a calibration line that is statistically indistinguishable from other clumped isotope calibrations at least with current precision we find no evidence for a consistent dolomite 47 offset these results further support a universal calibration for carbonate clumped isotope thermometry and enable new investigations into conditions of dolomite formation

hot or not impact of seasonally variable soil carbonate formation on paleotemperature and o isotope records from clumped isotope thermometry quantifying the timing and temperature of soil carbonate formation is important for interpreting isotopic records of earth surface temperature and soil water composition from paleosols pedogenic carbonates typically have been assumed to form at mean annual temperature but recent work suggests warm season bias in carbonate formation could impact the interpretation of d 18 o values and carbonate

surface rupture earthquakes over the last 1000 years in the wellington region new zealand and implications for ground shaking hazard the wellington region is cut by five active right lateral strike slip faults wairarapa wellington ohariu shepherds gully pukerua and wairau faults that have average recurrence intervals of meter scale surface rupture that range from 500 years to 5000 years and lateral slip rates that range from 1 to 10 mm yr only the wairarapa fault has ruptured since european settlement since circa a d 1840 paleoseismological studies on these faults have allowed the compilation of a complete record of surface rupture events over the past 1000 years in the wellington region within this time period there does not appear to be any temporal clustering of surface rupture events on adjacent faults the m 8 a d 1855 wairarapa earthquake did not trigger rupture on any other fault in the region the most recent surface faulting event on the wellington fault 290 440 cal years b p cal years are calendar years before a d 1950 does not coincide with rupture of any other onland fault and over 300 years separate the timing of the second most recent rupture on the wellington fault 660 720 cal years b p and the most recent rupture of the ohariu fault 1060 1140 cal years b p the most recent rupture of the shepherds gully pukerua fault is probably older than that of the ohariu fault the apparent nonclustering of surface rupture earthquakes in the wellington region has been documented only for the on land strike slip faults there are other possible seismogenic sources in the region and thus important issues remain to be addressed regarding the history of large earthquakes in the wellington region 1 the seismogenic potential and earthquake recurrence interval of the subduction thrust beneath wellington is not known 2 the timing of rupture events on the offshore portion of the wairau fault is not known and 3 paleoseismic data are not available for the section of the wellington fault north of the wellington hutt valley segment estimates of earthquake hazard in the wellington region for all return times greater than 50 years that incorporate paleoseismicity data are between one and two modified mercalli mm intensity units higher than the hazard based solely on the historical seismicity catalog and the hazard is spatially more variable using a deterministic attenuation model the level of shaking hazard approaches near maximum values within a return time of 500 years largely reflecting the recurrence interval 500 770 years of surface rupture earthquakes on the wellington fault inclusion of a plausible model for magnitude 8 subduction zone earthquakes does not affect the level of mm intensity in wellington region at return times greater than 500 years but does make a small contribution to the hazard at return times between 50 and 500 years

optimized sequential extraction for carbonates quantification and δ13c analysis of calcite dolomite and siderite siderite is present in diverse types of rocks and sediments but its quantification is cumbersome when present in relatively low contents a new analytical method for the sequential separation of different carbonate phases is presented the separation quantification and characterization of the carbonates is based on different kinetic reactions during acid digestion in combination with monitoring the solution composition and the concomitant release of co2 trapping the released gasses permits the isotopic characterization 13c of the different phases based on published rate laws an idealized model was built to identify ph and temperature conditions for optimal separation of the various carbonates by taking the size distribution of carbonate particles into consideration results from the theoretical survey were implemented in an extraction scheme which was optimized and evaluated by tests on pure mineral phases and their mixtures further tests on a diverse array of sediment and rock samples validated the specificity and reproducibility of the method

clumped isotope thermometry of magnesium carbonates in ultramafic rocks abstract magnesium carbonate minerals produced by reaction of h 2 o co 2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes including 1 deposition of ore grade massive vein cryptocrystalline magnesite 2 formation of hydrous magnesium carbonates in weathering environments and 3 metamorphic carbonate alteration of ultramafic rocks however the application of traditional geochemical and isotopic methods to infer temperatures of mineralization the nature of mineralizing fluids and the mechanisms controlling the transformation of dissolved co 2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved clumped isotope compositions of magnesium carbonates provide a means to determine primary mineralization or re equilibration temperature which permits the reconstruction of geologic processes that govern magnesium carbonate formation we first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite along with natural metamorphic magnesite and low temperature hydromagnesite precipitated within a mine adit we show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error in addition we employ carbonate clumped isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings cryptocrystalline magnesite vein deposits from california red mountain magnesite mine austria kraubath locality turkey tutluca mine eskisehir district and iran derakht senjed deposit exhibit broadly uniform 47 compositions that yield apparent clumped isotope temperatures that average 23 7 5 0 c based on oxygen isotope thermometry these clumped isotope temperatures suggest mineralization at shallow crustal depths in the presence of meteoric water hydrous magnesium carbonates from a 400 km latitudinal transect along the serpentinized peridotite bodies of the california coast ranges record clumped isotope temperatures between 14 2 and 22 7 2 8 c in agreement with historical maximum temperatures during the rainy season for california talc carbonate alteration of ultramafic rocks in greenland isua supracrustal belt and vermont ludlow yields clumped isotope alteration temperatures of magnesite and dolomite between 326 and 490 c broadly consistent with paragenesis and thermodynamic analysis for co 2 metasomatism of ultramafic rocks these metamorphic carbonates extend the applicability of clumped isotope thermometry to high temperature magnesium carbonate systems and indicate equilibrium blocking temperatures for magnesite of 490 c our study demonstrates the applicability of the clumped isotope approach to provide information on the formation of magnesium carbonates as ore resources surface records of climate and metamorphic assemblages

constraining the thermal history of the north american midcontinent rift system using carbonate clumped isotopes and organic thermal maturity indices abstract the midcontinent rift system mrs is a late mesoproterozoic 1 1 ga sequence of volcanic and sedimentary rocks exposed in the lake superior region of north america the mrs continues to be the focus of much research due to its economic mineral deposits as well as its archive of precambrian life and tectonic processes in order to constrain the post depositional thermal history of the mrs samples were analyzed for carbonate clumped isotope composition and organic thermal maturity clumped isotope values from sedimentary early diagenetic samples were partially reset during burial to temperatures between 68 and 75 c solid state reordering models indicate that maximum burial temperatures of 125 155 c would reset the clumped isotope values to the observed temperature range prior to the onset of regional cooling and uplift clumped isotope results from late stage veins in the white pine mine encompass a greater temperature range 49 116 c indicative of spatially variable hydrothermal activity and vein emplacement after burial temperatures fell below 100 c during regional cooling and uplift clumped isotope and organic thermal maturity data do not indicate significant spatial differences in thermal history along the mrs observed variability in bulk organic matter composition and biomarker indices are therefore more likely a result of shifts in primary productivity or early degradation processes these results demonstrate that the mrs experienced a spatially consistent relatively mild thermal history 125 155 c and is therefore a valuable archive for understanding the late mesoproterozoic environment

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

comparison of clumped isotope signatures of dolomite cements to fluid inclusion thermometry in the temperature range of 73 176 c abstract widespread application of the novel clumped isotope paleothermometer 47 using dolomite samples from shallow crustal settings has been hindered by a lack of adequate constraints on clumped isotope systematics in dolomites that formed at temperatures greater than 50 c consequently many high temperature applications involving diagenetic dolomites have required an assumption that the relationship between temperature and 47 in diagenetic dolomite resembles the theoretical temperature dependence for calcite here we present 47 results from dolomite cements for which precipitation temperatures were determined independently using fluid inclusion microthermometry we compare a rock based calibration for samples from the temperature range of 73 to 176 c to previously published laboratory derived calibrations for synthetic calcites this novel combination of approaches yields results that are broadly consistent with results reported from controlled laboratory experiments providing an important confirmation of the utility of clumped isotopes in real world systems our results suggest that the 47 of dolomite cements may provide key information in the reconstruction of burial and thermal histories and also in the recognition of potential petroleum reservoirs

temperature evolution and the oxygen isotope composition of phanerozoic oceans from carbonate clumped isotope thermometry abstract surface temperature is among the most important parameters describing planetary climate and habitability and yet there remains considerable debate about the temperature evolution of the earth s oceans during the phanerozoic eon 541 million years ago to present the time during which complex metazoan life radiated on earth here we critically assess the emerging record of phanerozoic ocean temperatures based on carbonate clumped isotope thermometry of fossil brachiopod and mollusk shells and we present new data that fill important gaps in the late paleozoic record we evaluate and reject the hypothesis that solid state reordering of 13c 18o bonds has destroyed the primary clumped isotope temperature signal of most fossils during sedimentary burial at elevated temperatures the resulting phanerozoic record which shows a general coupling between tropical seawater temperatures and atmospheric carbon dioxide co2 levels since the paleozoic indicates that tropical temperatures during the icehouse climate of the carboniferous period were broadly similar to present 25 30 c and suggests that benthic metazoans were able to thrive at temperatures of 35 40 c during intervals of the early and possibly the latest paleozoic when co2 levels were likely 5 10 higher than present day values equally important there is no resolvable trend in seawater oxygen isotope ratios 18 o over the past 500 million years indicating that the average temperature of oxygen exchange between seawater and the oceanic crust has been high 270 c since at least the early paleozoic which points to mid ocean ridges as the dominant locus of water rock interaction over the past half billion years

fabric variability associated with periglacial mass wasting at eagle summit alaska fabric analysis is a frequently applied technique and when used in concert with other tools aids the interpretation of glacigenic and colluvial depositional environments the research presented here focuses on its application to periglacial colluvium using a stratified systematic unaligned sampling framework in order to assess the variation of fabrics generated the range of possible variation in fabric is necessary information for its application to periglacial paleoenvironmental interpretation fabric strength and shape from 68 samples of 50 stones each on a range of microgeomorphic settings across terrain influenced by periglacial mass wasting in central alaska were analyzed in relation to local slope orientation clast characteristics organic mat thickness stone density distance downslope from the divide soil texture and soil moisture principal components analysis pca was used to reduce stone characteristics to three factors multiple regression analyses of the three factors and environmental variables with the fabric strength parameters as dependent variables indicate that stone characteristics particularly size and platyness are the most significant factors determining fabric strength no distinct fabric strength or shape was associated with specific landforms these results raise serious doubts as to the time cost effectiveness of the application of fabric analysis as a paleoenvironmental tool to identify periglacial landforms from their deposits

carbonate clumped isotope thermometry of deep sea corals and implications for vital effects here we calibrate the carbonate clumped isotope thermometer in modern deep sea corals we examined 11 specimens of three species of deep sea corals and one species of a surface coral spanning a total range in growth temperature of 2 25 c external standard errors for individual measurements ranged from 0 005 to 0 011 average 0 0074 which corresponds to 1 2 c external standard errors for replicate measurements of 47 in corals ranged from 0 002 to 0 014 average 0 0072 which corresponds to 0 4 2 8 c we find that skeletal carbonate from deep sea corals shows the same relationship of 47 the measure of 13 c 18 o ordering to temperature as does inorganic calcite in contrast the 13 c and 18 o values of these carbonates measured simultaneously with 47 for every sample differ markedly from equilibrium with seawater i e these samples exhibit pronounced vital effects in their bulk isotopic compositions we explore several reasons why the clumped isotope compositions of deep sea coral skeletons exhibit no evidence of a vital effect despite having large conventional isotopic vital effects

reducing uncertainties in carbonate clumped isotope analysis through consistent carbonate based standardization about a decade after its introduction the field of carbonate clumped isotope thermometry is rapidly expanding because of the large number of possible applications and its potential to solve long standing questions in earth sciences major factors limiting the application of this method are the very high analytical precision required for meaningful interpretations the relatively complex sample preparation procedures and the mass spectrometric corrections needed in this paper we first briefly review the evolution of the analytical and standardization procedures and discuss the major remaining sources of uncertainty we propose that the use of carbonate standards to project the results to the carbon dioxide equilibrium scale can improve interlaboratory data comparability and help to solve long standing discrepancies between laboratories and temperature calibrations the use of carbonates reduces uncertainties related to gas preparation and cleaning procedures and ensures equal treatment of samples and standards we present a set of carbonate standards of diverse composition discuss how they can be used to correct for mass spectrometric biases and demonstrate that their use significantly improves the comparability among four laboratories we propose that the use of these standards or of a similar set of carbonate standards will improve the comparability of data across laboratories

paleoclimate reconstruction using carbonate clumped isotope thermometry carbonate clumped isotope thermometry is a relatively new paleotemperature proxy based on measurements of the degree of ordering of 13 c and 18 o into bonds with each other making the 13 c 18 o 16 o 2 2 ion group in lattices of carbonate minerals this technique has several unusual properties that complement existing methods of paleoclimate reconstruction most importantly it is based on a homogeneous isotope exchange equilibrium and thus constrains temperature independent of the isotopic composition of waters from which carbonates grew this method also appears to be generally insensitive to vital effects that compromise many other paleothermometers based on the chemical properties of biominerals or organic matter at least for those organisms that have been subjected to systematic study to date corals and foraminifera however discrepancies among some calibrations particularly at low temperatures may point toward the existence of vital effects in mollusks and other organisms this review discusses the principles and calibrations of the technique its uses in combination with conventional stable isotope measurements to constrain the 18 o of past waters preservation of paleotemperatures in ancient materials as well as current problems in our understanding of calibrations and interlaboratory data comparisons

near equilibrium 13 c 18 o bonding during inorganic calcite precipitation under chemo stat conditions we report results of 13 c 12 c 18 o 16 o and 13 c 18 o clumped isotope analyses from a series of calcite precipitation experiments from aqueous solutions under laboratory conditions chemo stat precipitation experiments were performed to synthetically form calcite from aqueous solution onto 43 ca labeled calcite seed crystals formation rate was controlled during the experiments to investigate the effect of precipitation rate and temperature on 13 c 18 o bonding in calcite where rates ranged from 10 6 88 to 10 8 20 mol m 2 s 1 at three temperatures 10 20 and 30 c no relation was observed between precipitation rate and 13 c 18 o bonding proportion over the range of precipitation rates used the relation between 47 and temperature produced was comparable to calibration studies which report a relatively high sensitivity of 13 c 18 o bonding to temperature over the range investigated comparing solution conditions across multiple experimental data sets indicates an inverse relation between saturation state and 13 c 18 o bonding where high super saturation conditions are likely to be furthest from equilibrium 13 c 18 o partitioning carbon fractionation between calcite and hco 3 aq was found to be a temperature independent value of 1 6 the temperature dependent calcite water 18 o 16 o fractionation relation determined in this study is slightly different larger calcite h 2o value than those measured in several previous investigations significantly we observe a dependence of the 18o 16o isotope fractionation factor on growth rate taken together these findings suggest carbonate growth in our experiments approached equilibrium more closely than previous experiments of this type yet did not achieve full o isotope equilibrium

a 600 million year carbonate clumped isotope record from the sultanate of oman carbonate clumped isotope thermometry is a promising technique that has the potential to help decode the significance of the variability of both physical and geochemical compositions of ancient carbonate rocks this study utilizes a 600 million year record of marine carbonate rocks from the subsurface and surface of the sultanate of oman to explore how burial and exhumation affected the carbonate clumped isotope thermometer samples span 6 km of burial depth and include calcite and dolomite mineralogies and a range of carbonate rock textures we find evidence for two broad patterns in the physical and geochemical behavior of carbonate rocks during burial the first group of carbonates yield water 18 o vsmow compositions slightly enriched or equal to an expected ice free seawater composition of 1 2 and display good to fair textural preservation suggesting that cementation and lithification occurred within tens of meters of the sediment water interface temperatures from the second group sit on the present day geotherm yield highly enriched water 18 o vsmow compositions and display fair to poor textural preservation we find no evidence for solid state reordering in paired analyses of calcites and dolomites our results contribute to a growing body of work that indicates that the seawater 18 o vsmow composition has not changed significantly over 600 myr and was not 6 in the ediacaran

carbon and oxygen stable isotopic signatures of methanogenesis temperature and water column stratification in holocene siderite varves abstract manganoan siderite fe mn co 3 occurs in abundance of up to 19 dry weight as the sole endogenic carbonate within a succession of holocene organic rich varved sediments from freshwater otter lake ol michigan radiocarbon dating and varve counts from a 7 m piston core constrain periods of major siderite accumulation to sediments older than 1200 cal yr bp sediment petrography suggests that siderite was a seasonal precipitate confined to the summer layer of the varve couplet bulk sediment chemistry reveals cycles in abundance of manganese and aluminum coincident with centennial scale cycles of siderite accumulation siderite 13 c and 18 o are enriched when the mineral is abundant and depleted when it is least abundant samples with high abundance of siderite precipitated in oxygen isotopic equilibrium with modern lake water but are 13 c enriched relative to modern waters samples from intervals of low siderite abundance are 13 c and 18 o depleted relative to equilibrium with modern lake water these data suggest that abundant siderite precipitation occurred when the ol water column was ferruginous iron meromictic allowing for enhanced ferrous iron concentrations and dissolved inorganic carbon dic enriched in 13 c below the chemocline where methanogenesis in waters and sediments influenced dic composition seasonal siderite precipitation was triggered by water column alkalinity fluctuations driven by summer calcite dissolution manganese substitution in siderite lowered kinetic barriers to low temperature mineral precipitation climate changes and basin filling influenced lake stratification and the rate of siderite precipitation the siderite occurrence reported here displays remarkable similarity to its occurrence in paleogene maar lake deposits suggesting that further studies of holocene lacustrine siderites may provide insight into ancient sedimentary systems and environments

micromorphology and stable isotope geochemistry of historical pedogenic siderite formed in pah contaminated alluvial clay soils tennessee u s a abstract alluvial clay soil samples from six boreholes advanced to depths of 400 450 cm top of limestone bedrock from the chattanooga coke plant ccp site were examined micromorphologically and geochemically in order to determine if pedogenic siderite feco3 was present and whether siderite occurrence was related to organic contaminant distribution samples from shallow depths were generally more heavily contaminated with polycyclic aromatic hydrocarbons pahs than those at greater depth the upper 1 m in most boreholes consisted of mixtures of anthropogenically remolded clay soil fill containing coal clinker cinder grains and limestone gravel most layers of coarse fill were impregnated with creosote and coal tar most undisturbed soil below 1 m depth consisted of highly structured clays exhibiting fine subangular blocky ped structures as well as redox related features pedogenic siderite was abundant in the upper 2 m of most cores and in demonstrably historical 100 years old soil matrices two morphologies were identified 1 sphaerosiderite crystal spherulites ranging from 10 to 200 m in diameter and 2 coccoid siderite comprising grape like clusters of crystals 5 20 m in diameter the siderite formed in both macropores and within fine grained clay matrices indicates development of localized anaerobic low eh conditions possibly due to microbial degradation of organic contaminants stable isotope compositions of the siderite have 13c values spanning over 25 7 to 18 vpdb indicating fractionation of dic by multiple microbial metabolic pathways but with relatively constant 18o values 4 8 0 66 vpdb defining a meteoric sphaerosiderite line msl calculated isotope equilibrium water 18o values from pedogenic siderites at the ccp site are from 1 to 5 per mil lighter than the groundwater 18o values that we estimate for the site if confirmed by field studies in progress this observation might call for a reevaluation of low temperature siderite water 18o fractionations investigations at the ccp site thus provide valuable information on the geochemical conditions under which siderite can form in modern soils and thus insight on controls on siderite formation in ancient soils

temperature dependence of oxygen and clumped isotope fractionation in carbonates a study of travertines and tufas in the 6 95 c temperature range conventional carbonate water oxygen isotope thermometry and the more recently developed clumped isotope thermometer have been widely used for the reconstruction of paleotemperatures from a variety of carbonate materials in spite of a large number of studies however there are still large uncertainties in both 18o and 47 based temperature calibrations for this reason there is a need to better understand the controls on isotope fractionation especially on natural carbonates in this study we analyzed oxygen carbon and clumped isotopes of a unique set of modern calcitic and aragonitic travertines tufa and cave deposits from natural springs and wells together these samples cover a temperature range from 6 to 95 c travertine samples were collected close to the vents of the springs and from pools and tufa samples were collected from karstic creeks and a cave the majority of our vent and pool travertines and tufa samples show a carbonate water oxygen isotope fractionation comparable to the one of tremaine et al 2011 with some samples showing higher fractionations no significant difference between the calcite water and aragonite water oxygen isotope fractionation could be observed the 47 data from the travertines show a strong relationship with temperature and define the regression 47 0 044 0 005 106 t2 0 205 0 047 the ph of the parent solution mineralogy and precipitation rate do not appear to significantly affect the 47 signature of carbonates compared to the temperature effect and the analytical error the tufa samples and three biogenic calcites show an excellent fit with the travertine calibration indicating that this regression can be used for other carbonates as well this work extends the calibration range of the clumped isotope thermometer to travertine and tufa deposits in the temperature range from 6 c to 95 c

meltwater pulse recorded in last interglacial mollusk shells from bermuda the warm climate of bermuda today is modulated by the nearby presence of the gulf stream current however iceberg scours in the florida strait and the presence of ice rafted debris in bermuda rise sediments indicate that during the last deglaciation icebergs discharged from the laurentide ice sheet traveled as far south as subtropical latitudes we present evidence that an event of similar magnitude affected the subtropics during the last interglacial potentially due to melting of the greenland ice sheet using the clumped isotope paleothermometer we found temperatures 10 c colder and seawater 18o values 2 lower than modern in last interglacial cittarium pica shells from grape bay bermuda in contrast last interglacial shells from rocky bay bermuda record temperatures only slightly colder and seawater 18o values similar to modern likely representing more typical last interglacial conditions in bermuda outside of a meltwater event the significantly colder ocean temperatures observed in grape bay samples illustrate the extreme sensitivity of bermudian climate to broad scale ocean circulation changes they indicate routine meltwater transport in the north atlantic to near equatorial latitudes which would likely have resulted in disruption of the atlantic meridional overturning circulation these data demonstrate that future melting of the greenland ice sheet a potential source of the last interglacial meltwater event could have dramatic climate effects outside of the high latitudes

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

devils hole paleotemperatures and implications for oxygen isotope equilibrium fractionation subaqueous calcite in devils hole nevada was growing continuously from slightly super saturated groundwater providing a 570 kyr long o18 paleoclimate record due to its very slow growth it has been assumed to have grown under conditions of isotopic equilibrium however its holocene o18 value is 1 5 higher than predicted by laboratory precipitation based oxygen isotope thermometer calibrations the suggestion that devils hole calcite anchors the isotope thermometer to more 18o enriched values has stirred a debate as to which paleothermometer calibration is relevant for paleoclimate and casts doubt on the validity of o18 based paleotemperatures we used clumped isotopes to test the assumptions of the devils hole alternative 18o thermometer carbonate clumped isotopes are a temperature proxy that measures the abundance of 13c18o bonds in caco3 this proxy is independent of the water composition and therefore gives independent estimates of temperatures when calcite forms at thermodynamic and isotopic equilibrium we find that devils hole water paleotemperatures were constant at 30 6 2 6 c between 27 and 180 ka similarly to the modern groundwater temperature of 32 8 34 3 c the proximity of the devils hole clumped isotope data to values expected based on modern groundwater temperatures supports the notion that devils hole calcite grew under equilibrium conditions therefore the commonly used laboratory based o18 temperature calibrations should be reconsidered the constant water temperature over the glacial interglacial cycles indicates that the long devils hole o18 record reflects only variations in the groundwater o18 values and as such represents a valuable archive of paleoclimate and isotope paleohydrology

calibration of the carbonate clumped isotope paleothermometer for otoliths paleothermometry is an essential tool for understanding past changes in climate the carbonate clumped isotope thermometer is a temperature proxy related to ordering of 13 c and 18 o in the carbonate lattice based on measurements of 13 c 18 o 16 o in co 2 produced by acid digestion of carbonate this thermometer has been previously calibrated for inorganic calcite and aragonitic corals ghosh p adkins j affek h balta b guo w f schauble e a schrag d and eiler j m 2006 c 13 o 18 bonds in carbonate minerals a new kind of paleothermometer geochim cosmochim acta70 6 1439 1456 here we determine the relationship between growth temperatures of aragonitic fish otoliths and abundances of 13 c 18 o 16 o produced by acid digestion of those otoliths our calibration is based on analyses of otoliths from six species from four genera of modern fish sampled from a latitudinal transect of the atlantic ocean between 54 s and 65 n plus one species from the tropical western pacific the temperatures at which fish otoliths precipitated were estimated by the mean temperature in the waters in which they lived averaged over their estimated lifetimes estimated growth temperatures of our samples vary between 2 and 25 c our results show that the abundance of 13 c 18 o 16 o in co 2 produced by acid digestion of fish otolith aragonite is a function of growth temperature following the relationship 47 0 0568x10 6 t 2 where 47 is the enrichment in per mil of 13 c 18 o 16 o in co 2 relative to the amount expected for a stochastic random distribution of isotopes among all co 2 isotopologues and t is the temperature in kelvin this relationship closely approaches that previously documented for inorganic calcite and aragonitic coral ghosh et al 2006

constraining temperatures of formation and composition of dolomitizing fluids in the upper devonian nisku formation alberta canada with clumped isotopes abstract three dolomite phases in the burial dolomitization system of the nisku formation in central alberta canada were measured for carbonate clumped isotopes independent temperature constraints using fluid inclusions and traditional oxygen isotope geothermometry allow us to test the application of this method using a new calibration curve extrapolated to higher temperatures these three phases of dolomite correspond to three diagenetic stages in the burial history the oldest phase is replacive gray matrix dolomite formed during relatively shallow burial depths at average clumped isotope temperatures 47t of 80 7 c previous temperature estimates from standard oxygen isotope geothermometry ranged from 50 to 80 c a calculated 18o h2o of 3 1 4 vsmow points to precipitation from devonian seawater modified by evaporation and or water rock interaction the first phase of saddle dolomite cement formed by pressure solution during intermediate burial depths yielded average 47t of 96 4 c previously calculated at 80 c and 18o h2o of 4 1 vsmow a second phase of saddle dolomite formed in association with thermochemical sulphate reduction during deep burial records average 47t of 151 5 c comparable to fluid inclusion temperatures ranging from 125 to 145 c the average 18o h2o of the fluid that formed this saddle dolomite phase is calculated as 8 1 vsmow suggesting much more advanced water rock interaction 47t are consistent with previous temperature estimates from a combination of geological data conventional o isotope and fluid inclusion thermometry another important finding is that the 47 signatures are preserved even after reaching deeper burial and or during uplift and cooling which points to a closure temperature in dolomites in excess of 180 c thus dolomite appears to be a better phase for clumped isotope analysis than calcite for rocks that have been exposed to higher temperatures upon further burial this study demonstrates the power of the clumped isotope thermometer to reconstruct complex diagenetic histories in burial diagenetic environments where multiple generations of diagenetic cements can be analyzed individually

middle cretaceous greenhouse hydrologic cycle of north america we present a paleolatitudinal precipitation reconstruction for the greenhouse setting of mid latitude north america based on the oxygen isotopic composition of sphaerosiderites found in middle cretaceous wetland paleosols our reconstructed middle cretaceous d 18 o values of precipitation are 4 less than values from comparable modern low elevation coastal settings free of monsoons the data fit a conceptual model in which the precipitation source for the eastern margin of the cretaceous western interior seaway of north america is an 18 o enriched oceanic coastal jet in this subtropical tropical setting midcretaceous precipitation rates are interpreted to range from 2500 to 4100 mm yr

a paired apatite and calcite clumped isotope thermometry approach to estimating cambro ordovician seawater temperatures and isotopic composition the secular increase in 18 o values of both calcitic and phosphatic marine fossils through early phanerozoic time suggests either that 1 early paleozoic surface temperatures were high in excess of 40 c tropical mat 2 the 18 o value of seawater has increased by 7 8 vsmow through paleozoic time or 3 diagenesis has altered secular trends in early paleozoic samples carbonate clumped isotope analysis in combination with petrographic and elemental analysis can deconvolve fluid composition from temperature effects and therefore determine which of these hypotheses best explain the secular 18 o increase clumped isotope measurements of a suite of calcitic and phosphatic marine fossils from late cambrian to middle late ordovician aged strata the first paired fossil study of its kind document tropical sea surface temperatures near modern temperatures 26 38 c and seawater oxygen isotope ratios similar to today s ratios

seasonal bias in the formation and stable isotopic composition of pedogenic carbonate in modern soils from central new mexico usa in order to better calibrate pedogenic carbonate as a proxy for past environments we compared the stable isotopic composition of soil co 2 soil water and pedogenic carbonate in young soils from central new mexico usa seasonal changes in the 13 c value of soil co 2 the 18 o value of soil water and the soil temperature were monitored to establish the timing of isotopic equilibrium with the carbonate calcite solubility was calculated from measured temperatures and co 2 concentrations in the soil this approach allowed us to determine the conditions associated with pedogenic carbonate formation carbon isotope equilibrium oxygen isotope equilibrium and minimum calcite solubility all occurred simultaneously during warm dry conditions in may 2008 when soil co 2 concentrations were low it is therefore concluded that pedogenic carbonate forms during warm dry periods and does not record mean growing season conditions as typically assumed the seasonal bias in pedogenic carbonate formation may explain the occurrence of pedogenic carbonate in monsoon climates and its absence in regions where annual precipitation is more uniformly distributed the implications of the seasonal bias for stable isotope based paleoenvironmental reconstructions are that paleoelevations may have been previously over or underestimated paleoatmospheric co 2 concentrations likely have been signifi cantly overestimated and pedogenic carbonate provides a c 4 biased record of paleovegetation especially in dry soils

effects of improved 17o correction on interlaboratory agreement in clumped isotope calibrations estimates of mineral specific offsets and temperature dependence of acid digestion fractionation the clumped isotopic composition of carbonate derived co denoted is a function of carbonate formation temperature and in natural samples can act as a recorder of paleoclimate burial or diagenetic conditions the absolute abundance of heavy isotopes in the universal standards vpdb and vsmow defined by four parameters r r r and impact calculated values here we investigate whether use of updated and more accurate values for these parameters can remove observed interlaboratory differences in the measured t relationship using the updated parameters we reprocess 14 published calibration data sets measured in 11 different laboratories representing many mineralogies bulk compositions sample types reaction temperatures and sample preparation and analysis methods exploiting this large composite data set n 1 253 sample replicates we investigate the possibility for a universal clumped isotope calibration we find that applying updated parameters improves the t relationship reduces residuals within most labs and improves overall agreement but does not eliminate all interlaboratory differences we reaffirm earlier findings that different mineralogies do not require different calibration equations and that cleaning procedures method of pressure baseline correction and mass spectrometer type do not affect interlaboratory agreement we also present new estimates of the temperature dependence of the acid digestion fractionation for based on combining reprocessed data from four studies and new theoretical equilibrium values to be used in calculation of the empirical transfer function overall we have ruled out a number of possible causes of interlaboratory disagreement in the t relationship but many more remain to be investigated

the climate of the late cretaceous new insights from the application of the carbonate clumped isotope thermometer to western interior seaway macrofossil abstract we apply the carbonate clumped isotope thermometer 47 to macrofossils from the baculites compressus 73 5 ma and the hoploscaphites nebrascensis 67 ma ammonite zones of the western interior seaway wis of north america and nearby coeval terrestrial and open marine environments the carbonate clumped isotope thermometer is based on a single phase isotope exchange equilibrium that promotes the clumping of two heavy isotopes together within a single carbonate molecule as temperature decreases due to the thermometer s isotopic independence from water coupled measurements of 47 and the bulk oxygen isotopic composition of a carbonate 18 o c enable the reconstruction of both paleotemperature and the isotopic composition of the water in which the organisms grew before applying the technique to the aragonite shells of fossil marine organisms mostly ammonites but also some gastropods bivalves and one belemnite we measure the clumped isotopic composition of modern nautilus and cuttlefish two of the nearest living relatives to the cretaceous ammonites modern cephalopods exhibit disequilibrium isotope effects with respect to 47 but not 18 o c therefore a simple correctional scheme is applied to the late cretaceous macrofossil data before reconstructing paleotemperatures diagenesis is also assessed by visual preservation and previously measured sr concentrations cochran et al 2003 temperatures reconstructed for the late cretaceous western interior seaway range from 16 4 3 5 c for an offshore interior seaway environment from the h nebrascensis zone to 24 2 0 4 c for the b compressus ammonite zone the seaway itself has an isotopic composition of approximately 1 relative to vsmow the expectation for an ice free global ocean average while a nearby freshwater environment has an isotopic composition approaching 20 we compare the attributes of the reconstructed climate to predictions based on late cretaceous climate models and previous reconstructions of the seaway and also assess the sensitivity of our results to the modern cephalopods correction by comparisons to suitable modern analogs finally our clumped isotope data are consistent with cooling between the late campanian and maastrichtian as also seen in benthic foraminfera 18 o

microbial influence on the oxygen isotopic composition of diagenetic siderite abstract numerous early diagenetic siderite concretions previously described have been interpreted as the results of microbially mediated reactions interpretation of oxygen isotope data for such material requires an understanding of the effect of temperature on fractionation processes however whilst equilibrium fractionation of oxygen isotopes between siderite and water has been measured down to 33 c extrapolation to lower temperatures may be invalid furthermore inorganic measurements may not be applicable to microbial systems the specific iron reducing microorganism geobacter metallireducens has been cultured anaerobically in the laboratory using acetate as an organic substrate and amorphous feooh as an electron acceptor the acetate is oxidised to co2 with concurrent iron reduction and extracellular siderite precipitation rhombohedral siderite crystals up to 25 m in size have been precipitated over a range of temperatures 18 40 c stable isotopic analysis of these crystals and the solutions from which they precipitate shows that this microbial precipitation of siderite has an associated isotopic fractionation different from the published equilibrium and which is not simply a function of temperature in all cases 18o values of siderite are lower than predicted by inorganic equilibrium fractionation data this may explain the numerous anomalously low 18o values reported for early diagenetic marine siderites and previously attributed to mechanisms such as mixing with meteoric water sediment water interaction recrystallisation or variable isotopic fractionation despite a lack of supporting evidence

clumped isotope signatures in modern brachiopod carbonate abstract we present a temperature to 47 relationship for naturally occurring modern brachiopods which was established using a suite of thirteen brachiopod specimens from twelve sampling localities that span a mean annual seawater temperature range of 0 8 to 29 0 c sample locations and depths were selected to maximize the range of temperatures covered by the calibration while minimizing the seasonal temperature variability impacting the samples linear least squares regression analysis yields the following relationship expressed using the ghosh et al 2006 reference frame 47 0 0478 0 0099 10 6 t 2 0 1164 0 1203 n 13 r 2 0 91 95 ci this equation lies within the 95 confidence interval of the original relationship determined using synthetic calcite ghosh et al 2006 but is in better agreement with the newly revised calibration of zaarur et al 2013 however despite this broad agreement our equation has a shallower slope than the equations for synthetic calcites and yields temperatures at the warm end of the calibration temperature range 47 0 640 that are as much as 3 1 c offset from those predicted using the equation of zaarur et al 2013 on the other hand our new equation has a steeper slope than the henkes et al 2013 equation for modern brachiopods and mollusks this finding is consistent with the hypothesis that differences in the protocols employed by laboratories that use different temperatures of phosphoric acid digestion cause the observed discrepancies between the 47 values reported by various laboratories