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

sub ice topography in patriot hills west antarctica first results of a newly developed high resolution fm cw radar system we present a newly developed high resolution frequency modulated continuous wave fm cw radar system for sounding the sub ice topography the system working in the frequency range from 200 to 400 mhz was developed to measure thickness and internal layers in cold ice with a resolution better than 1 m this system has the potential to measure accumulation rates an important input for improved knowledge of the mass balance of polar ice sheets first measurements for the test calibration and optimization of the new ice sounder were made in december 2005 near the ellsworth mountains specifically in patriot hills west antarctica at 80 18 s 81 22 w the complete radar system was installed on a ski mounted support frame and towed by hand across the ice surface the measurement results show the capability of this system to measure ice thickness up to 1000 m and to define internal layers within the ice body

a method for computing shallow ice core depths sipre style hand augers usually recover core sections whose bottom is somewhat shallower than the drill depth a procedure for calculating the range of possible core depths is presented in the field the drill barrel is lowered down the hole by means of a series of rigid extension rods the apparatus is then rotated to drill through debris left behind by the prior run and into fresh firn or ice care is taken to ensure that the total penetration of debris and firn does not exceed about half the length of the drill barrel otherwise the barrel s capacity for core and chips will be exceeded and the drill likely jammed the entire apparatus is then recovered the workers record the run number the total drill length barrel and extensions the exposed length of extensions above the hole top at the end of drilling and the length of recovered core the cycle is then repeated an example is shown in table i these data are then used to calculate drill depth which is drill length minus the exposed length plus an adjustment if drilling is from the base of a pit distance drilled is then obtained by comparison with the drill depth of the prior run the apparent core loss is the distallce drilled minus the length of recovered core the actual core loss is not readily calculated it is the sum of true core loss ground up core and the collapse of friable strata and the amount of core

new geochemical support for mixing zone dolomitization at golden grove barbados dolomite occurs in the golden grove reef terrace of late pleistocene age in southeastern barbados where fore reef lithologies have been partially to completely dolomitized interpretation of the possible modes of formation of this dolomite has been a subject of disagreement for over a decade among the points of contention are the timing of deposition dolomitization and dolomite cement precipitation and the relationship of replacement dolomite with dolomite cement data from this study indicate that dolomitization occurred during a single relative sea level fall following reef development at marine oxygen isotope stage 7 3 at approximately 216 ka replacement dolomitization affected both micritic matrix and skeletal grains during or after replacement dolomitization dolomite and calcite cements filled primary and secondary pores the cement paragenesis comprises early dolomite cement complexly banded cements of alternating calcite and dolomite late dolomite cement of near stoichiometric composition and a final phase of blocky calcite cement replacement dolomitization and cement precipitation represent a continuum of processes resulting from progressive modification of diagenetic fluids stable carbon and oxygen isotope and strontium elemental compositions of replacive dolomite dolomite cements and calcite cements indicate that dolomitization occurred in a mixing zone between marine and meteoric groundwaters occupying the reef terrace shortly after deposition dolomite oxygen isotope values range from 0 18 to 3 85 pdb and become progressively more depleted throughout the paragenesis indicating a greater influence of meteoric water through time remarkably depleted carbon isotope compositions for both replacement dolomite and dolomite cement 9 53 to 23 04 pdb originated from oxidation of thermogenic methane advected from the underlying accretionary complex methane was oxidized in marine waters that subsequently mixed with meteoric waters as evidenced by a progressive enrichment in carbon isotope composition throughout the paragenesis dolomite strontium contents are substantially elevated above those expected for marine dolomitization ranging from 640 to 1650 ppm and increasing throughout the paragenesis meteoric water provided the excess strontium as aragonite to calcite transformation in the exposed reef terrace increased the fluid sr ca ratio the continuum of geochemical compositions between the replacement dolomite and dolomite cement argues for their genetic association these new data provide additional support to the mixing zone interpretation for golden grove and that the model of mixing zone dolomitization remains viable

evolutionary driven of gephyrocapsa coccolith isotopic vital effects over the past 400 ka abstract coccolithophores play important roles in marine biochemistry due to the processes of calcification and photosynthesis coccoliths are produced intracellularly and cells produce coccoliths with stable isotopes distinct from theoretically precipitated inorganic calcite due to the influences of coccolithophore physiology which are the so called vital effects the coccolith isotopic vital effects show large variations between species and hamper the use of coccolith isotopes in paleoceanography in addition learning the coccolith isotopic vital effects can help to better understand the carbon fractionation in coccolithophore cell so as to provide a new insight in reconstructing sea water carbonate system e g from alkenone 13 c or directly from coccolith 13 c in geological past in the present study we investigated the morphological parameters growth rate and coccolith stable isotope compositions of gephyrocapsa the most universal alkenone producing coccolithophore across the pleistocene these data allow us to estimate the influences of gephyrocapsa morphology as well as the growth rate on coccolith vital effects the results showed that gephyrocapsa morphology as well as coccolith isotopes varied with species and morphotype changes which were evolutionarily forced over the past 400 ka the small gephyrocapsa morphotypes g caribbeanica and gephyrocapsa

accumulation over the greenland ice sheet from historical and recent records water accumulation defined as precipitation minus evaporation was estimated over all of greenland as part of a program to understand changes in ice sheet mass and elevation over 360 historical and recent point accumulation estimates on the greenland ice sheet were evaluated and 276 estimates that were judged to be high quality were used to develop the accumulation map the data set includes 99 points developed as part of four investigations of the past 5 15 years these are judged to have the greatest accuracy using kriging the average accumulation over greenland is estimated to be 30 g cm 2 yr 1 for the interior part of the ice sheet above 1800 m elevation where most of the data were acquired the average accumulation is also estimated to be 30 g cm 2 yr 1 there are still many areas on the ice sheet including northwest southeast and southern greenland where accumulation is highly uncertain exceeding the mean ice sheet uncertainty at a point of 20 25 in these regions further sampling will be required to reduce uncertainty in both regional and ice sheet wide accumulation

mg ca sr ca and ca isotope ratios in benthonic foraminifers related to test structure mineralogy and environmental controls we analysed mg ca sr ca and ca isotope ratios of benthonic foraminifers from sediment core tops retrieved during several research cruises in the atlantic ocean in order to improve the understanding of isotope fractionation and element partitioning resulting from biomineralisation processes and changes in ambient conditions species include foraminifers secreting tests composed of hyaline low magnesium calcite porcelaneous high magnesium calcite as well as aragonite our results demonstrate systematic isotope fractionation and element partitioning patterns specific for these foraminiferal groups calcium isotope fractionation is similar in porcelaneous and hyaline calcite tests and both groups demonstrate the previously described anomaly with enrichment of heavy isotopes around 3 4 degrees c gussone and filipsson 2010 calcium isotope ratios of the aragonitic species hoeglundina elegans on the other hand are about 0 4 parts per thousand lighter compared to the calcitic species which is in general agreement with stronger fractionation in inorganic aragonite compared to calcite however the low and strongly variable sr content suggests additional processes during test formation and we propose that transmembrane ion transport or a precursor phase to aragonite may be involved porcelaneous tests composed of high mg calcite incorporate higher amounts of sr compared to hyaline low mg calcite in agreement with inorganic calcite systematics but also porcelaneous tests with reduced mg ca show high sr ca while calcium isotopes sr ca and mg ca in benthonic foraminifers primarily appear to fractionate and partition with a dominant inorganic control delta ca 44 40 temperature and growth rate dependencies of benthonic foraminifer tests favour a dominant contribution of light ca by transmembrane transport relative to unfractionated seawater ca to the calcifying fluid thus controlling the formation of foraminiferal delta ca 44 40 and sr ca proxy signals c 2015 elsevier ltd all rights reserved less

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

regional and temporal variation of accumulation around northgrip derived from ground penetrating radar during the summer of 2003 a ground penetrating radar survey around the north greenland icecore project northgrip deep ice core drilling site 75806 0 n 42820 0 w 2957 m a s l was carried out using a shielded 250 mhz radar system the drill site is located on an ice divide roughly 300 km north northwest of the summit of the greenland ice sheet more than 430 km of profiles were measured covering a 10 km by 10 km area with a grid centered on the drilling location and eight profiles extending beyond this grid seven internal horizons within the upper 120 m of the ice sheet were continuously tracked containing the last 400 years of accumulation history based on the age depth and density depth distribution of the deep core the internal layers have been dated and the regional and temporal distribution of accumulation rate in the vicinity of northgrip has been derived the distribution of accumulation shows a relatively smoothly increasing trend from east to west from 145 kg m 2 a 1 to 200 kg m 2 a 1 over a distance of 50 km across the ice divide the general trend is overlain by small scale variations on the order of 2 5 kg m 2 a 1 km 1 i e around 1 5 of the accumulation mean the temporal variations of the seven periods defined by the seven tracked isochrones are on the order of 4 of the mean of the last 400 years i e at northgrip 7k g m 2 a 1 if the regional accumulation pattern has been stable for the last several thousand years during the holocene and ice flow has been comparable to today advective effects along the particle trajectory upstream of northgrip do not have a significant effect on the interpretation of climatically induced changes in accumulation rates derived from the deep ice core over the last 10 kyr

measurements of total carbon dioxide and alkalinity by potentiometric titration in the geosecs program abstract approximately 6000 determinations of the alkalinity and total carbon dioxide content of seawater have now been made in the atlantic pacific and indian oceans as part of the geosecs program by a computer controlled potentiometric titration technique the equations used to locate the equivalence points of the carbonic acid system on this titration curve were developed in 1971 but have not previously been published these functions may be represented by f 1 v 2 v v 0 n h k 1 c v 0 v v 0 h h s o 4 h f b o h 4 1 h k 1 c f 2 v 0 v v 0 h h s o 4 h f h c o 3 upon inspection these functions are analogous to the modified gran functions of hansson and jagner 25 with the omission of the contributions of oh and co 3 2 and with the contribution of b oh 4 being assessed at a chlorinity of 19 for all samples reprocessing the original titration e m f volume data with appropriate corrections and modified gran functions reveals an error of about 12 mol kg in the geosecs total carbon dioxide data in addition the protonation of dissolved phosphate species during the titration results in a contribution to measured total carbon dioxide equal to the total phosphate concentration differences in the application of the geosecs functions between the atlantic and the pacific indian oceans expeditions are also to be found so that the error deriving from this source for the atlantic expedition was only 5 mol kg the application of the correct functions increases precision enabling smaller differences such as those attributable to fossil fuel carbon dioxide potentially to be observed and increases accuracy so that the error in titrator total carbon dioxide previously diagnosed by takahashi 14 can be logically accounted for

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

calculation of coccolith volume and its use in calibration of carbonate flux estimates abstract estimates of coccolith volume help in determining total coccolith carbonate fluxes and the relative contributions of various coccolith species it is argued here that the best approach to deriving such coccolith volumes is to calculate shape factors k s for each species separately based on reconstruction of cross profiles and to determine mean sizes from measurement of size variation in the sample of interest then volume k s l 3 values of k s are given for the most important extant coccolith species based on reconstruction of cross sections followed by calculation of a volume of rotation using an iterative routine implemented in an image analysis package substantial errors ca 50 are inevitable in such calculations but the resultant data are nonetheless of value coccolith assemblages from north atlantic 47 n 20 w jgofs 1989 sediment trap samples are analysed as a test case calculated coccolith pic fluxes constitute 30 80 of the chemically determined total pic fluxes

isotope techniques for tracing migration of gases in sedimentary basins the isotopic composition of methane is primarily dependent on the stage of maturation of organic matter present in the hydrocarbon source rocks and is not changed during migration the isotopic composition of in situ methane can be estimated from the maturity of the source organic matter migrated methane from deeper more mature sources is recognized by its relative 13 c enrichment compared to indigenous methane examples are presented in this paper to evaluate the migration pattern of gases in sedimentary basins

genetic and temporal relations between formation waters and biogenic methane upper devonian antrim shale michigan basin usa abstract controversy remains regarding how well geochemical criteria can distinguish microbial from thermogenic methane natural gas in most conventional deposits has migrated from a source rock to a reservoir rarely remaining associated with the original or cogenetic formation waters we investigated an unusual gas reservoir the late devonian antrim shale in which large volumes of variably saline water are coproduced with gas the antrim shale is organic rich of relatively low thermal maturity extensively fractured and is both source and reservoir for methane that is generated dominantly by microbial activity this hydrogeologic setting permits integration of chemical and isotopic compositions of coproduced water and gas providing a unique opportunity to characterize methane generating mechanisms the well developed fracture network provides a conduit for gas and water mass transport within the antrim shale and allows invasion of meteoric water from overlying aquifers in the glacial drift steep regional concentration gradients in chemical and isotopic data are observed for formation waters and gases dilute waters grade into dense brines 300 000 ppm over lateral distances of less than 30 km radiogenic 14c and 3h and stable isotope 18o and d analyses of shallow antrim shale formation waters and glacial drift groundwaters indicate recharge times from modern to 20 000 yr bp carbon isotope compositions of methane from antrim shale wells are typical of the established range for thermogenic or mixed gas 13c 47 to 56 however the unusually high 13c values of co2 coproduced with methane 22 and dissolved inorganic carbon dic in formation waters 28 require bacterial mediation the d values of methane and coproduced formation water provide the strongest evidence of bacterial methanogenesis methane ethane propane ratios and 13c values for ethane indicate 1 the presence of a thermogenic gas component that increases basinward and 2 progressive bacterial oxidation of ethane as the antrim shale subcrop is approached multiple episodes of pleistocene glaciation over northern michigan appear critical to the development of these gas deposits loading of thick ice sheets may have provided hydraulic head that enhanced dilation of preexisting fractures and influx of meteoric water the physical erosion cycle of repeated glacial advances and retreats exhumed the antrim shale around the northern margin of the michigan basin subjecting it to near surface physiochemical and biochemical processes the chemical and hydrologic relations demonstrated in the antrim shale reservoir suggest a dynamic connection between pleistocene glacial history of the midcontinent region and development of recoverable microbially generated natural gas reserves

the impact of mg contents on sr partitioning in benthic foraminifers foraminiferal calcite mg ca mg cacc is used in paleoceanographic studies to reconstruct temperature furthermore the mg cacc is influenced by different seawater mg ca mg casw foraminiferal calcite sr ca sr cacc can potentially be used to reconstruct sr ca ratios of seawater sr casw as these elements are the most abundant of all elements incorporated into the calcium carbonate of the foraminiferal tests they potentially might affect each other s incorporation to investigate the effects of the mg concentration in the test on sr incorporation we conducted a culture study with two species of benthic foraminifera producing carbonate tests with different mg content foraminifers grew under controlled conditions in different mg casw whereas sr casw was kept constant by analyzing sr cacc of cultured specimens with laser ablation inductively coupled plasma mass spectrometry la icp ms we show that sr cacc increases with increasing mg cacc we explain this observation by a stress in the crystal lattice caused by elevated mg cacc which may be compensated for by the additional incorporation of sr we discuss this finding in the context of biomineralization and evaluate the reliability of sr cacc as a possible sr casw proxy

effects of midlatitude westerlies on the paleoproductivity at the agulhas bank slope during the penultimate glacial cycle evidence from coccolith sr ca ratios modern primary productivity on the agulhas bank off south africa has been proposed to be linked to the midlatitude westerlies a paleoproductivity record from this area may therefore resolve temporal changes in the westerly dynamics accordingly we produced a coccolith sr ca based paleoproductivity record from core md96 2080 agulhas bank slope during the penultimate glacial interglacial cycle deriving the productivity signal from sr ca requires a correction for a temperature effect here constrained using mg ca sea surface temperatures from the foraminifer globigerina bulloides from core md96 2080 phases of depressed productivity coincided with periods of stratification in the same core indicated by high relative abundances of the coccolithophore florisphaera profunda and with low relative abundances of the upwelling indicator g bulloides in the nearby cape basin these observations collectively suggest that productivity was regulated by upwelling throughout this region we infer that as in the present periods of low productivity result from a more northerly position of the westerlies potentially accompanied by subtropical front displacements and blockage of upwelling promoting easterlies productivity minima also coincide with periods of increased ice rafted detritus ird deposition on the agulhas plateau which also indicates extreme northward positions of the westerlies the influence of the westerlies appears to be obliquity conditioned as productivity minima and ird maxima occur during low obliquity intervals the dynamic connection between productivity and the westerlies is supported by coeval salinity changes in the south indian gyre that likewise respond sensitively to a poleward contraction of the westerlies

climate proxies from sr ca of coccolith calcite calibrations from continuous culture of emiliania huxleyi abstract continuous culture of the coccolithophorid emiliania huxleyi reveals that coccolith sr ca ratios depend on temperature and growth rate at a constant temperature of 18 c coccolith sr ca ratios increased nearly 15 as growth rate increased from 0 1 to 1 5 divisions per day and calcification rate increased from 1 5 to 50 pg calcite per cell per day when temperature increased from 7 to 26 c sr ca ratios increased by more than 25 i e 1 1 c although the range in growth and calcification rates was the same as for experiments at constant temperature the temperature dependence of sr ca ratios in coccoliths is consistent with that observed in planktonic foraminifera and abiogenic calcites suggesting that it is controlled by thermodynamic processes however the positive correlation of coccolith sr ca with temperature contrasts with field studies in the equatorial pacific where sr ca ratios are highest at the locus of maximum upwelling and productivity despite depressed temperatures this paradox may reflect different calcification rate effects between e huxleyi and the other species dominating assemblages in the equatorial pacific sediments which may be resolved by new techniques for separation of monospecific coccolith samples from sediments models of crystal growth indicate that kinetic effects on sr partitioning in calcite due to surface enrichment could explain the sr ca variations observed in constant temperature experiments but not the larger amplitude calcification rate effects observed in equatorial pacific sediments despite the dual influence of temperature and growth rate on coccolith sr ca coccolith sr ca correlates with b the slope of the dependence of carbon isotope fractionation in biomarkers ep on co2 aq at a range of growth rates and temperatures consequently using coccolith sr ca in combination with alkenone ep may improve paleo co2 determinations

spatial and temporal variability of snow accumulation using ground penetrating radar and ice cores on a svalbard glacier a 50 mhz ground penetrating radar was used to detect horizontal layers in the snowpack along a longitudinal profile on nordenskjoldbreen a svalbard glacier the profile passed two shallow and one deep ice core sites two internal radar reflection layers were dated using parameters measured in the deep core radar travel times were converted to water equivalent yielding snow accumulation rates along the profile for three time periods 1986 99 1963 99 and 1963 86 the results show 40 60 spatial variability in snow accumulation over short distances along the profile the average annual accumulation rate for 1986 99 was found to be about 12 higher than for the period 1963 86 which indicates increased accumulation in the late 1980s and 1990s

cenozoic pelagic sr ca records exploring a link to paleoproductivity 1 recent studies have revealed that sr ca ratios of coccolithophores may be affected by productivity here we compile published sr ca data from bulk carbonate fine fraction sediment and planktonic foraminiferal sr ca records that span the past 60 myr and attempt to place these records into a paleoceanographic framework we account for changes in seawater sr ca ratios using the curve of lear et al 2003 and discuss our observations with respect to changes in the partitioning coefficient of sr through time we discuss limitations associated with postburial processes temporal changes in the coccolith planktonic foraminiferal rain ratio and the coccolith species composition of the sediment despite these caveats we are able to show that in the bulk and fine fraction carbonate records there are two broad periods of enhanced partitioning of sr relative to today the oligocene and the middle to late miocene early pliocene because these are two intervals for which we can cite evidence for a relatively productive ocean on the regional or global scale we believe that the sr ca ratios of bulk carbonate can be explained at least in part by the effects of oceanic nutrient levels on sr uptake during calcification of coccoliths which make up the vast majority of these sediments within the limits of the inferred seawater sr ca record the results of this study contribute a geologic perspective to recent laboratory and field studies that have raised the possibility that sr incorporation into biogenic calcite is controlled by biogeochemical processes

characteristics of accumulation around the epica deep drilling site in dronning maud land antarctica based on ground penetrating radar profiles we analyze area wide spatial and temporal characteristics of accumulation rate in the vicinity of the epica european project for ice coring in antarctica deep drilling site in dronning maud land antarctica edml an area of 1600 km 2 is covered by 500 km of radar profiles organized in a star like pattern with eight 20 25 km legs and a 10 km grid with 1 3 km spacing each pattern being centred on the edml drilling location distributions of density cumulative mass age and the electromagnetic wave speed with depth are available from physical ice core records nine internal reflection horizons are continuously tracked within the upper 110 m of ice over the whole area yielding a spatial picture of accumulation rate history over 1000 years the mean accumulation rate over the last 153 years varies between 50 and 75 kg m 2 a 1 over 50 km perpendicular to the ice divide the spatial average is 61 kg m 2 a 1 this general pattern is overlain by small scale variations of accumulation rate on the order of 10 of the mean maximum local gradients in accumulation rate are 2 3 kg m 2 a 1 km 1 about five times the regional accumu lation rate gradient comparison of topography and accumulation rate along a 20 km profile in the direction of the mean winds indicates that variations in accumulation rate over short distances are linked to surface undulations our results show that advected spatial variations of accumulation rate are on the same order and even exceed temporal changes over the investigated periods ice flow and upstream effects therefore might influence accumulation rates reconstructed from the edml ice core

li partitioning into coccoliths of emiliania huxleyi evaluating the general role of vital effects in explaining element partitioning in biogenic carbonates

sr ca variations in cretaceous carbonates relation to productivity and sea level changes abstract we present high resolution sr ca measurements on coccolith dominated pelagic carbonates of berriasian valanginian albian santonian and campanian maastrichtian age from dsdp sites and tethyan land sections carbonate sr ca varies by up to 80 over both long and short timescales and may reflect either temporal variations in seawater sr ca or variable sr partitioning in biogenic carbonates numerical models of seawater sr and ca budgets indicate that while sea level changes can cause comparably large variations in the seawater sr ca ratio the timing and pattern of predicted sr ca variations agrees poorly with the carbonate record reef crises unrelated to sea level changes may also elevate seawater sr ca and in some cases the record of reef crises corresponds to increasing carbonate sr ca changes in sr partitioning likely due to changes in calcareous nannoplankton productivity also appear to control carbonate sr ca in these records cretaceous carbonate sr ca broadly covaries with indicators of productivity derived from microfossil ecology recent studies in sediment core tops and cultures have shown that sr partitioning in coccolith carbonate is strongly influenced by changes in coccolithophorid growth and calcification rate where the effects of changing seawater sr ca can be constrained by independent geological data carbonate sr ca measurements could provide a valuable perspective on changes in the productivity of calcareous nannoplankton and variations in the carbonate and carbon cycle in the cretaceous

mississippian paleocean chemistry from biotic and abiotic carbonate muleshoe mound lake valley formation new mexico u s a abstract it has been proposed that phanerozoic variation in the mg ca ratio of seawater has resulted in variation in the primary mineralogies of shallow water carbonates between aragonite and calcite dominated seas to test this hypothesis this study estimates the mississippian oceanic mg ca and sr ca ratios from the composition of marine carbonate cements and crinoidal carbonate both of which have been suggested to faithfully record seawater chemistry the early mississippian tournaisian visean muleshoe mound lake valley fm alamogordo nm u s a lends itself well to this endeavor because it contains abundant crinoids and marine carbonate cement stable isotope and elemental analyses as well as cathodoluminescence characteristics elucidate the diagenetic history of the bioherm and identify the least diagenetically altered materials for reconstruction of paleoseawater chemistry isotopic analyses document two diagenetic trends one meteoric and one burial diverging from values similar to literature estimates of mississippian marine calcite 1 5 18o 4 5 13c the burial diagenetic trend follows from this origin to more negative oxygen values 7 18o 3 13c the meteoric diagenetic trend is defined by a meteoric calcite line at 3 18o similarity of non luminescent marine cement and non luminescent crinoid isotopic and elemental compositions suggests that crinoidal carbonate was completely replaced by cement in the marine environment average elemental ratios for least altered marine cements are mg ca 11 mmol mol sr ca 0 2 mmol mol mn ca 0 2 mmol mol and fe ca 0 4 mmol mol early mississippian seawater is estimated to have had a mg ca ratio of 0 2 0 3 mol mol this mg ca ratio is compatible with the early mississippian being an interval of calcite sea conditions and compares well with the devonian estimate from marine cements 0 5 though it is 5 10 times lower than estimates from mass balance modeling the sr ca for early mississippian seawater was between 0 5 and 0 9 mmol mol which is much lower than previous estimates of 6 mmol mol from brachiopod calcite and argues for the development of a sr sink aragonite in the latest devonian to earliest mississippian

abiotic and biotic controls on methane formation down to 2 5 km depth within the precambrian fennoscandian shield abstract despite a geological history characterised by high temperature and pressure processes and organic carbon deprived crystalline bedrock large amounts of hydrocarbons are found in deep groundwaters within precambrian continental shields in many sites methane comprises more that 80 of the dissolved gas phase reaching concentrations of tens of mmol l 1 in this study we used isotopic methods to study the carbon isotope systematics and sources of crustal methane within the fennoscandian shield the main study sites were the outokumpu deep drill hole and the pyhasalmi mine in finland both of which allow groundwater sampling down to 2 5 km depth and have been previously studied for their groundwater chemistry and microbiology we show that the differences in the amount and isotopic composition of methane are related to the availability of carbon sources as well as processes behind the incorporation of hydrogen and carbon via abiotic and biotic pathways into hydrocarbon molecules supported by previously reported occurrences and isotopic data of deep groundwater methane in lithologically different locations in finland and sweden we show that methane formation is controlled by microbial methanogenesis and abiotic reactions as well as lithology with the metasedimentary environments being the most favourable for methane occurrence rather than a thermogenic relic crustal methane within the fennoscandian shield is more likely the result of low temperature formation from ancient organic compounds or their inorganic intermediates such as graphite such crustal gases are characterised by the lack of major amounts of c 2 hydrocarbons and 13 c rich methane further microbiological and isotopic geochemical evidence suggest that microbial methane is more common at depths shallower than 1 5 km

nine centuries of microparticle deposition at the south pole abstract the analysis of microparticles in a 101 m core from amundsen scott south pole station antarctica has revealed a substantial increase in total particle concentration between approximately 1450 and 1850 a d a period encompassing the latest neoglacial interval or little ice age it is likely that this reflects a simultaneous increase in the concentration of particulate material in the antarctic atmosphere this is important climatologically for the antarctic atmosphere may represent the closest approximation to the natural background aerosol thus cores from east antarctica may contain long and detailed records of the natural global background aerosol such records are unavailable from any other medium additionally a cyclical variation which appears to be annual has been detected in the south pole particle record these features allow construction of a relative time scale for ice cores older than 100 yr from regions of low accumulation 1 where many traditional techniques are not applicable this is especially significant as the comparison of climatic data extracted from ice cores with other records of proxy data depends upon the ability to assign an accurate time scale to the ice core an estimated nine century record of net annual accumulation at the south pole has been compiled and the calculated error in the time scale is 90 yr

sr mg ratios of modern marine calcite empirical indicators of ocean chemistry and precipitation rate holocene biotic and abiotic marine calcite have a similar range of mg contents 0 to 22 and 4 to 21 mol mgco3 respectively yet biotic calcite has sr2 concentrations that are consistently 1250 ppm higher than those of abiotic calcite as in laboratory experiments a positive linear relation is observed between dsr and calcite mg content this produces two distinct linear trends on a plot of sr2 vs mg2 concentrations principal axes of variation for both trends have similar slopes yet distinctly different sr2 concentration intercepts biotic y 0 024x 1298 r2 0 70 abiotic y 0 027x 47 r2 0 77 the similar slopes of these trends reflect the constancy of mgca and srca ratios of modern seawater equations describing the dependence of dsr on calcite mg content are derived from both trends biotic dsr 3 16 x 10t 6 ppm mg 0 169 abiotic dsr 3 52 x 10 6 ppm mg 0 0062 characterization of sr mg trends for holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater mgca and srca ratios the relatively high sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms calcites precipitated from seawater in laboratory experiments have dsr values that are similar to those of biotic marine calcite suggesting that both precipitate at approximately the same rate our estimates of surface area normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded ph stat experiments we conclude that the dsr values for biotic and experimental marine calcite are kinetically controlled whereas the lower precipitation rates of abiotic marine calcite yield dsr values that approximate equilibrium conditions experimentally derived equations describing the relation between dsr and calcite precipitation rate indicate that the offset in sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates however observations of naturally occurring marine cements suggest that the five order of magnitude offset best represents natural system processes

dependence of antarctic surface mass balance on temperature elevation and distance to open ocean the latest compilations of surface mass balance mean annual surface temperature and elevation for the antarctic ice sheet derived from data sets of approximately 1500 700 and 105 points respectively have been used to obtain areally integrated means for 24 ice drainage systems and 329 grid point values covering the whole ice sheet monthly summaries of remotely sensed sea ice data for 1973 1976 have been used to obtain mean annual distance to open ocean linear and second order regression analyses of surface balance on 1 temperature for the entire ice sheet 2 elevation for the conterminous grounded ice and 3 distance to the open ocean for the ice shelves including ice rises and attached islands have been made using both system means and grid point values these analyses show correlation coefficients of between 0 63 and 0 81 and they provide bases for descriptive models of the present antarctic ice sheet as well as for predictive models of the response of the ice sheet to air temperature changes and variations in meridional mass and energy transfers extrapolation to other ice sheets past and present may be possible but should be made cautiously linear models are recommended for paleoclimatic reconstructions of ice sheets in upper mid latitudes and second order models are recommended for those in high latitudes system means are shown to be reliable for these purposes incidental results are new estimates of the mean annual surface temperature for the whole ice sheet 36 c and mean surface elevation for the conterminous grounded ice 2290 m

a comparison of radio echo sounding data and electrical conductivity of the grip ice core the depth of reflecting layers in arctic ice sheets has been determined by electromagnetic echo sounding using a varying distance between transmitter and receiver to determine the radar wave velocity the depth of the radar reflecting layers is compared with a profile of electrical conductivity measurements ecms from the greenland ice core project grip ice core in order to determine the velocity of the radar waves in the ice cap by using several reflecting layers it is possible to isolate the firn correction of the wave velocity and to estimate the accuracy of the calculated electromagnetic wave velocity the measured firn correction is compared with the correction calculated from the density profile and a comparison between the depth profiles of ecm and radar based on the corrected electromagnetic wave velocity is presented this profile shows that acid layers which originate from major volcanic eruptions show up as reflecting radar horizons

visual stratigraphic dating of the gisp2 ice core basis reproducibility and application annual layers are visible in the greenland ice sheet project 2 ice core from central greenland allowing rapid dating of the core changes in bubble and grain structure caused by near surface primarily summertime formation of hoar complexes provide the main visible annual marker in the holocene and changes in cloudiness of the ice correlated with dustiness mark wisconsinan annual cycles both markers are evident and have been intercalibrated in early holocene ice layer counts are reproducible between different workers and for one worker at different times with 1 error over century length times in the holocene reproducibility is typically 5 in wisconsinan ice age ice and decreases with increasing age and depth cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50 000 years visible observations are not greatly degraded by brittle ice or many other core quality problems allowing construction of long consistently sampled time series high accuracy requires careful study of the core by dedicated observers

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

multiyear accumulation and temperature history near the north greenland ice core project site north central greenland this paper presents a comparison of two independent methods of estimating subseasonal accumulation across the interior of greenland these methods high resolution snow pit studies and atmospheric modeling have differing spatial and temporal resolution but both can estimate net accumulation for subseasonal and shorter periods the snow pit approach is based on a documented relationship between high resolution snow pit profiles of oxygen stable isotope ratio 18o and multiyear special sensor microwave imager ssm i 37 ghz brightness temperature records comparison of ssm i data to profiles obtained during the 1995 alfred wegener institut north greenland traverse field season shows that 18o data from snow in north central greenland are a reliable high resolution temperature proxy this enables determination of accumulation amount rate and timing from approximately july 1991 through june 1995 across this 220 km long transect of the ice sheet precipitation estimates derived from early modeling based on european centre for medium range weather forecasts data show a similar average seasonal pattern but a diminished magnitude of accumulation 56 for these sites the slope of the multiyear t versus correlation was evaluated for each site on the basis of the observed and calculated temperature history from the nearby north greenland ice core project ngrip site automatic weather station these data should assist interpretation of the paleoclimatic record in the ngrip deep core

flow at ice divide triple junctions 2 three dimensional views of isochrone architecture from ice penetrating radar surveys 1 ground based surveys of ice divide triple junctions in two antarctic ice rises the fletcher promontory and berkner island have been carried out using low frequency ice penetrating radars these surveys have focused on understanding the internal layer architecture at and around the triple junctions with a particular emphasis on understanding how the raymond effect operates a variety of features have been observed including raymond cupolas under the junctions bump stacks of varying amplitude with distance from the divide double bumps crooked stacks implying divide motion and the presence of ridges containing weak and strong bump stacks it was generally not possible to elucidate the three dimensional structure by correlation of pick crossovers so instead a least squares cross correlation technique was used which computes nominal age surfaces using radial basis function interpolation double bumps are absent from the central cupola of fletcher promontory permitting us to infer that the ice here has thinned by around 500 m in the past 5000 years estimates of the age scale suggest that there will be recoverable eemian ice a technique for inferring the velocity profile at divides using layer traces and assumed velocities in the flanks is presented

sr partitioning in the benthic foraminifera ammonia aomoriensis and amphistegina lessonii the shallow water benthic foraminifera ammonia aomoriensis and amphistegina lessonii were grown at different seawater sr ca and the test sr ca ratio was determined by laser ablation inductively coupled plasma mass spectrometry a aomoriensis test sr ca is positively correlated with seawater sr ca the linear regression has a slope of 0 17 representing the overall sr partitioning coefficient kdsr the slope remains unchanged if seawater ca concentration is changed in order to change the seawater sr ca in the case of a lessonii the slopes of the linear regressions representing kdsr differ from one another i e 0 16 if the sr concentration is changed and 0 32 if the ca level is changed this difference in kdsr can be explained by the relative to a aomoriensis high mg content of a lessonii ca 40 mmol mol distorting the calcite lattice and weakening the discrimination against sr the mg content of a aomoriensis is too low ca 4 mmol mol to observe the influence on sr partitioning all data are compatible with a recently developed model for minor element partitioning in foraminifera nehrke et al 2013 mewes et al 2015a on the whole our data confirm the model applicability of the model to sr and dependence of the calcite sr ca on seawater sr ca as opposed to seawater sr concentration and improve our understanding of the model influence of calcite mg ca on sr partitioning

origin and migration of hydrocarbon gases and carbon dioxide bekes basin southeastern hungary the bekes basin is a sub basin within the pannonian basin containing about 7000 m of post cretaceous sedimentary rocks natural gases are produced from reservoirs precambrian to tertiary in age located on structural highs around the margins of the basin gas composition and stable carbon isotopic data indicate that most of the flammable gases were derived from humic kerogen contained in source rocks located in the deep basin the depth of gas generation and vertical migration distances were estimated using quantitative source rock maturity carbon isotope relationships for methane compared to known neogene source rock maturity depth relationships in the basin these calculations indicate that as much as 3500 m of vertical migration has occured in some cases isotopically heavy 7 0 co2 is the predominant species present in some shallow reservoirs located on basin margin structural highs and has probably been derived via long distance vertical and lateral migration from thermal decompositon of carbonate minerals in mesozoic and older rocks in the deepest parts of the basin a few shallow reservoirs 2000m contain isotopically light 50 to 60 0 methane with only minor amounts of c2 homologs 3 v v this methane is probably mostly microbial in origin above normal pressures occuring at depths greater than 1800 m are believed to be the principal driving force for lateral and vertical gas migration these pressures are caused in part by active hydrocarbon generation undercompaction and thermal decomposition of carbonates

late 20th century increase in south pole snow accumulation a compilation of the 37 year history of net accumulation at the south pole mosley thompson et al 1995 suggests an increase in net annual accumulation since 1965 this record is sporadic and its quality is compromised by spatially restricted observations and nonsystematic measurement procedures results from a new spatially extensive network of 236 accumulation poles document that the current 5 year 1992 1997 average annual net accumulation at the south pole is 84 5 8 9 mm water equivalent w e this accumulation rate reflects a 30 increase since the 1960s when the best although not optimal records indicate that it was 65 mm w e identification of two prominent beta radioactivity horizons 1954 1955 and 1964 1965 in six firn cores confirms an increase in accumulation since 1965 viewed from a longer perspective of accumulation provided by ice cores and a snow mine study the net accumulation of the 30 year period 1965 1994 is the highest 30 year average of this millennium limited data suggest this recent accumulation increase extends beyond the south pole region and may be characteristic of the high east antarctic plateau enhanced accumulation over the polar ice sheets has been identified as a potential early indicator of warmer sea surface temperatures and may offset a portion of the current rise in global sea level

microbial production and modification of gases in sedimentary basins a geochemical case study from a devonian shale gas play michigan basin an expanded data set for gases produced from the antrim shale a devonian black shale in the michigan basin united states has allowed for a detailed examination of the related chemical and isotopic compositional changes in the solid gas liquid systems that discriminate between microbial and thermogenic gas origin in the antrim shale economic microbial gas deposits are located near the basin margins where the shale has a relatively low thermal maturity and fresh water infiltrates the permeable fracture network the most compelling evidence for microbial generation is the correlation between deuterium in methane and coproduced water along the basin margins there is also a systematic enrichment in 13c of ethane and propane with decreasing concentrations that suggests microbial oxidation of these thermogenic gas components microbial oxidation accounts not only for the shift in 13c values for ethane but also in part for the geographic trend in gas composition as ethane and higher chain hydrocarbons are preferentially removed this oxidation is likely an anaerobic process involving a syntrophic relationship between methanogens and sulfate reducing bacteria the results of this study are integrated into a predictive model for microbial gas exploration based on key geochemical indicators that are present in both gas and coproduced water one unequivocal signature of microbial methanogenesis is the extremely positive carbon isotope values for both the dissolved inorganic carbon in the water and the coproduced co2 gas in contrast the 13c value of methane is of limited use in these reservoirs as the values typically fall between the commonly accepted fields for thermogenic and microbial gas in addition the confounding isotopic and compositional overprint of microbial oxidation increasing the values to typically thermogenic values may obscure the distinction between methanogenic and thermogenic gas

point measurements of mass balance of the greenland ice sheet using precision vertical global positioning system gps surveys rates of ice sheet thickening or thinning in greenland are measured using the coffee can technique this entails computing the difference in the vertical velocity of markers anchored in firn and the long term rate of snow accumulation the velocities are obtained from repeat surveys using the global positioning system gps with corrections for densification and along slope flow this difference is the local mass balance for two sites in western greenland camp century and a site just south of the egig line crawford point results show ice sheet thinning a third west greenland site inland from upernavik is close to balance two sites dye 2 in western greenland and summit are thickening slowly

global and local forcing of early toarcian seawater chemistry a comparative study of different paleoceanographic settings paris and lusitanian basins 1 the early toarcian was characterized by two large perturbations to the carbon cycle a positive trend associated with increased organic matter burial and ocean anoxia and a pronounced negative carbon isotope excursion cie we contrast the geochemical evolution in the carbonate phases of two successions one from the paris basin sancerre core comprising black shales the other from the lusitanian basin peniche section with very minor lithological expression of bottom water anoxia our aim was to identify whether these carbon cycle perturbations were related and differentiate between the common global versus regional expressions of the biogeochemical response and ocean chemistry our results highlight contrasts in timing of different phases of anoxia in both locations through the widely documented negative cie widespread anoxic conditions were not a necessary prerequisite for generating a pronounced cie as required by the recycling so called kuspert model the production of carbonate simultaneously dropped during the 13c negative shift in both locations likely in response to lowered seawater saturation rate induced by substantial absorption of co2 from the atmosphere the recovery interval was accompanied by a rapid reestablishment of seawater alkalinity and primary and carbonate productivity in epicontinental seas as evidenced by high 13c and sr ca in contrast with the more open ocean regime in the lusitanian basin our results confirm that parallels can be draw between the ocean productivity response and feedback during the toarcian cie and the petm both events are characterized by ocean acidification and reduced pelagic calcification followed by a peak in nearshore coccolith productivity which could have helped the recovery from the perturbation

hydrocarbon seep carbonates of a miocene forearc east coast basin north island new zealand an ancient hydrocarbon seep province of 14 isolated authigenic carbonate deposits has been identified in fine grained deep marine siliciclastic strata of the miocene east coast basin north island new zealand these forearc sediments have been uplifted and complexly deformed into accretionary ridges adjacent to the still active hikurangi convergent margin older active and passive margin strata mid cretaceous to oligocene in age underlie the neogene sequence and contain oil and gas prone source rocks older mesozoic meta sedimentary rocks constitute the backstop against which the current phase of subduction related sedimentation has accumulated 24 ma present the seep carbonates up to 10 m thick 200 m across archive methane signatures in their depleted carbon isotopes to 13c 51 7 pdb and contain chemosynthesis based paleocommunities e g worm tubes bathymodioline mussels and vesicomyid lucinid and thyasirid bivalves typical of other cenozoic and modern seeps northern and southern sites are geographically separated and exhibit distinct lithological and faunal differences structural settings are variable seep associated lithologies also are varied and suggest carbonate development in sub seafloor seafloor and physically reworked diapiric expansion gas explosion gravity slide or debris flow settings similar to italian apennine seep deposits of overlapping ages peculiar attributes of the new zealand miocene seep deposits are several including digitate thrombolites of clotted microbial micrite encased in thick isopachous horizons and botryoids of aragonite seep plumbing features are also well exposed at some sites displaying probable gas explosion breccias filled with aragonite tubular concretions fluid conduits and carbonate cemented thin sandstone beds and burrows within otherwise impermeable mudstones a few seeps were large enough to develop talus debris piles on their flanks which were populated by lucinid bivalves and terebratulid brachiopods firmgrounds and hardgrounds were common as evidenced by trace fossil associations or caryophyllid coral thickets atop some seep carbonate deposits thus the new zealand examples show strong evidence of formation in sediments at or just beneath the seafloor but some were clearly exhumed by erosion to sustain later non seep epifaunal and boring paleocommunities

relationship between coccolith sr ca ratios and coccolithophore production and export in the arabian sea and sargasso sea coccolithophore caco3 production can account for 20 80 of biogenic carbonate exported from the photic zone and coccoliths are a dominant biogenic carbonate in many deep sea sediments a new method for picking individual coccoliths from sediment traps and sediments for analysis using secondary ion mass spectrometry ion probe allows us to make precise sr ca and mg ca determinations on coccoliths from single species even in samples where material is limited there are large biological effects in sr ca partitioning in coccoliths that have been related to variations in coccolithophore productivity in sediment traps from the sargasso sea at bermuda and arabian sea in the somali basin we can identify sr ca variations in several species that are consistent with inferred seasonal variations in coccolithophore productivity in surface waters in the arabian sea coccolith sr ca ratios in calcidiscus leptoporus and helicosphaera carteri are lowest during the nonproductive intermonsoon they are highest during the upwelling of southwest monsoon and during the nutrient entrainment from strong winds of the northeast monsoon these sr ca variations match seasonal trends in coccolith export flux furthermore sr ca variations in c leptoporus are larger and this species also has the greater variation in export flux between southwest monsoon and intermonsoon seasons at bermuda a 1996 fall bloom driven by passage of a warm mode water eddy induced a large increase in sr ca of c leptoporus coincident with an increase of c leptoporus export over an annual series for 2004 highest sr ca ratios of c leptoporus in the summer months match the typical summer peak in surface standing stock of this species and the stimulation of its productivity by mesoscale cyclonic eddies and eddy eddy interactions high sr ca did not coincide with the highest export of c leptoporus coccoliths likely because cyclonic eddies unlike mode water eddies are dominated by small phytoplankton with low export efficiency these data confirm a relationship between coccolith sr ca ratios and productivity sr ca ratios of the smaller and more slowly sinking emiliania huxleyi at bermuda show very small o4 seasonal sr ca variations in contrast nutrientlimited culture experiments for this species reveal significant 435 increases in sr ca with nitrate stimulated growth

comparative study of stable carbon and hydrogen isotopes of alkane gases sourced from the longtan and xujiahe coal bearing measures in the sichuan basin china abstract two sets of coal bearing measures the upper triassic xujiahe formation t 3 x and the upper permian longtan formation p 2 l have been extensively developed in the sichuan basin sw china and some large gas fields related to these coal bearing measures have been discovered the stable carbon and hydrogen isotopic composition of alkane gases sourced from the two sets of coal bearing measures t 3 x and p 2 l gases have been investigated in this study the main controls on the gas composition and isotopic abundances of gases in the sichuan basin have been identified and distinguished on the basis of their molecular and isotopic composition the carbon and hydrogen isotopic compositions of methane 13 c c1 42 5 to 26 8 d c1 173 to 107 vary widely and show a positive correlation with the thermal maturity of the source rocks the 13 c c2 value of the t 3 x and p 2 l gases in the sichuan basin ranged from 28 2 to 21 3 and showed less variations with increasing maturity from r o values of 1 2 to 2 8 however these 13 c c2 values differ greatly from that of oil associated gas in the sichuan basin thus we provide further evidence that the value of 13 c c2 is a useful parameter to distinguish coal derived and oil associated gases the hydrocarbon gases in the xujiahe and jurassic reservoirs in contrast showed little isotopic difference indicating that secondary migration has little influence on their carbon and hydrogen isotope compositions in addition the 13 c values of p 2 l co 2 2 6 to 3 3 may reflect an origin from dissolution of the carbonates in the reservoir by acidic fluids containing h 2 s

coccolithophore productivity response to greenhouse event of the paleocene eocene thermal maximum abstract during the paleocene eocene thermal maximum petm rapid release of isotopically light c to the ocean atmosphere system elevated the greenhouse effect and warmed temperatures by 5 7 c for 105 yr the response of the planktic ecosystems and productivity to the dramatic climate changes of the petm may represent a significant feedback to the carbon cycle changes but has been difficult to document we examine sr ca ratios in calcareous nannofossils in sediments spanning the petm in three open ocean sites as a new approach to examine productivity and ecological shifts in calcifying plankton the large heterogeneity in sr ca among different nannofossil genera indicates that nannofossil sr ca reflects primary productivity driven geochemical signals and not diagenetic overprinting elevated sr ca ratios in several genera and constant ratios in other genera suggest increased overall productivity in the atlantic sector of the southern ocean during the petm dominant nannofossil genera in tropical atlantic and pacific sites show sr ca variations during the petm which are comparable to background variability prior to the petm despite acidification of the ocean there was not a productivity crisis among calcifying phytoplankton we use the pandora ocean box model to explore possible mechanisms for petm productivity change if independent proxy evidence for more stratified conditions in the southern ocean during the petm is robust then maintenance of stable or increased productivity there likely reflects increased nutrient inventories of the ocean increased nutrient inventories could have resulted from climatically enhanced weathering and would have important implications for burial rates of organic carbon and stabilization of climate and the carbon cycle

calcium isotopes in deep time potential and limitations abstract calcium is an essential element in the biogeochemical cycles that regulate the long term climate state of earth the removal of co2 from the ocean atmosphere system is controlled by the burial of carbonate sediments caco3 ultimately linking the global calcium and carbon cycles this fundamental link has driven the development of the stable calcium isotope proxy with application to both ancient skeletal and non skeletal bulk carbonate sediments calcium isotope ratios 44 40ca have been used to track long term changes in seawater chemistry e g aragonite vs calcite seas and to elucidate short term climatic perturbations associated with mass extinction events however developments in the calcium isotope proxy have shown that 44 40ca values in carbonate minerals also are sensitive to changes in precipitation rates mineralogy and diagenesis thereby complicating the application of the proxy to the reconstruction of global cycles first inorganic carbonate precipitation experiments have demonstrated that carbonate 44 40ca values are sensitive to precipitation rates with higher rates generally leading to larger fractionation second 44 40ca values are sensitive to carbonate mineralogy with inorganic aragonite and calcite being on average 1 5 and 0 9 depleted relative to contemporaneous seawater respectively the effects of both changes in carbonate mineralogy and precipitation rates affect primary and secondary minerals but are particularly pronounced during carbonate diagenesis where relatively slow rates of recrystallization and neomorphism can lead to significant changes in bulk sediment 44 40ca values third changes in faunal composition expressed in skeletal fossil archives can lead to large changes in carbonate 44 40ca values that are decoupled from changes in global cycles nevertheless when these factors are appropriately considered the application of calcium isotopes in ancient carbonate sediments becomes a powerful tool for understanding biogeochemical processes that operate over many scales from diagenetic changes within the sediment pore space to regional changes across ancient carbonate platforms and to global changes in seawater chemistry through time importantly the processes that contribute to variability in carbonate 44 40ca values are likely to impact other carbonate bound proxies highlighting the potential for calcium isotopes as a tool to better understand the variability of other isotope systems

occurrence and geochemistry of natural gases piceance basin northwest colorado the piceance basin is a hydrocarbon rich province that has natural gas production from reservoirs ranging in age from late jurassic to eocene and large undeveloped resources of natural gas in coal beds and tight sandstone reservoirs of cretaceous age gases from all producing intervals are of predominantly thermal origin and become isotopically heavier delta isotope 13 c 1 51 3 to 29 1 o oo and chemically drier c 1 c 1 5 0 26 to 1 00 with increasing thermal maturity of reservoirs r o 0 45 to 2 40 over a depth range of 1100 to 11 702 ft 335 3567 m scatter in trend is attributed to source rock differences and considerable vertical and lateral migration based on chemical and isotopic composition three major types of gases can be distinguished those generated from mixed type ii and iii kerogens those from dispersed type iii kerogen and those from coal gases generated from mixed type ii and iii kerogens are produced from the upper jurassic morrison formation the lower cretaceous cedar mountain formation the upper cretaceous dakota sandstone the upper cretaceous mancos b producing interval and marginal marine sandstones of the upper cretaceous iles producing interval these gases are associated with minor amounts of oil and probably were generated from kerogen in the marine mancos shale gases generated from dispersed type iii kerogen are produced from nonmarine sandstones of the upper cretaceous williams fork producing inter al and from thermally immature reservoirs in the overlying paleocene and eocene fort union and wasatch formations these nonassociated gases contain large amounts of co 2 and probably were generated from carbonaceous shales in the williams fork producing interval their presence in immature fort union and wasatch reservoirs implies considerable vertical migration the third type of gas is methane rich is produced by devolatilization of humic coal and is generally in coal beds of the cameo fairfield zone of the williams fork producing interval these gases are not the major source for adjacent sandstone reservoirs a fourth distinct type of isotopically light thermogenic gas occurs in immature reservoirs of the eocene green river formation this gas is inferred to have migrated from u identified deeper more mature source rocks

cellular calcium pathways and isotope fractionation in emiliania huxleyi the marine calcifying algae emiliania huxleyi coccolithophores was grown in laboratory cultures under varying conditions with respect to the environmental parameters of temperature and carbonate ion concentration co32 concentration the ca isotope composition of e huxleyi s coccoliths reveals new insights into fractionation processes during biomineralization the temperature dependent ca isotope fractionation resembles previous calibrations of inorganic and biogenic calcite and aragonite unlike inorganically precipitated calcite the co32 concentration of the medium has no significant effect on the ca isotope composition of the coccoliths these results indicate a decoupling of the chemical properties of the bulk medium and the calcifying vesicle cellular ca pathways of e huxleyi indicate that fractionation cannot occur at the crystal surface as occurs during inorganic precipitation the dominant processes leading to the observed ca isotope fractionation pattern in e huxleyi are most likely the dehydration of the ca aquocomplex at the plasma membrane and the attachment of dissolved ca to proteins of ca channels the independence of ca isotope fractionation from co32 and the small temperature dependence of e huxleyi are also important for defining the isotopic signature of the oceanic ca sink since coccolithophores contribute to about half the global caco3 production a relatively uniform isotopic composition of the oceanic ca sink is further supported

seasonal cycles in biogenic production and export in northern bay of bengal sediment traps sediment traps in the northern and north central bay of bengal are characterized by highly seasonal fluxes and unusually high efficiency of organic carbon export however the mechanism for high export production remains under debate to evaluate the relationships between production in the photic zone and export processes responsible for the fluxes into the traps over an annual cycle we examine a series of indicators of production regime set in surface waters these indicators include communities of planktic foraminifera and coccolithophores stable isotopic chemistry of foraminifera and coccoliths and the sr ca ratios in coccoliths coccolith and foraminiferal assemblages confirm that the bay of bengal is a region of high productivity coccolithophore communities are dominated to an unusually high degree 90 by the lower photic zone dweller florisphaera profunda a species adapted to high nutrient and low light conditions typical of stratified waters like those induced by the strong halocline in the bay of bengal cyclonic eddy pumping and strong winds during the southwest monsoon swm increase the relative abundance of upwelling indicator species like foraminifera globigerina bulloides and the upper photic coccolithophores globigerina oceanica and emiliania huxleyi however while upwelling and eddy pumping do coincide with high opal and coccolith export in both traps peak organic carbon export precedes the onset of eddy pumping and upwelling indicators these data suggest an alternate mode of production in the bay of bengal which is not driven by upwelling but rather high production deeper in the water column probably by taxa adapted to lower light levels in both traps the pulses of organic carbon export coincide with elevated fluxes of planktonic foraminifera which likely reflect increased primary production consequently while major export pulses of organic carbon coincide with pulses of lithogenic export the pulses of organic carbon export are not likely to reflect simple scavenging of suspended organic carbon by lithogenic pulses rather they reflect increased organic carbon production nonetheless some seasonal changes increase in coccolith export efficiency during the swm are suggested by coccolith sr ca ratios in the northern trap coccolith carbonate export is decoupled from the main pulse of organic carbon export consequently ballasting of organic carbon aggregates by coccolith carbonate does not play a major role in the seasonal cycle of organic carbon export from the photic zone to shallow 800 m traps

effects of quaternary sea level cycles on strontium in seawater abstract the effects of quaternary sea level changes on the sr budget of the ocean are investigated using coupled numerical models of the seawater sr and ca budgets glacial interglacial sea level cycles influence the sr concentration of seawater directly through the periodic exposure and weathering of aragonite on continental shelves and indirectly by modulating the location and extent of carbonate deposition in the ocean as sea level recedes brief pulses of sr are added to the ocean from recrystallization of shelf aragonite this flux at its maximum is nearly ten times larger than the combined riverine and hydrothermal influx the large shelf recrystallization fluxes during glacial maxima produce rapid increases in the sr ca ratio of seawater despite the long residence time of sr in the ocean variations in the ratio of aragonitic vs calcitic sedimentation also influence on the sr content of seawater because the sr partitioning coefficient is higher in aragonite however this effect is minor compared to shelf aragonite recrystallization based on a variety of sensitivity tests the amplitude of sr ca variations ranges from 1 to 3 and is maximized by constant rates of total carbonate deposition extensive aragonite recrystallization and carbonate budgets which include dissolution of shelf carbonates such variation is sufficient to produce up to 1 5 c errors in paleotemperatures calculated from coral sr ca ratios since the last glacial maximum

occurrence frequency of thickness of annual snow accumulation layers at south pole this paper describes the frequency analysis of 2000 annual snow accumulation layers at the south pole it proposes application of this analysis to objective extraction of meteorological parameters from the south pole snow accumulation record we have compared the 200 year snow mine accumulation record of giovinetto and schwerdtfeger and a 2000 layer pit and core record obtained in 1982 frequency analysis of the number of occurrences of layers with respect to thickness or mass of the layer showed the logarithms of thickness or mass to be normally distributed this lognormality is quite robust arbitrary partitioning of the data by depth or systematic partition of the data by densification or firn ice transition does not destroy the lognormality of the accumulation series the geometric standard deviation of the mass of annual layers was the same as the geometric standard deviation of the thickness of these same layers as the layers densified from firn to ice this agrees with kapteyn s theory of transformability of lognormal distributions we have also compared the snow accumulation and marine aerosol sodium accumulation in recent annual layers with the station meteorological record and the surface aerosol record the amounts of snow and sodium accumulated are proportional to the number of warmings salt storms in most years of this short record the accumulation record may be transformable to provide an index of this meridional transport we propose that the magnitude of snow accumulation with respect to frequency of that accumulation provides an objective criterion for comparing individual years of meteorological history and that the geometric standard deviation of accumulation provides an objective index for estimation of climatic fluctuation during the period of accumulation

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

topographic control of regional accumulation rate variability at south pole and implications for ice core interpretation snow accumulation rates are known to be sensitive to local changes in ice sheet surface slope because of the effect of katabatic winds these topographic effects can be preserved in ice cores that are collected at non ice divide locations the trajectory of an ice core site at south pole is reconstructed using measurements of ice sheet motion to show that snow was probably deposited at places of different surface slope during the past 1000 years recent accumulation rates derived from shallow firn cores vary along this trajectory according to surface topography so that on a relatively steep flank mean annual accumulation is 18 smaller than on a nearby topographic depression these modern accumulation rates are used to reinterpret the cause of accumulation rate variability with time in the long ice core record as an ice dynamics effect and not a climate change signal the results highlight the importance of conducting ancillary ice dynamics measurements as part of ice coring programs so that topographic effects can be deconvolved from potential climate signals

age estimates of isochronous reflection horizons by combining ice core survey and synthetic radar data 1 ice core records and ice penetrating radar data contain complementary information on glacial subsurface structure and composition providing various opportunities for interpreting past and present environmental conditions to exploit the full range of possible applications accurate dating of internal radar reflection horizons and knowledge about their constituting features is required on the basis of three ice core records from dronning maud land antarctica and surface based radar profiles connecting the drilling locations we investigate the accuracies involved in transferring age depth relationships obtained from the ice cores to continuous radar reflections two methods are used to date five internal reflection horizons 1 conventional dating is carried out by converting the travel time of the tracked reflection to a single depth which is then associated with an age at each core location and 2 forward modeling of electromagnetic wave propagation is based on dielectric profiling of ice cores and performed to identify the depth ranges from which tracked reflections originate yielding an age range at each drill site statistical analysis of all age estimates results in age uncertainties of 5 10 years for conventional dating and an error range of 1 16 years for forward modeling for our radar operations at 200 and 250 mhz in the upper 100 m of the ice sheet comprising some 1000 1500 years of deposition history final age uncertainties are 8 years in favorable cases and 21 years at the limit of feasibility about one third of the uncertainty is associated with the initial ice core dating the remaining part is associated with radar data quality and analysis

improved method to determine radio echo sounding reflector depths from ice core profiles of permittivity and conductivity we present a technique that modifies and extends down hole target methods to provide absolute measures of uncertainty in radar reflector depth of origin we use ice core profiles to model wave propagation and reflection and then cross correlate the model results with radio echo sounding res data to identify the depth of reflector events stacked traces recorded with res near the epica drill site in dronning maud land antarctica provide reference radargrams and dielectric properties along the deep ice core form the input data to a forward model of wave propagation that produces synthetic radargrams cross correlations between synthetic and res radargrams identify differences in propagation wave speed they are attributed to uncertainties in pure ice permittivity and are used for calibration removing conductivity peaks results in the disappearance of related synthetic reflections and enables the unambiguous relation of electric signatures to res features we find that i density measurements with attenuation or dielectric profiling are too noisy below the firn ice transition to allow clear identification of reflections ii single conductivity peaks less than 0 5 m wide cause the majority of prominent reflections beyond a travel time of about 10 s 900 m depth and iii some closely spaced conductivity peaks within a range of 1 2m cannot be resolved within the res or synthetic data our results provide a depth accuracy to allow synchronization of age depth profiles of ice cores by res modeling of isochronous internal structures and determination of wave speed and of pure ice properties the technique successfully operates with dielectric profiling and electrical conductivity measurements suggesting that it can be applied at other ice cores and drill sites

high resolution hyperspectral based continuous mineralogical and total organic carbon analysis of the eagle ford group and associated formations in south texas hyperspectral sensing is used to generate mineral maps of a fine grained vertical eagle ford group cored section and underlying buda limestone and del rio formation in south texas this technology produces a map that shows the distribution of minerals on the core surface three different cameras within the hyperspectral core imaging system were used to image a 99 1 m 325 ft core a 1 line scan camera which produces a high resolution red green blue 120 m natural color photograph of the dry core from the visible light spectrum 2 short wave infrared swir spectrometer 300 500 m resolution and 3 long wave infrared lwir spectrometer 300 500 m resolution in 2016 the introduction of a new high resolution lwir spectrometer made it possible to identify minerals in cores that were not detected by previous swir systems high resolution hyperspectral imaging technology using both the swir and lwir spectra provides a significant step toward quantifying mineralogy and total organic carbon hyperspectral imaging is a powerful tool for studying textural and fabric relationships because it detects and highlights the major mineralogical changes that occur between depositional beds and among depositional features calcite compositional variations and cyclicity appear to be closely related the sr rich calcite appears to indicate a smaller allochem size dominance as well as the slower sedimentation rates that are required for nannofossils to settle from suspension finally the observed diagnostic cyclicity of the lower eagle ford can be related to coccolithophore productivity

exploring foraminiferal sr ca as a new carbonate system proxy in present day paleoclimate research one of the most pressing challenges is the reconstruction of atmospheric co2 concentrations a variety of proxies for several components of the marine inorganic carbon system have been developed in this context e g b isotopes b ca u ca to allow reconstruction of past seawater ph hco3 and co32 and thereby facilitate estimates of past atmospheric pco2 based on culture experiments using the benthic foraminifera ammonia sp we describe a positive correlation between sr ca and the carbonate system namely dic bicarbonate ion concentration foraminiferal sr ca ratios provide potentially additional constraints on the carbonate system proxy because the analysis of foraminiferal carbonate sr ca is straightforward and not easily contaminated applying our calibration to a published dataset of paleo sr ca suggests the validity of sr ca as a carbonate system proxy furthermore we explore how our data can be used to advance conceptual understanding of the foraminiferal biomineralization mechanism

coccolith strontium to calcium ratios in emiliania huxleyi the dependence on seawater strontium and calcium concentrations in recent studies the sr ca ratio of coccolithophore calcite was used as a proxy for past coccolithophore growth and calcification rates since sr and ca concentrations in seawater have not remained constant through time interpretation of sr ca data from the coccolith dominated sedimentary record requires knowledge about the incorporation of seawater sr into coccolith calcite during coccolithogenesis here we show that sr ca of emiliania huxleyi coccoliths is linearly related to seawater sr ca meaning that the sr exchange coefficient does not change with changing seawater sr ca the exchange coefficient for sr in this study 0 39 is close to values presented in the literature and is high compared with values obtained by inorganic precipitation experiments this suggests a strong effect of cell physiology on biogenic calcite precipitation in coccolithophores we present a conceptual model based on the transmembrane transport of sr and ca which explains the offset

cretaceous calcareous dinoflagellate cysts as recorder of δ44 40caseawater and paleo temperature using sr ca thermometry abstract we evaluate the potential of calcareous dinoflagellates as archives for sr ca based paleo temperature reconstructions and 44 40caseawater fluctuations on sediments from ocean drilling program expedition 113 hole 690c weddell sea southern ocean between 73 and 68 ma sr ca ratios of two cretaceous dinoflagellate species pirumella krasheninnikovii and orthopithonella globosa show a pronounced decrease consistent with a significant drop in sea surface temperature as reflected by the 18o of planktic foraminifers the apparent temperature sensitivity of the dinoflagellate cysts sr ca is 0 06 and 0 08 mmol mol c 1 using 18o derived paleo sea surface temperatures which is significant and large enough to resolve paleoenvironmental temperature changes at current analytical precision as the chemical composition of the cyst calcite appears to have a good preservation the sr ca of calcareous dinoflagellates has a potential to serve as paleo temperature proxy although the chemical composition of the cretaceous seawater and potential impacts on the cyst geochemistry is pending further inspection the ca isotope composition of the two dinoflagellate species shows identical trends of increasing 44 40ca between 73 and 67 ma the planktic foraminifer archaeoglobigerina australis and the benthic foraminifer nuttallides truempyi reveal the same increase of about 0 4 but are offset relative to the dinoflagellates by about 0 5 presumably due to species specific ca isotope fractionation bulk carbonate sediment shows significant scatter likely caused by changes in faunal composition and does not reproduce the trend revealed by the dinoflagellate and foraminifer records these observations demonstrate the importance of taxon specific records and careful determination of fractionation factors of selected archives and highlight complications arising from utilizing less suitable archives such as bulk sediments for 44 40caseawater reconstructions our records indicate strong changes in the marine ca cycle associated with the global temperature decrease towards the end of the cretaceous

snow dunes and glazed surfaces in antarctica new field and remote sensing data as part of the international trans antarctic scientific expedition project the italian antarctic programme undertook two traverses from the terra nova station to talos dome and to dome c along the traverses the party carried out several tasks drilling glaciological and geophysical exploration the difference in spectral response between glazed surfaces and snow makes it simple to identify these areas on visible near infrared satellite images integration of field observation and remotely sensed data allows the description of different mega morphologic features wide glazed surfaces sastrugi glazed surface fields transverse dunes and megadunes topography global positioning system ground penetrating radar and detailed snow surface surveys have been carried out providing new information about the formation and evolution of mega morphologic features the extensive presence up to 30 of glazed surface caused by a long hiatus in accumulation with an accumulation rate of nil or slightly negative has a significant impact on the surface mass balance of a wide area of the interior part of east antarctica the aeolian processes creating these features have important implications for the selection of optimum sites for ice coring because orographic variations of even a few metres per kilometre have a significant impact on the snow accumulation process remote sensing surveys of aeolian macro morphology provide a proven high quality method for detailed mapping of the interior of the ice sheet s prevalent wind direction and could provide a relative indication of wind intensity

spatial variability at shallow snow layer depths in central dronning maud land east antarctica spatial variability at swallow snow layer depths in central dronning maud land east antarctic

controls on stable strontium isotope fractionation in coccolithophores with implications for the marine sr cycle abstract the controls on stable sr isotope fractionation into the calcite produced by the coccolithophore species emiliania huxleyi coccolithus pelagicus spp braarudii and gephyrocapsa oceanica are investigated each species has been cultured under controlled laboratory conditions at a range of temperatures 10 25 c to test the potential of 88 86 sr as a proxy for growth rate and or sea surface temperature coccolithophores are one of the most abundant pelagic calcifiers since sr substitutes to some degree for ca in their calcite coccoliths coccolithophores represent a significant output of sr from seawater potentially influencing the 88 86 sr mass balance in the modern oceans the coccoliths are investigated for their 88 86 sr sr ca and 18 o measured as function of temperature as temperature is increased all species show a negative stable sr isotopic fractionation related to a temperature controlled growth rate we infer the shift of 88 86 sr to lighter values as indicative of a kinetic control on the isotope fractionation revealing the potential of 88 86 sr as a proxy for growth rate which in these experiments is primarily dictated by temperature the results from these experiments indicate that coccolithophore calcite incorporates sr with a very light 88 86 sr isotope composition as low as 0

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

radar internal layers from the greenland summit ice penetrating radar measurements made over the summit region of greenland show returns from internal layers which can be used to augment the interpretation of climate information from the two deep cores recently recovered from this area these reflecting surfaces believed to represent isochrones give information about the stress regime near the summit and may aid in a better calibration of the age depth scale between the two cores particularly in the lowest 10 of ice thickness where there is currently disagreement the approximate depth at which internal echoes become discontinuous corresponds with the observations of steep inclinations and overturned folds on the scale of centimeters in the core samples however the deepest internal layers which can be distinguished in the profiles place constraints on the scale and location of high angle or overturned folds

a top down and bottom up comparison of paleoproductivity proxies calcareous nannofossil sr ca ratios and benthic foraminiferal accumulation rates we investigate whether a relationship exists between organic matter production at the sea surface recorded by nannofossil carbonate sr ca and its consumption on the seafloor measured by benthic foraminiferal accumulation rates bfar a mid pliocene 3 67 3 90 ma section of ocean drilling program site 926 in the northwestern tropical atlantic was sampled where previous work established that the calcareous nannoplankton assemblages vary with insolation linked changes in surface water productivity our results reveal that coarse fraction nannofossil sr ca varies with changes in assemblage composition and may be predominantly controlled by the geochemistry of the warm water oligotrophic genus discoaster bfar also have a positive relationship with sr ca and discoaster abundances implying times of relatively low surface water nutrients coincide with enhanced bfar this result is opposite of what one would expect given the assumption of a direct relationship between primary and export production we speculate that the bfar are stimulated by enhanced organic carbon export associated with ballasting by nannofossil assemblages dominated volumetrically by large robust taxa such as discoaster species these results highlight the complexity of interpretations of bulk nannofossil sr ca ratios as well as bfar data with respect to paleoproductivity

microbial generation of economic accumulations of methane within a shallow organic rich shale although methane of bacterial origin is ubiquitous in marine and freshwater sediments economic accumulations of bacterial gases occur mainly at depths of several kilometres in tertiary basins that had high sedimentation rates1 2 here we present an integration of geochemical and isotopic data from gas and water extracted from the upper devonian antrim shale along the northern margin of the michigan basin which demonstrates that significant volumes of bacterial gas have been generated in organic rich shales at depths of less than 600 metres the antrim shale is mainly a self sourced reservoir in contrast to conventional gas deposits that have migrated from a source to a reservoir and has become one of the most actively exploited gas reservoirs3 in the united states the gas forming processes operating at shallow depths in the antrim shale are not unique4 and an understanding of these processes should lead to the identification and development of other economic non conventional gas deposits around the world

stable carbon isotope geochemistry of adsorbed alkane gases in near surface soils of the saurashtra basin india abstract the stable carbon isotopic compositions of light hydrocarbon gases adsorbed in near surface soil and sediments from the saurashtra basin were characterized for their origin and maturity saurashtra is considered geologically prospective for oil and gas reserves however a major part of the basin is covered by the deccan traps hindering the exploration of mesozoic hydrocarbon targets surface geochemical prospecting based on micro seepage of hydrocarbons from subsurface accumulations could be advantageous in such areas in light of this 150 soil samples were collected from the northwestern part of saurashtra around the jamnagar area where a thick sedimentary sequence of about 2 3 km exists under 1 1 5 km of deccan basalt the concentration of acid desorbed alkane gases from soil samples was found to vary in ppb as methane c 1 3 518 ethane c 2 0 430 propane c 3 0 331 i butane ic 4 0 297 n butane nc 4 2 116 i pentane ic 5 0 31 and n pentane nc 5 0 23 respectively fifteen samples with high concentrations of alkane gases were measured for their 13 c 1 13 c 2 and 13 c 3 compositions using gas chromatography combustion isotope ratio mass spectrometry gc c irms the values for methane varied from 27 to 45 4 ethane from 20 9 to 27 6 and propane from 20 4 to 29 1 versus the vienna peedee belemnite vpdb the carbon isotope ratio distribution pattern represents isotopic characteristics pertaining to hydrocarbon gases derived from thermogenic sources comparisons of carbon isotopic signatures and compositional variations with the standard carbon isotopic models suggest that hydrocarbon gases found in the shallow depths of the study area are not of bacterial origin but are formed thermally from deeply buried organic matter likely to be mainly a terrestrial source rock with a partial contribution from a marine source these gases may have migrated to the near surface environment where they represent an admixture of thermally generated hydrocarbon gases from mixed sources and maturity the maturity scale 13 c versus log ro applied to the surface sediment samples of the jamnagar area indicated the source material to be capable of generating oil and gas the detection of thermogenic alkane gases in near surface sediments offers the possibility of hydrocarbons at depth in saurashtra

a cenozoic seawater sr ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes a cenozoic multi species record of benthic foraminiferal calcite sr ca has been produced and is corrected for inter specific offsets typically less than 0 3 mmol mol and for the linear relationship between decreasing benthic foraminiferal sr ca and increasing water depth the water depth correction determined from holocene late glacial maximum and eocene paleowater depth transects is not vert similar0 1 mmol mol km the corrected cenozoic benthic foraminiferal sr ca record ranges from 1 2 to 2 0 mmol mol and has been interpreted in terms of long term changes in seawater sr ca enabling issues related to higher resolution variability in sr ca to be ignored we estimate that seawater sr ca was not vert similar1 5 times modern values in the late cretaceous but declined rapidly into the paleogene following a minimum in the eocene seawater sr ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late miocene by assuming scenarios for changing seawater calcium concentration and using published carbonate accumulation rate data combined with suitable values for sr partition coefficients into carbonates the seawater sr ca record is used to estimate global average river sr fluxes these fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity tectonic outgassing to calculate changes in global average river 87sr 86sr through the cenozoic the absolute magnitude of sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties nevertheless our results suggest that river sr flux increased from 35 ma to the present day roughly two fold accompanied by an overall increase in 87sr 86sr by not vert similar0 to 0 001 between 75 and 35 ma river 87sr 86sr also increased by not vert similar0 001 to 0 002 but was accompanied by a decrease two to three fold in river sr flux

source and migration of light hydrocarbons indicated by carbon isotopic ratios carbon isotopic ratios can distinguish among different sources of methane and can be used to correlate maturity of sediments with the methane this technique has been applied to several wells and the isotopic values have been used to suggest the sources of the methane and whether the methane migrated into the area comparison of the isotopic ratio changes in ethane propane and butanes indicated that isotopic fractionation of methane by migration is not a major factor the significant changes in methane isotopic ratio and the small changes in the isotopic ratios of these heavier hydrocarbons suggest that although diffusion is not the sole process in migration the time for migration is moderate

trace metal mg ca and sr ca analyses of single coccoliths by secondary ion mass spectrometry here we present the first multi species comparison of modern and fossil coccolith trace metal data obtained from single liths we present both trace metal analyses sr ca mg and al and distribution maps of individual paleogene fossil coccoliths obtained by secondary ion mass spectrometry sims we use this data to determine the effects of variable coccolith preservation and diagenetic calcite overgrowths on the recorded concentrations of strontium and magnesium in coccolith calcite the analysis of coccoliths from deep ocean sediments spanning the eocene oligocene transition demonstrates that primary coccolith calcite is resistant to the neomorphism that is common in planktonic foraminifera from similar depositional environments instead where present diagenetic calcite forms distinct overgrowths over primary coccolith calcite rather than replacing this calcite diagenetic overgrowths on coccoliths are easily distinguished in sims analyses on the basis of relatively higher mg and lower sr concentrations than co occurring primary coccolith calcite this interpretation is confirmed by the comparable sims analyses of modern cultured coccoliths of coccolithus braarudii further with diagenetic calcite overgrowth being the principle source of bias in coccolith based geochemical records we infer that lithologies with lower carbonate content deposited below the palaeo lysocline are more likely to produce geochemical records dominated by primary coccolith calcite than carbonate rich sediments where overgrowth is ubiquitous the preservation of primary coccolith carbonate in low carbonate lithologies thus provides a reliable geochemical archive where planktonic foraminifera are absent or have undergone neomorphism

temperature dependence of the strontium distribution coefficient in calcite an experimental study from 408 degrees to 2008 degrees c and application to natural diagenetic calcites abstract the temperature dependence of sr coprecipitation with calcite was determined experimentally in solutions with sr ca ratios and ionic strengths closely resembling marine pore fluids aragoniteto calcite and dolomite to calcite transformations were conducted over a temperature range from 40 to 200 c temperature dependence of the distribution coefficient of strontium in calcite dcsr is significant dcsr in aragonite to calcite experiments varied from 0 046 at 40 c to 0 068 at 200 c dcsr in dolomite to calcite experiments varied from 0 034 at 40 c to 0 062 at 200 c experimental values of dcsr are somewhat dependent on the precursor phase the experimental results are applied to natural diagenetic and hydrothermal calcites recovered from the sediment covered middle valley part of the juan de fuca ridge spreading center ocean drilling program holes 857c and 858d low mg calcites from hole 858d have sr contents appropriate for their present day in situ temperatures and pore water sr values in contrast high mg calcites from hole 858d that precipitated from supersaturated pore waters at inferred high growth rates have elevated sr contents relative to calculated equilibrium values the sr contents of calcites from hole 857c are close to predicted equilibrium values in some instances but are substantially different in others deviations from predicted equilibrium sr contents especially in nodules are attributed to the formation of mixed generations of carbonate precipitating with increasing burial depths and temperatures through pore waters with variable sr composition