distribution of rocks on the gusev plains and on husband hill mars 1 the population of rocks larger than 15 cm in diameter was measured at 36 locations imaged by the spirit rover over 4 km of the traverse across the gusev plains and husband hill in gusev crater on mars the rock population observed on plains surfaces is consistent with impact fragmentation of rubbly fractured volcanics and reveals little evidence for modification by secondary processes or weathering interpretation of counts from husband hill suggest an influence by bedrock for rocks larger than 0 5 m across but the distribution of smaller rocks is consistent with ejecta possessing contributions from pre plains impact events results indicate plains surfaces experienced only tens of centimeters of eolian erosion deposition since the hesperian whereas meters rather than tens of meters of erosion modified husband hill since the early hesperian

calcium isotope ratios in the world s largest rivers a constraint on the maximum imbalance of oceanic calcium fluxes 1 the oceanic mass balance of calcium ca is defined by a balance between the inputs rivers and hydrothermal and outputs bulk carbonate of ca large rivers were analyzed for ca isotope ratios 44ca 42ca expressed as ca to investigate the source and cycling of riverine ca and to add an isotopic mass balance constraint to the oceanic budget of ca the new data account for approximately one third of the total ca supplied to the oceans by rivers inter sample and seasonal variability was assessed by analyzing more than one sample for many rivers the range in the ca of large rivers at high water stand is extremely narrow at 0 27 variations in ca do not correlate with proxies for carbonate silicate or evaporite derived ca and are more likely related either to inherent variability in the lithological sources of ca or to process related fractionation the spread in riverine ca overlaps with the spread in marine limestone ca consistent with most riverine ca coming from the recycling of limestones the ca isotope composition of continental runoff has an average ca value of 0 38 0 04 identical to recent 5 m yr bulk carbonate ooze 0 33 0 13 2s d isotopic mass balance constrains that the input and output fluxes of ca to and from the oceans are balanced to within 15 over time scales similar to the residence time of ca in the oceans 1 m yr a greater imbalance between the fluxes would result in a detectable difference between the ca value of bulk carbonate and the riverine input at the current level of uncertainty the input and output fluxes could be imbalanced over much shorter time scales such as glacial interglacial cycles in which case the ocean carbonate system will not yet have responded because of the long residence time of ca the maximum current flux imbalance of 15 would be sufficient to account for the total variations in ca concentration over the tertiary such an interpretation is not unique but is the simplest interpretation given the similarity between the input and output isotopic compositions and rules out hypotheses of extreme imbalance in the recent global biogeochemical cycle of ca

surficial deposits at gusev crater along spirit rover traverses the mars exploration rover spirit has traversed a fairly flat rock strewn terrain whose surface is shaped primarily by impact events although some of the landscape has been altered by eolian processes impacts ejected basaltic rocks that probably were part of locally formed lava flows from at least 10 meters depth some rocks have been textured and or partially buried by windblown sediments less than 2 millimeters in diameter that concentrate within shallow partially filled circular impact depressions referred to as hollows the terrain traversed during the 90 sol martian solar day nominal mission shows no evidence for an ancient lake in gusev crater

accuracy of stable mg and ca isotope data obtained by mc icp ms using the standard addition method the standard addition method is evaluated to verify the accuracy and precision of mg and ca isotope data with complex matrices using the standard sample bracketing technique and analysis by mc icp ms the 44ca 42ca ratio of seawater expressed as 44 42ca relative to srm915a was determined as 0 93 0 03 95 confidence in agreement with estimates obtained by the double spike method using standard addition the seawater 26mg 24mg ratio expressed as 26mg relative to the dsm3 standard was determined as 0 80 0 06 95 confidence in agreement with previous estimates four terrestrial silicate rocks morb flood basalt glacial flour and granodiorite and olivine mineral separates from an island basalt are shown to exhibit no scatter within the error of the method averaging a 26mg of 0 20 0 05 95 confidence although a number of silicate rock data for mg isotope ratios have already been reported this is the first detailed effort to validate the accuracy of such data and test for residual analytical artifact after chemical purification of samples data regressions were evaluated statistically using the mean square weighted deviate mswd demonstrating that the uncertainty on individual data points are generally over estimated the external two standard deviation uncertainty on individual data points is estimated by monte carlo simulation as b0 075 about a factor of two improvement on early publications of mg isotope data the consistency of the standard addition estimates of 26mg in silicate rocks imply that if any residual matrix effects are present then they must be less than the spread of the data 0 11 given the diverse range of matrices in each of the samples the 26mg values of the silicate rocks suggest that mg isotope ratios in silicate material may only have a very restricted range the 26mg values of silicate material in the present study falls between the average values reported by teng et al teng f z wadhwa m helz r t 2007 investigation of magnesium isotope fractionation during basalt differentiation implications for a chondritic composition of the terrestrial mantle earth and planetary science letters 261 84 92 doi 10 1016 j epsl 2007 06 004 and wiechert and halliday wiechert u halliday a n 2006 non chondritic magnesium and the origins of the inner terrestrial planets earth and planetary science letters 256 360 371 doi 10 1016 j epsl 2007 01 007 and given the spread of published 26mg values for chondritic material a chondritic composition for terrestrial mg cannot be ruled out we suggest that some of the small discrepancies between our data and analysis of the same samples in earlier studies may have arisen because the chemical purification of mg prior to analysis can easily induce analytical artifact this method could be expanded to the isotope ratios of other elements which also rely on correcting for mass bias using the standard sample bracketing method where similar analytical discrepancies may also exist

clathrites archives of near seafloor pore fluid evolution δ44 40ca δ13c δ18o in gas hydrate environments aragonitic clathrites are methane derived precipitates that are found at sites of massive near seafloor gas hydrate clathrate accumulations at the summit of southern hydrate ridge cascadia margin these platy carbonate precipitates form inside or in proximity to gas hydrate which in our study site currently coexists with a fluid that is highly enriched in dissolved ions as salts are excluded during gas hydrate formation the clathrites record the preferential incorporation of 18o into the hydrate structure and hence the enrichment of 16o in the surrounding brine we measured 18o values as high as 2 27 relative to peedee belemnite that correspond to a fluid composition of 1 18 relative to standard mean ocean water the same trend can be observed in ca isotopes ongoing clathrite precipitation causes enrichment of the 44ca in the fluid and hence in the carbonates carbon isotopes confirm a methane source for the carbonates our triple stable isotope approach that uses the three main components of carbonates ca c o provides insight into multiple parameters influencing the isotopic composition of the pore water and hence the isotopic composition of the clathrites this approach provides a tool to monitor the geochemical processes during clathrate and clathrite formation thus recording the evolution of the geochemical environment of gas hydrate systems

riverine evidence for a fractionated reservoir of ca and mg on the continents implications for the oceanic ca cycle analysis of river water rock travertine and soil from the high altitude negligible vegetation setting of the southern tibetan plateau demonstrates that ca and mg isotope ratios are fractionated during weathering dissolved ca in the two rivers studied is derived primarily by limestone dissolution 44 42ca in the rivers averages 0 43 and is statistically distinct from limestone at 0 31 the range in 44 42ca in these small rivers is 0 43 equivalent to the entire range in 44 42ca recorded in marine carbonate over the last 80 ma precipitation of isotopically light travertine with a 44 42ca of 0 21 enriches solute ca in heavy isotopes the mg isotope composition of the rivers is intermediate between limestone and silicate rock averaging 1 5 silicate soil has a 26mg of 0 03 heavier than silicate rock by 0 5 these fractionations in the soil create a companion groundwater reservoir of heavy ca and light mg seasonal variations in ca and mg isotope ratios in the dissolved load are small but define an array which can be modelled as a mixture between a fractionated groundwater reservoir and surface runoff reflecting the isotopic composition of the lithology fractionation of ca during the weathering of the continents is of importance to the global cycle of ca the riverine input of ca to the oceans dominated by carbonate weathering is controlled not only by the composition of the primary continental crust but also by the size and composition of a fractionated reservoir on the continents the impact on the oceanic cycle of ca depends on the relative residence times of dissolved ca in the ocean and the storage time of fractionated ca

crater morphometry on the mafic floor unit at jezero crater mars comparisons to a known basaltic lava plain at the insight landing site

hydrothermal fluid fluxes calculated from the isotopic mass balance of thallium in the ocean crust abstract hydrothermal fluids expelled from the seafloor at high and low temperatures play pivotal roles in controlling seawater chemistry however the magnitude of the high temperature water flux of mid ocean ridge axes remains widely disputed and the volume of low temperature vent fluids at ridge flanks is virtually unconstrained here we determine both high and low temperature hydrothermal fluid fluxes using the chemical and isotopic mass balance of the element thallium tl in the ocean crust thallium is a unique tracer of ocean floor hydrothermal exchange because of its contrasting behavior during seafloor alteration at low and high temperatures and the distinctive isotopic signatures of fresh and altered morb and seawater the calculated high temperature hydrothermal water flux is 0 17 2 93 1013 kg yr with a best estimate of 0 72 1013 kg yr this result suggests that only about 5 to 80 of the heat available at mid ocean ridge axes from the crystallization and cooling of the freshly formed ocean crust is released by high temperature black smoker fluids the residual thermal energy is most likely lost via conduction and or through the circulation of intermediate temperature hydrothermal fluids that do not alter the chemical budgets of tl in the ocean crust the tl based calculations indicate that the low temperature hydrothermal water flux at ridge flanks is 0 2 5 4 1017 kg yr this implies that the fluids have an average temperature anomaly of only about 0 1 to 3 6 c relative to ambient seawater if these low temperatures are correct then both sr and mg are expected to be relatively unreactive in ridge flank hydrothermal systems and this may explain why the extent of basalt alteration that is observed for altered ocean crust appears insufficient to balance the oceanic budgets of 87sr 86sr and mg

large fractionation of calcium isotopes during cave analogue calcium carbonate growth we have measured 44 42ca of laboratory precipitated calcite grown in an experimental setup that closely replicates stalagmite formation calcium solutions were dripped onto two different substrates in tightly controlled conditions and calcite precipitated due to rapid co2 degassing with seeded glass slides as the substrate we observe a ca isotope ratio in the calcite which is 0 5 per amu lower than that in the growth solution this fractionation is generally almost twice that observed in previously published calcite growth experiments and indicates a large kinetic effect on ca isotopes in the stalagmite growth environment the precipitate forming near the spot where the drip lands shows slightly greater solution to precipitate fractionation than calcite further from the drip reflecting a decrease in this kinetic fractionation as precipitation continues we interpret these results in the context of the model of fantle and depaolo 2007 which involves surface entrapment of light ca isotopes to decrease calcite 44 42ca and depletion of ca from the solution in the direct vicinity of the growing calcite to increase calcite 44 42ca in the stalagmite setting the second of these effects is minimized so that calcite ca isotope ratios are unusually light this interpretation suggests that stalagmite ca isotope ratios should decrease with the saturation state of the drip water i e with the growth rate of calcite ca isotopes might therefore allow reconstruction of surface entrapment of trace metals and isotopes more generally and might for instance allow an assessment of the appropriate relationship between oxygen isotope fractionation and temperature for periods of past growth in stalagmites

calcium isotope fractionation in ikaite and vaterite abstract we investigated the isotopic composition of calcium in the metastable calcium carbonate polymorphs vaterite and ikaite the synthetic vaterite precipitates show a smaller degree of ca isotope fractionation than calcite or aragonite at comparable temperatures and revealed no significant temperature sensitivity between 10 and 50 c ikaite the water bearing ca carbonate modification caco 3 6h 2 o was precipitated at 2 c in controlled laboratory experiments and in addition recovered from marine sediments and sea ice synthetic and natural ikaites show similar values of ca isotope fractionation in general ikaite is less depleted in heavy isotopes compared to calcite or aragonite at low temperatures the observed offset of vaterite and ikaite to calcite or aragonite precipitated at similar temperatures is presumably mainly related to differences in precipitation rates and regimes which seem however to be typical for the growth of these carbonate minerals small differences in ca isotope ratios of naturally formed ikaites from different locations seem to be related to different geochemical conditions in the respective sediment settings

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

ca isotope stratigraphy across the cenomanian turonian oae 2 links between volcanism seawater geochemistry and the carbonate fractionation factor abstract the ca isotope composition of marine carbonate rocks offers potential to reconstruct drivers of environmental change in the geologic past this study reports new high precision ca isotope records ca 44 40 2 sd 0 04 for three sections spanning a major perturbation to the cretaceous ocean climate system known as ocean anoxic event 2 oae 2 central colorado usa portland 1 core southeastern france pont d issole and hokkaido japan oyubari yezo group in addition we generated new data for selected samples from eastbourne england english chalk where a previous ca isotope study was completed using different methodology blattler et al 2011 strata of the yezo group contain little carbonate 1 wt on average and accordingly did not yield a clear ca 44 40 signal the portland core and the pont d issole section display comparable ca 44 40 values which increase by 0 10 0 15 at the onset of oae 2 and then decrease to near initial values across the event the eastbourne ca 44 40 values are higher than previously reported they are also higher than the ca 44 40 values for the portland core and the pont d issole section but define a similar pattern according to a numerical model of the marine ca cycle elevated hydrothermal inputs have little impact on seawater ca 44 40 values elevated riverine chemical weathering inputs produce a transient negative isotope excursion which significantly differs from the positive isotope excursions observed in the portland pont d issole and eastbourne records a decrease in the magnitude of the carbonate fractionation factor provides the best explanation for a positive shift in ca 44 40 values especially given the rapid nature of the excursion because a decrease in the fractionation factor corresponds to an increase in the ca co3 ratio of seawater we tentatively attribute the positive ca isotope excursion to transient ocean acidification i e a reduction in the concentration of co 3 2 during co2 uptake recent studies utilizing a variety of isotope proxies e g nd os and pb implicate eruption of the caribbean large igneous province as a likely source of increased co2 moreover integration of c ca and os isotope data reveals new information about the timing of events during the onset of oae 2

calcium and magnesium isotope systematics in rivers draining the himalaya tibetan plateau region lithological or fractionation control abstract in rivers draining the himalaya tibetan plateau region the 26mg 24mg ratio has a range of 2 and the 44ca 42ca ratio has a range of 0 6 the average 26 mg values of tributaries from each of the main lithotectonic units tethyan sedimentary series tss high himalayan crystalline series hhcs and lesser himalayan series lhs are within 2 standard deviation analytical uncertainty 0 14 the consistency of average riverine 26 mg values is in contrast to the main rock types limestone dolostone and silicate which range in their average 26 mg values by more than 2 tributaries draining the dolostones of the lhs differ in their 44 42 ca values compared to tributaries from the tss and hhcs the chemistry of these river waters is strongly influenced by dolostone solute mg ca close to unity and both 26 mg 1 31 and 44 42 ca 0 64 values are within analytical uncertainty of the lhs dolostone these are the most elevated 44 42 ca values in rivers and rock reported so far demonstrating that both riverine and bedrock 44 42 ca values may show greater variability than previously thought although rivers draining tss limestone have the lowest 26 mg and 44 42 ca values at 1 41 and 0 42 respectively both are offset to higher values compared to bedrock tss limestone the average 26 mg value of rivers draining mainly silicate rock of the hhcs is 1 25 lower by 0 63 than the average silicate rock these differences are consistent with a fractionation of 26 mg values during silicate weathering given that the proportion of mg exported from the himalaya as solute mg is small the difference in 26mg 24mg ratios between silicate rock and solute mg reflects the 26mg 24mg isotopic fractionation factor silicate dissolved mg between silicate and dissolved mg during incongruent silicate weathering the value of silicate dissolved mg of 0 99937 implies that in the tss solute mg is primarily derived from silicate weathering whereas the source of ca is overwhelmingly derived from carbonate weathering the average 44 42 ca value in hhcs rivers is within uncertainty of silicate rock at 0 39 the widespread hot springs of the high himalaya have an average 26 mg value of 0 46 and an average 44 42 ca value of 0 5 distinct from riverine values for 26 mg but similar to riverine 44 42 ca values although rivers draining each major rock type have 44 42 ca and 26 mg values in part inherited from bedrock there is no correlation with proxies for carbonate or silicate lithology such as na ca ratios suggesting that ca and mg are in part recycled however in spite of the vast contrast in vegetation density between the arid tibetan plateau and the tropical lesser himalaya the isotopic fractionation factor for ca and mg between solute and rocks are not systematically different suggesting that vegetation may only recycle a small amount of ca and mg in these catchments the discrepancy between solute and solid ca and mg isotope ratios in these rivers from diverse weathering environments highlight our lack of understanding concerning the origin and subsequent path of ca and mg bound as minerals in rock and released as cations in rivers the fractionation of ca and mg isotope ratios may prove useful for tracing mechanisms of chemical alteration ca isotope ratios of solute riverine ca show a greater variability than previously acknowledged the variability of ca isotope ratios in modern rivers will need to be better quantified and accounted for in future models of global ca cycling if past variations in oceanic ca isotope ratios are to be of use in constraining the past carbon cycle

assessment of insight landing site predictions comprehensive analysis of remote sensing data used to select the interior exploration using seismic investigations geodesy and heat transport insight landing site correctly predicted the atmospheric temperature and pressure profile during entry and descent the safe landing surface and the geologic setting of the site the smooth plains upon which the insight landing site is located were accurately predicted to be generally similar to the mars exploration rover spirit landing site with relatively low rock abundance low slopes and a moderately dusty surface with a 3 10 m impact fragmented regolith over hesperian to early amazonian basaltic lava flows the deceleration profile and surface pressure encountered by the spacecraft during entry descent and landing compared well within 1 of the envelope of modeled temperature profiles and the expected surface pressure orbital estimates of thermal inertia are similar to surface radiometer measurements and materials at the surface are dominated by poorly consolidated sand as expected thin coatings of bright atmospheric dust on the surface were as indicated by orbital albedo and dust cover index measurements orbital estimates of rock abundance from shadow measurements in high resolution images and thermal differencing indicated very low rock abundance and surface counts show 1 4 area covered by rocks slopes at 100 to 5 m length scale measured from orbital topographic and radar data correctly indicated a surface comparably smooth and flat as the two smoothest landing sites opportunity and phoenix thermal inertia and radar data indicated the surface would be load bearing as found

degradation of 100 m scale rocky ejecta craters at the insight landing site on mars and implications for surface processes and erosion rates in the hesperian and amazonian rocky ejecta craters recs at the interior exploration using seismic investigations geodesy and heat transport insight landing site on elysium planitia mars provide constraints on crater modification and rates for the hesperian and amazonian the recs are between 10 m and 1 2 km in diameter and exhibit five classes of preservation class 1 represents pristine craters with sharp rims and abundant ejected rocks from classes 2 to 5 rims become more subdued craters are infilled and the ejecta become discontinuously distributed high resolution imaging science experiment digital elevation models indicate a maximum depth to diameter ratio of 0 15 which is lower than pristine models for craters of similar size the low ratio is related to the presence of a loosely consolidated regolith and early stage eolian infill rim heights have an average height to diameter ratio of 0 03 for the most pristine class the size frequency distribution of recs plotted using cumulative and differential methods indicates that crater classes within the diameter range of 200 m to 1 2 km are separated by 100 to 200 myr smaller craters degrade faster with classes separated by 100 myr rim erosion can be entirely modeled by nonlinear diffusional processes using the calculated timescales and a constant diffusivity of 8 10 7 m 2 year for craters 200 to 500 m in diameter diffusion models only partly capture depth related degradation which requires eolian infill depth degradation and rim erosion rates are 10 2 to 10 3 m myr respectively the rates are consistent with relatively slow modification that is typical of the last two epochs of martian history

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

experimental studies of seismoelectric conversions in fluid saturated porous media when seismic waves generate a relative fluid solid motion in a fluid saturated porous medium the moving charges streaming current in the electric double layer induce an electromagnetic em field this paper first experimentally confirms that the coupling between the seismic wave and the electromagnetic field in the kilohertz range is electrokinetic in nature seismoelectric signals are measured in homogeneous cylindrical porous rock samples and multilayered models the seismoelectric signals in homogeneous rock are electric fields that move along with the acoustic wave the mechanism of the seismoelectric conversion is completely different from the piezoelectric effect of quartz grains the seismoelectric sensitivity with respect to salinity of the saturant has been experimentally determined the amplitude of seismoelectric signals increases as the saturant conductivity decreases the seismoelectric effects are generated by two different mechanisms both the em radiation and the electric potential generated at an interface and within a porous medium respectively were measured as the p wave at ultrasonic frequencies passes through the layered models our experimental results demonstrate that seismoelectric effects exist and are measurable in the kilohertz range the paper concludes with a comparison of experimental data and modeled data in a three layer porous model seismoelectric measurements could be an effective means of obtaining transport coefficients such as hydraulic permeability and other porous rock properties

interpreting the ca isotope record of marine biogenic carbonates an 18 million year record of the ca isotopic composition 44 42ca of planktonic foraminiferans from odp site 925 in the atlantic on the ceara rise provides the opportunity for critical analysis of ca isotope based reconstructions of the ca cycle 44 42ca in this record averages 0 37 0 05 1 sd and ranges from 0 21 to 0 52 the record is a good match to previously published neogene ca isotope records based on foraminiferans but is not similar to the record based on bulk carbonates which has values that are as much as 0 25 lower bulk carbonate and planktonic foraminiferans from core tops differ slightly in their 44 42ca i e by 0 06 0 06 n 5 while the difference between bulk carbonate and foraminiferan values further back in time is markedly larger leaving open the question of the cause of the difference modeling the global ca cycle from downcore variations in 44 42ca by assuming fixed values for the isotopic composition of weathering inputs 44 42caw and for isotope fractionation associated with the production of carbonate sediments sed results in unrealistically large variations in the total mass of ca2 in the oceans over the neogene alternatively variations of 0 05 in the ca isotope composition of weathering inputs or in the extent of fractionation of ca isotopes during calcareous sediment formation could entirely account for variations in the ca isotopic composition of marine carbonates ca isotope fractionation during continental weathering such as has been recently observed could easily result in variations in 44 42caw of a few tenths of permil likewise a difference in the fractionation factors associated with aragonite versus calcite formation could drive shifts in sed of tenths of permil with shifts in the relative output of calcite and aragonite from the ocean until better constraints on variations in 44 42caw and sed have been established modeling the ca2 content of seawater from ca isotope curves should be approached cautiously

chemical weathering mass loss and dust inputs across a climate by time matrix in the hawaiian islands we determined the total mass loss and rate of chemical weathering from three minimally eroded hawaiian lava flows that are 10 170 and 350 ka old using a backhoe we sampled the entire weathering zone at 28 sites and measured the depletion or enrichment of each major element in each soil horizon relative to parent material we were able to assess the influence of both climate and substrate age on chemical weathering because each flow crosses a precipitation gradient from 600 to 2500 mm yr 1 mass loss rates were highest for the 0 10 ka interval under the wettest climatic conditions 54 t km 2 yr 1 and decreased to near zero in the wet sites during the 10 170 and 170 350 ka intervals not surprisingly weathering rates were lower in drier sites 24 t km 2 yr 1 from 0 10 ka to b 2tk m 2 yr 1 thereafter however the effects of precipitation were non linear there was a precipitation threshold below which mass loss was relatively small and above which mass loss was substantial but insensitive to increased rainfall chemical weathering rates depend on tectonic uplift erosion climate rock type or some combination thereof by working on stable uneroded surfaces of a single rock type across a well constrained precipitation gradient we were able to identify another potential driver the rate of dust deposition although hawai i is one of the least dusty places in the northern hemisphere dust inputs reached 82 of the total mass loss from the weathering zone at some sites and averaged 30 on the 170 ka flow this highlights the potential importance of dust as a component of observed weathering fluxes from catchments worldwide

spirit mars rover mission overview and selected results from the northern home plate winter haven to the side of scamander crater spirit mars rover mission overview and selected results from the northern home plate winter haven to the side of scamander crater

constraints on ripple migration at meridiani planum from opportunity and hirise observations of fresh craters 1 observations of fresh impact craters by the opportunity rover and in high resolution orbital images constrain the latest phase of granule ripple migration at meridiani planum to have occurred between 50 ka and 200 ka opportunity explored the fresh resolution crater cluster and concepcion crater that are superposed on and thus younger than the ripples these fresh craters have small dark pebbles scattered across their surfaces which are most likely fragments of the impactor suggesting that the dark pebbles and cobbles observed by opportunity at meridiani planum are a lag of impactor derived material either meteoritic or secondary impactors from elsewhere on mars two larger fresh rayed craters in meridiani planum bracket ripple migration secondaries from ada crater are clearly superposed on and secondaries from an unnamed 0 84 km diameter crater have been modified and overprinted by the ripples three methods were used to estimate the age of these craters and thus when the latest phase of ripple migration occurred the inactivity of the ripples over the past 50 ka at meridiani is also consistent with other evidence for the stability of the ripples the lack of observed eolian bed forms in craters that formed in the past 20 years and little evidence for much dune motion in the past 30 yr on mars observations of crater morphology and their interaction with the ripples allow the development of a general time scale for craters in meridiani planum over the past million years

234u 238u activity ratios in freshwaters as tracers of hydrological processes the strengbach watershed vosges france abstract 234u 238u and 87sr 86sr isotopic ratios as well as major and trace u ba sr rb element concentrations were analyzed in dissolved loads of the strengbach stream vosges france in order to constrain the sources of u isotopes 234u 238u to river waters the variations of the 234u 238u activity ratios along the stream indicate a clear dependence between the 234u 238u activity ratios of the surface waters and the different types of rocks forming the watershed with near equilibrium values for the waters draining granites and high 234u 238u disequilibria 1 4 for those flowing over carbonates the high 234u 238u disequilibria are related to a supply of 234u enriched groundwaters located within the carbonate rocks the 234u 238u activity ratios of the waters at the outlet of the catchment collecting the sources of the stream on the granitic lithology decrease from 1 02 to 0 96 when the discharge of the stream increases such a tendency requires mixing between a water body enriched in 234u which weathered the granitic bed rock at secular equilibrium and a water with a 234u 238u activity ratio below unity representing a mobilization of u from material that has already been weathered comparison of the geochemical characteristics of waters collected during the year and those collected during a flood event reveals the involvement of two different weathered end members depending on the hydrological conditions during the year the dissolved u transported by the river originates from bed rock and deep horizons of the weathering profile whereas a significant part of u during the flood event is supplied by superficial horizons of soils probably complexed by organic colloids these results outline the potential of 234u 238u activity ratios to investigate hydrological processes and emphasize that their use as tracers of rock weathering should be made cautiously

calcium isotopes in the global biogeochemical ca cycle implications for development of a ca isotope proxy abstract at the earth s surface calcium ca is a critical element at a variety of scales it is soluble in natural waters a biological nutrient and a major constituent of the dominant mineral sink for carbon in the ocean caco3 there is a 4 variation in the ca isotopic composition 44ca 40ca expressed as 44ca of various ca reservoirs on earth suggesting ca isotopes as a promising tracer of ca cycling in both the present and the past fifteen years of high precision ca isotope measurements has revealed much about the behavior of ca isotopes in the earth surface environment but there remain fundamental questions concerning how ca isotopes are used to elucidate the marine and terrestrial ca cycles the current work presents a data compilation of over 70 published ca isotope studies totaling over 2600 measurements presented on a common delta scale that includes data on rivers and groundwater dust soils and soil pore fluids vegetation rainwater silicate minerals rocks and authigenic marine minerals carbonates sulfates and phosphates both modern and ancient the data compilation suggests that 1 there is a significant difference between carbonate 0 60 and silicate 44ca 0 94 2 riverine 44ca 0 88 does not simply reflect the compiled carbonate 44ca and 3 terrestrial vegetation exhibits the largest range of ca isotopic compositions 3 5 in the terrestrial setting we discuss these observations in the context of the global ca cycle exploring the extent to which seawater 44ca variability is feasible and how we can achieve accurate reconstructions of seawater 44ca over geologic time scales the current study presents simple mass balance models that quantify the leverage of inputs to change the ca isotopic composition of the ocean as this directly impacts the manner in which ca isotopes are interpreted although ca fractionates isotopically in the modern system during continental cycling the 44ca range of riverine inputs to the ocean is considerably smaller than the variability observed in putative seawater proxies such as nannofossil ooze and marine barite in the terrestrial realm plants exhibit a wide 44ca range and there is evidence that ca fluxes via biomass degradation are significant at the catchment scale we therefore assess the ability of the continental biosphere to influence riverine and consequently seawater 44ca a steady state biosphere has little leverage to alter riverine 44ca except in cases where the 44ca of the recycling flux is isotopically distinct from the 44ca of the uptake flux a non steady state biosphere can substantially impact both soil and riverine 44ca driving exchangeable ca either heavier or lighter depending on the magnitude of the recycling flux relative to the uptake flux based on estimates of the size of the global biosphere 1 5 1015 mol ca we suggest a decaying biosphere has the potential to impact riverine 44ca by tenths of a permil over time scales in the marine realm we evaluate the effect of a variable fractionation factor accompanying global removal of ca from the ocean on seawater 44ca and suggest methods by which such a mechanism can be recognized in the rock record experimental data suggest that there is considerable leverage

the calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance calcium isotope ratios relative to seawater were studied in natural waters in order to constrain the ca isotopic flux to the oceans and to discuss the oceanic ca budget this study includes the analysis of 1 ca isotopes in continental waters at the regional scale of the upper rhine valley and 2 the determination of the 44ca values of some major rivers and hydrothermal vents the data indicate that the global 44ca variability of the studied waters with a maximal range of 1 is limited and must be linked to mass fractionation processes at the scale of a small watershed aubure vosges france the 44ca river flux changes due to the variation of the proportion of waters resulting from chemical alteration of rocks and biologically fractionated soil solutions ca isotopes could therefore be an important tool to quantify the impact of the plants and the biosphere on the river water chemistry at the regional scale of the rhine valley as well as at the global scale of world rivers the 44ca variability of river samples ranges from 0 5 to 1 without any relationship with the lithology of the watershed or the climate similarly the 44ca value of hydrothermal vents is also uniform and close to the mean value of river waters consequently the 44ca flux to the ocean should remain rather constant through time with a mean of 1 1 0 2 this value confirms that the ca budget of the present day seawater is in steady state this was not necessarily the case in the past non steady state periods should have been due to intensity variations of incoming and outcoming ca fluxes rather than to the variations in their isotopic signatures

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

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

seawater calcium isotope ratios across the eocene oligocene transition during the eocene oligocene transition eot ca 34 ma earth s climate cooled significantly from a greenhouse to an icehouse climate while the calcite caco3 compensation depth ccd in the pacific ocean increased rapidly fluctuations in the ccd could result from various processes that create an imbalance between calcium ca sources to and sinks from the ocean e g weathering and caco3 deposition with different effects on the isotopic composition of dissolved ca in the oceans due to differences in the ca isotopic composition of various inputs and outputs we used ca isotope ratios 44 40ca of coeval pelagic marine barite and bulk carbonate to evaluate changes in the marine ca cycle across the eot we show that the permanent deepening of the ccd was not accompanied by a pronounced change in seawater 44 40ca whereas time intervals in the neogene with smaller carbonate depositional changes are characterized by seawater 44 40ca shifts this suggests that the response of seawater 44 40ca to changes in weathering fluxes and to imbalances in the oceanic alkalinity budget depends on the chemical composition of seawater a minor and transient fluctuation in the ca isotope ratio of bulk carbonate may reflect a change in isotopic fractionation associated with caco3 precipitation from seawater due to a combination of factors including changes in temperature and or in the assemblages of calcifying organisms

bayesian inversion of joint sh seismic and seismoelectric data to infer glacier system properties abstract in glacial studies properties such as glacier thickness and the basement permeability and porosity are key to understand the hydrological and mechanical behaviour of the system the seismoelectric method could potentially be used to determine key properties of glacial environments here we analytically model the generation of seismic and seismoelectric signals by means of a shear horizontal seismic wave source on top of a glacier overlying a porous basement considering a one dimensional setting we compute the seismic waves and the electrokinetically induced electric field we then analyse the sensitivity of the seismic and electromagnetic data to relevant model parameters namely depth of the glacier bottom porosity permeability shear modulus and saturating water salinity of the glacier basement moreover we study the possibility of inferring these key parameters from a set of very low noise synthetic data adopting a bayesian framework to pay particular attention to the uncertainty of the model parameters mentioned above we tackle the resolution of the probabilistic inverse problem with two strategies 1 we compute the marginal posterior distributions of each model parameter solving multidimensional integrals numerically and 2 we use a markov chain monte carlo algorithm to retrieve a collection of model parameters that follows the posterior probability density function of the model parameters given the synthetic data set both methodologies are able to obtain the marginal distributions of the parameters and estimate their mean and standard deviation the markov chain monte carlo algorithm performs better in terms of numerical stability and number of iterations needed to characterize the distributions the inversion of seismic data alone is not able to constrain the values of porosity and permeability further than the prior distribution in turn the inversion of the electric data alone and the joint inversion of seismic and electric data are useful to constrain these parameters as well as other glacial system properties furthermore the joint inversion reduces the uncertainty of the model parameters estimates and provides more accurate results

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

stable calcium isotopic composition of meteorites and rocky planets abstract new measurements of mass dependent calcium isotope effects in meteorites lunar and terrestrial samples show that earth moon mars and differentiated asteroids e g 4 vesta and the angrite and aubrite parent bodies are indistinguishable from primitive ordinary chondritic meteorites at our current analytical resolution 0 07 sd for the 44 ca 40 ca ratio in contrast enstatite chondritic meteorites are slightly enriched in heavier calcium isotopes ca 0 5 and primitive carbonaceous chondritic meteorites are depleted in heavier calcium isotopes ca 0 5 the calcium isotope effects cannot be easily ascribed to evaporation or intraplanetary differentiation processes the isotopic variations probably survive from the earliest stages of nebular condensation and indicate that condensation occurred under non equilibrium undercooled nebular gas conditions some of this early high temperature calcium isotope heterogeneity is recorded by refractory inclusions niederer and papanastassiou 1984 and survived in planetesimals but virtually none of it survived through terrestrial planet accretion the new calcium isotope data suggest that ordinary chondrites are representative of the bulk of the refractory materials that formed the terrestrial planets enstatite and carbonaceous chondrites are not the enrichment of light calcium isotopes in bulk carbonaceous chondrites implies that their compositions are not fully representative of the solar nebula condensable fraction

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

crater gradation in gusev crater and meridiani planum mars 1 the mars exploration rovers investigated numerous craters in gusev crater and meridiani planum during the first 400 sols of their missions craters vary in size and preservation state but are mostly due to secondary impacts at gusev and primary impacts at meridiani craters at both locations are modified primarily by eolian erosion and infilling and lack evidence for modification by aqueous processes effects of gradation on crater form are dependent on size local lithology slopes and availability of mobile sediments at gusev impacts into basaltic rubble create shallow craters and ejecta composed of resistant rocks ejecta initially experience eolian stripping which becomes weathering limited as lags develop on ejecta surfaces and sediments are trapped within craters subsequent eolian gradation depends on the slow production of fines by weathering and impacts and is accompanied by minor mass wasting at meridiani the sulfate rich bedrock is more susceptible to eolian erosion and exposed crater rims walls and ejecta are eroded while lower interiors and low relief surfaces are increasingly infilled and buried by mostly basaltic sediments eolian processes outpace early mass wasting often produce meters of erosion and mantle some surfaces some small craters were likely completely eroded buried craters 100 m in diameter on the hesperian aged floor of gusev are generally more pristine than on the amazonian aged meridiani plains this conclusion contradicts interpretations from orbital views which do not readily distinguish crater gradation state at meridiani and reveal apparently subdued crater forms at gusev that may suggest more gradation than has occurred

relative contributions of silicate and carbonate rocks to riverine sr fluxes in the headwaters of the ganges abstract exhumation of the himalayan tibetan orogen is implicated in the marked rise in seawater 87sr 86sr ratios since 40 ma however both silicate and carbonate rocks in the himalaya have elevated 87sr 86sr ratios and there is disagreement as to how much of the 87sr flux is derived from silicate weathering most previous studies have used element ratios from bedrock to constrain the proportions of silicate and carbonate derived sr in river waters here we use arrays of water compositions sampled from the head waters of the ganges in the indian and nepalese himalaya to constrain the end member element ratios the compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two component mixing of silicate and carbonate derived components and lie on a plane in multicomponent composition space key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes na 0 for carbonate and constant ca na for silicate the fractions of sr derived from silicate and carbonate sources are then calculated by mass balance in sr ca mg na composition space comparison of end member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low mg trace calcite in silicate rocks may explain discrepancies in sr ca na mg covariation alternatively composition dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation ratio diagrams however the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained silicates are calculated to provide 50 of the dissolved sr flux from the head waters of the ganges assuming that discrepancies between ca mg na covariation and the silicate rock compositions arise from addition of trace calcite if the ca mg na mixing plane is rotated by composition dependent secondary calcite deposition this estimate would be increased moreover when 87sr 86sr ratios of the sr inputs are considered silicate sr is responsible for 70 16 1 of the 87sr flux forcing changes in seawater sr isotopic composition since earlier studies predict that silicate weathering generates as little as 20 of the total sr flux in himalayan river systems this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

crust stratigraphy and heterogeneities of the first kilometers at the dichotomy boundary in western elysium planitia and implications for insight lander abstract insight landed on mars on november 26 2018 in western elysium planitia the mars crust beneath the lander is subject to complex geologic history next to the great topographic and crustal dichotomy of mars understanding this part of the martian crust in the subsurface would aid future investigations of the internal structure of the planet based on seismic datasets collected by the seismic experiment for interior structure seis instrument here we investigate the subsurface structure and composition from the analysis of mineralogy and morphology of exposures in impact craters as well as on scarps and knobs in the general region of elysium planitia using a combination of orbital datasets we identify exposures of subsurface materials with distinct composition and physical properties we find olivine and pyroxene detections associated with small impact craters 1 5 7 km rim in the vicinity of insight lander as well as in the transition unit and elysium volcanic unit fe mg phyllosilicates have been identified in the central peak of the 51 km diameter kalpin crater and on knobs in the transition unit between the dichotomy and the plains in addition eroded meter scale layered unit subject to erosion has been identified in six impact craters to the north east of the landing site including kalpin crater massive bedrock and layered weak materials co occur in the transition unit indicating a complex origin these results together suggest both materials with altered composition and layered deposit occur as distinct geologic units beneath the basaltic lava flow units through analogy with terrestrial sedimentary rocks or clay bearing sediments we suggest physically weak materials exist beneath the lava flow units in the general region of elysium planitia the spatial distribution and continuity of these materials are unclear due to the lack of exposures within the lava flow unit where the insight lander is located these subsurface materials of distinct physical properties may result in increased attenuation or reverberations of seismic waves to be collected by seis the findings suggest a close investigation of the potential effects of subsurface stratigraphy on seismic data would help inform future data interpretation and understanding of the internal structure of mars

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

the impact of water rock interaction and vegetation on calcium isotope fractionation in soil and stream waters of a small forested catchment the strengbach case this study aims to constrain the factors controlling the calcium isotopic compositions in surface waters especially the respective role of vegetation and water rock interactions on ca isotope fractionation in a continental forested ecosystem the approach is to follow changes in space and time of the isotopic composition and concentration of ca along its pathway through the hydro geochemical reservoirs from atmospheric deposits to the outlet of the watershed via throughfalls percolating soil solutions and springs the study is focused on the strengbach catchment a small forested watershed located in the northeast of france in the vosges mountains the 44 40ca values of springs brooks and stream waters from the catchment are comparable to those of continental rivers and fluctuate between 0 17 and 0 87 soil solutions however are significantly depleted in lighter isotopes 44 40ca 1 00 1 47 whereas vegetation is strongly enriched 44 40ca 0 48 to 0 19 these results highlight that vegetation is a major factor controlling the calcium isotopic composition of soil solutions with depletion in light calcium in the soil solutions from deeper parts of the soil compartments due to preferential 40ca uptake by the plants rootsystem however mass balance calculations require the contribution of an additional ca flux into the soil solutions most probably associated with water rock interactions the stream waters are marked by a seasonal variation of their 44 40ca with low 44 40ca in winter and high 44 40ca in spring summer and autumn for some springs nourishing the streamlet a decrease of the 44 40ca value is observed when the discharge of the spring increases with in addition a clear covariation between the 44 40ca and corresponding h4sio4 concentrations high 44 40ca values and low h4sio4 concentrations at high discharge low 44 40ca values and high h4sio4 concentrations at low discharge these data imply that during dry periods and low water flow rate the source waters carry a ca isotopic signature from alteration of soil minerals whereas during wet periods and high flow rates admixture of significant quantities of 40ca depleted waters vegetation induced signal from uppermost soil horizons controls the isotopic composition of the source waters this study clearly emphasizes the potential of ca isotopes as tracers of biogeochemical processes at the water rock vegetation interface in a small forested catchment

the stable calcium isotopic composition of rivers draining basaltic catchments in iceland calcium isotopic compositions 44 42ca were measured in icelandic rivers draining a range of catchment types the 44 42ca values of the rivers ranged from 0 45 to 0 67 which in all cases was higher than the 44 42ca value of basaltic rock standards 0 42 0 03 a single explanation was unable to satisfactorily explain the 44 42ca values of all rivers rather it was found that the rivers formed three distinct groups based on the extent of glacial coverage in each catchment the ca isotopic composition of rivers draining catchments with less than 10 glacial cover could be explained by the mixing of water sources basalt derived solutes meltwater taken to represent meteorological precipitation inputs and hydrothermal water however fractionation of 44 42ca in these catchments cannot unequivocally be ruled out in catchments with greater than 22 glacial cover ca isotopic compositions could not be explained by a mixture of water sources and instead reflected a fractionation process most likely the precipitation of ca bearing secondary minerals or the adsorption ion exchange of ca onto mineral surfaces the fractionation factor for this process was calculated to be 0 9999 the third group of rivers with partially glaciated 10 21 catchments grouped with glaciated catchments with respect to their sr geochemistry and with non glaciated catchments with respect to their ca geochemistry the difference in the controls of ca isotope fractionation between glaciated and unglaciated catchments was attributed to different weathering regimes

calcium isotopic ratios and rare earth element abundances in refractory inclusions from the allende cv3 chondrite abstract refractory inclusions in primitive meteorites are the oldest objects formed in the solar system they exhibit large mass dependent isotopic effects in many elements including si mg and ca indicative of their complex origin we report data for both mass dependent and mass independent e ca isotopic effects and rare earth element ree abundances in six refractory inclusions from the allende cv3 meteorite our data reveal large mass dependent ca isotopic effects in these refractory inclusions with 44 40 ca ranging from 5 60 to 0 35 relative to nist srm 915a which are significantly lower than that of the bulk silicate earth 44 40 ca 1 05 0 04 importantly 44 40 ca is correlated with ree patterns refractory inclusions with group ii ree patterns have lighter ca isotope compositions compared to those with group i ree patterns specifically the studied refractory inclusions form negative 44 ca 40 ca tm er and 44 ca 40 ca nd er trends implying segregation of up to 3 of an ultrarefractory evaporation residue from a chondritic reservoir prior to the formation of refractory inclusions this residue would have to be characterized by high 44 ca 40 ca and low tm er and nd er at 2 levels of 0 5 and 1 5 for e 40 44 ca and e 43 44 ca respectively the six refractory inclusions studied show no detectable 40 ca or 43 ca anomalies relative to the terrestrial standards however five out of the six refractory inclusions do show a 48 ca excess of several e units clearly resolvable from the terrestrial standards

40k 40ca isotopic constraints on the oceanic calcium cycle the contributions of crustal silicates to the oceanic calcium cycle are investigated using high precision 40 k 40 ca measurements in archean and proterozoic carbonates river waters and a series of terrestrial and extraterrestrial mafic ultramafic samples using a multidynamic data collection scheme with strict controls on instrumental mass fractionation we show that a reproducibility of 0 35 e units 2 is obtained for the 40 ca 44 ca ratio using the thermofinnigan triton this represents an improvement by a factor of 3 compared with previous generations of data well defined excesses of 40 ca from 40 k decay were found in river waters draining the himalayas but not in the mississippi and columbia rivers all marine carbonate samples ranging in age from archean to recent show no discernable effects of 40 k decay to within the limit of 0 35 e units 2 in 40 ca 44 ca our results therefore indicate that the ca isotopic composition of seawater has remained constant and indistinguishable from that of the mantle for the past 3 5 ga despite the influx of radiogenic calcium delivered by weathering of the high k ca components of the continental crust thus over most of geologic time the contributions of the high k ca sources from the continents are far below the contributions of hydrothermal sources mass balance constraints indicate that unless the present day contribution of continental silicates is much less than 8 of the river ca flux the total hydrothermal flux of calcium must exceed the input from high temperature vents at ridge axes by at least one order of magnitude the present day oceanic mass balance requires a high input of calcium 4 15 10 12 mol ca yr at low temperature hydrothermal sites

corrigendum to calcium isotopes in the global biogeochemical ca cycle implications for development of a ca isotope proxy earth sci rev 129 2014 148 177

variations in the marine ca cycle over the past 20 million years a 20 million year marine ca isotope record is constructed based on measurements of 36 nannofossil ooze samples from dsdp site 590 the ca isotopic composition d 44 ca relative to our bbulk earthq average of carbonate ooze samples varies between 0 2 and 0 9 and the inferred d 44 ca of seawater calcium varies between 1 1 and 0 4 modern seawater value is 0 95 on our scale fluctuations in the seawater ca isotope ratio occur in 2 to 4 million year intervals and indicate that the supply and removal of ca from the oceans are seldom in balance the ca isotope record is used to reconstruct past weathering fluxes and marine calcium concentrations the inferred marine concentration of ca fluctuates by about f20 on 2 4 million year time scales and by about f50 over the 20 million year record these variations are presumably superimposed on the previously inferred 100 million year variations the seawater ca concentration was about 0 5 times present at 20 ma and generally increased until 6 ma 1 7 times present local maxima in seawater calcium concentrations occur at 6 4 and 4 ma preceding periods of enhanced marine productivity and high mass accumulation rates at site 590 while the calculated calcium concentrations are sensitive to the assumed d 44 ca value for the weathering flux the 2 4 million year features of the derived

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

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

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

calcium isotope record of phanerozoic oceans implications for chemical evolution of seawater and its causative mechanisms a total of 280 brachiopods of ordovician to cretaceous age complemented by published data from belemnites and planktonic foraminifera are used to reconstruct the evolution of calcium isotope composition of seawater 44 40casw over the phanerozoic the compiled 44 40casw record shows a general increase from 1 3 nist srm 915a at the beginning of the ordovician to 2 at present superimposed on this trend is a major long term positive excursion from the early carboniferous to early permian as well as several short term mostly negative oscillations a numerical model of the global cycles of calcium carbon magnesium and strontium was used to estimate whether the recorded 44 40casw variations can be explained by varying magnitudes of input and output fluxes of calcium to the oceans the model uses the record of marine 87sr 86sr ratios as proxy for seafloor spreading rates a record of oceanic mg ca ratios to estimate rates of dolomite formation and reconstructed atmospheric co2 discharge and erosion rates to estimate continental weathering fluxes the model results indicate that varying magnitudes of the calcium input and output fluxes cannot explain the observed 44 40casw trends suggesting that the isotope signatures of these fluxes must also have changed as a possible mechanism we suggest variable isotope fractionation in the sedimentary output flux controlled by the dominant mineralogy in marine carbonate deposits i e the oscillating calcite aragonite seas the ultimate control of the calcium isotope budget of the phanerozoic oceans appears to have been tectonic processes specifically variable rates of oceanic crust production that modulated the hydrothermal calcium flux and the oceanic mg ca ratio which in turn controlled the dominant mineralogy of marine carbonates hence the 44 40casw as to the causes of the short term oscillations recorded in the secular 44 40casw trend we tentatively propose that these are related to variable rates of dolomite formation and or to changing chemical composition of the riverine flux in particular and ratios induced by variable proportions of silicate vs carbonate weathering rates on the continents

the source of calcium in wet atmospheric deposits ca sr isotope evidence tracing the origin of calcium in wet atmospheric deposits is important for environmental studies since it is a dominant acid neutralising cation and an essential nutrient here we present the first calcium isotope ratio measurements for rain and snow samples from northeastern and southern locations france switzerland luxembourg california and japan suggest a carbonate origin only at a local scale in a forested watershed vosges mountains france the ca isotopic compositions of rainwater indicate that the rainwater becomes admixed with throughfall solution which is a mixing product of ca from dissolved atmospheric dust particles and leave excretions if this proves to be widely true the contribution of ca from the canopy could be very important for the neutralisation of acid rain and of the corresponding soil system in forested watersheds in such cases ca and sr cycles are decoupled in the lower atmosphere in contrast to sr isotopes ca isotopes can be applied to tracing processes occurring in the biosphere

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

erosion of ejecta at meteor crater arizona new methods for estimating erosion at meteor crater arizona indicate that continuous ejecta deposits beyond 1 4 1 2 crater radii from the rim 0 25r 0 5r have been lowered less than 1 m on the average this conclusion is based on the results of two approaches coarsening ofunweathered ejectainto surface lag deposits and calculation of the sediment budget within a drainage basin on the ejecta preserved ejecta morphologies beneath thin alluvium revealed by ground penetrating radar provide qualitative support for the derived estimates although slightly greater erosion 2 3 m of less resistant ejecta locally has occurred such deposits were limited in extent particularly beyond 0 25r 0 5r from the present rim subtle but preserved primary ejecta features e g distal ejecta lobes and blocks further support our estimate of minimal erosion of ejecta since the crater formed 50 000 years ago unconsolidated deposits formed during other sudden extreme events e g landslides exhibit similarly low erosion over the same time frame the common factor is the presence of large fragments or large fragments in a matrix of finer debris at meteor crater fluvial and eolian processes remove surrounding fines leaving behind a surface lag of coarse grained ejecta fragments that armor surfaces and slow vertical lowering

a laboratory seismoelectric measurement for the permafrost model with a frozen unfrozen interface 1 in this study a laboratory seismoelectric measurement for the permafrost model with a frozen unfrozen interface is presented the measurements obtained experimentally confirms that an electric double layer can be formed at the interface due to the electric and mechanical differences of the frozen and unfrozen media and seismoelectric conversion em waves originted from the relative motion of the charges in the electric double layer can be observed at n 10 khz frequency band this suggests a potential application for non destructive detection of the frost depth

calcium isotope fractionation in selected modern and ancient marine carbonates the calcium isotope composition 44 42ca was analyzed in modern cretaceous and carboniferous marine skeletal carbonates as well as in bioclasts non skeletal components and diagenetic cements of cretaceous and carboniferous limestones in order to gain insight in ca2 aq caco3 isotope fractionation mechanisms in marine carbonates splits of samples were analyzed for sr mg fe and mn concentrations and for their oxygen and carbon isotopic composition biological carbonates generally have lower 44 42ca values than inorganic marine cements and there appears to be no fractionation between seawater and marine inorganic calcite a kinetic isotope effect related to precipitation rate is considered to control the overall discrimination against 44ca in biological carbonates when compared to inorganic precipitates this is supported by a well defined correlation of the 44 42ca values with sr concentrations in cretaceous limestones that contain biological carbonates at various stages of marine diagenetic alteration no significant temperature dependence of ca isotope fractionation was found in shells of cretaceous rudist bivalves that have recorded large seasonal temperature variations as derived from 18o values and mg concentrations the reconstruction of secular variations in the 44 42ca value of seawater from well preserved skeletal calcite is compromised by a broad range of variation found in both modern and cretaceous biological carbonates independent of chemical composition or mineralogy despite these variations that may be due to still unidentified biological fractionation mechanisms the 44 42ca values of cretaceous skeletal calcite suggest that the 44 42ca value of cretaceous seawater was 0 3 0 4 lower than that of the modern ocean

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

evaluating the ca isotope proxy the use of ca isotopes as a proxy for mass flux imbalances in the ca cycle is evaluated critically a compiled ca isotope record for the last 45 ma derived from bulk nannofossil ooze and with a temporal resolution of 0 5 ma and an interpretation of the record are presented in the context of the global ca cycle this analysis which assumes that nannofossil ooze records isotopic variations in seawater indicates a dynamic ca cycle in the cenozoic such dynamic behavior has serious implications for the c cycle and suggests feedbacks between the ca and c cycles to stabilize or buffer the oceanic carbon reservoir alternative applications of the ca isotope proxy are investigated using numerical models to determine the extent to which ca isotopes are sensitive to other aspects of the ca cycle the results of the simulations are applied to specific cases in the cenozoic the simulations illustrate how variations in the global fractionation factor between calcium carbonate and seawater can produce trends similar to those observed when comparing previously published ca isotopic compositions of marine barite to the nannofossil ooze record the large drop in the 44 ca value of bulk nannofossil ooze near the eocene oligocene boundary can be reconciled in two ways either as a substantial increase in weathering relative to sedimentation or as an indicator of changing depositional mode within the ocean though the preferred interpretation is not clear at present it is evident that ca isotopes stand to be a unique proxy for ca cycling once the isotope systematics are elucidated

geophysical applications of electrokinetic conversion in volume 1 of geophysics 1936 r r thompson of humble oil and refining company proposed that the coupling of seismic and electrical energy can be used as an exploration tool subsequent efforts were directed toward using electric field antennas as geophones small scale studies concluded that antennas are not as sensitive as conventional geophones and their response is highly variable depending on the local soil conditions by 1959 martner and sparks of pan american petroleum reported in geophysics a systematic study of seismoelectric coupling using explosives at various depths their results were the first to show that the conversion of seismic to electromagnetic energy at the water table could be detected using surface antennas no studies have systematically explored the full potential of electroseismic methods using the same level of experimental sophistication used in seismic exploration

boron and calcium isotope composition in neoproterozoic carbonate rocks from namibia evidence for extreme environmental change the level and evolution of atmospheric carbon dioxide throughout earth s history are key issues for palaeoclimate reconstructions especially during times of extreme climate change such as those that marked the neoproterozoic the carbon isotope ratios of marine carbonates are crucial in the correlation and identification of neoproterozoic glacial deposits and they are also used as a record for biogeochemical cycling and potential proxy for atmospheric pco2 likewise the boron and calcium isotope compositions of marine carbonates are potential proxies for palaeo seawater ph and the ratio of calcium fluxes into and out of seawater respectively and together they may be used to estimate atmospheric carbon dioxide here we use b and ca isotopes to estimate palaeoenvironmental conditions in the aftermath of a major neoproterozoic glaciation in namibia the validity of the b and ca isotope variation in the ancient marine carbonates is evaluated using the oxygen isotope composition of the carbonates and its correlation to the carbon isotope variation a negative 2 7 to 6 2 11b excursion occurs in the postglacial carbonates and is interpreted to reflect a temporary decrease in seawater ph associated variations in 44ca values ranging between 0 35 and 1 14 are linearly coupled with the carbon isotope ratios and imply enhanced postglacial weathering rates the reconstructed seawater ph and weathering profiles indicates that high atmospheric co2 concentrations were likely during the melt back of neoproterozoic glaciations and precipitation of cap carbonates however the b isotope trend suggests that these concentrations rapidly ameliorated and they do not co vary with 13c thus models attempting to link long lived negative 13c excursions to elevated pco2 need to be reconsidered

calcium isotope fractionation in calcite and aragonite abstract calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite precipitation temperatures ranged from 0 to 28 c calcium isotope fractionation shows a temperature dependence in accordance with previous observations 1000 ln cc 1 4 0 021 t c for calcite and 1000 ln ar 1 9 0 017 t c for aragonite within uncertainty the temperature slopes are identical for the two polymorphs however at all temperatures calcium isotopes are more fractionated in aragonite than in calcite the offset in 44 40 ca is about 0 6 the underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals or to different ca reaction behavior at the solid liquid interface recently the observed temperature dependence of the ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting lemarchand et al 2004 we show that this mechanism can in principle also be applied to caco 3 precipitation in natural environments in normal marine settings following this model ca isotope fractionation in marine ca carbonates is primarily controlled by precipitation rates on the other hand the larger ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates the rate control model of ca isotope fractionation predicts a strong dependence of the ca isotopic composition of carbonates on ambient co 3 2 concentration while this model is in general accordance with our observations in marine carbonates cultured specimens of the planktic foraminifer orbulina universa show no dependence of ca isotope fractionation on the ambient co 3 2 concentration the latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water

calcium isotope δ 44 40 ca fractionation along hydrothermal pathways logatchev field mid atlantic ridge 14 45 n we investigate the logatchev hydrothermal field at the mid atlantic ridge 14 degrees 45 n to constrain the calcium isotope hydrothermal flux into the ocean during the transformation of seawater to a hydrothermal solution the ca concentration of pristine seawater ca sw increases from about 10 mm to about 32 mm in the hydrothermal fluid endmember ca hydend and thereby adopts a delta ca 44 40 hydend of 0 95 0 07 parts per thousand relative to seawater sw and a sr 87 sr 86 isotope ratio of 0 7034 4 we demonstrate that delta ca 44 40 hydend is higher than that of the bedrock at the logatchev field from mass balance calculations we deduce a delta ca 44 40 of 1 17 0 04 parts per thousand sw for the host rocks in the reaction zone and 1 45 0 057 parts per thousand sw for the isotopic composition of the entire hydrothermal cell of the logatchev field the values are isotopically lighter than the currently assumed delta ca 44 40 for bulk earth of 0 92 0 187 parts per thousand sw skulan j depaolo d j and owens t l 1997 biological control of calcium isotopic abundances in the global calcium cycle geochim cosmochim acta 61 12 2505 2510 and challenge previous assumptions of no ca isotope fractionation between hydrothermal fluid and the oceanic crust zhu p and macdougall j d 1998 calcium isotopes in the marine environment and the oceanic calcium cycle geochim cosmochim acta 62 10 1691 1698 schmitt a d chabeaux f and stille p 2003 the calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance earth planet sci lett 6731 1 16 here we propose that ca isotope fractionation along the fluid flow pathway of the logatchev field occurs during the precipitation of anhydrite two anhydrite samples from the logatchev hydrothermal field show an average fractionation of about delta 44 4c ca 0 57 parts per thousand relative to their assumed parental solutions ca isotope ratios in aragonites from carbonate veins from odp drill cores indicate aragonite precipitation directly from seawater at low temperatures with an average delta ca 44 40 of 1 54 0 08 parts per thousand sw the relatively large fractionation between the aragonite precipitates and seawater in combination with their frequent abundance in weathered mafic and ultramafic rocks suggest a reconsideration of the marine ca isotope budget in particular with regard to ocean crust alteration c 2008 elsevier ltd all rights reserved

seismoelectric and seismomagnetic measurements in fractured borehole models seismoelectric and seismomagnetic fields generated by seismic waves in fluid saturated fractured borehole models are experimentally investigated with an electrode and a hall effect sensor in a borehole with a horizontal fracture the stoneley and flexural waves induce seismoelectric and seismomagnetic fields on the borehole wall and an electromagnetic wave propagating at light speed at the horizontal fracture in a borehole with a vertical fracture the acoustic field generated by a monopole or dipole source is similar to that in a borehole without a vertical fracture however the acoustic wave propagating along the vertical fracture induces seismoelectric and seismomagnetic fields whose apparent velocities are equal to that of a stoneley wave experimental results show that two different kinds of electric and magnetic fields are generated by acoustic waves in borehole models with horizontal and or vertical fractures one is an electromagnetic wave propagating with light speed the second is a stationary or localized seismoelectric and seismomagnetic field seismoelectric and seismomagnetic measurements might be a new logging technique for exploring fractures in a borehole

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

localization and physical properties experiments conducted by spirit at gusev crater the precise location and relative elevation of spirit during its traverses from the columbia memorial station to bonneville crater were determined with bundle adjusted retrievals from rover wheel turns suspension and tilt angles and overlapping images physical properties experiments show a decrease of 0 2 per mars solar day in solar cell output resulting from deposition of airborne dust cohesive soil like deposits in plains and hollows bright and dark rock coatings and relatively weak volcanic rocks of basaltic composition volcanic impact aeolian and water related processes produced the encountered landforms and materials

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

the impact of biotic abiotic interfaces in mineral nutrient cycling a study of soils of the santa cruz chronosequence california abstract biotic abiotic interactions between soil mineral nutrients and annual grassland vegetation are characterized for five soils in a marine terrace chronosequence near santa cruz california a mediterranean climate with wet winters and dry summers controls the annual cycle of plant growth and litter decomposition resulting in net above ground productivities of 280 600 g m 2 yr 1 the biotic abiotic a b interface separates seasonally reversible nutrient gradients reflecting biological cycling in the shallower soils from downward chemical weathering gradients in the deeper soils the a b interface is pedologically defined by argillic clay horizons centered at soil depths of about one meter which intensify with soil age below these horizons elevated solute na ca mg ca and sr ca ratios reflect plagioclase and smectite weathering along pore water flow paths above the a b interface lower cation ratios denote temporal variability due to seasonal plant nutrient uptake and litter leaching potassium and ca exhibit no seasonal variability beneath the a b interface indicating closed nutrient cycling within the root zone whereas mg variability below the a b interface denotes downward leakage resulting from higher inputs of marine aerosols and lower plant nutrient requirements the fraction of a mineral nutrient annually cycled through the plants compared to that lost from pore water discharge is defined their respective fluxes fj plants qj plants qj plants qj discharge with average values for k and ca fk plants 0 99 fca plants 0 93 much higher than for mg and na fmg plants 0 64 fna plants 0 28 the discrimination against rb and sr by plants is described by fractionation factors ksr ca 0 86 krb k 0 83 which are used in rayleigh fractionation mixing calculations to fit seasonal patterns in solute k and ca cycling krb k and k 24 mg 22 mg values derived from isotope data in the literature fall within fractionation envelopes bounded by inputs from rainfall and mineral weathering ksr ca and k 44 ca 40 ca fractionation factors fall outside these envelopes indicating that ca nutrient cycling is closed to these external inputs small net positive k and ca fluxes 6 14 mol m 2 yr 1 based on annual mass balances indicate that the soils are accumulating mineral nutrients probably as a result of long term environmental disequilibrium

size frequency distributions of rocks on mars and earth analog sites implications for future landed missions the size frequency distribution of rocks at the viking landing sites and a variety of rocky locations on the earth that formed from a number of geologic processes all have the general shape of simple exponential curves which have been combined with remote sensing data and models on rock abundance to predict the frequency of boulders potentially hazardous to future mars landers and rovers rock data from the near field of the viking landers where dimensions can be measured accurately in stereo images and estimates from the far field of viking 1 have convex up curved shapes on log log graphs of cumulative frequency per square meter or cumulative fractional area versus diameter the rock data show a sharp drop off at large diameters and a progressive approach to a plateau with decreasing diameter approaching the total rock coverage which can be fit well with simple exponential functions similar shaped size frequency distributions of rocks are found at a wide variety of rocky surfaces on the earth and can be fit well with simple exponential functions this distribution is compatible with fracture and fragmentation theory which provides a physical basis for its wide application a combined fit to rock area data at both viking sites was made with a general exponential function in which the pre exponential is the total area covered by rocks simple linear height versus diameter relationships were also derived from height diameter ratios at the viking sites which suggest that rockier areas on mars have higher standing rocks than less rocky areas height was then substituted into the general exponential function derived for diameter yielding the cumulative fractional area of rocks versus height for any given total rock coverage on mars results indicate that most of mars is rather benign with regard to hazards from landing on large rocks for total rock coverage of 8 equivalent to modal rock coverage on mars and the viking 1 site without the outcrops about 1 of the surface is covered by 20 cm or higher rocks a lander designed to accommodate landing on 0 5 m high boulders such as the mars pathfinder airbag system could land on a surface covered by about 20 rocks similar to the viking 2 site which is rockier than 95 of the planet with 1 of the surface covered by rocks of 0 5 m or higher

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

reconciling the elemental and sr isotope composition of himalayan weathering fluxes insights from the carbonate geochemistry of stream waters determining the relative proportions of silicate vs carbonate weathering in the himalaya is important for understanding atmospheric co2 consumption rates and the temporal evolution of seawater sr however recent studies have shown that major element mass balance equations attribute less co2 consumption to silicate weathering than methods utilizing ca sr and 87sr 86sr mixing equations to investigate this problem we compiled literature data providing elemental and 87sr 86sr analyses for stream waters and bedrock from tributary watersheds throughout the himalaya mountains in addition carbonate system parameters pco2 mineral saturation states were evaluated for a selected suite of stream waters the apparent discrepancy between the dominant weathering source of dissolved major elements vs sr can be reconciled in terms of carbonate mineral equilibria himalayan streams are predominantly ca2 mg2 hco3 waters derived from calcite and dolomite dissolution and mass balance calculations demonstrate that carbonate weathering contributes 87 and 76 of the dissolved ca2 and sr2 respectively however calculated ca sr ratios for the carbonate weathering flux are much lower than values observed in carbonate bedrock suggesting that these divalent cations do not behave conservatively during stream mixing over large temperature and pco2 gradients in the himalaya the state of calcite and dolomite saturation was evaluated across these gradients and the data show that upon descending through the himalaya 50 of the streams evaluated become highly supersaturated with respect to calcite as waters warm and degas co2 stream water ca mg and ca sr ratios decrease as the degree of supersaturation with respect to calcite increases and mg2 ca2 and hco3 mass balances support interpretations of preferential ca2 removal by calcite precipitation on the basis of patterns of saturation state and pco2 changes calcite precipitation was estimated to remove up to 70 of the ca2 originally derived from carbonate weathering accounting for the nonconservative behavior of ca2 during riverine transport brings the ca sr and 87sr 86sr composition of the carbonate weathering flux into agreement with the composition of carbonate bedrock thereby permitting consistency between elemental and sr isotope approaches to partitioning stream water solute sources these results resolve the dissolved sr2 budget and suggest that the conventional application of two component ca sr and 87sr 86sr mixing equations has overestimated silicate derived sr2 and hco3 fluxes from the himalaya in addition these findings demonstrate that integrating stream water carbonate mineral equilibria divalent cation compositional trends and sr isotope inventories provides a powerful approach for examining weathering fluxes