δ44 40ca variability in shallow water carbonates and the impact of submarine groundwater discharge on ca cycling in marine environments shallow water carbonates from florida bay the florida reef tract and a mexican caribbean fringing reef at punta maroma were studied to determine the range of ca isotope variation among a cohort of modern carbonate producers and to look for local scale ca cycling effects the total range of ca isotope fractionation is 0 4 at punta maroma yielding an allochem weighted average 44 40 ca value of 1 12 consistent with bulk sediment from the lagoon with a value of 1 09 these values are virtually identical to bulk carbonate sediments from the florida reef tract 1 11 and from one location in florida bay 1 09 near a tidal inlet in the florida keys no evidence was found for the 0 6 fractionation between calcite and aragonite which has been observed in laboratory precipitation experiments combining these results with carbonate production modes and 44 40 ca values for pelagic carbonates taken from the literature we calculate a weighted average value of 1 12 0 11 2 for the global scale ca output flux into carbonate sediments the 44 40 ca value of the input ca flux from rivers and hydrothermal fluids is 1 01 0 04 2 mean calculated from literature data that have been corrected for inter laboratory bias assuming that the ocean ca cycle is in steady state we calculate a 44 40 ca value of 1 23 0 23 2 for submarine groundwater discharge sgd on a global scale the sgd ca flux rivals river flows and mid ocean ridge hydrothermal vent inputs as a source of ca to the oceans it has the potential to differ significantly in its isotopic value from these traditional ca inputs in the geological past and to cause small changes in the 44 40 ca value of oceans through time in the innermost water circulation restricted region of northeastern florida bay sediments and waters exhibit a 0 7 gradient in 44 40 ca values decreasing towards the florida everglades this lowering of 44 40 ca is predominantly caused by local scale ca inputs from sgd which has a high ca concentration 450 mg l and low 44 40 ca value 0 96 mixing calculations show that ca inputs from sgd and surface water runoff from the florida everglades contribute between 8 and 60 of the dissolved ca to the studied waters with salinities between 30 and 14 respectively similar degrees of circulation restriction between epeiric seas and oceans in the geological past may have also led to overprinting of sedimentary carbonate 44 40 ca values in nearshore regions of epeiric seas due to local scale cycling of seawater through coastal carbonate aquifers local ca cycling effects may explain some of the scatter in 44 40 ca values present in the ca isotope evolution curve of phanerozoic oceans

biological markers in lower jurassic synrift lacustrine black shales hartford basin connecticut u s a abstract the east berlin formation lower jurassic hartford basin connecticut u s a is distinctive for its six cyclic units of lacustrine black shale and gray mudstone separated by playa and fluvial redbeds the black shales are each about a meter thick and were deposited in subtropical thermally strastified oligomictic lakes the youngest of which lakes 3 through 6 were large enough to flood most of the basin and attained depths of several tens of meters the saturate fractions of solvent extracts of organic rich black shales from each of the six lakes collected at fresh roadcuts near east berlin are dominated by extended homologous series of n alkanes alkylcyclohexanes and branched chain alkanes a striking feature of the black shales is the presence of a series of extended tricyclic terpanes from c20 to at least c41 hopanes are either not detectable or present only in subordinate quantities relative to the tricyclic terpanes the samples are depleted in hopanes in part because of the elevated maturity level mid to late oil window tricyclic terpane concentrations may also have been enhanced by fractionation effects related to oil expulsion out of the black shales in addition the original organic matter may have been exceptionally rich in tricyclic terpane precursors i e fossil lipids of prokaryotes present in anoxic moderately saline alkaline lakes

organic geochemical studies of a messinian evaporitic basin northern apennines italy ii isoprenoid and n alkyl thiophenes and thiolanes abstract series of n alkyl and isoprenoid thiophenes and thiolanes most of which have not been previously reported have been identified in an extract from a messinian upper miocene marl layer deposited under hypersaline euxinic conditions the identifications were based on mass spectra and chromatographic data of synthesized reference compounds and on comparison of mass spectra relative retention times and response on the fpd their specific structures and their distribution patterns show similarities with those of the alkanes inorganic sulphur is therefore considered to be incorporated into specific lipid moieties from archae bacterial and or algal input during diagenesis a biosynthetic origin of these compounds is also possible however the organic sulphur compounds encountered are thought to be indicators of a hypersaline depositional environment

radiogenic and stable sr isotope ratios 87 sr 86 sr δ 88 86 sr as tracers of riverine cation sources and biogeochemical cycling in the milford sound region of fiordland new zealand this study reports radiogenic sr isotope ratios 87sr 86sr stable sr isotope ratios 88 86sr and major ion concentrations for river rock sediment soil and plant samples collected from the cleddau and hollyford catchments in the milford sound region of fiordland new zealand the catchments primarily drain gabbro but some tributaries access limestone and volcanogenic sediments the goal of the study was to understand controls on riverine 88 86sr values in a landscape with multiple factors that may influence chemical weathering including dense vegetation high rainfall and abundant freshly eroded holocene fluvio glacial and landslide debris rivers draining gabbro have higher 88 86sr values than bedrock by as much as 0 14 and the 88 86sr values strongly correlate with molar ca sr ratios r2 0 69 leaching of rocks and sediment reveals no evidence for the preferential dissolution of minerals having high 88 86sr values and ca sr ratios in stream sr isotope fractionation seems unlikely because comparison against 87sr 86sr and ca sr ratios demonstrates that riverine 88 86sr values conservatively trace water mass mixing the riverine data are best explained by the input of soil water which is distinct from potential bedrock end members i e silicates and carbonates based on 88 86sr but indistinguishable in terms of ca sr and 87sr 86sr while strontium isotope fractionation during secondary mineral formation and pedogenesis is possible clay mineral formation is minor and most soils are poorly developed instead soil water 88 86sr values more likely reflect plant uptake plant samples yielded a wide range of 88 86sr values but on average they are lower than those for bedrock consistent with the expectation that plants preferentially incorporate lighter sr isotopes mass balance constraints together with 87sr 86sr ratios indicate that soil water 88 86sr values are 0 30 higher than bedrock 88 86sr values and mixing calculations show that the plant fractionated soil water pool contributes 27 of the riverine sr for tributaries accessing limestone and volcanogenic sediments ca sr and 87sr 86sr ratios appear consistent with two component mixing between silicate and carbonate weathering but 88 86sr values reveal a third contribution from soil water inputs similar to gabbro catchments the results of this study suggest that sr isotopes behave conservatively during water mass mixing and stream transport but non conservatively in soil where plant uptake can elevate soil water 88 86sr values relative to bedrock plant uptake or related biogeochemical processes such as ion exchange on organic matter surfaces also appear to modify soil water ca sr ratios many studies use 87sr 86sr and ca sr ratios to apportion riverine solutes between silicate and carbonate weathering but ca sr ratios may be non conservative in densely vegetated areas the stable sr isotope tracer shows promise for resolving riverine cation sources as well as effects from biological cycling

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

organic geochemistry of a lower jurassic synrift lacustrine sequence hartford basin connecticut u s a abstract synrift terrestrial strata of the lower jurassic east berlin formation hanford basin connecticut u s a record cyclical expansion and contraction of major lakes six of which were deep enough to develop anoxic bottom waters we have studied one representative lacustrine sequence in detail sampling a new roadcut near the village of east berlin the section examined is 4 m thick with a gray silstone at the base deposited in shallow water overlain by an organic rich black shale deep water succeeded in turn by another gray siltstone deposited as the lake waters gradually receded the upper gray siltstone is chemically distinct from the lower siltstone as it contains small amounts of corrensite analcime and gypsum reflecting the increasing salinity and alkalinity of the contracting lake the samples in the center of the black shale unit contain laminae of thermally altered yellowish orange fluorescing mottled telalginite the fluorescence properties indicate a peak oil generation maturity level confirmed by a vitrinite reflectance of 1 13 and a methylphenanthrene index of 1 08 the other samples have less organic matter becoming increasingly lean towards the top and bottom of the sequence samples in the middle of the black shale unit are distinguished by the presence of an homologous series of tricyclic terpanes extending from c20 to at least c41 and by the near absence of hopanes and steranes moving upsection into the gray siltstone the samples contain markedly lessextractable organic material eom and the concentration of tricyclic terpanes relative to hopanes steadily decreases in the uppermost sample hopanes are the predominant terpanes moving downsection from the black shale into the lower gray siltstone eom and the ratio of tricyclic terpanes also decrease except in the lowermost samples which contain terpane distributions like those of the middle part of the black shale this likely is migrated material because bitumen fills microfractures and extensive megafractures the lack of hopanes and steranes in the black shales cannot simply be a maturation effect as these biomarkers appear in the adjacent beds instead the manual terpane distributions may indicate a changing depositional environment documenting the geochemical evolution of the lake or more likely they may result from fractionation during expulsion of petroleum from these mature source rocks

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

modal variability in the southeast pacific basin energetics of the 2009 event abstract we study the barotropic variability in the southeast pacific basin in particular focusing on the extreme event during the fourth quarter of 2009 a 3 year integration of a barotropic shallow water model forced with wind stress anomalies generates localized variability that is similar in spatial extent and amplitude as the observed anomalous event an eigenmode analysis of the same model shows the presence of several free modes in the southeast pacific but projection of the modal patterns on the model output shows that their amplitudes are low instead the mode is interpreted as an almost free mode the modal excitation accounts for a considerable fraction 23 on average of the kinetic energy input by the wind stress in the southeast pacific basin increasing to 38 for the anomalous event in 2009 surprisingly a similar but weaker event during the third quarter of 2008 appears to have been more significant from an energetics point of view with almost 50 of the energy being input into the mode key areas of energetic dissipation appear to be the eltanin fracture zone the crest of the east pacific rise and the chile rise east pacific rise intersection

sedimentology and organic properties of lower tertiary lacustrine source rocks lunpola basin central tibetan plateau implications for hydrocarbon potential abstract the tertiary lacustrine niubao formation is well exposed in the middle western part of the lunpola basin central tibetan plateau where crude oil was once discovered during drilling campaigns sedimentological organic petrographic and geochemical work was performed on the upper and middle members of this formation in order to investigate its hydrocarbon source rock potential sedimentological analyses indicate that both members were deposited in relatively deep lake conditions away from the influence of big stream system with the upper niubao formation unf having higher sand content the two members contain abundant high quality type i kerogen derived mainly from plankton algae and bacteria compared with samples of the middle niubao formation mnf unf samples also contain more type ii and type iii kerogens of terrestrial origin biomarkers of source rock extracts suggest that a long standing anoxic stratified and saline ancient lake occupid the basin during deposition of the two members which was conducive to the preservation of organic matter however higher gammacerane content and the presence of carotane in mnf samples imply a more saline lake condition rock eval t max and biomarker parameters reveal marginal maturity and immaturity for samples from mnf and unf respectively therefore mnf has better source rocks of higher maturity might be the main hydrocarbon generating member of the basin similar diagnostic biomarkers and biomarker parameters reported in the crude oil also imply its affiliation with the source rocks of mnf

biogeochemistry of stable ca and radiogenic sr isotopes in a larch covered permafrost dominated watershed of central siberia stable ca and radiogenic sr isotope compositions were measured in different compartments stream water soil solutions rocks soils and soil leachates and vegetation of a small permafrost dominated watershed in the central siberian plateau the sr and ca in the area are supplied by basalt weathering and atmospheric depositions which significantly impact the sr isotopic compositions only vegetation significantly fractionates the calcium isotopes within the watershed these fractionations occur during ca uptake by roots and along the transpiration stream within the larch trees and are hypothesised to be the result of chromatographic processes and ca oxalate crystallisations during ca circulation or storage within plant organs biomass degradation significantly influences the ca isotopic compositions of soil solutions and soil leachates via the release of light ca and organic and organo mineral colloids are thought to affect the ca isotopic compositions of soil solutions by preferential scavenging of 40ca the imprint of organic matter degradation on the 44 40ca of soil solutions is much more significant for the warmer south facing slope of the watershed than for the shallow and cold soil active layer of the north facing slope as a result the available stock of biomass and the decomposition rates appear to be critical parameters that regulate the impact of vegetation on the soil water system in permafrost areas finally the obtained 44 40ca patterns contrast with those described for permafrost free environments with a much lower 44 40ca fractionation factor between soils and plants suggesting specific features of organic matter decomposition in permafrost environments the biologically induced ca isotopic fractionation observed at the soil profile scale is not pronounced at the scale of the streams and large rivers in which the 44 40ca signature may be controlled by the heterogeneity of lithological sources

lithium in tektites and impact glasses implications for sources histories and large impacts abstract lithium li abundances and isotope compositions were determined in a representative suite of tektites moldavites muong nong type tektites and an australite ivory coast tektites and bediasites impact related glasses libyan desert glass zhamanshinites and irghizites a glass fragment embedded in the suevite from the ries impact crater and sedimentary materials in order to test a possible susceptibility of li to fractionation during hypervelocity impact events and to de convolve links to their potential parental sources the overall data show a large spread in li abundance 4 7 58 ppm li and 7 li values 3 2 to 26 0 but individual groups of tektites and impact glasses have distinctive li compositions most importantly any significant high temperature li isotope fractionation can be excluded by comparing sedimentary lithologies from central europe with moldavites instead we suggest that li isotope compositions in tektites and impact related glasses are probably diagnostic of the precursor materials and their pre impact geological histories the muong nong type tektites and australite specimen are identical in terms of li concentrations and 7 li and we tentatively endorse their common origin in a single impact event evidence for low temperature rayleigh fractionation which must have operated prior to impact induced melting and solidification is provided for a subset of muong nong type tektites although li isotope variations in most tektites are broadly similar to those of the upper continental crust libyan desert glass carries high 7 li 24 7 which appears to mirror the previous fluvial history of parental material that was perhaps deposited in lacustrine environment or coastal seawater lithium isotopes in impact related glasses from the zhamanshin crater define a group distinct from all other samples and point to melting of chemically less evolved mafic lithologies which is also consistent with their major and trace element patterns extreme shock pressures and the related extreme post shock temperatures alone appear not to have any effect on the li isotope systematics therefore useful information on parental lithologies and magmatic processes may be retrieved from analyses of martian and lunar meteorites moreover lack of significant li depletion in tektites provides further constraints on the loss of moderately volatile elements during the moon forming impact

molecular isotopic characterisation of hydrocarbon biomarkers in palaeocene eocene evaporitic lacustrine source rocks from the jianghan basin china immature organic matter in lacustrine source rocks from the jianghan basin eastern china was studied for distributions and stable carbon isotopic compositions 13 c of hydrocarbon biomarkers all of the bitumens contain isorenieratane 13 c ca 17 indicating the presence of chlorobiaceae and thus periods of euxinic conditions extended into the photic zone aliphatic hydrocarbon fractions are dominated by pristane and phytane and contain relatively low amounts of 4a and 4 methylsteranes c 30 13 c ca 16 believed to originate from 4 methylsterols in dinoflagellates 13 c values of gammacerane ca 24 and c 30 17 21 h hopane ca 23 are consistent with an origin from bacterivorous ciliates that fed on chlorobiaceae the bitumens contain low relative amounts of organo sulphur compounds one rock contains c 37 and c 38 n alkanes 13 c ca 36 derived from alkadienes and alkenones of prymnesiophytes the distributions of hydrocarbon biomarkers suggest that they were initially sulphurised during early diagenesis and later released during early thermal maturation

paradox in bulk and molecular geochemical data and implications for hydrocarbon migration in the inter salt lacustrine shale oil reservoir qianjiang formation jianghan basin central china abstract this study analyzes the bulk and molecular geochemical data of 56 core samples of the eocene qianjiang formation a confined source rock unit embedded with salt intervals formed in a hypersaline lacustrine setting in central china these source rocks within a single evaporative cycle collected from a recent shale oil exploration well are highly laminated consisting of both intra and inter salt shales both organic pores and matrix pores serve as storage for hydrocarbon generated from kerogen within the source rock because the contrast in density between kerogen and oil conversion of kerogen to oil inevitably leads to the increase in pore pressure and oil expulsion from kerogen within the same source rock unit impregnation of source rocks by expelled oils from nearby mature source rocks or from the organic rich laminae within the same source rock units leads to anomalous rock eval pyrolysis data characterized by an abnormally high s1 peak a high production index pi a suppressed tmax and other anomalies it is contradictory that both rock eval pyrolysis data and sterane isomerization ratios of the studied inter salt shale samples indicate strong impact of allochthonous hydrocarbons in the source rocks whereas most aliphatic biomarker parameters obtained from the solvent extracts of these shales still provide useful information on the vertical variation in organic source input and depositional environment of the host rocks this study provides insights into the bulk and molecular geochemical data interpretation particularly in the inter salt shale oil system evaluation in inferring the prevailing directions and pathways of diagenetic fluid movement and hydrocarbon migration

ca sr and ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence in hawaii abstract nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus p and calcium ca from minerals at depth and concentrate those nutrients at the surface here we use soil chemistry and stable isotopes of the alkaline earth elements ca strontium sr and barium ba to test the hypothesis that biolifting of p has been an important pedogenic process across a soil climosequence developed on volcanic deposits at kohala mountain hawaii the geochemical linkage between these elements is revealed as generally positive site specific relationships in soil mass gains and losses particularly for p ba and ca using the ratio of immobile elements titanium and niobium ti nb to link individual soil samples to a restricted compositional range of the chemically and isotopically diverse volcanic parent materials at sites where p is enriched in surface soils relative to abundances in deeper soils the isotope compositions of exchangeable ca sr and ba in the shallowest soil horizons 10 cm depth at those sites is consistently heavier than the volcanic parent materials the isotope compositions of exchangeable ca and sr trend toward heavier compositions with depth more gradually reflecting increasing leakiness from these soils in the order ba

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

elucidating modern geochemical cycles at local regional and global scales using calcium isotopes abstract in earth s surface environment calcium ca is an important mobile metal that is actively and passively transported in solution and within organic and mineral phases being cycled and recycled during various biogeochemical processes with the development of modern mass spectrometric techniques small variations in the stable and radiogenic isotopic compositions of ca can be measured revealing insight in these complex biogeochemical cycles and tracing and quantifying components across a range of spatial and temporal scales similar to other more routine isotope systems more than three decades of work reveal systematic variations in the partitioning of ca isotopes due to both abiotic and biological processes an overview of processes that fractionate ca isotopes at local regional and global scales is outlined here we present detailed examples of instances in which ca isotopes have provided unique insight into the functioning of earth surface processes and the cycling of ca at multiple scales future studies should target questions for which ca isotopic analysis provide unique insight and when combined with other isotope and trace element multi proxy studies better constrain the system of interest at the same time we challenge the scientific community to explore new frontiers including polar regions and other extreme environments

atmospheric contribution to cations cycling in highly weathered catchment guadeloupe lesser antilles abstract the important fertilizing role of atmospheric dust and particularly african dust in tropical rainforests is increasingly recognized but still poorly quantified to better evaluate dust input into the caribbean basin we sampled critical zone compartments of a small forested volcanic catchment in guadeloupe soils parent rock atmospheric dust plants soil solutions stream and rain waters the aims of this study are to track sources of cation nutrients ca mg k sr developed on highly weathered soil in the rainforest of guadeloupe to quantify plant recycling of these nutrients and to identify constraints on regolith development and its associated nutrient pool in the quiock creek catchment a large isotopic range of 87sr 86sr and end values was observed despite the small scale of observation sr isotopic composition of the dissolved load varied from 0 7084 in rainfall to 0 7110 in soil solution whereas it ranges between 0 7068 and 0 7153 for soil samples and between 0 7096 and 0 7102 for plants the nd isotopic composition varied between 8 39 in near surface soil samples to 2 71 in deeper soil all samples had an intermediate signature between that of the bedrock endmember 87sr 86sr 0 7038 end 4 8 and the atmospheric endmember sea salt 87sr 86sr 0 7092 and saharan dust 87sr 86sr 0 7187 end 11 5 the regolith was built on pyroclastic deposits but because of extreme leaching the regolith has lost its original bedrock signature and inherited an exogenous atmospheric signature our results show that only the chemical weathering of the fresh near surface minerals can provide nutrients to the ecosystem first 30 cm however this dust weathering is too low to sustain the tropical forest ecosystem on its own the cationic mass balance at the catchment scale as well as the sr isotopic signature show that cation and sr fluxes are of atmospheric origin only and that original bedrock no longer participates in nutrient cycles the vegetation reflects the 87sr 86sr of the dissolved pool of atmospheric sr at the soil plant scale the cation nutrient fluxes provided by vegetation litter fall leaf excretion are major compared to input and output fluxes the annual ca k sr and mg fluxes within the vegetation are respectively 31 28 20 and 3 times greater than the exported fluxes at the outlet of the basin the residence time of nutrients in the vegetation is 16 years for k and close to 45 years for sr ca and mg these results emphasize the highly efficient vegetative turnover that dominates the nutrient cycle in the quiock creek catchment this first characterization of biogeochemical cycles in the guadeloupean rainforest suggests that the forest community of quiock creek is sustained by a small near surface nutrient pool disconnected from the deep volcanic bedrock we also demonstrated that even with efficient nutrient recycling saharan dust plays a significant role in maintaining ecosystem productivity in guadeloupe over long time scales

strontium isotope composition as a tracer of calcium sources in two forest ecosystems in belgium the two main sources of ca in forest ecosystems are mineral weathering release and atmospheric inputs we use the 87 sr 86 sr isotopic ratio sr is used as a proxy for ca to determine the ca contribution from atmospheric deposition input in two forest ecosystems beech stands growing on soils formed from parent materials with contrasting total ca contents and isotopic ratios pleistocene loess in central belgium acid leached soil and lower devonian shales in the ardenne massif of high belgium ochreous brown earth the 87 sr 86 sr ratio and the ca and sr contents were measured in bulk precipitation in vegetation beechwood growth rings and leaves and in main soil horizons total acid extractable and labile pools the relative contributions of atmospheric input and soil mineral weathering to vegetation were calculated using mixing equations calculations based on sr isotope ratios of bulk precipitation end member 1 87 sr 86 sr close to ocean water 0 7090 0 1 m hcl extractable soil fraction end member 2 and beech wood mixing compartment indicate that about 43 central belgium and 39 ardennes of sr uptake originates from atmospheric inputs for ca the contributions of atmospheric input are 75 and 78 respectively these estimations are however very sensitive to the choice of the appropriate 87 sr 86 sr and sr ca ratios for the weathering end member the isotopic composition of the mineral source is estimated from the soil mineralogical composition and the relative weatherability of the sr bearing minerals due to soil processes mineral weathering element recycling and geomorphological events addition of allochtonous minerals to the autochtonous pool inherited from the local bedrock the distribution of minerals in both soil profiles is heterogeneous and varies from horizon to horizon which horizons are relevant and which soil pool total soil acidextractable fraction or labile pool should be selected for isotopic measurement of the weathering end member is therefore open to uncertainty the choice of the appropriate 87 sr 86 sr and sr ca ratios for the weathering end member is discussed our results emphasize the importance of the atmospheric contribution of ca for tree mineral nutrition in the studied forest stands suggesting that these ecosystems on acid soils are sensitive to chemical changes in the atmospheric environment e g acid depositions associated with decreasing input of atmospheric cations our results support therefore

peculiarities of salt lake sediments as potential source rocks in china abstract hypersaline lake sediments are widely distributed in china and can be good sources for petroleum the palaeogene sediments of the jianghan basin in eastern china are a typical example composed of salt lake evaporite clastic facies in fault subsided basins their organic matter is variable but is dominated by type ii kerogen the biological marker characteristics of core extracts and oils from the jianghan basin include i low oep values for n alkanes and occasionally an even odd predominance ii a high concentration of phytane iii a relatively high gammacerane 17 h 21 h hopane ratio and iv abundant mainly nickel porphyrins sample guang 33 k 33 is typical of the immature oils found in the jianghan basin geological and geochemical data both indicate that it was generated from source rocks in the maturity range r 0 0 45 0 55 its characteristics are similar to those of immature source rocks with high concentrations of phytane steranes triterpanes and nickel porphyrins and for an oil extremely low values for molecular parameters of maturity such as c 29 20s 20s 20r 14 h 17 h steranes c 32 22s 22s 22r 17 h 21 h hopanes and dpep dpep etio porphyrins

ca isotope constraints on chemical weathering processes evidence from headwater in the changjiang river china abstract this study aims to clarify the relationship between chemical weathering of rocks and the carbon budget of rivers and better understand the weathering mechanisms of plateau watersheds we chose to study the jinsha river which originates from the tibetan plateau and also is in the upper reaches of the changjiang river analysis of hydrochemistry radiogenic strontium isotope and stable calcium isotopes were conducted of the jinsha river water samples which were collected along its mainstream and main tributaries in the summer the results show that the water chemistry of the mainstream waters is dominated by evaporite weathering which have low 87sr 86sr values 0 7098 0 7108 and wide range of sr contents 2 70 9 35 mol l in contrast tributaries of the jinsha river have higher 87sr 86sr 0 7090 0 7157 and lower sr contents 1 mol l moreover the ca isotopic compositions in the mainstream 0 87 1 11 are heavier than the tributaries 0 68 0 88 and could not be fully explained by the conventional mixing of different sources we suggest that secondary carbonate precipitation fractionates ca isotopes in the jinsha river and fractionation factors are between 0 99935 and 0 99963 at least 66 of ca was removed in the mainstream of the jinsha river through secondary mineral precipitation and the average value is 35 in the tributaries the results highlight that evaporite weathering results in more carbonate precipitation influencing ca transportation and cycling in the riverine system constrained by stable ca isotopic compositions and water chemistry

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

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

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

influence of afforestation on soil the case of mineral weathering abstract although concerns have been raised that increased nutrient demand by fast growing tree species could deplete soil nutrient pools recent research suggests that some species are able to obtain nutrients via soil mineral weathering hybrid poplars which are fast growing and nutrient demanding species are increasingly used in intensive silvicultural settings understanding whether hybrid poplars have an effect on long term nutrient availability and can promote soil mineral weathering is therefore important we investigated the levels of base cations i e k ca mg and na of surface soils 0 20 cm in 13 hybrid poplar plantations in quebec and compared the results with those of adjacent abandoned agricultural fields to evaluate whether exchangeable base cation pools and non exchangeable pools i e those in the crystal lattice of minerals were being depleted we used a sequential leach with diluted salt bacl 2 for exchangeable and weak acid solutions hcl and hno 3 for non exchangeable levels of exchangeable and non exchangeable cations were not statistically different between land use types exploratory analyses however revealed trends toward a greater depletion of ca mg and na in non exchangeable forms following afforestation the depletion of these non exchangeable base cations due to afforestation occurred at sites where greater levels were initially present in soil the results suggest increased soil mineral weathering due to greater amounts of minerals susceptible to dissolution and in part high clay content based on ca mg and k concentrations of the different leaches and their molar ratios ca al fe mg al fe and k al fe we propose a lesser role of soil mineral weathering on ca cycling than mg and k which could lead to faster depletion of exchangeable ca pools of the surface soil due to fast growth and high ca demand by the poplars

constraining seasonal active layer dynamics and chemical weathering reactions occurring in north slope alaskan watersheds with major ion and isotope δ34sso4 δ13cdic 87sr 86sr δ44 40ca and δ44 42ca measurements abstract rising air temperatures in the arctic may destabilize a large pool of organic carbon stored in permafrost thereby causing a positive feedback to global climate warming permafrost thaw could also deepen hydrologic flow paths and expose previously frozen rock and mineral fragments to chemical weathering future shifts in the inorganic solute geochemistry of arctic rivers may signal changes in soil processes that also affect organic carbon storage tracing permafrost thaw with dissolved riverine loads requires understanding the spatial and seasonal variation of chemical weathering reactions and other biogeochemical phenomena that affect elemental mass transport to help identify connections between mineral weathering and active layer processes we studied the major ion and isotope 34 s so4 13 c dic 87 sr 86 sr 44 40 ca and 44 42 ca geochemistry of five streams draining the north slope of alaska continuous permafrost underlies all streams but the atigun river roche moutonnee creek and trevor creek primarily drain bare bedrock outcrops in the brooks range while the upper kuparuk river and imnavait creek primarily drain tundra in total we collected 546 water samples spanning the spring freshet through fall freeze up in 2009 and 2010 we also analyzed snow rock sediment soil and plant samples major ion ratios and 13 c dic values point to the overall dominance of carbonate weathering by carbonic and sulfuric acids with additional influences from atmospheric deposition plant decay sulfate salt dissolution and silicate weathering by carbonic acid 13 c dic values may also reflect partial equilibration with soil and atmospheric co 2 all streams display large seasonal variations in major ion ratios and 13 c dic values that are consistent with progressive deepening of the seasonally thawed zone over the summer in the mountain watersheds carbonate weathering dominates during the spring and summer while sulfate salt primarily caso 4 and mgso 4 dissolution dominates during the fall riverine 34 s so4 values reveal that the sulfate salts are secondary precipitates we propose a conceptual model where cryoconcentration in soils during the late fall and winter causes secondary mineral formation at depth and re exposure during subsequent thaw seasons produces the observed geochemical signals in rivers the tundra streams lack definitive evidence for sulfate salt dissolution presumably because thick peat soils limit the exposure and weathering of underlying glacial sediment where the salts are expected to form and dissolve appearance of a sulfate salt dissolution signal in tundra streams may correlate with future permafrost degradation carbonate weathering dominates riverine 87 sr 86 sr ratios but the compositional heterogeneity of bedrock limits interpretation of the data all rivers have higher 44 40 ca values compared to bedrock likely due to plant uptake of lighter ca isotopes in the tundra watersheds freshet 44 40 ca values were 0 10 0 20 lower than summer and fall values these trends likely reflect contributions from plant decay as comparison between 44 40 ca and 44 42 ca values suggests that all isotopic variation is mass dependent with minimal radiogenic 40 ca inputs from the weathering of old silicate minerals with high k ca ratios

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

immature oil and condensate modification of hydrocarbon generation model for terrestrial organic matter petroleum has been found in canadian frontier basins in reservoirs which have undergone low levels of thermal alteration vitrinite reflectance 0 6 ro paraffin indices stable carbon and hydrogen isotope contents pristane to nc17 ratios and diterpenoid biologic markers have been used to assess the level of maturity of the hydrocarbons in the reservoir independently of the level of maturity of the reservoir itself and of the surrounding shale units in the tertiary of the beaufort mackenzie basin naphthenic oils and condensates have been generated from terrestrially derived organic matter in source rocks juxtaposed with the reservoir at reflectance levels of 0 4 to 0 6 ro however condensates discovered in reservoirs which are th rmally immature on the labrador shelf have undergone extensive vertical migration and can be classed as conventional mature to overmature condensates hydrocarbons discovered in the lower cretaceous of the beaufort mackenzie basin and also those of the scotian shelf are more or less in place in that they are at a level of thermal alteration about equivalent to that of the reservoirs in which they are trapped the source for the early oils and condensates is considered to be resinite occurring dispersed in coal fragments the proportion of resinite liptinite and vitrinite in the organic matter of terrestrial source rocks strongly controls both the level of thermal alteration necessary for the section to function as an effective source rock and the ultimate product gas oil or condensate which will be generated

hydrocarbon generation potential and miocene pliocene paleoenvironments of the kangal basin central anatolia turkey abstract this study deals with the organic geochemical characteristics hydrocarbon generative potential and miocene pliocene paleoenvironments of the kangal coal district which developed in a limnic depositional environment and contains the hamal etyemez and kalburcayiri coal fields in the southern part of the sivas basin central anatolia around kalburcayiri the average thickness of each of the two coal seams approximately 10 m are currently being exploited based on open cast methods the coal from which is used by the nearby lignite fired kangal power station an attempt was made to elucidate depositional conditions through proximate and ultimate analyses coal petrography and the geochemical characteristics of the kangal coals these coals have a huminite reflectance value of rmax 0 40 accordingly from the standpoint of coal rank this is a dull brown coal of the subbituminous c type huminite is the most widespread maceral type while gelinites are the most often encountered macerals relative to liptinites the proportion of inertinites is high on the basis of maceral composition the depositional environment of the kangal coals was determined to be either a forest swamp or a lake bottom the distributions of the c27 and c28 c29 steranes for all these coal samples are very similar c29 c27 c28 tricyclic terpanes have low concentrations in all samples of the kangal coals and are dominated by low molecular weight compounds c20 c24 with a maximum at c23 total organic carbon toc wt values of the kalburcayiri samples are 4 64 30 64 wt in the hamal samples 0 83 2 53 wt and in the etyemez samples 8 91 10 39 wt on the basis of tmax values the samples are in the immature early mature stage according to rock eval pyrolysis data the coals have hydrocarbon source rock potential but the coaly shales and other organic matter rich levels have no hydrocarbon source rock potential the high inertinite levels and high vitrinite inertinite ratios suggest that the kangal coals have more potential for gas generation than oil

calcium isotopes in a proglacial weathering environment damma glacier switzerland the biogeochemical cycling and isotopic fractionation of calcium during the initial stages of weathering were investigated in an alpine soil chronosequence damma glacier switzerland this site has a homogeneous silicate lithology and minimal biological impacts due to sparse vegetation cover calcium isotopic compositions obtained by tims using a 43ca 46ca double spike were measured in the main ca pools during this very early stage of weathering the young soils which have formed 44 42ca 0 44 44 42ca 0 44 were indistinguishable to the rocks from which they were derived 44 42ca 0 44 44 42ca 0 44 and stream water 44 42ca 0 48 44 42ca 0 48 was also within error of the average rock this lack of variation indicates that the dissolution of the bulk silicate rock does not strongly fractionate ca isotopes the only ca pool which was strongly fractionated from bulk rock was vegetation which exhibited an enrichment of light ca isotopes significant ca isotope fractionation between bulk rock and the dissolved flux of ca is likely to only occur where the ca biogeochemical cycle is dominated by secondary processes such as biological cycling adsorption and secondary mineral precipitation

coupled δ44 40ca δ88 86sr and 87sr 86sr geochemistry across the end permian mass extinction event abstract we report high resolution high precision 44 40ca 88 86sr and 87sr 86sr records spanning the permian triassic boundary ptb from the meishan and dajiang carbonate successions in south china the goal of the study was to understand the behavior of ca and sr isotopes during a time period in earth history characterized by severe biological and environmental perturbations including a major mass extinction flood basalt volcanism ocean acidification and sea level fluctuations dajiang displays negative 44 40ca and 88 86sr excursions and invariant 87sr 86sr ratios in the

the ca isotopic composition of dust producing regions measurements of surface sediments in the black rock desert nevada dust is a relatively unconstrained flux in the geochemical cycle of ca the isotopic composition of dust derived ca has not been studied though it is an important part of any attempt at deciphering ca isotope based proxy records accordingly this study reports the elemental and calcium isotope geochemistry of 30 surface upper 0 5 cm sediments from an arid dust producer the black rock desert in northwestern nevada geochemical data for sequential water and 0 5 n hcl leaches meant to sample mobile ca and selected leached residues are presented along with x ray diffraction xrd determinations of major mineralogy bulk playa sediments have ca concentrations between 0 28 and 40 wt median 6 8 wt and calcite concentrations of 2 32 isotopically ca sampled by water leaches 60 of total ca though the degree of fractionation w a varies between 0 and 0 6 acid leaches which are the primary component of mobile ca in the sediments have 44casrm 915a values of 0 78 0 08 similar to the 44ca of modern nannofossil ooze and modern rivers this means that dust produced in closed continental basins likely has little isotopic leverage to change the ocean s isotopic composition and suggests that the ca isotopic composition of dust is tied to rivers weathering in addition while the ca concentration data in the water leach suggest that evaporative evolution controls the amount of ca in this reservoir the isotope data are inconsistent with this conclusion instead we hypothesize that adsorption of ca on clays controls the ca isotope systematics in the water leach this hypothesis requires that there is no significant isotopic fractionation during evaporite mineral precipitation and may suggest that sorption at rates appropriate for natural systems might fractionate differently than sorption at laboratory rates

dinoflagellate origin for sedimentary 4α methylsteroids and 5α h stanols biological marker compounds provide useful tools for evaluating the depositional environments of recent and ancient sediments and petroleums1 largely through established relationships between the organic matter of sediments and source organisms1 2 such relationships are best tested and explored by investigating the lipid components of natural populations of autochthonous biota that can be clearly recognized as contributors to underlying bottom sediments in this context we have studied the lipids of the freshwater dinoflagellate peridinlum lomnickii woloszynska order peridiniales class dinophyceae collected from the waters of priest pot3 a eutrophic lake in the english lake district its distributions of both 4 methylsterols and 4 methylstanones closely resemble those of the underlying bottom sediments demonstrating that dinoflagellates are important contributors of these sedimentary compounds the 4 methylsteroidal hydrocarbons found in ancient sediments and petroleums4 6 are presumably diagenetic products of such 4 methylsteroids and therefore reflect dino flagellate inputs to the original depositional environments furthermore the prominence of 5 h cholestan 3 ol in p lomnickii suggests that dinoflagellates may be the long sought direct biological source of sedimentary 5 h stanols

calcium isotope constraints on the uptake and sources of ca2 in a base poor forest a new concept of combining stable δ44 42ca and radiogenic eca signals abstract plant available reserves of major base cations ca 2 and mg 2 decreased markedly in soils over the past century thus posing a potential threat to forest ecosystem health trees are thought to obtain dissolved ca 2 ions mainly from an easily accessible soil water reservoir also termed the exchangeable cation pool the status of ca reserves in this soil pool is sensitive to anthropogenic perturbations such as soil acidification induced by acid rain and or excessive timber harvesting here we show that in a base poor forest of the northeastern usa i e wachusett mountain massachusetts the exchangeable ca pool of deeper mineral soils has a unique isotope signature that is significantly enriched in the radiogenic 40 ca due to the dissolution of k rich silicate minerals such as biotite using a simple isotope mass balance and assuming that the input of ca from biotite has a e ca signature of 16 the results of our calculation indicate that the weathering of biotite may supply a sizeable fraction up to 25 of ca 2 ions into the exchangeable cation pool of deeper mineral soils importantly samples of local vegetation i e woody tissues of red oak show no detectable excess of the radiogenic 40 ca and based on our model the upper limit of a possible biotite derived ca contribution in vegetation is estimated at 5 we also found no evidence of the radiogenic 40 ca signal in the samples of forest floor and the uppermost organic rich soils 0 15 cm depth which in turn suggest that over the long term development of the forest and its organic matter accumulation the vegetation growth must have also relied primarily on the non radiogenic ca sources based on our experimental data such sources may include i wet atmospheric deposition ii the organically complexed ca in topsoil horizons and iii chemical weathering and or fungal mediated dissolution of apatite and ca rich plagioclase hence our stable and radiogenic ca isotope data indicate that the studied base poor forest is able to bypass the exchangeable cation pool of deeper i e below 15 cm mineral soils and still manages to meet its nutritional requirements with respect to ca another important implication of this study is that the organically complexed ca in the topsoil horizon 0 15 cm depth has to be tightly bound to the ion exchange sites otherwise the large radiogenic 40 ca signatures present in the exchangeable cation pool of deep mineral soils would be swamped by the downward gravitational flux of non radiogenic ca from the decaying organic matter and litterfall hence the limited mobility of the organically complexed ca in soils and its tight biological cycling could explain the lack of a significant impact of vegetation on the ca isotope systematics observed in large rivers

onocerane and other triterpenoids in late cretaceous sediments from the upper benue trough nigeria tectonic and palaeoenvironmental implications abstract the aliphatic hydrocarbon bitumen fraction has been investigated in late cretaceous outcrop samples from the upper benue trough inundated by the sea only during the maximum mid cretaceous transgression thermal maturity in nearly all formations is pre oil window indicating only limited mainly tertiary burial the santonian deformation a significant thermal influence to the south west appears to have had little effect here onocerane i is the dominant triterpenoid in the pindiga formation but is absent elsewhere its origin is uncertain but it appears to be associated with deposition in a restricted basin possibly a brackish lagoon receiving dominantly terrestrial organic input a review of possible natural product precursor compounds suggests onoceradiene from a fern like plant was a likely source even carbon number predominance of n alkanes in the range c 16 to c 22 in some formations is tentatively interpreted to indicate hypersalinity

quantitative strontium isotope models for weathering pedogenesis and biogeochemical cycling abstract isotopes of strontium sr are a useful tracer for weathering atmospheric fluxes cation biocycling and pedogenesis we present basic models for application of strontium isotopes to the soil vegetation atmosphere system the mathematical formulations fall into the general categories of 1 steady state models in which isotopic ratios remain constant over the time scale of interest and 2 time dependent models in which isotope ratios change through time in the steady state models fluxes of sr and other elements to the system are constant steady state models can be used to infer short term weathering rates from river and stream isotope compositions to determine fluxes to a single or multiple layer soil exchange solution system and to quantify nutrient fluxes to vegetation time dependent models involve a change in isotopic ratio from some initial value to a new value over the time period of interest in some cases the change may represent a shift from one steady state situation to a new one after a shift in one or more of the fluxes feeding the system examples of applications of time dependent models include identifying the dominant cation sources to an evolving soil exchange solution system and calculating weathering rates by measuring the isotopic compositions of primary soil minerals we use time dependent models to explain differences in the isotopic ratios of labile and carbonate sr from arid sites in hawaii with a basalt parent material isotopic signature and new mexico with an atmospheric isotopic signature these models suggest that the difference is due to a combination of low atmospheric strontium fluxes and high weathering rates in the hawaiian profile compared to the new mexico calcrete profile

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 rapid resetting of the ca isotopic signatures of calcite at ambient temperature during its congruent dissolution precipitation and at equilibrium abstract this study provides direct experimental evidence of the resetting of the calcium ca isotope signatures of calcite in the presence of an aqueous fluid during its congruent dissolution precipitation and at equilibrium at ambient temperatures over week long timescales batch reactor experiments were performed at 25 c in aqueous nacl solutions air or co2 gas mixtures were bubbled through this fluid to fix ph during congruent calcite dissolution the fluid became enriched in isotopically heavy ca and the ca isotope composition continued to become heavier after the fluid attained bulk chemical equilibrium with the mineral the 44 42ca composition of the fluid was up to 0 8 higher than the dissolving calcite at the end of the dissolution experiments calcite precipitation was provoked by increasing the reactor fluid ph after chemical equilibrium had been attained via dissolution rayleigh isotope fractionation effects were observed immediately after the ph was increased and rapid calcite precipitation occurred however isotopic exchange continued after the system chemically equilibrated eradicating this rayleigh signal taken together these observations 1 confirm dynamic mineral fluid equilibrium i e dissolution and precipitation occur at equal non zero rates at equilibrium and 2 indicate that isotopic compositions of calcite can readily equilibrate even when this mineral is in bulk chemical equilibrium with its coexisting fluid this latter observation suggests the preservation of paleo environmental isotopic signatures in calcite may require a combination of the isolation of the fluid mineral system from external chemical input and or the existence of a yet to be defined calcite dissolution precipitation inhibition mechanism

calcium isotopes in the marine environment and the oceanic calcium cycle abstract a systematic investigation of 44 ca 40 ca ratios in the oceanic ca cycle indicates that the average ca isotopic composition of input and output are quite different suggesting that the present ocean is not in a steady state our data show that sea water has uniform 44 ca 40 ca as expected from the long residence time of ca in the oceans it also exhibits the heaviest isotopic composition among all samples measured consistent with recent results by skulan et al 1997 and must be maintained at this value by strong biogenic isotope fractionation during the precipitation of caco 3 our measurements show that the riverine input is variable the most radiogenic river waters we have measured lowest 44 ca 40 ca are from ganges tributaries which also have high 87 sr 86 sr although there does not appear to be a systematic correlation between ca and sr isotopic compositions based on available data there is also significant isotopic variability among samples of caco 3 precipitated from the present ocean with coccolith oozes showing the most highly fractionated isotopic values relative to seawater among foraminifera ca isotopes exhibit species dependent fractionation effects but also appear to display systematic temperature dependent fractionation within inidividual species

impact of a base metal smelter on the geochemistry of soils of the flin flon region manitoba and saskatchewan the regional dispersal patterns of six trace metals as cd cu hg pb zn emitted from the base metal smelter at flin flon were examined in surface soils and at depth using an extensive regiona

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

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

novel cyclised and aromatised diagenetic products of β carotene in the green river shale abstract a suite of novel diagenetic products of carotene has been identified in an extract of a sample from the green river shale identification is mainly based on comparison of mass spectra with those of diagenetic products of another carotenoid isorenieratene these compounds were formed by i cyclisation and aromatisation of the polyene isoprenoid chain ii explusion of toluene and m xylene from the polyene isoprenoid chain and iii aromatisation of the 1 1 5 trimethylcyclohex 5 enyl moieties resulting in 1 2 dimethylbenzene end groups reduction of the double bonds of carotene is the most important diagenetic process however as judged from the high relative amount of carotane 63 of quantified diagenetic products of carotene these results indicate that the fossilisation potential of carotenoids is greater than previously thought

controls on deposition of aquatic and terrestrial organic matter in the lacustrine namling oiyug basin oligocene miocene southern tibet abstract the namling oiyug basin is the only cenozoic lake basin that has hydrocarbon potential in southern tibet china coal was once exploited in the basin from the early miocene mangxiang formation which also hosts oil prone source rock layers herein a combined investigation of sedimentological features and organic geochemistry is performed on a measured outcrop section of the mangxiang formation to study the lake basin types as well as the depositional history of aquatic and terrestrial organic matter om there are two periods in the lake basin evolution history the balanced fill and overfilled stages in the balanced fill basin stage oil prone laminated shale was deposited in a relatively deep lake environment with total organic carbon toc contents around 5 wt and hi values up to 316 mg hc g toc indicating hydrogen poor type ii kerogen with transition to type iii kerogen comparison between maceral composition and geochemical properties suggests that the relative low hi values are results of thermal maturity the high value of the gammacerane index indicates water stratification of the lake in this stage water and sediment input approximately equaled potential accommodation the lake was relatively stable and hosted large amounts of lacustrine algae and accumulated om with low terrestrial input in an anoxic environment after the onset of the thrusting the potential accommodation was decreased large volumes of clastic sediments also drained into the lake from the surrounding area resulting in an overfilled lake basin during this stage peat was deposited in freshwater environment with 30 wt toc low hi and type iii om the high pr ph 3 implies oxic conditions

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

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

tightly coupled records of ca and c isotope changes during the hirnantian glaciation event in an epeiric sea setting abstract a 44 40 ca excursion of 0 5 is recorded during the hirnantian glaciation event in carbonate rocks of the monitor range section in nevada the timeframe for the glaciation is 1 03 0 2 ma the 44 40 ca changes are synchronous with lithofacies and biofacies indicators of sea level change and co vary negatively with a large positive 13 c excursion of 7 that was previously interpreted to reflect local c cycling effects in circulation restricted waters of the epeiric martin ridge basin the synchronousness of the ca and c isotope excursions is inconsistent with what we know of ca and c geochemical cycles in the modern ocean because the residence time of ca is longer than that of c a box model is used to illustrate that the negative 44 40 ca excursion would take longer to recover than the positive 13 c excursion if the relative timescales of the hirnantian ca and c cycles were scaled similarly to those in the ocean today one way to speed up the timescale of the ca isotope response is to decrease the size of the ca reservoir this is what is accomplished when seawater circulation is restricted between oceans and epeiric seas approximately 30 of the 0 5 shift in hirnantian 44 40 ca values may be attributed to lower sea surface temperatures in the tropics during glaciation the remainder is attributed to local ca cycling effects in the martin ridge basin which include an increase in isotopically light ca inputs by submarine groundwater discharge sgd and a larger kinetic isotope fractionation effect due to increased carbonate precipitation rate the hypothesized increase in carbonate precipitation rate may have been caused by high photosynthesis rates maintained by high nutrient fluxes from sgd which increased the local carbonate saturation state of the waters additionally the conditions in this setting may have fostered a suite of organisms employing a calcification mechanism that involved microenvironments bacterial or algal surfaces biofilms or sedimentary pore fluids where biological activity could effectively alter the carbonate chemistry in very small c reservoirs a similar scenario was presented by laporte et al 2009 to explain the bulk of the anomalously large 7 positive 13 c excursion in the same section the strong negative coupling between the stratigraphic records of ca and c isotope changes in the martin ridge basin may serve as a tool to identify other epeiric sea settings in the rock record where similar physical and ecological attributes developed during periods of restricted circulation brought on by low sea level

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

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

application of biological markers in the assessment of paleoenvironments of chinese non marine sediments abstract in this study we employ molecular organic geochemical data for 22 representative sediment samples from chinese non marine sedimentary basins in an attempt to characterize and assess the non marine depositonal paleoenvironments the samples investigated include oilshale shale mudstone and sodium sulphate rich sediments ranging in age from cretaceous to tertiary it is evidenced by geological and geochemical data that those sediments studied originate from lacustrine environments ranging from freshwater brackish fresh water to hypersaline the aliphatic fractions of the sediment extracts were analyzed by gc and gc ms and relative abundance of compounds and compound classes of normal acyclic and cyclic alkanes were measured from mass chromatograms the results reveal significant differences in the chemical features of the various sample groups which enable them to be characterized and identified in terms of source and or environment related parameters the diagnostic parameters that allow this assessment are the relative abundances of n alkanes acyclic isoprenoid alkanes and 4 methyl steranes hopane sterane ratio gammacerane and homohopane indexes etc in this study data interpretation was also assisted by pattern recognition through principal component analysis the results show that the sample groups of different environmental origin could be unambiguously distinguished on scores plot

δ44ca evolution in a carbonate aquifer and its bearing on the equilibrium isotope fractionation factor for calcite abstract to improve understanding of ca isotope transport during water rock interaction on the continents we measured dissolved 44 ca values along a 236 km flow path in the madison aquifer south dakota where fluids have chemically evolved according to dolomite and anhydrite dissolution calcite precipitation and ca for na ion exchange over a timescale spanning 15 kyr we used a reactive transport model employing rate data constrained from major ion mass balances to evaluate the extent to which calcite precipitation and ion exchange fractionate ca isotopes elevated 44 ca values during the initial and final stages of water transport possibly result from calcite precipitation under supersaturated conditions and ca for na ion exchange respectively however for the bulk of the flow path 44 ca values evolve by mixing between anhydrite and dolomite dissolution with no fractionation during calcite precipitation under saturated conditions we attribute the absence of ca isotope fractionation to the long timescale of water rock interaction and slow rate of calcite precipitation which have enabled fluids to chemically and isotopically equilibrate with calcite we therefore conclude that the equilibrium ca isotope fractionation factor between calcite and water cal w is very close to zero to the extent that the madison aquifer typifies other groundwater systems where calcite slowly precipitates from solutions at or near chemical equilibrium this study suggests that groundwater contributions to 44 ca variability on the continents can be modeled according to simple mixing theory without invoking isotope discrimination

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

effects of biogeochemical processes on magnesium isotope variations in a forested catchment in the vosges mountains france abstract this study investigates the potential of mg isotopes as tracers of biogeochemical processes in a small forested catchment located on sandstones extremely poor in mg bearing minerals the average 26 mg is 0 63 0 12 and 0 0 14 for local rainwater and bedrock respectively from the c horizon to the upper eluvial e horizon soil 26 mg from 0 0 0 14 to 0 25 0 14 is close to the bedrock value while more than 70 of mg is lost suggesting a small isotopic shift during illite dissolution the surface soil horizon a h 26 mg is close to plant 26 mg and especially to the grass 26 mg value 0 49 the bulk 26 mg of trees and grass 0 32 and 0 41 respectively are higher than the average 26 mg values of the soil exchangeable fraction 0 92 to 0 42 and of rainwater 0 65 within plants roots are enriched in heavy isotopes whereas light isotopes are preferentially translocated and stored in the above ground parts in norway spruce the older needles forming the annual litterfall are isotopically lighter and strongly depleted in mg compared to more recent needles soil solution 26 mg shifts seasonally from low values lower than rainwater and close to litterfall during a high rainfall period in spring to higher values close to soil 26 mg in dryer periods of winter or summer at the watershed scale streamwater 26 mg varies between 0 85 0 14 and 0 08 0 14 and 26 mg values decrease linearly with discharge the high streamwater 26 mg at low flow close to bedrock 26 mg most likely reflects dissolution processes in the deep saprolite in relation to the very long water residence time conversely we suggest that low stream level 26 mg values are at least partly related to the contribution of surface flows from wet areas using a simple mass and isotopic balance approach we compute that mineral dissolution rates in the soil 0 35 kg mg ha 1 year 1 presently compensate for mg losses from the soil

biological marker composition of typical source rocks and related crude oils of terrestrial origin in the people s republic of china a review abstract typical source rocks and related crude oils of terrestrial origin in china come from five major environments a sedimentary formations in large lake basins in china s interior plate b lacustrine clastic rocks in fault subsidence basins c saline lake strata in fault subsidence basins d lagoonal lacustrine volcano clastic rocks in intermontane basins and e paralic coal bearing formations of the platform facies each has its specific biomarker characteristics as follows 1 environment a is poor in gammacerane and triterpane of higher plant origin 2 environment b contains abundant biomarkers especially hopanoid and steroid hydrocarbons with some triterpanes of higher plant origin 3 environment c has extremely high amounts of phytane and series of s compounds with high ratios of phytane pristane and gammacerane c30 hopane and sometimes high even carbon predominance of n alkanes 4 environment d contains abundant isoprenoid alkanes and carotanes carotane and carotane and 5 environment e is rich in biomarkers of high plants such as diterpenoid and aromatized terpenoid hydrocarbons

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

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

a sequential extraction to determine the distribution of apatite in granitoid soil mineral pools with application to weathering at the hubbard brook experimental forest nh usa abstract mineral weathering in soils is an important source of many nutrients to forest ecosystems apatite a ca phosphate mineral occurs in trace amounts in virtually all igneous and metamorphic rocks and is often found as small mineral inclusions in more weathering resistant silicate minerals to better understand the distribution of apatite in soils and its exposure to soil solutions a sequential extraction method was developed to selectively dissolve minerals from soils so that the amount of apatite in contact with soil solutions versus that armored by silicate minerals could be quantified the use of three molarities of hno3 0 01 0 1 and 1 m at three temperatures 0 10 or 20 c was explored and it was found that apatite congruently dissolved in 1 m hno3 at all three temperatures but did not completely dissolve in weaker hno3 solutions soil horizons glacial till i e soil parent material and individual minerals separated from till collected from the hubbard brook experimental forest hbef nh were subjected to a 4 step sequential extraction chemical analyses of the extracts indicate that 1 m nh4cl ph 7 20 c removes exchangeable ions 1 m hno3 at 20 c primarily dissolves apatite in contact with solutions 1 m hno3 at 200 c primarily dissolves biotite and chlorite and apatite armored by them and a mixture of concentrated hno3 hcl and hf at 200 c dissolves the more refractory minerals including muscovite alkali feldspar plagioclase feldspar and quartz and apatite armored by these minerals this extraction method was applied to soil profiles from hbef to demonstrate that it could be used to interpret the abundance of apatite and other minerals as a function of depth approximately 70 of the apatite in the hbef soil parent material is exposed to soil solutions the remaining 30 is armored in more weathering resistant micas and feldspars in the upper soil horizons the only apatite that has not been weathered from the soil occurs as inclusions in micas and feldspars and thus the rate of dissolution of apatite in weathered soil horizons is controlled by silicate mineral dissolution

isotopically heavy carbon in the c21 to c25 regular isoprenoids in halite rich deposits from the sdom formation dead sea basin israel abstract a series of miocene pliocene halite deposits with extremely low organic carbon contents from the sdom formation dead sea basin israel have been studied distributions and 13c contents of biomarkers have been determined using gc ms and irm gcms analyses respectively the hydrocarbon fractions consist mainly of pristane phytane and c21 to c25 regular isoprenoids the predominance of c21 regular isoprenoids in the dead sea halites and other hypersaline deposits indicate that these components could be derived from ether bound membrane lipids of halophilic archaea the lack of intact ether bound lipids in the polar fractions indirectly infers that such components have already been released at early stages of diagenesis their 13c contents are enriched in 13c by up to 7 compared to the biomarkers of presumed phytoplanktonic origin i e steranes and hopanes within the same sediment sample in agreement with a source other than algae and cyanobacteria thus tentatively assigned as halophilic archaea based on biomarker distributions 13c contents and mineral compositions these sediments appear to have been deposited in a salinity stratified water body with a bottom water brine continual evaporation and deposition of the higher salts i e carnallites are favourable conditions for the growth of halophilic archaeal communities

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

calcium and strontium isotope dynamics in three polluted forest ecosystems of the czech republic central europe abstract calcium and strontium isotope ratios were used to identify ca sources for bulk soil soil solutions and runoff in the stressed forest ecosystems of central europe all three study sites are underlain by ca poor crystalline bedrock orthogneiss leucogranite and serpentinite respectively but differ in historical rates of acid deposition udl the spruce die back affected site at the czech polish border underlain by orthogneiss received six times more acidifying compounds from the atmosphere than lys and plb two paired catchments near the czech german border the paired catchments near the czech german border whose forests were only mildly damaged by industrial pollution differ in their acid buffering capacity extremely low for lys leucogranite extremely high for plb serpentinite at the spruce die back affected catchment udl 19 years of monthly hydrochemical monitoring revealed six times higher atmospheric deposition and runoff fluxes of ca compared to the paired catchments lys and plb across the three sites the mean 44ca values increased in the order spruce bark 0 84

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

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

the major ion δ44 40ca δ44 42ca and δ26 24mg geochemistry of granite weathering at ph 1 and t 25 c power law processes and the relative reactivity of minerals abstract we dissolved boulder creek granodiorite in a plug flow reactor for 5794 h at ph 1 and t 25 c the primary purpose of the experiment was to identify controls on dissolved 44 40ca 44 42ca and 26 24mg values during granite weathering herein we also examine the origin of ca and mg isotopic variability among minerals composing the boulder creek granodiorite and we constrain fundamental characteristics of granite weathering important for quantifying the elemental and isotopic geochemistry of the reactor output nine ca bearing minerals display an 8 80 range of 44 40ca values and a 0 51 range of 44 42ca values three mg bearing minerals display a 1 53 range of 26 24mg values these ranges expressed at the mineralogical scale are higher than the ranges thus far reported for bulk igneous rocks most of the 44 40ca variability reflects 40ca enrichment in k feldspar and to a lesser extent biotite due to the radioactive decay of 40k over the 1 7 ga age of the rock whereas the entire range of 44 42ca values reflects mass dependent isotope fractionation during igneous differentiation and crystallization the range of 26 24mg values may represent either fractionation during the chloritization of biotite or interaction of the boulder creek granodiorite with mg rich metamorphic fluids having low 26 24mg values the elemental and isotopic composition of the reactor output varied substantially during the experiment we synthesize the mineralogical and fluid data using coupled mass conservation equations solved at non steady state model calculations reveal an intricate balance between increasing specific surface area and decreasing mineral concentrations while surface area normalized dissolution rate constants were time invariant specific surface area increased as a power law function of time through positive feedbacks between mechanical disaggregation chemical dissolution and mineral depletion variations in dissolved 44 40ca 44 42ca and 26 24mg values reflect conservative mixing rather than fractionation apatite and calcite initially control 44 40ca and 44 42ca values followed by biotite titanite epidote hornblende and plagioclase the release of radiogenic 40ca clearly defines the period where biotite dissolution dominates the brucite layer of chlorite initially controls 26 24mg values followed by biotite the tot layer of chlorite and hornblende through direct isotopic tracking these results demonstrate that trace minerals such as apatite and calcite in the case of ca and brucite in the case of mg dominate elemental release during the incipient stages of granite weathering the results further show that biotite dissolution dominates the middle stages of granite weathering and that plagioclase dissolution only becomes important during relatively late stages the ca and mg isotope variations associated with these stages are distinct and potentially resolvable in soil mineral weathering studies

assessment of hydrocarbon source rock potential of polish bituminous coals and carbonaceous shales abstract we analyzed 40 coal samples and 45 carbonaceous shale samples of varying thermal maturity vitrinite reflectance 0 59 to 4 28 from the upper carboniferous coal bearing strata of the upper silesian lower silesian and lublin basins poland to evaluate their potential for generation and expulsion of gaseous and liquid hydrocarbons we evaluated source rock potential based on rock eval pyrolysis yield elemental composition atomic h c and o c and solvent extraction yields of bitumen an attempt was made to relate maceral composition to these source rock parameters and to composition of the organic matter and likely biological precursors a few carbonaceous shale samples contain sufficient generation potential pyrolysis assay and elemental composition to be considered potential source rocks although the extractable hydrocarbon and bitumen yields are lower than those reported in previous studies for effective type iii source rocks most samples analysed contain insufficient capacity for generation of hydrocarbons to reach thresholds required for expulsion primary migration to occur in view of these findings it is improbable that any of the coals or carbonaceous shales at the sites sampled in our study would be capable of expelling commercial amounts of oil inasmuch as a few samples contained sufficient generation capacity to be considered potential source rocks it is possible that some locations or stratigraphic zones within the coals and shales could have favourable potential but could not be clearly delimited with the number of samples analysed in our study because of their high heteroatomic content and high amount of asphaltenes the bitumens contained in the coals are less capable of generating hydrocarbons even under optimal thermal conditions than their counterpart bitumens in the shales which have a lower heteroatomic content

recent advances in petroleum geochemistry applied to hydrocarbon exploration this paper presents a critical review of recent advances in the study of generation maturation and migration of petroleum the different source potentials for generating hydrocarbons depend on the type of kerogen in addition to the classic types i ii and iii a residual oxidized organic matter is also observed which has no potential for hydrocarbon generation coal is widely considered as a potential source for gas but some coals may generate sizeable amounts of oil as well the development of routine analytical tools particularly pyrolysis makes possible the preparation of geochemical logs that are the basis for screening samples and for interpreting other analyses among optical techniques the major subjects of discussion concern the nature of amorphous organ c matter which may encompass different chemical types of kerogen and the applicability of vitrinite reflectance techniques to type i and ii kerogens following important advances in identification of biological markers in sediments and crude oils these markers are used for oil source rock correlation and proposed for reconstruction of depositional environment and subsequent thermal evolution migration of hydrocarbons is now better understood and the importance of a hydrocarbon phase migration is widely recognized overpressuring of pore fluids is mainly responsible for expulsion of petroleum geologic models of basin evolution subsidence compaction thermal history and geochemical models hydrocarbon generation and migration become progressively available their integration int a comprehensive model should be one of the major developments in future petroleum exploration

silicate versus carbonate weathering in iceland new insights from ca isotopes to trace sources of ca in icelandic rivers we report elemental and ca isotope data for rivers high and low temperature groundwater basalt hydrothermal calcite including iceland spar and stilbite and heulandite which are two types of zeolites commonly formed during low grade metamorphism of basalt in agreement with previous research we find that rivers have higher 44 40ca values than basalt with a maximum difference of 0 40 this difference may reflect isotope fractionation in the weathering zone i e preferential uptake of 40ca during clay mineral formation adsorption and other geochemical processes that cycle ca however calcite 44 40ca values are also up to 0 40 higher than bedrock values and on a diagram of 44 40ca versus sr ca nearly all waters plot within a plausible mixing domain bounded by the measured compositions of basalt and calcite with glacial rivers plotting closer to calcite than non glacial rivers calcite and heulandite form during hydrothermal alteration of basalt in the deep lava pile and often occur together in metabasalts now exposed at the surface because heulandite 44 40ca values are 1 2 lower than basalt we suggest that 40ca uptake by heudlandite explains the relatively high 44 40ca values of calcite and that calcite weathering in turn elevates riverine 44 40ca values high mechanical erosion rates are known to facilitate the exposure and weathering of calcite which explains the isotopic contrast between glacial and non glacial watersheds using a mixing model we find that calcite weathering provides 0 65 of the ca in non glacial rivers and 25 90 of the ca in glacial rivers with silicate weathering providing the remainder icelandic hydrothermal calcite contains mantle carbon noting that zeolite facies metamorphism and hydrothermal fluid circulation are ubiquitous characteristics of basaltic eruptions and assuming that hydrothermal calcite in other basaltic settings also contains mantle carbon we suggest that the contribution of basalt weathering to long term co2 drawdown and climate regulation may be less significant than previously realized

the stable cr isotopic compositions of chondrites and silicate planetary reservoirs abstract the depletion of chromium in earth s mantle 2700 ppm in comparison to chondrites 4400 ppm indicates significant incorporation of chromium into the core during our planet s metal silicate differentiation assuming that there was no significant escape of the moderately volatile element chromium during the accretionary phase of earth stable cr isotope compositions expressed as the difference in 53 cr 52 cr from the terrestrial reference material srm979 53 52 cr srm979 values of planetary silicate reservoirs might thus yield information about the conditions of planetary metal segregation processes when compared to chondrites the stable cr isotopic compositions of 7 carbonaceous chondrites 11 ordinary chondrites 5 hed achondrites and 2 martian meteorites determined by a double spike mc icp ms method are within uncertainties indistinguishable from each other and from the previously determined 53 52 cr srm979 value of 0 124 0 101 for the igneous silicate earth extensive quality tests support the accuracy of the stable cr isotope determinations of various meteorites and terrestrial silicates reported here the uniformity in stable cr isotope compositions of samples from planetary silicate mantles and undifferentiated meteorites indicates that metal silicate differentiation of earth mars and the hed parent body did not cause measurable stable cr isotope fractionation between these two reservoirs our results also imply that the accretionary disc at least in the inner solar system was homogeneous in its stable cr isotopic composition and that potential volatility loss of chromium during accretion of the terrestrial planets was not accompanied by measurable stable isotopic fractionation small but reproducible variations in 53 52 cr srm979 values of terrestrial magmatic rocks point to natural stable cr isotope variations within earth s silicate reservoirs further and more detailed studies are required to investigate whether silicate differentiation processes such as partial mantle melting and crystal fractionation can cause stable cr isotopic fractionation on earth and other planetary bodies

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

testing the groundwater ridging hypothesis of streamflow generation during snowmelt in a forested catchment hydrometric and isotopic techniques were used to test the groundwater ridging hypothesis of stream flow generation during snowmelt in a forested catchment on the canadian shield the catchment contains a central wetland that drains to an ephemeral channel hydrograph separation using 2h as a tracer indicated that approximately 60 of total stream flow during snowmelt was supplied by pre event water this was supported by hydrometric results however contrary to the groundwater ridging hypothesis the response of water table levels in near stream areas to initial melt inputs failed to promote a rapid flux of ground water to the wetland and stream all stream flow originated as saturation overland flow from the wetland and groundwater flow during much of the melt was directed down the catchment s main axis and back under hillslopes surrounding the wetland and channel although the hydrograph separation indicated pronounced short term variations in pre event discharge from the catchment groundwater fluxes to the wetland remained relatively invariant following initiation of surface saturation streamflow fluctuations appear to have been generated by displacement of water held in surface storage induced by melt and rainwater inputs to the wetland this stored water had an isotopic signature intermediate between that of event and pre event water suggested oscillations in pre event runoff were an artifact of the mixing model approach to hydrograph separation rather than the result of rapid changes in groundwater fluxes to the wetland

chemical molecular and isotopic differentiation of organic facies in the tertiary lacustrine duaringa oil shale deposit queensland australia abstract total organic matter extractable organic matter bitumen and pyrolysates released on low temperature sealed tube pyrolysis of kerogen were analysed chemically and isotopically based on bulk bitumen and biomarker parameters the sediments are immature to a depth of approx 1300 m within the terrestrial and lacustrine depositional environments of the tertiary duaringa basin various organic facies have been classified according to inorganic input and maceral abundances of organic matter derived from land plant and algal sources the latter derived mainly from pediastrum and with a varying botryococcus content the lacustrine upper lamosite is chemically and isotopically distinct from the lower lamosite due to a changing algal community relative contributions from allochthonous land plants and for the lower lamosite a slightly more saline and restricted lake environment the lower lamosite is associated with the highest concentrations of c 28 c 30 4 methylsteranes and 13 c depletion in toc in the upper lamosite there is a strong positive correlation between botryococcus content and 13 c enrichment the organically lean claystones have sources nearly identical to the lamosites but the organic matter is diluted due to rapid influx of siliciclastics the terrestrial facies the cannel coal and carbonaceous shales are mainly distinguished from the lacustrine facies by higher relative proportions of c 29 steranes c 30 4 methylsteranes and 13 c values for the pyrolysed hydrocarbons intermediate between the two lamosite facies the carbonaceous oil shale has a composite geochemical signature intermediate between the two end members lamosite and cannel coal oleanane and ring a degraded triterpanes derived from lupane arborane and oleanane skeletons are distributed throughout all organic facies representing both autochthonous and allochthonous higher plant inputs higher concentrations of oleanane and des a lupane are associated with the terrestrial facies hopanes dominate over steranes in all organic facies and their concentration ranges are independent of facies for the lamosites the aliphatic biopolymer algaenan is implicated as the dominant source for n alkanes from analysis of their yields homologue abundances and individual 13 c values in the terrestrial facies resinites are paraffinic and are a major source for the n alkanes released on pyrolysis compound specific analysis of extractable and pyrolysate hydrocarbons allowed deconvolution of different source inputs to free lipids and kerogen for the lamosites low molecular weight n alkanes in the bitumen are derived mainly from a pediastrum source while botryococcus is associated with waxy n alkanes however the situation is reversed in the kerogen pediastrum algeanan has a longer average alkyl chain length than botryococcus algaenan the magnitude of the isotopic differences between single n alkanes released at different temperatures is useful in determining multiplicity of sources

changing sources of base cations during ecosystem development hawaiian islands 87 sr 86 sr evidence from a soil chronosequence in the hawaiian islands demonstrates that the atmosphere supplies 85 of putatively rock derived sr in older sites initially bedrock is the dominant source for sr and other lithophile elements such as ca but high rates of weathering and leaching of the substrate by 20 ka lead to a shift to atmospheric sources the loss of weathering inputs coincides with other physio chemical changes in the soil and results in a steep decline of base cations in the soil pool while these patterns imply the potential for limitation of biological productivity by low base cation supply the atmosphere provides a supply of base cations in excess of nutritional needs even after nearly all rock derived base cations have been leached from the soil this raises the possibility that p limitation in terrestrial ecosystems may develop at least as much because of low rates of atmospheric deposition of p relative to ca k and other rock derived elements as because of its chemical interaction in soil

characterisation of sedimentary organic matter by bulk and molecular geochemical proxies an example from oligocene maar type lake enspel germany abstract characterisation of organic matter composition of fossil lake sediments is important in reconstruction of fossil ecosystems and paleoclimates high time resolved organic matter analysis is needed to characterize sediments from small lake environments due to their rapidly changing environmental conditions a suitable technique for rapid analysis of organic matter in such sediments is rock eval pyrolysis in small lakes however routine interpretation of rock eval data can be misleading lack of tributaries capable of transporting larger woody fragments into small lakes causes a bias towards the input of lipid rich leaf waxes and cuticles this hydrogen rich and oxygen depleted terrigenous organic matter hi 250 600 mg hc g toc and oi 20 40 mg co 2 g toc can easily be misinterpreted as being of algal origin differentiation of terrigenous plant derived hydrogen rich organic matter from algal organic matter is readily achieved by including c n elemental ratios and lipid biomarker data

global variability of chromium isotopes in seawater demonstrated by pacific atlantic and arctic ocean samples abstract seawater chromium cr isotope and concentration data are presented from multiple sites in the arctic ocean and three locations in the atlantic and pacific oceans a 2400 m profile illustrates the heterogeneity of 53cr in the arctic ocean with depth and water mass source pacific vs atlantic the highest 53cr values occur in pacific sourced waters which also have the lowest cr concentration chromium concentration and 53cr data from these locations in conjunction with published data for the south atlantic ocean yield a simple logarithmic function as predicted by rayleigh fractionation in a closed system the observed cr isotope signature is hypothesized to arise from fractionation during the reduction of cr vi in surface waters and oxygen minimum zones scavenging of isotopically light cr iii to deeper water and sediment and subsequent release of this seawater derived cr iii back into seawater either as organic complexes with cr iii or after oxidation to cr vi the isotopic fractionation factor e associated with cr cycling in seawater is estimated to be 0 80 0 03 2 samples from the sea ice affected surface mixed layer of the arctic ocean 10 m depth deviate from the general trend and samples proximal to rivers illustrate geographic variation in 53cr values for continental runoff but prompt loss of this signature away from the source

constraining soil mineral weathering 87sr 86sr for calcium apportionment studies of a deciduous forest growing on soils developed from granitoid igneous rocks abstracts we used 87 sr 86 sr as a proxy for ca to apportion the contribution of atmospheric deposition and soil mineral weathering sources to the ca pools in trees in a small forested watershed of southern quebec the effects of topography and forest stand composition were assessed by dividing the watershed into three study zones representing two elevations and differences in tree species apportionment calculations show that all tree species studied contained ca that is dominantly sourced from soil mineral weathering averaging 85 due to the presence in the soils of easily weathered ca bearing minerals such as calcite and apatite as well as the relatively deep rooting habits reaching the mineral soil of the tree species calcium pools in trees are shifted towards the atmospheric component on hilltops due to the filtering of dry aerosols of the tree canopies which are more exposed to atmospheric circulation than trees at the bottom of the slopes although some variability in soil bulk chemistry and mineralogy in the watershed obscures the full extent of this phenomenon the buildup and recycling of ca in the soil vegetation system with the forest floor acting as the major accessible ca pool for the tree roots must be considered when interpreting apportionment calculations this work supports other ca cycling models in forests suggesting that topography can influence the balance of ca captured from atmospheric sources by trees even in cases where mineral weathering is the dominant source of ca nutrition in trees

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

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