climatic dependence of stable carbon and oxygen isotope signals recorded in speleothems from soil water to speleothem calcite abstract understanding the relationship between stable isotope signals recorded in speleothems 13 c and 18 o and the isotopic composition of the carbonate species in the soil water is of great importance for their interpretation in terms of past climate variability here the evolution of the carbon isotope composition of soil water on its way down to the cave during dissolution of limestone is studied for both closed and open closed conditions with respect to co 2 the water entering the cave flows as a thin film towards the drip site co 2 degasses from this film within approx 10 s by molecular diffusion subsequently chemical and isotopic equilibrium is established on a time scale of several 10 100 s the 13 c value of the drip water is mainly determined by the isotopic composition of soil co 2 the evolution of the 18 o value of the carbonate species is determined by the long exchange time t ex between oxygen in carbonate and water of several 10 000 s even if the oxygen of the co 2 in soil water is in isotopic equilibrium with that of the water dissolution of limestone delivers oxygen with a different isotopic composition changing the 18 o value of the carbonate species consequently the 18 o value of the rainwater will only be reflected in the drip water if it has stayed in the rock for a sufficiently long time after the water has entered the cave the carbon and oxygen isotope composition of the drip water may be altered by co 2 exchange with the cave air exchange times ex co 2 of about 3000 s are derived thus only drip water which drips in less than 3000 s onto the stalagmite surface is suitable to imprint climatic signals into speleothem calcite deposited from it precipitation of calcite proceeds with time constants p of several 100 s different rate constants and equilibrium concentrations for the heavy and light isotopes respectively result in isotope fractionation during calcite precipitation since t ex p exchange with the oxygen in the water can be neglected and the isotopic evolution of carbon and oxygen proceed analogously for drip intervals t d p the isotopic compositions of both carbon and oxygen in the solution evolve linearly in time the calcite precipitated at the apex of the stalagmite reflects the isotopic signal of the drip water for long drip intervals when calcite is deposited from a stagnant water film long drip intervals may have a significant effect on the isotopic composition of the dic in this case the isotopic composition of the calcite deposited at the apex must be determined by averaging over the drip interval such processes must be considered when speleothems are used as proxies of past climate variability

a terrestrial u th dated stable isotope record of the penultimate interglacial abstract here we present the first u series dated stable oxygen isotope record in continental europe that covers the entire tripartite penultimate interglacial i e marine isotope stages 7 5 to 7 1 this record was obtained from a u rich stalagmite from spannagel cave in the austrian alps which is largely devoid of kinetic isotope fractionation effects which comprised previously studied flowstone from this site composed of dense columnar calcite this speleothem apparently grew without significant interruption for ca 50 ka albeit at a very slow rate the age model was established based on 23 individual u th tims dates using a combination of a bayesian approach which includes additional information using stratigraphic constraints and the mixed effect regression model the resulting record shows three prominent maxima in 18 o mis 7 5 7 3 and 7 1 separated by a long earlier and a shorter later cold period mis 7 4 and 7 2 respectively the mid points of the transitions into the three warm phases occurred at 240 3 215 2 and 200 3 ka and the mis 7 6 transition was dated to 190 3 ka the timing of these climate transitions is supported by other samples from the same cave and agrees within analytical uncertainties with u th dated evidence from corals marine aragonitic sediments and submerged stalagmites as well as with orbitally tuned deep sea records good agreement was also found with new speleothem data from china as far as mis 7 1 and 7 5 are concerned whereas mis 7 3 apparently started earlier and mis 7 2 lasted longer than in the alps comparing the european speleothem data with antarctic ice cores reveals obvious differences in age the latter suggesting an earlier start and a generally shorter duration of the three warm episodes in essence this study underscores the great potential of speleothems as accurate and precise chronometers of pleistocene climate change and emphasizes the need for similar studies in other continents including submerged caves in order to improve the imperfect chronological framework of mis 7

calibration of the calcite water oxygen isotope geothermometer at devils hole nevada a natural laboratory abstract the 18 o of ground water 13 54 0 05 and inorganically precipitated holocene vein calcite 14 56 0 03 from devils hole cave 2 in southcentral nevada yield an oxygen isotopic fractionation factor between calcite and water at 33 7 c of 1 02849 0 00013 1000 ln calcite water 28 09 0 13 using the commonly accepted value of calcite water t of 0 00020 k 1 this corresponds to a 1000 ln calcite water value at 25 c of 29 80 which differs substantially from the current accepted value of 28 3 use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in devils hole that is 8 c lower than the measured ground water temperature alternatively previously published fractionation factors would yield a 18 o of water from which the calcite precipitated that is too negative by 1 5 using a temperature of 33 7 c several lines of evidence indicate that the geochemical environment of devils hole has been remarkably constant for at least 10 ka accordingly a re evaluation of calcite water oxygen isotopic fractionation factor may be in order assuming the devils hole oxygen isotopic value of calcite water represents thermodynamic equilibrium many marine carbonates are precipitated with a 18 o value that is too low apparently due to a kinetic isotopic fractionation that preferentially enriches 16 o in the solid carbonate over 18 o feigning oxygen isotopic equilibrium

the influence of temperature ph and growth rate on the δ18o composition of inorganically precipitated calcite abstract the oxygen isotope composition of carbonate minerals varies with temperature as well as other environmental variables for carbonates that precipitate slowly under conditions that approach thermodynamic equilibrium the temperature dependence of 18 o uptake is the dominant signal and the measured 18 o content can be used as a paleotemperature proxy in the more common case where carbonate minerals grow in a regime where they are not in isotopic equilibrium with their host solution their oxygen isotope compositions are a convolution of multiple environmental variables here we present results from calcite growth experiments demonstrating the occurrence of large 2 non equilibrium oxygen isotope effects under conditions relevant to biogenic calcite growth and many natural inorganic systems we show that these non equilibrium effects vary systematically with ph and crystal growth rate an isotopic ion by ion crystal growth model quantifies the competing roles of temperature ph and growth rate and provides a general description of calcite water oxygen isotope fractionation under non equilibrium conditions the crystal growth model results show that 1 there are both equilibrium and kinetic contributions to calcite oxygen isotopes at biogenic growth rates 2 calcite does not directly inherit the oxygen isotope composition of dic even at fast growth rates 3 there is a kinetically controlled variation of about 1 per ph unit between ph 7 7 and 9 3 at constant growth rate for inorganic calcite as well as biogenic calcite and 4 extreme light isotope enrichments in calcite in alkaline environments are likely due to disequilibrium among dic species in aqueous solution the model can be extended to 13 c uptake into carbonates as well as clumped isotopes but additional data are needed to constrain the kinetic fractionation factors for carbon isotopes the experimental and model results constitute an important step in separating the relative influence of inorganic and biologic processes on isotopic fractionation and may aid the development of new paleoproxies based on non equilibrium effects

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

carbon and oxygen isotope study of the active water carbonate system in a karstic mediterranean cave implications for paleoclimate research in semiarid regions abstract in a semiarid climatic zone such as the eastern mediterranean region annual rainfall variations and fractionation processes in the epikarst zone exert a profound influence on the isotopic compositions of waters seeping into a cave consequently the isotopic compositions of speleothems depositing from cave waters may show complex variations that need to be understood if they are to be exploited for paleoclimate studies this is confirmed by a four year study of the active carbonate water system in the soreq cave israel the 18o smow values of cave waters range from 6 3 to 3 5 the highest 18o values occur at the end of the dry season in waters dripping from stalactites and reflect evaporation processes in the epikarst zone whereas the lowest values occur in rapidly dripping fast drip waters at the peak of the rainy seasons however even fast drip waters are about 1 5 heavier than the rainfall above the cave which is taken to reflect the mixing of fresh with residual evaporated water in the epikarst zone 13c pdb values of dissolved inorganic carbon dic vary from 15 6 to 5 4 with fast drip waters having lower 13c values mostly 15 6 to 12 and higher dic concentrations relative to pool and stalactite drip water the low 13c values of fast drip waters and their supersaturation with respect to calcium carbonate indicates that the seepage waters have dissolved both soil co2 derived from overlying c3 type vegetation and marine dolomite host rock the 18o pdb values of various types of present day low magnesium calcite lmc speleothems range from 6 5 to 4 3 and 13c values from 13 to 5 5 and are not correlated with speleothem type an analysis of 18o values of present day calcite rafts and pool waters shows that they form in oxygen isotope equilibrium similarly the measured ranges of 13c and 18o values for all types of present day speleothems are consistent with equilibrium deposition at cave temperatures the 13c 18o range of contemporary lmc thus reflects the variations in temperatures and isotopic compositions of the presentday cave waters the 10 variation in the 13c values in waters can be modeled by a simple rayleigh calculation of the carbon isotope fractionation accompanying co2 degassing and carbonate precipitation these variations may obscure the differences in the carbon isotopic composition of speleothems that could arise when vegetation cover changes from c3 to c4 type plants this consideration emphasizes that it is necessary to characterize the full range of 13c values associated with contemporaneous speleothems in order to clarify the effects of degassing from those due to differing vegetation types isotopic studies of a number of different types of fossil lmc speleothems show many of them to exhibit isotopic trends that are similar to those of present day lmc but others show both higher and lower 18o ranges in particular the higher 18o range has been shown by independent age measurements to be associated with a period of drier conditions the results of the study thus indicate that it is necessary to work on a well calibrated cave system in semiarid climates and that the fossil speleothem record should be obtained from different types of contemporaneous deposit in order to fully characterize the 18o 13c range representative of any given climatic period

reorganization of the north atlantic oscillation during early holocene deglaciation laurentide ice sheet retreat continued into the mid holocene speleothem based precipitation records suggest the cessation of melt led to the establishment of the present precipitation patterns associated with the north atlantic oscillation

disequilibrium carbon and oxygen isotope fractionation in recent cave calcite comparison of cave precipitates and model data abstract speleothem proxy data provide important information in continental palaeo climate research due to their precise chronology and wide geographic distribution despite a continuously growing number of field and numerical studies designed to study stable isotope fractionation effects many aspects remain a matter of debate here carbon and oxygen isotope ratios from cave drip water and calcite precipitates sampled on watch glasses in the bunker cave western germany are compared with the values expected for isotopic equilibrium furthermore the field data are compared with the results of a numerical model simulating stalagmite growth and stable isotope ratios two drip sites with different drip rates were investigated drip site ts 1 is characterised by a high drip rate and drip water of this site is characterised by a high saturation index with respect to calcite ts 1 shows no evidence of prior calcite precipitation conversely drip site ts 8 shows a low drip rate and drip water from this site is characterised by a low saturation index ts 8 shows evidence of prior calcite precipitation whereas the mean 13 c dic values of the drip water are significantly different between the two drip sites the mean 18 o drip water values are similar calcite precipitation rates are higher at watch glass site u i corresponding to drip site ts 1 this is probably due to the higher si calcite and drip rate the 18 o and 13 c values of the calcite precipitated on watch glasses u iv corresponding to drip site ts 8 are significantly higher than those of the calcite collected on watch glasses u i calcite precipitation occurs close to isotopic equilibrium at watch glass site u i whereas the calcite precipitated at watch glass site u iv shows clear evidence of isotopic disequilibrium the results suggest that cave calcites precipitated at lower drip rates have higher 13 c and 18 o values than predicted by equilibrium precipitation furthermore our data show that stalagmites from the same cave which are fed by drip water with similar 18 o values may have different 18 o calcite values the 13 c and 18 o values predicted by the numerical model are generally lower by 1 9 and 0 8 respectively than those of the natural cave calcite nevertheless the first order trends observed in the cave data are well reproduced by the model the offset between cave and model data is probably due to the fractionation factors used in the model

the evolution of 13 c and 18 o isotope composition of dic in a calcite depositing film of water with isotope exchange between the dic and a co 2 containing atmosphere and simultaneous evaporation of the water implication to climate proxies from stalagmites a theoretical model abstract the most widely applied climate proxies in speleothems are the isotope compositions of carbon and oxygen expressed by 13c and 18o values however mechanisms which are not related to climate changes overlay the climate signal one is the temporal increase of both 13c and 18o values by kinetic processes during precipitation of calcite isotope exchange between dic in the water and the co2 in the surrounding cave atmosphere can also change isotope composition here we present a theoretical model of the temporal isotope evolution of dic in a thin water layer during precipitation of calcite and simultaneous isotope exchange with the cave atmosphere and simultaneous evaporation of water the exchange of oxygen isotopes in the dic with those in the water is also considered for drip times for tdrip dic t drip e c eq c 0 e t drip eq atm 0 t drip in atm eq water 0 e w t drip t ev t drip water the first term on the right hand side is the contribution from precipitation of calcite the second stems from isotope exchange with the co2 of the cave atmosphere and the third results from isotope exchange between oxygen in the dic and the oxygen in the water e are kinetic parameters is the time scale of precipitation eq atm 0 and eq water 0 are the differences between the corresponding initial value 0 and the value eq atm water if dic were in isotope equilibrium with the atmosphere or in the case of oxygen with the water respectively in atm and water are the time scales of approach to isotope equilibrium by the exchange reactions ceq is the concentration of dic in chemical equilibrium with the co2 in the cave atmosphere and c0 is the initial concentration when the water drips to the stalagmite tev is the time needed for complete evaporation of the water layer ew is the fractionation between water vapor and fluid water for times tdrip 0 2 we find a further increase of dic tdrip until a maximum is passed and a final value is reached if eq atm 0 and eq water 0 are both zero exchange has no influence on the isotope composition for drip times tdrip eq atm 0 is about zero in summer time when most of the co2 comes from the vadose zone ground air and about 12 in winter time in well ventilated caves when most of the co2 stems from earth s atmosphere outside the cave therefore 13c may be affected by isotope exchange for the 18o equilibrium between the dic and the oxygen in the water as well as the oxygen in the co2 of the atmosphere is likely in summer time in winter time co2 from the atmosphere outside the cave with of about 6 vpdb may imprint small signals

testing theoretically predicted stalagmite growth rate with recent annually laminated samples implications for past stalagmite deposition annually laminated stalagmites deposited over the last 30 160 years are analysed to determine their growth rate three natural and artificial cave sites in england france and belgium were chosen for their wide range of variability in growth rate determining variables and multiple samples were taken from each site the annual nature of laminae deposition within the stalagmite calcite was confirmed by comparison to the date of cave void opening 14c analyses or by using dated event horizons measured stalagmite growth rate was determined from annual laminae thickness measurements and compared to that theoretically predicted from the chemical kinetics of the calcite precipitation reaction a good agreement is observed between empirical observations and theoretical predictions although two complicating factors variations in calcite porosity and seasonal cessation of the water supply to the samples both affect the growth rate implications for the extraction of palaeoclimate information from stalagmite growth rate are discussed

large kinetic isotope effects in modern speleothems the application of stable isotopes in speleothem records requires an understanding of the extent to which speleothem calcite isotopic compositions refl ect the compositions of the cave waters from which they precipitate to test for equilibrium precipitation modern speleothem calcite was grown on glass plates so that the carbon and oxygen isotope composition of the calcite and the water from which it precipitated could be directly compared the plates were placed on the tops of three actively growing stalagmites that occupy a 1 m 2 area in harrison s cave barbados west indies only some of the plate 13 c values and none of the plate 18 o values correspond to equilibrium values indicating signifi cant kinetic isotope effects during speleothem calcite growth we investigate herein mechanisms that may account for the kinetic isotope effects on each plate speleothem calcite was deposited with distinct 18 o and 13 c compositions that increase progressively away from the growth axis with up to 6 6 13 c and 1 7 18 o enrichments the positive 13 c

the influence of kinetics on the oxygen isotope composition of calcium carbonate paleotemperature reconstructions rely on knowledge of the equilibrium separation of oxygen isotopes between aqueous solution and calcium carbonate although oxygen isotope separation is expected on theoretical grounds the temperature dependence remains uncertain because other factors such as slow exchange of isotopes between dissolved co2 species and water can obscure the temperature signal this is problematic for crystal growth experiments on laboratory timescales and for interpreting the oxygen isotope composition of crystals formed in natural settings we present results from experiments in which inorganic calcite is precipitated in the presence of 0 25 m dissolved bovine carbonic anhydrase ca the presence of dissolved ca accelerates oxygen isotope equilibration between the dissolved carbon species co2 h2co3 hco3 co32 and water thereby eliminating this source of isotopic disequilibrium during calcite growth the experimental results allow us to isolate for the first time kinetic oxygen isotope effects occurring at the calcite water interface we present a framework of ion by ion growth of calcite that reconciles our new measurements with measurements of natural cave calcites that are the best candidate for having precipitated under near equilibrium conditions our findings suggest that isotopic equilibrium between calcite and water is unlikely to have been established in laboratory experiments or in many natural settings the use of ca in carbonate precipitation experiments offers new opportunities to refine oxygen isotope based geothermometers and to interrogate environmental variables other than temperature that influence calcite growth rates

atmospheric pco 2 control on speleothem stable carbon isotope compositions abstract the stable carbon isotope compositions of c3 plants are controlled by the carbon isotope composition of atmospheric co2 13ca and by the stomatal response to water stress these relationships permit the reconstruction of ancient environments and assessment of the water use efficiency of forests it is currently debated whether the 13c values of c3 plants are also controlled by atmospheric pco2 here i show that globally averaged speleothem 13c values closely track atmospheric pco2 over the past 90 kyr after accounting for other possible effects this coupling is best explained by a c3 plant 13c sensitivity of 1 6 0 3 100 ppmv co2 during the quaternary this is consistent with 20th century european forest tree ring 13c records providing confidence in the result and suggesting that the modest pco2 driven increase in water use efficiency determined for those ecosystems and simulated by land surface models accurately approximates the global average response the 13c signal from c3 plants is transferred to speleothems relatively rapidly thus the effect of atmospheric pco2 should be subtracted from new and existing speleothem 13c records so that residual 13c shifts can be interpreted in light of the other factors known to control spleleothem 13c values furthermore global average speleothem 13c shifts may be used to develop a continuous radiometric chronology for pleistocene atmospheric pco2 fluctuations and by correlation ice core climate records

if martian ice caps flow ablation mechanisms and appearance abstract assuming that the northern ice cap of mars is thick enough to flow like terrestrial ice sheets a model is presented that explains i the origins movement and spiral nature of the scarp trough complexes ii the reentrant valleys like chasma boreale and iii the layered terrain accumulation and ablation are discussed in relation to the scarps and a model is developed relating them to ice flow and scarp velocities and to the particle paths within the ice cap a brief summary of terrestrial ice sheet flow and mass balance is given in order to illustrate and clarify the concepts used to model the martian ice caps

sea land oxygen isotopic relationships from planktonic foraminifera and speleothems in the eastern mediterranean region and their implication for paleorainfall during interglacial intervals the oxygen and carbon stable isotope compositions of cave speleothems provide a powerful method for understanding continental climate change here we examine the question of the regionality of this isotopic record and its linkage with the marine isotopic record in the eastern mediterranean em region the study presents a new accurately dated 250 kyr 18o and 13c record determined from speleothems of the peqiin cave northern israel its comparison with the continuous 185 kyr isotopic record of the soreq cave speleothems from central israel reveals striking similarities thus a strong regional climatic signal brought about by variations in temperature and rainfall amount is reflected in both cave records low 18o minima in the peqiin profile for the last 250 to 185 kyr period interglacial marine isotopic stage 7 match the timing of sapropels 9 to 7 and are indicative of high rainfall in the em region at these times the combined soreq and peqiin 18o record for the last 250 kyr excellently matches the published globigerinoides ruber g ruber marine 18o record for the em sea with the isotopic compositional difference g ruber speleothems remaining relatively constant at 5 6 0 7 thus establishing for the first time a robust exploitable link between the land and the marine isotopic records the correspondence of low 18o speleothem values and high cave water stands with low g ruber 18o values during interglacial sapropel events indicates that these periods were characterized by enhanced rainfall in the em land and sea regions by use of sea surface temperatures derived from alkenone data as a proxy for land temperatures at the soreq cave we calculate the paleorainfall 18o values and its amounts maximum rainfall and lowest temperature conditions occurred at the beginning of the sapropel events and were followed by decrease in rainfall and increase in temperatures leading to arid conditions the record for the last 7000 yr shows a trend toward increasing aridity and agrees well with climatic and archeological data from north africa and the middle east

waxing and waning of the perennial north polar h2o ice cap of mars over obliquity cycles abstract the perennial north polar h2o ice cap of mars is investigated with the dynamic thermodynamic ice sheet model sicopolis computational results for flow velocities ice temperatures and surface accumulation ablation rates are presented for the steady state with present conditions as well as for transient scenarios over idealized obliquity cycles with periods of 1 3 myr and 125 kyr the transient simulations lead to a stop and go type dynamics with a cold and almost stagnant modern ice cap and a warmer flowing ice cap for past large obliquity periods the most likely scenario for the present ice cap comprises an ice volume of 1 2 million km3 a maximum thickness of 3 km the absence of pronounced local isostasy h2o ice accumulation rates of the order of tenth mm water equivalent w e per earth year yr flow velocities of the order of mm yr and an ice base far below pressure melting

a flow model for the polar caps of mars a mechanical model with circular symmetry is examined to test the hypothesis that the martian ice caps are composed of flowing water ice together with some rock debris in contrast with most or all previous models no assumption of a steady state is made instead the accumulation and ablation is assumed to be insignificant and it is suggested that after a sufficient time the profile would have settled down to a particular collapsing form calculated by halfar 1983 higher modes of flow would have decayed relatively quickly to calculate the time constant it is necessary to consider carefully the distribution of temperature with depth the time constant is sensitive to the grain size which is assumed to be 1 10 mm and is a significant unknown as is also the effect of preferred crystal orientation apart from this the main uncertainty is the value of the upward heat flux with a heat flux of 30 mw m 2 the water ice hypothesis is consistent with an age of about 10 7 years for both the north and the south polar caps the north cap being the younger by a factor of about 7

modelling fractionation of stable isotopes in stalagmites abstract high resolution 13c and 18o profiles recorded in precisely dated speleothems are widely used proxies for the climate of the past both 13c and 18o depend on several climate related effects including meteorological processes processes occurring in the soil zone above the cave and isotope fractionation processes occurring in the solution layer on the stalagmite surface here we model the latter using a stalagmite isotope and growth model and determine the relationship between the stable isotope values in speleothem calcite and cave parameters such as temperature drip interval water p co 2 and a mixing coefficient describing mixing processes between the solution layer and the impinging drop the evolution of 13c values is modelled as a rayleigh distillation process and shows a pronounced dependence on the residence time of the solution on the stalagmite surface and the drip interval respectively the evolution of 18o values in contrast is also influenced by buffering reactions between the bicarbonate in the solution and the drip water driving the 18o value of the bicarbonate towards the value expected for equilibrium isotope fractionation between drip water and calcite this attenuates the dependence of the 18o values on drip interval the temperature dependence of 18o however is more pronounced than for 13c and in a similar range as expected for fractionation under equilibrium conditions we also investigate the isotopic enrichment of the 13c and 18o values along individual growth layers and thus the slopes expected for hendy tests the results show that a positive hendy test is only possible if isotope fractionation occurred under disequilibrium conditions however a negative hendy test does not exclude that isotope fractionation occurred under disequilibrium conditions a more reliable indicator for disequilibrium fractionation is the enrichment of the 13c values along an individual growth layer

basal mechanics of ice stream b west antarctica 2 undrained plastic bed model based on the results of our studies of the physical conditions beneath ice stream b we formulate a new analytical ice stream model the undrained plastic bed model henceforth the upb model mathematically the upb model is represented by a non linear system of four coupled equations which express the relationships among ice sliding velocity till strength water storage in till and basal melt rate we examine this system of equations for conditions of ice stream stability over short timescales that permit holding ice stream geometry constant less than hundreds of years temporal variability is introduced into the upb model only by the direct dependence of till void ratio changes e t on the basal melting rate m r since till strength b e and ice stream velocity u b b change as long as till void ratio varies the first condition for ice stream stability is that of constant till water storage 0 the second condition for ice stream stability arises from the feedback between ice stream velocity till strength and the basal melting rate which depends on shear heating m r u b b this is the weak till condition which requires that in a steady state till strength is a small fraction of the gravitational driving stress b n 1 1 d the salient feature of the upb model is its ability to produce two thermo mechanically controlled equilibrium states one with a strong bed and slow ice velocities ice sheet mode and one with a weak bed and fast ice velocities ice stream mode this bimodality of basal conditions is consistent with the available observations of subglacial conditions beneath slow and fast moving ice in west antarctica basal conditions that do not correspond to these two steady states may occur transiently during switches between the two stable modes the upb model demonstrates that ice streams may be prone to thermally triggered instabilities during which small perturbations in the basal thermal energy balance grow leading to generation or elimination of the basal conditions which cause ice streaming

the role of silicate surfaces on calcite precipitation kinetics abstract the aim of this study is to illuminate how calcite precipitation depends on the identity and structure of the growth substrate calcite was precipitated at 25 c from supersaturated aqueous solutions in the presence of seeds of either calcite or one of six silicate materials augite enstatite labradorite olivine basaltic glass and peridotite rock calcite saturation was achieved by mixing a cacl2 rich aqueous solution with a nahco3 na2co3 aqueous buffer in mixed flow reactors containing 0 5 2 g of mineral rock or glass seeds this led to an inlet fluid calcite saturation index of 0 6 and a ph equal to 9 1 although the inlet fluid composition flow rate and temperature were identical for all experiments the onset of calcite precipitation depended on the identity of the seeds present in the reactor calcite precipitated instantaneously and at a constant rate in the presence of calcite grains calcite precipitated relatively rapidly on labradorite olivine enstatite and peridotite mainly composed of mg olivine surfaces but more slowly on augite and basaltic glass calcite precipitation rates however became independent of substrate identity and mass over time and all rates approach 10 9 68 0 08 mol s for 10 day long experiments and 10 9 21 0 2 mol s for 70 day long experiments scanning electron microscope images showed olivine enstatite and peridotite surfaces to be covered extensively with calcite coatings at the end of the experiments less calcite was found on labradorite and augite and the least on basaltic glass in all cases calcite precipitation occurs on the mineral rock or glass surfaces calcite precipitation on these surfaces however negligibly affects the dissolution rates of the silicate grains these results support ultramafic and basalt carbonation as a long term carbon storage strategy as calcite readily precipitates on the surfaces of minerals contained in these rocks without inhibiting their dissolution

isotope disequilibrium effects the influence of evaporation and ventilation effects on the carbon and oxygen isotope composition of speleothems a model approach abstract in order to improve the understanding of variations of speleothem 18o and 13c values in the context of palaeoclimate research it is important to quantify the isotope fractionation processes influencing the 18o and 13c values of stalagmites here we present an extended version of speleothem stable isotope model that accounts for evaporation and condensation effects during precipitation of calcite the isolution model allows to calculate the effect of evaporation on 18ocalcite and 13ccalcite values in dependence on relative humidity and wind velocity our results reveal that evaporation may have a significant effect on 18ocalcite and 13ccalcite due to the loss of h2o from the solution layer and the related increase of the ca2 concentration this leads to higher precipitation rates and consequently larger isotope fractionation effects the effect on speleothem 18ocalcite and 13ccalcite can be as high as changes caused by variations of temperature drip interval pco2 drip and pco2 cave furthermore the change of pco2 cave due to ventilation effects may also affect speleothem 18ocalcite and 13ccalcite values because of the effect of pco2 cave on the equilibrium concentrations of the co2 h2o caco3 system and thus the calcite precipitation rate the variability of other cave parameters temperature drip interval pco2 drip pco2 cave can have a comparable effect on 18ocalcite and 13ccalcite values depending on the magnitude of variability we validated the isolution model by modelling the 18ocalcite values from a cave analogue experiment and successfully reproduced the values for high temperatures

impacts of cave air ventilation and in cave prior calcite precipitation on golgotha cave dripwater chemistry southwest australia abstract speleothem trace element chemistry is an important component of multi proxy records of environmental change but a thorough understanding of hydrochemical processes is essential for its interpretation we present a dripwater chemistry dataset pco2 alkalinity ca sicc mg and sr from an eight year monitoring study from golgotha cave building on a previous study of hydrology and dripwater oxygen isotopes treble et al 2013 golgotha cave is developed in quaternary aeolianite and located in a forested catchment in the mediterranean type climate of southwest western australia all dripwaters from each of the five monitored sites become supersaturated with respect to calcite during most of the year when cave ventilation lowers pco2 in cave air in this winter ventilation mode prior calcite precipitation pcp signals of increased mg ca and sr ca in dripwater are attributed to stalactite deposition a fast dripping site displays less evolved carbonate chemistry implying minimal stalactite growth phenomena which are attributed to minimal degassing because of the short drip interval 30 s we employ hydrochemical mass balance modelling techniques to quantitatively investigate the impact of pcp and co2 degassing on our dripwater initially we reverse modelled dripwater solutions to demonstrate that pcp is dominating the dripwater chemistry at our low flow site and predict that pcp becomes enhanced in underlying stalagmites secondly we forward modelled the ranges of solution mg ca variation that potentially can be caused by degassing and calcite precipitation to serve as a guide to interpreting the resulting stalagmite chemistry we predict that stalagmite trace element data from our high flow sites will reflect trends in original dripwater solutes preserving information on biogeochemical fluxes within our system by contrast stalagmites from our low flow sites will be dominated by pcp effects driven by cave ventilation our poorly karstified system allows us to highlight and quantify these in cave pcp processes which are otherwise masked at sites where karstification is more developed and hydrogeology is more complex our modelling also shows enhanced co2 source production in the unsaturated zone that is attributed to deeply rooted vegetation and increasing bioproductivity which we link to forest recovery after fires impacted our site during 2006 ce

the asian monsoon over the past 640 000 years and ice age terminations oxygen isotope records from chinese caves characterize changes in both the asian monsoon and global climate here using our new speleothem data we extend the chinese record to cover the full uranium thorium dating range that is the past 640 000 years the record s length and temporal precision allow us to test the idea that insolation changes caused by the earth s precession drove the terminations of each of the last seven ice ages as well as the millennia long intervals of reduced monsoon rainfall associated with each of the terminations on the basis of our record s timing the terminations are separated by four or five precession cycles supporting the idea that the 100 000 year ice age cycle is an average of discrete numbers of precession cycles furthermore the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands and is nearly in anti phase with summer boreal insolation these observations indicate that insolation in part sets the pace of the occurrence of millennial scale events including those associated with terminations and unfinished terminations records of the asian monsoon have been extended to 640 000 years ago and confirm both that the 100 000 year ice age cycle results from integral numbers of precessional cycles and that insolation influences the pacing of major millennial scale climate events prior records of the asian monsoon have revealed cyclic variations over hundreds of thousands of years probably driven by variations in insolation caused by the precession of earth s orbit hai cheng and colleagues now provide a speleothem record from chinese cave samples that extends earlier records to 640 000 years ago close to the maximum age possible with uranium thorium dating this spectacular record confirms that the characteristic 100 000 year ice age cycle corresponds to an integral number four or five of precession cycles and that insolation influences millennial scale variations in monsoon strength

interpretation of speleothem calcite δ13c variations evidence from monitoring soil co2 drip water and modern speleothem calcite in central texas we studied the sources and transport of carbon in two active karst systems in central texas inner space cavern is and natural bridge north and south caverns nb to provide new insights into the interpretation of speleothem cave calcite deposit carbon isotope compositions we have determined the 13c values of soil co2 13cs in grassland and savanna above these caves with 13c values of cave drip water 13chco3 and modern speleothem calcite grown on artificial substrates 13ccc we compare 13chco3 values from direct drip sites where water was sampled immediately upon discharging from the cave ceiling to values from indirect sites where water was sampled after flowing along a prolonged path within the cave that allowed for longer co2 degassing and have found that direct drip sites yield consistently lower 13chco3 values the 13chco3 values of direct drip water below savanna 10 6 0 5 and 12 6 0 2 in nb and is respectively are indistinguishable from is or similar to nb calculated 13chco3 values in equilibrium with measured soil co2 beneath trees 13 5 to 11 3 for juniper trees above nb and 13 6 to 12 6 for mixed oak and elm trees above is respectively at is the 13chco3 values of direct drip water are higher below grassland 9 7 0 3 than below savanna 12 6 0 2 these results suggest that the 13chco3 values of drip waters that initially enter the caves are controlled by deep rooted plants where present and are minimally influenced by host rock dissolution and or prior calcite precipitation pcp the 13chco3 values of indirect drip water vary seasonally with relatively low values during the summer 10 8 0 8 and 9 2 0 4 under juniper savanna at nb and under grassland at is respectively that are similar to the direct drip 13chco3 values 10 6 0 5 and 9 7 0 3 under savanna at nb and under grassland at is respectively the relatively high 13chco3 values of indirect drip sites during the winter 13chco3 8 6 0 8 at nb and 8 0 0 1 at is result from co2 degassing of water along in cave flow paths we also present decade long records of modern calcite 13c values from direct and indirect drip sites at is the 13ccc values vary seasonally with lower values during the summer and higher values during the winter and with smaller amplitude variations at the direct drip site such seasonal variations can be used as a geochronological tool in some speleothems that do not contain visible lamina the summer 13ccc values of direct drip calcite are similar to 13ccc values predicted from soil co2 collected beneath trees above that drip site the occurrence of highest 13ccc values during the winter when cave co2 concentrations are low highlights the significance of ventilation driven changes in cave air pco2 modern calcite 13c values are also negatively correlated with drip rate which suggests that 13ccc variations are controlled by kinetic effects during degassing and calcite precipitation associated with the drip water exposure time to a low pco2 environment in all at the caves we investigated variability in speleothem 13ccc values primarily reflect presence absence of deep rooted vegetation and kinetic isotope effects we therefore infer that increased aridity may result in higher 13c values of vegetation lower drip rates and more drip water degassing and thus higher 13ccc values of speleothem calcite

caribbean hydroclimate and vegetation history across the last glacial period abstract we present a new speleothem trace element and stable isotope record which extends previous paleoclimate evidence from cuban speleothems to the last 96 ka multiple proxies were used to reconstruct caribbean hydroclimate and vegetation variability on orbital to millennial timescales in particular our proxies indicate a shift to more abundant c4 compared to c3 vegetation and or reduced soil activity during the last glacial maximum our results confirm the close link of caribbean precipitation to north atlantic climate variability insolation and the strength of the amoc the associated variations in caribbean ssts and the shift of the itcz led to substantial changes of the hydrological cycle during heinrich stadials and the younger dryas climatic conditions in cuba were comparably cool and or dry in contrast warm dansgaard oeschger cycles were accompanied by wetter conditions this is in agreement with previous evidence for the holocene when north atlantic cold warm events coincided with drier wetter conditions in cuba however our record suggests that this connection was less dominant during mis 4 to 2 displayed by a weaker response of cuban precipitation proxies to north atlantic climatic shifts than during mis 5 in particular we hypothesize that this weaker connection was mediated by the southerly shifted itcz inducing a weakening of the northern branch of the caribbean low level jet which usually transports moisture into the northern caribbean this is strikingly evident during the deglacial when driest and or coolest conditions prevailed in western cuba from hs 1 into the younger dryas including the bolling allerod interstadial

north iberian temperature and rainfall seasonality over the younger dryas and holocene abstract several stalagmite records have yielded important but discontinuous insights into northern iberian climate since the last glacial here we present the first continuous iberian stalagmite based reconstruction of climate since the bolling allerod interstadial from a single stalagmite sample gar 01 from la garma cave cantabria the 13 5 ka gar 01 record provides the opportunity for replication continuation and aggregation of previously published records from northern spain the gar 01 record reveals shifts in oxygen isotope ratios that are inexplicable by appealing to a single control i e exclusively temperature rainfall amount etc herein we explore the potential role of rainfall and temperature seasonality shifts on the new 18o record using a simple monte carlo approach to estimate the seasonal distribution of rainfall and the annual temperature range at 100 year timeslices across the record this model is corroborated by intervals of monthly resolved laser ablation trace element data providing glimpses into past iberian seasonality shifts the most salient features of the modelled results include extremely dry younger dryas winters 12 9 11 6 ka bp and several intervals during the mid holocene with almost no summer rainfall e g at 4 2 and 9 0 ka bp by 1 6 ka bp a near modern rainfall seasonality was established according to the modelling results seasonal rainfall and temperature distribution variability can account for 95 of the record the model presented here provides a new tool for extracting critical missing seasonality information from stalagmite 18o records intervals where the model does not converge may represent transient climate anomalies with unusual origins that warrant further investigation

monitoring bunker cave nw germany a prerequisite to interpret geochemical proxy data of speleothems from this site summary monitoring cave environments is important to understand processes in karst systems if stalagmites from a specific cave are used as archives of past climate variability a quantitative understanding of the soil karst speleothem system is crucial the monitoring program performed in bunker cave nw germany which includes monthly collection of climatological data as well as air and water samples from the cave and the overlying soil since 2006 is a prerequisite for the interpretation of speleothem data from the cave in terms of climate variability the results show that bunker cave is a homogeneously ventilated cave with rather low pco2 values of 580 1200 ppmv which lacks strong seasonal variations the 18o value of cave drip water reflects the mean annual composition of the rain water and the seasonal variability is strongly attenuated indicating a well mixed karst aquifer hence stalagmites from bunker cave should be well suited to record interannual decadal climate trends seven drip sites in two cave chambers show three different types of discharge behaviour including slow seasonal drip fast seasonal drip and seepage flow the drip rate patterns of most drip sites are consistent with the main infiltration events taking into account a delay of several months an instantaneous response to precipitation i e piston flow is not observed for any drip site indicating a specific water capacity threshold in the soil karst aquifer prior calcite precipitation pcp was also identified especially during times of low discharge though pcp is not as pronounced at bunker cave as in other caves it probably has an influence on the mg ca ratios of the stalagmites

forward modeling of ice topography on mars to infer basal shear stress conditions 1 understanding the history of ice caps on mars could reveal important information about martian geologic and climatic history to do this an ice reconstruction model is needed that operates over complex topography and can be constrained with a limited number of free parameters in this study we developed a threshold sliding model for ice cap morphology based on the classic model of nye later incorporated into the models of reeh and colleagues we have updated the nye reeh model with a new numerical algorithm although the model was originally developed to model perfectly plastic deformation it is applicable to any ice body that deforms when a threshold basal shear stress is exceeded the model requires three inputs a digital elevation model of bed topography a mask grid that defines the position of the ice terminus and a function defining the threshold basal shear stress to test the robustness of the model the morphology of the greenland ice sheet is reconstructed using an empirical equation between threshold basal shear stress and ice surface slope the model is then used to reconstruct the morphology of ice draping impact craters on the margins of the south polar layered deposits using an inferred constant basal shear stress of 0 6 bar for the majority of the examples this inferred basal shear stress value is almost 1 3 of the average basal shear stress calculated for the greenland ice sheet what causes this lower basal shear stress value on mars is unclear but could involve the strain weakening behavior of ice

speleothem calcite farmed in situ modern calibration of δ18o and δ13c paleoclimate proxies in a continuously monitored natural cave system abstract understanding the relationships between speleothem stable isotopes 13 c 18 o and in situ cave forcing mechanisms is important to interpreting ancient stalagmite paleoclimate records cave studies have demonstrated that the 18 o of inorganically precipitated low temperature speleothem calcite is systematically heavier than the 18 o of laboratory grown calcite for a given temperature to understand this apparent offset rainwater cave drip water groundwater and modern naturally precipitated calcite farmed in situ were grown at multiple locations inside hollow ridge cave in marianna florida high resolution micrometeorological air chemistry time series and ventilation regimes were also monitored continuously at two locations inside the cave supplemented with periodic bi monthly air gas grab sample transects throughout the cave cave air chemistry and isotope monitoring reveal density driven airflow pathways through hollow ridge cave at velocities of up to 1 2 m s 1 in winter and 0 4 m s 1 in summer hollow ridge cave displays a strong ventilation gradient in the front of the cave near the entrances resulting in cave air that is a mixture of soil gas and atmospheric co 2 a clear relationship is found between calcite 13 c and cave air ventilation rates estimated by proxies pco 2 and 222 rn calcite 13 c decreased linearly with distance from the front entrance to the interior of the cave during all seasons with a maximum entrance to interior gradient of 13 c caco3 7 a whole cave hendy test at multiple contemporaneous farming sites reveals that ventilation induces a 1 9 0 96 13 c offset between calcite precipitated in a ventilation flow path and calcite precipitated on the edge or out of flow paths this interpretation of the hendy test has implications for interpreting 13 c records in ancient speleothems calcite 13 c caco3 may be a proxy not only for atmospheric co 2 or overlying vegetation shifts but also for changes in cave ventilation due to dissolution fissures and ceiling collapse creating and plugging ventilation windows farmed calcite 18 o was found to exhibit a 0 82 0 24 offset from values predicted by both theoretical calculations and laboratory grown inorganic calcite unlike 13 c caco3 oxygen isotopes showed no ventilation effects i e 18 o caco3 appears to be a function of growth temperature only although we cannot rule out a small effect of unmeasured gradients in relative humidity evaporation accompanying ventilation our results support the findings of other cave investigators that water calcite fractionation factors observed in speleothem calcite are higher that those measured in laboratory experiments cave and laboratory calcite precipitates may differ mainly in the complex effects of kinetic isotope fractionation combining our data with other recent speleothem studies we find a new empirical relationship for cave specific water calcite oxygen isotope fractionation across a range of temperatures and cave environments 1000 ln 16 1 10 3 t 1 24 6 with a fractionation temperature dependence of 18 o t 0 177 c lower than the currently accepted 0 206 c

reconstruction of the glacial ice covers of greenland and the canadian arctic islands by three dimensional perfectly plastic ice sheet modelling a three dimensional perfectly plastic ice sheet model developed for determining the surface elevations and the flow pattern of an ice sheet with given bottom topography and ice margin positions is applied to the reconstruction of the glacial ice covers of greenland and the canadian arctic islands in the northern regions two different reconstructions have been performed with ice margins along the present 600 and 200 m sea depth contours respectively in central greenland the ice margin is considered to be at the outermost ice margin deposits on the coastal shelf to the west and at the present 200 m sea depth contour to the east the main conclusions to be drawn from the reconstructions are 1 the flow pattern of the glacial ice cover of greenland shows a great resemblance to the present one the central ice divide being displaced less than 50 km from its present position and being no more than 200 m higher than today 2 the main ice divide of the ice sheet covering the canadian arctic islands the innuitian ice sheet was located over the highlands of eastern ellesmere island with local domes positioned over the present ice caps indicating that even the deep ice of wisconsin age in these ice caps is of local origin this is also the case for the devon island ice cap 3 even in the not very likely case of a rather extensive glacial ice cover in north west greenland the ice flow pattern upstream of the camp century deep drill site would not have changed radically compared to the present flow pattern thus it is concluded that even advanced ice margins in late wisconsin time could at most have resulted in an elevation of the deposition site of the late wisconsin ice at camp century 600 m higher than at present the consequences of this conclusion are discussed

palaeoclimatic interpretation of high resolution oxygen isotope profiles derived from annually laminated speleothems from southern oman high resolution stable isotope profiles of three contemporaneously deposited stalagmites from a shallow cave in southern oman provide an annually resolved record of indian ocean monsoon rainfall variability for the past 780 years uranium series age dating and counts of annual growth bands enable an excellent age calibration although modern speleothems do not grow in perfect isotopic equilibrium oxygen isotope ratios 18o are a proxy for the amount of monsoon rainfall this is supported by the statistically significant correlation between 18o and the thickness of annual bands whereas 18o is inversely correlated with annual band thickness additionally overlapping 18o profiles are very similar in pattern and range indicating that sample specific noise did not blur the climatic signal the longest oxygen isotope profile derived from stalagmite s3 clearly shows the transition at 1320 ad from a generally wetter medieval warm period to a drier little ice age that lasted from approximately ad 1320 1660 in southern oman the decrease in monsoon rainfall since the 1960s is also obvious in meteorological records from northern africa and india indicating that our speleothem based rainfall records do not only reflect local monsoon rainfall variability

changes in greenland ice sheet elevation attributed primarily to snow accumulation variability the response of grounded ice sheets to a changing climate critically influences possible future changes in sea level recent satellite surveys over southern greenland show little overall elevation change at higher elevations but large spatial variability using satellite studies alone it is not possible to determine the geophysical processes responsible for the observed elevation changes and to decide if recent rates of change exceed the natural variability here we derive changes in ice sheet elevation in southern greenland for the years 1978 88 using a physically based model of firn densification and records of annual snow accumulation reconstructed from 12 ice cores at high elevation our patterns of accumulation driven elevation change agree closely with contemporaneous satellite measurements of ice sheet elevation change and we therefore attribute the changes observed in 1978 88 to variability in snow accumulation similar analyses of longer ice core records show that in this decade the greenland ice sheet exhibited typical variability at high elevations well within the long term natural variability our results indicate that a better understanding of ice sheet mass changes will require long term measurements of both surface elevation and snow accumulation

variable winter moisture in the southwestern united states linked to rapid glacial climate shifts the last glacial period was characterized by large rapid climate fluctuations an analysis of a speleothem from new mexico shows that the coldest conditions over greenland coincide with increased winter precipitation in the southwestern united states which can be attributed to a southward displacement of the polar jet stream and the north american storm track

reconstruction of temperature in the central alps during the past 2000 yr from a δ18o stalagmite record the precisely dated isotopic composition of a stalagmite from spannagel cave in the central alps is translated into a highly resolved record of temperature at high elevation during the past 2000 yr temperature maxima during the medieval warm period between 800 and 1300 ad are in average about 1 7 8c higher than the minima in the little ice age and similar to present day values the high correlation of this record to d 14 c suggests that solar variability was a major driver of climate in central europe during the past 2 millennia d 2005 elsevier b v all rights reserved

speleothem record from pentadactylos cave cyprus new insights into climatic variations during mis 6 and mis 5 in the eastern mediterranean abstract a new paleoclimate record from cyprus gives valuable insights into climatic variations during marine isotope stages mis 6 5 for the east mediterranean region two stalagmites from pentadactylos cave in the kyrenia mountain range 800 m altitude in cyprus grew from 174 6 0 7 to 112 2 0 5 ka bp with major hiatuses at 163 142 and 132 128 ka during early mis6 the stalagmite suggests through a relatively low growth rate 57 5 mm ka and variable but rather negative d18o that climate conditions were highly variable on a millennial scale with wet and cold climate conditions during sapropel 6 deposition at the end of mis6 141 132 ka growth rate varied from 123 to 18 mm ka and less negative 18 o c suggests general dry cold conditions followed by a growth stop during h11 the onset of mis5e is marked by the highest growth rate 217 mm ka the most negative 18o values at the onset and during the eemian wet period in cyprus are driven mostly by the source effect sapropel 5 and enhanced rainfall amounts stable conditions during mis 5e were rather short as shown in the growth and isotopic signal consistent with other em records after 122 ka growth decreased drastically 8 2 mm ka and a slow deterioration of the soil cover is suggested from continuously less negative 13c values fluid inclusion d18o shows a clear shift 4 5 between end mis 6 and mis 5e clumped isotopes measurements indicate kinetic effects between calcite and water of up to 1 after correction for kinetic effects using 47 a minimum estimate for the mis 6 5 temperature shift in the em is ca 9 c similarly drastic changes in rainfall amounts are inferred from measured fluid inclusion and calculated water d18o

spatial distribution of helium isotopes in volcanic gases and thermal waters along the vanuatu new hebrides volcanic arc we report the first helium isotope survey of volcanic gases hot springs and some olivine phenocrysts along the vanuatu island arc from tanna in the south to vanua lava in the north low co2 content and low 3he 4he ratios in thermal fluids of epi 4 0 0 1 ra efate 4 5 0 1 ra and pentecost 5 3 0 5 ra islands coherently indicate reduced mantle gas leakage and crustal contamination by radiogenic helium on these extinct volcanic systems of the former pliocene arc instead presently active vanuatu volcanoes display 3he 4he and c 3he ratios typical of subduction related volcanic arcs 3he 4he ratios range from 6 4 0 5 ra in southernmost tanna and 7 23 0 09 ra in northernmost vanua lava to typical morb values in the central islands of gaua 7 68 0 06 ra ambrym 7 6 0 8 ra and ambae 7 2 ra in groundwaters 7 9 1 4 ra in olivine phenocrysts and 8 0 0 1 ra in summit fumaroles of aoba volcano on ambrym however we discover that hydrothermal manifestations separated by only 10 15 km on both sides of a major e w transverse fault zone crossing the island are fed by two distinct helium sources with different 3he 4he signatures while fluids in southwest ambrym baiap and sesivi areas have typical arc ratios 7 6 0 8 ra fluids on the northwest coast buama bay area display both higher 3he 4he ratios 9 8 0 2 ra in waters to 10 21 0 08 ra in bubbling gases and lower c 3he ratios that evidence a hotspot influence we thus infer that the influx of indian morb mantle beneath the central vanuatu arc from which ambrym magmas originate also involves a 3he rich hotspot component possibly linked to a westward influx of samoan hotspot material or another yet unknown local source this duality in magmatic he source at ambrym fits with the bimodal composition and geochemistry of the erupted basalts implying two distinct magma sources and feeding systems more broadly the wide he isotopic variations detected along the vanuatu arc further verify the complex tectonic and magmatic framework of this intra oceanic island arc

north polar region craterforms on mars geometric characteristics from the mars orbiter laser altimeter abstract this study focuses on topographic characterization of ice associated north polar region impact craters and several enigmatic polar craterforms using new information from the mars orbiter laser altimeter mola an instrument aboard the mars global surveyor mgs orbiter we find that for ice associated craters the topography reveals several surprising results not previously apparent from orbital images alone first geometric properties for several impact craters associated with ice and frost deposits suggest that cavity infill is as high as 80 of reconstructed preerosion levels second craters associated with ice also demonstrate unique cavity geometries relative to their nonpolar counterparts finally in some cases ice associated impact features are anomalously deep on the basis of depths modeled from the best available scaling laws we suggest that burial of these impact features by either episodic advance of the polar cap margin or by continuous deposition at the highest rates previously estimated for the north polar region of mars has occurred subsequent stripping has exhumed the features leaving behind cavity infill deposits and a few of these display topographic levels above the surrounding preimpact surface in at least one case cavity interior deposits show layering with a typical thickness of 10 m suggesting episodic deposition and ablation of materials as in the polar layered terrain in addition to ice associated craters we investigated the topography of several enigmatic polar craterforms in particular a few craterforms within 150 km of the permanent north polar cap appear to resemble simple effusive lava shield volcanoes found on earth their geometric properties cannot be reconciled with previous suggestions that they were manifestations of martian hydromagmatic processes i e maar volcanism mola s initial measurements of impact craters and other craterforms in the north polar latitudes of mars support the concept of a geologically recent surface with evidence of effusive volcanism and enhanced sedimentation in addition the measured impact crater depths for ice associated craters suggest at least a few cases of enhanced excavation and thus a possibly weaker target relative to the typical northern hemisphere plains

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

modelling the δ18o value of cave drip water and speleothem calcite abstract stable isotope signals recorded in speleothems have provided important insights about past climate variability in recent years quantitative reconstruction of mean annual temperature and the amount of precipitation however remains difficult because the stable isotope signals are influenced by various processes here we present a drip water model which shows how these climate parameters affect the oxygen isotope signal of cave drip water in the model the dependence of the 18 o value of drip water on mean annual temperature is established by correlation to the amount of winter precipitation and winter temperature application of the model to two caves in western germany reveals a strong influence of winter rainfall on the oxygen isotope composition of cave drip water in this region assuming equilibrium isotope fractionation between drip water and calcite we provide a function relating the 18 o value of speleothem calcite to mean annual surface temperature this function shows a clear anticorrelation between temperature and the 18 o value of speleothem calcite which has been previously reported for several caves in central and northern europe by inverse application of this function we tentatively reconstruct average temperatures for the period between 6 and 1 5 ka from the 18 o signals of two stalagmites from atta and bunker cave western germany the resulting temperature curves are very sensitive to the value used for the correlation between the amount of winter precipitation and winter temperature since this correlation was probably not constant in the past the reconstructed temperature curves are associated with substantial uncertainty

chasma boreale mars topographic characterization from mars orbiter laser altimeter data and implications for mechanisms of formation 1 chasma boreale a large reentrant in the north polar cap of mars is distinct in scale detailed topography and orientation from the spiraling troughs that characterize the majority of the polar cap we use new high resolution mars orbiter laser altimeter mola data and mars orbiter camera moc and viking images of the chasma region to assess hypotheses of origin of chasma boreale these hypotheses include formation by glacial flow and ablation by eolian processes such as katabatic winds and sublimation by outflow of meltwater or by a combination of two or more of these processes we find that these new data support initial formation by outflow of meltwater with later modification by katabatic winds and sublimation on the basis of our analysis we suggest a possible scenario in which outflow has occurred in several stages the outflow appears to have begun near an enclosed depression at the head of the chasma meltwater migrated within and below the ice down the regional slope and eventually broke out to the surface removal of material by melting caused subsidence and erosion of the polar deposits forming the chasma which has subsequently undergone modification by eolian and sublimation processes the outflow deposited most of its sediment in the form of a lobe that stratigraphically overlies the polygonal plains mapped at the mouth of the chasma and scoured some of the circumpolar sediment mantle in the surrounding region the lowest portions of the north polar basin received the rest of the sediment as a deposit a few meters thick mola data also reveal evidence for similar events of smaller magnitude elsewhere on the margins of the polar cap

vegetation and environmental changes in tropical south america from the last glacial to the holocene documented by multiple cave sediment proxies abstract 18 o values in speleothems have been utilized to document past changes in south american monsoon intensity however changes in regional vegetation and ecosystems have not been part of this discussion and other cave proxies such as speleothem 13 c values a useful proxy for vegetation reconstruction have been neglected due to interpretive complexities here we report 13 c values and 87sr 86sr ratios in stalagmites together with xrf derived elemental chemistry 13 corg values and carbon content from a sedimentary profile from the same cave where the stalagmites were collected in combination with a previously published 18 o record this enables us to clarify climate and environmental shifts that occurred between the last glacial maximum and the holocene in central south america we show that vegetation was sparse during the last glacial period in spite of a previously inferred strong monsoon and that changes in atmospheric pco2 combined with local hydrological and temperature feedbacks may have determined vegetation development during this time

martian impact craters correlations of ejecta and interior morphologies with diameter latitude and terrain abstract the premise of this study is that global analysis of crater morphologies can discriminate between the effects of impact energy atmosphere and subsurface volatiles based on the correlation between morphology and latitude diameter and terrain this study focuses on seven ejecta and nine interior morphologies associated with 3819 craters 8 km in diameter distributed across the entire martian surface this data set is sufficiently large to provide statistically viable results on a global scale the results of the analyses indicate that changes in ejecta and interior morphology correlate with increases in crater diameter excavation depths corresponding to these diameters are calculated from depth diameter relationships and are compared to the theoretical distribution of subsurface volatiles the different ejecta morphologies can be described by impact into material with varying proportions of volatiles and the latidudinal variations seen for rampart crater morphologies correlate well with the proposed latitude depth relationship for ice and brines across the planet many of the interior structres show distributions indicative of terrain dependent influences for example the concentrations of central pit craters around ancient impact basins and on alba patera suggest that volatiles preferentially collect in these areas however central peak and peak ring interior morphologies show little relationship to planetary properties and probably result from changes in impact energy thus many of the unique morphologies associated with martian impact craters result from the presence of subsurface volatiles

investigation of the stable isotope fractionation in speleothems with laboratory experiments many speleothems show evidence for calcite precipitation under disequilibrium conditions to improve the understanding of these kinetic processes several laboratory experiments were performed to study the fractionation of stable oxygen and carbon isotopes during the precipitation of calcite carbonate was precipitated under controlled conditions from both a body of standing water beaker experiments and a solution flowing along a channel channel experiments at a relative humidity of 100 slow degassing of co2 simulated by the beaker experiments results in 18o values in equilibrium with the solution in contrast the 13c values show a significant enrichment inversely proportional to the height of the solution in the beakers fast degassing of co2 simulated by the channel experiments showed an enrichment of both 13c and 18o and a slope of 13c 18o of 1 4 0 6 these results represent experimental evidence for the hendy effect which is manifested in i a progressive increase in 18o and 13c away from the growth axis and ii a positive correlation between 18o and 13c along a single growth layer of a stalagmite

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

the instability of a south polar cap on mars composed of carbon dioxide abstract if the martian south polar cap were composed of solid carbon dioxide would it be sufficiently stable against collapse under its own weight this question is examined in the light of new experiments on the creep of solid carbon dioxide and new high resolution topographic mapping of the south polar cap the conclusion from a simple model is that with the strongest of three flow laws compatible with the measurements co 2 is strong enough to support a cap of this material with thickness about 1800 m for 10 7 years or more which is the age suggested by the cratering record however none of the three possible flow laws will allow a 3000 m cap the thickness suggested by stereogrammetry to survive for 10 7 years indicating that the south polar ice cap is probably not composed of pure co 2 ice

viscous relaxation of craters within the martian south polar layered deposits abstract the south polar layered deposits pld are of fundamental importance to martian climatology as they may comprise the largest reservoir of near surface water on mars the south pld exhibit relatively young crater retention surface ages which are widely attributed to recent resurfacing however we show that both constructional and destructional resurfacing mechanisms such as dust deposition and water ice sublimation respectively are inconsistent with the size depth and spatial distributions of south pld craters we demonstrate that another process viscous creep relaxation of dusty water ice is more compatible with the observed cratering of south pld surfaces the results of our finite element relaxation simulations suggest that despite their apparent youthfulness the pld have been stable for at least several hundred million and perhaps even over a billion years consequently our modeling implies that the time scales for the formation and preservation of the layers characteristic of the south and possibly north pld are much longer than generally assumed

simulating speleothem growth in the laboratory determination of the stable isotope fractionation δ13c and δ18o between h2o dic and caco3 abstract here we present novel cave analogue experiments directly investigating stable carbon and oxygen isotope fractionation between the major involved species of the carbonate system hco3 co2 caco3 and h2o in these experiments which were performed under controlled conditions inside a climate box a thin film of solution flew down an inclined marble or glass plate after different distances of flow and thus residence times on the plate ph electrical conductivity supersaturation with respect to calcite precipitation rate as well as the 18o and 13c values of the dissolved inorganic carbon dic and the precipitated caco3 were obtained progressive precipitation of caco3 along the plate is accompanied by degassing of co2 and stable isotope fractionation and the system is driven out of isotope equilibrium we observe a strong enrichment of the 13c values with increasing residence time and a smaller enrichment in 18o the temporal evolution of the 18o and 13c values of both the dic and the precipitated caco3 can be explained by a rayleigh fractionation model but the observed enrichment in 13c values is much larger than expected based on isotope equilibrium fractionation factors our setup enables to determine the fractionation between caco3 and hco3 i e ecaco3 hco3 carbon isotope fractionation 13ecaco3 hco3 is strongly negative for all experiments and much lower than equilibrium isotope fractionation 0 1 in addition 13ecaco3 hco3 decreases with increasing residence time on the plate and thus decreasing supersaturation with respect to calcite thus isotope fractionation depends on precipitation rate and consequently occurs under kinetic conditions this is in contrast to previous studies which found no rate dependence and no or even a positive carbon isotope fractionation between caco3 and hco3 oxygen isotope fractionation 18ecaco3 hco3 is also negative and dependent on precipitation rate since no literature values for 18ecaco3 hco3 are available we calculated 18ecaco3 hco3 using equilibrium oxygen isotope fractionation factors between water and calcite and water and hco3 respectively at the beginning of the plate the fractionation is in agreement with the fractionation calculated using fractionation factors determined in cave systems the observed fractionation between caco3 and water 1000ln18 is also in good agreement with the values determined in cave systems and shows a very similar temperature dependence 1000 ln 18 16 516 1 267 10 3 t 26 141 4 356 however with progressive precipitation of caco3 along the plate the system is forced out of isotope equilibrium with the water and 1000ln18 increases the large negative rate dependent isotope fractionations observed in this study suggest that precipitation of speleothem calcite is strongly kinetically controlled and may thus have a large effect on speleothem 18o and 13c values since these values may erroneously be interpreted as reflecting changes in past temperature precipitation and or vegetation density these results have important implications for paleoclimate reconstructions from speleothems

a novel application of triple oxygen isotope ratios of speleothems abstract we present triple oxygen isotope data from speleothems obtained by an o2 co2 pt catalyzed oxygen isotope equilibration method the high precision 9 per meg or better 1 sd of our new speleothem 17o carbonate 17o anomaly data is sufficient to resolve subtle hydroclimatic signals in addition we determined triple oxygen isotope fractionation factors through two sets of modern paired carbonate dripwater samples collected at a temperature of 17 1 c which is prerequisite to the calculation of triple oxygen isotope compositions of parent meteoric waters at cave sites from speleothem proxy data based on this calibration we back calculated triple oxygen isotope compositions of parent waters across well characterized climate transitions using speleothem proxy data from three regions resulting oxygen isotope data closely track the global meteoric water line gmwl providing a preliminary validation of the method our speleothem 17o data indicate a 21 per meg difference between marine isotope stage 5d and 5e in samples from central asia and a 15 per meg difference between the middle holocene and last glacial maximum in samples from the eastern mediterranean suggesting a shift in moisture source and or fractionation history unexpectedly there were no measurable 17o differences between glacial and interglacial samples from both the south american western amazon and asian southern china monsoon domains implying consistent moisture source conditions across glacial and interglacial cycles at least in terms of relative humidity remarkably 17o values from the western amazonian samples are significantly higher 20 per meg than those from asian monsoon regions suggesting lower relative humidity along moisture trajectories in the western amazon during the middle holocene and last glacial period similarly 17o values of the eastern mediterranean samples are significantly higher 19 55 per meg than those of coeval samples from central asia implying different hydrological environments or moisture sources despite being in the same westerly circulation domain speleothem 17o data may thus provide new and important constraints for understanding regional and global hydroclimate dynamics

modification of secondary craters on the martian south polar layered deposits secondary crater fields are important stratigraphic markers that can shed light on resurfacing processes that have occurred since their formation we examine the morphologies of secondary craters formed from the ejection of material from two large impacts on the martian south polar layered deposits spld mcmurdo crater at 84 5 s 0 w and an unnamed impact at 80 8 s 284 w the morphologies of these secondary craters allow us to impose constraints on the modification history of the spld we have quantified crater morphologies using data sets from the mars global surveyor and mars odyssey missions we find a complete lack of secondary craters smaller than 300 m in diameter in both crater fields which implies that at least the upper 30 m of the deposits have been resurfaced since the time of these impacts secondary crater depth to diameter ratios are low average of 0 016 indicating that significant degradation has occurred since their emplacement we find that vertical resurfacing alone is not enough to explain the observed depth to diameter distribution and suggest that viscous relaxation of craters coupled with a small amount of vertical resurfacing best fits the data in the mcmurdo field high depth to diameter craters are found preferentially on steeper terrain associated with scarps cutting through the secondary field this observation suggests that crater modification exhibits a dependence on slope we comment on possible mechanisms that may explain this observation the morphologies of secondary craters on the spld point to modification processes without lunar parallel and not yet fully modeled for mars

stable isotope variations in modern tropical speleothems evaluating equilibrium vs kinetic isotope effects applications of speleothem calcite geochemistry in climate change studies require the evaluation of the accuracy and sensitivity of speleothem proxies to correctly infer paleoclimatic information the present study of harrison s cave barbados uses the analysis of the modern climatology and groundwater system to evaluate controls on the c and o isotopic composition of modern speleothems this new approach directly compares the 18 o and 13 c values of modern speleothems with the values for their corresponding drip waters in order to assess the degree to which isotopic equilibrium is achieved during calcite precipitation if modern speleothems can be demonstrated to precipitate in isotopic equilibrium then ancient speleothems suitable for paleoclimatic studies from the same cave environment may also have been precipitated in isotopic equilib rium if modern speleothems are precipitated out of isotopic equilibrium then the magnitude and direction of the c and o isotopic offsets may allow specific kinetic and or equilibrium isotopic fractionation mechanisms to be identified carbon isotope values for the majority of modern speleothem samples from harrison s cave fall within the range of equilibrium values predicted from the combined use of 1 calcite water fractionation factors from the literature 2 measured temperatures and 3 measured 13 c values of the dissolved inorganic carbon of drip waters calcite samples range from 0 8 higher to 1 1 lower than predicted values the 13 c depletions are likely caused by kinetically driven departures in the fractionation between hco3 aq and caco3 from equilibrium conditions caused by rapid calcite growth 13 c enrichments can be accounted for by rayleigh distillation of the hco3 aq reservoir during degassing of 13 c depleted co2 modern speleothems from harrison s cave are not in o isotopic equilibrium with their corresponding drip waters and are 0 2 to 2 3 enriched in 18 o relative to equilibrium values 18 o variations in modern calcite are likely controlled by kinetically driven changes in the fractionation between hco3 aq and caco3 from equilibrium conditions to nonequilibrium conditions consistent with rapid calcite growth in contrast to 13 c 18 o values of modern calcite may not be affected by rayleigh distillation during degassing because co2 hydration and hydroxylation reactions will buffer the o isotopic composition of the hco3 aq reservoir if the effects of rayleigh distillation manifest themselves in the o isotopic system they will result in 18 o enrichment in the hco3

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

ancient glaciation on mars a large number of anomalous landforms on mars can be attributed to glaciation including the action of ice and meltwater glacial landscapes are concentrated south of lat 33 and in the northern plains suggesting vast austral and boreal ice sheets crater densities on the glaciated terrains indicate that the final glacial epoch occurred late in martian history thus mars may have had a relatively warm moist climate and dense atmosphere much later than previously believed

influence of ice rheology and dust content on the dynamics of the north polar cap of mars abstract the evolution and dynamics of the north polar cap residual ice cap layered deposits complex of mars is simulated with a thermomechanical ice sheet model we consider a scenario with ice free initial conditions at 5 ma before present due to the large obliquities which prevailed prior to this time the north polar cap is then built up to its present shape driven by a parameterized climate forcing surface temperature surface mass balance based on the obliquity and eccentricity history the effects of different ice rheologies and different dust contents are investigated it is found that the build up scenarios require an accumulation rate of approximately 0 15 0 2 mm a 1 at present the topography evolution is essentially independent of the ice dynamics due to the slow ice flow owing to the uncertainties associated with the ice rheology and the dust content flow velocities can only be predicted within a range of two orders of magnitude likely present values are of the order of 0 1 1 mm a 1 and a strong variation over the climatic cycles is found for all cases computed basal temperatures are far below pressure melting

modelling stalagmite growth and δ13c as a function of drip interval and temperature abstract growth and stable isotope composition of stalagmites are affected by climate changes to understand the underlying mechanisms we developed a time dependent multi box model that describes stalagmite growth and stable isotope fractionation of carbon under disequilibrium conditions the model takes variations of the drip interval temperature and the amount of mixing between the impinging drops and the solution on top of the stalagmite into account which allows to quantify the influence of these parameters to calculate the variations of 13c the multi box model was calibrated by comparison with an existing growth model the results show that drip interval temperature and the mixing coefficient do have a significant influence on 13c however considering the higher natural variability of the drip interval this parameter might have the largest influence

precise dating of dansgaard oeschger climate oscillations in western europe from stalagmite data the signature of dansgaard oeschger events millennial scale abrupt climate oscillations during the last glacial period is well established in ice cores and marine records but the effects of such events in continental settings are not as clear and their absolute chronology is uncertain beyond the limit of 14 c dating and annual layer counting for marine records and ice cores respectively here we present carbon and oxygen isotope records from a stalagmite collected in southwest france which have been precisely dated using 234u 230th ratios we find rapid climate oscillations coincident with the established dansgaard oeschger events between 83 000 and 32 000 years ago in both isotope records the oxygen isotope signature is similar to a record from soreq cave israel and deep sea records indicating the large spatial scale of the climate oscillations the signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western europe an important site in human cultural evolution we also find evidence for a long phase of extremely cold climate in southwest france between 61 2 0 6 and 67 4 0 9 kyr ago

comment on maximilian hansen denis scholz bernd r schone christoph spotl simulating speleothem growth in the laboratory determination of the stable isotope fractionation δ13c and δ18o between h2o dic and caco3 chemical geology 509 2019 20 44 abstract in this comment it is shown that analysis of the fractionation constants of the dic describing the enrichment of 13c and 18o along the flow path of a thin water layer flowing down an inclined marble plate precipitating calcite in analogy to precipitation to speleothems enables one to decide whether the rayleigh distillation model or the kinetic model is valid appropriate analysis of etot values for carbon and oxygen as reported by hansen et al 2019 reveals the validity of the kinetic model and allows determining the constants ekin and this is in contrast to findings of hansen and coauthors and gives a deeper understanding of the meaning of kinetic fractionation during precipitation of calcite

oxygen isotope fractionation between calcite and fluid as a function of growth rate and temperature an in situ study the 18o content of carbonates expressed as 18o is widely used in paleothermometry yet it is clear from comparison of experimental results and natural carbonate samples that chemical isotopic equilibrium is not always achieved in nature this observation underscores the importance of exploring possible effects of growth rate on isotopic fractionation which is the focus of this study in situ secondary ion mass spectrometry sims analyses of 18o were performed on single crystals of experimentally grown calcite the change in growth rate v over time within each crystal was monitored by addition of multiple rare earth element ree spikes into the fluid from which the calcite grew the values of 18o in bulk calcites and experimental fluids were measured by stable isotope ratio mass spectrometers the average sims 18o overlaps with those determined by conventional mass spectrometry within analytical uncertainty the fractionation factor expressed as 18o approaches its equilibrium value in slowly grown calcites v 0 02 nm s and decreases by 1 5 with increasing growth rate from 10 3 to 0 34 nm s here 18o 103 ln 18o and 18o 18o 16o calcite 18o 16o fluid our results provide the first in situ evidence that under equilibrium conditions 18o may be depleted in the near surface region of calcite relative to the bulk crystal lattice and that this 18o depleted zone can be captured during rapid crystal growth crystal growth rate is therefore a potentially important consideration when using 18o in natural carbonates as a proxy for ocean and terrestrial temperature

holocene climate variability in central germany and a potential link to the polar north atlantic a replicated record from three coeval speleothems here we present high resolution trace element and stable isotope records from three coeval holocene stalagmites from the herbstlabyrinth cave system central germany all stalagmites were precisel