modification and preservation of environmental signals in speleothems speleothems are primarily studied in order to generate archives of climatic change and results have led to significant advances in identifying and dating major shifts in the climate system however the climatological meaning of many speleothem records cannot be interpreted unequivocally this is particularly so for more subtle shifts and shorter time periods but the use of multiple proxies and improving understanding of formation mechanisms offers a clear way forward

effects of regolith megaregolith insulation on the cooling histories of differentiated asteroids the cooling histories and in particular the core cooling rates of differentiated asteroids are calculated employing a variety of thermal conductivity structures in order to simulate the potential insulating effects of regolith and megaregolith brecciated impact rubble layers the regolith is assumed to have thermal conductivity 0 005 the unbrecciated mantle conductivity and its thickness in our most typical model is assumed to be 0 003 the parent body radius the megaregolith if present is assumed to have thermal conductivity 0 1 that of unbrecciated mantle we find that a combination of relatively thick megaregolith and regolith can potentially reduce the core cooling rate by more than a factor of 10 below the rate predicted by models with conventional thermal conductivity structure for any given measured cooling rate the radius implied for the parent asteroid can potentially be reduced by a factor of 5 from the radius predicted by models with conventional thermal conductivity structure realistically the regolith and megaregolith thicknesses required to engender these extreme effects were probably seldom generated except perhaps within the largest asteroids where even if generated they would quickly be reduced by compaction and sintering nonetheless our results for models with plausible regolith and megaregolith thicknesses indicate that most of the iron meteorites and the pallasites probably formed in relatively small r less than 50 km parent bodies we have parameterized our results so that effects of intermediate configurations can readily be calculated the parameterization also facilitates evaluation of additional variables e g the initial temperature the concentrations of long lived radioactive heat sources etc albeit these variables are far less crucial than the thermal conductivity structure our results indicate that the insulation of even a thin regolith causes metallalographic cooling rates to be relatively uniform and practically independent of depth within a given asteroid stochastic differences in cratering regolith production histories may have engendered radically different cooling rates from asteroids of similar radius or similar cooling rates from asteroids of different radius

comparative stable isotope geochemistry of ni cu zn and fe in chondrites and iron meteorites high precision ni isotopic variations are reported for the metal phase of equilibrated and unequilibrated ordinary chondrites carbonaceous chondrites iron meteorites mesosiderites and pallasites we also report new zn and cu isotopic data for some of these samples and combine them with literature fe cu and zn isotope data to constrain the fractionation history of metals during nebular vapor solid and planetary metal sulfide silicate phase changes the observed variations of the 62ni 58ni 61ni 58ni and 60ni 58ni ratios vary linearly with mass difference and define isotope fractionation lines in common with terrestrial samples this implies that ni was derived from a single homogeneous reservoir while no 60ni anomaly is detected within the analytical uncertainties ni isotopic fractionation up to 0 45 per mass difference unit is observed the isotope compositions of ni and zn in chondrites are positively correlated we suggest that in ordinary chondrites exchange between solid phases in particular metal and silicates and vapor followed by mineral sorting during accretion are the main processes controlling these isotopic variations the positive correlation between ni and zn isotope compositions contrasts with a negative correlation between ni and zn and cu isotope compositions which when taken together do not favor a simple kinetic interpretation the observed transition element similarities between different groups of chondrites and iron meteorites are consistent with the genetic relationships inferred from oxygen isotopes iiia pallasites and iva l chondrites copper is an exception which we suggest may be related to separate processing of sulfides either in the vapor or during core formation

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

towards radiocarbon calibration beyond 28 ka using speleothems from the bahamas we present a new speleothem record of atmospheric 14c between 28 and 44 ka that offers considerable promise for resolving some of the uncertainty associated with existing radiocarbon calibration curves for this time period the record is based on a comprehensive suite of ams 14c ages using new low blank protocols and u th ages using high precision mc icpms procedures atmospheric 14c was calculated by correcting 14c ages with a constant dead carbon fraction dcf of 22 7 5 9 based on a comparison of stalagmite 14c ages with the intcal04 reimer et al 2004 calibration curve between 15 and 11 ka the new 14c speleothem record shows similar structure and amplitude to that derived from cariaco basin foraminifera hughen et al 2004 2006 and the match is further improved if the latter is tied to the most recent greenland ice core chronology svensson et al 2008 these data are however in conflict with a previously published 14c data set for a stalagmite record from the bahamas gb 89 24 1 beck et al 2001 which likely suffered from 14c analytical blank subtraction issues in the older part of the record the new bahamas speleothem 14c data do not show the extreme shifts between 44 and 40 ka reported in the previous study beck et al 2001 causes for the observed structure in derived atmospheric 14c variation based on the new speleothem data are investigated with a suite of simulations using an earth system model of intermediate complexity data model comparison indicates that major fluctuations in atmospheric 14c during marine isotope stage 3 is primarily a function of changes in geomagnetic field intensity although ocean atmosphere system reorganisation also played a supporting role

a stalagmite record of holocene indonesian australian summer monsoon variability from the australian tropics oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave kni 51 located in the eastern kimberley region of tropical western australia represent the first absolute dated high resolution speleothem record of the holocene indonesianeaustralian summer monsoon iasm from the australian tropics stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic holocene iasm which strengthened in the early holocene decreased in strength by 4 ka with a further decrease from w2 to 1 ka before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka the relationships between the kni 51 iasm reconstruction and those from published speleothem time series from flores and borneo in combination with other data sets appear largely inconsistent with changes in the position and or organization of the intertropical convergence zone itcz instead we argue that the el nino southern oscillation enso may have played a dominant role in driving iasm variability since at least the middle holocene given the muted modern monsoon rainfall responses to most el nino events in the kimberley an impact of enso on regional monsoon precipitation over northwestern australia would suggest non stationarity in the long term relationship between enso forcing and iasm rainfall possibly due to changes in the mean state of the tropical pacific over the holocene

ams carbon 14 dating of microbial carbonates in holocene coral reefs western luzon philippines abstract microbial carbonates microbialites occurred in the holocene coral reefs at paraoir the philippines these microbialites appeal grayish to buff in color with a stromatolitic to thrombolitic structures and encrust on corals directly or on a thin layer of calcareous red algae or encrusting foraminifera that covered the corals first the microbialites only occur in the lower earlier parts of the holocene reef sequence where heliopora coerulea dominated no microbial carbonates were observed in the upper younger part of the holocene reefs that is interpreted to grow in water depth shallower than 6 m on the basis of coral community samples of microbial carbonate and associated coral were dated by ams 14 c the results show that the microbialites formed about 10 to 7 5 kyr bp nearly coeval to or a few hundred years younger than the corals on which the microbialites encrusted ams 14 c ages of samples recovered at reef margins are consistent to 230 th ages of corals associated with the microbialites but those recovered in the back reef are much older that the previously published 230 th ages of corals and interpreted to be reworked into the backreef it is proposed that the microbialites at paraoir formed in early holocene on reef slope when the deglacial sea level was rising rapidly after 7 5 kyr bp when the sea level rise slowed down and coral reefs caught up with sea level the condition became favorable to corals prospered in shallow water and no longer suitable for microbialite formation

elevated and variable values of 13c in speleothems in a british cave system 13c isotope variations in speleothems have been investigated for samples from the british isles where plants which use the hatch slack or c4 photosynthetic pathway are not present the range of 13c expected in speleothem carbonate formed in isotopic equilibrium with soil co2 derived from the overlying c3 vegetation should thus fall in the range 12 to 6 forty one actively growing speleothem samples from low discharge sites were analysed from stump cross caverns yorkshire england ten percent have 13c greater than 6 in addition a large range of 13c was observed 8 06 1 38 a 1 variability of 17 with adjacent samples having 13c differing by a maximum of 4 74 similar findings were obtained from a review of analyses of late quaternary speleothem samples from the british isles with 75 of flowstone samples and 57 of high flow stalagmite samples exhibiting elevated 13c three possible processes are proposed as possible causes of elevated 13c in speleothems firstly fractionation may occur between the stalactite and stalagmite due to evaporation or degassing secondly degassing of the groundwaters may have occurred within the aquifer before reaching the cave void allowing release of some co2 from the water whilst remaining saturated in calcium finally the elevated 13c may be due to short water residence times in the soil such that equilibrium between soil water and soil co2 is not reached evidence presented here demonstrates that any one of these mechanisms may be important in the karst areas of the british isles caution is needed before interpreting the 13c signal within speleothems in terms of palaeovegetation

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

stable isotope stratigraphy of holocene speleothems examples from a cave system in rana northern norway high precision tims u series dates and continuous stable oxygen and carbon isotope profiles of a 4000 year stalagmite record from rana northern norway are presented and compared with data from two other speleothems from the same cave the dating results yield ages from 3875 34 to 296 3 years before ad2000 with 2s errors from 0 5 to 1 the overall growth rate is 35 mm ka corresponding to a temporal resolution of 29 years mm the stalagmite is tested for isotopic equilibrium conditions where all hendy tests except one indicate isotopic equilibrium or quasi equilibrium deposition both the stable oxygen and carbon isotope records reveal a strong and abrupt enrichment in the near top measurements this corresponds in time to the opening of a second cave entrance in the late 1960s which caused changes in the cave air circulation the stable oxygen isotope signal is enriched compared to the modern value over the last 300 years indicating a negative response to temperature changes likewise the stable carbon isotope record is enriched in this period however both of the stable isotope records are shown to be significantly enriched compared to the isotope ranges displayed by other stalagmites in the same cave and this questions the reliability of the proxy records derived from the presented stalagmite still a general good correspondence of large scale fluctuations is found between the three stable oxygen isotope records from this cave the stable carbon isotope records show large variations within the cave and are believed to be governed by soil zone conditions percolation pathways and possibly driprates q 2001 elsevier science b v all rights reserved

climatic and local effects on stalagmite δ13c values at lianhua cave china abstract carbon isotopes in speleothems may serve as indicators of vegetative change climatic conditions and karst processes in many recent studies of chinese stalagmites however carbon isotopes have often been neglected or underutilized in interpreting paleoenvironments here we present a continuous decadal scale 13 c record 819 measurements of the mid to late holocene from a precisely dated 10 230 th dates aragonite stalagmite from lianhua cave hunan province china compared to coeval stalagmites from other chinese caves the average 13 c value 3 6 of stalagmite a1 is higher by 2 7 variations in the 13 c values 0 1 to 6 0 reflect changes in both vegetative productivity and inorganic processes which respond to climatic processes the 13 c record of stalagmite a1 can be subdivided into three intervals 1 warm humid stage 6 6 to 3 8 ka 2 transitional stage 3 8 to 1 6 ka and 3 cool arid stage 1 6 ka to present comparisons with other stalagmite and paleoclimatic records demonstrate that these intervals are generally consistent with changes in regional vegetation and climatic conditions

a high resolution record of holocene climate change in speleothem calcite from cold water cave northeast iowa high precision uranium thorium mass spectrometric chronology and 18o 13c isotopic analysis of speleothem calcite from cold water cave in northeast iowa have been used to chart mid holocene climate change significant shifts in 18o and 13c isotopic values coincide with well documented holocene vegetation changes temperature estimates based on 18o 16o ratios suggest that the climate warmed rapidly by about 3 c at 5900 years before present and then cooled by 4 c at 3600 years before present initiation of a gradual increase in 13c at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present

generation of a heavy mineral glacial indicator dispersal train from a diabase sill nipigon region northwestern ontario the heavy clinopyroxene mineral pigeonite forms a glacial indicator dispersal train originating from diabase intrusions in the nipigon region of northwestern ontario analysis and interpretation of the pigeonite dispersal pattern adjacent to the up ice portion of the diabase provides a number of insights into the nature of glacial erosion of bedrock and the generation of heavy mineral dispersal trains bedrock erosion and entrainment rates at the time of pigeonite dispersal train formation were high 3 14 mm a 1 suggesting that bedrock erosion was rapid yet spatially and temporally restricted contrasting erosion rates between the diabase and surrounding greenstone lithologies suggests that modern shield topography is not an assemblage of equilibrium bedforms with respect to the ice sheet this agrees with hypothesized low total erosion of shield bedrock during the pleistocene pigeonite grain size coarsens over the diabase source indicating that most of the pigeonite was quarried from outcrops as coar

hf w sm nd and rb sr isotopic evidence of late impact fractionation and mixing of silicates on iron meteorite parent bodies abstract we report the first sm nd and rb sr isotopic analyses of silicate inclusions in four iie iron meteorites miles weekeroo station a and b and watson we also report the hf w isotopic composition of a silicate inclusion from watson and 182 w 184 w of the host feni metal in all four iies the host metal in watson has a negative w value 2 21 0 24 similar to or higher than other iron meteorites 1 35 and consistent with segregation of metal from silicate early in solar system history however the large silicate inclusion in the watson iie iron yielded a chondritic w value 0 50 0 55 thus indicating a lack of equilibration with the feni host within the practical lifetime of activity of the parent 182 hf 50 ma one of the silicate inclusions in miles is roughly chondritic in major element composition has a present day nd of 10 3 relatively non radiogenic 87 sr 86 sr 0 714177 13 and a t chur age of 4270 ma two silicate inclusions from weekeroo station and one from watson exhibit fractionated sm nd and rb sr ratios and more radiogenic 87 sr 86 sr 0 731639 12 to 0 791852 11 and non radiogenic nd values 5 9 to 13 4 the silicate inclusion in watson has a t chur age of 3040 ma in agreement with previously determined 4 he and 40 ar gas retention ages indicative of a late thermal event a later event is implied for the two silicate inclusions in weekeroo station which yield indistinguishable t chur ages of 698 and 705 ma silicate inclusions in iie iron meteorites formed over a period of 3 billion yr by impacts involving an h chondrite parent body and an feni metal parent body the lile enriched nature of some of these silicates suggests several stages of melting mixing and processing however there is little evidence to suggest that the silicates in the iie irons were ever in equilibrium with the host feni metal

the cosmic molybdenum ruthenium isotope correlation dauphas et al astrophys j 565 2002 640 644 reported molybdenum isotopic anomalies in differentiated and bulk primitive meteorites it is shown here that these isotopic anomalies correlate with one another in exactly the way expected from nucleosynthesis theory if different regions of the nebula received different contributions of s process matter synthesized in lowmass agb stars furthermore when bulk measurements are grouped by meteorite class the molybdenum isotopic anomalies correlate with the ruthenium isotopic anomalies recently reported by chen et al lunar planet sci xxxiv 2003 1789 again indicating a heterogeneous distribution of s process matter as molybdenum is only moderately siderophile most of the molybdenum presently in the mantle was delivered before the completion of core formation in contrast because ruthenium is highly siderophile nearly all of the mantle ruthenium was delivered by a late veneer after the end of core formation thus the fact the silicate earth lies on the mo ru cosmic correlation supports the idea that the earth accreted homogeneously stated otherwise the feeding zone of the earth did not change drastically with time as both the bulk of the earth and the late veneer accreted from material from the same mo ru isotopic reservoir d 2004 elsevier b v all rights reserved

timing and dynamics of the last deglaciation from european and north african δ13c stalagmite profiles comparison with chinese and south hemisphere stalagmites abstract the last deglaciation and its climatic events such as the bolling allerod ba and the younger dryas yd have been clearly recorded in the 13 c profiles of three stalagmites from caves from southern france to northern tunisia the three 13 c records dated by thermal ionization mass spectrometric uranium thorium method tims show great synchroneity and similarity in shape with the chinese cave 18 o records and with the marine tropical records leading to the hypothesis of an in phase between 15 5 and 16 ka 0 5 ka postglacial warming in the northern hemisphere up to at least 45 n the ba transition appears more gradual in the speleothem records than in the greenland records and the allerod seems warmer than the bolling showing here close similarities with other marine and continental archives a north south gradient is observed in the ba trend it cools in greenland and warms in our speleothem records several climatic events are clearly recognizable a cooler period at about 14 ka older dryas od the intra allerod cold period at about 13 3 ka the yd cooling onset between 12 7 and 12 9 0 3 ka similar to the ba the yd displays a gradual climate amelioration just after its onset at 12 75 0 25 ka up to the preboreal and is punctuated by a short climatic event at 12 15 ka even though the southern hemisphere stalagmite records seem to indicate that the postglacial warming started about 3 ka 1 8 ka earlier in new zealand 41 s and about 1 to 2 ka earlier in south africa 24 1 s large age uncertainties essentially due to slow growth rates make the comparison still perilous the overall 13 c speleothem record seems to follow a baseline temperature increase controlled by the increase in insolation and punctuated by cold events possibly due to the n america freshwater lake discharges

the δ18o and δ13c records in an aragonite stalagmite from furong cave chongqing china a 2000 year record of monsoonal climate abstract a 7 cm long aragonite stalagmite fr0510 1 from furong cave chongqing was dated by 210pb and 230th methods revealing a 2000 year record of climate history under the influence of the east asian monsoon the fr0510 1 record resembles dongge cave da record on 10 100 year scales but quite different from the wanxiang cave wx42b record indicating that while stalagmite 18o record represents local regional moisture change spatial variability of the monsoonal rainfall over eastern china must take into account during the past 2000 years climate in chongqing was relatively wet in the intervals of 50 bc ad 250 ad 1150 1450 and ad 1600 1950 and relatively dry during the periods of ad 250 1150 and ad 1450 1600 dry conditions were prevailing over the medieval warm period whereas wet climates were dominant during the most time of the little ice age in chongqing area

nickel isotopic studies in meteorites abstract we have analyzed the nickel isotopic composition of meteoritic materials by high precision mass spectrometry the samples analyzed include almost all meteorite types for which large isotopic anomalies have been reported for oxygen silver magnesium and titanium these samples are c 1 c 3 l ll h and e chondrites ivb irons eagle station pallasite and inclusion matrix and whole rock samples of the allende meteorite the result is that we have not found any anomaly for nickel isotopic compositions within our accuracy of 0 7 for 61 ni 60 ni 0 4 0 08 for 62 ni 60 ni and 1 1 5 for 64 ni 60 ni

oxygen and carbon isotopic systematics of aragonite speleothems and water in furong cave chongqing china abstract to understand oxygen and carbon stable isotopic characteristics of aragonite stalagmites and evaluate their applicability to paleoclimate the isotopic compositions of active and fossil aragonite speleothems and water samples from an in situ multi year october 2005 july 2010 monitoring program in furong cave located in chongqing of china have been examined the observations during october 2005 june 2007 show that the meteoric water is well mixed in the overlying 300 500 m bedrock aquifer reflected by relatively constant 18o 0 11 0 14 1 of drip waters in the cave which represents the annual status of rainfall water active cave aragonite speleothems are at oxygen isotopic equilibrium with drip water and their 18o values capture the surface water oxygen isotopic signal aragonite to calcite transformation since the last glaciation is not noticeable in furong stalagmites our multi year field experiment approves that aragonite stalagmite 18o records in this cave are suitable for paleoclimate reconstruction with high u 0 5 7 2 ppm and low th 20 1270 ppt the furong aragonite stalagmites provide very precise chronology as good as 20s yrs 2 of the climatic variations since the last deglaciation the synchroneity of chinese stalagmite 18o records at the transition into the bolling allerod t ba and the younger dryas from furong hulu and dongge caves supports the fidelity of the reconstructed east asian monsoon evolution however the furong record shows that the cold older dryas od occurred at 14 0 thousand years ago agreeing with greenland ice core 18o records but 200 yrs younger than that in the hulu record the od age discrepancy between chinese caves can be attributable to different regionally climatic environmental conditions or chronological uncertainty of stalagmite proxy records which is limited by changes in growth rate and subsampling intervals in absolute dating seasonal dissolved inorganic carbon 13c variations of 2 3 in the drip water and 5 7 in the pool and spring waters are likely attributed to variable degrees of co2 degassing in winter and summer the variable 13c values of active deposits from 11 to 0 could be caused by kinetically mediated co2 degassing processes the complicated nature of pre deposition kinetic isotopic fractionation processes for carbon isotopes in speleothems at furong cave require further study before they can be interpreted in a paleoclimatic or paleoenvironmental context

carbon isotopic records from stalagmites and the signification of paleo ecological environment in the area of guangxi guizhou china high resolution carbon isotopic records in millennial centennial and decadal timescales from three stalagmites from three different caves under a similar monsoon climate in guangxi guizhou china provided detailed information on the paleo ecological environmental conditions in the past 15 000 years the results indicate that during the glacial period or cold dry period such as heinrich event h1 and younger dryas event karst development was poor as was pedogenesis c3 vegetation didn t grow well resulting in c4 plants dominating and with heavy 13c values in stalagmites in a warm humid stage c3 vegetation grew well and predominated with negative 13c values the 13c records from stalagmites could be indicative of sensitive vegetation changes and reflective of climate changes in precipitation temperature etc the 13c records may also be used to distinguish different effects from nature or human activity particularly since the late holocene human activities have increased disturbances to environment even more than natural factors forest vegetation was destroyed c4 plants became dominant and rock desertification was aggravated because of severe water and soil loss all resulting in sharply increasing 13c values of stalagmites that are heavier than pre middle holocene 13c values

comparison of speleothem δ18o records from eastern china with solar insolation ice core and marine records similarities and discrepancies on different time scales abstract four 230 th dated 18 o records in three stalagmites one from dragon spring stalagmite l12 and two from golden lion caves stalagmites jsd 01 and jsd 02 located in libo county southeast guizhou china are presented these records cover age ranges of 0 75 2 ka late holocene 9 9 6 ka early holocene 87 9 88 2 ka and 93 8 95 2 ka late pleistocene they fit well with the published dongge cave record from the same area where the climate has been much influenced by the east asian monsoon the agreement reinforces the role of stalagmite 18 o as a proxy for regional precipitation or monsoon strength on millennial or longer time scales the 18 o record of dongge cave resembles those of sanbao cave in hubei and hulu cave in jiangsu of china the matching of these records with the northern hemisphere solar insolation variations points to the importance of insolation in affecting the east asian summer monsoon strength on 10 3 10 4 yr scales while the monsoon variations as depicted by these chinese speleothem 18 o records show a strong coupling to insolation s precession component 23 kyr period other climate records of global significance extracted from oceanic and terrestrial deposits e g deep sea sediments polar ice cores cave deposits from non monsoonal regions do not although the latter records were thought to be also influenced by the large changes in global ice volume they show variations modulated chiefly by insolation due to earth s eccentricity change 100 kyr period it is hypothesized that precession variations control the distribution of solar insolation between the northern and southern hemispheres the itcz position and the modulation of low latitude summer monsoon variability increasing rainfall and or summer winter precipitation ratio brought about by strong summer monsoons leads to 18 o depletion in stalagmites grown in monsoonal regions one should use caution to compare speleothem 18 o records with other paleoclimate records reflecting pleistocene ice ages on 10 4 10 5 yr timescales

high precision and high resolution carbonate 230th dating by mc icp ms with sem protocols abstract to facilitate the measurement of u th isotopic compositions suitable for high precision and high resolution 230th dating of coral and speleothem carbonates secondary electron multiplier sem protocol techniques for multicollector inductively coupled plasma mass spectrometry mc icp ms have been developed the instrumental sensitivities are 1 2 with a precision of 1 2 2 for abundance determination of 50 200 fg 234u 1 4 ng 238u or 230th this method features chemistry refinements improvements to procedural and instrumental blanks spectral inference reductions and careful consideration of non linear sem behavior measurement consistency of this mc icp ms combined with previous mass spectrometric results on u th standards and a variety of carbonates demonstrates the validity of the sem protocol method for fossil corals a routine u th isotopic determination at permil level precision requires only 10 50 mg of carbonate as little as 200 mg of young coral with an age of less than 20 yr can be dated with a precision of 0 3 0 8 yr about 20 200 mg speleothem samples with sub ppm to ppm u are required to earn a 5 precision on ages from 5 to 100 kyr requirement of small sample size 10 100s mg carbonate can permit high temporal resolution to date speleothems with slow growth rates i e 1 10 mm kyr this high precision 230th chronology is critical to accurately establish age models date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography the u th isotopic determination techniques described here can also be applied to different environmental samples such as waters rocks and sediments

interhemispheric anti phasing of rainfall during the last glacial period abstract we have obtained a high resolution oxygen isotopic record of cave calcite from caverna botuvera 27 13 s 49 09 w southern brazil which covers most of the last 36 thousand years ka with an average resolution of a few to several decades the chronology was determined with 46 u th ages from two stalagmites tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change we interpret our record in terms of meteoric precipitation changes hence the variability of south american monsoon sam intensity the oxygen isotopic profile broadly follows local insolation changes and shows clear millennial scale variations during the last glacial period with amplitudes as large as 3 but with smaller centennial scale shifts 1 during the holocene the overall record is strikingly similar to but strongly anti correlated with a number of records from the northern hemisphere we compared our record to other precisely dated contemporaneous records from hulu cave eastern china minima in 18o wet periods intense sam at our site are synchronous with maxima in 18o dry periods weak east asian monsoon eam in eastern china within precise dating errors and vice versa this anti phased precipitation relationship between two low latitude locations may be interhemispheric in extent based on comparison with records from other sites precipitation anti phasing may be related to north south shifts in the mean position of the intertropical convergence zone itcz and asymmetry in hadley circulation in two hemispheres associated not with seasonal changes as observed today but with millennial scale climate shifts the millennial scale atmospheric see saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor s greenhouse properties

fossil records of high level of 60fe in chondrules from unequilibrated chondrites abstract the short lived now extinct nuclide sln 60fe which decays to 60ni with a half life of 2 62 ma is uniquely of stellar origin hence its solar system initial abundance yields information about the source of slns and the astrophysical environment in which the solar system was born only a few chondrules 19 from unequilibrated ordinary chondrites have reported resolved 60ni excesses using in situ secondary ion mass spectrometry implying fe 60 fe 56 0 6 10 7 in the early solar system and among these very few 3 have higher excesses implying fe 60 fe 56 7 10 7 mishra et al 2010 mishra and goswami 2014 telus et al 2012 at variance multi collector inductively coupled plasma mass spectrometer studies of bulk samples and mineral separates from differentiated meteorites angrites achondrites and chondrules suggest a low abundance of 60fe 56fe of 1 4 10 8 which would rule out the need for an external seeding of the early solar with stellar 60fe quitte et al 2011 tang and dauphas 2012 two semarkona chondrules and one efremovka chondrule analyzed in the present study have mass fractionation corrected excess of up to 75 permil and give 60fe isochrons with initial 60fe 56fe ratios of 7 8 3 7 10 7 3 8 1 6 10 7 and 2 2 1 1 10 7 2 for efremovka ch 1 semarkona ch 12 and semarkona ch j5 respectively the higher values of 60fe 56fe ratios seen in the chondrules of these least altered meteorites samples concur with and lend greater credence to the suggestion of a massive star as the source of 60fe and possibly of other short lived nuclides to the early solar system however no definitive explanation e g sample bias effects of metamorphism 60fe heterogeneity to the apparent disagreement with studies of bulk chondrules and chondrule fragments has been found

182w and 187re 187os systematics of iron meteorites chronology for melting differentiation and crystallization in asteroids w isotopic compositions measured by n tims in five iron meteorite groups are used in conjunction with 187re 187os isotopic data to constrain the timing of metal segregation and crystallization respectively in the iron meteorite parent bodies fractionation of the parent isotope 182hf half life 9 2 ma from the daughter 182w likely occurred during segregation of metal from silicate in the iron meteorite parent bodies if w isotopic equilibrium was achieved between silicate and metal during metal segregation then the w isotopic compositions in the irons should record the timing of this event samples were taken from the five largest iron meteorite groups including the four magmatic groups iiab iiiab iva and ivb and the nonmagmatic iab iiicd group together these groups comprise approximately 90 by weight of iron meteorites classified so far with the exception of the iva group the groups have well defined 187re 187os isochron ages which are interpreted as the time of crystallization of the metal of their parent bodies within each magmatic group samples that crystallized both early and late in the sequence of each core were analyzed to evaluate possible evolution of the w isotopic composition during crystallization all the samples examined display very similar w values within a narrow range of compositions between 5 1 and 3 1 witzation began less than a few percent of additional metal was segregated to the cores moreover the average w values for the five groups have no resolvable difference ranging from 4 08 0 69 iva to 3 30 0 15 iab iiicd these data indicate that all of the iron meteorite parent bodies underwent metal segregation within 5 ma of each other apparently independent of their composition size and time of crystallization of the metal in all groups except the iiiab group there is a resolvable time interval between the timing of metal segregation as constrained by the w isotopic data and the initiation of core crystallization as given by the re os isotopic systematics

δ18o δ13c elemental content and depositional features of a stalagmite from yelang cave reflecting climate and vegetation changes since late pleistocene in central guizhou china abstract a 13 5 cm long stalagmite from yelang cave in central guizhou provides another example of ams 14 c dating on stalagmites which are not suitable for 230 th u dating due to very low u content and low 230 th 232 th ratio this record duplicates the published stalagmite record of 20120824 13 from the same cave zhao et al 2015 not only on 18 o and 13 c records but also on major growth hiatuses facilitating speleothem 18 o and 13 c as climate and vegetation proxies respectively based on the two stalagmite records climate and vegetation conditions can be deciphered as follow relatively cool and dry climates with c4 dominated plants during 33 4 36 ka very cold and dry climates with poor vegetation coverage during the last glacial maximum cold and dry climates with poor vegetation during younger dryas warming and very wet climates with the best vegetation mainly c3 plants coverage during 9 11 5 ka bp corresponding to a maximum insolation drying climate and decreased vegetation intensity from 9 ka to 8 ka relatively good vegetation coverage during 5 6 ka the summer monsoon strength decreased from 5 ka to 1 5 ka bp but increased during the medieval warm period to produce wet climates and abundant vegetation and strongly decadal variations in moisture budget and strong deforestation due to human impact during the past 600 years high fe mn and al contents from detritus caused dark bands near the hiatuses strong positive correlation of mg and sr with high mg sr values 23 in this study reflects source control on the mg and sr variations so that mg sr is not a function of cave temperature in such a case for pure calcite without detrital influence mg sr may register changes in cave temperature with higher mg sr indicating warmer temperature this study calls for the attention to find out climatic conditions in central guizhou during the bolling allerod warming and the middle holocene 6 8 ka intervals because of lacking deposition during these intervals in yelang cave using stalagmite 18 o alone to decipher climatic conditions on decadal to millennial scales needs to consider multiple factors such as amount source and temperature effects on the 18 o

timing and climatic impact of greenland interstadials recorded in stalagmites from northern turkey a 50 kyr long exceptionally well dated and highly resolved stalagmite oxygen 18o and carbon 13c isotope record from sofular cave in northwestern turkey helps to further improve the dating of greenland interstadials gi 1 and 3 12 timing of most gi in the sofular record is consistent within 10 to 300 years with the iconic hulu cave record larger divergences 500 years between sofular and hulu are only observed for gi 4 and 7 the sofular record differs from the most recent ngrip chronology by up to several centuries whereas age offsets do not increase systematically with depth the sofular record also reveals a rapid and sensitive climate and ecosystem response in the eastern mediterranean to gi whereas a phase lag of 100 years between climate and full ecosystem response is evident finally results of spectral analyses of the sofular isotope records do not support a 1 470 year pacing of gi

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

microsegregation rates of liquid fe ni s metal in natural silicate metal systems a combined experimental and numerical study we present results of an image based numerical model aimed at quantifying the microsegregation and flow of liquid metal in meteorites prior to the onset of silicate melting the sample material is the h6 chondrite kernouve the model utilizes the observed geometry of two distinct chondrite textures associated with grain scale melt segregation in the following 1 the undeformed natural state and 2 during deformation and partial melting under controlled laboratory conditions the numerical simulations recover liquid metal segregation rates of 10 6 to 10 4 m s 1 for matrix permeabilities k of 10 12 k 10 10 m2 and pressure gradients of 1 and 104 pa m 1 the velocity flow field is position dependent across the sample reflecting initial grain scale heterogeneity and anisotropy in the spatial distribution of metal prior to melting in addition to porous flow we use a coupled brinkman navier stokes solution to quantify liquid metal segregation through deformation induced microscale veins melt flow velocities in veins are several orders faster than matrix flow implying that a combination of porous grain scale flow feeding into a network of small scale cracks and veins during the initial stages of partial melting may be an extremely efficient mechanism for segregating liquid metal from silicate matrix in planetesimals undergoing deformation this mechanism may be temporary and confined only to the earliest stages of melt microsegregation because with increasing temperature the onset of silicate melting shuts off liquid metal segregation by creeping matrix flow the point at which this occurs marks an important transition in the mode and style of internal differentiation

a 6000 year high resolution climatic record from a stalagmite in xiangshui cave guilin china middle to late holocene palaeoclimate change has been reconstructed at high resolution by the analysis of the carbon and oxygen isotopes from a thermal ionization mass spectrometric tims u th dated stalagmite from xiangshui cave near guilin guangxi province china the carbon and oxygen isotopic records from the stalagmite suggest that changes in the asian monsoon since the middle holocene 6000 bp can be divided into two periods 1 an interval from 6000 to 3800 bp when a strong east asian summer monsoon gradually weakened and climate was relatively warm and humid 2 a cool period from 3800 to 373 bp when the east asian summer monsoon was relatively weak and the winter monsoon was probably relatively strong this cooler interval was interspersed with a number of short warm periods a this interpretation is largely based upon the general increase in 6180 values of the stalagmite between 6000 and 3800 bp and shifts in 6180 about a relatively heavy mean value between 3800 and 373 bp the 6000 to 380

spatial variations of monsoonal rain in eastern china instrumental historic and speleothem records abstract we select four caves and their nearby cities in the monsoonal region of china for studying the relationships among precipitation temperature summer monsoon intensity and stalagmite 18o the instrumental historic and stalagmite 18o records from these areas show strong spatial disparities on annual to decadal scales so that climatic conditions in a single location cannot represent these of the entire eastern china on time scales

changes in climate and vegetation of central guizhou in southwest china since the last glacial reflected by stalagmite records from yelang cave abstract two stalagmites 6 cm and 18 cm long from yelang cave 26 2 28 n 105 44 11 e in central guizhou of china have been dated by icp ms 230th u 210pb and ams 14c dating methods low u but high th contents in the young stalagmites were difficult to apply 230th u dating instead ams 14c dating solved the chronological problem of these stalagmites both stalagmites had fast growth rates during holocene optimum and the last 600 years but absent growth between 4 and 8 ka the 18o record of stalagmite 20120824 13 agrees well with the dongge 18o records on centennial or longer scales showing dry climates during the last glacial maximum lgm and younger dryas and wet climates during holocene optimum following the solar insolation trend the summer monsoon strength decreased from 4 12 ka to 1 5 ka but increased during the medieval warm period to produce wet climates and abundant vegetation in the study area the 18o record during the last 600 years exhibits strongly decadal variations twelve light 18o excursions on decadal scales during the last 600 years can be identified agreeing with the local dry wet index record the pacific decadal oscillation pdo strongly affects decadal variability of the moisture budget in the study area with cold pdo la nina condition in favor of stronger easm and wet climates the 13c record indicates that natural vegetation in the study area was strongly destroyed by human activity after the reign of emperor yong zheng ad 1722 1735 of qing dynasty since then the karst desertification in central guizhou has been strongly developed due to rapidly increased population and land use

isotopic characterization of rapid climatic events during ois3 and ois4 in villars cave stalagmites sw france and correlation with atlantic and mediterranean pollen records abstract we present a new mid latitude speleothem record of millennial scale climatic variability during ois3 from the villars cave that combined with former published contemporaneous samples from the same cave gives a coherent image of the climate variability in sw france between 55 ka and 30 ka the 0 82 m long stalagmite vil stm27 was dated with 26 tims u th analyses and its growth curve displays variations that are linked with the stable isotopes both controlled by the climatic conditions it consists in a higher resolved replicate of the previously published vil stm9 and vil stm14 stalagmites where dansgaard oeschger do events have been observed the good consistency between these three stalagmites and the comparison with other palaoeclimatic reconstructions especially high resolution pollen records odp 976 from the alboran sea monticchio lake record from southern italy and the nearby md04 2845 atlantic ocean record permits to draw a specific climatic pattern in sw france during the ois3 and to see regional differences between these sites main features of this period are 1 warm events corresponding to greenland interstadials gis that are characterized by low speleothem 13 c high temperate pollen percentages warm temperatures and high humidity among these events gis 12 is the most pronounced one at villars characterized by an abrupt onset at 46 6 ka and a duration of about 2 5 ka the other well individualized warm event coincides with gis 8 which is however much less pronounced and occurred during a cooler period as shown by a lower growth rate and a higher 13 c 2 cold events corresponding to greenland stadials gs that are clearly characterized by high speleothem 13 c low temperate pollen abundance low temperature and enhanced dryness particularly well expressed during gs coinciding with heinrich events h5 and h4 the main feature of the villars record is a general cooling trend between the do 12 event 45 5 ka and the synchronous stop of the three stalagmites at 30 ka 1 with a first well marked climatic threshold at 41 ka after which the growth rate and the diameter of all stalagmites slows down significantly this climatic evolution differs from that shown at southern mediterranean sites where this trend is not observed the 30 ka age marks the second climatic threshold after which low temperatures and low rainfalls prevent speleothem growth in the villars area until the lateglacial warming that occurred at 16 5 0 5 ka this 15 ka long hiatus as the older villars growth hiatus that occurred between 67 4 and 61 ka are linked to low sea levels reduced ocean circulation and a southward shift of the polar front that likely provoked local permafrost formation these cold periods coincide with both low summer 65 n insolation low atmospheric co 2 concentration and large ice sheets development especially the fennoscandian

pt re os systematics of group iiab and iiiab iron meteorites the pt re os isotopic and elemental systematics of 13 group iiab and 23 group iiiab iron meteorites are examined as has been noted previously for iron meteorite groups and experimental systems solid metal liquid metal bulk distribution coefficients d values for both iiab and iiiab systems show dos dre dpt 1 during the initial stages of core crystallization assuming closed system crystallization the latter stages of crystallization for each core are generally characterized by dpt dre dos the processes governing the concentrations of these elements are much more complex in the iiiab core relative to the iiab core several crystallization models utilizing different starting parameters and bulk distribution coefficients are considered for the re os pair each model has flaws but in general the results suggest that the concentrations of these elements were dominated by equilibrium crystallization and subsequent interactions between solid metal and both equilibrium and evolved melts late additions of primitive metal to either core were likely minor or nonexistent the 187re 187os systematics of the iiab and iiiab groups are consistent with generally closed system behavior for both elements since the first several tens of ma of the formation of the solar system consistent with short lived chronometers the re os isochron ages for the complete suites of iiab and iiiab irons are 4530 50 ma and 4517 32 ma respectively and are similar to previously reported re os ages for the lower ni endmembers of these two groups both isochrons are consistent with but do not require crystallization of the entire groups within 10 30 ma of the initiation of crystallization the first high precision 190pt 186os isochrons for iiab and iiiab irons are presented the pt os isochron ages for the iiab and iiiab irons calculated using the current best estimate of the for 190pt are 4323 80 ma and 4325 26 ma respectively the re os and pt os ages do not overlap within the uncertainties the younger apparent ages recorded by the pt os system likely reflect error in the 190pt decay constant the slope from the pt os isochron is combined with the age from the re os isochron for the iiiab irons to calculate a revised of 1 415 10 12 a 1 for 190pt although additional study of this decay constant is still needed

climatic fluctuations during the lia and post lia in the kumaun lesser himalaya india evidence from a 400 y old stalagmite record this paper presents the first stable isotope delta o 18 and delta c 13 data of a similar to 400 years 1590 2006 ad long annual to decadal resolution speleothem record collected from the indian lesser himalaya the data show a variation from 2 7 to 5 9 parts per thousand in delta o 18 and 5 3 to 8 8 parts per thousand in delta c 13 the isotopic analyses indicate that the climate during this period can be divided into two stages a wet phase during the little ice age lia 1590 1850 ad and comparatively dry phase during the post lia after 1850 ad however the record also documents the minor dry events during the lia and a wet episode after the lia within the age uncertainty the dry spells during the lia are linked with the historical drought events in the indian subcontinent and similar latitudes the isotopic record is consistent with a number of previous studies in the areas influenced by the westerlies but appears to be conflicting to the regions dominated by the indian summer monsoon ism this may be due to the possible changes in the strength of westerlies in the study area and added by negative anomaly of north atlantic oscillation nao during the lia c 2012 elsevier ltd and inqua all rights reserved

climate and environmental changes during the past millennium in central western guizhou china as recorded by stalagmite zjd 21 abstract stalagmite zjd 21 12 3 cm long was collected from zhijin cave in zhijin county guizhou china its 210pb profile and seven 230th 234u dates indicate that the stalagmite has grown continuously for the past 1100 years the 18o record of zjd 21 indicates that 18o in the stalagmite was mainly influenced by rainfall amount and or summer winter rain ratio with lighter values corresponding to wetter climatic conditions and or more summer monsoonal rains the zjd 21 18o record suggests 1 dry warm climates during ad 950 1100 overlapping with most of the medieval warm period mwp in europe 2 strengthening of the summer monsoon from the mwp toward the beginning of the little ice age lia at ad 1250 3 relatively wet cold conditions occurred between ad 1250 and 1500 shown by relatively light 18o values 4 the summer monsoon intensity strongly declined referred by the increase 18o trend from ad 1500 to ad 1600 perhaps resulting in dry cold conditions and 5 a strongly enhancement of the summer monsoon intensity appeared from ad 1700 to 1950 reflecting wet cold conditions during the late period of the lia on decadal scales the monsoonal climate of central western guizhou can be either warm wet and cold dry or warm dry and cold wet the 13c variations in zjd 21 on decadal to centennial scales respond mainly to vegetation changes with heavier values reflecting lesser amount of forest coverage prior to ad 1700 the 13c generally co varied with 18o reflecting the expected more extensive vegetation growth lighter 13c under wetter climate lighter 18o however during the past 300 years the 13c increased sharply showing an opposite trend to that of 18o this observation strongly suggests that a decline of surface vegetation due to an artificial deforestation might have occurred an occurrence coincident with the large scale immigration into central western guizhou in connection with copper mining activities during the reign of emperor yongzheng of qing dynasty since the late 1890s especially in the past 50 years population surge has led to serious karst rocky desertification in the area

nickel isotopes in iron meteorites nucleosynthetic anomalies in sulphides with no effects in metals and no trace of 60fe iron 60 decays to 60ni with a half life of 1 49 myrs such that ni isotopic studies of iron meteorites have the potential to provide powerful new constraints on the energy budgets and time scales of planetesimal melting differentiation and core formation we report high resolution mc icpms ni isotope compositions for the fe ni metal phase from 33 iron meteorites as well as for 10 coexisting sulphides the isotopic composition of every metal sample is indistinguishable from that of the standard within uncertainties whereas several sulphides show an excess of 61ni correlated with a deficit in 60ni these latter effects are not explicable by currently known analytical artefacts nor can they be readily explained by spallation reactions or radioactive decay based on our sampling they seem more prevalent in but not exclusive to non magmatic iron meteorites and could reflect admixing of less than 0 4 ppm pure s process component into normal ni on meteorite parent bodies sulphides do not show the excess 60ni expected from their high fe ni ratios if they formed within the first few million years of the solar system the data provide evidence that sulphides in iron meteorites crystallized more than 10 myrs after the start of the solar system

extremely large variations of atmospheric 14c concentration during the last glacial period a long record of atmospheric 14c concentration from 45 to 11 thousand years ago ka was obtained from a stalagmite with thermal ionization mass spectrometric 230th and accelerator mass spectrometric 14c measurements this record reveals highly elevated 14c between 45 and 33 ka portions of which may correlate with peaks in cosmogenic 36cl and10be isotopes observed in polar ice cores superimposed on this broad peak of 14c are several rapid excursions the largest of which occurs between 44 3 and 43 3 ka between 26 and 11 ka atmospheric 14c decreased from 700 to 100 per mil modulated by numerous minor excursions carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle

east asian summer monsoon variations in the past 12 5 ka high resolution delta o 18 record from a precisely dated aragonite stalagmite in central china due to possible aragonite to calcite transformation resulting in alteration in isotopic signatures and a bias in age dating aragonite speleothems are often excluded from paleoclimatic archives however aragonite stalagmites contain ppm level uranium content making them much easier to date achieving higher age dating precisions than calcite stalagmites in this regard provided aragonite to calcite transformation did not occur aragonite stalagmites are potentially well suited for holocene climate research given their climate proxies can be placed into a better constrained chronological framework in this paper we present high precision u th dates and o isotopic time series for a 82 cm long continuous growth aragonite stalagmite lh2 from lianhua cave hunan province china and discuss east asian summer monsoon easm variability for the last 12 5 ka bp before present the u th dated delta o 18 sequence with a mean 16 year resolution and the growth rate pattern of lh2 show that easm experienced a strengthening stage a strong stage and a weakening stage during the last 12 5 ka during the yd 12 5 11 5 ka bp heavy delta o 18 values and low growth rate indicate a weak monsoon period during the preboreal from similar to 11 5 to 10 6 ka bp delta o 18 values decreased dramatically similar to 1 94 parts per thousand reflecting abrupt strengthening of the monsoon from 10 6 to 4 2 ka bp the record is characterized by the lightest delta o 18 values and high growth rates suggesting a strong monsoon period the summer monsoon weakened substantially after 4 2 ka bp as inferred from gradually increasing delta o 18 values and decreasing growth rate overall the intensity of the easm is regulated by summer insolation at 30 degrees n during the last 12 5 ka although oxygen isotope fractionation is different between aragonite h2o and calcite h2o because of rayleigh fractionation law the overall temporal pattern of delta o 18 values from aragonite stalagmite lh2 is concordant with other high resolution holocene calcite stalagmite records from south china the comparison among these records shows that the holocene optimum was synchronous across asian continental region influenced by the easm and indian summer monsoon ism lasting from similar to 10 6 to 4 2 ka bp as reflected by consistently lighter delta 18 ovalues among all these records regardless of their latitudinal difference these records do not support previously reported asynchronism between easm and ism in details the long term delta o 18 trend in lh2 is punctuated by a number of centennial fluctuations for instance two weak monsoon events occurred at 9232 57 yr bp and 8137 21 yr bp correlating in time with cooling events in greenland ice cores the latest weak monsoon event centered at 302 8 yr bp which is related to the little ice age lia in addition the monsoon intensity derived from our record also shows a strong connection with latitudinal migration of the inter tropical convergence zone itcz as recorded in the cariaco basin sediments spectral analysis of delta o 18 values shows that significant peaks match with solar periodicities of 208 yr de vries cycle 86 yr gleissberg cycle or related to delta c 14 production suggesting shorter term monsoon variations are forced by solar radiation overall our study suggests that the delta o 18 record in the aragonite stalagmite is highly consistent with those derived from calcite stalagmites suggesting that aragonite stalagmites are suitable for palaeoclimate reconstruction especially for the holocene period as aragonite calcite transformation has not occurred c 2013 elsevier ltd all rights reserved

a high resolution record of atmospheric 14c based on hulu cave speleothem h82 abstract the development of a calibration of atmospheric radiocarbon 14c is a significant scientific goal because it provides the means to link the numerous 14c dated paleoclimate records to a common timescale with absolutely dated records and thereby improve our understanding the relationships between the carbon cycle and climate change currently few calibration datasets that directly sample the atmospheric 14c reservoir are available beyond the end of the dendro dated holocene tree ring record at 12 6 kyr bp before 1950 ad in the absence of suitable true atmospheric records 14c calibrations beyond this age limit are based largely on marine data that are complicated by the marine reservoir effect which may have varied over the glacial cycle in this paper we present a high resolution record of u th series and 14c measurements from hulu cave speleothem h82 spanning 10 6 26 8 kyr bp corrections for detrital 230th are negligible and the contribution of 14c free geologic carbon to the speleothem calcite is small 5 6 and is stable across major climate shifts the time series provides a 16 kyr record of atmospheric 14c as well as an updated age model for the existing hulu cave 18o record the 14c data are in good overall agreement with existing marine and terrestrial 14c records but comparisons with the cariaco basin marine 14c record through the deglacial interval reveal that the cariaco reservoir age appears to have varied during parts of the younger dryas and heinrich stadial 1 cold events this highlights the importance of developing extended high resolution marine and terrestrial 14c records as a means of detecting changes in ocean circulation over the glacial cycle

modeling speleothem δ13c variability in a central sierra nevada cave using 14c and 87sr 86sr abstract carbon isotopes in speleothems can vary in response to a number of complex processes active in cave systems that are both directly and indirectly related to climate progressing downward from the soil zone overlying the cave these processes include soil respiration fluid rock interaction in the host limestone degassing of co2 and precipitation of calcite upflow from the speleothem drip site and calcite precipitation at the drip site here we develop a new approach to independently constrain the roles of water rock interaction and soil processes in controlling stalagmite 13c this approach uses the dead carbon proportion dcp estimated from coupled 14c and 230th u measurements in conjunction with sr isotope analyses on stalagmite calcite from a central sierra nevada foothills cave in california a region characterized by a highly seasonal mediterranean type climate to determine the roles of water rock interaction and soil processes in determining stalagmite 13c increases in stalagmite dcp between 16 5 and 8 8 ka are coincident with decreased 13c indicating a varying yet substantial contribution from the soil organic matter som reservoir likely due to significantly increased average age of som in the soil veneer above the cave during wet climatic intervals we use geochemical and isotope mixing models to estimate the host carbonate contribution throughout the 13c time series and determine the degree of degassing and calcite precipitation that occurred prior to precipitation of stalagmite calcite the degree of degassing and prior calcite precipitation we calculate varies systematically with other climate indicators with less degassing and prior calcite precipitation occurring during wetter climatic intervals and more during drier intervals modeled 13c values and degassing calculations suggest that some degree of prior calcite precipitation is necessary at all time intervals to explain measured stalagmite 13c values even during relatively wet intervals these results illustrate the importance of constraining degassing and prior calcite precipitation in the interpretation of speleothem 13c records particularly those from caves that formed in seasonal semi arid to arid environments

nickel isotope heterogeneity in the early solar system article i nfo ni of bulk iron and chondritic meteorites carbonaceous chondrites have variable positive e 62 ni 0 05 to 0 25 whereas ordinary chondrites have negative e 62 ni 0 04 to 0 09 the ni isotope compositions of iron meteorites overlap with those of chondrites and define an array with negative slope in the e 60 ni versus e 62 ni diagram the ni isotope compositions of the volatile depleted group ivb irons are similar to those of the refractory co cv carbonaceous chondrites whereas the other common magmatic iron groups have ni isotope compositions similar to ordinary chondrites only enstatite chondrites have identical ni isotope compositions to earth and so appear to represent the most appropriate terrestrial building material differences in e 62 ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed but some of the e 60 ni variability could reflect a radiogenic component from the decay of 60 fe comparison of the e 60 ni of iron and chondritic meteorites with the same e 62 ni allows us to place upper limits on the 60 fe 56 fe of planetesimals during core segregation we estimate that carbonaceous

characterising the nickel isotopic composition of organic rich marine sediments new ni stable isotope data 60ni determined by double spike mc icp ms for two geologically distinct suites of organic rich marine sediments from the sinemurian pliensbachian s p global stratotype section and point gssp robin hood s bay uk and the devonian mississippian exshaw formation west canada sedimentary basin is presented herein these sediments yield 60ni values of between 0 2 and 2 5 and predominantly have ni isotopic compositions that are heavier than those of abiotic terrestrial and extraterrestrial samples 0 15 and 0 27 and in some cases present day seawater 1 44 and dissolved ni from riverine input 0 80 in addition the observed degree of isotopic fractionation in the marine sediments is far greater than that of these other sample matrices however a strong similarity is exhibited between the 60ni values of the organic rich sediments studied here and those of ferromanganese crusts 0 9 2 5 suggesting that factors ubiquitous to the marine environment are likely to play a key role in the heightened level of isotopic fractionation in these sample matrices a lack of correlation between the ni stable isotope compositions of the organic rich sediments and ni abundance suggests that isotopic fractionation in these sediments is not controlled by incorporation or enrichment of ni during sediment accumulation further no relationship is observed between 60ni and toc concentrations or bottom water redox conditions indicating that the organic carbon reservoir and levels of oxygenation at the sediment water interface do not exert a primary control on ni isotope fractionation in marine sediments following examination of these relationships it is therefore more likely that the heavy ni isotope compositions of marine sediments are controlled by the weathering environment and the dominant sources of dissolved ni into the global ocean reservoir

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

trace element studies of silicate rich inclusions in the guin ungr and kodaikanal iie iron meteorites a devitrified glass inclusion from the guin ungr iron consists of cryptocrystalline feldspars pyroxenes and silica and is rich in sio2 al2o3 and na2o it contains a rutile grain and is in contact with a large cl apatite the latter is very rich in rare earth elements rees 80 x ci which display a flat abundance pattern except for eu and yb which are underabundant the devitrified glass is very poor in rees light rare earth elements lrees and deficits in eu and yban ultrarefractory pattern the genetic models suggested so far cannot explain what is observed and consequently we offer a new model for silicate inclusion formation in iie and related irons nebular processes and a relationship with e meteorites guin or ca al rich inclusions cais kodaikanal are indicated a sequence of condensation cas tin or refractory pyroxene rich liquids and vapor solid elemental exchange can be identified that took place beginning under reducing and ending at oxidizing conditions phosphate rutile formation alkali and fe 2 metasomatism metasomatic loss of rees from glasses

response of a modern cave system to large seasonal precipitation variability abstract speleothems are capable of providing information on the response of middle and low latitude terrestrial environments to global climate change during the pleistocene and holocene multiproxy speleothem studies however have demonstrated that complex interactions can occur in cave settings between processes that are directly and indirectly related to climate change thorough and extended monitoring of modern cave environments is necessary in order to fully understand how each cave responds to these processes on seasonal and interannual timescales and how environmental signals are preserved in speleothem carbonate regular environmental monitoring began at black chasm cavern in the sierra nevada foothills california during the winter of 2006 2007 monthly measurements of cave air temperature humidity and p co 2 in black chasm demonstrate that the cave is ventilated in the winter months when cold dense surface air sinks into the cave cave drip water flow nearly ceases during the late summer and autumn increases substantially during the winter and spring and responds within hours to storm events during the height of the rainy season rainwater and drip water 18 o and 2 h are controlled by variations in surface air temperature and moisture source while rainfall source influences rainwater isotopes through individual storm events it has less influence on drip water isotopic composition due to mixing of recharge waters delivered by different rainfall events in the epikarst variations in drip water chemistry 13 c mg ca and sr ca indicate that the greatest level of calcite precipitation upflow from the drip water collection site prior calcite precipitation occurs during the autumn october november when drip rates are slow and cave air p co 2 is low the least prior calcite precipitation occurs during the summer july august when drip rates are slow but cave air p co 2 is at a maximum while p co 2 is a primary control on prior calcite precipitation during all seasons the predominant influence of drip rate variability on prior calcite precipitation is evident when considering only those seasons winter spring and autumn characterized by low cave air p co 2 thus drip rate variability and in turn rainfall amount should provide the primary control on trace element variations ultimately captured in speleothem calcite the isotopic and chemical variability observed in black chasm drip waters supports previous interpretations of speleothem paleoclimate proxy records from a nearby cave where such monitoring is not feasible observations of the modern cave environment at black chasm provide a reference point for the interpretation of stalagmite proxy records from similar seasonal mediterranean climates

dead carbon in stalagmites carbonate bedrock paleodissolution vs ageing of soil organic matter implications for 13c variations in speleothems twenty one 14c accelerator mass spectrometric analyses were obtained for three holocene stalagmites from the uamh an tartair cave sutherland scotland in order to estimate the past dead carbon proportion dcp results show that the dcp increases from 22 to 38 from 3780 years ago to the present because 13c variation is small within each sample it is concluded that this dcp increase is the product of the ageing of soil organic matter related to peat bog development above the cave that produced older soil co2 and not from a more intense dissolution of the surrounding carbonates which would have led to a 13c increase comparison with samples from other sites in europe shows no intersite correlation between dcp and 13c but a relatively good intersite correlation is observed between dcp and average site temperature thus temperature may be a major factor controlling the production of old soil organic matter co2 and therefore the dead carbon content of seepage water in contrast to the scotland stalagmites two other holocene samples from sites in southern france and belgium exhibit a good correlation between 13c and dcp which can be explained in terms of variations in the intensity of limestone dissolution consequently 13c variations observed in stalagmites are not always due to changes in the vegetation type c3 c4 as has been commonly assumed 13c 12c variations in speleothem calcite may also be controlled by the soil organic matter age and in some cases by the intensity of the limestone dissolution conversely a largely constant speleothem 13c signal as observed for the scotland stalagmites does not necessarily imply that surface climate and vegetation conditions were stable since the dcp variations in this case are clearly related to the peat bog development during stalagmite growth

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

climate variability in central china over the last 1270 years revealed by high resolution stalagmite records oxygen and carbon isotopic variations in the upper section of a stalagmite sf 1 from buddha cave 33 40 n 109 05 e dated by 230th 234u 210pb and lamination counting to a time resolution as fine as 1 3 years have recorded climate changes in central china for the last 1270 years the changes include those corresponding to the medieval warm period little ice age and 20th century warming lending support to the global extent of these events the isotopic records also show cycles of 33 22 11 9 6 and 7 2 years the 33 year cycle could well represent the 35 year periodicity of climate fluctuations previously recognized in china and europe cycles of 22 11 and 9 6 years have often been associated with the sunspot or lunar orbit variations the 7 2 year cycle was recently identified also in tree ring records from an area close to buddha cave these cycles suggest that external forcing e g solar irradiance may affect the summer monsoon over eastern china the general consistency between the climate characteristics inferred from the stable isotope records of sf 1 and those from other proxy records underscores the value of stalagmites as recorders of paleoclimate

chinese stalagmite δ 18 o controlled by changes in the indian monsoon during a simulated heinrich event carbonate cave deposits in india and china are assumed to record the intensity of monsoon precipitation because the 18 o of the carbonate tracks the isotopic signature of precipitation these records show spatially coherent variability throughout the last ice age and suggest that monsoon strength was altered during the millennial scale climate variations known as dansgaard oeschger events and during the heinrich cooling events here we use a numerical climate model with an embedded oxygen isotope model to assess what caused the shifts in the oxygen isotope signature of precipitation during a climate perturbation designed to mimic a heinrich event our simulations show that a sudden increase in north atlantic sea ice extent during the last glacial period leads to cooling in the northern hemisphere reduced precipitation over the indian basin and weakening of the indian monsoon the precipitation is isotopically heavier over india and the water vapour exported to china is isotopically enriched our model broadly reproduces the enrichment of 18 o over northern india and east asia evident in speleothem records during heinrich events we therefore conclude that changes in the 18 o of cave carbonates associated with heinrich events reflect changes in the intensity of indian rather than east asian monsoon precipitation

speleothem evidence for temporal spatial variation in the east asian summer monsoon since the medieval warm period published annual to decadal resolution stalagmite d 18 o records since ad 900 from six caves dongge furong heshang buddha shihua and wanxiang in china were analyzed to detect temporal and spatial variability of the east asian summer monsoon strength which strongly affects wet dry conditions in eastern china the empirical mode decomposition method was used to obtain trends of the six cave records after the base trend was determined d 18 o anomalies of each record were computed by subtracting the base trend mean d 18 o anomaly values of the detrended time series for each cave record were calculated for four periods i medieval warm period mwp ad 900 1250 ii little ice age phase 1 lia 1 ad 1250 1550 iii little ice age phase 2 lia 2 ad 1550 1850 and iv modern period md ad 1850 2000 from these anomalies the temporal and spatial variability of wet dry conditions has been identified positive values of the mean d 18 o anomalies indicating drier conditions appeared in the lower yangtze river drainage area and southeast coast area during md 1 lia 1 and mwp whereas negative values existed in north south and yangtze areas of eastern china during lia 2 the results agree with the dryness wetness index reconstructed by chinese historic records in general these results illustrate that wet and dry conditions in different regions of eastern china could be opposite under monsoon influence so that no single speleothem d 18 o record could represent the monsoonal climate in this vast region climatic patterns in the monsoonal region can be either a combination of warm wet and cold dry or a combination of cold wet and warm dry on annual to centennial scales a 128 year periodic cycle exists in all six cave records whereas 64 year possibly a harmonic of 128 year periodicity and 42 year periodicities appear in shihua heshang and dongge records these cycles may reflect the influence of solar activity on the east asian summer monsoon copyright 2012 john wiley sons ltd