mineral composition and structure of the stalagmite laminae from chulerasim cave indian himalaya and the significance for palaeoclimatic reconstruction many noteworthy properties of climate recorded by stalagmites can result from their mineralogy and fabric as well as their mode of occurrence in this study x ray diffraction xrd and scanning electron microscope sem investigations were carried out for a well laminated stalagmite from chulerasim cave north india to identify the mineral composition and structure of the laminae as some early reported stalagmite laminae from thailand and southwestern china the laminae of this stalagmite are composed of alternating compact and porous sub layers the xrd results confirm that the stalagmite is composed mainly of primary aragonite which corrects the previous interpretation the sem results show that the compact sub layer is composed of elongated columnar aragonites with a general longitudinal orientation parallel to the vertical growth axis and the coalescence of the aragonite crystals is well developed leaving few inter crystalline voids the compact sub layer may have formed in quasi equilibrium conditions and provides the main carrier of climate proxies the porous sub layer is made up of needles drusy and fibrous aragonites intersecting each other accordingly the coalescence is low with many inter crystalline voids which suggests a short hiatus between two adjacent compact sub layers therefore the growth of alternation of compact porous sub layers may not be successive and they may have formed in different seasons the results suggest that for stalagmite palaeoclimate research cave monitoring should be performed to reveal when and how the compact sub layers were formed

relative precipitation rates of aragonite and mg calcite from seawater temperature or carbonate ion control the temperature and degree of carbonate mineral supersaturation co3 2 ion concentration of seawater are the two most likely controlling variables on the compositions of recent marine carbonate cements the relative importance of these variables is difficult to assess in nature because they have similar trends with depth 0 1500 m and latitude in modern oceans we carried out laboratory experiments to investigate the relative growth rates of calcite mg calcite and aragonite in seawater as functions of both temperature 5 25 and 37 c and of carbonate ion concentration 2 5 to 15 times supersaturated with respect to calcite the precipitation rates of aragonite relative to those of calcite increase strongly with increasing temperature and are not affected greatly by changes in saturation state at 5 c calcite precipitation rates are nearly equivalent to those of aragonite regardless of the degree of saturation at both 25 and 37 c aragonite precipitation rates are much more rapid than those of calcite up to a factor of 4 except at very low saturation states calcite compositions vary from less than 5 mol mgco3 at 5 c to 14 mol mgco3 at 37 c our results suggest that the well documented shift toward precipitation of lower mol mg calcite and the decrease in abundance of aragonite cements with increasing oceanic depth and latitude can be attributed largely to lower temperatures

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

accelerated melting of himalayan snow and ice triggers pronounced changes in a valley peatland from northern india 1 the himalayan region of northern india depends on monsoon rains together with snow and glacial melt to supply life sustaining water to one of the world s most densely populated areas here we provide high resolution pollen and diatom evidence from a peat deposit in the pinder valley that shows a synchronous and abrupt ecosystem turnover toward a wetter state in the last two centuries that exceeded changes recorded over the last three millennia contrary to expectations there was no relationship between recent proxy changes and summer monsoon precipitation strong relationships however were found with winter climate data we link this recent unprecedented wetness to marked warming at higher elevations resulting in increased seasonal runoff and associated climatic feedbacks in this snow and ice melt dominated region in contrast to the expected desiccation and decomposition of most peat systems with warming this site has instead become the wettest in its ca 3500 year history

the mediaeval warm period drought recorded in lake huguangyan tropical south china the geochemistry of dated sediment cores from lake huguangyan 21o9 n 110o17 e tropical south china reveals distinct stratigraphical patterns in total organic and inorganic carbon toc tic biogenic silica bs and total nitrogen tn over the past 1400 years in this hydrologically closed lake tic variations may reeect changes in the precipitation evaporation ratio which controls the evaporative enrichment of carbonate toc bs and tn in the sediment are proxy indicators of lake productivity and nutrient input which we believe are linked to local precipitation high tic content correlates with low concentrations of toc bs and tn and indicates two drought episodes dated to ad 670 760 and ad 880 1260 in the sediments of lake huguan gyan local historical chronicles support these data suggesting that the climate of tropical south china was dry during the mediaeval warm period mwp and wet during the little ice age lia the detected mwp drought is temporally correlated with evidence for lower precipitation on the guliya china and quelccaya peru ice caps and with increased salinity in moon lake us great plains

inter mineral fe isotope variations in mantle derived rocks and implications for the fe geochemical cycle iron isotope and major and minor element compositions of coexisting olivine clinopyroxene and orthopyroxene from eight spinel peridotite mantle xenoliths olivine magnetite amphibole and biotite from four andesitic volcanic rocks and garnet and clinopyroxene from seven garnet peridotite and eclogites have been measured to evaluate if inter mineral fe isotope fractionation occurs in high temperature igneous and metamorphic minerals and if isotopic fractionation is related to equilibrium fe isotope partitioning or a result of open system behavior there is no measurable fractionation between silicate minerals and magnetite in andesitic volcanic rocks nor between olivine and orthopyroxene in spinel peridotite mantle xenoliths there are some inter mineral differences up to 0 2 in 56fe 54fe in the fe isotope composition of coexisting olivine and clinopyroxene in spinel peridotites the fe isotope fractionation observed between clinopyroxene and olivine appears to be a result of open system behavior based on a positive correlation between the 56feclinopyroxene olivine fractionation and the 56fe value of clinopyroxene and olivine there is also a significant difference in the isotopic compositions of garnet and clinopyroxene in garnet peridotites and eclogites where the average 56feclinopyroxene garnet fractionation is 0 32 0 07 for six of the seven samples the one sample that has a lower 56feclinopyroxene garnet fractionation of 0 08 has a low ca content in garnet which may reflect some crystal chemical control on fe isotope fractionation the fe isotope variability in mantle derived minerals is interpreted to reflect subduction of isotopically variable oceanic crust followed by transport through metasomatic fluids isotopic variability in the mantle might also occur during crystal fractionation of basaltic magmas within the mantle if garnet is a liquidus phase the isotopic variations in the mantle are apparently homogenized during melting processes producing homogenous fe isotope compositions during crust formation

crystallization history of enriched shergottites from fe and mg isotope fractionation in olivine megacrysts abstract martian meteorites are the only samples available from the surface of mars among them olivine phyric shergottites are basalts containing large zoned olivine crystals with highly magnesian cores fo 70 85 and rims richer in fe fo 45 60 the northwest africa 1068 meteorite is one of the most primitive enriched shergottites high initial 87 sr 86 sr and low initial e 143 nd it contains olivine crystals as magnesian as fo 77 and is a major source of information to constrain the composition of the parental melt the composition and depth of the mantle source and the cooling and crystallization history of one of the younger magmatic events on mars 180 ma in this study fe mg isotope profiles analyzed in situ by femtosecond laser ablation mc icp ms are combined with compositional profiles of major and trace elements in olivine megacrysts the cores of olivine megacrysts are enriched in light fe isotopes 56 fe irmm 14 0 6 to 0 9 and heavy mg isotopes 26 mg dsm 3 0 0 2 relative to megacryst rims and to the bulk martian isotopic composition 56 fe 0 0 05 26 mg 0 27 0 04 the flat forsterite profiles of megacryst cores associated with anti correlated fractionation of fe mg isotopes indicate that these elements have been rehomogenized by diffusion at high temperature we present a 1 d model of simultaneous diffusion and crystal growth that reproduces the observed element and isotope profiles the simulation results suggest that the cooling rate during megacryst core crystallization was slow 43 21 c year and consistent with pooling in a deep crustal magma chamber the megacryst rims then crystallized 1 2 orders of magnitude faster during magma transport toward the shallower site of final emplacement megacryst cores had a forsterite content 3 2 1 5 mol higher than their current composition and some were in equilibrium with the whole rock composition of nwa 1068 fo 80 1 5 nwa 1068 composition is thus close to a primary melt i e in equilibrium with the mantle from which other enriched shergottites derived

iron isotope differences between earth moon mars and vesta as possible records of contrasted accretion mechanisms the iron isotope compositions of shergotty nakhla chassigny snc meteorites thought to come from mars eucrites and diogenites assumed to sample asteroid 4 vesta and rocks from the moon and earth have been measured using high precision plasma source mass spectrometry the means of eight samples from mars and nine samples from vesta are within error identical despite a range of rock types they are lighter by 0 1 in 57fe 54fe compared to the average of 13 terrestrial mantle derived rocks the latter value is identical within uncertainty with a previously published mean of 46 igneous rocks from the earth the average for 14 lunar basalts and highland plutonic rocks covering a broad spectrum of major element composition is heavier by 0 1 in 57fe 54fe relative to our estimate for the earth s mantle and therefore 0 2 heavier than the eucrites diogenites and snc meteorites however the data scatter somewhat and the apollo 15 green glass and apollo 17 orange glass are identical to samples from mars and vesta there is no clear relationship between petrological characteristics and fe isotope composition despite a wide spectrum of samples instead contrasted planetary isotopic signatures are clearly resolved statistically after evaluating alternative scenario it appears that the most plausible explanation for the heavier fe in the earth and moon is that both objects grew via processes that involved partial vaporisation leading to kinetic iron isotope fractionation followed by minor loss this is consistent with the theory in which the moon is thought to have originated from a giant impact between the proto earth and another planet combined with numerical simulations fe isotope data can offer the potential to provide constraints on the processes that occurred in planetary accretion

petrographic and isotopic evidence for holocene long term climate change and shorter term environmental shifts from a stalagmite from the serra do courel of northwestern spain and implications for climatic history across europe and the mediterranean abstract a small stalagmite from cova da arcoia in the serra do courel of northwestern spain provides a record both of general climate change across the holocene and of shorter term shifts between wetter and drier conditions nineteen u series dates from 9 3 ka to the present provide a chronology of the stalagmite with uncertainties of commonly only decades and at the most only 200 years these dates constrain the age of 18 petrographic surfaces that are of two types one type e inferred to result from dissolution during enhanced flow of water and the other type l inferred to result from lesser flow aragonite is more abundant in the earlier parts of the stalagmite and calcite is more abundant in the later part values of 13 c range from 5 6 to 1 3 relative to vpdb but are greatest beneath type l surfaces values of 18 o range from 5 4 to 4 4 relative to vpdb and have a weak but statistically significant correlation with 13 c greater abundance of aragonite greater values of 13 c and lesser frequency of type e surfaces early in the stalagmite suggest a drier and perhaps warmer early to middle holocene whereas greater abundance of calcite and frequent type e surfaces higher in the stalagmite suggest wetter conditions later in the holocene 18 o data are most compatible with this general conclusion however a prominent type e surface records the 8 2 ka event as an isolated wetter episode in the otherwise dry early holocene much of the stalagmite s aragonite and calcite suggests normal stalagmite growth in moderate climatic conditions however the near or complete cessation of growth at type l surfaces and greater 13 c greater 18 o and lesser fluorescence of aragonite beneath those surfaces combine to suggest at least six century scale episodes of strikingly dry conditions on the other hand evidence of dissolutional erosion at type e surfaces suggests at least ten distinct episodes of much wetter conditions these combine to suggest highly variable climate across the holocene at the scale of decades to a few centuries the record from this stalagmite is similar to records from greenland ice cores and from pollen and or stalagmite records from france northernmost spain and more broadly from northern or atlantic facing europe in contrast it suggests trends nearly opposite those in records from eastern and southern spain suggesting that the serra do courel is north of but perhaps not far from the boundary between atlantic and mediterranean regions of holocene climate trends in the iberian peninsula that general antiphasal relationship between northwestern spain and regions to the south and east extends to the specific observation that four of the most pronounced wetter events in the stalagmite s record coincide with periods of widespread drought and or cultural collapse in the mediterranean and middle east

monsoon reconstruction from radiocarbon dated tropical indian speleothems the potential of tropical speleothems as a climate proxy has been investigated amplitudes of 180 and 813c variations are found to be large and are likely to be primarily controlled by past rainfall contribution from past temperature variations seems to be relatively small the amount effect in rainfall has been observed and quantified by analysing rainwater samples collected during a monsoon season a tentative chronology to these speleothems is asssigned by the 14c radiometric dating method assuming that the variations in the 180 of cave carbonates are solely due to the past variations in rainfall a history of the latter has been reconstructed a high resolution rainfall reconstruction up to the last 3400 years is now available from gupteswar cave orissa subject to validation of dates by the u th method it is observed that in a tropical speleothem 513c is dominantly controlled by rainfall the study has shown that tropical indian speleothems faithfully record the annual monsoon rainfall in the

a pollen record of holocene climatic changes from the dunde ice cap qinghai tibetan plateau pollen preserved in ice cores from the dunde ice cap provides a sensitive record of holocene climatic changes and vegetational response in the northern qinghai tibetan plateau at time scales ranging from millennia to centuries and decades pollen analysis of the annually resolvable ice layers for a 30 yr period 1957 1986 suggests that total pollen concentration is correlated positively with summer precipitation and negatively with summer temperature thus it is a sensitive indicator of moisture availability and vegetation density in the steppe and desert regions around dunde high pollen concentrations between 10 000 and 4800 yr b p suggest that the summer monsoon probably extended beyond its present limit to reach dunde and westernmost tibet in response to orbital forcing the summer monsoon retreated time transgressively across the qinghai tibetan plateau during the middle holocene relatively humid periods occurred at 2700 2200 1500 800 and 600 80 yr b p probably as a result of neoglacial cooling prominent pollen changes during the medieval warm period 790 620 yr b p and the little ice age 330 80 yr b p suggest that the vegetation in the qinghai tibetan plateau region is sensitive to abrupt century scale climatic changes such as those anticipated in scenarios of greenhouse warming

the little ice age recorded by sediment chemistry in lake erhai southwest china on the basis of concentrations of 21 major and minor elements in a well dated sediment core from the deepwater part of lake erhai principal component analysis pca reveals three main factors cont

coupled lithium and iron isotope fractionation during magmatic differentiation abstract in this study we investigated fe and li isotope fractionation between mineral separates of olivine pheno and xenocrysts including one clinopyroxyene phenocryst and their basaltic hosts samples were collected from the canary islands teneriffa la palma and some german volcanic regions vogelsberg westerwald and hegau all investigated bulk samples fall in a tight range of li and fe isotope compositions 56 fe wr 0 06 0 17 and 7 li ma 2 5 5 2 assuming 7 li of the olivine free matrix is virtually identical to that of the bulk sample for mass balance reasons in contrast olivine phenocrysts display highly variable but generally light fe and mostly light li isotope compositions compared to their respective olivine free basaltic matrix which was considered to represent the melt with 56 fe ol 0 24 to 0 14 and 7 li ol 10 5 to 6 5 respectively single olivine crystals from one sample display even a larger range of 56 fe ol between 0 7 and 0 1 one single clinopyroxene phenocryst displays the lightest li isotope composition 7 li cpx 17 7 but no fe isotope fractionation relative to melt the olivine phenocrysts show variable mg and ni correlated in most cases that range between 0 89 and 0 74 and between 300 and 3000 g g respectively these olivines likely grew by fractional crystallization in an evolving magma one sample from the vogelsberg volcano contained olivine xenocrysts mg 0 89 and ni 3000 g g in addition to olivine phenocrysts this sample displays the highest li and the second highest fe isotope fractionation between olivine and melt 7 li ol melt 13 56 fe ol melt 0 29 our data i e the variable olivine at constant whole rock and matrix isotope compositions strongly indicate disequilibrium i e kinetic fe and li isotope fractionation between olivine and melt for li also between cpx and melt during fractional crystallization 7 li ol melt is correlated with the li partitioning between olivine and melt i e with li ol li melt indicating li isotope fractionation due to preferential faster diffusion of 6 li into olivine during fractional crystallization olivine with low 7 li ol melt also have low 56 fe ol melt indicating that fe isotope fractionation is also driven by diffusion of isotopically light fe into olivine potentially as fe mg inter diffusion the lowest 56 fe ol melt 0 40 was observed in a sample from westerwald germany with abundant magnetite indicating relatively oxidizing conditions during magma differentiation this may have enhanced equilibrium fe isotope fractionation between olivine and melt or fine dispersed magnetite in the basalt matrix may have shifted its fe isotope composition towards higher 56 fe the decoupling of li and fe isotope fractionation in cpx is likely due to faster diffusion of li relative to fe in cpx implying that the large investigated cpx phenocryst resided in the magma for only a short period of time which was sufficient for li but not for fe diffusion the absence of any equilibrium fe isotope fractionation between the investigated cpx phenocryst and its basaltic host may be related to the similar fe 3 fe 2 of cpx and melt in contrast to cpx the generally light fe isotope composition of all investigated olivine separates implies the existence of equilibrium in addition to diffusion driven isotope fractionation between olivine and melt on the order of 0 1

speleothem evidence for changes in indian summer monsoon precipitation over the last 2300 years speleothems from a well ventilated dolomitic cave in the pokhara valley central nepal preserve a mineralogic record of indian summer monsoon variability over the past 2300 yr annually deposited aragonite layers formed between 2300 and 1500 yr b p indicating reduced monsoon precipitation and increased cave aridity whereas alternating calcite aragonite laminae deposited after 1500 yr b p record elevated summer monsoon precipitation and increased cave humidity dense optically clear calcite layers deposited from 450 5 to 360 20 yr b p 1550 to 1640 a d indicate a less evaporative cave environment and suggest moister and or cooler conditions possibly related to climatic change associated with the onset of the little ice age

equilibrium high temperature fe isotope fractionation between fayalite and magnetite an experimental calibration abstract the iron isotopic fractionation factor between magnetite and fayalite was measured at high temperature in a piston cylinder apparatus for the first time the three isotope method matsuhisa j goldsmith j r and clayton r n 1978 mechanisms of hydrothermal crystallisation of quartz at 250 c and 15 kbar geochim cosmochim acta 42 173 182 has been used to determine equilibrium fractionation between two minerals directly the experimentally determined temperature dependent iron isotope fractionation between fayalite and magnetite is described by 10 3 ln 57 mag fa 57 fe mag fa 0 30 0 024 10 6 t 2 the equation predicts measurable fractionation at magmatic temperatures our work bears on the magnitude of fe isotope fractionation attending differentiation in magmatic systems and provides a new isotope thermometer for co existing fayalite and magnetite

stalagmite evidence from belize indicating significant droughts at the time of preclassic abandonment the maya hiatus and the classic maya collapse abstract paleoenvironmental data from a stalagmite from western belize provide a 3300 year record of droughts that impacted the maya civilization at least four times across a span of 1500 years and the most sustained period of drought coincided with the collapse of classic maya civilization the stalagmite which comes from macal chasm in the vaca plateau provides reliably dated reflectance color luminescence and c and o stable isotope records for the period from 1225 b c to the present the record thus encompasses the maya preclassic classic and postclassic periods the maya civilization peaked in population density and socioeconomic complexity during the classic period extending from a d 25 to 900 but it declined abruptly over the years from a d 750 and 900 the stalagmite record indicates that a series of droughts which collectively form the most prolonged dry interval in the 3300 year record lasted from a d 700 to 1135 and thus coincided with the collapse of the maya civilization in addition two earlier droughts evident in the stalagmite record coincided with the preclassic abandonment and the maya hiatus two earlier declines in maya civilization a drought in the mid 1400s recorded in post classic documents is also evident in the stalagmite record collectively these findings illustrate the dependence of mayan civilization on water supplies and the impact of declining water resources on a vibrant civilization

iron and magnesium isotopic constraints on the origin of chemical heterogeneity in podiform chromitite from the luobusa ophiolite tibet we present high precision measurements of iron fe and magnesium mg isotopic compositions of olivine orthopyroxene and chromite separates from harzburgites dunites and chromitites in the mantle section of the luobusa ophiolite southern tibet to investigate the origins of podiform chromitite two harzburgites in the zedong ophiolite southern tibet are also reported for comparison the olivine and orthopyroxene in the luobusa and zedong harzburgites have similar fe and mg isotopic compositions with fe 56 values ranging from 0 to 0 083 in olivine from 0 034 to 0 081 in orthopyroxene and mg 26 values ranging from 0 25 parts per thousand to 0 20 parts per thousand in olivine from 0 29 parts per thousand to 0 26 parts per thousand in orthopyroxene respectively the olivines of two dunites from the luobusa display small fe and mg isotopic variations with fe 56 values of 0 014 parts per thousand and 0 116 parts per thousand and mg 26 values of 0 21 parts per thousand and 0 29 parts per thousand all chromites in the luobusa chromitites have lighter fe isotopic compositions than the coexisting olivines with fe 56 values ranging from 0 247 parts per thousand to 0 043 parts per thousand in chromite and from 0 146 parts per thousand to 0 215 parts per thousand in olivine fe 56 chr ol 0 294 to 0 101 parts per thousand the chromite mg 26 values span a significant range from 0 41 parts per thousand to 0 14 parts per thousand large disequilibrium fe and mg isotope fractionation between chromite and olivine as well as positive correlation of chromite fe 56 values with their mgo contents could be attributed to fe mg exchange between chromite and olivine in the disseminated chromitites the higher modal abundances of olivine than chromite would result in a more extensive fe mg exchange whereas chromite in the massive chromitite where olivine is rare could not be affected by this process

late cretaceous neo tethyan slab roll back evidence from zircon u pb o and whole rock geochemical and sr nd fe isotopic data of adakitic plutons in the himalaya tibetan plateau

lithium isotopes in global mid ocean ridge basalts abstract the lithium isotope compositions of 30 well characterized samples of glassy lavas from the three major mid ocean ridge segments of the world spanning a wide range in radiogenic isotope and elemental content and sea floor physical parameters have been measured the overall data set shows a significant range in 7li 1 6 to 5 6 with no global correlation between li isotopes and other geochemical or tectonic parameters the samples with the greatest lithophile element depletion n morb k2o tio2

timing and nature of holocene glacier advances at the northwestern end of the himalayan tibetan orogen abstract holocene glacial chronostratigraphies are developed for four glaciated valleys at the northwestern end of the himalayan tibetan orogen using geomorphic mapping and cosmogenic 10be surface exposure dating the study areas include the hamtah valley in the lahul himalaya and the karzok lato and upper stok valleys in zanskar five local glacial stages are dated to 10 4 6 1 3 3 2 1 0 9 0 7 0 4 and 0 3 0 2 ka based on 49 new moraine boulder ages large age dispersions are evident for each of the local glacial stages this is especially the case for 6 1 3 3 and 2 1 0 9 ka which is likely a result of prior and or incomplete exposures in very young moraine boulders an additional compilation of 187 published 10be moraine boulder ages help define seven himalayan holocene regional glacial stages hhs for the northwestern end of the himalayan tibetan orogen these hhs date to 10 9 9 3 8 2 7 4 6 9 4 3 4 5 2 8 2 7 1 8 1 8 0 9 and

luminescent microbanding in speleothems high resolution chronology and paleoclimate when illuminated by ultraviolet light many calcite speleothems stalagmites stalactites flowstones display luminescence caused by the presence of organic humic substances occluded in the calcite the amplitude of luminescence varies in a banded pattern parallel to growth layering through 14 c and thermal ionization mass spectrometry uranium series dating we show that cyclical oscillations in the luminescence have periodicities ranging from a few days to 10 5 yr a well defined annual cycle is present in many vadose zone speleothems and can be used to define the chronology of short term events this cycle is probably a response to hydrological events in the recharge to the cave longer term oscillations are inferred to be controlled by climate through its effect on organic activity in the overlying soil

nature and origin of organic matter in carbonates from speleothems marine cements and coral skeletons organic matter in speleothem calcite marine carbonate cements and aragonitic coral skeletons was studied to determine its location molecular structure functionality and effect on mineral growth sem analyses showed that inorganically precipitated carbonates incorporate during growth adsorbed organic matter between submicroscopic subunits of the crystals whereas biologically secreted carbonates incorporate biogenic tissue between the crystals molecular fluorescence spectroscopy indicated that low molecular weight fulvic acids are the most important constituents of the organic matter the fulvic acids are probably derived from soils speleothem calcite dissolved organic matter marine carbonates and biological decay products aragonitic coral skeleton

high frequency holocene glacier fluctuations in the himalayan tibetan orogen abstract holocene glacial chronostratigraphies in glaciated valleys spread throughout the himalayan tibetan orogen including the himalaya tibet pamir and tian shan are developed using a landsystems approach detailed geomorphic mapping and new and published 10be surface exposure dating new studies in the kulti valley of lahul and the parkachik valley of the nun kun massif of the himalaya of northern india define three glacier advances at 14 7 12 2 0 5 ka in addition to one historically dated late 19th century advance in the kulti valley and one late holocene advance at 0 2 ka in the parkachik valley three major climatic groups subdivided into five climatic zones are defined across the orogen using cluster analysis ca and principal component analysis pca to identify glaciated regions with comparable climatic characteristics to evaluate the timing and extent of holocene glacier advances across these regions our regional analyses across the himalayan tibetan orogen suggest at least one lateglacial 15 3 11 8 ka and five himalayan tibetan holocene glacial stages hths at 11 5 9 5 8 8 7 7 7 0 3 2 2 3 1 0 and

lithium isotopic composition of alaskan type intrusion and its implication abstract to determine whether fractionation of li isotopes could occur at high temperatures we examined major element and li isotopic compositions of olivine from the xiadong intrusion an alaskan type complex in the central asian orogenic belt olivine in thirteen dunites displaying characteristic cumulus textures yielded large variations in li concentration 0 10 to 11 18 ppm and isotopic composition 7 li 7 18 to 34 41 these variations are too large to be attributed entirely to diffusive processes the correlations between li elemental or isotopic composition and differentiation indices such as fo and mno contents of olivine and nio content of chromite suggest probable li isotope fractionation during early stage of differentiation we speculate that while li behaves mildly incompatible during differentiation 7 li is preferentially incorporated into olivine relative to 6 li during early stage crystallization from arc magmas relatively high li concentrations and low 7 li in arc magmas might be the result of substantial olivine fractionation prior to eruption

lithium isotope geochemistry of the hawaiian plume results from the hawaii scientific drilling project and koolau volcano 1 we determined lithium isotopic compositions of mauna loa and mauna kea basalts from the 3 1 km drill hole of the hawaiian scientific drilling project hsdp for comparison li isotopic ratios were also determined for basalts from koolau volcano these two suites of samples define geochemical extremes in the range of hawaiian shield lavas the 400 ka record of mauna kea in the hsdp core shows temporal fluctuations between low 7li 4 relative to the l svec standard and high 7li 5 6 suggesting that the source components in the hawaiian plume are heterogeneous in li isotopic composition based on sio2 content and isotopic ratios of he li nd hf and pb three geochemical groups are identified in mauna kea lavas mauna kea basalts between 1900 and 2500 mbsl have relatively low 7li of about 4 they are low sio2 lavas distinguished by the highest 3he 4he and 208pb 204pb and low 176hf 177hf and 143nd 144nd like basalt from loihi seamount this mauna kea group is considered to originate from the core of the plume above 1900 mbsl high 7li lavas with high sio2 contents appear in both the submarine and subaerial sections they are marked by low 3he 4he and high 176hf 177hf the 7li rich signature of some samples 7li up to 5 7 is indicative of recycled oceanic crust in the plume this magma group defines the kea component the low sio2 lavas in the subaerial section have low 7li 4 3he 4he and 208pb 204pb their 7li values overlap the range of 7li in unaltered mid ocean ridge basalt morb and are consistent with upper mantle material entrained by the plume or contamination of plume derived magmas by the pacific lithosphere the 7li of koolau lavas mostly fall within the range of 4 5 0 3 exceptions are two samples that have 7li of 2 3 the lightest isotopic values may indicate subducted li that was isotopically fractionated during slab dehydration in contrast to other isotopic systems most koolau samples however resemble mauna kea samples in li isotopic composition mauna loa samples have 7li values of 3 5 to 4 9 within the range of the koolau and mauna kea lavas based on these data the loa trend volcanoes and kea trend volcanoes have largely overlapping li isotopic compositions in summary the hawaiian plume is not highly variable in li isotopic composition 7li is typically 4 with perturbations by subducted components to lower and higher ratios 2 5 to 5 7 the overlap of most hawaiian basalt and morb in their range of li isotopic ratios suggests minor influence of recycled oceanic crust in the plume and perhaps similar li isotopic ratios in the upper and lower mantle

precipitation variability in the indian central himalaya during last ca 4 000 years inferred from a speleothem record impact of indian summer monsoon ism and westerlies abstract we report the first high resolution stalagmite record from indian central himalaya by using a combined oxygen and carbon isotopic study spanning the last 4000 years in addition to the multi decadal events the stalagmite data also provide information on the variability in the intensity of precipitation indian summer monsoon ism and westerlies in north indian hills during the late holocene the 18o values show strong variability between 2 1 and 8 9 the extremely high variability points to the monsoon from two different sources compared to other similar aged caves which are primarily controlled by one monsoon such as the east asian summer monsoon easm although ism has penetrated into some parts in the areas of easm in the past or the westerlies therefore we suggest that the westerlies played an important role in the late holocene climate of the indian himalaya as the source of the westerlies is mediterranean atlantic the north atlantic oscillation nao which was responsible for comparatively stronger westerlies in southern europe may have brought higher precipitation to the north indian hills the stronger westerlies may also have resulted in the highest precipitation between 0 5 and 0 25 ka bp 1450 1700 ad a part of the lia in contrast to the weakening of the indian summer monsoon ism in peninsular india the stalagmite has also recorded the driest period peaking at 3 2 ka bp which may be nearly synchronous with the final collapse of the harappan culture in northwest india

discerning crystal growth from diffusion profiles in zoned olivine by in situ mg fe isotopic analyses mineral zoning is used in diffusion based geospeedometry to determine magmatic timescales progress in this field has been hampered by the challenge to discern mineral zoning produced by diffusion from concentration gradients inherited from crystal growth a zoned olivine phenocryst from kilauea iki lava lake hawaii was selected for this study to evaluate the potential of mg and fe isotopes for distinguishing these two processes microdrilling of the phenocryst 300 m drill holes followed by mc icpms analysis of the powders revealed negatively coupled mg and fe isotopic fractionations 26mg from 0 1 to 0 2 and 56fe from 1 2 to 0 2 from core to rim which can only be explained by mg fe exchange between melt and olivine the data can be explained with ratios of diffusivities of mg and fe isotopes in olivine scaling as d2 d1 m1 m2 with mg 0 16 and fe 0 27 la mc icpms and mc sims fe isotopic measurements are developed and are demonstrated to yield accurate 56fe measurements within precisions of 0 2 1 sd at spatial resolutions of 50 m 56fe and 26mg stay constant with fo in the rim late stage overgrowth whereas in the core original phenocryst 56fe steeply trends toward lighter compositions and 26mg trends toward heavier compositions with higher fo a plot of 56fe vs fo immediately distinguishes growth controlled from diffusion controlled zoning in these two regions the results are consistent with the idea that large isotopic fractionation accompanies chemical diffusion in crystals whereas fractional crystallization induces little or no isotopic fractionation the cooling timescale inferred from the chemical isotope zoning profiles is consistent with the documented cooling history of the lava lake in the absence of geologic context in situ stable isotopic measurements may now be used to interpret the nature of mineral zoning stable isotope measurements by la mc icpms and mc sims can be used as standard petrologic tools to identify samples for diffusion based geospeedometry

late quaternary climatic variability in the central ganga plain a multi proxy record from karela jheel lake abstract a multi proxy study involving phytoliths diatoms thecamoebians and sponge spicules was carried out on a trench profile 260 cm deep from karela lake in the central ganga plain to reconstruct climatic variations since ca 17 000 cal bp the testate amoebae record indicate spells of winter monsoon between ca 17 000 cal bp and 13 700 cal bp increased diversity of diatoms testate amoebae and sponge spicules in addition to low humidity aridity index iph values suggest strengthened monsoon inducing the expansion of lake margin and high primary productivity during ca 13 700 to 4300 cal bp further between ca 4300 and 2900 cal bp higher iph values and related responses of other studied proxies show a stressed lake ecosystem since ca 2900 cal bp area of the lake was reduced responding to low intensity of the indian summer monsoon anthropogenic activities may also have played a role in the lake shrinking at least during some parts of this duration

relation between eurasian snow cover snow depth and the indian summer monsoon an observational study abstract satellite derived snow cover data for 22 yr and snow depth data for 9 yr over eurasia have been analyzed to reexamine the possible relation of snow with the indian summer monsoon in contrast to the previous studies that use snow cover averaged over all of eurasia as a single number the frequency of occurrence of snow at each grid point over eurasia is correlated with the indian summer monsoon rainfall thus specific geographical regions over eurasia that are responsible for the well known inverse relationship between eurasian snow cover and indian monsoon rainfall are delineated it is found somewhat surprisingly that western eurasia is the only geographical region for which a significant inverse correlation exists between winter snow cover and subsequent summer monsoon rainfall however composites for high and low snow cover over eurasia show spatially homogeneous large scale patterns of snow cover and surface temperature anomalies winters of high and low snow cover for eurasia are found t

summer monsoon precipitation variations in central china over the past 750 years derived from a high resolution absolute dated stalagmite abstract a 2 3 year resolution record of stalagmite oxygen isotope variations from the south flank of the qinling mountains central china has revealed the asian summer monsoon asm precipitation variations in the investigated area over the past 750 years the summer monsoon precipitation gradually increased since 1249 ad reaching its highest values in the period 1535 1685 ad and then decreased with substantial decadal to centennial scale fluctuations the monsoon precipitation increased again between 1920 and 1970 ad three intervals of high monsoon precipitation were identified 1535 1685 ad 1755 1835 ad and 1920 1970 ad three intervals of low precipitation were inferred in 1249 1325 ad 1390 1420 ad and 1890 1915 ad the 18 o composition and lithological features of the stalagmite coincidently indicate a wetter climate during the little ice age lia which is also confirmed by climate records from chinese historical documents within this area a comparison with other high resolution speleothem records indicates regional differences in monsoon precipitation variability from the south to the north of central china in the last 750 years on decadal to centennial scale power spectrum analysis of the 18 o record shows significant 117 8 34 6 14 10 3 and 6 year periodicities these periodicities are widely observed in the climate records from asm controlled areas of china and are consistent with the gleissburg periodicity br ckner periodicity sunspot periodicity of solar activity and el nino southern oscillation enso periodicity these correlations suggest that both solar activity and enso periodicity may have had important influences on asm precipitation in china over the past 750 years

indian summer monsoon during the last two millennia abstract the monsoon is a large scale feature of the tropical atmospheric circulation affectingpeople and economies in the world s most densely populated regions future trends due to naturalvariabilityandhuman inducedclimatechangesareuncertain palaeoclimaterecordscanimprove ourunderstanding of monsoon dynamics and thereby reduce this uncertainty palaeoclimate records haverevealed a dramatic decrease in the asian summer monsoon since the early holocene maximum9kabp herewefocusonthelast2ka wheresomerecordsindicateanincreasingtrendinthesummermonsoon analysing globigerina bulloides upwelling records from the arabian sea we nd theweakest monsoon occurred 1500 a bp with an increasing trend towards the present copyright 2010 john wiley sons ltd keywords monsoon holocene tropics india arabian sea introduction earth s climate is changing as a result of both natural andanthropogenic causes one region of the world that isparticularly susceptible to shifts in climate and extremeweather events is the indian subcontinent in this denselypopulated region both droughts and oods as well as trends inthe seasonal receipt of rainfall have the potential to bedevastating from economic agricultural and public healthperspectives the southwest indian monsoon is the maincontributor to india s yearly rainfall budget therefore unravelling past trends of the monsoon rains is critical tounderstanding future monsoon trends india ishome tooneofthelongesttimeseriesofinstrumentalclimate observations the all india monsoon rainfall index spanning 1844 to the present sontaake et al 1993 parthasarathy et al 1994 this record is remarkable bothfor showing an absence of a long term trend and for showing alarge variation in rainfall from one year to the next records ofthe atmospheric circulation such as the indian monsoon index imi based on the arabian sea winds are much shorter andspan only the past 50 a wang et al 2001 these records alsoindicate large variations from one year to the next and do notreveal a trend blending appropriate instrumental records withpalaeo observations from ocean sediments cave deposits orotherproxies canprovidealongerperspectiveonthemonsoonand its natural variability than otherwise would be available the monsoon is the result of both the seasonally changingthermal contrast between the land and ocean and the seasonalmigration of the intertropical convergence zone itcz whichreaches its northernmost location in summer exacerbating thethermally driven pressure gradient gadgil 2003 duringwinter the air over the land is cooler and denser than the airover the water this creates a surface pressure contrast that isenhanced by the position of the itcz over the ocean south ofthe continent of india resulting in a dry northeasterly wind thatblows across the continent in spring the continent warmsquickly compared to the surrounding water the winds thenreverse and a southwesterly wind blows across the arabiansea bringing moisture laden air towards india the south westerly winds that bring the monsoon rains also causeupwelling and sea surface cooling in the arabian sea producing a distinctive fossil record that can be tied to themonsoon winds via well known physical mechanisms a variety of indian and asian summer monsoon indices havebeen developed from instrumental records in general throughout india and asia in summer stronger winds overthe ocean and increased rainfall over land are correlated withthe large scale atmospheric circulation fig 1 the webster yang index wyi is a broad scale index of the monsooncirculation covers a large continuous area 40 1108 e 0 208n and measures the difference in strength between low level 850hpa and upper level 200hpa winds webster and yang 1992 in contrast the imi measures the arabian sea windsby subtracting the low level 850hpa zonal wind over land 20 308 n 60 908 e from the low level 850hpa winds in

iron isotopic compositions of adakitic and non adakitic granitic magmas magma compositional control and subtle residual garnet effect abstract here we present iron fe isotopic compositions of 51 well characterized adakitic and non adakitic igneous rocks from the dabie orogen central china and panama costa rica central america twelve i type non adakitic granitoid samples from the dabie orogen yield 56fe ranging from 0 015 to 0 184 the good correlations between 56fe and indices of magma differentiation e g sio2 feot mg and fe3 fe suggest fe2 rich silicate and oxide minerals dominated fractional crystallization with 56femelt crystal 0 06 may account for the 56fe variation in these samples one a type granite sample from the dabie orogen has 56fe as high as 0 447 likely indicating less magnetite crystallization and an increase in 103ln melt with magma na k ca mg combined with the literature data most high silica sio2 71 wt granitic rocks define a good positive linear correlation between 56fe and na k ca mg 56fe 0 0062 na k ca mg 0 130 r2 0 66 given that fractional crystallization also tends to increase 56fe with na k ca mg this correlation can serve as the maximum estimate of the magma compositional control on fe isotope fractionation low mg adakitic samples lma have 56fe ranging from 0 114 to 0 253 the melt compositional control on lma 56fe could be insignificant due to their limited na k ca mg variation except for one sample that may be affected by late differentiation 14 out of 15 lma have 56fe increasing with dy yb n reflecting a subtle but significant effect of residual garnet proportion this serves as evidence for that source mineralogy may play an important role in fractionating fe isotopes during partial melting dabie and central america high mg adakitic samples have homogeneous fe isotopic compositions with mean 56fe of 0 098 0 038 2sd n 11 and 0 085 0 045 2sd n 11 respectively these samples have undergone melt mantle interaction which may neutralize the possible 56fe variation of their pristine magmas derived by partial melting of eclogitic rocks

environmental controls on the petrology of a late holocene speleothem from botswana with annual layers of aragonite and calcite abstract a carbonate stalagmite from drotsky s cave in northwestern botswana consists of alternating layers of calcite and aragonite layer counts and radiocarbon ages indicate that the calcite aragonite pairs are annual layers representing about 1500 years of deposition the annual layering probably resulted from highly seasonal rainfall comparison of the uppermost layers of the speleothem with meteorological records shows that precipitation of caco3 in drotsky s cave was controlled by climate thickness of calcite layers correlates with rainfall suggesting that calcite precipitation was largely dependent on the quantity of water supplied to the speleothem by contrast thickness of aragonite layers correlates with temperature although variation in temperature cannot explain greater aragonite abundance on the sides of the speleothem compared to its center mg ca ratios in calcite layers increase upward to the bases of overlying aragonite layers and analyses of cave waters suggest that fluid mg ca ratios reach levels sufficient to cause aragonite precipitation increasing evaporation which caused greater ionic strength and supersaturation resultant increasing mg ca ratios in the fluid and perhaps increasing temperature probably combined to cause aragonite precipitation detailed petrographic analysis suggests that each annual cycle of caco3 precipitation began with relatively intense fluid flow sometimes sufficient to dissolve some of the underlying aragonite before precipitation of calcite calcite precipitation under a thick fluid layer allowed euhedral crystals to form at first but thinning of the fluid to a film allowed only flatly terminated calcite crystals by season s end as fluid flow diminished increasing evaporation increasing mg ca ratios in the fluid and perhaps increasing temperature combined to cause aragonite precipitation to begin particularly on the sides of the speleothem in some years fluid flow diminished to the point that dust accumulated on aragonite surfaces before the onset of the next year s precipitation p

climatic variability in central indian himalaya during the last 1800 years evidence from a high resolution speleothem record stable isotopes from a u th dated aragonite stalagmite from the central kumaun himalaya provide evidence of variation in climatic conditions in the last similar to 1800 years the delta o 18 and delta c 13 values vary from 4 3 parts per thousand to 7 6 parts per thousand and 3 4 parts per thousand to 9 1 parts per thousand respectively although the stalagmite was not grown in isotopic equilibrium with cave drip water a clear palaeoclimatic signal in stalagmite delta o 18 values is evident based on the regional climate data the stalagmite showed a rapid growth rate during 830 910 ad most likely the lower part of medieval warm period mwp and 1600 1640 ad the middle part of little ice age lia two distinct phases of reduced precipitation are marked by a 2 parts per thousand shift in 8180 values towards the end of mwp similar to 1080 1160 ad and after its termination from similar to 1210 to 1440 ad the lia similar to 1440 1880 ad is represented by sub tropical climate similar to modern conditions whereas the post lia was comparatively drier the inter tropical convergence zone itcz was located over the cave location during wetter warmer conditions when it shifted southward precipitation over the study area decreased a prominent drop in delta o 18 and delta c 13 values during the post lia period may also have been additionally influenced by anthropogenic activity in the area c 2013 elsevier ltd and inqua all rights reserved

el nino and related monsoon drought signals in 523 year long ring width records of teak tectona grandis l f trees from south india abstract we present a 523 year a d 1481 2003 tree ring width index chronology of teak tectona grandis l f from kerala southern india prepared from three forest sites dendroclimatological investigations indicate a significant positive relationship between the tree ring index series and indian summer monsoon rainfall ismr and related global parameters like the southern oscillation index soi a higher frequency of occurrence of low tree growth is observed in years of deficient indian monsoon rainfall droughts associated with el nino since the late 18th century prior to that time many low tree growth years are detected during known el nino events probably related to deficient indian monsoon rainfall the general relationship between ismr and el nino is known to be negative and the spatial correlations between our kerala tree ring chronology and sea surface temperatures ssts over the nino regions follow similar patterns as those for ismr this relationship indicates strong enso related monsoon signals in the tree ring records these tree ring chronologies with a high degree of sensitivity to monsoon climate are useful tools to understand the vagaries of monsoon rainfall prior to the period of recorded data

iron isotope fractionation in planetary crusts we present new high precision iron isotope data d 56 fe vs irmm 014 in per mil for four groups of achondrites one lunar meteorite 11 martian meteorites 32 howardite eucrite diogenite meteorites heds and eight angrites angrite meteorites are the only planetary materials other than earth moon system significantly enriched in the heavy isotopes of fe compared to chondrites by an average of 0 12 in d 56 fe while the reason for such fractionation is not completely understood it might be related to isotopic fractionation by volatilization during accretion or more likely magmatic differentiation in the angrite parent body we also report precise data on martian and hed meteorites yielding an average d 56 fe of 0 00 0 01 stannern trend eucrites are isotopically heavier by 0 05 in d 56 fe than other eucrites we show that this difference can be ascribed to the enrichment of heavy iron isotopes in ilmenite during igneous differentiation preferential dissolution of isotopically heavy ilmenite during remelting of eucritic crust could have generated the heavy iron isotope composition of stannern trend eucrites this supports the view that stannern trend eucrites are derived from main group eucrite source magma by assimilation of previously formed asteroidal crust these new results show that iron isotopes are not only fractionated in terrestrial and lunar basalts but also in two other differentiated planetary crusts we suggest that igneous processes might be responsible for the iron isotope variations docu

iron isotope fractionation during crystallization and sub solidus re equilibration constraints from the baima mafic layered intrusion sw china abstract to better understand fe isotope fractionation between mafic minerals and oxides during crystallization of mafic magma and sub solidus re equilibration the fe isotopes of whole rocks and separated minerals olivine clinopyroxene magnetite and ilmenite of the baima mafic layered intrusion sw china have been investigated the separated minerals show a systematical decrease in 57 fe values from magnetite 0 15 to 0 51 to olivine 0 11 to 0 15 and clinopyroxene 0 35 to 0 05 and then to ilmenite 0 82 to 0 10 demonstrating regular fractionation between these minerals except for a few of samples most of the olivine and clinopyroxene are similar to those of mantle xenoliths in fe isotopes indicating that fe isotope equilibrium reached during magma crystallization was well preserved by contrast the fe isotopes of the magnetite and ilmenite may be evidently modified by sub solidus re equilibration via the fe 3 versus ti 4 and fe 2 exchange between the oxides furthermore the sub solidus re equilibration in fe isotope is strongly controlled by the proportions of magnetite and ilmenite in rocks therefore although the 57 fe ilm of the lower zone rocks with magnetite ilmenite ratios as high as 6 10 was reduced evidently by the sub solidus re equilibration the magnetite preserved their original fe isotope compositions by contrast the fe isotopes of both most magnetite and ilmenite in the middle zone had been markedly modified by sub solidus re equilibration owing to the moderate magnetite ilmenite ratios 4 7 the decreases of both 57 fe mt and 57 fe ol upwards in the cyclic units of the lower zone reveal that extensive early fractional crystallization of the magnetite resulted in depletion of heavier fe isotopes in the magma on the other hand early crystallization of olivine and clinopyroxene gave rise to the slight elevation of 57 fe ol values upwards in the cyclic units of the middle and upper zones the stratigraphic reversals in the 57 fe mt and 57 fe ol values suggest multiple magma recharges additionally the 57 fe ol values in the base of the lower zone 0 10 to 0 15 indicate that the parental magma were heavy in fe isotope due to extensive silicate mineral fractionation at depth this study indicates fractionation in fe isotope between silicates and oxides during magma crystallization and sub solidus re equilibration

in situ fe isotope ratio determination in fe ti oxides and sulfides from drilled gabbros and basalt from the iodp hole 1256d in the eastern equatorial pacific abstract in situ fe isotope measurements have been carried out to estimate the impact of the hydrothermal metamorphic overprint on the fe isotopic composition of fe ti oxides and fe sulfides of the different lithologies of the drilled rocks from iodp hole 1256d eastern equatorial pacific 15 ma crust formed at the east pacific rise most igneous rocks normally have a very restricted range in their 56fe 54fe ratio in contrast fe isotope compositions of hot fluids 300 c from mid ocean ridge spreading centers define a narrow range that is shifted to lower 56fe values by 0 2 0 5 as compared to igneous rocks therefore it is expected that mineral phases that contain large amounts of fe are especially affected by the interaction with a fluid that fractionates fe isotopes during exsolution precipitation of those minerals we have used a femtosecond uv laser ablation system to determine mineral 56fe 54fe ratios of selected samples with a precision of one key observation is that the temperature dependent inter mineral fractionations of fe isotopes between magnetite and ilmenite are systematically shifted towards higher values when compared to theoretically expected values while synthesized well equilibrated magnetite ilmenite pairs are compatible with the theoretical predictions theoretical considerations including factors of different aqueous fe chlorides and rayleigh type fractionations in the presence of a hydrous chlorine bearing fluid can explain this observation the disagreement between observed and theoretical equilibrium fractionation the fact that magnetite in contrast to ilmenite shows a slight downhole trend in the 56fe values and the observation of small scale heterogeneities within single mineral grains imply that a general re equilibration of the magnetite ilmenite pairs is overprinted by kinetic fractionation effects caused by the interaction of magnetite ilmenite with hydrothermal fluids penetrating the upper oceanic crust during cooling or incomplete re equilibration at low temperatures furthermore the observation of significant small scale variations in the 56fe 54fe ratios of single minerals in this study highlights the importance of high spatial resolution analyses of stable isotope ratios for further investigations

the absence of lithium isotope fractionation during basalt differentiation new measurements by multicollector sector icp ms we report measurements of the isotopic composition of lithium in basalts using a multicollector magnetic sector plasma source mass spectrometer mc icp ms this is the first application of this analytical technique to li isotope determination external precision of multiple replicate and duplicate measurements for a variety of sample types averages 1 1 2 population the method allows for the rapid 8 min sample analysis of small samples 40 ng li relative to commonly used thermal ionization methods the technique has been applied to a suite of samples from kilauea iki lava lake hawaii the samples range from olivine rich cumulitic lava to sio2 and k2o enriched differentiated liquids and have 7li per mil deviation of sample 7li 6li relative to the l svec standard of 3 0 to 4 8 the data indicate a lack of per mil level li isotope fractionation as a result of crystal liquid fractionation at temperatures greater than 1050 c this conclusion has been tacitly assumed but never demonstrated and is important to the interpretation of li isotope results from such geochemically complex environments as island arcs

intermediate chromitite in kizildag ophiolite se turkey formed during subduction initiation in neo tethys abstract chromitites in the kizildag ophiolite mostly occur in the mantle harzburgites and some of them in crustal cumulate dunites olivine in both the dunites and chromitites is highly magnesian fo 90 5 92 8 and 90 2 96 1 respectively while the coexisting chromite varies widely in composition cr 52 9 68 6 and 57 1 76 2 respectively placing it between high al and high cr varieties concentrations of ni v and ga in the chromite ni 741 1310 ppm v 521 1227 ppm ga 20 51 ppm are also highly variable straddling the range of high al and high cr chromite olivine in the dunites and chromitites has a large range of li concentrations 0 27 2 47 ppm and 7li values 7 20 29 90 based on the calculated al2o3 12 1 17 2 wt contents feo mgo values 0 92 1 57 and trace element concentrations of the parental magmas of the dunites and chromitites it is suggested that they are transitional between morb and boninitic melts and should have been derived by mixing of geochemically and spatially distinct magmas generated by partial melting of different sources the li isotopic compositions of olivine from the dunites and chromitites except kz14 38 and kz15 38 are neither controlled by diffusion nor fractional crystallization and thus may be intrinsic features of their parental melts the range of 7li values of olivine in the dunites and chromitites is analogous to that of arc lavas and marine sediments indicating that the chromitites record various degrees of melt penetration the wide range of li isotopic variations in olivine and chemistry in chromite from the kizildag chromitites suggest that the parental melts were originated in a proto forearc mantle during subduction initiation

diffusion driven extreme lithium isotopic fractionation in country rocks of the tin mountain pegmatite abstract lithium concentrations and isotopic compositions in the country rocks amphibolites and schists of the tin mountain pegmatite show systematic changes with distance to the contact both li and 7 li decrease dramatically along a 10 m traverse from the pegmatite into amphibolite with li concentration decreasing from 471 to 68 ppm and 7 li decreasing from 7 6 to 19 9 rubidium and cs also decrease from the pegmatite contact into the country rock but only within the first 2 m of the contact after which their concentrations remain constant neither mixing between pegmatite fluids and amphibolite nor li isotope fractionation by rayleigh distillation during fluid infiltration is a likely explanation of these observations due to the extremely light isotopic composition required for the amphibolite end member in the mixing model 7 li 20 and the similarly extreme isotopic fractionation required in a rayleigh distillation model rather these variations are likely due to isotopic fractionation accompanying li diffusion from the li rich pegmatite li 450 to 730 ppm into amphibolites li 20 ppm the fact that other alkali element concentrations vary only within 2 m of the contact reflects the orders of magnitude faster diffusion of li relative to heavier elements quartz mica schists in contact with the pegmatite also show large variations in both li and 7 li as a function of distance from contact 1 wt to 70 ppm and 10 8 to 18 6 respectively but over a longer distance of 30 m lithium concentrations of the schist decrease from 1 wt adjacent to the contact to 70 ppm 300 m from the contact the latter is a typical concentration in metapelites the nature of the 7 li variations in the schists is different than in the amphibolites schists within the first 2 m of the contact have nearly identical 7 li of 10 which mimics that of the estimated bulk pegmatite 8 to 11 at a distance of 30 m the 7 li reaches the lowest value in the schists of 18 6 similar to the lowest amphibolite measured at a distance of 300 m the 7 li climbs back to 2 5 which is within the range of 7 li of other schists in the region and metapelites worldwide the behavior of li in the schists can also be modeled by li diffusion with the effective diffusion coefficient in the schist being 10 times greater than that in the amphibolite the effective diffusion coefficients of li in the amphibolite and schist are 2 orders of magnitude greater that those in minerals which implicates the importance of fluid assisted grain boundary diffusion over solid state diffusion in transporting li through these rocks

fe isotope fractionation during partial melting on earth and the current view on the fe isotope budgets of the planets reply to the comment of f poitrasson and to the comment of b l beard and c m johnson on iron isotope fractionation during planetary differentiation by s weyer a d anbar g p brey c munker k mezger and a b woodland abstract in their comments on our recent paper s weyer a d anbar g p brey c muncker k mezger a b woodland iron isotope fractionation during planetary differentiation earth planet sci lett 240 2005 251 264 poitrasson f poitrasson does planetary differentiation really fractionate iron isotopes a comment on iron isotope fractionation during planetary differentiation by s weyer a d anbar g p brey c munker k mezger a b woodland epsl vol 240 251 264 earth planet sci lett this issue 2007 and beard and johnson b l beard c m johnson comment on iron isotope fractionation during planetary differentiation by s weyer et al earth planet sci letts v240 pages 251 264 earth planet sci lett this issue 2007 argued that there is currently no evidence that the fe isotope composition fractionates during silicate differentiation on planets based on the investigation of crustal materials they claim that differences in the fe isotope compositions of planets can be best explained by their different accretion histories however based on a compilation of fe isotope analyses from recent studies we show that there is increasing evidence for a systematically lighter fe isotope composition of the terrestrial upper mantle compared to basalts and that fe isotope fractionation during partial melting is the most likely process responsible for this isotopic difference additionally we show that the average value and also the observed range of fe isotope compositions of basalts and other differentiated rocks from the earth and the moon are very similar thus there is currently little evidence that the moon is isotopically heavier than the earth as earlier proposed by poitrasson et al f poitrasson a halliday d lee s levasseur n teutsch iron isotope differences between earth moon mars and vesta as possible records of contrasted accretion mechanisms earth planet sci lett 223 2004 253 266 however most likely the crust of the earth and the moon is isotopically heavier than that of mars and the hed parent body from our current stage of knowledge it is difficult to decide if the different crustal values mirror bulk planetary differences differences in the silicate portion of the planets or differences in isotope fractionation during partial melting among planets

iron and lithium isotope systematics of the hekla volcano iceland evidence for fe isotope fractionation during magma differentiation abstract in this study potential iron isotope fractionation by magmatic processes in the earth s crust was systematically investigated high precision iron isotope analyses by mc icp ms were performed on a suite of rock samples representative for the volcanic evolution of the hekla volcano iceland the whole series of hekla s rocks results from several processes i basaltic magmas rise and induce partial melting of meta basalts in the lower part of the icelandic crust the resulting dacitic magma evolves to rhyolitic composition through crystal fractionation during this differentiation the 56 54feirmm 014 values increase successively from 0 051 0 021 for the primitive dacites to 0 168 0 021 for the rhyolites this increase can be described by a rayleigh fractionation model using a constant bulk fractionation factor between all mineral phases m and the silicate liquid l of 56 54fem l 0 1 ii the basaltic magma itself differentiates by crystal fractionation to basaltic andesite composition no fe isotope fractionation was found in this series all basalts and basaltic andesites have an average 56 54feirmm 014 value of 0 062 0 042 2sd n 9 identical to mean terrestrial basaltic values reported in previous studies this observation is consistent with the limited removal of iron from the remaining silicate melt through crystal fractionation and small mineral melt fe isotope fractionation factors expected at temperatures in excess of 1050 c iii andesites are produced by mixing of basaltic andesite with dacitic melts the iron isotope composition of the andesites is matching that of the basaltic andesites and the less evolved dacites in agreement with a mixing process in the hekla volcanic suite li concentrations are positively correlated with indicators of magma differentiation all hekla rocks have 7li values typical for the upper mantle and demonstrate the absence of resolvable li isotope fractionation during crystal fractionation as a fluid mobile trace element li concentrations and isotopes are a potential tracer of magma fluid interaction at hekla li concentrations and isotope compositions do not indicate any extensive fluid exsolution hence the heavy fe isotope composition of the dacites and rhyolites can be predominately attributed to fractional crystallisation iron isotope analyses on single samples from other icelandic volcanoes torfajokull vestmannaeyjar confirm heavy fe isotope enrichment in evolving magmas our results suggest that the iron isotope composition of highly evolved crust can be slightly modified by magmatic processes

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

lithium isotope evidence for subduction enriched mantle in the source of mid ocean ridge basalts the process of plate tectonics continually returns material from the earth s surface to its interior a major goal of geochemists has been to see if convective flow within the earth ever allows such compositionally distinctive material to return to the surface a study of lithium isotope variations in the upper mantle now provides firm evidence for such a recycled signature in the chemical compositions of some submarine lavas that sample the convecting interior of the earth yet the recycled signature they record appears to arise not from former crustal plates themselves as was expected but from mantle material influenced by the subducting crust at convergence zones the fate of the plates themselves thus remains elusive recycled crustal materials returned from the earth s surface to the mantle by subduction have long been invoked to explain compositional heterogeneity in the upper mantle1 yet increasingly problems have been noted with this model2 3 the debate can be definitively addressed using stable isotope ratios which should only significantly vary in primitive mantle derived materials as a consequence of recycling here we present data showing a notable range in lithium isotope ratios in basalts from the east pacific rise which correlate with traditional indices of mantle heterogeneity for example 143nd 144nd ratios such co variations of stable and radiogenic isotopes in melts from a normal ridge segment provide critical evidence for the importance of recycled material in generating chemical heterogeneity in the upper mantle contrary to many models however the elevated lithium isotope ratios of the enriched east pacific rise lavas imply that subducted ocean crust is not the agent of enrichment instead we suggest that fluid modified mantle which is enriched during residency in a subduction zone is mixed back into the upper mantle to cause compositional variability

panigarh cave stalagmite evidence of climate change in the indian central himalaya since ad 1256 monsoon breaks and winter southern jet depressions abstract variations in petrography stable isotopes reflectance and luminescence along the central growth axis of a 14 5 cm stalagmite from panigarh cave indicate cooler and slightly wetter conditions in the himalayan foothills of northern india during the little ice age lia which lasted from ad 1489 1889 based on deposition of calcite and ad 1450 1820 based on rapid changes in 18o values conditions were warmer and drier during the preceding medieval climate anomaly mca and also in the post lia periods as evidenced by deposition of aragonite a review of currently existing stalagmite and other proxy data from south and east asia reveals a broad spatial pattern in precipitation over south and east asia during the lia with northern areas showing generally increased precipitation and southern areas reduced precipitation during the mca and after the lia the records suggest this pattern was reversed weaker ism during the lia brought drought conditions to the core ism area but triggered more monsoon breaks that brought higher precipitation to the himalayas at the same time the weaker ism may also have pushed more depressions along the path of the southern winter jet which brought more winter precipitation to the himalayas and therefore a lia wetter in our study area

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

the earliest lunar magma ocean differentiation recorded in fe isotopes recent high precision isotopic measurements show that the isotopic similarity of earth and moon is unique among all known planetary bodies in our solar system these observations provide fundamental constraints on the origin of earth moon system likely a catastrophic giant impact event however in contrast to the isotopic composition of many elements e g o mg si k ti cr and w the fe isotopic compositions of all lunar samples are significantly different from those of the bulk silicate earth such a global fe isotopic difference between the moon and earth provides an important constraint on the lunar formation such as the amount of fe evaporation as a result of a giant impact origin of the moon here we show through high precision fe isotopic measurements of one of the oldest lunar rocks 4 51 0 10 gyr4 51 0 10 gyr dunite 72 415 compared with fe isotope results of other lunar samples from the apollo program and lunar meteorites that the lunar dunite is enriched in light fe isotopes complementing the heavy fe isotope enrichment in other lunar samples thus the earliest olivine accumulation in the lunar magma ocean may have been enriched in light fe isotopes this new observation allows the fe isotopic composition of the bulk silicate moon to be identical to that of the bulk silicate earth by balancing light fe in the deep moon with heavy fe in the shallow moon rather than the moon having a heavier fe isotope composition than earth as a result of giant impact vaporization

a 5000 yr record of climate change in varved sediments from the oxygen minimum zone off pakistan northeastern arabian sea the upper holocene marine section from a kasten core taken from the oxygen minimum zone off karachi pakistan at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1 2 mm yr and a unique record of monsoonal climatic variability covering the past 5000 years our chronostratigraphy is based on varve counts verified by conventional and ams 14 c dating individual hemipelagic varve couplets are about 0 8 1 5 mm thick with light colored terrigenous laminae a deposited mainly during the winter monsoon alternating with dark colored laminae b rich in marine organic matter coccoliths and fish debris that reflect deposition during the high productivity season of the late summer monsoon august october precipitation and river runoff appear to control varve thickness and turbidite frequency we infer that precipitation decreased in the river watershed indicated by thinning varves after 3500 4000 yr b p this is about the time of increasing aridification in the near east and middle east as documented by decreasing nile river runoff data and lake level lowstands between turkey and northwestern india this precipitation pattern continued until today with precipitation minima about 2200 1900 yr b p 1000 yr b p and in the late middle ages 700 400 yr b p and precipitation maxima in the intervening periods as documented by spectral analysis the thickness of varve couplets responds to the average length of a 250 yr cycle a 125 yr cycle the gleissberg cycle of solar activity 95 yr and a 56 yr cycle of unknown origin higher frequency cycles are also present at 45 39 29 31 and 14 yr the sedimentary gray value also shows strong variability in the 55 yr band plus a 31 yr cycle because high frequency cyclicity in the enso band ca 3 5 and 5 yr is only weakly expressed our data do not support a straightforward interaction of the pacific enso with the monsoon driven climate system of the arabian sea

did the indo asian collision alone create the tibetan plateau it is widely believed that the tibetan plateau is a late cenozoic feature produced by the indo asian collision however because tibet was the locus of continental accretion and subduction throughout the mesozoic crustal thickening during that time may also have contributed to growth of the plateau this portion of the geologic history was investigated in a traverse through the central lhasa block southern tibet together with earlier studies our mapping and geochronological results show that the lhasa block underwent little north south shortening during the cenozoic rather our mapping shows that 60 crustal shortening perhaps due to the collision between the lhasa and qiangtang blocks occurred during the early cretaceous this observation implies that a significant portion of southern tibet was raised to perhaps 3 4 km elevation prior to the indo asian collision

iron isotope systematics of the panzhihua mafic layered intrusion associated with giant fe ti oxide deposit in the emeishan large igneous province sw china

chemical weathering since the little ice age recorded in lake sediments a high resolution proxy of past climate because of the different geochemical behaviour of rubidium and strontium in earth surface processes variations of the rb sr ratios in lake sediments were used as a geochemical proxy of chemical weathering and past climate in a single watershed low magnetic susceptibility low caco3 low sr concentration and hence high rb sr ratio in the lake sediments indicate weak chemical weathering under a cold but wet climate during the little ice age lia in the closed daihai lake watershed the concordant change in both sr and caco3 concentrations with 18o values in the dunde ice core suggests that weak chemical weathering during the wet lia was controlled by air temperature after the lia however precipitation played a dominant role in chemical weathering copyright 2001 john wiley sons ltd

the role of stratotypes in stratigraphy part 3 the wood committee the berkeley school of north american mammalian stratigraphic paleontology and the status of provincial golden spikes abstract the north american land mammal ages defined in 1941 by the wood committee provide good examples of the use of strict nominal stratotypes in fixing the names and establishing the minimum durations of provincial biochronologic units the lithostratigraphic type sections of each age served a name bearing and exemplary function not a boundary defining function despite some inconsistencies in their work the common charge that the wood committee defined many of their ages as lithochrons is a myth nevertheless the potential or actual temporal overlap of some of the original nominal stratotypes of the ages is a significant problem and their redefinition is permissible in order to preserve the original intentions of the wood committee the berkeley school of north american mammalian stratigraphic paleontology has been the most influential force in theoretical discussions in this field since the 1960s d e savage retained most of the oppelian views of r m kleinpell while m o woodburne and d r prothero departed from that tradition and adopted some of the views of h d hedberg and w a berggren thus emphasizing single taxon definitions datum planes and boundary stratotype definitions for stages however recommendations by members of the berkeley school that we turn our land mammal ages into formal stages are ironic because their own writings show they still hold the anti hedbergian view that stages are flexible biostratigraphic biochronostratigraphic entities nevertheless in partial agreement with at least some members of the berkeley school the transformation of our provincial biochronologic units into golden spike defined ages stages would defeat their purpose which is to summarize our evolving knowledge of the true sequence of important paleobiological events in each major fossil group that occurred in a given province in principle and in practice hedberg s attempt to restrict the terms age stage to golden spike defined entities has failed however hedbergians and traditional stratigraphic paleontologists can find common ground if they will admit that aurichronologic and biochronologic units are both legitimate subcategories of geochronologic units if so hedberg s major program would be vindicated in that golden spikes would still be used to define the phanerozoic standard global geochronologic units while traditional stratigraphic paleontologists would retain the ability to modify the boundaries of their provincial ages stages as they saw fit provided that such modifications did not violate the strict nominal stratotypes of those ages stages

stalagmite based high resolution precipitation variability for past four centuries in the indian central himalaya chulerasim cave re visited and data re interpretation abstract although the variations in 18 o and 13 c and the u th dating in the speleothems are considered as key proxies improved dating with better quality resolution as well as composition of stalagmites and growth rate along with the cave monitoring are equally important for understanding the high resolution precipitation variability in the past with a total of six dates on a 11 5 cm long stalagmite we re interpret the decadal to century scale climatic changes with multi year droughts from the indian central himalaya between ca 1622 and 1950 ad the sample is composed of aragonite both compact sub layers and porous sub layers although the age model of this young speleothem may be within age uncertainty owing to the high 230 th 23 2 th isotope ratios yet the distinction of this study lies in recording various historical drought events which are otherwise never reported from the himalayan foothills additionally the sample consists of reasonable amount of u 2 ppm thus the age correction requirement may be minimum the higher growth rate and comparatively lower values of 18 o and 13 c are observed during the little ice age lia until ca 1820 ad indicating its being wet in the himalayan foothills in contrast to the peninsular india and other regions which are solely influenced by the indian summer monsoon ism this is mainly because the monsoon trough moves from the plains to the himalayan foothills during break monsoon conditions and provides more orographic precipitation in form of the westerlies in the south facing himalayan slopes the post lia period from ca 1820 ad onwards is interpreted as comparatively drier than the lia

tree ring based spring temperature patterns over the past four centuries in western himalaya a network of 12 tree ring width chronologies of himalayan cedar cedrus deodara from the western himalayan region india has been used to reconstruct mean spring march may temperature variations back to a d 1600 the most conspicuous feature of the temperature reconstruction is the long term cooling trend since the late 17th century that ended early in the 20th century the warmest 30 yr mean for the 20th century was recorded during 1945 1974 however this warming in the context of the past four centuries is well within the range of natural variability since warmer springs of greater magnitude occurred in the later part of the 17th century 1662 1691

a 900 year 600 to 1500 a d record of the indian summer monsoon precipitation from the core monsoon zone of india 1 we present a near annually resolved record of the indian summer monsoon ism rainfall variations for the core monsoon region of india that spans from 600 to 1500 a d from a 230th dated stalagmite oxygen isotope record from dandak cave our rainfall reconstruction which spans the medieval warm period mwp and the earliest portion of the little ice age lia indicates that the short instrumental record of ism underestimates the magnitude of monsoon rainfall variability periods of severe drought lasting decades occurred during the 14th and mid 15th centuries and coincided with several of india s most devastating famines

late holocene climate response and glacial fluctuations revealed by the sediment record of the monsoon dominated chorabari lake central himalaya we studied a periglacial lake situated in the monsoon dominated central himalaya where an interplay of monsoonal precipitation and glacial fluctuations during the late holocene is well preserved a

iron isotope fractionation during magmatic differentiation in kilauea iki lava lake magmatic differentiation helps produce the chemical and petrographic diversity of terrestrial rocks the extent to which magmatic differentiation fractionates nonradiogenic isotopes is uncertain for some elements we report analyses of iron isotopes in basalts from kilauea iki lava lake hawaii the iron isotopic compositions 56fe 54fe of late stagemeltveins are 0 2 permil per thousand greater than values for olivine cumulates olivine phenocrysts are up to 1 2 per thousand lighter than those of whole rocks these results demonstrate that iron isotopes fractionate during magmatic differentiation at both whole rock and crystal scales this characteristic of iron relative to the characteristics of magnesium and lithium for which no fractionation has been found may be related to its complex redox chemistry in magmatic systems and makes iron a potential tool for studying planetary differentiation

controls on dissolved inorganic carbon and δ13c in cave waters from desoto caverns implications for speleothem δ13c assessments abstract unraveling the factors controlling the carbon chemistry and transport of carbon within extant karst systems has important implications concerning the assessment of time series 13c records of speleothems here we report the results of a 3 year study of total dissolved inorganic carbon dic and 13cdic from cave waters at desoto caverns southeastern usa that offer valuable insight on carbon transport and the accompanied isotope fractionations from end member sources to speleothems dic and 13cdic values of cave waters range from 0 2 to 6 0 mm and 2 7 to 12 9 vpdb respectively dic and 13cdic of seasonal drips show seasonal albeit noisy variability and are inversely related 13cdic 2 49 dic 0 64 r2 0 84 a shallow pool fed by multiple drips shows a bimodal 13cdic distribution with an isotopically heavier mode during winter 4 to 5 vpdb relative to summer months 9 to 10 vpdb a multi year trend of decreasing water availability during the study period is not reflected in a response of cave water carbon chemistry suggesting that rainfall amount may not be a significant controlling factor of the carbon chemistry coupled cave air winter ventilation summer stagnation and varying co2 fluxes through the soil horizon and epikarst exert the strongest influence on seasonal dic and 13cdic variability measured values of high dic and low 13cdic from cave waters collected during the summer early fall closely approximate isotopic equilibrium conditions conversely low dic and high 13cdic values during winter early months indicate kinetically enhanced isotopic fractionations within the cave waters the kinetically enhanced isotopic fractionation of hco 3 partitioned between degassed co2 and precipitated caco3 1000 ln co 2 hco 3 caco 3 ar hco 3 2 is greater by about a factor of two 6 7 0 3 relative to the same isotopic fractionation under equilibrium conditions 3 1 on the basis of 14c mass balance and paired 14c u th measurements we estimate that on average about 23 of c delivered annually by the drips to the aragonite stalagmites is derived from 14c dead dolomite cap while the remainder of 77 is derived from 14c live biomass 13c measurements of aragonite n 12 sampled from the tips of active speleothems during the summer months are consistent with theoretical aragonite 13c values calculated using the shallow pool summer early fall data thus confirming the 13c seasonality in both drips and coeval aragonite 13c values of an active stalagmite section spanning the last 200 years show a normal distribution with a mean of 7 1 1 2 n 81 and a mode of 7 to 8 that are statistically indistinguishable from the annual mean and mode of all dripwaters thus secular time series 13c records of stalagmites at desoto caverns with resolving power 10 1 year will likely carry the imprints of drip annual means that record climate driven 13c seasonal biases

lithium isotopic systematics of granites and pegmatites from the black hills south dakota to study li isotopic fractionation during granite differentiation and late stage pegmatite evolution li isotopic compositions and concentrations have been measured for the s type harney peak granite the spatially associated tin mountain pegmatite and possible metasedimentary source rocks in the black hills south dakota the harney peak granite is isotopically heterogeneous with 7 li varying from 3 1 to 6 6 the 7 li values of proterozoic metasedimentary rocks that are possible sources of the harney peak granite range from 3 1 to 2 5 and overlap with post archean shales and the harney peak granite for the granite suite there is no correlation between 7 li and elements indicative of degrees of granite differentiation sio2 li rb etc the li isotopic composition of the harney peak granite therefore appears to res ect the source composition minerals from the zoned tin mountain pegmatite have extremely high li contents and heavier li isotopic compositions than the granite or surrounding black hills metasedimentary rocks the heavier compositions may res ect li isotopic fractionation resulting from extensive crystal melt fractionation lithium concentrations decrease in the order spodumene 3 7 wt muscovite 0 2 to 2 0 wt plagioclase 100 1100 ppm quartz 30 140 ppm plagioclase muscovite and spodumene in all zones display a relatively narrow range in 7 li of 7 9 to 11 4 in contrast quartz is isotopically heavier and more variable 14 7 to 21 3 with 7 li showing an inverse correlation with li concentration this correlation res ects the mixing of isotopically heavy li in quartz and lighter li in s uid inclusions as documented by s uid inclusion compositions

lithium isotopic composition of submarine basalts implications for the lithium cycle in the oceans abstract we have measured the li isotope composition of young pristine basalts from active ocean ridge crests of progressively older basalts along a dredging transect and a limited number of hydrothermally altered basalts the data significantly extend our limited knowledge of the isotopic abundance ratio of li in geological material fresh mid ocean ridge basalts have 6li values of between 3 4 and 4 7 relative to isotope standard l svec during low temperature weathering on the seafloor the isotopic composition of the rock becomes increasingly heavier due to addition of seawater li 6li 32 3 the oldest 46 m y and most altered rock studied has an isotopic composition of 14 a linear relationship exists between 6li and the inverse of li concentration suggesting that li in weathered basalts can be regarded as a two component mixture of basaltic li and seawater derived li that has been incorporated in alteration minerals most likely secondary clays such as smectite and phillipsite the inferred li isotopic composition of the alteration endmember indicates an apparent isotopic fractionation factor of 1 019 relative to the seawater source thus li uptake by secondary minerals from the low temperature weathering process and by analogy incorporation in similar authigenic minerals in marine sediments provides a mechanism for preferential removal of the lighter li isotope from ocean water however isotopic fractionation due to authigenic clay formation alone cannot account for the isotopic difference between seawater and its principal sources unless the hydrothermal flux is comparable to the river flux alternatively more important sinks of6li must exist if the steady state isotopic composition of li in ocean water is to be maintained

isotope fractionation by chemical diffusion between molten basalt and rhyolite abstract experimental diffusion couples were used to study chemical diffusion between molten rhyolite and basalt with special emphasis on the associated fractionation of calcium and lithium isotopes diffusion couples were made by juxtaposing firmly packed powders of a natural basalt suny morb and a natural rhyolite lake county obsidian and then annealing them in a piston cylinder apparatus for times ranging from 0 1 to 15 7 h temperatures of 1350 1450 c and pressures of 1 2 1 3 gpa profiles of the major elements and many trace elements were measured on the recovered quenched glasses the diffusivities of all elements except lithium were found to be remarkably similar while the diffusivity of lithium was two to three orders of magnitude larger than that of any of the other elements measured chemical diffusion of calcium from molten basalt into rhyolite was driven by a concentration ratio of 18 and produced a fractionation of 44ca from 40ca of about 6 because of the relatively low concentration of lithium in the natural starting materials a small amount of spodumene lialsi2o6 was added to the basalt in order to increase the concentration difference between basalt and rhyolite which was expected to increase the magnitude of diffusive isotopic fractionation of lithium the concentration ratio between li doped basalt and natural rhyolite was 15 and the resulting diffusion of lithium into the rhyolite fractionated 7li from 6li by about 40 we anticipate that several other major rock forming elements such as magnesium iron and potassium will also exhibit similarly larger isotopic fractionation whenever they diffuse between natural melts with sufficiently large differences in the abundance of these elements

the leading mode of indian summer monsoon precipitation variability during the last millennium 1 the internally generated intraseasonal variability of the indian summer monsoon is characterized by intermittent periods of enhanced active and deficient break precipitation which produce a quasi east west precipitation dipole over the indian subcontinent here we present multicentennial length and near annually resolved reconstructions of monsoon precipitation inferred from absolute dated and instrumentally calibrated speleothem oxygen isotope records from regions central and northeast india that have diametric responses to active break monsoon circulation patterns on centennial timescales ad 1400 2008 precipitation variability from these two regions exhibit opposing behavior oscillating between periods with a persistently active dominated ad 1700 to 2007 and a break dominated ad 1400 to 1700 regime the switch between these regimes occurs abruptly within decades at a time ad 1650 1700 when a proxy record of upwelling intensity from the arabian sea suggest an abrupt increase in the monsoon winds on the basis of these observations we hypothesize that the frequency distribution of active break periods varies on centennial timescales implying a leading role of internal dynamics in governing the ism response to slowly evolving changes in the external boundary conditions

a study of clay pore water and sporopollens for characterizing paleoenvironments in the hebei plain northern china abstract we developed a clay pore water cpw isotopic method for tracing paleoenvironments characterized by sporopollens the thick clayey layers have the advantage of preserving pore water regardless of whether the water is inherent in the clayey layers or not therefore the clayey layers are a suitable target from which paleoenvironmental information can be extracted sediment sporopollens as well as cpw deuterium and oxygen isotopes were investigated in drilling cores obtained from a 130 m borehole at a field site in hengshui in the north china plain our interpretation of 18 o in cpw was consistent with sporopollens climate indices indicating that cpw was an effective proxy for obtaining paleoenvironmental information sporopollens species were abundant in the cores but the quantity of each species was low furthermore mean annual temperature and precipitation curves were established using a pollen climatic response surface model the results indicated two warm humid periods 5 2 0 m 22 6 11 m and one cold dry period 8 8 6 4 m in the holocene as well as two warm humid periods 90 6 83 m 110 6 108 2 m and three cold dry periods approximately 40 m 66 4 56 8 m approximately 100 m in the late pleistocene data derived from the sporopollens and cpw cumulatively elucidate the environmental change in northern china

the little ice age in the himalaya a review of glacier advance driven by northern hemisphere temperature change northern hemisphere cooling between 1400 and 1900 in the common era ce resulted in the expansion of glaciers during a period known as the little ice age lia early investigation of recent advances of himalayan glaciers assumed that these events were synchronous with lia advances identified in europe based on the appearance and position of moraines and without numerical age control however applications of quaternary dating techniques such as terrestrial cosmogenic nuclide dating have allowed researchers to determine numerical ages for these young moraines and clarify when glacial maxima occurred this paper reviews geochronological evidence for the last advance of glaciers in the himalaya the 66 ages younger than 2000 years 0 2000 ce calculated from 138 samples collected from glacial landforms demonstrate that peak moraine building occurred between 1300 and 1600 ce slightly earlier than the coldest period of northern hemisphere air temperatures the timing of lia advances varied spatially lik

palaeoclimatic conditions in the late pleistocene wadda lake eastern kumaun himalaya india abstract an episode of neotectonic activity on an east west trending fault in the zone of active intracrustal north almora thrust in the eastern kumaun himalaya resulted in the formation of a lake around 36 000 yr b p a 13 m continuous sequence made up largely of carbonaceous mud represents the lake that disappeared around 10 000 yr b p due to the revival of neotectonic activity on the basis of radiocarbon dating it appears that the rate of sedimentation varied from time to time during the existence of the lake palaeomagnetic studies show normal polarity except for a major deviation in the upper part of the section palynological investigations testify to the occurrence of three temperate humid and at least two well defined arid climatic phases which are correlated with previously documented late quaternary climatic changes as recorded in the himalaya as well as in tibet around 10 000 yr b p widespread deposition of a tectonically induced debris flow occurred in the lake basin at the terminal stage of the lake s life the two events ca 36 000 and 10 000 yr b p thus seem to represent two major neotectonic events in the kumaun lesser himalaya

reconstruction of little ice age glacier area and equilibrium line attitudes in the central and western himalaya abstract glacial changes during the little ice age lia in the himalayan mountains are important for understanding changes in the monsoonal and westerly climate of the so called the third pole however knowledge of these changes and their dynamics remains limited because of the region s geographical inaccessibility in addition to geopolitical reasons in this study we used high resolution three dimensional images from google earth to identify lateral and terminal moraines as delineators of paleoglacier boundaries and mapped the boundaries of both modern and lia glaciers arcgis 9 3 software was applied to map data and to calculate glacier lengths and areas modern glacier surface elevation data were derived from srtm shuttle radar topography mission records three methods the toe to headwall altitude ratio thar the toe to summit altitude method tsam and the toe to ridge altitude method tram were used to estimate equilibrium line altitude ela the transient snowlines tsl of ninety one modern glaciers were acquired using landsat 8 oli images in late summer to evaluate the reliability of the calculated elas our results showed that the total length and total area of two hundred and twenty glaciers in the central and western himalaya cwh had decreased respectively by 35 and 31 since the lia the tram method was the preferred method for the reconstruction of elas the mean depression of elas from the lia to the first decade of the 21st century as reconstructed using the tram method was 123 m the ela depression and rate of change of glacier length and glacier area displayed generally increasing trends from west to east along the central and western himalaya suggesting that the moisture was most likely transported from an easterly direction these changes were more intensive on southern than northern slopes suggesting that southerly and westerly precipitation likely increased over the same period we speculated that the cwh had been influenced by both the indian summer monsoon ism and westerlies since the lia ism moisture as in modern times was the main factor controlling the distribution of glaciers during the lia further precipitation carried by the westerlies likely intensified along southerly pathways along the cwh during the lia

annual to sub annual resolution of multiple trace element trends in speleothems this study aims to establish evidence for the widespread existence of preserved high resolution trace element variations in speleothems that may have climatic significance ion microprobe analysis of speleothems reveals that annual to sub annual variations in element chemistry exist at five shallow western european cave sites crag cave county kerry and ballynamintra county waterford ireland uamh an tartair sutherland scotland grotte pere noel belgium grotta di ernesto ne italy with widely varying climatic geomorphic and geological settings the variations are not restricted to species mg sr and ba known to substitute directly for ca in the calcite lattice but include h f na and p phosphorus as phosphate displays the greatest variability and may have the most significance as a proxy for the seasonal temperature cycle because of its role as a nutrient element the technique allows estimation of growth rate of speleothems at any interval of interest which is one of several possible uses in palaeoclimatology

past monsoon rainfall variations in peninsular india recorded in a 331 year old speleothem an actively growing stalagmite collected from a cave located in the hills of the western ghats in the uttar kannada district of karnataka india has been studied for stable isotope ratios of oxygen and carbon width of growth layers and grey level changes distinct carbonate layers alternate coarse and compact are seen in cross section each couplet of compact and coarse layer is found to represent a single year a total of 331 such couplets has been counted indicating that the stalagmite started growing in ad 1666 and continued until it was sampled stable isotope ratios of oxygen i 18o and carbon i 13c show variations ranging from 13 6 to 7 9 and from 2 7 to 1 6 respectively we have reconstructed past rainfall changes of the cave site using the amount effect in i 18o of rain speleothem i 18o and instrumental rainfall data from the associated climate subdivision show a significant correlation r 0 62 decadal average several sharp spikes of enrichment and depletion in 18o are indicative of the past deficiency and excess in rainfall most of the severe drought years recorded independently by meteorological observations are found registered in the stalagmite layers during the 331 year period rainfall was highest at ad 1666 and lowest around ad 1900 the stalagmite generated past rainfall record can serve as a reasonable proxy for testing monsoon models

forcing of the asian monsoon on the tibetan plateau evidence from high resolution ice core and tropical coral records 1 climatic influences on snow accumulation across the tibetan plateau are examined using records of net snow accumulation an and oxygen isotopic ratios 18o since 1801 from two ice cores from opposite sides of the plateau from 1880 to the 1990s summer monsoon precipitation has been a significant component of the annual accumulation on the dasuopu glacier in the himalayas but during the latter part of the little ice age 1810 to 1880 total an was 30 higher than the summer monsoon amounts in northern india this was possibly the result of increased early winter snowfall as westerly low pressure systems linked to the north atlantic pushed farther east along the himalayas than they normally do today the decades of high accumulation and the colder temperatures allowed excess snow and ice to persist late into each year which may have weakened the subsequent asian summer monsoon consequently precipitation in the northeast tibetan plateau where the dunde ice cap is located may have been affected primarily by eurasian continental processes rather than tropical meteorology during this time since the onset of the recent warming over the last century the south asian summer monsoon intensified and influenced summer climate farther to the north and west and expressions of tropical pacific and indian oceanic atmospheric processes are noticeable in the dunde net accumulation record the dunde and dasuopu glaciers which are located on the northern and southern rims of the tibetan plateau were situated in regions of environmental transition as the northern hemisphere climate shifted from a neoglacial to a warming climate mode which is something to consider when interpreting the longer ice core climate records

a 164 ka record of environmental change in the american southwest from a carlsbad cavern speleothem abstract a horizontal core 2 8 m in length drilled from the georgia giant column in carlsbad cavern provides climate information for the last 164 ka forty six alpha spectrometric u series ages determined at intervals of 7 6 cm along the core indicate five periods of deposition and five hiatuses the longest from 136 to 110 ka variations in growth rate 0 to 70 mm ka in the abundance of aragonite chalcedony and fe bearing phases and in 13c indicate that glacial intervals of the last 164 ka ois 6 4 and 2 were much wetter than today as were the colder substages 5d and 5b of ois 5 by contrast during the two warmest periods of the past 164 ka namely ois 5e and 1 there was no deposition on either side of the speleothem suggesting conditions as dry or drier than today the record from carlsbad parallels data from many other sites in the southwestern usa and northern mexico and data from marine sediments and ice cores demonstrating the extent to which ice sheet fluctuations influenced conditions in southern new mexico detailed correlation of 13c values in the georgia giant which range from 6 6 to 0 9 relative to pdb with distant speleothem records and with data from ice cores further documents the linkage of southwestern climate with global scale extent of glaciation values of 18o in the georgia giant core range from 9 7 to 4 7 relative to pdb and average 6 6 18o depleted carbonate in the georgia giant during ois 6 at a time when the world s oceans were enriched in 18o suggests that precipitation during cold intervals was brought largely by pacific air masses in fall winter and spring as a result of the southward displacement of the polar jet stream by the growth of the laurentide ice sheet termination ii marking the end of the penultimate glaciation is well defined in the core s 18o data analytical uncertainties in the radiometric ages do not preclude a start of termination ii as late as 128 ka as suggested by specmap data however data from the georgia giant core are more compatible with an earlier start like that obtained from devils hole and vostok data raising the possibility that early warming was widespread in the u s southwest region by 145 ka

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

fe isotope systematics of coexisting amphibole and pyroxene in the alkaline igneous rock suite of the ilimaussaq complex south greenland abstract the ilimaussaq intrusion south greenland provides an exceptional test case for investigating the changes of stable fe isotope fractionation of solidus phases with changes in the fe 3 fe ratio of an evolving melt the intrusion comprises a sequence of four melt batches that were fed from the same parental alkali basaltic magma differentiation produced cumulate rocks that range from augite syenite phase i over peralkaline granite phase ii to agpaitic syenites phases iiia and iiib fe 3 fe ratios in amphiboles increase substantially from phase i to phase ii and iii rocks and mark a major change in the parental magma composition from augite syenites to peralkaline granites and agpaitic syenites before this transition olivine clinopyroxene and amphibole in augite syenite the most primitive rock type in the ilimaussaq complex have a uniform fe isotope composition that is identical to that of the bulk of igneous crustal rocks and approximated by the average isotopic composition of basalts 56 54 fe irmm 014 0 072 0 046 after the transition amphiboles in the peralkaline granites and agpaitic syenites yield significantly heavier fe isotope compositions with 56 54 fe irmm 014 values ranging from 0 123 to 0 237 contamination of the ilimaussaq magma by ongoing crustal assimilation as cause for this increase can be excluded on the grounds of nd isotope data large scale metasomatic overprint with an external fluid can also be dismissed based on amphibole o and li isotope systematics rather the increase towards heavy fe isotope compositions most likely reflects the change in chemical compositions of amphiboles calcic in augite syenite to sodic in the agpaitic syenites and their fe 3 fe ratios that mirror changes in the chemical composition of the melt and its oxygen fugacity a sensitive adjustment of equilibrium fe isotope fractionation factors to amphibole ferric ferrous ratios is also supported by beta factors calculated from mossbauer spetroscopy data comparison of the measured isotope fractionation between clinopyroxene and amphibole with that predicted from mossbauer data reveal fe isotope systematics close to equilibrium in augite syenites but fe isotopic disequilibrium between these two phases in phase iiia agpaitic syenites these results are in agreement with o and li isotope systematics while amphiboles in all ilimaussaq lithologies crystallized at temperatures between 650 and 850 c textural evidence reveals later clinopyroxene crystallization at temperatures as low as 300 400 c therefore isotopic equilibrium at crystallization conditions between these two phases can not be expected but importantly subsolidus reequilibration can also be dismissed