glacial interglacial temperature change in the tropical west pacific a comparison of stalagmite based paleo thermometers in the tropics geochemical records from stalagmites have so far mainly been used to qualitatively reconstruct changes in precipitation but several new methods to reconstruct past temperatures from stalagmite material have emerged recently i liquid vapor homogenization of fluid inclusion water ii noble gas concentrations in fluid inclusion water iii the partitioning of oxygen isotopes between fluid inclusion water and calcite and iv the abundance of the 13 c 18 o 16 o clumped isotopologue in calcite we present for the first time a direct comparison of these four paleo thermometers by applying them to a fossil stalagmite covering nearly two glacial interglacial cycles marine isotope stages mis 12 9 and to two modern stalagmites all from northern borneo the temperature estimates from the different methods agree in most cases within errors for both the old and recent samples reconstructed formation temperatures of the recent samples match within 2 sigma errors with measured cave temperatures however slight but systematic deviations are observed between noble gas and liquid vapor homogenization temperatures whereas the temperature sensitivity of fluid inclusion 18 o and clumped isotopes is currently debated we find that the calibration of tremaine et al 2011 for fluid inclusion 18 o and a synthetic calcite based clumped isotope calibration ziegler et al in prep yield temperature estimates consistent with the other methods all methods with the potential exception of clumped isotopes show excellent agreement on the amplitude of glacial interglacial temperature change indicating temperature shifts of 4 5 c this amplitude is similar to the amplitude of mg ca based regional sea surface temperature records when correcting for sea level driven changes in cave elevation our reconstruction of tropical temperature evolution over the time period from 440 to 320 thousand years ago ka adds support to the view that climate sensitivity to varying greenhouse forcing is substantial also in the deep tropics

high resolution stalagmite climate record from the yucatan peninsula spanning the maya terminal classic period the decline of the classic maya civilization was complex and geographically variable and occurred over a 150 year interval known as the terminal classic period tcp c e 800 950 paleoclimate studies based on lake sediments from the yucatan peninsula lowlands suggested that drought prevailed during the tcp and was likely an important factor in the disintegration of the classic maya civilization the lacustrine evidence for decades of severe drought in the yucatan peninsula however does not readily explain the long 150 year socio political decline of the classic maya civilization here we present a new absolute dated highresolution stalagmite 18o record from the northwest yucatan peninsula that provides a much more detailed picture of climate variability during the last 1500 years direct calibration between stalagmite 18o and rainfall amount offers the first quantitative estimation of rainfall variability during the terminal classic period our results show that eight severe droughts lasting from 3 to 18 years occurred during major depopulation events of classic maya city states during these droughts rainfall was reduced by 52 to 36 the number and short duration of the dry intervals help explain why the tcp collapse of the mayan civilization occurred over 150 years

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

a 9000 year carbon isotopic record of acid soluble organic matter in a stalagmite from heshang cave central china paleoclimate implications abstract organic matter preserved in speleothems has the potential to reflect the changes of the overlying vegetation and soil ecosystem here we report the first near 50 yr resolution acid soluble organic matter asom carbon isotope 13 c asom sequence derived from a laminated stalagmite hs 4 spanning the last 9 ky in heshang cave central china the 13 c asom values vary between 25 8 and 22 0 with lower values from 9 to 4 ka bp and less negative values from 4 to 0 ka bp we postulate that the 13 c asom sequence is mainly controlled by temperature and water balance temperature could affect both vegetation physiology and microbial degradation in soil horizons the influence of temperature on the 13 c asom is supported by the negative correlation r 0 48 p 13 c asom record and the paleotemperature record in the nearby dajiuhu peatland the water balance can affect the retention time of organic matter in soils under drier conditions the soil organic matter will be retained longer and is more likely to be biologically degraded resulting in more negative 13 c asom values our results reveal that 13 c asom in speleothems has the potential to reflect the response of vegetation and or soil processes to paleoclimate changes

phytoliths indicators of grassland dynamics during the late holocene in intertropical africa abstract the reconstruction of african tropical grassland history during the late holocene can be carried out using phytolith analysis fossil phytolith assemblages from lake guiers in the sahelian region of senegal and from lake sinnda in the guineo congolian region of congo were investigated the results are interpreted on the basis of modern phytolith assemblages from the same regions and compared to pollen data previously obtained tall or short grass associations are discriminated by their phytolith index iph saddle cross dumbel saddle while the density of shrubs and trees is indicated by relative proportions of the dicotyledon phytoliths the phytolith data emphasize that in the guineo congolian region around lake sinnda the driest phase of the late holocene occurred between 4000 and 1200 yr b p commencing with the opening of the dense forest and its replacement by a short grass savanna from ca 1000 yr b p wetter climatic conditions developed as represented by the setting up of a tall grass savanna woodland the modern shrub and tall grass savanna was developed ca 700 yr b p in the sahelian region around lake guiers the driest phase occurred after about 2000 yr b p and has not been followed by moister conditions a tall grass savanna woodland was gradually replaced by a shrub and short grass savanna which still occurs a short period of development of swampy vegetation which can be related to a lake level change interrupted the semi arid adaptation of the vegetation between about 2000 yr b p and the present

timing and structure of mega sacz events during heinrich stadial 1 a substantial strengthening of the south american monsoon system sams during heinrich stadials hs points toward decreased cross equatorial heat transport as the main driver of monsoonal hydroclimate variability at millennial time scales in order to better constrain the exact timing and internal structure of hs1 over tropical south america we assessed two precisely dated speleothem records from central eastern and northeastern brazil in combination with two marine records of terrestrial organic and inorganic matter input into the western equatorial atlantic during hs1 we recognize at least two events of widespread intensification of the sams across the entire region influenced by the south atlantic convergence zone sacz at 16 11 14 69 kyr b p and 18 1 16 66 kyr b p labeled as hs1a and hs1c respectively separated by a dry excursion from 16 66 to 16 11 kyr b p hs1b in view of the spatial structure of precipitation anomalies the widespread increase of monsoon precipitation over the sacz domain was termed mega sacz

varied response of western pacific hydrology to climate forcings over the last glacial period atmospheric deep convection in the west pacific plays a key role in the global heat and moisture budgets yet its response to orbital and abrupt climate change events is poorly resolved here we present four absolutely dated overlapping stalagmite oxygen isotopic records from northern borneo that span most of the last glacial cycle the records suggest that northern borneo s hydroclimate shifted in phase with precessional forcing but was only weakly affected by glacial interglacial changes in global climate boundary conditions regional convection likely decreased during heinrich events but other northern hemisphere abrupt climate change events are notably absent the new records suggest that the deep tropical pacific hydroclimate variability may have played an important role in shaping the global response to the largest abrupt climate change events

a 780 year annually resolved record of indian ocean monsoon precipitation from a speleothem from south oman 1 meteorological records of monsoon rainfall in the indian ocean are generally less than 100 years long the relative brevity of these records makes it difficult to investigate monsoon variation on decadal and centennial timescales to determine what factors influence the intensity of rainfall on these timescales or to place possible changes in the twentieth century into a broader historical context development of a geologic proxy for rainfall that records annual variation in the monsoon over much longer time periods than are covered by instrumental records would be a significant step forward we have developed an annually resolved record of monsoon rainfall variation for the past 780 years based on annual layer thickness and stable isotope analyses of a laminated stalagmite from southern arabia our results show that monsoon variation over the past century is not outside of the range of the past 800 years decreasing monsoon rainfall over the past century is related to increasing sea surface temperature in the indian ocean spectral analyses of the record are dominated by cycles that are similar to those observed in records of solar activity on centurial timescales decadal to interannual cycles in the record appear to originate in the tropical pacific ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 3354 meteorology and atmospheric dynamics precipitation 1854 1620 global change climate dynamics 3309 1699 global change general or miscellaneous keywords monsoon paleoclimate rainfall indian ocean speleothem oxygen isotopes

reconstruction of seasonal precipitation in hawai i using high resolution carbon isotope measurements across tree rings abstract determination of carbon isotope 13 c values of tree ring tissue is a well established method to reconstruct past climate variability at annual resolution but such records are limited in tropical latitudes due to the lack of well defined annual growth bands recent work has demonstrated the potential for high resolution intra ring 13 c records to help define ring boundaries in tropical environments and provide additional climate information at sub annual resolution here we present a high resolution intra ring carbon isotope 13 c record of the hawaiian endemic species sophora chrysophylla also known as m mane in order to assess the ability to extract seasonal climate information from these drought tolerant trees tree cores were sampled from high elevation m mane trees growing on the west side of mauna kea big island across our entire dataset 1986 2008 we identified a notable decreasing linear trend in the 13 c record of 0 061 year that can be attributed to changes in the 13 c value of atmospheric co 2 and p co 2 concentration associated with fossil fuel burning correcting for these affects yields a nearly flat 13 c record with a slope of 0 0075 year suggesting no long term trends in climate across the study period we observe a quasi periodic change in the 13 c values 13 c measured within each ring that averages 1 09 0 50 1 n 23 in amplitude these variations are interpreted as the intra annual isotopic signal in tree photosynthesis the 13 c variability correlates with the visible ring structure of the sample suggesting the presence of annual growth rings at this tropical high elevation site we applied these data to a model that relates the 13 c value to seasonal changes in precipitation in order to reconstruct annual changes in total summer may through october and winter november through april precipitation at the site across the 23 year record 1986 2008 n 579 13 c measurements reconstructed values for the ratio of summer to winter precipitation total summer precipitation and total winter precipitation correlate well with rainfall data collected from a nearby weather station r 0 65 0 36 and 0 70 respectively these results support application of this model to reconstruct inter annual changes in seasonal precipitation from long term tree ring chronologies they also demonstrate the potential of using m mane 13 c for future long term climate reconstructions

evaporation induced 18o and 13c enrichment in lake systems a global perspective on hydrologic balance effects growing pressure on sustainable water resource allocation in the context of global development and rapid environmental change demands rigorous knowledge of how regional water cycles change through time one of the most attractive and widely utilized approaches for gaining this knowledge is the analysis of lake carbonate stable isotopic compositions however endogenic carbonate archives are sensitive to a variety of natural processes and conditions leaving isotopic datasets largely underdetermined as a consequence isotopic researchers are often required to assume values for multiple parameters including temperature of carbonate formation or lake water delta o 18 in order to interpret changes in hydrologic conditions here we review and analyze a global compilation of 57 lacustrine dual carbon and oxygen stable isotope records with a topical focus on the effects of shifting hydrologic balance on endogenic carbonate isotopic compositions through integration of multiple large datasets we show that lake carbonate delta o 18 values and the lake waters from which they are derived are often shifted by 10 parts per thousand relative to source waters discharging into the lake the global pattern of delta o 18 and delta c 13 covariation observed in 70 of the records studied and in several evaporation experiments demonstrates that isotopic fractionations associated with lake water evaporation cause the heavy carbon and oxygen isotope enrichments observed in most lakes and lake carbonate records modeled endogenic calcite compositions in isotopic equilibrium with lake source waters further demonstrate that evaporation effects can be extreme even in lake records where delta o 18 and delta c 13 covariation is absent aridisol pedogenic carbonates show similar isotopic responses to evaporation and the relevance of evaporative modification to paleoclimatic and paleotopographic research using endogenic carbonate proxies are discussed recent advances in stable isotope research techniques present unprecedented opportunities to overcome the underdetermined nature of stable isotopic data through integration of multiple isotopic proxies including dual element c 13 excess values and clumped isotope temperature estimates we demonstrate the utility of applying these multi proxy approaches to the interpretation of paleohy droclimatic conditions in ancient lake systems understanding past present and future hydroclimatic systems is a global imperative significant progress should be expected as these modern research techniques become more widely applied and integrated with traditional stable isotopic proxies c 2015 elsevier ltd all rights reserved

barriers and bridges early human dispersals in equatorial se asia past environments of equatorial se asia must have played a critical role in determining the timing and trajectory of early human dispersal into and through the region however very few reliable terrestrial records are available with which to contextualize human dispersal events this circumstance coupled with a sparse archaeological record and the likelihood that much of the archaeological record is now submerged means we have an incomplete understanding of the role that geography climate and environment played in shaping human pre history in this region from a review of the literature we conclude that there must have been a substantial environmental barrier resulting in a genetic separation between east and west sundaland that persisted even though a terrestrial connection was present for most of the pleistocene this barrier is likely to be a north south corridor of open non forest vegetation and its existence may have encouraged the rapid dispersal of early humans through the interior of sundaland and on to sahul we conclude that more reliable terrestrial palaeoenvironmental records are required to better understand the links between past environments and dispersal events we highlight avenues of particular research value such as focusing on eastern sumatra western southern borneo and the islands in the java sea where the purported savanna corridor most probably existed and including edaphic factors in palaeovegetation modelling

carbon isotope signature of environmental change found in fossil ratite eggshells from a south asian neogene sequence a 10 m y long sequence of ratite e g ostrich eggshells from siwalik group sedimentary deposits of northern pakistan and india shows a dramatic 8 increase in the 13 c in biomineralogic calcite by 4 ma values of 13 c from ratite eggshell carbonate older than 7 ma are about the same as those from carbonate from contemporaneous fossil mammal tooth enamel and paleosols however after 4 ma the ratite eggshell carbonate 13 c values are 5 less than these coexisting materials these findings are evidence of the development of a c 3 c 4 vegetative mosaic probably mirroring the sedimentologic edaphic mosaic of the aggrading alluvial plain of the siwalik depositional system

guano derived δ 13 c based paleo hydroclimate record from gaura cu musca cave sw romania the 13c values of 23 unevenly spaced guano samples from a 17 cm long clay sediment profile in gaura cu musc cave gm in sw romania made it possible to preliminarily characterize the medieval warm period summer hydroclimate regime the beginning of the sequence ad 990 was rather wet for more than a century before becoming progressively drier after a brief yet distinct wet period around ad 1170 drier conditions with a possible shift from c3 to a mixed c3 dominated c4 type vegetation 2 lower 13c values prevailed for almost half a century before the climate became colder and wetter at the onset of the little ice age when bats left the cave the guano inferred wet and dry intervals from the gm cave are mirrored by changes in the color and amount of clay accumulated in the cave they also agree well with reconstructions based on pollen and charcoal from peat bogs and 13c and 18o on speleothems from other romanian sites overall these results indicate that the 13c of bat guano can provide a sensitive record of the short term coupling between local regional climate and the plant insect bat guano system

interglacial hydroclimate in the tropical west pacific through the late pleistocene records of atmospheric carbon dioxide concentration pco 2 and antarctic temperature have revealed an intriguing change in the magnitude of interglacial warmth and pco 2 at around 430 000 years ago 430 ka but the global climate repercussions of this change remain elusive here we present a stalagmite based reconstruction of tropical west pacific hydroclimate from 570 to 210 ka the results suggest similar regional precipitation amounts across the four interglacials contained in the record implying that tropical hydroclimate was insensitive to interglacial differences in pco 2 and high latitude temperature in contrast during glacial terminations drying in the tropical west pacific accompanied cooling events in northern high latitudes therefore the tropical convective heat engine can either stabilize or amplify global climate change depending on the nature of the climate forcing

radiocarbon dating of charcoal from tropical sequences results from the niah great cave sarawak and their broader implications subsamples of charcoal from a number of different excavation contexts at the early modern human homo sapiens site of niah great cave malaysia were accelerator mass spectrometry ams 14c dated samples were prepared using one of a number of different methods untreated control acid base acid aba and acid base wet oxidation with stepped combustion abox sc after bird et al 1999 the results show that for material younger than 25 ka bp there is little difference between the two chemical pretreatment methods and the control for charcoal beyond 25 ka bp however there are differences of up to 4000 a with abox sc ages being consistently older this is argued to be a more effective pretreatment method for decontaminating charcoal samples prior to radiocarbon dating for radiocarbon dating charcoals greater than 25 ka bp the abox sc pretreatment and combustion approach appears to be the most rigorous method for developing a robust chronological framework for tropical sequences and should be more widely applied in contexts where the material being dated is likely to be ancient the new chronology developed for niah cave based on this technique suggests that the earliest human evidence dates back to at least 45 ka bp and may extend significantly earlier than this based on the recent discovery of lithics 50 cm below the earliest dated charcoal copyright 2008 john wiley sons ltd

quality of topsar topographic data for volcanology studies at kilauea volcano hawaii an assessment using airborne lidar data abstract we use airborne lidar data for the summit area of kilauea caldera hawaii to explore the utility of topographic data collected by the topsar airborne interferometric radar for volcanology studies the lidar data are processed to a spatial resolution of 1 m pixel compared to topsar with a spatial resolution of 5 m over a variety of fresh volcanic surfaces pahoehoe and aa lava flows ash falls and fluvial fans topsar data are shown to have a typical vertical offset compared to the lidar data of no more than 2 3 m larger differences between the two data sets and topsar data drop outs are found to be concentrated around steep scarps such as the walls of pit craters and ground cracks associated with the southwest rift zone a comparison of these two data sets is used to explore the utility of topsar to interpret the topography of volcanic features close to the spatial resolution of topsar such as spatter ramparts fractures a perched lava flow and eroded ash deposits comparison of the topsar elevation and the lidar first return minus the return from the ground surface the so called bald earth data for vegetated areas reveals topsar penetration into the tree canopy is typically at least 10 and no more than 50 although a wide range of penetration values from 0 to 90 has been identified our results are significant because they show that topsar data for volcanoes can reliably be used to measure regional slopes and the thickness of lava flows and have value for the validation of coarser spatial resolution digital elevation data such as srtm in areas where lidar data have not been collected

oxygen isotope systematics in a multiphase weathering system in haiti abstract physical and chemical partial dissolution techniques have been applied to a suite of young karst bauxite and laterite samples from the southern peninsula of haiti the 18o values have been obtained for nine mineral species and range from 1 0 for anatase rutile to 33 4 for authigenic quartz on one hand results for quartz calcite kaolinite gibbsite and boehmite compare favourably with 18o values predicted from accepted mineral water fractionation factors assuming modern temperatures 25 2 c and water 18o values 3 1 0 5 on the other hand the 18o values measured for anatase illite smectite chlorite smectite and some iron oxide samples do not compare favourably with predicted values departures from expected values for these minerals may be related to crystallization from water with a different 18o value than modern water an imprecise knowledge of some mineralwater fractionation factors under surficial conditions or nonattainment of isotopic equilibrium between mineral and water during formation partial dissolution techniques hold considerable promise for obtaining quantitative 18o values of individual minerals in single samples of complex fine grained regolith material

a stable isotope study of lateritic bauxites abstract stable isotope analyses of gibbsitic samples from a number of lateritic bauxites suggest that the accepted oxygen and hydrogen isotope fractionation factors for the mineral at surficial temperatures are incorrect a new ox of 1 0143 0 002 and hy of 0 998 0 015 is proposed for gibbsite and in addition an ox of 1 0175 0 001 and hy of 0 975 0 008 is proposed for boehmite at surficial temperatures application of these fractionation factors suggests that gibbsite from many of the equatorial bauxites analyzed formed in equilibrium with meteoric waters similar to those which commonly accompany monsoon type rainfall these waters are generally depleted in 18o and d compared to precipitation derived from tradewinds the isotopic composition of gibbsite from the mid tertiary weipa bauxite in north queensland indicates equilibrium with waters similar in isotopic composition to modern groundwaters in the region this suggests that a monsoon type climate similar to that of the present has prevailed in the region since at least the mid tertiary the oxygen and hydrogen isotope composition of gibbsite from the paragominas deposit in brazil is markedly out of isotopic equilibrium with modern tradewind derived regional rainfall but in equilibrium with waters comparable to those derived from monsoonal rains this suggests that since the formation of the deposit the climate has changed and the monsoons no longer operate in the region thus the link between the isotopic composition of bauxite minerals and the nature of the climate prevailing during their formation can be used to define tropical regions which have previously experienced a monsoonal climate providing valuable information on the nature of atmospheric circulation in the past

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

speleothems and climate a special issue of the holocene speleothems cave dripstones are formed as a part of the meteoric water cycle and therefore vari ations in their growth rate and composition reflect environmental changes on the land surface above the cave since they are continental deposits and possess a remarkably accurate dating potential using tims u series techniques speleothems are important palaeoclimatic archives for the terrestrial environment complementing the marine and ice core records the climatic proxies that can be deciphered from speleothems are growth rate stable isotope composition d18o d13c organic humic matter and trace element composition as well as luminescent laminae which may display annual rhythms the nine papers in this special issue oftheholocene present the latest results in palaeoclimatic analysis from speleothems

a 2500 yr late holocene multi proxy record of vegetation and hydrologic changes from a cave guano clay sequence in sw romania we provide sedimentological geochemical mineral magnetic stable carbon isotope charcoal and pollen based evidence from a guano clay sequence in gaura cu musc cave sw romania from which we deduced that from 1230 bc to ad 1240 climate oscillated between wet and dry from 1230 bc to ad 1000 the climate was wetter than the present prompting flooding of the cave preventing bats from roosting and resulting in a slow rate of clay accumulation the second half of the medieval warm period mwp was generally drier the cave experienced occasional flash flooding in between which maternity bat roosts established in the cave one extremely wet event occurred around ad 1170 when fe mn and ti zr ratios show the highest values coincident with a substantial increase of sediment load in the underground stream the mineral magnetic characteristics for the second part of the mwp indicate the partial input of surface sourced sediments reflecting agricultural development and forest clearance in the area pollen and microcharcoal studies confirm that the overall vegetation cover and human land use have not changed much in this region since the medieval times

glacial interglacial changes in southern africa compound specific δ13c land plant biomarker and pollen records from southeast atlantic continental margin sediments this is part 2 of a study examining southwest african continental margin sediments from nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s representing two glacial mis 2 and 6a and two interglacial stages mis 1 and 5e contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 as indicators of land plant vegetation of different biosynthetic types were correlated with concentrations and distributions of pollen taxa in sediments of the same time horizons selected single pollen type data reveal details of vegetation changes but the overall picture is best illustrated by summing pollen known to predominantly derive from c4 plants or c4 plus cam plants the c4 plant signals in the biomarkers are recorded in the 13c data and in the abundances of c31 and c33n alkanes and the c32n alkanol calculated clusters of wind trajectories for austral summer and winter situations for the holocene and the last glacial maximum afford information on the source areas for the lipids and pollen and their transport pathways to the ocean this multidisciplinary approach provides clear evidence of latitudinal differences in leaf wax lipid and pollen composition with the holocene sedimentary data paralleling the current major phytogeographic zonations the northern sites congo fan area and northern angola basin get most of their terrestrial material from the congo basin and the angolan highlands dominated by c3 plants airborne particulates derived from the western and central south african hinterland dominated by deserts semideserts and savannah regions are rich in organic matter from c4 plants as can be expected from the present and glacial positions of the phytogeographic zones the carbon isotopic signatures of n alkanes and n alkanols both become isotopically more enriched in 13c from north to south in the northern part of the transect the relative importance of c4 plant indicators is higher during the glacials than in the interglacials indicating a northward extension of arid zones favoring grass vegetation in the south where grass rich vegetation merges into semidesert and desert the difference in c4 plant indicators is small

isotopic evidence for plio pleistocene environmental change at gona ethiopia abstract a 4 5 ma record of fluvial and lacustrine deposits is well exposed at gona in the afar depression of ethiopia we use isotopic values of pedogenic carbonate and fossil teeth to reconstruct plio pleistocene environmental change at gona an increase in 13c values of pedogenic carbonates since 4 5 ma points to a shift from woodlands to grassy woodlands in the early pliocene 10 4 to 3 9 vpdb to more open but still mixed environments in the late pleistocene 3 0 to 1 4 vpdb this pattern is also seen in isotopic records elsewhere in east africa however at 1 5 ma the higher proportion of c4 grasses at gona is largely a result of a local facies shift to more water limited environments the wide range of 13c values of pedogenic carbonate within single stratigraphic levels indicates a mosaic of vegetation for all time intervals at gona that depends on depositional environment elements of this mosaic are reflected in 13c values of both modern plants and soil organic matter and plio pleistocene soil carbonate indicating higher amounts of c4 grasses with greater distance from a river channel in both the modern and ancient awash river systems 18o values of pedogenic carbonates increase up section from 11 9 in the early pliocene to 6 4 vpdb in the late pleistocene the wide range of 18o values in paleovertisol carbonates from all stratigraphic levels probably reflects short term climate changes and periods of strong evaporation throughout the record based on the comparison between 18o values of plio pleistocene pedogenic carbonates and modern waters we estimate that there has been a 6 5 increase in mean annual 18o values of meteoric water since 4 5 ma 18o values of pedogenic carbonate from other east african records indicate a similar shift increasing aridity and fluctuations in the timing and source of rainfall are likely responsible for the changes in 18o values of east african pedogenic carbonates through the plio pleistocene

variability of indian monsoonal rainfall over the past 100 ka and its implication for c 3 c 4 vegetational change abstract oxygen and carbon isotope ratios of soil carbonate and carbon isotope ratios of soil organic matter som separated from three cores kalpi iitk and firozpur of the ganga plain india are used to reconstruct past rainfall variations and their effect on ambient vegetation the 18o values of soil carbonate 18osc analyzed from the cores range from 8 2 to 4 1 using these variations in 18osc values we are able for the first time to show periodic change in rainfall amount between 100 and 18 ka with three peaks of higher monsoon at about 100 40 and 25 ka the estimation of rainfall variations using 18o value of rainwater amount effect suggests maximum decrease in rainfall intensity 20 during the last glacial maximum the 13c values of soil carbonate 13csc and som 13csom range from 6 3 to 1 6 and 28 9 to 19 4 respectively implying varying proportions of c3 and c4 vegetations over the ganga plain during the last 100 ka the comparison between monsoonal rainfall and atmospheric co2 with vegetation for the time period 84 to 18 ka indicate that relative abundances of c3 and c4 vegetations were mainly driven by variations in monsoonal rainfall

impact of bolivian paleolake evaporation on the δ18o of the andean glaciers during the last deglaciation 18 5 11 7 ka diatom inferred δ18o values and hydro isotopic modeling abstract during the last deglaciation the bolivian altiplano 15 23 s 66 70 w was occupied by paleolake tauca covering at least 51 000 km 2 at its maximum highstand between 16 5 and 15 ka twenty five hundred years later after a massive regression a new transgressive phase produced paleolake coipasa smaller than tauca and restricted to the southern part of the basin these paleolakes were overlooked at the west by the sajama ice cap the latter provides a continuous record of the oxygen isotopic composition of paleo precipitation for the last 25 ka contemporaneously to the end of paleolake tauca around 14 3 ka the sajama ice cap recorded a significant increase in ice oxygen isotopic composition 18 o ice this paper examines to what extent the disappearance of lake tauca contributed to precipitation on the sajama summit and this specific isotopic variation the water 18 o values of paleolakes tauca and coipasa 18 o lake were quantitatively reconstructed from 18 5 to 11 7 ka based on diatom isotopic composition 18 o diatoms and ostracod isotopic composition 18 o carbonates retrieved in lacustrine sediments at a centennial time scale a strong trend appears abrupt decreases of 18 o lake during lake fillings are immediately followed by abrupt increases of 18 o lake during lake level stable phases the highest variation occurred at 15 8 ka with a 18 o lake decrease of about 10 concomitant with the lake tauca highstand followed 400 years later by a 7 increase in 18 o lake a simple hydro isotopic modeling approach reproduces consistently this rapid decrease increase feature moreover it suggests that this unexpected re increase in 18 o lake after filling phases can be partly explained by an equilibration of isotopic fluxes during the lake steady state based on isotopic calculations during lake evaporation and a simple water stable isotopes balance between potential moisture sources at sajama advection versus lake evaporation we show that total or partial evaporation from 5 to 60 of paleolake tauca during its major regression phase at 14 3 ka could explain the pronounced isotopic excursion at sajama ice cap these results suggest that perturbations of the local hydrological cycle in lacustrine areas may substantially affect the paleoclimatic interpretation of the near by isotopic signals e g ice core or speleothems

a 3 800 million year isotopic record of life from carbon in sedimentary rocks an increased ratio of 12c to 13c an indicator of the principal carbon fixing reaction of photosynthesis is found in sedimentary organic matter dating back to almost four thousand million years ago a sign of prolific microbial life not long after the earth s formation partial biological control of the terrestrial carbon cycle must have been established very early and was in full operation when the oldest sediments were formed

phytolith evidence for c4 dominated grassland since the early holocene at long pocket northeast queensland australia abstract preliminary phytolith analysis of ephemeral lake fill sediment at long pocket near toomba northeast queensland australia indicates that a c4 dominated grassland with a minor woody component has been present in the region since ca 8000 cal yr b p based on the modern distribution of c4 and c3 native grasses in australia this suggests that mean summer temperatures of at least 14 c ca 10 c cooler than present were maintained since the early holocene this interpretation is comparable with previous studies which together imply that the establishment of c4 dominated grasses in central and northeast australia occurred between the last glacial maximum most likely after ca 16 000 14 c yr b p and ca 7200 14 c yr b p ca 8000 cal yr b p taxonomic composition of the grassland appears relatively consistent since the early holocene at long pocket and includes phytoliths comparable with those from modern arundinoideae panicoideae and chloridoideae rare non grass phytoliths are also present a gradual decrease in abundance of saddle phytolith forms attributed to chloridoideae grasses from the base of the record at ca 6500 7000 cal yr b p suggests decreasing aridity throughout the holocene this trend could reflect a locally drawn out effect of the end of the postglacial arid period due to the well drained basalt flow catchment maintaining a local arid habitat for the chloridoideae grasses

key drivers controlling stable isotope variations in daily precipitation of costa rica caribbean sea versus eastern pacific ocean moisture sources abstract costa rica is located on the central american isthmus which receives moisture inputs directly from the caribbean sea and the eastern pacific ocean this location includes unique mountainous and lowland microclimates but only limited knowledge exists about the impact of relief and regional atmospheric circulation patterns on precipitation origin transport and isotopic composition therefore the main scope of this project is to identify the key drivers controlling stable isotope variations in daily scale precipitation of costa rica the monitoring sites comprise three strategic locations across costa rica heredia central valley turrialba caribbean slope and cano seco south pacific slope sporadic dry season rain is mostly related to isolated enriched events ranging from 5 8 to 0 9 18o by mid may the intertropical convergence zone reaches costa rica resulting in a notable depletion in isotope ratios up to 18 5 18o hysplit air mass back trajectories indicate the strong influence on the origin and transport of precipitation of three main moisture transport mechanisms the caribbean low level jet the colombian low level jet and localized convection events multiple linear regression models constructed based on random forests of surface meteorological information and atmospheric sounding profiles suggest that lifted condensation level and surface relative humidity are the main factors controlling isotopic variations these findings diverge from the recognized amount effect in monthly composite samples across the tropics understanding of stable isotope dynamics in tropical precipitation can be used to a enhance groundwater modeling efforts in ungauged basins where scarcity of long term monitoring data drastically limit current and future water resources management b improve the re construction of paleoclimatic records in the central american land bridge c calibrate and validate regional circulation models

calibration of the speleothem delta function an absolute temperature record for the holocene in northern norway the speleothem delta function sdf provides a new transfer function between the d18o signal of speleothem calcite and surface ground temperature the function is based on physical principles relating d18o of the calcite to thermodynamic fractionation and to the dripwater function which in turn relates d18o of dripwaters to that of the local precipitation and thus to the modification of source water in relationship to the geographical position of the site the sdf must be calibrated against at least two reliable and well dated palaeotemperature points the end product is a reconstruction of absolute cave and surface temperatures the technique is tested using a holocene speleothem from north norway sg93 dated by 12 tims u th dates the reconstructed temperature curve is presented and compared with the gisp2 ice core record and with the historic record in both cases the correlation with sg93 is impressive indicating the validity of the technique

monsoon source shifts during the drying mid holocene biomarker isotope based evidence from the core monsoon zone cmz of india abstract a better understanding of past variations of the indian summer monsoon ism that plays a vital role for the still largely agro based economy in india can lead to a better assessment of its potential impact under global climate change scenarios however our knowledge of spatiotemporal patterns of ism strength is limited due to the lack of high resolution continental paleohydrological records here we reconstruct centennial scale hydrological variability during the holocene associated to changes in the intensity of the ism based on a record of lipid biomarker abundances and compound specific stable isotopic composition of a 10 m long sediment core from saline alkaline lonar lake situated in the core monsoon zone of central india we identified three main periods of distinct hydrology during the holocene in central india the period between 10 1 and 6 cal ka bp was likely the wettest during the holocene lower average chain length acl index values 29 4 28 6 and negative 13 c wax values 34 8 to 27 8 of leaf wax n alkanes indicate the dominance of woody c 3 vegetation in the catchment and negative d wax values concentration weighted average 171 to 147 suggest a wet period due to an intensified monsoon after 6 cal ka bp a gradual shift to less negative 13 c wax values particularly for the grass derived n c 31 and appearance of the triterpene lipid tetrahymanol generally considered as a marker for salinity and water column stratification mark the onset of drier conditions at 5 1 cal ka bp an increasing flux of leaf wax n alkanes along with the highest flux of tetrahymanol indicate a major lowering of the lake level between 4 8 and 4 cal ka bp we find evidence for a transition to arid conditions indicated by high and strongly variable tetrahymanol flux in addition a pronounced shift to less negative 13 c wax values in particular for n c 31 25 2 to 22 8 during this period indicates a change of dominant vegetation to c 4 grasses in agreement with other proxy data such as deposition of evaporite minerals we interpret this period to reflect the driest conditions in the region during the last 10 1 ka this transition led to protracted late holocene arid conditions after 4 ka with the presence of a permanent saline lake supported by the sustained presence of tetrahymanol and more positive average d wax values 122 to 141 a late holocene peak of cyanobacterial biomarker input at 1 3 cal ka bp might represent an event of lake eutrophication possibly due to human impact and the onset of cattle livestock farming in the catchment a unique feature of our record is the presence of a distinct transitional period between 4 8 and 4 cal ka bp which was characterized by some of the most negative d wax values during the holocene up to 180 when all other proxy data indicate the driest conditions during the holocene these negative d wax values can as such most reasonably be explained by a shift in moisture source area and or pathways or rainfall seasonality during this transitional period we hypothesize that orbital induced weakening of the summer solar insolation and associated reorganization of the general atmospheric circulation as a possible southward displacement of the tropical rainbelt led to an unstable hydroclimate in central india between 4 8 and 4 ka our findings shed light onto the sequence of changes during mean state changes of the monsoonal system once an insolation driven threshold has been passed and show that small changes in solar insolation can be associated with major hydroclimate changes on the continents a scenario that may be relevant with respect to future changes in the ism system

the effect of species on lacustrine δ18odiatom and its implications for palaeoenvironmental reconstructions the oxygen isotope composition of diatom silica 18odiatom is increasingly being used to reconstruct climate from marine and lacustrine sedimentary archives although diatoms are assumed to precipitate their frustule in isotopic equilibrium with their surrounding water it is unclear whether internal processes of a given species affect the fractionation of oxygen between the water and the diatom we present 18odiatom data from two diatom size fractions 3 38 and 38 m characterized by different species in a sediment core from heart lake alaska differences in 18odiatom between the two size fractions varies from 0 to 1 2 with a mean offset of 0 01 n 20 fourier transform infrared spectroscopy confirms our samples consist of pure biogenic silica sio2 and 18odiatom trends are not driven by contamination the maximum offset is outside the range of error but the mean is within analytical error of the technique 1 06 demonstrating no discernible species dependent fractionation in 18odiatom we conclude that lacustrine 18odiatom measurements offer a reliable and valuable method for reconstructing 18owater considering the presence of small offsets in our two records we advise interpreting shifts in 18odiatom only where the magnitude of change is greater than the combined analytical error

a petrographic and geochemical record of climate change over the last 4600years from a northern namibia stalagmite with evidence of abruptly wetter climate at the beginning of southern africa s iron age abstract stalagmite dp1 a speleothem 1 6 m in length from dante cave in northeastern namibia provides a paleoclimate record of a gradual transition from wetter to drier conditions from 4 6 to 3 3 ka bp a variable but pronounced dry period from 3 3 to 1 8 ka and a wetter but variable period from 1 8 ka to the present this record is based on 30 u th radiometric dates and their resulting calculated growth rates and on c and o stable isotope data relative proportions of aragonite and calcite in layers measurements of stalagmite width along layers and observation of petrographic surfaces suggestive of changes from drier to wetter conditions and vice versa the stalagmite s first deposition which seemingly followed conditions too wet for deposition coincided with desiccation in the sahara and the end of the african humid period there gradual drying continued and led to a sustained very dry period from 3322 11 to 1786 10 bp a 2 3 ka bp dry period that dry period began and ended abruptly the abrupt transition from drier to wetter conditions at 1 8 ka coincides with the beginning of the iron age in southern africa suggesting that wetter conditions facilitated migrations and or changes in food production that may have contributed to a transition in human technologies and lifestyles this transition is coeval with transitions to colder conditions in ice core records from greenland and antarctica the dp1 record suggests considerable change over the past 1800 years with at least three wet dry cycles the wettest conditions may have occurred relatively recently between 230 and 100 bp a d 1720 and 1850 so that early european explorers may have seen and or heard reports of conditions among the wettest during the later holocene in southern africa

resolving seasonality in tropical trees multi decade high resolution oxygen and carbon isotope records from indonesia and thailand abstract dendrochronological techniques have found limited applications in the tropics because of invisible or indistinct banding in wood the seasonal cycles of rainfall and relative humidity in these regions while not sufficient to produce distinct visible rings may still generate seasonal signals in the oxygen isotopic composition of tree cellulose which can be used for climate reconstruction and chronology we explore this approach using trees from indonesia and thailand from three different families multi decade 18o records from javanese cross dated teak rings and bomb radiocarbon dated suar wood lacking visible rings demonstrate the reproducibility of the signal between trees grown at the same locality as well as from wider geographical regions these results confirm predictions that the trees oxygen isotopic signatures reflect an external climatic forcing high resolution 18o records reveal large seasonal cycles up to 4 for javanese suar samples and up to 18 for a thai podocarpus sample we show that the six 18o and 13c cycles measured on a podocarpus match the number of growth years for the period spanning the time of wounding and cutting of the wedge section this result demonstrates that the isotopic cycles found in this tree with indistinct annual rings are indeed seasonal and could be used for chronology we present evidence that stable isotope chronologies of tropical trees also contain insights in tropical tree physiology and growth dynamics

combined records from a stalagmite from barbados and from lake sediments in haiti reveal variable seasonality in the caribbean between 6 7 and 3 ka bp abstract the growth of a well dated stalagmite from barbados records high infiltration rates into the karst aquifer and hence increased rainfall intensity between 6 7 and 3 ka bp in agreement with records from lake miragoane haiti hodell et al 1991 reconstruction of the caribbean climate change over the past 10 500 years nature 352 790 793 mainly reflecting the insolation maximum of the northern hemisphere both the lake record and the stable isotope record of the stalagmite reveal additional centennial variability of recharge high oxygen isotope values in stalagmite calcite corresponding to reduced recharge are synchronous with periods of lower stable isotope values recorded in lake miragoane ostracods previously attributed to enhanced precipitation accordingly periods of increased recharge in barbados correspond to 18o enriched isotope values of ostracods which were attributed to higher evaporation precipitation ratios in the lakes we ascribe this apparent discrepancy to changes in seasonality i e winter periods of reduced temperature and relative humidity following summer months of increased precipitation at present such climate conditions occur during periods of enhanced northern atlantic oscillation nao if enhanced seasonality is a consequence of a nao situation the apparent discrepancy of high isotope values in lakes previously attributed to droughts can be reconciled with lower winter temperatures in the lakes further the correlation of solar intensity derived from 14c and 10be with the isotopic signals recorded in the lacustrine sediments suggests a solar forcing of the nao during the mid holocene

diatom phytolith and pollen records from a 10be 9be dated lacustrine succession in the chad basin insight on the miocene pliocene paleoenvironmental changes in central africa abstract a discontinuous 200 m long borehole drilled in the bol archipelago 13 n lake chad provided 25 samples which were dated using the 10 be 9 be method and analyzed for their micro biological content the dating provided ages ranging from 6 3 0 1 to 2 6 0 1 ma a period contemporaneous with the pliocene fossil localities located in the current djurab desert of chad 16 17 n well preserved diatom assemblages first occurred at 4 7 0 1 ma and were dominated by the freshwater planktonic genera aulacoseira and stephanodiscus until the end of the pliocene this supports the recurrence of lacustrine conditions at bol during all the pliocene the presence of pelite and argillaceous deposits in the core before 4 7 0 1 ma however suggests that the lake settled earlier at least since 6 3 0 1 ma the abundance of afromontane pollen taxa at 4 2 0 1 ma and the occurrence of trapeziform polylobate phytoliths throughout the sequence suggest significant vegetation inputs from the southern highlands while the importance of kaolinite in the clay sediments indicates a water supply predominantly from the south during the pliocene phytolith assemblages are all dominated by lobate grass silica short cells and by blocky and elongate types which attest to the presence of herbaceous dominated vegetation around bol and or in the southern drainage basin during the pliocene this result is also supported by the pollen assemblage described at 4 2 0 1 ma which shows highest affinity for the savanna biome moreover low values for the xerophytic grass phytolith index indicate the presence of humid loving mesophytic and aquatic grass communities in this vegetation at last significant variations in the abundance of blocky and elongate phytoliths are indicative of local alternations of fully lacustrine and marshy conditions at bol particularly between 3 6 and 2 7 ma the abundance of silicified bulliform cells combined with the absence of diatoms support a significant lacustrine reduction at bol favoring the increasing of local marshy vegetation

persistent multidecadal power of the indian summer monsoon article i nfo the instrumental record of indian summer monsoon ism precipitation displays two complete manifesta tions of an inferred multidecadal cycle hitherto no precipitation sensitive proxy record from the indian subcontinent has had the necessary resolution and length to adequately assess whether this observed feature is an inherent aspect of the ism system on longer timescales here we present compelling evidence for persistence of this cycle using a millennial length ad 600 1550 and sub annually resolved speleothem oxygen isotope record 18 o from dandak cave in east central india the record displays a high degree of correlation with a speleothem based asian monsoon reconstruction from wanxiang cave in north central china on annual to decadal timescales showing theregional significanceof these findings theobserved period inourmonsoonreconstructionissimilartothatassociatedwiththegleissbergsolarcycleandmultidecadalsea surface temperature variability in the north atlantic amo both of which are often cited as the prominent pacemakers of ism variability on multidecadal timescales we document transient coherence between ism precipitation amount and solar variability that persists exclusively in the century prior to and during the medieval climate anomaly nominally ad 950 1300 the non stationary nature of the sfv monsoon relationship presented here may be evidence of the time varying influence of tropical ocean atmosphere dynamics on the solar monsoon link however it is not possible to show with significance that this period of coherenceisanythingmorethananartifactoftwotimeserieswithsimilarspectra wetherefore areinclinedto interpret our record as evidence of a minimal role of solar variability in driving persistent multidecadal variability of the ism multidecadal sst variability in the north atlantic remains as the likely alternative driver for persistence of this cycle regardless of the causative mechanism s the amplitude and regional signature of the observed cycle in ism precipitation highlight its societal importance with respect to forecasting ism precipitation on multidecadal timescales

intensification of monsoon microclimate and asynchronous c4 appearance isotopic evidence from the indian siwalik sediments article i nfo analysis of the d h ratio of pedogenic clay and the 18 o 16 o ratio of carbonate nodules collected from siwalik sediments in india indicates three episodes of monsoon intensification at 11 ma 6 ma and 3 ma these episodes coincide with major pulses of tectonic uplift in the himalayas suggesting causal link between monsoon intensity and uplift in addition variation in the carbon isotope ratio of carbonate nodules and residual organic matter indicates a change in vegetation regime from pure c3 type to a mix of c3 c4 type during this time span isotopic analysis of samples collected from different locations of the himalayan siwalik shows that the late miocene c4 appearance was locally asynchronous by 3 ma similar to what is seen on a global scale the lack of synchronous emergence of c4 plants in various parts of siwalik probably indicates a combined effect of microclimate e g varying monsoon intensity and habitat disturbance e g forest fire in contrast subsequent expansion of c4 plants during the late miocene pliocene time could be entirely due to monsoon intensification that favoured c4 respiration in a warm and seasonally variable rainfall regime 2010 elsevier b v all rights reserved

a comparison of the palaeoclimate signals from diatom oxygen isotope ratios and carbonate oxygen isotope ratios from a low latitude crater lake the analysis of oxygen isotope ratios 18o from authigenic lake carbonates has become a well established palaeoclimate technique less common is the use of 18o in biogenic silica e g diatoms sponge spicules phytoliths but the technique is being increasingly utilised for non carbonate lakes this paper aims to compare 18odiatom with 18ocarbonate in a low latitude closed basin lake due to the influence of ph rarely are both carbonate and diatoms preserved in lake sediments in concentrations high enough to measure oxygen isotopes the 18o composition of both carbonate and silica should reflect the isotope composition and temperature of the lake water at the time of precipitation and hence theoretically they should be equivalent only one comparative study of 18odiatom and 18ocarbonate currently exists and that found differences between their 18o compositions probably because they precipitated in different seasons unless there is evidence to suggest that silica and carbonate precipitate at the same time their 18o records are likely to be different but complementary in this study we show that 18odiatom and 18ocalcite from lake tilo ethiopia show some similar broad climate trends however the 18odiatom curve is generally more variable and does not record two regional arid events picked up by the 18ocalcite data several possible reasons for this are discussed the precision of the 18odiatom extraction technique contamination of the diatom samples from tephra volcanic glass vital effects in the diatom samples differences in their respective equilibrium isotope fractionation rates and the possibility that the dominant diatom aulacoseira granulata and calcite precipitated in different seasons during this time currently the problems associated with the cleaning and extraction of 18odiatom suggests that details found in 18ocalcite records may be lost in 18odiatom records where contaminants such as tephra and clay minerals are difficult to remove

δd values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha abstract a set of lake surface sediment samples and aquatic macrophytes from the eastern and central tibetan plateau and a sediment core from koucha lake northeastern tibetan plateau were analysed for hydrogen isotope signals of aliphatic lipid biomarkers the d values of n alkanes were correlated with those of meteoric water in the summer months and showed increasing pearson correlation coefficients with increasing n alkane chain length r 0 80 for n c 31 while in samples from the most humid regions southeastern tibetan plateau the apparent enrichment factors between meteoric water and lipids are close to those reported for other humid sites e 135 for mid chain and 125 for long chain n alkanes they become smaller e 118 to 41 mean value 86 at sites with a negative moisture balance northeastern and central tibetan plateau and qaidam basin this might be caused by enrichment in deuterium of the source water used for lipid synthesis as a result of lake water evaporation and soil and leaf water evapotranspiration in the core from lake koucha decreasing d values of all n alkanes between 15 and 10 cal ka bp give evidence for an intensification of the asian summer monsoon at ca 9 cal ka bp a ca 15 shift towards higher d values of mid chain n alkanes suggests enhanced evaporation of the lake water which outweighs higher precipitation amounts because of a temperature increase during the early holocene monsoonal maximum only a few surface sediment samples show a significant offset between d values of mid chain n alkanes and n c 31 d mid n c31 and no systematic dependence between this offset and environmental parameters such as mean annual precipitation was found in the core available data for most samples also do not show a significant offset only a slight increase 15 of d mid n c31 at ca 10 0 cal ka bp and a decrease 17 at ca 6 8 cal ka bp might indicate wetter and drier conditions respectively however interpretation of d mid n c31 throughout the record is difficult because of a lack of reliable data for n c 31 in key sections of the core so more records are necessary to further test the potential applicability of d mid n c31 as a proxy for palaeo hydrological conditions

reassessment of lake victoria upper nile river paleohydrology from oxygen isotope records of lake sediment cellulose reconstruction of lake water 1 8 o from analysis of cellulose 1 8 o in two sediment cores from lake victoria east africa shows a large shift to lower values during the terminal pleistocene this shift records the transition from closed to open basin conditions following desiccation at the last glacial maximum although oxygen isotope analysis of cellulose from one core had placed this overflow at 8 ka 7200 1 4 c yr b p reevaluation of the age model for this core in addition to new stratigraphic and chronological evidence from a second core suggests that basin overflow was established much earlier ca 13 ka our refined view of the timing of lake victoria overflow inferred from the oxygen isotope records is consistent with other paleolimnological studies indicating that lake sediment cellulose is an effective and sensitive isotopic archive of major hydrologic events in this region

shifts in late paleozoic atmospheric circulation over western equatorial pangea insights from pedogenic mineral δ18o compositions the d 18 o values of pedogenic calcites phyllosilicates and iron oxyhydr oxides from fossil soils throughout the southwestern united states show systematic paleolatitudinal and temporal trends that indicate a significant change in soil moisture conditions and atmospheric circulation patterns over southwestern euramerica throughout latest pennsylvanian and early permian time a progressive depletion of as much as 6 in mineral 18 o values with increasing distance northward to 108 of the paleoequator indicates a weakening or disruption of zonal easterly flow over the study area by latest pennsylvanian time furthermore elevated d 18 o values suggest a proximal source of paleoprecipitation over the study area perhaps due to initiation of reversed equatorial flow over tropical southwestern euramerica coupling of the geographic and temporal trends defined by pedogenic mineral d 18 o values with those defined by climatically sensitive paleosol pedotypes in the study area along with overall elevated mineral d 18 o values provides some of the strongest evidence that northern hemisphere monsoonal circulation was well established over pangea by early permian time

oxygen isotopes in cellulose from modern and quaternary intertropical peatbogs implications for palaeohydrology abstract cellulose 18o values were measured in modern peatbog plants in recent peats and in mountain peatbog cores from burundi in a study of the hydrologic control of the frsol 18o 16o ratio in intertropical peat cellulose modern plants and waters were collected under various altitudes 800 2500 m a s l with mean annual relative humidity ranging from 0 72 to 0 82 the water 18o values i vary between 4 and 2 5 the cellulose water enrichment is of 25 3 0 5 for aquatic plants of 24 6 emergent plant species the scatter in the cellulose 18o values in vary between 4 and 2 5 the cellulose water enrichment is cellulose 18o values of emergent plantss tend to decrease with increasing elevation 0 6 to 0 07 per 100 m and relative humidity 0 5 to 0 1 per mean emergent plant 18o values are approximated within 0 6 by available cellulose 18o models relating cellulose 18o to the relative humidity h and the environmental water 18o except in a large swampy system peats were subsampled in core ka 2 kashiru burundi 3 28 s 29 34 e 890 cm long 2240 m a s l altitude and for control in the topmost 50 cm of core ku 2 kuruyangwe 3 35 s 29 41 e 2020 m a s l altitude similar 18o vaues 26 to 28 5 were found in the topmost 50 cm of both cores they compare well with the mean 18o for modern emergent plants at kashiru ams 14c dating showed that core ka 2 spans the last 30 ka celluloses are mainly derived from emergent plants and yield 18o values ranging from 19 to 29 with the highest values between 2 1 and 0 ka and the lowest values 19 to 23 5 between 6 and 4 5 ka for the period between 6 and 4 5 ka the models yield a decrease in in of 4 to 2 5 relative to present for an h increase of 6 to 11 before 11 7 ka the models yield a in value close to the present value for an h increase of 6

an isotopic study of paleosol carbonates from olduvai gorge the isotopic composition of paleosol carbonates from olduvai gorge can be used to give estimates of the paleoclimatic history of east africa during the plio pleistocene oxygen isotopes are indicative of major changes in the isotopic composition of meteoric water while carbon isotopes are indicative of major changes in the fraction of biomass using the hatch slack c4 photosynthetic pathway three major periods of climatic change in this terrestrial setting occurred at about 1 67 1 3 and 0 6 myr these involved major changes in flora as well as major changes in the isotopic composition of meteoric water overall the climate has become warmer and more arid over the past 2 2 myr

atmospheric circulation patterns during late pleistocene climate changes at lake malawi africa abstract the climate of tropical africa transitioned from an interval of pronounced orbitally paced megadroughts to more humid and stable conditions approximately 70 000 years ago scholz et al 2007 the regional atmospheric circulation patterns that accompanied these climatic changes however are unclear due to a paucity of continental paleoclimate records from tropical africa extending into the last interglacial we present a new 140 kyr record of the deuterium hydrogen isotopic ratio of terrestrial leaf waxes d wax from drill cores from lake malawi southeast africa that spans this important climatic transition d wax shifts from highly variable and relatively d depleted to more stable and d enriched around 56 ka contemporary with the onset of more humid conditions in the region moisture source and transport history dominate the d wax signal at lake malawi with local rainfall amount playing a secondary role for much of the paleorecord analysis of modern moisture sources for lake malawi suggests that d depletion of waxes during the megadroughts may have been caused by an enhanced contribution of the drier d depleted air mass currently located in central southern africa to the lake malawi catchment this d depleted air mass is associated with the descending limb of the hadley cell which implies significant changes in the hadley circulation during the megadroughts and related changes in the position of the intertropical convergence zone over africa these findings demonstrate the ability of d wax to serve as an atmospheric tracer when used in conjunction with additional proxy records for moisture balance and elucidate potential mechanisms for pronounced hydrological change in southeast africa during the late pleistocene

compound specific carbon isotope records of vegetation and hydrologic change in central sulawesi indonesia since 53 000 yr bp lake matano 2 29 1 s 121 20 e in central sulawesi the deepest and one of the largest lakes in indonesia provides an excellent opportunity to reconstruct long term hydrological and vegetation changes at the heart of the maritime continent within the tropical western pacific warm pool we measured the carbon isotopic composition of terrestrial leaf waxes 13cwax in new sediment cores from lake matano to understand regional variations in vegetation and their interactions with local and high latitude climate forcings during the past 53 kyr variations in 13cwax record the expansion and contraction of c3 versus c4 vegetation as well as changes in plants carbon and water use efficiency and by inference regional hydroclimate during marine isotope stages 1 and 3 more negative 13cwax values indicate that closed canopy c3 rainforests predominated in sulawesi reflecting a wetter less seasonal climate in contrast more positive 13cwax values record a terrestrial ecosystem with more abundant open canopy vegetation and possible expansion of c4 grasses between 29 and 14 ka bp indicating that during marine isotope stage 2 including the last glacial maximum the climate was more arid likely with increased precipitation seasonality in central sulawesi comparison of our record with other paleovegetation and paleohydrological records from sulawesi and nearby islands suggests coherent long term hydrological changes in central indonesia that appear to be sensitive to high latitude climate across glacial interglacial boundaries however variations in the amplitude of the response of vegetation to these glacial interglacial forcings highlight the importance of regional topographic control on climate and vegetation and suggest an important role for higher elevations in maintaining rainforest refugia during regionally arid time intervals when c4 savannas and grasslands expanded at lower elevations

tree ring cellulose δ18o of fokienia hodginsii in northern laos a promising proxy to reconstruct enso 1 a tree ring cellulose 18o chronology of fokienia hodginsii from 1951 to 2002 is established by four cores from four different trees to explore its potential for reconstructing climatic variations in northern laos this chronology is the first tree ring 18o chronology from laos as well as the first for this species we compare variations of tree ring cellulose 18o and ring width between cores the results suggest that the 18o time series are more strongly correlated between different trees than ring width time series are in addition correlation analysis shows a significantly negative correlation between tree ring cellulose 18o and the may october palmer drought severity index pdsi while the tree ring width indices have a poor correlation with pdsi the spatial correlation analysis between tree ring cellulose 18o and global sea surface temperature and the time series correlation analysis between tree ring cellulose 18o and the multivariate el nino southern oscillation enso index mei during the investigated period 1951 2002 reveal that enso has an important effect on tree ring cellulose 18o in laos our results indicate that the tree ring cellulose 18o of fokienia hodginsii is a promising proxy to reconstruct pdsi in southeast asian countries such as laos and to discuss their teleconnections with global atmospheric circulations such as enso

a review of the oxygen isotope composition of lacustrine diatom silica for palaeoclimate reconstruction diatom silica frustules are a form of biogenic opal and contain oxygen isotopes that are being increasingly used in palaeoclimate studies frustules are comprised of an inner tetrahedrally bonded silica skeleton si o si with an outer hydrous layer the hydrous layer is freely exchangeable and must be removed prior to oxygen isotope measurement using oxidising reagents and or high temperatures analysis of the oxygen isotope composition of diatom silica requires samples that are almost pure diatomite since extraction techniques will liberate oxygen from all the components in the sediment there is a generally acceptable protocol involving chemistry sieving and settling techniques and more recently laminar flow separation recent studies of lacustrine diatoms have shown that even a small proportion of contaminant can have a significant influence on the oxygen isotope value all lake sediments require their own specific procedure and every sample must be scrutinised by microscopy to check for the level of contamination prior to analysis where sediment cannot be purified sufficiently a semi quantitative assessment of the diatom content can facilitate mass balance techniques when robust preparation methods are used diatom silica offers an important palaeoclimate proxy providing an additional complementary rather than an alternative host of oxygen isotopes in carbonates in lacustrine isotope studies it is often assumed but rarely proven that diatom silica form in isotope equilibrium and hence empirically derived palaeotemperature equations usually made in vitro can be used most studies lack the detailed investigation of contemporaneous materials from natural waters of the region under study to test these equations further investigations need to be conducted in order to understand the systematic relationship between temperature water isotope composition and diatom isotope composition to enable quantitative interpretation of the sediment record experiments to test for vital effects and inter specific differences have so far revealed little variation it is useful to know when and where the diatom silica is formed in the modern environment so details of diatom ecology are important in the interpretation of isotope data here we show that valuable palaeoclimate data can be gained from the oxygen isotope composition of diatom silica 18odiatom especially since diatoms are abundant in many lakes sensitive to climate variation where other hosts e g carbonates are absent to date the most successful studies have been conducted in areas where the 18odiatom registers changes in the oxygen isotope composition of the lake water rather than temperature which is then related to other aspects of climate in these studies the range of values obtained is often greater than the error introduced by contaminating materials

the provenance of vegetation and environmental signatures encoded in vascular plant biomarkers carried by the ganges brahmaputra rivers organic matter carried by rivers and deposited in continental and marine sediments contains valuable information on past environmental conditions and their impact on the terrestrial biosphere in order to use sedimentary records to reconstruct past environmental conditions on the continents such as vegetation cover and type or precipitation intensity we need to understand the provenance of the organic signatures and how they are transferred and potentially modified by fluvial transport to the sedimentary reservoir in particular we need to understand how environmental conditions are imprinted in the composition of riverine particulate organic carbon here we investigate the stable carbon and hydrogen isotopic signatures of vascular plant leaf wax biomarkers in the modern day ganges and brahmaputra river complex one of the largest fluvial systems on earth the distribution of n alkanes and n alkanoic acids in ganges brahmaputra river sediments suggests that vascular plant inputs are consistently a significant component of the organic carbon pool molecular 13c measurements reveal that c3 vegetation inputs delivered by the himalayan rivers are partly degraded and replaced by mixed c3 c4 vegetation input in the floodplain the hydrogen isotopic composition of long chain c24 n alkanoic acids in combination with their stable c isotopic composition provides constraints on the isotopic composition of the environmental water used by higher plants within the drainage basin calculated compositions compare well with the depleted d isotopic ratios of the river water during the summer monsoon suggesting that h isotopic compositions of long chain alkanoic acids are a valuable proxy for the composition of summer monsoon moisture in the ganges brahmaputra basin detailed studies of the isotopic anatomy of modern river systems are critical for informed interpretation of marine sedimentary records in river influenced continental margins

concurrent purification of sterols triterpenols and alkenones from sediments for hydrogen isotope analysis using high performance liquid chromatography three methods are presented on how to purify acetylated sterols acetylated triterpenols and individual alkenones for hydrogen isotope analysis from marine and lacustrine sediments using reverse phase high performance liquid chromatography rp hplc the main advantages over previous hplc methods are reduced operator time increased automation and the ability to simultaneously purify multiple target compounds from a sample these gains are achieved primarily by acetylating compounds prior to purification rather than after and also by using a fraction collector with semi preparatory rather than analytic configuration the effectiveness of the method is demonstrated for i dinosterol and taraxerol in sediment from the brackish pond poza del diablo galapagos ii for di and tri unsaturated c37 and c38 alkenones in cultured emiliania huxleyi iii for brassicasterol and di tri and tetra unsaturated c37 alkenones in sediment from manito lake saskatchewan canada and iv for brassicasterol dinosterol and di tri and tetra unsaturated c37 alkenones in sediment from the great salt lake utah the purification process yields 80 90 recoveries and results in no measurable hydrogen isotope alteration

abrupt variations in south american monsoon rainfall during the holocene based on a speleothem record from central eastern brazil well dated high resolution oxygen isotope records of speleothems in central eastern brazil spanning from 1 3 to 10 2 kyr b p reveal that the occurrence of abrupt variations in monsoon precipitation is not random they show a striking match with bond events and a significant pacing at 800 yr a dominant periodicity present in sea surface temperature records from both the north atlantic and equatorial pacific oceans that is possibly related to periods of low solar activity high 14 c based on the atmospheric 14 c record the precipitation variations over central eastern brazil are broadly antiphased with the asian and indian monsoons during bond events and show marked differences in duration and structure between the early and late holocene our results suggest that these abrupt multicentennial precipitation events are primarily linked to changes in the north atlantic meridional overturning circulation amoc anomalous cross equatorial flow induced by negative amoc phases may have modulated not only the monsoon in south america but also affected el nino like conditions in the tropical pacific during the holocene

a 400 year record of hydroclimate variability and local enso history in northern southeast asia inferred from tree ring δ18o abstract we present here a chronology of tree ring cellulose 18 o for the period 1588 2002 based on individual measurements of seven fokienia hodginsii trees growing in northern laos response function analysis of meteorological data revealed that this oxygen isotope chronology has a significant negative correlation with monsoon season precipitation the water level of the mekong river and the palmer drought severity index pdsi our reconstructed monsoon season pdsi which accounts for 41 5 of pdsi variance showed that wetter phases occurred during the periods ad 1660 1695 and ad 1705 1790 that the main drier periods were ad 1630 1660 ad 1900 1940 and ad 1954 2002 and that there has been a trend of decreasing moisture during the monsoon season over the last 200 years a reduction in monsoon activity can also be seen in various tree ring oxygen isotope records from the himalaya tibet plateau and southeast asia rising sea surface temperatures over the tropical pacific and indian ocean could be responsible for this reduction in the asian summer monsoon by combining proxies sensitive to the el nino southern oscillation enso in northern laos and vietnam we were able to reconstruct the annual multivariate enso index mei and local enso event history and so improve our understanding of long term variations in enso and its influences on southeast asia

tufa as a record of perennial fresh water in a semi arid rift basin kapthurin formation kenya lithological and biological features of a fossiliferous tufa in the kapthurin formation baringo kenya reveal the presence of a lush wetland in a semiarid environment during the middle pleistocene ca 500 ka in this portion of the east african rift valley four geological sections each between 3 m and 8 m in thickness exposed over a distance of 0ae5 km reveal a 1 to 2 m thick paludal tufa which is composed of three carbonate beds two dark grey silty claystones and a reddish brown silty palaeosol high resolution stratigraphic analysis carbonate petrography stable isotope and elemental geochemistry clay mineralogy and fossil remains molluscs ostracods diatoms and charophytes reveal a ground water fed system that fluctuated in depth and periodically disappeared altogether oxygen isotope ratios d 18 o of tufa matrix range from 4ae5 to 8ae0 vienna pee dee belemnite and become more positive up section indicating the decreasing influence of fault related fluids and increasing residence time or freshness of wetland water rather than evaporative enrichment this spring was situated on a lake margin during low lake levels thrived during periods of increased ground water input and was ultimately replaced by an alkaline lake the wetland would appear to have existed during a cool interval within the generally warm marine isotope stage 13 or perhaps during the warm second half of marine isotope stage 13 the ground water source of this wetland arose through a fault system thus the position of the tufa deposit is controlled structurally but the timing and duration of the wetland system may have been influenced by both climatic and tectonic factors

late quaternary palaeoecology palynology and palaeolimnology of a tropical lowland swamp rawa danau west java indonesia abstract sedimentological limnological and palynological analyses of a sediment core from a lowland site in west java indonesia provide a detailed palaeoenvironmental record for the late glacial and the holocene the record suggests open vegetation under inferred drier climatic conditions for the late glacial however there is no unequivocal evidence for cooler conditions at this time the onset of the holocene coincides with a change to more humid climatic conditions with the development of a fern rich closed forest vegetation type dramatic changes in diatom community composition provide a striking record of habitat change associated with lake shallowing but this process appears to be a result of basin in filling rather than variations in precipitation evaporation balance associated with climatic fluctuations evidence for human impact on the vegetation development is restricted to the last few hundred years

paleoclimatic reconstruction in northern oman based on carbonates from hyperalkaline groundwaters abstract a paleoclimatic reconstruction for the past 35 000 years for northern oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs high ph groundwaters ph up to 11 9 discharge from the mantle sequence of the oman ophiolite as the product of modern low temperature serpentinization under arid climatic conditions hyperalkaline discharge occurs at the surface uptake of atmospheric co 2 precipitates characteristic laminated travertines accompanied by strong kinetic depletion of 13 c and 18 o pluvial climates supporting a shallow bicarbonate groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite replaced roots and stems all such carbonates have modern initial 14 c contents allowing radiocarbon dating and paleoclimatic reconstruction for the late pleistocene and holocene our reconstruction shows a dominantly wet late pleistocene up to 19 000 yr b p when a phase of climatic deterioration began leading to a period of hyperaridity which dominated from ca 16 300 to 13 000 yr b p the early holocene pluvial occurred from 12 500 to ca 6500 yr b p and was followed by renewed climatic deterioration and the current phase of hyperaridity comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the a rub al khali of central saudi arabia and the summer insolation driven monsoon record of east africa and the arabian sea is remarkably good

carbon isotopic evidence from paleosols for mixed c3 c4 vegetation in the bogota basin colombia abstract pollen reconstructions in the bogota basin colombia indicate the expansion of tropical high altitude grassland paramo at the expense of andean forests during glacial intervals the carbon isotopic composition 13c of soil organic matter som can be a useful indicator of changes in vegetation affecting grasslands because it distinguishes between two groups of grasses c3 and c4 adapted to different ecological environments values of som 13c were determined in four weathering profiles containing both modern holocene soils and paleosols formed during the last glacial stage these profiles are located along an altitudinal transect in the bogota basin extending from 2550 to 3100 m values of som 13c in the topsoil horizons reflect those of the native c3 vegetation that currently dominates the ecosystems in the colombian andes although c4 grasses are currently negligible in the basin elevated som 13c values indicative of c4 plants were found in two holocene soils environmental changes or ancient agricultural activities could explain the increased abundance of these plants in the basin during the late holocene isotopic values in the studied paleosols revealed the presence of a mixed c3 c4 vegetation in the basin during the last glacial stage thus indicating the expansion of c4 grasses we hypothesized that lowered pco2 and possibly reduced rainfall resulted in the colonization of the tropical andes by lowland c4 grasses despite of prevailing cooler temperatures

major environmental changes recorded by lacustrine sedimentary organic matter since the last glacial maximum near the equator lagoa do caco ne brazil sediment samples collected along a 6 m core drilled in the deepest part of the lagoa do caco ne brazil have been investigated in order to determine source s and degradation conditions of the organic matter om with special emphasis on paleoenvironmental implications bulk organic geochemistry rock eval pyrolysis c n determination 13c and 15n measurement and petrography combined with sedimentological evidence and radiocarbon dates allowed to identify four major intervals documenting major environmental changes that occurred during the last 20 000 years the first interval dating back to the end of the last glacial maximum lgm contains well preserved om derived from higher plants this material was most probably produced in an ephemeral palustrine system and rapidly buried by sands this level is thought to have been deposited under relatively arid climate conditions associated with strong but episodic rainfalls between 19 240 and 17 250 cal years bp the climate appears to have been more humid and seasonality more pronounced as suggested by the presence of a permanent lake after a drastic environmental change dating back to 17 250 cal years bp the sediment became truly lacustrine with restricted mineral input and highly degraded higher plant derived organic matter after that a stepwise improvement in the preservation of om occurred as revealed by several pronounced shifts in the rock eval tps2 signal these changes could document abrupt climatically driven changes during the late glacial finally around 5610 cal years bp environmental conditions approaching those prevailing today were established minor climatic changes during the holocene were probably buffered by a high water table which might explain the lack of paleoenvironmental fluctuations

stable isotope proxy records in tropical terrestrial environments abstract the tropics refers to an area that is loosely equatorial characterized by relatively high temperatures at low altitude comparatively low seasonal contrast in temperatures and generally high or highly seasonal rainfall the stable isotopes of carbon oxygen and hydrogen are increasingly important tools of relevance to understanding trajectories and mechanisms of past environmental change in the tropics in the case of carbon this is because at the broadest level the carbon isotope composition of organic and carbon containing inorganic proxy materials formed in the tropics can be read as being derived from the balance between c3 tree and c4 grass photosynthesis hence providing a relative measure of vegetation type and indirectly climate likewise changes in the oxygen and hydrogen isotope composition of many proxy materials again at the broadest level can be read as indicative of changes in hydrological conditions and or altitude in the past this review provides an entry point into the literature relating to the use of stable isotopes as terrestrial environmental proxies for past environmental change with a focus on the measurement and interpretation of stable isotope data from the wide range of proxy materials preserved in tropical environments

rapid post mortem maturation of diatom silica oxygen isotope values 1 oxygen isotope values of diatom silica 18odiatom are increasingly used as paleoclimate proxies however the magnitude and timing of post mortem alteration of 18odiatom values has been unclear in freshwater diatom silica from a human made pond in northern new mexico post mortem alteration of 18odiatom values occurs within one year of sediment burial diatom silica collected antemortem has an average 18odiatom value of 21 5 vsmow 1 3 n 23 whereas diatom silica from two sediment cores from the same freshwater environment records significantly higher 18odiatom values 28 9 0 8 n 13 the difference in ante and post mortem 18odiatom values indicate post mortem alteration of diatom silica oxygen that results in a 7 increase in 18o values this study demonstrates that 18odiatom values reach mature values within 0 5 years of frustule death initial diatom 18o values that record growing conditions are rapidly overwritten during silica maturation and the mature diatom 18o values approach isotopic equilibrium for quartz water the rapid post mortem alteration of diatom 18o values explains much of the disparate data regarding silica water fractionation for diatom silica and has a profound effect on the use of diatom silica 18o values as a paleoclimate proxy in lacustrine and marine environments

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

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

a model of fossil tooth and bone diagenesis implications for paleodiet reconstruction from stable isotopes abstract diagenesis of structural carbonate in biogenic apatite in the postmortem environment is modeled as a process of water mineral interaction both closed and open system model calculations suggest that 13 c of structural carbonate in biogenic apatite is much more resistant to diagenetic modification than 18 o apatite structural carbonate retains an original 13 c signal in closed system diagenesis for open systems 13 c of biogenic apatite with very low porosity such as tooth enamel can survive most diagenesis and retain a primary isotopic signature on the hand 18 o of structural carbonate in biogenic apatite may not be a reliable indicator of the original isotopic ratios except in a diagenetic system with low temperature and very low water biomineral ratio application of the model to teeth and carbonate cement in sediments from the badlands south dakota illustrates that 13 c values of enamel samples preserve the original signal whereas 13 c values of dentine represent varying extents of diagenesis 18 o values of fossil teeth may record an early or late part of their water biomineral interaction history during diagenesis

millennial scale trends in west pacific warm pool hydrology since the last glacial maximum models and palaeoclimate data suggest that the tropical pacific climate system plays a key part in the mechanisms underlying orbital scale and abrupt climate change atmospheric convection over the western tropical pacific is a major source of heat and moisture to extratropical regions and may therefore influence the global climate response to a variety of forcing factors the response of tropical pacific convection to changes in global climate boundary conditions abrupt climate changes and radiative forcing remains uncertain however here we present three absolutely dated oxygen isotope records from stalagmites in northern borneo that reflect changes in west pacific warm pool hydrology over the past 27 000 years our results suggest that convection over the western tropical pacific weakened 18 000 20 000 years ago as tropical pacific and antarctic temperatures began to rise during the early stages of deglaciation convective activity as inferred from oxygen isotopes reached a minimum during heinrich event 1 ref 10 when the atlantic meridional overturning circulation was weak pointing to feedbacks between the strength of the overturning circulation and tropical pacific hydrology there is no evidence of the younger dryas event in the stalagmite records however suggesting that different mechanisms operated during these two abrupt deglacial climate events during the holocene epoch convective activity appears to track changes in spring and autumn insolation highlighting the sensitivity of tropical pacific convection to external radiative forcing together these findings demonstrate that the tropical pacific hydrological cycle is sensitive to high latitude climate processes in both hemispheres as well as to external radiative forcing and that it may have a central role in abrupt climate change events

stable isotope geochronology of the australian regolith australian regolith profiles can be assigned to one of three post palaeozoic age groups on the basis of the oxygen isotope composition of authigenic clay minerals developed in the profile systematic variations in the isotopic composition of meteoric waters and therefore of the authigenic regolith minerals that formed in equilibrium with them are a result of the continent s drift from high to low latitudes and changes in global climate residual clays collected in situ from regolith profiles of post mid tertiary age have 18o values between 17 5 and 21 3 with the exception of samples from northern australia north of approximately 20 s which have anomalously low values because meteoric waters in northern australia are largely derived from monsoonal rain the high 18o values of post mid tertiary residual clays are consistent with australia s northward drift to low warm latitudes during this time compared with the much higher latitudes it occupied for most of its post palaeozoic history late tertiary residual clays have 18o values that are indistinguishable from all other post mid tertiary clays indicating that further subdivision of the sample groups is not feasible on a continent wide scale comparison with hypothetical modern clays in equilibrium with modern meteoric waters confirms that there has been very little change in the isotopic composition of meteoric waters in australia since the mid tertiary pre mid tertiary clays have lower 18o values between 10 0 and 17 5 which are consistently lower than post mid tertiary clays 18o values of less than 14 to 15 are thought to reflect weathering events during much earlier geologic periods perhaps early or mid mesozoic when australia was at high latitude and the australian climate was humid and cool to cold several workers have documented the existence of very old regolith profiles and land surfaces in australia and support for the above hypothesis comes from three analyses of clays from profiles of stratigraphically demonstrable pre late mesozoic age which have 18o values between 10 2 and 12 3 regolith profiles composed of low 18o clays 15 are widespread in australia and it is possible that a much greater part of the modern landscape than previously recognized developed in the early or mid mesozoic the 18o values of transported i e sedimentary kaolinites reveals that the major source for many tertiary kaolinitic sediments was this postulated pre late mesozoic low 18o regolith the stableisotope evidence that much of the australian regolith formed in comparatively cold conditions suggests that contrary to some traditional interpretations lateritization and deep weathering phenomena are not solely the result of weathering in tropical or sub tropical climates the hydrogen isotope composition of the clays range from 115 to 50 however it is inferred that the majority of clays have undergone some post formational hydrogen isotope exchange which renders their d composition unsuitable for dating purposes

clumped isotope evidence for diachronous surface cooling of the altiplano and pulsed surface uplift of the central andes spatially extensive paleoelevation records of the altiplano plateau are critical to determining the geodynamic mechanisms that formed and support high elevations over a broad area prior stable isotope data reveal a climate history for the northern bolivian altiplano that has been interpreted to show rapid surface uplift of 2 5 1 0 km between 10 and 6 ma this study applies clumped isotope paleothermometry to paleosol carbonates formed at both a low elevation site and temporally overlapping high elevation sites in the southern altiplano eastern cordillera during the middle to late miocene surface paleotemperature decreased by 14 c in the southern altiplano eastern cordillera relative to stable low elevation paleotemperatures implying surface elevation increase of 1 9 0 7 km between 16 and 13 ma and an additional 0 7 0 6 km between 13 and 9 ma both the large magnitude of surface temperature decrease and earlier onset 7 4 myr in the south as compared to the north suggest rapid elevation increase by piecemeal removal of lower lithosphere beneath the plateau and possible northward lower crustal flow

decadal scale rainfall variability in ethiopia recorded in an annually laminated holocene age stalagmite an annually laminated uranium series dated holocene stalagmite from southeast ethiopia has been analysed for growth rate and 13c and 18o variations at annual to biennial resolution in order to provide the first long duration proxy record of decadal scale rainfall variability in this climatically sensitive region our study site 10 n is climatically influenced by both summer june august and spring march may rainfall caused by the annual movement of the inter tropical convergence zone itcz and modulated by large scale anomalies in the atmospheric circulation and in ocean temperatures here we show that stalagmite growth episodic throughout the last 7800 years demonstrates decadal scale 8 25 yr variability in both growth rate and 18o a hydrological model was employed and indicates that this decadal variability is due to variations in the relative amounts of rainfall in the two rain seasons our record unique in its combination of length a total of 1000 years annual chronology and high resolution 18o shows for the first time that such decadal scale variability in rainfall in this region has occurred through the holocene which implies persistent decadal scale variability for the large scale atmospheric and oceanic driving factors

a strong control of the south american seesaw on the intra seasonal variability of the isotopic composition of precipitation in the bolivian andes water stable isotopes d in tropical regions are a valuable tool to study both convective processes and climate variability provided that local and remote controls on d are well known here we examine the intra seasonal variability of the event based isotopic composition of precipitation ddzongo in the bolivian andes zongo valley 16 20 s 67 47 w from september 1st 1999 to august 31st 2000 we show that the local amount effect is a very poor parameter to explain ddzongo we thus explore the property of water isotopes to integrate both temporal and spatial convective activities we first show that the local convective activity averaged over the 7 8days preceding the rainy event is an important control on ddzongo during the rainy season 40 of the ddzongo variability is captured this could be explained by the progressive depletion of local water vapor by unsaturated downdrafts of convective systems the exploration of remote convective controls on ddzongo shows a strong influence of the south american seesaw sass which is the first climate mode controlling the precipitation variability in tropical south america during austral summer our study clearly evidences that temporal and spatial controls are not fully independent as the 7 day averaged convection in the zongo valley responds to the sass our results are finally used to evaluate a water isotope enabled atmospheric general circulation model lmdz iso using the stretched grid functionality to run zoomed simulations over the entire south american continent 15 n 55 s 30 85 w we find that zoomed simulations capture the intra seasonal isotopic variation and its controls though with an overestimated local sensitivity and confirm the role of a remote control on d according to a sass like dipolar structure 2011 elsevier b v

increasing australian indonesian monsoon rainfall linked to early holocene sea level rise the australian indonesian summer monsoon affects rainfall variability across the indo pacific region reconstructions of monsoon strength from stalagmites show that precipitation increased from 11 000 to 7 000 years ago as rising global sea level caused the flooding of the indonesian continental shelf the australian indonesian summer monsoon affects rainfall variability and hence terrestrial productivity in the densely populated tropical indo pacific region it has been proposed that the main control of summer monsoon precipitation on millennial timescales is local insolation1 2 3 but unravelling the mechanisms that have influenced monsoon variability and teleconnections has proven difficult owing to the lack of high resolution records of past monsoon behaviour here we present a precisely dated reconstruction of monsoon rainfall over the past 12 000 years based on oxygen isotope measurements from two stalagmites collected in southeast indonesia we show that the summer monsoon precipitation increased during the younger dryas cooling event when atlantic meridional overturning circulation was relatively weak4 monsoon precipitation intensified even more rapidly from 11 000 to 7 000 years ago when the indonesian continental shelf was flooded by global sea level rise5 6 7 we suggest that the intensification during the younger dryas cooling was caused by enhanced winter monsoon outflow from asia and a related southward migration of the intertropical convergence zone8 however the early holocene intensification of monsoon precipitation was driven by sea level rise which increased the supply of moisture to the indonesian archipelago

stalagmite stable isotope record of recent tropical cyclone events we present a 23 yr stalagmite record 1977 2000 of oxygen isotope variation associated with 11 tropical cyclones tcs from actun tunichil muknal cave in central belize high resolution microsampling yielded a record of monthly to weekly temporal resolution that contains abrupt decreases negative excursions in calcite 18 o values that correspond with recent tc rain events nearby a logistic discriminant model reliably identifi ed tc proxy signals using the measurable parameters 18 o and 13 c values and single point changes in 18 o value the logistic model cor rectly identifi ed 80 of excursions as tc events and incorrectly classifi ed only 1 of nearly 1200 nonstorm sampling points in addition to enabling high resolution tc frequency reconstruction this geologic proxy also provides information about the intensity of individual tcs a multiple regression predicted tc intensity r 2 0 465 p 0 034 using sampling frequency and excursion amplitude consistent with previous low resolution studies we found that the decadal average 18 o value was lower during the 1990s when several tcs produced rainfall in the area but higher during the 1980s when only one tc struck longer accurately dated high resolution speleo them stable isotope records may be a useful new tool for paleotempestology to clarify associa tions between highly variable tc activity and the dynamic range of quaternary climate

multi proxy evidence for human induced deforestation and cultivation from a late holocene stalagmite from middle java indonesia abstract speleothem multi proxy records have proved highly useful in reconstructing past changes in climatic and environmental conditions as well as karst processes and in distinguishing between the numerous potential driving forces that influence these proxies there is lack of such terrestrial proxies from the tropical indo pacific for the first time we present an annual to decadal scale multi proxy record of 377 samples including stable isotopes 18o 13c and trace elements mg ca sr ca from a holocene calcite stalagmite from bribin cave gunung kidul regency middle java indonesia that has grown over the last 4000 years 11 230th dates 18o values average 7 with high frequency variability of up to 1 and hint at relatively stable overall climatic conditions in the tropical indo pacific region during the late holocene the 13c values of stalagmite jb2 are low 13 at the beginning of the record suggesting a c3 dominated rainforest cover strong positive covariation with mg ca and sr ca ratios is a stringent indication of a dominant natural control by prior calcite precipitation and water rock interaction however 13c values increase dramatically by 4 from 1 1 ka to 0 5 ka clear evidence of an anthropogenic influence through deforestation and cultivation

paleovegetational history in the kashmir basin india derived from 13c 12c ratio in paleosols abstract the presence of a series of humus rich layers identified as paleosols in the loess sediments in the kashmir basin in northwestern india indicate phases of climatic amelioration in the past stable carbon isotope ratios of the organic fraction of paleosols from three locations show that almost all the paleosols supported significant c 4 type vegetation which is characteristic of water stressed and relatively hot dry environments limited measurements of stable carbon isotope ratio in modern soils show an estimated c 4 type vegetation contribution of less than 25 which is tenable given the temperate climate of the basin today in the light of some recently published tl thermoluminiscence dates for loess sedimentation in kashmir these findings suggest significant ecological changes most likely related to water stress and temperature there during the past 300 kyr 1kyr 1000years

spatial temporal changes in andean plateau climate and elevation from stable isotopes of mammal teeth abstract paleoelevation constraints from fossil leaf physiognomy and stable isotopes of sedimentary carbonate suggest that significant surface uplift of the northern andean plateau on the order of 2 5 1 km occurred between 10 3 and 6 4 ma independent spatial and temporal constraints on paleoelevation and paleoclimate of both the northern and southern plateau are important for understanding the distribution of rapid surface uplift and its relation to climate evolution across the plateau this study focuses on teeth from modern and extinct mammal taxa including notoungulates pyrotheres and litopterns spanning 29 ma to present collected from the altiplano and eastern cordillera of bolivia 16 2 s to 21 4 s and lowland brazil tooth enamel of large water dependent mammals preserves a record of surface water isotopes and the type of plants that animals ingested while their teeth were mineralizing previous studies have shown that the 18o of modern precipitation and surface waters decrease systematically with increasing elevations across the central andes our results from high elevation sites between 3600 and 4100 m show substantially more positive 18o values for late oligocene tooth samples compared to

a 1500 year el nino southern oscillation and rainfall history for the isthmus of panama from speleothem calcite received 25 february 2004 revised 28 may 2004 accepted 6 august 2004 published 30 october 2004 1 the effect of the el nino southern oscillation enso on tropical rainfall variations of the past 2 millennia is largely unknown high resolution monsoon records are sparse despite the role of enso in generating global hydrologic anomalies in modern climate to investigate the relationship between enso and the central american monsoon we generated a high resolution 2 9 years sample oxygen isotope monsoon rainfall record from a u th dated stalagmite 180 b c to 1310 a d from the isthmus of panama we present evidence for a weakened monsoon during the high medieval 1100 1200 a d and the classic maya collapse 750 950 a d rainfall decreased and was more variable after 550 a d and the period 900 1310 a d was drier than the preceding millennium a weaker monsoon corresponds with increased el nino variability and our data display statistical variance in the enso band we conclude that enso variation has forced isthmian rainfall and may have contributed to hemispheric climatic anomalies at this time index terms 1040 geochemistry isotopic composition chemistry 1620 global change climate dynamics 3309 1854 hydrology precipitation 3354 3344 meteorology and atmospheric dynamics paleoclimatology 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 keywords paleoclimate el nino southern oscillation speleothem medieval climatic anomaly intertropical convergence zone panama