insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

the 2002 2003 el nino recorded in australian cave drip waters implications for reconstructing rainfall histories using stalagmites 1 a 30 month study of drip hydrochemistry from kooringa cave eastern australia revealed a clear geochemical response to the 2002 2003 el nino through the drought drip discharge fell to base flow drip ca2 concentrations fell by half and drip mg ca and sr ca increased in a co varying pattern calcite mg ca and sr ca predicted from drip waters displayed a marked increase through and just beyond the period of greatest moisture deficit the results suggest that stalagmites from shallow caves in drought sensitive eastern australia potentially preserve a valuable record of el nino la nina history

solar forcing of holocene droughts in a stalagmite record from west virginia in east central north america 1 elevated sr ca ratios and 13c values in holocene age stalagmite bcc 002 from east central north america record six centennial scale droughts during the last five north atlantic ocean ice rafted debris ird episodes previously ascribed to solar irradiance minima spectral and cross spectral analyses of the multi decadal resolution sr ca and 13c time series yield coherent 200 and 500 years periodicities the former is consistent with the de vries solar irradiance cycle cross spectral analysis of the sr ca and ird time series yields coherent periodicities of 715 and 455 years which are harmonics of the 1 450 500 year ird periodicity these coherencies corroborate strong visual correlations and provide convincing evidence for solar forcing of east central north american droughts and strengthen the case for solar modulation of mid continent climates moisture transport across north america may have lessened during droughts because of weakened north south temperature and pressure gradients caused by cooling of the tropical pacific and atlantic oceans

experimental deformation of partially molten westerly granite under fluid absent conditions with implications for the extraction of granitic magmas the mechanical behavior of partially molten westerly granite was investigated in the temperature range 800 1100 c 250 mpa confining pressure by means of constant strain rate creep and stress relaxation tests the only water in the samples came from the breakdown of hydrous phases biotite minor chlorite and muscovite and alteration products of feldspars thus the amount of melt was controlled by the test temperature and ranged from 3 at 800 c to 50 at 1100 c over that temperature range strength decreased from 500 mpa to less than 1 mpa and a preliminary constitutive flow law for the partially molten rock was obtained to allow extrapolation to low strain rates the comparative viscosity of the melt alone was estimated at 950 and 1000 c from the distance it could be made to penetrate into a porous sand under a known pressure gradient under all conditions deformation of the matrix of solid grains was by brittle fracture only samples containing up to 10 vol melt failed with the formation of a shear fault zone at higher melt fractions melt filled pores collapsed by shear enhanced compaction squeezing the melt into axial cracks above 40 vol melt unfractured solid grains were carried about passively in the flowing liquid there was no evidence of a rheologically critical melt percentage in this system by analogy with the uniaxial compaction of water saturated soils a simple model is erected to describe a two stage process for the extraction of granitic melts from their protoliths with the aid of nonhydrostatic stress shear enhanced compaction is inferred to drive melt into a network of melt filled veins whereupon porous flow through the high permeability vein network allows rapid drainage of melt to higher crustal levels

trace elements in speleothems as recorders of environmental change speleothems are now established as important palaeoenvironmental archives and contain a number of suitable proxies although trace elements have been much less widely used than oxygen and carbon isotopes the complexity of the cave environment helps to explain this since the fluids from which speleothems form vary greatly in composition in space even within a cave chamber seasonally and over longer periods understanding the forcing factors for this variability is the key to decoding the significance of the trace element records a variety of techniques are available for trace element work and it is important to understand the strengths and limitations of each and also to seek an understanding e g by micro imaging techniques of whether the elements are associated with inclusions in the caco3 or are isolated within the crystal lattice for some elements there is a more or less predictable relationship between element ratios to ca in the water and in the calcite individual trace elements may be derived from atmospheric deposition superficial deposits or bedrock and can be recycled in soil processes before being transferred to the cave some components show an instantaneous response to water infiltration whereas others are only leached by slow flowing seepage waters changing in the proportion of water from fracture fed and seepage flow aquifer compartments is an important factor in influencing trace element supply high flows lead to higher fluxes of soil derived colloidally transported elements conversely under relatively dry conditions degassing of co2 results in prior calcite precipitation upflow of the site of speleothem deposition and leads to higher ratios of sr ca and mg ca some trace element variations in speleothems over time are induced during crystal growth whereby faster growth leads to a greater departure from equilibrium element partitioning despite the demonstrated temperature dependence of mg partitioning into calcite attempts at deriving palaeotemperature records from speleothems have been so far confounded by variations in solution mg ca and or crystallographic effects a number of case studies have effectively used trace elements such as speleothem mg as records of palaeo aridity using supporting arguments from modern monitoring or covariations with other parameters such as stable isotopes sr and u isotopes can also be indicators of palaeohydrology although sr isotope variations can also reflect varying aeolian input considerable progress has been made in decoding the meaning of annual trace element variations using criteria for understanding dripwater hydrology and ph this should lead in the future to more specific interpretations of how seasonality evolves through time

dry late glacial and early holocene climate in arid central asia indicated by lithological and palynological evidence from bosten lake china abstract stratigraphical and chronological investigations of four sediment cores from bosten lake the largest inland freshwater lake in china provide a reliable regional environmental evolution record since the late glacial the stratigraphy of the four cores has been well correlated according to their lithology and chronology osl and 14c dates pollen and grain size data from bosten lake show evidence for a dry regional climate during late glacial and early holocene 16 8 cal ka bp indicated by a thick layer of aeolian sand deposit 100 cm although the climate became humid after 8 cal ka bp analysis of pollen assemblages pollen a c ratio and ephedra percentage also indicates that the climate was relatively dry in the bosten lake area between 8 and 6 cal ka bp while afterwards more humid conditions ca 6 1 5 cal ka bp are assumed comparison with other lake records from arid central asia influenced by the westerly winds generally supports the assumption of late glacial to early holocene dry climates in westerly dominated regions hence they contrast the holocene climate development in monsoon asia relatively wet conditions during the late holocene 6 1 5 cal ka bp might be induced by stronger westerly circulation

the generation of sodic granite magmas western palmer land antarctic peninsula subduction related mesozoic to cainozoic granites s l in western palmer land antarctic peninsula have similar chemical compositions to archean tonalite trondhjemite granodiorite ttg suites phanerozoic slab melts adakites and to experimental partial melts of basaltic material in equilibrium with amphibole pyroxene garnet they are predominantly sodic metaluminous and most have al2o3 15 wt and y 36 km between triassic and tertiary times the initial nd t of the magmatism increased and sr t decreased suggesting that new continental crust was produced during this period underplating by mafic magma was an important crustal growth mechanism in the arc the generation of abnormally thick crust and its subse quent fusion is considered to be a consequence of ca 180 ma of subduction and associated magmatism in the region an implication of the model is that dense garnet amphibolite and eclogite residues from partial melting of the lower crust will accumulate in theory the setting was appropriate for such residues to detach from the base of the crust and to sink into the convecting mantle such a process would leave the rest of the crust enriched in large ion lithophile elements lree but depleted in hree y

holocene climate and vegetation changes inferred from pollen records of lake aibi northern xinjiang china a potential contribution to understanding of holocene climate pattern in east central asia abstract this research focuses on the reconstructions of the lake hydrologic variations and the basin wide vegetation changes over past 13 870 years based on pollen data of 195 samples and the lithologic variations obtained from lake aibi in the western part of xinjiang area our results showed that lake or swamp environment did not come into existence until 13 870 cal bp and swamp or wetland environment dominated the depression of the basin between 13 870 and 7430 cal bp under ameliorated basin wide moisture conditions the following period between 7430 and 3620 cal bp witnessed lake transgression in the depression and vegetation amelioration within the basin the moisture conditions were continuously ameliorated from 3620 cal bp onward leading to further lake transgression and further basin wide vegetation amelioration a dry interval from 1400 to 1150 cal bp interrupted the late holocene wet epoch of the past 3600 years our synthesized regionally averaged moisture index of xinjiang area indicates that a gradual wetting climate dominated the mid to late holocene in xinjiang area this wetting trend in xinjiang area is hypothesized to have been associated with the winter warming and winter wetting trends in northern europe the gradual increase of winter insolation in mid to late holocene might have enhanced evaporation in the north atlantic ocean and injected more moisture to the westerlies system therefore bringing more precipitation to the downwind area including xinjiang

holocene moisture changes in western china central asia inferred from stalagmites abstract central asia lies at the convergence between the mediterranean and asian monsoon climates and there is a complex interaction between the westerlies with the monsoon to form the climate of that region and its variability the region is highly vulnerable to changes in rainfall highlighting the need to understand the underlying controls we present a stalagmite based 18 o record from kesang cave in western china using mc icp ms u series dating and stable isotope analysis stalagmite calcite 18 o largely documents changes in the 18 o of precipitation 18 o in stalagmites was low during the early and middle holocene 10 0 3 0 ka bp and shifted to higher values between 3 0 and 2 0 ka bp after 2 0 ka bp 18 o fluctuates with distinct centennial scale variations drawing from results of state of the art atmospheric general circulation model simulations for the preindustrial period and 9 ka bp we propose that changes in moisture source regions and the wetter climate both contributed to the isotopic depletion of precipitation during the early and middle holocene multiple records from surrounding regions indicate a generally wetter climate during the early and mid holocene supporting our interpretation on the speleothem 18 o changes in precipitation seasonality do not appear to be a viable explanation for the observed changes nor increased penetration of monsoonal moisture to the study site we speculate that the climatic regime shifted around 3 0 2 0 ka bp towards a drier climate resulting in temperature having dominant control on precipitation 18 o the demise of three settlements around 500ad at the margin of tarim basin coincided with a period of decreased precipitation and increased temperature that likely affected local water resources underscoring the potential impact of climate on human habitation in this region

thermal and dynamical regimes of single and two phase magmatic flow in dikes finite element calculations of magma flow in dikelike channels with length to width ratios of 1000 1 or more have been used to investigate the coupling between thermal and dynamical regimes due to temperature dependent viscosity and dissipation steady state solutions with realistic thermal and dynamical parameter values have been obtained the models show that the onset of solidification on the boundaries of a basaltic or andesitic dike as predicted by idealized laminar flow models can be prevented or significantly delayed by a small amount of transverse flow induced by rising bubbles boundary roughness or turbulence this effect will reduce the critical initial widths of dikes estimated by bruce and huppert 1989 in the absence of transverse flow the bulk temperature of the magma may actually increase slightly with distance along the dike as a result of viscous dissipation even while solidification is occurring on the walls of the dike with converging or necking dike walls it is found that boundary temperatures fall to a minimum and then increase with distance along a dike even if viscous heating is neglected for viscous heating to offset significant rates of heat loss 2 kw m2 in a plane parallel 1 m wide basaltic dike an average flow velocity of 2 7 m s driven by a pressure gradient of 1 7 mpa km is required a 7 void fraction caused by exsolution of volatiles or chamber gas in the magma will produce this pressure gradient the ease of producing such a gradient by reducing the density of the magmatic column with addition of a gas phase makes it likely that flows of basaltic magma could be maintained in dikes tens of kilometers long furthermore a gas phase may be important for the propagation of the fracture prior to the initial injection of magma during dike emplacement rapid transport of more silicic magmas through dikes is inhibited by the requirement of large driving pressure gradients exceeding several hundred megapascals per kilometer however the pressure gradient can be substantially reduced if the magma is a heterogenous mixture of a predominantly silicic component with a more mafic component pipe flow experiments involving molten polymers that exhibit dynamical similarity to magmas strongly suggest that unmixing occurs when a two component magma mixture in which the components have different viscosities rises within a dike within a few dike widths of the inlet the less viscous mafic component encapsulates the more viscous silicic part effectively lubricating the passage of the more viscous component compositional variations in the obsidian dome volcano support the occurrence of this pressure reduction or self lubrication mechanism such a self lubrication process often may be necessary to permit very viscous magmas to reach earth s surface if so chemical and lithologic zoning would be anticipated as a common feature of near surface intrusions or lava flows that are characterized by a high silica and or high crystal content such as at deadman dome in long valley california

the wiley glacier complex antarctic peninsula pluton growth by pulsing of granitoid magmas early cretaceous gabbro quartz diorite granodiorite and tonalite granodiorite plutons of the wiley glacier complex in the antarctic peninsula magmatic arc were emplaced in a zone of syn magmatic extensional shearing the oldest component pluton is the creswick gap quartz diorite granodiorite pluton and this is cut by slightly younger hornblende gabbro of the moore point pluton these plutons form the wall rock to the burns bluff tonalite granodiorite pluton the youngest component of the complex the burns bluff pluton comprises tonalite granodiorite sheets which at the plutons margins are interleaved with screens of mylonite wall rock the moore point hornblende gabbro has nd141 of ca 4 and sr141 of ca 1 it is predominantly mantle in origin although its parent magma assimilated some continental crust during emplacement the creswick gap pluton has nd141 between ca 4 quartz diorite and ca 1 granodiorite and sr141 from ca 1 quartz diorite to ca 22 granodiorite this pluton contains both mantle and crustal components we suggest that the quartz diorite facies fractionated from a similar parent magma to that of the moore point gabbro whilst the granodiorite fractionated from a gabbro quartz diorite magma during continued crustal assimilation geochemical variations within the creswick gap pluton cannot be generated by afc models some of the granodiorite samples have chemical characteristics which typify partial melts of amphibole garnet bearing crust we conclude that the pluton comprises fractionates of basaltic magma and crustal partial melt the burns bluff tonalite granodiorite sheets have nd141 between ca 4 and ca 2 and sr141 from ca 5 to ca 31 their isotopic and chemical compositions suggest that some are fractionates of basalt gabbro magma others are predominantly partial melts of amphibole garnet bearing crust and some are mixtures of these two magma types the chemical and isotopic compositions of the burns bluff plutons constituent tonalite sheets and its dyke like internal structure suggest that it grew incrementally via the addition of melt batches from a variety of crustal and mantle sources the growth of this pluton via dyking may reflect magma pulsing associated with transtensional movement along the creswick gap shear zone moreover the burns bluff pluton may be a frozen conduit system for structurally higher plutons in the antarctic peninsula batholith

seasonal dripwater mg ca and sr ca variations driven by cave ventilation implications for and modeling of speleothem paleoclimate records a 4 year study in a central texas cave quantifies multiple mechanisms that control dripwater composition and how these mechanisms vary at different drip sites we monitored cave air compositions in situ calcite growth dripwater composition and drip rate every 4 6 weeks three groups of drip sites are delineated groups 1 3 based on geochemical variations in dripwater composition quantitative modeling of mineral solution reactions within the host carbonate rock and cave environments is used to identify mechanisms that can account for variations in dripwater compositions the covariation of mg ca and sr ca and sr isotopes is key in delineating whether mg ca and sr ca variations are dictated by water rock interaction i e calcite or dolomite recrystallization or prior calcite precipitation pcp group 1 dripwater compositions reflects a narrow range of the extent of water rock interaction followed by varying amounts of prior calcite precipitation pcp group 2 dripwater compositions are controlled by varying amounts of water rock interaction with little to no pcp influence group 3 dripwater compositions are dictated by variable extents of both water rock interaction and pcp group 1 drip sites show seasonal variations in dripwater mg ca and sr ca whereas the other drip sites do not in contrast to the findings of most previous dripwater mg ca sr ca studies these seasonal variations at group 1 drip sites are independent of changes in water flux i e rainfall and or drip rate and instead significantly correlate with changes in cave air co2 concentrations these results are consistent with lower cave air co2 related to cool season ventilation of the cave atmosphere enhancing calcite precipitation and leading to dripwater geochemical evolution via pcp group 1 dripwater mg ca and sr ca seasonality and evidence for pcp as a mechanism that can account for that seasonality have two implications for many other regions where seasonal ventilation of caves is likely 1 speleothem trace element records may provide seasonal signals and 2 such records may be biased toward recording climate conditions during the season when calcite is depositing additionally we use our results to construct a forward model that illustrates the types of speleothem mg ca and sr ca variations that would result from varying controls on dripwater compositions the model provides a basis for interpreting paleodripwater controls from high frequency mg ca and sr ca variations for speleothems from caves at which long term monitoring studies are not feasible 2011 elsevier ltd all rights reserved

association of the northern hemisphere circumglobal teleconnection with the asian summer monsoon during the holocene in a transient simulation this paper provides another look at the response of the asian summer monsoon asm to insolation forcing and oceanic feedback during the holocene using a fully coupled general circulation ocean atmosphere model forced by earth s orbital variations the model results revealed a recurrent circumglobal teleconnection cgt pattern in the summertime june july august mid latitude circulation of the northern hemisphere during the holocene the cgt index showed a decreasing trend before 5 ka bp and a slight increasing trend afterwards affected by the combined effects of summer insolation indian summer monsoon ism north atlantic and indian ocean western pacific ocean sea surface temperature sst the cgt showed a close relationship with asm precipitation and surface air temperature during the holocene and therefore could act as a bridge linking the asm to insolation high latitude forcing north atlantic sst and low latitude forcing tropical ocean sst we emphasize that the mid latitude atmospheri

intracrustal derivation of na rich andesitic and dacitic magmas an example from volcan ollague andean central volcanic zone andesitic and dacitic lavas erupted from quaternary stratovolcanoes in the central volcanic zone cvz of the andes have major and trace element compositions similar to proposed melts of subducted mid ocean ridge basalt and na rich trondjhemites tonalites and granodiorites ttg in early archean high grade gneiss terrains suites of lavas from individual volcanoes have average la yb of 25 45 sr y of 30 65 yb contents of 1 5 1 1 ppm and na 2 o contents 3 8 wt with lavas erupted on the volcanic front displaying the most affinity to the early archean suites because slab melting is not involved in the derivation of the cvz magmas these data indicate that rocks with early archean ttg compositions can also be produced through intracrustal differentiation processes isotopic major element and ree data from volcan ollague are consistent with a model incorporating contamination of mantle derived basaltic magmas in garnet bearing deep continental crust to produce basaltic andesite magma followed

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

two mathematical models of mg and sr partitioning into solution during incongruent calcite dissolution implications for dripwater and speleothem studies abstract positive correlation between sr ca and mg ca in cave dripwaters and speleothem is often attributed to prior calcite precipitation pcp where exclusion of mg and sr from calcite precipitated upstream of the dripwater speleothem site results in enrichment in the mg ca and sr ca ratios of residual effluent modelling predicts that pcp will produce a straight line correlation in graphs of ln sr ca vs ln mg ca with a theoretical slope that is given by kd sr 1 kd mg 1 calculated to be 0 88 0 13 regardless of rock or absolute dripwater composition sinclair et al submitted for publication while this makes the correlation slope potentially diagnostic for pcp mg and sr are also preferentially released from calcite during incongruent calcite dissolution icd and it is possible that icd produces a similar correlation between ln sr ca and ln mg ca to examine this possibility mathematical formulations for two different mechanisms of icd are presented model 1 simulates net dissolution as a dynamic kinetic process where forward and reverse reactions compete dissolution is congruent but ions are fractionated by a simultaneous reverse reaction where new calcite forms with sr ca and mg ca ratios that are determined by the solution composition and kd sr and kd mg model 2 simulates leaching of mg and sr from a fresh calcite surface by tracking the dissolution of a thin layer where high ion mobility allows the calcite to maintain a homogenous composition controlled by kd sr and kd mg in both models generalised kinetic equations are used in the derivations meaning that the results are not specific to a particular kinetic model in both models of icd the mathematics predict that under conditions that may prevail during dissolution of limestone the correlation between ln sr ca and ln mg ca is approximately linear with a slope given by kd sr 1 kd mg 1 thus this property is not specific to just pcp however for both pcp and icd this slope is universal expected to occur regardless of kinetics and the absolute composition of solution or host rock a correlation slope of 0 88 in either karst waters or speleothem is therefore diagnostic for calcite water interaction

controls on trace element sr mg compositions of carbonate cave waters implications for speleothem climatic records abstract at two caves clamouse s france and ernesto ne italy cave drip and pool waters were collected and sampled at intervals over a 2 3 year period mg ca and sr ca concentration ratios corrected for marine aerosols are compared with those of bedrocks and in some cases aqueous leachates of soils and weathered bedrocks cave waters do not lie along mixing lines between calcite and dolomite of bedrock carbonate but typically show enhanced and covarying mg ca and sr ca four factors are considered as controlling processes 1 the much faster dissolution rate of calcite than dolomite allows for the possibility of increase of mg ca if water rock contact times are increased during drier conditions a theoretical model is shown to be comparable to experimental leachates 2 prior calcite precipitation along a flow path is a powerful mechanism for generating enhanced and covarying mg ca and sr ca ratios this mechanism requires the solution to lose co 2 into pores or caverns 3 incongruent dolomite dissolution has only limited potential and is best regarded as two separate processes of dolomite dissolution and calcite precipitation 4 selective leaching of mg and sr with respect to ca is shown to be important in leachates from ernesto where it appears to be a phenomenon of calcite dissolution in general selective leaching can occur whenever ca is sequestered into precipitates due to freezing or drying of soils or if there is derivation of excess sr and mg from non carbonate species the ernesto cave has abundant water supply which in the main chamber is derived from a reservoir with year round constant p co 2 of around 10 2 4 and no evidence of calcite precipitation in the karst above the cave two distinct but overlying trends of enhanced and covarying mg ca and sr ca away from the locus of bedrock compositions are due to calcite precipitation within the cave and at a variable drip site due to enhanced selective leaching at slow drip rates mg enhancement in the first chamber is due to a more dolomitic bedrock and longer residence times the clamouse site has a less abundant water supply and presents geochemical evidence of prior calcite precipitation both in the cave and in overlying porous dolomite dedolomitized limestone bedrock initial p co 2 values as high as 10 1 are inferred experimental incubations of clamouse soils which generated enhanced p co 2 and precipitated caco 3 had compositions similar to the karst waters calcite precipitation is inferred to be enhanced in drier conditions hydrological controls on cave water chemistry imply that the trace element chemistry of speleothems may be interpretable in palaeohydrological terms drier conditions tends to promote not only longer mean residence times enhancing dolomite dissolution and hence mg ca but also enhances degassing and calcite precipitation leading to increased mg ca and sr ca

continental crust crustal underplating and low q upper mantle beneath an oceanic island arc a detailed structural model of the crust subducting slab and underlying upper mantle across the northern izu ogasawara bonin island arc system is derived from a marine seismic reflection and ocean bottom seismographic refraction survey and subsequent forward modeling combined with tomographic inversion the model indicates that the crust is thickest beneath the presently active rift zone and a granitic crust may have formed in the mid crust a highly attenuative mantle that is one with low quality q seems to be confined mainly beneath the presently active rift zone in contrast high p wave velocity persists in the lower crust between the forearc and eastern margin of the back arc basin suggesting a large scale magma input responsible for the arc formation

a persistent holocene wetting trend in arid central asia with wettest conditions in the late holocene revealed by multi proxy analyses of loess paleosol sequences in xinjiang china abstract there are significant differences in the interpretation of the moisture precipitation history of arid central asia aca during the holocene as inferred on one hand from speleothem oxygen isotope records and on the other from lake sediments here we present the results of measurements of climatically sensitive magnetic properties and soil color from four well dated loess paleosol sequences from the northern slopes of the tienshan mountains and the yili river valley xinjiang china in the core area of aca our results demonstrate that the characteristic holocene paleosol indicating relatively moist conditions generally formed after 6 ka 1 ka 1000 cal yr bp in the study region and that the accumulation of unweathered loess prevailed during the early holocene indicating a dry climate at that time the magnetic proxies further reveal a trend of generally increasing moisture since the last glacial maximum with the wettest climate occurring during the late holocene this trend of increasing moisture during the holocene is representative of the xinjiang region and possibly of the whole of the core area of aca and is in marked contrast both to the mid holocene moisture maximum observed in the east asian summer monsoon region and to the general decrease in the strength of the indian summer monsoon since the early holocene our findings are supported by the results of a climate simulation which indicate a trend of increasing summer and winter precipitation during the holocene in the core area of aca caused mainly by an increase in the strength of the westerlies effected by an increasing latitudinal insolation gradient and by a negative trend of the arctic oscillation ao or north atlantic oscillation nao

trend of increasing holocene summer precipitation in arid central asia evidence from an organic carbon isotopic record from the ljw10 loess section in xinjiang nw china abstract due to the lack of reliable climatic proxies the variability of precipitation in westerlies dominated arid central asia aca during the holocene is debated here we present a high resolution ca 100 years per sample organic carbon isotopic composition 13corg record from bulk samples from the lujiaowan10 section in the northern piedmont of the tienshan mountains xinjiang province northwestern china a robust chronology is provided by k feldspar pirir dating during the early to middle holocene from 12 ka to 6 ka 1 ka 1000 years ago the 13corg values are relatively invariant with an average of around 22 5 after about 6 ka the 13corg values exhibit an overall negative trend with the most negative value of 25 2 occurring in the uppermost part of the section within the interval of holocene soil formation our investigation of the relationship between modern climatic variables and surface soil 13corg values from the region reveals a significant negative correlation between surface soil 13corg and summer precipitation amount june to august therefore we used the calibration model between summer precipitation amount and surface soil 13corg to quantitatively reconstruct the holocene summer precipitation history of the study area our results indicate that summer precipitation in the region was the lowest ca 85 mm during the early to middle holocene 12 6 ka however after 6 ka the precipitation increased continuously to about 137 mm per year at the present our reconstruction is generally consistent with climate simulation results and with regional effective moisture records thus we conclude that the highest summer precipitation and therefore the wettest climate occurred in the late holocene decreasing northern hemisphere summer insolation may have effected a change in the cgt circumglobal teleconnection from a positive to negative phase and together with more negative trends in ao arctic oscillation or nao north atlantic oscillation may have been responsible for the observed pattern of summer precipitation evolution

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

himalayan strain reservoir inferred from limited afterslip following the gorkha earthquake great himalayan earthquakes are rare analysis of surface motions in the months after the 2015 gorkha earthquake reveals negligible aseismic slip implying that stress may be stored in the crust to be tapped during future great earthquakes

spatial variability in cave drip water hydrochemistry implications for stalagmite paleoclimate records the identification of vadose zone hydrological pathways that most accurately transmit climate signals through karst aquifers to stalagmites is critical for accurately interpreting climate proxies contained within individual stalagmites a three year cave drip hydrochemical study across a spectrum of drip types in crag cave sw ireland reveals substantial variability in drip hydrochemical behaviour stalagmites fed by very slow drips 2 ml min sites apparently unconnected with local meteorological events water from these drips was typically undersaturated with respect to calcite and thus did not result in calcite deposition data presented here suggest that drips in this flow regime also experience flow re routing and blocking and that any stalagmites developed under such drips are unsuitable as mid to high resolution paleoclimate proxies most drip sites demonstrated seasonal ca2 and mg2 variability that was probably linked to water excess prior calcite precipitation along the flowpath affected the chemistry of slowly dripping sites while dilution predominantly controlled the water chemistry of the more rapidly dripping sites this research underscores the importance of understanding drip hydrology prior to selecting stalagmites for paleoclimate analysis and before interpreting any subsequent proxy data

controls on trace element partitioning in cave analogue calcite abstract we report trace element data from a series of carbonate growth experiments in cave analogue conditions in the laboratory with the goal of better understanding environmental controls on trace element incorporation in stalagmites the experimental setup closely mimics natural processes e g precipitation driven by co2 degassing low ionic strength solution thin solution film but with a tight control on growth conditions temperature pco2 drip rate calcite saturation index and the composition of the initial solution calcite is dissolved in deionized water in a 20 000 ppmv pco2 environment with trace elements li na mg co sr cd ba u at appropriate concentrations to mimic natural cave drip waters this solution is dripped onto glass plates coated with seed calcite in a lower pco2 environment at 7 15 25 and 35 c and drip rates of 2 6 and 10 drips per minute d sr was shown to be statistically invariant over the full range of temperature and growth rate studied no relationship between sr ca and growth rate is therefore expected in stalagmite samples over comparable growth rates d mg has a relationship with temperature defined by d mg 0 01e0 02 0 006 t but temperature is not expected to be the dominant control on mg ca in cave calcite due to the larger impact of calcite precipitation on mg ca over short timescales in conditions where temperature is well buffered the fraction of calcium remaining in solution f is likely to be the dominant control on mg ca and other trace element ratios but differences in the response of trace elements to f and t may allow their combined use to assess past cave conditions high cd castalagmite is particularly indicative of low amounts of prior calcite precipitation and cd ca would be a useful addition to trace element studies of natural stalagmites significant scatter is observed in trace element ratios during the laboratory experiments which cannot be explained by simple rayleigh distillation this scatter is well explained by solution mixing and by the mixing of calcite with different fractions of calcite growth accounting for the effects of mixing on trace element concentrations or ratios may help to achieve more robust interpretations of stalagmite chemistry as part of a multi proxy approach to assessment of past environments

controls on the spatial and temporal variability of vadose dripwater geochemistry edwards aquifer central texas abstract a 4 yr study of spatial and temporal variability in the geochemistry of vadose groundwaters from caves within the edwards aquifer region of central texas offers new insights into controls on vadose groundwater evolution the relationship between vadose and phreatic groundwaters and the fundamental influence of soil composition on groundwater geochemistry variations in sr isotopes and trace elements mg ca and sr ca ratios of dripwaters and soils from different caves as well as phreatic groundwaters provide the potential to distinguish between local variability and regional processes controlling fluid geochemistry and a framework for understanding the links between climatic and hydrologic processes the sr isotope compositions of vadose cave dripwaters mean 87sr 86sr 0 7087 and phreatic groundwaters mean 87sr 86sr 0 7079 generally fall between values for host carbonates mean 87sr 86sr 0 7076 and exchangeable sr in overlying soils mean 87sr 86sr 0 7088 dripwaters have lower mg ca and sr ca ratios and higher 87sr 86sr values than phreatic groundwaters dripwater 87sr 86sr values also inversely correlate with both mg ca and sr ca ratios mass balance modeling combined with these geochemical relationships suggest that variations in fluid compositions are predominantly controlled by groundwater residence times and water rock interaction with overlying soils and host aquifer carbonate rocks consistent differences in dripwater geochemistry i e 87sr 86sr mg ca and sr ca between individual caves are similar to compositional differences in soils above the caves while these differences appear to exert significant control on local fluid evolution geochemical and isotopic variations suggest that the controlling processes are regionally extensive temporal variations in 87sr 86sr values and mg ca ratios of dripwaters from some sites over the 4 yr interval correspond with changes in both aquifer and climatic parameters these results have important implications for the interpretation of trace element and isotopic variations in speleothems as paleoclimate records as well as the understanding of controls on water chemistry for both present day and ancient carbonate aquifers

a high resolution record of holocene environmental and climatic changes from lake balikun xinjiang china implications for central asia a high resolution record of holocene environmental and climatic change in the balikun area was reconstructed from a sediment core from the lake balikun multiproxy data show that the climate was extremely arid during the early holocene before 8 6 cal ka bp moisture began to increase after 8 6 cal ka bp and the climate was humid between 7 9 and 4 3 cal ka bp a significant dry event occurred around 4 3 3 8 cal ka bp the climate became generally wet during the late holocene after 3 8 cal ka bp the holocene pollen and geophysical records do not indicate a wet early holocene making it evident that there was no early holocene humid period associated with peak asian monsoon strength regional comparisons indicate that this region has a different pattern of holocene environmental and climatic change from the asian monsoonal area and south siberia

comparison of high resolution sub annual records of trace elements in a modern 1911 1992 speleothem with instrumental climate data from southwest australia high spatial resolution measurements of mg p u sr ba and na using 193 nm excimer laser ablation inductively coupled plasma mass spectrometry has revealed clearly resolvable annual cycles in a modern speleothem from southwestern australia the age of this stalagmite is established by the dates of emplacement and removal of the boardwalk where it grew 1911 1992 this chronological constraint allows for the first confident comparison between the instrumental climate record and speleothem trace element content eleven laser ablation transects across a 0 5 mm wide section of the speleothem growth axis were measured cycles that could be matched between adjacent transects were stacked into a master record to minimise variability between tracks and permit greater confidence in comparing the trace elements to the instrumental climate record p and u positively and mg inversely mimic the sudden 20 decrease in annual rainfall experienced by this region since 1965 we argue that p from seasonal vegetation decay is transported to the speleothem before it is mineralised in the soil owing to the low p retention capacity of southwest australian soils both vegetation activity and the transport of vegetation derived hpo42 are sensitive to rainfall groundwater p concentration may also influence the transport of u through the strong affinity between phosphate and uranyl ions mg appears to be sensitive to groundwater residence time as this affects drip water mg ca composition by preferential loss of ca during drier episodes when calcite precipitates before reaching the stalagmite the effects of groundwater residence time may also be important for sr on inter annual scales however the behaviour of sr on the annual cycle is opposite to mg but compatible with ba and na which are shown to depend on speleothem growth rate

seasonal trace element and stable isotope variations in a chinese speleothem the potential for high resolution paleomonsoon reconstruction abstract we report the presence of clear annual cycles in trace element mg ca sr ca ba ca and u ca and stable isotope 18o and 13c composition in an annually banded stalagmite from heshang cave hubei province china 30 44 n 110 42 e through a combination of micromilling and in situ analysis la mc icpms we measured geochemical variations across 16 annual growth bands to assess their potential as seasonal resolution paleomonsoon proxies to facilitate comparison with modern climatic and environmental data we created composite annual cycles for each proxy by stacking 6 well defined years speleothem 18o variations 10 8 to 8 5 are controlled by seasonal variations in temperature and drip water 18o which lead to maximum values during may around the time of summer monsoon onset this provides a chronological marker which can be used to constrain the timing of the other geochemical cycles the composite cycles reveal a strong positive correlation between mg ca sr ca ba ca and 13c values in the micromilled section r2 0 65 0 98 with minimum values occurring around may maximum u ca values occur at the same time we present simple models which show that these correlations as well as the observed ranges of mg ca 14 1 to 22 4 mmol mol sr ca 0 2 to 0 4 mmol mol and 13c 12 5 to 10 7 may be fully explained by progressive co2 degassing and calcite precipitation from an initially saturated solution using realistic initial conditions for heshang cave t 18 c mg casolution 0 84 mol mol sr casolution 0 69 mmol mol 13ctdic 16 75 we find that the observed relationships can be produced by using dmg 0 016 and dsr 0 30 within the range of expected values the model suggests that the fraction of ca removed from the solution ranges from 0 to 30 to produce the observed seasonal cycles this variation may be due to two related processes which occur during drier periods 1 increased prior precipitation of calcite in the epikarst or on the cave ceiling and or 2 a greater degree of co2 degassing and calcite precipitation on stalagmite surfaces when drip rates are lower both mechanisms would have the effect of enriching speleothem mg ca sr ca ba ca and 13c values during drier periods past variations in heshang carbonate chemistry may therefore be useful as seasonal resolution proxies for past rainfall

the gangotri granite garhwal himalaya laccolithic emplacement in an extending collisional belt the gangotri miocene leucogranite is composed of several laccoliths 6 7 km long 1 5 2 km thick which can be divided into two sets of lenses the southern lenses intruded in the lower part of the high himalaya sedimentary cover and the northern lenses intruded in an older porphyritic biotite bearing granite in both cases the magmatic fabric is commonly weak with no dominant stretching direction although a rough e w trend is present in the northern lenses the magnetic fabric is characterized by the fact that drastic changes in the direction in the magnitude of the magnetic parameters or in the fabric type planar or linear may take place over very short distances measurements of preferred orientations in thin sections indicate that the strain regime was largely dominated by a coaxial component for both sets of lenses in agreement with the large dispersion observed in both the field and magnetic lineations the comparison of the granite and host rock structures shows that the leucogranite emplacement dates the onset of the extensional tectonism in the high himalaya range and is not related to a southward directed thrust event associated with the main central thrust this is exemplified by the vertical attitude of the feeder dikes that intrude the metasedimentary rocks beneath die southern lenses the presence of these dikes indicates in turn that magma ascent occurred by fracture propagation the spatial disposition of the southern lenses could have resulted either from the disruption of a single laccolithic intrusion by crustal scale boudinage due to a northern gravity backslide of the top of the tibetan slab or from the intrusion of independent laccoliths the use of the elastic bending theory of pollard and johnson 1973 shows that in both hypotheses the current laccolith sizes are compatible with a laccolithic mode of magma emplacement however neither the density contrast between the magma and its enclosing rocks nor the lithological boundary between the tibetan slab and the overlying tibetan metasedimentary series controlled the level of magma emplacement rather flat lying collapse structures which intersected the upward propagating magma dikes are the most likely causes of magma arrest such a mechanism was favored by the schist rich lithology of the metasedimentary host rocks in addition field relationships indicate that the melt supply through the dike system was a continuous rather than pulsed process existing numerical treatments on the rates of magma transport through fractures show that in such a case the laccoliths could have been built in less than 100 years this short time of emplacement the small size of the laccoliths and their peripheral disposition relative to the badrinath granite suggest that the gangotri lenses may represent the initial stage of pluton accretion in the high himalaya which ultimately gave rise to a much larger massif such as the manaslu granite

mg sr and sr isotope geochemistry of a belgian holocene speleothem implications for paleoclimate reconstructions in this study variations in mg ca sr ca and 87sr 86sr ratios in a holocene belgian speleothem cave secondary carbonate deposit are interpreted in terms of changes in water residence time and changes in weathering processes possibly induced by changes in west european climate a stalagmite from the pere noel cave belgium was dated with the tims u th method and was deposited between 13 and 2 ka bp the 1000 mg ca ratio varies between 4 9 and 26 and displays short term changes but no significant long term trend the 1000 sr ca ratio varies between 0 09 and 0 31 and displays both short term changes and a long term decreasing trend from 12 9 to 3 5 ka in parallel the sr isotopic composition of the speleothem decreases from 0 7090 at 12 9 ka to 0 7088 at 3 5 ka the sr isotope ratio is higher than expected from the overlying limestone 87sr 86sr 0 7081 which implies an external source of radiogenic sr most probably from a silicate phase short term and long term changes in mg ca sr ca as well as long term changes of 87sr 86sr ratios can be explained by changes in the dissolution and precipitation processes of the host limestone these processes are controlled by changes in water residence times linked to changes in the water excess precipitation minus evapo transpiration c 2000 elsevier science b v all rights reserved

holocene environmental and climatic changes inferred from wulungu lake in northern xinjiang china abstract sedimentological geochemical and palynological data from wulungu lake in northern xinjiang china are used to reconstruct environmental and climate changes since 9550 cal yr bp high abundance of sparganium and poaceae low md median diameter and 13 c organic values indicate aridity between 9550 and 6730 cal yr bp high md and 13 c organic values and the prevalence of desert steppe and steppe vegetation between 4200 and 560 cal yr bp indicate that effective moisture increased after 6730 cal yr bp peaking at 4200 and 560 cal yr bp low md values a negative excursion of 13 c org and the transition from steppe to desert vegetation since 560 cal yr bp reflect a decrease in effective moisture during the latest holocene late holocene human activities were indicated by sharp increase in the abundance of pediastrum then variations in carbonate contents indicate that temperature was generally high between 9550 and 7740 cal yr bp low between 7740 and 6730 cal yr bp intermediate between 6730 and 560 cal yr bp and low during the last 560 yr regional comparison indicates that the asian monsoon did not extend to wulungu lake and westerlies were the main factor in determining the moisture availability during the holocene

structure of the 8200 year cold event revealed by a speleothem trace element record abrupt first order shifts in strontium and phosphorus concentrations in stalagmite calcite deposited in western ireland during the 8200 year event the major cooling episode 8200 years before the present are interpreted as responses to a drier climate lasting about 37 years both shifts are centered on 8330 80 years before the present coinciding with a large oxygen isotope anomaly and a change in the calcite petrography in this very high resolution monthly record antipathetic second order oscillations in phosphorus and strontium reveal decreased growth rates and increased rainfall seasonality growth rate variations within the event reveal a two pronged structure consistent with recent model simulations

geodynamic evolution of the antarctic peninsula during mesozoic times and its bearing on weddell sea history this review of the tectonic evolution of the antarctic peninsula during mesozoic times highlights four main events 1 late triassic late jurassic extension 2 late jurassic early cretaceous dextral transpression 3 early cretaceous extension and 4 mid cretaceous compression magmatism was virtually continuous during much of this period with the exception of possible breaks in the known record in early jurassic and late jurassic early cretaceous times the second of these breaks corresponded to the first compressional event there was no apparent hiatus in the magmatic record during the mid cretaceous compressional event although there was a significant change in the pattern of sedimentation in the larsen basin on the eastern margin of the weddell sea at about that time the tectonic evolution of the peninsula is compared to and puts some constraints on existing weddell sea models the late triassic late jurassic arc extension correlates with initial rifting in the weddell sea region during sinistral motion between east and west gondwana however there is no known record of large scale pre mid jurassic transcurrent deformation in the antarctic peninsula that would have been consistent with rotation of west antarctic crustal blocks in the initial rifting period the peninsula wide late jurassic early cretaceous compressional event may correlate with the major change in gondwana plate motions from e w to n s african reference frame separation of east and west gondwana this change probably resulted in formation of an ocean continent boundary along the northern margin of the weddell sea embayment and initial seafloor spreading geological data do not seem to support subduction of southwestern proto weddell sea oceanic lithosphere beneath the eastern margin of the peninsula at that time cretaceous arc extension was coeval with the initial seafloor spreading phase in the weddell sea mid cretaceous arc compression linked to a global increase in ocean floor spreading rates and a superplume event correlates with a change from ne sw to nw se spreading in the weddell sea

evidence for holocene changes in australian indonesian monsoon rainfall from stalagmite trace element and stable isotope ratios abstract trace element and stable isotope ratios from an active stalagmite lr06 b1 recovered from liang luar cave on the island of flores eastern indonesia are used to reconstruct the position of the austral summer inter tropical convergence zone and australian indonesian summer monsoon variability during the holocene uranium series dating of the stalagmite shows that it commenced growth 12 640 years ago with hiatuses spanning 8 560 to 6 420 and 3 670 to 2 780 years ago stalagmite mg ca and sr ca ratios correlate significantly with one another and with 18 o and 13 c throughout the record this suggests that the mg ca and sr ca ratios are dominated by prior calcite precipitation a process whereby degassing in the vadose zone during periods of low recharge causes deposition of calcite and disproportionate loss of ca 2 ions relative to mg 2 and sr 2 upstream of the stalagmite the degree of initial 234 u 238 u disequilibrium also appears to have been controlled by recharge to the overlying aquifer together with the mg ca sr ca and 18 o values the initial uranium isotope activity ratios 234 u 238 u i imply a generally drier early holocene coincident with a lower sea level and lower southern hemisphere summer insolation comparison of speleothem 18 o time series from flores and borneo shows that they vary in unison for much of the holocene however there is a significant decrease in the borneo 18 o record 6 000 to 4 000 years ago that does not occur in the flores record this anomaly may be related to a change in the australian indonesian summer monsoon circulation in response to a protracted positive phase of the indian ocean dipole under this scenario stronger upwelling off of western indonesia would based on present day effects result in reduced summer convective activity over flores and a subsequent northward shift of the intertropical convergence zone

holocene east asian summer monsoon records in northern china and their inconsistency with chinese stalagmite δ18o records abstract monsoon precipitation over china exhibits large spatial differences it has been found that a significantly enhanced east asian summer monsoon easm is characterized by increased rainfall in northern china and by reduced rainfall in southern china and this relationship occurs on different time scales during the holocene this study presents results from a diverse range of proxy paleoclimatic records from northern china where precipitation variability is traditionally considered as an easm proxy our aim is to evaluate the evolution of the easm during the holocene and to compare it with all of the published stalagmite 18 o records from the asian monsoon region in order to explore the potential mechanism s controlling the chinese stalagmite 18 o we found that the intensity of the easm during the holocene recorded by the traditional easm proxy of moisture or precipitation records from northern china is significantly different from the chinese stalagmite 18 o records the easm maximum occurred during the mid holocene challenging the prevailing view of an early holocene easm maximum mainly inferred from stalagmite 18 o records in eastern china in addition all of the well dated holocene stalagmite 18 o records covering a broad geographical region exhibit a remarkably similar trend of variation and are statistically well correlated on different time scales thus indicating a common signal however in contrast with the clear consistency in the 18 o values in all of the cave records both instrumental and paleoclimatic records exhibit significant spatial variations in rainfall on decadal to centennial time scales over eastern china in addition both paleoclimatic records and modeling results suggest that holocene east asian summer monsoon precipitation reached a maximum at different periods in different regions of china thus the stalagmite 18 o records from the easm region should not be regarded as a reliable indicator of the strength of the east asian summer monsoon furthermore modern observations indicate that the moisture for precipitation in the east asian monsoon region is mainly derived from the indian ocean the moisture transport route from the indian ocean to the east asian monsoon region during the holocene is almost identical to that of modern precipitation therefore the strong correlation of 18 o records in the easm and indian summer monsoon ism regions and the similarity of the pattern of latitudinal changes in 18 o values in stalagmites and in modern meteoric precipitation along the water vapor transport route further suggests that the stalagmite 18 o records from the easm region are essentially a signal of the isotopic composition of precipitation which is determined mainly by changes in the 18 o of atmospheric vapor in the upstream source region over the indian ocean and indian monsoon region via the upstream depletion mechanism finally the main trends of the stalagmite 18 o records are strongly correlated with the known evolution of the ism and therefore these records reflect the history of the ism rather than that of the easm our findings support the conclusion that easm variability is mainly controlled by northern hemisphere summer insolation and was strongly modulated by ice volume during the last deglaciation and early holocene which delayed the response of the easm maximum to peak insolation forcing

east asian hydroclimate modulated by the position of the westerlies during termination i speleothem oxygen isotope records have revolutionized our understanding of the paleo east asian monsoon yet there is fundamental disagreement on what they represent in terms of the hydroclimate changes we report a multiproxy speleothem record of monsoon evolution during the last deglaciation from the middle yangtze region which indicates a wetter central eastern china during north atlantic cooling episodes despite the oxygen isotopic record suggesting a weaker monsoon we show that this apparent contradiction can be resolved if the changes are interpreted as a lengthening of the meiyu rains and shortened post meiyu stage in accordance with a recent hypothesis model simulations support this interpretation and further reveal the role of the westerlies in communicating the north atlantic influence to the east asian climate

late pleistocene and holocene palaeoenvironments in and around the middle caspian basin as reconstructed from a deep sea core this article has been made available through open access by the brunel open access publishing fund

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

evidence for solar influence in a holocene speleothem record pere noel cave se belgium abstract we present a decadal centennial scale holocene climate record based on trace elements contents from a 65 cm stalagmite from belgian pere noel cave pere noel pn stalagmite covers the last 12 7 ka according to u th dating high spatial resolution measurements of trace elements sr ba and mg were done by laser ablation inductively coupled plasma mass spectrometry la icp ms trace elements profiles were interpreted as environmental and climate changes in the han sur lesse region power spectrum estimators and continuous wavelet transform were applied on trace elements time series to detect any statistically significant periodicities in the pn stalagmite spectral analyses reveal decadal to millennial periodicities i e 68 75 133 136 198 209 291 358 404 602 912 1029 and 2365 2670 yr in the speleothem record results were compared to reconstructed sunspot number data to determine whether solar signal is presents in pn speleothem the occurrence of significant solar periodicities i e cycles of gleissberg de vries unnamed 500 years eddy and hallstatt supports for an impact of solar forcing on pn speleothem trace element contents moreover several intervals of significant rapid winter change were detected during the holocene at 10 3 9 3 9 5 around 8 2 6 4 6 2 4 7 4 5 and around 2 7 ka bp those intervals are similar to the cold winter events evidenced in different natural paleoclimate archives suggesting common climate forcing mechanisms related to changes in solar irradiance

moisture evolution in central asia since 26 ka insights from a kyrgyz loess section western tian shan abstract central asia ca is located in the hinterland of the eurasian continent and faces an extreme risk of continued aridification under the current global warming trend to predict future climate change in ca paleoclimate studies provide essential references however the mechanisms underlying climate changes in ca remain relatively poorly known here we investigate moisture variations in ca as recorded in a 6 m loess section in the western tian shan kyrgyzstan which has accumulated since 26 ka based on the radiometric ams 14c dating we reconstructed the evolution of the wind regime and moisture conditions in the western tian shan with a modified grain size index gsim and a new l proxy l while the frequency dependent magnetic susceptibility fd redness a and yellowness b did not provide reliable paleoclimatic indicators due to weak pedogenesis and other controlling factors the gsim records demonstrated a precipitation maximum in summer before 15 ka shifting to a maximum in spring after 15 ka probably associated with large scale modulation of the latitudinal climatic zones and atmospheric circulation in response to retreat of the northern hemisphere ice sheets based on the l records we place emphases on the important role of temperature modulated evaporation in moisture evolution across ca however this has only influenced moisture evolution in spring and summer with little effect on winter moisture conditions moreover the l records may also indicate that atmospheric humidity can partly affect the long term effective moisture variations

crustal growth of the antarctic peninsula by accretion magmatism and extension a subduction accretion model incorporating new geophysical data is presented to explain the geology of the antarctic peninsula from late palaeozoic to cenozoic time according to the model the peninsula consists of overlapping accretionary magmatic and extensional regimes that were diachronous across the peninsula and have built the crust to its present form the crust which contains a small proportion of sialic basement was mainly formed by accretionary and magmatic processes and modified to its present shape by extension the gondwanide orogeny for the antarctic peninsula is interpreted in terms of the accretionary processes

climatic and atmospheric circulation pattern variability from ice core isotope geochemistry records altai tien shan and tibet several firn ice cores were recovered from the siberian altai belukha plateau central tien shan inilchek glacier and the tibetan plateau zuoqiupu glacier bomi from 1998 to 2003 the comparison analyses of stable isotope geochemistry records obtained from these firn ice cores identified the physical links controlling the climate related signals at the seasonal scale variability the core data related to physical stratigraphy meteorology and synoptic atmospheric dynamics were the basis for calibration validation and clustering of the relationships between the firn ice core isotope geochemistry and snow accumulation air temperature and precipitation origin the mean annual accumulation in water equivalent was 106 g cm 2 a 1 at inilchek glacier 69 g cm 2 a 1 at belukha and 196 gc m 2 a 1 at zuoqiupu the slopes in regression lines between the d 18 o ice core records and air temperature were found to be positive for the tien shan and altai glaciers and negative for southeastern tibet where heavy amounts of isotopically depleted precipitation occur during summer monsoons the technique of coupling synoptic climatology and meteorological data with d 18 o and d excess in firn core records was developed to determine climate related signals and to identify the origin of moisture in altai two thirds of accumulation from 1984 to 2001 was formed from oceanic precipitation and the rest of the precipitation was recycled over aral caspian sources in the tien shan 87 of snow accumulation forms by precipitation originating from the aral caspian closed basin the eastern mediterranean and black seas and 13 from the north atlantic

87sr 86sr and sr ca in speleothems for paleoclimate reconstruction in central china between 70 and 280 kyr ago limestone cave deposits speleothems provide archives for past changes in regional climates over a range of timescales while 18o and 13c in speleothem calcite have been commonly used for reconstruction of paleoclimates we report here further efforts in the use of 87sr 86sr and sr ca signals in speleothem calcite to deduce paleomonsoon variability near the loess plateau of central china a two end member mass balance model of concentration and isotopic composition of strontium in a cave system is used to estimate variation of the 87sr 86sr ratio in sediments overlying a limestone cave we show that this ratio reflects climate driven variations in the provenance and the extent of chemical weathering of the epikarstic sediments the measurements of 87sr 86sr made on a well dated stalagmite sfl from buddha cave 33o40n 109o05 e show ratios of 0 71092 to 0 71133 0 00001 as 2 during relatively cold periods e g marine isotope stage mis 5b 5d and 8 lower than ratios of 0 71133 to 0 71194 during relatively warm periods e g mis 5a 5c 5e and 7 as changes in the sr ca ratio may affect speleothem 87sr 86sr we show that the direct use of speleothem 87sr 86sr is less ideal than our modeled 87sr 86sr for the exogenic sr source above the cave as a paleomonsoon proxy using the 18o 13c sr ca and 87sr 86sr records of the stalagmite we reconstruct the variability of the east asian monsoon for the time period between 70 and 280 kyr ago the results show that summer monsoons were more intense during interglacial periods than during glacial periods

variation in carbon isotopic composition over the past ca 46 000 yr in the loess paleosol sequence in central kazakhstan and paleoclimatic significance abstract we present a high resolution record of 13 c org variation from two loess sequences in central kazakhstan the variation shows that the vegetation was persistently dominated by c 3 plants over the past ca 46 000 yr the 13 c org signature was most likely an indicator of moisture and the moisture variation in central kazakhstan was associated with the precipitation in western europe the 13 c org indicated that moisture variation exhibited five stages decreasing during stage 1 ca 46 000 ca 31 500 yr bp increasing during stage 2 ca 31 500 ca 25 500 yr bp again decreasing during stage 3 ca 25 500 ca 19 000 yr bp fluctuating along a constant line during stage 4 ca 19 000 ca 5000 yr bp and increasing during stage 5 last ca 5000 yr our comparison demonstrated a general similarity between the 13 c org indicated moisture variation in central kazakhstan and the reconstructed precipitation variation in western europe the similarity implies that the moisture of the past ca 46 000 yr in central kazakhstan has been controlled or modulated by westerlies that brought water vapor from the north atlantic not only to western europe but also to central kazakhstan

evidence of rainfall variations in southern brazil from trace element ratios mg ca and sr ca in a late pleistocene stalagmite trace element ratios in the bt2 stalagmite from botuveracave southern brazil are explored as a proxy for changes in the local rainfall recharge during the last 116 ky bp mg ca and sr ca ratios measured with an electron microprobe are signif icantly positively correlated with one another throughout the entire record and vary in a way that is very consistent with variations of d 18 o in the same speleothem during the last glacial period we suggest that prior calcite precipitation in the vadose zone of the cave system is the main factor affecting the incorporation of mg and sr into calcite of the stalagmite this interpretation is supported by trace element correlation patterns and by results from a hydrochemistry study performed in a cave located in the same region and in a similar environmental setting therefore we conclude that higher lower mg ca and sr ca values are associated with lower higher levels of recharge into the karstic aquifer as such conditions lead to an increase decrease in the volume of calcite precipitated in the unsaturated zone above the cave during dry wet climate periods trace element variations point to generally dryer wetter conditions during lower high phases of summer insolation in the southern hemisphere these periods coincide with decreased increased activity of the south american summer monsoon as revealed by d 18 o stalagmite records in addition trace element variations show that rather wet conditions persisted through out most of the last glacial period from approximately 70 to 17 ky bp we suggest that during this period the glacial boundary conditions especially ice volume buildup in the northern hemisphere played an important role for monsoon rainfall inten sification in the region 2007 elsevier ltd all rights reserved

dry early holocene revealed by sand dune accumulation chronology in bayanbulak basin xinjiang nw china understanding the holocene climate changes especially moisture variation and their mechanisms in the semiarid arid central asia sca is very important as water availability is crucial for sustainable developments in this area this study presents chronostratigraphy of an aeolian sedimentary sequence from bayanbulak basin xinjiang nw china aiming to infer the holocene moisture history in the sca luminescence dating technique was selected to construct the age framework of the study section since the luminescence signal intensity of quartz from the samples was too low to be detected feldspar was used as an alternative dosimeter a newly developed post infrared ir ir stimulated luminescence irsl pirir dating protocol on k feldspar was applied to determine the ages of samples a set of tests on luminescence characteristics was performed and demonstrate that this method is suitable and the resultant ages are reliable combined with the stratigraphic investigation on the sand dune palaeosol section the results imply a very dry climatic condition characterized by sand dune accumulation at similar to 9 8 kyr and a wet interval of 5 1 6 kyr when a soil layer was formed this moisture variation pattern is consistent with that inferred from many lacustrine records in the sca suggesting a widespread dry period at 11 8 kyr the present results appear to challenge a new stalagmite delta o 18 sequence located nearby to bayanbulak basin which instead suggested a humid early holocene

holocene moisture evolution across the mongolian plateau and its surrounding areas a synthesis of climatic records abstract based on the review of 26 high standard holocene climatic reconstructions mainly pollen based from the mongolian plateau and its surrounding areas temporal and spatial patterns of the holocene moisture evolution are synthesized the regionally averaged moisture history from the summer monsoon influenced semiarid belt in china i e region a demonstrates that the moisture index curve is broadly in agreement with the synthesized east asian monsoon strength curve both following the general trend of the west tropical pacific sst that is in turn the delayed response to the northern hemispheric summer solar insolation the regionally averaged moisture indices from the winter monsoon dominated southern siberia including lake baikal area and the altai mountains i e region b exhibit a general declining trends since 10 6 9 6 cal kyr bp being largely consistent with the trends of the annual precipitation and the warm season temperature in the russian plain the consistency might be attributable to the holocene declining trend of the warm season temperature in north atlantic region the predominant feature of the regionally averaged moisture index from the westerlies affected northern xinjiang i e region c is a persistent increasing trend since 8 cal kyr bp the wetting trend of northern xinjiang during the past 8000 years might be attributable to the increasing trend of winter insolation and to the associated increasing trend of cold season temperature in northwestern europe the chronological correspondences between dry phases and warm intervals in the arid areas of the mongolian plateau i e northern mongolian plateau within mongolia and southern mongolian plateau within china region d lend a support to the proposal that the mid holocene dry phase was most likely the result of mid holocene high warm season temperature

causes of early holocene desertification in arid central asia paleoclimate records of effective moisture precipitation minus evaporation or p e show a dry low effective moisture period in mid latitude arid semi arid central asia during the early holocene 11 000 8 000 years ago relative to the middle and late holocene in contrast to evidence for greater than present precipitation at the same time in the south and east asian monsoonal areas to investigate the spatial differences in climate response over mid latitude central asia and monsoonal asia we conducted a series of simulations with the community climate system model version 3 coupled climate model for the early middle and late holocene the simulations test the climatic impact of all important forcings for the early holocene including changes in orbital parameters the presence of the remnant laurentide ice sheet and deglacial freshening of the north atlantic model results clearly show the early holocene patterns indicated by proxy records including both the decreased effective moisture in arid central asia which occurs in the model primarily during the winter months and the increase in summer monsoon precipitation in south and east asia the model results suggest that dry conditions in the early holocene in central asia are closely related to decreased water vapor advection due to reduced westerly wind speed and less evaporation upstream from the mediterranean black and caspian seas in boreal winter as an extra forcing to the early holocene climate system the laurentide ice sheet and meltwater fluxes have a substantial cooling effect over high latitudes especially just over and downstream of the ice sheets but contribute only to a small degree to the early holocene aridity in central asia instead most of the effective moisture signal can be explained by orbital forcing decreasing the early holocene latitudinal temperature gradient and wintertime surface temperature we find little evidence for regional subsidence related to a stronger summer asian monsoon in forcing early holocene aridity in central asia as has been previously hypothesized

production of jurassic rhyolite by anatexis of the lower crust of patagonia abstract the mid jurassic marifil and chon aike volcanic rocks of eastern patagonia are part of one of the largest silicic igneous provinces known rb sr geochronology indicates eruptive ages of 175 190 ma for the marifil complex mostly toarcian aalenian the majority of the rocks are isotopically uniform with initial 87sr 86sr 0 7067 0 0003 and endt 4 2 primary magmas of andesitic composition were generated by partial melting of mafic grenvillian lower crust indentified by depleted mantle model ages of 1150 1600 ma lower crustal pyroxene granulite xenoliths can be modelled as residual jurassic source although they may alternatively be co genetic cumulates the dacite rhyolite suite formed by crystal liquid fractionation processes from the primary andesites involving multistage crystallization and re melting during magma ascent with the later stages of evolution being explicable by fractional crystallization of plagioclase amphibole and accessory minerals the province represents large scale lower crustal reworking associated with the unique tectonic and igneous environment of gondwana break up

inconsistency between records of δ18o and trace element ratios from stalagmites evidence for increasing mid late holocene moisture in arid central asia the interpretation of trace element calcium ratios of speleothems as indicators of local hydroclimatic variability in the vicinity of caves has led to controversy in reconstructing the evolution of

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

holocene moisture variations over the arid central asia revealed by a comprehensive sand dune record from the central tian shan nw china abstract arid central asia aca is one of the largest arid desert areas in the world and its climate is dominated by the westerlies in this study we examined sand dune evolution from the bayanbulak basin in the tian shan xinjiang nw china aiming to infer the holocene moisture history of the aca combined with stratigraphic observation and environmental proxies analysis grain size magnetic susceptibility and total organic content large numbers of luminescence ages from multiple sites eight sections 79 samples were applied to reconstruct the evolution of the sand dune accumulation in the study basin the overall results imply very dry conditions characterized by sand dune accumulation at 12 6 5 ka a wet interval between 6 5 and 0 8 ka when soil formation occurred and decreased moisture during the last 0 8 ka this moisture variation pattern is generally consistent with that inferred from many lacustrine records in the core zone of aca suggesting a widespread dry period in the early to middle holocene and relatively wet middle to late holocene thus the moisture history derived from the current sand dune system contrasts with that in asian monsoon areas which are characterized by a strong monsoon high precipitation in the early and mid holocene and a weak monsoon low precipitation and dry climate during the late holocene our results strongly suggest that the winter solar insolation and the external boundary conditions such as atmospheric co2 concentration ice sheets and meltwater fluxes have been major influential factors triggering the holocene moisture evolution in the core zone of aca