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

centennial to decadal scale monsoon precipitation variability in the semi humid region northern china during the last 1860 years records from stalagmites in huangye cave we developed a composite oxygen isotopic record of cave calcite for the last 1860 years based on three stalagmites from the huangye cave in eastern gansu province northern china the d 18 o values reflect monsoon precipitation changes with lower d 18 o values representing higher precipitation and vice versa three intervals of high precipitation were identified at ad 138 450 ad 730 1200 and ad 1860 1960 two intervals of low precipitation occurred at ad 1320 1410 and ad 1530 1860 the reconstructed monsoon precipitation variations correlate well with other records further east in the eastern yellow river basin suggesting synchronous precipitation changes during the late holocene in the semi humid region of northern china on decadal to centennial scales peak periods of warfare in dynastic transition times such as at ad 391 420 ad 601 630 ad 1111 1140 ad 1351 1380 and ad 1621 1650 correspond to sharp declines in precipitation or temperature in semi humid northern china indicating a strong connection between climatic and societal changes our study suggests that climatic deterioration in semi humid northern china has played an important role in chinese societal evolution

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

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

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 holocene indian monsoon variability over the southern tibetan plateau and its teleconnections abstract a high resolution stalagmite oxygen isotope record from tianmen cave located in the south central tibetan plateau characterizes detailed climatic variations between 8 7 and 4 3 ka bp on centennial and decadal time scales with a temporal resolution of 3 to 7 years the tianmen record is in good agreement with speleothem records from asian monsoon regions i e dongge cave dykoski et al 2005 wang et al 2005 qunf cave fleitmann et al 2003 upwelling records from the arabian sea gupta et al 2003 gupta et al 2005 and peat bog records from southeast tibetan plateau hong et al 2003 indicating that the indian summer monsoon ism gradually weakened as northern hemisphere summer insolation declined during the early mid holocene and that ism intensity rather than temperature dominates the precipitation 18o on centennial to decadal time scales in the southern tp on centennial to decadal time scales the detrended tianmen record correlates well with the greenland ice core record further confirming the mechanistic connection between the ism and high northern latitude temperature changes meanwhile the tianmen record bears significant solar activity cycles suggesting that the solar output changes may affect the variability of the ism and likely the position of the intertropical convergence zone itcz as well moreover due to joint effects of changes in monsoon precipitation moisture source and temperature the tianmen 18o record shows much larger amplitude changes than speleothem 18o records from low elevation asian monsoon regions which is similar to the previously reported marine isotope stage mis 5 record cai et al 2010 suggesting heightened sensitivity of precipitation isotope composition to climate changes over the high elevation regions and further demonstrating that the stable isotope lapse rate may change under different climatic conditions

climate change and cultural response around 4000 cal yr b p in the western part of chinese loess plateau new data suggest that dramatic environmental change in the western loess plateau of china corresponded with substantial changes in human demography ca 4000 cal yr b p these data demonstrate that a rapid climatic transition from wet to dry led to an ecologically devastated period between 4090 and 3600 cal yr b p the sudden reduction in the number of archaeological sites during this period namely a reduction in the total number of sites and a contraction of the areal distribution of sites points to declining agricultural productivity associated with widespread aridification beginning at 4000 cal yr b p 2005 published by university of washington

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

role of seasonal transitions and westerly jets in east asian paleoclimate abstract the summer rainfall climate of east asia underwent large and abrupt changes during past climates in response to precessional forcing glacial interglacial cycles as well as abrupt changes to the north atlantic during the last glacial however current interpretations of said changes are typically formulated in terms of modulation of summer monsoon intensity and do not account for the known complexity in the seasonal evolution of east asian rainfall which exhibits sharp transition from the spring regime to the meiyu and then again from the meiyu to the summer regime we explore the interpretation that east asian rainfall climate undergoes a modulation of its seasonality during said paleoclimate changes following previous suggestions we focus on role of the westerly jet over asia namely that its latitude relative to tibet is critical in determining the stepwise transitions in east asian rainfall seasons in support of this linkage we show from observational data that the interannual co variation of june july august rainfall and upper tropospheric zonal winds show properties consistent with an altered timing of the transition to the meiyu summer and with more northward shifted westerlies for earlier transitions we similarly suggest that east asian paleoclimate changes resulted from an altered timing in the northward evolution of the jet and hence the seasonal transitions in particular the transition of the jet from south of the plateau to the north that determines the seasonal transition from spring rains to the meiyu in an extreme scenario which we speculate the climate system tended towards during stadial cold phases of d o stadials and periods of low northern hemisphere summer insolation the jet does not jump north of the plateau essentially keeping east asia in prolonged spring conditions we argue that this hypothesis provides a viable explanation for a key paleoproxy signature of d o stadials over east asia namely the heavier mean 18o of precipitation as recorded in speleothem records the southward jet position prevents the low level monsoonal flow which is isotopically light from penetrating into the interior of east asia as such precipitation there will be heavier consistent with speleothem records this hypothesis can also explain other key evidences of east asian paleoclimate changes in particular the occurrence of dusty conditions during north atlantic stadials and the southward migration of the holocene optimal rainfall

factors controlling the growth rate carbon and oxygen isotope variation in modern calcite precipitation in a subtropical cave southwest china abstract a prerequisite for using cave speleothems to reconstruct palaeoenvironmental conditions is an accurate understanding of specific factors controlling calcite growth in particular the isotopic partitioning of oxygen 18 o and carbon 13 c which are the most commonly used proxies an in situ monitoring study from april 2008 to september 2009 at xueyu cave chongqing sw china provides insight into the controls on calcite growth rates drip water composition cave air parameters and 18 o and 13 c isotopic values of modern calcite precipitation both cave air p co 2 and drip water hydrochemical characteristics show obvious seasonality driven by seasonal changes in the external environment calcite growth rates also display clear intra annual variation with the lowest values occurring during wet season and peak values during the dry season seasonal variations of calcite growth rate are primarily controlled by variations of cave air p co 2 and drip water rate seasonal 18 o vpdb and 13 c vpdb in modern calcite precipitates vary with more negative values in the wet season than in the dry season strong positive correlation of 18 o vpdb vs 13 c vpdb is due to simultaneous enrichment of both isotopes in the calcite this correlation indicates that kinetic fractionation occurs between parent drip water and depositing calcite likely caused by the variations of cave air p co 2 and drip rate influenced by seasonal cave ventilation kinetic fractionation amplifies the equilibrium fractionation value of calcite 18 o by 1 5 and 13 c by 1 7 which quantitatively reflects surface conditions during the cave ventilation season these results indicate that the cave monitoring of growth rate and 18 o and 13 c of modern calcite precipitation are necessary in order to use a speleothem to reconstruct palaeoenvironment

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

modeling climate shift of el nino variability in the holocene a coupled ocean atmosphere general circulation model is used to investigate climatic shift of el nino in the holocene the model simulates a reduced enso intensity in the early and mid holocene in agreement with paleoclimate record the enso reduction is proposed to be caused by both an intensified asian summer monsoon and a warm water subduction from the south pacific into the equatorial thermocline

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

extraordinary floods of 4100 4000 a bp recorded at the late neolithic ruins in the jinghe river gorges middle reach of the yellow river china abstract holocene palaeohydrological investigations were carried out in the middle reach of the jinghe river that drains the central part of the loess plateau a set of palaeoflood slackwater deposits was found interbedded in the holocene loess soil sequence within the cliff riverbanks both the sedimentary criteria and the analytical results show that this sediment was sourced from a suspended sediment load of floodwater the major cultural layer of a late neolithic settlement 4300 4000 a bp occurring at the same site is blanketed by this flood deposit directly slopewash with pottery shards charcoal and burnt earth occurs in between the palaeoflood slackwater deposit beds it indicates that each of the slackwater deposit beds has recorded one individual flood event and that these extraordinary floods occurred when the late neolithic people occupied the riverbank terrace land this pre historical settlement was abandoned after the floods eventually due presumably to repeated inundation by overbank floodwater the flood events were osl dated to between 4100 and 4000 a bp and checked by archaeological dating of the anthropogenic remains retrieved from the sequences peak discharges of the floods were estimated to between 19 500 and 22 000 m3 s 1 which is several times gauged maximum floods during the 4200 4000 a bp climatic event severe droughts were documented in china s monsoonal regions and great floods were known from an ancient legend this study provides a well dated sediment record of pre historical floods which occurred at the transition from the neolithic to the bronze age in the yellow river basin it shows that extraordinary floods were part of the abrupt climatic variability during the 4200 4000 a bp climatic event the highly variable unstable and catastrophic climate typified by both droughts and floods resulted in settlement abandonment and possibly the decline of the highly developed late neolithic civilizations in china s monsoonal regions

extraordinary floods related to the climatic event at 4200 a bp on the qishuihe river middle reaches of the yellow river china abstract palaeo hydrological study was carried out in the qishuihe river valley in the middle reaches of the yellow river several bedsets of flood slackwater deposit were identified in the holocene loess soil sequences on the riverbanks they were differentiated from aeolian loess and soils by the parallel and waving beddings and the distinctive stratigraphic breaks separating individual palaeoflood events chronology of the flood events was established by osl dating checked by archaeological identification of the anthropogenic remains retrieved from the sequences the results show that successive floods occurred between 4300 and 4000 a bp in association with the abrupt climatic event of 4200 a bp these overbank floods had the riverbank settlement inundated repeatedly another series of extraordinary floods occurred between 3200 and 3000 a bp when monsoonal climate shifted from the mid holocene climatic optimum toward late holocene dry conditions the climatic event of 4200 a bp and the climatic decline at 3100 a bp were believed to be characterized by droughts previously this work provides solid evidence that both severe droughts and extreme floods were parts of the climatic variability during abrupt climatic event and climatic decline in the semi arid to sub humid zones over the world

a high resolution record of holocene rainfall variations from the western chinese loess plateau antiphase behaviour of the african indian and east asian summer monsoons tropical monsoons are key mechanisms for transfer of heat and moisture to higher latitudes here we present a high resolution terrestrial proxy summer monsoon record for the southeast asian monsoon from a rapidly accumulating holocene loess soil sequence in the western chinese loess plateau we use magnetic and clastic grain size proxies to make quantitative estimates of holocene rainfall and identify variations in winter monsoon intensity our record reveals cyclical millennial and multimillennial rainfall changes as with the northwest african southwest asian monsoon records a short arid interval at 12 5 to 11 5 ka bp the younger dryas and subsequent summer monsoon intensification are recorded however at 6 ka bp the southeast asian summer monsoon weakened when the northwest african southwest asian monsoons strengthened and then from 5 ka bp intensified when northwest africa southwest asia became dry these antiphase monsoonal relationships may reflect competition between sea surface temperature changes and solar forcing the intensity of the southeast asian winter monsoon intensified from 9 ka bp onwards varying in its phase relationships with summer monsoon intensity after 2 25 ka bp extreme climatic instability is indicated by both climate proxies

investigating the long term palaeoclimatic controls on the δd and δ18o of precipitation during the holocene in the indian and east asian monsoonal regions abstract this paper aims to achieve an improved understanding of the long term change trends of precipitation d and 18 o values d p and 18 o p in the asian monsoonal region and their relationship with the corresponding humidity trends during the holocene to do this we first review the observed modern spatial pattern of summer precipitation distribution in the east asian summer monsoon easm region under different easm intensities and the relationship between modern observed 18 o p values and corresponding precipitation amounts on monthly and inter annual timescales in the easm and indian summer monsoon ism regions second we compare holocene lacustrine and marine compound specific hydrogen isotopic records of n alkanes n alkanoic acid d n lacustrine authigenic carbonate and cave stalagmite oxygen isotopic records 18 o c and 18 o s from the asian monsoonal region all of which are closely related to d p and 18 o p variations the results demonstrate that in both the ism and easm regions all of these isotopic records exhibit roughly similar long term characteristics i e they were all more negative during the early holocene and early mid holocene ca 11 6 ka b p b p means before present present 1950 ad and then became more positive towards the late holocene third we compare representative paleo humidity records from the asian monsoonal region the results confirm that in the ism region a humid interval occurred in the early holocene and early mid holocene ca 11 6 ka b p and subsequently the climate became more arid towards the late holocene this indicates an enhanced ism during the early holocene and early mid holocene ca 11 6 ka b p and an ism of decreasing intensity towards the late holocene on a holocene orbital scale both 18 o p and d p appear to be controlled by an amount effect in the ism region consistent with the region s inter annual modern 18 o p data this evidence indicates that both 18 o p and d p paleo records are significantly related to paleo humidity in the ism region in contrast holocene humidity variations in the easm region exhibit clear spatial differences a humid mid holocene interval ca 8 3 ka b p occurred in southern and northern china but an arid interval from ca 7 3 ka b p occurred in central china in the middle reaches of the yangtze river based on precipitation distribution patterns under different easm intensities in the easm region over the past few decades we conclude that easm intensity was enhanced during the mid holocene ca 8 3 ka b p relative to the ism intensity the response of easm intensity to summer insolation was relatively slow in the easm region the relationship between climate and 18 o p and d p is more complex consistent with analyses of regional inter annual modern 18 o p data this evidence demonstrates that both 18 o p and d p paleo records cannot be used directly as paleo humidity i e precipitation amount or easm intensity indicators in the easm region further comparison and analyses demonstrate that the coupled variations in west east equatorial pacific temperature gradients and the west pacific subtropical high wpsh played an important role in determining easm intensity during the holocene

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

the 9 2 ka event in asian summer monsoon area the strongest millennial scale collapse of the monsoon during the holocene numerous holocene paleo proxy records exhibit a series of centennial millennial scale rapid climatic events unlike the widely acknowledged 8 2 ka climate anomaly the likelihood of a significant climate excursion at around 9 2 cal ka bp which has been notably recognized in some studies remains to be fully clarified in terms of its magnitude and intensity as well as its characteristics and spatial distributions in a range of paleoclimatic records in this study a peat sediment profile from the dajiuhu basin in central china was collected with several geochemical proxies and a pollen analysis carried out to help improve understanding of the climate changes around 9 2 cal ka bp the results show that the peat development was interrupted abruptly at around 9 2 cal ka bp when the chemical weathering strength decreased and the tree pollen declined this suggests that a strong drier regional climatic event occurred at around 9 2 cal ka bp in central china which was in turn probably connected to the rapid 9 2 ka climate event co developing worldwide in addition based on the synthesis of our peat records and the other holocene hydrological records from asian summer monsoon asm region we further found that the 9 2 ka event probably constituted the strongest abrupt collapse of the asian monsoon system during the full holocene interval the correlations between asm and the atmospheric 14c production rate the north atlantic drift ice records and greenland temperature indicated that the weakened asm event at around 9 2 cal ka bp could be interpreted by the co influence of external and internal factors related to the changes of the solar activity and the atlantic meridional overturning circulation amoc

centennial to decadal scale monsoon precipitation variations in the upper hanjiang river region china over the past 6650 years abstract the upper hanjiang river region is the recharge area of the middle route of south to north water transfer project the region is under construction of the hanjiang weihe river water transfer project in china monsoon precipitation variations in this region are critical to water resource and security of china in this study high resolution monsoon precipitation variations were reconstructed in the upper hanjiang river region over the past 6650 years from 18 o and 13 c records of four stalagmites in xianglong cave the long term increasing trend of stalagmite 18 o record since the middle holocene is consistent with other speleothem records from monsoonal china this trend follows the gradually decreasing northern hemisphere summer insolation which indicates that solar insolation may control the orbital scale east asian summer monsoon easm variations despite the declined easm intensity since the middle holocene local precipitation may not have decreased remarkably as revealed by the 13 c records a series of centennial to decadal scale cyclicity was observed with quasi millennium quasi century 57 36 and 22 year cycles by removing the long term trend of stalagmite 18 o record increased monsoon precipitation during periods of 4390 3800 a bp 3590 2960 a bp 2050 1670 a bp and 1110 790 a bp had caused four super floods in the upper reach of hanjiang river dramatically dry climate existed in this region during the 5 0 ka and 2 8 ka events coinciding with notable droughts in other regions of monsoonal china remarkably intensified and southward westerly jet together with weakened summer monsoon may delay the onset of rainy seasons resulting in synchronous decreasing of monsoon precipitation in china during the two events during the 4 2 ka event and the little ice age the upper hanjiang river region was wet which was similar to the climate conditions in central and southern china but was the opposite of drought observed in northern china we propose that weakened summer monsoon and less strengthened or normal westerly jet may cause rain belt stay longer in the southward region which reduced rainfall in northern china but enhanced it in central and southern china

transfer of inland salts to the marine environment at the head of spencer gulf south australia upper spencer gulf is linked by a narrow tidal channel to an extensive system of salt marshes channels and salt pans overlying cainozoic sediments of the pirie torrens basin in arid south australia the gulf here is characterised by a vigorous tidal regime with a spring range of 3 4 m current velocities reaching 1 0 m s 1 and salinities greater than that estimated from evaporation alone we suggest that the anomalously high salinities are maintained by input from interstitial brines from the northern salt pan corridor and by the scavenging effect of surface water after occasional heavy rains these processes are particularly important in buffering the salinity of tidal waters in winter when evaporation is reduced our hypothesis is based on the distribution of total salts major ions selected trace elements and the 87sr 86sr isotopic ratio in samples of surface and interstitial water collected during 1986 1988 and on oceanographic measurements of the tidal regime a removal rate of the order of 10 kg s 1 of total salts from inland brines to tidal water has been derived from hydrodynamical simulations of the system

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

the eastward shift of the walker circulation in response to global warming and its relationship to enso variability this study investigates the global warming response of the walker circulation and the other zonal circulation cells represented by the zonal stream function in cmip3 and cmip5 climate models the changes in the mean state are presented as well as the changes in the modes of variability the mean zonal circulation weakens in the multi model ensembles nearly everywhere along the equator under both the rcp4 5 and sres a1b scenarios over the pacific the walker circulation also shows a significant eastward shift these changes in the mean circulation are very similar to the leading mode of interannual variability in the tropical zonal circulation cells which is dominated by el nino southern oscillation variability during an el nino event the circulation weakens and the rising branch over the maritime continent shifts to the east in comparison to neutral conditions vice versa for a la nina event two thirds of the global warming forced trend of the walker circulation can be explained by a long term trend in this interannual variability pattern i e a shift towards more el nino like conditions in the multi model mean under global warming further interannual variability in the zonal circulation exhibits an asymmetry between el nino and la nina events el nino anomalies are located more to the east compared with la nina anomalies consistent with this asymmetry we find a shift to the east of the dominant mode of variability of zonal stream function under global warming all these results vary among the individual models but the multi model ensembles of cmip3 and cmip5 show in nearly all aspects very similar results which underline the robustness of these results the observed data era interim reanalysis from 1979 to 2012 shows a westward shift and strengthening of the walker circulation this is opposite to what the results in the cmip models reveal however 75 of the trend of the walker circulation can again be explained by a shift of the dominant mode of variability but here towards more la nina like conditions thus in both climate change projections and observations the long term trends of the walker circulation seem to follow to a large part the pre existing dominant mode of internal variability

oceanographic controls on shallow water temperate carbonate sedimentation spencer gulf south australia spencer gulf is a large ca 22 000 km2 shallow 60 m water depth embayment with active heterozoan carbonate sedimentation gulf waters are metahaline salinities 39 to 47 and warm temperate ca 12 to 28 c with inverse estuarine circulation the integrated approach of facies analysis paired with high resolution monthly oceanographic data sets is used to pinpoint controls on sedimentation patterns with more confidence than heretofore possible for temperate systems biofragments mainly bivalves benthic foraminifera bryozoans coralline algae and echinoids accumulate in five benthic environments luxuriant seagrass meadows patchy seagrass sand flats rhodolith pavements open gravel sand plains and muddy seafloors the biotic diversity of spencer gulf is remarkably high considering the elevated seawater salinities echinoids and coralline algae traditionally considered stenohaline organisms are ubiquitous euphotic zone depth is interpreted as the primary control on environmental distribution whereas seawater salinity temperature hydrodynamics and nutrient availability are viewed as secondary controls luxuriant seagrass meadows with carbonate muddy sands dominate brightly lit seafloors where waters have relatively low nutrient concentrations ca 0 to 1 mg chl a m 3 low diversity bivalve dominated deposits occur in meadows with highest seawater salinities and temperatures 43 to 47 up to 28 c patchy seagrass sand flats cover less illuminated seafloors open gravel sand plains contain coarse bivalve bryozoan sediments interpreted as subphotic deposits in waters with near normal marine salinities and moderate trophic resources 0 5 to 1 6 mg chl a m 3 to support diverse suspension feeders rhodolith pavements coralline algal gravels form where seagrass growth is arrested either because of decreased water clarity due to elevated nutrients and associated phytoplankton growth 0 6 to 2 mg chl a m 3 or bottom waters that are too energetic for seagrasses currents up to 2 m sec 1 muddy seafloors occur in low energy areas below the euphotic zone the relationships between oceanographic influences and depositional patterns outlined in spencer gulf are valuable for environmental interpretations of other recent and ancient particularly neogene high salinity and temperate carbonate systems worldwide

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

groundwater evaporation from salt pans examples from the eastern arabian peninsula summary the major groundwater resources of the arabian peninsula are stored in the large sedimentary basins in its eastern part evaporation from continental salt pans playas is an important process in water resources assessments of its upper principal aquifers the upper mega aquifer system as it constitutes a significant sink however literature values on evaporation rates vary widely and usually report about coastal salt pans where seawater evaporation is assumed the present study applies different methods to provide a comprehensive picture of groundwater evaporation from salt pans of the upper mega aquifer system a remote sensing approach provided the spatial distribution and total salt pan area of about 36 500 km 2 hydrochemical and isotopic investigations revealed that from about 10 3600 km 2 1600 km 2 of the mapped salt pan area seawater evaporates to estimate the groundwater evaporation rate from continental salt pans a laboratory column experiment was set up implying a mean annual evaporation rate of about 42 mm 13 mm in situ analysis of water table fluctuations in the field suggested about 3 mm a 1 originate from recently infiltrated rainwater leading to an annual net groundwater evaporation of 39 mm 13 mm relating this number to the mapped salt pan area from which groundwater evaporates provides a total annual groundwater loss of 1 3 km 3 0 5 km 3 for the upper mega aquifer system

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

hydrogeologic processes in saline systems playas sabkhas and saline lakes abstract pans playas sabkhas salinas saline lakes and salt flats are hydrologically similar varying only in their boundary conditions thus in evaluating geochemical processes in these systems a generic water and solute mass balance approach can be utilized a conceptual model of a coastal sabkha near the arabian gulf is used as an example to illustrate the various water and solute fluxes analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha but contribute only a small volume of the water local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge to rainfall ratio of more than 50 the contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha because of a short residence time of water steady state flow is expected within a short time 50 000 years the solute composition of the brine in a closed saline system depends largely on the original composition of the input water the high total ion content in the brine limits the efficiency of water rock interaction and absorption because most natural systems are hydrologically open the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation thus during the hot dry season months minerals exhibit retrograde solubility so that gypsum anhydrite and calcite precipitate evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone e g halite and carnallite provided that the relative humidity of the atmosphere is less than the activity of water the slope of the fresh brine water interface in saline lake systems is shallower than in fresh seawater interface because of the greater density difference between the fresh brine water bodies the interface between sabkha brines and seawater slopes seaward unlike normal marine fresh water systems that slope landward moreover the brine seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha s brine

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

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

chemical mechanical coupling observed for depleted oil reservoirs subjected to long term co2 exposure a case study of the werkendam natural co2 analogue field geological storage of co2 is one of the most promising technologies to rapidly reduce anthropogenic emissions of carbon dioxide in order to ensure storage integrity it is important to understand the effect of long term co2 brine rock interactions on the mechanical behaviour of a storage complex as most of these reactions are too slow to reproduce on laboratory timescales we studied a natural co2 analogue reservoir the rot fringe sandstone werkendam field the netherlands 125 135 ma of co2 exposure and its unreacted counterpart we focused on co2 induced mineralogical and porosity permeability changes and their effect on mechanical behaviour of both intact rock and simulated fault gouge overall co2 exposure did not lead to drastic mineralogical changes the co2 exposed material shows a stronger dependence of permeability on porosity which is attributed to differences in diagenesis closed system diagenesis and hydrocarbon emplacement taking place before co2 charging the limited extent of reaction was in part the result of bitumen coatings protecting specific mineral phases from reaction in local mm sized zones displaying significant anhydrite cement dissolution enhanced porosity was observed for most of the reservoir the long term mechanical behaviour after co2 exposure could be described by the behaviour of the unreacted sandstone while these more porous zones had a lower rock strength in addition co2 exposure did not affect the fault friction behaviour and slip is expected to result in stable sliding simple stress path calculations predict that reservoir failure due to depletion and injection is unlikely even for the porous zones nor will fault reactivation occur for realistic injection scenarios

timing and structure of the 8 2 kyr b p event inferred from δ18o records of stalagmites from china oman and brazil oxygen isotope records of stalagmites from china and oman reveal a weak summer monsoon event with a double plunging structure that started 8 21 0 02 kyr b p an identical but antiphased pattern is also evident in two stalagmite records from eastern brazil indicating that the south american summer monsoon was intensifi ed during the 8 2 kyr b p event these records demonstrate that the event was of global extent and synchronous within dating errors of 50 years in comparison with recent model simulations it is plausible that the 8 2 kyr b p event can be tied in changes of the atlantic meridional overturning circulation triggered by a glacial lake draining event this in turn affected north atlantic climate and latitudinal position of the intertropical convergence zone resulting in the observed low latitude monsoonal precipitation patterns

sea surface temperatures and ice rafting in the holocene north atlantic climate influences on northern europe and greenland abstract the oceanographic conditions in the high latitude north atlantic ocean during the holocene were reconstructed through analyses of sea surface temperature sst alkenone unsaturation ratios and ice rafting mineralogy and grain size from two sediment sequences one recovered from the reykjanes ridge at 59 n and the other from the norwegian sea at 68 n comparison of our records to published ice core and terrestrial proxy climate data sets suggests that atmospheric temperature changes over northern europe and greenland were coupled to sst variability and ice rafting the records outline four major climatic phases i an early holocene thermal maximum that lasted until approximately 6 7 kyr bp ii a distinctly cooler phase associated with increased ice rafting between 6 5 and 3 7 kyr bp iii a transition to generally warmer but relatively unstable climate conditions between 3 7 and 2 kyr bp and iv a second distinct sst decline that took place between 2 and 0 5 kyr bp in contrast to the dominant control of northern hemisphere summer insolation on early holocene climate development via strong seasonality the trigger for the onset of relatively unstable climatic conditions in the north atlantic at 3 7 kyr bp is not straightforward however it is possible that this change was triggered by late holocene winter insolation increase at high northern latitude and or by inter hemispheric changes in orbital forcing the late holocene neoglaciation trend which is characteristic of numerous terrestrial archives in northern europe may not only be attributed to a gradual decrease in orbitally forced summer temperature but also to increase snow precipitation at high northern latitudes during generally milder winters

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

depositional frequency of german subfossil oaks climatically and non climatically induced fluctuations in the holocene a highly resolved record of the depositional frequency of subfossil trees since 8263 bc in the valley of the river main is presented different aspects of forest dynamics are explored including depositional anomal ies phases of low or zero departures changes in forest density based on tree growth trend classes gtcs and regeneration using mean lifespan ml data this reveals a number of climatically induced environmental changes that are synchronous with events in the north atlantic region and therefore may reflect a facet of the north atlantic climate system three periods are recognized 1 pre 3500 bc when depositional frequency was dominated by climatic events with notable anomalies at 6200 and 4100 bc 2 between 3500 and 1200 bc when climatically triggered events were enhanced by forest clearances especially marked anomalies occurring around 2700 2300 and 1700 bc and 3 post 1200 bc when the climatic information is obscured by human activities

a high resolution stalagmite record of the holocene east asian monsoon from mt shennongjia central china high resolution oxygen isotope 18o profiles of six stalagmites from sanbao cave in hubei province central china established with 1413 oxygen isotope data and 65 230th ages provide a continuous history of east asian summer monsoon easm intensity for the period from 13 0 2 thousand years before present ky bp relative to ad 1950 the 18o record includes four distinct stages in the evolution of the easm 1 an abrupt transition 11 5 ky bp into the holocene 2 a period of gradual increase in monsoon intensity 11 5 9 5 ky bp 3 the maximum humid period 9 5 6 5 ky bp and 4 a period of gradual decline in monsoon intensity 6 5 0 2 ky bp comparison of sanbao with regional records of comparable resolution reveals that the timing of the beginning and end of the holocene optimum as defined by the minimum in 18 o was similar in the indian and east asian monsoon systems this supports the idea that shifts in the monsoon tied to shifts in the mean position of the inter tropical convergen

the enso asian monsoon interaction in a coupled ocean atmosphere gcm abstract in this study the authors evaluate the el nino southern oscillation enso asian monsoon interaction in a version of the hadley centre coupled ocean atmosphere general circulation model cgcm known as hadcm3 the main focus is on two evolving anomalous anticyclones one located over the south indian ocean sio and the other over the western north pacific wnp these two anomalous anticyclones are closely related to the developing and decaying phases of the enso and play a crucial role in linking the asian monsoon to enso it is found that the hadcm3 can well simulate the main features of the evolution of both anomalous anticyclones and the related sst dipoles in association with the different phases of the enso cycle by using the simulated results the authors examine the relationship between the wnp sio anomalous anticyclones and the enso cycle in particular the biennial component of the relationship it is found that a strong el nino event tends to be followed by a more rapid decay and i

palaeosol development in the chinese loess plateau as an indicator of the strength of the east asian summer monsoon evidence for a mid holocene maximum the interpretation of the stalagmite delta o 18 record from southern china as an indicator of east asian summer monsoon easm rainfall amount or intensity is strongly debated soil development in the chinese loess plateau clp situated in the modern summer monsoon domain has long been treated as a direct and reliable easm proxy in this study we compiled 81 loess and 229 palaeosol dates from 77 profiles across the clp and synthesized the data statistically in order to investigate the easm history during the holocene the resulting history of holocene loess deposition and palaeosol development demonstrates that 1 loess deposition decreased and palaeosol formation increased across the clp after 11 5 ka 1 ka 1000 cal yr bp revealing a gradually intensified easm during the early holocene 2 numerous palaeosols developed in the clp between 8 8 ka and 3 4 ka indicating a generally strong easm during the mid holocene 3 the number of palaeosol dates decreased rapidly at around 3 ka suggesting a sudden retreat of the easm in the late holocene these trends of easm evolution are broadly consistent with variations in aeolian sand activity in the four main sandlands the mu us otindag horqin and hulun buir sandlands along the modern monsoon fringe in northern china and are supported by a wide range of independent evidence in addition we also found that high loess deposition and stronger aeolian activity occurred at similar to 5 ka representing a weak easm event within the context of an overall strong mid holocene easm the strong mid holocene easm revealed by palaeosol development in the clp and aeolian sand activity in the sandlands in northern china contrasts with the early holocene easm maximum suggested by stalagmite delta o 18 data from southern china our results are compatible with the proposal that the stalagmite delta o 18 variations in china do not result from changes in easm rainfall amount or intensity but instead reflect changes in moisture source driven by variations in atmospheric oceanic circulation c 2014 elsevier ltd and inqua all rights reserved

the stratigraphy of coastal carbonate banks and holocene sea levels of northern spencer gulf south australia abstract stratigraphic and chronologic studies of the coastal sediments of northern spencer gulf in the vicinity of redcliff are described two pleistocene marine units are recognised beneath an extensive holocene peritidal sequence the holocene sequence is dominated by sediments of the posidonia australis seagrass facies which form a distinctive carbonate bank fringing the coastline peritidal sedimentation commenced prior to 6600 radiocarbon yrs b p and a 2 5 m higher relative sea level existed from about 6000 until around 1700 yrs b p the subsequent relative fall to present level probably resulted from local tectonic uplift after the regression mangrove and samphire colonization and beach ridge progradation occurred over the former seagrass bank