evolution of the indian summer monsoon and terrestrial vegetation in the bengal region during the past 18 ka the indian summer monsoon ism is a major global climatic phenomenon long term precipitation proxy records of the ism however are often fragmented and discontinuous impeding an estimation of the magnitude of precipitation variability from the last glacial to the present to improve our understanding of past ism variability we provide a continuous reconstructed record of precipitation and continental vegetation changes from the lower ganges brahmaputra meghna catchment and the indo burman ranges over the last 18 000 years 18 ka the records derive from a marine sediment core from the northern bay of bengal nbob and are complemented by numerical model results of spatial moisture transport and precipitation distribution over the bengal region the isotopic composition of terrestrial plant waxes dd and d13c of n alkanes are compared to results from an isotope enabled general atmospheric circulation model isocam for selected time slices pre industrial mid holocene and heinrich stadial 1 comparison of proxy and model results indicate that past changes in the dd of precipitation and plant waxes were mainly driven by the amount effect and strongly influenced by ism rainfall maximum precipitation is detected for the early holocene climatic optimum ehco 10 5 6 ka bp whereas minimum precipitation occurred during the heinrich stadial 1 hs1 16 9 15 4 ka bp the isocam model results support the hypothesis of a constant moisture source i e the nbob throughout the study period relative to the pre industrial period the model reconstructions show 20 more rain during the mid holocene 6 ka bp and 20 less rain during the heinrich stadial 1 hs1 respectively a shift from c4 plant dominated ecosystems during the glacial to subsequent c3 c4 mixed ones during the interglacial took place vegetation changes were predominantly driven by precipitation variability as evidenced by the significant correlation between the dd and d13c alkane records when compared to other records across the ism domain precipitation and vegetation changes inferred from our records and the numerical model results provide evidence for a coherent regional variability of the ism from the last glacial to the present

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

high resolution holocene environmental changes in the thar desert northwestern india sediments from lunkaransar dry lake in northwestern india reveal regional water table and lake level fluctuations over decades to centuries during the holocene that are attributed to changes in the southwestern indian monsoon rains the lake levels were very shallow and fluctuated often in the early holocene and then rose abruptly around 6300 carbon 14 years before the present 14c yr b p the lake completely desiccated around 4800 14c yr b p the end of this 1500 year wet period coincided with a period of intense dune destabilization the major harrapan indus civilization began and flourished in this region 1000 years after desiccation of the lake during arid climate and was not synchronous with the lacustral phase

how the north atlantic multidecadal oscillation may have influenced the indian summer monsoon during the past two millennia 1 observations have indicated that the north atlantic sst variations have persistent effects on the indian summer monsoon rainfall at multidecadal and longer timescales the question of how such influences may have been achieved is addressed in this study using both instrumentation data of the 20th century and proxy records of the last 2000 years major results show that the north atlantic sst anomalies strongly affect the tibetan plateau surface temperature and heat sources the latter cause changes in the meridional temperature gradient between tibetan plateau and the tropical indian ocean through the thermal wind effect the meridional temperature gradient anomalies change the lower tropospheric zonal winds and the monsoon circulation and rainfall citation feng s and q hu 2008 how the north atlantic multidecadal oscillation may have influenced the indian summer monsoon during the past two millennia geophys res lett 35 l01707 doi 10 1029 2007gl032484

multi centennial scale sst and indian summer monsoon precipitation variability since the mid holocene and its nonlinear response to solar activity indian summer monsoon ism shows a weak correlation with solar variability in the 20th century however such climatological observations on solar activity monsoon relationship are very short and

modelling the influence of north atlantic multidecadal warmth on the indian summer rainfall 1 ensemble experiments with an atmospheric general circulation model reveal that a positive warm ocean phase of the atlantic multidecadal oscillation amo increases indian summer rainfall the intensification is driven by extratropical north atlantic warmth with some cancellation associated with monsoon weakening in response to tropical north atlantic warmth mechanistically warm extratropical north atlantic ssts increase local rainfall inducing an arching extratropical wavetrain response the latter leads to intensified northern subsidence of monsoon mean meridional streamflow as well as widespread low surface pressure over north africa the middle east and the western indian ocean contributing to a strengthened indian monsoon trough and increased monsoon rainfall warm tropical north atlantic ssts primarily increase local tropical atlantic rainfall that induces a tropically confined response consisting of low level easterly wind anomalies over the indian ocean and dynamically induced subsident drying over india

el nino as a mediator of the solar influence on climate 1 using a climate model of intermediate complexity we simulate the response of the el nino southern oscillation enso system to solar and orbital forcing over the holocene solar forcing is reconstructed from radiocarbon production rate data using various scaling factors to account for the conflicting estimates of solar irradiance variability as estimates of the difference since the maunder minimum range from 0 05 to 0 5 of the solar constant we consider these two extreme scenarios along with the intermediate case of 0 2 we show that for large or moderate forcings the low pass filtered east west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing with a short phase lag about a decade wavelet analysis shows a statistically significant enhancement of the century to millennial scale enso variability for even a moderate irradiance forcing in contrast the 0 05 case displays no such enhancement orbitally driven insolation forcing is found to produce a long term increase of enso variability from the early holocene onward in accordance with previous findings when both forcings are combined the superposition is approximately linear in the strong scaling case overall the sea surface temperature response is of the magnitude required and is persistent enough to induce important climatic perturbations worldwide the results suggest that enso may plausibly have acted as a mediator between the sun and the earth s climate a comparison to key holocene climate records from the northern hemisphere subtropics and midlatitudes shows support for this hypothesis

hydroclimatic shifts in northeast thailand during the last two millennia the record of lake pa kho the southeast asian mainland is located in the central path of the asian summer monsoon a region where paleoclimatic data are still sparse here we present a multi proxy toc c n delta c 13 bio

climate and anthropogenic controls on the carbon cycle of xingyun lake china abstract the organic and inorganic carbon cycles in lakes are responsive to both natural climate variability and human induced environmental changes here we present an 8600 year sediment record from xingyun lake in yunnan china that provides insight into carbon cycling and lake primary productivity using stable isotope measurements of organic carbon and nitrogen carbon to nitrogen ratio inorganic carbon isotopes and mass accumulation rates of carbon nitrogen and calcite the early to middle holocene is characterized by relative stability in most proxies although some variation in organic carbon isotopes reflects fluctuating terrestrial organic matter inputs the middle to late holocene from 5300 to 3300 years bp is marked by amplified variability in nearly all proxies and suggests either increased c4 vegetation or increased primary productivity these changes are coincident with declining lake levels and increased aridity throughout the indian summer monsoon region after 3300 years bp the greatest variability is in nitrogen isotopes and coincides closely with human settlement in the region these changes are accompanied by further indications of increased primary productivity suggesting eutrophic lake conditions while we cannot definitively link human activity to these changes the balance of evidence suggests that other mechanisms are unlikely this study supports previous work that anthropogenic activities began measurably impacting the landscape in southwestern china within the last few millennia

ground viscosity and stiffness measurements for near surface seismic velocity in land surveys the weathering layer can often distort the seismic signal due to it passing through rapid velocity and density changes dispersion scattering and inelastic absorption in a simple spring dashpot model for the earth response an equivalent medium groups these complex phenomena into two parameters only these are called ground viscosity and ground stiffness the most recent controllers for vibrators can estimate both parameters to validate these measurements saudi aramco conducted an experiment measuring ground viscosity and stiffness from two different vibrator control systems over an area of varying terrain conditions including unconsolidated sand and limestone outcrop the two systems measured different values but detected similar trends that correlated well with weathering conditions and surface geology e g lower viscosity values on the outcrop than on the sand the ratio of ground viscosity to ground stiffness can approximate the shallow s wave velocity which we converted into p wave velocity through calibration with sparse uphole data static corrections incorporating this velocity information somewhat improved the focusing of seismic time sections this new approach does not require additional acquisition efforts and can model shallow complex formations in arid areas where classical static methods often fail

multidecadal and multicentennial variability of the meridional overturning circulation the variability of the meridional overturning circulation moc simulated in a multimillenial control integration of the kiel climate model kcm displays enhanced variability relative to the red background at decadal and centennial timescales the multidecadal variability is the model s version of the atlantic multidecadal variability amv often referred to as atlantic multidecadal oscillation amo while multidecadal variability originates in the north atlantic multicentennial variability is driven in the southern ocean both multidecadal and multicentennial variability are associated with considerable changes in sea ice extent this may be important to understand the different evolution of sea ice cover in the northern and southern hemisphere during the most recent decades with a strong decline observed in the north and almost no trend in the south

a mid to late holocene record of palaeoclimatic changes from nal sarovar a palaeodesert margin lake in western india with a view to obtain palaeoclimatic data from a climatically sensitive region we have studied core samples from nal sarovar a large shallow lake lying within the palaeodesert margin of thar in western india a combination of c n ratios and 13c on a radiocarbon dated core section have been used as climatic proxies a high resolution record extending back to ca 6 6 ka bp has been reconstructed the data indicate that in the past climate has varied from drier to wetter than present on time scales of few hundreds to few thousands of years there are however significant differences on the timing of these wet and dry periods when compared with the available data from lakes farther north in rajasthan further it looks unlikely that during the 6 6 ka the catchment areas of nal sarovar experienced such a significant increase in rainfall as has been suggested for the rajasthan lakes interestingly drier periods in nal sarovar data appear to correlate well with periods of glacier expansion in eurasia indicating that the palaeoclimatic variations recorded in nal sarovar are a regional feature 1997 john wiley sons ltd

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

the near surface information gap for time and depth imaging the shallowest few hundred metres of the earth cannot be adequately imaged by conventional seismic when tuned for deeper targets adding independent measurements such as uphole or shallow refraction surveys reduces this information gap but in some arid areas such as saudi arabia the near surface complexities are not well resolved even in this way the joint tomographic inversion of different wave types can contribute to reducing these ambiguities further by complementing the different penetration ranges and propagation directions of reflected refracted and diving waves here we demonstrate the weakness of diving waves when used alone and the value of complementing them by available reflected and refracted arrivals

north atlantic oscillation dynamics recorded in greenland ice cores carefully selected ice core data from greenland can be used to reconstruct an annual proxy north atlantic oscillation nao index this index for the past 350 years indicates that the nao is an intermittent climate oscillation with temporally active coherent and passive incoherent phases no indication for a single persistent multiannual nao frequency is found in active phases most of the energy is located in the frequency band with periods less than about 15 years in addition variability on time scales of 80 to 90 years has been observed since the mid 19th century

aeolian sediments on the north eastern tibetan plateau abstract aeolian sediments on the tibetan plateau are an important archive of palaeoclimatic information this study presents a detailed analysis of sediments from the donggi cona catchment on the north eastern part of the tibetan plateau long and short distance sediment transport leads to a complex pattern of aeolian sediment deposition that depends on climatic changes as well as on the availability of sediments based on the largest dataset of osl datings 51 from a single catchment on the tibetan plateau so far different periods of increased sediment transport have been reconstructed increased aeolian deposition in this high elevation environment started in the early holocene with the accumulation of sands from around 10 5 to 7 ka loess sediments have been preserved from a period from 10 5 to 7 5 ka both archives are related to the strengthening of the asian summer monsoons characterized by wetter and warmer climate this change in climate supported the trapping of aeolian sediments under full monsoon conditions from around 9 ka onwards fluvial processes resulted in erosion of the aeolian archives and the formation of colluvial sediments until 6 ka a dry and cooler climate resulted in the reactivation of dune sands from 3 ka to present possibly in combination with stronger human influence aeolian sediments on the tibetan plateau therefore indicate two different climatic modes during the early holocene wetter conditions were favourable to retain aeolian sediments the reactivation of sediment in the late holocene due to small scale disturbances in the vegetation cover points to a cooler and drier climate

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

indian summer monsoon variability in southern india during the last deglaciation evidence from a high resolution stalagmite δ 18 o record abstract we present a high resolution record of indian summer monsoon ism variability during the last deglacial period the record is based on high precision measurements of oxygen isotopes 18o in 263 sub samples from a 18 cm long stalagmite vspm1 sample collected from the valmiki cave in the southern india the chronological framework is based on high precision u th dating in 8 sub samples at regular intervals the stalagmite exhibits a variable growth rate ranging from 0 03 to 0 80 mm yr with 9 years as an average sampling resolution for 18o x ray diffraction analysis shows that the sample is composed of aragonite mineral the 18o record provides a strong evidence of abrupt changes in ism activity between approximately 15 610 and 13 160 yr bp before 1950 ad highly negative 18o values at 15 610 and 15 250 yr bp are suggestive of a wet climate followed by less negative 18o at 15 240 to 14 750 yr bp indicating relatively dry climate these dry and arid conditions are punctuated by two wet events at 15 030 and 14 910 yr bp a marked increase in 18o between approximately 14 660 and 14 370 yr bp suggests weakening in ism activity followed by a gradual decrease in 18o between 14 370 and 13 560 yr bp indicating strengthening of ism however we cannot rule out the possibility of some past flooding event influencing 18o of vspm1 wavelet analysis of 18o time series suggests strong influence of solar forcing on ism activity the amplitude variance of 18o reveal decadal to centennial scale variability in monsoonal activity during the last deglaciation

solar influence on the indian ocean monsoon through dynamical processes 1 the result of paleoclimate studies on the relationship between the indian monsoon and solar activity inferred from the analysis of stalagmites in oman is confirmed by using a modern meteorological dataset from 1958 1999 the present result suggests that the solar influence on monsoon activity is not due to a change in radiative heating in the troposphere but rather originates from the stratosphere through modulation of the upwelling in the equatorial troposphere which produces a north south seesaw of convective activity over the indian ocean sector during summer higher precipitation over arabia and india thus occurs during high solar activity

individual and combined influences of enso and the indian ocean dipole on the indian summer monsoon the relative influences of the enso and indian ocean dipole iod events on the indian summer rainfall were studied using observational data and an atmospheric general circulation model agcm the composite analysis of rainfall anomalies demonstrates that the iod while significantly influencing the indian summer monsoon rainfall also significantly reduces the impact of enso on the indian summer rainfall whenever these events with the same phase co occur the agcm experiments have shown that during an el nino event the walker circulation over the tropical indo pacific region is modulated a low level anomalous divergence center over the western pacific and an anomalous convergence zone over the equatorial indian ocean are induced furthermore an anomalous zone of convergence over the myanmar and south china regions is induced during an el nino event these zones of anomalous convergence are complemented by anomalous divergence over the indian region causing anomalous subsidence and weakened rainfall when a strong positive iod event simultaneously occurs with el nino the latter s influence on the indian monsoon is reduced by both poles of the iod through the following mechanism an anomalous divergence center as compared to the summers when an el nino alone occurs is introduced in the eastern tropical indian ocean from this center the anomalous divergent flow crosses the equator and this air while weakening the el nino induced divergence over the western pacific also leads to convergence over the indian monsoon region this results in the reduction of the enso induced subsidence and the related rainfall deficit over the eastern flank of the indian monsoon trough region and adjoining regions to the east on the other hand over the western part of the tropical indian ocean sector part of the anomalous ascending motion from the warm pole of the positive iod event subsides just to the north of the equator moves northward ascends and causes surplus rainfall this reduces the enso induced rainfall deficit over western india the western part of the monsoon trough and parts of pakistan the agcm experiments also demonstrate that positive iod events amplify the enso induced dryness over the indonesian region

hydroclimatic variability in southeast asia over the past two millennia abstract the spatiotemporal variability of the asian monsoon am over the last two millennia has been attributed to a combination of external solar and volcanic forcing and or internal coupled atmosphere ocean dynamics but the relative importance of these mechanisms remains unresolved the present knowledge of multidecadal to centennial scale am variability over mainland southeast asia is not well constrained despite substantial progress in understanding seasonal to decadal variability from tree ring records here we present the first high resolution stable isotope 13 c and 18 o speleothem record from northern laos spanning the common era 50 bce to 1880 ce the 13 c record reveals substantial centennial scale fluctuations primarily driven by local water balance notably the driest period at our site occurred from 1280 to 1430 ce during the time of the angkor droughts supporting previous findings that this megadrought likely impacted much of mainland southeast asia in contrast variations in stalagmite 18 o reflect changes in rainfall upstream from our study site interestingly the 18 o record exhibits a positive correlation with solar activity that persists after 1200 ce contrary to the findings in previous studies solar forced climate model simulations reveal that these 18 o variations may be driven by solar forced changes in upstream rainout over the tropical indian ocean which modify the 18 o of moisture transported to our study site without necessarily affecting local rainfall amount we conclude that future rainfall changes in mainland southeast asia are likely to be superimposed on multidecadal to centennial scale variations in background climate driven primarily by internal climate variability whereas solar forcing may impact upstream rainout over the indian ocean

speleothem based 1000 year high resolution record of indian monsoon variability during the last deglaciation abstract a high resolution record of the indian summer monsoon ism is generated using a 18 o time series from a stalagmite collected from the valmiki cave in southern india this record covers a time span of 1000 years from 15 700 to 14 700 yr bp before 1950 ad with an average sampling resolution of 5 years high amplitude 18 o variation in this record reflects abrupt changes in ism activity during the last deglaciation and suggest an age for the onset of termination 1a t1a at 14 800 yr bp in the indian sub continent this record shows evidence for strong changes in tropical climate during the last deglaciation coincident variability in vspm4 18 o with speleothems from southern china during termination 1a suggests that these caves reflect fluctuations in ism activity the variance in 18 o amplitude reveals significant multidecadal variability in ism activity our record reveals intervals of strong monsoon activity during the later phase of heinrich event 1 h1 and shows synchronous multidecadal variability between ism and east asian monsoon eam spectral analysis of 18 o time series in vspm4 reveals solar forcing and strong ocean atmospheric circulation control on ism dynamics during the studied time interval

lateglacial and holocene environmental changes in ganga plain northern india abstract stable isotope elemental geochemistry and pollen analysis of a sediment profile from sanai lake central ganga plain were used to document climatic oscillations during the last 15 000 yr in indian subcontinent micaceous sandy sediments at the base of the profile indicate an active channel and humid conditions before 15 000 14c yr bp the channel was abandoned during comparatively arid conditions 15 000 13 000 14c yr bp and converted into a swamp enhanced humidity around 13 000 14c yr bp led to submergence of marshes and establishment of a large lake a dry phase is also identified around an estimated age of 11 500 10 500 14c yr bp which might correspond to the younger dryas event witnessed globally the early to mid holocene climatic optimum 10 000 5800 14c yr bp is characterised by a lake environment occurence of warmth loving aquatic plants lower 18o values of gastropod aragonite heavier 13corg values indicate a sensitive response of the lake ecology to the climatic warming and increased rainfall this is followed by an arid event during 5000 2000 14c yr bp and from 1700 14c yr bp there is evidence of climatic amelioration the sequence and magnitude of the millenium scale climatic oscillations documented along the lake profile correlate well with records from other parts of the indian subcontinent indicating that the recorded changes are an expression of broad scale probably global and climatic change

geostatistical integration of near surface geophysical data accurate statics calculation and near surface related noise removal require a detailed knowledge of the near surface velocity field conventional seismic surveys currently are not designed to provide this information and 3d high resolution reflection refraction acquisition is not feasible for large survey areas satellite images and vibrator plate attributes are dense low cost data which can be used in spatially extrapolating velocities from sparse uphole data by geostatistics we tested this approach in two different areas of saudi arabia and found that the optimal recipe depends on the local geology

a practical review of geostatistical processing applied to geophysical data methods and applications nowadays geostatistics is commonly applied for numerous gridding or modelling tasks however it is still under used and unknown for classical geophysical applications this paper highlights the main geostatistical methods relevant for geophysical issues for instance to improve the quality of seismic data such as velocity cubes or interpreted horizons these methods are then illustrated through four examples the first example based on a gravity survey presents how a geostatistical interpolation can be used to filter out a global trend in order to better define real anomalies in the second case study dedicated to refraction surveying geostatistical filtering is used to filter out acquisition artefacts and identify the main geological structures the third one is an example of porosity being integrated geostatistically with a seismic acoustic impedance map the last example deals with geostatistical time to depth conversion the interest of performing geostatistical simulations is finally discussed

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

late holocene monsoon precipitation changes in southern china and their linkage to northern hemisphere temperature abstract observations and models suggest a latitudinal redistribution of precipitation as a result of ongoing global climatic warming however the dynamic link between temperature and regional precipitation in the course of natural climatic variability during the current interglacial period remains unclear especially in the monsoon regions of china here we present a reconstruction of a 5 year resolution summer monsoon rainfall record for the past 3200 years based on 622 pairs of 18o and 13c and 29 230th dates from a stalagmite wu37 from wulu cave in southern china a close similarity between the 18o and 13c records on centennial to decadal timescales suggests that calcite 18o is most likely a proxy associated with monsoon precipitation the record reveals that the little ice age 650 100 yr b p was a relatively humid period with two centennial scale wet events compared with the medieval warm period 1050 650 yr b p in contrast with previous observations in india and northern china monsoon precipitation variations indicated by our record and other cave records nearby were inversely related to changes in northern hemisphere nh temperature over the past two millennia in particular to variations in the thermal gradient between the northern and southern hemispheres this suggests that nh temperature has an important influence on summer precipitation in southern china via the interhemispheric thermal gradient and land ocean thermal contrast in addition we find that variations of monsoon rainfall in southern china on multi centennial to centennial timescales are inversely correlated with observed rainfall in the core monsoon region of india and in the northern fringe of the asian summer monsoon region in china this spatial pattern of rainfall variability can be interpreted as a result of the migration of the intertropical convergence zone that is likely dominated by the interhemispheric thermal gradient via cross equatorial airflows

the role of intraseasonal variability in the nature of asian monsoon precipitation abstract the structure of the mean precipitation of the south asian monsoon is spatially complex embedded in a broad precipitation maximum extending eastward from 70 e to the northwest tropical pacific ocean are strong local maxima to the west of the western ghats mountain range of india in cambodia extending into the eastern china sea and over the eastern tropical indian ocean and the bay of bengal bob where the strongest large scale global maximum in precipitation is located in general the maximum precipitation occurs over the oceans and not over the land regions distinct temporal variability also exists with time scales ranging from days to decades neither the spatial nor temporal variability of the monsoon can be explained simply as the response to the cross equatorial pressure gradient force between the continental regions of asia and the oceans of the southern hemisphere as suggested in classical descriptions of the monsoon monthly 1979 2005 and daily 1997 present rainfall estimates

a tree ring based reconstruction of the atlantic multidecadal oscillation since 1567 a d 1 we present a tree ring based reconstruction of the atlantic multidecadal oscillation amo which demonstrates that strong low frequency 60 100 yr variability in basin wide 0 70 n sea surface temperatures ssts has been a consistent feature of north atlantic climate for the past five centuries intervention analysis of reconstructed amo indicates that 20th century modes were similar to those in the preceding 350 yr and wavelet spectra show robust multidecadal oscillations throughout the reconstruction though the exact relationships between low frequency sst modes higher frequency 7 25 yr atmospheric modes e g north atlantic oscillation arctic oscillation and terrestrial climates must still be resolved our results confirm that the amo should be considered in assessments of past and future northern hemisphere climates

model evaluation of the coherence of a common source water oxygen isotopic signal recorded by tree ring cellulose and speleothem calcite oxygen isotopic compositions 18o of tree rings and speleothems inherit 18o of precipitation 18oppt and are used to reconstruct past variations in the amount of precipitation or temperature integration of 18o records of both the proxies for a multiproxy climate reconstruction necessitates understanding of the extent to which the initial 18oppt is modified in both the proxies before getting preserved in them a forward modeling approach assuming both the proxies have access to a common source water 18o signal is employed to assess the expected maximum correlation between the 18o records of the two proxies on interannual time scale and the factors influencing the correlation variations in the leaf temperature relative humidity 18o of atmospheric water vapor introduce variations in 18o of tree ring cellulose while the variations in the cave temperature and oxygen isotopic equilibrium disequilibrium conditions between calcite and drip water influence 18o of speleothem calcite variation introduced by these factors in 18o of individual proxies as compared to the variation in 18oppt is crucial in deciding the correlation between 18o records of the two proxies when the former is higher than or comparable with the latter finding one to one correspondence between the 18o records of the two proxies could be challenging modeling exercise revealed a favorable climatic condition at jagdalpur 19 08 n 82 03 e a potential tropical location for tree ring and speleothem based climate reconstruction for inheriting a common source water 18o signal in both the proxies 18o records of tree ring and annually resolved speleothem from jagdalpur could be integrated for the multiproxy climate reconstruction

holocene palaeoenvironmental changes in the thar desert an integrated assessment incorporating new insights from aeolian systems abstract due to the scarcity of geochemical and palaeoecological proxies in drylands dunes have often been used as geoproxies for late quaternary palaeoenvironmental reconstruction with chronologies commonly provided by luminescence dating owing to their widespread occurrence and location in a monsoonal regime dunes in the thar desert in south asia act as important archives of past landscape change previous reviews have assimilated dune age data from the thar and suggested a temporally and spatially complex record of sediment accumulation over the last 70 ka new luminescence age data presented in this study and from recent dunefield based investigations demonstrate a stronger holocene record of dune building in parts of the thar than previously suggested in this study the accumulation intensity ai methodology is applied to new and old data sets providing records of dune accumulation that can be analysed alongside other palaeoenvironmental records ai analysis demonstrates the significance of holocene dune accumulation in the thar landscape with accumulation peaks observed between 12 and 8 ka centred around 7 5 and 3 5 ka and in last two millennia the strengthening of the indian summer monsoon remains a significant influence on widespread dune accumulation in the early holocene but dunefields have also shown diverse and spatially intensive responses to sediment supply and anthropogenic disturbances during the late holocene additionally aeolian fluvial sequences associated with the ghaggar hakra palaeochannel along the northern margin of the thar also display dynamic geomorphic behaviour during the holocene the integration and interpretation of the ai data with published highly resolved geochemical proxies of palaeoclimate shows a complex relationship between geoproxy and geochemical records we suggest that process studies of geomorphologic systems and their diverse responses to the same environmental stimuli must be given due consideration before deriving palaeoenvironmental interpretations despite the presence of over a hundred holocene dune records from the thar there still remains marked spatial and temporal gaps further intensive investigations of distinct dunefields with a strong chronometric framework and geomorphological grasp are required to gain significant insights into wider thar landscape and palaeoenvironmental dynamics

late holocene asian summer monsoon dynamics from small but complex networks of paleoclimate data internal variability of the asian monsoon system and the relationship amongst its sub systems the indian and east asian summer monsoon are not sufficiently understood to predict its responses to a future warming climate past environmental variability is recorded in palaeoclimate proxy data in the asian monsoon domain many records are available e g from stalagmites tree rings or sediment cores they have to be interpreted in the context of each other but visual comparison is insufficient heterogeneous growth rates lead to uneven temporal sampling therefore computing correlation values is difficult because standard methods require co eval observation times and sampling dependent bias effects may occur climate networks are tools to extract system dynamics from observed time series and to investigate earth system dynamics in a spatio temporal context we establish paleoclimate networks to compare paleoclimate records within a spatially extended domain our approach is based on adapted linear and nonlinear association measures that are more efficient than interpolation based measures in the presence of inter sampling time variability based on this new method we investigate asian summer monsoon dynamics for the late holocene focusing on the medieval warm period mwp the little ice age lia and the recent period of warming in east asia we find a strong indian summer monsoon ism influence on the east asian summer monsoon during the mwp during the cold lia the ism circulation was weaker and did not extend as far east the most recent period of warming yields network results that could indicate a currently ongoing transition phase towards a stronger ism penetration into china we find that we could not have come to these conclusions using visual comparison of the data and conclude that paleoclimate networks have great potential to study the variability of climate subsystems in space and time

a 1400 year high resolution record of atmospheric circulation over the north atlantic and asia major ion series developed from new subannual scale sampling of an ice core from central greenland are calibrated with instrumental series of atmospheric sea level pressure recording major marine icelandic low and terrestrial siberian high atmospheric circulation systems to provide proxy records of atmospheric circulation over the past 1400 years examination of the proxy records reveals major changes in behaviour of these systems c ad 1400 multidecadal and centennial scale periodic components characterization of mean sea level pressure anomaly fields during the little ice age and the mediaeval warm period the potential role of solar forcing coupled ocean atmosphere associations and a perspective within which the characteristics of instrumental era climate can be assessed

evidence for solar forcing on the indian monsoon during the last millennium abstract solar influence on the intensity of the indian monsoon is demonstrated using a sediment core from the eastern arabian sea dating back to 1200 yr through pattern matching as well as spectral analysis of proxy records of monsoon and solar activity the intensity of the indian monsoon is found to have decreased during periods of solar minima during the last millennium periodicities of 200 20 105 15 and 60 10 yr are observed in the proxy records coinciding with those known for solar cycles the 60 yr periodicity observed in the instrumental rainfall data appears to be of solar origin and supports the hypothesis of solar control on the indian monsoon on a multi decadal time scale evidence for the presence of a coupled atmospheric forcing for the indian and east african monsoons on a centennial time scale is also seen

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

comparing state of the art near surface models of a seismic test line from saudi arabia we present a seismic test line provided by saudi aramco for various research teams to highlight a few major challenges in land data processing due to near surface anomalies we discuss state of the art methods used to compensate for shallow distortions including single layer multilayer plus minus refraction and tomostatics methods they are a starting point for the new technologies presented in other papers all dealing with the same challenging data described here the difficulties on the test line are mostly due to the assumption of vertical raypaths inherent in classical applications of near surface correction statics even the most detailed velocity depth model presents difficulties due to the complex raypath there is a need for methods which are based on more complex models and theories

corrigendum to introduction holocene climate and cultural evolution in late prehistoric early historic west asia quaternary research 66 2006 372 387

holocene climate and cultural evolution in late prehistoric early historic west asia abstract the precipitation climatology and the underlying climate mechanisms of the eastern mediterranean west asia and the indian subcontinent are reviewed with emphasis on upper and middle tropospheric flow in the subtropics and its steering of precipitation holocene climate change of the region is summarized from proxy records the indian monsoon weakened during the holocene over its northernmost region the ganges and indus catchments and the western arabian sea southern regions the indian peninsula do not show a reduction but an increase of summer monsoon rain across the holocene the long term trend towards drier conditions in the eastern mediterranean can be linked to a regionally complex monsoon evolution abrupt climate change events such as the widespread droughts around 8200 5200 and 4200 cal yr bp are suggested to be the result of altered subtropical upper level flow over the eastern mediterranean and asia the abrupt climate change events of the holocene radically altered precipitation fundamental for cereal agriculture across the expanse of late prehistoric early historic cultures known from the archaeological record in these regions social adaptations to reduced agro production in both dry farming and irrigation agriculture regions are visible in the archaeological record during each abrupt climate change event in west asia chronological refinement in both the paleoclimate and archaeological records and transfer functions for both precipitation and agro production are needed to understand precisely the evident causal linkages

holocene variations of monsoon rainfall in rajasthan two reconstructed histories of the monsoon rainfall in rajasthan show that the monsoon was weak or absent in latest glacial time with the advent of holocene climatic patterns fresh water lakes formed in dune fields and the pollen rain preserved in these reservoirs provides a basis for the reconstruction of the monsoon history the two reconstructions separated by only 150 km have some features in common and some striking differences both show maximum monsoon amounts in the early holocene with a roughly two thirds decrease to the present both show salinization in sub boreal time both show long intervals of near complete desiccation in the last four millennia the shorter term variations however are not closely parallel these shorter term variations may be explained in terms of the behavior of the present day interannual variability

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

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

a mechanism for decadal changes of enso behavior roles of background wind changes this study explains why a number of el nino properties period amplitude structure and propagation have changed in a coherent manner since the late 1970s and why these changes had almost concurred with the pacific decadal climate shift evidence is presented to show that from the pre shift 1961 1975 to the post shift 1981 1995 epoch significant changes in the tropical pacific are found in the surface winds and temperature whereas changes in the thermocline are uncertain numerical experiments with the cane and zebiak model demonstrate that the decadal changes in the surface winds qualitatively reproduce the observed coherent changes in el nino properties the fundamental factor that altered the model s el nino is the decadal changes of the background equatorial winds and associated upwelling the annual cycle is also necessary for the mean state to modulate el nino from the pre to post shift epoch the changes in the background winds and upwelling modify the structure of the coupled mode eastward displacement of the equatorial westerly anomalies by reallocating anomalous atmospheric heating and sst gradient along the equator this structural change amplifies the enso cycle and prolongs the oscillation period by enhancing the coupled instability and delaying transitions from a warm to a cold state or vice versa the changes in the mean currents and upwelling reduce the effect of the zonal temperature advection while enhance that of the vertical advection thus the prevailing westward propagation is replaced by eastward propagation or standing oscillation our results suggest a critical role of the atmospheric bridge that rapidly conveys the influences of extratropical decadal variations to the tropics and the possibility that the pacific climate shift might have affected el nino properties in the late 1970s by changing the background tropical winds and the associated equatorial upwelling

paleomagnetic investigation of some volcanic rocks from the mcmurdo volcanic province antarctica paleomagnetic data for lava flows from sporadic but long lived eruptions in the mcmurdo sound region are combined with previously published geologic and geochronologic data to determine the general eruptive sequence of the area lava flows in the walcott bay area were erupted during the gauss normal matuyama reversed and brunhes normal polarity chrons the youngest flows on black island probably erupted near the boundary between the gilbert and gauss chrons the most recent activity was concentrated on the volcanic edifices of mounts morning and discovery and on ross island where mount erebus is currently active combining virtual geomagnetic poles calculated for 39 units sampled during this study with those of eight flows that were published previously yields a mean paleomagnetic pole at 87 3 n 317 3 e 95 6 3 the ancient geomagnetic field dispersion about this mean pole is 23 5 with upper and lower limits of 95 confidence equal to 27 4 and 20 5 respectively this value probably is a reasonable estimate of secular variation for the antarctic continent during pliocene and pleistocene time

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

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

high resolution holocene monsoon record from the eastern arabian sea through stable oxygen and carbon analyses of rapidly accumulating sediment cores from the eastern arabian sea we show that the excess of evaporation over precipitation e p steadily appears to have decreased during the last 10 000 to 2000 years most probably due to an increasing trend in the summer monsoon rainfall contrary to the land based paleoclimatic data from this region which indicate onset of aridity around 4000 years ago our results are consistent with the hypothesis that significant spatial variability in the monsoon rainfall observed today was persistent during most of the holocene alternatively the trend can be seen as an adjustment between two phases one between 10 000 and 6000 years ago of increasing precipitation and another between 3500 and 2000 years ago after the arid episode we also report a significant 700 year periodicity similar to that reported recently from the south china sea indicating that the centennial millennial scale response of the indian and chinese monsoons to high latitude forcing may be alike

oxygen isotopic composition of bulk carbonates in recent sediments from lake kuhai nw china and implications for hydroclimatic changes in headwater areas of the yellow river on the northeastern tibetan plateau abstract the water resource issue is one of the most significant problems in the yellow river basin and has received much attention from the public and government because of the dramatically decreased yellow river streamflow in the last several years in this study oxygen isotopic compositions of bulk carbonates from lake kuhai in the headwaters of the yellow river were evaluated as an indirect proxy of past yellow river streamflow in order to place the recent flow reduction in a long term context the results indicated that 18o values of bulk carbonates from core khc14 1 generally vary with changes in the yellow river streamflows related to the precipitation evaporation temperature ratio above the tangnaihai hydrological station over the past 50 years in general the yellow river streamflow in the headwaters area continued to decrease from the early 1980s to the late 1990s because of decreased precipitation and increased temperature then the streamflow increased with enhancing precipitation over the last two decades in addition 18o values of bulk carbonates in the lake kuhai core roughly correlate with the streamflows of the upper reaches of the yellow river recorded by tree ring width over the past 800 years the enriched 18obc values showed that the precipitation evaporation p e ratio or streamflow was very low and the climate might be very dry in the middle of the 1400s ce in the headwaters of the yellow river over the past 800 years our results suggested that changes in the p e ratio or streamflow of the upper reaches of the yellow river were dominated by variations in indian summer monsoon precipitation over a long time scale consistent with other records from the northeastern tibetan plateau

multidecadal variability of atmospheric methane 1000 1800 c e 1 we present a new high precision high resolution record of atmospheric methane from the west antarctic ice sheet wais divide ice core covering 1000 1800 c e a time period known as the late preindustrial holocene lpih the results are consistent with previous measurements from the law dome ice core the only other high resolution record of methane for this time period and confirm most of the observed variability multidecadal variability in methane concentrations throughout the lpih is weakly correlated or uncorrelated with reconstructions of temperature and precipitation from a variety of geographic regions correlations with temperature are dominated by changes in northern hemisphere high latitude temperatures between 1400 and 1600 c e during the onset of the little ice age times of war and plague when large population losses could have reduced anthropogenic emissions are coincident with short periods of decreasing global methane concentrations

a physical mechanism for north atlantic sst influence on the indian summer monsoon a link between the atlantic multidecadal oscillation amo and multidecadal variability of the indian summer monsoon rainfall is unraveled and a long sought physical mechanism linking atlantic climate and monsoon has been identified the amo produces persistent weakening strengthening of the meridional gradient of tropospheric temperature tt by setting up negative positive tt anomaly over eurasia during northern late summer autumn resulting in early late withdrawal of the south west monsoon and persistent decrease increase of seasonal monsoon rainfall on inter annual time scales strong north atlantic oscillation nao or north annular mode nam influences the monsoon by producing similar tt anomaly over eurasia the amo achieves the interdecadal modulation of the monsoon by modulating the frequency of occurrence of strong nao nam events this mechanism also provides a basis for explaining the observed teleconnection between north atlantic temperature and the asian monsoon in paleoclimatic proxies citation goswami b n m s madhusoodanan c p neema and d sengupta 2006 a physical mechanism for north atlantic sst influence on the indian summer monsoon

inter annual relationship between atlantic sea surface temperature anomalies and indian summer monsoon in this study the simultaneous inter annual relationships between sst anomalies over the northwest atlantic ocean and southwest monsoon rainfall over the monsoon core region have been examined using monthly sst and atmospheric data for the period 1951 2005 statistical analyses reveal significant inter annual simultaneous relationship between the sst anomalies over north atlantic and rainfall over the monsoon core region but with significant epochal variations the relationship has become stronger after mid 1970s when the el nino indian monsoon relationship has weakened positive sst anomalies over the north atlantic ocean shift the north atlantic jet northwards and the associated circulation changes in the upper troposphere influence indian monsoon through the circumglobal teleconnection across central asia the present study thus highlights the important role of north atlantic ocean as an important source of inter annual variability of the indian summer monsoon

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

the primacy of multidecadal to centennial variability over late holocene forced change of the asian monsoon on the southern tibetan plateau abstract the nature of multidecadal to centennial variability of the asian monsoon is largely unknown hindering our understanding of how the modern precipitation regime compares to preindustrial variability as well as how the asian monsoon may change in coming decades here we use the sediment record from a closed basin lake in southern tibet ngamring tso along with other published paleoclimatic records to assess summer monsoon precipitation variability over the 20th century and during the late holocene 4100 cal yr bp to present the first principal component of the ngamring tso grain size record which is highly correlated with median grain size correlates significantly with observed summer june september precipitation from ce 1940 to 2007 grain size decreased with increasing summer precipitation and increased with decreasing summer precipitation satellite images of ngamring tso reveal larger lake area in the 1970s and 2000s and smaller lake area in the 1980s and 1990s suggesting monsoon precipitation induced changes in lake depth or area likely govern grain size variability in the context of the last 4100 yr prolonged periods of relatively weak summer monsoon precipitation occurred from 2800 2600 cal yr bp 2500 2300 cal yr bp and 1600 400 cal yr bp a trend toward increased summer precipitation began around 1000 cal yr bp with above average summer precipitation from 400 cal yr bp to present peaking between 200 100 cal yr bp ce 1750 1850 dry and wet periods are coincident with dry and wet periods in other south central tibetan lake sediment records that reflect precipitation or moisture balance and with regional proxies of the ism and easm indicating south central tibet is influenced by both monsoon subsystems however western tibet lake sediment records do not covary with the ngamring tso record suggesting the spatial variability in tibet precipitation that occurs on interannual timescales today may also characterize precipitation on multidecadal and centennial timescales during the late holocene 20th century precipitation variability in southern tibet falls within the range of natural variability in the last 4100 yr and does not show a clear trend of increasing precipitation as projected by models instead it appears that poorly understood multidecadal to centennial internal modes of monsoon variability remained influential throughout the last 4100 yr thus substantial multidecadal to centennial scale hydroclimatic variability will complicate our ability to project and prepare for anthropogenic changes in the region s monsoon precipitation

painting the near surface using geology geophysics and satellites a smooth interpolation of a sparse uphole survey may be the main tool available for modeling the near surface in desert areas an uphole survey does not properly define sharp near surface velocity changes associated with lithologic and topographic variations such as cliffs canyons or outcrops which may be delineated by satellite imagery instead we present a patchy interpolation technique to build a consistent near surface model the algorithm is based on k means clustering to integrate geological geophysical and remote sensing information a somewhat arbitrary aspect of the method is the choice of how many clusters are used in segregating the data linking this parameter to surface geologic formations may be inadequate because p or s wave velocities are unlikely to have a sufficiently unique correlation with geologic age and lithology we suggest an empirical criterion improvement in the seismic stack section achieved by processing with parameters derived by various clustering choices and data t

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

seismic refraction traveltime inversion for static corrections in a glaciated shield rock environment a case study a traveltime inversion technique is applied to model the upper 40 m of the subsurface of a glaciated shield rock area in order to calculate static corrections for a multi azimuth multi depth walk away vertical seismic profile and a surface seismic reflection profile first break information from a seismic refraction survey is used in conjunction with a ray tracing program and an iterative damped least squares inversion algorithm to create a two dimensional model of the subsurface the layout of the seismic survey required crooked seismic lines and substantial gaps in the source and receiver coverage to be accounted for additionally there is substantial topographical variation and a complex geology consisting of glaciofluvial sediment and glacial till overlying a crystalline bedrock the resolution and reliability of the models is measured through a parameter perturbation technique normalized 2 values root means square traveltime residuals and comparison to known geology

abrupt changes in indian summer monsoon strength during the last 900 years and their linkages to socio economic conditions in the indian subcontinent abstract abrupt shifts in indian summer monsoon ism precipitation largely affected regional hydrometeorology accelerating socio economic and cultural adaptations of agrarian economies in south asia in the last millennium linking ism variability to human history in the indian subcontinent is still limited by the scarcity of high resolution paleoclimatic data for the period encompassing the last 1000 years or earlier we present a new high resolution oxygen isotope proxy record from the wah shikar cave northeastern india and identified abrupt shifts in the ism that had profound impact on human societies during the last 900 yrs the ism was strong during the medieval climate anomaly mca and the current warm period cwp and show multiple shifts during the little ice age lia the abrupt shifts in the ism were more frequent during warm intervals showing a secular trend with few exceptions during the cold periods intervals of prolonged summer monsoon weakening are correlated to the decline of major dynasties in india possibly due to decrease in agriculture productivity declining economy and societal crisis changes in atmospheric temperature due to volcanic eruptions and sun spot activity have played major role in the onset of the lia and other prolonged weak intervals of the ism during the last 900 yrs

vibrator attribute leading velocity estimation accurate knowledge of the near surface velocity macromodel is vital for hydrocarbon exploration and reservoir characterization that utilize seismic data because this model is crucial for statics and depthing however determination of near surface velocities using direct measurements via uphole surveys is economically prohibitive consequently geophysicists face a problem when determining how to interpolate between sparse near surface well control when near surface velocity varies laterally with lithology that in turn does not vary equally in all directions therefore techniques are needed to estimate near surface velocity using other available data in order to minimize the associated risk resulting from incomplete knowledge of the near surface velocity model

sixty year quasi period of the asian monsoon around the last interglacial derived from an annually resolved stalagmite δ18o record abstract the 60 year quasi periodic variability of the asian monsoon in the mid late holocene has been found to be widespread in instrumental and various terrestrial records however whether this period exists in the older interglacial periods remains to be further studied this paper is based on an 1840 mm long stalagmite with clear annual laminae with a growth rate of about 1 mm yr from yongxing cave china that allows for the reconstruction of the asian monsoon evolution sequence during the period 123 20 121 21 kyr bp the stalagmite record closely tracks the 65 n solar insolation changes as a whole indicating the dominant control of solar insolation on the asian summer monsoon after removing the solar insolation signal from the yx108 record the 18o residuals 18o show 28 multidecadal monsoon cycles the average amplitude of these fluctuations is larger than 0 8 with a duration typically ranging from 50 to 80 yr about 64 yr on average which is very similar to the mid late holocene asian monsoon variability further wavelet analysis displays a significant quasi periodicity of 60 years throughout the studied period providing further evidence for assessing whether the 60 year quasi periodic variability of the asian monsoon found in the holocene exists in older periods our study thus suggests that this quasi periodic variability not only occurred during the modern period but also existed in the last interglacial and their influence may even be an intrinsic characteristic of the asian monsoon system during glacial interglacial cycles we manifested that the interactions between solar activity and the atlantic multidecadal oscillation may be the main reason for the 60 year quasi period of the asian monsoon

late holocene indian summer monsoon precipitation history at lake lugu northwestern yunnan province southwestern china abstract knowledge of late holocene precipitation variability in the northwestern yunnan province is important for understanding the indian summer monsoon ism dynamics in this study we present a proxy record of the ism precipitation history at lake lugu covering the last 2 900 years based on grain size and carbon nitrogen c n ratio in the northwestern yunnan province the results show centennial variations in ism precipitation with two remarkably dry intervals from 750 to 1167 ad and from 1733 ad to the present and two relatively wet intervals from 898 bc to 750 ad and from 1167 to 1733 ad a comparison between the record at lake lugu and the pollen record at lake erhai both in the northwestern yunnan province suggests that dry climate conditions prevailed during the medieval warm period mwp and over the last 100 200 years whereas relatively humid conditions prevailed during the little ice age lia these characteristics are generally similar to those of the climate patterns in extensive areas dominated by the ism e g southwestern southern china southeastern southern tibetan plateau northeastern india himalayas southern oman and equatorial eastern africa but anti phased with the climate patterns in the wide areas dominated by the east asian summer monsoon easm e g northern northeastern china and north central japan we speculate that both the variations in the sea surface temperature sst over the tropical indo pacific ocean the ocean atmosphere coupling processes and the migration of the mean position of the intertropical convergence zone itcz should be responsible for the hydroclimatic contrasts over the asian summer monsoon asm region on centennial timescales during the last 2 000 years

high resolution mid holocene indian summer monsoon recorded in a stalagmite from the kotumsar cave central india abstract the indian summer monsoon ism a significant part of the global monsoon system is driven by several climate forcing parameters with the growing pace of global climate change scenario there is need to focus on generating more high resolution records of past monsoon the ism reconstructions from core monsoon zone cmz of india which represents all india summer monsoon rainfall are useful for a better understanding of its past variability such reconstructions from the cmz are rather sparse and require detailed study based on various climate proxies here we focus on the reconstruction of ism variability during the mid holocene based on stalagmite oxygen isotope ratios from the kotumsar cave central india we show that with decreasing insolation monsoon started declining at the beginning of the mid holocene from 8 5 to 6 5 ka bp which is also observed in the previous ism reconstructions with coarser resolutions however a gradual increase in the rainfall is observed from 6 5 to 5 6 ka bp a feature which is also noted in the east asian monsoon reconstruction from the dongge cave our record mainly emphasizes on the occurrence of several abrupt weak monsoon events throughout the mid holocene the occurrence of 8 2 and 5 9 ka abrupt weak monsoon events suggest that ism variability is tightly bound to north atlantic oscillation nao we also demonstrate that ism during the mid holocene was partly sensitive to el nino southern oscillation enso and displayed an inverse relationship

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

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

linking holocene drying trends from lonar lake in monsoonal central india to north atlantic cooling events abstract we present the results of biogeochemical and mineralogical analyses on a sediment core that covers the holocene sedimentation history of the climatically sensitive closed saline and alkaline lonar lake in the core monsoon zone in central india we compare our results of c n ratios stable carbon and nitrogen isotopes grain size as well as amino acid derived degradation proxies with climatically sensitive proxies of other records from south asia and the north atlantic region the comparison reveals some more or less contemporaneous climate shifts at lonar lake a general long term climate transition from wet conditions during the early holocene to drier conditions during the late holocene delineating the insolation curve can be reconstructed in addition to the previously identified periods of prolonged drought during 4 6 3 9 and 2 0 0 6 cal ka that have been attributed to temperature changes in the indo pacific warm pool several additional phases of shorter term climate alteration superimposed upon the general climate trend can be identified these correlate with cold phases in the north atlantic region the most pronounced climate deteriorations indicated by our data occurred during 6 2 5 2 4 6 3 9 and 2 0 0 6 cal ka bp the strong dry phase between 4 6 and 3 9 cal ka bp at lonar lake corroborates the hypothesis that severe climate deterioration contributed to the decline of the indus civilisation about 3 9 ka bp

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

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