indian ocean summer monsoon iosm dynamics within the past 4 ka recorded in the sediments of lake nam co central tibetan plateau china abstract in september 2008 several cores 68 cm 115 cm length water depth 93 m were retrieved from lake nam co southern central tibetan plateau 4718 m a s l this study focuses on the interpretation of high resolution partly 0 2 cm data from three gravity cores and the upper part of a 10 4 m long piston core i e the past 4000 cal bp in terms of lake level changes hydrological variations in the catchment area and consequently variations in monsoon strength a wide spectrum of sedimentological geochemical and mineralogical investigations was carried out results are presented for xrf core scans grain size distribution xrd measurements and sem image analyses these data are complemented by an age depth model using 210pb and 137cs analyses as well as eleven ams 14c ages this model is supported by excellent agreement between secular variations determined on one of the gravity cores to geomagnetic field models this is a significant improvement of the chronology as most catchments of lacustrine systems on the tibetan plateau contain carbonates resulting in an unknown reservoir effect for radiocarbon dates the good correlation of our record to the geomagnetic field models confirms our age depth model and indicates only insignificant changes in the reservoir effect throughout the last 4 ka high summer monsoonal activity i e moist environmental conditions was detected in our record between approximately 4000 and 1950 cal bp as well as between 1480 and 1200 cal bp accordingly lower monsoon activity prevails in periods between the two intervals and thereafter this pattern shows a good correlation to the variability of the indian ocean summer monsoon iosm as recorded in a peat bog 1000 km in ne direction from lake nam co this is the first time that such a supra regional homogenous monsoon activity is shown on the tibetan plateau and beyond finally our data show a significant lake level rise after the little ice age lia in lake nam co which is suggested to be linked to glacier melting in consequence of rising temperatures occurring on the whole tibetan plateau during this time

role of deep sea temperature in the carbon cycle during the last glacial 1 to characterize the response of earth s climate system to increases in atmospheric co2 climate modelers define climate sensitivity as the change in global mean temperature in response to prescribed forcing here we turn this approach around and use estimates of ocean temperature change to investigate the mechanisms driving co2 variations over the last glacial new records provide evidence of a link between deep ocean temperature and atmospheric co2 over the last glacial cycle two mechanisms simultaneously couple pco2 and deep ocean temperature the temperature dependent solubility of co2 in seawater and the atmospheric co2 dependent radiative forcing of temperature each of these forcing mechanisms leaves a unique slope of covariation between co2 and deep ocean temperature which we estimate using numerical models of climate and the carbon cycle the pco2 t slopes derived from paleoclimate data differ between the deglaciation and shorter 5 kyr duration events in marine isotope stage 3 mis 3 revealing different mechanisms driving atmospheric co2 variability the amplitude of changes over the deglaciation coincides with estimates for co2 forcing of temperature however co2 changes during mis 3 can be explained solely by temperature dependent solubility driving variations in atmospheric pco2 the deep water temperature changes during mis 3 may reflect changes in the temperature or relative contribution of antarctic bottom water and play a role in the bipolar seesaw

palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

monsoon fluctuations in two 20 000 yr b p oxygen isotope pollen records off southwest india abstract two marine pollen diagrams for sediments off the southwest coast of india provide a 20 000 yr history of the nearby continental vegetation determined by the monsoon climate within the framework of the isotopic stratigraphy two important phases of the evolution of the monsoon climate are a very arid period about 22 000 18 000 yr b p and a very humid period culminating at 11 000 yr b p the very arid period corresponds to the lowest pollen representation of mangrove vegetation which is used here as an indirect indicator of monsoonal runoff this aridity is due to a very weak southwest airflow a great reduction of summer monsoonal rainfall and reduced runoff of the western ghats rivers the extension of the monsoon over india after the last glacial maximum has been a gradual process following the northward progression of the intertropical convergene zone the very humid period corresponding to the highest pollen representation of mangrove vegetation and the heaviest summer rainfall is a climatic response to the maximum summer insolation of the northern hemisphere at 11 000 yr b p

characteristics of late quaternary monsoonal glaciation on the tibetan plateau and in east asia abstract glaciers fed by monsoonal precipitation are mainly located on the tibetan plateau and easternmost asia these are characterized by simultaneous accumulation and ablation in summer season the southeast part of the tibetan plateau experiences monsoonal precipitation in excess of 1000 mm yr resulting in maritime temperate glaciers in contrast precipitation in the middle and northwest part of the tibet plateau decreases from 1000 to 200 mm yr resulting in the formation of continental cold glaciers during the last glacial the regions of heavy monsoonal precipitation were restricted to the southeast corner of the plateau the westerly weak precipitation zone shifted southward and occupied the major northwest part of the plateau where the extreme continental type glaciers greatly expanded in the eastern margin of asia including taiwan central japan hokkaido and probably mount changbai maritime type glaciers were more extensive because of higher monsoonal precipitation especially heavy snowfall in northwest japan owing to the rich moisture content of the winter monsoon over the japan sea the millennial scale monsoon intensity and glacial cycle in the tibetan plateau are strongly affected by the precession cycle and the orbit inclination cycle which dominate the solar irradiance variation in low latitudes as the high radiation and strong monsoon caused the warmer and wetter climate during 40 30 ka the low radiation produced a weak monsoon and large depression of temperature and precipitation around 21 ka this climatic pattern differs from that in the high latitudes where the eccentricity cycle is prominent the temperature during the last glacial maximum lgm was 6 9 c lower than today on the tibetan plateau and the equilibrium line altitude was depressed by about 1000 m in the southeast part and in the east south and west margins of the plateau where precipitation was high the equilibrium line depression was 500 300 m in the inner and especially the west part of the plateau this variation in equilibrium lines might be caused by the combined effect of the decrease in precipitation the expansion of extreme continental glaciers and the active uplift of glaciated mountains the estimation of a glaciated area of about 350 000 km2 in the tibetan plateau and roughly 500 000 km2 in high asia based on observations of prominent features of lgm glacier extension may be the direct evidence that shows there was no quaternary unified ice sheet developed in the tibetan plateau

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

initiation of fennoscandian ice sheet retreat during the last deglaciation although the retreat history of the southern margin of the laurentide ice sheet during the last deglaciation has been well known for several decades1 3 and recently supported by evidence from accelerator mass spectrometer ams radiocarbon dating of meltwater in the gulf of mexico4 and the north atlantic subtropical gyre5 the retreat history of the fennoscandian ice sheet before 13kyr ago is still poorly documented from ams 14c dating and isotopic analysis of a rapidly deposited series of supra till sediments in the norwegian channel north sea we find that the southern margin of the fennoscandian ice sheet was in retreat by 15 kyr bp before present approximately 2 000 yr earlier than previously supposed oxygen isotope analyses in the channel sediments confirm earlier evidence from deep norwegian sea sediment cores for low salinity due to ice sheet discharge beginning 15 14 5 kyr bp ref 6 recent recalibration of the 14c timescale indicates that the onset of deglaciation within the norwegian sea occurred during an interval of rapidly increasing summer insolation beginning 18 000 calendar yr bp ref 7 suggesting that ice sheet retreat may have been caused by increasing insolation acting on a particularly climate sensitive ice sheet configuration fresh water and icebergs discharged into the norwegian sea at this time reached the north atlantic and may have contributed to a brief interval of extreme oceanic cooling8 and reduced production of north atlantic deep water9 10 these factors may also have helped to briefly reverse the deglaciation trend erie interstade already underway in north america

cultivation and human impact at 6000 cal yr b p in tropical lowland forest at niah sarawak malaysian borneo this paper describes palynological evidence for what appears to be comparatively large scale human impact in the catchment of the sungai niah in the wet tropical lowland swamp forests of sarawak malaysian borneo close to the great cave of niah pollen associated with cleared landscapes and rice cultivation is evident in the sedimentary record from before 6000 cal yr b p human activity seems to have been associated with changes in sedimentary regime with peat dominated environments being replaced diachronously by clay dominated deposition this may reflect anthropogenic soil erosion in the catchment of the sungai niah

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

a 50 000 year record of late pleistocene tropical vegetation and human impact in lowland borneo abstract there has been considerable uncertainty about the nature of pleistocene environments colonised by the first modern humans in island se asia and about the vegetation of the last glacial maximum lgm in the region here the palynology from a series of exposures in the great cave of niah sarawak malaysian borneo spanning a period from ca 52 000 to 5000 bp is described vegetation during this period was climate driven and often highly unstable interstadials are marked by lowland forest sometimes rather dry and at times by mangroves stadials are indicated by taxa characteristic of open environments or as at the lgm by highly disturbed rather open forest stadials are also characterised by taxa now restricted to 1000 1600 m above sea level suggesting temperature declines of ca 7 9 c relative to present by comparison with modern lapse rates the practice of biomass burning appears associated with the earliest human activity in the cave

later pleistocene holocene climate conditions of qinghai xizhang plateau tibet based on carbon and oxygen stable isotopes of zabuye lake sediments abstract we present a time series of carbon and oxygen stable isotope records of the last 30 000 14c years throughout the last glacial postglacial cycle from western qinghai xizhang tibet plateau a 20 m core drilled in the south basin of zabuye salt lake was analyzed for inorganic and organic carbon and total sulfur contents 13c and 18o values of carbonates our results indicate that climatic changes have led to a drastic negative shift of stable isotope ratios at the transition between the last full glacial and the postglacial phase during later pleistocene times 16 2 kyr bp and a rapid positive shift at the transition from pleistocene to holocene 10 6 kyr bp the first shift is marked by the drop of 18ocarb values of about 10 from 2 to 8 and 13ccarb values of about 3 from 5 to 2 the second shift which occurred at the transition from pleistocene to holocene was of similar magnitude but in the opposite direction isotope data combined with total organic and inorganic carbon contents and the lithological composition of the core suggest this lake was an alluvial pre lake environment prior to ca 28 14c kyr bp during ca 28 16 2 14c kyr bp zabuye lake was likely a moderately deep lake with limited outflow the cool and arid glacial climate led the lake level to drop drastically extended residence time overwhelmed the lower temperature and caused a steady increase of 13ccarb and 18ocarb values and total inorganic carbon content in the sediments during ca 16 2 10 6 14c kyr bp this lake probably overflowed and received abundant recharge from melting glaciers when the deglaciation was in its full speed a spike of markedly enhanced 13ccarb and 18ocarb is seen at 11 5 kyr bp probably due to the isotopic effects left behind by the short but severe younger dryas yd event after ca 10 6 14c kyr bp zabuye lake probably closed its surface outflow due to strong desiccation and drastic climate warming the early and middle holocene were characterized by unstable climatic conditions with alternating warmer cooler episodes as indicated by the severe fluctuations of total organic carbon 13c and 18o values a hypersaline salt lake environment was finally formed at zabuye after 5 14c kyr bp when the mirabilite and halite concentrations steadily increased and became the dominant minerals in the sediments severe imbalance of inflow outflow resulted in the drastic increase of total sulfur 13ccarb and 18ocarb values and dominance of halite in the lake since ca 3 8 kyr bp to present

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

the last deglaciation event in the eastern central arctic ocean oxygen isotope records of cores from the central arctic ocean yield evidence for a major influx of meltwater at the beginning of the last deglaciation 15 7 thousand years ago 16 650 calendar years b c the almost parallel trends of the isotope records from the arctic ocean the fram strait and the east greenland continental margin suggest contemporaneous variations of the eurasian arctic and greenland laurentide ice sheets or increased export of low saline waters from the arctic within the east greenland current during the last deglaciation on the basis of isotope and carbon data the modern surface and deep water characteristics and seasonally open ice conditions with increased surface water productivity were established in the central arctic at the end of termination lb about 7 2 thousand years ago or 6 000 calendar years b c

a re evaluation of the vegetation history of the eastern pyrenees france from the end of the last glacial to the present abstract fourteen pollen records obtained from 10 sites in the eastern pyrenees are presented along with the results of 40 new radiocarbon dates of samples obtained from these sites the data 784 pollen spectra provide a more comprehensive evaluation of the vegetation history of the region than has hitherto been possible the salient elements of the regional plant succession are described in the light of a study of regional pollen rain vegetation relationships vegetational developments during the last glacial interglacial transition and the holocene are compared with those of other regions in france and the western mediterranean this approach therefore provides a new synthesis of published and unpublished information over a large area a consistent and coherent pattern emerges and the new evidence indicates a number of previously held views on the vegetation history of the pyrenees to be erroneous

do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific 1 the paleoceanographic recording fidelity of pelagic sediments is limited by chemical diagenesis and physical mixing bioturbation and horizontal sediment transport diagenesis and bioturbation are relatively well studied but the effects of physical sedimentation have been largely ignored modeling u series isotopes e g 230th can potentially quantify horizontal sediment movement but model horizontal sediment focusing often equals or exceeds the vertical particle rain we find no evidence of this level of sediment focusing in the equatorial pacific from geophysical data or sediment core comparisons the overestimate of sediment focusing by 230th is probably caused by poor model assumptions that sediment does not fractionate does not sort according to size during transport and that 230th cannot leak from slowly accumulating sediments both assumptions are weak u series methods do hold promise to quantify sediment focusing if properly calibrated with calibration the trade offs between seeking high sedimentation rates for better time resolution and the blurring by horizontal sediment focusing can be better assessed

anomalously mild younger dryas summer conditions in southern greenland the first late glacial lake sediments found in greenland were analyzed with respect to a variety of environmental variables the analyzed sequence covers the time span between 14400 and 10500 calendar yr b p and the data imply that the conditions in southernmost greenland during the younger dryas stadial 12800 11550 calendar yr b p were characterized by an arid climate with cold winters and mild summers preceded by humid conditions with cooler summers climate models imply that such an anomaly may be explained by local climatic phenomenon caused by high insolation and fohn effects it shows that regional and local variations of younger dryas summer conditions in the north atlantic region may have been larger than previously found from proxy data and modeling experiments

a δ 13 c record of late quaternary climate change from tropical peats in southern india stable isotope ratios of carbon in soils or lake sediments1 3 and of oxygen and hydrogen in peats4 5 have been found to reflect past moisture variations and hence to provide valuable palaeoclimate records previous applications of the technique to peat have been restricted to temperate regions largely because tropical climate variations are less pronounced making them harder to resolve here we present a 13c record spanning the past 20 kyr from peats in the nilgiri hills southern india because the site is at high altitude 2 000 m above sea level it is possible to resolve a clear climate signal we observe the key climate shifts that are already known to have occurred during the last glacial maximum 18 kyr ago and the subsequent deglaciation in addition we observe an arid phase from 6 to 3 5 kyr ago and a short wet phase about 600 years ago the latter appears to correspond to the mediaeval warm period which previously was believed to be confined to europe and north america6 7 our results therefore suggest that this event may have extended over the entire northern hemisphere

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

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

stability of phase h in the mgsio 4 h 2 alooh sio 2 system abstract the newly described hydrous phase h mgsio 4 h 2 is stable to the pressures and temperatures of the earth s lower mantle suggesting that the earth s lower mantle may participate in the cycling of water we present the results of ab initio calculations on the stability of this phase within the phase h alooh sio 2 system between 20 and 60 gpa exploring the wide pressure and temperature stability field of this mineral we find that hydrogen in phase h is bonded in a single well at all pressures and only the pure phase results in pressure induced symmetrization while the solid solution maintains asymmetric bonding to high pressure substitutions on octahedral sites are locally charge balanced by h furthermore small amounts of al h in sio 2 stabilize the cacl 2 structure of sio 2 to pressures as low as 20 gpa while phase h and alooh form an ideal mixture at all pressures considered the resulting structure is stable relative to the anhydrous assemblage of the earth s lower mantle by 16 19 kj mol in alumina rich phase h this increases the stability of the mineral by 800 k relative to the pure substance making it potentially stable under lower mantle temperatures along typical geotherms

the low latitude monsoon climate during dansgaard oeschger cycles and heinrich events during the last 100 000 years dansgaard oeschger cycles d o cycles and heinrich events have been the dominant signal of past climate variability over greenland and the north atlantic the succession of stadials cold and interstadials warm associated with these cycles has been documented in records from the entire northern hemisphere south america new zealand antarctica the south atlantic and the southern ocean evidently climate forcing in the d o band affects both hemispheres the origin and cause of these teleconnected patterns is still unknown even if a large proportion of the cooling in europe and northern asia during heinrich events is a meteorological response to cold surface water in the north atlantic resulting from the surge of the laurentian and scandinavian ice sheets but this does not imply that the d o cycles are a priori caused by the collapse of these large icesheets a severe challenge to a primary origin from the northern ice sheet and north atlantic comes from the observation that warming in antarctica and the circumpolar current leads the north atlantic changes by some 1500 years charles et al 1996 blunier et al 1998 in the second part of the paper we investigate new deep sea records from the low latitude monsoon system mainly corroborating the result of schulz et al 1998 that the indian monsoon showed d o variability the abundance of eolian dust indicating continental humidity aridity in core 70kl from the arabian sea shows humid intervals which seem to correlate with temperature maxima in the antarctic vostok ice core apparently the low frequency sub milankovitch variability of the monsoon is associated with the southern hemisphere the d o scale component in the monsoonal climate on the other hand shows a succession of short humid intervals the sequence is most closely comparable to the greenland temperature record and to the stadial interstadial succession in the pacific santa barbara basin odp 893 in order to understand the global forcing of climate change in the d o band it appears necessary to quantify the phase relationships not only between d o cycles in the polar ice cores bender et al 1994 blunier et al 1998 steig et al 1998 but also between the low latitude pacific indian ocean and the high latitude records

millennial reoccurrence of century scale abrupt events of east asian monsoon a possible heat conveyor for the global deglaciation high resolution sediment records from the south china sea reveal a winter monsoon dominated glacial regime and a summer monsoon dominated holocene regime during the last glacial cycle a fundamental change between regimes occurred during deglaciation through a series of millennial reoccurrences of century scale changes in the east asian monsoon eam climate these abrupt events centered at 17 0 15 9 15 5 14 7 13 5 13 9 13 3 12 1 11 5 and 10 7 14c ka correlate well with the millennial scale events in the santa barbara basin and the arabian sea i e a relationship between eam and el nino southern oscillation systems the abrupt increases in summer monsoon imply enhanced heat transport from low latitude sea area to the midlatitude high latitude land area the phase relationship between events of eam and ice sheet may reflect a faster eam response and a slower ice sheet response to the insolation change a far reaching conclusion is that the eam might have triggered the northern hemisphere deglaciation

human used upper montane ecosystem in the horton plains central sri lanka a link to lateglacial and early holocene climate and environmental changes abstract this study utilizes radiocarbon dated pollen spores sphagnum spp macrofossils and total organic carbon proxies to examine variability of past climate environment and human activity in montane rainforest grassland and wetland of the horton plains hp central sri lanka since the last glacial maximum lgm the lgm is largely characterized by grasslands and xerophytic herbs dominated open habitats arid lgm punctuated climatic ameliorations which took place in short episodes humans appear to have reached the hp ecosystem after 18 000 cal yrs bp occasionally the first intertropical convergence zone itcz induced changes in south west monsoon swm rains occurred at low latitudes between 16 200 and 15 900 cal yrs bp suggesting an onset of monsoon rains after this event monsoon rains weakened for several millennia except the period 13 700 13 000 cal yrs bp but human activity seems to have continued with biomass burning and clearances by slash and burn very large size grass pollen grains which are morphologically similar to pollen from closer forms of oryza nivara were found after 13 800 cal yrs bp early holocene extreme and abrupt climate changes seem to have promoted the forms of o nivara populations in association with humans new data from the hp would therefore be most interesting to investigate the dispersal and use of domesticated rice in south asia

burial of different types of organic carbon in core 17962 from south china sea since the last glacial period abstract total organic carbon toc black carbon bc and land derived organic carbon loc extracted from marine sediment core 17962 from the southern south china sea and analyzed by pyrolysis gas chromatography elemental analyzers and mass spectroscopy can be interpreted in terms of regional land biomass burning climatic conditions vegetation cover and ocean paleoproductivity carbon from terrestrial sources including bc and loc appears to be a significant component of toc 3 1 39 3 range 16 5 average for bc 4 4 56 6 range 14 6 average for loc the production of bc and loc was only slightly higher during the last maximum glaciation lgm than during the holocene therefore dramatic changes in climate and vegetation cover do not seem to have occurred at the pleistocene holocene boundary paleoproductivity data calculated from marine organic carbon proved to be more accurate than those calculated from toc and exhibit the same pattern of temporal variation however the glacial interglacial contrast in the refined palaeoproductivity is less evident than that calculated from toc

orbital insolation forcing of the indian monsoon a motor for global climate changes abstract both modern and ancient indian summer monsoons are driven by transequatorial pressure differences directly coupled with the insolation difference between the northern and southern subtropical hemispheres a high resolution record of upwelling and dust flux from the western arabian sea resembles an insolation based indian summer monsoon index this index and the observed monsoonal climate variations share major elements on the orbital obliquity and precessional band with the specmap marine oxygen isotope record representing global ice volume the long term evolution of the index mirrors almost exactly the insolation changes at 65 n showing that the forcing of low latitude climate variability has a structure similar to that of the insolation forcing in the high northern latitudes moreover insolation forcing in the low latitudes directly controls atmospheric processes in the african indian and asian monsoon being responsible for a huge amount of transequatorial water vapour and therefore latent heat transport millennial scale variability of the monsoonal climate is concentrated at periodicities near 1100 1450 1750 and 2300 years these cycles are not strictly periodic but occur in bands with specific activity phases and amplitude increases during warm stages and interstadials for the 1100 and 1750 yr cycles whereas the 1450 yr cycle dominates the cold intervals

changing moisture sources over the last 330 000 years in northern oman from fluid inclusion evidence in speleothems speleothems from hoti cave in northern oman provide a record of continental pluvial periods over the last 330 000 yr periods of rapid speleothem deposition occurred from 6000 to 10 500 78 000 to 82 000 120 000 to 135 000 180 000 to 200 000 and 300 000 to 330 000 yr ago with little or no growth during the intervening periods during each of these five pluvial periods d values of water extracted from speleothem fluid inclusions dfi are between 60 and 20 vsmow and 18o values of speleothem calcite 18oc are between 12 and 4 to vpdb these values are much more negative than modern rainfall for d or modern stalagmites for 18o previous work on the isotopic composition of rainfall in oman has shown that northern and southern moisture sources are isotopically distinct combined measurements of the d values of fluid inclusion water with calculated 18o values from peak interglacial speleothems indicate that groundwater was predominantly recharged by the southern indian ocean moisture source when the monsoon rainfall belt moved northward and reached northern oman during each of these periods

a paleoindian response to younger dryas climate change abstract late quaternary changes in north american vegetation and geography reflect the influence of changing climate induced by the retreating ice sheets orbitally driven seasonal insolation patterns increasing carbon dioxide concentrations and relatively rapid internal variations at regional scales these climate changes resulted in ecosystem variability that impacted human access to resources we use paleoenvironmental and archaeological records from 14 000 to 10 000 cal yr bp for new england and maritime canada ne m to propose the impact of rapid climate change on human resource procurement and technology paleoenvironmental reconstructions for the younger dryas chronozone ydc 12 900 11 600 cal yr bp show ecologic responses to colder than earlier conditions at roughly the same time 13 000 11 000 cal yr bp we surmise that fluted points were used to hunt large mammals including caribou which inhabited regions with sub arctic like vegetation environmental changes associated with rapid regional warming at the end of the ydc coincided with the abandonment of fluting technology as conditions warmed vegetation changes led to shifts in animal populations which may be reflected in the development of other point styles by paleoindians and subsequent human groups

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

isotopic fingerprints of paleoclimates during the last 30 000 years in deep confined groundwaters of southern india isotopic and geochemical evidence of paleoclimates especially for the last glaciation has been obtained from deep confined groundwaters of southern india the 13c 18o chloride and deuterium analyses of groundwaters show distinct excursions inferred to be related to climatic variations the arid climatic episode associated with the last glaciation 18 000 2000 yr b p is conspicuously identified by signatures of relatively enriched 13c 10 to 12 pdb and 18o 5 3 to 4 8 smow values and high chloride concentration 80 to 160 mg l the transition from an arid to humid period ca 12 000 8000 yr b p is shown by a decreasing trend in the 13c 9 5 to 17 and 18o 4 5 to 6 3 contents of groundwaters the late holocene since 4000 yr b p marked by a more humid but unstable climate is identified by further depletion of 13c 13 to 20 and 18o 5 2 to 6 3 similar variation between 18o and chloride values in confined groundwaters further demonstrates two distinct climatic excursions arid and humid governed by the amount effect this is the first time that isotopic and geochemical signatures related to changing paleoclimates have been identified in the confined groundwaters of the southern indian landmass

relationship of environmental changes in central sri lanka to possible prehistoric land use and climate changes abstract a radiocarbon dated pollen analysed peat sequence from the horton plains 2000 m a s l in central sri lanka together with physical and chemical parameters organic carbon mineral magnetics carbon isotopes and phytoliths indicates major environmental changes during the last 24 000 years the results suggest that a mobile life form i e a hunter forage culture predominated in an open landscape associated with xerophytic vegetation e g chenopodium spp at 17 5 ka bp incipient management of cereal plants and slash and burn techniques seem to have prevailed between 17 5 and 13 ka bp which was indigenous and associated with grazing evidence of systematic cereal cultivation in the form of oat and barley pollen grains is found from the late pleistocene 13 ka bp this is the earliest evidence of farming activities noted in sri lanka as well as in south asia after 13 ka bp cereal cultivation was associated with an increase in humidity with a later abrupt increase in aridity agricultural land use decreased from 8 to 3 6 ka bp when the area appears to have been almost deserted after a severe middle holocene arid phase i e 5 4 3 6 ka bp the agricultural activity with a limited extension was again initiated by 2 9 ka bp during the next 900 years cultivation ceased allowing the upper montane rain forest to dominate between 0 2 and 0 15 ka bp new phases of agricultural activities were undertaken and potato cultivation took place lately between 1950 and 1969 ad

the variation of the southwest monsoon from the high resolution pollen record in heqing basin yunnan province china for the last 2 78 ma abstract a high resolution pollen record has been obtained from the heqing basin of yunnan province china the 737 72 m long continuous lacustrine sequence covers the last 2 78 ma according to the results of ams 14 c and magnetostratigraphy dating seven pollen ecological groups several high percentage pollen taxa and two palynological diversity indices d total and h total are combined to reconstruct synthetically the palaeoclimatic evolution in the heqing region of yunnan province according to the palaeoclimatic changes eight major variations of the southwest monsoon occurred during the periods 2 780 2 729 ma 2 608 1 447 ma and 0 342 0 118 ma the climate was predominantly relative warm and dry indicating a rather weak southwest monsoon between 2 729 and 2 608 ma the climate was mostly humid with increased rainfall seasonality mirroring a relative strong southwest monsoon from 1 447 to 0 342 ma the southwest monsoon gradually strengthened and its intensity achieved its maximum strength within wet phases between 0 991 and 0 342 ma the southwest monsoon during the period 0 118 ma 11 83 ka bp fluctuated greatly with a pattern of weak strong weak the spectral analysis of mesic conifer pollen percentages revealed that the climate and the southwest monsoon in the heqing region have been dominated by the 100 ka eccentricity period and also influenced by the other major orbital and sub orbital frequencies including 400 ka eccentricity obliquity 41 and 29 ka periods 23 ka precession and 10 ka

a 20 ka sediment record from the hajar mountain range in n oman and its implication for detecting arid humid periods on the southeastern arabian peninsula abstract playa like sediments from the hajar mountain range in northern oman 22 83 n 59 00 e 1050 m asl document variations of the paleoenvironmental and paleoclimate conditions over the last 20 ka based on high resolution sediment sampling and their osl dating sedimentation rates were calculated and used as a proxy for paleorainfall the results show that the glacial to lateglacial was characterized by arid conditions with a following transitional period of even less rainfall at 10 5 ka sedimentation rates increases abruptly indicating the onset of the early holocene humid period ehhp rainfall reaches its maximum at 9 8 ka ehhp 2 and a decreasing sedimentation rate after 8 ka characterizes the arid period of the middle to late holocene variations of the hydrological regime are associated with the intensity of the boreal summer indian monsoon and its related position of the itcz for the onset of the ehhp a northerly shift of the itcz is postulated thus confirming earlier results from the southern arabian peninsula

multiple thermal maxima during the holocene the astronomical theory of climatic change provides an alternative to the traditional chronology for holocene climatic change which calls for one thermal maximum about 6000 years ago the theory predicts a series of maxima during the holocene one for each season because the relation of the perihelion to the spring equinox changes with a 22 000 year period late summer insolation would have been greatest 5000 years ago whereas early summer insolation would have been greatest 13 000 years ago climatic reconstructions based on the response of ecosystems to late summer climate indicate a later holocene thermal maximum than paleoclimatic data sensitive to early summer climate in southern idaho three different vegetation types indicate thermal maxima at different times during the holocene depending on the climatic variable controlling each type

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

systematic variations in c o and sr isotopes and elemental concentrations in neoproterozoic carbonates in namibia implications for a glacial to interglacial transition abstract we analyzed c o and sr isotopic compositions of neoproterozoic cap carbonates overlying a glacial deposit in namibia to trace environmental changes following the glaciation the three isotopic records showed coherent and phased changes that corresponded to the stratigraphic variation a lower rhythmite unit had three intervals which were distinguished by isotopic variations and mineral type in the basal interval 13 c increased exponentially from a negative value 4 3 pee dee belemnite pdb 13 c values were relatively constant in the middle interval and increased again to positive values in the top interval indicating a phased removal of 13 c depleted carbon from the surface ocean the gradual increase to larger values 6 in the upper stromatolite unit was interpreted to reflect a change in seawater composition resulting from biological activity after environmental recovery from the glacial episode 18 o values and sr isotopic ratios decreased in the basal interval and approached stable values in the middle interval they increased in the upper interval and fluctuated in the stromatolite unit on the basis of geochemical screening criteria for detecting diagenetic alteration of sr isotopes the middle interval of the rhythmite unit with a minimum 87 sr 86 sr ratio of 0 70685 was interpreted to have retained the primary value or to have the least altered sr isotopic composition the basal interval which had ratios 0 718 at its base as high as those of old sialic rocks was interpreted as having altered sr isotopic ratios the high sr isotopic ratios at the base of this interval gradually decreased to near the minimum value at the top of the interval and other isotopic compositions and trace element concentrations showed systematic variations such systematic variations except for the variation in na concentration can be explained by a progressive diagenetic fluid rock interaction alternatively they might reflect a compositional transition from a local transport limited water following the glaciation to global well mixed seawater

synchroneity of tropical and high latitude atlantic temperatures over the last glacial termination a high resolution western tropical atlantic sea surface temperature sst record from the cariaco basin on the northern venezuelan shelf based on mg ca values in surface dwelling planktonic foraminifera reveals that changes in sst over the last glacial termination are synchronous within 30 to 90 years with the greenland ice sheet project 2 air temperature proxy record and atmospheric methane record the most prominent deglacial event in the cariaco record occurred during the younger dryas time interval when ssts dropped by 3 to 4 c a rapid southward shift in the atmospheric intertropical convergence zone could account for the synchroneity of tropical temperature atmospheric methane and high latitude changes during the younger dryas