organic carbon fractions and estimation of organic carbon storage in the lake sediments in inner mongolia plateau china organic carbon oc in lake sediments plays an important role in terrestrial ecosystem carbon cycle the inner mongolia plateau contains a number of shallow and freshwater lakes with a total lake area of more than 8 000 km2 accounting for an approximate 10 of the total lake area in china the inner mongolia plateau lakes act as important oc sink in mid high latitude regions in this study heavy and light fractions of oc and oc species were analyzed in sediments from four typical lakes in the inner mongolia plateau meanwhile to identify oc origins allochthonous and autochthonous oc were calculated based on a binary model furthermore total organic carbon toc storage active carbon pool acp and stable carbon pool scp over the past 150 years were estimated in the inner mongolia plateau the dominating direct findings of the current research are that heavy fraction oc plays a key role as carbon sink in mid high latitude regions due to its percentage of more than 90 in toc the percentages of allochthonous oc in toc are high 86 4 66 7 and 72 5 in daihai lake dh dalinuoer lake dlne and hulunhu lake hlh respectively which indicates that allochthonous oc is dominant in dh dlne and hlh the range of humin is 62 15 84 03 in these four lakes the average oc accumulation rate calculated in this work is 1 37 g c m 2 year 1 in these four lakes comparatively oc storages in sediments from lakes in the inner mongolia plateau are relatively more stable than from those lakes located in tropical and sub tropical regions an estimate of the toc burial scp and acp in lake sediments would be 1 64 1012 1 52 1012 and 1 20 1011 g c respectively over the past 150 years in the inner mongolia plateau

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

an interannual link between arctic sea ice cover and the north atlantic oscillation this work investigates links between arctic surface variability and the phases of the winter djf north atlantic oscillation nao on interannual time scales the analysis is based on era reanalysis and model data from the ec earth global climate model our study emphasizes a mode of sea ice cover variability that leads the nao index by 1 year the mechanism of this leading is based on persistent surface forcing by quasi stationary meridional thermal gradients associated thermal winds lead a slow adjustment of the pressure in the following winter which in turn feeds back on the propagation of sea ice anomalies the pattern of the sea ice mode leading nao has positive anomalies over key areas of south davis strait labrador sea the barents sea and the laptev ohkostsk seas associated to a high pressure anomaly over the canadian archipelago baffin bay and the laptev east siberian seas these anomalies create a quasi annular quasi steady positive gradient of sea ice anomalies about coastal line when leading the positive nao phase and force a cyclonic vorticity anomaly over the arctic in the following winter during recent decades in spite of slight shifts in the modes spectral properties the same leading mechanism remains valid encouraging actual models appear to reproduce the same mechanism leading model s nao relative to model areas of persistent surface forcing this indicates that the link between sea ice and nao could be exploited as a potential skill source for multi year prediction by addressing the key problem of initializing the phase of the nao ao arctic oscillation

hydrogen index and carbon isotopes of lacustrine organic matter as lake level indicators abstract optical and geochemical techniques were applied to organic matter of late quaternary sediments from lakes victoria and rukwa east africa variations in total organic carbon toc and hydrogen content expressed as hydrogen index hi can be related to known changes in lake level and used to identify periods of very low water or subaerial exposure in basinal sequences toc and hi both decline as an exposure surface is approached mainly due to the selective removal of unstable components by bacterial respiration and inorganic oxidation inert organic material of very low hi is typically concentrated at the overlying transgression surface the carbon isotopic composition of the particulate organic matter tends to be less negative in sediments associated with exposure surfaces although weathering may be partially responsible isotopic variations are mainly due to changes in the relative importance of material from plants using c4 photosynthesis such as grasses and sedges growing around the shore and on the exposed lake muds and of material from planktonic algae and terrestrial c3 plants

proxy climate and geomagnetic palaeointensity records extending back to ca 75 000 bp derived from sediments cored from lago grande di monticchio southern italy as part of a multi disciplinary study of maar lake sediments magnetic properties of some 3000 samples from two long cores extracted from the bottom sediments of lago grande di monticchio located in southern italy have been measured and the results connected with lithological palynological and geochemical data obtained from the same cores a time scale based on microlaminations radiocarbon and arar age determinations see companion papers in this special issue of quaternary science reviews dates the base of the longer 51 m core at about 76 ka before the present the strengths of anhysteretic remanence saturation isothermal remanence and susceptibility are highly sensitive to the contrast between stadial and interstadial conditions showing almost flip flop transitions at oxygen isotope stage 5a 4 and stage 2 1 boundaries as previously observed for lac du bouchet another maar lake site located in the haute loire province of france on the other hand these laboratory installed magnetizations vary smoothly through sediment deposited during stadials a prolonged period of heavy modelled precipitation starting at 25 ka bp coincides with a marked decrease in measured magnetic intensities possibly associated with the consequent increase in lake level and lake water chemistry the natural remanent magnetization is dominated by climatic and environmental influences nevertheless a weak signal attributed to variations in the palaeointensity of the geomagnetic field has been isolated and it shows good broad scale agreement with that previously reported for lac du bouchet

mineral magnetism of lacustrine sediments and holocene palaeoenvironmental changes in dali nor area southeast inner mongolia plateau china mineral magnetic measurements and analysis of total organic carbon toc and carbon nitrogen c n were performed on two ams 14c dated lacustrine sequences recovered from xiaoniuchang and jiangjunpaozi 42 n 117 e the two sites lie in the dali nor area of southeast inner mongolia plateau where the semi humid climate transforms into a semi arid one sirm low frequency magnetic susceptibility lf irm20mt hirm and irm20mt sirm may largely reflect the erosion of catchment materials and dilution effect of organic matter on deposited magnetic minerals irm 100mt sirm and irm 300mt sirm likely indicate the aeolian activities sirm lf positively correlated to sand percentage of sediments is diagnostic of changes of lake levels or effective humidity complemented by the data of toc and c n and of previously accomplished analyses of grain size loss on ignition loi and pollen the variations in mineral magnetism reveal holocene palaeoenvironmental changes conditions were quite dry and cool before 9970 years bp and then humidified in jiangjunpaozi the effective humidity maximised prior to 8000 years bp and subsequently declined in the two sites the less wet but warmer conditions persisted in jiangjunpaozi until 6600 years bp and xiaoniuchang until 5600 years bp deterioration occurred since then and culminated during 4300 1300 years bp in jiangjunpaozi and 3000 730 years bp in xiaoniuchang which was followed by a moderate but probably very short amelioration in the two sites

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

terminal pleistocene holocene palaeoenvironmental changes revealed by mineral magnetism measurements of lake sediments for dali nor area southeastern inner mongolia plateau china abstract mineral magnetic properties sirm arm hirm and s ratios are presented for two ams 14c dated pit sequences of lake sediments recovered from haoluku and liuzhouwan 43 n 117 e the two sites fall in the semi humid to semi arid climate transition zone dali nor area of the southeast inner mongolia plateau china complemented by data for loss on ignition loi total organic carbon toc carbon nitrogen c n grain size and pollen these mineral magnetic measurements provide additional insights into environmental changes occurring at this area over the last 13 500 years conditions were extremely dry and windy as shown by the low sirm arm and hirm and high s ratios before 13 500 yr bp the environment began to ameliorate gradually since then and a further humidification occurred at 10 300 yr bp in haoluku the northern site and at 9400 yr bp in liuzhouwan the southern one as implied by the increased but only moderately high sirm arm and hirm and decreased s ratios as indicated by the remarkably increased sirm arm hirm and s ratios a deterioration commenced at 5600 yr bp in haoluku and at 4700 yr bp in liuzhouwan in haoluku conditions have been generally dry and windy since 5600 yr bp despite a minor amelioration at 4500 3000 yr bp a short but marked amelioration occurred at 1200 700 yr bp in liuzhouwan s ratios seem to be a reliable indicator of environmental aridity for this area

transport of surface freshwater from the equatorial to the subtropical north atlantic ocean abstractthe transport of low salinity water northward in the tropical and subtropical north atlantic ocean influences upper ocean stratification vertical mixing and sea surface temperature sst in this study satellite and in situ observations are used to trace low salinity water northward from its source in the equatorial atlantic and to examine its modification through air sea fluxes and vertical mixing in contrast to gridded climatologies which depict a gradual northward dispersal of surface freshwater from the equatorial atlantic satellite observations and direct measurements from four moorings in the central tropical north atlantic show a distinct band of surface freshwater moving northward from the equatorial atlantic during boreal fall through spring with drops in sea surface salinity sss of 0 5 2 5 psu in the span of one to two weeks as the low sss front passes the ultimate low latitude source of the low sss water is found to be primarily amazon river discharge west of 40 w and rainfall

observed linkages between the northern annular mode north atlantic oscillation cloud incidence and cloud radiative forcing the signature of the northern annular mode north atlantic oscillation nam nao in the vertical and horizontal distribution of tropospheric cloudiness is investigated in cloudsat and calipso data from june 2006 to april 2011 during the northern hemisphere winter the positive polarity of the nam nao is marked by increases in zonally averaged cloud incidence north of 60 n decreases between 25 and 50 n and increases in the subtropics the tripolar like anomalies in cloud incidence associated with the nam nao are largest over the north atlantic ocean basin middle east and are physically consistent with the nam nao related anomalies in vertical motion importantly the nam nao related anomalies in tropospheric cloud incidence lead to significant top of atmosphere cloud radiative forcing anomalies that are comparable in amplitude to those associated with the nam nao related temperature anomalies the results provide observational evidence that the most prominent pattern of northern hemisphere climate variability is significantly linked to variations in cloud radiative forcing implications for two way feedback between extratropical dynamics and cloud radiative forcing are discussed

mineral magnetic tracing of aeolian dust in southwest pacific sediments abstract reliable magnetic signatures were sought to trace aeolian dust in tasman sea sediments where the aeolian fraction had also been chemically isolated modern dust samples from eastern australia were found to have a strong ferrimagnetic signal and a weaker antiferromagnetic afm background the ferrimagnetic component could not be detected in the deep sea sediments where a finer biogenic magnetite component prevails over a background afm and two other authigenic components the modern dust is thought to be unrepresentative of prehistoric dust probably as the result of contamination from local agricultural soils the afm component in the sediments however was found to be highly correlated with the independently determined aeolian concentration except in intervals with a high magnetic susceptibility high fd signal possibly from an authigenic component because of the non aeolian contribution to magnetic hardness sirm irm 300 and different relationships observed in different cores the magnetic tracing of aeolian dust is currently only valid as a measure of relative changes in concentration in sediments with similar chemistry and low frequency dependence of susceptibility

drought and dust deposition in the west african sahel a 5500 year record from kajemarum oasis northeastern nigeria a high resolution multiproxy palaeolimnological record from the manga grasslands northeastern nigeria spanning the last 5500 calendar years reveals the episodic deterioration in sahelian climate as significant biogeophysical thresholds were crossed desert dust deposition began to increase 4700 cal bp rainfall during the summer monsoon season declined permanently after 4100 cal bp a further significant change in atmospheric circulation giving rise to multidecadal to centennial scale droughts and enhanced dust deposition occurred 1500 cal bp hence the post 1968 sahel drought is not unique the prolonged arid episode that occurred around 1200 1000 cal bp in ethiopia the sahel and tropical mexico may have been linked to an abrupt cooling event in the north atlantic and to a cluster of intense el nino southern oscillation events in the eastern equatorial pacific

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

sedimentation in lake malawi east africa during the past 10 000 years a continuous paleoclimatic record from the southern tropics a suite of piston cores recovered from lake malawi 9 14 s 34 35 e east africa in 1986 has been analyzed for major and minor elements organic c and n calcium carbonate and diatoms an internally consistent stratigraphy was constructed from calcium carbonate abundance and variations in the two most abundant diatom genera stephanodiscus and melosira with age control obtained primarily from 14c dating of the carbonate differences with time in fe abundance in a transect of cores from different water depths have been interpreted to reflect changes in chemocline depth the depth to the chemocline was on the order of 100 m shallower than present prior to 3500 yr b p indicating less seasonality carbonate production and preservation appears to be related to climatically induced changes in both salinity and chemical distributions in the water column the carbonate which precipitates from surface waters is most abundant during the interval from about 10 000 to 6000 yr b p this micrite most likely represents periods of low lake level when salinity increased and carbonate precipitation was enhanced sedimentary evidence suggests that lake levels were 100 150 m lower than present during this period this record is different from climatic trends in northern intertropical africa but appears to also be related to changes in insolation and monsoon circulation this is the northernmost basin in africa reported to exhibit a southern hemisphere response to the early holocene northern hemisphere summer insolation maximum the climatic hingeline north of lake malawi 9 s implied by our results is significantly south of that indicated by general circulation model simulations however the cores show evidence for periods of abrupt climate change during the interval of generally arid climate

paleoenvironmental implications of rock magnetic properties of late quaternary sediment cores from the eastern equatorial atlantic rapid and nondestructive rock magnetic measurements of late quaternary sediment cores from the senegal continental slope and the sierra leone rise in the eastern equatorial atlantic correlate strongly with the specmap oxygen isotope master curve and carbonate content the rock magnetic paleoclimatic relationship results from differences in the concentration accumulation rate grain size and composition of magnetic minerals between glacials and interglacials at both sites magnetic mineral assemblages of glacial episodes are characterized by higher concentrations and accumulation rates of magnetic minerals by coarser grained ferrimagnetic minerals e g magnetite and by a lower ratio of ferrimagnetic to antiferromagnetic e g goethite hematite minerals by serving as a sensitive tracer for various deep sea sedimentary components rock magnetic properties can provide insights into changing sediment sources and fluxes and therefore are a useful addition to more traditional chemically and mineralogically based paleoceanographic techniques

a revised 30 000 year paleoclimatic and paleohydrologic history of lake albert east africa abstract new geochemical and palynological data and a sedimentological reinterpretation of two cores from lake albert allow a revision of the paleoclimatic and paleohydrologic history of northwest uganda over the last 30 000 14 c yr bp our findings document one and possibly three periods of significantly reduced inflow to the nile river system from the white nile based on sediment fabric and mineralogy shifts in percentages of total organic carbon toc and total organic nitrogen ton hydrogen index hi and 13 c and 15 n as well as poor preservation of sporopollenin and siliceous microfossils we recognize two mature paleosols that formed between 18 000 and 12 500 14 c yr bp at the surface of exposed lacustrine muds a thin fossiliferous zone between the two soils documents a brief period of flooding lake albert was below the level of the coring site and thus a closed basin for several thousand years during the late pleistocene around 12 500 14 c yr bp the younger vertisol was flooded by a major rise in lake level relatively deep water conditions were established soon after this transgression but an apparent change in sedimentation rate sometime between 8 000 and 3 400 14 c yr bp may reflect another briefer period of low water which resulted in interruption of sedimentation at the coring site palynological data document a rapid and abrupt shift to drier conditions around lake albert from 11 400 to 9 900 14 c yr bp coincident with the cool younger dryas event of the northern hemisphere geochemical evidence suggests that throughout the terminal pleistocene and early holocene and again in the late holocene the water column was relatively well mixed with little tendency to persistent anoxia

a rock magnetic record from lake baikal siberia evidence for late quaternary climate change rock magnetic measurements of sediment cores from the academician ridge region of lake baikal siberia show variations related to late quaternary climate change based upon the well dated last glacial interglacial transition variations in magnetic concentration and mineralogy are related to glacial interglacial cycles using a conceptual model interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals the variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods we also infer an increased contribution of eolian sediment during the colder windier and more arid glacial conditions when extensive loess deposits were formed throughout europe and asia eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals variations in magnetic concentration and mineralogy of lake baikal sediment correlate to the specmap marine oxygen isotope record the high degree of correlation between baikal magnetic concentration mineralogy and the specmap oxygen isotope record indicates that lake baikal sediment preserves a history of climate change in central asia for the last 250 ka this correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method future work must include providing better age control and additional climate proxy data thereby strengthening the correlation of continental and marine climate records

holocene landscape evolution of the manga grasslands ne nigeria evidence from palaeolimnology and dune chronology this paper presents a synthesis of results from investigations into palaeolimnology and dune chronology in the manga grasslands and adjacent areas of ne nigeria in order to reconstruct the evolution of this semi arid landscape since the late glacial a marked wet phase gave way to a fall in lake levels during the late glacial dune emplacement was active at this time to the south of the manga grasslands but seems to have been absent from the grasslands themselves wet conditions prevailed during much of the early to mid holocene accompanied by periods of significant barchanoid dune reactivation a marked deterioration in climate and vegetation commenced around 4 1 ka bp leading to the formation of the present day semi arid landscape the data suggest that there have been major changes in humidity in this part of subsaharan west africa during the late glacial to holocene and that the relationship between changes in precipitation and aeolian activity is complex

a multiproxy lake record from inner mongolia displays a late holocene teleconnection between central asian and north atlantic climates in order to study how the holocene central asian climate is coupled to the global climate system a 4 24 m long lake core from western inner mongolia in china was studied using a multiproxy approach sedimentology and geochemical parameters such as gypsum and dolomite content presence of lakeshore sand changing to aeolian sand and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late holocene aridification is linked to the southward retreat of the northern boundary of the asian summer monsoon leaving central asia under the influence of the westerly belt the weakening of the asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation the weakening summer insolation also likely increased the intensity of the siberian high pressure system further promoting aridification of central asia on a shorter time scale the multiproxy record shows the climate to have been relatively dry during the medieval warm period ad 800 1100 with the ensuing humid environment at the end of this period gradually turning to become extremely dry ad 1100 1550 at the little ice age maximum switches in the north atlantic oscillation caused these changes through a teleconnection in the form of westerlies these westerlies provided most of central asia s moisture after the retreat of the asian summer monsoon the central asian climate therefore corresponds closely with late holocene european climate changes

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

the dry holocene megathermal in inner mongolia the paleoclimate since 14 kyr bp 14c age was reconstructed based on a 16 22 m long sediment core collected from lake yanhaizi a saline lake located near the northern limit of the east asian summer monsoon in inner mongolia coarse sediments were deposited there during a shrinkage phase of the lake when sand dunes reactivated these sediments have low organic carbon contents but high maturity indices indicating that they were deposited in an arid environment by contrast based on high organic contents and low maturity indices fine sediments were deposited during periods of high lake stand in a humid environment it was in general dry between 8 0 and 4 3 kyr bp the above dry and wet phases are consistent with those recovered from the arid semiarid transition zone elsewhere but are unlike the widely perceived humid holocene megathermal reported in east china and the newly reconstructed record in the alpine retreat lake in taiwan the discrepancy may be due to a relative insensitivity to humidity changes in these two areas since they have both been under the total influence of the summer monsoon on the other hand much enhanced evaporation over higher monsoon precipitation at lake yanhaizi reduces the effective humidity in the warm climate near the northern boundary of the summer monsoon this also accounts for the fact the high temperature holocene megathermal as revealed in the okinawa trough and the northern south china sea is correlated to the dry phases at lake yanhaizi conversely the 4 2 kyr bp coldest period in the holocene corresponds to a wet phase at lake yanhaizi

reconstruction of last glacial to early holocene monsoon variability from relict lake sediments of the higher central himalaya uttrakhand india abstract proglacial lake sediments at goting in the higher central himalaya were analyzed to reconstruct the summer monsoon variability during the last glacial to early holocene sedimentary structures high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced fluctuating monsoonal conditions optically stimulated luminescence osl dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka during this period goting basin witnessed moderate to strengthened monsoon conditions around 25 ka 23 5 ka 22 5 ka 22 ka 18 ka 17 ka 16 5 ka and after14 5 13 ka the last glacial phase ended with the deposition of outwash gravel dated at 11 ka indicating glacial retreat and the onset of holocene condition additionally centennial scale fluctuations between 16 5 ka and 12 7 ka in the magnetic and geochemical data are seen a close correspondence at the millennial scale between our data and that of continental and marine records from the indian sub continent suggests that goting basin responded to periods of strengthened monsoon during the last glacial to early holocene we attribute the millennial scale monsoon variability to climatic instability in higher northern latitudes however centennial scale abrupt changes are attributed to the result of albedo changes on the himalaya and tibetan plateau

new evidence on deglacial climatic variability from an alpine lacustrine record in northwestern yunnan province southwestern china abstract new deglacial pollen and conifer stoma records from tiancai lake northwestern yunnan province southwestern china an alpine lake in the southwest monsoon region are presented in this study based on these records the lithology of core tcyl1 and pca analysis of pollen data between 21 and 11 5 ka bp calibrated 14 c years the deglacial vegetation and climate changes are discussed in detail the results show that tiancai lake was above the upper limit of picea abies forest a treeline in the study area between 21 and 11 5 ka bp and the climate was colder and drier than that of the holocene during this period eight significant vegetation changes are recorded that are considered to be responses to changing temperatures and variations in the southwest monsoon in southwestern china the heinrich event 1 h1 the bolling allerod warm period ba and the younger dryas cold event yd are all clearly detected in this record in addition this study finds that the initial late glacial warming in northwestern yunnan province was at 18 7 ka bp which is coincident with the climate records in monsoonal central asia the indian ocean the tropical and subtropical pacific ocean and antarctica and is a response to solar insolation changes a noted temperature increase between 15 8 and 14 4 ka bp occurred at the end of the h1 and before the ba which indicates a strong pre bolling warming based on the study we consider that the hypothesis about a slowdown of the ocean s thermohaline circulation is sufficient to explain these late glacial abrupt events

asynchronous evolution of the indian and east asian summer monsoon indicated by holocene moisture patterns in monsoonal central asia abstract the numerical meta analysis of 92 proxy records 72 sites of moisture and or temperature change confirms earlier findings that the dominant trends of climatic evolution in monsoonal central asia since the last glacial roughly parallel changes in northern hemisphere summer insolation i e the period following the last glacial maximum was characterized by dry and cold conditions until 15 cal kyr bp followed by a warm wet period coincident with the bolling allerod warm period and terminated by a cold dry reversal during the younger dryas period after an abrupt increase at the start of the holocene warm and wet conditions prevailed until ca 4 cal kyr bp when moisture levels and temperatures started to decrease ordination of moisture records reveals strong spatial heterogeneity in moisture evolution during the last 10 cal kyr the indian summer monsoon ism areas northern india tibetan plateau and southwest china exhibit maximum wet conditions during the early holocene while many records from the area of the east asian summer monsoon indicate relatively dry conditions especially in north central china where the maximum moisture levels occurred during the mid holocene we assign such phenomena to strengthened hadley circulation centered over the tibetan plateau during the early holocene which resulted in subsidence in the east asian monsoonal regions leading to relatively dry conditions our observations of the asynchronous nature of the two asian monsoon subsystems on millennial time scales have also been observed on annual time scales as well as implied through the spatial analysis of vertical air motion patterns after strong ascending airflows over the tibetan plateau area that were calculated from ncep ncar reanalysis data for the last 30 years analogous with the early holocene the enhancement of the ism in a future warming world will result in an increase in the asynchronous nature of the monsoon subsystems this trend is already observed in the meteorological data from the last 15 years

sedimentological and carbonate data evidence for lake level variations during the past 3700years from a southern indian lake abstract over the years several proxies have been developed to reconstruct rainfall variability however most rely on indirect approaches to provide qualitative paleorainfall estimate in an attempt to obtain a more direct measure of paleorainfall shankar et al 2006 explored the rock magnetic properties of lake sediments from thimmannanayakanakere tk in tropical southern india they proposed the use of magnetic susceptibility as a proxy for rainfall in the tropics warrier and shankar 2009 provided geochemical evidence in support of this proposition here sedimentological and carbonate data is provided as further evidence to bolster shankar et al s 2006 proposition high low values of lf indicate high low rainfall in the region of tk during the past 3700 years particle size variations suggest that the sand was high low during arid humid periods when the tk lake level was low high hence a negative correlation is documented between sand and lf along with other rock magnetic parameters hirm an indicator of magnetically hard minerals like haematite and goethite is suggestive of a relatively arid climate the high low hirm values in tk sediments indicate arid humid conditions for this reason sand is positively correlated with hirm by contrast fine silt and clay contents are low during low rainfall periods and vice versa thus both fine silt and clay contents are positively correlated with lf and other rock magnetic parameters but negatively correlated with hirm magnetic minerals reside principally in the fine silt fraction of tk sediments as evidenced from the positive correlation between fine silt content and magnetic susceptibility carbonate content too is indicative of paleorainfall conditions being high low during arid humid climatic conditions based on the lf sand and carbonate data we have inferred lake level variations in tk during the past 3700 years

grain size in sediments from lake sugan a possible linkage to dust storm events at the northern margin of the qinghai tibetan plateau samples of surface deposits in the lake sugan catchment as well as surface lake sediments eolian materials occulted in the lake ice cover and airborne dust were collected for grain size analysis the results show that the coarse fraction of the lake sediments could be transported by ambient winds and to a lesser extent by river flow in the study area sediment cores were retrieved from lake sugan in december 2000 and 210pb and 137cs dating and grain size analyses were performed on these samples 210pb ages and the volume percentage of the fraction of lake sediments 63 m were used to reconstruct the dust storm history from 1957 to 2000 observational data for dust storm events collected at a local meteorological station largely agrees with the reconstructed trend for the past 44 years suggesting that lake sediments can be employed to trace the dust storm history of the northern qinghai tibetan plateau

a multi proxy record of environmental changes during the holocene from the haolaihure paleolake sediments inner mongolia abstract the east central inner mongolia is located near the present day limit of the asian summer monsoon asm influence and therefore sensitive to both regional and global climate change here we present the high resolution proxy record of regional paleoclimate evolution over the past 12 2 cal ka bp based on analyses of grain size and organic geochemical proxies i e toc tn c n 13c and 15n preserved in sediments from the haolaihure paleolake the multi proxy record reveals a cool and dry period from 12 2 to 8 7 cal ka bp and a relatively warm and wet stage from 8 7 to 2 2 cal ka bp interrupted by a short interval of reduced precipitation at 4 6 3 7 cal ka bp after 2 2 cal ka bp the regional environment deteriorated as climate shifted to generally cooler and drier conditions in the area with a brief return to a warm and wet climate during the medieval warm period the record also indicates severe drought in the region during the younger dryas event comparison with other proxy paleoclimate records in inner mongolia south china and central asia suggests that the environmental conditions in the east central inner mongolia were primarily controlled by the asm in the early to mid holocene while the westerlies appeared to be a major driver of environmental changes in the late holocene six of the eight cool and dry events recorded in haolaihure paleolake sediments are in phase with the ice rafting events in the north atlantic and were possibly caused by weakening of both the asm and the westerlies

climate and seismicity in the higher central himalaya during 20 10 ka evidence from the garbayang basin uttaranchal india abstract in the trans himalaya the trans himadri fault thf controlled the extent of past glaciers the rivers were impounded by glacial debris resulting in the formation of lakes that recorded regional climatic and seismic events one such lake formed at garbayang where the upper 28 m lacustrine succession spanned an age range of 20 10 ka magnetic susceptibility and sedimentological data suggest that the region experienced high amplitude low frequency millennial scale climate changes during the period 20 3 and 13 2 ka followed by low amplitude high frequency changes from 13 2 11 1 ka a sudden drop in magnetic susceptibility and elemental concentration of layers dated at 11 12 ka suggests cooling associated with the younger dryas occurrence of faulted strata seismites during 20 17 and 14 13 ka suggests recent activation of the thf this is noteworthy as the thf has been considered dormant since its last reactivation at 11 ma further the luminescence dates suggest that radiocarbon ages on organic carbon are grossly overestimated due to a hard water effect caused by the dominance of limestone in the lake catchment this implies that earlier radiocarbon based palaeoenvironmental reconstruction in the region will need revalidation

holocene environmental changes as recorded by mineral magnetism of sediments from anguli nuur lake southeastern inner mongolia plateau china abstract two cores one 1141 cm long an s and the other 885 cm long an a were retrieved from anguli nuur lake 41 18 24 n 114 20 27 e 1315 masl one of the largest lakes in the transition zone between a semi humid and semi arid climate parallel to the present limit of the southeast monsoon along the southeastern inner mongolia plateau in north china mineral magnetic parameters lf arm irm300mt sirm and irm 300mt were measured on an s and two additional parameters arm and hirm and four inter parametric ratios arm sirm irm300mt sirm irm 300mt sirm and sirm lf were calculated potential sources of these lake sediments catchment soils and dune materials close to the lake and in a distant sand plain were sampled and the magnetic properties of the surface material specimens were measured a chronological model was developed for an s by comparing and combining ams14c dates of an s with 137cs 210pb and ams14c dates of an a with the help of surface material magnetism the magnetic data of an s in combination with particle size toc and c n and pollen analyses indicate the environmental changes during the last 10 000 years around this lake conditions began to ameliorate at 10 900 cal yr bp 9600 14c yr bp and thus relatively wet and warm environments prevailed during 10 900 8900 cal yr bp 9600 8000 14c yr bp the holocene optimum or the wettest and warmest conditions was during 8900 7400 cal yr bp 8000 6500 14c yr bp the environment began to deteriorate from 7400 cal yr bp 6500 14c yr bp and the driest and coolest conditions occurred during 2200 480 cal yr bp there may have been a minor amelioration after 480 cal yr bp the inferred changes in palaeoenvironmental conditions around anguli nuur lake are broadly in agreement with those around most other sites on the inner mongolia plateau

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

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

rock magnetism of greigite bearing sediments from the dead sea israel summary detailed magnetostratigraphic investigations were carried out on five sediment cores obtained from three sites on the northwestern shore of the dead sea israel the sediments are heterogeneous composed of fine clastic layers alternating with authigenic aragonite the magnetic remanence is carried by ti magnetite and greigite reflecting a detrital as well as an authigenic phase directions of the characteristic remanent magnetization were obtained from stepwise af demagnetization of the natural remanent magnetization and subsequent principle component analysis the acquisition of a gyroremanent magnetization in a noticeable amount of the samples could be linked to core disturbances the depth age models based on ams 14c datings on plant remains yielded an age of 10 04 ka cal bp for the base of the longest profile from site ein gedi a continuous lacustrine sediment sequence the profiles from the two other sites representing near shore sedimentation are interrupted by a hiatus in sedimentation comparison of the inclination and declination records from all dead sea cores and nearby sited lakes suggest that low frequency variations documented in the dead sea sediments are likely of geomagnetic origin

winter north atlantic low cloud anomalies associated with the northern hemisphere annular mode ship observations of low cloud anomalies over the atlantic ocean from jan 1956 through mar 1995 are linearly related to the northern hemisphere annular mode nam and to the corresponding anomalies of surface pressure surface wind and sea surface temperature sst positive nam anomalies are associated with coherent cloud anomaly patterns a band of increased bad weather stratiform cloud along the storm track between 40 n and 50 n positive anomalies of precipitating stratiform and convective clouds together with negative anomalies of fair weather stratiform clouds north of this band and negative anomalies of cumulonimbus with weak increases in fair weather stratiform clouds south of this band near 10 n positive nam anomalies are associated with increased trade winds and increases in both fair weather and bad weather stratiform clouds resulting in an increase of total low cloud amount low cloud anomalies are also related to anomalies in sst and surface wind divergence