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

chemical and physical denudation in the amazon river basin we present major and trace element data on the suspended and dissolved phases of the amazon river and its main tributaries the sr isotopic composition of the dissolved load is also reported special attention is paid to the abundances of ree and to their fractionation between the dissolved and suspended phase the rivers of the amazon basin are among the richest in dissolved ree and are similar to the rivers of the congo system however a greater range of fractionation between lree and hree is reported here at a global scale the rivers have intermediate patterns between those of the congo system and those of high ph rivers such as the indus and mississippi rivers only few elements rb u ba k na sr and ca are mobilized by silicate weathering these elements are strongly depleted in the suspended phase with respect to upper continental crust in the dissolved load these elements are controlled by atmospheric inputs and the weathering of the main lithologies we propose a model based on mass budget equations that allow the proportions derived from the different sources to be calculated as a consequence silicate carbonate and evaporite weathering rates can be estimated as well as the consumption of co2 by weathering of each of these lithologies physical weathering rates can be estimated by two complementary approaches on the one hand the multi year average of suspended sediments yields can be used to estimate physical denudation on the other hand we have developed a steady state model of erosion that allows us to calculate physical erosion rates on the basis of the dissolved load of rivers a mean crustal composition is assumed in this model for the rock sources of the drainage basins comparison of the rates predicted by the model to the observed rates shows good agreement for the lowland rivers but a strong discrepancy for the rivers derived from the andes andean rivers solimoes madeira and amazon have observed sediment yields much greater than those predicted according to the steady state model of chemical and physical weathering two interpretations can account for this inconsistency the first is that these rivers are not in steady state and hence that the soils are being destroyed the second requires that the local continental crust is different from the average continental crust of taylor and mclennan and contains a large proportion of sedimentary rocks using the measured sediment yields and assuming a steady state we can estimate the amount of sediment recycling for each drainage basin for the amazon at santarem we find that at least 25 of the mass of the upper continental crust of the amazon drainage basin is constituted of recycled material

mid late holocene vegetation response to climatic drivers and biotic disturbances in the banni grasslands of western india abstract tropical grasslands and savannas are globally extensive and are of significant environmental economic and ecological importance these ecosystems are anticipated to be particularly sensitive to future changes in climate and understanding how these systems have responded to climatic changes in the past can provide us with insights into their potential responses to future global change in this study the temporal dynamics of c 3 c 4 vegetation changes in response to changes in moisture availability local fire events and changing levels of herbivory in a summer rainfall region of western india are reconstructed for the past 4600 cal yr bp paleodata such as stable carbon isotope of bulk organic matter 13 c org oxygen isotope from carbonate shells 18 o shell macro charcoal and herbivore dung fungal spores are reported from the retrieved cores of two wetland sites located in the banni grasslands of western india results show that vegetation in the banni was composed mostly of c 3 vegetation from 4600 to 2500 cal yr bp after which there was a decline in c 3 vegetation from the late holocene to the present there was a mix of both c 3 and c 4 vegetation with c 4 grasses being more abundant in the ecosystem these shifts were coincident with rainfall changes from more mesic conditions during 4600 to 2500 cal yr bp to more arid conditions towards the present as indicated by 18 o shell isotope data the period of increase in c 4 vegetation also coincides with a period of increased biotic disturbances in the ecosystem particularly fire given the current scenarios of global warming recurrent drought events and increased anthropogenic use of similar ecosystems such studies can provide us insights into potential future trajectories of these ecosystems

stable isotope and radiocarbon balances of two tibetan lakes sumxi co longmu co from 13 000 bp hydrologic and climatic changes in western tibet since 13 000 bp are inferred from mineralogical and isotopic analyses of lacustrine sediments from the sumxi longmu co basin the interpretation is based on isotope data from the modern system carbon isotope chemistry is complex because of the presence of old limestones on the watershed sediments contain detrital and authigenic calcites the proportions of which are quantitatively estimated by x ray diffractometry stable isotope contents of the authigenic calcite are reconstructed from mass balance equations the high 13c contents up to 6 are attributed to an enhancement of calcite precipitation from water surface during freezing periods the 18o content is related to residence time and evaporation the validity of 14c dates obtained from different types of material is discussed our record in good agreement with paleobiological data from the same material shows the sudden establishment of wet warm conditions at 10 000 bp which culminated at 7500 6000 bp after a brief reversal event at 7900 bp maximum aridity for the whole holocene is recorded at 4300 bp

environmental changes since 8 4 ka reflected in the lacustrine core sediments from nam co central tibetan plateau china the tibetan plateau induces and enhances the asian monsoon that influences the plateau itself east china and even the whole of asia pursuing the changing monsoon history and its impact in this environment sensitive area is a key for understanding the climatic changes here we present the initial results from core sed iments in nam co central tibet to elucidate the holocene environment changes in this area the studied lake nam co is the second largest lake with an elevation of 4718 m water area of 2015 km 2 and catchment area of 10 610 km 2 by using echo seismic profiling and hydro echosounding we investigated the bathymetric dis tribution of the whole lake one 332 cm long piston core was successfully taken in the east part of the lake at 60 m water depth twelve ams 14 c dates from top to bottom of this core established a good time sequence toc tn n alkanes grain size clay minerals fe mn sr ba and caco3 content were analysed with sampling intervals from 1 cm to 10 cm results showed that since 8400 yr bp the environment changes in this region indicate three stages the early stage 8400 6900 yr bp was characterized by slight shifting from warm to cold with a cold dry interval at 8100 7800 yr bp the middle stage was from 6900 to 2900 yr bp during which cli mate changed from warm humid to cold dry however around 2900 yr bp the climate once was slightly cold but strongly dry the late stage from 2900 yr bp to present was characterized by a general tendency toward cold dry the first temperature decline was around 1700 1500 yr bp following which temperature increased once before decreasing again around 600 300 yr bp which might be the result of the little ice age

uniform postglacial slip rate along the central 600 km of the kunlun fault tibet from 26al 10be and 14c dating of riser offsets and climatic origin of the regional morphology late pleistocene holocene sinistral slip rates on several segments of the kunlun fault in northeastern tibet have been determined these determinations are based on the measured displacement of alluvial surfaces whose surface ages were determined by cosmogenic 2 6 al and 1 0 be dating of quartz pebbles and by 1 4 c dating of charcoal in the west at three sites along the xidatan dongdatan segment of the fault near 94 e terrace riser offsets ranging from 24 to 110 m with cosmogenic ages ranging from 1800 to 8200 yr yield a mean left lateral slip rate of 11 7 1 5 mm yr 1 field observations indicate minimum offsets of 9 12 m this offset when combined with the long term slip rate indicates that great earthquakes m 8 rupture this segment of the fault with a recurrence interval of 800 1000 yr at two sites along the dongxi anyemaqin segment of the fault near 99 e terrace riser offsets ranging from 57 to 400 m with 1 4 c ages ranging from 5400 to 37 000 yr bp yield a minimum slip rate of 10 mm yr 1 at one site the 1937 january 7 m 7 5 and the penultimate earthquakes produced 4 m of left slip and 0 4 m of reverse slip the maximum recurrence interval of earthquakes with such characteristic slip is thus 400 yr farther east near 100 5 e along the maqen segment of the fault the 180 m offset of a lateral moraine emplaced between the last glacial maximum 20 ka and 11 100 yr bp yields a mean slip rate of 12 5 2 5 mm yr 1 the slip rates are constant within uncertainty throughout the 600 km of the kunlun fault that we studied the average slip rate is 11 5 2 0 mm yr 1 extrapolating this rate to the reminder of the fault we conclude that most 80 per cent of the 300 morphological offsets measured in the field or on spot satellite images post date the last glacial maximum most of the terraces we studied were deposited during the humid period of the early holocene optimum 9 5 ka the formation of younger terraces reflects late holocene climate change

the pleistocene and holocene records of the mazarron basin se spain abstract here we reconstructed the evolution of the mazarron basin during the pleistocene and holocene in this regard we studied 9 cores with the aim to 1 define a chronological framework 2 obtain data on the palaeoenvironment and 3 establish the relationship with recent tectonics a total of 158 samples were recovered for amino acid racemization aar dating 4 for radiocarbon dating 14c and 332 for sedimentological and palaeontological determination and 110 for determination of the mineralogical content these approaches allowed us to elucidate the evolutionary phases of the palaeo landscape of the mazarron basin a fault controlled graben affected by diverse faults mainly those of las moreras and rella the ages of the records and the facies correlation indicate that las moreras fault controlled sedimentation during marine isotope stage mis 7 whereas the rella fault was strongly active during the middle holocene during mis7 a brackish lagoon developed in the western area overlying alluvial fan deposits later the area was uplifted thereby becoming exposed to erosion the activity of the rella fault allowed sedimentation in the western part of the mazarron basin during the middle holocene while in the upper holocene sedimentation occurred in the eastern part the holocene transgression was reflected in a temporarily floodable marsh in the hinterland with changing salinity conditions from brackish to euhaline waters along the sea front the marine influence was evident but not dominant thus the mazarron basin during the holocene was brackish to highly euhaline with variable biological diversity linked to a narrow and probably discontinuous communication with the sea with restricted circulation and long flushing times which was reflected by the significant presence of halite the record ended with recent alluvial anthropic sediments

implications of radiocarbon ages of organic and inorganic carbon in coastal lakes in florida for establishing a reliable chronology for sediment based paleoclimate reconstruction coastal lake sediments are valuable paleoclimate archives provided that they can be accurately dated here we report radiocarbon ages of bulk sediment organic matter om plants shells particulate om and dissolved om from coastal lakes in florida bulk sediment om yielded ages that are consistently older than contemporaneous plants and shells indicating significant radiocarbon deficiencies in sedimentary om in these lakes the data show that the om radiocarbon deficiency varies over time and with location making it impossible to determine a proper correction factor for radiocarbon ages of bulk sediments from these lakes as a result we consider ages obtained from bulk sediment om from these lakes unreliable the age reversals in bulk sediment om observed in the sediment cores are likely caused by rapid increases in erosion and sedimentation resulting from large storm events the data also show that sedimentation rate can vary considerably within a given lake implying that an age depth model established for one core cannot be directly applied to other cores despite their close proximity analyses of shells from one of the lakes suggest that fresh brackish water shells may serve as a good substrate for radiocarbon dating owing to a small reservoir effect on inorganic carbon

a 14 ka high resolution δ18o lake record reveals a paradigm shift for the process based reconstruction of hydroclimate on the northern tibetan plateau abstract the influence of the mid latitude westerlies mlw competing with the asian summer monsoons asm over the tibetan plateau tp remains a matter of discussion on how and to which extent both atmospheric systems have been controlling hydro climate during the holocene depleted oxygen isotopes in lake deposits were commonly interpreted in terms of enhanced summer monsoon moisture supply implying a migration of the asm deep into the interior of the plateau during holocene periods in order to test this relationship we used a high resolution oxygen isotope record mean 20 yr resolution in combination with carbonates and mineral phases titanium flux grain size and ostracod abundances derived from a 6 84 m long sediment core in the endorheic kuhai lake basin north eastern tp the results confirm 1 continuous positive co variance between enriched 18ocarb and total carbonates during the last 14 ka indicative of dominant seasonal influence on multi decadal to centennial scale isotopic signatures in lake water and respective carbonate precipitation 2 negative co variance between allochthonous sediment flux and 18ocarb and carbonates attributed to relative increase of flux rates during non summer seasons 3 correspondence of lake level variations with carbonate mineral phases and the occurrence disappearance of ostracod assemblages and 4 inverse relationships between isotopic signatures in asm dominated and mlw controlled lake records across the tp enriched 18ocarb in kuhai lake sediments was primarily a result of high evaporation during the summer seasons while asm related rainfall amount did not play an important role likely counterbalanced by isotopic signatures from different water sources conversely depleted 18ocarb was mainly attributed to water supply during non summer seasons of colder temperatures and generally light isotopic signatures from mlw derived sources this finding may lead to a paradigm shift in such way that depleted 18o in carbonates is primarily not the result from asm related rainfall as previously assumed the reconstructed hydro climatic history of kuhai lake indicates the dominance of westerly derived climate during the younger dryas interval 12 8 11 5 ka under very shallow pond like conditions despite climate amelioration during the early holocene 11 5 7 5 ka hydrological conditions remained unstable with frequent alternations between dominance of summer and winter seasons during the middle holocene 7 5 5 5 ka the lake experienced highest lake levels dominated by summer monsoon related water supply assigned to the holocene hydro climatic optimum frequent high amplitude fluctuations afterwards 5 1 2 9 ka refer to cooling drying events under enhanced mlw influence accompanied by a strong lake level decline the late holocene 2 9 ka present period experienced moderate isotopic variations and fluctuating lake levels in response to variable influence of summer or winter related hydro climatic conditions this seesaw like pattern with amplitudes of 10 in 18ocarb resembles fluctuations in cave records and variations between air and seawater dole effect high correspondence with cooling events derived from north atlantic drift ice and meltwater discharge indicate close ties to northern hemispheric climate transmitted by the mlw across the tp

on the hydraulic properties of coarse textured sediments at intermediate water contents 1 a modified steady state head control method was used to obtain on identical samples direct measurements of soil moisture retention volumetric water content versus matric potential and unsaturated hydraulic conductivity k as a function of both and the minimum values for the undisturbed coarse textured samples were as low as 400 cm whereas the values were as low as 0 04 of the 79 samples 41 contained a high gravel fraction 2 mm size that ranged from 20 to 71 by weight the remaining samples were sandy with very little gravel fraction we examined similarities and differences between the two soil types in their retention and k slopes for the intermediate moisture regime the retention data for the gravelly soils fell within a narrower range than for the sandy type the water capacity d d estimates for the two soil types showed similar variability although both soils are coarse textured important differences were noted in two integral measures for and k measurements the mean and variance for the campbell pore size distribution parameter b and k slope estimates for the gravelly type were larger than those for the sandy type a unique relation was noted between b and the relationship was similar for the two soil types with a very dissimilar particle size distribution

ostracods and stable isotopes of a late glacial and holocene lake record from the ne tibetan plateau abstract ostracod assemblage changes and stable isotopes of ostracod shells were used to reconstruct the salinity history of lake donggi cona on the northeastern tibetan plateau in response to the late glacial and holocene climate history brackish and relatively unstable conditions were inferred for the earlier part of the late glacial between 18 9 and 13 4 cal ka bp and for the early to mid holocene 11 9 6 8 cal ka bp a saline lake existed in the intervening period probably representing colder and drier conditions during the greenland stadial 1 younger dryas in north atlantic region freshwater conditions similar to the present stage of lake donggi cona were established for the first time at 6 8 cal ka bp this inference and the implied increase in moisture availability in the latter half of the holocene is in contrast to most climate records from the tibetan plateau which suggest drier and colder conditions however three lake records from the eastern tibetan plateau including our new record show that the holocene insolation driven monsoonal weakening and temperature decrease caused a catchment specific opposite response of the moisture availability in comparison to those at the majority of sites catchments with relatively low precipitation at present experienced apparently a moisture availability increase during the colder second half of the holocene in contrast to the inferred drier conditions at predominantly generally wetter sites the increase in moisture availability at relatively dry sites mainly results from the lowered temperature and evaporation but is probably further controlled by a complex of factors including the amount and timing of precipitation the altitudes of the lake basins and upper reaches and the existence or development of glaciers snow fields and frozen ground in a given catchment our record from lake donggi cona suggests that the recently observed reduction in yellow river discharge in response to present global warming will likely continue or even increase under warmer climatic conditions in the future

aeolian process and climatic changes in loess records from the northeastern tibetan plateau response to global temperature forcing since 30 ka the response of surface processes to global climatic changes since the last glacial is critical to understanding the mechanism of climatic changes on the tibetan plateau in this study loess from the northeastern tibetan plateau netp was closely spaced dated to provide an independent high resolution record of dust accumulation processes and millennial scale climatic changes optically stimulated luminescence ages reveal episodes of rapid dust deposition at approximately 12 3 ka 16 ka 21 23 ka 25 28 ka and possibly also at 30 33 ka these episodes are broadly correlated with high latitude and marine records cold climatic events such as the younger dryas heinrich event 1 and the last glacial maximum this correlation implies that dust storms in the netp represent episodic aridification and wind strengthening which is ascribed to the southward shift of the polar front and the intensification of the siberian high pressure cell that was forced by millennial scale cooling in high northern latitudes

climate variability on the south eastern tibetan plateau since the lateglacial based on a multiproxy approach from lake naleng comparing pollen and non pollen signals a multi proxy lateglacial environmental record is described from lake naleng 31 10 degrees n 99 75 degrees e 4200 m above sea level situated on south eastern tibetan plateau to gain deeper insights into the hydrological and palaeoclimate development since 17 7 cal ka bp palynological reconstructions of variations in mean annual precipitation map and temperature mat sedimentological data and sediment chemistry including weathering indicators provide a multi faceted picture of local and regional environmental changes since the lateglacial principal component analyses of all parameters provide information on interrelationships between each parameters which help to evaluate their traceability to temperature and precipitation and to estimate their usability as proxy indicators for local and or regional variations during the lateglacial from 17 7 to 14 0 cal ka bp lake naleng experienced cold and dry climate conditions with low biological productivity and supply of unaltered fine grained material due to the high supply of glacier milk during the second half of the lateglacial climate conditions changed abruptly increases in mat from 4 to 2 2 degrees c and map from 500 mm to 820 mm between 14 0 and 13 0 cal ka bp indicate a climate amelioration this time interval can be correlated to the bolling allerod b a warming period in the north atlantic region and is followed by the younger dryas cold reversal indicated by abrupt decreases of mat from 2 2 to 5 degrees c and map from 820 to 650 mm the onset of the holocene at about 11 5 cal ka bp is indicated by rises in reconstructed mat from 5 to about 03 degrees c and map from 600 mm to 950 mm which led to an increased supply of weathered material and higher biological productivity between 5 0 and 3 0 cal ka bp mat increases to about 0 2 degrees c and map rises to maximum values of about 1000 mm followed by slightly decreasing mat and map between 3 0 and 0 cal ka bp the biogeochemical parameters total organic carbon toc c n delta c 13 org and weathering indicators e g the chemical index of alteration cia and sr ba are directly erosion of soils or indirectly changing provenance related to moisture availability on the south eastern tp and shows matching regional climate oscillations since the lateglacial in comparison to other lateglacial records from the tp map reconstructions from lake naleng indicate wetter climate conditions in the south eastern part of the tp and dryer conditions farther away from moisture sources c 2015 elsevier ltd all rights reserved

reduced early holocene moisture availability in the bayan har mountains northeastern tibetan plateau inferred from a multi proxy lake record abstract a late glacial and holocene lake sediment record from the northeastern tibetan plateau was investigated using ostracod and geochemical analysis after lake koucha was established about 16 cal ka bp oligohaline conditions gradually converted to mesohaline conditions about 10 cal ka bp clearly suggesting that the water body was a closed basin lake from about 10 cal ka bp the salinity of the lake rose continuously until hyperhaline levels were reached about 7 5 cal ka bp this increase in salinity was accompanied by a falling lake level extreme rainfall and flooding events in a generally dry climate hit the shallow saline lake around 8 5 cal ka bp causing a unique thin gravel containing layer within the continuous fine grained lake sediments the age control of our record does not allow us to correlate this event exactly to the widely recorded 8 2 cal ka bp event however the recovered sediments from lake koucha provide strong evidence that climate changes around 8 5 cal ka bp had significant environmental implications in northeastern tibet after about 7 3 cal ka bp the available moisture significantly increased causing a continuous salinity decline until the present day freshwater conditions of a through flow lake were established about 6 5 cal ka bp in lake koucha this major shift from a shallow saline to a deeper freshwater lake was probably accompanied by a fundamental change from a macrophyte dominated to a phytoplankton dominated lake a slight reduction in available moisture in comparison to the periods before and afterward was recorded between 4 3 and 2 0 cal ka bp in phase with numerous records from monsoonal asia the reconstructed overall change in moisture availability from dry conditions before about 7 3 cal ka bp to wetter conditions afterwards contradicts most palaeoclimate records from the tibetan plateau and its surroundings which show that wetter conditions in the early holocene were replaced by drier and probably cooler conditions in the mid and late holocene however in the semi arid region of lake koucha with a mean annual precipitation of about 500 mm the insolation driven strengthened monsoon in the early holocene may have resulted in a temperature rise and higher evaporation rates which outweighed the increase in precipitation and therefore led to significantly lower moisture availability our record provides further evidence for a regionally non uniform response of the available moisture evolution to the overall monsoonal signal in the holocene climate history of central asia

vegetational responses to monsoon variability during late holocene inferences based on carbon isotope and pollen record from the sedimentary sequence in dzukou valley ne india abstract the study aims to identify regional vegetational changes during the late holocene from the dzukou valley in north eastern ne india and the potential relationship of these vegetation dynamics with climatic shifts the investigations utilize a combination of 13corg of organic matter lipid biomarker n alkane as well as pollen data derived from 1 4 m sedimentary profile spanning the last 3150 cal bp the 13corg values during late holocene range from 29 1 to 27 7 suggesting that organic carbon was derived exclusively from c3 vegetation the profile is characterized by a homologous series of n alkanes ranging in chain length from n c18 to n c35 with maxima at n c29 the generated proxy data reveal three phases of climatic and vegetation shifts with the first phase from 3150 cal bp to 2300 cal bp being characterised by relatively high 13corg values and occupied by pine oak forest indicating a comparatively dry climatic conditions subsequently the second phase from 2300 cal bp to 1000 cal bp shows an increase in arboreal pollen tree elements and gradually decreasing trend of 13corg with a total shift of 1 4 suggesting moist climatic conditions during the third phase from 1000 cal bp onwards the precipitation declined till date as suggested by increasing trend in 13corg values and good recovery of pinus oak forest pollens this study provides significant insights into the use of 13corg and biomarkers along with pollen data to understand the influence of fluctuating rainfall in a high rainfall zone in altering the floristic composition within a region thus the study has provided ground for further investigations to address issues related to biodiversity loss extent of endemism in high rainfall zones dominated by single types c3 and or c4 of vegetation

late quaternary lacustrine ostracoda and their implications for hydro climatic variation in northeastern tibetan plateau abstract ostracoda from non marine waters have a significant potential role in monitoring ecological conditions and reconstructing paleoenvironments during the last decades the increase in research on ostracods on the tibetan plateau tp has been achieved although there are still taxonomical and ecological problems in their application in quaternary studies the aim of this review is to summarize the occurrences of ostracods in surface samples from four selected lakes qinghai lake lake donggi cona lake kuhai and hala lake along the modern monsoon marginal zone on the northeast tibetan plateau and to compare the ostracod associations in sediment cores from different sites with available proxy data after re evaluation of chronologies in order to reconstruct hydroclimatic conditions and monsoon influence during the late quaternary comprehensive reanalysis of ostracod data from selected lakes including 3 closed and 1 open lake basins on the northeastern tp shows that their occurrence and disappearance responded sensitively to salinity and related water depth changes during the late quaternary this could lead to a re interpretation of other proxy data related to hydro climatic interpretation ostracod based reconstructions of lake level changes along the modern summer monsoon marginal zone of the northeastern tp during the late quaternary indicate an overestimation of the contribution from monsoonal rainfall to strong lake level changes while the glacier snow meltwater supply was underestimated in previous studies this inference sheds more light on moisture source and the interplay between westerlies and asian summer monsoon on the northern tp

the influence of 14c reservoir age on interpretation of paleolimnological records from the tibetan plateau there is a great deal of controversy regarding the fate of glaciers and ice fields on the tibetan plateau in the face of continued anthropogenic global warming paleoclimate reconstructions and spatial analyses aimed at mapping past climate changes are the key to understanding the climatic response of the tibetan plateau to changing conditions specifically the numerous lakes distributed across the tibetan plateau can provide high resolution spatial and temporal climate reconstructions to investigate past changes in the climate system in this paper we review the primary limitation to exploiting these valuable paleoclimate archives errors in radiocarbon based age models we review the techniques that have been used to estimate 14 c reservoir ages on the tibetan plateau and compile the published 14 c reservoir ages to examine their spatial and temporal patterns and to assess the imposed chronological uncertainties using site specific evaluations of bangong co and lake qinghai we demonstrate that 14 c age model uncertainties permit equally probable and contrasting interpretations of existing paleoclimate records we also examine 14 c induced uncertainties in the spatial climatic response on the tibetan plateau to 1 the termination of the last glacial maximum and 2 the holocene thermal maximum we conclude with recommendations for reducing uncertainties in future lake based paleoclimate studies on the tibetan plateau

the interplay between relative sea level rise and sediment supply at the distal part of the nile littoral cell during holocene sea level rise coastal areas became transitional environments as marine incursion covered the land changing conditions resulted in dynamic depositional environments that recorded the migration and stabilization of modern shorelines these processes are viewed in the zevulun plain haifa bay israel record located in the northern edge of the nile littoral cell sedimentological and palaeontological analyses combined with dating enabled the reconstruction of the holocene chrono stratigraphical frame the results reveal an unconformity representing a long period of exposure and erosion during the last glacial the interplay between relative sea level rise and sediment supply was first set out by the deposition of alluvial sediments evidence of the hydrological system reactivation and base level landward migration sea flooding of the zevulun plain started about 7 8 cal ka bp and the coastline was pushed eastward nile driven sands transported by longshore currents formed dunes that blocke

revisiting growth and decline of late quaternary mega lakes across the south central tibetan plateau abstract lake basins record critical interactions between the hydrosphere cryosphere and atmosphere their sediments and shoreline landforms archive timing duration and intensity of past climatic variability and environmental impacts over a variety of timescales thousands of lake systems spread across the internally drained tibetan plateau today of which many are only the salty remains of much more expansive paleolakes in the past this study presents new shoreline ages integrated with quantitative digital topographic analysis and regional geomorphic evidence to reconstruct the sizes and extents of late quaternary rift lake systems for the south central tibetan plateau this study presents optically stimulated luminescence osl and the first k feldspar post infrared infrared pirir stimulated luminescence ages for zabuye caka and dawa tso and tests if these lakes were once part of a singular pleistocene mega lake established across four n s rift systems our new results show that two large but separate paleolake systems developed in the latest pleistocene earliest holocene and no lake larger than 6460 km2 has existed since at least 41 ka in the lunggar region early holocene paleolakes expanded up to 7 modern 220 335 km3 with two to four fold asymmetric lake expansion in the west compared to the east findings corroborate earlier investigations implying that dramatic runoff increase and or evapotranspiration reduction prompted rapid earliest holocene lake expansion precipitation variability in combination with permafrost degradation temperature and wind strength governed paleolake moisture balance open system lake behavior and evolving drainage configurations across complex topography explain delayed onsets of lake regression and punctuated lake decline this suggests abrupt holocene climate shifts are not necessarily required for punctuated lake decline lastly unique geomorphological and paleoclimatic similarities between tibetan and east african rift lakes highlight the potential for some tibetan paleolakes to function as natural climate amplifiers over both short and geologic timescales

source and biolability of ancient dissolved organic matter in glacier and lake ecosystems on the tibetan plateau the tibetan plateau is the world s largest and highest plateau and holds the largest mass of ice on earth outside the icesheets of greenland and antarctica as well as abundant lakes this study examined the molecular and isotopic signatures of dissolved organic matter dom along with its biolability in glacier ice glacier fed streams and alpine lakes on the tibetan plateau the aim was to assess the sources of dom and the potential of dom to provide a carbon subsidy to downstream ecosystems tibetan glaciers and glacier streams exhibited low dissolved organic carbon doc concentrations 17 7 27 9 lm and ancient doc radiocarbon ages 749 2350 ybp the optical properties stable carbon isotope ratios d 13 cdoc and the molecular composition fourier transform ion cyclotron resonance mass spectrometry of tibetan glacier dom are consistent with data from other glacier systems around the world the geochemical signatures and the ancient apparent ages of tibetan glacier dom suggest a significant fraction is derived from the atmospheric deposition of pre aged possibly fossil fuel derived organics within the tibetan alpine lakes doc was also ancient 525 675 ybp due to either inputs of pre aged organics from glacier runoff direct deposition or due to the aging of organics in situ i e a radiocarbon reservoir effect the glacier ice and glacier stream sites exhibited high biolability of doc and so provide a carbon subsidy to downstream environments that will change as glaciers on the tibetan plateau recede

lateglacial and holocene variation in aeolian sediment flux over the northeastern tibetan plateau recorded by laminated sediments of a saline meromictic lake predominantly laminated lake sediments from a saline closed basin lake on the northeastern tibetan plateau were investigated using a multi proxy approach 14c accelerator mass spectrometry dating smear slide analysis loss on ignition grain size x ray diffraction elemental concentration ostracod assemblages stable isotopes of ostracod shells to trace the regional environmental and climatic history in the lateglacial and holocene before about 15 cal ka bp small saline water bodies probably filled the basin under unstable cold and harsh environmental conditions soon after about 14 9 cal ka bp a relatively deep saline lake was established probably as a result of runoff from melting snow ice and frozen ground in the lake s catchment large changes in flux of aeolian material to the lake were recorded during this initial period of formation of lake kuhai highest lake levels a low sediment accumulation rate and less saline conditions were maintained between about 12 8 and 7 1 cal ka bp when the aeolian influx diminished significantly after about 7 1 cal ka bp the aeolian influx remained at a moderate level apart from a strongly increased dust delivery to the lake between about 6 1 and 5 4 cal ka bp and a minor short lived period of slightly enhanced aeolian influx at about 2 7 cal ka bp the strongly enhanced dust input to the lake between 6 1 and 5 4 cal ka bp represented the largest influx of aeolian material to lake kuhai during the entire holocene however evidence for climatic deterioration during this period is not seen at most other palaeoclimate sites on the tibetan plateau but instead a significant increase in aridity has been recorded at numerous sites in the northern foreland of the tibetan plateau and on the chinese loess plateau the large dust input to lake kuhai between 6 1 and 5 4 cal ka bp probably did not result from a severe climate deterioration on the tibetan plateau itself but from the pronounced aridity in its northern and eastern foreland in contrast the increase in dust influx about 2 7 cal ka bp seems to correspond to a brief warming spell recorded at other sites on the tibetan plateau too a slight increase in lake level and decrease in salinity after about 0 6 cal ka bp suggests a slightly higher effective moisture during the final lake stage accompanied by a somewhat larger dust influx this apparent contradiction possibly results from enhanced human activities on the northeastern tibetan plateau during the last 600 years copyright 2009 john wiley sons ltd

variability of gardner s α for coarse textured sediments vadose zone soils in arid regions often contain a high gravel fraction 2 mm size this paper examines for coarse textured soils variability of the slope of gardner s 1958 unsaturated hydraulic conductivity k versus matric potential relation k kse the steady state head control method was used to obtain unsaturated k for tensions as high as 386 cm a total of 79 samples were analyzed in the laboratory the gravel fraction for the 41 gravelly samples ranged from 20 to 71 by weight the remaining 38 samples were sandy with no gravel fraction the measured k values for the gravelly samples fall within a narrow range and are well within the range of measured k values for the sandy samples the bulk of both gravelly and sandy samples can be described using a single slope exponential model gardner s and the intercept k0 are based on a least squares fit to the late time measurements at lower the mean and variance of for the gravelly samples are lower compared with the sandy type the values for the gravelly soils follow a normal distribution whereas the k0 estimates and the laboratory measured ks follow lognormal distributions for the sandy type k0 and ks follow lognormal distributions the values appear to be related to the median particle diameter d50 and the slope of the particle size distribution a clear reduction in variability of is apparent with an increase in d50 suggesting that the unsaturated k and variability for the gravelly soils can be estimated within narrow ranges the flow weighted characteristic pore size m is clearly dependent on the soil type m values for the gravelly soils are characterized by a smaller mean and variance than for the sandy type this helps explain the finding that the range in unsaturated k for the gravelly soils is less than for the sandy type at higher tensions the mean and variance of and lnk0 as well as the cross correlation between and lnk0 are important inputs to stochastic models of unsaturated flow the implications of their variability on flow in heterogeneous media are discussed

correcting laboratory measured moisture retention data for gravels vadose zone soils in desert environments often contain a high gravel fraction 2 mm size laboratory measurements of moisture retention are typically made on the fine fraction 2 mm size the measurements are then corrected for field conditions by accounting for the gravel fraction in the sample a frequently used correction procedure for gravelly soils is tested a total of 23 samples containing gravel fractions up to 80 by weight were analyzed in the laboratory retention data on 2 mm size fraction were obtained and compared with measurements on bulk soil and gravel field samples results indicate that for the relatively wet moisture regime considered in this study retention data for gravelly soils can be estimated reasonably well by correcting the pressure cell measurements for the field bulk density and the fraction of fines present in the field samples further work is needed on testing the correction procedure for the dry moisture regime

understanding the variability in freshwater radiocarbon reservoir offsets a cautionary tale abstract freshwater resources in past diets can lead to inaccuracies when attempts are made to ascertain their radiocarbon ages or those of the consumers radiocarbon reservoir effects may lead to significant age offsets when the bones or other tissues of these consumers are radiocarbon dated a number of recent studies have investigated freshwater reservoir offsets however no study thus far has satisfactorily obtained a ubiquitous freshwater reservoir correction due to variability in the ecosystems analysed this study tests the possibility of predicting freshwater reservoir effects from the carbonate alkalinity of the water with measurements on modern fish bone and water samples a predictive capability would be especially valuable in the absence of well preserved archaeological fish bone we surveyed samples from lakes and rivers in varying geological settings in britain and ireland modern fish bone and water samples were analysed to investigate modern radiocarbon offsets from the atmosphere archaeological fish bone was also analysed to examine past reservoir offsets at selected sites stable carbon and nitrogen isotope values were measured to aid in interpretation of any variability in the offsets large freshwater reservoir offsets were measured in some modern and archaeological samples maximum offset 1638 14 c years the freshwater reservoir offsets in the fish bone were highly correlated with alkalinity of water in modern lake sites analysed however a high amount of variation within and between fish species was also evident in the results precluding the possibility of providing regional corrections for freshwater reservoir offsets from alkalinity although this still may provide a general guideline the variability is thought to be due to differences in the diet of individual fish

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

geomorphological and palaeoclimate dynamics recorded by the formation of aeolian archives on the tibetan plateau abstract aeolian sediments are an important archive for palaeoclimate reconstructions on the tibetan plateau the accumulation of aeolian sediments and the formation of palaeosols are used as a proxy for dry and wet phases respectively during the last decade the number of osl optically stimulated luminescence ages of aeolian sediments has been rapidly increasing this study summarises the results from more than 300 individual osl ages despite the widespread occurrence of aeolian sediments on the tibetan plateau nearly all osl samples are located on the northeastern and the southern part in most regions the strongest accumulation occurred during the late glacial and in the early holocene this coincides with the strengthening of the asian summer monsoon on the tibetan plateau and wetter climate conditions after the relatively dry glacial times the development of a sufficient vegetation cover acting as a sediment trap seems to be an important requirement for the preservation of aeolian archives short dry periods like the younger dryas led to a more enhanced aeolian accumulation without destruction of previously formed archives in some regions the formation of palaeosols occurred mainly during the wet early and mid holocene but the number of ages is relatively small in contrast a second phase of aeolian accumulation during the late holocene was related to the weakening of the asian summer monsoon and drier climate conditions this indicates that the reaction of aeolian accumulation on the tibetan plateau depends on the previous climate state a comparison between the osl ages from aeolian sands and loess deposits yields a different timing of deposition of these two sediment types while the sand deposits in different basins resemble wet and dry phases loess deposits show no common signal between the analysed areas this indicates an influence of local factors such as varying source areas and erosive processes on the slopes in general the aeolian archives in the high mountain environment are governed by numerous factors besides the climatic influence

holocene environmental changes in lake bangong basin western tibet part 1 chronology and stable isotopes of carbonates of a holocene lacustrine core abstract a 12 4 m core collected from the eastern part of lake bangong is analyzed for mineralogy radiometric chronology and stable isotope contents of authigenic inorganic carbonate isotopic compositions of the modern lake waters and of its major tributaries are first presented radiocarbon activity of these waters show that equilibrium with the atmospheric co2 is not reached because of admixture of dead carbon in solution in the system a model is thus developed to correct the radiocarbon ages of fossil material of aquatic origin for this ageing the core provides a continuous holocene record changes in mineralogy of bulk sediments and in 13c and 18o contents of authigenic carbonates reveal extremely large changes in environmental conditions induced by climate changes and or local hydrological factors e g closure opening of the lake system controlled by the altitude of the outflow sill the eastern basin of lake bangong was closed before 9 6 and after 1 2 ka b p in response to aridity on the catchment wet warm conditions attributed to the monsoon influence were established suddenly at 9 6 ka b p and maintained until 6 2 ka b p although minor reversal events occurred between 8 6 and 7 7 ka b p the return towards aridity is non linear dry spells at 6 2 3 9 3 2 and 1 3 ka b p are alternated with short term periods with positive precipitation evaporation balance

inverse relationship between south west and north east monsoon during the late holocene geochemical and sedimentological record from ennamangalam lake southern india abstract the southern peninsula of the indian sub continent is characterized by moisture source from both the south west sw and north east ne monsoon however the long term climate variability associated with these two moisture sources and their relative contribution in the region is less known in this study we have used a multiproxy approach geochemistry clay mineralogy and end member mixing analyses of the grain size parameters on the radiocarbon dated sediment profile from ennamangalam lake southern india to reconstruct the past moisture sources in the region based on our systematic investigation we have identified three hydrological stages in the region stage 1 ca 4800 to 3150 cal bp relative drier condition marked by low detrital content and higher contribution of relatively fine grained end member em 2 stage 2 ca 3150 to 1640 cal bp transition phase high sedimentation rate as compared to the preceding stage and stage 3 1640 cal bp to present represented by enhanced detrital content intense chemical weathering shown by increasing cia and continuous declining value of mg al and dominance of em 1 characterized by coarse grain sediments indicating high energy condition due to the intense precipitation the regional comparison of paleoclimate records demonstrate that the increase in precipitation observed in ennamangalam region during the late holocene is in contrast to the records from the core monsoon zone the overview of regional records indicate an inverse relationship between the south west and the north east monsoon strength during the late holocene affected by the increasing enso variability

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

high resolution osl dating of aeolian activity at qinghai lake northeast tibetan plateau abstract qinghai lake is the largest lake on the tibetan plateau tp located between the extremely arid qaidam basin to the west and the severely desertified gonghe basin to the south extensive aeolian sediment at qinghai lake is ideal material to reconstruct regional aeolian activity and to better understand the relationship between desertification and climatic change in the lake basin aeolian sand accumulation is usually accompanied by erosion hence depositional hiatuses and disconformities must be identified for reliable reconstruction of regional aeolian activity to date the low density of age sampling around qinghai lake has hindered identification of hiatuses in this study we report the first high density osl dating 41 osl ages were obtained from two aeolian sand sections dongwei dw and niaodao nd sand accumulation trends recorded in the high density osl sampling sections were consistent with previously published probability density function pdf ages for the northeast tp the middle holocene 7 to 4 ka was characterized by very low accumulation rates with rapid sedimentation in the late glacial to early holocene 14 to 7 ka and the late holocene after 4 ka a 3 ka hiatus in accumulation between 7 to 4 ka was identified in the dw section but the nd section showed successive accumulation since the late glacial 14 ka on sub orbital and millennial scales our environmental reconstructions are consistent with previously published aeolian data and paleoshorelines records the combined evidence shows strong aeolian activity since 14 ka to 9 ka initiation of pedogenesis at 9 to 7 ka intensified soil development between 7 ka and 4 ka with the most intense pedogenesis and least aeolian activity between 6 to 4 ka relatively weak paleosol formation from 4 to 2 ka and renewed aeolian activity after 2 ka

developing inorganic carbon based radiocarbon chronologies for holocene lake sediments in arid nw china abstract inorganic carbonates are often used to establish radiocarbon 14c chronologies for lake sediments when terrestrial plant remains tpr are rare or when bulk organic matter is insufficient for dating a problem that is common for many lakes in arid regions however the reservoir effect re as well as old carbon contributed from the lakes catchment make it difficult to establish reliable chronologies here we present a systematic study of inorganic 14c ages of two lake sediment sequences one from a small enclosed saline lake lake gahai in qaidam basin and the other from a large freshwater lake lake bosten in xinjiang modern dissolved inorganic carbon dic of the lakes paleo lake sediments exposed in the catchment and mollusk shells in core sediments from lake gahai were dated to assess the re and the contribution of pre aged carbon to the old ages in the cores we propose a statistical regression to assess more than one re for the 14c carbonate ages within our sedimentary sequences old radiocarbon ages contributed by detrital carbonates were assessed by comparing the ages of mollusk shells with those of carbonates at the same sediment depths we established the re of the authigenic component and assessed detrital old carbon contributions to our two sites and this was used to correct the 14c ages based on this approach we developed age models for both cores and tested them using 210pb ages in both cores and tpr based 14c ages recovered from lake bosten we further tested our age models by comparing carbonate based oxygen isotope 18o records from both lakes to an independently dated regional speleothem 18o record our results suggest if sedimentary sequences are densely dated and the re and the contribution of old carbon from detrital carbonates can be ascertained robust chronological frameworks based on carbonate based 14c determinations can be established

basin morphology and seismic stratigraphy of lake donggi cona north eastern tibetan plateau china basin morphology and depositional stratigraphy of lake donggi cona on the north eastern tibetan plateau has been studied with echo depth sounding and shallow seismic sub bottom profiling the basin is a pull apart structure situated at the highly active kunlun fault it is characterised by a 92 m deep graben structure in the western part of the lake basin and a shallow eastern lake part the latter filled up with fluvial sediments from a large alluvial plain three prominent morphological levels were identified at 24 m 39 m and 57 m below present lake level they were partly created by basin subsidence while the deposition of prograding delta sediments primarily formed the morphological steps the inherited tectonic structures control on going neotectonic activity which seems to have only minor influence on present basin morphology the basin is filled by sediments of at least 30 m thickness in the depocentre three major depositional units can be distinguished in comparison with lithological changes in a sediment core they give evidence of pronounced lake level fluctuations and dramatic changes in lake volume a numerical age datum of w19 cal ka bp at the base of the sediment core allows a tentative reconstruction of late glacial to holocene lake development a very low base level preceded a time of delta formation during higher lake level i e w26 m lower than present during last glacial maximum creating a lake of only 18 of its present size at the transition to holocene the lake level rose very quickly changing to a deep lake environment thus transgression may have promoted maximum lake stands

last glacial holocene geochronology of sediment cores from a high altitude tibetan lake based on ams 14c dating of plant fossils implications for paleoenvironmental reconstructions abstract we obtained three sediment cores from a high altitude lake lake pumoyum co altitude 5020 m asl on the southern tibetan plateau for reconstruction of environmental changes during the last glacial holocene transition in this study we established the first reliable chronology for sediment cores from lake pumoyum co ca 18 5 cal ka bp at the bottom by 14c analyses of terrestrial plant residue concentrates prc 125 m and aquatic plant residues the calibrated ages of the prc fraction in the surface sediment were nearly modern 0 1 0 1 cal ka bp and the 13c values 22 to 24 were agreed well with those of modern terrestrial c3 plants in addition we estimated 14c reservoir ages of macrophyte remains from changes in their 13c values the major climate boundary layers in the cores transitions to bolling allerod 14 5 0 5 cal ka bp younger dryas 12 8 0 1 cal ka bp and preboreal 11 6 cal ka bp were confirmed by our new 14c chronology the transition to the bolling allerod warm phase from the last glacial 14 5 0 5 cal ka bp coincided with an obvious lithologic boundary a rapid decrease in the abundance of the macrophyte remains in the lake pumoyum co sediment cores

chemical and isotopic o h c composition of surface waters in the catchment of lake donggi cona nw china and implications for paleoenvironmental reconstructions abstract the oxygen hydrogen and carbon isotope ratios and major and trace element concentrations of surface waters are reported for the catchment of lake donggi cona qinghai province china the chemistry of the surface waters in the southeastern catchment is reflecting the dissolution of carbonate rocks whereas thermal waters add sodium and chlorine to the waters in the northern catchment the dongqu river draining the southeast catchment contributes 87 to 94 to the water budget of the lake thermal waters and waters from the northern catchment add 6 to 13 the combination of hydrogen and oxygen isotopes provides evidence that only small amounts of recycled lake water contribute to the precipitation in the catchment most of the moisture may be transported by the east asian summer monsoon or an eastern branch of the south asian monsoon into the donggi cona region from oxygen isotope ratios it is calculated that about 45 of the lake water input is evaporated and 55 leaves the lake through a channeled outflow the carbon isotope ratios identifies microbial respiration of organic matter probably in soils and sediments of the catchment as the major source of dissolved inorganic carbon in most surface waters and the lake an isotope effect from biological processes in the lake is minor and can be neglected in order to explain isotope ratios of inorganic carbon in lake water the results imply that oxygen isotope ratios in the lake sediment archives mainly mirror the relation between precipitation and evaporation p e which may be controlled by changes in the global water cycle like monsoon intensity or by tectonically driven local changes affecting the outflow flux a comparison between lake archives based on ostracod shells and the modern system indicates similar 18o values for the lake water since 4 3 ka but different 13cdic values this discrepancy between carbon isotope ratios in ostracod shells and modern lake water samples may be due to thermal waters with high 13cdic emerging near the coring site it is suggested that carbon isotopes of ostracods from a sediment drill core reflect the activity of a local thermal spring at the lake bottom whereas oxygen isotopes provide evidence for an open lake system since about 11 ka and that the climate and environment of the donggi cona region changed very little over the last 4300 years

modern hydrology and late holocene history of lake karakul eastern pamirs tajikistan a reconnaissance study abstract lake karakul in the pamirs tajikistan is a deep brackish water lake in a closed basin at almost 4000 m above sea level water samples from the catchment area and lake karakul and a 104 cm sediment core from its shallow eastern sub basin were investigated and provide a first lake record from the region spanning the last 4200 cal yr bp multi proxy analyses revealed the following a relatively high meltwater inflow from glaciers snow fields and frozen ground in the catchment as a result of relatively warm conditions was reconstructed for the period between 4200 and 3500 cal yr bp the shift to colder climatic conditions around 3500 cal yr bp was probably abrupt total organic carbon values displayed the most dramatic drop for the entire core within less than 40 years in contrast the subsequent re establishment of warmer conditions occurred gradually over several centuries a higher meltwater supply to the lake and warmer conditions were recorded since ca 1900 cal yr bp with two slightly colder intervals between 1200 and 800 cal yr bp and between 400 and 100 cal yr bp the abrupt shift to significantly colder and drier conditions around 3500 cal yr bp in the eastern pamirs is seen also in records from the aral sea and the guliya ice core from the western tibetan plateau however more palaeoclimate studies in this highly continental part of central asia are needed to assess the spatial and temporal patterns of the holocene climate in the region

holocene variations in the asian monsoon inferred from the geochemistry of lake sediments in central tibet we present a record of monsoon variations for the early and middle holocene that is inferred from the geochemistry of sediment cores from ahung co a lake in central tibet the resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal which eliminates errors associated with the lake hard water effect we made down core geochemical measurements of carbonate organic carbon c n and 13c of bulk organic matter 13c and 18o of carbonate and dolomite proxy calibration and modern water balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation we find that lake level and monsoon precipitation have been decreasing at ahung co since the early holocene 7500 cal yr b p superimposed on this trend are rapid declines in monsoon rainfall at 7000 7500 and 4700 cal yr b p and seven century scale wet dry oscillations the cores do not contain sediment from the last 4000 yr surface sediments from the lake accumulated during the 20th century however from this we argue that lake levels have risen again recently following a late holocene dry period

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

multi decadal periods of enhanced aeolian activity on the north eastern tibet plateau during the last 2ka abstract the north eastern tibetan plateau is regarded as key area for the understanding of the holocene paleoclimate in central asia during the last decade a special emphasis has been placed on multi decadal to millennial scale climate fluctuations especially in the context of the recent climate change however most reconstructions are based on lake sediments tree rings and speleothems whereas only little information from terrestrial archives is included this study presents multi decadal scale climate fluctuations based on optical stimulated luminescence osl ages from aeolian sediments from three catchment areas six phases of enhanced aeolian accumulation during the last 2000 years each lasting around 80 200 years were identified the first three phases 1630 1725 ce 1450 1530 ce and 1250 1350 ce occurred during the little ice age the other three 750 950 ce 390 540 ce 50 225 ce during the so called dark ages cooling aeolian processes were strongly reduced during the medieval climate anomaly a comparison with other proxy records indicates that the formation of aeolian archives on the north eastern tibetan plateau during the late holocene is facilitated by cool and dry climate conditions during times of weaker asian summer monsoon and probably enhanced westerlies the results show that short term climate fluctuations can be reconstructed from non continuous and heterogeneous terrestrial archives in a semi arid environment provided a sufficient number of osl ages from aeolian sediments is available

mineralogy and geochemistry of the holocene lacustrine sediments in nam co tibet abstract the carbonates clays and major chemical compositions of lacustrine sediments in nam co lake were examined by x ray diffraction scanning electron microscopy and chemical analysis carbonates include monohydrocalcite mhc first report from china and in a high altitude lake low mg calcite and traces of dolomite mhc in nam co is developed in water 1 8 g l with high mg ca molar ratios 10 03 15 03 high ph 8 04 9 72 and the presence of bacteria algae diatom and ostracoda illite and mg chlorite provide a strong evidence for physical weathering in the holocene most ca and sr in sediments originate from carbonates as the molar ratios of ca and co32 are all less than 1 and the curve of sr is very similar to that of ca however most of the mg fe and rb are from clays the lake water shifted from a fresh water environment to an evaporative alkaline environment by 2 06 cal ka bp there was a depositional event that the depositional rate changed from 0 134 to 1 639 mm a at about 2 cal ka bp

organic matter geochemical signatures of sediments of lake ngoring qinghai tibetan plateau a record of environmental and climatic changes in the source area of the yellow river for the last 1500 years abstract the climate history of the source area of the yellow river sayr is important to understanding the pacing and processes of climate evolution on the northeastern qinghai tibetan plateau qtp to date results of research in this alpine region are limited herein we provide a first lacustrine record from the largest freshwater lake on the qtp that archives climatic and environmental variations in the sayr for the last 1500 yr the bulk organic carbon and nitrogen isotopic compositions 13corg and 15ntot are combined with atomic carbon nitrogen c n ratios to indicate that the sedimentary organic matter in lake ngoring originates from autochthonous algae and that the terrestrial input is minor comparison of the record of organic carbon isotope values with published records of ice accumulation rate iar of dunde and guliya glaciers from the northern qtp the total solar irradiance tsi 18o variations in the greenland ice core and biologically sensitive indicators c37 4 alkenone crenarchaeol and bgdgt concentrations from lake qinghai indicate that variations in the 13corg values in lake ngoring sediments reflect lake level fluctuations that are associated with variations in the amount of precipitation and glacier meltwater on the sayr high lake level phases indicated by positive shifts of 13corg values correspond to higher values of the north atlantic oscillation index naoi and lower values of the southern oscillation index soipr this relation suggests that the hydrologic history in the sayr is linked to changes in the indian monsoon and the westerlies and that both air masses delivered more moisture to the sayr during high tsi stages in contrast variations in the 15ntot values resemble the multiple paleoclimate proxy records obtained from ice cores peat sequences lake sediments and integrated paleo records from other qtp sites suggesting that the 15ntot values archived in lake ngoring sediments provide a history of past lake water temperature variations that is consistent with the variation history of the temperature dependent parameters from regional paleo climatic studies global climatic events including the dark ages cold period the medieval climate anomaly the little ice age and modern warming in 20th century could be clearly observed in the 15ntot variations in general the 13corg and 15ntot values in lake ngoring sediments appear to be useful indicators for paleo environment and paleo climate reconstructions in alpine oligotrophic freshwater lakes such as this one

spectral attenuation of track line noise satellite airborne and marine geophysical surveys usually sample features better along track than across track in maps this aliasing together with errors in along track data processing produce a systematic washboard effect across the survey lines known as track line noise in regions covered by two line surveys at different azimuths the combined data generate maps with this noise orthogonal to both survey azimuths statistical efforts to minimize random noise will only be partially effective in attenuating systematic track line noise we present a method that exploits the spectral differences resulting from the different survey azimuths to reduce this systematic noise in each survey only two of the spectral quadrants are normally contaminated combining the four least contaminated quadrants from both surveys generates a map of minimal track line noise this method is used to improve the recovery of geoid undulations from satellite altimetry of the barents sea in the arctic

late glacial and holocene development of lake donggi cona north eastern tibetan plateau inferred from sedimentological analysis abstract sediments of lake donggi cona on the northeastern tibetan plateau were studied to infer changes in the lacustrine depositional environment related to climatic and non climatic changes during the last 19 kyr the lake today fills a 30 8 km big and 95 m deep tectonic basin associated with the kunlun fault the study was conducted on a sediment core transect through the lake basin in order to gain a complete picture of spatio temporal environmental change the recovered sediments are partly finely laminated and are composed of calcareous muds with variable amounts of carbonate micrite organic matter detrital silt and clay on the basis of sedimentological geochemical and mineralogical data up to five lithological units lu can be distinguished that document distinct stages in the development of the lake system the onset of the lowermost lu with lacustrine muds above basal sands indicates that lake level was at least 39 m below the present level and started to rise after 19 ka possibly in response to regional deglaciation at this time the lacustrine environment was characterized by detrital sediment influx and the deposition of siliciclastic sediment in two sediment cores upward grain size coarsening documents a lake level fall after 13 cal ka bp possibly associated with the late glacial younger dryas stadial from 11 5 to 4 3 cal ka bp grain size fining in sediment cores from the profundal coring sites and the onset of lacustrine deposition at a litoral core site 2 m water depth in a recent marginal bay of donggi cona document lake level rise during the early to mid holocene to at least modern level in addition high biological productivity and pronounced precipitation of carbonate micrites are consistent with warm and moist climate conditions related to an enhanced influence of summer monsoon at 4 3 cal ka bp the lake system shifted from an aragonite to a calcite dominated system indicating a change towards a fully open hydrological lake system the younger clay rich sediments are moreover non laminated and lack any diagenetic sulphides pointing to fully ventilated conditions and the prevailing absence of lake stratification this turning point in lake history could imply either a threshold response to insolation forced climate cooling or a response to a non climatic trigger such as an erosional event or a tectonic pulse that induced a strong earthquake which is difficult to decide from our data base

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

reconstructing human landscape interactions in the ancient mediterranean harbour of cartagena spain here we sought to reconstruct the pleistocene and holocene evolution of cartagena bay therefore 16 borehole cores were analysed with the following aims 1 to define a chronological framework 2 to obtain data on the palaeoenvironment and 3 to establish the relationship with human activities especially focused on the reconstruction of the carthago nova also known as qart hadasht conquest a total of 147 samples were recovered for amino acid racemisation aar dating 32 for radiocarbon dating 14c and 159 for sedimentological palaeontological and biomarker determination these approaches allowed us to elucidate the evolutionary phases of the palaeolandscape in cartagena the simultaneous use of aar and 14c dating allowed the discrimination of spurious ages and the establishment of a chronological scale during the marine isotope stages mis 7 and 5 the sea level sl in cartagena bay was almost the same as today an alluvial plain developed in the northern area and a delta was formed by

reconstructed late quaternary hydrological changes from lake tso moriri nw himalaya abstract we present the results of our investigations on the radiocarbon dated core sediments from the lake tso moriri nw himalaya aimed at reconstructing palaeohydrological changes in this climatically sensitive region based on the detailed geochemical mineralogical and sedimentological analysis we recognise several short term fluctuations superimposed upon seven major palaeohydrological stages identified in this lake since 26 cal ka stage i 20 2 cal ka shallow lake characterised by input of coarse grained detrital sediments stage ii 20 2 16 4 cal ka lake deepening and intensification of this trend ca 18 cal ka stage iii 16 4 11 2 cal ka rising lake levels with a short term wet phase 13 1 11 7 cal ka stage iv 11 2 8 5 cal ka early holocene hydrological maxima and highest lake levels inferred to have resulted from early holocene indian monsoon intensification as records from central asia indicate weaker westerlies during this interval stage v 8 5 5 5 cal ka mid holocene climate deterioration stage vi 5 5 2 7 cal ka progressive lowering of lake level stage vii 2 7 0 cal ka onset of modern conditions the reconstructed hydrological variability in lake tso moriri is governed by temperature changes meltwater inflow and monsoon precipitation increased runoff a regional comparison shows considerable differences with other palaeorecords from peninsular india during late holocene

spatial variability of 14c reservoir effects in tibetan plateau lakes abstract radiocarbon dating of lake sediments is often hampered by the presence of a lake reservoir effect lre also dead carbon or old carbon effect especially in dry and cold regions with a sparse plant cover in the catchment the tibetan plateau became a hotspot of the palaeoenvironmental and climate research community in recent years and the assessment of present day lres is a crucial prerequisite for the establishment of reliable radiocarbon age depth relationships for lake sediment cores this paper examines the spatial variability of lres within individual lakes through a discussion of new data for lake donggi cona and a compilation of previously published data for five additional lakes where lre data are available for different sites lake reservoir effects for lake donggi cona on the northeastern tibetan plateau were determined for shells of aquatic snails collected alive close to the lake s shore the largest determined lre of 20 000 14 c years is significantly larger than previously reported lres from the central part of the lake and larger than any previously published lre for the tibetan plateau relatively low lres in the central regions of lakes higher lres towards the margins and high lres in tributaries and spring waters are apparently a common pattern of tibetan plateau lakes the differences in lres within individual lakes or catchment areas are attributed to the more prolonged exchange of the lake water s dissolved inorganic carbon with the atmospheric co 2 in central lake regions on the one hand and the increasing influence of 14 c free or poor stream and groundwater due to the dissolution of carbonaceous basement rocks towards its margins generally higher lres were recorded in the three tectonically active lake regions of the six examined catchments and it is speculated that rising crustal co 2 further contributes to the lres in these catchments in addition to these observations and inferences elevated 14 c levels of the atmosphere as a result of nuclear bomb testing are often ignored if lres for modern materials are reported by convention relative to the atmospheric 14 c activity of the year 1950 lre data reported in this way represent unrealistic minimum estimates

paleolakes in the gobi region of southern mongolia abstract numerous lakes and remnants of paleolakes exist in western and southern mongolia for six basins in the area detailed geomorphological maps were compiled based on extensive field studies and remote sensing datasets several phases of high and low lake levels were reconstructed and dated by radiocarbon and optically stimulated luminescence during the marine isotope stage mis 6 lakes in southern and western mongolia mostly disappeared in contrast large paleolakes existed during the last interglacial mis 5e and lasted probably until the beginning of the last glacial these huge lakes were caused by a strong east asian summer monsoon which reached southern and even western mongolia during the mis 3 the monsoon was considerably weaker and most of the lakes were relatively small or even disappeared higher lake levels of this period were only recorded at the orog nuur however at this time the lake was fed by glacial melt water from the khangai mountains the mis 2 was again a very dry period the previously supposed phase of synchronous high lake levels and glaciations in southern and western mongolia is not supported by the data presented here during the holocene lakes in the western and southern part of the study area evolved differently early holocene high lake levels were reconstructed for the western lakes while most of the southern lakes had highest lake levels in the mid holocene these differences can be attributed to different moisture bearing atmospheric systems in the late holocene lake levels were generally low and in the last 50 years most lakes completely disappeared due to a strong human usage of the water resources

mid to late holocene paleoenvironmental changes inferred from organic geochemical proxies in lake tangra yumco central tibetan plateau investigations of the paleoclimate and paleoenvironmental changes in the tibetan plateau in recent years have led to many significant achievements however high resolution lake records from the mid to late holocene have not been determined for the central tibetan plateau which is in the transition zone between the indian summer monsoon ism system and the westerlies in this study we analyzed the distribution and compound specific carbon isotope compositions delta c 13 of sedimentary n alkanes and the bulk sediment total organic matter toc total nitrogen tn and c n ratios to reconstruct the paleoenvironmental changes over the past 6 cal ka bp using a 376 cm sediment core from the southern basin of tangra yumco central tibetan plateau our results indicated that clear stepwise decreases in lake productivity and lake level occurred during the mid to late holocene based on decreases in delta c 13 values of mid chain n alkanes and paq an n alkane based proxy additionally the variations in the toc tn and c n ratios revealed generally increased inputs of allochthonous organic matter over the past 6 cal ka bp when our findings at tangra yumco were compared with records from the central tibetan plateau and adjacent regions we found generally consistent patterns of lake environmental changes over the past 6 cal ka bp suggesting that the climate of the central tibetan plateau was primarily influenced by the ism system at the millennial time scale therefore our results depict the evolution of the ism over the past 6 cal ka bp in the central tibetan plateau which corresponds to summer solar insolation and the migrations of the intertropical convergence zone itcz we also propose that the climate of the north atlantics influenced the climate of the central tibetan plateau through some indirect climatic mechanisms

holocene lake level variations of longmu co western qinghai tibetan plateau longmu co is surrounded by conspicuous regressive shorelines attesting to high water levels in the past in this study we dated paleoshoreline sediments around the lake using optically stimulated luminescence osl infrared stimulated luminescence irsl and radiocarbon dating then explored the forces that drove holocene lake level variations we found that 1 osl irsl ages are consistent with geomorphic sequences and some extant cosmogenic and u th shoreline ages however inorganic evaporite crust 14c ages are much older than corresponding osl irsl ages due to varying lake reservoir effects and should be used with caution 2 the highest lake levels of longmu co 160 145 m above present lasted from 12 8 to 11 3 ka two periods of abrupt lake level declines occurred at 11 3 and 7 4 ka lake level dropped 44 and 45 m respectively with a gradual regression of 18 m between these two intervals the lake expanded moderately from 7 to 5 5 ka then declined once more after 5 5 ka with this regression accelerating during the last 1 5 ka 3 the deglacial lake level transgression was likely due to glacier melt waters the indian summer monsoon reached the longmu co watershed and brought precipitation during the early holocene middle to late holocene lake regression was caused by the retreat of the monsoon and consequent environmental deterioration

response of lake catchment processes to holocene climate variability evidences from the ne tibetan plateau abstract investigating the so called third pole environment tpe became a major concern during the last decades since it was recognized that the high altitude region of the tibetan plateau tp is a key area for the understanding of cause effect mechanisms driven by climate change and geodynamic processes studies on the hydro climatic evolution during the late quaternary were mainly carried out by single lake records or alternatively by individual terrestrial sites integrated source to sink studies considering lake catchment interactions were extremely seldom utilized we investigated such relationships in the kuhai basin on the north eastern tibetan plateau and analysed sedimentary processes based on 30 onshore sections and three sediment cores from different locations and water depth in the lake basin grain size variations ostracod assemblages geochemical proxies and absolute dating luminescence radiocarbon 210pb 137cs were applied as key indicators that reveal interacting sediment fluxes under different hydro climatic settings during the younger dryas interval and the holocene our results indicate that wind induced transportation processes and allocation of respective aeolian sands in the catchment are attributed to distinct phases of reduced effective moisture availability during summer time those phases corresponded to weak summer monsoon influence during the younger dryas interval the early holocene 11 6 7 5 ka dry cold interlude dci ca 4 5 3 0 ka dark ages cold period dacp ca 1 8 1 1 ka and the little ice age lia ca 0 6 0 1 ka contemporaneous low lake levels during these periods corresponded with respective aeolian sand flux and variable composition of mixed sediments fluvial and aeolian in lake deposits different flux rates at the core sites could be assigned to local conditions in respect to inflow behaviour of individual drainage systems and nearshore morphology aeolian deposits in the catchment were not always preserved and underwent re mobilisation during succeeding episodes and or erosion during phases of high water availability wetter climatic conditions during the mid holocene ca 7 5 5 1 ka roman warm period rwp ca 2 8 1 5 ka and medieval climate anomaly mca ca 0 9 0 6 ka revealed significant lake level rise due to enhanced river discharge well documented by highest suspended flux rates disappearance of ostracod communities at core sites and very low sand input climate shifts during the holocene were linked to variations in effective moisture supply under the influence of the asian summer monsoon asm and the interplay with the mid latitude westerlies mlw cold dry phases were likely a response to north atlantic climatic anomalies transmitted by the mlw across the tp