reduction in northward incursions of the south asian monsoon since 1400 ad inferred from a mt everest ice core 1 a highly resolved mt everest ice core reveals a decrease in marine and increase in continental air masses related to relatively high summer surface pressure over mongolia and reduction in northward incursions of the summer south asian monsoon since 1400 ad previously published proxy records from lower sites south of the himalayas indicate strengthening of the monsoon since this time these regional differences are consistent with a south north seesaw in convective activity in the asian monsoon region and reflect a southward shift in the mean summer position of the monsoon trough since 1400 ad the change in monsoonal circulation at 1400 ad is synchronous with a reduction in solar irradiance and the onset of the lia this demonstrates a hemispheric scale circulation reorganization at this time and the potential for future large shifts in monsoonal circulation

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

oxygen and carbon isotopes in modern fresh water ostracod valves assessing vital offsets and autecological effects of interest for palaeoclimate studies abstract the isotopic composition of modern benthic ostracod and mollusc carbonate the oxygen isotope composition of lake water 18ow the carbon isotope composition of dissolved inorganic carbon 13cdic and water temperatures were monitored during a year at different water depths in two lakes ammersee and starnberger see southern germany the aim was to test whether the valves are built in isotopic equilibrium and how seasonal water temperatures are recorded in the shells we find systematic offsets between 18o of valve carbonate compared to 18o expected for a theoretical calcite formed in isotopic equilibrium offsets are higher than 2 for different species of the candona group 1 5 for cytherissa lacustris and around 0 8 for limnocythere inopinata and darwinula stevensoni they seem to be constant for all instars of a species and temperature independent mean water temperatures of the calcification period are readily reflected in the valve 18o if corrected for the offsets 13c of valve carbonate is mainly controlled by 13c of the dissolved carbonate in ambient lake water but seems to be biased by micro habitat effects and vital offsets the study provides information on the seasonality of valve formation thus potentially allowing the quantification of temporal and spatial water temperature gradients from specific 18o records

precipitation at lake qinghai ne qinghai tibet plateau and its relation to asian summer monsoons on decadal interdecadal scales during the past 500 years knowledge of the variability of precipitation at lake qinghai and its relation to the asian summer monsoons is helpful in constraining global climatic dynamics based on the high resolution precipitation indicators of 13 c of the organic matter 13 corg c n atomic ratio and the detrended total organic carbon content tocdetrended we found that the trend of precipitation at lake qinghai is inversely correlated to that of the indian summer monsoon ism inferred from layer thickness of a stalagmite s3 in southern oman on decadal interdecadal scales the chinese drought flood d f indices which can indicate the dryness wetness over large geographic areas are also used to indicate the intensity of the monsoon rainfall the d f index of xining near lake qinghai is synchronous with those of the regions in northern china where the east asian summer monsoon easm dominates while it is anti phase with those of southwestern china where ism prevails these materials suggest that during the past 500 years the source of moisture to lake qinghai on decadal interdecadal scales is controlled mainly by the easm but not by the ism it is also suggested that the intensity of easm is inversely related to that of the ism on decadal interdecadal scales the decadal interdecadal variability of enso may be responsible for the inverse relationship between the intensity of easm and that of ism 2007 elsevier b v all rights reserved

tree ring evidence of little ice age glacier advances in southern tibet the history of late holocene glacier fluctuations in eastern tibet was studied by determining the ages of trees growing on glacier deposits maximum tree ages yield minimum ages of ad 1760 and 1780 for moraine formation at the maximum extent of the little ice age glacier advances in two glacier forefields subsequent moraines could be dated to the beginning of the nineteenth and the beginning of the twentieth century larch trees from a third glacier forefield in southeastern tibet show evidence of glacier activity from 1580 to 1590 from the end of the eighteenth to the beginning of the nineteenth century and from 1860 to 1880 one glacier at mt gyalaperi recently advanced in both 1951 and 1987 periods of glacier advances can partly be correlated with periods of growth reductions in chronologies of total ring width and maximum latewood density derived from trees growing on slopes above the glacier valleys correlation functions with meteorological data suggest that maximum latewood density of subalpin

the mediaeval warm period drought recorded in lake huguangyan tropical south china the geochemistry of dated sediment cores from lake huguangyan 21o9 n 110o17 e tropical south china reveals distinct stratigraphical patterns in total organic and inorganic carbon toc tic biogenic silica bs and total nitrogen tn over the past 1400 years in this hydrologically closed lake tic variations may reeect changes in the precipitation evaporation ratio which controls the evaporative enrichment of carbonate toc bs and tn in the sediment are proxy indicators of lake productivity and nutrient input which we believe are linked to local precipitation high tic content correlates with low concentrations of toc bs and tn and indicates two drought episodes dated to ad 670 760 and ad 880 1260 in the sediments of lake huguan gyan local historical chronicles support these data suggesting that the climate of tropical south china was dry during the mediaeval warm period mwp and wet during the little ice age lia the detected mwp drought is temporally correlated with evidence for lower precipitation on the guliya china and quelccaya peru ice caps and with increased salinity in moon lake us great plains

palaeo water depth estimation for a 600 year record from nam co tibet using an ostracod based transfer function a modern training set of ostracods from the large slightly saline lake nam co on the southeastern tibetan plateau is presented in total 44 samples covering the largest part of the lake and water depth from 2 to 93 m were taken there are eight ostracod species in surface sediments of nam co leucocytherella sinensis leucocythere dorsotuberosa fabaeformiscandona gyirongensis candona xizangensis candona candida ilyocypris cf mongolica eucypris gyirongensis and limnocythere inopinata in order of mean dominance a morphological variant of l dorsotuberosa the forma postilirata is an indicator form of deep water below the thermocline the 36 samples comprise a sufficient number of ostracods for analysis covering water depths between 3 7 and 89 3 m two transfer function models based on weighted average binomial regression wa br and weighted average partial least square regression wa pls using the programs excel and c2 were established to estimate past water depths of nam co transfer functions were applied to ostracod data from two short cores from nam co covering approximately the past 600 years model results show a lake level minimum occurring during the little ice age lia between about 1490 and 1760 ad this minimum corresponds to results from previous stable isotope analysis and indicates a lake level which was about 5 m below the present day level the more exact transfer function model wa pls was set up using c2 and revealed a higher correlation index r o f 0 91 and a lower standard error of 6 7 m however the more selective because of using indicator taxa only wa br model using excel r 0 88 standard error 10 6 m seems to represent palaeo water depths better at least for the studied short cores

a general cooling trend on the central tibetan plateau throughout the holocene recorded by the lake zigetang pollen spectra abstract a 741 cm long laminated sediment core covering the last 10 800 years was collected from lake zigetang central tibetan plateau 90 9 e 32 0 n 4560 m a s l and analysed palynologically at 69 horizons biome reconstruction suggests a dominance of temperate steppe vegetation mainly artemisia and poaceae on the central tibetan plateau during the first half of the holocene 10 8 4 4 cal ka bp while alpine steppes with desert elements mainly cyperaceae poaceae chenopodiaceae and characteristic high alpine herb families tend to dominate the second half 4 4 0 cal ka bp the artemisia cyperaceae ratio a semi quantitative measure for summer temperature indicates a general cooling trend throughout the holocene dense temperate steppe vegetation and maximum desert plant withdrawal however indicate that a suitable balance of wet and warm conditions for optimum vegetation growth likely occurred during the middle holocene 7 3 4 4 cal ka bp severe early holocene cold events have been reconstructed for 8 7 8 3 and 7 4 cal ka bp

ostracod distribution and habitat relationships in the kunlun mountains northern tibetan plateau abstract surface sediment samples were collected from the lakes heihai kusai haiding nuur and yan hu and from streams and ponds in the kunlun mountains at the northern margin of the tibetan plateau to investigate the sub fossil ostracod micro crustacean fauna of the region among 65 collected samples 46 ostracod shell rich samples were used to study the relationship between the ostracod distribution and specific conductivity sc of the water which ranged from 0 6 to 53 0 ms cm 1 a total of eleven ostracod species was identified from this region with about half of the species restricted to the tibetan plateau and its adjacent mountain areas and the other half representing holarctic taxa tonnacypris cf estonica and tonnacypris tonnensis are reported from the tibetan plateau for the first time leucocythere sp is the dominant species and ilyocypris cf bradyi is also relatively abundant the other seven species were recorded with limited abundances apparently due to lower sc tolerances leucocythere sp was recorded over the full sc range from 0 6 to 53 ms cm 1 eucypris mareotica is a typical brackish and saline water species which was found at sample sites with high sc 2 8 53 0 ms cm 1 in contrast leucocythere dorsotuberosa candona candida and eucypris afghanistanensis prefer freshwater to slightly oligohaline waters with sc 1 the sc optimum and tolerance range for each species were determined and compared to earlier reported data from other regions of central asia the results indicate that species assemblage data from fossil ostracod shells have a large potential to provide information on past sc levels and more general climate determined moisture conditions

carbon and oxygen isotope variations among lacustrine ostracods implications for palaeoclimatic studies large ranges of 13c 12c and 18o 16o ratios are found among modem ostracods from lakes in jamaica and mexico if their calcite carapaces grew in isotopic equilibrium with the lake water then the main period of carapace formation was probably in the cooler and or wetter months differences in 13c and 18 o values between ostracods from different sites relate to spatial variations in the composition of the lake water and differences between species at the same site probably reflect differences in organic photosynthesis or decay among the micro habitats occupied by the species there nevertheless remain significant variations in both 13c and 18o among modern valves of the same species at the same site a consequence of the temporal and spatial variation in lake water and the fact that ostracods form their carapace over a short period individual valves from a 1 cm section of a sediment core show that the isotopic effects of changes in the rainfall versus evaporation status of a lake over a period of c

the holocene salinity history of bosten lake xinjiang china inferred from ostracod species assemblages and shell chemistry possible palaeoclimatic implications abstract a sediment core from bosten lake the largest freshwater lake in the tianshan mountains and in the northwesternmost province of china provided a high resolution record of environmental change covering the last 8500 cal a bp higher salinity levels of bosten lake were reconstructed from assemblages the stable isotope composition and sr ca and mg ca ratios of ostracod shells between 7800 and 5600 cal a bp a period of low and moderate salinities between 5600 and 4900 cal a bp was followed by the re establishment of higher salinities between 4900 and 4300 cal a bp since then bosten lake has recorded fluctuating conditions with a number of multi centennial phases of low and moderate salinities although the salinity lake level relationship of bosten lake is not fully understood a higher salinity at the core site seems to correspond to periods of higher lake levels this contradictory interpretation is explained tentatively by the changing distance of the core site to the freshwater providing river mouth with changing lake levels and potentially resulting lateral shifts of the salinity distribution pattern within the lake assuming this explanation is correct the record from bosten lake reflects higher moisture availability and a strong climatic influence of the indian monsoon in the early mid holocene until about 4000 cal a bp and more unstable drier conditions susceptible to minor changes in the regional circulation patterns and temperature variations afterwards

holocene environments from stable isotope stratigraphy of ostracods and authigenic carbonate in chilean altiplano lakes abstract sediment cores from three shallow 4000 m a s l paleoclimatic profiles show coherency within tropical subtropical circulation patterns climatic signals however are partially masked by local environmental systems results suggest similar arid mid holocene to less arid late holocene trends in the three lakes although each lake shows distinct response characteristics linked to differences in regional moisture balance isotopic signatures for each lake group in discrete 18o vs 13c populations high isotopic variability results from episodic flooding and brine evolution in the shallow lakes laguna seca 18 11 s 69 14 w 4500 m a s l is characterized by a diverse ostracod assemblage of at least 8 species indicating highest moisture levels among the three sites high 13c values are the result of continuous evasion of co2 derived from volcanically charged groundwaters and springs plus the formation of travertine and photosynthetic activity in the lake a 3 decrease in 18o about 4 7 m suggests an abrupt shift to wetter conditions at the transition from mid to late holocene lagunas miscanti 23 44 s 67 46 w 4140 m a s l and del negro francisco 27 28 s 69 14 w 4125 m a s l each contain only one ostracod species limnocythere sappaensis attesting to higher salinities although sediment facies and ostracod continuity and abundances imply a history of higher effective moisture at laguna del negro francisco sediment cores from each lake document more arid conditions in the lower sections with a sharp shift to wetter conditions in the upper sections highly variable isotope values at the transition from mid to late holocene suggest rapid short term climate shifts during this transition this overall trend can be correlated from laguna seca laguna miscanti and laguna del negro francisco to lago titicaca implying climatic coherency along the altiplano isotopic profiles show second order fluctuations and drought events that suggest short term variability along the transect in order to explain differences in the effective moisture among the three sites we postulate interactions of regional air masses in the north convective tropical precipitation dominates laguna seca as for lakes in the titicaca region effective moisture for lagunas del negro francisco and miscanti follows a south to north gradient generated by cold air masses from cut offs of pacific westerlies colliding with moist tropical air masses coherent shifts in the past therefore imply changes in available tropical air mass moisture

interplay between redox conditions and hydrological changes in sediments from lake nam co tibetan plateau during the past 4000 cal bp inferred from geochemical and micropaleontological analyses abstract this study focuses on the analysis of lake sediments retrieved from the deepest part of lake nam co tibetan plateau one gravity core of 115 cm length covering the last 4000 cal bp was analyzed for geochemical and biological parameters high organic content at 4000 cal bp and the coinciding presence of pyrite framboids until 2000 cal bp point to hampered decomposition of organic material due to anoxic conditions within the lake sediments at the same time sedimentological and biological proxies suggest a rather high lake level but still 5 m below the recent one with less saline lake water due to enhanced monsoonal activity during this time a change in the source of organic matter to lowered input of terrestrial components is observed a rather quick shift to a dry environment with less monsoonal influence and a lake level 15 m lower than today at 2000 cal bp lead to the oxygenation of sediment the degradation of organic matter and the absence of pyrite oscillations of the lake level thereafter were of minor amplitude and not able to establish anoxia at the lake bottom again a wet spell between 1500 cal bp and 1150 cal bp is visible in proxies referring to catchment hydrology and the ostracod based water depth transfer function gives only a slightly elevated lake level the last 300 years are characterized by low toc and rising tn values reflecting enhanced nutrient supply and hence an advancing influence of human activity in the catchment decreasing toc tn values point to a complete shift to almost solely aquatic biomass production these results show that hydrological variations in terms of lake level change based on monsoonal strength can be linked to redox conditions at the lake bottom of nam co comparison with other archives over larger parts of the tibetan plateau and beyond exhibits a rather homogeneous climatic pattern throughout the late holocene

the little ice age recorded by sediment chemistry in lake erhai southwest china on the basis of concentrations of 21 major and minor elements in a well dated sediment core from the deepwater part of lake erhai principal component analysis pca reveals three main factors cont

millennial scale holocene climate variability in the nw china drylands and links to the tropical pacific and the north atlantic abstract a loess paleosol sequence and a lake sediment record from the central hexi corridor in the drylands of nw china show patterns of persistent millennial to centennial scale climate variability during the holocene epoch which can be well correlated with abrupt climatic events reported from the north atlantic and the asian monsoon dominated regimes our results show that the drylands in nw china might have been regulated both by the westerlies and by the east asian summer monsoon easm in a roughly synchronous manner it seems that cold dry intervals in the central hexi corridor may generally correspond to cooling phases in high latitudes of the northern hemisphere and that cold warm wet intervals largely correlate with relatively warm phases in northern high latitudes a candidate mechanism involving nao ao and enso dynamics is tentatively proposed to account for this synchroneity climatic patterns may be spatially different in the nw china drylands in response to the changing predominant control of either the westerlies or the easm depending on the contrast of their relative strengths glacier meltwater discharges associated with alpine warming may be partly responsible at least for the two records discussed in this paper for such spatial heterogeneity of climatic changes during the holocene more work is needed to evaluate the individual roles and combined impacts of the easm the westerlies and alpine glacier meltwater regulation on the nw china dryland dynamics

speleothem evidence for changes in indian summer monsoon precipitation over the last 2300 years speleothems from a well ventilated dolomitic cave in the pokhara valley central nepal preserve a mineralogic record of indian summer monsoon variability over the past 2300 yr annually deposited aragonite layers formed between 2300 and 1500 yr b p indicating reduced monsoon precipitation and increased cave aridity whereas alternating calcite aragonite laminae deposited after 1500 yr b p record elevated summer monsoon precipitation and increased cave humidity dense optically clear calcite layers deposited from 450 5 to 360 20 yr b p 1550 to 1640 a d indicate a less evaporative cave environment and suggest moister and or cooler conditions possibly related to climatic change associated with the onset of the little ice age

a 2540 year record of moisture variations derived from lacustrine sediment sasikul lake on the pamir plateau although the pamir plateau is an ideal place to investigate paleo environmental changes in the westerlies dominated high central asia there are only few holocene records from this region we present a sub centennially resolved lacustrine record of moisture variations from sasikul lake central pamir plateau based on geochemical sedimentological and mineralogical proxies our results show that generally dry conditions at sasikul lake during the past 2540 years were interrupted by a pronounced wet period between ad 1550 and 1900 corresponding to the little ice age lia more negative values of carbonate 18o lower total inorganic carbon tic and sand content during the lia all indicate a relatively wet period with higher lake level higher tic during the medieval warm period mwp ad 950 1200 reveals a lower lake level relative to the lia low 18o during this time is probably attributed to changes in the isotopic composition of input water and or upstream moisture sources the significant incr

stable isotope and ostracode species assemblage evidence for lake level changes of nam co southern tibet during the past 600 years abstract ostracode species assemblages and stable oxygen and carbon isotopes of shells from two 210 pb dated short cores of 78 cm and 47 cm length taken from lake nam co southern tibet provide information about lake level history of the past approximately 600 years at decadal resolution a transfer function is applied to reconstruct paleo water depths from modern ostracodes ostracode assemblages and isotope data from five species allow a subdivision into phases of lake level evolution before 1600 ad relatively low oxygen isotope values and high abundances of deep water 30 m ostracodes i e leucocythere dorsotuberosa leucocythere dorsotuberosa f postilirata suggest a lake level 10 m higher than today between 1600 ad and 1800 ad more positive oxygen isotope values and higher abundances of shallow water ostracodes i e ilyocypris cf mongolica candona xizangensis suggest a lake level approximately 40 m below modern level between 1800 ad and 1920 ad oxygen isotopes are characterized by a trend to more negative values followed by a trend to more positive ones these trends are interrupted by several short term fluctuations but overall oxygen isotope values suggest a drop in lake level a clearer lake level picture is provided by species assemblages that suggest a continuously increasing lake level since 1900 ad precipitation data from meteorological stations nearby show an increase in precipitation in the last 30 years the low lake level between 1600 ad and 1800 ad is contemporary to the little ice age during that cold period meltwater input into the lake decreased this underlines the sensitivity of the level of lake nam co to temperature changes on the tibetan plateau

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

trace element variability in single ostracod valves as a proxy for hydrochemical change in nam co central tibet during the holocene ostracod shells belonging to three taxa leucocytherella sinensis huang 1982 leucocythere dorsotuberosa huang 1982 and l dorsotuberosa f postilirata sensu pang 1985 were collected from two sediment cores from lake nam co on the central tibetan plateau two variants of la icp ms laser ablation inductively coupled plasma mass spectrometry spot and line scan analyses were used to investigate trace element concentrations mg sr ba u and rare earth elements rees in single ostracod shells the results suggest that the line scan method can provide better precision than the spot analysis and is therefore preferred no significant difference in trace element composition between taxa was detected in our study fluctuations of mg ca and sr ca in the shells show good agreement with the reported lake level changes during the holocene indicating that ostracod mg and sr can be related to palaeohydrochemical processes in this area a high correlation between ba ca and sr ca was detected in our study perhaps implying that both metals were controlled by the same mechanisms a possible relationship between ostracod u ca and the past redox conditions on the lake bottom is discussed relatively low and constant la ca was observed which could be due to the ree characteristics in the lake water or ostracod biological processes or even the associated fe mn and or organic contaminants future studies on more specimens from this area especially shells from living ostracods are essential to investigate the potential of ostracod ba u and rees for use as palaeoenvironmental indicators

isotopic composition of dissolved inorganic carbon in a large polluted river the vistula poland abstract the vistula is a large lowland temperate river receiving high loads of pollutants from a densely populated catchment on the other hand the river is to a relatively small extent affected by channelisation and damming this study is the first attempt to characterise stable isotope aspects of dissolved inorganic carbon in the vistula which is a major source of pollution to the baltic sea isotopic composition of dic and other chemical properties were measured biweekly at the upper reach and monthly at the mouth of the river two longitudinal samplings were performed in hydrological summer and winter conditions short term and short range observations were carried out in an anthropogenically influenced urban reach at cracow most water samples from the vistula and its tributaries analysed in this study had 13 c dic values around the range 12 to 11 typical for european lowland rivers fed by groundwaters on carbonate areas variablity of 13 c dic in this river system is limited except for the impoundments and the specific hydrological conditions the few impoundments that exist on the vistula intensify the photosynthesis respiration cycle as well as the exchange of co 2 with the atmosphere enhanced contribution of biogenic carbon during floods is reflected by lowering of 13 c dic low flows facilitate photosynthetic assimilation and evasion of co 2 into the atmosphere resulting in positive shifts of 13 c dic principal component analysis confirmed that 13 c dic variability at the fixed cross section in cracow reflected releases and withdrawals of co 2 from the riverine dic pool the apparent 13 c dic variability depends to some extent on the spatio temporal context of observations diurnality can be very pronounced in the impounded anthropogenically influenced reaches in warm periods interpretation of the observed riverine 13 c dic patterns can be difficult as the spatial and temporal variabilities combine resulting in convoluted isotopic signals isotopic investigations into the nature of riverine carbon cycling should be supplemented by discharge records and by observations of the parameters influenced by the photosynthesis respiration cycle dissolved oxygen ph p co 2 and of those conservative with respect to biological processes electrical conductivity stable isotope composition of water

spring hydroclimate reconstruction on the south central tibetan plateau inferred from juniperus pingii var wilsonii shrub rings since 1605

twentieth century climatic warming in china in the context of the holocene development of an annual mean temperature series of china for the period of ad 1880 1998 indicated that 1998 was thie wanrest year since 1880 during 1998 temperature was 1 38c higher than the normal 1961 90 annual mean temperatures of china were found using a weighted average of 10 regional series whliich covei ed the xvhole lanid ai ea of the coutliry fromii xinjiang and tibet ii the west to tailwan i the ecast gaps in temperatture obseivations were filled by using ice core i 0 and tie iing data for thice regions in the west and docuimenitary data for scven regions in the east since 1 951 only obser x ational data were usecl fiftyyear mean teiimperatture anomnalies were calculated trom the ninth to trwentietlh cernturies the series do not show any conisistenit warm peiliod in west china durinig the mediaeval warmii period ad 900 to 1300 but temiperatures in east china in at 850 1099 anid 1200 99 were abouit 0 2c higher than the average for recent years centurv mean ternperatures combin

climatic variation in the linxia basin ne tibetan plateau from 13 1 to 4 3 ma the stable isotope record the 13 c and 18 o values of carbonates and 13 corg values c and c n ratios of organic matter from lacustrine and fluvial sediments were measured from two stratigraphic sections in the linxia basin on the northeastern margin of the tibetan plateau diagenesis when present is early limited to small spatial scales and restricted stratigraphic intervals a strong correlation exists between dolomite content and the 18 o values of micritic carbonate suggesting that carbonates are primary precipitates from lake water and that 18 o values reflect changes in the lake environment with more positive values derived from evaporated and more saline lake water the first part of this record is characterized by strong oscillations between dry and wet conditions accompanied by changes in the lake system between hydrographically closed and open states 13 1 8 0 ma the most severe aridity occurred from 9 6 to 8 5 ma after 8 0 ma a more stable and less arid climate dominated the region and the drainage system was open 8 0 5 3 ma after 5 3 ma climate became gradually drier and or cooler 5 3 4 3 ma the organic matter preserved in the linxia basin is most likely a mixture of terrestrial c3 plant matter and lake algae a correlation between c n and 13 corg indicates that a significant percentage of the organic matter is derived from terrestrial sources the organic matter has undergone selective degradation during which the c n ratios and organic carbon percentage decreased the 13 corg values are relatively stable throughout the 13 1 to 4 3 ma interval ranging from 24 to 29 vpdb suggesting that c4

holocene east asian monsoon variation inferred from species assemblage and shell chemistry of the ostracodes from hulun lake inner mongolia a sediment core from hulun lake inner mongolia was analyzed for species assemblages and shell chemistry of ostracodes to investigate changes in the hydrology and climate of the east asian summer monsoon margin during the holocene darwinula stevensoni was abundant ilyocypris spp scarce littoral ostracodes absent and mg ca sr ca and 18o were low 11 100 to 8300 yr ago indicating high lake levels and cool fresh waters darwinula stevensoni declined largely ilyocypris spp throve littoral ostracodes were rare and chemical indicators remained in low values 8300 to 6200 yr ago suggesting that the lake continued high stands but water became warm the lake then contracted and water became cool brackish 6200 to 4300 yr ago littoral ostracodes flourished 4300 to 3350 yr ago marking the lowest lake levels of the entire holocene the lake level recovered and water salinity decreased 3350 to 1900 yr ago from 1900 to 500 yr ago the lake maintained the preceding status albeit lowered stands and increased salinities 1100 to 800 yr ago during the recent 500 yr the lake expanded and water salinity decreased the data imply that the east asian summer monsoon did not intensify until 8300 yr ago and weakened dramatically 4300 to 3350 yr ago

prehistoric maritime migration in the pacific islands an hypothesis of enso forcing long distance human migration across the pacific ocean occurred during the late holocene and originated almost entirely in the west as prevailing tradewinds blow from the east the mechanisms of p

the holocene paleolimnology of lake issyk kul kyrgyzstan trace element and stable isotope composition of ostracodes the stable isotope and trace element geochemistry of ostracode shells from lake issyk kul kyrgyzstan provide an important new paleoclimate record for central asia the n 18 o n 13 c sr ca mg ca and u ca composition of shells from the species candona neglecta found in two piston cores constrains the paleohydrology of the lake from 8700 to 1000 calendar yr before present these data combined with robust chronologies based on 16 ams 14 c dates suggest that the region went from a relatively moist climate in the early holocene to a more arid climate in the late holocene intense freshwater input presumably glacial runoff flowed into the lake from 8700 to 8300 cal yr bp as evident from the n 18 o and n 13 c values from 8300 to 6900 cal yr bp n 18 o and sr ca values indicate that the lake was relatively fresh and an open basin and u ca values suggest that the lake was well mixed with well oxygenated bottom waters there is a transition zone between 6900 and 4900 cal yr bp when n 18 o and sr ca values rapidly increase and mg ca and u ca values rapidly decrease during this period the lake evolved from an open freshwater well mixed lake to a closed more saline less well mixed lake for the remainder of the record n 18 o sr ca mg ca and u ca are relatively constant implying conditions similar to modern conditions although the slight increasing trend in sr ca may suggest an increase in salinity over this period the n 13 c values were approximately in equilibrium with atmospheric co2 in the early part of the record but became relatively negative in the later part of the record this indicates that the dominant mechanism controlling the isotopic composition of dissolved inorganic carbon shifted from exchange with the atmosphere to variations in biological productivity fl 2001 elsevier science b v all rights reserved

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

palynological evidence for holocene environmental change in the changjiang yangtze river delta china abstract holocene vegetation changes in response to climate fluctuations and human impacts are reviewed on the basis of pollen analyses from borehole cores taken from the changjiang yangtze river delta china and other previously reported data during the earliest holocene 10 930 9000 cal yr bp the climate was warm and wet allowing thermophilous hardwoods to occupy mid and low elevations surrounding a palaeo changjiang estuary the climate became gradually cooler and cool tolerant conifers grasses and ferns became dominant until 7600 cal yr bp when the estuary became a delta a mid holocene climatic optimum occurred between 7600 and 4800 cal yr bp when evergreen and broadleaved deciduous trees flourished at mid and low elevations surrounding the delta front prodelta after this time climate became cooler again until 1340 cal yr bp during this period evergreen and broadleaved deciduous trees were replaced by conifers and grasses inhabiting the inter subtidal flat delta front this development of conifer grassland vegetation was shortly interrupted between 3860 and 3200 cal yr bp when thermophilous tree cover increased and open vegetation with scattered conifers was reduced since 1340 cal yr bp the vegetation has been similar to that at present under warm wet conditions human impacts are recognized by the first appearance of fagopyrum and a sudden increase in herb pollen at 4500 and 1340 cal yr bp respectively

distribution and formation of monohydrocalcite from surface sediments in nam co lake tibet abstract carbonate minerals oxygen and carbon isotopes and mg ca from surface sediments and soils were examined in nam co lake central tibet this paper provides information of the irregular distribution and formation of monohydrocalcite a metastable mineral carbonates of soils surrounding nam co lake consist of calcite with minor dolomite carbonates in surface sediments in nam co lake consist mainly of calcite and monohydrocalcite all of the monohydrocalcite and most of the calcite in surface sediments are authigenic the monohydrocalcite is distributed irregularly in nam co lake because of inhomogeneous features of lake water the variable micro environment high precipitation rate and or nucleation mg ions could play a greater role in the precipitation of monohydrocalcite than that of phosphate ions because the amount of phosphate ions could be much lower than mg ions in the 4781 m altitude altiplano lake with poor nutrients the presence of monohydrocalcite occurs at 2 1 ka bp corresponding with the sharp increase of precipitation rate from 0 134 mm y to 1 639 mm y high precipitation rate and or nucleation is necessary for water molecule infiltration into the crystal lattice of monohydrocalcite the 18 o v pdb and 13 c v pdb of carbonate minerals mixed with calcite and monohydrocalcite range from 5 3 to 8 0 with an average of 6 5 and from 2 8 to 4 5 with an average of 3 73 respectively 18 o v pdb and 13 c v pdb of calcite range from 8 0 to 10 6 with an average of 8 09 and from 2 8 to 4 2 with an average of 3 25 respectively monohydrocalcite possibly has more positive values of 18 o and 13 c than those of calcite

pipe soil interaction model for current induced pipeline instability on a sloping sandy seabed as offshore exploitation moves to deeper waters ocean currents become the prevailing hydrodynamic loads on pipelines and at the same time a sloping seabed is always encountered the prediction of lateral soil resistance is vital in evaluating pipeline on bottom stability unlike previous pipe soil interaction models used mainly for horizontal seabed conditions a pipe soil interaction model for current induced downslope and upslope instabilities is proposed by using the limit equilibrium approach the coulomb s theory of passive earth pressure for the sloping seabed is incorporated in the derivation the model verification with existing full scale tests shows good agreement between the experimental results and predicted ones parametric study indicates that the effect of slope angle on pipeline lateral soil resistance is significant in the examined range of slope angle from 15 to 15 the critical pipeline embedment and corresponding passive pressure decrease approximately linearly with increasing slo

water depth related ostracod distribution in lake pumoyum co southern tibetan plateau abstract a modern training set covering 55 surface sediment samples from pumoyum co a freshwater lake on the southern tibetan plateau was analysed in order to quantify relationships between ostracod species distribution and environmental conditions the extensive data set referring to nine ostracod species includes physico chemical parameters for water depths ranging between 1 m and 62 m canonical correspondence analysis suggests that water depth significantly controls the spatial distribution of modern ostracods in the lake on this basis an ostracod based water depth transfer function was established for reconstructing palaeo lake levels the transfer function presents a good correlation between measured and estimated water depth r2 0 87 with a root mean square error of prediction of 15 5 m this transfer function was applied to fossil ostracod associations of 38 sediment samples from a gravity core which covers the last 6 ka bp three stages of lake level fluctuations since 6 ka bp were inferred a low lake level 25 m compared to the present 65 m depth between 6 0 ka bp and 4 3 ka bp a fluctuating lake level 25 to 5 m from 4 3 to 2 0 ka bp and a rise from a low level 25 m to that of present day within the last two millennia together with other proxies including ostracod diversity and grain size as well as total organic carbon and total inorganic carbon content of the gravity core sediments the water depth transfer function was used to reconstruct past climate change in the pumoyum co area as a response to indian monsoon dynamics

ostracod shell chemistry as proxy for paleoenvironmental change abstract the application of ostracod shell chemistry as a paleoenvironmental tool has grown within the past decades most studies have investigated mg and sr in ostracod shells as proxies for temperature and salinity and the use of a wide range of trace elements as prospective paleoenvironmental indicators has yet to be developed for lacustrine systems only a few preliminary studies have used trace metals in paleolimnological studies such as cd ba and zn as paleonutrient indicators or mn fe and u as redox and oxygenation indicators this paper reviews the state of the art of geochemical analyses in microfossils such as ostracods foraminifera and corals and provides insights in new trace element proxies with the goal to promote the use of trace elements in ostracod shells as paleoenvironmental proxies in paleoceanography foraminifera and corals are most prominently used to reconstruct past climate conditions well established proxies such as 18o mg ca and sr ca provide information about changes in sea surface temperatures in addition a great number of new proxies have been developed recently such as radiogenic isotopes and redox sensitive trace elements in paleolimnology ostracod shell chemistry is widely used to assess paleohydrological changes reconstruction of temperature and salinity changes in lake environments is often achieved by oxygen isotopes as well as mg ca and sr ca ratios but depending on the hydrological and geological settings of the lake system local calibrations are needed to assess which proxy is suited to reflect which processes new proxies need to be tested by novel techniques that recently have become available compared to conventional instrumentation used in ostracod shell chemistry methods such as laser ablation icp ms and nanosims allow single shell analysis and provide high resolution data the potential of ostracods in paleolimnology is not yet fully assessed but can be developed by learning from paleoceanographic studies

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

zr rb ratio in the chinese loess sequences and its implication for changes in the east asian winter monsoon strength abstract the long term dust accumulation sequences on the chinese loess plateau clp provide a valuable opportunity to study the evolution of east asian winter monsoon strength grain size of bulk samples of loess deposits though widely used is a modified measure of the strength of winter monsoon wind due to modification by post depositional weathering and pedogenesis this study proposes a new and reliable geochemical climate proxy that records the variability of the east asian winter monsoon on the clp six loess paleosol sections on the plateau were selected for measuring concentrations of the trace elements zr and rb as well as grain size variations of the zr rb ratio in all the sections encompassing the last 130 ka display a generally similar pattern to that of mean grain size of bulk samples mgsb though a positive correlation exists between the zr rb ratio and mgsb the correlation coefficient decreases in southern and eastern sections where intense pedogenesis occurred in the relatively warm and humid climates long term zr rb variation in the lingtai section exhibits amplitudes and frequencies similar to those in mgsb and the mean grain size of quartz particles mgsq accepted as a more reliable proxy than mgsb in the upper loess paleosol sequence over the past 2 6 ma however for the underlying red clay formation in the interval from about 7 2 6 ma b p the mgsb record is relatively stable whereas both the zr rb ratio and mgsq show distinct variability and display amplitudes similar to those observed in the overlying loess paleosol sequence these results demonstrate that the zr rb ratio reflects original eolian grain size and may serve as a reliable index of the strength of east asian winter monsoon winds

chemical evolution of groundwater in the river danube deposits in the southern part of the pannonian basin hungary processes controlling the groundwater chemical composition were studied in the river danube deposits in the southeastern part of hungary phreeqm a combined geochemical and one dimensional transport model and phreeqe netpath and wateqf geochemical computer codes were used to simulate these processes the main processes controlling water chemistry are equilibrium with calcite undersaturation in dolomite and albite weathering in the recharge area ion exchange along the flow path and ion exchange and mixing with old water at the end of the flow path ion exchange seems to be the most important process controlling groundwater chemistry along the flowpath in the fluvial sediments studied isotopic data support the geochemical model the groundwater ages adjusted for the modeled c mass transfer range from 3300 to 20 200 a b p cation exchange suggests that displacement of a former aqueous solution by the present groundwater occurred this displacement is attributed to tectonic and paleoclimatic events at the end of the pleistocene

an account of the techniques using ostracodes in palaeolimnology in australia abstract ostracodes are common in australian waters especially in saline lakes where they are particularly diverse this makes them indispensable tools for australian palaeolimnological studies especially since many australian lakes are saline the following types of subjective information can be obtained from the study of australian fossil ostracode faunas without knowledge of the ecology or taxonomy of their living representatives the search for a life assemblage can lead to detection of the presence of water currents and the effects of reworking in addition to the identification of particular facies such as a lake shoreline or a desiccation phase rate of sedimentation can be estimated as well as the amount of sediment compaction of drying information on water oxygenation and acidification can be obtained and finally presence of seasonality affecting lakes can be identified with additional reference to the ecology of particular species permanency of lake water can be assessed and so can the variability of rainfall and even at times the detection of whether a lake was close to a summer winter rainfall boundary shell ornamentation can inform on water depth in addition salinity data can be obtained as well as some information on water chemistry and temperature the latter from trace elements mg sr and stable isotope 18 o studies of ostracode shells

holocene climatic and environmental changes in the arid and semi arid areas of china a review this paper reviews recently published literature most of which was published in chinese and searches for regional patterns of holocene changes useful in depicting global patterns the holocene in the xinjiang region can be divided into three stages a warming and dry early stage from 11 similar to 10 to 8 similar to 7 ka bp a warm and wet middle stage from 8 similar to 7 to 4 5 similar to 3 ka bp and a fluctuating cool and dry late stage since 4 5 similar to 3 ka bp the holocene in the northern tibetan plateau can also be divided into three stages a warming and wet stage from 10 5 similar to 10 to 5 similar to 4 ka bp followed by a variable drying and probably warm stage 5 similar to 4 to 3 ka bp and ending with a cool and dry stage since 3 ka bp in the inner mongolian plateau the early holocene from 10 5 similar to 9 5 to 8 similar to 7 5 ka bp was warming and dry and a warm and wet climate occurred from 7 5 to 3 5 during which the best time was 6 3 3 8 ka bp the climate has been variably drying and probably cooling since 3 5 ka bp in the northwestern part of the loess plateau several holocene palaeosols have been identified 10 9 7 5 5 4 3 and 2 7 2 ka bp with the 7 5 5 ka bp palaeosol being most strongly expressed the best developed palaeosol equivalent in major valleys is a swamp wetland facies deposited between 8885 and 3805 c 14 yr bp under an extremely wet regime the climate has fluctuated significantly at least three times around a dry and probably cool regime after the swamp wetland facies depositional period our summary shows that the holocene climatic optimum occurred nearly contemporaneously 8 5 ka bp at all sites in the xinjiang region in the inner mongolian plateau and in the northwestern part of the loess plateau a warming and wet early holocene 10 8 ka bp in the northern tibetan plateau is most likely related to high effective soil moisture resulting from snow and ice melting we propose here that the middle holocene climatic optimum 8 5 ka bp in arid to semi arid china was primarily a delayed response of the low latitude oceans to high latitude peak insolation 9 8 ka bp

ostracod calcite records the 18 o 16 o ratio of the bicarbonate and carbonate ions in water abstract the 18 o of ostracod valves is widely used to infer water 18 o and temperature however ostracod 18 o appears sensitive to other environmental variables in addition there is species dependent ostracod calcite 18 o enrichment relative to slowly precipitated inorganic calcite under the same conditions together these uncertainties complicate ostracod paleoclimate reconstructions this study presents a new understanding of the causes of ostracod 18 o variations based on a global database of published ostracod 18 o values in lake marine and coastal environments and from culture experiments the database includes associated field experiment host water parameters including temperature 1 to 32 c water 18 o 13 2 to 4 3 vsmow ph 6 9 10 4 salinity 0 72 g kg calcite saturation states 0 6 26 and dissolved inorganic carbon concentration dic 0 9 54 3 mmol kg the data show that 1 the 18 o of marine and non marine ostracods reflects the 18 o 16 o of the sum of host water co 3 2 and hco 3 ions for example at a given temperature the 18 o of non marine ostracods decreases by 4 to 6 as co 3 2 dic reaches 70 depending on the ostracod species in low co 3 2 dic settings i e high hco 3 co 3 2 ostracod 18 o 16 o is close to the 18 o 16 o of hco 3 ions which explains why on average ostracod 18 o is higher than the 18 o of inorganic calcite precipitated slowly under the same conditions 2 taxonomic offsets in ostracod 18 o vary with the host water co 3 2 dic in environments where hco 3 co 3 2 i e most freshwater lakes the 18 o 16 o of candonids is indistinguishable from the 18 o 16 o of hco 3 ions difference of 0 10 0 16 while the 18 o 16 o of cyprids is lower than the 18 o 16 o of hco 3 ions by 0 77 to 0 32 cytherids by 0 88 0 29 and limnocytherids by 1 12 0 05 3 the sensitivity of ostracod 18 o to co 3 2 dic also varies with taxonomy for each percent increase in co 3 2 dic candonids 18 o decreases by 0 098 0 024 cyprids by 0 075 0 004 cytherids by 0 057 0 012 and limnocytherids by 0 058 0 005 4 the similarity in 18 o 16 o between ostracod calcite and the sum of host water hco 3 and co 3 2 despite species specific offsets suggests rapid precipitation of a finite dic pool in the ostracod calcifying fluid we propose an ostracod 18 o model whereby the more negative the 18 o 16 o of a given species relative to the sum of co 3 2 and hco 3 the greater the isotopic equilibrium between the dic pool and h 2 o in the ostracod calcifying fluid 5 higher host water salinities and ph induce higher co 3 2 dic resulting in lower ostracod 18 o which explains the variable salinity and ph effects on ostracod 18 o our database and ostracod 18 o model shows that ostracod 18 o records from closed basin environments likely reflect high or variable co 3 2 dic rather than water temperature and 18 o alone our study reconciles contradictory observations of controls on ostracod 18 o and paves the way for improved paleo environmental interpretations and reconstructions of past water co 3 2 dic

late holocene temperature fluctuations on the tibetan plateau abstract proxy data of palaeoclimate like ice cores tree rings and lake sediments document aspects of climate changes on the tibetan plateau during the last 2000 years the results show that the tibetan plateau experienced climatic episodes such as the warm intervals during ad 800 1100 and 1150 1400 the little ice age between ad 1400 and 1900 and an earlier cold period between the 4th and 6th centuries in addition temperatures varied from region to region across the plateau a warm period from ad 800 to 1100 in the northeastern tibetan plateau was contemporaneous with cooling in the southern tibetan plateau which experienced warming between ad 1150 and 1400 large scale trends in the temperature history from the northeastern tibetan plateau resemble those in eastern china more than the trends from the southern plateau the most notable similarities between the temperature variations of the tibetan plateau and eastern china are cold phases during ad 1100 1150 1500 1550 1650 1700 and 1800 1850

late quaternary transition from lacustrine to a fluvio lacustrine environment in the north western nam co tibetan plateau china abstract holocene sediments from a 9 m high outcrop at the gangyasang qu s entry into lake nam co on the south eastern tibetan plateau were studied in a multiproxy approach the lowermost part of the section is of early holocene age and consists of varved sediments deposited in a proglacial lake geomorphological investigations of fossil beach ridges and fossil cliff lines in the littoral zone of nam co indicate a late pleistocene lake level high of 29 m above the present level a warming is visible in ostracode rich silts deposited after 9 6 ka bp an ostracode based transfer function estimates a lake level 28 m higher than today from this time until about 5 2 ka bp a late pleistocene lake level high was accompanied by an increase in lake size causing nam co to overflow into the lower course of gangyasang qu where a bay with slack water conditions formed between 4 2 and 1 3 ka bp the lake level was approximately 10 m higher than today the progradation of the gangyasang qu delta into nam co and the decreasing lake level shifted the study site into a fluvio lacustrine environment the sandy character and relatively low numbers of ostracode valves in the topmost sediments indicate increased fluvial activity possibly due to a temporary increase in flood frequency this facies lasted at least until 1 3 ka bp when the lake level of nam co dropped again and the river incised more than 10 m into the underlying fluvio lacustrine and lacustrine sediments

paleoclimatic implications of an 850 year oxygen isotope record from the northern tibetan plateau oxygen isotope records from the sediments of hydrologically closed lakes are commonly interpreted in terms of changing effective precipitation we compare an 850 year long oxygen isotope record derived from ostracode carbonate from the sediments of sugan lake in the northern tibetan plateau with tree ring and ice core evidence for changing temperature precipitation and isotopic composition of the lake s inflow taking into account all of these independent records we show that variations in the carbonate delta o 18 values could not have been the result of varying effective precipitation alone changes in water temperature and in the delta o 18 of source waters also played a significant role where independent records of temperature precipitation or the isotopic composition of input waters are unavailable care should be taken to avoid simplistic interpretations of carbonate stable isotope records as these may contribute to incorrect paleoclimatic reconstructions

climatic signals in the chinese loess record for the last glacial the influence of northern high latitudes and the tropical pacific the high resolution shagou loess section near the northwest limit of the east asian summer monsoon northwest china was analyzed the timescale of this section was set up based on a grain size age model and age controls the record of the shagou section shows that the millennial scale oscillations are superimposed on an orbital scale trend which can be correlated with the variations found in greenland and the sulu sea differences in the corresponding dansgaard oeschger cycles between the records in greenland and the chinese loess sections including the orbital scale trend the timing and the amplitude suggest that the climatic signals in chinese loess might not be singularly regulated by the north atlantic the differences in trend and amplitude can be reasonably explained when compared with the sulu sea record this suggests that the western tropical pacific also exerted an important influence on climatic signals found in the chinese loess record possibly countering the impact of high latitude factors during the last glacial

microhabitat preferences and stable carbon isotopes of endobenthic foraminifera clue to quantitative reconstruction of oceanic new production seventeen surface sediment samples from the north atlantic ocean off ne greenland between 76 and 81 n and nine samples from the south atlantic ocean close to bouvet island between 48 and 55 s were taken with the aid of a multiple corer and investigated for their live rose bengal stained benthic foraminiferal content within the upper 15 cm of sediment preferentially endobenthic melonis barleeanum m zaandami and bulimina aculeata as well as preferentially epibenthic lobatula lobatula were counted from 1 cm thick sediment slices each and analyzed for stable carbon and oxygen isotopic compositions of their calcareous tests live and dead specimens were counted and measured separately the carbon isotopic composition of the foraminifera was compared to that of the dissolved inorganic carbon dic of simultaneously sampled bottom water during a period of one month one station off ne greenland was replicately sampled once every week and samples were processed as above live specimens of lobatula lobatula are confined to the uppermost two centimeters of sediment live specimens of melonis spp are found down to eight centimeters within the sediment but with a distinct sub surface maximum between two and five centimeters the down core distribution of live bulimina aculeata shows a distinct surface maximum in the top centimeter and constant but low numbers down to 11 cm subbottom depth the average stable carbon isotopic composition d13c per mil vpdb of live l lobatula off ne greenland is by 0 4 0 1 per mil higher than the d13cdic of the ambient bottom water at the time of sampling there is evidence that this species calcify before the ice free season when bottom water d13cdic is supposed to be higher this would reconfirm the one to one relationship between d13c of ambient water dic and cibicids widely used by paleoceanographers live m barleeanum show a negative offset from bottom water dic of 1 7 0 6 per mil in the uppermost sediment and of 2 2 0 5 per mil in three to four centimeters subbottom depth all d13c values of live melonis spp decrease within the upper four centimeters regardless of the time of sampling and site investigated the offset of live b aculeata from bottom water d13cdic values of eight stations rather constantly amounts 0 6 0 1 per mil no matter what subbottom depth the specimens are from at one station however where is strong indication of elevated organic carbon flux the negative offset averaged over all sub bottom depths increases to 1 5 0 2 per mil buliminids actively move within the sediment and by this either record an average isotope signal of the pore water or the signal of one specific calcification depth the recorded signal however depends on the organic carbon flux and reflects general but site specific pore water d13cdic values if compared with epibenthic d13c values from the same site not influenced by pore water and related phytodetritus layer effects bulimina d13c values bear some potential as a paleoproductivity proxy specimens of melonis spp seem to prefer a more static way of life and calcify at different but individually fix depths within the sediment although live specimens thus record a stratified pore water d13c signal there is no means yet to correct for bioturbational and early diagenetic effects in fossil faunas