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

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

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

the distribution of apparent dose as determined by optically stimulated luminescence in small aliquots of fluvial quartz implications for dating young sediments abstract we noted recently murray et al 1995 that quartz samples taken from in channel fluvial deposits have apparent doses ranging over several orders of magnitude we suggested that these dose distributions are best explained by a mixture of a small number of poorly bleached grains and a larger number of well bleached grains in this paper we examine the distribution of apparent dose in small aliquots each composed of 2000 grains of different particle size fractions 63 90 m 90 125 m 125 180 m 180 212 m 212 250 m diameter from two samples collected from the murrumbidgee river new south wales australia the samples are of known burial age the first being 70 years old and the second being its modern equivalent 0 2 gy the difference in the lowest apparent dose in the two samples is considered to be the result of their different burial times we suggest a method for dating recently deposited

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

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

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

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

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

fluid drainage from the edge of a porous reservoir we report theoretical and experimental studies to describe buoyancy driven fluid drainage from a porous medium for configurations where the fluid drains from an edge we first study homogeneous porous systems to investigate the influence of heterogeneities we consider the case where the permeability varies transverse to the flow direction exemplified by a v shaped hele shaw cell finally we analyse a model where both the permeability and the porosity vary transverse to the flow direction in each case a self similar solution for the shape of these gravity currents is found and a power law behaviour in time is derived for the mass remaining in the system laboratory experiments are conducted in homogeneous and v shaped hele shaw cells and the measured profile shapes and the mass remaining in the cells agree well with our model predictions our study provides new insights into drainage processes such as may occur in a variety of natural and industrial activities including the geological storage of carbon dioxide

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

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

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

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

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