applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

the source and paleoclimatic implication of hydrogen isotopic composition of n alkanes in sediments from the yixian formation western liaoning province ne china abstract hydrogen isotopic composition of n alkanes was measured in sediments from an excavated profile of the early cretaceous yixian formation in liaoning province ne china aiming to assess the significance of the d value of n alkanes in ancient lacustrine sediments as the indicator for determining the source inputs of organic matters and paleoclimatic conditions the d values of n alkanes are in the range of 250 to 85 and display an obvious three stage variation pattern through the profile which is consistent with the distribution of the dominated n alkanes and the profile of their 13 c values the d and 13 c values of n alkanes suggest that short chain n alkanes are primarily derived from photosynthetic bacteria and algae n c 29 and n c 31 are mainly originated from terrestrial higher plants n c 28 and n c 30 may be derived from the same precursor but via the different biological mechanism of hydrogen isotopic fractionation while the source inputs of medium chain n alkanes are more complicated with n c 23 being derived from some specific algae or biosynthesized by various aquatic organisms the paleoclimatic conditions are reconstructed via two approaches the reconstructed hydrogen isotopic values of lake water and meteoric water expressed as d lw and d mw respectively were at the intervals of 51 8 to 17 0 and 118 1 to 43 5 respectively indicating a general climate transition from semi arid to arid the calculated d lw mw values vary from 37 0 to 89 1 and display a similar but a significant large scale variation trend with the d c 23 long 28 8 to 85 0 long represents long chain n alkanes and d mid long 15 4 to 43 4 mid represents medium chain n alkanes values the discrepancy may be attributed to the source input overlap for n alkanes and the uncertainties of e water lipid values the coupling of d c 23 long d mid long and d lw mw values with the paleoclimatic evidence indicates that the d values of n alkanes could be more sensitive to the change of paleoclimatic conditions

reconstruction of past precipitation δ18o using tree ring cellulose δ18o and δ13c a calibration study near lac d annecy france abstract two sets of living oaks quercus r growing under different hydrological situations were sampled near lac d annecy france the stable isotope composition of the latewood cellulose was analysed in terms of oxygen and carbon isotopic composition for the period 1971 2001 and compared to the nearby monthly meteorological temperature relative humidity and isotopic composition of precipitation records a linear regression shows that 60 of the cellulose oxygen isotopic composition inter annual variations are due to changes in precipitation isotopic composition and relative humidity the small slope between cellulose versus precipitation oxygen isotopic composition suggests a significant contribution of local continental recycling and questions the common assumption that vapour oxygen isotopic composition is at equilibrium with precipitation isotopic composition in europe during the growing season finally the combined use of tree ring oxygen and carbon isotopic composition records enables to account for leaf water enrichment due to stomata stress and to provide a reconstruction r 2 0 64 of the summer precipitation isotopic composition

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

empirical relationship between leaf wax n alkane δd and altitude in the wuyi shennongjia and tianshan mountains china implications for paleoaltimetry article i nfo estimating past elevation not only provides evidence for vertical movements of the earth s lithosphere but also increases our understanding of interactions between tectonics relief and climate in geological history development of biomarker hydrogen isotope based paleoaltimetry techniques that can be applied to a wide range of sample types is therefore of continuing importance here we present leaf wax derived n alkane d dwax values along three soil altitudinal transects at different latitudes in the wuyi shennongjia and tianshan mountains in china to investigate dwax gradients and the apparent fractionation between leaf wax and precipitation ewax p we findthatsoil dwax trackaltitudinal variationsof precipitation d along the three transects that span variable environment conditions and vertical vegetation spectra an empirical dwax altitude relation is therefore established in which the average dwax lapse rate of 2 27 0 38 100 m is suitable for predicting relative paleoelevation change relative uplift the application of this empirical gradient is restricted to phases in the mountain uplift stage whenthe atmospheric circulation had not distinctly changed and to when the climate was notarid anempirical dwax latitude altitudeformulaisalsocalculated dwax 3 483lat 0 0227alt 261 5 which gives the preliminary spatial distribution pattern of dwax in modern china meanvalue of ewax p intheextreme humid wuyimountainsisquite negative 154 compared to the humid shennongjia 129 and the arid but with abundant summer precipitation tianshan mountains 130 which suggests aridity or water availability in the growing season is the primary factor controlling soil sediment ewax p along the tianshan transects values of ewax p are speculated to be constant with altitude while along the wuyi and shennongjia transects ewax p are also constant at the low mid altitudes but become slightly more negative at high altitudes which could be attributed to overestimates of precipitation d or the vegetation shift to grass conifer additionally a reversal of altitude effect in the vertical variation of dwax was found in the alpine zone of the tianshan mountains which might be caused by atmospheric circulation change with altitude this implies that the paleo circulation pattern and its changes should alsobe evaluated whenstable isotope based paleoaltimetry is applied

soil n alkane δd and glycerol dialkyl glycerol tetraether gdgt distributions along an altitudinal transect from southwest china evaluating organic molecular proxies for paleoclimate and paleoelevation abstract organic molecular proxies provide a record of the hydrogen isotopic composition of ambient precipitation and paleoenvironmental temperature in terrestrial settings two classes of organic biomarkers are commonly utilized to reconstruct these past environmental conditions straight chained normal alkanes n alkanes and branched glycerol dialkyl glycerol tetraethers brgdgts we measured the dn alkane and the ratio of cyclisation and methylation indexes of branched tetraethers cbt mbt from surface soils along a 1000 km transect along the southeast margin of the tibetan plateau to assess how these proxies record changes in climate parameters that are related to elevation despite variations in ecosystem abundance weighted dnc27 31 data record the d of precipitation across the orogen and indicate minimal change in apparent fractionation en alkane water 133 with elevation n alkane d mirrors the pattern of rayleigh distillation of an air mass undergoing rainout as moisture moves from the bay of bengal into the se margin of the tibetan plateau soil tetraether temperatures provide a reliable measure of modern temperature with an mbt cbt calculated temperature lapse rate 5 8 c km close to the moist adiabat these data reflect ground level conditions that are independent of the shape of the orogen or the source of moisture in combination with a rayleigh distillation model that incorporates temperature and precipitation isotope data paired tetraether temperature and leaf wax isotope data produce a reliable record of changes in environmental conditions associated with modern elevation change across the largest orogen however some tetraether calibrations may impart systematic temperature bias most notably in cold or dry climates these calibration uncertainties can result in underestimates of paleoelevations by up to 1 5 2 km paired isotopic and temperature paleoelevation reconstructions can minimize errors associated with an individual proxy method however we recommend that application of tetraether temperature paleoelevation reconstruction take potential calibration biases into account in paleoelevation estimates

sources and occurrence of c12c22n alkane distributions with even carbon number preference in sedimentary environments abstract the occurrence of c12 c22n alkanes with a strong even carbon number preference is reported in recent and miocene sediments encompassing marine and freshwater systems deposited under oxic and anoxic conditions it is therefore shown that these n alkanes can be found in a wider type of sedimentary environment than those previously described the occurrence in some cases of a parallel distribution of c14 c20n alk 1 enes is also illustrated a variety of biological sources including both marine and freshwater bacteria as well as fungi and yeast species is suggested to account for such distributions

palaeoenvironmental changes in the padul basin granada spain over the last 1 ma based on the biomarker content the n alkane components of sediments were measured in 530 samples taken from a 107 m long core in the padul basin andalusia spain covering from the lower pleistocene ca 1 ma to the mid holocene ca 4 5 ka b p we show that the relative percentages of the high molecular weight n alkanes c27 c29 and c31 are useful tools to reconstruct the ancient vegetation and palaeoclimatological evolution of this basin on the basis of these proxies we distinguished twelve long term climatic periods linked to alternating dry humid scenarios 6 dry episodes alternating with 5 humid episodes were interpreted in the pleistocene record together with a final episode covering the holocene dry scenarios produced the recession of forests and the development of grasses whereas the inverse pattern was interpreted during humid phases the good correlation with the guadix baza basin record showed that in most cases dry periods coexisted with warm conditions while humid ones were linked to temperate colder conditions only during the last long term dry episode of the pleistocene which coincided with the end of the last glacial period did low temperatures concur the relative percentages of the high molecular weight n alkanes also indicate rapid changes in vegetation produced by short scale arid cycles during the last glacial period 100 ka b p which are linked to the heinrich events and younger dryas this interpretation has been confirmed by previous pollen analysis performed in the padul basin likewise a correlation was observed with marine isotope stages mis these results show that vegetation responds to long term cycles orbital scale and millennial scale global cycles therefore climatic variations in the padul basin responded to global climatic changes although with local climatic effects good correspondence was also observed with elemental isotopic and other molecular organic proxies thereby amplifying the palaeoclimatological knowledge of the padul basin during the pleistocene especially in some spans that were previously unclear

calibration of modern sedimentary δ2h plant wax water relationships in greenland lakes abstract sedimentary plant wax distributions and isotopic compositions are powerful widely applied paleoenvironmental proxies however there is conflicting evidence on the behavior of these proxies at high latitude sites where extreme climate and light conditions may uniquely influence plant physiology and growth here we present modern sedimentary n alkane and n alkanoic acid abundances and compound specific 2h and 13c isotope values from a 22 lake transect extending from northwest to southernmost greenland covering a large latitudinal and climatic gradient sedimentary plant waxes are similar in abundance and carbon isotopic composition across the transect suggesting no major differences in biologic sources there are strong correlations r 0 8 0 9 between 2h values of many long chain sedimentary waxes and those of modelled precipitation with n alkanes more tightly correlated to precipitation than n alkanoic acids data presented here also demonstrate that 2h values of mid chain sedimentary waxes do not strongly correlate to the 2h values of lake water when it decouples isotopically from precipitation i e in glacier fed and evaporatively enriched lakes this calls into question the common interpretation that mid chain sedimentary waxes can be ascribed to aquatic plants we contextualize our greenland data with an updated global dataset of 2h values of modern sedimentary waxes and precipitation this update adds 100 lakes from recently published literature to the seminal review presented by sachse et al 2012 this large new compilation suggests a global average apparent fractionation including arctic data between n c28 alkanoic acids and annual precipitation ec28 ann of 99 and between n c29 alkanes and annual precipitation ec29 ann of 121 the latter value is remarkably consistent with the value first reported by sachse et al 2012

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

hydrogen isotopic ratios of plant wax n alkanes in a peat bog deposited in northeast china during the last 16 kyr abstract based on paleoclimatic reconstructions using various proxies the holocene climate optimum 10 5 6 ka has been characterized as a warmer and wetter period in most of east asia the summer monsoons associated with the east asian monsoon evidently intensified and extended further inland from the pacific ocean a source region of moisture a notable exception to this general pattern exists in northeast china where less wet conditions are recorded we determined molecular compositions of individual plant wax hydrocarbons and their hydrogen isotope compositions d values in a radiocarbon dated peat core recovered from the hani marsh in jilin province china and confirmed that the temperature dependent effective precipitation in northeast china decreased during the holocene climate optimum a combination of p aq an indicator of the relative contribution of aquatic to terrestrial plants and the difference in d between low c 23 c 25 and c 27 and high molecular weight c 31 n alkanes in the hani peat bog indicates a dramatic change in vegetation from the deglaciation to the holocene no significant differences were observed between the d values of low and high molecular weight n alkanes with relatively high d values and low p aq during the early holocene indicating that all n alkanes were produced by evapotranspiration sensitive terrestrial plants during that time however lower d values of mid chain n alkanes c 23 c 25 and c 27 relative to the long chain n alkane c 31 together with higher p aq values during the deglaciation 14 11 ka suggest an increase in the contribution of aquatic plants and a higher water level during the period the study demonstrates that northeast china was under a markedly wetter climate condition during the late deglaciation for the 16 kyr record in the hani peat sequence we infer that moisture delivery by the east asian monsoon was relatively invariable in northeast china but increased evaporation during the warmer holocene climate optimum reduced the effective precipitation defined by the balance between precipitation and evaporation

biomarkers challenge early miocene loess and inferred asian desertification 1 fine grained miocene sediments from tianshui basin northeastern tibetan plateau have received intense attention recently because these sediments were identified as loess the presence of early miocene loess pushes the timing of initiation of inland asian desertification from 8 ma back to 22 ma however mudflat distal fan and shallow lake sediments of miocene have also been reported in tianshui basin consequently the origin of these fine grained miocene sediments in this area remains controversial here we investigate then alkane biomarker characteristics of neogene sediments from a north south transect of exposures within tianshui basin and compare these molecular distributions with those published quaternary loess to help resolve the disputed origin we found thatn c23 and n c25 alkanes sourced from either aquatic macrophytes or palustrine plants are ubiquitous in the miocene sediments from tianshui basin but are largely absent in quaternary loess this striking difference between n alkane distributions in the tianshui samples and the quaternary loess casts doubt on an eolian origin for the tianshui samples and challenges the hypothesis of an early miocene onset of asian interior desertification

molecular paleoclimatology reconstruction of climate variabilities in the late quaternary abstract lipid class compounds were studied in the deep sea surface sediments from the central pacific across a latitudinal transect at 175 e 48 n 15 s and a box core from the western tropical pacific to discuss their utility as paleoclimatological indicators higher concentrations of c25 c35 n alkanes were observed in the higher latitudes in the north pacific their latitudinal distributions are similar to the spatial distributions of the observed soil dust concentrations observed in the central north pacific atmosphere suggesting that the sedimentary c25 c35 n alkanes are atmospherically transported from terrestrial higher plants and can be used as an indicator of terrestrial input to ocean environments downcore distributions of total c25 c35 n alkanes suggest that terrestrial input doubled over the western tropical pacific at the lgm and decreased by a factor of two at the last deglaciation period in comparison with the holocene the latitudinal distributions of c17 c20 n alkanes and pristane are higher in the high latitudes and equatorial region probably reflecting the higher primary productivity in surface waters of these oceans the downcore profiles of these compounds as well as total organic carbon long chain alkenones and dinosterol suggest that biological production decreased significantly during the deglaciation period and slightly increased during the lgm compared with that of the holocene the downcore uk37 record suggests that the sst was almost constant over the last 20 000 y which agrees well with the climap results and foraminifera 18o although it disagrees with results from coral sr ca ratios and 18o records

middle to late holocene environmental changes in the depositional system of the tropical brackish bolgoda lake coastal southwest sri lanka abstract the tropical bolgoda lake is one of the largest lagoonal estuaries in sri lanka organic constituents in this lake were investigated using 28 surface sediments three cores from the lake and four short cores from mangrove mud elemental and molecular compositions of sediments and living organic matter om were determined using cns elemental analysis and gas chromatography mass spectrometry respectively chronology of events was determined using accelerated mass spectrometry ams 14 c data for bulk oms woods and mollusk shells the history of bolgoda lake can be divided into two major chrono stratigraphic divisions namely a lower sedimentary succession from ca 7 0 cal ky b p to 2 5 cal ky b p and an upper sedimentary succession from ca 2 5 cal ky b p to the recent according to the sapropelic depositional system concentrations of the mangrove biomarker taraxone increased significantly at ca 7 0 cal ky b p the lower part of the sediment sequence had moderate productivity and was mainly deposited under marine terrestrial influence in oxygen poor anoxic conditions during mid holocene sea level highstands a drastic increase in total organic carbon toc content reaching 29 was found in one of the bolgoda cores this increase occurred because of sea level regression at about 2 5 cal ky b p this change was probably caused by development of a beach rock sandbar and the estuary system changed to a semi closed lake due to the sea level regression as a result aquatic vascular plants predominate in this depositional system after ca 2 5 cal ky b p toc content decreased slightly but relatively high toc contents were maintained in the muddy sediments in moderately sized and shallow 1 2 m tropical estuaries lagoons such as bolgoda lake drastic changes in toc contents may be the most sensitive indicator of sea level variations increase in higher plant om with higher n c 29 n c all and n c 37 n c all alkane ratios also suggest a climatic transition from wetter to somewhat drier after the middle holocene accumulations of pyrogenic polycyclic aromatic hydrocarbons pahs in the modern sediments record anthropogenic activity after european settlement in the 15th century

paleoclimatic significance of δd and δ13c values in pinon pine needles from packrat middens spanning the last 40 000 years we compared two approaches to interpreting dd of cellulose nitrate in pinon pine needles pinus edulis preserved in packrat middens from central new mexico usa one approach was based on linear regression between modern dd values and climate parameters and the other on a deterministic isotope model modified from craig and gordon s terminal lake evaporation model that assumes steady state conditions and constant isotope effects one such effect the net biochemical fractionation factor was determined for a new species pinon pine regressions showed thatdd values in cellulose nitrate from annual cohorts of needles 1989 1996 were strongly correlated with growing season may august precipitation amount and d 13 c values in the same samples were correlated with june relative humidity the deterministic model reconstructed dd values of meteoric water used by plants after constraining relative humidity effects with d 13 c values growing season temperatures were estimated via modern correlations with dd values of meteoric water variations of this modeling approach have been applied to tree ring cellulose before but not to macrofossil cellulose and comparisons to empirical relationships have not been provided results from fossil pinon needles spanning the last40 000 years showed no significant trend in dd values of cellulose nitrate suggesting either no change in the amount of summer precipitation based on the transfer function or dd values of meteoric water or temperature based on the deterministic model however there were significant differences in d 13 c values and therefore relative humidity between pleistocene and holocene published by elsevier science b v

seismic slip and down dip strain rates in wadati benioff zones the rate of accumulation of seismic moment in wadati benioff zones is used to estimate strain rates in subducting slabs that are sinking through the asthenosphere between depths of 75 and 175 kilometers a typical down dip strain rate is about 10 15 per second which implies that slabs in this depth range typically accumulate strain of order 10 1 this result is in accord with geometrical arguments that subducted slabs must experience large membrane strains to deform to their observed shapes mantle seismicity repeated catastrophic shear failure is apparently a primary mechanism by which large membrane strains accumulate in the cold cores of subducting slabs slabs are penetratively deformed and they have low flexural rigidity compared to oceanic plates at the earth9s surface

the huguang maar lake a high resolution record of palaeoenvironmental and palaeoclimatic changes over the last 78 000 years from south china abstract a series of seven piston cores from the huguang maar lake situated near the south china sea coastline provides insight into regional palaeoenvironmental and palaeoclimatic changes in southern china over the last 78 000 years the data set comprises a high resolution record of magnetic susceptibility dry density and water content total organic carbon and inorganic carbon total nitrogen biogenic silica bsio2 and palynological results the time scale was developed by ams 14c dating of 17 terrestrial plant macro fossils during the last glacial the huguang record is characterised by an alternation of more temperate and humid periods from 78 to 58 and 48 to 40 5 ka bp and periods with predominance of grassland vegetation and possibly lowered lake level from 58 to 48 and ca 40 5 to 15 ka bp the huguang data have been compared to regional marine and terrestrial records in order to discuss variability of the south east asian monsoon system for most of the last glacial period the huguang proxies do not exhibit marked millennial scale variability as known from some long se asian and many north atlantic records this picture changes at about 15 cal ka bp when the huguang and greenland records appear to correlate well a short climatic reversal which is assumed to reflect a younger dryas type event is well recorded in the huguang record during the holocene the huguang multi proxy data show a much higher variability than during the last glacial stage probably reflecting at least for the early mid holocene fluctuations in monsoon activity however the last 4000 years of the sediment record are clearly influenced by enhanced human activity and thus difficult to interpret in terms of palaeoclimate change

climate variability in the past 19 000 yr in ne tibetan plateau inferred from biomarker and stable isotope records of lake donggi cona abstract we investigated 4 84 m long sediment record spanning over the late glacial and holocene from lake donggi cona to be able to reconstruct circulation pattern on the tibetan plateau tp presently lake donggi cona is located at the boundaries of westerlies and asian monsoon circulations in the northeastern tp however the exact timing and stimulating mechanisms for climatic changes and monsoon shifts in this region are still debated we used a 19 ka long stable isotope record of sedimentary n alkanes to address this discrepancy by providing insights into paleohydrological conditions the d of n c 23 is influenced by lake water evaporation the d values of sedimentary n c 29 are mainly controlled by moisture source and temperature changes long chain n alkanes dominate over the core whereas three mean clusters i e microbial aquatic and terrestrial can be inferred multi proxies suggest five major episodes in the history of lake donggi cona the lake donggi cona record indicates that the late glacial 18 4 14 8 cal ka bp was dominated by low productivity of mainly microbial and aquatic organisms relatively low d values suggest low temperatures and moist conditions eventually caused by stronger westerlies winter monsoon and melt water influence likely the shift 17 9 cal ka bp from microbial to enhanced aquatic input suggests either a change from deep to shallow water lake or a break in local stratification between 14 8 and 13 0 cal ka bp variable climatic conditions prevailed although the westerlies weekend the increase in temperature enhanced the permafrost and snow melting displayed by a high sedimentary accumulation rate higher d values indicate increasingly arid conditions with higher temperatures which eventually lead to high evaporative conditions and lowest lake levels low vegetation cover and high erosion rates led to high sediment accumulation resulting in stratification followed by anoxia in the terminal lake from 13 0 to 9 2 cal ka bp lowered values of d along with high contents of terrestrial organic matter marked the early holocene warming indicating a further strengthening of summer precipitation and higher lake levels a cooling trend was observed in the mid holocene between 9 2 and 3 0 cal ka bp accompanied by higher moisture availability displayed by lowered d values caused by reduced evaporative conditions due to a drop in temperature and recovering westerlies after 3 0 cal ka bp a decrease in lake productivity and cold and semi arid conditions prevailed suggesting lower lake levels and reduced moisture from recycled air masses and westerlies we propose that the summer monsoon was the predominant moisture source during the bolling allerod warm complex and early holocene followed by westerlies in mid to late holocene period stable carbon isotope values 32 indicate the absence of c 4 type vegetation in the region contradicting with their presence in the lake qinghai record the d record from lake donggi cona highlights the importance of the interplay between westerlies and summer monsoon circulation at this location which is highly dynamic in northeastern plateau compared to the north atlantic circulation and insolation changes consequently lake donggi cona might be an important anchor point for environmental reconstructions on the tibetan plateau

diatom and geochemical evidence of mid to late holocene climatic changes at lake holzmaar west eifel germany abstract changes in diatom assemblages geochemistry and stable carbon isotope composition of bulk organic matter in a varved sediment section from lake holzmaar west eifel germany were used to infer mid to late holocene climatic changes and human impact from 6340 to 1470 cal yr bp shifts in total lacustrine primary production were derived from 13 c org values changes in non siliceous algae biomass productivity were deduced from accumulation rates of organic matter diatom valve accumulation rates and biogenic opal accumulation rates were used as proxies for diatom productivity and for siliceous phytoplankton abundance respectively based on weighted averaging of relative diatom abundance in subsamples qualitative changes in past trophic status were inferred accumulation rates of minerogenic material and the toc tn molar ratio permitted the deduction of past changes in allochthonous matter influx diatom assemblage composition showed statistically significant changes around 5130 3660 and 2900 cal yr bp whereas planktonic diatom productivity was subject to distinct shifts around 5900 5130 4500 3600 2660 and approximately 1630 cal yr bp and siliceous phytoplankton biomass changed ca 6100 4500 2660 1900 and 1700 cal yr bp causally determined changes in diatom assemblage composition and productivity for example due to shifts in nutrient ratios and or concentrations invoked by changes in lake circulation patterns precipitation rates and or erosion rates are discussed glacier fluctuations and lake level changes reported from other study sites in western europe support the finding that reconstructed lacustrine processes are at least indirectly linked to climate palynological and archaeological evidence however has shown a strong superimposition of lacustrine processes with local regional anthropogenic activity since the iron age

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

paleohydrological changes in the eastern mediterranean region during the early to mid holocene recorded in plant wax n alkane distributions and δ13ctoc new data from tenaghi philippon ne greece abstract holocene climate dynamics have strongly influenced precipitation patterns in the eastern mediterranean region this holds particularly true for the 8 2 kyr bp climatic event arguably the strongest perturbation of early to mid holocene climate here we present a biomarker record of leaf wax derived n alkane distributions and stable isotopic composition of total organic carbon 13 c toc along with palynological data from the fen peat archive of tenaghi philippon tp ne greece spanning the interval from 8 7 to 7 5 kyr bp our record documents the response of in situ vegetation within the philippi peatland to changing hydrological conditions and addresses the applicability of organic proxies such as the aquatic index p aq average chain length acl and 13 c toc as indicators of peat surface moisture conditions at the study site the long chain n alkanes n c 27 n c 29 and n c 31 typical of vascular terrestrial plants dominated the peat sequence a period of relatively dry surface conditions indicated by low values of p aq and elevated acl values in concert with elevated 13 c toc values preceded the 8 2 kyr bp climatic event from ca 8 7 to 8 2 kyr bp slightly wetter more humid conditions suggested by an increase in p aq as well as reduced acl and 13 c toc values characterized the interval of the 8 2 kyr bp climatic event notably the increase in surface wetness as indicated by the biomarker record coincided with a marked rise in fern spore proportion as well as increasing proportion of pollen from aquatic taxa following the 8 2 kyr bp event a distinct change in paleohydrology at tp became apparent from ca 7 9 kyr bp onward an increase in the abundance of the mid chain length n alkanes n c 23 and n c 25 indicative of an increased contribution from aquatic plants to the sediment together with a steep increase in p aq and a decrease in acl as well as variation in 13 c toc imply considerably elevated surface moisture levels likely caused by the increased activity of the karstic system of the surrounding mountains collectively the biomarker proxies and pollen data reveal a concise picture of changing moisture conditions at tp in response to the 8 2 kyr bp climatic event

paleoclimate changes of the last 1000 yr on the eastern qinghai tibetan plateau recorded by elemental isotopic and molecular organic matter proxies in sediment from glacial lake ximencuo abstract total organic carbon corg and nitrogen ntot concentrations and isotope compositions and n alkane and n alkan ol molecular biomarker compositions were measured in two parallel sediment cores from lake ximencuo a typical glacial lake on the eastern qinghai tibetan plateau qtp to reconstruct local climatic variations during the past 1000 yr concentrations of corg and ntot vary similarly with changes in precipitation recorded by tree rings in dulan northeastern qtp indicating their close relation to precipitation carbon preference index cpi values of c22 c33 n alkanes and c22 c28 n alkan 1 ols and average chain length acl values of c27 c33 n alkanes generally negatively correlate with 13corg and 15ntot and also vary comparably with the oxygen isotope temperature record from the dunde ice core northeastern qtp these patterns indicate that high cpi values and negative shifts of the 13corg and 15ntot correspond to warmer conditions that favor the growth of vascular land plants and that lower values and positive shifts correspond to cooler conditions in the lake ximencuo locality this observation contradicts previous interpretations from peat and modern soil studies that conclude that the cpi indices were controlled by microbial degradation under different climate conditions here we propose that the changes of organic matter sources under different climate regimes combined with physiological adjustments of vascular plants to different air temperatures might yield different cpi responses to climate changes in glacial plateau lakes air temperature and precipitation increases and decreases reconstructed in this 1000 yr study were generally independent of each other but they both occurred at centennial or multi centennial scales the interaction between subtropical asian monsoon and mid latitude westerly atmospheric circulation systems probably dominated the local precipitation variations in the lake ximencuo catchment whereas solar insolation volcanism and greenhouse gas variations were likely responsible for the air temperature changes that are recorded in the lake sediments and that are consistent with regional temperature variations in the eastern qtp

lake change and its implication in the vicinity of mt qomolangma everest central high himalayas 1970 2009 high elevation inland lakes are a sensitive indicator of climate change the extents of lakes in mt qomolangma region have been extracted using the object based image processing method providing 6 24 images during 1970 2009 combined with data from five meteorological stations and three periods glacier data the inter annual and intra annual lake changes and responses to climate and glacier change have been analyzed the results show that the lakes have shrunk overall with clear inter annual and intra annual fluctuations during 1970 2009 in general there appeared a trend of slight shrinkage in the 1970s distinct shrinkage around 1990 general expansion in 2000 and accelerated decrease after 2000 lake peiku and neighboring lakes show a highly consistent change trend correlation coefficients of 0 68 0 91 with larger lakes having smaller shrinkage rates which implies a higher stability in the order of peiku langqiang cuochuolong lake peiku the largest lake decreased 10 38 km2 3 69 or 0 27 km2 year 1 during 1970 2009 the changes in lake peiku indicate that precipitation is its main source of supply with glacier melt water a key supplement meanwhile lake como chamling reduced by 13 12 km2 19 79 during 1974 2007 with strong shrinkage expansion shrinkage expansion fluctuations overall lakes in the vicinity of mt qomolangma are a sensitive good indicator to climate change

spatial patterns of soil n alkaneδd values on the tibetan plateau implications for monsoon boundaries and paleoelevation reconstructions 1 between 2010 and 2011 this project collected and analyzed forty nine superficial soil samples for wax derivedn alkane d values dwax along a south to north transect of the tibetan plateau from the southern plateau and nepalese himalayas passing through the nam co basin to qilian mountains twenty two paired river water samples were also collected from northeastern tibet during this period and analyzed for d drw the drw and dwaxvalues become progressively more negative northward from 27 5 n and reach a minimum at 30 6 n nam co basin north of the nam co basin to 35 n isotope values increase due to increasing contributions from the year round westerlies and recycled moisture from the plateau relatively high and constant dwax and drw values prevail in areas north of 35 n in northeastern tibet results show that these dwaxvalues vary considerably with location and relate closely to the influences of the summer monsoon and circulation changes these changes track the spatial variability of isotopes from modern river water and precipitation at large spatial scales paleoelevation reconstructions should take into account the impact of mixing between continental and monsoon derived moisture on the relationships with elevation and dwax and linear isotopic lapse rates for central northeastern tibet based on extended and more sensitive relative to 18o dwax and drw values we infer that in the past the westerlies reached further south to the north piedmont of the nyainqentanglha range and that indian summer monsoon moisture pushes across the tanggula mountains and approaches the kunlun mountains

hydrogen isotope ratios of palmitic acid in lacustrine sediments record late quaternary climate variations the rich paleoclimate information preserved in lacustrine sedimentary organic matter can be difficult to extract because of the mixed terrestrial and aquatic inputs herein we demonstrate that compound specific hydrogen isotope analysis of palmitic acid pa a ubiquitous compound in lacustrine sediments captures the d signals of lake water samples collected across a diverse range of 33 north american lakes show a strong correlation between water and dpa values at crooked pond massachusetts the dpa changes in a 14 k y sediment record parallel temperature trends inferred from fossil pollen downcore changes reveal differences between climatic trends in new england and in greenland that are consistent with important regional differences in climate controls

hydrological changes of the past 1400 years recorded in δd of sedimentary n alkanes from poyang lake southeastern china hydrogen isotopic compositions d of plant leaf wax have been increasingly used for paleohydrological reconstructions over various geological timescales here we analyzed downcore variations of

a rapid hydroclimate change and its influence on the songliao basin during the santonian campanian transition as recorded by compound specific isotopes abstract reconstruction of the paleoclimate and paleoenvironment of the songliao basin has important theoretical and practical significance to reveal the regional continental climate characteristics and continental organic matter accumulation under the cretaceous greenhouse climate conditions here we report the composition of biomarkers and the stable carbon and hydrogen isotope compositions of n alkanes from nenjiang formation sediments in the songliao basin which provide information on the source of organisms paleoenvironmental conditions and paleoclimate changes during the late cretaceous our hydrogen isotope records of n alkanes displayed a significantly negative shift indicating that a dramatically wet climate occurred during the santonian campanian transition a wet climate such as that during a prolonged rainfall event had a significant impact on the lake and resulted in the lake level increasing and the salinity decreasing in the surface water during this period however the freshwater input increased the salinity difference between the upper and lower water layers which caused stable water stratification to occur in the lake in addition the high total organic carbon toc content indicates high primary productivity because of increased precipitation carrying more terrigenous nutrients into the lake which resulted in eutrophication during this period notably the increased aryl isoprenoid ratios and the occurrence of isorenieratane indicates that photic zone euxinia pze was enhanced during the santonian campanian transition which was possibly due to the dramatic change in the hydroclimate we speculate that the large freshwater input promoted the formation of pze in the lake then pze restricted the habitat available for aerobic organisms which had fatal effects on the lake ecosystem

preservation of lipid hydrogen isotope ratios in miocene lacustrine sediments and plant fossils at clarkia northern idaho usa abstract we measured d h ratios of individual lipids isolated from plant fossils and water lain sediments from the miocene clarkia lacustrine deposit 15 20 ma in northern idaho usa in order to assess the preservation potential of lipid hydrogen isotope ratios distinct n alkyl lipid profiles in plant fossils platanus quercus salix and the sedimentary matrix demonstrate the high degree of lipid preservation as previously reported our data suggest that original hydrogen isotope ratios of carbon bound hydrogen in lipids may have been preserved after 15 20 million years of burial in the water lain lacustrine sediment because d values of individual lipids show large variations between different fossil genera and between fossils and sediments and hydrogen isotope values of fossil lipids differ by more than 123 from the associated sediment water these data are consistent with minimal isotopic exchange between carbon bound hydrogen in lipids and sediment water hydrogen our results validate the use of lipid hydrogen isotope ratios for paleoecological studies over an extended geological time period

ecological development of lake donggi cona north eastern tibetan plateau since the late glacial on basis of organic geochemical proxies and non pollen palynomorphs organic geochemical proxy data from surface sediment samples and a sediment core from lake donggi cona were used to infer environmental changes on the northeastern tibetan plateau spanning the last 18 4 kyr long chain n alkanes dominate the aliphatic hydrocarbon fraction of the sediment extract from most surface sediment samples and the sediment core unsaturated mid chain n alkanes nc23 1 and nc25 1 have high abundances in some samples especially in core samples from the late glacial and early holocene toc contents organic biomarker and non pollen palynomorph concentrations and results from organic petrologic analysis on selected samples suggest three major episodes in the history of lake donggi cona before ca 12 6 cal ka bp samples contain low amounts of organic matter due to cold and arid conditions during the late glacial after 12 6 cal ka bp relatively high contents of toc and concentrations of botryococcus fossils as well as enhanced concentrations of mid chain n alkanes and n alkenes suggest a higher primary and macrophyte productivity than at present this is supported by high contents of palynomorphs derived from higher plants and algae and was possibly triggered by a decrease of salinity and amelioration of climate during the early holocene since 6 8 cal ka bp lake donggi cona has been an oligotrophic freshwater lake proxy data suggest that variations in insolation drive ecological changes in the lake with increased aquatic productivity during the early holocene summer insolation maximum short term drops of toc contents or biomarker concentrations at 9 9 cal ka bp after 8 0 and between 3 5 and 1 7 cal ka bp can possibly be related to relatively cool and dry episodes reported from other sites on the north eastern tibetan plateau which are hypothesized to occur in phase with northern hemisphere cooling events

δd values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha abstract a set of lake surface sediment samples and aquatic macrophytes from the eastern and central tibetan plateau and a sediment core from koucha lake northeastern tibetan plateau were analysed for hydrogen isotope signals of aliphatic lipid biomarkers the d values of n alkanes were correlated with those of meteoric water in the summer months and showed increasing pearson correlation coefficients with increasing n alkane chain length r 0 80 for n c 31 while in samples from the most humid regions southeastern tibetan plateau the apparent enrichment factors between meteoric water and lipids are close to those reported for other humid sites e 135 for mid chain and 125 for long chain n alkanes they become smaller e 118 to 41 mean value 86 at sites with a negative moisture balance northeastern and central tibetan plateau and qaidam basin this might be caused by enrichment in deuterium of the source water used for lipid synthesis as a result of lake water evaporation and soil and leaf water evapotranspiration in the core from lake koucha decreasing d values of all n alkanes between 15 and 10 cal ka bp give evidence for an intensification of the asian summer monsoon at ca 9 cal ka bp a ca 15 shift towards higher d values of mid chain n alkanes suggests enhanced evaporation of the lake water which outweighs higher precipitation amounts because of a temperature increase during the early holocene monsoonal maximum only a few surface sediment samples show a significant offset between d values of mid chain n alkanes and n c 31 d mid n c31 and no systematic dependence between this offset and environmental parameters such as mean annual precipitation was found in the core available data for most samples also do not show a significant offset only a slight increase 15 of d mid n c31 at ca 10 0 cal ka bp and a decrease 17 at ca 6 8 cal ka bp might indicate wetter and drier conditions respectively however interpretation of d mid n c31 throughout the record is difficult because of a lack of reliable data for n c 31 in key sections of the core so more records are necessary to further test the potential applicability of d mid n c31 as a proxy for palaeo hydrological conditions

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

hydrogen isotope ratios of lacustrine sedimentary n alkanes as proxies of tropical african hydrology insights from a calibration transect across cameroon abstract hydrogen isotope values d of sedimentary aquatic and terrestrial lipid biomarkers originating from algae bacteria and leaf wax have been used to record isotopic properties of ancient source water i e precipitation and or lake water in several mid and high latitude lacustrine environments in the tropics however where both processes associated with isotope fractionation in the hydrologic system and vegetation strongly differ from those at higher latitudes calibration studies for this proxy are not yet available to close this gap of knowledge we sampled surface sediments from 11 lakes in cameroon to identify those hydro climatological processes and physiological factors that determine the hydrogen isotopic composition of aquatic and terrestrial lipid biomarkers here we present a robust framework for the application of compound specific hydrogen isotopes in tropical africa our results show that the d values of the aquatic lipid biomarker n c17 alkane were not correlated with the d values of lake water carbon isotope measurements indicate that the n c17 alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis we demonstrate that the d values of the n c29 alkane were correlated with the d values of surface water i e river water and groundwater which on large spatial scales reflect the isotopic composition of mean annual precipitation such a relationship has been observed at higher latitudes supporting the robustness of the leaf wax lipid d proxy on a hemispheric spatial scale in contrast the d values of the n c31 alkane did not show such a relationship but instead were correlated with the evaporative lake water d values this result suggests distinct water sources for both leaf wax lipids most likely originating from two different groups of plants these new findings have important implications for the interpretation of long chain n alkane d records from ancient lake sediments in particular a robust interpretation of palaeohydrological data requires knowledge of the vegetation in the catchment area as different plants may utilise different water sources our results also suggest that the combination of carbon and hydrogen isotopes does help to differentiate between the metabolic pathway and or growth form of organisms and therefore the source of hydrogen used during lipid biosynthesis

paleoaltimetry of the tibetan plateau from d h ratios of lipid biomarkers abstract the past elevation of the land surface provides a unique constraint on the underlying lithospheric structure during mountain and plateau formation development of new paleoaltimetry techniques that can be applied to a wide variety of sample types is therefore of continuing importance this study evaluates organic substrates that preserve the d ratio of surface waters as a new approach to reconstruct paleoaltimetry we measured the hydrogen isotope composition of n alkanes from epicuticular plant waxes preserved in lacustrine deposits to reconstruct the d of precipitation in cenozoic basins that have been elevated as part of the tibetan plateau n alkane d and carbonate 18 o inferred water compositions from the eocene miocene lunpola basin and miocene hoh xil basin plot near or at enriched values relative to the global meteoric water line as expected for evaporative lakewater and leafwater systems that have the same precipitation source n alkane d based water compositions are nearly identical to the minimum carbonate 18 o based values demonstrating that plant wax d is minimally affected by evaporation compared to lacustrine calcite 18 o this agreement strongly supports the presence of similar precipitation isotopic compositions in both archives despite different isotope systems source water reservoirs archive materials modes of incorporation and diagenetic processes paleoelevations for each basin and time period were calculated from precipitation isotope ratios using the isotope altitude relationship derived from both a simple thermodynamic model and modern precipitation sampling from the plateau region our new results from the hoh xil basin suggest 1700 to 2600 m of uplift may have occurred some time between the late eocene and early miocene the timing of this uplift is consistent with late oligocene compressional deformation of the hoh xil basin and northward growth of the tibetan plateau however the calculated uplift is not a unique solution from the paleoisotope data because of uncertainties in eocene and miocene moisture sources and isotope gradients for the northern plateau our results demonstrate the utility of lipid based estimates of paleoelevation and expand the types of deposits amenable to paleoaltimetry analysis

characterisation of n alkanes and their hydrogen isotopic composition in sediments from lake qinghai china the distributions of n alkanes and their hydrogen isotopic composition dd in surface and core sediments from the saline qinghai lake were measured to assess whether or not biological source information was recorded in the dd values of n alkanes the results indicate that the n alkane distributions between shallow water surface and core sediments were similar and closer to those of terrestrial herbaceous plants from the qinghai lake surrounding areas rather than the aquatic plants living in the lake the n alkanes in the surface and core sediments had similar mean dd values ranging from 185 to 133 and 163 to 142 respectively the mean dd values of n alkanes in the sediments showed that the even n alkanes were heavier in d compared with the odd homologues

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

assessment of the difference between mid and long chain compound specific δdn alkanes values in lacustrine sediments as a paleoclimatic indicator abstract previous studies have proposed that the difference between compound specific hydrogen isotopic composition of n alkanes d n alkanes of possible terrestrial origin and aquatic origin in lacustrine sediments is an indicator of hydroclimatic conditions for a lake environment e g terrestrial evapotranspiration of the lake drainage area or evaporation inflow ratio for the lake sachse d radke j gleixner g 2004 hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability geochimica et cosmochimca acta 68 4877 4889 sachse d radke j gleixner g 2006 d values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record organic geochemistry 37 469 483 mugler i sachse d werner m xu b q wu g j yao t d gleixner g 2008 effect of lake evaporation on d values of lacustrine n alkanes a comparison of nam co tibetan plateau and holzmaar germany organic geochemistry 39 711 729 and this proposed indicator has been applied to a paleoclimatic study of koucha lake kcl on the northeastern tibetan plateau netp however the application was not very successful due to an apparent discrepancy between the reconstructed possible hydroclimatic variation based on the proposed indicator and precipitation amount variation based on pollen in the same lake aichner b herzschuh u wilkes h vieth a bohner j 2010a d values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha organic geochemistry 41 779 790 we report new compound specific d n alkanes data for sediments since the last glacial from hurleg lake klk and genggahai lake ggh both also on the netp ca 300 km apart together d n alkanes data from the three lakes were analyzed to assess the difference between mid chain and long chain compound specific d n alkanes values in the sediments as a paleoclimatic indicator our results indicate that mid chain n c 23 and n c 25 and long chain n c 27 n c 29 and n c 31 n alkanes as compounds representative of aquatic and terrestrial origins respectively were valid only for klk correspondingly the use of differences between mid chain and long chain compound specific d n alkanes as a possible paleoclimatic indicator was feasible only for this lake hence our results emphasize the complex relationship between the chain length of lacustrine n alkanes and their actual origins and suggest that the correlation analysis of d n alkanes data for different chain length could be part of the possible evaluation method for the application of lacustrine compound specific d n alkanes data in paleoclimatic studies

transfer and early diagenesis of biogenic silica oxygen isotope signals during settling and sedimentation of diatoms in a temperate freshwater lake lake holzmaar germany abstract we have investigated the transfer of oxygen isotope signals of diatomaceous silica 18odiatom from the epilimnion 0 7 m through the hypolimnion to the lake bottom 20 m in freshwater lake holzmaar germany sediment traps were deployed in 2001 at depths of 7 and 16 m to harvest fresh diatoms every 28 days the 7 m trap collected diatoms from the epilimnion being the main zone of primary production while the 16 m trap collected material already settled through the hypolimnion also a bottom sediment sample was taken containing diatom frustules from approximately the last 25 years the 18odiatom values of the 7 m trap varied from 29 4 in spring autumn to 26 2 in summer according to the temperature dependence of oxygen isotope fractionation and represent the initial isotope signal in this study remarkably despite the short settling distance 18odiatom values of the 7 and the 16 m trap were identical only during spring and autumn seasons while from april to september 18odiatom values of the 16 m trap were roughly 1 5 enriched in 18o compared to those of the 7 m trap isotopic exchange with the isotopically lighter water of the hypolimnion would shift the 18odiatom value to lower values during settling from 7 to 16 m excluding this process as a cause for the deviation dissolution of opal during settling with intact organic coatings of the diatom cells and near neutral ph of the water should only cause a minor enrichment of the 16 m values nevertheless opal from the bottom sediment was found to be 2 5 enriched in 18o compared to the weighted average of the opal from the 7 m trap thus resuspension of bottom material must have contributed to the intermediate 18odiatom signal of the 16 m trap during summer dissolution experiments allowed further investigation of the cause for the remarkably enriched 18odiatom value of the bottom sediment experiments with different fresh diatomaceous materials show an increase of opaline 18o at high ph values which is remarkably reduced when organic coatings of the cells still exist or at near neutral ph in contrast high ph conditions do not affect the 18odiatom values of sub fossil and even fossil opal ir analyses show that the 18o enrichment of the sedimentary silica is associated with a decrease in si oh groups and the formation of si o si linkages this indicates a silica dehydroxylation process as cause for the isotopic enrichment of the bottom sediment silica dissolution and dehydroxylation clearly induce a maturation process of the diatom oxygen isotope signal presumably following an exponential behaviour with a rapid initial phase of signal alteration the dynamics of this process is of particular importance for the quantitative interpretation of sedimentary 18odiatom values in terms of palaeothermometry

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

high relief topography of the nima basin in central tibetan plateau during the mid cenozoic time abstract there remains inconsistence of uplift history of the tibetan plateau here we estimated paleoelevation of mid cenozoic nima basin located in central tibet using multi proxies they included meteoric water and vegetation isotope proxies based on hydrogen and carbon isotopic compositions d and 13c respectively of terrestrial plant wax lipid of n alkanes and temperature proxy derived from microbial membrane lipid of branched glycerol dialkyl glycerol tetraethers brgdgts lipid analysis on sedimentary rocks in the nima basin yielded 222 12 and 30 0 0 7 for d and 13c of n c29 alkane respectively and brgdgt derived mean annual air temperature maat of 21 5 3 1 c for the paleo basin using the sea level meteoric water 18o and miocene siwalik paleovegetation 13c as low elevation references values of d and 13c of n c29 alkane in this study suggested paleoelevations of 4546 m and 2800 m respectively whereas by using a subtropical sea surface temperature as a reference brgdgt derived maats suggested a paleoelevation of 893 m we believed that the three estimates reflect a high relief topography in the study basin during the mid cenozoic representing elevations of orographic barrier of southerly oceanic moisture basin catchment and basin lake level respectively this scenario implies a low elevation of the basin relative to the lhasa terrane located to the south during the mid cenozoic hence challenging the classical crustal thickening models assuming a simple crustal thickening uplift relationship

effect of lake evaporation on δd values of lacustrine n alkanes a comparison of nam co tibetan plateau and holzmaar germany compound specific hydrogen isotope ratio values of lacustrine n alkanes from two contrasting ecosystems the semiarid to arid nam co central tibet and the humid holzmaar germany were compared in order to assess whether or not these environmental conditions are recorded in the isotopic signatures of biomarkers increased evaporation of lake water at nam co is recorded by the n alkanes of aquatic origin hence isotopic enrichment results in a di erence between terrestrial and aquatic n alkanes in the opposite direction 68 from that known for humid climate conditions 30 predominating at holzmaar based on this isotopic di erence between terrestrial and aquatic n alkanes evaporation to inflow ratio e i values were estimated and suggest that the isotopic di erence is indicative of the general hydroclimatic characteristics of a lake system moreover the comparison with e i values calculated with actual stable water isotope data showed that the dd values of aquatic and terrestrial lacustrine n alkanes serve as a proxy for the relative isotopic di erences between lake and inflow waters and can be used to assess the proportion of water undergoing evaporation relative to the inflow and thus to reconstruct the lake water balance in the past 2008 published by elsevier ltd

rapid northward shift of the indian monsoon on the tibetan plateau at the end of the little ice age variations in the indian monsoon im and westerlies ws significantly affect the climate on the tibetan plateau tp and have widespread ecological and socioeconomic impacts on the whole of asian society so far however the rate and magnitude of changes in the im have still remained unclear here we report for the first time that the im rapidly shifted northward at the end of the little ice age lia we used sediment proxies for humidity and moisture sources from the taro co lake which is located in the transition zone between the ws and im our comprehensive survey of climate records for the tp and its peripheral mountain ranges revealed that the northern boundary of the im i e the southern boundary of the ws lay along the southern slope of the gandise range 29 5 n in the late lia in contrast it passed quickly over the gandise range by at least 1 5 in latitude at the end of the lia our results suggest that this rapid climatic shift was potentially triggered by the counteracting effects of blocking by the tp and its marginal orography which hindered the northward movement of the im and the pulling thermal gradient of the tp

using distributions and stable isotopes of n alkanes to disentangle organic matter contributions to sediments of laguna potrok aike argentina when using biomarkers such as n alkanes as tools for paleo environmental reconstructions it is imperative to determine their specific sources for each setting toward that goal we analyzed a set of various potential organic matter om sources such as aquatic and terrestrial plants dust and soils from laguna potrok aike lpa and surrounding areas in southern patagonia we determined chain length distributions and hydrogen d and carbon 13c isotopic compositions of n alkanes of different om sources in order to quantify their relative contributions to lake sediments our results reveal that the mid chain n alkane n c23 is predominantly produced by submerged aquatic plants whereas long chain n alkanes n c29 n c31 are derived from various terrestrial sources we estimated their relative contributions to the sediment using two approaches i e based on the n alkane distributions and their d and 13c values both approaches result in similar estimates of aquatic and terrestrial contributions for mid and long chain n alkanes to the sediment 62 73 of the mid chain n c23 alkanes originate from aquatic sources while 66 77 of the long chain n alkanes originate from dust and 14 30 from terrestrial plants our study shows that mid chain n alkanes such as the n c23 alkane in lpa are derived mainly from aquatic macrophytes and thus have the potential to record changes in lake water isotopic composition in contrast the n c29 alkane reflects the isotopic signal of various terrestrial sources from southern patagonia

quaternary paleoenvironmental change on the tibetan plateau and adjacent areas western china and western mongolia abstract this paper summarises the nature of climatic change during the last glacial interglacial cycle on the tibetan plateau and adjacent areas the results are derived from inland glacier fluctuations lake level changes and dust loess records of central asia including tibet these are based on our field investigations from 1988 to 1998 and literature surveys the changing extents of different climatic controlled geomorphic landscapes and vegetation zones help to provide estimates of the magnitude of climatic change features such as ice wedge casts loess and palaeosols ela reconstruction s and palaeobotanical data are used to help reconstruct palaeoprecipitation and palaeotemperatures weathering characteristics the overlying strata and some luminescence dates indicate that there are two main glacial ice advances during the last glacial cycle these correspond to marine oxygen isotope stages ois 2 and 4 in some areas as the eastern or northern margin of the tibetan plateau remnants of older glaciations are preserved higher lake levels in the deserts of central asia and on the tibetan plateau are dated to 40 to 25 ka ois 3 and to late glacial early to mid holocene periods our work supports the view that in many areas of central asia cold phases during the last glacial correspond with the maximum extent of glaciers and the periglacial activity the last glaciation produced large alluvial fans alternating with periods of high lake stands on the tibetan plateau however at the northern margin of the plateau in the qaidam basin and in some particular desert areas in western china high lake levels occurred also during the pleistocene and are related with alluvial fans

a 15 ka lake water δd record from genggahai lake northeastern tibetan plateau and its paleoclimatic significance abstract the mid chain and long chain n alkanes in sediments of genggahai lake on the northeastern tibetan plateau have been assigned as being predominantly from aquatic plants thus at the lake compound specific hydrogen isotopic data for mid and long chain n alkanes d n alkanes are indicators of the variation in lake water d d lw genggahai d lw is determined by the local meteoric water d d mw and by lake surface evaporation as evidenced by modern observational data and the broad correlation between genggahai d lw and average lake water depth during the past 15 ka with more negative d lw values corresponding to greater average water depth as demonstrated by the mid and long chain d n alkanes data the most negative interval of genggahai d lw was during the early holocene an overall trend towards more positive values from the early to the late holocene clearly indicates the long term evolutionary history of local d mw which could be related to the intensity of the indian summer monsoon ism via the rainfall amount effect therefore the record of d lw at genggahai during the past 15 ka which resembles that of stalagmite 18 o records from the core ism region apparently reflects the long term evolution of ism intensity furthermore several short term positive excursions in genggahai d lw values during the late holocene reflect enhanced lake surface evaporation via an isotopic enrichment mechanism that apparently resulted from periods of weakened ism intensity our results highlight the fact that unambiguous source determination of n alkanes is vital for determining the paleoclimatic significance of lacustrine d n alkanes data

spatial gradients in plant leaf wax d h across a coastal salt marsh in southern california coastal salt marsh ecosystems contain strong environmental gradients that are anticipated to influence the d h ratios recorded in the leaf waxes of salt tolerant plants we characterized the molecular and hydrogen isotopic composition of alkanes in plant and sediment samples as well as the d h ratios of environmental and plant waters across an elevation and inundation gradient in a southern californian coastal salt marsh we sampled the dominant salt marsh plant species salicornia virginica arthrocnemum subterminale and jamuea carnosa all succulents as well as monanthochloe littoralis and limonium californicum nonsucculents plant xylem water hydrogen isotopic compositions indicate a shift in source waters from meteoric influences at upland sites dd value 20 to seawater dominated values 0 at lowland areas we found leaf water d enrichment relative to xylem water ranging from mean dd values of 54 upland to 28 lowland interpreted as a reduction of transpiration with increasing inundation time this has the effect of increasing the net fractionation between source water and leaf wax product across the environmental gradient from mean values of 101 upland to 134 lowland with an attenuated signal recorded in the dd values of plant leaf wax n alkanes 122 to 136 these results constrain the hydrogen isotopic composition of salt marsh organic matter that may contribute to marine carbon budgets of the santa barbara basin and further indicate the potential for plant leaf waxes to resolve paleoenvironmental change including sea level change in sediment cores from salt marsh ecosystems

oxygen 18 and carbon 13 records for the last 14 000 years from lacustrine carbonates of siling co lake in the qinghai tibetan plateau to understand paleoenvironmental changes for the central qinghai tibetan plateau we analyzed stable isotopes of oxygen and carbon from calcium carbonates in a bottom sediment core collected from siling co lake five conventional and two tams 14c dates indicate that the core recovered sediments of the last 14 000 years calcium carbonates in the sediments seem to be primary carbonates precipitated chemically in the lake and not clastic particles from limestones distributed around the lake because of large variation of isotopic ratios isotopic covariance since 6 000 yr bp and similarity between dates from total calcium carbonates and organic carbon their isotopic composition therefore reflects that of the lake water we present the following paleoenvironmental history over the last 14 000 years in the central part of the plateau from secular variations of 18o 13c and caco3 content throughout the core 1 desiccation was dominant during the latter part of the last glacial stage 14 000 to 11 000 yr bp 2 the last glacial stage abruptly terminated at 11 000 yr bp 3 a temperate and stable climate was dominant from 11 000 to 5 000 yr bp 4 climatic conditions fluctuated from 5 000 to the present including two strong desiccation periods 5 000 to 4 000 yr bp and 3 000 to 2 000 yr bp and an intermediate period of heavy rainfall 4 000 to 3 000 yr bp this period is also characterized by a covariant o and c isotopic trend

a six year isotopic record of lake evaporation at a mine site in the canadian subarctic results and validation an isotopic method is applied in conjunction with a water balance method and the penman combination method to estimate evaporation from a small high closure low outflow lake near yellowknife northwest territories canada 62803 0 n 111824 0 w the study provides baseline hydrological information for assessment of tailings pond design and management at nearby mine sites and notably enables intercomparison of several field based evaporation methods and a standard climate approach in a subarctic setting a non steady isotope mass balance method is applied to estimate evaporation over time intervals ranging from five days to three weeks based on isotopic surveys of lakewater groundwater precipitation and atmospheric moisture during the open water periods of 1991 to 1996 use of a relatively high precision non steady technique in contrast to the commonly employed approach assuming steady state is feasible in the present setting owing to pronounced seasonal evaporative enrichment in lake water 20 30 times analytical uncertainty of d 18 o a comparative analysis reveals that the isotopic method is conservative relative to the penman combination method but less conservative than standard water balance although estimates for the open water period are in agreement to within 20 in both cases interannual variability in evaporation is revealed to be 30 50 greater than predicted from standard pan to lake algorithms and of the same order of magnitude as the annual snow water equivalent 155 175 mm which has important implications for the design and management of tailings ponds in the area 1998 john wiley sons ltd