TY - JOUR A1 - Wang, Xinxin A1 - Huang, Xianyu A1 - Sachse, Dirk A1 - Hu, Yu A1 - Xue, Jiantao A1 - Meyers, Philip A. T1 - Comparisons of lipid molecular and carbon isotopic compositions in two particle-size fractions from surface peat and their implications for lipid preservation JF - Environmental earth sciences N2 - Knowledge of the possible impacts of early diagenesis on lipid biomarkers in geologic settings is important for robust applications of lipid proxies for paleoclimate reconstructions. In this study, molecular distributions and carbon isotopic compositions of lipids were compared in two particle-size fractions (<0.3 mm and >0.3 mm) of twelve surface peat samples collected from Dajiuhu peatland, central China. The average chain length (ACL) values of long-chain n-alkanes, n-fatty alcohols, n-fatty acids and n-alkan-2-ones show no significant differences between the finer and coarser fractions. In contrast, the carbon preference index values of long-chain n-alkanes, n-fatty alcohols and n-alkan-2-ones have relatively smaller values in the finer fractions than in the coarser ones. Stanols were also more abundant in the finer fractions. In addition, the delta C-13 values of odd-numbered n-alkanes (C-23-C-33) were generally less negative in the finer fractions. Our results indicate that (1) the finer fractions probably experienced stronger degradation than the coarser fractions; (2) the less negative delta(CC)-C-13 values of odd-numbered n-alkanes (C-23-C-33) in the finer fractions were largely a result of greater heterotrophic reworking during degradation; (3) ACL values of long-chain n-alkyl lipids (n-alkanes, n-fatty alcohols and n-fatty acids, n-alkan-2-ones) appear to be reliable proxies to trace lipid sources and their associated paleoenvironmental signals in peat deposits. KW - Peat KW - Lipids KW - Compound-specific carbon isotope KW - Particle-size fractions KW - Decomposition Y1 - 2016 U6 - https://doi.org/10.1007/s12665-016-5960-3 SN - 1866-6280 SN - 1866-6299 VL - 75 SP - 375 EP - 385 PB - Springer CY - New York ER - TY - JOUR A1 - Wang, Xinxin A1 - Huang, Xianyu A1 - Sachse, Dirk A1 - Ding, Weihua A1 - Xue, Jiantao T1 - Molecular Paleoclimate Reconstructions over the Last 9 ka from a Peat Sequence in South China JF - PLoS one N2 - To achieve a better understanding of Holocene climate change in the monsoon regions of China, we investigated the molecular distributions and carbon and hydrogen isotope compositions delta C-13 and delta D values) of long-chain n-alkanes in a peat core from the Shiwangutian SWGT) peatland, south China over the last 9 ka. By comparisons with other climate records, we found that the delta C-13 values of the long-chain n-alkanes can be a proxy for humidity, while the dD values of the long-chain n-alkanes primarily recorded the moisture source dD signal during 9-1.8 ka BP and responded to the dry climate during 1.8-0.3 ka BP. Together with the average chain length ACL) and the carbon preference index CPI) data, the climate evolution over last 9 ka in the SWGT peatland can be divided into three stages. During the first stage 9-5 ka BP), the delta C-13 values were depleted and CPI and Paq values were low, while ACL values were high. They reveal a period of warm and wet climate, which is regarded as the Holocene optimum. The second stage 5-1.8 ka BP) witnessed a shift to relatively cool and dry climate, as indicated by the more positive delta C-13 values and lower ACL values. During the third stage 1.8-0.3 ka BP), the delta C-13, delta D, CPI and Paq values showed marked increase and ACL values varied greatly, implying an abrupt change to cold and dry conditions. This climate pattern corresponds to the broad decline in Asian monsoon intensity through the latter part of the Holocene. Our results do not support a later Holocene optimum in south China as suggested by previous studies. Y1 - 2016 U6 - https://doi.org/10.1371/journal.pone.0160934 SN - 1932-6203 VL - 11 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Voss, Katalyn A. A1 - Bookhagen, Bodo A1 - Sachse, Dirk A1 - Chadwick, Oliver A. T1 - Variation of deuterium excess in surface waters across a 5000-m elevation gradient in eastern Nepal JF - Journal of hydrology N2 - The strong elevation gradient of the Himalaya allows for investigation of altitude and orographic impacts on surface water delta O-18 and delta D stable isotope values. This study differentiates the time- and altitude-variable contributions of source waters to the Arun River in eastern Nepal. It provides isotope data along a 5000-m gradient collected from tributaries as well as groundwater, snow, and glacial-sourced surface waters and time-series data from April to October 2016. We find nonlinear trends in delta O-18 and delta D lapse rates with high-elevation lapse rates (4000-6000 masl) 5-7 times more negative than low-elevation lapse rates (1000-3000 masl). A distinct seasonal signal in delta O-18 and delta D lapse rates indicates time-variable source-water contributions from glacial and snow meltwater as well as precipitation transitions between the Indian Summer Monsoon and Winter Westerly Disturbances. Deuterium excess correlates with the extent of snowpack and tracks melt events during the Indian Summer Monsoon season. Our analysis identifies the influence of snow and glacial melt waters on river composition during low-flow conditions before the monsoon (April/May 2016) followed by a 5-week transition to the Indian Summer Monsoon-sourced rainfall around mid-June 2016. In the post-monsoon season, we find continued influence from glacial melt waters as well as ISM-sourced groundwater. KW - stable isotopes KW - Himalaya KW - glacier KW - snow KW - precipitation KW - seasonality Y1 - 2020 U6 - https://doi.org/10.1016/j.jhydrol.2020.124802 SN - 0022-1694 SN - 1879-2707 VL - 586 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Vogeli, Natalie A1 - Najman, Yani A1 - van der Beek, Peter A1 - Huyghe, Pascale A1 - Wynn, Peter M. A1 - Govin, Gwladys A1 - van der Veen, Iris A1 - Sachse, Dirk T1 - Lateral variations in vegetation in the Himalaya since the Miocene and implications for climate evolution JF - Earth & planetary science letters N2 - The Himalaya has a major influence on global and regional climate, in particular on the Asian monsoon system. The foreland basin of the Himalaya contains a record of tectonics and paleoclimate since the Miocene. Previous work on the evolution of vegetation and climate has focused on the central and western Himalaya, where a shift from C3 to C4 vegetation has been observed at similar to 7 Ma and linked to increased seasonality, but the climatic evolution of the eastern part of the orogen is less well understood. In order to track vegetation as a marker of monsoon intensity and seasonality, we analyzed delta C-13 and 8180 values of soil carbonate and associated delta C-13 values of bulk organic carbon from previously dated sedimentary sections exposing the syn-orogenic detrital Dharamsala and Siwalik Groups in the west, and, for the first time, the Siwalik Group in the east of the Himalayan foreland basin. Sedimentary records span from 20 to 1 Myr in the west (Joginder Nagar, Jawalamukhi, and Haripur Kolar sections) and from 13 to 1 Myr in the east (Kameng section), respectively. The presence of soil carbonate in the west and its absence in the east is a first indication of long-term lateral climatic variation, as soil carbonate requires seasonally arid conditions to develop. delta C-13 values in soil carbonate show a shift from around -10 parts per thousand to -2 parts per thousand at similar to 7 Ma in the west, which is confirmed by delta C-13 analyses on bulk organic carbon that show a shift from around -23 parts per thousand to -19 parts per thousand at the same time. Such a shift in isotopic values is likely to be associated with a change from C3 to C4 vegetation. In contrast, delta C-13 values of bulk organic carbon remain at 23 parts per thousand o in the east. Thus, our data show that the current east -west variation in climate was established at similar to 7 Ma. We propose that the regional change towards a more seasonal climate in the west is linked to a decrease of the influence of the Westerlies, delivering less winter precipitation to the western Himalaya, while the east remained annually humid due to its proximity to the monsoonal moisture source. (C) 2017 Elsevier B.V. All rights reserved. KW - Himalaya KW - stable carbon isotopes KW - paleovegetation KW - Siwalik KW - pre-Siwalik KW - monsoon Y1 - 2017 U6 - https://doi.org/10.1016/j.epsl.2017.04.037 SN - 0012-821X SN - 1385-013X VL - 471 SP - 1 EP - 9 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Schwab, Valerie F. A1 - Garcin, Yannick A1 - Sachse, Dirk A1 - Todou, Gilbert A1 - Sene, Olivier A1 - Onana, Jean-Michel A1 - Achoundong, Gaston A1 - Gleixner, Gerd T1 - Dinosterol delta D values in stratified tropical lakes (Cameroon) are affected by eutrophication JF - Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry N2 - In freshwater settings, dinosterol (4 alpha,23,24-trimethyl-5 alpha-cholest-22E-en-3 beta-ol) is produced primarily by dinoflagellates, which encompass various species including autotrophs, mixotrophs and heterotrophs. Due to its source specificity and occurrence in lake and marine sediments, its presence and hydrogen isotopic composition (delta D) should be valuable proxies for paleohydrological reconstruction. However, because the purity required for hydrogen isotope measurements is difficult to achieve using standard wet chemical purification methods, their potential as a paleohydrological proxy is rarely exploited. In this study, we tested delta D values of dinosterol in both particulate organic matter (POM) and sediments of stratified tropical freshwater lakes (from Cameroon) as a paleohydrological proxy, the lakes being characterized by variable degrees of eutrophication. In POM and sediment samples, the delta D values of dinosterol correlated with lake water delta D values, confirming a first order influence of source water delta D values. However, we observed that sedimentary dinosterol was D enriched from ca. 19 to 54% compared with POM dinosterol. The enrichment correlated with lake water column conditions, mainly the redox potential at the oxic-anoxic interface (E-h OAI). The observations suggest that paleohydrologic reconstruction from delta D values of dinosterol in the sediments of stratified tropical lakes ought to be sensitive to the depositional environment, in addition to lake water delta D values, with more positive dinosterol delta values potentially reflecting increasing lake eutrophication. Furthermore, in lake sediments, the concentration of partially reduced vs. non-reduced C-34 botryococcenes, stanols vs. stenols, and bacterial (diploptene, diplopterol and beta beta-bishomohopanol) vs. planktonic/terrestrial lipids (cholesterol, campesterol and dinosterol) correlated with Eh OAI. We suggest using such molecular proxies for lake redox conditions in combination with dinosterol delta D values to evaluate the effect of lake trophic status on sedimentary dinosterol delta D values, as a basis for accurately reconstructing tropical lake water delta D values. (C) 2015 Elsevier Ltd. All rights reserved. KW - Hydrogen KW - Isotope KW - Fractionation KW - Biomarkers KW - Dinosterol KW - Lake KW - Redox potential KW - Paleoenvironmental KW - Proxy Y1 - 2015 U6 - https://doi.org/10.1016/j.orggeochem.2015.08.003 SN - 0146-6380 VL - 88 SP - 35 EP - 49 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Schwab, Valerie F. A1 - Garcin, Yannick A1 - Sachse, Dirk A1 - Todou, Gilbert A1 - Sene, Olivier A1 - Onana, Jean-Michel A1 - Achoundong, Gaston A1 - Gleixner, Gerd T1 - Effect of aridity on delta C-13 and delta D values of C-3 plant- and C-4 graminoid-derived leaf wax lipids from soils along an environmental gradient in Cameroon (Western Central Africa) JF - Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry N2 - The observation that the hydrogen isotope composition (delta D) of leaf wax lipids is determined mainly by precipitation delta D values, has resulted in the application of these biomarkers to reconstruct paleoclimate from geological records. However, because the delta D values of leaf wax lipids are additionally affected by vegetation type and ecosystem evapotranspiration, paleoclimatic reconstruction remains at best semi-quantitative. Here, we used published results for the carbon isotope composition (delta C-13) of n-alkanes in common plants along a latitudinal gradient in C-3/C-4 vegetation and relative humidity in Cameroon and demonstrated that pentacyclic triterpene methyl ethers (PTMEs) and n-C-29 and n-C-31 in the same soil, derived mainly from C-4 graminoids (e.g. grass) and C-3 plants (e.g. trees and shrubs), respectively. We found that the delta D values of soil n-C-27, n-C29 and n-C-31, and PTMEs correlated significantly with surface water delta D values, supporting previous observations that leaf wax lipid delta D values are an effective proxy for reconstructing precipitation delta D values even if plant types changed significantly. The apparent fractionation (epsilon(app)) between leaf wax lipid and precipitation delta D values remained relatively constant for C-3-derived long chain n-alkanes, whereas eapp of C-4-derived PTMEs decreased by 20 parts per thousand along the latitudinal gradient encompassing a relative humidity range from 80% to 45%. Our results indicate that PTME delta D values derived from C-4 graminoids may be a more reliable paleo-ecohydrological proxy for ecosystem evapotranspiration within tropical and sub-tropical Africa than n-alkane delta D values, the latter being a better proxy for surface water delta D values. We suggest that vegetation changes associated with different plant water sources and/or difference in timing of leaf wax synthesis between C-3 trees of the transitional class and C-3 shrubs of the savanna resulted in a D depletion in soil long chain n-alkanes, thereby counteracting the effect of evapotranspiration D enrichment along the gradient. In contrast, evaporative D enrichment of leaf and soil water was significant enough to be recorded in the delta D values of PTMEs derived from C-4 graminoids, likely because PTMEs recorded the hydrogen isotopic composition of the same vegetation type. KW - Evapotranspiration KW - D-enrichment KW - Pentacyclic triterpene methyl ethers KW - PTMEs KW - n-Alkane KW - Compound-specific isotope KW - Paleo KW - Climate KW - Proxy Y1 - 2015 U6 - https://doi.org/10.1016/j.orggeochem.2014.09.007 SN - 0146-6380 VL - 78 SP - 99 EP - 109 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Scheingross, Joel S. A1 - Hovius, Niels A1 - Dellinger, M. A1 - Hilton, R. G. A1 - Repasch, M. A1 - Sachse, Dirk A1 - Grocke, D. R. A1 - Vieth-Hillebrand, Andrea A1 - Turowski, Jens M. T1 - Preservation of organic carbon during active fluvial transport and particle abrasion JF - Geology N2 - Oxidation of particulate organic carbon (POC) during fluvial transit releases CO2 to the atmosphere and can influence global climate. Field data show large POC oxidation fluxes in lowland rivers; however, it is unclear if POC losses occur predominantly during in-river transport, where POC is in continual motion within an aerated environment, or during transient storage in floodplains, which may be anoxic. Determination of the locus of POC oxidation in lowland rivers is needed to develop process-based models to predict POC losses, constrain carbon budgets, and unravel links between climate and erosion. However, sediment exchange between rivers and floodplains makes differentiating POC oxidation during in-river transport from oxidation during floodplain storage difficult. Here, we isolated inriver POC oxidation using flume experiments transporting petrogenic and biospheric POC without floodplain storage. Our experiments showed solid phase POC losses of 0%-10% over similar to 10(3) km of fluvial transport, compared to similar to 7% to >50% losses observed in rivers over similar distances. The production of dissolved organic carbon (DOC) and dissolved rhenium (a proxy for petrogenic POC oxidation) was consistent with small POC lasses, and replicate experiments in static water tanks gave similar results. Our results show that fluvial sediment transport, particle abrasion, and turbulent mixing have a minimal role on POC oxidation, and they suggest that POC losses may accrue primarily in floodplain storage. Y1 - 2019 U6 - https://doi.org/10.1130/G46442.1 SN - 0091-7613 SN - 1943-2682 VL - 47 IS - 10 SP - 958 EP - 962 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Sarkar, Saswati A1 - Wilkes, Heinz A1 - Prasad, Sushma A1 - Brauer, Achim A1 - Riedel, Nils A1 - Stebich, Martina A1 - Basavaiah, Nathani A1 - Sachse, Dirk T1 - Spatial heterogeneity in lipid biomarker distributions in the catchment and sediments of a crater lake in central India JF - Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry N2 - The basin-scale spatial variability in lipid biomarker proxies in lacustrine sediments, which are established tools for studying continental environmental change, has rarely been examined. It is often implicitly assumed that a lake sediment core provides an average integral of catchment sources. Here we evaluated the distribution of lipid biomarkers in a modern ecosystem and compared it with the sedimentary record. We analyzed lipid biomarkers in terrestrial and aquatic organisms and in lake surface sediments from 17 locations within the saline-alkaline Lonar crater lake in central India. Terrestrial vegetation and lake surface sediments were characterized by relatively high average chain length (ACL) index values (29.6-32.8) of leaf wax n-alkanes, consistent with suggestions that plants in drier and warmer climates produce longer chain alkyl lipids than plants in cooler and humid areas. A heterogeneous spatial distribution of ACL values in lake surface sediments was found: at locations away from the shore, the values were highest (31 or more), possibly indicating different sources and/or transport of terrestrial biomarkers. In floating, benthic microbial mats and surface sediment, n-heptadecane, carotenoids, diploptene, phytol and tetrahymanol occurred in large amounts. Interestingly, these biomarkers of a unique bacterial community were found in substantially higher concentrations in nearshore sediment samples. We suggest that human influence and subsequent nutrient supply resulted in increased primary productivity, leading to an unusually high concentration of tetrahymanol in the nearshore sediments. In summary, the data showed that substantial heterogeneity existed within the lake, but leaf wax n-alkanes in a core from the center of the lake represented an integral of catchment conditions. However, lake level fluctuation may potentially affect aquatic lipid biomarker distributions in lacustrine sediments, in addition to source changes. Y1 - 2014 U6 - https://doi.org/10.1016/j.orggeochem.2013.11.009 SN - 0146-6380 VL - 66 SP - 125 EP - 136 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Sarkar, Saswati A1 - Prasad, Sushma A1 - Wilkes, Heinz A1 - Riedel, Nils A1 - Stebich, Martina A1 - Basavaiah, Nathani A1 - Sachse, Dirk T1 - Monsoon source shifts during the drying mid-Holocene: Biomarker isotope based evidence from the core 'monsoon zone' (CMZ) of India JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - A better understanding of past variations of the Indian Summer Monsoon (ISM), that plays a vital role for the still largely agro-based economy in India, can lead to a better assessment of its potential impact under global climate change scenarios. However, our knowledge of spatiotemporal patterns of ISM strength is limited due to the lack of high-resolution, continental paleohydrological records. Here, we reconstruct centennial-scale hydrological variability during the Holocene associated to changes in the intensity of the ISM based on a record of lipid biomarker abundances and compound-specific stable isotopic composition of a 10 m long sediment core from saline alkaline Lonar Lake, situated in the core 'monsoon zone' of central India. We identified three main periods of distinct hydrology during the Holocene in central India. The period between 10.1 and 6 cal ka BP was likely the wettest during the Holocene. Lower average chain length (ACL) index values (29.4-28.6) and negative delta C-13(wax) values (-34.8 parts per thousand to -27.8 parts per thousand) of leaf wax n-alkanes indicate the dominance of woody C-3 vegetation in the catchment, and negative delta D-wax values (concentration weighted average) (-171 parts per thousand to -147 parts per thousand) suggest a wet period due to an intensified monsoon. After 6 cal ka BP, a gradual shift to less negative delta C-13(wax) values (particularly for the grass derived n-C-31) and appearance of the triterpene lipid tetrahymanol, generally considered as a marker for salinity and water column stratification, mark the onset of drier conditions. At 5.1 cal ka BP an increasing flux of leaf wax n-alkanes along with the highest flux of tetrahymanol indicate a major lowering of the lake level. Between 4.8 and 4 cal ka BP, we find evidence for a transition to arid conditions, indicated by high and strongly variable tetrahymanol flux. In addition, a pronounced shift to less negative delta C-13(wax) values, in particular for n-C-31 (-25.2 parts per thousand to -22.8 parts per thousand), during this period indicates a change of dominant vegetation to C-4 grasses. In agreement with other proxy data, such as deposition of evaporite minerals, we interpret this period to reflect the driest conditions in the region during the last 10.1 ka. This transition led to protracted late Holocene arid conditions after 4 ka with the presence of a permanent saline lake, supported by the sustained presence of tetrahymanol and more positive average delta D-wax values (-122 parts per thousand to -141 parts per thousand). A late Holocene peak of cyanobacterial biomarker input at 1.3 cal ka BP might represent an event of lake eutrophication, possibly due to human impact and the onset of cattle/livestock farming in the catchment. A unique feature of our record is the presence of a distinct transitional period between 4.8 and 4 cal ka BP, which was characterized by some of the most negative delta D-wax values during the Holocene (up to -180 parts per thousand), when all other proxy data indicate the driest conditions during the Holocene. These negative delta D-wax values can as such most reasonably be explained by a shift in moisture source area and/or pathways or rainfall seasonality during this transitional period. We hypothesize that orbital induced weakening of the summer solar insolation and associated reorganization of the general atmospheric circulation, as a possible southward displacement of the tropical rainbelt, led to an unstable hydroclimate in central India between 4.8 and 4 ka. KW - Indian Summer Monsoon KW - Holocene KW - Lonar Lake KW - Lipid biomarkers KW - Compound-specific stable isotopic KW - composition Y1 - 2015 U6 - https://doi.org/10.1016/j.quascirev.2015.06.020 SN - 0277-3791 VL - 123 SP - 144 EP - 157 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Sachse, Dirk A1 - Kahmen, Ansgar A1 - Gleixner, Gerd T1 - Significant seasonal variation in the hydrogen isotopic composition of leaf-wax lipids for two deciduous tree ecosystems (Fagus sylvativa and Acer pseudoplatanus) N2 - Compound specific hydrogen isotope ratios (delta D) of long chain sedimentary n-alkanes, which mostly originate from the leaf waxes of higher terrestrial plants, are increasingly employed as paleoclimate proxies. While soil water is the ultimate hydrogen source for these lipids and the isotopic fractionation during biosynthesis of lipids is thought to remain constant, environmental parameters and plant physiological processes can alter the apparent hydrogen isotopic fractionation between leaf-wax lipids and a plant's source water. However, the magnitude and timing of these effects and their influence on the isotopic composition of lipids from higher terrestrial plants are still not well understood. Therefore we investigated the seasonal variability of leaf-wax n-alkane delta D values for two different temperate deciduous forest ecosystems that are dominated by two different tree species, Beech (Fagus sylvatica) and Maple (Acer pseudoplatanus). We found significant seasonal variations for both tree species in n-alkane delta D values of up to 40%. on timescales as short as one week. Also, the isotopic difference between different n-alkanes from the same plant species did vary significantly and reached up to 50 parts per thousand at the same time when overall n-alkane concentrations were lowest. Since delta D values of soil water at 5 and 10 cm depth, which we assume represent the delta D value of the major water source for the investigated beech trees, were enriched in autumn compared to the spring by 30 parts per thousand, whereas n-alkane delta D values increased only by 10 parts per thousand, we observed variations in the apparent fractionation between beech leaf derived n-alkanes and soil water of up to 20 parts per thousand on a seasonal scale. This observed change in the apparent fractionation was likely caused by differences in leaf water isotopic enrichment. Based on mechanistic leaf water models we conclude that changes in the isotopic difference between water vapor and soil water were the most likely reason for the observed changes in the apparent fractionation between n- alkanes and soil water. The large variability of n-alkane concentrations and delta D values over time implies a continuous de nova synthesis of these compounds over the growing season with turnover times possibly as short as weeks. The signal to reach the soil therefore represents an integrated record of the last weeks before leaf senescence. This holds true also for the sedimentary record of small catchment lakes in humid, temperate climates, where wind transport of leaf-wax lipids is negligible compared to transfer through soil and the massive input of leaves directly into the lake in autumn. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/01466380 U6 - https://doi.org/10.1016/j.orggeochem.2009.02.008 SN - 0146-6380 ER - TY - JOUR A1 - Sachse, Dirk A1 - Dawson, Todd E. A1 - Kahmen, Ansgar T1 - Seasonal variation of leaf wax n-alkane production and delta H-2 values from the evergreen oak tree, Quercus agrifolia JF - Isotopes in environmental and health studies N2 - In order to understand the timing of leaf wax synthesis in higher plants, we analysed the variability in leaf wax n-alkane concentration, composition (expressed as average chain length (ACL)), and delta H-2(wax) values as well as plant source water delta H-2 values (xylem and leaf water) in the evergreen tree Quercus agrifolia over a period of 9 months, beginning with leaf flush. We identified three distinct periods of leaf development with the first month following leaf flush being characterized by de novo synthesis and possibly removal of n-alkanes. During the following 3 months, n-alkane concentrations increased sevenfold and delta H-2(wax) and ACL values increased, suggesting this period was the major leaf wax n-alkane formation period. During the remaining 4 months of the experiment, stable values suggest cessation of leaf wax n-alkane formation. We find that n-alkane synthesis in Q. agrifolia takes place over 4 months, substantially longer than that observed for deciduous trees. KW - leaf wax KW - oak tree KW - hydrogen-2 KW - isotope ecology KW - n-alkanes Y1 - 2015 U6 - https://doi.org/10.1080/10256016.2015.1011636 SN - 1025-6016 SN - 1477-2639 VL - 51 IS - 1 SP - 124 EP - 142 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Sachse, Dirk A1 - Billault, Isabelle A1 - Bowen, Gabriel J. A1 - Chikaraishi, Yoshito A1 - Dawson, Todd E. A1 - Feakins, Sarah J. A1 - Freeman, Katherine H. A1 - Magill, Clayton R. A1 - McInerney, Francesca A. A1 - van der Meer, Marcel T. J. A1 - Polissar, Pratigya A1 - Robins, Richard J. A1 - Sachs, Julian P. A1 - Schmidt, Hanns-Ludwig A1 - Sessions, Alex L. A1 - White, James W. C. A1 - West, Jason B. A1 - Kahmen, Ansgar ED - Jeanloz, R T1 - Molecular Paleohydrology interpreting the Hydrogen- Isotopic Composition of Lipid Biomarkers from Photosynthesizing Organisms JF - Annual review of earth and planetary sciences JF - Annual Review of Earth and Planetary Sciences N2 - Hydrogen-isotopic abundances of lipid biomarkers are emerging as important proxies in the study of ancient environments and ecosystems. A decade ago, pioneering studies made use of new analytical methods and demonstrated that the hydrogen-isotopic composition of individual lipids from aquatic and terrestrial organisms can be related to the composition of their growth (i.e., environmental) water. Subsequently, compound-specific deuterium/hydrogen (D/H) ratios of sedimentary biomarkers have been increasingly used as paleohydrological proxies over a range of geological timescales. Isotopic fractionation observed between hydrogen in environmental water and hydrogen in lipids, however, is sensitive to biochemical, physiological, and environmental influences on the composition of hydrogen available for biosynthesis in cells. Here we review the factors and processes that are known to influence the hydrogen-isotopic compositions of lipids-especially n-alkanes-from photosynthesizing organisms, and we provide a framework for interpreting their D/H ratios from ancient sediments and identify future research opportunities. KW - paleoclimate KW - paleoclimate proxy KW - deuterium KW - organic geochemistry Y1 - 2012 SN - 978-0-8243-2040-9 U6 - https://doi.org/10.1146/annurev-earth-042711-105535 SN - 0084-6597 VL - 40 IS - 1 SP - 221 EP - 249 PB - Annual Reviews CY - Palo Alto ER - TY - JOUR A1 - Romero-Viana, Lidia A1 - Kienel, Ulrike A1 - Wilkes, Heinz A1 - Sachse, Dirk T1 - Growth-dependent hydrogen isotopic fractionation of algal lipid biomarkers in hypersaline Isabel Lake (Mexico) JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - In this study, we evaluated the potential of the hydrogen isotopic composition of algal lipid biomarkers as a proxy for past hydroclimatic variability in hypersaline Isabel Lake, Mexico (Eastern Pacific). We compared rainfall variability recorded in the region over the last 65 years with changes in delta D values of the most abundant compounds preserved in the uppermost 16 cm of lake sediment. Changes in delta D values of the 1,15-C-32 diol (delta D-diol), a specific biomarker of algal populations, were related to rainfall variability; specifically, n-alkyl diols were more deuterium-enriched (depleted) during wetter (drier) periods. Strikingly, neither the magnitude of lipid biomarker isotopic changes over interannual timescales (of up to 70-80 parts per thousand) nor the direction of that variability can be explained by changes in delta D values of the water source or salinity fluctuations (approximately 30 on the practical salinity scale) controlled by seasonal rainfall. However, changes in sedimentary biomarker composition, higher total organic carbon content and less negative delta C-13 values of the 1,15-C-32 diol indicate enhanced algal growth during wetter periods. We find that these conditions result in less negative delta D values of n-alkyl diols. We hypothesize that due to higher lipid demand during enhanced algal growth, an increasing proportion of hydrogen for lipid synthesis is derived from the cytosol via oxidation of polysaccharides, which may cause a deuterium enrichment of the acetogenic compounds. This study has significant implications for paleohydrological reconstructions using algal lipid delta D values, particularly in highly seasonal environments such as Isabel Lake. In such environments, delta D values of specific algal lipid biomarkers may not record the full seasonal cycle in source water delta D but appear to be mainly controlled by the physiological state of algal populations. Our data provide the first evidence that changes in D/H fractionation due to algal growth conditions can be recorded in sediments. For paleoclimate reconstructions in such environments, algal growth conditions should be constrained with additional proxy data (delta C-13 values of the same biomarkers), as the net D/H fractionation between water and lipids may not have been constant over time. Y1 - 2013 U6 - https://doi.org/10.1016/j.gca.2012.12.017 SN - 0016-7037 VL - 106 IS - 4 SP - 490 EP - 500 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Romero-Viana, Lidia A1 - Kienel, Ulrike A1 - Sachse, Dirk T1 - Lipid biomarker signatures in a hypersaline lake on Isabel Island (Eastern Pacific) as a proxy for past rainfall anomaly (1942-2006 AD) JF - Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences N2 - Isabel Lake is a hypersaline crater-lake on Isabel Island, Mexico, situated in the eastern tropical Pacific, an area highly sensitive to hydrological changes. Today, annual rainfall mostly occurs during the wet season, from June to October, when the northern edge of the Intertropical Convergence Zone (ITCZ) extends over the island. In order to evaluate the potential of sedimentary lipid biomarker signatures as a proxy of past hydro-climatic variability we have performed a calibration analysis comparing changes in biomarker distribution in the upper 16 cm of the sediment core with a regional instrumental data set. Annual laminations present in the sediment sequence allow for precise chronological control (1942-2006), More than 80 different lipid compounds were identified in the sediment and could be assigned to three major groups of source organisms: (1) algal populations; (2) a mixed community of ciliates, bacteria and cyanobacteria; and (3) photosynthetic sulfur bacteria. We found that the observed changes in the. relative contribution of the different lipid biomarkers to the sediment record were determined by the regional rainfall variability over the last 65 years. The planktonic community of Isabel Lake was highly sensitive to salinity fluctuations related to rainfall variability; seasonal precipitation results in freshwater input into the lake, driving an annual algal bloom and a relative decrease in the abundance of the more halotolerant populations of (cyano) bacteria and ciliates. Consequently, the concentration ratio between the two most abundant biomarkers in the Isabel Lake sediments, n-alkyl diols and tetrahymanol (which we define as the DiTe index), representing algal and ciliate planktonic populations, respectively, was significantly correlated with the seasonal rainfall anomaly (r = 0.68, p < 0.01). We propose that the DiTe index is a proxy of changes in the aquatic ecosystem of Isabel Lake and, by extension, regional hydrological changes in a sensitive climatic area of the eastern tropical Pacific. KW - Lipid KW - biomarkers KW - Diol KW - Tetrahymanol KW - ENSO KW - Salinity KW - Paleoclimate KW - Mexico Y1 - 2012 U6 - https://doi.org/10.1016/j.palaeo.2012.06.011 SN - 0031-0182 VL - 350 IS - 18 SP - 49 EP - 61 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Rohrmann, Alexander A1 - Strecker, Manfred A1 - Bookhagen, Bodo A1 - Mulch, Andreas A1 - Sachse, Dirk A1 - Pingel, Heiko A1 - Alonso, Ricardo N. A1 - Schildgen, Taylor F. A1 - Montero, Carolina T1 - Can stable isotopes ride out the storms? The role of convection for water isotopes in models, records, and paleoaltimetry studies in the central Andes JF - Earth & planetary science letters KW - stable isotopes KW - Andes KW - precipitation KW - convection KW - paleoaltimetry KW - TRMM satellite data Y1 - 2014 U6 - https://doi.org/10.1016/j.epsl.2014.09.021 SN - 0012-821X SN - 1385-013X VL - 407 SP - 187 EP - 195 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Rohrmann, Alexander A1 - Sachse, Dirk A1 - Mulch, Andreas A1 - Pingel, Heiko A1 - Tofelde, Stefanie A1 - Alonso, Ricardo N. A1 - Strecker, Manfred T1 - Miocene orographic uplift forces rapid hydrological change in the southern central Andes JF - Scientific reports N2 - Rainfall in the central Andes associated with the South American Monsoon and the South American Low-Level Jet results from orographic effects on atmospheric circulation exerted by the Andean Plateau and the Eastern Cordillera. However, despite its importance for South American climate, no reliable records exist that allow decoding the evolution of thresholds and interactions between Andean topography and atmospheric circulation, especially regarding the onset of humid conditions in the inherently dry southern central Andes. Here, we employ multi-proxy isotope data of lipid biomarkers, pedogenic carbonates and volcanic glass from the Eastern Cordillera of NW Argentina and present the first long-term evapotranspiration record. We find that regional eco-hydrology and vegetation changes are associated with initiation of moisture transport via the South American Low-Level Jet at 7.6 Ma, and subsequent lateral growth of the orogen at 6.5 Ma. Our results highlight that topographically induced changes in atmospheric circulation patterns, not global climate change, were responsible for late Miocene environmental change in this part of the southern hemisphere. This suggests that mountain building over time fundamentally controlled habitat evolution along the central Andes. Y1 - 2016 U6 - https://doi.org/10.1038/srep35678 SN - 2045-2322 VL - 6 SP - 4283 EP - 4306 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Riedel, Nils A1 - Stebich, Martina A1 - Anoop, Ambili A1 - Basavaiah, Nathani A1 - Menzel, Philip A1 - Prasad, Sushma A1 - Sachse, Dirk A1 - Sarkar, Saswati A1 - Wiesner, Martin T1 - Modern pollen vegetation relationships in a dry deciduous monsoon forest: A case study from Lonar Crater Lake, central India JF - Quaternary international : the journal of the International Union for Quaternary Research N2 - As part of ongoing research on Holocene lacustrine sediments of Lonar Crater Lake (central India), pollen assemblages in lake surface sediment and soil samples were studied to unravel pollenevegetation relationships, including pollen transport processes in tropical dry deciduous forest vegetation. Furthermore, palynological results were compared with geochemical proxies and spatial features of the lake sediments and the vegetation. The obtained data reveal strong differences in pollen assemblages and pollen concentrations between and within the studied trapping media. Local arboreal vegetation is adequately represented in the soil samples, but is less represented in the lake surface sediment samples. The composition of the lacustrine pollen assemblages is mainly influenced by patterns of transport through surface and channel runoff. Besides the relevance of our new data for reliable interpretation of fossil pollen spectra extracted from Lonar sediment cores, the results of this study are of general importance for the understanding of Quaternary pollen assemblages from tropical lacustrine archives, as well as for the implementation and selection of suitable approaches for quantitative pollen based environmental reconstructions in south Asia and beyond. (C) 2015 Elsevier Ltd and INQUA. All rights reserved. KW - Tropical dry deciduous forests KW - Modern pollen/vegetation relationships KW - Lonar Lake KW - Central India Y1 - 2015 U6 - https://doi.org/10.1016/j.quaint.2015.01.046 SN - 1040-6182 SN - 1873-4553 VL - 371 SP - 268 EP - 279 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Repasch, Marisa A1 - Wittmann, Hella A1 - Scheingross, Joel S. A1 - Sachse, Dirk A1 - Szupiany, Ricardo A1 - Orfeo, Oscar A1 - Fuchs, Margret A1 - Hovius, Niels T1 - Sediment Transit Time and Floodplain Storage Dynamics in Alluvial Rivers Revealed by Meteoric 10Be JF - Journal of Geophysical Research: Earth Surface N2 - Quantifying the time scales of sediment transport and storage through river systems is fundamental for understanding weathering processes, biogeochemical cycling, and improving watershed management, but measuring sediment transit time is challenging. Here we provide the first systematic test of measuring cosmogenic meteoric Beryllium-10 (10Bem) in the sediment load of a large alluvial river to quantify sediment transit times. We take advantage of a natural experiment in the Rio Bermejo, a lowland alluvial river traversing the east Andean foreland basin in northern Argentina. This river has no tributaries along its trunk channel for nearly 1,300 km downstream from the mountain front. We sampled suspended sediment depth profiles along the channel and measured the concentrations of 10Bem in the chemically extracted grain coatings. We calculated depth-integrated 10Bem concentrations using sediment flux data and found that 10Bem concentrations increase 230% from upstream to downstream, indicating a mean total sediment transit time of 8.4 ± 2.2 kyr. Bulk sediment budget-based estimates of channel belt and fan storage times suggest that the 10Bem tracer records mixing of old and young sediment reservoirs. On a reach scale, 10Bem transit times are shorter where the channel is braided and superelevated above the floodplain, and longer where the channel is incised and meandering, suggesting that transit time is controlled by channel morphodynamics. This is the first systematic application of 10Bem as a sediment transit time tracer and highlights the method's potential for inferring sediment routing and storage dynamics in large river systems. KW - meteoric 10Be KW - sediment transit time KW - river sediment KW - floodplains KW - sediment routing Y1 - 2019 U6 - https://doi.org/10.1029/2019JF005419 SN - 2169-9011 SN - 2169-9003 VL - 125 PB - Wiley CY - Hoboken, NJ ER - TY - JOUR A1 - Rach, Oliver A1 - Kahmen, Ansgar A1 - Brauer, Achim A1 - Sachse, Dirk T1 - A dual-biomarker approach for quantification of changes in relative humidity from sedimentary lipid D/H ratios JF - Climate of the past : an interactive open access journal of the European Geosciences Union N2 - Past climatic change can be reconstructed from sedimentary archives by a number of proxies. However, few methods exist to directly estimate hydrological changes and even fewer result in quantitative data, impeding our understanding of the timing, magnitude and mechanisms of hydrological changes. Here we present a novel approach based on delta H-2 values of sedimentary lipid biomarkers in combination with plant physiological modeling to extract quantitative information on past changes in relative humidity. Our initial application to an annually laminated lacustrine sediment sequence from western Europe deposited during the Younger Dryas cold period revealed relative humidity changes of up to 15% over sub-centennial timescales, leading to major ecosystem changes, in agreement with palynological data from the region. We show that by combining organic geochemical methods and mechanistic plant physiological models on well characterized lacustrine archives it is possible to extract quantitative ecohydrological parameters from sedimentary lipid biomarker delta H-2 data. Y1 - 2017 U6 - https://doi.org/10.5194/cp-13-741-2017 SN - 1814-9324 SN - 1814-9332 VL - 13 SP - 741 EP - 757 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Rach, Oliver A1 - Engels, S. A1 - Kahmen, A. A1 - Brauer, Achim A1 - Martin-Puertas, C. A1 - van Geel, B. A1 - Sachse, Dirk T1 - Hydrological and ecological changes in western Europe between 3200 and 2000 years BP derived from lipid biomarker delta D values in lake Meerfelder Maar sediments JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - One of the most significant Late Holocene climate shifts occurred around 2800 years ago, when cooler and wetter climate conditions established in western Europe. This shift coincided with an abrupt change in regional atmospheric circulation between 2760 and 2560 cal years BP, which has been linked to a grand solar minimum with the same duration (the Homeric Minimum). We investigated the temporal sequence of hydroclimatic and vegetation changes across this interval of climatic change (Homeric climate oscillation) by using lipid biomarker stable hydrogen isotope ratios (ED values) and pollen assemblages from the annually-laminated sediment record from lake Meerfelder Maar (Germany). Over the investigated interval (3200-2000 varve years BP), terrestrial lipid biomarker ED showed a gradual trend to more negative values, consistent with the western Europe long-term climate trend of the Late Holocene. At ca. 2640 varve years BP we identified a strong increase in aquatic plants and algal remains, indicating a rapid change in the aquatic ecosystem superimposed on this long-term trend. Interestingly, this aquatic ecosystem change was accompanied by large changes in ED values of aquatic lipid biomarkers, such as nC(21) and nC(23) (by between 22 and 30%(0)). As these variations cannot solely be explained by hydroclimate changes, we suggest that these changes in the Wag value were influenced by changes in n-alkane source organisms. Our results illustrate that if ubiquitous aquatic lipid biomarkers are derived from a limited pool of organisms, changes in lake ecology can be a driving factor for variations on sedimentary lipid MN values, which then could be easily misinterpreted in terms of hydro climatic changes. (C) 2017 Elsevier Ltd. All rights reserved. KW - Holocene KW - Climate dynamics KW - Paleoclimatology KW - Western Europe KW - Continental biomarkers KW - Organic geochemistry KW - Stable isotopes KW - Vegetation dynamics Y1 - 2017 U6 - https://doi.org/10.1016/j.quascirev.2017.07.019 SN - 0277-3791 VL - 172 SP - 44 EP - 54 PB - Elsevier CY - Oxford ER -