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 - GEN 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 T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 543 KW - n-alkaline distributions KW - East-Asian monsoon KW - lacustrine sedimentary sequence KW - intertropical convergence zone KW - Western Nanling mountains KW - North-Atlantic climate KW - delta-D values KW - summer monsoon KW - isotopic composition KW - hydrogen isotopes Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-411608 SN - 1866-8372 IS - 543 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 - GEN 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 T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1119 KW - meteoric 10Be KW - sediment transit time KW - river sediment KW - floodplains KW - sediment routing Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-494324 SN - 1866-8372 IS - 1119 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 - GEN 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 T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 660 KW - delta-D values KW - hydrogen-isotopic composition KW - Dryas cold period KW - n-alkanes record KW - leaf water KW - Younger Dryas KW - seasonal variation KW - Lake sediments KW - Central Europe KW - climate varibility Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-418731 SN - 1866-8372 IS - 660 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 - TY - JOUR A1 - Rach, Oliver A1 - Brauer, Achim A1 - Wilkes, Heinz A1 - Sachse, Dirk T1 - Delayed hydrological response to Greenland cooling at the onset of the Younger Dryas in western Europe JF - Nature geoscience N2 - The general warming trend of the last deglaciation was interrupted by the Younger Dryas, a period of abrupt cooling and widespread environmental change(1-10). Ice core records suggest the abrupt cooling began 12,846 years ago in Greenland(10), about 170 years before the significant environmental and vegetation change in western Europe(7) classically defined as the Younger Dryas. However, this difference in timing falls within age model uncertainties. Here we use the hydrogen isotope composition of lipid biomarkers from precisely dated varved sediments from Lake Meerfelder Maar to reconstruct hydroclimate over western Europe. We observe a decrease in the hydrogen isotope values of both aquatic and terrestrial lipids 12,850 years ago, indicating cooling climate in this region synchronous with the abrupt cooling in Greenland. A second drop occurs 170 years later, mainly in the hydrogen isotope record of aquatic lipids but to a lesser extent in the terrestrial lipids, which we attribute to aridification, as well as a change in moisture source and pathway. We thus confirm that there was indeed a lag between cooling and substantial hydrologic and environmental change in western Europe. We suggest the delay is related to the expansion of sea ice in the North Atlantic Ocean and the subsequent southward migration of the westerly wind system(9). We further suggest that these hydrological changes amplified environmental change in western Europe at the onset of the Younger Dryas. Y1 - 2014 U6 - https://doi.org/10.1038/NGEO2053 SN - 1752-0894 SN - 1752-0908 VL - 7 IS - 2 SP - 109 EP - 112 PB - Nature Publ. Group CY - New York ER - TY - JOUR A1 - Prasad, Sushma A1 - Anoop, A. A1 - Riedel, N. A1 - Sarkar, Saswati A1 - Menzel, P. A1 - Basavaiah, Nathani A1 - Krishnan, R. A1 - Fuller, D. A1 - Plessen, Birgit A1 - Gaye, B. A1 - Roehl, U. A1 - Wilkes, H. A1 - Sachse, Dirk A1 - Sawant, R. A1 - Wiesner, M. G. A1 - Stebich, M. T1 - Prolonged monsoon droughts and links to Indo-Pacific warm pool: A Holocene record from Lonar Lake, central India JF - Earth & planetary science letters N2 - Concerns about the regional impact of global climate change in a warming scenario have highlighted the gaps in our understanding of the Indian Summer Monsoon (ISM, also referred to as the Indian Ocean summer monsoon) and the absence of long term palaeoclimate data from the central Indian core monsoon zone (CMZ). Here we present the first high resolution, well-dated, multiproxy reconstruction of Holocene palaeoclimate from a 10 m long sediment core raised from the Lonar Lake in central India. We show that while the early Holocene onset of-intensified monsoon in the CMZ is similar to that reported from other ISM records, the Lonar data shows two prolonged droughts (PD, multidecadal to centennial periods of weaker monsoon) between 4.6-3.9 and 2-0.6 cal ka. A comparison of our record with available data from other ISM influenced sites shows that the impact of these PD was observed in varying degrees throughout the ISM realm and coincides with intervals of higher solar irradiance. We demonstrate that (i) the regional warming in the Indo-Pacific Warm Pool (IPWP) plays an important role in causing ISM PD through changes in meridional overturning circulation and position of the anomalous Walker cell; (ii) the long term influence of conditions like El Nino-Southern Oscillation (ENSO) on the ISM began only ca. 2 cal ka BP and is coincident with the warming of the southern IPWP; (iii) the first settlements in central India coincided with the onset of the first PD and agricultural populations flourished between the two PD, highlighting the significance of natural climate variability and PD as major environmental factors affecting human settlements. KW - Indian summer monsoon KW - ENSO KW - prolonged droughts KW - Holocene KW - Lonar Lake Y1 - 2014 U6 - https://doi.org/10.1016/j.epsl.2014.01.043 SN - 0012-821X SN - 1385-013X VL - 391 SP - 171 EP - 182 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Olen, Stephanie M. A1 - Bookhagen, Bodo A1 - Hoffmann, Bernd A1 - Sachse, Dirk A1 - Adhikari, Danda P. A1 - Strecker, Manfred T1 - Understanding erosion rates in the Himalayan orogen: A case study from the Arun Valley JF - Journal of geophysical research : Earth surface N2 - Understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution. Denudation rates derived from terrestrial cosmogenic nuclides (TCNs) are commonly used to quantify erosion and bridge tectonic (Myr) and climatic (up to several kiloyears) time scales. However, how the processes of erosion in active orogens are ultimately reflected in Be-10 TCN samples remains a topic of discussion. We investigate this problem in the Arun Valley of eastern Nepal with 34 new Be-10-derived catchment-mean denudation rates. The Arun Valley is characterized by steep north-south gradients in topography and climate. Locally, denudation rates increase northward, from <0.2mmyr(-1) to similar to 1.5mmyr(-1) in tributary samples, while main stem samples appear to increase downstream from similar to 0.2mmyr(-1) at the border with Tibet to 0.91mmyr(-1) in the foreland. Denudation rates most strongly correlate with normalized channel steepness (R-2=0.67), which has been commonly interpreted to indicate tectonic activity. Significant downstream decrease of Be-10 concentration in the main stem Arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample. This results in Be-10 concentrations and denudation rates that do not uniformly represent the upstream catchment area. We observe strong impacts on Be-10 concentrations from local, nonfluvial geomorphic processes, such as glaciation and landsliding coinciding with areas of peak rainfall rates, pointing toward climatic modulation of predominantly tectonically driven denudation rates. Y1 - 2015 U6 - https://doi.org/10.1002/2014JF003410 SN - 2169-9003 SN - 2169-9011 VL - 120 IS - 10 SP - 2080 EP - 2102 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Nieto-Moreno, Vanesa A1 - Rohrmann, Alexander A1 - van der Meer, Marcel T. J. A1 - Damste, Jaap S. Sinninghe A1 - Sachse, Dirk A1 - Tofelde, Stefanie A1 - Niedermeyer, Eva M. A1 - Strecker, Manfred A1 - Mulch, Andreas T1 - Elevation-dependent changes in n-alkane delta D and soil GDGTs across the South Central Andes JF - Earth & planetary science letters N2 - Surface uplift of large plateaus may significantly influence regional climate and more specifically precipitation patterns and temperature, sometimes complicating paleoaltimetry interpretations. Thus, understanding the topographic evolution of tectonically active mountain belts benefits from continued development of reliable proxies to reduce uncertainties in paleoaltimetry reconstructions. Lipid biomarker-based proxies provide a novel approach to stable isotope paleoaltimetry and complement authigenic or pedogenic mineral proxy materials, in particular outside semi-arid climate zones where soil carbonates are not abundant but (soil) organic matter has a high preservation potential. Here we present delta D values of soil-derived n-alkanes and mean annual air temperature (MAT) estimates based on branched glycerol dialkyl glycerol tetraether (brGDGT) distributions to assess their potential for paleoelevation reconstructions in the southern central Andes. We analyzed soil samples across two environmental and hydrological gradients that include a hillslope (26-28 degrees S) and a valley (22-24 degrees S) transect on the windward flanks of Central Andean Eastern Cordillera in NW Argentina. Our results show that present-day n-alkane delta D values and brGDGT-based MAT estimates are both linearly related with elevation and in good agreement with present-day climate conditions. Soil n-alkanes show a delta D lapse rate (A(delta D)) of -1.64 parts per thousand/100 m (R-2 = 0.91, p < 0.01) at the hillslope transect, within the range of delta D lapse rates from precipitation and surface waters in other tropical regions in the Andes like the Eastern Cordillera in Colombia and Bolivia and the Equatorial and Peruvian Andes. BrGDGT-derived soil temperatures are similar to monitored winter temperatures in the region and show a lapse rate of Delta T = -0.51 degrees C/100 m (R-2 = 0.91, p < 0.01), comparable with lapse rates from in situ soil temperature measurements, satellite derived land-surface temperatures at this transect, and weather stations from the Eastern Cordillera at similar latitude. As a result of an increasing leeward sampling position along the valley transect lapse rates are biased towards lower values and display higher scatter (Delta(delta D) = -0.9 parts per thousand/100 m, R-2 = 0.76, p < 0.01 and Delta T = -0.19 degrees C/100 m, R-2 = 0.48, p < 0.05). Despite this higher complexity, they are in line with lapse rates from stream-water samples and in situ soil temperature measurements along the same transect. Our results demonstrate that both soil n-alkane delta D values and MAT reconstructions based on brGDGTs distributions from the hillslope transect (Delta(delta D) = -1.64 parts per thousand/100 m, R-2 = 0.91, p < 0.01 and Delta T = -0.51 degrees C/100 m, R-2 = 0.91, p < 0.01) track the direct effects of orography on precipitation and temperature and hence the combined effects of local and regional hydrology as well as elevation. (C) 2016 Elsevier B.V. All rights reserved. KW - South Central Andes KW - leaf-wax n-alkane delta D KW - branched GDGTs KW - MAT(mr) paleothermometer KW - paleoaltimetry proxies KW - attitudinal transects Y1 - 2016 U6 - https://doi.org/10.1016/j.epsl.2016.07.049 SN - 0012-821X SN - 1385-013X VL - 453 SP - 234 EP - 242 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Nelson, Daniel B. A1 - Knohl, Alexander A1 - Sachse, Dirk A1 - Schefulss, Enno A1 - Kahmen, Ansgar T1 - Sources and abundances of leaf waxes in aerosols in central Europe JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - Atmospheric transport is an understudied mechanism for leaf wax hydrogen isotope applications that contributes to mobilizing and depositing these compounds on the surface of the Earth. While previous efforts have identified the importance of atmospheric leaf wax deposition in remote marine locations, the processes are not well constrained on land in temperate latitudes where lakes are common and sedimentary leaf wax hydrogen isotope values are an attractive tool for understanding past precipitation changes. This work presents results from a field study that was conducted in 2010 and 2011 at Hainich National Park, Germany in order to evaluate the quantity and sources of leaf waxes in the atmosphere. Aerosols were sampled at approximately weekly intervals inside the forest canopy, and n-alkane distributions and hydrogen isotope values were compared with those from major tree species surrounding the sampling site. Despite sampling in what was expected to be a major production center, the distribution and hydrogen isotope values of atmospheric n-alkanes bore little resemblance to those of the local vegetation. Comparison with local meteorological data and to 10-day and 36-h back air mass trajectories indicated shifting effects of winds and temperature, and that mesoscale transport processes were more important than longrange mechanisms. Back trajectories also highlighted source effects, with easterly winds coinciding with relatively lower leaf wax hydrogen isotope values from more continental regions. These results suggest that leaf wax aerosols average over spatial scales that exceed typical surface catchment areas for small lake systems, even in forested areas, yet that the area over which these compounds are derived is still relatively regional. Depositional fluxes were also estimated in order to assess the potential importance of atmospheric transport to sedimentary archives. Although difficult to constrain, these estimates suggest that atmospheric deposition may be non-negligible for lake systems in cases where inputs from rivers or surface runoff are limited. Together, these observations provide new insights on how leaf waxes from different sources are integrated during aeolian transport and the spatial scales over which these processes occur. KW - Hydrogen isotopes KW - Leaf wax KW - Aerosols KW - n-Alkanes KW - Biomarkers KW - Lakes KW - Sediments Y1 - 2016 U6 - https://doi.org/10.1016/j.gca.2016.11.018 SN - 0016-7037 SN - 1872-9533 VL - 198 SP - 299 EP - 314 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Menges, Johanna A1 - Huguet, C. A1 - Alcaniz, Josep M. A1 - Fietz, Susanne A1 - Sachse, Dirk A1 - Rosell-Mele, A. T1 - Influence of water availability in the distributions of branched glycerol dialkyl glycerol tetraether in soils of the Iberian Peninsula JF - Biogeosciences Y1 - 2014 U6 - https://doi.org/10.5194/bg-11-2571-2014 SN - 1726-4170 SN - 1726-4189 VL - 11 IS - 10 SP - 2571 EP - 2581 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Menges, Johanna A1 - Hovius, Niels A1 - Andermann, Christoff A1 - Lupker, Maarten A1 - Haghipour, Negar A1 - Märki, Lena A1 - Sachse, Dirk T1 - Variations in organic carbon sourcing along a trans-Himalayan river determined by a Bayesian mixing approach JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - Rivers transfer particulate organic carbon (POC) from eroding mountains into geological sinks. Organic carbon source composition and selective mobilization have been shown to affect the type and quantity of POC export, but their combined effects across complex mountain ranges remain underexplored. Here, we examine the variation in organic carbon sourcing and transport in the trans-Himalayan Kali Gandaki River catchment, along strong gradients in precipitation, rock type and vegetation. Combining bulk stable nitrogen, and stable and radioactive organic carbon isotopic composition of bedrock, litter, soil and river sediment samples with a Bayesian end-member mixing approach, we differentiate POC sources along the river and quantify their export. Our analysis shows that POC export from the Tibetan segment of the catchment, where carbon bearing shales are partially covered by aged and modern soils, is dominated by petrogenic POC. Based on our data we re-assess the presence of aged biospheric OC in this part of the catchment, and its contribution to the river load. In the High Himalayan segment, we observed low inputs of petrogenic and biospheric POC, likely due to very low organic carbon concentrations in the metamorphic bedrock, combined with erosion dominated by deep-seated landslides. Our findings show that along the Kali Gandaki River, the sourcing of sediment and organic carbon are decoupled, due to differences in rock organic carbon content, soil and above ground carbon stocks, and geomorphic process activity. While the fast eroding High Himalayas are the principal source of river sediment, the Tibetan headwaters, where erosion rates are lower, are the principal source of organic carbon. To robustly estimate organic carbon export from the Himalayas, the mountain range should be divided into tectono-physiographic zones with distinct organic carbon yields due to differences in substrate and erosion processes and rates. KW - particulate organic carbon KW - Himalaya KW - rivers KW - carbon cycle KW - stable KW - isotopes KW - erosion KW - end-member mixing Y1 - 2020 U6 - https://doi.org/10.1016/j.gca.2020.07.003 SN - 0016-7037 VL - 286 SP - 159 EP - 176 PB - Elsevier CY - New York [u.a.] ER - TY - JOUR A1 - Menges, Johanna A1 - Hovius, Niels A1 - Andermann, Christoff A1 - Dietze, Michael A1 - Swoboda, Charlie A1 - Cook, Kristen L. A1 - Adhikari, Basanta R. A1 - Vieth-Hillebrand, Andrea A1 - Bonnet, Stephane A1 - Reimann, Tony A1 - Koutsodendris, Andreas A1 - Sachse, Dirk T1 - Late holocene landscape collapse of a trans-himalayan dryland BT - human impact and aridification JF - Geophysical research letters N2 - Soil degradation is a severe and growing threat to ecosystem services globally. Soil loss is often nonlinear, involving a rapid deterioration from a stable eco-geomorphic state once a tipping point is reached. Soil loss thresholds have been studied at plot scale, but for landscapes, quantitative constraints on the necessary and sufficient conditions for tipping points are rare. Here, we document a landscape-wide eco-geomorphic tipping point at the edge of the Tibetan Plateau and quantify its drivers and erosional consequences. We show that in the upper Kali Gandaki valley, Nepal, soil formation prevailed under wetter conditions during much of the Holocene. Our data suggest that after a period of human pressure and declining vegetation cover, a 20% reduction of relative humidity and precipitation below 200 mm/year halted soil formation after 1.6 ka and promoted widespread gullying and rapid soil loss, with irreversible consequences for ecosystem services. KW - geomorphology KW - paleoclimate KW - human activity KW - Tibetan plateau KW - late Holocene Y1 - 2019 U6 - https://doi.org/10.1029/2019GL084192 SN - 0094-8276 SN - 1944-8007 VL - 46 IS - 23 SP - 13814 EP - 13824 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Meese, Bernd A1 - Bookhagen, Bodo A1 - Olen, Stephanie M. A1 - Barthold, Frauke Katrin A1 - Sachse, Dirk T1 - The effect of Indian Summer Monsoon rainfall on surface water delta D values in the central Himalaya JF - Hydrological processes N2 - Stable isotope proxy records, such as speleothems, plant-wax biomarker records, and ice cores, are suitable archives for the reconstruction of regional palaeohydrologic conditions. But the interpretation of these records in the tropics, especially in the Indian Summer Monsoon (ISM) domain, is difficult due to differing moisture and water sources: precipitation from the ISM and Winter Westerlies, as well as snow- and glacial meltwater. In this study, we use interannual differences in ISM strength (2011-2012) to understand the stable isotopic composition of surface water in the Arun River catchment in eastern Nepal. We sampled main stem and tributary water (n = 204) for stable hydrogen and oxygen isotope analysis in the postmonsoon phase of two subsequent years with significantly distinct ISM intensities. In addition to the 2011/2012 sampling campaigns, we collected a 12-month time series of main stem waters (2012/2013, n = 105) in order to better quantify seasonal effects on the variability of surface water delta O-18/delta D. Furthermore, remotely sensed satellite data of rainfall, snow cover, glacial coverage, and evapotranspiration was evaluated. The comparison of datasets from both years revealed that surface waters of the main stem Arun and its tributaries were D-enriched by similar to 15 parts per thousand when ISM rainfall decreased by 20%. This strong response emphasizes the importance of the ISM for surface water run-off in the central Himalaya. However, further spatio-temporal analysis of remote sensing data in combination with stream water d-excess revealed that most high-altitude tributaries and the Tibetan part of the Arun receive high portions of glacial melt water and likely Winter Westerly Disturbances precipitation. We make the following two implications: First, palaeohydrologic archives found in high-altitude tributaries and on the southern Tibetan Plateau record a mixture of past precipitation delta D values and variable amounts of additional water sources. Second, surface water isotope ratios of lower elevated tributaries strongly reflect the isotopic composition of ISM rainfall implying a suitable region for the analysis of potential delta D value proxy records. KW - Himalaya KW - palaeoclimate records KW - snow melt KW - stream water KW - water isotopes Y1 - 2018 U6 - https://doi.org/10.1002/hyp.13281 SN - 0885-6087 SN - 1099-1085 VL - 32 IS - 24 SP - 3662 EP - 3674 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Kahmen, Ansgar A1 - Schefuss, Enno A1 - Sachse, Dirk T1 - Leaf water deuterium enrichment shapes leaf wax n-alkane delta D values of angiosperm plants I experimental evidence and mechanistic insights JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - Leaf wax n-alkanes of terrestrial plants are long-chain hydrocarbons that can persist in sedimentary records over geologic timescales. Since meteoric water is the primary source of hydrogen used in leaf wax synthesis, the hydrogen isotope composition (delta D value) of these biomarkers contains information on hydrological processes. Consequently, leaf wax n-alkane delta D values have been advocated as powerful tools for paleohydrological research. The exact kind of hydrological information that is recorded in leaf wax n-alkanes remains, however, unclear because critical processes that determine their delta D values have not yet been resolved. In particular the effects of evaporative deuterium (D)-enrichment of leaf water on the delta D values of leaf wax n-alkanes have not yet been directly assessed and quantified. Here we present the results of a study where we experimentally tested if and by what magnitude evaporative D-enrichment of leaf water affects the delta D of leaf wax n-alkanes in angiosperm C3 and C4 plants. Our study revealed that n-alkane delta D values of all plants that we investigated were affected by evaporative D-enrichment of leaf water. For dicotyledonous plants we found that the full extent of leaf water evaporative D-enrichment is recorded in leaf wax n-alkane delta D values. For monocotyledonous plants we found that between 18% and 68% of the D-enrichment in leaf water was recorded in the delta D values of their n-alkanes. We hypothesize that the different magnitudes by which evaporative D-enrichment of leaf water affects the delta D values of leaf wax n-alkanes in monocotyledonous and dicotyledonous plants is the result of differences in leaf growth and development between these plant groups. Our finding that the evaporative D-enrichment of leaf water affects the delta D values of leaf wax n-alkanes in monocotyledonous and dicotyledonous plants albeit at different magnitudes - has important implications for the interpretation of leaf wax n-alkane delta D values from paleohydrological records. In addition, our finding opens the door to employ delta D values of leaf wax n-alkanes as new ecohydrological proxies for evapotranspiration that can be applied in contemporary plant and ecosystem research. Y1 - 2013 U6 - https://doi.org/10.1016/j.gca.2012.09.003 SN - 0016-7037 VL - 111 SP - 39 EP - 49 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Kahmen, Ansgar A1 - Sachse, Dirk A1 - Arndt, Stefan K. A1 - Tu, Kevin P. A1 - Farrington, Heraldo A1 - Vitousek, Peter M. A1 - Dawson, Todd E. T1 - Cellulose delta O-18 is an index of leaf-to-air vapor pressure difference (VPD) in tropical plants JF - Proceedings of the National Academy of Sciences of the United States of America N2 - Cellulose in plants contains oxygen that derives in most cases from precipitation. Because the stable oxygen isotope composition, delta O-18, of precipitation is associated with environmental conditions, cellulose delta O-18 should be as well. However, plant physiological models using delta O-18 suggest that cellulose delta O-18 is influenced by a complex mix of both climatic and physiological drivers. This influence complicates the interpretation of cellulose delta O-18 values in a paleo-context. Here, we combined empirical data analyses with mechanistic model simulations to i) quantify the impacts that the primary climatic drivers humidity (e(a)) and air temperature (T-air) have on cellulose delta O-18 values in different tropical ecosystems and ii) determine which environmental signal is dominating cellulose delta O-18 values. Our results revealed that e(a) and T-air equally influence cellulose delta O-18 values and that distinguishing which of these factors dominates the delta O-18 values of cellulose cannot be accomplished in the absence of additional environmental information. However, the individual impacts of e(a) and T-air on the delta O-18 values of cellulose can be integrated into a single index of plant-experienced atmospheric vapor demand: the leaf-to-air vapor pressure difference (VPD). We found a robust relationship between VPD and cellulose delta O-18 values in both empirical and modeled data in all ecosystems that we investigated. Our analysis revealed therefore that delta O-18 values in plant cellulose can be used as a proxy for VPD in tropical ecosystems. As VPD is an essential variable that determines the biogeochemical dynamics of ecosystems, our study has applications in ecological-, climate-, or forensic-sciences. KW - stable isotopes KW - plant-water relations KW - paleoecology KW - climate change KW - Hawaii Y1 - 2011 U6 - https://doi.org/10.1073/pnas.1018906108 SN - 0027-8424 VL - 108 IS - 5 SP - 1981 EP - 1986 PB - National Acad. of Sciences CY - Washington ER - TY - JOUR A1 - Kahmen, Ansgar A1 - Dawson, Todd E. A1 - Vieth, Andrea A1 - Sachse, Dirk T1 - Leaf wax n-alkane delta D values are determined early in the ontogeny of Populus trichocarpa leaves when grown under controlled environmental conditions JF - Plant, cell & environment : cell physiology, whole-plant physiology, community physiology N2 - The stable hydrogen isotope ratios (delta D) of leaf wax n-alkanes record valuable information on plant and ecosystem water relations. It remains, however, unknown if leaf wax n-alkane delta D values record only environmental variation during the brief period of time of leaf growth or if leaf wax n-alkane delta D values are affected by environmental variability throughout the entire lifespan of a leaf. To resolve these uncertainties, we irrigated Populus trichocarpa trees with a pulse of deuterium-enriched water and used compound-specific stable hydrogen isotope analyses to test if the applied tracer could be recovered from leaf wax n-alkanes of leaves that were at different stages of their development during the tracer application. Our experiment revealed that only leaf wax n-alkanes from leaves that had developed during the time of the tracer application were affected, while leaves that were already fully matured at the time of the tracer application were not. We conclude from our study that under controlled environmental conditions, leaf wax n-alkanes are synthesized only early in the ontogeny of a leaf. Our experiment has implications for the interpretation of leaf wax n-alkane delta D values in an environmental context, as it suggests that these compounds record only a brief period of the environmental variability that a leaf experiences throughout its life. KW - cuticle KW - plant water relations KW - stable isotopes Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-3040.2011.02360.x SN - 0140-7791 VL - 34 IS - 10 SP - 1639 EP - 1651 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Jambrina-Enriquez, Margarita A1 - Sachse, Dirk A1 - Valero-Garces, Blas L. T1 - A deglaciation and Holocene biomarker-based reconstruction of climate and environmental variability in NW Iberian Peninsula: the Sanabria Lake sequence JF - Journal of paleolimnolog N2 - The molecular biomarker composition of two sediment cores from Sanabria Lake (NW Iberian Peninsula) and a survey of modern plants in the watershed provide a reconstruction of past vegetation and landscape dynamics since deglaciation. During a proglacial stage in Lake Sanabria (prior to 14.7 cal ka BP), very low biomarker concentration and carbon preference index (CPI) values similar to 1 suggest that the n-alkanes could have derived from eroded ancient sediment sources or older organic matter with high degree of maturity. During the Late glacial (14.7-11.7 cal ka BP) and the Holocene (last 11.7 cal ka BP) intervals with higher biomarker and triterpenoid concentrations (high %nC(29) , nC(31) alkanes), higher CPI and average carbon length (ACL), and lower P-aq (proportion of aquatic plants) are indicative of major contribution of vascular land plants from a more forested watershed (e.g. Mid Holocene period 7.0-4.0 cal ka BP). Lower biomarker concentrations (high %nC(27) alkanes), CPI and ACL values responded to short phases with decreased allochthonous contribution into the lake that correspond to centennial-scale periods of regional forest decline (e.g. 4-3 ka BP, Roman deforestation after 2.0 ka, and some phases of the LIA, seventeenth-nineteenth centuries). Human activities in the watershed were significant during early medieval times (1.3-1.0 cal ka BP) and since 1960 CE, in both cases associated with relatively higher productivity stages in the lake (lower biomarker and triterpenoid concentrations, high %nC(23) and %nC(31) respectively, lower ACL and CPI values and higher P-aq). The lipid composition of Sanabria Lake sediments indicates a major allochthonous (watershed-derived) contribution to the organic matter budget since deglaciation, and a dominant oligotrophic status during the lake history. The study constrains the climate and anthropogenic forcings and watershed versus lake sources in organic matter accumulation processes and helps to design conservation and management policies in mountain, oligotrophic lakes. KW - Plant n-alkanes KW - Lipid biomarker KW - Sanabria Lake KW - n-Alkanes KW - Holocene KW - Lateglacial KW - Iberian Peninsula Y1 - 2016 U6 - https://doi.org/10.1007/s10933-016-9890-6 SN - 0921-2728 SN - 1573-0417 VL - 56 SP - 49 EP - 66 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Hoffmann, Bernd A1 - Kahmen, Ansgar A1 - Cernusak, Lucas A. A1 - Arndt, Stefan K. A1 - Sachse, Dirk T1 - Abundance and distribution of leaf wax n-alkanes in leaves of Acacia and Eucalyptus trees along a strong humidity gradient in northern Australia JF - Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry N2 - Environmental parameters such as rainfall, temperature and relative humidity can affect the composition of higher plant leaf wax. The abundance and distribution of leaf wax biomarkers, such as long chain n-alkanes, in sedimentary archives have therefore been proposed as proxies reflecting climate change. However, a robust palaeoclimatic interpretation requires a thorough understanding of how environmental changes affect leaf wax n-alkane distributions in living plants. We have analysed the concentration and chain length distribution of leaf wax n-alkanes in Acacia and Eucalyptus species along a 1500 km climatic gradient in northern Australia that ranges from subtropical to arid. We show that aridity affected the concentration and distribution of n-alkanes for plants in both genera. For both Acacia and Eucalyptus n-alkane concentration increased by a factor of ten to the dry centre of Australia, reflecting the purpose of the wax in preventing water loss from the leaf. Furthermore, Acacian-alkanes decreased in average chain length (ACL) towards the arid centre of Australia, whereas Eucalyptus ACL increased under arid conditions. Our observations demonstrate that n-alkane concentration and distribution in leaf wax are sensitive to hydroclimatic conditions. These parameters could therefore potentially be employed in palaeorecords to estimate past environmental change. However, our finding of a distinct response of n-alkane ACL values to hydrological changes in different taxa also implies that the often assumed increase in ACL under drier conditions is not a robust feature for all plant species and genera and as such additional information about the prevalent vegetation are required when ACL values are used as a palaeoclimate proxy. Y1 - 2013 U6 - https://doi.org/10.1016/j.orggeochem.2013.07.003 SN - 0146-6380 VL - 62 IS - 9 SP - 62 EP - 67 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Hoffmann, Bernd A1 - Feakins, Sarah J. A1 - Bookhagen, Bodo A1 - Olen, Stephanie M. A1 - Adhikari, Danda P. A1 - Mainali, Janardan A1 - Sachse, Dirk T1 - Climatic and geomorphic drivers of plant organic matter transport in the Arun River, E Nepal JF - Earth & planetary science letters KW - plant wax biomarker KW - leaf wax delta D KW - carbon cycle KW - remote sensing KW - erosion Y1 - 2016 U6 - https://doi.org/10.1016/j.epsl.2016.07.008 SN - 0012-821X SN - 1385-013X VL - 452 SP - 104 EP - 114 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Hernandez, Martin A. A1 - Gleixner, Gerd A1 - Sachse, Dirk A1 - Alvarez, Hector M. T1 - Carbon Allocation in Rhodococcus jostii RHA1 in Response to Disruption and Overexpression of nlpR Regulatory Gene, Based on C-13-labeling Analysis JF - Frontiers in microbiology N2 - Nitrogen lipid regulator (NlpR) is a pleiotropic regulator that positively controls genes associated with both nitrogen and lipid metabolism in the oleaginous bacterium Rhodococcus jostii RHA1. In this study, we investigated the effect of nlpR disruption and overexpression on the assimilation of C-13-labeled glucose as carbon source, during cultivation of cells under nitrogen-limiting and nitrogen-rich conditions, respectively. Label incorporation into the total lipid extract (TLE) fraction was about 30% lower in the mutant strain in comparison with the wild type strain under low-nitrogen conditions. Moreover, a higher C-13 abundance (similar to 60%) into the extracellular polymeric substance fraction was observed in the mutant strain, nlpR disruption also promoted a decrease in the label incorporation into several TLE-derivative fractions including neutral lipids (NL), glycolipids (GL), phospholipids (PL), triacylglycerols (TAG), diacylglycerols (DAG), and free fatty acids (FFA), with the DAG being the most affected. In contrast, the nlpR overexpression in RHA1 cells under nitrogen-rich conditions produced an increase of the label incorporation into the TLE and its derivative NL and PL fractions, the last one being the highest C-13 enriched. In addition, a higher C-13 enrichment occurred in the TAG, DAG, and FFA fractions after nlpR induction, with the FFA fraction being the most affected within the TLE. Isotopic-labeling experiments demonstrated that NlpR regulator is contributing in oleaginous phenotype of R. jostii RHA1 to the allocation of carbon into the different lipid fractions in response to nitrogen levels, increasing the rate of carbon flux into lipid metabolism. KW - Rhodococcus KW - RHA1 KW - NlpR KW - regulation KW - C-13-glucose KW - lipid metabolism Y1 - 2017 U6 - https://doi.org/10.3389/fmicb.2017.01992 SN - 1664-302X VL - 8 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Garcin, Yannick A1 - Schwab, Valerie F. A1 - Gleixner, Gerd A1 - Kahmen, Ansgar A1 - Todou, Gilbert A1 - Sene, Olivier A1 - Onana, Jean-Michel A1 - Achoundong, Gaston A1 - Sachse, Dirk T1 - Hydrogen isotope ratios of lacustrine sedimentary n-alkanes as proxies of tropical African hydrology insights from a calibration transect across Cameroon JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - Hydrogen isotope values (delta 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 delta D values of the aquatic lipid biomarker n-C(17) alkane were not correlated with the delta D values of lake water. Carbon isotope measurements indicate that the n-C(17) alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis. We demonstrate that the delta D values of the n-C(29) alkane were correlated with the delta 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 delta D proxy on a hemispheric spatial scale. In contrast, the delta D values of the n-C(31) alkane did not show such a relationship but instead were correlated with the evaporative lake water delta 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 delta 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. Y1 - 2012 U6 - https://doi.org/10.1016/j.gca.2011.11.039 SN - 0016-7037 VL - 79 IS - 4 SP - 106 EP - 126 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Garcin, Yannick A1 - Schefuss, Enno A1 - Schwab, Valerie F. A1 - Garreta, Vincent A1 - Gleixner, Gerd A1 - Vincens, Annie A1 - Todou, Gilbert A1 - Sene, Olivier A1 - Onana, Jean-Michel A1 - Achoundong, Gaston A1 - Sachse, Dirk T1 - Reconstructing C-3 and C-4 vegetation cover using n-alkane carbon isotope ratios in recent lake sediments from Cameroon, Western Central Africa JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - Trees and shrubs in tropical Africa use the C-3 cycle as a carbon fixation pathway during photosynthesis, while grasses and sedges mostly use the C-4 cycle. Leaf-wax lipids from sedimentary archives such as the long-chain n-alkanes (e.g., n-C-27 to n-C-33) inherit carbon isotope ratios that are representative of the carbon fixation pathway. Therefore, n-alkane delta C-13 values are often used to reconstruct past C-3/C-4 composition of vegetation, assuming that the relative proportions of C-3 and C-4 leaf waxes reflect the relative proportions of C-3 and C-4 plants. We have compared the delta C-13 values of n-alkanes from modern C-3 and C-4 plants with previously published values from recent lake sediments and provide a framework for estimating the fractional contribution (areal-based) of C-3 vegetation cover (f(C3)) represented by these sedimentary archives. Samples were collected in Cameroon, across a latitudinal transect that accommodates a wide range of climate zones and vegetation types, as reflected in the progressive northward replacement of C-3-dominated rain forest by C-4-dominated savanna. The C-3 plants analysed were characterised by substantially higher abundances of n-C-29 alkanes and by substantially lower abundances of n-C-33 alkanes than the C-4 plants. Furthermore, the sedimentary delta C-13 values of n-C-29 and n-C-31 alkanes from recent lake sediments in Cameroon (-37.4%) to 26.5%) were generally within the range of delta C-13 values for C-3 plants, even when from sites where C-4 plants dominated the catchment vegetation. In such cases simple linear mixing models fail to accurately reconstruct the relative proportions of C-3 and C-4 vegetation cover when using the delta C-13 values of sedimentary n-alkanes, overestimating the proportion of C-3 vegetation, likely as a consequence of the differences in plant wax production, preservation, transport, and/or deposition between C-3 and C-4 plants. We therefore tested a set of non-linear binary mixing models using delta C-13 values from both C-3 and C-4 vegetation as end-members. The non-linear models included a sigmoid function (sine-squared) that describes small variations in the f(C3) values as the minimum and maximum delta C-13 values are approached, and a hyperbolic function that takes into account the differences between C-3 and C-4 plants discussed above. Model fitting and the estimation of uncertainties were completed using the Monte Carlo algorithm and can be improved by future data addition. Models that provided the best fit with the observed delta C-13 values of sedimentary n-alkanes were either hyperbolic functions or a combination of hyperbolic and sine-squared functions. Such non-linear models may be used to convert delta C-13 measurements on sedimentary n-alkanes directly into reconstructions of C-3 vegetation cover. (C) 2014 Elsevier Ltd. All rights reserved. Y1 - 2014 U6 - https://doi.org/10.1016/j.gca.2014.07.004 SN - 0016-7037 SN - 1872-9533 VL - 142 SP - 482 EP - 500 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Garcin, Yannick A1 - Deschamps, Pierre A1 - Menot, Guillemette A1 - de Saulieu, Geoffroy A1 - Schefuss, Enno A1 - Sebag, David A1 - Dupont, Lydie M. A1 - Oslisly, Richard A1 - Brademann, Brian A1 - Mbusnum, Kevin G. A1 - Onana, Jean-Michel A1 - Ako, Andrew A. A1 - Epp, Laura Saskia A1 - Tjallingii, Rik A1 - Strecker, Manfred A1 - Brauer, Achim A1 - Sachse, Dirk T1 - Early anthropogenic impact on Western Central African rainforests 2,600 y ago JF - Proceedings of the National Academy of Sciences of the United States of America N2 - A potential human footprint on Western Central African rainforests before the Common Era has become the focus of an ongoing controversy. Between 3,000 y ago and 2,000 y ago, regional pollen sequences indicate a replacement of mature rainforests by a forest-savannah mosaic including pioneer trees. Although some studies suggested an anthropogenic influence on this forest fragmentation, current interpretations based on pollen data attribute the "rainforest crisis" to climate change toward a drier, more seasonal climate. A rigorous test of this hypothesis, however, requires climate proxies independent of vegetation changes. Here we resolve this controversy through a continuous 10,500-y record of both vegetation and hydrological changes from Lake Barombi in Southwest Cameroon based on changes in carbon and hydrogen isotope compositions of plant waxes. delta C-13-inferred vegetation changes confirm a prominent and abrupt appearance of C-4 plants in the Lake Barombi catchment, at 2,600 calendar years before AD 1950 (cal y BP), followed by an equally sudden return to rainforest vegetation at 2,020 cal y BP. delta D values from the same plant wax compounds, however, show no simultaneous hydrological change. Based on the combination of these data with a comprehensive regional archaeological database we provide evidence that humans triggered the rainforest fragmentation 2,600 y ago. Our findings suggest that technological developments, including agricultural practices and iron metallurgy, possibly related to the large-scale Bantu expansion, significantly impacted the ecosystems before the Common Era. KW - Western Central Africa KW - late Holocene KW - rainforest crisis KW - paleohydrology KW - human activity Y1 - 2018 U6 - https://doi.org/10.1073/pnas.1715336115 SN - 0027-8424 VL - 115 IS - 13 SP - 3261 EP - 3266 PB - National Acad. of Sciences CY - Washington ER - TY - GEN A1 - Garcin, Yannick A1 - Deschamps, Pierre A1 - Menot, Guillemette A1 - de Saulieu, Geoffroy A1 - Schefuss, Enno A1 - Sebag, David A1 - Dupont, Lydie M. A1 - Oslisly, Richard A1 - Brademann, Brian A1 - Mbusnum, Kevin G. A1 - Onana, Jean-Michel A1 - Ako, Andrew A. A1 - Epp, Laura Saskia A1 - Tjallingii, Rik A1 - Strecker, Manfred A1 - Brauer, Achim A1 - Sachse, Dirk T1 - No evidence for climate variability during the late Holocene rainforest crisis in Western Central Africa REPLY T2 - Proceedings of the National Academy of Sciences of the United States of America Y1 - 2018 U6 - https://doi.org/10.1073/pnas.1808481115 SN - 0027-8424 VL - 115 IS - 29 SP - E6674 EP - E6675 PB - National Acad. of Sciences CY - Washington ER - TY - GEN A1 - Garcin, Yannick A1 - Deschamps, Pierre A1 - Menot, Guillemette A1 - de Saulieu, Geoffroy A1 - Schefuss, Enno A1 - Sebag, David A1 - Dupont, Lydie M. A1 - Oslisly, Richard A1 - Brademann, Brian A1 - Mbusnum, Kevin G. A1 - Onana, Jean-Michel A1 - Ako, Andrew A. A1 - Epp, Laura Saskia A1 - Tjallingii, Rik A1 - Strecker, Manfred A1 - Brauer, Achim A1 - Sachse, Dirk T1 - Human activity is the most probable trigger of the late Holocene rainforest crisis in Western Central Africa Reply T2 - Proceedings of the National Academy of Sciences of the United States of America Y1 - 2018 U6 - https://doi.org/10.1073/pnas.1805582115 SN - 0027-8424 VL - 115 IS - 21 SP - E4735 EP - E4736 PB - National Acad. of Sciences CY - Washington ER - TY - JOUR A1 - Gamarra, B. A1 - Sachse, Dirk A1 - Kahmen, A. T1 - Effects of leaf water evaporative H-2-enrichment and biosynthetic fractionation on leaf wax n-alkane H-2 values in C3 and C4 grasses JF - Plant, cell & environment : cell physiology, whole-plant physiology, community physiology N2 - Leaf wax n-alkane H-2 values carry important information about environmental and ecophysiological processes in plants. However, the physiological and biochemical drivers that shape leaf wax n-alkane H-2 values are not completely understood. It is particularly unclear why n-alkanes in grasses are typically H-2-depleted compared with plants from other taxonomic groups such as dicotyledonous plants and why C3 grasses are H-2-depleted compared with C4 grasses. To resolve these uncertainties, we quantified the effects of leaf water evaporative H-2-enrichment and biosynthetic hydrogen isotope fractionation on n-alkane H-2 values for a range of C3 and C4 grasses grown in climate-controlled chambers. We found that only a fraction of leaf water evaporative H-2-enrichment is imprinted on the leaf wax n-alkane H-2 values in grasses. This is interesting, as previous studies have shown in dicotyledonous plants a nearly complete transfer of this H-2-enrichment to the n-alkane H-2 values. We thus infer that the typically observed H-2-depletion of n-alkanes in grasses (as opposed to dicots) is because only a fraction of the leaf water evaporative H-2-enrichment is imprinted on the H-2 values. Our experiments also show that differences in n-alkane H-2 values between C3 and C4 grasses are largely the result of systematic differences in biosynthetic fractionation between these two plant groups, which was on average -198 and-159 parts per thousand for C3 and C4 grasses, respectively. We present novel and exciting data on how leaf wax n-alkane 2H values from grasses are affected by plant physiological (leaf water evaporative 2H-enrichment) or biochemical processes (biosynthetic hydrogen isotope fractionation). These results are very interesting because they shed new light on how naturally observed differences between 2H values from C3 and C4 grasses and dicots can be explained by systematic differences in the biosynthesis of n-alkanes between these plant group (i.e. largely driven by NADPH origins). KW - biosynthetic fractionation KW - C3 and C4 grasses KW - deuterium KW - leaf water evaporative H-2-enrichment KW - leaf wax n-alkanes Y1 - 2016 U6 - https://doi.org/10.1111/pce.12789 SN - 0140-7791 SN - 1365-3040 VL - 39 SP - 2390 EP - 2403 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Engels, Stefan A1 - Brauer, Achim A1 - Buddelmeijer, Nico A1 - Martin-Puertas, Celia A1 - Rach, Oliver A1 - Sachse, Dirk A1 - Van Geel, Bas T1 - Subdecadal-scale vegetation responses to a previously unknown late-Allerod climate fluctuation and Younger Dryas cooling at Lake Meerfelder Maar (Germany) JF - Journal of quaternary science N2 - Lake Meerfelder Maar (MFM) is the northernmost Western European sediment record with annual laminations across the Younger Dryas (YD), and the onset of the YD in the record of MFM has previously been defined as an increase in non-arboreal pollen abundance at ca. 12 680 varve a BP. Here we present a palynological record at unprecedented subdecadal resolution for MFM, covering the Allerod-YD transition. Our results show a fluctuation in pollen accumulation rates (PARs) before the onset of the YD, with lower rates between ca. 12 725 and 12 685 varve a BP. The fluctuation in PARs occurs simultaneous with a previously undescribed short fluctuation in sediment composition and varve thickness, as well as with changes in biogeochemical proxies. The combined evidence indicates signs of climatic instability ca. 45 years before the onset of the YD. The PAR records of Betula and Pinus furthermore show earlier and more abrupt changes at the onset of the YD than the percentage-records do. Finally, heliophilous herbaceous taxa show a delayed increase following the onset of the YD of ca. 145 years. This paper illustrates the potential to identify previously unrecognized climate variability and vegetation change when using subdecadal-resolution analyses. Copyright (C) 2016 John Wiley & Sons, Ltd. KW - climate instability KW - Lateglacial KW - Meerfelder Maar KW - pollen accumulation rates KW - vegetation change Y1 - 2016 U6 - https://doi.org/10.1002/jqs.2900 SN - 0267-8179 SN - 1099-1417 VL - 31 SP - 741 EP - 752 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Dietze, Elisabeth A1 - Mangelsdorf, Kai A1 - Andreev, Andreev A1 - Karger, Cornelia A1 - Schreuder, Laura T. A1 - Hopmans, Ellen C. A1 - Rach, Oliver A1 - Sachse, Dirk A1 - Wennrich, Volker A1 - Herzschuh, Ulrike T1 - Relationships between low-temperature fires, climate and vegetation during three late glacials and interglacials of the last 430 kyr in northeastern Siberia reconstructed from monosaccharide anhydrides in Lake El’gygytgyn sediments JF - Climate of the Past N2 - Landscapes in high northern latitudes are assumed to be highly sensitive to future global change, but the rates and long-term trajectories of changes are rather uncertain. In the boreal zone, fires are an important factor in climate-vegetation interactions and biogeochemical cycles. Fire regimes are characterized by small, frequent, low-intensity fires within summergreen boreal forests dominated by larch, whereas evergreen boreal forests dominated by spruce and pine burn large areas less frequently but at higher intensities. Here, we explore the potential of the monosaccharide anhydrides (MA) levoglucosan, mannosan and galactosan to serve as proxies of low-intensity biomass burning in glacial-to-interglacial lake sediments from the high northern latitudes. We use sediments from Lake El'gygytgyn (cores PG 1351 and ICDP 5011-1), located in the far north-east of Russia, and study glacial and interglacial samples of the last 430 kyr (marine isotope stages 5e, 6, 7e, 8, 11c and 12) that had different climate and biome configurations. Combined with pollen and non-pollen palynomorph records from the same samples, we assess how far the modern relationships between fire, climate and vegetation persisted during the past, on orbital to centennial timescales. We find that MAs attached to particulates were well-preserved in up to 430 kyr old sediments with higher influxes from low-intensity biomass burning in interglacials compared to glacials. MA influxes significantly increase when summergreen boreal forest spreads closer to the lake, whereas they decrease when tundra-steppe environments and, especially, Sphagnum peatlands spread. This suggests that low-temperature fires are a typical characteristic of Siberian larch forests also on long timescales. The results also suggest that low-intensity fires would be reduced by vegetation shifts towards very dry environments due to reduced biomass availability, as well as by shifts towards peatlands, which limits fuel dryness. In addition, we observed very low MA ratios, which we interpret as high contributions of galactosan and mannosan from biomass sources other than those currently monitored, such as the moss-lichen mats in the understorey of the summergreen boreal forest. Overall, sedimentary MAs can provide a powerful proxy for fire regime reconstructions and extend our knowledge of long-term natural fire-climate-vegetation feedbacks in the high northern latitudes. KW - molecular tracers KW - organic aerosols KW - emission factors KW - carbonaceous aerosols KW - pollen records KW - core PG1351 KW - biomass KW - holocene KW - levoglucosan KW - charcoal Y1 - 2020 U6 - https://doi.org/10.5194/cp-16-799-2020 SN - 1814-9332 SN - 1814-9324 VL - 16 IS - 2 SP - 788 EP - 818 PB - Copernicus Publications CY - Göttingen ER - TY - GEN A1 - Dietze, Elisabeth A1 - Mangelsdorf, Kai A1 - Andreev, Andreev A1 - Karger, Cornelia A1 - Schreuder, Laura T. A1 - Hopmans, Ellen C. A1 - Rach, Oliver A1 - Sachse, Dirk A1 - Wennrich, Volker A1 - Herzschuh, Ulrike T1 - Relationships between low-temperature fires, climate and vegetation during three late glacials and interglacials of the last 430 kyr in northeastern Siberia reconstructed from monosaccharide anhydrides in Lake El’gygytgyn sediments T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Landscapes in high northern latitudes are assumed to be highly sensitive to future global change, but the rates and long-term trajectories of changes are rather uncertain. In the boreal zone, fires are an important factor in climate-vegetation interactions and biogeochemical cycles. Fire regimes are characterized by small, frequent, low-intensity fires within summergreen boreal forests dominated by larch, whereas evergreen boreal forests dominated by spruce and pine burn large areas less frequently but at higher intensities. Here, we explore the potential of the monosaccharide anhydrides (MA) levoglucosan, mannosan and galactosan to serve as proxies of low-intensity biomass burning in glacial-to-interglacial lake sediments from the high northern latitudes. We use sediments from Lake El'gygytgyn (cores PG 1351 and ICDP 5011-1), located in the far north-east of Russia, and study glacial and interglacial samples of the last 430 kyr (marine isotope stages 5e, 6, 7e, 8, 11c and 12) that had different climate and biome configurations. Combined with pollen and non-pollen palynomorph records from the same samples, we assess how far the modern relationships between fire, climate and vegetation persisted during the past, on orbital to centennial timescales. We find that MAs attached to particulates were well-preserved in up to 430 kyr old sediments with higher influxes from low-intensity biomass burning in interglacials compared to glacials. MA influxes significantly increase when summergreen boreal forest spreads closer to the lake, whereas they decrease when tundra-steppe environments and, especially, Sphagnum peatlands spread. This suggests that low-temperature fires are a typical characteristic of Siberian larch forests also on long timescales. The results also suggest that low-intensity fires would be reduced by vegetation shifts towards very dry environments due to reduced biomass availability, as well as by shifts towards peatlands, which limits fuel dryness. In addition, we observed very low MA ratios, which we interpret as high contributions of galactosan and mannosan from biomass sources other than those currently monitored, such as the moss-lichen mats in the understorey of the summergreen boreal forest. Overall, sedimentary MAs can provide a powerful proxy for fire regime reconstructions and extend our knowledge of long-term natural fire-climate-vegetation feedbacks in the high northern latitudes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1439 KW - molecular tracers KW - organic aerosols KW - emission factors KW - carbonaceous aerosols KW - pollen records KW - core PG1351 KW - biomass KW - holocene KW - levoglucosan KW - charcoal Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516843 SN - 1866-8372 IS - 2 ER - TY - JOUR A1 - Crausbay, Shelley A1 - Genderjahn, Steffi A1 - Hotchkiss, Sara A1 - Sachse, Dirk A1 - Kahmen, Ansgar A1 - Arndt, Stefan K. T1 - Vegetation dynamics at the upper reaches of a tropical montane forest are driven by disturbance over the past 7300 years JF - Arctic, antarctic, and alpine research : an interdisciplinary journal N2 - We assessed tropical montane cloud forest (TMCF) sensitivity to natural disturbance by drought, fire, and dieback with a 7300-year-long paleorecord. We analyzed pollen assemblages, charcoal accumulation rates, and higher plant biomarker compounds (average chain length [ACL] of n-alkanes) in sediments from Wai 'anapanapa, a small lake near the upper forest limit and the mean trade wind inversion ('IWI) in Hawai`i. The paleorecord of ACL suggests increased drought frequency and a lower awl elevation from 2555-1323 cal yr B.P. and 606-334 cal yr B.P. Charcoal began to accumulate and a novel fire regime was initiated ca. 880 cal yr B.P., followed by a decreased fire return interval at ca. 550 cal yr B.P. Diebacks occurred at 2931, 2161, 1162, and 306 cal yr B.P., and two of these were independent of drought or fire. Pollen assemblages indicate that on average species composition changed only 2.8% per decade. These dynamics, though slight, were significantly associated with disturbance. The direction of species composition change varied with disturbance type. Drought was associated with significantly more vines and lianas; fire was associated with an increase in the tree fern Sadleria and indicators of open, disturbed landscapes at the expense of epiphytic ferns; whereas stand-scale dieback was associated with an increase in the tree fern Cibotium. Though this cloud forest was dynamic in response to past disturbance, it has recovered, suggesting a resilient TMCF with no evidence of state change in vegetation type (e.g., grassland or shrubland). Y1 - 2014 U6 - https://doi.org/10.1657/1938-4246-46.4.787 SN - 1523-0430 SN - 1938-4246 VL - 46 IS - 4 SP - 787 EP - 799 PB - Institute of Arctic and Alpine Research, University of Colorado CY - Boulder ER - TY - JOUR A1 - Aichner, Bernhard A1 - Ott, Florian A1 - Slowinski, Michal A1 - Norygkiewicz, Agnieszka M. A1 - Brauer, Achim A1 - Sachse, Dirk T1 - Leaf wax n-alkane distributions record ecological changes during the Younger Dryas at Trzechowskie paleolake (northern Poland) without temporal delay JF - Climate of the past : an interactive open access journal of the European Geosciences Union N2 - While of higher plant origin, a specific source assignment of sedimentary leaf wax n-alkanes remains difficult. In addition, it is unknown how fast a changing catchment vegetation would be reflected in sedimentary leaf wax archives. In particular, for a quantitative interpretation of n-alkane C and H isotope ratios in terms of paleohydrological and paleoecological changes, a better understanding of transfer times and dominant sedimentary sources of leaf wax n-alkanes is required. In this study we tested to what extent compositional changes in leaf wax n-alkanes can be linked to known vegetation changes by comparison with high-resolution palynological data from the same archive. We analyzed leaf wax n-alkane concentrations and distributions in decadal resolution from a sedimentary record from Trzechowskie paleolake (TRZ, northern Poland), covering the Late Glacial to early Holocene (13 360-9940 yr BP). As an additional source indicator of targeted n-alkanes, compound-specific carbon isotopic data have been generated in lower time resolution. The results indicated rapid responses of n-alkane distribution patterns coinciding with major climatic and paleoecological transitions. We found a shift towards higher average chain length (ACL) values at the Allerod-Younger Dryas (YD) transition between 12 680 and 12 600 yr BP, co-evaled with a decreasing contribution of arboreal pollen (mainly Pinus and Betula) and a subsequently higher abundance of pollen derived from herbaceous plants (Poaceae, Cyperaceae, Artemisia), shrubs, and dwarf shrubs (Juniperus and Salix). The termination of the YD was characterized by a successive increase in n-alkane concentrations coinciding with a sharp decrease in ACL values between 11 580 and 11 490 yr BP, reflecting the expansion of woodland vegetation at the YD-Holocene transition. A gradual reversal to longer chain lengths after 11 200 yr BP, together with decreasing n-alkane concentrations, most likely reflects the early Holocene vegetation succession with a decline of Betula. These results show that n-alkane distributions reflect vegetation changes and that a fast (i.e., subdecadal) signal transfer occurred. However, our data also indicate that a standard interpretation of directional changes in biomarker ratios remains difficult. Instead, responses such as changes in ACL need to be discussed in the context of other proxy data. In addition, we find that organic geochemical data integrate different ecological information compared to pollen, since some gymnosperm genera, such as Pinus, produce only a very low amount of n-alkanes and for this reason their contribution may be largely absent from biomarker records. Our results demonstrate that a combination of palynological and n-alkane data can be used to infer the major sedimentary leaf wax sources and constrain leaf wax transport times from the plant source to the sedimentary sink and thus pave the way towards quantitative interpretation of compound-specific hydrogen isotope ratios for paleohydrological reconstructions. Y1 - 2018 U6 - https://doi.org/10.5194/cp-14-1607-2018 SN - 1814-9324 SN - 1814-9332 VL - 14 IS - 11 SP - 1607 EP - 1624 PB - Copernicus CY - Göttingen ER -