TY - JOUR A1 - Repasch, Marisa A1 - Scheingross, Joel S. A1 - Hovius, Niels A1 - Vieth-Hillebrand, Andrea A1 - Mueller, Carsten W. A1 - Höschen, Carmen A1 - Szupiany, Ricardo N. A1 - Sachse, Dirk T1 - River organic carbon fluxes modulated by hydrodynamic sorting of particulate organic matter JF - Geophysical research letters N2 - Rivers regulate the global carbon cycle by transferring particulate organic carbon (POC) from terrestrial landscapes to marine sedimentary basins, but the processes controlling the amount and composition of fluvially exported POC are poorly understood. We propose that hydrodynamic sorting processes modify POC fluxes during fluvial transit. We test this hypothesis by studying POC transported along a similar to 1,200 km reach of the Rio Bermejo, Argentina. Nanoscale secondary ion mass spectrometry revealed that POC was either fine, mineral-associated organic matter, or coarse discrete organic particles. Mineral-associated POC is more resistant to oxidation and has a lower particle settling velocity than discrete POC. Consequently, hydraulic sorting and downstream fining amplify the proportion of fine, mineral-associated POC from similar to 55% to similar to 78% over 1,220 km of downstream transit. This suggests that mineral-associated POC has a greater probability of export and preservation in marine basins than plant detritus, which may be oxidized to CO2 during transit. KW - compound-specific stable isotopes KW - carbon fluxes KW - rivers KW - NanoSIMS; KW - sediment transport KW - hydrodynamic sorting Y1 - 2022 U6 - https://doi.org/10.1029/2021GL096343 SN - 0094-8276 SN - 1944-8007 VL - 49 IS - 3 PB - American Geophysical Union CY - Washington 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 - 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 - 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 - 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 - Dietze, Elisabeth A1 - Mangelsdorf, Kai A1 - Andreev, Andrei 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 - Dietze, Elisabeth A1 - Mangelsdorf, Kai A1 - Andreev, Andrei 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 - JOUR A1 - Aichner, Bernhard A1 - Makhmudov, Zafar A1 - Rajabov, Iljomjon A1 - Zhang, Qiong A1 - Pausata, Francesco Salvatore R. A1 - Werner, Martin A1 - Heinecke, Liv A1 - Kuessner, Marie L. A1 - Feakins, Sarah J. A1 - Sachse, Dirk A1 - Mischke, Steffen T1 - Hydroclimate in the Pamirs Was Driven by Changes in Precipitation-Evaporation Seasonality Since theLast Glacial Period JF - Geophysical research letters N2 - The Central Asian Pamir Mountains (Pamirs) are a high-altitude region sensitive to climatic change, with only few paleoclimatic records available. To examine the glacial-interglacial hydrological changes in the region, we analyzed the geochemical parameters of a 31-kyr record from Lake Karakul and performed a set of experiments with climate models to interpret the results. delta D values of terrestrial biomarkers showed insolation-driven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive delta D shifts driven by changes in precipitation seasonality were observed at ca. 31-30, 28-26, and 17-14 kyr BP. Multiproxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer evaporation, triggered higher lake levels during those episodes, possibly synchronous to northern hemispheric rapid climate events. We conclude that seasonal changes in precipitation-evaporation balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant. KW - climate KW - biomarker KW - geochemistry KW - modelling KW - paleoclimate KW - hydrology Y1 - 2019 U6 - https://doi.org/10.1029/2019GL085202 SN - 0094-8276 SN - 1944-8007 VL - 46 IS - 23 SP - 13972 EP - 13983 PB - American Geophysical Union CY - Washington 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 - 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 - 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 - 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 - 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 - Aichner, Bernhard A1 - Hilt, Sabine A1 - Perillon, Cecile A1 - Gillefalk, Mikael A1 - Sachse, Dirk T1 - Biosynthetic hydrogen isotopic fractionation factors during lipid synthesis in submerged aquatic macrophytes: Effect of groundwater discharge and salinity JF - Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry N2 - Sedimentary lipid biomarkers have become widely used tools for reconstructing past climatic and ecological changes due to their ubiquitous occurrence in lake sediments. In particular, the hydrogen isotopic composition (expressed as delta D values) of leaf wax lipids derived from terrestrial plants has been a focus of research during the last two decades and the understanding of competing environmental and plant physiological factors influencing the delta D values has greatly improved. Comparatively less attention has been paid to lipid biomarkers derived from aquatic plants, although these compounds are abundant in many lacustrine sediments. We therefore conducted a field and laboratory experiment to study the effect of salinity and groundwater discharge on the isotopic composition of aquatic plant biomarkers. We analyzed samples of the common submerged plant species, Potamogeton pectinatus (sago pondweed), which has a wide geographic distribution and can tolerate high salinity. We tested the effect of groundwater discharge (characterized by more negative delta D values relative to lake water) and salinity on the delta D values of n-alkanes from P. pectinatus by comparing plants (i) collected from the oligotrophic freshwater Lake Stechlin (Germany) at shallow littoral depth from locations with and without groundwater discharge, and (ii) plants grown from tubers collected from the eutrophic Lake Muggelsee in nutrient solution at four salinity levels. Isotopically depleted groundwater did not have a significant influence on the delta D values of n-alkanes in Lake Stechlin P. pectinatus and calculated isotopic fractionation factors epsilon(l/w) between lake water and n-alkanes averaged -137 +/- 9%(n-C-23), -136 +/- 7%(n-C-25) and -131 +/- 6%(n-C-27), respectively. Similar epsilon values were calculated for plants from Lake Muggelsee grown in freshwater nutrient solution (-134 +/- 11% for n-C-23), while greater fractionation was observed at increased salinity values of 10 (163 +/- 12%) and 15(-172 +/- 15%). We therefore suggest an average e value of -136 +/- 9% between source water and the major n-alkanes in P. pectinatus grown under freshwater conditions. Our results demonstrate that isotopic fractionation can increase by 30-40% at salinity values 10 and 15. These results could be explained either by inhibited plant growth at higher salinity, or by metabolic adaptation to salt stress that remain to be elucidated. A potential salinity effect on dD values of aquatic lipids requires further examination, since this would impact on the interpretation of downcore isotopic data in paleohydrologic studies. (C) 2017 Elsevier Ltd. All rights reserved. Y1 - 2017 U6 - https://doi.org/10.1016/j.orggeochem.2017.07.021 SN - 0146-6380 VL - 113 SP - 10 EP - 16 PB - Elsevier CY - Oxford 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 - 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 - 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 -