TY - JOUR A1 - Garcin, Yannick A1 - Schildgen, Taylor F. A1 - Acosta, Veronica Torres A1 - Melnick, Daniel A1 - Guillemoteau, Julien A1 - Willenbring, Jane A1 - Strecker, Manfred T1 - Short-lived increase in erosion during the African Humid Period BT - evidence from the northern Kenya Rift JF - Earth & planetary science letters N2 - The African Humid Period (AHP) between similar to 15 and 5.5 cal. kyr BP caused major environmental change in East Africa, including filling of the Suguta Valley in the northern Kenya Rift with an extensive (similar to 2150 km(2)), deep (similar to 300 m) lake. Interfingering fluvio-lacustrine deposits of the Baragoi paleo-delta provide insights into the lake-level history and how erosion rates changed during this time, as revealed by delta-volume estimates and the concentration of cosmogenic Be-10 in fluvial sand. Erosion rates derived from delta-volume estimates range from 0.019 to 0.03 mm yr(-1). Be-10-derived paleo-erosion rates at similar to 11.8 cal. kyr BP ranged from 0.035 to 0.086 mm yr(-1), and were 2.7 to 6.6 times faster than at present. In contrast, at similar to 8.7 cal. kyr BP, erosion rates were only 1.8 times faster than at present. Because Be-10-derived erosion rates integrate over several millennia; we modeled the erosion-rate history that best explains the 10Be data using established non-linear equations that describe in situ cosmogenic isotope production and decay. Two models with different temporal constraints (15-6.7 and 12-6.7 kyr) suggest erosion rates that were 25 to 300 times higher than the initial erosion rate (pre-delta formation). That pulse of high erosion rates was short (similar to 4 kyr or less) and must have been followed by a rapid decrease in rates while climate remained humid to reach the modern Be-10-based erosion rate of,similar to 0.013 mm yr(-1). Our simulations also flag the two highest Be-10-derived erosion rates at 11.8 kyr BP related to nonuniform catchment erosion. These changes in erosion rates and processes during the AHP may reflect a strong increase in precipitation, runoff, and erosivity at the arid-to-humid transition either at 15 or similar to 12 cal. kyr BP, before the landscape stabilized again, possibly due to increased soil production and denser vegetation. KW - northern Kenya Rift KW - Baragoi KW - paleo-delta KW - African Humid Period KW - erosion KW - Be-10 Y1 - 2017 U6 - https://doi.org/10.1016/j.epsl.2016.11.017 SN - 0012-821X SN - 1385-013X VL - 459 SP - 58 EP - 69 PB - Elsevier CY - Amsterdam 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 - JOUR A1 - Diaz, Nathalie A1 - Dietrich, Fabienne A1 - Sebag, David A1 - King, Georgina E. A1 - Valla, Pierre G. A1 - Durand, Alain A1 - Garcin, Yannick A1 - de Saulie, Geoffroy A1 - Deschamps, Pierre A1 - Herman, Frederic A1 - Verrecchia, Eric P. T1 - Pedo-sedimentary constituents as paleoenvironmental proxies in the Sudano-Sahelian belt during the Late Quaternary (southwestern Chad Basin) JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - Climate and environmental changes since the Last Glacial Maximum in the tropical zone of West Africa are usually inferred from marine and continental records. In this study, the potential of carbonate pedo-sedimentary geosystems, i.e. Vertisol relics, to record paleoenvironmental changes in the southwestern part of Chad Basin are investigated. A multi-dating approach was applied on different pedogenic organo-mineral constituents. Optically stimulated luminescence (OSL) dating was performed on the soil K-rich feldspars and was combined with radiocarbon dating on both the inorganic (C-14(inorg)) and organic carbon (C-14(org)) soil fractions. Three main pedo-sedimentary processes were assessed over the last 20 ka BP: 1) the soil parent material deposition, from 18 ka to 12 ka BP (OSL), 2) the soil organic matter integration, from 11 cal ka to 8 cal ka BP (C-14(org)), and 3) the pedogenic carbonate nodule precipitation, from 7 cal ka to 5 cal ka BP (C-14(inorg)). These processes correlate well with the Chad Basin stratigraphy and West African records and are shown to be related to significant changes in the soil water balance responding to the evolution of continental hydrology during the Late Quaternary. The last phase affecting the Vertisol relics is the increase of erosion, which is hypothesized to be due to a decrease of the vegetation cover triggered by (i) the onset of drier conditions, possibly strengthened by (ii) anthropogenic pressure. Archaeological data from Far North Cameroon and northern Nigeria, as well as sedimentation times in Lake Tilla (northeastern Nigeria), were used to test these relationships. The increase of erosion is suggested to possibly occur between c. 3 cal ka and 1 cal ka BP. Finally, satellite images revealed similar geosystems all along the Sudano-Sahelian belt, and initial C-14(inorg) ages of the samples collected in four sites gave similar ages to those reported in this study. Consequently, the carbonate pedo-sedimentary geosystems are valuable continental paleoenvironmental archives and soil water balance proxies of the semiarid tropics of West Africa. (C) 2018 Elsevier Ltd. All rights reserved. KW - Pedogenic carbonate nodules KW - Vertisol genesis KW - Soil water balance KW - Optical methods KW - Radiogenic isotopes KW - Quaternary KW - Monsoon KW - Western Africa Y1 - 2018 U6 - https://doi.org/10.1016/j.quascirev.2018.05.022 SN - 0277-3791 VL - 191 SP - 348 EP - 362 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Sebag, David A1 - Garcin, Yannick A1 - Adatte, Thierry A1 - Deschamps, Pierre A1 - Menot, Guillemette A1 - Verrecchia, Eric P. T1 - Correction for the siderite effect on Rock-Eval parameters BT - Application to the sediments of Lake Barombi (southwest Cameroon) JF - Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry N2 - Originally developed for use in the petroleum industry, Rock-Eval pyrolysis is a technique commonly applied to lake sediments to infer paleoenvironmental reconstructions. The standard Rock-Eval parameters provide information on the amount of total organic and inorganic carbon (TOC and MinC, respectively), and are usually interpreted as proxies for the source (aquatic or terrestrial) of the primary production of organic matter (Hydrogen Index vs Oxygen Index). Although this method usually provides valuable evidence, the common presence of siderite in tropical lake sediments can alter the primary signal of the sedimentary organic matter (SOM). Indeed, the CO2 and CO released by the pyrolysis of siderite are integral to the calculation of the SOM-related standard Rock-Eval parameters. In this study, we analyze sediments from a core collected in the Lake Barombi (southwest Cameroon) and describe the impact of siderite on standard Rock-Eval parameters. We propose a workflow that allows standard Rock-Eval parameters to be corrected, based on the analysis of thermograms. The proposed corrections provide siderite-effect-free parameters, accurately reflecting the changes in sedimentary organic matter composition. (C) 2018 Elsevier Ltd. All rights reserved. KW - Organic geochemistry KW - Rock-Eval pyrolysis KW - Van Krevelen diagram KW - Siderite KW - Tropical lake KW - Western Central Africa Y1 - 2018 U6 - https://doi.org/10.1016/j.orggeochem.2018.05.010 SN - 0146-6380 VL - 123 SP - 126 EP - 135 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Deino, A. L. A1 - Dommain, René A1 - Keller, C. B. A1 - Potts, R. A1 - Behrensmeyer, A. K. A1 - Beverly, E. J. A1 - King, J. A1 - Heil, C. W. A1 - Stockhecke, M. A1 - Brown, E. T. A1 - Moerman, J. A1 - deMenocal, P. A1 - Deocampo, D. A1 - Garcin, Yannick A1 - Levin, N. E. A1 - Lupien, R. A1 - Owen, R. B. A1 - Rabideaux, N. A1 - Russell, J. M. A1 - Scott, J. A1 - Riedl, S. A1 - Brady, K. A1 - Bright, J. A1 - Clark, J. B. A1 - Cohen, A. A1 - Faith, J. T. A1 - Noren, A. A1 - Muiruri, V. A1 - Renaut, R. A1 - Rucina, S. A1 - Uno, K. T1 - Chronostratigraphic model of a high-resolution drill core record of the past million years from the Koora Basin, south Kenya Rift: Overcoming the difficulties of variable sedimentation rate and hiatuses JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - The Olorgesailie Drilling Project and the related Hominin Sites and Paleolakes Drilling Project in East Africa were initiated to test hypotheses and models linking environmental change to hominin evolution by drilling lake basin sediments adjacent to important archeological and paleoanthropological sites. Drill core OL012-1A recovered 139 m of sedimentary and volcaniclastic strata from the Koora paleolake basin, southern Kenya Rift, providing the opportunity to compare paleoenvironmental influences over the past million years with the parallel record exposed at the nearby Olorgesailie archeological site. To refine our ability to link core-to-outcrop paleoenvironmental records, we institute here a methodological framework for deriving a robust age model for the complex lithostratigraphy of OL012-1A. Firstly, chronostratigraphic control points for the core were established based on 4 Ar/39Ar ages from intercalated tephra deposits and a basal trachyte flow, as well as the stratigraphic position of the Brunhes-Matuyama geomagnetic reversal. This dataset was combined with the position and duration of paleosols, and analyzed using a new Bayesian algorithm for high-resolution age-depth modeling of hiatus-bearing stratigraphic sections. This model addresses three important aspects relevant to highly dynamic, nonlinear depositional environments: 1) correcting for variable rates of deposition, 2) accommodating hiatuses, and 3) quantifying realistic age uncertainty with centimetric resolution. Our method is applicable to typical depositional systems in extensional rifts as well as to drill cores from other dynamic terrestrial or aquatic environments. We use the core age model and lithostratigraphy to examine the inter connectivity of the Koora Basin to adjacent areas and sources of volcanism. (C) 2019 Elsevier Ltd. All rights reserved. KW - Pleistocene KW - Paleolimnology KW - East Africa KW - Sedimentology KW - Radiogenic isotopes KW - Bayesian modeling KW - paleosol KW - Tephrostratigraphy KW - Magnetostratigraphy KW - Kenya Rift Y1 - 2019 U6 - https://doi.org/10.1016/j.quascirev.2019.05.009 SN - 0277-3791 VL - 215 SP - 213 EP - 231 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Melnick, Daniel A1 - Yildirim, Cengiz A1 - Hillemann, Christian A1 - Garcin, Yannick A1 - Ciner, T. Attila A1 - Perez-Gussinye, Marta A1 - Strecker, Manfred T1 - Slip along the Sultanhani Fault in Central Anatolia from deformed Pleistocene shorelines of palaeo-lake Konya and implications for seismic hazards in low-strain regions JF - Geophysical journal international N2 - Central Anatolia is a low-relief, high-elevation region where decadal-scale deformation rates estimated from space geodesy suggest low strain rates within a stiff microplate. However, numerous Quaternary faults have been mapped within this low-strain region and estimating their slip rate and seismic potential is important for hazard assessments in an area of increasing infrastructural development. Here we focus on the Sultanhani Fault (SF), which constitutes an integral part of the Eskisehir-Cihanbeyli Fault System, and use deformed maximum highstand shorelines of palaeo-lake Konya to estimate tectonic slip rates at millennial scale. Some of these shorelines were previously interpreted as fault scarps, but we provide conclusive evidence for their erosional origin. We found that shoreline-angle elevations estimated from differential GPS profiles record vertical displacements of 10.2 m across the SF. New radiocarbon ages of lacustrine molluscs suggest 22.4 m of relative lake-level fall between 22.1 +/- 0.3 and 21.7 +/- 0.4 cal. kaBP, constraining the timing of abrupt abandonment of the highstand shoreline. Models of lithospheric rebound associated with regressions of the Tuz Golu and Konya palaeolakes predict only similar to 1 m of regional-scale uplift across the Konya Basin. Dislocation models of displaced shorelines suggest fault-slip rates of 1.5 and 1.8 mm yr(-1) for planar and listric fault geometries, respectively, providing reasonable results for the latter. We found fault scarps in the Nasuhpinar mudflat that likely represent the most recent ground-breaking rupture of the SF, with an average vertical displacement of 1.2 +/- 0.5 m estimated from 54 topographic profiles, equivalent to a M similar to 6.5-6.9 earthquake based on empirical scaling laws. If such events were characteristic during the ultimate 21 ka, a relatively short recurrence time of similar to 800-900 yr would be needed to account for the millennial slip rate. Alternatively, the fault scarp at Nasuhpinar might represent a larger earthquake requiring more frequent smaller events to account for the millennial rate. The relatively fast slip rate of the SF over the past 21 ka is unlikely to have persisted over longer timescales and might reflect spatiotemporal variations in deformation rates within kinematically-linked fault systems within Central Anatolia, or a transient perturbation to the local stress field or fault strength. Such perturbation might have been related to climatically controlled changes in surface and near-surface loads and by interactions among the different tectonic processes that have been proposed to drive the overall slow uplift and associated extension in the Central Anatolian Plateau. KW - Seismic cycle KW - Geomorphology KW - Continental neotectonics KW - Earthquake hazards KW - Tectonics and climatic interactions Y1 - 2017 U6 - https://doi.org/10.1093/gji/ggx074 SN - 0956-540X SN - 1365-246X VL - 209 SP - 1431 EP - 1454 PB - Oxford Univ. Press 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 - 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 - 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 - 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 -