@article{KahmenSchefussSachse2013,
  author    = {Kahmen, Ansgar and Schefuss, Enno and Sachse, Dirk},
  title     = {Leaf water deuterium enrichment shapes leaf wax n-alkane delta D values of angiosperm plants I experimental evidence and mechanistic insights},
  series = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society},
  volume    = {111},
  journal   = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0016-7037},
  doi       = {10.1016/j.gca.2012.09.003},
  pages     = {39 -- 49},
  year      = {2013},
  abstract  = {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.},
  language  = {en}
}
@article{GarcinSchefussSchwabetal.2014,
  author    = {Garcin, Yannick and Schefuss, Enno and Schwab, Valerie F. and Garreta, Vincent and Gleixner, Gerd and Vincens, Annie and Todou, Gilbert and Sene, Olivier and Onana, Jean-Michel and Achoundong, Gaston and Sachse, Dirk},
  title     = {Reconstructing C-3 and C-4 vegetation cover using n-alkane carbon isotope ratios in recent lake sediments from Cameroon, Western Central Africa},
  series = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society},
  volume    = {142},
  journal   = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0016-7037},
  doi       = {10.1016/j.gca.2014.07.004},
  pages     = {482 -- 500},
  year      = {2014},
  abstract  = {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.},
  language  = {en}
}
@article{GarcinDeschampsMenotetal.2018,
  author    = {Garcin, Yannick and Deschamps, Pierre and Menot, Guillemette and de Saulieu, Geoffroy and Schefuss, Enno and Sebag, David and Dupont, Lydie M. and Oslisly, Richard and Brademann, Brian and Mbusnum, Kevin G. and Onana, Jean-Michel and Ako, Andrew A. and Epp, Laura Saskia and Tjallingii, Rik and Strecker, Manfred and Brauer, Achim and Sachse, Dirk},
  title     = {Early anthropogenic impact on Western Central African rainforests 2,600 y ago},
  series = {Proceedings of the National Academy of Sciences of the United States of America},
  volume    = {115},
  journal   = {Proceedings of the National Academy of Sciences of the United States of America},
  number    = {13},
  publisher = {National Acad. of Sciences},
  address   = {Washington},
  issn      = {0027-8424},
  doi       = {10.1073/pnas.1715336115},
  pages     = {3261 -- 3266},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@misc{GarcinDeschampsMenotetal.2018,
  author    = {Garcin, Yannick and Deschamps, Pierre and Menot, Guillemette and de Saulieu, Geoffroy and Schefuss, Enno and Sebag, David and Dupont, Lydie M. and Oslisly, Richard and Brademann, Brian and Mbusnum, Kevin G. and Onana, Jean-Michel and Ako, Andrew A. and Epp, Laura Saskia and Tjallingii, Rik and Strecker, Manfred and Brauer, Achim and Sachse, Dirk},
  title     = {No evidence for climate variability during the late Holocene rainforest crisis in Western Central Africa REPLY},
  series = {Proceedings of the National Academy of Sciences of the United States of America},
  volume    = {115},
  journal   = {Proceedings of the National Academy of Sciences of the United States of America},
  number    = {29},
  publisher = {National Acad. of Sciences},
  address   = {Washington},
  issn      = {0027-8424},
  doi       = {10.1073/pnas.1808481115},
  pages     = {E6674 -- E6675},
  year      = {2018},
  language  = {en}
}
@misc{GarcinDeschampsMenotetal.2018,
  author    = {Garcin, Yannick and Deschamps, Pierre and Menot, Guillemette and de Saulieu, Geoffroy and Schefuss, Enno and Sebag, David and Dupont, Lydie M. and Oslisly, Richard and Brademann, Brian and Mbusnum, Kevin G. and Onana, Jean-Michel and Ako, Andrew A. and Epp, Laura Saskia and Tjallingii, Rik and Strecker, Manfred and Brauer, Achim and Sachse, Dirk},
  title     = {Human activity is the most probable trigger of the late Holocene rainforest crisis in Western Central Africa Reply},
  series = {Proceedings of the National Academy of Sciences of the United States of America},
  volume    = {115},
  journal   = {Proceedings of the National Academy of Sciences of the United States of America},
  number    = {21},
  publisher = {National Acad. of Sciences},
  address   = {Washington},
  issn      = {0027-8424},
  doi       = {10.1073/pnas.1805582115},
  pages     = {E4735 -- E4736},
  year      = {2018},
  language  = {en}
}