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 - 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 - 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 - 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 - 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 -