@article{KruegerFoersterTrauthetal.2021, author = {Kr{\"u}ger, Johanna and Foerster, Verena Elisabeth and Trauth, Martin H. and Hofreiter, Michael and Tiedemann, Ralph}, title = {Exploring the Past Biosphere of Chew Bahir/Southern Ethiopia: Cross-Species Hybridization Capture of Ancient Sedimentary DNA from a Deep Drill Core}, series = {Frontiers in Earth Science}, journal = {Frontiers in Earth Science}, publisher = {Frontiers in Earth Science}, address = {Lausanne, Schweiz}, issn = {2296-6463}, doi = {10.3389/feart.2021.683010}, pages = {1 -- 20}, year = {2021}, abstract = {Eastern Africa has been a prime target for scientific drilling because it is rich in key paleoanthropological sites as well as in paleolakes, containing valuable paleoclimatic information on evolutionary time scales. The Hominin Sites and Paleolakes Drilling Project (HSPDP) explores these paleolakes with the aim of reconstructing environmental conditions around critical episodes of hominin evolution. Identification of biological taxa based on their sedimentary ancient DNA (sedaDNA) traces can contribute to understand past ecological and climatological conditions of the living environment of our ancestors. However, sedaDNA recovery from tropical environments is challenging because high temperatures, UV irradiation, and desiccation result in highly degraded DNA. Consequently, most of the DNA fragments in tropical sediments are too short for PCR amplification. We analyzed sedaDNA in the upper 70 m of the composite sediment core of the HSPDP drill site at Chew Bahir for eukaryotic remnants. We first tested shotgun high throughput sequencing which leads to metagenomes dominated by bacterial DNA of the deep biosphere, while only a small fraction was derived from eukaryotic, and thus probably ancient, DNA. Subsequently, we performed cross-species hybridization capture of sedaDNA to enrich ancient DNA (aDNA) from eukaryotic remnants for paleoenvironmental analysis, using established barcoding genes (cox1 and rbcL for animals and plants, respectively) from 199 species that may have had relatives in the past biosphere at Chew Bahir. Metagenomes yielded after hybridization capture are richer in reads with similarity to cox1 and rbcL in comparison to metagenomes without prior hybridization capture. Taxonomic assignments of the reads from these hybridization capture metagenomes also yielded larger fractions of the eukaryotic domain. For reads assigned to cox1, inferred wet periods were associated with high inferred relative abundances of putative limnic organisms (gastropods, green algae), while inferred dry periods showed increased relative abundances for insects. These findings indicate that cross-species hybridization capture can be an effective approach to enhance the information content of sedaDNA in order to explore biosphere changes associated with past environmental conditions, enabling such analyses even under tropical conditions.}, language = {en} } @article{OwenMuiruriLowensteinetal.2018, author = {Owen, Richard Bernhart and Muiruri, Veronica M. and Lowenstein, Tim K. and Renaut, Robin W. and Rabideaux, Nathan and Luo, Shangde and Deino, Alan L. and Sier, Mark J. and Dupont-Nivet, Guillaume and McNulty, Emma P. and Leet, Kennie and Cohen, Andrew and Campisano, Christopher and Deocampo, Daniel and Shen, Chuan-Chou and Billingsley, Anne and Mbuthia, Anthony}, title = {Progressive aridification in East Africa over the last half million years and implications for human evolution}, 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 = {44}, publisher = {National Academy of Sciences}, address = {Washington}, issn = {0027-8424}, doi = {10.1073/pnas.1801357115}, pages = {11174 -- 11179}, year = {2018}, abstract = {Evidence for Quaternary climate change in East Africa has been derived from outcrops on land and lake cores and from marine dust, leaf wax, and pollen records. These data have previously been used to evaluate the impact of climate change on hominin evolution, but correlations have proved to be difficult, given poor data continuity and the great distances between marine cores and terrestrial basins where fossil evidence is located. Here, we present continental coring evidence for progressive aridification since about 575 thousand years before present (ka), based on Lake Magadi (Kenya) sediments. This long-term drying trend was interrupted by many wet-dry cycles, with the greatest variability developing during times of high eccentricity-modulated precession. Intense aridification apparent in the Magadi record took place between 525 and 400 ka, with relatively persistent arid conditions after 350 ka and through to the present. Arid conditions in the Magadi Basin coincide with the Mid-Brunhes Event and overlap with mammalian extinctions in the South Kenya Rift between 500 and 400 ka. The 525 to 400 ka arid phase developed in the South Kenya Rift between the period when the last Acheulean tools are reported (at about 500 ka) and before the appearance of Middle Stone Age artifacts (by about 320 ka). Our data suggest that increasing Middle- to Late-Pleistocene aridification and environmental variability may have been drivers in the physical and cultural evolution of Homo sapiens in East Africa.}, language = {en} } @article{KhiderEmileGeayMcKayetal.2019, author = {Khider, D. and Emile-Geay, J. and McKay, N. P. and Gil, Y. and Garijo, D. and Ratnakar, V and Alonso-Garcia, M. and Bertrand, S. and Bothe, O. and Brewer, P. and Bunn, A. and Chevalier, M. and Comas-Bru, L. and Csank, A. and Dassie, E. and DeLong, K. and Felis, T. and Francus, P. and Frappier, A. and Gray, W. and Goring, S. and Jonkers, L. and Kahle, M. and Kaufman, D. and Kehrwald, N. M. and Martrat, B. and McGregor, H. and Richey, J. and Schmittner, A. and Scroxton, N. and Sutherland, E. and Thirumalai, Kaustubh and Allen, K. and Arnaud, F. and Axford, Y. and Barrows, T. and Bazin, L. and Birch, S. E. Pilaar and Bradley, E. and Bregy, J. and Capron, E. and Cartapanis, O. and Chiang, H-W and Cobb, K. M. and Debret, M. and Dommain, R{\´e}ne and Du, J. and Dyez, K. and Emerick, S. and Erb, M. P. and Falster, G. and Finsinger, W. and Fortier, D. and Gauthier, Nicolas and George, S. and Grimm, E. and Hertzberg, J. and Hibbert, F. and Hillman, A. and Hobbs, W. and Huber, M. and Hughes, A. L. C. and Jaccard, S. and Ruan, J. and Kienast, M. and Konecky, B. and Le Roux, G. and Lyubchich, V and Novello, V. F. and Olaka, L. and Partin, J. W. and Pearce, C. and Phipps, S. J. and Pignol, C. and Piotrowska, N. and Poli, M-S and Prokopenko, A. and Schwanck, F. and Stepanek, C. and Swann, G. E. A. and Telford, R. and Thomas, E. and Thomas, Z. and Truebe, S. and von Gunten, L. and Waite, A. and Weitzel, N. and Wilhelm, B. and Williams, J. and Winstrup, M. and Zhao, N. and Zhou, Y.}, title = {PaCTS 1.0: A Crowdsourced Reporting Standard for Paleoclimate Data}, series = {Paleoceanography and paleoclimatology}, volume = {34}, journal = {Paleoceanography and paleoclimatology}, number = {10}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2572-4517}, doi = {10.1029/2019PA003632}, pages = {1570 -- 1596}, year = {2019}, abstract = {The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community-sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate data sets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive-specific properties and distinguished reporting standards for new versus legacy data sets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate data sets. Since such goals are at odds with present practices, we discuss a transparent path toward implementing or revising these recommendations in the near future, using both bottom-up and top-down approaches.}, language = {en} } @article{AichnerMakhmudovRajabovetal.2019, author = {Aichner, Bernhard and Makhmudov, Zafar and Rajabov, Iljomjon and Zhang, Qiong and Pausata, Francesco Salvatore R. and Werner, Martin and Heinecke, Liv and Kuessner, Marie L. and Feakins, Sarah J. and Sachse, Dirk and Mischke, Steffen}, title = {Hydroclimate in the Pamirs Was Driven by Changes in Precipitation-Evaporation Seasonality Since theLast Glacial Period}, series = {Geophysical research letters}, volume = {46}, journal = {Geophysical research letters}, number = {23}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0094-8276}, doi = {10.1029/2019GL085202}, pages = {13972 -- 13983}, year = {2019}, abstract = {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.}, language = {en} } @article{MengesHoviusAndermannetal.2019, author = {Menges, Johanna and Hovius, Niels and Andermann, Christoff and Dietze, Michael and Swoboda, Charlie and Cook, Kristen L. and Adhikari, Basanta R. and Vieth-Hillebrand, Andrea and Bonnet, Stephane and Reimann, Tony and Koutsodendris, Andreas and Sachse, Dirk}, title = {Late holocene landscape collapse of a trans-himalayan dryland}, series = {Geophysical research letters}, volume = {46}, journal = {Geophysical research letters}, number = {23}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0094-8276}, doi = {10.1029/2019GL084192}, pages = {13814 -- 13824}, year = {2019}, abstract = {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.}, language = {en} } @misc{SachseBillaultBowenetal.2012, author = {Sachse, Dirk and Billault, Isabelle and Bowen, Gabriel J. and Chikaraishi, Yoshito and Dawson, Todd E. and Feakins, Sarah J. and Freeman, Katherine H. and Magill, Clayton R. and McInerney, Francesca A. and van der Meer, Marcel T. J. and Polissar, Pratigya and Robins, Richard J. and Sachs, Julian P. and Schmidt, Hanns-Ludwig and Sessions, Alex L. and White, James W. C. and West, Jason B. and Kahmen, Ansgar}, title = {Molecular Paleohydrology interpreting the Hydrogen- Isotopic Composition of Lipid Biomarkers from Photosynthesizing Organisms}, series = {Annual review of earth and planetary sciences}, volume = {40}, journal = {Annual review of earth and planetary sciences}, number = {1}, editor = {Jeanloz, R}, publisher = {Annual Reviews}, address = {Palo Alto}, isbn = {978-0-8243-2040-9}, issn = {0084-6597}, doi = {10.1146/annurev-earth-042711-105535}, pages = {221 -- 249}, year = {2012}, abstract = {Hydrogen-isotopic abundances of lipid biomarkers are emerging as important proxies in the study of ancient environments and ecosystems. A decade ago, pioneering studies made use of new analytical methods and demonstrated that the hydrogen-isotopic composition of individual lipids from aquatic and terrestrial organisms can be related to the composition of their growth (i.e., environmental) water. Subsequently, compound-specific deuterium/hydrogen (D/H) ratios of sedimentary biomarkers have been increasingly used as paleohydrological proxies over a range of geological timescales. Isotopic fractionation observed between hydrogen in environmental water and hydrogen in lipids, however, is sensitive to biochemical, physiological, and environmental influences on the composition of hydrogen available for biosynthesis in cells. Here we review the factors and processes that are known to influence the hydrogen-isotopic compositions of lipids-especially n-alkanes-from photosynthesizing organisms, and we provide a framework for interpreting their D/H ratios from ancient sediments and identify future research opportunities.}, language = {en} } @article{BookhagenStrecker2012, author = {Bookhagen, Bodo and Strecker, Manfred}, title = {Spatiotemporal trends in erosion rates across a pronounced rainfall gradient: Examples from the southern Central Andes}, series = {Earth \& planetary science letters}, volume = {327}, journal = {Earth \& planetary science letters}, number = {8}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2012.02.005}, pages = {97 -- 110}, year = {2012}, abstract = {The tectonic and climatic boundary conditions of the broken foreland and the orogen interior of the southern Central Andes of northwestern Argentina cause strong contrasts in elevation, rainfall, and surface-process regimes. The climatic gradient in this region ranges from the wet, windward eastern flanks (similar to 2 m/yr rainfall) to progressively drier western basins and ranges (similar to 0.1 m/yr) bordering the arid Altiplano-Puna Plateau. In this study, we analyze the impact of spatiotemporal climatic gradients on surface erosion: First, we present 41 new catchment-mean erosion rates derived from cosmogenic nuclide inventories to document spatial erosion patterns. Second, we re-evaluate paleoclimatic records from the Calchaquies basin (66 W, 26 S), a large intermontane basin bordered by high (> 4.5 km) mountain ranges, to demonstrate temporal variations in erosion rates associated with changing climatic boundary conditions during the late Pleistocene and Holocene. Three key observations in this region emphasize the importance of climatic parameters on the efficiency of surface processes in space and time: (1) First-order spatial patterns of erosion rates can be explained by a simple specific stream power (SSP) approach. We explicitly account for discharge by routing high-resolution, satellite derived rainfall. This is important as the steep climatic gradient results in a highly non-linear relation between drainage area and discharge. This relation indicates that erosion rates (ER) scale with ER similar to SSP1.4 on cosmogenic-nuclide time scales. (2) We identify an intrinsic channel-slope behavior in different climatic compartments. Channel slopes in dry areas (< 0.25 m/yr rainfall) are slightly steeper than in wet areas (> 0.75 m/yr) with equal drainage areas, thus compensating lower amounts of discharge with steeper slopes. (3) Erosion rates can vary by an order of magnitude between presently dry (similar to 0.05 mm/yr) and well-defined late Pleistocene humid (similar to 0.5 mm/yr) conditions within an intemontane basin. Overall, we document a strong climatic impact on erosion rates and channel slopes. We suggest that rainfall reaching areas with steeper channel slopes in the orogen interior during wetter climate periods results in intensified sediment mass transport, which is primarily responsible for maintaining the balance between surface uplift, erosion, sediment routing and transient storage in the orogen.}, language = {en} }