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The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and evolution in Africa through the analysis of sediment cores that have recorded environmental changes in the Chew Bahir basin. In this statistical project we consider the Chew Bahir palaeolake to be a dynamical system consisting of interactions between its different components, such as the waterbody, the sediment beneath lake, and the organisms living within and around the lake. Recurrence is a common feature of such dynamical systems, with recurring patterns in the state of the system reflecting typical influences. Identifying and defining these influences contributes significantly to our understanding of the dynamics of the system. Different recurring changes in precipitation, evaporation, and wind speed in the Chew Bahir basin could result in similar (but not identical) conditions in the lake (e.g., depth and area of the lake, alkalinity and salinity of the lake water, species assemblages in the water body, and diagenesis in the sediments). Recurrence plots (RPs) are graphic displays of such recurring states within a system. Measures of complexity were subsequently introduced to complement the visual inspection of recurrence plots, and provide quantitative descriptions for use in recurrence quantification analysis (RQA). We present and discuss herein results from an RQA on the environmental record from six short (< 17 m) sediment cores collected during the CBDP, spanning the last 45 kyrs. The different types of variability and transitions in these records were classified to improve our understanding of the response of the biosphere to climate change, and especially the response of humans in the area. [ABSTRACT FROM AUTHOR]

Annual laminae (varves) in lake sediments are typically visually identified, measured and counted, although numerous attempts have been made to automate this process. The reason for the failure of most of these automated algorithms for varve counting is the complexity of the seasonal laminations, typically rich in lateral facies variations and internal heterogeneities. In the manual counting of varves, the investigator acquired and interpreted flexible numbers of complex decision criteria to understand whether a particular simple lamination is a varve or not. Fuzzy systems simulate the flexible decision making process in a computer by introducing a smooth transition between true varve and false varve. In our investigation, we use an adaptive neuro fuzzy inference system (ANFIS) to detect varves on the basis of a digital image of the sediment. The results of the application of the ANFIS to laminated sediments from the Meerfelder Maar (Eifel, Germany) and from a landslide-dammed lake in the Quebrada de Cafayate of Argentina are compared with manual varve counts and possible reasons for the differences are discussed. [ABSTRACT FROM AUTHOR]

Abstract: The late Cenozoic climate of East Africa is punctuated by episodes of short, alternating periods of extreme wetness and aridity, superimposed on a regime of subdued moisture availability exhibiting a long-term drying trend. These periods of extreme climate variability appear to correlate with maxima in the 400-thousand-year (kyr) component of the Earth''s eccentricity cycle. Prior to 2.7Ma the wet phases appear every 400kyrs, whereas after 2.7Ma, the wet phases appear every 800kyrs, with periods of precessional-forced extreme climate variability at 2.7–2.5Ma, 1.9–1.7Ma, and 1.1–0.9Ma before present. The last three major lake phases occur at the times of major global climatic transitions, such as the onset of Northern Hemisphere Glaciation (2.7–2.5Ma), intensification of the Walker Circulation (1.9–1.7Ma), and the Mid-Pleistocene Revolution (1.0–0.7Ma). High-latitude forcing is required to compress the Intertropical Convergence Zone so that East Africa becomes locally sensitive to precessional forcing, resulting in rapid shifts from wet to dry conditions. These periods of extreme climate variability may have provided a catalyst for evolutionary change and driven key speciation and dispersal events amongst mammals and hominins in East Africa. [Copyright &y& Elsevier]

The chronology of multiple landslide deposits and related lake sediments in the semi-arid eastern Argentine Cordillera suggests that major mass movements cluster in two time periods during the Quaternary, i.e. between 40 and 25 and after 5 14C kyr BP. These clusters may correspond to the Minchin (maximum at around 28–27 14C kyr BP) and Titicaca wet periods (after 3.9 14C kyr BP). The more humid conditions apparently caused enhanced landsliding in this environment. In contrast, no landslide-related damming and associated lake sediments occurred during the Coipasa (11.5–10 14C yr BP) and Tauca wet periods (14.5–11 14C yr BP). The two clusters at 40–25 and after 5 14C kyr BP may correspond to periods where the El Nin˜o–Southern Oscillation (ENSO) and Tropical Atlantic Sea Surface Temperature Variability (TAV) were active. This, however, was not the case during the Coipasa and Tauca wet periods. Lake-balance modelling of a landslide-dammed lake suggests a 10–15% increase in precipitation and a 3–4°C decrease in temperature at ∼30 14C kyr BP as compared to the present. In addition, time-series analysis reveals a strong ENSO and TAV during that time. The landslide clusters in northwestern Argentina are therefore best explained by periods of more humid and more variable climates. [Copyright &y& Elsevier]

Variations in the temporal and spatial distribution of solar radiation caused by orbital changes provide a partial explanation for the observed long-term fluctuations in African lake levels. The understanding of such relationships is essential for designing climate-prediction models for the tropics. Our assessment of the nature and timing of East African climate change is based on lake-level fluctuations of Lake Naivasha in the Central Kenya Rift (0°55′S 36°20′E), inferred from sediment characteristics, diatoms, authigenic mineral assemblages and 17 single-crystal 40Ar/39Ar age determinations. Assuming that these fluctuations reflect climate changes, the Lake Naivasha record demonstrates that periods of increased humidity in East Africa mainly followed maximum equatorial solar radiation in March or September. Interestingly, the most dramatic change in the Naivasha Basin occurred as early as 146 kyr BP and the highest lake level was recorded at about 139–133 kyr BP. This is consistent with other well-dated low-latitude climate records, but does not correspond to peaks in Northern Hemisphere summer insolation as the trigger for the ice-age cycles. The Naivasha record therefore provides evidence for low-latitude forcing of the ice-age climate cycles. [Copyright &y& Elsevier]

Lake sediments in 10 Ethiopian, Kenyan, and Tanzanian rift basins suggest that there were three humid periods at 2.7 to 2.5 million years ago (Ma), 1.9 to 1.7 Ma, and 1.1 to 0.9 Ma, superimposed on the longer-term aridification of East Africa. These humid periods correlate with increased aridity in northwest and northeast Africa and with substantial global climate transitions. These episodes could have had important impacts on the speciation and dispersal of mammals and hominins, because a number of key events, such as the origin of the genus Homo and the evolution of the species Homo erectus, took place in this region during that time. [ABSTRACT FROM AUTHOR]

The Chew Bahir Drilling Project (CBDP) aims to test hypothesized linkages between climate and human evolution, dispersal and technological innovation by the acquisition and analysis of long (~280 m) sediment cores that have recorded environmental change in the Chew Bahir basin, southern Ethiopia. In this time-series analysis project, we consider the Chew Bahir palaeolake to be a dynamical system consisting of interactions between its different components, such as the waterbody, the sediment beneath lake, and the organisms living within and around the lake, and humans within the lake catchment. Recurrence is a common feature of such dynamical systems, with recurring patterns in the state of the system reflecting typical influences. Identifying and defining these influences contributes significantly to our understanding of the dynamics of the system.We use methods of linear and nonlinear time series analysis, such as change point detection, semblance analysis and recurrence plots, to identify and classify recurring types of variability and transitions on the time scales of human life spans. For example, we investigate the rapidness of transitions, possible precursor events, and tipping points in our palaeoenvironmental data and discuss their possible impact on the living conditions of humans in the region. First results of the analysis show that we indeed find, as an example, recurring threshold-type transitions, when the Chew Bahir system switched from one stable mode to another, such as from stable wet to dry conditions. Such a rapid change of climate in response to a relatively modest change in forcing appears to be typical of tipping points in complex systems such as the Chew Bahir. If this is the case then the 14 dry events idenfified at the end of the African Humid Period (15–5 kyr BP) could represent precursors of an imminent tipping point that, if properly interpreted, would allow predictions to be made of future climate change in the Chew Bahir basin. [ABSTRACT FROM AUTHOR]

Abstract: Owen et al. [Owen, R.B., Potts, R., Behrensmeyer, A.K., Ditchfield, P., 2008, Diatomaceous sediments and environmental change in the Pleistocene Olorgesailie Formation, southern Kenya Rift Valley. Palaeogeography, Palaeoclimatology, Palaeoecology, 269, 17–37], Diatomaceous sediments and environmental change in the Pleistocene Olorgesailie Formation, southern Kenya Rift, Palaeogeography Palaeoclimatology Palaeoecology, 269, 17–37) argued that diatom assemblage variations in the Olorgesailie Formation indicate considerable environmental instability with both wetter and drier periods, contradicting the proposed period of lake stability and wet climatic conditions between ca. 1.1 and 0.9million years ago as proposed by Trauth et al. [Trauth, M.H., Maslin, M.A., Deino, A., Strecker, M.R., 2005. Late Cenozoic moisture history of East Africa. Science 309, 2051–2053., Trauth, M.H., Maslin, M.A., Deino, A., Bergner, A.G.N., Dühnforth, M., Strecker, M.R., 2007. High- and low-latitude forcing of Plio-Pleistocene East African climate and human evolution. Journal of Human Evolution 53, 475–486]. Contrary to the interpretation of our work by Owen et al. [Owen, R.B., Potts, R., Behrensmeyer, A.K., Ditchfield, P., 2008, we never said that the proposed periods of large lakes were characterized by stable conditions. [Copyright &y& Elsevier]

Abstract: The water-level record from the 300m deep paleo-lake Suguta (Northern Kenya Rift) during the African Humid Period (AHP, 15–5ka BP) helps to explain decadal to centennial intensity variations in the West African Monsoon (WAM) and the Indian Summer Monsoon (ISM). This water-level record was derived from three different sources: (1) grain size variations in radiocarbon dated and reservoir corrected lacustrine sediments, (2) the altitudes and ages of paleo-shorelines within the basin, and (3) the results of hydro-balance modeling, providing important insights into the character of water level variations (abrupt or gradual) in the amplifier paleo-Lake Suguta. The results of these comprehensive analyses suggest that the AHP highstand in the Suguta Valley was the direct consequence of a northeastwards shift in the Congo Air Boundary (CAB), which was in turn caused by an enhanced atmospheric pressure gradient between East Africa and India during a northern hemisphere insolation maximum. Rapidly decreasing water levels of up to 90m over less than a hundred years are best explained by changes in solar irradiation either reducing the East African–Indian atmospheric pressure gradient and preventing the CAB from reaching the study area, or reducing the overall humidity in the atmosphere, or a combination of both these effects. In contrast, although not well documented in our record we hypothesize a gradual end of the AHP despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the Suguta Valley. The abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during October. Whether or not this is the case, the water-level record from the Suguta Valley demonstrates the importance of both orbitally-controlled insolation variations and short-term changes in solar irradiation as factors affecting the significant water level variations in East African rift lakes. [Copyright &y& Elsevier]

How do we convert variabilities and trends in hundreds of potential parameters that are typically analyzed in the framework of a scientific drilling project to actual climate proxies? Using the case study from the Chew Bahir core from the southern Ethiopian Rift, we will show that deciphering climate information from lake sediments is challenging, because of the complex relationship between climate parameters and sediment composition. Establishing a reliable climate proxy for a new terrestrial archive requires the stepwise development of a profound understanding of both climate-controlled and non-climate controlled processes in the catchment. As a contribution towards an enhanced understanding of human-climate interactions the Chew Bahir Drilling Project, as part of HSPDP (Hominin Sites and Paleolakes Drilling Project) recovered 280 m-long sediment records from a deep, tectonically-bound basin in the southern Ethiopian rift in late 2014. The Chew Bahir record covers the past ~600 ka of environmental history, a critical time period that includes the transition to the Middle Stone Age, and the origin and dispersal of modern Homo sapiens. By deconvolving the relationship between sedimentological processes and geochemical parameters and strongly climate-controlled processes in the Chew Bahir basin, such as weathering (incongruent dissolution), transportation and authigenic mineral alteration, site-specific indicators for climate shifts on different magnitudes are being developed to eventually provide a detailed and reliable climate record. This study uses a multi indicator approach including whole rock and clay mineral analyses (XRD), XRF geochemistry and sedimentology such as grain size analysis. We will illustrate how sensitively the degree of authigenic transformation in especially clay minerals and zeolites has recorded even subtle shifts in the hydrochemistry of paleolake and porewaters, thereby representing a robust tool for differentiating contrasting chemical environments controlled by climatic change. The precise time resolution, largely continuous record and (eventually) a detailed understanding of site specific proxy formation, will give us a continuous record of environmental history on decadal to orbital timescales. Our data enable us to test current hypotheses of the impact of a variety of climate shifts on human evolution and dispersal. [ABSTRACT FROM AUTHOR]

Sedimentary ancient DNA (sedaDNA) has been proven to be a useful tool forpaleoenvironmental studies, but only a handful exist for tropical regions. We here presentsedaDNA analyses dating back to 1800 AD on two sediment cores from two craterlakes from the Kenyan Rift Valley. These alkaline-saline lakes have experienceddifferent climatic and anthropogenic influences. New data were retrieved from asediment core from Lake Kageinya (formerly known as Lake Eight), located in theremote, non-influenced anthropogenically, hot and hyper-arid Suguta Valley. Inthis study we used sedaDNA to study the temporal succession of Brachionus spp.rotifer haplotypes. The results are compared to previously published data fromLake Sonachi, a well-studied lake in the humid and colder mountainous region ofKenya near Naivasha town, now supported by a 210Pb age chronology. Both recordsexpand well beyond the onset of substantial anthropogenic impact on the regions.The results revealed that climate is the main driver for haplotype changes in bothlakes rather than an anthropogenic impact. During prolonged dry periods haplotypecomposition remained constant and at low diversity such as from 1910 to the late 1960s.Sudden changes and the emergence of new haplotypes are observed when climatebecame more humid, but also more variable (before 1910 and from 1960s onwards).Progressive changes in haplotype composition during such variable climates could reflectlocal adaptation and/or is the result of immigration of new haplotypes after theeradication of previous populations during extreme environmental conditions. Theseresults imply that sedaDNA in tropical lake sediments, despite of adverse chemicalconditions, is preserved at least back to 1800 AD and its analysis provides a goodcomplementary paleoenvironmental proxy for paleo-limnological reconstructions. [ABSTRACT FROM AUTHOR]