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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]

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]

The sediments of the Chew Bahir playa lake in southern Ethiopia were cored down to 280 m depth in the context of HSPDP (Hominin Sites and Paleolakes Drilling Project) and CRC (Collaborative Research Center) 806 "Our way to Europe" projects. The main aim is to reconstruct the paleoenvironmental conditions during the development of anatomically modern humans (AMH) and to test hypotheses about human evolution, dispersal and technological innovation. Based on several dating methods (14C, Ar/Ar, optical stimulated luminescence, chemical fingerprints of tephras) the composite core is shown to cover the last ~600 ka and therefore brackets the time period of important steps in cultural evolution, from Late Acheulean to Middle/Late Stone Age technologies, the origin of AMH, as well as the most recent "Out of Africa" human dispersal events. The multiproxy record of the composite core (e.g., chemical and physical sediment properties, stable C, O and Sr isotope ratios of carbonates, microfossil assemblages and biomarkers) indicates long- and short-time hydroclimatic changes mainly driven by orbital controlled insolation (mostly the Earth's precession ~15-25 ka, but also eccentricity ~90-120 ka). We compare our Chew Bahir data with results from other long marine and terrestrial paleoclimatic records. Here we focus on particularly strong wet and dry fluctuations at Chew Bahir during the last 200 ka to test established hypotheses for human dispersal and technological innovation. The record indicates that at least some of the human dispersal waves have taken place during wetter environmental conditions offering green corridors in East Africa, one of the source regions of our ancestors. [ABSTRACT FROM AUTHOR]