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Six sites in Ethiopia and Kenya, all adjacent to key paleoanthropological sites have been investigated as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP), aiming at an enhanced understanding of climatic influences on human physical and cultural evolution. The recovered sediment cores from the six sites all together span the last ~3.5 Ma. The sediment core records archive environmental change during diverse milestones in human evolution, and times of dispersal and technological and cultural innovation. The 280 m-long Chew Bahir lacustrine record, recovered from a tectonically-bound basin in the southern Ethiopian rift in late 2014, covers the past ~600 ka of environmental history, a time period that includes the transition to the Middle Stone Age, and the origin and dispersal of modern Homo sapiens. Developing a continuous climate history based on sediment core composition is not straightforward because on one hand some indicators might only be preserved intermittently and on the other hand the physical and chemical properties of the sedimentary deposits do not have a linear relationship to climate. Here we present the first outcome of our ongoing work on deciphering direct paleoenvironmental information from authigenic mineral transformations in the long (~280 m) Chew Bahir sediment cores. First results suggest mineralogical and geochemical indicators record wet, dry and hyper-arid climate intervals. Preliminary work suggests that the most extreme evaporative phases are represented by authigenic mineral assemblages including Mg-enriched clays, low-temperature authigenic illite and euhedral analcime. SEM and Energy Dispersive Spectrometer (EDS) analyses confirm that the variations in the analcime abundance that are evident in the XRD dataset seem to be distinctly formed deltoidal icositetrahedrons. These are known to form in highly saline and alkaline brines (pH 9 and higher) and can be associated with pronounced arid phases. Understanding and determining the degree of authigenic mineral alteration in the Chew Bahir records will enable interpretation of µXRF-derived indicators (e.g. K correlated with aridity), and provide direct paleohydrologic data. Together with a well-constrained age-model, our growing understanding of site-specific proxy formation and the establishment of climate proxies for Chew Bahir will provide a robust environmental history on decadal to orbital timescales. [ABSTRACT FROM AUTHOR]

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]

There is ongoing debate concerning whether or not changes in the eastern African climate, both long-term and short-term, affected the evolution, dispersal, cultural development, and technological innovations of Homo sapiens – and if so, in what way. We present the wavelet spectral analysis results of a ∼620 kyr record of environmental change from the Chew Bahir (CHB) basin in the southern Ethiopian rift, approximately 120 km from the Omo-Kibish fossil locality, which boasts one of the oldest documented appearances of H. sapiens. Our results indicate that the long-term wet-dry changes in the eastern African climate recorded in the CHB sediments were mainly caused by changes in orbital eccentricity, with relatively dry but variable climates occurring during eccentricity minima within the 400 kyr eccentricity cycle, and increased precipitation, interspersed with distinctly dryer phases associated with orbital precession, during eccentricity maxima. Such insolation-forced precipitation changes would have affected the habitat of H. sapiens in the region; the transition from Acheulean to Middle Stone Age (MSA) documented in the Olorgesailie Basin of southern Kenya coincides with a distinct eccentricity minimum with reduced precipitation and repeated abrupt climatic transitions. In contrast, at the time of the subsequent, first documented occurrence of H. sapiens in eastern Africa the climate was distinctly wetter and less variable. • Orbitally controlled variation in insolation have caused wet-dry climate cycles in the CHB over the las 620 kyrs. • The climate of the CHB was characterized by a long term drying trend coinciding with an increase in variability. • Short term increases of variability correspond to changes in eccentricity translating into fast climate transitions. • During the transition from Acheulean to MSA technologies the climate of the CHB was highly variable. [ABSTRACT FROM AUTHOR]

Despite eastern Africa being a key location in the emergence of Homo sapiens and their subsequent dispersal out of Africa, there is a paucity of long, well-dated climate records in the region to contextualize this history. To address this issue, we dated a ∼293 m long composite sediment core from Chew Bahir, south Ethiopia, using three independent chronometers (radiocarbon, 40Ar/39Ar, and optically stimulated luminescence) combined with geochemical correlation to a known-age tephra. The site is located in a climatically sensitive region, and is close to Omo Kibish, the earliest documented Homo sapiens fossil site in eastern Africa, and to the proposed dispersal routes for H. sapiens out of Africa. The 30 ages generated by the various techniques are internally consistent, stratigraphically coherent, and span the full range of the core depth. A Bayesian age-depth model developed using these ages results in a chronology that forms one of the longest independently dated, high-resolution lacustrine sediment records from eastern Africa. The chronology illustrates that any record of environmental change preserved in the composite sediment core from Chew Bahir would span the entire timescale of modern human evolution and dispersal, encompassing the time period of the transition from Acheulean to Middle Stone Age (MSA), and subsequently to Later Stone Age (LSA) technology, making the core well-placed to address questions regarding environmental change and hominin evolutionary adaptation. The benefits to such studies of direct dating and the use of multiple independent chronometers are discussed. • Four independent dating methods applied to ∼293 m lake core from southern Ethiopia. • Reveals 620 ka high-resolution sedimentary record near key fossil hominin sites. • Mean accumulation rate of 0.47 mm/a comparable to other African lacustrine sediments. • Accumulation rate fell to 0.1 mm/a during MIS 2, likely due to reduced sediment supply. • Use of multiple independent chronometers is a powerful approach in lake settings. [ABSTRACT FROM AUTHOR]

Cores from terrestrial archives, such as the lacustrine sediments from the Chew Bahir basin in southern Ethiopia, which cover the last ~600 ka, often reflect both local, regional and global climate influences. In our analysis we were able to identify several time windows in which the Chew Bahir climate is in resonance with regional and global climate change.As a contribution to understanding and differentiating these connections recorded in the Chew Bahir sediments, we have correlated the 2nd principal component of the MSCL based color reflectance values representing wet conditions in the Chew Bahir basin, with the wetness index from ocean core ODP 967 from the eastern Mediterranean Sea. The correlation between these two time series was calculated using the Spearman correlation coefficient in a sliding window. Episodes with high correlation between the two records of wetness could indicate a strong link between both regions, possibly through an increased outflow of the river Nile into the eastern Mediterranean Sea due to higher precipitation values on the Ethiopian plateau.Our preliminary results show that when correlating the two records, two distinct temporal units can be distinguished. Between ~570 ka and ~350 ka the correlation is dominated by cycles that correspond with orbital precession whereas the second unit (after 350 ka) reveals a strong influence of atmospheric CO2. This observation suggests that both orbital precession and atmospheric CO2. may cause a synchronization of different regions in the African climate system, possibly depending on boundary conditions which are still to be identified.As a next step we'll investigate the nonlinear relationships between the two records by focusing on the transition between the two main observed phases. The transition around ~350 kyrs however, is not only highly interesting from a climatic perspective, but it is also a noteworthy period for human cultural evolution as a transition from Acheulean to Middle Stone Age (MSA) technologies takes place at this time. So far our results outline that during this climatically and evolutionary relevant episode a relatively stable, long-lasting, pan-African wet phase may have existed, with possible green corridors connecting the habitats of hominins, and ample resources supporting large population sizes. [ABSTRACT FROM AUTHOR]