The Chew Bahir Drilling Project: A Half-Million Year Climate Record from the Southern Ethiopian Rift, Crucible of Human Evolution
Final Report Abstract
In Nov–Dec 2014 we have collected two parallel sediment cores, HSPDP-CHB14 2A (4°45'40.32"N 36°46'0.48"E) and 2B (4°45'40.68"N 36°46'1.20"E) in the Chew Bahir basin, southern Ethiopian rift, 266.38 and 278.58 m long. These cores were obtained within the Chew Bahir Drilling Project (CBDP) as part of the ICDP-funded Hominin Sites and Paleolakes Drilling Project (HSPDP) the aim of which is to test hypothesized linkages between climate change and mammalian (including hominin) evolution in tropical-subtropical eastern Africa. The analysis of the 292.87 m long composite core of the CBDP with more than 90% recovery included, among other methods, Multi-Sensor Core Logging (MSCL), including magnetic susceptibility, p-wave velocity, gamma-ray density as well as the color scans, X-ray fluorescence (XRF) scans, and X-ray diffraction (XRD) analyses. The analysis of the the ~620 kiloyear (kyr) environmental record from the Chew Bahir basin has five main results, corresponding to the scientific questions asked in the initial proposal: First, the results from the analysis revealed three distinct climatic phases that are associated with milestones in hominin/human evolution, innovation and dispersal. During Phase I, a major mammalian turnover and the onset of the demise of Homo erectus and Acheulean technology in eastern Africa coincides with a long-term drying trend. After ~413 kiloyears before present (kyr BP) (Phase II) an increasingly orbitally-paced, wetter, eastern African climate is paralleled by the emergence of H. sapiens. With the onset of Phase III at ~195 kyr BP, rapid climate oscillations superimposed on a long-term drying trend coincide with the rapid expansion of cultural capacity, that might have buffered H. sapiens from severe environmental challenges. At the same time, humid pulses may have propelled major migration events out of Africa. Second, we find a tight correlation between moisture availability across Africa to Walker and Hadley Circulation variability that were most likely driven by changes in Earth's eccentricity. Our results demonstrate that low latitude insolation rather than glacial-interglacial cyclicity was the predominant driver of pan-African climate change during the mid to late Pleistocene. We argue that these low-latitude climate processes governed the dispersion and evolution of vegetation, as well as mammals, in eastern and western Africa, ultimately by increasing resource-rich and stable ecotonal settings that have long thought to have been the preferred habitats of hominins. Third, documented wet phases at CHB, compared with other sedimentological records of northeastern Africa of the last 200–60 kyrs, indicate recurrent availability of favorable living conditions in the lowlands of the East African Rift System and adjacent regions for H. sapiens, which would have provided opportune corridors for our species to disperse into the Levant and Arabia. Increasing aridity in the lowlands of the southern Ethiopian rift valley starting during marine isotope stage (MIS) 4 and intensifying since 60 kyr BP may have induced H. sapiens to develop, test and use new strategies to survive: living in high mountain refugia as well as the use of new tools. Fourth, we used nonlinear time series analysis methods to distinguish two types of variability and transitions in eastern African climate, which we also find in eastern Mediterranean climate. Type 1 variability reflects the influence of precessional forcing at times of maximum (~400 kyr) eccentricity, causing cyclical (~23 kyr) variations in climate and relatively moderate transitions from wet to dry (and back) over several hundreds of years. Type 2 variability seems to be linked with minimum eccentricity, with century-millennium-scale variations with progressively increasing frequencies and extremely rapid transitions between wet and dry within a few decades or years. Fifth, according to our results concerning the causes of the Acheulean to Middle-Stone Age technology we find that this transition coincides with a distinct eccentricity minimum with reduced precipitation and repeated abrupt climatic transitions. In contrast, at the time of the subsequent first documented appearance of H. sapiens in eastern Africa the climate was distinctly wetter and less variable.
Publications
- (2015) Environmental Change and Human Occupation of Southern Ethiopia and Northern Kenya during the last 20,000 years. Quaternary Science Reviews, 129, 333-340
Foerster, V., Vogelsang, R., Junginger, A., Asrat, A., Lamb, H.F., Schaebitz, F., Trauth, M.H.
(See online at https://doi.org/10.1016/j.quascirev.2015.10.026) - (2016). The Hominin Sites and Paleolakes Drilling Project: Inferring the Environmental Context of Human Evolution from Eastern African Rift Lake Deposits. Scientific Drilling, 21, 1–16
Cohen, A.S. , Campisano, C., Arrowsmith, R., Asrat, A., Behrensmeyer, A.K., Deino, A., Feibel, C., Hill, A., Johnson, R., Kingston, J., Lamb, H., Lowenstein, T., Noren, A., Olago, D., Owen, R.B., Potts, R., Reed, K., Renaut, R., Schäbitz, F., Tiercelin, J.-J., Trauth, M.H., Wynn, J., Ivory, S., Brady, K., O’Grady, R., Rodysill, J., Githiri, J., Russell, J., Foerster, V., Dommain, R., Rucina, S., Deocampo, D., Russell, J., Billingsley, A., Beck, C., Dorenbeck, G., Dullo, L., Feary, D., Garello, D., Gromig, R., Johnson, T., Junginger, A., Karanja, M., Kimburi, E., Mbuthia, A., McCartney, T., McNulty, E., Muiruri, V., Nambiro,E., Negash, E.W., Njagi, D., Wilson, J.N., Rabideaux, N., Raub, T., Sier, M.J., Smith, P., Urban, J., Warren, M., Yadeta, M., Yost, C., Zinaye, B.
(See online at https://doi.org/10.5194/sd-21-1-2016) - (2017) The Hominin Sites and Paleolakes Drilling Project: High-Resolution Paleoclimate Records from the East African Rift System and Their Implications for Understanding the Environmental Context of Hominin Evolution. PaleoAnthropology, 2017, 1-43
Campisano, C.J., Cohen, A.S., Arrowsmith, J.R., Asrat, A., Behrensmeyer, A.K. Brown, E.T., Deino, A.L. Deocampo, D.M., Feibel, C.S., Kingston, J.D., Lamb, H.F., Lowenstein, T.K., Noren, A., Olago, D.O., Owen, R.B., Pelletier, J.D., Potts, R., Reed, K.E., Renaut, R.W., Russell, J.M., Russell, J.L., Schäbitz, F., Stone, J.R., Trauth, M.H., Wynn, J.G.
(See online at https://doi.org/10.1130/abs/2017am-295426) - (2018) Abrupt or Gradual? Change Point Analysis of the Late Pleistocene-Holocene Climate Record from Chew Bahir, Southern Ethiopia. Quaternary Research, 90, 321–330
Trauth, M.H., Foerster, V., Junginger, A., Asrat, A., Lamb, H., Schaebitz, F.
(See online at https://doi.org/10.1017/qua.2018.30) - 2018. Towards an understanding of climate proxy formation in the Chew Bahir basin, southern Ethiopian Rift. Palaeogeography, Palaeoclimatology, Palaeoecology, 501, 111-123
Foerster, V., Deocampo, D.M., Asrat, A., Günter, C., Junginger, A., Kraemer, H., Stroncik, N.A., Trauth, M.H.
(See online at https://doi.org/10.1016/j.palaeo.2018.04.009) - (2019) Classifying past climate change in the Chew Bahir basin, southern Ethiopia, using recurrence quantification analysis. Climate Dynamics, 53(5), 2557–2572
Trauth, M.H., Asrat, A., Duesing, W., Foerster, V., Kraemer, K.H., Marwan, N., Maslin, M.A., Schaebitz, F.
(See online at https://doi.org/10.1007/s00382-019-04641-3) - (2020) Determining the pace and magnitude of lake level changes in southern Ethiopia over the last 20,000 years using Lake Balance Modelling and SEBAL. Frontiers in Earth Science, 8, 197
Fischer, M.L, Markowska, M., Bachofer, F., Foerster, V., Asrat, A., Zielhofer, C., Trauth, M.H., Junginger, M.
(See online at https://doi.org/10.3389/feart.2020.00197) - Recurring types of variability and transitions in the ~620 kyr record of climate change from the Chew Bahir basin, southern Ethiopia, Quaternary Science Reviews
Trauth, M.H., Asrat, A., Cohen, A., Duesing, W., Foerster, V., Kaboth-Bahr, S., Kraemer, H., Lamb, H., Marwan, N., Maslin, M., Schaebitz, F.
(See online at https://doi.org/10.1016/j.quascirev.2020.106777) - Multiband wavelet age modeling (MUBAWA) for a ~293 m (~600 kyr) sediment core from Chew Bahir basin, southern Ethiopian Rift. Frontiers in Earth Science
Duesing, W., Berner, N., Deino, A.L., Foerster, V., Kraemer, H., Marwan, N., Trauth, M.H.
(See online at https://doi.org/10.3389/feart.2021.594047)
