Trends, rhythms and events in East African climate: statistical analysis of the paleoclimare records of the long sediment cores of the Chew Bahir basin
Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
Final Report Abstract
We have statistically analyzed the environmental changes over the past ~620,000 years in eastern Africa, derived from long (~278 m) sediment cores from the Chew Bahir basin, southern Ethiopian rift. These cores were obtained 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 project has four main results, corresponding to the four scientific questions asked in the proposal. First, we developed a wavelet-based age-depth modeling technique to generate an absolute age model by tuning the scanned coloring of the sediment, reflecting the alternating wet and dry conditions in the basin, to their probable cause, cyclical (~23 kyr) changes in insolation, which in turn result from changes in the Earth's orbital parameters (climate precession). The age model generated in this way complements the age model for the long sediment cores from the Chew Bahir Basin, based on radiometric age dating and an age model obtained by means of traditional tuning using the technique of Hays et al. (1976). Second, we used multivariate statistical methods to detect similarities and differences between three eastern African sites, including Chew Bahir, six western African sites, and one southeastern African site, which revealed that low-latitude insolation rather than glacialinterglacial cyclicity (mainly controlled by the obliquity of the earth's axis, which varies with a ~41 kyr cycle) was the predominant driver of pan-African climate change during the mid to late Pleistocene. Third, we analyzed the long-term trends and shifts in the variability in the Chew Bahir using wavelet power spectral analysis, which revealed that the long-term variations in eastern African climate were due mainly to changes in the long period (~400 kyr) of changes in the earth's orbital eccentricity. Relatively dry but variable climates occurred during the minima of this cycle, and wet climates occured during the maxima, interspersed with distinctly drier phases associated with orbital precession. 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. The different types of variability and the transitions between those types had important effects on the availability of water, and could have transformed eastern Africa’s environment considerably, which would have had important implications for the shaping of the habitat of H. sapiens and the direct ancestors of this species. The surprise of the project is the presumed, but so far not shown in this clarity, importance of the long period (~400 kyr) of the earth's eccentricity cycle, which is reflected in two episodes with relatively humid and stable conditions (~600–470 kyr BP and 340–150 kyr BP), interrupted by an episode with very unstable conditions (~470–340 kyr BP). This episode of relative unstability coincides with the genetically determined multiregional appearance of H. sapiens and (possibly associated) cultural transition from the Acheulean to the Middle Stone Age technology between ~500 and 300 thousand years ago. A closer look at this connection between climate change and human development is to be examined in a pan-African perspective in the course of a follow-up project.
Publications
- (2018) Abrupt or Gradual? Change Point Analysis of the Late Pleistocene-Holocene Climate Record from Chew Bahir, Southern Ethiopia. Quaternary Research
Trauth, M.H., Foerster, V., Junginger, A., Asrat, A., Lamb, H., Schaebitz, F.
(See online at https://doi.org/10.1017/qua.2018.30) - (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) - 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)
