ALBERT

Description: The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and hominin evolution in Africa through the analysis of sediment cores that have recorded environmental changes in the Chew Bahir basin (CHB). In this statistical project we used recurrence plots (RPs) together with a recurrence quantification analysis (RQA) to distinguish two types of variability and transitions in the Chew Bahir aridity record and compare them with the ODP Site 967 wetness index from the eastern Mediterranean. The first type of variability is one of slow variations with cycles of ∼20 kyr, reminiscent of the Earth’s precession cycle, and subharmonics of this orbital cycle. In addition to these cyclical wet-dry fluctuations in the area, extreme events often occur, i.e. short wet or dry episodes, lasting for several centuries or even millennia, and rapid transitions between these wet and dry episodes. The second type of variability is characterized by relatively low variation on orbital time scales, but significant century-millennium-scale variations with progressively increasing frequencies. Within this type of variability there are extremely fast transitions between dry and wet within a few decades or years, in contrast to those within Type 1 with transitions over several hundreds of years. Type 1 variability probably reflects the influence of precessional forcing in the lower latitudes at times with maximum values of the long (400 kyr) eccentricity cycle of the Earth’s orbit around the sun, with the tendency towards extreme events. Type 2 variability seems to be linked with minimum values of this cycle. There does not seem to be a systematic correlation between Type 1 or Type 2 variability with atmospheric CO2 concentration. 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.

Description: Eastern Africa and Arabia were major hominin hotspots and critical crossroads for migrating towards Asia during the late Pleistocene. To decipher the role of spatiotemporal environmental change on human occupation and migration patterns, we remeasured the marine core from Meteor Site KL 15 in the Gulf of Aden and reanalyzed its data together with the aridity index from ICDP Site Chew Bahir in eastern Africa and the wet-dry index from ODP Site 967 in the eastern Mediterranean Sea using linear and nonlinear time series analysis. These analyses show major changes in the spatiotemporal paleoclimate dynamics at 400 and 150 ka BP (thousand years before 1950), presumably driven by changes in the amplitude of the orbital eccentricity. From 400 to 150 ka BP, eastern Africa and Arabia show synchronized wet-dry shifts, which changed drastically at 150 ka BP. After 150 ka BP, an overall trend to dry climate states is observable, and the hydroclimate dynamics between eastern Africa and Arabia are negatively correlated. Those spatio-temporal variations and interrelationships of climate potentially influenced the availability of spatial links for human expansion along those vertices. We observe positively correlated network links during the supposed out-of-Africa migration phases of H. sapiens. Furthermore, our data do not suggest hominin occupation phases during specific time intervals of humid or stable climates but provide evidence of the so far underestimated potential role of climate predictability as an important factor of hominin ecological competitiveness.

Description: Situated within a 1.07 million-year-old meteorite crater, Lake Bosumtwi in Ghana stands as a pivotal location for comprehending climatic, ecological and environmental fluctuations within the sub-Saharan region of West Africa. The region's susceptibility to seasonal environmental shifts and climate oscillations is heightened by the annual movements of the tropical rain belt driven by atmospheric circulation. Yet, there is no satisfying age-depth model available for the entire sedimentary sequence strongly limiting our understanding of changes in this circulation pattern and associated (broad-scale) environmental responses during the last million years in the local to regional context of Lake Bosumtwi. To overcome this, we statistically examine the cyclicity in total natural gamma ray (NGR) data on a core from the lake's centre and create a cyclostratigraphic age-depth model. The calculated maximum age of 946 ka agrees well with the meteorite impact age (∼10 % offset). In order to refine this purely statistical approach, we also perform a correlative age-depth model using 33 tie points accounting for the complexity of climatic and environmental imprints to the NGR record that may exceed direct insolation related effects. Special attention is paid to the core's robustly dated (14C, OSL, U/Th) uppermost part covering the last 200 ka. Here, high NGR and co-varying K counts coincide with warm periods (except of the water-saturated and unconsolidated Holocene part) and the inverse for glacials and stadials. Based on this, we define tie points for correlating our NGR data to the age-depth model of a NE Atlantic SST record. Comparing our results to the correlation target, other global climate records and Sahara dust flux data reveals striking similarities and supports a proxy understanding with increased in wash of K-enriched terrigenous material from the crater rims in warm and moist periods (high NGR) and K-depleted dust input in stadials possibly contributing to low NGR values in addition to reduced input of K-enriched sediments from the crater rims. Our correlative age model results in precession amplitudes matching eccentricity well, providing further support especially because an over-tuning is unlikely with the used 33 tie points. Overall we provide crucial chronological context to numerous datasets along with environmental constrains that can be used to study the potential habitat availability of early anatomically modern humans in West Africa.