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Abstract:

Long-held views of high-altitudes as natural ecosystems characterized by late anthropogenic transformation processes have recently been challenged by studies carried out on the world’s high plateaus. This is all the more relevant in light of the demanding question where prehistoric populations retreated to, especially during arid intervals, when lowlands may have become uninhabitable. In this presentation we introduce an interdisciplinary approach for the reconstruction of Quaternary abiotic, biotic and cultural changes in African model highland environments of southern Ethiopia. The Bale Mountains represent the largest afro-alpine ecosystem of the continent. They are characterized by a very high biodiversity including a large number of endemic species and they host relevant archives to reconstruct the coupled landscape and human history. First results of a joint Ethio-European research unit (“The Mountain Exile Hypothesis”, funded by the Deutsche Forschungsgemeinschaft) summarized here, comprise archeological, archeozoological, soil biogeochemical and glacial chronological studies and concentrate on the earliest human occupation and persistent use of the available resources. The Bale Mountains feature the oldest evidence for humans in high-altitudes. Late Pleistocene hunter-gatherers must have been very familiar with the then glaciated environment. In immediate vicinity to valley glaciers, high-quality obsidian was regularly and repeatedly extracted from primary outcrops located above 4200 m asl, the highest known occurrences in Ethiopia. Settlement and subsistence activities concentrated on the ice-free areas with access to melt-water. Prehistoric foragers were moreover capable of developing unique subsistence strategies for sustainable and continuous survival and to satisfy the higher caloric demands of living in these altitudes. The associated Middle Stone Age material culture shows the existence of networks to lowlands, but at the same time exhibit the development of distinctive and independent technological traditions.

Abstract:

The high-altitude regions of African tropical environments are among the least studied areas regarding the dispersal and colonization of anatomically modern humans across and out of Africa. Human colonization of high altitude regions is considered a relatively recent process, not least as high-altitude environments are usually perceived as unfavorable for human subsistence and are believed to have functioned as a migration barrier due to their physiological and ecological challenges, including high-altitude hypoxia, cold stress and lack of sufficient resources. Although it is not yet clear when and how human population dispersed into the high-altitude mountains of tropical Africa, our new findings suggest that specialized hunter-gatherer successfully colonized and exploited a wide range of ‘harsh’ landscapes of the Bale Mountains (>3800m asl) in the southeastern Ethiopian Highlands during the Late and Terminal Pleistocene up to Middle and Late Holocene. Moreover, ongoing archaeological research in the northwestern part of the Bale Mountains provides new perspectives on human colonization of high-altitude tropical environments and the relationship between human adaptation and climate changes at least during three separate time periods between 31,000 cal. BP and 4,000 cal BP.

Abstract:

Today’s ice caps and glaciers in Africa are restricted to the highest peaks, but during the Pleistocene, several mountains on the continent were extensively glaciated. However, little is known about regional differences in the timing and extent of past glaciations and the impact of paleoclimatic changes on the afro-alpine environment and settlement history. Here, we present a glacial chronology for the Ethiopian Highlands in comparison with other East African Mountains. In the Ethiopian Highlands, glaciers reached their maximum 42 to 28 ka thousand years ago before the global Last Glacial Maximum. The local maximum was accompanied by a temperature depression of 4.4° to 6.0°C and a ~700-m downward shift of the afro-alpine vegetation belt, reshaping the human and natural habitats. The chronological comparison reveals that glaciers in Eastern Africa responded in a nonuniform way to past climatic changes, indicating a regionally varying influence of precipitation, temperature, and orography on paleoglacier dynamics.

Abstract:

In this study, we synthesize terrestrial and marine proxy records, spanning the past 620 ky, to decipher pan-African climate variability and its drivers and potential linkages to hominin evolution. We find a tight correlation between moisture availability across Africa to El Niño Southern Ocean oscillation (ENSO) variability, a manifestation of theWalker Circulation, that was most likely driven by changes in Earth’s eccentricity. Our results demonstrate that low-latitude insolation was a prominent driver of pan-African climate change during the Middle 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 by increasing resource-rich and stable ecotonal settings thought to have been important to early modern humans.

Abstract:

The preservation of archaeological remains and environmental information in a sediment accumulation can vary in caves and rockshelters, depending on external climatic conditions, and the circumstances within the shelter. Several sediment stratigraphies in the Horn of Africa are characterized by erosion layers, discordances and chronological gaps, that create uncertainties about the impact of climatic and environmental shifts on human settlements. Archaeological sites in Ethiopia that preserve information about human occupation during the Upper Pleistocene and Holocene often deal with major gaps during a period corresponding to MIS 2. In this study we present the first results of sedimentological, geochemical analyses and radiocarbon dating at Sodicho Rockshelter (1930 m above sea level) that provide evidence on high altitude settlement during this mentioned chronostratigraphic gap and subsequent time slices. This new archaeological site in the southwestern Ethiopian Highlands hosts a 2-m-long sediment record. So far, a stratigraphy has been excavated that dates back to ∼27 ka, including several settlement phases of Late Pleistocene and Holocene hunter-gatherers and providing information on environmental changes. A multiproxy approach was chosen to establish a first general stratigraphy of the site and to disentangle the sediment composition as well as site formation processes. The results suggest a variation of allochthonous and autochthonous geogenic deposits, and anthropogenic accumulation processes. With the help of radiocarbon dating, anthropogenic layers were dated covering the arid Last Glacial Maximum (LGM, ∼21 ± 2 ka). The occupation phases were interrupted in cause of environmental changes. The most prominent is the accumulation of reddish, archaeological sterile deposits that can be chronologically associated with the African Humid Period (AHP, ∼15–5 ka BP). Geochemical records point to dry spells within this humid phase, suggesting correlations with regional climate signals of lacustrine sediments. These sediment accumulations of past wet conditions are covered by alternating layers of Holocene volcanic fallout and sediments with preserved cultural material. Our study provides a preliminary impression of still poorly understood time periods of human occupation in the southwestern Ethiopian Highlands. The data obtained from Sodicho Rockshelter could validate the current state of knowledge and partially reduce the chronostratigraphic gap.