Project Database

Abstract:

Fire plays a critical role shaping both the distribution and composition of the Afroalpine and Afromontane communities. Some plant communities are resilient to certain fire regimes, presenting post-fire traits such as resprouting, as is evident in the sub-Alpine Ericaceous zone, while others lacking these strategies are more fire-prone. The fire regime concept includes the biological role in fire occurrence because some of the parameters driving fire regimes – frequency, type or intensity - are often regulated by the vegetation through its structure, flammability and connectivity.

Abstract:

East Africa is an underrepresented region in respect of monitoring the stable isotopic composition of precipitation (δ18Oprec and δ2Hprec). In 2017, we collected precipitation samples from ten weather stations located along an altitudinal transect ranging from 1304 to 4375 m a.s.l. The δ18Oprec and δ2Hprec values varied from –8.7 to +3.7‰ and –38 to +29‰, respectively. The local meteoric water line is characterised by a lower slope, a higher intercept and more positive d-excess values (δ2H = 5.3 ± 0.2 * δ18O + 14.9 ± 0.9) compared to the global meteoric water line. Both altitude and amount of precipitation clearly correlate with our isotope data. However, the δ18Oprec and δ2Hprec values show at the same time a seasonal pattern reflecting rainy versus dry season. More enriched isotope values prevailed shortly after the end of the dry season; more depleted isotope values coincided with high precipitation amounts recorded in May, August and September. Moreover, HYSPLIT trajectories reveal that during the dry season water vapour originates primarily from the Arabian Sea, whereas during the wet season it originates primarily from the Southern Indian Ocean. These findings challenge the traditional amount effect interpretation of paleoclimate isotope records from East Africa and rather point to a previously underestimated source effect.

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.

Abstract:

Large forms of sorted patterned ground belong to the most prominent geomorphic features ofperiglacial and permafrost environments of the mid-latitudes and polar regions, but they were hitherto unknownin the tropics. Here, we report on relict large sorted stone stripes (up to 1000 m long, 15 m wide, and 2 m deep)on the ca. 4000 m high central Sanetti Plateau of the tropical Bale Mountains in the southern Ethiopian High-lands. These geomorphic features are enigmatic since forms of patterned ground exceeding several metres arecommonly associated with distinct seasonal ground temperatures, oscillating around 0◦C. To systematicallyinvestigate present frost phenomena and relict periglacial landforms in the Bale Mountains, we conducted ex-tensive geomorphological mapping. The sorted stone stripes were studied in more detail by applying aerialphotogrammetry, ground-penetrating radar measurements, and36Cl surface exposure dating. In addition, weinstalled ground temperature data loggers between 3877 and 4377 m to analyse present frost occurrence andseasonal ground temperature variations. Superficial nocturnal ground frost was measured at 35–90 d per year,but the ground beneath the upper few centimetres remains unfrozen the entire year. Seasonal frost occurrencewould require a mean annual ground temperature depression of about 11◦C, corresponding to an air tempera-ture decrease of about 6–8◦C (relative to today) as inferred from a simple statistical ground temperature modelexperiment. Our results suggest the formation of the large sorted stone stripes under past periglacial conditionsrelated to lateral and vertical frost sorting in the course of cyclic freezing and thawing of the ground. It is likelythat the stone stripes formed either in proximity to a former ice cap on the Sanetti Plateau over the last glacial pe-riod due to seasonal frost heave and sorting or they developed over multiple cold phases during the Pleistocene.Although certain aspects of the genesis of the large sorted stone stripes remain unresolved, the presence of thesegeomorphic features provides independent evidence besides glacial landforms for unprecedented palaeoclimaticand palaeoenvironmental changes in the tropical Bale Mountains during the (Late) Pleistocene.