This study explores the emergence of Oldowan technology in the northeastern part of the Koobi Fora Formation, focusing on a poorly understood spatial and temporal context. It highlights the dynamic interplay between hominins, landscapes, and climate during the late Pliocene. The archaeological findings present a comprehensive analysis of stone artifacts from the FwJj52 locality that spans the terminal Pliocene- earliest Pleistocene. The technological patterns at the archeological site FwJj52 align with early Oldowan sites, emphasizing an astute understanding of raw material properties by hominins in the region.

Chrono-stratigraphic investigations reveal that the FwJj52 represents a unique locality, corresponding to the Tulu-Bor and Burgi Members of the Koobi Fora Formation, the latter member containing a stratigraphic interval largely absent in the geologic record of East Turkana due to a widespread unconformity. Multi-proxy geochronology (paleomagnetism, tephrostratigraphy) establishes a robust late Pliocene age estimate for the artifact-bearing horizons from FwJj52. Paleoenvironmental proxies (e.g., phytoliths, microcharcoals, plant biomarkers, pedogenic carbonates, soil geochemistry) indicate the area around FwJj52 experienced significant environmental changes. This includes shifts from humid floodplains to semi-arid plains alternating with paleoriver systems, probably triggered by the retreat of paleo-lake shorelines. 

This Interdisciplinary approach, combining archaeology, chrono-stratigraphy, and paleoenvironmental reconstructions, unveils a complex paleoecological narrative, indicating changes in vegetation, water availability, and climate, coinciding with the emergence of Oldowan stone tool technology in East Turkana. The landscape and climatic shifts we document in the northeastern Turkana Basin, Kenya mirror broader trends in eastern Africa during the late Pliocene, influenced by orbitally- forced climate change, tectonics, and reorganizations of paleogeography. These changes had cascading effects on ecosystems, including the expansion of grasslands and alterations in plant and animal species composition in the late Pliocene.

Paleogeographical and paleoecological shifts in the late Pliocene in eastern Africa likely imposed selective pressures on early hominins that could have influenced their behavior. This study emphasizes the reciprocal relationship between landscapes and tool-making endeavors, suggesting that the environments associated with ancient river systems acted as both witnesses to, and catalysts for, the evolution of stone tool technology.

How to cite: Palcu, D. V., Braun, D. R., Advokaat, E., Archer, W. S., Bobe, R., Carvalho, S., Forrest, F., Hammond, A. S., Kinyanjui, R., Martini, A., Mason, P., Patterson, D. B., Sier, M., Srivastava, P., Uno, K., Villaseñor, A., Wynn, J., Jovane, L., and Harris, J. W. K. and the Koobi Fora Research & Training Program (KFRTP): Hominin Technology Flourished amid Pliocene Environmental Variance in the Turkana Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6186, https://doi.org/10.5194/egusphere-egu24-6186, 2024.

In the backdrop of the global freshwater crisis exacerbated by human activities and climate change, our study addresses the need to understand the forces shaping lacustrine ecosystems in Eastern Africa, particularly within the East African Rift System (EARS). The Lake Elmenteita basin in the Central Kenya Rift represents the intricate interplay between intense geotectonic forces and escalating human activities. This study aims to unravel the complex interactions shaping this critical ecosystem, with a particular emphasis on the geotectonic aspects that underpin the lake's environmental dynamics. Lake Elmenteita is ecologically vital, supporting a diverse habitat including numerous bird species and serving as a primary food source for up to half a million flamingos.

Our research employs a multidisciplinary approach, integrating tectonic geomorphology, geological remote sensing, geochemistry, soil science, and micropaleontology. This approach is designed to differentiate the lake's natural geological influences from anthropogenic impacts.

Field investigations have demonstrated that tectonic activity controls mobilization of soils and sediments, primarily through processes of uplift and exhumation. Additionally, fault zones are correlated with hydrothermal activity influencing element mobilization and distribution. This is particularly evident through fault-controlled thermal springs along the lake shore and within its catchment, notably in areas like the Kinangop Plateau. Here, intensive agriculture amidst complex faulting has heightened vulnerability to soil erosion. The geological diversity, marked by erodable trachytic tuffs and more resistant basaltic sources, dictates distinct erosion patterns, further compounded by deforestation. This deforestation is visible in Landsat time series data from 1984 to 2023, and particularly severe in the basaltic regions of the Aberdare Range, and trachytic regions of the Kingangop plateau indicating a correlation with increased agricultural activity.

Remote sensing analysis, using multispectral (Aster, Landsat, Sentinel) and topographic  (TanDEM-X, Copernicus DEM) data, has been instrumental in mapping the lake's geological diversity and intricate fault network. The analysis highlights active fault zones, such as those along the NW sector of the Sattima fault and the Gilgil segment of the Kijabe fault. These faults are crucial in shaping the drainage patterns of the Kinangop plateau and influencing the hydrology of the lake.

The preliminary findings of this study place a spotlight on the dominant role of geotectonic processes in the environmental makeup of Lake Elmenteita, while also acknowledging the significant, albeit secondary, impact of human activities. By closely examining these combined forces, the research aims to contribute substantially to the understanding and management of this sensitive ecosystem. This insight is vital not only for Lake Elmenteita but also for other lacustrine systems within rift environments.

How to cite: Kübler, S., Rosca, C., Junginger, A., Muiruri, V., and Dusingizimana, M. W.: Geotectonic Influences on the Lake Elementeita Ecosystem (Central Kenya Rift): Insights from Field and Space-Based Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5407, https://doi.org/10.5194/egusphere-egu24-5407, 2024.

Lake Elmenteita located in the central Kenyan Rift System is a shallow (ca. 1 m deep on average), hyper-saline and alkaline playa lake of international bio-ecological importance, as emphasized by its classification as RAMSAR site (2005) and UNESCO world heritage site of “outstanding universal value” (2011). Unusually high rainfall and anthropogenic influence (deforestation, agriculture, sewage loading) are current drivers of changes in water level, composition and quality as well as the dramatic decline in riparian habitats. Identifying individual sources of both, elemental nutrients (P, N, Mg, Si, Zn) and potentially toxic elements (heavy metals, e.g., Cs, Mo, Pb, Sb, Cu) to the lake is imperative for ecosystem monitorization and development of biodiversity conservation strategies.

Here, we present dissolved element concentrations in water samples collected in July 2022 from the 1) central, 2) northern (discharge of rivers Kariandusi and Mereroni), and 3) southern (dominated by tectonically modulated volcanic hot-springs) part of the lake, as well as from 4) river Mereroni and 5) an additional hot-spring in the eastern part of the catchment. Data was acquired in the field and at the laboratories of the Isotope Geochemistry Group, Tübingen University. Results show compositional differences between hot springs and riverine influx (e.g., Cs: 0.03 ng/g Mereroni river vs. 3.3 ng/g S-hot springs), and also between Mereroni river water and northern shore waters (e.g., Sb: 0.063 ng/g Mereroni river vs. 0.92 ng/g N-shore; Cu: 0.925 ng/g Mereroni river vs. 27.3 ng/g N-Shore). Accompanied by observed compositional heterogeneities within the lake itself, our findings suggest that several sources and processes govern the elemental influx and distribution. Using geochemical indices, we will propose elemental dispersion vectors, main sources, and in-lake processes with the aim to unfolding the impact of recent anthropogenic signals from volcano-tectonic elemental origins to the lake.

How to cite: Rosca, C., Kübler, S., Muiruri, V., and Junginger, A.: Resolving volcanic from anthropogenic metal input to modern lake Elmenteita, Kenya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10665, https://doi.org/10.5194/egusphere-egu24-10665, 2024.

Lake Victoria, Africa’s largest lake, is located between the eastern and western branches of the East African Rift System, and its immense size but relatively shallow depth distinguish it from other lakes in eastern Africa. The Lake Victoria ecosystem serves as a stark example of the devastating impact human activities and anthropogenic eutrophication can have on freshwater biodiversity. However, despite its global significance as a case study of human-induced biodiversity loss, our understanding of the long-term ecological dynamics of the Lake Victoria ecosystem has remained surprisingly limited. Lake sediments provide valuable insights into the long-term ecological dynamics of Lake Victoria and the complex interplay between hydroclimatic variability, nutrient cycles, and biotic communities, which is crucial for deciphering the trajectories of the lake’s ecosystem evolution under multiple abiotic and biotic stressors in the past and future.

We present in a comprehensive paleolimnological study a detailed reconstruction of the changes in aquatic primary production and phytoplankton communities in Lake Victoria over the past 17 ka, based on novel bio-geochemical analyses of four well-dated sediment cores along a depth transect. Sedimentary pigments and biogenic silica were analyzed to infer aquatic productivity. Changes in sediment composition are supported by X-ray Fluorescence (XRF)-derived element geochemistry, ¹³C and ¹⁵N, and sedimentary phosphorus fraction analyses. In this study, we make use of this exceptionally extensive multivariate dataset to gain a more accurate view on environmental changes in LV from the latest Pleistocene to Holocene times.

Our comprehensive study of Lake Victoria's primary production patterns reveals a profound influence of regional hydroclimate changes on the lake's mixing and nutrient regime, ultimately driving the dynamics of primary producer communities. From its initial wetland phase (16.7 – 14.5 ka), Lake Victoria transitioned to an exorheic, productive system during the wetter Holocene with increased monsoonal activity. This period is marked by two distinct phases of elevated diatom production (11 – 9 ka and 7 – 4 ka). In the late Holocene, drier conditions with reduced water column mixing prevailed, leading to the emergence of a cyanobacteria-dominated phytoplankton community. Overall, these shifts in primary producer dominance underscore the lake's ecosystem sensitivity to hydroclimate variability. Our findings provide invaluable insights into the magnitude and direction of changes in Lake Victoria over time, highlighting the profound impact of natural and anthropogenic factors on the lake's aquatic ecosystem.

How to cite: Wienhues, G., Lami, A., Bernasconi, S., Vogel, H., Cohen, A., and Grosjean, M.: Exploring past primary production and its linkage with hydroclimate changes in Lake Victoria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15595, https://doi.org/10.5194/egusphere-egu24-15595, 2024.

The role that climate played in human evolution has been controversially discussed among scientists for decades. Inspired by these discussions, the Hominin Sites Paleolakes Drilling Project (HSPDP) conducted five deep drilling campaigns adjacent to key hominin fossil sites in eastern Africa, including the Chew Bahir Basin in southern Ethiopia. Analysis of the Chew Bahir lacustrine sedimentary record revealed that over the past 620,000 years, phases of environmental stability and instability occurred contemporaneously with milestones in human history, including pulsed dispersal events out of Africa coinciding with potential humid periods. Although proxies from Chew Bahir sediments have provided important qualitative information about relative changes in environmental conditions, we still lack quantitative information on water availability and an understanding of the dominant climatic forcings controlling water balance. Here we present the first radiogenic strontium isotope (⁸⁷Sr/⁸⁶Sr) record covering the past 50,000 years from four Chew Bahir sediment short cores (CB01, CB03, CB05, CB06) and one long core HSPDP-CHB-1A in a resolution of 100 to 1000 years measured on fish bones, endogenic calcites, and ostracods. We interpret the Sr isotope proxy to reflect water provenance changes, particularly controlled by the varying contribution of water overflowing from a series of lakes further north in Ethiopia. Our new Sr-isotope record shows a remarkable correlation with global sea level variability and does not show a pattern of precession paced cycles. Superimposed on this pattern, we see concurrent excursions in the Sr-isotope record of centennial- to millennial scale events such as Heinrich Event 1 (H1) or the Younger Dryas (YD). As Chew Bahir dominantly receives Indian Ocean moisture, the most likely driver of moisture availability in this part of eastern Africa is the temperature of western Indian Ocean surface water that varies in pace with glacial-interglacial climate change. Also on shorter time scales, reduced Indian Ocean surface temperatures correspond to reduced moisture in the tropical rainbelt resulting in dry conditions around H1 and the YD. Where other paleohydrological proxy data from lake fossils can be comparatively noisy because of the high spatial and seasonal variability in such tropical systems, the relatively conservative hydrochemistry of the Sr isotope signal in lakes like Chew Bahir makes this proxy relatively insensitive to seasonal variability while it faithfully captures decadal to longer time scale signals.

How to cite: Zachow, C., Vonhof, H., Galer, S. J. G., Foerster, V., Markowska, M., and Junginger, A.: Indian ocean sea surface temperature control on the 50,000-year strontium isotope Chew Bahir lake record, Eastern Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11537, https://doi.org/10.5194/egusphere-egu24-11537, 2024.

The directly dated RRMarch2021 age model (Roberts et al., Quaternary Science Reviews, 2021) for the ~290 m long composite core from Chew Bahir, southern Ethiopia, has provided a valuable chronology for long-term climate changes in northeastern Africa. However, the age model has limitations on shorter time scales (less than 1–2 precession cycles), especially in the time range <20 kyr BP and between ~155–428 kyr BP. To address those constraints we developed a partially orbitally tuned age model. A comparison with the ODP Site 967 record of the wetness index from the eastern Mediterranean, 3,200 km away but connected to the Ethiopian plateau via the River Nile, suggests that the partially orbitally tuned age model offers some advantages compared to the exclusively directly dated age model, with the limitation of the reduced significance of (cross)spectral analysis results of tuned age models in cause-effect studies. The availability of this more detailed age model is a prerequisite for further detailed spatiotemporal correlations of climate variability and its potential impact on the exchange of different populations of Homo sapiens in the region.

How to cite: Trauth, M. H., Fischer, M. L., Foerster, V., Marwan, N., Roberts, H. M., and Schaebitz, F.: Combining orbital tuning and direct dating approaches to age-depth model development for Chew Bahir, Ethiopia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5046, https://doi.org/10.5194/egusphere-egu24-5046, 2024.