North Africa is one of the most vulnerable regions on Earth to anthropogenically-driven climate change, but also one of the least equipped to deal with the consequences. Predictions of precipitation levels over the forthcoming centuries diverge, not only in magnitude, but also in the sign of change. One key aspect of this uncertainty comes from the role of Atlantic Ocean sea surface temperatures (SST), which are known to exert a strong control over precipitation in North Africa and are implicated in both the major Sahelian drought of the late 20^th century and extreme droughts associated with the Heinrich events of the last glacial period.

To better understand how African hydroclimate responds to SST variability across a range of climate states, we reconstruct changes in the ocean and atmosphere through the transition from the Pliocene epoch (when atmospheric CO₂ levels were comparable to present) into the cooler Pleistocene. We present data from Ocean Drilling Project Site 659, which is situated in the subtropical North Atlantic beneath the major modern summer Saharan dust plume. Our dust accumulation and X-ray fluorescence core scan data record repeated shifts between highly arid conditions and humid intervals with vegetated or “Green Sahara” conditions over much of northern Africa. The amplitude of these humid events is modulated by both global climate state and variability in solar insolation, with three unusually long intervals of low dust emissions (each lasting ca. 100 kyr) occurring at times when insolation variability was weak. We also present new paired alkenone-derived SST estimates and multi-species planktonic foraminiferal isotope records from 3.5–2.3 Myr ago to explore the role of North Atlantic dynamics in driving African hydroclimate variability. Our records help to develop the environmental framework needed to assess evolutionary outcomes on land and improve our understanding of the mechanisms driving precipitation variability in North Africa.

How to cite: Crocker, A., Jewell, A., Mitsunaga, B., Buchanan, S., Westerhold, T., Röhl, U., Xuan, C., Russell, J., Herbert, T., and Wilson, P.: Did the North Atlantic Ocean play a role driving Green Sahara conditions during the Late Pliocene and Early Pleistocene?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10095, https://doi.org/10.5194/egusphere-egu23-10095, 2023.

The Early Mid-Pleistocene Transition (EMPT) between 1,200–700 ka represents a major global climate transition from dominantly 41,000-year to 100,000-year glacial cycles. The forces and mechanisms behind this transition, and the response of African environments, is not well understood. The active volcanism and tectonics of the East African Rift System (EARS) add complexity to environmental systems and can erase important proxy records, inhibiting studies of lacustrine dynamics. As a result, there is minimal understanding of how this transition impacted the region’s lake systems, with implications for hominin migration. At paleolake Suguta in the northern Kenya Rift, however, flood basalts cap lacustrine EMPT-aged deposits and help preserve these strata and their valuable paleoenvironmental record. This research presents a high-resolution reconstruction of hydrological change from approximately 930 to 830 ka during the EMPT at the Suguta-Turkana Valley in the northern Kenya Rift. Paleolake dynamics are reconstructed from a 41 m sedimentary section using diatom morphology, sedimentology, and x-ray fluorescence analysis. Lake levels varied during the EMPT, particularly from ~885–830 ka, ranging from deep stratified lakes, shallow, well-mixed lakes, and complete desiccation. This record identifies hydroclimate variability at several thousand year-resolution within the Suguta-Turkana Valley during the EMPT, illuminating a period where generally little is known about terrestrial environmental change.

How to cite: Robakiewicz, E., Owen, R. B., Deino, A., Trauth, M., and Junginger, A.: Variable Hydroclimate in the Suguta-Turkana Valley, Kenya during the Early Middle-Pleistocene Transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14071, https://doi.org/10.5194/egusphere-egu23-14071, 2023.

Which routes did Homo sapiens take when spreading from Africa to Eurasia? The climatic conditions changed and with them the living conditions. Over the past twelve years, a research team has deciphered the complex interplay of cultural innovations, mobility and environmental changes funded by the German Research Foundation (Collaborative Research Center 806 "Our Way to Europe"). Our working group in Bonn specifically investigated when and where migration corridors or barriers existed  from a paleoecological and paleoclimatological point of view. It turned out that the Levant, as the only permanent land bridge between Africa and Eurasia during the Quaternary, was the key region as a migration corridor for modern humans. Cores from the Dead Sea Deep Drilling Project (ICDP) were investigated, in which the environmental and climate history of the last 200 ka is excellently preserved and documented. In particular, pollen analysis allows changes in vegetation cover to be identified and environmental and climatic conditions to be reconstructed. These data illustrate that the Levant could only have served as a corridor when, under more favorable conditions, for example, neither deserts nor dense forests impeded the spread of modern humans.

How to cite: Litt, T.: Paleoecology/paleoclimate of the Levant and its impact on the spread of modern humans from Africa to Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5707, https://doi.org/10.5194/egusphere-egu23-5707, 2023.

The study of the mid-Holocene climate tipping point in tropical and subtropical Africa is the subject of current research, not only because there is a comparatively simple but nonlinear relationship between the change in cause (orbital forcing) and the accelerated response of the monsoon system, but also because the African monsoon is an example of a potentially positive evolution of living conditions for humans: modeling results suggest that the Sahel is expanding northward in the wake of human-induced recent global warming, with green belts spreading northward. New literature distinguishes tipping elements such as the African monsoon according to the nature of the cause and the response of the climate system. Research here focuses primarily on tipping points of the type, which is characterized by a critical slowing down and a decreasing recovery from perturbations. The African monsoon, on the other hand, is an example of the tipping point of the type, which is characterized by flickering before the transition. The two types also differ in the nature of their early warning signals (EWS). These EWS are increasingly becoming the focus of research, as they are particularly important for predicting possible tipping of climate in the future of our planet. For the African monsoon system, flickering between two stable states near the transition has been predicted by modeling, but has not yet been demonstrated on paleoclimate time series.

The paleoenvironmental record from the Chew Bahir Basin in the southern Ethiopian Rift, which documents the climate history of eastern Africa of the past ~620 ka with decadal resolution in some parts provides the possibility to examine the termination of the African Humid Period (AHP, ~15–5 kyr BP) with regard to the possible occurrence of EWS. Thanks to six well-dated short sediment cores (<17 m, <47 kyr BP) and two long cores (~290 m, <620 ka BP) we can not only study the last climate transition at ~5.5 kyr BP in detail, but also similar transitions including possible EWS long before the first occurrence of Homo sapiens at ~318 ka BP on the African continent. The analysis of the Chew Bahir record reveals a rapid (~880 yr) change of climate at ~5.5 kyr BP in response to a relatively modest change in orbital forcing that appears to be typical of climate tipping points. If this is the case then 14 dry events at the end of the AHP and 7 wet events after the transition, each of them 20–80 yrs long and recurring every 160±40 yrs, could indeed indicate a pronounced flickering between wet and dry conditions at the end of the AHP, providing significant EWS of an imminent tipping point. Compared to the low-frequency cyclicity of climate variability before and after the termination of the AHP, the flickering occurs on time scales equivalent to a few human generations and it is very likely (albeit speculative) that people were conscious of these changes and adapted their lifestyles to the rapid changes in water and food availability.

How to cite: Trauth, M. H., Asrat, A., Fischer, M. L., Hopcroft, P. O., Foerster, V., Kaboth-Bahr, S., Lamb, H. F., Marwan, N., Maslin, M. A., Schäbitz, F., and Valdes, P. J.: Early Warning Signals for the Termination of the African Humid Period(s), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5277, https://doi.org/10.5194/egusphere-egu23-5277, 2023.

The Okavango rift zone/delta and the Makgadikgadi paleo-megalake form a dynamic system in northern Kalahari, where tectonic activity, climate change, sedimentation, and biota have interacted in a complex pattern. Previous research suggested that the region may have been a hotspot for hominid evolution.

Here we present results from the first scientific deep drilling project (OKAMAK) in the northern Kalahari, Botswana. Two drill cores, OKA (230 meters) and MAK (210 m), were drilled in the Okavango delta and Makgadikgadi paleolake. Cores recovered shallow and deep-water sands, muds and evaporitic lithologies of the Cenozoic Kalahari Group extending across the unconformity into the Cretaceous/Jurassic Karoo Group sandstones.

We discuss initial stratigraphy, chronologies and paleoenvironmental information for this novel sedimentary record, present hypotheses to be tested on the complex climate of the region, history of river piracy, evolution of the delta and infilling phases of Makgadikgadi and assess the international collaborative potential of this yet to be fully understood region within a future multi-platform ICDP-IODP initiative.

How to cite: Giosan, L., Canales, J. P., Ivory, S., Shen, Z., De Jonge, C., Eglinton, T., Lattaud, J., Russo, N., Haghipour, N., Filip, F., Khonde, N., Carter, A., Garzanti, E., Ando, S., Franchi, F., Kgosiemang, K., Burrough, S., Thomas, D., Mapeo, R., and Laletsang, K. and the OKAMAK Extended Team: When the desert was a lake: Tectonics, climate, river piracy and hominids in the Kalahari, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1586, https://doi.org/10.5194/egusphere-egu23-1586, 2023.

The Guinea Dome, located in the eastern tropical North Atlantic, is produced by cyclonic circulation associated with the eastward North Equatorial Countercurrent, the northward Mauritanian Current and the westward North Equatorial Current, which causes the uplift of the isotherms in the Guinea Dome. This oceanographic feature is important for the regional atmosphere-ocean dynamics, and its variability was suggested to be linked with precipitation changes in North Africa, at least at a decadal scale. Characterizing the development of the dome through the Holocene will contribute to understand the prominent environmental changes that occurred regionally during this period, as evidenced by the green-to-desert Sahara transition at the end of the African Humid Period (ca. 6,000 years ago).

A 35cm sediment multicore, extracted southwest off Cabo Verde during the iMirabilis2 scientific cruise, at a water depth of 4,394 m, is being investigated. We present planktonic foraminifera counts and X-ray fluorescence (XRF) scanning data to reconstruct palaeoceanographic and sediment input changes during the Holocene. An age-depth model for the sediment core was established with three samples dated by the radiocarbon method, indicating that the sediment was deposited from 11,180 to 1,257 calibrated years before present (cal. BP).

Planktonic foraminifera results show a gradual but important change in the assemblages throughout the core, where the abundance of species preferring warmer waters increase by 44% towards the top of the core. These results are interpreted as warming of the surface water masses during the Holocene, as a result of reduced influence of the Guinea Dome due to its change of location to a more southern position and/or as a consequence of a weakening of the dome. X-ray fluorescence scan variations along the core show that the faunal shift is encompassed by differences in the terrigenous sediment supply, indicating changes in the inland climate regime. For instance, changes in the Ti/Fe, Ti/Al and Al/Ca ratios are proxies for the fluvial/aeolian sedimentary input and the hinterland climate variability. An increase of the high river discharge indicators is displayed between 10 and 6 kyr BP, probably as a consequence of the increased precipitation that took place during the African Humid Period.

Further ongoing geochemical analyses of foraminifera shells will provide information regarding the temperature, salinity and productivity of both, the mixed layer and the sub-thermocline, which will improve the characterization of the variability that the Guinea Dome experienced during the Holocene.

How to cite: Pérez-Rodríguez, I., Hansteen, T. H., Schindlbeck-Belo, J. C., Nürnberg, D., Kutterolf, S., Huvenne, V. A. I., Barnhill, K. A., Simon-Lledó, E., Evans, S., Vinha, B., Mosquera Giménez, Á., and Orejas, C.: Holocene oceanographic variability linked to the Guinea Dome development recorded in a deep-sea sediment core off Cabo Verde, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5829, https://doi.org/10.5194/egusphere-egu23-5829, 2023.

Climate over Kenya is rather heterogeneous and exceptionally dry for a region located in the tropics. This is related to various large-scale drivers, such as Lake Victoria, the complex topography, and the vicinity to the ocean. In consequence water resources are scarce and several stakeholders depend on these. Hence, it is important to understand how precipitation amounts and patterns change under global warming. A special focus is on Mount Kenya, one of the most important freshwater towers in Kenya. To investigate these changes, we employ the Weather Research and Forecasting (WRF) model V3.8.1 to downscale a 30-year period for the present and the future climate, based on global climate simulations. The present period covers the years 1981–2010, and the future is run once for the mitigation scenario RCP2.6 and for the high-emission scenario RCP8.5 for the years 2071–2100.

Changes in precipitation and temperature are well noticeable in the region of Mount Kenya. The projection indicates an increase in precipitation for the two rainy seasons (March to May, and October to November), while precipitation is reduced in the dry season. Extreme precipitation around Mount Kenya shows increases in the future during the rainy season, whereby the two different scenarios show a similar increase in extreme precipitation. This result is a bit surprising and needs further investigation. As expected, temperatures are projected to increase over all of Kenya, and particularly along the slopes of Mount Kenya in all months. For temperature there is a clear difference in the warming between the two scenarios, as RCP8.5 shows a much stronger change in temperature than RCP2.6. The summit of Mount Kenya reaches temperatures in the future that today are found at an elevation of around 3,200 m above sea level (a.s.l.). This warming can substantially affect the endemic vegetation along the slopes of Mount Kenya. Assuming that the tree line is limited by temperature and not precipitation, as the latter is abundant, it could move from around 3,000 m a.s.l. up to 3,700 m a.s.l. The strong increase in temperature further affects the remaining glacier, which is currently an important water storage during dry months. The projected increase in precipitation over entire Kenya will therefore increase water availability and reduce fire danger. Nevertheless, the combined increase in temperature and precipitation could affect human and animal wellbeing, as heat stress may be increased.

All these results are based on a single regional and global climate model. Preliminary results indicate that the rainy season is clearly underestimated in the present simulation, compared to simulations obtained by a downscaling of the reanalysis ERA5. This indicates that important components of the atmosphere are not correctly captured by the model. These could include land-atmosphere interactions, misrepresentation of land cover, biases in sea surface temperatures and related changes in the atmospheric circulations. Thus, the atmospheric circulation and interactions with the land surface have to be assessed in further studies.

How to cite: Messmer, M., González Rojí, S. J., Raible, C. C., and Stocker, T. F.: Influence of climate and atmospheric circulation changes on water balance of Mount Kenya and surroundings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6585, https://doi.org/10.5194/egusphere-egu23-6585, 2023.