Africa is the world’s second largest continent, encompassing diverse ecosystems in numerous climate classifications, ranging from tropical forests to subarctic drylands on its highest mountain peaks. All these different environments underwent tremendous climatic fluctuations in the geological past, causing severe environmental changes. Further, Africa is one of the most vulnerable continents to future climate change, with widespread and till now uncertain impacts on African environments and society, as predicted by the recent IPCC report.
This session aims to convene studies about climate and environmental variabilities in Africa on various time scales, in past and future. The session will be open for studies from marine and continental records, using any kind of archive and proxy data, such as sedimentological records, tree rings, speleothems, ice cores, fossil pollen as well as modern monitoring data and modeling studies.
vPICO presentations: Fri, 30 Apr
The hypothesis of a connection between the onset (or intensification) of Northern Hemisphere Glaciation (NHG), the stepwise increase in African aridity (and climate variability) and an important mammalian (including hominin) species turnover is a textbook example of the initiation of a scientific idea and its propagation in science. It is, however, also an example of the persistent popularity of a hypothesis despite mounting evidence against it. The first part of our work analyzes of the history of the scientific idea by seeking its roots, including coincidental meetings and exchanges between of scientists, at project meetings, conferences and workshops. The consequences of this idea are examined and its influence on subsequent scientific investigations both before and after it has been falsified. In the second part of our investigation, we examine why the idea that the high latitudes have a major control on the climate of the low latitudes and thus early human evolution persists. For this purpose, an attempt is made to understand the original interpretation of the data, with special consideration of the composition of the scientific team and their scientific backgrounds and persuasions. Some of the key records in support of the hypothesis of a step-wise transition will be statistically re-analyzed by fitting change-point models to the time series to determine the midpoint and duration of the transition – in case such a transition is found in the data. A critical review of key publications in support of such a connection and a statistical re-analysis of key data sets leads to three conclusions: (1) Northern Hemisphere Glaciation is a gradual process between ~3.5–2.5 Ma, not an abrupt onset, either at ~2.5 Ma, nor at ~2.8 Ma, or any other time in the Late Cenozoic Era, (2) the trend towards greater aridity in Africa during this period was also gradual, not stepwise in the sense of a consistent transition of a duration of ≤0.2 Ma, and (3) accordingly, a step-wise change in environmental conditions cannot be used to explain an important mammalian (including hominin) species turnover.
How to cite: Trauth, M. H., Asrat, A., Berner, N., Bibi, F., Foerster, V., Grove, M., Kaboth-Bahr, S., Maslin, M. A., Mudelsee, M., and Schaebitz, F.: Northern Hemisphere Glaciation, African Climate and Evolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-805, https://doi.org/10.5194/egusphere-egu21-805, 2021.
Within eastern Africa, Ethiopia stands out for its steep topography, resulting in an altitudinal zonation of climate and vegetation. To understand future vegetation changes, we need information on past vegetation covers and vegetation responses to environmental and climatic changes. Pollen studies are available for low and high elevations in Ethiopia, but they are low in number and limited in spatial coverage. In addition, explicit research to altitudinal patterns of environmental changes are missing. However, archaeological evidence from SW Ethiopia suggests vertical migration of humans in response to humidity fluctuations, highlighting the need for research to spatial dynamics of human activities and vegetation in Ethiopia. On the other hand, sedimentological evidence suggests a millennia long agricultural history in Ethiopia’s highlands and several authors identify this region as a center of plant domestication.
It is clear that a thorough understanding of the past vegetation cover and its alteration by humans and climate is missing for Ethiopia. These research gaps impede identification of the timing and location of the onset of agriculture in the ancient Ethiopian landscape, resulting in poor understanding of e.g. contemporary degraded landforms. In our study, we aim to reconstruct and quantify the vegetation history along an altitudinal gradient in the Southern Ethiopian Rift Valley and to identify the role of man and climate on this evolution. Therefore, several lakes and swamps are selected as study sites along an altitudinal gradient (1100-3000 m a.s.l.) in the Gamo Highlands near the city of Arba Minch, along the Southern Ethiopian Rift Valley. Here, we will present the results of pollen, charcoal and NPP analyses from two wetland sites situated at 2300 and 3000 m a.s.l. The records show an increase of Afromontane forest taxa around 13 ka BP, at the expense of Montane ericaceous taxa. At 8 ka BP, a shift in the composition of the Afromontane forest is observed, together with a change in the fungal assemblage and decrease of grasses. Around 6 ka BP, Wooded grassland taxa increase simultaneously with Delitschia fungal spores. Montane forest taxa increase again at 2.5 ka BP, together with a shift in fungal spores, followed by an increase in charcoal accumulation during the last millennium. Most of the observed transitions can be linked to other vegetation records from Ethiopia, and reflect responses to climatic changes such as the African Humid Period. However, the exact timing and nature of the vegetation changes differs substantially between records, and asks for a denser sampling of palaeoecological records across Ethiopia. In this study, we will link the reconstructed vegetation changes with anthropogenic and natural driving forces, and come up with a reconstruction of the long-term landscape development in the study area in SW Ethiopia.
How to cite: Augustijns, F., Broothaerts, N., and Verstraeten, G.: Reconstructing vegetation changes in the Ethiopian Highlands: 18000 years of Afromontane vegetation dynamics recorded in high altitude wetlands., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1340, https://doi.org/10.5194/egusphere-egu21-1340, 2021.
The formation of the East African Rift System led to the emergence of large topographical contrasts in southern Ethiopia. This extreme topography is in turn responsible for an extreme gradient in the distribution of precipitation between the dry lowlands (~500 mm a-1) in the surrounding of Lake Turkana and the moist western Ethiopian Highlands (~2,000 mm a-1). As a consequence, the prevailing vegetation is fractionated into a complex mosaic that includes desert scrubland along the Lake Turkana shore, woodlands and wooded grasslands in the Omo-River lowlands and the paleo-lake Chew Bahir catchment, afro-montane forests of the Ethiopian Highlands, and afro-alpine heath in most elevated parts. During the past 25 ka, southern Ethiopia has been exposed to significant climate changes, from a dry and cold Last Glacial Maximum (LGM, 25-18 ka BP) to the African Humid Period (AHP, 15-5 ka BP), and back to present-day dry conditions. These shifts in temperature and precipitation may have affected the vegetation pattern and landscape in the area, but environmental data especially from LGM times are rare. This is because in times of a dry climate the paleo-lake Chew Bahir was dried up and hence the climate record in lake sediments was interrupted.
In this study, we investigate the hydrological conditions during the LGM using a previously-developed lake balance model (LBM) for southern Ethiopia, which is now coupled with a new predictive vegetation model (PVM) to better understand the biosphere-hydrosphere interactions and thus possible precipitation thresholds. The PVM is based on the method of boosted regression trees using elevation and monthly precipitation as input to predict land-cover, tree-cover and vegetation greenness for a ~1 km grid covering the Omo-River, paleo-lake Chew Bahir, Lake Chamo and Lake Abaya catchments. We linked the PVM and the resulting land surface parameters with the LBM to model the impact of a changing land-cover to the actual evaporation. Furthermore, we used the glycerol dialkyl glycerol tetraethers (GDGT) based paleo-temperature and tropical lapse rate reconstructions from Mount Kenya to consider the orographic temperature distribution in southern Ethiopia during the LGM. Using both, we simulated different precipitation amounts from 100% to 50% compared to the modern-day multi-annual averages and their effect on vegetation and lake levels of paleo-lake Chew Bahir. Our biosphere-hydrosphere modelling approach suggests 25 to 30% lower moisture availability during the LGM compared to the modern conditions and provides a high-resolution spatial reconstruction of the potential prevailing vegetation in the southern Ethiopian region.
How to cite: Fischer, M. L., Bachofer, F., Trauth, M. H., and Junginger, A.: How dry was the LGM? A Biosphere-Hydrosphere modelling approach for the paleo-lake Chew Bahir and Omo-River catchment in southern Ethiopia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5923, https://doi.org/10.5194/egusphere-egu21-5923, 2021.
The advent of pastoralism in Eastern Africa is one of the most significant cultural transformations in the continent’s history. Traditionally, herding origins and its spreading routes have been studied in the lowlands and described as a complex and lengthy process that began before 4 ka BP and lasted until 1.3 ka BP. This cultural transition has long been argued to have been a process involving both environmental change and population movements. Given the current patchy archaeological data, most studies studies conclude that no single factor can be identified as a driver of the onset of herding in Eastern Africa, but almost all evidence is from lowland areas. The higher elevations of the Eastern African mountains are sensitive to climate and environmental change, so may be ideal for testing hypotheses of human-environmental relationships. However, the history of pastoralism in the African highlands, especially its connection with regional herding migrations and Holocene climate change, has thus far been poorly explored with few available records.
In this contribution, we provide evidence of early pastoral activities at high altitude in the Bale Mountains of southwest Ethiopia. We present a 4000-year multiproxy palaeoecological lacustrine sequence from Garba Guracha, a cirque lake at 3950 m asl, combining palaeoclimatic and palaeoenvironmental proxies. Our record indicates the distinctive presence of faecal fungal spores (Sporormiella, Cercospora, Podospora) and the expansion of pollen and sedaDNA from ruderal plants as early as 3.5 ka. To our knowledge, this is the highest altitude record of early animal husbandry traces on the continent. Coeval with the expansion of pastoralism indicators in Garba Guracha, we find important changes in the lake’s diatom community, as well as climate fluctuations reconstructed from biomarkers; these may be critical for understanding human occupation at high altitudes. However, archaeological studies conducted in the Garba Guracha basin have proved unfruitful in finding permanent settlements of herders, suggesting hypotheses of seasonal resource use.
We discuss different scenarios of pastoral expansion on the Eastern African highlands under changing local climates, as well as the general context of pastoralist migration across Eastern Africa.
How to cite: Gil-Romera, G., Bittner, L., Grady, D. A., Epp, L. S., Ossendorf, G., Fekadu, M., Zech, M., Opgenoorth, L., Miehe, G., and Lamb, H. F.: The highest altitude paleoecological record of early pastoralism in Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12530, https://doi.org/10.5194/egusphere-egu21-12530, 2021.
The Turkana Basin is world famous for its extensive outcrops that provide insights into the paleoclimate and paleolandscapes in which hominins evolved over the past ~4 Ma. The Nachukui Formation, part of the Omo Group, reflects basin-wide dynamic processes of interlaced sequences including floodplains, deltas, and river systems throughout the Plio-Pleistocene. Paleosols associated with floodplains of the fluvial systems provide a valuable window into better understanding key intervals within this record and are frequently associated with fossiliferous fluvial sequences. This study analyzed three paleosols taken from outcrops of the Kaitio and Natoo Members of the Nachukui Formation. In particular, the Kaitio Mmb was assumed to be simply a lacustrine environment deposited during the longest-lived part of Paleolake Lorenyang (~1.7-2 Ma). However, recent studies have worked to provide a more comprehensive understanding of this member, indicating it was a far more dynamic lacustrine margin than previously recognized. This research builds upon this stratigraphic framework to integrate paleosol-based geochemical proxies to better reconstruct the paleoclimate and paleoenvironment of West Turkana Kaitio (WTK). This includes 1) x-ray fluorescence (XRF) elemental analysis of bulk sediment, and 2) stable isotope analysis on both bulk sediment and pedogenic carbonates. These data allowed us to make estimates of mean annual precipitation (MAP), vegetation type, and paleotemperatures. Using the CalMag and CIA-K weathering indices, the MAP estimates range from 351-933 mm of rain/year, with the means for both proxies ranging from 351-917 mm with an average MAP of 761.75 mm. The CIA-K weathering index produced MAP values of 503-933 mm with an average 812.88 mm. Compared to modern average rainfall values in the basin (324.1-151.6 mm/yr), our MAP estimates indicate the basin experienced more precipitation in the Plio-Pleistocene than it does today. Pairing the geochemical data with our sedimentological assessment allowed us to better characterize these paleosols for a more in depth understanding of the depositional environment of the Kaitio Member.
How to cite: Manning, M., Beck, C., and Beverly, E.: Analysis of paleosol-based proxies from the Turkana Basin through paleo-landscape and paleoclimate reconstruction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3453, https://doi.org/10.5194/egusphere-egu21-3453, 2021.
The Turkana Basin in northern Kenya contains a robust record of hominin fossils, including Nariokotome Boy (discovered from the NK3 site), the most complete H. erectus specimen found to date. Understanding the paleoenvironmental context in which hominins such as H. erectus evolved has been an objective of decades of research in eastern Africa. Here, we present a study using grain size analyses to infer the paleoenvironmental conditions responsible for the deposition of the sedimentary sequences directly associated with NK3. We resampled a ~14 m interval at from the West Turkana Kaitio (WTK13) core, collected as part of the Hominin Sites and Paleolakes Drilling Project. This interval ties directly to the outcrop where Nariokotome Boy was recovered. By sampling continuously at 0.5 cm intervals (~7 yrs/sample), we document the paleoenvironment in ultra high-resolution (i.e. a scale relevant to a hominin life) that directly correlates to the NK3 site. Over 350 sediment samples were pre-treated to remove carbonate, biogenic silica, and other organic material from detrital material. Grain size distributions were measured on a Malvern Mastersizer 3000 using wet suspension. Based on these analyses, the interval was dominated by silt, which was further investigated using end-member modeling. A four end-member solution explained on average 99% of the population variability. The bottom of the interval was more coarse-grained, with an abrupt fining transition at 38.83 meter below surface (mbsf), which corresponds with the transition out of a tuffaceous interval (Natoo tuff) and into a pedogenically modified interval. This correlation is significant as the top of this tuff is the surface upon which Nariokotome Boy was recovered. Previous facies and grain size analyses revealed and quantified Turkana’s dynamic lake level history. However, our grain size analysis provides unprecedented resolution for the paleoenvironment during which Nariokotome Boy lived. Our 0.5 cm sampling resolution enables us to quantify depositional changes on a scale comparable with previous descriptive facies analyses and to refine transitions between paleosols, fluvial deposits, and lacustrine deposition at the interface of these three paleoenvironments enabling us to reconstruct a dynamic lakeshore environment during the lifetime of the Nariokotome Boy.
How to cite: O'Reilly, C., Beck, C. C., van der Lubbe, J. H., Feibel, C. S., Wegter, B., and Cohen, A. S.: High-resolution records of grain-size and depositional environment correlated to the Homo erectus Nariokotome Boy site, West Turkana, Kenya, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16309, https://doi.org/10.5194/egusphere-egu21-16309, 2021.
Lake Victoria (LV), Africa’s largest lake is situated in the African Great Rift Valley. Due to its shallowness (max.68 m; mean 40 m) and limited river inflow, LV is very sensitive to variations in climate and lake level fluctuations. As a result, LV has undergone repeated low stand periods, or even complete desiccation during the Late Pleistocene with profound effects on the aquatic ecosystem. One example is the emergence of a unique biodiversity of endemic cichlid species following the lake’s last desiccation event during the last glacial and subsequent refilling commencing ~15,000 years ago.
In an interdisciplinary project we aim at reconstructing linkages between paleoenvironmental variability, disturbances and adaptive species radiation by combining approaches from paleogenomics, paleoecology and paleolimnology. For this purpose, four sediment cores along a depth-transect (near-shore to offshore), covering ca. the past 14,000 years, are analyzed.
We present first paleolimnological results of long-term changes of using (isotope-)geochemical indicators including: Sedimentary pigments and biogenic silica to infer aquatic productivity supported by micro X-ray Fluorescence (XRF) derived element geochemistry, 13C and 15N, and sedimentary phosphorus fraction analyses providing information on changes in sediment composition.
The results suggest that the infilling of the LV basin was a long-term step-wise process. This is shown by elevated and variable indicators for lithogenic input (e.g Ti, Zr and K) and interpreted as mobilization of substrate from the shorelines by a dynamic lake level prior to its stabilization in the Early and Mid-Holocene. This process is mainly reflected in the core taken at the greatest water depth (65 m). Simultaneously, the aquatic productivity (BSi and chloropigments) increased rapidly after the refilling of the lake basin in the Late-Glacial. A gradual drying of the climate and a following shift to a more oxygenated water column is observed in the Mid-to Late Holocene indicated by a decline in chemically weathered material (e.g Rb/K & K/Al ratios) and abundance of Mn.
How to cite: Wienhues, G., Temoltzin-Loranca, Y., Vogel, H., and Grosjean, M.: Multiproxy paleolimnological reconstruction of Lake Victoria’s environmental history, East Africa , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7946, https://doi.org/10.5194/egusphere-egu21-7946, 2021.
In order to disentangle natural climate variability from anthropogenically caused variations, environmental reconstructions of the past 2000 years have gained renewed scientific interest during the last ~20 years. Whereas climatic and environmental changes during this period, such as the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are fairly well expressed in western Europe and the North Atlantic area, knowledge about equivalent changes in African climate and environment (e.g. changes in temperature and precipitation, monsoonal activity and resulting vegetation feedbacks) can be much improved. Here we present new results from Lake Chala, a crater lake in equatorial East Africa, based on sedimentary grain-size distributions. Notwithstanding the relatively minor clastic mineral component, we are able to discriminate between different aeolian and fluviatile sources of terrigenous material and to reconstruct temporal trends in their contribution to the sediment. This can be linked to both local environmental dynamics and changes in the large-scale monsoonal systems over the East African landmass. Our findings point to arid conditions during the MCA and humid conditions during the LIA, in support of regional hydroclimate history as reconstructed from other moisture-balance proxies. The results of this study form an important piece of the puzzle to better understand past changes in African environments, which is a key aspect in the debate about future climate change in one of the most climate-sensitive regions on the planet.
How to cite: Meyer, I., Papadimitriou, I., Verschuren, D., and De Batist, M.: Lake Chala 2k: the last two millennia of environmental change in equatorial East Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5020, https://doi.org/10.5194/egusphere-egu21-5020, 2021.
To understand the driving processes for changes in African ecosystems and related problems such as soil degradation, it is crucial to gain insight in the relative importance of human disturbance and climate change. Madagascar is known for its particularly high erosion rates in the central highlands, yet the role of human disturbance versus natural processes are not well understood and is a topic of ongoing debate. Recent studies have challenged the traditional view that the currently observed intense erosion processes and sediment fluxes in Madagascar are mainly driven by recent large-scale deforestation. However, at present almost no quantitative data is available to couple vegetation dynamics and sediment fluxes over time in Madagascar. This study aims to provide more insight in landscape changes (vegetation changes, sediment mobilization and deposition) in central Madagascar, and in the specific role of man and climate. The study focuses on the 1800 km² catchment of Lake Alaotra, located ca 200 km northeast of Antananarivo. Lake Alaotra is formed in a graben system in the highlands of Madagascar, and is the largest freshwater lake of the country (400 km²). A pollen record from the lake was used to reconstruct regional vegetation changes. Radiocarbon dates of extracted pollen provide a detailed chronostratigraphic framework. Augerings and radiocarbon dates from floodplains and marshes in the catchment were used to reconstruct the sediment deposition history. The pollen record and charcoal data shows the vegetation changes over the last 3000 years. The main observed shift in vegetation is a transition from a woodland/grassland mosaic towards an open grassland, starting ca 1850 years ago, which coincides with the onset of human activities. Data on floodplain sedimentation show an increase in accumulation rates in the last 600 years, from ca 1 mm yr-1 to ca 30 mm yr-1, which can be linked to increased hillslope erosion rates during that time period. The sedimentation wave, however, does not reach Lake Alaotra nor the surrounding marshes as floodplains act as a buffer. Overall, this study provides a spatial and temporal integrated reconstruction of vegetation changes in the Lake Alaotra catchment and the link with sediment mobilization and deposition, thereby providing a better understanding of environmental changes in central Madagascar and its driving forces.
How to cite: Broothaerts, N., Razanamahandry, V. F., Brosens, L., Campforts, B., Jacobs, L., Razafimbelo, T., Rafolisy, T., Verstraeten, G., Bouillon, S., and Govers, G.: Vegetation changes and sediment transfers in the catchment of Lake Alaotra, Madagascar, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2123, https://doi.org/10.5194/egusphere-egu21-2123, 2021.
Palaeoproxy records during the Last Glacial Maximum (LGM) in Southern Africa have not offered consistent results regarding hydroclimate of the region. Similarly, models from the Palaeoclimate/Coupled Modelling Intercomparison Project (PMIP/CMIP) show varying results with regards to the movement of the Southern Hemisphere (SH) Westerlies. An equator-wards shift in the SH Westerlies has long been used to account for increased precipitation in Southern Africa during the LGM. Palynological studies have supported this narrative citing the presence of higher precipitation species during the LGM as evidence of increased precipitation. This project uses the fossil charcoal and pollen assemblages from Elands Bay Cave (EBC) and Boomplaas Cave (BPC) to quantify the change in Mean Annual Temperature (MAT) and Total Annual Precipitation (TAP) using the recalibrated age models at both sites to understand the change in hydroclimate of the region. These sites are both spatially and temporally ideal to track changes in the SH Westerlies with both sites recording floral assemblages from the Last Glacial Period, the LGM, and deglaciation at EBC in the Winter Rainfall Zone (WRZ) and BPC in the Year-round Rainfall Zone (YRZ). Both rainfall zones receive precipitation from mid-latitude frontal systems associated with the SH Westerlies. The YRZ is associated with both the mid-latitude frontal systems and tropical disturbances. A database of the modern-day distribution of the taxa identified in the stratigraphy at EBC and BPC was created using the Global Biodiversity Information Facility and paired with modern climate data from WorldClim to perform a Weighted Average – Partial Least Squares (WA-PLS) regression to predict MAT and TAP. Most of the WA-PLS regression models predict temperatures around 7°C at the LGM, consistent with regional records. The predicted TAP at the LGM is mostly lower than that of the Last Glacial Period. In the case of EBC in the WRZ, decreased precipitation is consistent with a decrease in intensity of the frontal system and/or a polewards shift in the SH Westerlies at the LGM. Similarly, decreased precipitation in BPC in the YRZ implies decrease in intensity of frontal systems and/or a polewards shift in the SH Westerlies. This poleward shift in the SH Westerlies has been demonstrated in some climate models, the parameters of which need further interrogation.
How to cite: Khumalo, W., Hare, V., and Pickering, R.: Effect of Southern Hemisphere Westerlies on hydroclimate and seasonality from the Last Glacial Maximum: Using the fossil charcoal and pollen records from Elands Bay Cave and Boomplaas Cave, South Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11197, https://doi.org/10.5194/egusphere-egu21-11197, 2021.
During the Holocene (0-11.7 ka BP), the subtropical regions of Africa were characterized by very significant climatic changes. These changes were evidenced by variations in lake levels which reflect the balance between precipitation and evaporation (P-E) at the watershed scale. These climatic conditions are mainly associated with the dynamics of the African summer monsoon in relation with the location of the Intertropical Convergence Zone (ITCZ), which is modulated by summer insolation induced by the Earth's orbital parameters. This mechanism explains the wetter conditions observed from 11 ka BP to 5.5 ka BP in the Sahelo-Saharan zone. This period, called "Green Sahara" or "African Humid Period", was characterized by a green landscape, covered by grasslands and trees, dotted with numerous lakes, and incised by large river networks.
Despite the numerous studies carried out on the African Humid Period, there is a scarcity of data for quantifying source and origin of precipitation. The Lake Chad Basin (BLT) is a key region for paleoclimatic research because of its position reflecting main tropical atmospheric mechanisms and its endorheic morphology amplifying climatic signals. More particularly, the crater palaeolakes of Trou au Natron (Pic Toussidé) and Era Kohor (Emi Koussi) in the Tibesti mountains offer unique sedimentary archives that may record the climatic history of the Sahara.
This work aims to reconstruct the evolution of these crater palaeolakes, thanks to the oxygen isotopic composition of diatoms (18Odiatom), from the termination of the last deglaciation until the African Humid Period. The identification of the fossil diatom assemblages combined with the 18Odiatom values should give insights on the evolution of the limnological parameters, the relative depth, the chemistry, and the water isotopic composition of these palaeolakes.
The measurement of 18Odiatom is carried out using the IR-laser fluorination-isotope ratio mass spectrometry technique at the CEREGE stable isotope laboratory, after dehydration under a flow of nitrogen gas. The diatoms are purified at the CEREGE micropaleontology laboratory after decarbonation and organic matter oxidation. The taxonomic determination of diatoms is carried at CEREGE (France) and at the University of N’Djamena (Chad).
Preliminary results from the two Tibesti mountains records cover the Holocene wet period. They show significant variations in the d18Odiatom values and a distinct evolution of ecosystems as demonstrated by taxonomic assemblage of fossil diatoms. These results are compared with a reconstruction of the d18Odiatom from Lake Chad for the same period. This comparison evidenced substantial data for the reconstruction of the Holocene wet period, in terms of origin of water inflows in the basin, eg Tropical versus Mediterranean and lowland versus mountainous atmospheric processes, and on the reconstruction of the migration and the position of the ITCZ. These two questions are still speculative and will certainly provide data for global climate circulation models which are struggling to reproduce the climate in Saharan latitudes.
How to cite: Abdallah Nassour, Y., Florence, S., Abderamane, M., Jean-Charles, M., Christine, P., Martine, C., Corrine, S., Anne, A., Philipp, H., Michele, D., and Stefan, K.: The Holocene African Humid Period from Tibesti mountains (Chad): Contribution of the fossil assemblage and the oxygen isotopic composition from lacustrine diatoms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12322, https://doi.org/10.5194/egusphere-egu21-12322, 2021.
On glacial to interglacial time scales, northern Africa fluctuated between arid to hyperarid states and much wetter conditions called African Humid Periods (AHP). These AHP are characterized by a major transformation of the Saharan hydrological cycle, favoring the development of vast fluvial networks, tropical flora and fauna in a region previously hyperarid. In the present-day context of global warming, it is crucial to understand the environmental mechanisms and responses associated with these dramatic swings between two extreme climatic states in order to improve the climatic projections. Numerous studies have been focused on the last AHP, which occurred at the beginning of the Holocene and corresponds to a period when insolation - governed by precession – and obliquity both reached their maximum almost synchronously, thus complicating the distinction of their respective roles. The study of older AHP corresponding to different orbital configurations is likely to provide some answers. However, finding climatic archives allowing the reconstruction of past changes in the Saharan hydrological cycle on longer timescales remains challenging (e.g., discontinuity of continental archives, preservation of tracers…). In this study, we propose to circumvent this difficulty by studying the Saharan dust deposited in marine sediments of the northeastern Atlantic tropical ocean. In fact, past modifications of Saharan dust deposited off West Africa can provide precious information on changes in environmental conditions in their source areas (aridity, weathering), as well as on changes in the characteristics of their atmospheric transport (pathways and strength). Here, we present a unique high-resolution (1 sample/200yrs) multi-proxy characterization of the dust deposited continuously through the last 240ka - a period punctuated by eight AHP - in the marine core MD03-2705 (18°05N; 21°09W; 3085 mbsl) retrieved from a bathymetric dome, 300 meters above the surrounding seafloor. Considering this particular environmental setting, the terrigenous fraction in this record is assumed to be predominantly of eolian origin. We combine the 230Th-normalized dust flux1 together with grain-size distribution, clay mineralogy and geochemical compositions in order to explore changes in the Saharan hydroclimate and atmospheric circulation over North Africa on millennial to orbital timescales, with a particular focus on the mechanisms associated with the recurrence of the AHP.
1Skonieczny et al., 2019 – Science Advances 5 (1) - eaav1887
How to cite: Leblanc, M., Skonieczny, C., Bory, A., Bout-Roumazeilles, V., Miska, S., Abraham, R., Delattre, M., Nouet, J., and Malaizé, B.: Hydroclimate and atmospheric circulation over North Africa through the last two climatic cycles reconstructed from dust deposited off West Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8608, https://doi.org/10.5194/egusphere-egu21-8608, 2021.
The Western Mediterranean region including the North African desert margin is considered one of the most sensitive areas to future climate changes. In order to refine long-term scenarios for hydrological and environmental responses to future climate changes in this region, it is important to improve our knowledge about past environmental responses to climatic variability at centennial to millennial timescales. During the last two decades, the recovery and compilation of Holocene records from the subtropical North Atlantic and the Mediterranean Sea have improved our knowledge about millennial-scale variability of the Western Mediterranean palaeoclimate. The variabilities appear to affect regional precipitation patterns and environmental systems in the Western Mediterranean, but the timescales, magnitudes and forcing mechanisms remain poorly known. To compare the changes in Holocene climate variability and geomorphological processes across temporal scales, we analysed a 19.63-m long sediment record from Lake Sidi Ali (33°03’ N, 5°00’ W, 2080 m a.s.l.) in the sub-humid Middle Atlas that spans the last 12,000 years (23 pollen-based radiocarbon dates accompanied with 210Pb results). We use calibrated XRF core scanning records with an annual to sub-decadal resolution to disentangle the complex interplay between climate changes and environmental dynamics during the Holocene. Data exploration techniques and time series analysis (Redfit, Wavelet) revealed long-term changes in lake behaviour. Three main proxy groups were identified (temperature proxies: 2ky, 1ky and 0.7ky cycles; sediment dynamic proxies: 3.5ky, 1.5ky cycles; hydrological proxies: 1.5ky, 1.2ky, 0.17ky cycles). For example, redox sensitive elements Fe and Mn show 1ky cycles and higher values in the Early Holocene and 1.5ky cycles and lower values in the Mid- to Late Holocene. All groups show specific periodicities throughout the Holocene, demonstrating their particular climatic and geomorphological dependencies. Furthermore, we discuss these periodicities relating to global and hemispheric drivers, such as the North Atlantic Oscillation (NAO), El-Niño Southern Oscillation (ENSO), Innertropical Convergence Zone variability (ITCZ) and North Atlantic cold relapses (Bond events).
How to cite: Schmidt, J., Kertscher, C., Reichert, M., Ballasus, H., Schneider, B., Dietze, E., Tjallingii, R., Benkkadour, A., Mikdad, A., Werther, L., Bolland, A., Pichat, S., von Suchodoletz, H., Fletcher, W., Mischke, S., and Zielhofer, C.: Centennial to millennial-scale variability of Holocene climate and environmental dynamics in the western Mediterranean (Lake Sidi Ali, Middle Atlas, Morocco), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8650, https://doi.org/10.5194/egusphere-egu21-8650, 2021.
The southwest of Morocco is considered to be an area of refuge within the Mediterranean region, hosting the endemic tropical Argan tree. This region is presently subject to severe droughts, desertification, and land degradation, and likely facing increased climate variability and socio-economic stress in the future. Here, we use the stable hydrogen and carbon isotope composition (δD and δ13C) of plant-waxes in a high-resolution marine sediment core (GeoB8601-3) collected off Cape Ghir in southwestern Morocco, in combination with published data on pollen and XRF element ratios from the same archive. We aim to reconstruct the hydroclimate and vegetation history during the last 3000 years. Stable carbon isotope compositions of leaf waxes (δ13Cwax) show that natural vegetation in southwestern Morocco consists of C3 plants. Minor variations in δ13Cwax were positively correlated to changes in stable hydrogen isotope compositions of leaf waxes (δDwax) before 700 CE. Changes in rainfall amounts and water use efficiency indicate a clear vegetation response to precipitation changes and thus to climate forcing. After 700 CE, δDwax and δ13Cwax became de-coupled suggesting that the plant wax discharge and their isotope signals were no longer solely controlled by climate; the waxes likely mainly originate from the lowlands and carry an enriched (dry) δD signal but a depleted 13C signature. The depletion of δ13Cwax correlates with the increase of Argan pollen concentration in the record. The period between ~700 and 900 CE coincides with the Arabization of Morocco which had an impact on the demographic composition of the country leading to new agricultural habits and, as a result, on the land-use triggering a higher erosion of lowland material by the Souss River.
How to cite: Baqloul, A., Schefuß, E., Kölling, M., Dupont, L., Groeneveld, J., Zhao, X., Reddad, H., Bouchaou, L., and Bouimetarhan, I.: Climate and land-use effects on hydrological and vegetation signals during the last three millennia in southwestern Morocco, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5417, https://doi.org/10.5194/egusphere-egu21-5417, 2021.
Abstract: Changes in the global oceanic system have already negatively affected the world’s marine life and the livelihoods of many coastal communities across the world, including in the Middle East' and Eastern Africa's Least Developed Countries (LDCs). Coastal communities in Somalia and Yemen for instance, have been particularly affected by extreme environmental events (EEEs), with an increase in the frequency of tropical cyclones over the past 20 years. Using expert elicitation as a method to generate data to assess and quantify a specific issue in the absence of sufficient and/or reliable data, the authors interviewed selected specialists in or from Somalia and Yemen, from diverse fields of expertise related to climate change, extreme environmental events, disaster risk reduction, and humanitarian affairs. Ten experts followed the elicitation protocol and answered a specific series of questions in order to better quantify the expectable mid-to-long-term climatic and humanitarian levels of risks, impacts, and consequences that climate change and related issues (e.g., sea-level rise, tropical cyclones, and sea surge) may generate in coastal areas along the Gulf of Aden's coastal cities of Aden and Bossaso, in Yemen and Somalia, respectively.
The findings indicate that there is cause for significant concern as climate change is assessed by all interviewees - irrespective of their background -, as very likely to hold a negative to a devastating impact on (fresh) water security, food security, public health, social conflicts, population displacement, and eventually political stability; and to strongly worsen the humanitarian situations in Somalia and Yemen, both in the medium-term (i.e., 2020-2050) and the long-term (i.e., 2020-2100). The authors call on the scientific community to further research the issue of climate change in the understudied coastal areas of the Gulf of Aden, and on the international community to pro-actively and urgently help the local populations and relevant authorities to rapidly and strongly build up their adaptation capacities, especially in the niche of coastal EEEs.
How to cite: Lambert, L., Almehdhar, M., and Haji, M.: Climate Change, Humanitarian Risks, and Social-Political (In)stability Along the Gulf of Aden: Expert Elicitation for the Case of Somalia and Yemen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7575, https://doi.org/10.5194/egusphere-egu21-7575, 2021.
The Sahel is Northern African region between the equator and the Sahara desert. It is home to a belt of semi-arid grassland that stretches from the Atlantic and across the continent westward towards the Red Sea. The monsoon type rainfall season that occurs in this region is influenced by the way that moisture transport along this belt region combines along the Inter Tropical Convergence Zone (ITCZ). The Sahel is one of the most productive crop areas of Africa, and if the rains fail – it has long lasting implications for its community. Due to its planetary location dry conditions pervade the Sahel for most of the year, with food production and livelihoods reliant on the summer monsoon rainy season between July and September. In this study we use (where available) up to 100 years of re-analysis records (GPCC rainfall, NCAR wind and HadiSST ocean data) together with an accurate signal decomposition approach (dominant frequency state analysis, DFSA). With this we assess how the teleconnection influence of the Pacific ENSO and the Atlantic dipole mechanisms influence the dry and wet Sahel rain conditions. The severe Sahelian drought of the 1980’s is shown to be a compounded sequence of drying dynamic effects that combined to occur suddenly over the span of 5-10 years. Our work indicates that dry and wet conditions appear to be related to land-air evaporation and condensation in the vicinity of the Sahel river catchments, with the land locked Lake Chad catchment having a particularly sensitive arid climate. Our latest finding’s help explain how the Atlantic and Pacific physical mechanism influence the Sahel monsoon and its extremes. With an assessment of agricultural data we also show how agricultural growth in the region is impacted by these factors. We present and discuss Africa dry and wet rainfall epoch forecasts over the next 30 years for Sahel based on stable and altered climate hysteresis scenarios.
How to cite: Bruun, J. T., Sheen, K., and Collins, M.: Mechanisms and effects of dry and wet Sahel epochs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3465, https://doi.org/10.5194/egusphere-egu21-3465, 2021.
Terrestrial signals in marine sediment archives are frequently used for paleoclimate reconstructions. A little is known about the origin of terrestrial components such as pollen and spores, organic and inorganic elements in the sedimentary archives. The aims of this study is to investigate the geographic distribution pattern of pollen and spores in southern Morocco in relation to environmental gradients, and different transport mechanisms in order to link temporal variations in marine sediment cores to environmental changes in southern Morocco. Pollen taxa of Argania spinosa, Cichorioideae, Poaceae and Cyperaceae exhibit high percentages and concentrations in the semi-arid Souss Massa basin and the relatively humid Tensift basin accompanied with higher values of Fe/Ca and Ti/Al. Moreover, the simulation between distribution of Olea/Phillyrea and Ti/Al ratio suggests that Olea/Phillyrea are mainly dispersed by wind transport. However, Artemisia and Quercus distributions are limited to the south of High Atlas and the northern Anti Atlas. Chenopodiaceae, Caryophyllaceae , and Amaranthaceae (CCA) show a maximum percentages in littoral sites especially of Souss and Draa basins according to the important production of pollen quantities, the high values of CCA from north to south of study area are indicated the starts of Saharan-type climate with increasing values of Acacia, Ziziphus, Asphodelus and Tamarix taxa may indicate plants adaptation to droughts, and/or a dominant aeolian transport. The South of Morocco which is known by higher wind inflows and low rainfall during the year occurring as occasional events during the winter, we conclude that pollen are primarily transported by the NE trade winds and occasionally with rivers in the basins.
How to cite: Tadoumant, S., Bouimetarhan, I., Koelling, M., Baqloul, A., and Bouchaou, L.: Modern pollen distributions and their relationship with environmental gradient in Southern Morocco, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10196, https://doi.org/10.5194/egusphere-egu21-10196, 2021.
Atmospheric rivers (ARs) are long, narrow, and transient corridors of enhanced water vapour content in the lower troposphere, often connected to the warm sector of extratropical cyclones and associated with strong low-level winds. These features play a major role in the global water cycle and drive weather extremes in many parts of the world. Here, we investigated the characteristics of landfilling ARs, including their frequency and magnitude over Morocco for the period 1979–2020. We used ECMWF ERA5 reanalysis data to detect and track landfilling ARs, and compared different gridded precipitation products (i.e. Integrated Multi-satellite Retrievals for GPM (IMERG), ERA5 Land, and CHIRPS) with a set of gauging stations datasets distributed across Morocco. We assessed AR association with rainfall at the annual and seasonal scales, as well as for extreme rainfall events, in different datasets. Preliminary results indicate that around 20 ARs/year make landfall or have their centroids within 200 km from Morocco. AR occurrence varies spatially and seasonally with highest occurrences in winter (DJF) across northern regions and spring (MAM) in the southern part of country. Rainfall events of up to 250 mm/year are driven by ARs; with the southernmost and driest regions receiving most of their rainfall from ARs. This paper will provide an overview of extreme rainfall and wind associated with ARs across Morocco.
How to cite: Khouakhi, A., Driouech, F., Slater, L., Waine, T., Chafki, O., and Raji, O.: Extreme weather associated with atmospheric rivers over Morocco, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13018, https://doi.org/10.5194/egusphere-egu21-13018, 2021.
Following the high temperatures recorded in the Sahel during 2010 and most recently in May 2013 in the northern part of Senegal where the temperature oscillated between 45 and 50 degrees, significant human deaths were recorded. A good understanding of the dynamics of these heat waves thus become necessary not only to improve the prediction of these events, but also to better assess the impact of future climate change on the occurrence and intensification of these heat waves. To address this issue, simulated CMIP5 daily bias-corrected temperature data interpolated on a 0.5° grid over 1950-2099 have been used by focusing on 3 RCP (Representative Concentration Pathways) scenarios, RCP8.5, RCP4.5 and RCP2.6 . The heat waves in Senegal are defined by relying on exceeding of a moving percentile relative to maximum, minimum and mean temperature during 3 consecutive days over the MAM (March-April-May), the hottest season of the year. Senegal is characterized by a steep zonal temperature gradient from the coast to hinterland. In RCP8.5, the general temperature increase present for the last 60 years (+1.5°C) will continue and reach ~ +5°C in 2100. In this context, at the end of the century the mean temperatures of the western coastal zone will be similar to the present ones of the eastern continental zone, and the warmest spring seasons recorded over the last 15 years will be the norm around 2040. Then exceptional and yet unknown intense heat waves are planned and policy and decision makers will have to anticipate reliable adaptation strategies.
How to cite: Sambou, M. J. G., Pohl, B., Janicot, S., Famien, A. M., Roucou, P., Badiane, D., and Gaye, A. T.: Heat Waves Evolution in Senegal under Climate Change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12310, https://doi.org/10.5194/egusphere-egu21-12310, 2021.
Recent studies in Kinshasa show how much air pollution is present in this large megalopolis of 13 million inhabitants, with levels even exceeding the recommended values (WHO, 2018).
From May 2017 to November 2019, the University of Kinshasa (UniKin: -4.42°S, 15.31°E) has equipped itself with a low-cost instrument operating in single-axis mode. Studies based on measurements made with this instrument have demonstrated the presence of NO2 with highest vertical column densities (VCDs) in June, July and August (R. Yombo, 2020). With this low-cost instrument, information such as aerosol and NO2 profile, which have major impacts on the determination of VCDs could not be obtained, leading to considerable uncertainties in the results obtained.
This work therefore supports the first one as described above, by presenting first results of a new MAX-DOAS (multi-axis differential optical absorption spectroscopy) system built at the IASB, in Belgium, and installed in Kinshsasa at the same location in November 2019. We first present the new MAX-DOAS, which is based on compact Avantes spectrometer (280-550 nm, 0.7 nm FWHM), a small computer, and a scanner. We describe the analyses for aerosol extinction, HCHO and NO2 using FRM4-DOAS. For these two molecules, we compare with model simulations (GEOS-Chem) and satellite observations (OMI, TROPOMI).
How to cite: Yombo, R., Merlaud, A., Pinardi, G., Mahieu, E., Friedrich, M., Hendrick, F., Fayt, C., Van Roozendael, M., Bopili Mbotia Lepiba, R., Buenimio Lomami, D., and Mbungu Tsumbu, J.-P.: MAX-DOAS measurements of NO2 and HCHO in the city of Kinshasa from 2019-2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-261, https://doi.org/10.5194/egusphere-egu21-261, 2020.
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