Search

Middle and Late Holocene sediments have not been extensively sampled in Lake Tanganyika, and much remains unknown about the response of the Rift Valley's largest lake to major environmental shifts during the Holocene, including the termination of the African Humid Period (AHP). Here, we present an integrated study (sedimentology, mineralogy, and geochemistry) of a radiocarbon-dated sediment core from the Kavala Island Ridge (KIR) that reveals paleoenvironmental variability in Lake Tanganyika since the Middle Holocene with decadal to centennial resolution. Massive blue-gray sandy silts represent sediments deposited during the terminal AHP (~5880–4640 cal yr BP), with detrital particle size, carbon concentrations, light stable isotopes, and mineralogy suggesting an influx of river-borne soil organic matter and weathered clay minerals to the lake at that time. Enhanced by the AHP's warm and wet conditions, chemical weathering and erosion of Lake Tanganyika's watershed appears to have promoted considerable nutrient recharge to the lake system. Following a relatively gradual termination of the AHP over the period from ~4640 cal yr BP to ~3680 cal yr BP, laminated and organic carbon-rich sediments began accumulating on the KIR. δ15Nbulk, C/N, and hydrogen index data suggest high relative primary production from a mix of algae and cyanobacteria, most likely in response to nutrient availability in the water column under a cooler and seasonally dry climate from ~3680 to 1100 cal yr BP. Sediments deposited during the Common Era show considerable variability in magnetic susceptibility, total organic carbon content, carbon isotopes, and C/N, consistent with dynamic hydroclimate conditions that affected the depositional patterns, including substantial changes around the Medieval Climate Anomaly and Little Ice Age. Data from this study highlight the importance of sedimentary records to constrain boundary conditions in hydroclimate and nutrient flux that can inform long-term ecosystem response in Lake Tanganyika. [ABSTRACT FROM AUTHOR]

The city of Fez in northern Morocco is situated on northeastern parts of the Saïs Plain, an alluvial basin. It is spreading southwesterly onto Pleistocene sediments consisting primarily of alluvial, channel-fill conglomerates and overbank deposits, as well as Holocene tufas. As urban development expands, human activities are increasingly eradicating these deposits, about which little is known. This study focuses on the clay-mineral composition of these Pleistocene overbank deposits, informally known as the “Red” and “Yellow” units, as well as of the Holocene tufas. In contrast to previous research that has emphasized the industrial uses of nearby Miocene marls. The objective of this study is to examine these Pleistocene and Holocene rocks to determine the likely origins, either inherited or neoformed, of the included clay minerals by comparing their compositions with those of nearby substrata.The clay-mineral analysis indicates a prevalence of smectites with varying amounts of illite, kaolinite, sepiolite, and chlorite. The presence of smectite and sepiolite likely reflects neoformation in areas of alkaline sedimentation during Quaternary semi-arid Mediterranean climates, when alkaline terrestrial environments rich in calcrete were widespread. Conversely, illite and chlorite appear to be predominantly inherited minerals within the studied units, transported by wind and water. Illite is largely sourced from Jurassic carbonates, whereas chlorite derives primarily from Miocene marine marls. Radiocarbon dating of two tufa samples indicated an age range between 6.7 and 5.6 ka Cal. B.P., aligning with the African Humid Period. The presence of significant quantities of kaolinite in the surface soils suggests that these soils formed during this humid period and are likely equivalent to the Holocene tufa deposits.

pH is one of the major parameters governing peat functioning, and pH variations in modern peatlands affect carbon and methane production and consumption. Paleo-pH reconstructions have been limited thus far, but they could help to better understand peat functioning in variety of settings and also serve as an indirect proxy for climatic and environmental variations such as precipitation. Bacterial hopanes and branched Glycerol Dialkyl Glycerol Tetraethers (brGDGTs) were investigated in a 10-ka peat record from North-East Cameroon (NGaoundaba, Western Central Africa). Recently developed pH proxies using the hopane ββ/(αβ + ββ) ratio and the brGDGT cyclization ratio (CBT peat) were applied and compared with previously published bulk organic data from the same core. Different hypotheses are usually proposed to explain the high abundance of the "thermally mature" C 31 αβ hopane in peats: acid-catalyzed isomerization of ββ to αβ isomers with or without biological mediation or the direct input of C 31 αβ hopanes by bacteria. In the NGaoundaba peat deposit, the opposite variation in the ββ/(αβ + ββ) ratio of C 30 and C 31 hopanes and the carbon isotopic composition of C 31 ββ and αβ hopanes suggest that an eventual transformation of C 31 ββ to αβ isomers is not possible without biological mediation. A linear correlation between hopane- and brGDGT-reconstructed pH is observed, suggesting a similar response to environmental changes for these two independent proxies. A large increase in reconstructed pH values coincides with changes in vegetation and precipitation at the end of the African Humid Period (AHP). Lower pH values are observed during the AHP, coinciding with a period of increased precipitation and consistent with bulk organic data and slightly higher C 31 ββ hopane δ13C values compared to middle and late Holocene. Bulk organic data indicate an interruption of the AHP by a drier intermission that coincides with a decrease in reconstructed pH values, probably reflecting a decrease in evapotranspiration. Variations in pH values could be interpreted in terms of preservation of peat organic matter and might reflect past changes in methane cycling in the investigated peatland. The present study reinforces the idea that reconstruction of pH in peat deposits represents a promising proxy of environmental change, enabling a better understanding of changes in peat functioning over large timescales and various locations. [ABSTRACT FROM AUTHOR]

Fossil diatoms and litho-stratigraphic changes in the Guern El Louläilet depressions, NW of the Great Western Erg, Algeria, were analysed to infer paleoenvironmental changes in the northern Algerian Sahara during the Early and Middle Holocene. Analysis was based on calcareous diatomite collected from four outcrops within the depressions. The diatom flora consists of brackish and epiphytic taxa, such as Epithemia argus, with percentages of some freshwater and planktonic species, mainly Cyclotella distinguenda. Results provide evidence for two Holocene lacustrine episodes related to the African Humid Period. The first episode (Early to Middle Holocene) was characterized by abrupt development of shallow-water conditions, with extensive littoral zones and evaporative periods that coincided with high salt concentrations in warm, alkaline water (swampy conditions). A second episode (Middle to Late Holocene?), with brackish water and alkaline conditions, coincided with a decline in lake water level that is attributed to drier conditions. Our findings are consistent with those of other studies from the area and demonstrate similar environmental changes occurred after 9300 cal yr BP at sites within the region. The main drivers of the African Humid Period were the northward shift of the Intertropical Convergence Zone (ITCZ) and expansion of summer monsoonal rains. Our study sites were located in the northern Sahara, where variations in the position of the Intertropical Convergence Zone (ITCZ) did not affect rainfall. Early and Middle Holocene climate fluctuations detected in this study may have been caused by intensification of winter precipitation in the south-central Mediterranean and its penetration southward. [ABSTRACT FROM AUTHOR]

This study analyses diatom assemblages from a Nile Delta core (B-1) to probe Holocene hydroclimate changesand their influence on the ecological habitats of the delta coast, with a further focus on the effects of relative sea-level rise. We found that the freshwater diatom Aulacoseira granulata varied in tandem with hydroclimate pulses in the Nile watershed, driven by the shift of the Intertropical Convergence Zone (ITCZ), therefore serving as a proxy for palaeo-Nile flow. Based on the ecological affinities of diatom taxa, we defined 5 diatom assemblages (I-V). Assemblage I (>10.0-8.5 ka BP) shows high A. granulata abundance (60–80%), implying peak Nile flow during the African Humid Period (AHP), at least 3 times greater than that of the recent past. Assemblage II (8.5-7.5 ka BP) sees decreased A. granulata (20–40%) and emergence of freshwater diatoms with benthic-oligotrophic characteristics (e.g. Epithemia gibba), suggesting reduced Nile flow and a delta estuary where the habitat became shallower with lower nutrient content. Assemblage III (7.5-6.0 ka BP) shows A. granulata resurgence (50–80%), reflecting Nile hydroclimate variability post-AHP due to the migration of the Intertropical Convergence Zone (ITCZ). The high-resolution- diatom spectra of B-1 also revealed major habitat changes, from saline to fluvial-dominated environments, around 6.0 ka BP. Assemblage IV (6.0-3.2 ka BP) indicates a notable Nile flow decline and freshwater community proliferation, coinciding with coastal habitat expansion and delta progradation due to RSL stablisation and basin-wide aridification. Assemblage V (3.2-2.0 ka BP) is marked by drought-tolerant diatoms (Nitzchia amphibia, Hantzschia amphioxys and Cavinula cocconeiformis), indicating intensified aridification. • Holocene diatom communities of Nile Delta were established for reconstruction of ecological habitat. • Five stages of diatom assemblages were identified in relation to basin-wide palaeo-hydroclimate change. • Holocene sea-level was established for tracking diatom-based coastal dynamics. • Aulacoseira granulata was used as for palaeo-Nile flow proxy. [ABSTRACT FROM AUTHOR]

Knowledge of past environmental change and prehistoric settlement dynamics in the Sahel east of the Nile is limited due to the scarcity of suitable sedimentary archives and archaeological sites. Here we present tufa-based paleoenvironmental records from the area of NW Butana (central Sudan, ∼55 km southeast of the Nile River) which show that increased rainfall and spring activity occurred in several discrete intervals during the last ∼30,000 years. Lithostratigraphic data combined with phytolith, malacological, paleopedological, and stable carbon isotope records revealed humidity peaks during late MIS3 and the early and middle Holocene. Gaps in lithological records correlated with dry periods of the Last Glacial Maximum and Younger Dryas. Minor wet pulses coinciding with Late Glacial interstadials indicate an early intensification of the African monsoon, which implies that a sharp climatic boundary existed between the Sahel and the Sahara during this period. These new paleoenvironmental records, together with archaeological evidence from Butana, provide a unique opportunity for understanding human ecology in the eastern Sahel. The peoples who inhabited this dryland area 30+ km from the Nile Valley could not rely on its relatively predictable resources of riverine, floodplain and lake habitats. New models of subsistence and settlement, and strategies of adaptations to seasonal and interannual environmental variability are needed. • A robust chronology of monsoon rainfall intensifications in the eastern Sahel. • Wet periods correspond to the late MIS3, Late Glacial, and early-middle Holocene. • Dry periods correlate with the LGM and Younger Dryas. • Sharp climatic boundary existed between the Sahel and the Sahara during the LG. • Springs provided resources for people who inhabited hinterlands during the AHP. [ABSTRACT FROM AUTHOR]

Abstract Low-altitude lakes in eastern Africa have long been investigated and have provided valuable information about the Late Quaternary paleohydrological evolution, such as the African Humid Period. However, records often suffer from poor age control, resolution, and/or ambiguous proxy interpretation, and only little focus has been put on high-altitude regions despite their sensitivity to global, regional, and local climate change phenomena. Here we report on Last Glacial environmental fluctuations at about 4000 m asl on the Sanetti Plateau in the Bale Mountains (SE Ethiopia), based on biogeochemical and palynological analyses of laminated lacustrine sediments. After deglaciation at about 18 cal kyr BP, a steppe-like herb-rich grassland with maximum Chenopodiaceae/Amaranthaceae and Plantago existed. Between 16.6 and 15.7 cal kyr BP, conditions were dry with a desiccation layer at ~ 16.3 cal kyr BP, documenting a temporary phase of maximum aridity on the plateau. While that local event lasted for only a few decades, concentrations of various elements (e.g. Zr, HF, Nb, Nd, and Na) started to increase and reached a maximum at ~ 15.8–15.7 cal kyr BP. We interpret those elements to reflect allochthonous, aeolian dust input via dry northerly winds and increasingly arid conditions in the lowlands. We suggest an abrupt versus delayed response at high and low altitudes, respectively, in response to Northern Hemispheric cooling events (the Heinrich Event 1). The delayed response at low altitudes might be caused by slow negative vegetation and monsoon feedbacks that make the ecosystem somewhat resilient. At ~ 15.7 cal kyr BP, our record shows an abrupt onset of the African Humid Period, almost 1000 years before the onset of the Bølling–Allerød warming in the North-Atlantic region, and about 300 years earlier than in the Lake Tana region. Erica pollen increased significantly between 14.4 and 13.6 cal kyr BP in agreement with periodically wet and regionally warm conditions. Similarly, intense fire events, documented by increased black carbon, correlate with wet and warm environmental conditions that promote the growth of Erica shrubs. This allows to conclude that biomass and thus fuel availability is one important factor controlling fire events in the Bale Mountains.

A widely hypothesized but complex transition from widespread fluvial activity to predominantly aeolian processes is inferred on Mars based on remote sensing data observations of ancient landforms. However, the lack of analysis of in situ martian fluvial deposits hinders our understanding of the flow regime nature and sustainability of the martian fluvial activity and the hunt for ancient life. Studying analogs from arid zones on Earth is fundamental to quantitatively understanding geomorphic processes and climate drivers that might have dominated during early Mars. Here we investigate the formation and preservation of fluvial depositional systems in the eastern Sahara, where the largest arid region on Earth hosts important repositories of past climatic changes. The fluvial systems are composed of well‐preserved single‐thread sinuous to branching ridges and fan‐shaped deposits interpreted as deltas. The systems' configuration and sedimentary content suggest that ephemeral rivers carved these landforms by sequential intermittent episodes of erosion and deposition active for 10–100s years over ∼10,000 years during the late Quaternary. Subsequently, these landforms were sculpted by a marginal role of rainfall and aeolian processes with minimum erosion rates of 1.1 ± 0.2 mm/yr, supplying ∼96 ± 24 × 1010 m3 of disaggregated sediment to adjacent aeolian dunes. Our results imply that similar martian fluvial systems preserving single‐thread, short distance source‐to‐sink courses may have formed due to transient drainage networks active over short durations. Altogether, this study adds to the growing recognition of the complexity of interpreting climate history from orbital images of landforms. Plain Language Summary: Mars is currently a dry and cold desert, but rivers preserved in inverted topography suggest that water once flowed during its early history. However, how sustained and how frequently these rivers flowed remains uncertain. Here we study ancient fluvial systems (rivers and deltas) from the eastern Sahara that formed during the late Quaternary, in much wetter conditions than those prevailing today in this desert and which bear striking analogies to martian systems. We find that rivers and deltas, now preserved as ridges, record short distance source‐to‐sink high‐energy systems formed due to heavy rainfall events. Our observations and measurements of the meandering systems within the deltaic features suggest that such wet conditions might have spanned tens to a few hundred years over a total duration of ∼10,000 years. Since the wet conditions ceased, arid conditions prevailed, and the aeolian processes resumed, sculpting ridges out of ancient channels. Our results imply that martian fluvial systems may have been associated with similar local and heavy runoff conditions that lasted 10–100s years over thousands of years, possibly sufficient to support habitability. A shift toward arid environments led to the sculpting of fluvial ridges and the widespread formation of dunes across the modern martian landscape. Key Points: Ancient depositional rivers in southern Egypt record ephemeral fluvial systems formed due to intense rainfall over ∼10 kaThese fluvial systems suggest tens to hundreds of years of river activitySimilar martian systems imply that early Mars's surface was punctuated by local and transient drainage systems fed over short durations [ABSTRACT FROM AUTHOR]

Low-altitude lakes in eastern Africa have long been investigated and have provided valuable information about the Late Quaternary paleohydrological evolution, such as the African Humid Period. However, records often suffer from poor age control, resolution, and/or ambiguous proxy interpretation, and only little focus has been put on high-altitude regions despite their sensitivity to global, regional, and local climate change phenomena. Here we report on Last Glacial environmental fluctuations at about 4000 m asl on the Sanetti Plateau in the Bale Mountains (SE Ethiopia), based on biogeochemical and palynological analyses of laminated lacustrine sediments. After deglaciation at about 18 cal kyr BP, a steppe-like herb-rich grassland with maximum Chenopodiaceae/Amaranthaceae and Plantago existed. Between 16.6 and 15.7 cal kyr BP, conditions were dry with a desiccation layer at ~ 16.3 cal kyr BP, documenting a temporary phase of maximum aridity on the plateau. While that local event lasted for only a few decades, concentrations of various elements (e.g. Zr, HF, Nb, Nd, and Na) started to increase and reached a maximum at ~ 15.8–15.7 cal kyr BP. We interpret those elements to reflect allochthonous, aeolian dust input via dry northerly winds and increasingly arid conditions in the lowlands. We suggest an abrupt versus delayed response at high and low altitudes, respectively, in response to Northern Hemispheric cooling events (the Heinrich Event 1). The delayed response at low altitudes might be caused by slow negative vegetation and monsoon feedbacks that make the ecosystem somewhat resilient. At ~ 15.7 cal kyr BP, our record shows an abrupt onset of the African Humid Period, almost 1000 years before the onset of the Bølling–Allerød warming in the North-Atlantic region, and about 300 years earlier than in the Lake Tana region. Erica pollen increased significantly between 14.4 and 13.6 cal kyr BP in agreement with periodically wet and regionally warm conditions. Similarly, intense fire events, documented by increased black carbon, correlate with wet and warm environmental conditions that promote the growth of Erica shrubs. This allows to conclude that biomass and thus fuel availability is one important factor controlling fire events in the Bale Mountains. [ABSTRACT FROM AUTHOR]

Understanding long-term (centennial–millennial scale) ecosystem stability and dynamics are key to sustainable management and conservation of ecosystem processes under the currently changing climate. Fossil pollen records offer the possibility to investigate long-term changes in vegetation composition and diversity on regional and continental scales. Such studies have been conducted in temperate systems, but are underrepresented in the tropics, especially in Africa. This study attempts to synthesize pollen records from Nigeria (tropical western Africa) and nearby regions to quantitatively assess Holocene regional vegetation changes (turnover) and stability under different climatic regimes for the first time. We use the squared chord distance metric (SCD) to assess centennial-scale vegetation turnover in pollen records. Results suggest vegetation in most parts of Nigeria experienced low turnover under a wetter climatic regime (African Humid Period), especially between ~8000 and 5000 cal year BP. In contrast, vegetation turnover increased significantly under the drier climatic regime of the late-Holocene (between ~5000 cal year BP and present), reflecting the imp role of moisture changes in tropical west African vegetation dynamics during the Holocene. Our results are consistent with records of vegetation and climatic changes in other parts of Africa, suggesting the Holocene pattern of vegetation change in Nigeria is a reflection of continental-scale climatic changes. [ABSTRACT FROM AUTHOR]

The Kalokol Basin on the west side of Lake Turkana, northern Kenya, has yielded three sites dating to the African Humid Period (AHP), a wet phase with intermittent dry spells that characterised the African climate c. 15.0–5.5 kya. Drawing on the chronological and lithic datasets from the three sites, this paper examines human settlement successions and the associated lithic technology in the region during the AHP. The radiocarbon dates signify at least six episodes of human settlement, occurring approximately 13.6–13.3, 11.24–10.77, 10.24–10.20, 7.27–7.02, 6.26–6.00 and 3.61–3.47 kya. The notion of 'settlement' as applied here implies either long-term or short-term human activities at the sites. During these successive settlements, people employed similar survival strategies: they exploited local stone raw materials, consumed aquatic resources from the lake using specialised bone points and settled near riparian settings. Their lithic technology is best characterised by preferential knapping of locally available chert and chalcedony and the production of geometric microliths and a range of flakes from expedient and formal cores. The finds from the Kalokol Basin contribute to improving our understanding of human adaptive strategies in the wider Lake Turkana Basin during the AHP. [ABSTRACT FROM AUTHOR]

The greening of the Sahara, associated with the African Humid Period (AHP) between ca. 14,500 and 5,000 y ago, is arguably the largest climate-induced environmental change in the Holocene; it is usually explained by the strengthening and northward expansion of the African monsoon in response to orbital forcing. However, the strengthened monsoon in Early to Middle Holocene climate model simulations cannot sustain vegetation in the Sahara or account for the increased humidity in the Mediterranean region. Here, we present an 18,500-y pollen and leaf-wax δD record from Lake Tislit (32° N) in Morocco, which provides quantitative reconstruction of winter and summer precipitation in northern Africa. The record from Lake Tislit shows that the northern Sahara and the Mediterranean region were wetter in the AHP because of increased winter precipitation and were not influenced by the monsoon. The increased seasonal contrast of insolation led to an intensification and southward shift of the Mediterranean winter precipitation system in addition to the intensified summer monsoon. Therefore, a winter rainfall zone must have met and possibly overlapped the monsoonal zone in the Sahara. Using a mechanistic vegetation model in Early Holocene conditions, we show that this seasonal distribution of rainfall is more efficient than the increased monsoon alone in generating a green Sahara vegetation cover, in agreement with observed vegetation. This conceptual framework should be taken into consideration in Earth system paleoclimate simulations used to explore the mechanisms of African climatic and environmental sensitivity. [ABSTRACT FROM AUTHOR]

Aim: Palaeoecological data provide an essential long‐term perspective of ecological change and its drivers in oceanic islands. However, analysing the effects of multi‐scalar and potentially co‐occurring disturbances is particularly challenging in dry islands. Here, we aim to identify the ecological consequences of the integrated impacts of a regional drying trend, volcanic eruptions and human mass migrations in a spatially constrained environment—a small, dry oceanic island in Macaronesia. Location: Brava Island, Republic of Cabo Verde. Taxa: Terrestrial vegetation and fungi. Methods: We use palaeoecological analyses applied to a caldera soil profile that dates back to 9700 cal yr BP (calibrated years before the present). Analyses include pollen (vegetation history), non‐pollen palynomorphs (changes in fern and fungal communities), grain‐size distribution, loss‐on‐ignition and geochemistry (sedimentology and erosion regimes), microscopic tephra shards (volcanic ash deposition) and charcoal (fire regime). Results: A regional drying trend after c. 4000 cal yr BP caused increased erosion but had limited immediate impacts on highland grassland vegetation. The expansion of fern‐rich woody scrubland was contemporaneous with significant deposition of volcanic ash and erosion between 1800 and 650 cal yr BP. About 300 cal yr BP, exogenous plants expanded, grazing and fires increased, and there was a decrease of native vegetation cover. Main conclusions: Throughout the Holocene, highland vegetation in Brava was characterized by the presence of open landscapes dominated by herbaceous species (e.g. Poaceae, Forsskaolea), with some presence of woody native taxa (e.g. Ficus, Dodonaea). A regional drying trend was a driver of erosion since the Mid Holocene but did not have an immediate influence on highland vegetation. Tephra deposition is a possible driver of vegetation change. Inter‐island mass migration after volcanic events in Fogo Island c. 1680 CE potentially triggered land use change and intensification, causing a reduction of native vegetation in Brava. [ABSTRACT FROM AUTHOR]

Northern Africa’s past climate is characterized by a prolonged humid period known as the African Humid Period (AHP), giving origin to the “Green Sahara” and supporting human settlements into areas that are now desert. The spatial and temporal extent of climate change associated with the AHP is, however, subject to ongoing debate. Uncertainties arise from the complex nature of African climate, which is controlled by the strength and interactions of different monsoonal systems, resulting in meridional shifts in rainfall belts and zonal movements of the Congo Air Boundary. Here, we examine a ∼12,500-years record of hydroclimate variability from Lake Dendi located in the Ethiopian highlands based on a combination of plant-wax-specific hydrogen (δD) and carbon (δ13C) isotopes. In addition, pollen data from the same sediment core are used to investigate the response of the regional vegetation to changing climate. Our δD record indicates high precipitation during peak AHP (ca. 10 to 8 ka BP) followed by a gradual transition toward a drier late Holocene climate. Likewise, vegetation cover changed from predominant grassland toward an arid montane forest dominated by Juniperus and Podocarpus accompanied by a general reduction of understory grasses. This trend is corroborated by δ13C values pointing to an increased contribution of C3 plants during the mid-to late Holocene. Peak aridity occurred around 2 ka BP, followed by a return to a generally wetter climate possibly linked to enhanced Indian Ocean Monsoon strength. During the last millennium, increased anthropogenic activity, i.e., deforestation and agriculture is indicated by the pollen data, in agreement with intensified human impact recorded for the region. The magnitude of δD change (40‰) between peak wet conditions and late Holocene aridity is in line with other regional δD records of East Africa influenced by the CAB. The timing and pace of aridification parallels those of African and Indian monsoon records indicating a gradual response to local insolation change. Our new record combining plant-wax δD and δ13C values with pollen highlights the sensitive responses of the regional vegetation to precipitation changes in the Ethiopian highlands.

The Ethiopian rift is known for its diverse landscape, ranging from arid and semi-arid savannahs to high and humid mountainous regions. Lacustrine sediments and paleo-shorelines indicate water availability fluctuated dramatically from deep fresh water lakes, to shallow highly alkaline lakes, to completely desiccated lakes. To investigate the role lakes have played through time as readily available water sources to humans, an enhanced knowledge of the pace, character and magnitude of these changes is essential. Hydro-balance models are used to calculate paleo-precipitation rates and the potential pace of lake level changes. However, previous models did not consider changes in hydrological connectivity during humid periods in the rift system, which may have led to an overestimation of paleo-precipitation rates. Here we present a comprehensive hydro-balance modeling approach that simulates multiple rift lakes from the southern Ethiopian Rift (lakes Abaya, Chamo, and paleo-lake Chew Bahir) simultaneously, considering their temporal hydrological connectivity during high stands of the African Humid Period (AHP, ~15–5 ka). We further used the Surface Energy Balance Algorithm for Land (SEBAL) to calculate the evaporation of paleo-lake Chew Bahir's catchment. We also considered the possibility of an additional rainy season during the AHP as previously suggested by numerous studies. The results suggest that an increase in precipitation of 20–30% throughout the southern Ethiopian Rift is necessary to fill paleo-lake Chew Bahir to its overflow level. Furthermore, it was demonstrated that paleo-lake Chew Bahir was highly dependent on the water supply from the upper lakes Abaya and Chamo and dries out within ~40 years if the hydrological connection is cut off and the precipitation amount decreases to present day conditions. Several of such rapid lake level fluctuations, from a freshwater to a saline lake, might have occurred during the termination of the AHP, when humid conditions were less stable. Fast changes in fresh water availability requires high adaptability for humans living in the area and might have exerted severe environmental stress on humans in a sub-generational timescale.

The African Humid Period (∼11,000–5,000 years before present) was the most recent of several precessionally paced wet intervals during which an increase in the Northern Hemisphere summer incoming solar radiation intensifies the West African Monsoon leading to dramatic changes over northern Africa. However, insolation anomaly alone is not sufficient and feedbacks are essential for further amplification of the monsoon. The most significant feedbacks derive from the land surface, arising from changes to vegetation, soil properties, and distribution of surface water. We show that in contrast to previous studies that have explored the individual impacts of these feedbacks, a modern climate model yields a much greater increase in precipitation in response to their collective effect. Agreement with proxies is improved while the desert‐steppe transition is pushed further northward than in any previous study. In the West African Sahel, intensities of summer daily mean and extreme precipitation increase by 150% and 90%, respectively. Plain Language Summary: From approximately 11,000 to 5,000 years before present, the summer monsoon over northern Africa was considerably stronger than what it is today and as such this period has come to be called the African Humid Period. As a result of this, lakes, wetlands, and rivers sprung up in the now arid regions of northern Africa and made it possible for vegetation to migrate northward which "greened the Sahara." It is widely understood that the greater amount of summer solar radiation impinging on this region, arising from a modest variation in the Earth's orbital configuration at that time, kick‐started this intensification. However, while this may have triggered the strengthening of the monsoon, it was not by itself sufficient to intensify it to the degree suggested by proxies that register the strength of palaeomonsoons. The interaction between the atmosphere and the greener and wetter land surface could have further invigorated the monsoon, but based on the results from modeling experiments performed thus far, it has been thought that even this additional interaction is not sufficient. Here, we show that land‐atmosphere interaction does however have the potential to strengthen the monsoon sufficiently to obtain agreement with proxy estimates. Key Points: Thus far, few studies have explored the combined effect of feedbacks from mid‐Holocene vegetation, soil, and lakes on precipitationWe find much greater impact on precipitation from the combined feedbacks than previously reportedAgreement with proxies improves with feedbacks and modeled precipitation can sustain prescribed vegetation over all of northern Africa [ABSTRACT FROM AUTHOR]

A comprehensive understanding of the relationship between land cover, climate change and disturbance dynamics is needed to inform scenarios of vegetation change on the African continent. Although significant advances have been made, large uncertainties exist in projections of future biodiversity and ecosystem change for the world's largest tropical landmass. To better illustrate the effects of climate–disturbance–ecosystem interactions on continental‐scale vegetation change, we apply a novel statistical multivariate envelope approach to subfossil pollen data and climate model outputs (TraCE‐21ka). We target paleoenvironmental records across continental Africa, from the African Humid Period (AHP: ca 14 700–5500 yr BP) – an interval of spatially and temporally variable hydroclimatic conditions – until recent times, to improve our understanding of overarching vegetation trends and to compare changes between forest and grassy biomes (savanna and grassland). Our results suggest that although climate variability was the dominant driver of change, forest and grassy biomes responded asymmetrically: 1) the climatic envelope of grassy biomes expanded, or persisted in increasingly diverse climatic conditions, during the second half of the AHP whilst that of forest did not; 2) forest retreat occurred much more slowly during the mid to late Holocene compared to the early AHP forest expansion; and 3) as forest and grassy biomes diverged during the second half of the AHP, their ecological relationship (envelope overlap) fundamentally changed. Based on these asymmetries and associated changes in human land use, we propose and discuss three hypotheses about the influence of anthropogenic disturbance on continental‐scale vegetation change. [ABSTRACT FROM AUTHOR]

A Late Pleistocene lacustrine sedimentary succession has recently been discovered and investigated in Northwest Africa (Morocco, Anti-Atlas, Agadir-Tissint Feija). By integrating new radiometric 230Th/U and OSL ages and new clay mineral analyses with previous sedimentological evidence, we significantly refine the origin and the timing of this succession and its significance for African paleoenvironments and paleoclimate. The sedimentary succession reflects the evolution of a paleolake, referred to as paleolake Tissint, that indicates the abrupt establishment of a wet period at ∼60 ka and a gradual return to drier conditions at ∼50 ka. Establishment of this paleolake coincides with a peak of precession-forced high summer insolation centered around ∼60 ka suggesting that orbital parameters triggered humid conditions in northwest Africa during this time interval. Comparing this observation with others from the literature, it appears that continental-scale wet conditions prevailed across North, Central and East Africa at that time and add evidence in support of a 60–50 ka African Humid Period (AHP). Given that the Holocene African Humid Period was associated with "Green Sahara" conditions, wet conditions between 60 and 50 ka likely sustained coeval greening, at least partially, of the Sahara region. In northwest Africa, the 60–50 ka AHP is affected by Heinrich Event HE6 which via adjustment of the Atlantic Meridional Ocean Circulation (AMOC) seems to have delayed the onset of this AHP. In a similar way, the younger Heinrich Event 5a resulted in short-term regional aridification about 55 ka ago that briefly interrupted the generally wetter period. Finally, as the AHP between ∼60 ka and ∼ 50 ka coincides with a major Human dispersal out of Africa; these particular conditions may have offered a climatic window of opportunity for Homo sapiens to open migration routes across Africa towards the Levant. • U/Th and OSL ages date the occurrence of paleolake Tissint to between ∼60 and ∼ 50 ka. • African Humid Period related to a 60-ka-centered insolation peak derived from precession variation. • Heinrich event 6 (∼60 ka) delayed the onset of humidification in northwest Africa. • Heinrich event 5a (∼55 ka) triggered short-term aridification in northwest Africa within the 60–50 ka humid interval. • The 60–50 ka AHP may have facilitated the 60 ka human dispersal out of Africa. [ABSTRACT FROM AUTHOR]

The mid- to late Holocene aridification pattern of NW Africa remains a matter of controversial debate. While many marine climate reconstructions indicate a relatively abrupt aridification at ∼5.5 ka BP, terrestrial palaeoclimate records rather show a spatially and temporally heterogeneous transition towards the modern arid state. To bridge conflicting evidence, we analysed high-resolution (sub-seasonal) ontogenetic oxygen isotope (δ18O) records and bulk 87Sr/86Sr ratios of bivalve shells and fish otoliths of estuarine-associated species. Samples were excavated from archaeological deposits formed during the mid- to late Holocene in a large palaeo-estuary east of the Banc d’Arguin, Mauritania. The mid-Holocene (∼5.2 ka BP) δ18O records indicated unrealistically high water temperatures when assuming a modern value for δ18OSeawater, suggesting a substantial input of isotopically lighter water to the study area. Respective salinity estimates consistently indicated persistent monsoonal discharge. Moreover, 87Sr/86Sr ratios of bivalve shells deviated considerably from the rather stable global seawater composition, further supporting the presence of significant terrestrial runoff between 5.0 and 5.3 ka BP. Altogether, our results support doubts regarding an abrupt termination of the African Humid Period (AHP) in the coastal areas of NW Africa, and show that fully marine conditions were established along the Banc d’Arguin by ∼3.0 ka BP.

We present new high‐resolution oxygen isotope (δ18O) records from three NW African speleothems located at ~31°N. The present‐day rainfall patterns at 31°N in NW Africa are linked to negative winter North Atlantic Oscillation phases. However, on multimillennial time scales, our δ18O records, together with other hydroclimate records, provide new evidence of humid conditions during the mid‐Holocene, a period that was presumably characterized by arid climate. Thus, the apparent increase in moisture during the mid‐Holocene is interpreted better as an increase in summer rainfall. This is most likely linked to the expansion of the West African summer monsoon fringe during the African Humid Period, which terminated in our record abruptly around 4 Kyr BP. The temporospatial difference with speleothem records from N Morocco suggests that the High‐Atlas Mountains might have been a topographic barrier to further expansion of the West African summer monsoon fringe into higher latitudes. Plain Language Summary: The Holocene African Humid Period in North Africa, characterized by the expansion of vegetation into the Green Sahara, has been linked to the intensification of the West African summer monsoon (WASM). However, the temporospatial pattern of the African Humid Period, especially the northernmost expansion of the WASM, remain a matter of controversy, largely owing to the lack of precisely dated and high‐resolution paleoclimatic records. This study presents new high‐resolution paleoclimate data based on speleothem oxygen isotope records from a key site at ~31°N in NW Africa. Our data suggest that the WASM expanded to 31°N in NW Africa during the mid‐Holocene and terminated abruptly at 4 Kyr BP. Key Points: Holocene rainfall variability in NW Africa is inferred from precisely dated and high‐resolution speleothem δ18O recordsThe West African summer monsoon expanded to 31°N in NW Africa during the mid‐HoloceneThe African Humid Period ended with an abrupt interval of megadrought around 4 Kyr BP in NW Africa [ABSTRACT FROM AUTHOR]

The Sahara was significantly greener 11-5 kya and during multiple earlier interglacial periods. But the mechanisms related to the greening of the Sahara remain uncertain as most climate models severely underestimate past wet conditions over north Africa. The variations in the African monsoon related to the greening of the Sahara are thought to be associated with the variations in the inter-hemispheric differential heating of Earth, caused by orbital variations. However, how orbital variations affect regional climate is not well understood. Using recent theory that relates the position of the tropical rain belt to the atmospheric energy budget, we study the effect of orbital forcing during the mid-Holocene on the African monsoon in simulations provided by the third phase of the Paleo Model Intercomparison Project (PMIP3). We find that energy fluxes in the African sector are related to orbital forcing in a complex manner. Contrary to generally accepted theory, orbital modulation of seasonal differential heating alone is shown to be a weak driver of African monsoon variations. Instead, net atmospheric heating near the equator, which modulates the intensity and extent of seasonal migrations of the tropical rain belt, is an important but overlooked driver of African monsoon variations. A conceptual framework that relates African monsoon variations to both equatorial and inter-hemispheric differential solar heating is presented. • Both hemispherically symmetric and asymmetric insolation changes affect Monsoons. • Inter-hemispheric solar heating alone is a weak driver of the African monsoon. • Equatorial solar heating is potentially an important driver of the African monsoon. • The relation of orbital forcing to regional heating is complex and poorly understood. [ABSTRACT FROM AUTHOR]

The African Humid Period (AHP), spanning ∼15-5 ka, was characterize across East Africa by increased precipitation. Wetter climate conditions created environments favorable to human occupation in what are today harsh, resource-limited places to inhabit. The Turkana Basin is a striking example of this. Throughout the AHP, lake levels intermittently rose ∼100 m establishing hydrologic connectivity from Lake Turkana into the Nile drainage system via an outlet to the northwest. This study presents new, high-resolution data from West Turkana outcrops of the Late Pleistocene/Holocene Galana Boi Formation. This research complements existing lake-level curves and allows for landscape reconstruction through lateral facies associations. The Kabua Gorge area contains both well-exposed stratigraphic sections and multiple archaeological sites to the north and west of the outcrops. This creates the opportunity to tie the archaeology closely to paleoenvironmental reconstructions from the geological record. The depositional environment is characterized by a dynamic fluctuating lake margin, consisting of at least four phases of inundation. Highstand Phase 4 is distinct within the Kabua Gorge sequence because it is comprised of black clay containing 2–10% total organic carbon, pedogenic overprinting, pedogenic carbonate nodules, and a diverse molluscan fauna. Deposition of this unit is indicative of an organic-rich, reducing lacustrine environment that was subsequently overprinted by pedogenesis. This unit grades laterally basinward from organic-rich paleosols to lacustrine silts characterized by abundant freshwater diatom taxa. By coupling sedimentology, diatom assemblage data, δ13C and δ18O isotope geochemistry of pedogenic carbonates, and a radiocarbon chronology for the area, the paleoenvironment of Kabua Gorge is interpreted as a shallow marshy embayment connected to the main body of a freshwater Lake Turkana. The landscape is a highly dynamic one, varying on a scale of 100s of meters. Sediments were deposited during periods of inundation and then pedogenically modified during brief periods of subaerial exposure to form Vertisols. Archaeological sites in the early part of the AHP at Kabua Gorge are closely associated in age with lacustrine highstands. Hence, we propose that the lagoonal marsh environment of Phase 4 would likewise have been a resource-rich area for human occupation during the AHP. Potential resources drawing humans to the area include access to fresh water and fishing grounds. Ultimately, understanding the paleoenvironmental dynamics at Kabua Gorge provides a window into the broader ecosystems in which humans culturally evolved from the Late Pleistocene to present. •Increase moisture of African Humid Period promoted littoral wetlands at Lake Turkana. •Multiproxy paleoenvironment reconstruction of marsh associated with archaeology. •Marshes were a significant source of aquatic resources for humans in Turkana Basin. •δ13C of pedogenic carbonate interpreted as tracking significant C 4 wetland vegetation. [ABSTRACT FROM AUTHOR]

The shift toward wetter climatic conditions during the African Humid Period (AHP) transformed previously marginal habitats into environments conducive to human exploitation. The Turkana Basin provides critical evidence for a dynamic climate throughout the AHP (~15–5 kyr BP), as Lake Turkana rose ~100 m multiple times to overflow through an outlet to the Nile drainage system. New data from West Turkana outcrops of the late-Pleistocene to early-Holocene Galana Boi Formation complement and extend previously established lake-level curves. Three lacustrine highstand sequences, characterized by laminated silty clays with ostracods and molluscs, were identified and dated using AMS radiocarbon on molluscs and charcoal. This study records the earliest evidence from the Turkana Basin for the onset of AHP by at least 13.9 kyr BP. In addition, a depositional hiatus corresponds to the Younger Dryas (YD), reflecting the Turkana Basin's response to global climatic forcing. The record from Kabua Gorge holds additional significance as it characterized the time period leading up to Holocene climatic stability. This study contributes to the paleoclimatic context of the AHP and YD during which significant human adaptation and cultural change occurred. [ABSTRACT FROM AUTHOR]

Mineralogical compositions and grain-size distributions combined with 87Sr/86Sr and ε Nd values of the detrital fraction were studied on cores recovered from the Gulf of Aden (MD92-1002) and the Red Sea (MD92-1008) basins in order to document past changes in Indian monsoon and northwesterly winds during the last glacial-interglacial transition (the last 20 ka), encompassing the African Humid Period (AHP). The ε Nd vs. 87Sr/86Sr plot indicates that sediments result from the mixing of two main sedimentary sources corresponding to the Afar volcanic rocks in Ethiopia and to the Arabian-Nubian Shield. Variations of sediment isotopic and mineralogical composition point to a diminution of the volcanic source contribution during the last deglaciation. Changes of mineral-accumulation rates and grain-size distributions denote a decline in the aridity of the source regions during the Holocene, particularly of the Afar volcanic region. In this area, the reduction of detrital supply, from 15 cal ka BP, can be explained by an increase of precipitations during the AHP, which resulted in an expansion of the vegetation cover and lake extensions in East Africa. In the Arabian Peninsula, precipitations were confined to the south, allowing sediments to be transported even during the Holocene. Our data suggest that the southwest monsoon was not the main carrier of aeolian sediments to the Red Sea and Gulf of Aden basins, but the Northwesterlies. In the Red Sea, the isotopic and mineralogical tracers reveal a contribution from Saharan dust between 16 and 12 cal ka BP, transported from the Nile catchment after aridification during Heinrich event 1. [ABSTRACT FROM AUTHOR]

Elemental XRF analysis carried out on an 8 m long core from the Nile Delta reveals a gradual increase in the Ca/Ti ratio between 5000 and 4000 cal BP which is linked to the progressive development of hyper-aridity in this region. The increase results from elevated flux of aeolian material entering the Nile river system from calcareous source rock geologies in the dryer Egyptian Sahara. The most major increase in hyper-aridity occurs around 4000 cal BP. Such a perspective suggests a locally abrupt, regionally time-transgressive inception of hyper-aridity in this region at the end of the African Humid Period. After this time, reorganisation of wind circulation meant that less Saharan-derived aeolian material entered the Nile Valley, and the contribution of aeolian material in the Nile's sedimentary signal was also dwarfed by an increase in Blue Nile sedimentary flux. Chronological control is provided by two radiocarbon dates and the top and bottom of a well-constrained pottery horizon that dates from the period of occupation of two nearby archaeological sites: Kom al-Ahmer and Kom Wasit. [ABSTRACT FROM AUTHOR]

Climate model simulations of the mid‐Holocene (MH) consistently underestimate northern African rainfall for reasons not fully understood. While most models incorporate orbital forcing and vegetation feedbacks, they neglect dust reductions associated with greater vegetation cover. Here we simulate the MH climate response to reduced Saharan dust using CESM CAM5‐chem, which resolves direct and indirect dust aerosol effects. Direct aerosol effects increase Saharan and Sahel convective rainfall by ~16% and 8%. In contrast, indirect aerosol effects decrease stratiform rainfall, damping the dust‐induced total rainfall increase by ~13% in the Sahara and ~59% in the Sahel. Sensitivity experiments indicate the dust‐induced precipitation anomaly in the Sahara and Sahel (0.27 and 0.18 mm/day) is smaller than the anomaly from MH vegetation cover (1.19 and 1.08 mm/day). Although sensitive to dust radiative properties, sea surface temperatures, and indirect aerosol effect parameterization, our results suggest that dust reductions had competing effects on MH African rainfall. Plain Language Summary: Six thousand years ago, changes in Earth's orbit led to greater summer season solar radiation over northern Africa. The increase in energy resulted in higher rainfall amounts, widespread vegetation, and reduced dust aerosols over regions that today are desert. In this study we use a climate model, CESM CAM5‐chem, that accounts for the ways dust aerosols interact with sunlight and cloud droplets to examine how the reduction in Saharan dust during this past humid time affected rainfall. When dust aerosols are reduced in the model, more sunlight reaches the surface, the Sahara warms, and convective rainfall from the West African Monsoon increases. However, through dust‐cloud droplet interactions, the same reduction in dust decreases nonconvective rainfall, which is less prevalent during the monsoon season but still important, and thus dampens the total rainfall increase. Overall, dust reduction leads to a rainfall response that is dependent on rainfall type. Lastly, we compare the rainfall response of reducing dust to that of increasing vegetation cover and find that while important, the response from dust is considerably weaker. Key Points: Changes in direct dust aerosol effects from reduced mid‐Holocene Saharan dust loading increase convective rainfall in northern AfricaChanges in indirect dust aerosol effects weaken total precipitation increases by limiting stratiform rainfall, particularly in the SahelThe African rainfall response to total dust aerosol effects is lower than a previous study and substantially less than vegetation forcing [ABSTRACT FROM AUTHOR]

Abstract Multi-proxy analyses of an 8 m sediment core from Lake Hayk, a closed, freshwater lake in the north-central highlands of Ethiopia, provide a record of changing lake level and inferred regional climatic change for the last 15.6 cal ka years. Between ca. 15.6–15.2 cal ka BP, a lowstand was synchronous with Heinrich Event 1 and an intense drought across Eastern Africa. At ca. 15.2 cal ka BP a lake began to develop at the core site in response to wetter conditions, at the onset of the African Humid Period (AHP). However, in contrast to other lakes in eastern Africa, Hayk lake level fell around ca. 14.8 cal ka BP, indicating a climate shift towards aridity. The lake began filling again at ca. 12.3 cal ka BP and reached maximum water depth between ca. 12.0–10.0 cal ka BP. Lake level declined slowly during the Holocene, culminating in the termination of the AHP at Hayk between ca. 5.2–4.6 cal ka BP. In the late Holocene, ca. 2.2–1.3 cal ka BP, Lake Hayk was again deep and fresh with some evidence of short-term lake level variability. The palaeo-record from Lake Hayk indicates that while it experienced, to a broad degree, the same glacial-interglacial dynamics and sub-millennial shifts in climate found in other palaeolimnological records from eastern Africa, there are offsets in timing and rate of response. These differences reflect chronological discrepancies between records, as well as the varying climate sensitivities and site-specific factors of individual lake basins. This record highlights the different responses by lakes in a climatically vulnerable area of Ethiopia. Highlights • Discrepancies in the timing of the Younger Dryas Stadial proper. • No evidence for the catastrophic shift in climate centred at 8.2 ka. • Diatom evidence suggesting relatively rapid AHP termination. • High-resolution evidence of millennial to multi-decadal variability at Lake Hayk. • Regional discrepancies in the timing and expression of climatic events. [ABSTRACT FROM AUTHOR]

Abstract We present X-Ray Fluorescence (XRF) Scanner measurements from a 6 m long sediment core (GeoB12624-1) on the upper slope of Tanzania to reconstruct the climatic evolution in East Africa since the Last Glacial Maximum (LGM). Log-ratios of Fe/Ca and Ti/Ca are indicative for sediment discharge of the Rufiji River, which is controlled by climatic conditions in the Rufiji catchment area. The most significant changes in major elemental composition occurred at 15.1 and 7.4 ka highlighted by the regime shift index values. The data set records distinct precipitation peaks during the early Holocene. This corresponds a maximum in the Northern Hemisphere (NH) summer insolation and results in a transition from the arid LGM to the humid early Holocene. Our geochemical record also indicates that this climatic transition was interrupted by two severe droughts that occurred during NH cold intervals: the Heinrich stadial 1 (HS1) and the Younger Dryas (YD). Through a comparison with other nearby paleoclimatic records, we suggest that arid climatic conditions only occurred in East Africa north of 8–10°S, whereas in southern East Africa around 15–20°S increased humidity during the HS1 and YD prevailed. We thus conclude that these two drought events were caused by a southward migration of the Intertropical Convergence Zone (ITCZ) which was fostered by the NH cooling during the HS1 and YD. Hence, our new geochemical record clearly documents that the East African climate not only responded to low-latitude insolation forcing on sub-orbital time scales, but also, was strongly influenced by high-latitude cooling during the HS1 and YD periods. Highlights • High-resolution climatic record from the Tanzanian upper slop since the LGM. • Climatic transition in East Africa following the summer insolation since the LGM. • The YD and HS1 drought throughout East Africa responding to shift of the ITCZ. • SSTs in the Indian Ocean playing a minor role in controlling East African climate. [ABSTRACT FROM AUTHOR]

We used a change point analysis on a late Pleistocene–Holocene lake-sediment record from the Chew Bahir basin in the southern Ethiopian Rift to determine the amplitude and duration of past climate transitions. The most dramatic changes occurred over 240 yr (from ~15,700 to 15,460 yr) during the onset of the African Humid Period (AHP), and over 990 yr (from ~4875 to 3885 yr) during its protracted termination. The AHP was interrupted by a distinct dry period coinciding with the high-latitude Younger Dryas stadial, which had an abrupt onset (less than ~100 yr) at ~13,260 yr and lasted until ~11,730 yr. Wet-dry-wet transitions prior to the AHP may reflect the high-latitude Dansgaard-Oeschger cycles, as indicated by cross-correlation of the potassium record with the NorthGRIP ice core record between ~45–20 ka. These findings may contribute to the debates regarding the amplitude, and duration and mechanisms of past climate transitions, and their possible influence on the development of early modern human cultures. [ABSTRACT FROM AUTHOR]

A 12 m long sediment sequence was recovered from the eastern Dendi Crater lake, located on the central Ethiopian Plateau and in the region of the Blue Nile headwaters. 24 AMS radiocarbon dates from bulk organic carbon samples indicate that the sediment sequence spans the last ca. 12 cal kyr BP. Sedimentological and geochemical data from the sediment sequence that were combined with initial diatom information show only moderate change in precipitation and catchment runoff during that period, probably due to the elevated location of the study region in the Ethiopian highlands. Less humid conditions prevailed during the Younger Dryas (YD). After the return to full humid conditions of the African Humid Period (AHP), a ~2 m thick tephra layer, probably originating from an eruption of the Wenchi crater 12 km to the west of the lake, was deposited at 10.2 cal kyr BP. Subsequently, single thin horizons of high clastic matter imply that short spells of dry conditions and significantly increased rainfall, respectively, superimpose the generally humid conditions. The end of the AHP is rather gradual and precedes relatively stable and less humid conditions around 3.9 cal kyr BP. Subsequently, slightly increasing catchment runoff led to sediment redeposition, increasing nutrient supply, and highest trophic states in the lake until 1.5 cal kyr BP. A highly variable increase in clastic matter indicates fluctuating and increasing catchment runoff over the last 1500 years. The data from Lake Dendi show, in concert with other records from the Nile catchment and the Eastern Mediterranean Sea (EMS), that the Blue Nile discharge was relatively high between ca. 10.0 and 8.7 cal kyr BP. Subsequent aridification peaked with some regional differences between ca. 4.0 and 2.6 cal kyr BP. Higher discharge in the Blue Nile hydraulic regime after 2.6 cal kyr BP is probably triggered by more local increase in rainfall, which is tentatively caused by a change in the influence of the Indian Ocean monsoon. [ABSTRACT FROM AUTHOR]

During the African Humid Period (AHP; c. 15–5.5 ka), the rivers and lakes of much of the continent swelled due to changes in monsoonal rainfall driven by Earth's orbital precession. This period witnessed the growth of diverse fisher-forager communities, whose members adapted their settlement patterns and created new technologies in order to take advantage of aquatic resources. Around Lake Turkana in northern Kenya, numerous surface sites have been documented along former shorelines dating to the AHP. Relatively few have been excavated and dated however, and just three – all from the eastern basin – have published faunal analyses. Here, we present archaeofaunal assemblages from the Kalokol region of the western basin, where three sites with microlithic technology, bone harpoons, and radiocarbon dates falling within the AHP were excavated. We present a detailed taphonomic assessment of the fish assemblages and a comparison with both natural and anthropogenic, and ancient and modern, fish bone accumulations. Taxa identified at the Kalokol sites are discussed in terms of the occupants' possible fishing technologies and strategies, drawing on ethological and ethnographic data. Our analysis, combining our data with those published from the eastern basin, enables a broader discussion of how people may have responded to fluctuating AHP environments in the Turkana Basin. [ABSTRACT FROM AUTHOR]

As riverine and lacustrine environments expanded across north tropical Africa during early Holocene times, certain characteristic fishing or “aquatic hunting” strategies became widespread. This paper investigates one such strategy and an associated technology: selective fishing and barbed bone “harpoon” points in the Turkana Basin, northwest Kenya. These tools have a geographically widespread distribution across Africa, primarily north of the equator, and can shed light on hunter-gatherer technology and resource acquisition in the face of environmental and social change. Interviews with contemporary Turkana fishers highlight near-shore fishing practices analogous to those of early Holocene hunter-gatherers. For example, Turkana fishers exploiting deltaic “yellow waters” have traditionally employed selective harpoon-like tools to acquire large aquatic fauna like Lates niloticus (Nile perch) and Synodontis sp. (catfish), while using non-selective traps, hooks and nets to catch smaller and deeper-water species. These practices have changed over several decades in response to local socioeconomic and environmental shifts. Today these selective strategies show a marked seasonality and regional variability that the archaeological record of this region has thus far been ill-equipped to investigate. Through carefully constructed analogy, this preliminary work contributes to a better understanding of human technological and behavioral responses to shifting lakeshore environments today and during early Holocene times. [ABSTRACT FROM AUTHOR]

The climate changes associated with the Holocene wet phase in the Sahara, the African Humid Period, are subject to ongoing debate discussing interactions between climate and vegetation and possible feedbacks between vegetation, albedo, desertification, and dust. However, very little attention has been given to the role of fire in shaping the land cover, although it is known that fires are important in the formation and consolidation of the African savanna. To fill this gap, we investigated the interaction between precipitation changes, vegetation shifts, and fire occurrence in West Africa by combining stable isotope measurements on plant waxes with pollen and micro-charcoal counts of marine sediments retrieved offshore of Cape Blanc. Our study focuses on the roles of fire at the dry limit of savanna during the Holocene evolution of precipitation changes indicating that the impact of fire during a relative wet climate differs from that during aridification. During the humid early Holocene, increased savanna extension and diversification ran parallel to increased fire occurrence. In contrast, after aridification of northern Africa started at the end of the African Humid Period, a maximum in fire occurrence correlated with a deterioration of the vegetation promoting desertification. [ABSTRACT FROM AUTHOR]

In Africa, the early Holocene was characterized by wetter, warmer conditions than today, followed by rapid aridification at ~5.2 ka. However, a lack of lowland vegetation records has prevented a detailed evaluation of forest response to Holocene climate change. Additionally, although modern vegetation communities are linked to human disturbance, few studies have addressed how prehistoric human activities helped engineer the character of modern African ecosystems. Understanding the architecture of lowland and highland forests is important to prevent further degradation from climate/land-use change. We present an 11,000 yr fossil pollen record from Lake Edward, Uganda. We show that Guineo-Congolian forests dominated the highlands and lowlands in equatorial East Africa in the early Holocene, highlighting the importance of rainfall and temperature in controlling forest communities. These forests remained until ~5.2 ka, when the climate became drier. The lacustrine ecosystem response to aridification was abrupt; however, forest decreased gradually, replaced by deciduous woodlands. Woodlands dominated until after an arid period at 2 ka; however, forest did not recover. Increased disturbance indicators and grasses suggest that the arrival of Iron Age people resulted in the modern fire-tolerant vegetation. Although late Holocene climate played a role in vegetation opening, the modern ecosystem architecture in East Africa is linked to early human activities. [ABSTRACT FROM PUBLISHER]

The abrupt change in North Atlantic dust deposition found in sediment records has been associated with a rapid large scale transition of Holocene Saharan landscape. We hypothesize that gradual changes in the landscape may have caused this abrupt shift in dust deposition either because of the non-linearity in dust activation or because of the heterogeneous distribution of major dust sources. To test this hypothesis, we investigate the response of North Atlantic dust deposition to a prescribed 1) gradual and spatially homogeneous decrease and 2) gradual southward retreat of North African vegetation and lakes during the Holocene using the aerosol-climate model ECHAM-HAM. In our simulations, we do not find evidence of an abrupt increase in dust deposition as observed in marine sediment records along the Northwest African margin. We conclude that such gradual changes in landscape are not sufficient to explain the observed abrupt changes in dust accumulation in marine sediment records. Instead, our results point to a rapid large-scale retreat of vegetation and lakes in the area of significant dust sources. [ABSTRACT FROM AUTHOR]