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Abstract: Bush encroachment is a significant phenomenon in savanna environments as it affects wildlife and local livelihoods by preventing new pasture generation. In this article we present a 2000-year record of vegetation change in the Dara range of the Mago National Park, southwestern Ethiopia, an area inhabited by Mursi agro-pastoralists. We use an interdisciplinary approach to understand whether bush encroachment in this area is a recent event or a transitional state of the savanna and describe the local understanding of encroachment as a species-specific process. The vegetation record was obtained from a fossil hyrax midden, a type of sediment already used in Southern Africa but never before in East Africa. Six encroaching phases, led by Capparaceae and Grewia, were found over the last two millennia. The system proved to be resilient, with alternating open and encroached phases, and showed a non-linear response to environmental change, thereby fitting the control theory hypothesis for hysteresis loops. Determining the thresholds conditioning the system''s resilience could help to improve savanna management for both local people and National Park authorities. [Copyright &y& Elsevier]

Abstract: High-resolution seismic data from Lake Tana, the source of the Blue Nile in northern Ethiopia, reveal a deep sedimentary sequence divided by four strong reflectors. Data from nearshore cores show that the uppermost strong reflector represents a stiff silt unit, interpreted as a desiccation surface. Channel cuts in this surface, bordered by levee-like structures, are apparent in the seismic data from near the lake margin, suggesting fluvial downcutting and over-bank deposition during seasonal flood events. Periphytic diatoms and peat at the base of a core from the deepest part of the lake overlie compacted sediments, indicating that desiccation was followed by development of shallow-water environments and papyrus swamp in the central basin between 16,700 and 15,100cal BP. As the lake level rose, open-water evaporation from the closed lake caused it to become slightly saline, as indicated by halophytic diatoms. An abrupt return to freshwater conditions occurred at 14,750cal BP, when the lake overflowed into the Blue Nile. Further reflection surfaces with downcut structures are identifiable in seismic images of the overlying sediments, suggesting at least two lesser lake-level falls, tentatively dated to about 12,000 and 8000cal BP. Since Lake Victoria, the source of the White Nile, was also dry until 15,000cal BP, and did not reach overflow until 14,500cal BP, the entire Nile system must have been reduced to intermittent seasonal flow until about 14,500cal BP, when baseflow was re-established with almost simultaneous overflow of the headwater lakes of both the White and Blue Nile rivers. Desiccation of the Nile sources coincides with Heinrich event 1, when cessation of northward heat transport from the tropical Atlantic disrupted the Atlantic monsoon, causing drought in north tropical Africa. The strong reflectors at deeper levels in the seismic sequence of Lake Tana may represent earlier desiccation events, possibly contemporaneous with previous Late Pleistocene Heinrich events. [Copyright &y& Elsevier]

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]

A comparison of a 6450 14C yr δ18O and δ13C record of authigenic calcite from Lake Awassa, Ethiopia, with other proxy climate records in the area suggests that the lake records long-term regional climate changes. Co-varying and increasing δ18O and δ13C values from ∼4800 BP suggest an aridification of climate after the early Holocene insolation maximum. After 4000 BP, humid conditions return until after ∼2800 BP when δ18O increases again, reflecting more arid conditions recorded elsewhere in Ethiopia. In addition to these long-term changes, there are abrupt decreases in both δ18Ocalcite and δ13Ccalcite immediately after tephra layers. The likeliest explanation for these abrupt decreases in isotopes is the effect of tephra on the lake''s catchment vegetation. δ18O, δ13C and lake-level measurements from Lake Awassa since the 1970s suggest that the lake is currently isotopically sensitive to short-term (annual–decadal) climate change. However, during this period, the catchment has undergone progressive deforestation that may have caused an increase in runoff. Caution is therefore required when reconstructing palaeoclimates as a contemporary lake may not always be a good analogue for lake hydrology in the past. [Copyright &y& Elsevier]

Abstract Establishing agricultural activity using pollen analysis is one of the prime challenges of a palaeoecological investigation. Here we report combined pollen and archaeobotanical data originating from a waterlogged off-site organic-rich fill radiocarbon dated to ∼8 ka Cal BP located between the two occupation mounds at Neolithic-Chalcolithic Çatalhöyük, south central Turkey in order to investigate the record of Early Chalcolithic agricultural activity. Pollen results indicate extremely high abundances of Cerealia-type pollen (30->70%) and critical measurements of these show them to be Triticum -type, Avena / Triticum -type, Secale -type and Hordeum -type. Pollen data are also compared with archaeobotanical data retrieved from the same sediment matrix and show high abundances of Triticum and Hordeum grains, awns, spikelet forks and glume bases. Archaeobotanical and pollen data are therefore unequivocal in showing the presence of cereals throughout the period of deposition, and although preservation of archaeobotanical cereal plant remains is typically poor, the presence of glume wheats, including emmer/'New Type' wheat and domesticated barley, is consistent with cereal data from on-site excavation deposits at Çatalhöyük. Pollen data also include high occurrences of clusters of Cerealia-type, Chenopodiaceae, Poaceae and Asteraceae and point to local deposition that is best explained as the anthers being deposited at the coring site attached to cereal or other herbaceous waste material. Archaeobotanical data in addition to very high percentage values of individual Cerealia-type pollen grains and clusters of Cerealia-type pollen and other non-arboreal pollen types suggest that the margins of the Çatalhöyük site were probably used for early stage crop processing activities as well as a waste site. Although radiocarbon dating of this organic-rich fill suggests that it was deposited over a very short time period (∼300 years) during the Early Chalcolithic, the data highlight the importance of adopting complementary palynological and archaeobotanical approaches in order to better understand the taphonomy of micro and macrofossil deposits associated with archaeological sites. While more distant, regional pollen sites in south-central Anatolia have difficulty registering Neolithic-Chalcolithic cereal cultivation, this study shows that if a pollen core site is located too close to an archaeological site, then pollen assemblages can be overwhelmed and 'swamped' by the products of local cereal processing and the inclusion of domestic waste material thus rendering it difficult to elucidate meaningful data on local agricultural activity. Highlights • Comparison of archaeobotanical and pollen analytical data from on- and off-site deposits at Neolithic-Chalcolithic Çatalhöyük. • Replicated very high percentage values (30–78%) of Cerealia-type pollen recorded from two sediment cores. • Quantitative measurements of Cerealia-type pollen grains. • Highlights the importance of taphonomical pathways for microfossil (pollen) and macrofossil (archaeobotanical) material. • Importance of site selection when undertaking palaeoecological investigations in close proximity to archaeological sites. [ABSTRACT FROM AUTHOR]

Abstract The lakes of the eastern Africa Rift often contain great thicknesses of sediment that may provide continuous records of environmental change over decadal to million-year timescales. However interpretation of these changes is greatly compromised without a reliable chronology. Luminescence dating has not been used extensively in lacustrine settings; instead previous studies have often relied upon radiocarbon dating, using extrapolation beyond the upper limit of that technique, and employing opportunistic sampling of tephra and palaeomagnetic signatures where possible. This study from Lake Tana, Ethiopia, demonstrates that recent advances in luminescence methodology can provide long chronologies for lake sediments that are not dependent on the intermittent presence of dateable material, as is the case for radiocarbon and tephra-based methods. Specifically, this study generates luminescence ages that agree with independent chronology based on radiocarbon dating in the upper part of the core, and extends significantly beyond the range of radiocarbon dating to provide one of the longest independently dated lacustrine sediment records in eastern Africa, thus demonstrating the tremendous potential of luminescence for constructing lacustrine sediment chronologies over 100,000 year timescales. Highlights • Recent advances make it timely to apply luminescence methods to date lake sediments. • Luminescence dating can provide long chronologies throughout lake sediment cores. • The application of luminescence dating to sediments from Lake Tana is discussed. • One of the longest independently dated lake records in eastern Africa. • Demonstrates the contribution luminescence dating can make to lacustrine studies. [ABSTRACT FROM AUTHOR]

Abstract Archaeological findings, numerical human dispersal models and genome analyses suggest several time windows in the past 200 kyr (thousands of years ago) when anatomically modern humans (AMH) dispersed out of Africa into the Levant and/or Arabia. From close to the key hominin site of Omo-Kibish, we provide near continuous proxy evidence for environmental changes in lake sediment cores from the Chew Bahir basin, south Ethiopia. The data show highly variable hydroclimate conditions from 116 to 66 kyr BP with rapid shifts from very wet to extreme aridity. The wet phases coincide with the timing of the North African Humid Periods during MIS5, as defined by Nile discharge records from the eastern Mediterranean. The subsequent record at Chew Bahir suggests stable regional hydrological setting between 58 and 32 kyr (MIS4 and 3), which facilitated the development of more habitable ecosystems, albeit in generally dry climatic conditions. This shift, from more to less variable hydroclimate, may help account for the timing of later dispersal events of AMH out of Africa. Highlights • Multiproxy record from S Ethiopia extends knowledge about environment and climate of past 116,000 yrs during human expansion. • Hydroclimate during Marine Isotope Stage (MIS) 5 was much more variable (frequency and amplitude) than during MIS 3 and 4. • Earth system models and model simulations of intermediate complexity emulate corresponding amplitude shifts in hydroclimate. • Environment was arid during MIS 3 and 4, but permanent lake water bodies existed as inferred from our biological proxies. [ABSTRACT FROM AUTHOR]

Abstract Lake Suigetsu (Japan) is a key site for radiocarbon (14C) calibration and palaeo-environmental reconstruction in East Asia. Here we present a description of the sediment (micro)facies, which in combination with a new approach to varve interpolation allows construction of a revised varve based chronology that extends the previous 2012 varve based chronology by ∼10 ka, back to ∼50 ka BP. Challenges in varve counting and interpolation, which were previously discussed in detail only for the Last Glacial-Interglacial Transition, are described here back to ∼50 ka BP. Furthermore, the relative merits of varve counting by μXRF scanning and by thin-section microscopy are discussed. Facies analysis reveals four facies zones, their transitions driven by both local and climatic controls. The lamination quality of the sediment is highly variable and varve interpolation reveals that in the analysed time interval, on average, only 50% of the annual cycles are represented by seasonal layers. In the remaining years seasonal layers are indistinguishable, i.e. either did not form or were not preserved. For varve interpolation an advanced version of the Varve Interpolation Program was used, which enabled the construction of the longest, purely varve dated chronology published, despite long intervals of poor lamination quality. The calculated interpolation uncertainty is +8.9% and −4.6%, which is well within expectations considering the high degree of interpolation and the length of the record. Highlights • New facies and microfacies data from Lake Suigetsu are presented. • Analysis covers the time frame from 50 to 10 ka BP. • Detailed description varve characteristics for the complete analysed interval. • Discussion of μXRF as a tool for varve counting compared to microscope counting. • Detailed discussion of strength and weaknesses of the Suigetsu varve chronology. [ABSTRACT FROM AUTHOR]

Our understanding of the impact of climate-driven environmental change on prehistoric human populations is hampered by the scarcity of continuous paleoenvironmental records in the vicinity of archaeological sites. Here we compare a continuous paleoclimatic record of the last 20 ka before present from the Chew Bahir basin, southwest Ethiopia, with the available archaeological record of human presence in the region. The correlation of this record with orbitally-driven insolation variations suggests a complex nonlinear response of the environment to climate forcing, reflected in several long-term and short-term transitions between wet and dry conditions, resulting in abrupt changes between favorable and unfavorable living conditions for humans. Correlating the archaeological record in the surrounding region of the Chew Bahir basin, presumably including montane and lake-marginal refugia for human populations, with our climate record suggests a complex interplay between humans and their environment during the last 20 ka. The result may contribute to our understanding of how a dynamic environment may have impacted the adaptation and dispersal of early humans in eastern Africa. [ABSTRACT FROM AUTHOR]

Abstract: Event layers in lake sediments are indicators of past extreme events, mostly the results of floods or earthquakes. Detailed characterisation of the layers allows the discrimination of the sedimentation processes involved, such as surface runoff, landslides or subaqueous slope failures. These processes can then be interpreted in terms of their triggering mechanisms. Here we present a 40 ka event layer chronology from Lake Suigetsu, Japan. The event layers were characterised using a multi-proxy approach, employing light microscopy and μXRF for microfacies analysis. The vast majority of event layers in Lake Suigetsu was produced by flood events (362 out of 369), allowing the construction of the first long-term, quantitative (with respect to recurrence) and well dated flood chronology from the region. The flood layer frequency shows a high variability over the last 40 ka, and it appears that extreme precipitation events were decoupled from the average long-term precipitation. For instance, the flood layer frequency is highest in the Glacial at around 25 ka BP, at which time Japan was experiencing a generally cold and dry climate. Other cold episodes, such as Heinrich Event 1 or the Late Glacial stadial, show a low flood layer frequency. Both observations together exclude a simple, straightforward relationship with average precipitation and temperature. We argue that, especially during Glacial times, changes in typhoon genesis/typhoon tracks are the most likely control on the flood layer frequency, rather than changes in the monsoon front or snow melts. Spectral analysis of the flood chronology revealed periodic variations on centennial and millennial time scales, with 220 yr, 450 yr and a 2000 yr cyclicity most pronounced. However, the flood layer frequency appears to have not only been influenced by climate changes, but also by changes in erosion rates due to, for instance, earthquakes. [Copyright &y& Elsevier]

The African Humid Period of the early to mid-Holocene (12,000–5000 years ago) had dramatic ecological and societal consequences, including the expansion of vegetation and civilization into the “green Sahara.” While the humid period itself is well documented throughout northern and equatorial Africa, mechanisms behind observed regional variability in the timing and magnitude of the humid period remain disputed. This paper presents a new hydrogen isotope record from leaf waxes (δD wax) in a 15,000-year sediment core from Lake Tana, Ethiopia (12°N, 37°E) to provide insight into the timing, duration, and intensity of the African Humid Period over northeastern Africa. δD wax at Lake Tana ranges between −80‰ and −170‰, with an abrupt transition from D-enriched to D-depleted waxes between 13,000–11,500 years before present (13–11.5 ka). A similarly abrupt transition from D-depleted to D-enriched waxes occurs ca 8.5–8 ka and is followed by generally D-enriched waxes throughout the late Holocene. Trends in δD wax covary with changes in Northern Hemisphere summer insolation and reflect increased precipitation at Lake Tana during the AHP; however, the transition from D-depleted to D-enriched waxes occurs earlier at Lake Tana (ca 8 ka, vs 5 ka) than in many other regional records, and the amplitude of D-depletion during the AHP is larger at Lake Tana as well. We attribute this early enrichment to a reduction of moisture derived from westerly sources (the Congo Basin and Atlantic Ocean) which we suggest are D-depleted relative to moisture sourced from the east (Indian Ocean) and the north (Red Sea and Mediterranean Sea). Our new record highlights the importance of both the northward migration of the tropical rain belt as well as east-west migration of the Congo Air Boundary to precipitation source and amount during the African Humid Period. [ABSTRACT FROM AUTHOR]

Abstract: East African paleoenvironments are highly variable, marked by extreme fluctuations in moisture availability, which has far-reaching implications for the origin, evolution and dispersal of Homo sapiens in and beyond the region. This paper presents results from a pilot core from the Chew Bahir basin in southern Ethiopia that records the climatic history of the past 45 ka, with emphasis on the African Humid Period (AHP, ∼15–5 ka calBP). Geochemical, physical and biological indicators show that Chew Bahir responded to climatic fluctuations on millennial to centennial timescales, and to the precessional cycle, since the Last Glacial Maximum. Potassium content of the sediment appears to be a reliable proxy for aridity, showing that Chew Bahir reacted to the insolation-controlled humidity increase of the AHP with a remarkably abrupt onset and a gradual termination, framing a sharply defined arid phase (∼12.8–11.6 ka calBP) corresponding to the Younger Dryas chronozone. The Chew Bahir record correlates well with low- and high-latitude paleoclimate records, demonstrating that the site responded to regional and global climate changes. [Copyright &y& Elsevier]

Abstract: The high potential of the varved sediments of Lake Suigetsu, central Japan, to provide a purely terrestrial radiocarbon calibration model and a chronology of palaeoclimatic changes has been widely recognised for the last two decades. However, this potential has not been fully realised since the only available long sediment core from the lake (‘SG93’) was extracted from a single bore hole and was therefore interrupted by gaps of unknown duration between successive core sections. In the summer of 2006, a new sediment core (‘SG06’) was recovered from the lake. Four separate boreholes were drilled and the parallel sets of cores recovered were found to overlap completely, without gaps between segments. This new record provides the ability to test existing atmospheric radiocarbon calibration models, as well as to assess the scale of inter-regional leads and lags in palaeoclimatic changes over the last Glacial–Interglacial cycle. Multi-disciplinary analyses from SG06 are still ongoing, but a reliable description of the sedimentary sequence needs to be provided to the wider science community before major outputs from the project are released, thereby allowing fully-informed critical evaluation of all subsequent releases of data based on the SG06 record. In this paper, we report key litho-stratigraphic information concerning the SG06 sediment core, highlighting changes in the clarity of annual laminations (varves) with depth, and possible implications for the mechanism of the climate change. We also discuss the potential of the SG06 record to meet the fundamental goals of the INQUA-INTIMATE project. [Copyright &y& Elsevier]

Abstract: High-resolution diatom, sediment and pollen analyses of two sections from the annually laminated SG06 core from Lake Suigetsu were used to study the onset and termination of the late-glacial climate reversal in central Japan. Its broadly recognised counterpart is the Younger Dryas or Greenland Stadial-1 (ca. 12.85–11.65cal. kyr BP based on the NGRIP ice core records). Our study suggests that accumulation of the analysed late-glacial sediments occurred in a deep and relatively cold water meso-eutrophic lake with a strong mixing regime and relatively high silica content. Combining these results together with available pollen-based environmental reconstructions we suggest that climate cooling, together with an intensified winter monsoon and thicker snow cover could influence changes in regional vegetation, sedimentation processes and trophic status of the lake during the transition from the last interstadial to stadial around Lake Suigetsu. A decrease in total pollen concentration and increase in Fagus pollen percentage indicate local vegetation stress/disturbances and suggest that cooling started at least 2–3 decades prior to the major shift in the inorganic sediment (accumulation of detrital layers) and in diatom assemblages (change from Aulacoseira ambigua to Aulacoseira subarctica dominance), which took about 10years. The transition from the last stadial to the Holocene again shows that vegetation in the lake catchment area reacted first to the regional climate change, i.e. to the weakening of the winter monsoon and decrease in winter snow accumulation. The increase in the vegetation cover density and reduced volume of surface runoff associated with the decrease in melt water supply is likely responsible for the reduced soil erosion activity which caused the cessation in detrital layer accumulation and consequent decrease in the amount of nutrients brought to the lake and lowering of the water nutrient status. The latter process finally influenced changes in the diatom assemblages, including the return to dominance of A. subarctica ca. 30years after the virtual disappearance of detrital layers from the sediment. Our results demonstrate the rapid response of the Lake Suigetsu system to the global cooling and subsequent warming, and allow clear definition of the onset and termination of the late-glacial climate reversal. Despite the fact that the lake system shows a more abrupt shift from the warm to cold (and cold to warm) environments than terrestrial records of vegetation demonstrate, we do not see any delayed response of local vegetation to the climate change. This last conclusion is of particular importance for application of the SG06 pollen record for quantitative climate reconstruction. [Copyright &y& Elsevier]

Abstract: Since fire has been recognized as an essential disturbance in Mediterranean landscapes, the study of long-term fire ecology has developed rapidly. We have reconstructed a sequence of vegetation dynamics and fire changes across south-eastern Iberia by coupling records of climate, fire, vegetation and human activities. We calculated fire activity anomalies (FAAs) in relation to 3kacalBP for 10–8kacalBP, 6kacalBP, 4kacalBP and the present. For most of the Early to the Mid-Holocene uneven, but low fire events were the main vegetation driver at high altitudes where broadleaved and coniferous trees presented a highly dynamic post-fire response. At mid-altitudes in the mainland Segura Mountains, fire activity remained relatively stable, at similar levels to recent times. We hypothesize that coastal areas, both mountains and lowlands, were more fire-prone landscapes as biomass was more likely to have accumulated than in the inland regions, triggering regular fire events. The wet and warm phase towards the Mid-Holocene (between ca 8 and 6kacalBP) affected the whole region and promoted the spread of mesophytic forest co-existing with Pinus, as FAAs appear strongly negative at 6kacalBP, with a less important role of fire. Mid and Late Holocene landscapes were shaped by an increasing aridity trend and the rise of human occupation, especially in the coastal mountains where forest disappeared from ca 2kacalBP. Mediterranean-type vegetation (evergreen oaks and Pinus pinaster-halepensis types) showed the fastest post-fire vegetation dynamics over time. [Copyright &y& Elsevier]

There is ongoing debate concerning whether or not changes in the eastern African climate, both long-term and short-term, affected the evolution, dispersal, cultural development, and technological innovations of Homo sapiens – and if so, in what way. We present the wavelet spectral analysis results of a ∼620 kyr record of environmental change from the Chew Bahir (CHB) basin in the southern Ethiopian rift, approximately 120 km from the Omo-Kibish fossil locality, which boasts one of the oldest documented appearances of H. sapiens. Our results indicate that the long-term wet-dry changes in the eastern African climate recorded in the CHB sediments were mainly caused by changes in orbital eccentricity, with relatively dry but variable climates occurring during eccentricity minima within the 400 kyr eccentricity cycle, and increased precipitation, interspersed with distinctly dryer phases associated with orbital precession, during eccentricity maxima. Such insolation-forced precipitation changes would have affected the habitat of H. sapiens in the region; the transition from Acheulean to Middle Stone Age (MSA) documented in the Olorgesailie Basin of southern Kenya coincides with a distinct eccentricity minimum with reduced precipitation and repeated abrupt climatic transitions. In contrast, at the time of the subsequent, first documented occurrence of H. sapiens in eastern Africa the climate was distinctly wetter and less variable. • Orbitally controlled variation in insolation have caused wet-dry climate cycles in the CHB over the las 620 kyrs. • The climate of the CHB was characterized by a long term drying trend coinciding with an increase in variability. • Short term increases of variability correspond to changes in eccentricity translating into fast climate transitions. • During the transition from Acheulean to MSA technologies the climate of the CHB was highly variable. [ABSTRACT FROM AUTHOR]

In order to track changes in the relative abundance of C3 and C4 plants in savanna vegetation, C/N and δ13C values were measured on bulk organic material in an 8840 14C-year record from Lake Tilo, Ethiopia. Between 8840 and 2500 BP, high C/N ratios suggest that input to the lake was predominantly from terrestrial plants. The corresponding δ13C values thus provide a proxy for changes in catchment vegetation that are supported by pollen data. δ13C values in the early Holocene are relatively low, reflecting the dominance of C3 vegetation (woody plants) and a more humid climate. δ13C shows no response to a known regional arid interval at 7800 yr BP, suggesting that woody vegetation was able to survive relatively prolonged dry periods. A gradual, rather than sharp, δ13C response to the end of the early Holocene humid interval at ∼4500 yr BP further supports this. Higher δ13C values at ∼2800–2300 and ∼1000 yr BP correspond to increases in sedge pollen, thought to be growing in freshwater springs, exposed as lake-level fell. The C/N and δ13C composition of bulk organic material complements the pollen evidence and may be useful in other lakes in savanna regions as indicators of terrestrial vegetation change. [Copyright &y& Elsevier]

Despite eastern Africa being a key location in the emergence of Homo sapiens and their subsequent dispersal out of Africa, there is a paucity of long, well-dated climate records in the region to contextualize this history. To address this issue, we dated a ∼293 m long composite sediment core from Chew Bahir, south Ethiopia, using three independent chronometers (radiocarbon, 40Ar/39Ar, and optically stimulated luminescence) combined with geochemical correlation to a known-age tephra. The site is located in a climatically sensitive region, and is close to Omo Kibish, the earliest documented Homo sapiens fossil site in eastern Africa, and to the proposed dispersal routes for H. sapiens out of Africa. The 30 ages generated by the various techniques are internally consistent, stratigraphically coherent, and span the full range of the core depth. A Bayesian age-depth model developed using these ages results in a chronology that forms one of the longest independently dated, high-resolution lacustrine sediment records from eastern Africa. The chronology illustrates that any record of environmental change preserved in the composite sediment core from Chew Bahir would span the entire timescale of modern human evolution and dispersal, encompassing the time period of the transition from Acheulean to Middle Stone Age (MSA), and subsequently to Later Stone Age (LSA) technology, making the core well-placed to address questions regarding environmental change and hominin evolutionary adaptation. The benefits to such studies of direct dating and the use of multiple independent chronometers are discussed. • Four independent dating methods applied to ∼293 m lake core from southern Ethiopia. • Reveals 620 ka high-resolution sedimentary record near key fossil hominin sites. • Mean accumulation rate of 0.47 mm/a comparable to other African lacustrine sediments. • Accumulation rate fell to 0.1 mm/a during MIS 2, likely due to reduced sediment supply. • Use of multiple independent chronometers is a powerful approach in lake settings. [ABSTRACT FROM AUTHOR]

The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and hominin evolution in Africa through the analysis of sediment cores that have recorded environmental changes in the Chew Bahir basin (CHB). In this statistical project we used recurrence plots (RPs) together with a recurrence quantification analysis (RQA) to distinguish two types of variability and transitions in the Chew Bahir aridity record and compare them with the ODP Site 967 wetness index from the eastern Mediterranean. The first type of variability is one of slow variations with cycles of ∼20 kyr, reminiscent of the Earth's precession cycle, and subharmonics of this orbital cycle. In addition to these cyclical wet-dry fluctuations in the area, extreme events often occur, i.e. short wet or dry episodes, lasting for several centuries or even millennia, and rapid transitions between these wet and dry episodes. The second type of variability is characterized by relatively low variation on orbital time scales, but significant century-millennium-scale variations with progressively increasing frequencies. Within this type of variability there are extremely fast transitions between dry and wet within a few decades or years, in contrast to those within Type 1 with transitions over several hundreds of years. Type 1 variability probably reflects the influence of precessional forcing in the lower latitudes at times with maximum values of the long (400 kyr) eccentricity cycle of the Earth's orbit around the sun, with the tendency towards extreme events. Type 2 variability seems to be linked with minimum values of this cycle. There does not seem to be a systematic correlation between Type 1 or Type 2 variability with atmospheric CO 2 concentration. The different types of variability and the transitions between those types had important effects on the availability of water, and could have transformed eastern Africa's environment considerably, which would have had important implications for the shaping of the habitat of H. sapiens and the direct ancestors of this species. [ABSTRACT FROM AUTHOR]

We have investigated provenance and weathering proxies of the clay-size sediment exported from the Nile River basin over the last 110,000 years. Using neodymium isotope composition of sediments from both the Nile Deep Sea-Fan and Lake Tana, we show that the Nile River branches draining the Ethiopian Highlands have remained the main contributors of clays to the Nile delta during the Late Quaternary. We demonstrate that fluctuations of clay-size particle contribution to the Nile Delta are mainly driven by orbital precession cycle, which controls summer insolation and consequently the African monsoon intensity changes. Our results indicate that - over the last 110,000 years – the proportion of clays coming from Ethiopian Traps fluctuates accordingly to the intensity of the last 5 precession cycles (MIS 5 to MIS 1). However, there is a threshold effect in the transport efficiency during the lowest insolation minima (arid periods), in particular during the MIS3. Several arid events corresponding to the Heinrich Stadial periods are associated with small or negligible clay source changes while chemical weathering proxies, such as δ7Li, Mg/Ti and K/Ti, vary significantly. This suggests a straightforward control of weathering by hydro-climate changes over centennial to millennial timescales. Our data also suggests a significant but more progressive influence of the temperature decrease between 110kyr and 20kyr. Taken altogether, the observed tight coupling between past climate variations and silicate weathering proxies leads us to conclude that precipitation changes in northeast Africa can impact soil development over a few hundred years only, while the influence of temperature appears more gradual. • First Li and Nd coupled isotopic source-to-sink approach over the Nile basin. • Clay εNd fluctuates in phase with the last 5 precession cycles intensity. • Transport thresholds are observed at lowest insolation minima. • Synchronicity between Heinrich Stadials and chemical weathering proxies. • Decoupled effect of temperature and precipitation on clay δ7Li values. [ABSTRACT FROM AUTHOR]