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ABSTRACT Targeted melanoma therapies, including treatment with the small molecule drug dabrafenib, can become ineffective due to acquired drug resistance. Dabrafenib targets BRAF‐V600E, a mutation that is present in more than half of melanoma cancers. Therefore, drug discovery efforts need to explore alternative candidate molecules that selectively target and kill melanoma cells via mechanisms different to those of current drugs. Marine fungi are an underexplored resource for bioactive molecules. Mortiamide‐D, a seven amino acid cyclic peptide from Mortierella sp, is an example molecule with desirable features for drug development. We synthesized mortiamide‐D and three rationally designed analogs and observed modest micromolar activity against HT144 melanoma cells that are sensitive or resistant to dabrafenib. By contrast, mortiamide‐D and analogs did not kill noncancer HaCaT cells at these concentrations. Substitution of D‐Ile at position 7 with D‐Arg improved membrane permeability and enhanced potency against HT144 cells via a mode‐of‐action that includes perturbation of mitochondrial membrane potential. These studies suggest the potential of mortiamides as modifiable scaffolds for developing a new class of molecule for targeting melanoma cells. [ABSTRACT FROM AUTHOR]

The numerous dispersal events that have occurred during the prehistory of hominin lineages are the subject of longstanding and increasingly active debate in evolutionary anthropology. As well as research into the dating and geographic extent of such dispersals, there is an increasing focus on the factors that may have been responsible for dispersal. The growing body of detailed regional palaeoclimatic data is invaluable in demonstrating the often close relationship between changes in prehistoric environments and the movements of hominin populations. The scenarios constructed from such data are often overly simplistic, however, concentrating on the dynamics of cyclical contraction and expansion during severe and ameliorated conditions respectively. This contribution proposes a two-stage hypothesis of hominin dispersal in which populations (1) accumulate high levels of climatic tolerance during highly variable climatic phases, and (2) express such heightened tolerance via dispersal in subsequent low-variability phases. Likely dispersal phases are thus proposed to occur during stable climatic phases that immediately follow phases of high climatic variability. Employing high resolution palaeoclimatic data from Lake Tana, Ethiopia, the hypothesis is examined in relation to the early dispersal of Homo sapiens out of East Africa and into the Levant. A dispersal phase is identified in the Lake Tana record between c. 112,550 and c. 96,975 years ago, a date bracket that accords well with the dating evidence for H. sapiens occupation at the sites of Qafzeh and Skhul. Results are discussed in relation to the complex pattern of H. sapiens dispersal out of East Africa, with particular attention paid to the implications of recent genetic chronologies for the origin of non-African modern humans. [ABSTRACT FROM AUTHOR]

We describe the career of John Birks as a pioneering scientist who has, over a career spanning five decades, transformed palaeoecology from a largely descriptive to a rigorous quantitative science relevant to contemporary questions in ecology and environmental change. We review his influence on students and colleagues not only at Cambridge and Bergen Universities, his places of primary employment, but also on individuals and research groups in Europe and North America. We also introduce the collection of papers that we have assembled in his honour. The papers are written by his former students and close colleagues and span many of the areas of palaeoecology to which John himself has made major contributions. These include the relationship between ecology and palaeoecology, late-glacial and Holocene palaeoecology, ecological succession, climate change and vegetation history, the role of palaeoecological techniques in reconstructing and understanding the impact of human activity on terrestrial and freshwater ecosystems and numerical analysis of multivariate palaeoecological data. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic and geochemical core data spanning the last 17,000years are correlated with new seismic stratigraphy from Lake Tana, Ethiopia, to infer past lake-level change and hence effective precipitation. The data confirm that low lake-level coincides with Heinrich Event 1 (H1) in the North Atlantic, as previously shown from diatom and pollen evidence (Lamb et al., 2007). The lake deepened at 15.3calkyr BP and abruptly returned to freshwater conditions, when the lake overflowed into the Blue Nile. Low runoff and lake levels and therefore rainfall are inferred between 13.0 and 12.5calkyr BP and may represent southerly suppression of the ITCZ and the associated monsoon front at the time of the Younger Dryas. Two drought episodes occurred at 8.4 and 7.5calkyr BP, and are also interpreted as a southward shift in the monsoon front. The first of these events appears to have preceded and been more significant than the 8.2calkyr BP. Precipitation declined after 6.8calkyr BP, although we do not see an abrupt end to the African Humid Period. This period culminated in a dry episode at ~4.2calkyr BP, supporting the view that reduced Nile flow was a contributing factor to the demise of the Egyptian Old Kingdom. [Copyright &y& Elsevier]

Abstract: Lake Ashenge, a closed-basin lake near the northernmost penetration of summer monsoon rains, is well placed to provide a continental record of past changes in the strength of the African monsoon system. Diatom and oxygen isotope analyses of the lake sediments confirm that the overall trend of climate change during the past 17,000 years was driven by precessional forcing, punctuated by abrupt shifts that may be linked to changes in Atlantic surface temperatures. The lake level was low from at least 17.2 to 16.2 cal kyr BP, and then rose between 16.2 and 15.2 cal kyr BP, which may represent a temporary reactivation of the monsoonal circulation system following its reduced activity during the Last Glacial Maximum. The lake was significantly low between 13.6 and ~11.8 cal kyr BP coinciding approximately with the Younger Dryas, but beginning 900 years before its recognised onset in the Greenland ice-core record. A major sedimentary hiatus, covering the interval ~11.8 to 7.6 cal kyr BP, was probably caused by an early Holocene lowstand, the precise timing of which cannot be determined because pre-lowstand sediments were eroded from the core site. The lake filled to its overflow from 7.6 cal kyr BP until 5.6 cal kyr BP, when the sediments record an abrupt lake response to the regional transition to arid conditions that mark the end of African Humid Period. Evidence is also presented for climate changes which may have been associated with the rise and fall of Aksum, Ethiopia''s first great civilisation. [Copyright &y& Elsevier]

The oxygen and carbon isotope composition of sedimentary carbonates formed in Lake Hayq, a closed-basin lake in northern Ethiopia, suggests marked variation in the balance between precipitation and evaporation during the last 2000 years. Diatom stratigraphy shows that the lake remained deep enough to support planktonic taxa, and was never saline. The record suggests that rainfall was higher than that of the twentieth century during most of this time, especially during two short intervals centred on AD 700 and AD 1300. Climate was drier only around AD 800, and from AD 1750–1900. Similar, but slightly moister climate than today, with high interdecadal variability, prevailed from AD 800 to AD 1200, equivalent to the European ‘Mediaeval Warm Period’. A period of high effective precipitation followed, from AD 1200 to AD 1700, during the ‘Little Ice Age’. Pollen evidence suggests that increased forest cover from AD 1400 to AD 1750 was a response to higher rainfall; forest cover may have increased evaporative loss from the catchment, contributing to a subsequent trend of increasing lakewater δ18O values. The record shows similarities in the timing and direction of changes in proxy-climatic records from Lake Naivasha (Kenya) and from the Nile. [ABSTRACT FROM AUTHOR]

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]

A Holocene pollen record from Co. Clare, western Ireland, shows unusually high Ulmus pollen frequencies until about 2500 cal. BP, interrupted by four brief episodes of reduced Ulmus pollen between 6000 and 3000 cal. BP. Localized anthropogenic disturbance of the vegetation during this interval is inferred from higher magnetic susceptibility of the sediments, indicating soil erosion, and from increased Poaceae and Plantago pollen. The continued abundance of elm at several sites in Ireland, despite human impact, suggests that disease was a less significant factor in the reduction of Irish elm populations than elsewhere in northwestern Europe. It may be that the pathogen, its dispersal agent, or susceptible elm ecotypes were locally absent near the western range margin of elm, reinforcing the argument that the combined effects of human exploitation and a pathogen were necessary to cause the permanent elm decline at 6000 cal. BP in most of northwestern Europe. [ABSTRACT FROM AUTHOR]

Pollen and charcoal analysis of sediment cores from two lakes in the highlands of northern Ethiopia provide evidence that the vegetation has changed in response to human impact during the last 3000 years. The natural, pre-disturbance vegetation of the area was Podocarpus-Juniperus forest. At about 500 BC, following Semitic immigration to northern Ethiopia, the forests were cleared and replaced by a secondary vegetation of Dodonaea scrub and grassland that persisted for 1800 years. Grasslands were dominant from about AD 1200 to 1400, probably as a result of further intensification of grazing, perhaps exacerbated by drought. Juniperus forest, with Olea and Celtis, then expanded from AD 1400 to 1700, possibly because of drought-induced depopulation followed by increased rainfall. Deforestation and soil erosion has again intensified during the last three centuries. Since forest regrowth was possible after 1800 years of human impact, northern Ethiopia should again be capable of supporting forest under appropriate land management. [ABSTRACT FROM AUTHOR]

Pollen data from a 625 cm sediment core from Crescent Island Crater, a subbasin of Lake Naivasha, Kenya, provide an 1100-year record of vegetation change at a mean time resolution of 15 years. Earlier data from the same core show a record of lake depth (and thus inferred rainfall variation) in the form of changing sedimentary facies, supported by salinity inferences based on diatom and chironomid assemblages. Stratigraphic variation in the abundances of aquatic and semi-aquatic plants and chlorophyte algae generally supports the reconstructed lake depths. Woody Afromontane and woodland plant taxa decreased relative to Poaceae (grasses) during low rainfall periods, and increased during high rainfall periods. A decrease in the extent of lower montane forest coincident with favourable climatic conditions after about AD 1700 was probably caused by Kikuyu immigration and population expansion around that time, as indicated by simultaneous appearance of the food crop Zea mays (maize). Increases in ruderal herbaceous and exotic tree pollen during the twentieth century indicate increased local landscape disturbance during the colonial period. There is little direct pollen evidence for accelerating clearance of the montane forest during recent decades. [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]

Acquired drug resistance is the major cause for disease recurrence in cancer patients, and this is particularly true for patients with metastatic melanoma that carry a BRAF V600E mutation. To address this problem, we investigated cyclic membrane-active peptides as an alternative therapeutic modality to kill drug-tolerant and resistant melanoma cells to avoid acquired drug resistance. We selected two stable cyclic peptides (cTI and cGm), previously shown to have anti-melanoma properties, and compared them with dabrafenib, a drug used to treat cancer patients with the BRAF V600E mutation. The peptides act via a fast membrane-permeabilizing mechanism and kill metastatic melanoma cells that are sensitive, tolerant, or resistant to dabrafenib. Melanoma cells do not become resistant to long-term treatment with cTI, nor do they evolve their lipid membrane composition, as measured by lipidomic and proteomic studies. In vivo studies in mice demonstrated that the combination treatment of cTI and dabrafenib resulted in fewer metastases and improved overall survival. Such cyclic membrane-active peptides are thus well suited as templates to design new anticancer therapeutic strategies. [Display omitted] [ABSTRACT FROM AUTHOR]

The development and application of lacustrine paleotemperature proxies based on microbial membrane lipid structures, including the TEX 86 and branched glycerol dialkyl glycerol tetraether (brGDGT) paleothermometers, have greatly advanced our understanding of the late-glacial and postglacial temperature history of Africa. However, the currently available records are from equatorial and southern hemisphere sites, limiting our understanding of the spatial patterns of temperature change. Here we use the brGDGT paleotemperature proxy to reconstruct Late Pleistocene and Holocene temperatures from Lake Tana, Ethiopia (12°N, 37°E). Following the termination of Heinrich Stadial 1 at ~ 15 ka, Lake Tana experienced a 3.7 °C oscillation over 1.2 ky. Temperatures then increased abruptly by nearly 7 °C between 13.8 and 13.0 ka, followed by a slow warming trend that peaked during the mid Holocene. Temperatures subsequently cooled from ~ 6 ka to ~ 0.4 ka. These data indicate that temperature at Lake Tana was sensitive to climate changes caused by variations in the Atlantic Meridional Overturning Circulation during the Late Pleistocene, as well as to regional hydroclimatic changes and reorganizations of the monsoons. Our record suggests that late-glacial temperature changes in northeast Africa were linked to high-latitude northern hemispheric climate processes, but that subsequent post-glacial temperature variations were strongly influenced by tropical hydrology. [ABSTRACT FROM AUTHOR]

Paleoanthropologists have long speculated about the role of environmental change in shaping human evolution in Africa. In recent years, drill cores of late Neogene lacustrine sedimentary rocks have yielded valuable high-resolution records of climatic and ecosystem change. Eastern African Rift sediments (primarily lake beds) provide an extraordinary range of data in close proximity to important fossil hominin and archaeological sites, allowing critical study of hypotheses that connect environmental history and hominin evolution. We review recent drill-core studies spanning the Plio–Pleistocene boundary (an interval of hominin diversification, including the earliest members of our genus Homo and the oldest stone tools), and the Mid–Upper Pleistocene (spanning the origin of Homo sapiens in Africa and our early technological and dispersal history). Proposed drilling of Africa's oldest lakes promises to extend such records back to the late Miocene. High-resolution paleoenvironmental records are critical for understanding external drivers of human evolution. African lake basin drill cores play a critical role in enhancing hominin paleoenvironmental records given their continuity and proximity to key paleoanthropological sites. The oldest African lakes have the potential to reveal a comprehensive paleoenvironmental context for the entire late Neogene history of hominin evolution. [ABSTRACT FROM AUTHOR]

Understanding eastern African paleoclimate is critical for contextualizing early human evolution, adaptation, and dispersal, yet Pleistocene climate of this region and its governing mechanisms remain poorly understood due to the lack of long, orbitally-resolved, terrestrial paleoclimate records. Here we present leaf wax hydrogen isotope records of rainfall from paleolake sediment cores from key time windows that resolve long-term trends, variations, and high-latitude effects on tropical African precipitation. Eastern African rainfall was dominantly controlled by variations in low-latitude summer insolation during most of the early and middle Pleistocene, with little evidence that glacial–interglacial cycles impacted rainfall until the late Pleistocene. We observe the influence of high-latitude-driven climate processes emerging from the last interglacial (Marine Isotope Stage 5) to the present, an interval when glacial–interglacial cycles were strong and insolation forcing was weak. Our results demonstrate a variable response of eastern African rainfall to low-latitude insolation forcing and high-latitude-driven climate change, likely related to the relative strengths of these forcings through time and a threshold in monsoon sensitivity. We observe little difference in mean rainfall between the early, middle, and late Pleistocene, which suggests that orbitally-driven climate variations likely played a more significant role than gradual change in the relationship between early humans and their environment. [ABSTRACT FROM AUTHOR]

In eastern Africa, there are few long, high-quality records of environmental change at high altitudes, inhibiting a broader understanding of regional climate change. We investigated a Holocene lacustrine sediment archive from Lake Garba Guracha, Bale Mountains, Ethiopia, (3,950 m asl), and reconstructed high-altitude lake evaporation history using δ18O records derived from the analysis of compound-specific sugar biomarkers and diatoms. The δ18Odiatom and δ18Ofuc records are clearly correlated and reveal similar ranges (7.9‰ and 7.1‰, respectively). The lowest δ18O values occurred between 10–7 cal ka BP and were followed by a continuous shift towards more positive δ18O values. Due to the aquatic origin of the sugar biomarker and similar trends of δ18Odiatom, we suggest that our lacustrine δ18Ofuc record reflects δ18Olake water. Therefore, without completely excluding the influence of the 'amount-effect' and the 'source-effect', we interpret our record to reflect primarily the precipitation-to-evaporation ratio (P/E). We conclude that precipitation increased at the beginning of the Holocene, leading to an overflowing lake between ca. 10 and ca. 8 cal ka BP, indicated by low δ18Olake water values, which are interpreted as reduced evaporative enrichment. This is followed by a continuous trend towards drier conditions, indicating at least a seasonally closed lake system. [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]

In this study, we synthesize terrestrial and marine proxy records, spanning the past 620 ky, to decipher pan-African climate variability and its drivers and potential linkages to hominin evolution. We find a tight correlation between moisture availability across Africa to El Niño Southern Ocean oscillation (ENSO) variability, a manifestation of the Walker Circulation, that was most likely driven by changes in Earth's eccentricity. Our results demonstrate that low-latitude insolation was a prominent driver of pan-African climate change during the Middle to Late Pleistocene. We argue that these low-latitude climate processes governed the dispersion and evolution of vegetation as well as mammals in eastern and western Africa by increasing resource-rich and stable ecotonal settings thought to have been important to early modern humans. [ABSTRACT FROM AUTHOR]

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]

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]

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]

The present study aims to review palaeoecological evidence for environmental changes induced by human activities over the last few millennia in the montane landscapes of Morocco. The study is based on well-dated pollen and geochemical records from the Rif and the Middle Atlas mountains, to show spatial and temporal variation in the onset and intensity of exploitation of forest, soil and mineral resources. Before ca. 2000 BP, anthropogenic impact was minimal. At about that time, abrupt changes of the arboreal pollen proportions, with a decline in all tree taxa, indicate a reduction of the forest cover interpreted as being anthropogenic. In the Rif Mountains, increased influx of carbonates (Ca) in the sedimentary records indicates enhanced soil erosion coincident with the reduction in tree cover. In the Middle Atlas, reduced forest cover is linked to geochemical evidence for mining and metallurgy of lead (Pb), copper (Cu) and zinc (Zn). These industrial activities correspond to the expansion of the Roman Empire into Morocco at around AD 40 and show a decline when the Romans were displaced by the Vandals about five centuries later. [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]

The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high-resolution, multi-proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well-constrained chronology is required. This paper outlines the multiple geochronological techniques being applied - namely varve counting, radiocarbon dating, tephrochronology (including argon-argon dating) and optically stimulated luminescence ( OSL) - and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu ( SG06) varve chronology and the absolute ( Int Cal09 tree-ring) time scale, as derived using radiocarbon data from the uppermost (non-varved) portion of the core. This tie-point, defined as a distinct (flood) marker horizon in SG06 (event layer B-07-08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 Int Cal09 cal. years BP (68.2% probability range). [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]

During the past 25 ka, southern Ethiopia has undergone tremendous climatic changes, from dry and relatively cold during the Last Glacial Maximum (LGM, 25–18 ka) to the African Humid Period (AHP, 15–5 ka), and back to present-day dry conditions. As a contribution to better understand the effects of climate change on vegetation and lakes, we here present a new Predictive Vegetation Model that is linked with a Lake Balance Model and available vegetation-proxy records from southern Ethiopia including a new phytolith record from the Chew Bahir basin. We constructed a detailed paleo-landcover map of southern Ethiopia during the LGM, AHP (with and without influence of the Congo Air Boundary) and the modern-day potential natural landcover. Compared to today, we observe a 15–20% reduction in moisture availability during the LGM with widespread open landscapes and only few remaining forest refugia. We identify 25–40% increased moisture availability during the AHP with prevailing forests in the mid-altitudes and indications that modern anthropogenic landcover change has affected the water balance. In comparison with existing archaeological records, we find that human occupations tend to correspond with open landscapes during the late Pleistocene and Holocene in southern Ethiopia. [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]

Leads, lags, or synchronies in climatic events among different regions are key to understanding mechanisms of climate change, as they provide insights into the causal linkages among components of the climate system. The well-studied transition from the Lateglacial to early Holocene (ca. 16–10 ka) contains several abrupt climatic shifts, making this period ideal for assessing the spatio-temporal structure of climate change. However, comparisons of timings of past climatic events among regions often remain hypothetical because site-specific age scales are not necessarily synchronised to each other. Here we present new pollen data (n = 510) and mean annual temperature reconstruction from the annually laminated sediments of Lake Suigetsu, Japan. Suigetsu's 14C dataset is an integral component of the IntCal20 radiocarbon calibration model, in which the absolute age scale is established to the highest standard. Its exceptionally high-precision chronology, along with recent advances in cosmogenic isotope studies of ice cores, enables temporally coherent comparisons among Suigetsu, Greenland, and other key proxy records across regions. We show that the onsets of the Lateglacial cold reversal (equivalent to GS-1/Younger Dryas) and the Holocene were synchronous between East Asia and the North Atlantic, whereas the Lateglacial interstadial (equivalent to GI-1/Bølling-Allerød) started ca. two centuries earlier in East Asia than in the North Atlantic. Bimodal migration (or 'jump') of the westerly jet between north and south of the Tibetan plateau and Himalayas may have operated as a threshold system responsible for the abruptness of the change in East and South (and possibly also West) Asia. That threshold in Asia and another major threshold in the North Atlantic, associated with switching on/off of the Atlantic meridional overturning circulation (AMOC), were crossed at different times, producing a multi-centennial asynchrony of abrupt changes, as well as a disparity of climatic modes among regions during the transitional phases. Such disparity may have disturbed zonal circulation and generated unstable climate during transitions. The intervening periods with stable climate, on the other hand, coincided with the beginnings of sedentary life and agriculture, implying that these new lifestyles and technologies were not rational unless climate was stable and thus, to a certain extent, predictable. [Display omitted] • The Lateglacial cold reversals in Lake Suigetsu (Japan) and NGRIP were synchronous. • The Lateglacial interstadial in Lake Suigetsu began earlier than in Greenland. • 'Postglacial' in Asia started already at ca. 15.0 kyr BP. • S–N migration of the westerly jet generated abrupt deglacial warming in Asia. • Climatic stability was the key for humans to commence agriculture. [ABSTRACT FROM AUTHOR]

Biome reconstruction from pollen and plant macrofossil data provides an objective method to reconstruct past vegetation. Biomes for Africa and the Arabian peninsula have been mapped for 6000 years bp and provide a new standard for the evaluation of simulated palaeovegetation distributions. A test using modern pollen data shows the robustness of the biomization method, which is able to predict the major vegetation types with a high confidence level. The application of the procedure to the 6000 years data set (pollen and plant macrofossil analyses) shows systematic differences from the present that are consistent with the numerous previous regional and continental interpretations, while providing a more extensive and more objective basis for such interpretations. Madagascar, eastern, southern and central Africa show only minor changes in terms of biomes, compared to present. Major changes in biome distributions occur north of 15°N, with steppe in many low-elevation sites that are now desert, and temperate xerophytic woods/scrub and warm mixed forest in the Saharan mountains. These shifts in biome distributions imply significant changes in climate, especially precipitation, between 6000 years and present, reflecting a change in monsoon extent combined with a southward expansion of Mediterranean influence. [ABSTRACT FROM AUTHOR]

Six sites in Ethiopia and Kenya, all adjacent to key paleoanthropological sites have been investigated as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP), aiming at an enhanced understanding of climatic influences on human physical and cultural evolution. The recovered sediment cores from the six sites all together span the last ~3.5 Ma. The sediment core records archive environmental change during diverse milestones in human evolution, and times of dispersal and technological and cultural innovation. The 280 m-long Chew Bahir lacustrine record, recovered from a tectonically-bound basin in the southern Ethiopian rift in late 2014, covers the past ~600 ka of environmental history, a time period that includes the transition to the Middle Stone Age, and the origin and dispersal of modern Homo sapiens. Developing a continuous climate history based on sediment core composition is not straightforward because on one hand some indicators might only be preserved intermittently and on the other hand the physical and chemical properties of the sedimentary deposits do not have a linear relationship to climate. Here we present the first outcome of our ongoing work on deciphering direct paleoenvironmental information from authigenic mineral transformations in the long (~280 m) Chew Bahir sediment cores. First results suggest mineralogical and geochemical indicators record wet, dry and hyper-arid climate intervals. Preliminary work suggests that the most extreme evaporative phases are represented by authigenic mineral assemblages including Mg-enriched clays, low-temperature authigenic illite and euhedral analcime. SEM and Energy Dispersive Spectrometer (EDS) analyses confirm that the variations in the analcime abundance that are evident in the XRD dataset seem to be distinctly formed deltoidal icositetrahedrons. These are known to form in highly saline and alkaline brines (pH 9 and higher) and can be associated with pronounced arid phases. Understanding and determining the degree of authigenic mineral alteration in the Chew Bahir records will enable interpretation of µXRF-derived indicators (e.g. K correlated with aridity), and provide direct paleohydrologic data. Together with a well-constrained age-model, our growing understanding of site-specific proxy formation and the establishment of climate proxies for Chew Bahir will provide a robust environmental history on decadal to orbital timescales. [ABSTRACT FROM AUTHOR]

How do we convert variabilities and trends in hundreds of potential parameters that are typically analyzed in the framework of a scientific drilling project to actual climate proxies? Using the case study from the Chew Bahir core from the southern Ethiopian Rift, we will show that deciphering climate information from lake sediments is challenging, because of the complex relationship between climate parameters and sediment composition. Establishing a reliable climate proxy for a new terrestrial archive requires the stepwise development of a profound understanding of both climate-controlled and non-climate controlled processes in the catchment. As a contribution towards an enhanced understanding of human-climate interactions the Chew Bahir Drilling Project, as part of HSPDP (Hominin Sites and Paleolakes Drilling Project) recovered 280 m-long sediment records from a deep, tectonically-bound basin in the southern Ethiopian rift in late 2014. The Chew Bahir record covers the past ~600 ka of environmental history, a critical time period that includes the transition to the Middle Stone Age, and the origin and dispersal of modern Homo sapiens. By deconvolving the relationship between sedimentological processes and geochemical parameters and strongly climate-controlled processes in the Chew Bahir basin, such as weathering (incongruent dissolution), transportation and authigenic mineral alteration, site-specific indicators for climate shifts on different magnitudes are being developed to eventually provide a detailed and reliable climate record. This study uses a multi indicator approach including whole rock and clay mineral analyses (XRD), XRF geochemistry and sedimentology such as grain size analysis. We will illustrate how sensitively the degree of authigenic transformation in especially clay minerals and zeolites has recorded even subtle shifts in the hydrochemistry of paleolake and porewaters, thereby representing a robust tool for differentiating contrasting chemical environments controlled by climatic change. The precise time resolution, largely continuous record and (eventually) a detailed understanding of site specific proxy formation, will give us a continuous record of environmental history on decadal to orbital timescales. Our data enable us to test current hypotheses of the impact of a variety of climate shifts on human evolution and dispersal. [ABSTRACT FROM AUTHOR]

Investigations on short (≤18.8 m) sediment cores retrieved along a NW-SE transect across the Chew Bahir (CB) basin, Southern Ethiopian Rift, have shown that they can provide valuable climate information (Förster et al., 2012). The relationship between mineralogical and geochemical properties of the core samples is closely linked to the hydroclimate history of the region. During dry climate episodes both the illitization of the smectites and the octahedral Al-to-Mg substitution in the phyllosilicate materials has been documented. An enhanced potassium fixation during dry intervals is also linked to the increase in layer charge caused by the authigenic changes in octahedral composition (Förster et al., 2018). The ongoing work, a non-destructive spectral analysis of reflectance in a wide spectral range from 0.3 to 17 µm on selected core samples from both wet and dry intervals from the long (~280 m) cores from Chew Bahir basin supports this interpretation. The spectral range from 0.3 to 6 µm is suitable for investigating the absorption bands of OH, H2O, M-OH lattice vibrations as well as the crystal field transitions of transition metal ions. This allows a detailed examination and differentiation of various clay minerals as well as indications of single primary minerals (olivine and pyroxene). The wavelength range longward 7 µm provides further mineralogical data such as on the presence of feldspars and the results of the short-wave channel to be substantiated. First results show that the main mineralogical structure is characterized by montmorillonite (rare illite and kaolinite are also present). Strongly variable parts of calcite are also spectrally detectable. Characteristic reflectance minima (Christiansen features) close to 8 µm indicate the presence of Ca-rich plagioclase. The high variability of a band close to 1 µm is used together with the spectral information above 7 µm to identify the diverse individual minerals within the olivine, pyroxene and feldspar group minerals. The results are compared with µXRF scan data and will be further verified by petrographic data of the rocks in the catchment. Overall, the presented spectral study (0.3 to 17 µm) is a suitable and non-destructive method to examine the main mineralogical components of the samples. The results can be directly compared with hyperspectral remote sensing data that are available for the Chew Bahir basin.Förster, V., Junginger, A., Langkamp, O., Gebru, T., Asrat, A., Umer, M., Lamb, H., Wennrich, V., Rethemeyer, J., Nowaczyk, N., Trauth, M.H., Schäbitz, F. (2012) Climatic change recorded in the sediments of the Chew Bahir basin, southern Ethiopia, during the last 45,000 years, Quaternary International, 274, 25-37.Förster, V., Deocampo, D., Asrat, A., Günter, C., Junginger, A., Krämer, H., Stroncik, N., Trauth, M.H. (2018) Towards an understanding of climate proxy formation in the Chew Bahir basin, southern Ethiopian Rift. Palaeogeography, Palaeoclimatology, Palaeoecology, 501, 111-123. [ABSTRACT FROM AUTHOR]

The Chew Bahir Drilling Project (CBDP) aims to test hypothesized linkages between climate and human evolution, dispersal and technological innovation by the acquisition and analysis of long (~280 m) sediment cores that have recorded environmental change in the Chew Bahir basin, southern Ethiopia. In this time-series analysis project, we consider the Chew Bahir palaeolake to be a dynamical system consisting of interactions between its different components, such as the waterbody, the sediment beneath lake, and the organisms living within and around the lake, and humans within the lake catchment. Recurrence is a common feature of such dynamical systems, with recurring patterns in the state of the system reflecting typical influences. Identifying and defining these influences contributes significantly to our understanding of the dynamics of the system.We use methods of linear and nonlinear time series analysis, such as change point detection, semblance analysis and recurrence plots, to identify and classify recurring types of variability and transitions on the time scales of human life spans. For example, we investigate the rapidness of transitions, possible precursor events, and tipping points in our palaeoenvironmental data and discuss their possible impact on the living conditions of humans in the region. First results of the analysis show that we indeed find, as an example, recurring threshold-type transitions, when the Chew Bahir system switched from one stable mode to another, such as from stable wet to dry conditions. Such a rapid change of climate in response to a relatively modest change in forcing appears to be typical of tipping points in complex systems such as the Chew Bahir. If this is the case then the 14 dry events idenfified at the end of the African Humid Period (15–5 kyr BP) could represent precursors of an imminent tipping point that, if properly interpreted, would allow predictions to be made of future climate change in the Chew Bahir basin. [ABSTRACT FROM AUTHOR]

The sediments of the Chew Bahir playa lake in southern Ethiopia were cored down to 280 m depth in the context of HSPDP (Hominin Sites and Paleolakes Drilling Project) and CRC (Collaborative Research Center) 806 "Our way to Europe" projects. The main aim is to reconstruct the paleoenvironmental conditions during the development of anatomically modern humans (AMH) and to test hypotheses about human evolution, dispersal and technological innovation. Based on several dating methods (14C, Ar/Ar, optical stimulated luminescence, chemical fingerprints of tephras) the composite core is shown to cover the last ~600 ka and therefore brackets the time period of important steps in cultural evolution, from Late Acheulean to Middle/Late Stone Age technologies, the origin of AMH, as well as the most recent "Out of Africa" human dispersal events. The multiproxy record of the composite core (e.g., chemical and physical sediment properties, stable C, O and Sr isotope ratios of carbonates, microfossil assemblages and biomarkers) indicates long- and short-time hydroclimatic changes mainly driven by orbital controlled insolation (mostly the Earth's precession ~15-25 ka, but also eccentricity ~90-120 ka). We compare our Chew Bahir data with results from other long marine and terrestrial paleoclimatic records. Here we focus on particularly strong wet and dry fluctuations at Chew Bahir during the last 200 ka to test established hypotheses for human dispersal and technological innovation. The record indicates that at least some of the human dispersal waves have taken place during wetter environmental conditions offering green corridors in East Africa, one of the source regions of our ancestors. [ABSTRACT FROM AUTHOR]

Cores from terrestrial archives, such as the lacustrine sediments from the Chew Bahir basin in southern Ethiopia, which cover the last ~600 ka, often reflect both local, regional and global climate influences. In our analysis we were able to identify several time windows in which the Chew Bahir climate is in resonance with regional and global climate change.As a contribution to understanding and differentiating these connections recorded in the Chew Bahir sediments, we have correlated the 2nd principal component of the MSCL based color reflectance values representing wet conditions in the Chew Bahir basin, with the wetness index from ocean core ODP 967 from the eastern Mediterranean Sea. The correlation between these two time series was calculated using the Spearman correlation coefficient in a sliding window. Episodes with high correlation between the two records of wetness could indicate a strong link between both regions, possibly through an increased outflow of the river Nile into the eastern Mediterranean Sea due to higher precipitation values on the Ethiopian plateau.Our preliminary results show that when correlating the two records, two distinct temporal units can be distinguished. Between ~570 ka and ~350 ka the correlation is dominated by cycles that correspond with orbital precession whereas the second unit (after 350 ka) reveals a strong influence of atmospheric CO2. This observation suggests that both orbital precession and atmospheric CO2. may cause a synchronization of different regions in the African climate system, possibly depending on boundary conditions which are still to be identified.As a next step we'll investigate the nonlinear relationships between the two records by focusing on the transition between the two main observed phases. The transition around ~350 kyrs however, is not only highly interesting from a climatic perspective, but it is also a noteworthy period for human cultural evolution as a transition from Acheulean to Middle Stone Age (MSA) technologies takes place at this time. So far our results outline that during this climatically and evolutionary relevant episode a relatively stable, long-lasting, pan-African wet phase may have existed, with possible green corridors connecting the habitats of hominins, and ample resources supporting large population sizes. [ABSTRACT FROM AUTHOR]

Eastern African hydroclimate in the early Holocene created a lush landscape in what iscommonly referred to as the African Humid Period (AHP: ∼15 to 5 ka). The termination ofthe AHP was characterised by a climatic shift towards drier conditions. This resulted in thedesiccation of many lakes and may have pressured hunter-gather societies to move towardsconcentrated pastoralist settlements at the shores of the few remaining lake areas or rivervalleys. During the AHP, Lake Chew Bahir, in the East African Rift System, was presumablyexpansive with a paleo-shoreline ∼30 m higher than present day, and likely served as animportant freshwater source and refugia. Today it is a predominantly dry playamudflat with ephemeral swamps in the deltaic areas. Strontium (Sr) isotope ratios(87Sr/86Sr) preserved in carbonate-rich lacustrine strata provide regionally-specificrecords of past variability in weathering and regional drainage patterns. Duringhumid episodes, the Chew Bahir catchment expands northwards to include theChamo and Abaya catchments. As these catchments are dominated by volcaniclithology, with low Sr isotopic ratios, additional water inflow from here can potentiallychange the overall Sr isotope ratio of the lake water in Chew Bahir in a measurableway. This study aims to reconstruct the hydrobalance of paleolake Chew Bahir using athree-step approach. We first establish the Sr isotope ratio of the input end members bysampling modern waters from the Chew Bahir and adjacent catchments, includinggroundwater, lakes, springs and rivers. We then analyse the Sr isotope ratios of microfossilsfrom the time period of the most recent AHP lake level high-stand from three shortcores (CB05, CB06 and CB03) along a transect from the centre to the westernmargin of the Chew Bahir basin. Finally, we use the paleo Sr isotope record over thelast 15 ka to develop an isotopically-enabled hydrobalance model to quantify pastlake levels. Over the last ∼15 ka 87Sr/86Sr ranges from 0.7059 to 0.7066, withhigher values during the start of the AHP, decreasing towards the termination. Thissuggests a larger input of water entering paleolake Chew Bahir from the northerlycatchments and paleo-connectivity of these lake systems during humid periods.This study provides valuable data for reconstructing millennial-scale change inhydrobalance and freshwater availability, in a highly-sensitive climate region, overa key time period for the transition from hunter-gather societies to pastoralism. [ABSTRACT FROM AUTHOR]