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Here, we evaluate the ability of micro X‐ray fluorescence (µXRF) core scanning to identify non‐visible volcanic ash (cryptotephra) layers in sedimentary records. Its suitability is assessed using the annually resolved lacustrine sediments of Lake Suigetsu (Japan) for which there is high‐resolution ITRAX µXRF core scanning data, and a detailed crypto‐tephrostratigraphy (formerly established via density separation techniques). The studied core sections contain 10 visible and 30 cryptotephra markers that span a range of glass concentrations (from 1000 to >20 000 shards per gram of dried sediment) and compositions (basalts, trachy‐andesites, phonolites, trachytes and rhyolites), thus providing an ideal case study. The ITRAX core scanner produced recognisable µXRF elemental responses for the visible ash layers, including those just 1 mm thick. However, just 10% of the cryptotephra layers could be unequivocally identified. Although this study demonstrates that µXRF core scanning should not be used as an independent method within a similar geological setting, we show it can provide a powerful tool alongside traditional techniques. Where detected, µXRF profiles can verify and refine cryptotephra positions (here to a sub‐millimetre resolution), and help establish reworking signatures. These insights create possibilities for ultra‐precise synchronisation of records, improved chronological modelling and help generate more complete eruption histories. [ABSTRACT FROM AUTHOR]

Terrestrial plant macrofossils from the sedimentary record of Lake Suigetsu, Japan, provide the only quasi-continuous direct atmospheric record of radiocarbon (14C) covering the last 50 ka cal BP (Bronk Ramsey et al. 2012). Since then, new high precision data have become available on U-Th dated speleothems from Hulu Cave China, covering the same time range (Cheng et al. 2018). In addition, an updated varve-based chronology has also been published for the 2006 core from Lake Suigetsu (SG06) based on extended microscopic analysis of the sediments and improved algorithms for interpolation (Schlolaut et al. 2018). Here we reanalyze the radiocarbon dataset from Suigetsu based on the new varve counting information and the constraints imposed by the speleothem data. This enables the new information on the calendar age scale of the Suigetsu dataset to be used in the construction of the consensus IntCal calibration curve. Comparison of the speleothem and plant macrofossil records provides insight into the mechanisms underlying the incorporation of carbon into different types of record and the relative strengths of different types of archive for calibration purposes. [ABSTRACT FROM AUTHOR]

The varved sediment profile of Lake Suigetsu, central Japan, offers an ideal opportunity from which to derive a terrestrial record of atmospheric radiocarbon across the entire range of the 14C dating method. Previous work by Kitagawa and van der Plicht (1998a,b, 2000) provided such a data set; however, problems with the varve-based age scale of their SG93 sediment core precluded the use of this data set for 14C calibration purposes. Lake Suigetsu was re-cored in summer 2006, with the retrieval of overlapping sediment cores from 4 parallel boreholes enabling complete recovery of the sediment profile for the present "Suigetsu Varves 2006" project (Nakagawa et al. 2012). Over 550 14C determinations have been obtained from terrestrial plant macrofossils picked from the latter SG06 composite sediment core, which, coupled with the core's independent varve chronology, provides the only non-reservoir-corrected 14C calibration data set across the 14C dating range. Here, physical matching of archive U-channel sediment from SG93 to the continuous SG06 sediment profile is presented. We show the excellent agreement between the respective projects' 14C data sets, allowing the integration of 243 14C determinations from the original SG93 project into a composite Lake Suigetsu 14C calibration data set comprising 808 individual 14C determinations, spanning the last 52,800 cal yr. [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: 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]

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]

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: 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]

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]

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]