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Inorganic geochemistry is a powerful tool in paleolimnology. It has become one of the most commonly used techniques to analyze lake sediments, particularly due to the development and increasing availability of XRF core scanners during the last two decades. It allows for the reconstruction of the continuous processes that occur in lakes and their watersheds, and it is ideally suited to identify event deposits. How earth surface processes and limnological conditions are recorded in the inorganic geochemical composition of lake sediments is, however, relatively complex. Here, we review the main techniques used for the inorganic geochemical analysis of lake sediments and we offer guidance on sample preparation and instrument selection. We then summarize the best practices to process and interpret bulk inorganic geochemical data. In particular, we emphasize that log-ratio transformation is critical for the rigorous statistical analysis of geochemical datasets, whether they are obtained by XRF core scanning or more traditional techniques. In addition, we show that accurately interpreting inorganic geochemical data requires a sound understanding of the main components of the sediment (organic matter, biogenic silica, carbonates, lithogenic particles) and mineral assemblages. Finally, we provide a series of examples illustrating the potential and limits of inorganic geochemistry in paleolimnology. Although the examples presented in this paper focus on lake and fjord sediments, the principles presented here also apply to other sedimentary environments. • Inorganic geochemical proxies are not universally applicable. • Simple multivariate statistics allow associating elements with sediment components. • Variations in most elements reflect sediment grain size and provenance. • Log-ratios effectively reduce the limitations inherent to XRF core scanner analysis. [ABSTRACT FROM AUTHOR]

The sediment profile from Lake Gościąż in central Poland comprises a continuous, seasonally resolved and exceptionally well‐preserved archive of the Younger Dryas (YD) climate variation. This provides a unique opportunity for detailed investigation of lake system responses during periods of rapid climate cooling (YD onset) and warming (YD termination). The new varve record of Lake Gościąż presented here spans 1662 years from the late Allerød (AL) to the early Preboreal (PB). Microscopic varve counting provides an independent chronology with a YD duration of 1149+14/–22 years, which confirms previous results of 1140±40 years. We link stable oxygen isotopes and chironomid‐based air temperature reconstructions with the response of various geochemical and varve microfacies proxies especially focusing on the onset and termination of the YD. Cooling at the YD onset lasted ~180 years, which is about a century longer than the terminal warming that was completed in ~70 years. During the AL/YD transition, environmental proxy data lagged the onset of cooling by ~90 years and revealed an increase of lake productivity and internal lake re‐suspension as well as slightly higher detrital sediment input. In contrast, rapid warming and environmental changes during the YD/PB transition occurred simultaneously. However, initial changes such as declining diatom deposition and detrital input occurred already a few centuries before the rapid warming at the YD/PB transition. These environmental changes likely reflect a gradual increase in summer air temperatures already during the YD. Our data indicate complex and differing environmental responses to the major climate changes related to the YD, which involve different proxy sensitivities and threshold processes. [ABSTRACT FROM AUTHOR]

Investigating past interglacial climatic and environmental changes can enhance our understanding of the natural rates and ranges of climate variability under interglacial boundary conditions. However, comparing past interglacial palaeoclimate records from different regions and archives is often complicated by differing and uncertain chronologies. For instance, the duration of the Last Interglacial in Europe is still controversial as southern European palaeoclimate records suggest a duration of ~16 500–18 000 years, while a length of only ~11 000 years in northern‐central Europe was previously inferred from the analysis of partly annually laminated (varved) palaeolake sediments recovered at Bispingen, northern Germany. To resolve this discrepancy, we here present sediment microfacies, geochemistry and pollen data from a new sediment core from the Bispingen palaeolake sediment succession, covering the entire Last Interglacial (Eemian) and the earliest part of the Last Glacial (Weichselian). In particular, we provide evidence that the duration of the Last Interglacial at Bispingen must have been hitherto underestimated due to the investigation of an incomplete sediment core. Using microscopic varve counting and sedimentation rate estimates for non‐varved sections on the new sediment core, we show that the Eemian in northern‐central Europe probably lasted at least ~15 000 years, about 4000 years longer than previously thought. This new duration estimate is in much better agreement with results from southern European palaeoclimate records, clarifying the enigma of a steep trans‐European vegetation gradient for several millennia at the end of the Last Interglacial. [ABSTRACT FROM AUTHOR]

Marine sediments from continental margins provide high-resolution archives of marine and continental climate, in particular near large river mouths. The Zambezi is one of the largest rivers in East Africa, discharging large amounts of fine-grained sediments onto the western margin of the Mozambique Channel. Accurate reconstructions of past variations in river discharge can be retrieved from the depositional history of riverine sediments. In this study, sedimentation patterns along the Mozambique Margin are inferred from a series of sediment cores spanning the last 20 kyr. These cores were retrieved off the Zambezi Mouth from the shelf and from various depths at the continental slope to provide detailed information on the depositional history of this region. High-resolution X-ray fluorescence and magnetic susceptibility core scanning measurements as well as grain-size distributions of the lithogenic sediment fraction, and organic matter and carbonate content analyses resolve centennial--millennial timescale variations in sediment transport and deposition along the Mozambique Margin. Largest changes in lithogenic sediment deposition coincide with the flooding of the Mozambique Shelf. Due to deglacial sea-level rise and changes in oceanic currents, fine-grained, mainly Zambezi sediments were no longer primarily deposited south of the Zambezi Mouth, but increasingly deposited onto the Mozambique Shelf, and transported northwards over the shelf before spilling over to the slope. In addition, flooding of the shelf initiated remobilization and down-slope transport of coarse-grained, winnowed sediments. The Heinrich Event 1 and Younger Dryas are clearly indicated as events of increased fine-grained sediment deposition along the Mozambique Margin, possibly linked to increased riverine runoff from the Zambezi Catchment, which is in harmony with a southward shift of the Intertropical Convergence Zone (ITCZ) and associated African rainfall belts, causing wetter conditions. This study illustrates that interpreting marine and continental climate proxy records in the vicinity of river deltas in terms of climate change requires proper consideration of sea-level and oceanic circulation induced effects on the transport and deposition patterns of fine-grained sediments at continental slopes. [ABSTRACT FROM AUTHOR]

Abstract: A multi-proxy reconstruction of a sediment core from the Tatos basin in the Mauritian lowlands reveals a dynamic environmental history during the last 8000 years. Under influence of sea level rise, the basin progressed from a wetland to a shallow lake between 8000 and 2500 cal yr BP and it slowly changed back into a wetland after sea level reached its highest position at around 2500 cal yr BP. The groundwater level in the basin was strongly affected by sea level rise and precipitation-forced runoff through the porous volcanic bedrock. Millennial-scale precipitation changes in the Mauritian lowlands were derived from the pollen records of semi-dry forest and palm woodland. Salinity and environmental reconstructions based on diatoms, ostracods, stable isotopes and sediment composition showed numerous decadal and centennial droughts and wet events. Mauritius experienced wet conditions between ∼8000 and ∼6800 cal yr BP, followed by decreasing humidity from 6800 to 6000 cal yr BP. Dry conditions persisted until ∼1200 cal yr BP, after which wetter conditions have prevailed as recorded from Mauritian lowland and upland records. Climate dynamics reflects northern hemisphere monsoon activity and suggest that Mauritian rainfall and the Indian and Asian summer monsoons are linked, as both receive moisture from the southern equatorial Indian Ocean. The anti-phased relationship of climate dynamics between the Mauritian lowlands and western tropical Australia during the middle Holocene is interpreted as a prolonged configuration of a negative mode of the Indian Ocean Dipole (IOD). A negative IOD-like state is supported by decreased Asian summer monsoon rainfall, higher Austral-Indonesian summer monsoon rainfall and lower temperatures in the Kilimanjaro record. Conversely, repeated decadal-scale wet events in the Mauritian lowlands occurring every ∼350 years reflect short positive IOD-like events. The onset of ENSO climate variability followed an anomalously strong negative IOD-like event and shifted teleconnections from the tropical Indian Ocean to the Pacific Ocean. A shift in ENSO activity around ∼2600 cal yr BP signifies the decoupling of ENSO from the Atlantic ITCZ. Subsequently, the influence of ENSO on climate in the western Indian Ocean is indicated by increased storm frequency and drought events after 2660 cal yr BP in Mauritius and reduced monsoon activity in the western and eastern Indian Ocean. [Copyright &y& Elsevier]

Abstract: Sediments deposited on deep-sea fans are an excellent geological archive to reconstruct past changes in fluvial discharge. Here we present a reconstruction of changes in the regime of the Nile River during the Holocene obtained using bulk elemental composition, grain-size analyses and radiogenic strontium (Sr) and neodymium (Nd) isotopes from a sediment core collected on the Nile deep-sea fan. This 6-m long core was retrieved at water-depth and is characterized by the presence of a 5-m thick section of finely laminated sediments, which were deposited between 9.5 and 7.3ka BP and correspond to the African Humid Period (AHP). The data show distinct changes in eolian dust inputs as well as variations in discharge of the Blue Nile and White Nile. Sedimentation was mainly controlled by changes in fluvial discharge during the Holocene, which was predominantly forced by low-latitude summer insolation and by the location of the eastern African Rain Belt. The changes in relative contribution from the Blue Nile and White Nile followed changes in low-latitude spring/autumn insolation, which highlights the role of changes in seasonality of the precipitation on the Nile River regime. The relative intensity of the Blue Nile discharge was enhanced during the early and late Holocene at times of higher spring insolation (with massive erosion and runoff during the AHP at times of high summer insolation), while it was reduced between 8 and 4ka at times of high autumn insolation. The gradual insolation-paced changes in fluvial regime were interrupted by a short-term arid event at 8.5–7.3ka BP (also associated with rejuvenation of bottom-water ventilation above the Nile fan), which was likely related to northern hemisphere cooling events. Another arid event at 4.5–3.7ka BP occurred as the apex of a gradually drier phase in NE Africa and marks the end of the AHP. [Copyright &y& Elsevier]

Abstract: The sediments in the upwelling area off central Vietnam are totally bioturbated and display a low-diverse assemblage of bioturbational structures. During interglacial times (Marine Isotope Stage MIS 1, 5a, 5c, 5e), summer monsoon leads to pronounced upwelling and seasonally pulsed arrival of organic matter on the seafloor. These deposits are characterized by a 4-tier bioturbated zone with Zoophycos. Zoophycos producers used this seasonal food source and show a cache behavioral strategy. During glacial periods upwelling was weak and oxygenation of bottom water decreased as evidenced by bioturbational structures that show a decrease in size, penetration depth and diversity. Enlarged freshwater influx during glacial times fuelled primary production and led to estuarine circulation. The resultant oxygen minimum layer favored an increased deposition of organic matter that in turn affected sediment properties. During MIS 2 and 5b oxygenation was probably a little lower than today. During MIS 3 and 5d Chondrites-like burrows point to a stronger oxygen deficiency. During MIS 4 bottom water oxygenation was even lower and only biodeformational structures occur in soft sediment rich in benthic food. Based on these findings an ichnofabric model for food-rich, fairly soft deposits experiencing oxygen deficiency is suggested having biodeformational structures as low-oxygen end member. [Copyright &y& Elsevier]

Abstract: The abrupt transition from fluvial to marine deposition of incised-valley-fill sediments retrieved from the southeast Vietnamese shelf, accurately records the postglacial transgression after 14ka before present (BP). Valley-filling sediments consist of fluvial mud, whereas sedimentation after the transgression is characterized by shallow-marine carbonate sands. This change in sediment composition is accurately marked in high-resolution X-ray fluorescence (XRF) core scanning records. Rapid aggradation of fluvial sediments at the river mouth nearly completely filled the Mekong incised valley prior to flooding. However, accumulation rates strongly reduced in the valley after the river-mouth system flooded and stepped back. This also affected the sediment supply to deeper parts of the southeast Vietnamese shelf. Comparison of the Mekong valley-filling with the East Asian sea-level history of sub- and inter-tidal sediment records shows that the transgressive surface preserved in the incised-valley-fill records is a robust sea-level indicator. The valley was nearly completely filled with fluvial sediments between 13.0 and 9.5 kaBP when sea-level rose rather constantly with approximately 10 mm/yr, as indicated by the East Asian sea-level record. At shallower parts of the shelf, significant sediment reworking and the establishment of estuarine conditions at the final stage of infilling complicates accurate dating of the transgressive surface. Nevertheless, incised-valley-fill records and land-based drill sites indicate a vast and rapid flooding of the shelf from the location of the modern Vietnamese coastline to the Cambodian lowlands between 9.5 ka and 8.5 kaBP. Fast flooding of this part of the shelf is related with the low shelf gradient and a strong acceleration of the East Asian sea-level rise from 34 to 9 meter below modern sea level (mbsl) corresponding to the sea-level jump of melt water pulse (MWP) 1C. [Copyright &y& Elsevier]

Abstract: On-line analysis of split sediment cores by XRF core scanners has become increasingly popular in the past decade, because it allows nondestructive extraction of near-continuous records of element intensities from sediment cores with a minimum of analytical effort. A disadvantage of XRF core scanning relative to conventional geochemical analysis is the problematic conversion of core-scanner output to element concentrations. The main reason for this long-standing problem is the poorly constrained measurement geometry, attributable to inhomogeneity of the specimens (e.g. variable water content and grain-size distribution), irregularities of the split core surface, and in some setups, spatial variations in thickness of an adhesive pore-water film which forms directly below a protective foil covering the core surface. We propose a log-ratio calibration model for XRF core scanners, derived from a combination of XRF-spectrometry theory, principles of compositional data analysis, and empirical evidence. The log-ratio calibration model provides accurate and precise predictions of sediment composition (element concentrations) from XRF core-scanner output with a limited number of parameters, namely 2(D −1), where D equals the number of chemical elements whose concentrations are to be estimated. The model can accommodate the inherent non-linearity of the relation between (relative) intensities and concentrations, which is apparent from the fact that it provides unbiased estimates. An immediate corollary of our results is that log-ratios of element intensities, which are related to log-ratios of element abundances by a simple linear transformation, provide the most easily interpretable signals of relative changes in chemical composition. Consistent use of log-ratios of element intensities or concentrations should minimise the risk of drawing erroneous conclusions from geochemical proxies. The relative standard deviation (precision) of predicted element concentrations in core GeoB7920 is less than 2%. Stochastic simulations indicate that this level of precision can be attained with 40 randomly selected calibration specimens. Improved control over input errors and development of robust goodness-of-fit statistics allows XRF core scanning to be developed into a rigorous quantitative measurement technology. The log-ratio calibration equation derived in this study may be adapted to inter-laboratory and inter-instrument calibration as well. [Copyright &y& Elsevier]

Robust chronologies and time equivalent tephra markers are essential to better understand spatial palaeoenvironmental response to past abrupt climatic changes. Identification of well-dated and widely dispersed volcanic ash by tephra and cryptotephra (microscopic volcanic ash) provides time synchronous tie-points and strongly reduces chronological uncertainties. Here, we present the major, minor and trace element analyses of cryptotephra shards in the Dead Sea Deep Drilling sedimentary record (DSDDP 5017-1A) matching the Campanian Ignimbrite (CI). This geochemical identification expands the known dispersal range of the CI to the southeastern Mediterranean, over 2300 km from the volcanic source. Due to the CI eruption occurring near-synchronous with North Atlantic ice surge of Heinrich Event 4 (HE4), this tephra provides insights into regional responses to large-scale climatic change in the Mediterranean. In the Dead Sea, the CI layer is associated with wetter climatic conditions. This contrasts with the contemporaneous occurrence of the CI deposition and dry conditions in the central and eastern Mediterranean suggesting a possible climate time-transgressive expansion of HE4. Our finding underscores the temporal and spatial complexity of regional climate responses and emphasises the importance of tephra as a time marker for studying large-scale climatic changes verses regional variations. [ABSTRACT FROM AUTHOR]

The Altiplano-Puna Plateau of the Central Andes hosts numerous lakes, playa-lakes, and salars with a great diversity and abundance of carbonates forming under extreme climatic, hydrologic, and environmental conditions. To unravel the underlying processes controlling the formation of carbonates and their geochemical signatures in hypersaline systems, we investigated coupled brine-carbonate samples in a high-altitude Andean lake using a wide suite of petrographic (SEM, XRD) and geochemical tools (δ2H, δ18O, δ13C, δ11B, major and minor ion composition, aqueous modelling). Our findings show that the inflow of hydrothermal springs in combination with strong CO 2 degassing and evaporation plays an important role in creating a spatial diversity of hydro-chemical sub-environments allowing different types of microbialites (microbial mounds and mats), travertines, and fine-grained calcite minerals to form. Carbonate precipitation occurs in hot springs triggered by a shift in carbonate equilibrium by hydrothermal CO 2 degassing and microbially-driven elevation of local pH at crystallisation. In lakes, carbonate precipitation is induced by evaporative supersaturation, with contributions from CO 2 degassing and microbiological processes. Lake carbonates largely record the evaporitic enrichment (hence salinity) of the parent water which can be traced by Na, Li, B, and δ18O, although other factors (such as e.g., high precipitation rates, mixing with thermal waters, groundwater, or precipitation) also affect their signatures. This study is of significance to those dealing with the fractionation of oxygen, carbon, and boron isotopes and partitioning of elements in natural brine-carbonate environments. Furthermore, these findings contribute to the advancement in proxy development for these depositional environments. [ABSTRACT FROM AUTHOR]

Salt caverns result from solution mining of bedded or domal saline structures. Such caverns are gaining in importance as a temporary geological storage for fluctuating renewables with view to securing a stable energy supply.Generally, salt rocks are regarded as highly impermeable and their geomechanical and hydraulic properties are well constrained. However, to assure the integrity of caverns during operation and long term abandonment, knowledge of geochemical rock-water interactions in the transition zone between cavity and salt rock is necessary. Of special interest are intercalations of potassium-rich salt beds that show different characteristics in terms of dissolution-recrystallization reactions.Due to the inaccessibility of cavern walls, a set of lab-based experimental simulations were performed mimicking cavern leaching. In large hand specimen cm-sized cavities were created by coupling fresh water injection and brine removal. Afterwards, the samples were cut to expose the cavity and its surrounding rim. For the identification of mineral composition around the cavity two techniques were used.Micro X-ray Fluorescence mapping was employed to obtain information on element distribution to conclude on mineral compositions. Analyses were performed every 50 m on the rock surface around the cavern. The mapping results provide details on the distribution of the elements Na, Mg, Al, Si, S, Cl, K, Ca, Fe, Br, Sr and can be associated with the main salt-minerals assemblages. The XRF mapping results reveal a clear separation between Na, Mg and K salt layers. Furthermore, hyperspectral image analyses were used to characterize the spatial distribution of minerals due to their spectral footprints. Image spectroscopy covers the optical and short-wave infrared regions across the 400-2500 nm spectral range.First results are presented here, showing that these methods are promising in detecting mineral dissolution and precipitation reaction in salt and are, thus, useful tools in unravelling geochemical processes related to marginal areas of cavernous structures in salt deposits. [ABSTRACT FROM AUTHOR]

Reading the sediment record in terms of past climates is challenging since linking climate change to the associated responses of sedimentary systems is not always straightforward. Here we analyze the erosional response of landscapes on the Tibetan Plateau to interglacial climate forcing. Using the theory of dynamical systems on Holocene time series of geochemical proxies, we derive a sedimentary response model that accurately simulates observed proxy variation in three lake records. The model suggests that millennial variations in sediment composition reflect a self‐organization of landscapes in response to abrupt climate change between 11.6 and 11.9 ka BP. The self‐organization is characterized by oscillations in sediment supply emerging from a feedback between physical and chemical erosion processes, with estimated response times between 3,000 to 18,000 years depending on catchment topography. The implications of our findings emphasize the need for landscape response models to decipher the paleoclimatic code in continental sediment records. Plain Language Summary: Lake sediments are an important source of information on past climates. Reading the information is not always straightforward. Complex interactions in landscapes can affect the transmission of climatic signals to the sediment record. However, the exact nature of such complex interactions remains unknown. This study compares sediment deposits of three lakes on the Tibetan Plateau. The deposits are continuous records of landscape responses to climate change during the last 12,000 years. We identified a mathematical model that accurately simulates changes in sediment composition at all sites. The model simulations suggest that an abrupt warming at the end of the last glacial period destabilized the landscapes. This caused fluctuations in the transport of sediments, which persisted for several thousand years. Our findings present evidence for a long‐lasting impact of abrupt climate change on fundamental Earth surface processes. Key Points: We analyzed the propagation of climatic signals to Holocene sediment records of three well‐studied Tibetan lakes in a dynamical system frameworkHolocene variation in geochemical proxies mainly reflect site‐specific landscape responses to abrupt climate changeOur results indicate a feedback between physical and chemical erosion processes on interglacial timescale [ABSTRACT FROM AUTHOR]

To reconstruct naturally and anthropogenically induced environmental change in SE Europe since the Little Ice Age, we have examined five partially varved sediment cores from coastal Lake Vouliagmeni, Greece. Our reconstructions are based on a multi-proxy approach including microfacies analysis, X-ray fluorescence core scanning, radionuclide dating (210Pb, 137Cs, and 241Am), and palynological analysis (pollen, spores, and dinoflagellate cysts). A 131 -cm-long composite record that encompasses the past c. 300 years reveals 181 varves of endogenic and mixed clastic-biogenic types. The formation of these varves was controlled by seasonal variability in clastic input and primary productivity. The non-varved intervals consist of homogenous lake sediments and turbidite deposits. Based on a chronology developed through radionuclide dating, varve counting and exclusion of turbidites from the sequence, we have compared our proxy data with meteorological data and historical records of earthquakes and human activities. Our results suggest that the surroundings of Lake Vouliagmeni experienced relatively wet conditions during the late solar Maunder Minimum (1645–1715 AD) and relatively dry conditions during the Dalton Minimum (1790–1830 AD), which highlights the hydroclimatic heterogeneity in SE Europe during the Little Ice Age. The evaluation of historical documentation suggests that the majority of the turbidites is related to lake-slope instabilities following earthquake shocks. Human impact on Lake Vouliagmeni includes (i) a change in aquatic biota following the artificial connection of the lake to the sea at c. 1880 AD, and (ii) expansion of agricultural areas and reduction of natural forests around the lake due to population growth over the past 300 years. [ABSTRACT FROM AUTHOR]

The introduction and application of high resolution XRF core scanners has made an enormous contribution to palaeoclimate science over the last two decades. These core scanners have become essential analytical tools for the investigation of sedimentary and other natural cumulative records of environmental change. Their widespread adoption by the environmental and geoscience communities has had a significant impact on the ability to systematically record high resolution chemical profiles in marine and lake sediments and soils. The range of applications has broadened beyond sedimentology and palaeoclimatology and now extends into scanning samples of speleothems, corals, mumiyo mounds, rocks, sedimentary nodules, archaeological artefacts, tree sections and melt segregations. Other areas exploiting the capability of XRF core scanners are mineral exploration, geotechnical characterisation, soil remediation studies and carbon capture and storage research. As a consequence of their ability to efficiently determine detailed, non-destructive elemental records in sediments and soils, scientific papers published since the year 2000 now number more than 1000. [ABSTRACT FROM AUTHOR]

The trace-metal composition of sediments provides important information on (past) environmental conditions, such as bottom water oxygenation, marine productivity, sediment provenance, and pollution. Whereas major and minor elements are often routinely analyzed using X-Ray Fluorescence (XRF) core scanning, analysis of trace metals with the same method is not yet established as a routine procedure. Here, we used a recently developed state-of-the-art XRF detector with a core scanner (Avaatech) to examine the optimal settings for analyzing a suite of trace metals (V, Cr, Ni, Cu, Zn, Mo, and U). Settings were optimized for fast analyses of sediment cores by extensive testing of primary energy settings, filters, and exposure times on two eastern Mediterranean Sea sapropel layers that archive episodes of past sea-floor anoxia. We reveal the following most advantageous (i.e., optimized for analytical accuracy and time efficiency) settings: (1) V, Cr, Ni at 20 kV with aluminum primary beam filter, (2) Cu, Zn, and U at 30 kV with 'thick' (125 μm) palladium primary beam filter, and (3) Mo at 50 kV with copper primary beam filter. For these trace elements, generally, ≥30 s of measurement are required for obtaining reliable data. Synthetic mixtures show that matrix effects, which are inherent to XRF analyses, are of particular importance for V. A correction for these matrix effects on V (e.g., using Compton scattering) may be necessary for samples with a large variability in carbonate content. XRF core-scanning measurements on synthetically, laminated sediments show that trace metals with contrasting atomic weights and related XRF penetration depths (V and Mo) can be determined at sub-mm resolution. We show that intensity results from the new XRF detector can be converted into concentrations using multivariate log-ratio calibration, allowing a fast quantitative prediction of sedimentary trace metal content using XRF core scanning. [ABSTRACT FROM AUTHOR]

In-depth understanding of the reorganization of the hydrological cycle in response to global climate change is crucial in highly sensitive regions like the eastern Mediterranean, where water availability is a major factor for socioeconomic and political development. The sediments of Lake Lisan provide a unique record of hydroclimatic change during the last glacial to Holocene transition (ca. 24–11 ka) with its tremendous water level drop of ~ 240 m that finally led to its transition into the present hypersaline water body—the Dead Sea. Here we utilize high-resolution sedimentological analyses from the marginal terraces and deep lake to reconstruct an unprecedented seasonal record of the last millennia of Lake Lisan. Aragonite varve formation in intercalated intervals of our record demonstrates that a stepwise long-term lake level decline was interrupted by almost one millennium of rising or stable water level. Even periods of pronounced water level drops indicated by gypsum deposition were interrupted by decades of positive water budgets. Our results thus highlight that even during major climate change at the end of the last glacial, decadal to millennial periods of relatively stable or positive moisture supply occurred which could have been an important premise for human sedentism. [ABSTRACT FROM AUTHOR]

Highlights: [•] Degradation of IPL GDGTs in a reoxidized sediment was dependent on head group. [•] TEX86 of IPL, but not CL GDGTs, changed via production and differential degradation. [•] Good preservation of glyco GDGTs discourages use as biomarkers for live Archaea. [•] Harsh oxidation events can alter TEX86 and other proxy values of IPL GDGTs. [•] Distribution changes in IPL GDGTs can be caused by differential degradation. [Copyright &y& Elsevier]

Connecting pathways are essential for cultural and economic exchange. Commonly, historians investigate the role of routes for cultural development, whereas the environmental impacts of historical routes attract less attention. Here, we present a high-resolution reconstruction of the impact of the major trade route via Marchionis in the southern Baltic lowlands on landscape evolution since more than 800 years. We combine precisely dated annually laminated sediments from Lake Czechowskie alongside via Marchionis and pollen data at 5-year resolution together with historical data. The transformation from a quasi-natural to a cultural landscape occurred in three phases (1) an early phase until the mid-fourteenth century with slowly increasing human impact. (2) an intensification of environmental disturbance until (3) the mid-nineteenth century when via Marchionis became a modern traffic route with strong environmental impacts. Superimposed on the long-term development were repeated interruptions by short-term downturns related to societal crisis and political decisions. [ABSTRACT FROM AUTHOR]

Well-known for their geological and natural singularity, the Dead Sea brines evolved from a marine ingression of the Mediterranean during the Pliocene. Dead Sea brines are currently almost ten times more concentrated than seawater and have a unique chemical composition with high boron isotope values (δ 11 B brine = ∼57‰). However, little is known on how these values were attained and their underlaying driving processes. Here we use boron isotopes (δ 11 B) combined with B/Ca and B/Li of lacustrine authigenic aragonites from the deep basin drill-core ICDP 5017-1, and Ein Gedi and Masada profiles to reconstruct past brine conditions. Comparing reconstructed δ 11 B brine from two key periods of contrasting hydro-climatic regimes we find that the brines of the late Holocene Dead Sea were enriched in 11B (δ 11 B brine = ∼60‰) relative to its glacial precursor Lake Lisan (∼57‰). With the aid of boron cycle modelling, we quantify the main boron fluxes in the basin. We show that the post-glacial δ 11 B brine enrichment is best explained by overall reduction of freshwater inflow to the lake and coeval increase in 10B sink through boron co-precipitation in evaporitic deposits and boron loss in atmospheric water vapour, consistent with the onset of warmer and drier climate in the Eastern Mediterranean during the Holocene. On geological time scales, adsorption of 10B on clastic sediments has acted as an important 10B sink and can explain the evolution of the high δ 11 B brine values. • New boron, carbon, and oxygen isotope and Element/Ca data of aragonite from ICDP core 5017-1, Ein Gedi and Masada. • Boron geochemistry as a tool for tracing the geological evolution of Dead Sea brines from seawater. • Late glacial Lake Lisan and late Holocene Dead Sea boron budgets and processes. [ABSTRACT FROM AUTHOR]

This paper presents the results of multiproxy research (pollen, charcoal, plant macrofossil and testate amoebae) on the biogenic deposits core from Gorodetsky Moch, an ombrotrophic peatland in western Russia (Western Dvina Lakeland). We reconstructed the impact of disturbance on peatland development in the last 300 years by using chronology of the records based on 14C and 210Pb data set. The multiproxy reconstruction was compared with changes in the land cover using historical maps and Corona images, which provides a unique spatial analysis of past ecological and land-use changes. We aimed to determine the effect of local disturbances (drainage) and land-use changes (landscape openness) on the development of the peatland during the last 300 years. Our study suggests that human activity had a crucial impact on the development of the peatland in the last centuries. The analysis of testate amoebae and plant macrofossils revealed a clear disturbed layer in the second half of the 20th century CE. Most probably, the drainage of the peatland triggered changes in the community of testate amoebae and plants, thereby causing a functional shift in Sphagnum peatland ecosystem. The hydrological stress and vegetation composition shift led to the collapse of mixotrophic testate amoebae. However, the peatland showed strong resilience and recovered toward the end of the 20th century CE and the beginning of the 21st century CE, despite the lower water table. Our study shows an example of the peatland ecosystem that experienced a considerable stress but finally sustained the former function. [ABSTRACT FROM AUTHOR]

Varved lake sediments provide climatic records with seasonal to annual resolution and low associated age uncertainty. Robust and detailed comparison of well-dated and annually laminated sediment records is crucial for reconstructing abrupt and regionally time-transgressive changes as well as validation of spatial and temporal trajectories of past climatic changes. The VARved sediments DAtabase (VARDA) presented here is the first data compilation for varve chronologies and associated palaeoclimatic proxy records. The current version 1.0 allows detailed comparison of published varve records from 95 lakes. VARDA is freely accessible and was created to assess outputs from climate models with high-resolution terrestrial palaeoclimatic proxies. VARDA additionally provides a technical environment that enables us to explore the database of varved lake sediments using a connected data model and can generate a state-of-the-art graphic representation of a multisite comparison. This allows the reassessment of existing chronologies and tephra events to synchronize and compare even distant varved lake records. Furthermore, the present version of VARDA permits the exploration of varve thickness data. In this paper, we report in detail on the data-mining and compilation strategies for the identification of varved lakes and assimilation of high-resolution chronologies, as well as the technical infrastructure of the database. Additional palaeoclimatic proxy data will be provided in forthcoming updates. The VARDA graph database and user interface can be accessed online at https://varve.gfz-potsdam.de (last access: 15 September 2020), all datasets of version 1.0 are available at 10.5880/GFZ.4.3.2019.003 (Ramisch et al., 2019). [ABSTRACT FROM AUTHOR]

Varved lake sediments provide long climatic records with high temporal resolution and low associated age uncertainty. Robust and detailed comparison of well-dated and annually laminated sediment records is crucial for reconstructing abrupt and regionally time-transgressive changes as well as validation of spatial and temporal trajectories of past climatic changes. The VARved sediments DAtabase (VARDA) presented here is the first data compilation for varve chronologies and associated palaeoclimatic proxy records. The current version 1.0 allows detailed comparison of published varve records from 95 lakes. VARDA is freely accessible and was created to assess outputs from climate models with high-resolution terrestrial palaeoclimatic proxies. VARDA additionally provides a technical environment that enables to explore the database of varved lake sediments using a connected data-model and can generate a state-of-the-art graphic representation of multi-site comparison. This allows to reassess existing chronologies and tephra events to synchronize and compare even distant varved lake records. Furthermore, the present version of VARDA permits to explore varve thickness data. In this paper, we report in detail on the data mining and compilation strategies for the identification of varved lakes and assimilation of high-resolution chronologies as well as the technical infrastructure of the database. Additional paleoclimate proxy data will be provided in forthcoming updates. The VARDA graph-database and user interface can be accessed online at https://varve.gfz-potsdam.de, all datasets of version 1.0 are available at http://doi.org/10.5880/GFZ.4.3.2019.003 (Ramisch et al., 2019). [ABSTRACT FROM AUTHOR]

Tephra layers preserved in distal sedimentary archives represent chronicles of explosive volcanism that can complement the often more fragmentary information from near-source volcanic deposits to establish complete volcanic histories. With regard to these aspects, the Middle Pleistocene of the Eastern Mediterranean region stands out as it has a complex and diverse, but as yet largely unexplored record of volcanic eruptions. Here we present the first distal tephra record for the Eastern Mediterranean region spanning from 335 to 235 ka (corresponding to Marine Isotope Stages [MIS] 9 to 7e); our record has been derived from peat cores from the iconic terrestrial climate archive of Tenaghi Philippon (NE Greece). We have identified twenty-seven cryptotephra layers that represent eruptions from diverse Mediterranean sources. Six cryptotephra layers can be linked to Campanian volcanoes, and another six layers are tentatively correlated to Aeolian Arc volcanism. Of the ten cryptotephra layers that we have identified as deriving from the Aegean Arc, eight originate from Santorini volcano and two are tentatively attributed to either Kos or Milos. Five cryptotephra layers have yet unknown origins. Most of the identified cryptotephras represent previously undocumented eruptions. We provide age estimates for all cryptotephras and, by extension, for the underlying eruptions based on orbitally tuned pollen data from the same cores. The only cryptotephra layer in the 335–235 ka record from Tenaghi Philippon that represents a previously known eruption has a palynostratigraphically derived age of c. 289 ka and can be tentatively linked to the Seiano Ignimbrite from the Campanian Volcanic Zone; this represents the first time that this eruption can be traced beyond its proximal area. The documentation and geochemical characterization of tephra layers from different Mediterranean sources in the Tenaghi Philippon peat cores for MIS 9–7e is an important step towards the integration of regional Mediterranean tephrostratigraphic information for the Middle Pleistocene. • 27 cryptotephras found in Tenaghi Philippon cores for the 335–235 ka time interval • Glass geochemistry indicates Italian, Aegean Arc and yet unknown origins. • Identification of the Seiano Ignimbrite from the Campanian Volcanic Zone • Age estimates for yet unknown eruptions derived from orbitally tuned pollen data [ABSTRACT FROM AUTHOR]

The sedimentary record of the Dead Sea provides an exceptional high-resolution archive of past climate changes in the drought-sensitive eastern Mediterranean-Levant, a key region for the development of humankind at the boundary of global climate belts. Moreover, it is the only deep hypersaline lake known to have deposited long sequences of finely laminated, annually deposited sediments (i.e. varves) of varied compositions, including aragonite, gypsum, halite and clastic sediments. Vast efforts have been made over the years to decipher the environmental information stored in these evaporitic-clastic sequences spanning from the Pleistocene Lake Amora to the Holocene Dead Sea. A general characterisation of sediment facies has been derived from exposed sediment sections, as well as from shallow- and deep-water sediment cores. During high lake stands and episodes of positive water budget, mostly during glacial times, alternating aragonite and detritus laminae ('aad' facies) were accumulated, whereas during low lake stands and droughts, prevailing during interglacials, laminated detritus ('ld' facies) and laminated halite ('lh' facies) dominate the sequence. In this paper, we (i) review the three types of laminated sediments of the Dead Sea sedimentary record ('aad', 'ld' and 'lh' facies), (ii) discuss their modes of formation, deposition and accumulation, and their interpretation as varves, and (iii) illustrate how Dead Sea varves are utilized for palaeoclimate reconstructions and for establishing floating chronologies. Image 1 • The Dead Sea is the only deep hypersaline lake with varved sediments. • The chronological and paleoclimatic value of Dead Sea varves is demonstrated. • The interpretation of alternating aragonite-detritus laminae as varves is evaluated. • Lake monitoring confirms the interpretation of laminated halite as varves. • Distinguishing between annual and non-annual laminations requires micro-facies analyses. [ABSTRACT FROM AUTHOR]

Abstract Central European climate is strongly influenced by North Atlantic (Westerlies) and Siberian High circulation patterns, which govern precipitation and temperature dynamics and induce heterogeneous climatic conditions, with distinct boundaries between climate zones. These climate boundaries are not stationary and shift geographically, depending on long-term atmospheric conditions. So far, little is known about past shifts of these climate boundaries and the local to regional environmental response prior to the instrumental era. High resolution multi-proxy data (stable oxygen and carbon isotope ratios, S/Ca and Sr/Ca) from two Holocene stalagmites from Bleßberg Cave (Thuringia) are used here to differentiate local and pan-regional environmental and climatic conditions Central Germany through the Holocene. Carbon isotope and S/Ca and Sr/Ca ratios inform us on local Holocene environmental changes in and around the cave, while δ18O (when combined with independent records) serves as proxy for (pan-)regional atmospheric conditions. The stable carbon isotope record suggests repeated changes in vegetation density (open vs. dense forest), and increasing forest cover in the late Holocene. Concurrently, decreasing S/Ca values indicate more effective sulfur retention in better developed soils, with a stabilization in the mid-Holocene. This goes in hand with changes in effective summer infiltration, reflected in the Sr/Ca profile. Highest Sr/Ca values between 4 ka and 1 ka BP indicate intensified prior calcite precipitation resulting from reduced effective moisture supply. The region of Bleßberg Cave is sensitive to shifts of the boundary between maritime (Cfb) and continental (Dfb) climate and ideally suited to reconstruct past meridional shifts of this divide. We combined the Bleßberg Cave δ18O time series with δ18O data from Bunker Cave (western Germany) and a North Atlantic Oscillation (NAO) record from lake SS1220 (SW Greenland) to reconstruct the mean position of the Cfb-Dfb climate boundary. We further estimate the dynamic interplay of the North Atlantic Oscillation and the Siberian High and their influence on Central European climate. Repeated shifts of the Cfb-Dfb boundary over the last 4000 years might explain previously observed discrepancies between proxy records from Europe. Detailed correlation analyses reveal multi-centennial scale alternations of maritime and continental climate and, concurrently, waning and waxing influences of Siberian High and NAO on Central Europe. Highlights • U-series dated multi-proxy speleothem data from Bleßberg Cave, Thuringia cover the Holocene. • Local and pan-regional environmental and climatic changes are reconstructed. • Bleßberg Cave record is compared to data from W Germany and Greenland to infer maritime/continental climate regimes. • Waning/waxing of NAO and Siberian High influence on European climate is discussed for the last 4,000 years. [ABSTRACT FROM AUTHOR]

Abstract Based on diatom, aquatic pollen and non-pollen palynomorph (NPP), lake sediment microfacies, and X-ray fluorescence (XRF) analyses we define three main phases of lake basin development including a marshy phase (ca. 16,600–9400 cal. yr BP), lagoon phase (ca. 9400–5900 cal. yr BP) and freshwater lake phase (since ca. 5900 cal. yr BP). Marine influence on the lake system linked to global sea-level rise and the Holocene marine transgression reached a maximum between ca. 8000 and 6000 cal. yr BP. An increase of Aulacoseira subarctica at 5530 cal. yr BP marks the end of the Holocene Thermal Optimum (i.e. onset of Middle Holocene cooling) in the study region. Our results further suggest that freshwater Lake Kushu had a significant effect on the initial habitation of Rebun Island by sedentary hunter-gatherer populations. The reconstructed onset of stable freshwater conditions (ca. 5100 cal. yr BP) coincided with the appearance of the earliest permanent settlements during the Middle Jomon culture phase (ca. 5000–4000 cal. yr BP). On the other hand, there is evidence for human-induced changes in the limnological conditions. This includes enhanced sediment and nutrient input into Lake Kushu resulting in high eutrophication levels that caused strongly reduced diatom productivity and enhanced green algae growth, which can be attributed to human activities apparently associated with the Okhotsk (ca. 1450–950 cal. yr BP) and Classic Ainu (ca. 350–100 cal. yr BP) culture periods. Highlights • Evidence for a marshy, lagoon, and freshwater phase in the Lake Kushu basin • Lagoon phase highlights maximum Holocene sea level. • Diatom record marks end of Holocene Thermal Optimum conditions at 5530 cal. yr BP. • Onset of stable freshwater phase coincides with earliest permanent settlements. • Record of human impact on Lake Kushu during Okhotsk and Ainu culture periods [ABSTRACT FROM AUTHOR]

We analyzed a 10-m sediment core retrieved at 82 m water depth off the coast of the Tagus River (Western Iberian Margin, Portugal) to investigate a linkage between variations in benthic foraminiferal assemblages and Tagus River discharge over the last 5700 years. Benthic foraminiferal assemblages were studied at high resolution in combination with the stable carbon and oxygen isotopic composition of fossil shells of Nonion scaphum , bulk and molecular organic matter properties (TOC, TN, C/N ratio, δ 13 C TOC , δ 15 N bulk , and BIT index), magnetic susceptibility, and XRF analyses. Three periods of environmental changes were identified: 1) high Tagus River discharge in 5750–2200 calendar year before present (cal yr BP), 2) lower discharge characterized by intense upwelling conditions (2250–1250 cal yr BP), and 3) both intense upwelling and Tagus River discharge (1250 cal yr BP-present). The data reveal alternating intense upwelling periods, as shown by the dominance of Cassidulina carinata , Valvulineria bradyana , or Bulimina marginata , whereas periods of increased river discharge are indicated by increase of N. scaphum , Ammonia beccarii , and Planorbulina mediterranensis . The Tagus River discharge was the strongest during the first period, transporting riverine material further offshore and preventing the establishment of a mud belt on the mid-shelf (around 100 m depth). During the second period, a decrease in Tagus River discharge favored the formation of the Tagus mud belt and strongly influenced the benthic environment by creating an organic matter stock. During the third period, intense upwelling and increased Tagus River discharge were recorded by benthic foraminiferal distribution, with an increase of terrestrial elements present in the mud belt. Furthermore, our results showed that variations in benthic foraminiferal assemblages corresponded to the well-known climatic periods in the study area, such as the Roman Period, the Dark Ages, the Medieval Warm Period, and the Little Ice Age. Our study strongly suggests that benthic foraminiferal assemblages can be used as a bio-indicator to trace the influence of past river discharge. [ABSTRACT FROM AUTHOR]

A potential human footprint on Western Central African rainforests before the Common Era has become the focus of an ongoing controversy. Between 3,000 y ago and 2,000 y ago, regional pollen sequences indicate a replacement of mature rainforests by a forest-savannah mosaic including pioneer trees. Although some studies suggested an anthropogenic influence on this forest fragmentation, current interpretations based on pollen data attribute the "rainforest crisis" to climate change toward a drier, more seasonal climate. A rigorous test of this hypothesis, however, requires climate proxies independent of vegetation changes. Here we resolve this controversy through a continuous 10,500-y record of both vegetation and hydrological changes from Lake Barombi in Southwest Cameroon based on changes in carbon and hydrogen isotope compositions of plant waxes. δ13C-inferred vegetation changes confirm a prominent and abrupt appearance of C4 plants in the Lake Barombi catchment, at 2,600 calendar years before AD 1950 (cal y BP), followed by an equally sudden return to rainforest vegetation at 2,020 cal y BP. δD values from the same plant wax compounds, however, show no simultaneous hydrological change. Based on the combination of these data with a comprehensive regional archaeological database we provide evidence that humans triggered the rainforest fragmentation 2,600 y ago. Our findings suggest that technological developments, including agricultural practices and iron metallurgy, possibly related to the large-scale Bantu expansion, significantly impacted the ecosystems before the Common Era. [ABSTRACT FROM AUTHOR]

Accurate dating and unambiguous chronological correlation using cryptotephras provide a powerful tool to compare the varved sediment records of the lakes Głęboczek (JG), Czechowskie (JC) and Jelonek (JEL) (north-central Poland). For the last 140 years, micro-facies analyses and µ-XRF element scanning at seasonal resolution, as well as bulk elemental analyses (organic matter, carbonate) at sub-decadal to decadal resolution, were conducted for all three lakes records. All lakes are located in a region with low population density, and therefore, anthropogenic influences are negligible or only minor. The varve chronologies have been established independently for each record and were synchronized with the Askja AD 1875 cryptotephra. Comparison with monthly temperature data since 1870 and daily temperature data since 1951 revealed different responses of lake deposition to recent climate change. Varves are well preserved over the entire 140 years only at JG, while in the JC record two faintly varved intervals are intercalated and in the JEL record two non-varved intervals occur at the base and top of the profiles. These differences likely are due to variations in lake characteristics and their influence on lake-internal responses. JG is the smallest and best wind-sheltered lake, which favours varve preservation. JC’s attenuated sediment responses can likely be linked to lake productivity changes with respect to climate warming. JEL is lacking a direct sedimentological response to the observed temperature increase, which can be linked to lake size and water depth superimposing regional climate changes. Climate changes at the demise of the ‘Little Ice Age’ around 1900 and the recent warming since the 1980s are expressed in sediment proxies in the lakes with different response times and amplitudes. This detailed comparison study on three nearby lakes demonstrates the influence of local parameters such as lake and catchment size and water depth superimposed on more regional climate-driven changes. [ABSTRACT FROM AUTHOR]

Identifying climates favoring extreme weather phenomena is a primary aim of paleoclimate and paleohydrological research. Here, we present a well-dated, late Holocene Dead Sea sediment record of debris flows covering 3.3 to 1.9 cal ka BP. Twenty-three graded layers deposited in shallow waters near the western Dead Sea shore were identified by microfacies analysis. These layers represent distal subaquatic deposits of debris flows triggered by torrential rainstorms over the adjacent western Dead Sea escarpment. Modern debris flows on this escarpment are induced by rare rainstorms with intensities exceeding >30 mm h−1 for at least one hour and originate primarily from the Active Red Sea Trough synoptic pattern. The observed late Holocene clustering of such debris flows during a regional drought indicates an increased influence of Active Red Sea Troughs resulting from a shift in synoptic atmospheric circulation patterns. This shift likely decreased the passages of eastern Mediterranean cyclones, leading to drier conditions, but favored rainstorms triggered by the Active Red Sea Trough. This is in accord with present-day meteorological data showing an increased frequency of torrential rainstorms in regions of drier climate. Hence, this study provides conclusive evidence for a shift in synoptic atmospheric circulation patterns during a late Holocene drought. [ABSTRACT FROM PUBLISHER]

The strength of the North Atlantic Oscillation (NAO) is considered to be the main driver of climate changes over the European and western Asian continents throughout the last millennium. For example, the predominantly warm Medieval Climate Anomaly (MCA) and the following cold period of the Little Ice Age (LIA) over Europe have been associated with long-lasting phases with a positive and negative NAO index. Its climatic imprint is especially pronounced in European winter seasons. However, little is known about the influence of NAO with respect to its eastern extent over the Eurasian continent. Here we present speleothem records (δ 13 C, δ 18 O and Sr/Ca) from the southern rim of Fergana Basin (Central Asia) revealing annually resolved past climate variations during the last millennium. The age control of the stalagmite relies on radiocarbon dating as large amounts of detrital material inhibit accurate 230 Th dating. Present-day calcification of the stalagmite is most effective during spring when the cave atmosphere and elevated water supply by snow melting and high amount of spring precipitation provide optimal conditions. Seasonal precipitation variations cause changes of the stable isotope and Sr/Ca compositions. The simultaneous changes in these geochemical proxies, however, give also evidence for fractionation processes in the cave. By disentangling both processes, we demonstrate that the amount of winter precipitation during the MCA was generally higher than during the LIA, which is in line with climatic changes linked to the NAO index but opposite to the higher mountain records of Central Asia. Several events of strongly reduced winter precipitation are observed during the LIA in Central Asia. These dry winter events can be related to phases of a strong negative NAO index and all results reveal that winter precipitation over the central Eurasian continent is tightly linked to atmospheric NAO modes by the westerly wind systems. [ABSTRACT FROM AUTHOR]

The Holocene sediment record of Lake Tiefer See exhibits striking alternations between well-varved and non-varved intervals. Here, we present a high-resolution multi-proxy record for the past ~6000 years and discuss possible causes for the observed sediment variability. This approach comprises microfacies, geochemical and microfossil analyses and a multiple dating concept including varve counting, tephrochronology and radiocarbon dating. Four periods of predominantly well-varved sediment were identified at 6000–3950, 3100–2850 and 2100–750 cal. a BP and AD 1924–present. Except of sub-recent varve formation, these periods are considered to reflect reduced lake circulation and consequently, stronger anoxic bottom water conditions. In contrast, intercalated intervals of poor varve preservation or even extensively mixed non-varved sediments indicate strengthened lake circulation. Sub-recent varve formation since AD 1924 is, in addition to natural forcing, influenced by enhanced lake productivity due to modern anthropogenic eutrophication. The general increase in periods of intensified lake circulation in Lake Tiefer See since ~4000 cal. a BP presumably is caused by gradual changes in the northern hemisphere orbital forcing, leading to cooler and windier conditions in Central Europe. Superimposed decadal- to centennial-scale variability of the lake circulation regime is likely the result of additional human-induced changes of the catchment vegetation. The coincidence of major non-varved periods at Lake Tiefer See and intervals of bioturbated sediments in the Baltic Sea implies a broader regional significance of our findings. [ABSTRACT FROM AUTHOR]

The limited availability of high-resolution continuous archives, insufficient chronological control, and complex hydro-climatic forcing mechanisms lead to many uncertainties in palaeo-hydrological reconstructions for the Western Mediterranean. In this study we present a newly recovered 19.63 m long core from Lake Sidi Ali in the North African Middle Atlas, a transition zone of Atlantic, Western Mediterranean and Saharan air mass trajectories. With a multi-proxy approach based on magnetic susceptibility, carbonate and total organic C content, core-scanning and quantitative XRF, stable isotopes of ostracod shells, charcoal counts, Cedrus pollen abundance, and a first set of diatom data, we reconstruct Western Mediterranean hydro-climatic variability, seasonality and forcing mechanisms during the last 12,000 yr. A robust chronological model based on AMS 14 C dated pollen concentrates supports our high-resolution multi-proxy study. Long-term trends reveal low lake levels at the end of the Younger Dryas, during the mid-Holocene interval 6.6 to 5.4 cal ka BP, and during the last 3000 years. In contrast, lake levels are mostly high during the Early and Mid-Holocene. The record also shows sub-millennial- to centennial-scale decreases in Western Mediterranean winter rain at 11.4, 10.3, 9.2, 8.2, 7.2, 6.6, 6.0, 5.4, 5.0, 4.4, 3.5, 2.9, 2.2, 1.9, 1.7, 1.5, 1.0, 0.7, and 0.2 cal ka BP. Early Holocene winter rain minima are in phase with cooling events and millennial-scale meltwater discharges in the sub-polar North Atlantic. Our proxy parameters do not show so far a clear impact of Saharan air masses on Mediterranean hydro-climate in North Africa. However, a significant hydro-climatic shift at the end of the African Humid Period (∼5 ka) indicates a change in climate forcing mechanisms. The Late Holocene climate variability in the Middle Atlas features a multi-centennial-scale NAO-type pattern, with Atlantic cooling and Western Mediterranean winter rain maxima generally associated with solar minima. [ABSTRACT FROM AUTHOR]

Analyses of pollen, diatoms, XRF geochemistry, and pigments provide a unique window into how an insular ecosystem in Mauritius responded to an extreme drought event 4200 years ago. We provide a reconstruction of regional vegetation change and local wetland development under influence of sea level rise and inferred climate change between 4400 and 4100 cal. yr BP. Our multi-proxy data evidence a severe drought between 4190 and 4130 cal. yr BP, which ultimately led to mass mortality of larger vertebrates, including two species of giant tortoises and dodos in a <2-ha region. This prolonged drought around the Indian Ocean is recorded in many regions dependent on monsoon precipitation and is suggested to cause the collapse of human societies in East Africa and India. We demonstrate a direct relation between the mass mortality events in the Mare aux Songes (MAS) rock valley and the 4200 cal. yr BP drought. MAS represents a fresh water source that attracted and concentrated vertebrates. Abrupt increased aridity induced regional fires on Mauritius and caused decreased water levels, and a shrinking water surface resulting in further concentration of the animals in this coastal site. Upconing of the saline wedge underlying the fresh water source induced progressive salinization. The excrements of the animals produced hypertrophic conditions that, combined with salinization and high temperatures, created a suitable environment for potentially toxic cyanobacteria. These factors led to a deadly cocktail, resulting in the death of 100,000s of vertebrates by intoxication, dehydration, trampling, and miring, and promoted a unique conservation of fossils. The ‘4.2 ka megadrought’ likely induced similar bottlenecks elsewhere in the SW Indian Ocean region. [ABSTRACT FROM AUTHOR]

• Bent incised valleys formed at times of relatively stable, but lowered sea level. • Bent-incised valley-infill deposits display distinct fill architecture. • Fluvial, estuarine and marine conditions differ in depositional style. • Vertically stacked aggrading strata record pronounced sea-level rise. During times of lowered sea level, Mekong River and Red River incised valleys into the ancient coastal plains of the exposed shelves of the western South China Sea. The deglacial fill history of the incised valley was investigated by seismic surveys and sediment cores. The channels mainly exhibit a low-sinuosity course, but some channel segments are bent. The oldest part of the channel-bend fill exhibits shingled reflectors in Parasound seismic records documenting lateral channel migration typical of meandering rivers. Above, vertically stacked reflectors, which extend from the inner-bend side onto the cut-bank side document that the river-mouth channel turned to a mainly depositional mode. Vertical aggradation started when sea level was ~ 1–2 m below river water-level. During this phase, about two-third of the channel depth was filled by "fluvial-to-estuarine" mud having negative log(Ti/Ca) values as evidenced in XRF core scan data. Typically estuarine conditions developed when river water-level was approximate to sea level. Today channel bends form in estuaries within the zone of bedload convergence. Therefore, it is suggested that the studied channel bends represent antecedent, inherited features that formed during phases of prolonged phases of lowered, but relatively stable sea level to allow bends morphologically to develop. In fact, the bends occur not only in the western South China Sea but also in other areas of the world within a depth range that corresponds to times of retarded sea-level fall during MIS 5b, 5d, 4, and 3. [ABSTRACT FROM AUTHOR]

The varved sediment of Lake Gościąż (Central Poland) is one of the most detailed and complete climate archives of the Late Glacial and the Holocene in Central Europe. Here, we present microfacies analyses in combination with μXRF core scanning and a detailed varve chronology of a new and continuous GOS18 sediment record. This record presents six lithozones that mark the most prominent depositional and geochemical changes during the Holocene and Late Glacial. Varve boundaries and five main varve microfacies types were distinguished under petrographic microscope. Analysis provides detailed insights into depositional processes and its changes since the Late Glacial. Microfacies components were used to interpret processes leading to varve formation. A new and independent chronology is obtained by triple varve counting on petrographic thin sections that is complemented by 137Cs measurements and 14C AMS dating of terrestrial plant remains. The age-depth model consists of three parts: (1) the upper part (0–520 cm) that is primarily based on varve counting, (2) the middle part (520–758 cm) obtained through age-depth modelling and (3) the lower part (758–1897 cm) developed by varve counting. The bottom of the composite profile coincides with the onset of lacustrine sedimentation in the late Allerød at 12,834 +134/-233 varve yr BP. The largest shift in geochemistry, expressed by log(Ca/Ti) and log(Si/Ti) ratios show a rapid increase of calcite precipitation and primary productivity at 7940 +112/-168 varve yr BP. Possible triggers for this include local changes in hydrology as the formation of "Na Jazach" system due to the Ruda River development and fluctuations of lake water level. • Combining varve counting, radiometric methods and age-depth relation modeling. • Development of the new chronology for Lake Gościąż, central Poland. • Varve microfacies and their environmental implications from Allerød to present time. • Detailed insights into depositional processes and abrupt geochemical shifts. [ABSTRACT FROM AUTHOR]

In the comment on "Varves of the Dead Sea sedimentary record." Quaternary Science Reviews 215 (Ben Dor et al., 2019): 173–184. by R. Bookman, two recently published papers are suggested to prove that the interpretation of the laminated sedimentary sequence of the Dead Sea, deposited mostly during MIS2 and Holocene pluvials, as annual deposits (i.e., varves) is wrong. In the following response, we delineate several lines of evidence which coalesce to demonstrate that based on the vast majority of evidence, including some of the evidence provided in the comment itself, the interpretation of these sediments as varves is the more likely scientific conclusion. We further discuss the evidence brought up in the comment and its irrelevance and lack of robustness for addressing the question under discussion. • The interpretation of laminations in the sedimentary record of the Dead Sea is discussed. • There is robust evidence for interpreting laminated sedimentary sequences of the Dead Sea as varves. • The recent claims made to question annual aragonite deposition in the Dead Sea are shown to be premature and irrelevant. [ABSTRACT FROM AUTHOR]