This study investigates Holocene floodplain evolution and flooding phases as experienced in the Lower Meuse catchment, primarily based on grain-size distributions of channel-fill and floodplain deposits in sediment cores. The presence of post-depositional FeeMn concretions and resistant organic particulate materials impedes the direct use of grain-size data. By combining end-member modelling results with laboratory observations, we have constructed a Flood Energy Index (FEI), which allows identification of phases of past increased flooding from the grain-size signal. Since concretions and organic-rich sediments regularly occur in floodplain sediments, we emphasize that the quality of a grain-size dataset should be assessed prior to its use for reconstruction of flood events. We suggest that the new approach has potential to become standardized within paleoflood research. The temporal variation of FEI in Meuse sediment cores highlights multi-centennial flooding phases occurring at c. 8500, c. 8000, c. 7600, c. 7000 and c. 5900 cal BP within the fluvio-lacustrine environment (early-middle Holocene). The record of low flood activity in the Subboreal is attributed to a cooler and dryer climate anomaly after the Holocene Climatic Optimum. In the late Holocene, the first flooding phase occurring at c. 2800 cal BP can be linked to the 2.8 ka climate anomaly. During the last two thousand years, the variation of FEI index reveals oscillating flood regimes in the Lower Meuse floodplain. The last three recorded flooding phases most likely coincide with the Roman Period (c. 12 BCE-250 CE), the Medieval Warm Period (c. 950-1400 CE) and the Little Ice Age (c. 1400-850 CE). Despite uncertainty in the age-model, the rapid accumulation rate and amplified flood magnitudes imply increased fluvial instability during the late Holocene, indicating that humans exerted a profound influence on fluvial dynamics in the Meuse.
Asian climate is controlled by the Asian monsoons and westerlies. The Asian monsoons bring at times extensive moisture from the Indian Ocean and Pacific Ocean to southern and eastern Asia during summer. By contrast, the westerlies have limited ability to bring moisture to central Asia and western China due to the long distance to major moisture sources in the Atlantic Ocean (Figure 1). As such, westerlies-dominated (inland) Asia is generally dry, with current annual precipitation rarely exceeding 250 mm and prevailing arid to hyper-arid conditions, while monsoonal Asia tends to experience dry sub-humid to humid conditions. At present, the boundary between monsoonal versus westerlies dominated Asia, that is, the southeastern boundary of arid inland Asia, lies at the Asian summer monsoon northwestern limit (Figure 1, Chen et al., 2008), though this boundary may have shifted between glacials and interglacials (Yang et al., 2015).The Chinese Loess Plateau (CLP) lies within the current monsoonal Asia (Figure 1) and has the thickest loess deposits in Asia. These deposits are invaluable paleoclimate archives allowing reconstruction of East Asian monsoon and inland Asian aridification history back to 25-22 Ma (Guo et al., 2002;Porter, 2001;Qiang et al., 2011;Sun et al., 2010). In particular, loess magnetic parameters and grain-size have been widely used to infer East Asian summer and winter monsoon intensities since the Miocene (An et al., 1991;Lu et al., 2000;Sun et al., 2016). By contrast, dust accumulation rate (DAR) on the CLP has been suggested to indicate the degree of inland Asian aridification or desertification, based on the assumption that the vast deserts and gobi areas in interior Asia act as the CLP's primary dust source regions (
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<p>Lateglacial climatic oscillations exerted profound impacts on the earth surface. In the Lower Meuse Valley (southern Netherlands), geomorphological studies in the last decades mainly centered on Lateglacial vegetation evolution, channel pattern changes and river terrace formation. Little information has been reported with respect to the paleohydrology and its relation with local and regional climate system. This study investigates a sediment core that contains flood sediments deposited from the Aller&#248;d to the middleHolocene. We conducted grain-size analysis, thermogravimetric analysis (organic matter and calcium carbonate content), pollen counting, macro fossils analysis, and oxygen and carbon stable isotopes analysis of the biogenic carbonate. Plant species variations in each pollen assemblage zone represent the local and regional vegetation development. The pollen and macro fossil studies reveal that the core site was in a lake and marsh environment through the Aller&#248;d-early Holocene period. The oxygen isotope record is believed to have captured the intra-Aller&#248;d Cold Period, its synchronous variation with the carbon isotope record indicates a dominant evaporation effect on the lake during the warm Aller&#248;d period. By highlighting the coarser components (flood signal) of the fine and coarse end members, two flooding energy indexes were constructed separately. The hydrological processes in the first phase of the Younger Dryas were characterized by rapidly increased flooding conditions and high accumulation rates. In the second phase of the Younger Dryas, an addition of aeolian sediments to the core site complicates the paleoflood identification. This work expands the paleoflooding reconstruction to a more broadly deposition setting where only fine or coarse fluvial sediment is the dominant component. The nearly synchronous changes of the increased flooding with the abruptly enhanced westerlies at the Aller&#248;d-Younger Dryas transition indicates a link between the Lower Meuse catchment and the regional North Atlantic climatic system</p>
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