TY - JOUR A1 - Neugebauer, Ina A1 - Brauer, Achim A1 - Draeger, Nadine A1 - Dulski, Peter A1 - Wulf, Sabine A1 - Plessen, Birgit A1 - Mingram, Jens A1 - Herzschuh, Ulrike A1 - Brande, Arthur T1 - A Younger Dryas varve chronology from the Rehwiese palaeolake record in NE-Germany JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - The first 1400-year floating varve chronology for north-eastern Germany covering the late Allered to the early Holocene has been established by microscopic varve counts from the Rehwiese palaeolake sediment record. The Laacher See Tephra (LST), at the base of the studied interval, forms the tephrochronological anchor point. The fine laminations were examined using a combination of micro-facies and mu XRF analyses and are typical of calcite varves, which in this case provide mainly a warm season signal. Two varve types with different sub-layer structures have been distinguished: (I) complex varves consisting of up to four seasonal sub-layers formed during the Allered and early Holocene periods, and, (II) simple two sub-layer type varves only occurring during the Younger Dryas. The precision of the chronology has been improved by varve-to-varve comparison of two independently analyzed sediment profiles based on well-defined micro-marker layers. This has enabled both (1) the precise location of single missing varies in one of the sediment profiles, and, (2) the verification of varve interpolation in disturbed varve intervals in the parallel core. Inter-annual and decadal-scale variability in sediment deposition processes were traced by multi-proxy data series including seasonal layer thickness, high-resolution element scans and total organic and inorganic carbon data at a five-varve resolution. These data support the idea of a two-phase Younger Dryas, with the first interval (12,675-12,275 varve years BP) characterised by a still significant but gradually decreasing warm-season calcite precipitation and a second phase (12,275-11,690 varve years BP) with only weak calcite precipitation. Detailed correlation of these two phases with the Meerfelder Maar record based on the LST isochrone and independent varve counts provides clues about regional differences and seasonal aspects of YD climate change along a transect from a location proximal to the North Atlantic in the west to a more continental site in the east KW - Varve chronology KW - Micro-fades KW - Micro-XRF KW - Younger Dryas KW - North-eastern Germany Y1 - 2012 U6 - https://doi.org/10.1016/j.quascirev.2011.12.010 SN - 0277-3791 VL - 36 IS - 10 SP - 91 EP - 102 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Swierczynski, Tina A1 - Lauterbach, Stefan A1 - Dulski, Peter A1 - Delgado, Jose Miguel Martins A1 - Merz, Bruno A1 - Brauer, Achim T1 - Mid- to late holocene flood frequency changes in the northeastern Alps as recorded in varved sediments of Lake Mondsee (Upper Austria) JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - Annually laminated (varved) lake sediments with intercalated detrital layers resulting from sedimentary input by runoff events are ideal archives to establish precisely dated records of past extreme runoff events. In this study, the mid- to late Holocene varved sediments of Lake Mondsee (Upper Austria) were analysed by combining sedimentological, geophysical and geochemical methods. This approach allows to distinguish two types of detrital layers related to different types of extreme runoff events (floods and debris flows) and to detect changes in flood activity during the last 7100 years. In total, 271 flood and 47 debris flow layers, deposited during spring and summer, were identified, which cluster in 18 main flood episodes (FE 1-18) with durations of 30-50 years each. These main flood periods occurred during the Neolithic (7100-7050 vyr BP and 6470-4450 vyr BP), the late Bronze Age and the early Iron Age (3300-3250 and 2800-2750 vyr BP), the late Iron Age (2050-2000 vyr BP), throughout the Dark Ages Cold Period (1500-1200 vyr BP), and at the end of the Medieval Warm Period and the Little Ice Age (810-430 vyr BP). Summer flood episodes in Lake Mondsee are generally more abundant during the last 1500 years, often coinciding with major advances of Alpine glaciers. Prior to 1500 vyr BP, spring/summer floods and debris flows are generally less frequent, indicating a lower number of intense rainfall events that triggered erosion. In comparison with the increase of late Holocene flood activity in western and northwestern (NW) Europe, commencing already as early as 2800 yr BP, the hydro-meteorological shift in the Lake Mondsee region occurred much later. These time lags in the onset of increased hydrological activity might be either due to regional differences in atmospheric circulation pattern or to the sensitivity of the individual flood archives. The Lake Mondsee sediments represent the first precisely dated and several millennia long summer flood record for the northeastern (NE) Alps, a key region at the climatic boundary of Atlantic, Mediterranean and East European air masses, aiding a better understanding of regional and seasonal peculiarities of flood occurrence under changing climate conditions. (C) 2013 Elsevier Ltd. All rights reserved. KW - Varved lake sediments KW - Detrital layers KW - mu RF KW - Microfacies KW - Palaeofloods KW - Flood frequency Y1 - 2013 U6 - https://doi.org/10.1016/j.quascirev.2013.08.018 SN - 0277-3791 VL - 80 SP - 78 EP - 90 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Wolff, Christian Michael A1 - Kristen-Jenny, Iris A1 - Schettler, Georg A1 - Plessen, Birgit A1 - Meyer, Hanno A1 - Dulski, Peter A1 - Naumann, Rudolf A1 - Brauer, Achim A1 - Verschuren, Dirk A1 - Haug, Gerald H. T1 - Modern seasonality in Lake Challa (Kenya/Tanzania) and its sedimentary documentation in recent lake sediments JF - Limnology and oceanography N2 - From November 2006 to January 2010, a sediment trap that was cleared monthly was deployed in Lake Challa, a deep stratified freshwater lake on the eastern slope of Mt. Kilimanjaro in southern Kenya. Geochemical data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to characterize the effect of single parameters on productivity and sedimentation processes in the crater basin. During the southern hemisphere summer (November-March), when the water temperature is high and the lake is biologically productive (nondiatom algae), calcite predominated in the sediment trap samples. During the "long rain" season (March-May) a small amount of organic matter and lithogenic material caused by rainfall appeared. This was followed by the cool and windy months of the southern hemisphere winter (June-October) when diatoms were the main component, indicating a diatom bloom initiated by improvement of nutrient availability related to upwelling processes. The sediment trap data support the hypothesis that the light-dark lamination couplets, which are abundant in Lake Challa cores, reflect seasonal delivery to the sediments of diatom-rich particulates during the windy months and diatom-poor material during the wet season. However, interannual and spatial variability in upwelling and productivity patterns, as well as El Nino-Southern Oscillation (ENSO)-related rainfall and drought cycles, exert a strong influence on the magnitude and geochemical composition of particle export to the hypolimnion of Lake Challa. Y1 - 2014 U6 - https://doi.org/10.4319/lo.2014.59.5.1621 SN - 0024-3590 SN - 1939-5590 VL - 59 IS - 5 SP - 1621 EP - 1636 PB - Wiley CY - Waco ER -