Palaeolake Rehwiese, NE-Germany, Younger Dryas varved data set RW09

The first 1400-year floating varve chronology for north-eastern Germany covering the late Allerød 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 ?-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 Allerød 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 varves 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 - 11,640 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.

德国东北部首个覆盖阿勒罗德冰阶（Allerød）晚期至全新世（Holocene）早期的1400年浮动纹泥年代学（floating varve chronology），通过对Rehwiese古湖沉积记录的显微纹泥计数得以建立。研究层位底部的拉赫湖火山碎屑层（Laacher See Tephra, LST）构成了火山年代学锚点。本研究结合微相分析（micro-facies）与?-XRF分析对精细纹层开展观测，该类纹层以方解石纹泥（calcite varves）为典型特征，其信号主要反映暖季气候信息。研究识别出两种具有不同亚层结构的纹泥类型：（I）复合纹泥，由阿勒罗德冰阶与全新世早期形成的最多四层季节亚层构成；（II）简单双亚层纹泥，仅出现于新仙女木事件（Younger Dryas）期间。通过基于清晰界定的微标记层（micro-marker layers）对两条独立分析的沉积剖面（sediment profiles）开展纹泥层间对比（varve-to-varve comparison），本年代学的精度得到显著提升。该对比工作实现了两项核心目标：（1）精准定位其中一条沉积剖面中缺失的单条纹泥；（2）验证平行岩芯受扰动纹泥层位的纹泥插值（interpolation）结果。以每5条纹泥为分辨率的季节层厚度、高分辨率元素扫描以及总有机碳与总无机碳数据等多代用指标序列（multi-proxy data series），揭示了沉积过程的年际与十年际尺度变化特征。上述数据佐证了新仙女木事件存在两阶段演化的观点：第一阶段（12675~12275纹泥年代距今（varve years BP））以显著但逐渐减弱的暖季方解石沉积为特征，第二阶段（12275~11640纹泥年代距今（varve years BP））的方解石沉积仅表现为微弱状态。基于拉赫湖火山碎屑层等时线（isochrone）与独立纹泥计数结果，将上述两阶段与米尔费尔德玛珥湖记录（Meerfelder Maar record）进行详细对比，可为沿西起北大西洋沿岸区域、东至更为内陆站点的样带（transect）上新仙女木事件气候变化的区域差异与季节特征提供重要研究线索。