Diatoms, total organic carbon, and total nitrogen of sediment core Dethlingen, Germany

To provide insights into the long-term evolution of aquatic ecosystems without human interference, we here evaluate a decadal- to centennial-scale-resolution diatom record spanning about 12 ka of the Holsteinian interglacial (Marine Isotope Stage 11c). Using a partially varved sediment core from the Dethlingen palaeolake (northern Germany), which has previously been studied for palynological and microfacies signals, we document the co-evolution of the aquatic and surrounding terrestrial environment. The diatom record is dominated by the genera Stephanodiscus, Aulacoseira, Ulnaria and Fragilaria. Based on the diatom assemblages and physical sediment properties, the evolution of the Dethlingen palaeolake can be subdivided into three major phases. During the oldest phase (lasting ~1900 varve years), the lake was ~10-15 m deep and characterized by anoxic bottom-water conditions and a high nutrient content. The following ~5600 years exhibited water depths >20 m, maximum diatom and Pediastrum productivity, and a peak in allochtonous nutrient input. During this phase, water-column mixing became more vigorous, resulting in a breakdown of anoxia. The youngest lake phase (~4000-5000 years) was characterized by decreasing water depth, turbulent water conditions and decreased nutrient loading. Based on our palaeolimnological data, we conclude that the evolution of the Dethlingen palaeolake during the Holsteinian interglacial responded closely to (i) changes within the catchment area (as documented by vegetation and sedimentation) related to the transition from closed forests growing on nutrient-rich soils (mesocratic forest phase) to open forests developing on poor soils (oligocratic forest phase), and (ii) short-term climate variability as reflected in centennial-scale climate perturbations.

为揭示无人类干扰下水生生态系统的长期演化规律，本研究针对跨度约12千年的霍尔斯坦间冰期（Holsteinian interglacial，即海洋同位素阶段11c，Marine Isotope Stage 11c，简称MIS11c）十年至百年尺度分辨率硅藻记录展开评估。本研究依托德国北部德特林根古湖（Dethlingen palaeolake）的部分纹层沉积岩芯——该岩芯此前已被用于孢粉学（palynological）与微相（microfacies）信号研究——，揭示了水生环境与周边陆地环境的协同演化过程。该硅藻记录以冠盘藻属（Stephanodiscus）、海链藻属（Aulacoseira）、乌尔曼藻属（Ulnaria）以及脆杆藻属（Fragilaria）为优势类群。基于硅藻组合与沉积物物理性质，德特林根古湖的演化可划分为三个主要阶段。最古老的阶段（持续约1900个纹层年）中，湖泊水深约10-15米，底层水体处于缺氧状态且营养盐含量较高。随后的约5600年里，湖泊水深超过20米，硅藻与盘星藻属（Pediastrum）生产力达到峰值，外源营养盐输入量亦达顶峰。此阶段水体混合作用愈发强烈，最终导致底层缺氧环境被打破。最晚的湖泊演化阶段（持续约4000-5000年）则以水深逐渐降低、水体呈湍流状态以及营养盐负荷下降为特征。基于本研究的古湖沼学（palaeolimnological）数据，我们认为霍尔斯坦间冰期德特林根古湖的演化主要响应于两类驱动因素：其一为集水区（catchment area）内的环境变化——该变化由营养丰富土壤上的封闭森林（中营养森林阶段，mesocratic forest phase）向贫瘠土壤上的开放森林（贫营养森林阶段，oligocratic forest phase）过渡所引发，相关过程可通过植被与沉积记录得到印证；其二为以百年尺度气候扰动为表征的短期气候变异性。