Abstract The climate history of the source area of the Yellow River (SAYR) is important to understanding the pacing and processes of climate evolution on the northeastern Qinghai-Tibetan Plateau (QTP). To date, results of research in this alpine region are limited. Herein, we provide a first lacustrine record from the largest freshwater lake on the QTP that archives climatic and environmental variations in the SAYR for the last 1500 yr. The bulk organic carbon and nitrogen isotopic compositions (δ13Corg and δ15Ntot) are combined with atomic carbon/nitrogen (C/N) ratios to indicate that the sedimentary organic matter in Lake Ngoring originates from autochthonous algae and that the terrestrial input is minor. Comparison of the record of organic carbon isotope values with published records of ice accumulation rate (IAR) of Dunde and Guliya glaciers from the northern QTP, the total solar irradiance (TSI), δ18O variations in the Greenland ice core and biologically sensitive indicators (C37:4 alkenone, crenarchaeol and bGDGT concentrations) from Lake Qinghai indicate that variations in the δ13Corg values in Lake Ngoring sediments reflect lake level fluctuations that are associated with variations in the amount of precipitation and glacier meltwater on the SAYR. High lake level phases indicated by positive shifts of δ13Corg values correspond to higher values of the North Atlantic Oscillation Index (NAOI) and lower values of the Southern Oscillation Index (SOIpr). This relation suggests that the hydrologic history in the SAYR is linked to changes in the Indian monsoon and the Westerlies and that both air masses delivered more moisture to the SAYR during high TSI stages. In contrast, variations in the δ15Ntot values resemble the multiple paleoclimate proxy records obtained from ice cores, peat sequences, lake sediments, and integrated paleo-records from other QTP sites, suggesting that the δ15Ntot values archived in Lake Ngoring sediments provide a history of past lake-water temperature variations that is consistent with the variation history of the temperature-dependent parameters from regional paleo-climatic studies. Global climatic events including the Dark Ages Cold Period, the Medieval Climate Anomaly, the Little Ice Age and Modern Warming in 20th century could be clearly observed in the δ15Ntot variations. In general, the δ13Corg and δ15Ntot values in Lake Ngoring sediments appear to be useful indicators for paleo-environment and paleo-climate reconstructions in alpine oligotrophic freshwater lakes such as this one.

中文翻译：

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恩戈林湖（青藏高原）沉积物有机质地球化学特征：近1500年来黄河源区环境气候变化记录

摘要 黄河源区（SAYR）气候史对于了解青藏高原东北部（QTP）气候演变的节奏和过程具有重要意义。迄今为止，在这个高山地区的研究结果是有限的。在此，我们提供了青藏高原最大淡水湖的第一个湖泊记录，该记录记录了过去 1500 年 SAYR 的气候和环境变化。大量有机碳和氮同位素组成（δ13Corg 和 δ15Ntot）与原子碳/氮 (C/N) 比值相结合，表明 Ngoring 湖中的沉积有机质来源于本土藻类，陆地输入较少。有机碳同位素值记录与青藏高原北部邓德和古利亚冰川冰积累率（IAR）、太阳总辐照度（TSI）、格陵兰冰芯δ18O变化和生物敏感指标（C37）的公开记录比较:4 来自青海湖的烯酮、crenarchaeol 和 bGDGT 浓度）表明，恩戈林湖沉积物中 δ13Corg 值的变化反映了与 SAYR 上降水量和冰川融水量变化相关的湖水位波动。δ13​​Corg 值的正变化表示的高湖水位阶段对应于北大西洋涛动指数 (NAOI) 的较高值和南方涛动指数 (SOIpr) 的较低值。这种关系表明 SAYR 的水文历史与印度季风和西风带的变化有关，并且这两种气团在高 TSI 阶段向 SAYR 输送了更多水分。相比之下，δ15Ntot 值的变化类似于从冰芯、泥炭层序、湖泊沉积物和其他青藏高原地区的综合古记录中获得的多个古气候代理记录，表明在恩戈林湖沉积物中存档的 δ15Ntot 值提供了过去的历史湖水温度变化与区域古气候研究中温度相关参数的变化历史一致。全球气候事件包括黑暗时代寒冷时期、中世纪气候异常、在δ15Ntot变化中可以清楚地观察到20世纪的小冰河时代和现代变暖。总的来说，恩戈林湖沉积物中的 δ13Corg 和 δ15Ntot 值似乎是像这样的高山贫营养淡水湖中古环境和古气候重建的有用指标。