Deciphering timings and rates of abrupt climate changes over the Lateglacial-Holocene period: The Lake Suigetsu biomarker record.

过去的气候重建对于了解气候变异性的长期趋势和测试用于预测未来气候变化的气候模型至关重要。对不同区域超前-滞后关系的详细重建提供了关于全球气候变化背景下区域之间因果联系的重要信息。在这里，我们使用日本水月湖的年度分层沉积物岩心来研究晚冰期和全新世早期关键气候突变的时间和速率（即从末次冰期结束到现在的温暖期的时间框架）使用高分辨率（5-10年）的分子记录的本地（内湖）和集水区的变化，降水/蒸发变化在这个网站。晚冰期-全新世以来的一系列气候突变引起了世界范围内的广泛研究，并提出了一些对立的理论。早期的研究倾向于支持偏远地区之间气候变化的同步性，而最近在西太平洋和南极洲的研究报告的气候变化与北大西洋的气候变化是异步的。在亚洲季风区，也有人认为，在亚洲全新世开始时中断变暖的冷却期是由北大西洋海洋环流变化引发的，而最近对格陵兰冰的研究认为，亚洲季风变化的开始时间略早于北大西洋。Co-I先前的研究使用花粉数据重建了水月湖过去的植被和温度，报告了日本冷却开始的实质性延迟，并建议北大西洋环流和太阳强迫的综合作用是千年到百年尺度季风气候变化的主要驱动力。中国石笋记录表明，约8200年前（8.2 ka事件）的冷却期与格陵兰冰芯数据中检测到的冷却证据同步变化，但这一假设需要使用包括日本在内的其他地区的记录进行检查。研究相对事件时间的困难在于（i）高精度的年龄测定和（ii）变化代理的响应时间。水月湖是进行高精度年龄测定的理想地点，因为待分析的沉积物岩心具有非常好的放射性碳年代测定。对于后一点，花粉一直是唯一的气候代用数据产生的水月湖核心，而花粉是足以讨论几十年到百年尺度的变化，突然（年际到十年）的变化是比较困难的，因为相对较慢的响应时间植被气候变化。生物标志物（“化学化石”）可用于提供关于过去环境的信息，其途径是提供源投入、生产力变化的证据，以及最近（通过使用特定化合物中分析的同位素比率）温度和降水/蒸发变化的证据。生物标志物分析将在这里重建源输入，生产力（反映湖泊生物群对变化的反应），温度和降水的变化的时间和速度，提供补充和额外的信息，花粉数据提供。这项研究将有助于（i）了解十年到百年气候变化的性质和机制，（ii）提供一个精确的和准确的年代学冰川消退到全新世事件的边界。一个重要的结果将是水月湖全新世开始的时间。虽然格陵兰的冰被用来通过计算每年的冰层来确定全新世开始的时间，但缺乏保存在冰中的合适的化石，可以通过放射性碳来确定年代。不过，将利用大量陆生植物叶片遗骸以及沉积物中的年层计数，通过放射性碳测定水月湖的年代，其结果将对地质学家和气候学家的科学界产生重大意义和益处。

Past climate reconstructions are fundamental to understand long-term trends in climate variability and to test climate models used to predict future climate change. Detailed reconstruction of lead-lag relationships in different regions provides important information about causal links between regions in the context of global climate change. Here we use an annually laminated sediment core from Lake Suigetsu, Japan, to examine timings and rates of key abrupt climate changes across the Lateglacial and early Holocene (i.e. the timeframe from the end of the last glacial into the present warm period) using a high resolution (5-10 year) molecular record of autochthonous (within-lake) and catchment responses to change, and precipitation/evaporation variations at this site. A series of abrupt climate changes from the Lateglacial-Holocene has been intensively studied worldwide and several opposing theories proposed. Earlier studies tended to support synchrony of climate changes between remote regions whereas recent studies in the West Pacific and Antarctica report climate changes that are asynchronous to those in the North Atlantic. In monsoon Asia, it has also been suggested that a cooling period that interrupted the warming at the onset of the Holocene in Asia was triggered by North Atlantic ocean circulation changes whereas a more recent study of Greenland ice argues that monsoon changes started slightly earlier in Asia than in the North Atlantic. Previous research by the Co-I using pollen data to reconstruct past vegetation and temperature at Lake Suigetsu reported a substantial delay in this cooling onset in Japan and suggested a combined role of North Atlantic circulation and solar forcing as the main drivers of millennial to centennial scale monsoon climate changes. Chinese stalagmite records suggest a period of cooling around 8200 years ago (the 8.2 ka event) has synchronous changes to evidence for cooling detected in Greenland ice core data but this hypothesis needs to be checked using records from other regions, including Japan. Difficulties in studying relative event timings lie in (i) high-precision age determination and (ii) response time in proxies for change. Lake Suigetsu is an ideal site for high-precision age determination because the sediment core to be analysed is extremely well radiocarbon dated. For the latter point, pollen has been the only climate proxy data generated from the Lake Suigetsu core and while pollen is sufficient to discuss multi-decadal to centennial scale changes, abrupt (inter-annual to decadal) changes are more difficult because of relatively slow response times of vegetation to climate changes. Biomarkers ('chemical fossils') can be used to provide information on past environments via evidence for changes in source inputs, productivity and, more recently (via the use of isotope ratios analysed in specific compounds) changes in temperature and precipitation/evaporation. Biomarker analysis will be employed here to reconstruct timings and rates of changes in source inputs, productivity (reflecting lake biota responses to change), temperature and precipitation, providing complimentary and additional information to that provided by pollen data. This research will contribute to (i) understanding the nature and mechanism of decadal to centennial climate changes, and (ii) providing a precise and accurate chronology for deglacial to Holocene event boundaries. An important result will be the timing of the Holocene onset in Lake Suigetsu. While Greenland ice is used to determine the timing of the Holocene onset via counting annual ice layers, there is a lack of suitable fossils preserved in ice that can be dated by radiocarbon. Lake Suigetsu, however, will be dated by radiocarbon using a large number of terrestrial plant leaf remains as well as counting of annual layers in the sediment.The results will be of significant interest and benefit to the scientific community of geologists and climatologists.