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多变性的长期趋势和测试用于预测未来气候变化的气候模型是至关重要的。对不同区域的领先-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，我们使用来自日本Suigetsu湖的每年一次的层状沉积岩芯，利用该地点原地(湖内)和集水区对变化的响应以及降水/蒸发变化的高分辨率(5-10年)分子记录，研究了整个冰期和全新世早期(即从最后一次冰川结束到现在暖期的时间框架)关键突然气候变化的时间和速率。拉丁-全新世以来的一系列气候突变在世界范围内得到了广泛的研究，并提出了几种相反的理论。早期的研究倾向于支持偏远地区之间的气候变化同步，而最近在西太平洋和南极洲的研究报告称，气候变化与北大西洋的气候变化是不同步的。在亚洲季风，也有人认为，北大西洋环流变化触发了亚洲全新世开始时中断变暖的冷却期，而最近一项关于格陵兰冰的研究认为，季风变化在亚洲比在北大西洋开始得稍早。Co-I以前使用花粉数据重建Suigetsu湖过去的植被和温度的研究报告称，日本的这种冷却开始时间有很大延迟，并表明北大西洋环流和太阳强迫的共同作用是千年到百年尺度季风气候变化的主要驱动因素。中国的石笋记录表明，大约8200年前的一段冷却时期(8.2 ka事件)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来验证。研究相对事件时间的困难在于(I)高精度的年龄确定和(Ii)变化代理的响应时间。Suigetsu湖是高精度年龄测定的理想地点，因为要分析的沉积物岩心具有非常好的放射性碳测年。对于后一点，花粉是Suigetsu湖岩芯产生的唯一气候替代数据，虽然花粉足以讨论数十年至百年尺度的变化，但突然(年际至十年)变化更困难，因为植被对气候变化的响应时间相对较慢。生物标志物(“化学化石”)可以用来提供关于过去环境的信息，方法是提供来源投入、生产力变化的证据，以及最近(通过使用在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。生物标志物分析将被用来重建来源输入、生产力(反映湖泊生物群对变化的响应)、温度和降水的时间和变化速率，提供补充和补充花粉数据所提供的信息。这项研究将有助于(I)了解十年至百年气候变化的性质和机制，以及(Ii)提供准确的去冰期至全新世事件界线的年代学。一个重要的结果将是Suigetsu湖全新世的开始时间。虽然格陵兰冰被用来通过计算每年的冰层来确定全新世的开始时间，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。然而，Suigetsu湖将利用大量陆地植物叶子残骸和沉积物中的年层数进行放射性碳测年。这一结果将对地质学家和气候学家的科学界产生重大兴趣和好处。

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.