Evaluation of the potential of speleothems for reconstruction of (short-term) phases of extreme climate

本提案的目的是评估洞穴主题在重建过去（短期）阶段和极端气候事件（如特别低温、极端降雨量或极高风速）方面的潜力。这种极端事件很少发生，但往往造成巨大的破坏，可能对有关地区的人口和生态系统造成严重后果。更好地了解这种极端事件的原因和边界条件，将能够更好地预测未来极端事件的发生，这对于对人口的后果作出适当安排是必不可少的。洞穴主题提供精确的年代多代理记录，接近年度分辨率，因此具有作为此类事件档案的巨大潜力。然而，在洞穴上方的含水层中，洞穴中记录的替代信号有一定程度的平滑。因此，需要评估不同的洞穴系统和洞穴代表对过去极端事件重建的敏感性。本提案的重点是8.2 ka事件和过去2000年。8.2 ka事件是全新世最极端的气候异常，反映了间冰期气候状态下大量淡水涌入北大西洋的影响。在过去2000年中，确定了几个百年尺度的气候振荡（如中世纪暖期和小冰河期）。除了这些事件外，还观察到其他短暂的气候异常，如公元1342年7月历史性的圣马格达莱纳洪水或公元1540年欧洲前所未有的高温和干旱。有些事件是由火山爆发引发的，例如公元1816年没有夏天，这与公元1815年的坦博拉火山爆发有关。包括8.2 ka事件和最近2000年德国三个洞穴系统的几个洞穴主题是可用的。对于这三个洞穴，已经建立了长期的洞穴监测计划，这是了解洞穴系统中发生的过程和解释洞穴主题中记录的代理信号的先决条件。我们将以非常高的分辨率（~年）分析石笋相应剖面的稳定同位素和微量元素，并通过MC-ICPMS 230Th/ u测年对样品进行精确测年。利用基于气象和洞穴监测数据的定量正演模拟方法，确定最适合重建过去短期极端事件的代理。精确年代的高分辨率多代理记录和定量正演模拟方法相结合，为以下工作提供了坚实的基础：(1)确定重建过去短期极端事件的最合适代理；(2)比较不同洞穴主题的特定事件。这将有助于确定活动的时间、持续时间和结构。

The objective of this proposal is to evaluate the potential of speleothems for reconstruction of past (short-lived) phases and events of extreme climate, such as particularly low temperatures, extreme amounts of rainfall or very high wind speed. Such extreme events occur rarely, but they often cause great damage, which may have serious consequences for the population and ecosystems of the concerned region. A better understanding of the causes and boundary conditions of such extreme events will enable an improved prediction of the occurrence of future extremes, which is essential to make appropriate arrangements for the consequences for the population. Speleothems offer precisely dated multi-proxy records with near annual resolution, and consequently have great potential as archives of such events. However, the proxy signals recorded in speleothems are smoothed to a certain extent in the aquifer above the cave. Thus, the sensitivity of different cave systems and speleothem proxies for reconstruction of past extreme events needs to be evaluated. The focus of this proposal is on the 8.2 ka event and the last 2000 years. The 8.2 ka event was the most extreme climate anomaly of the Holocene and reflects the impact of dramatic freshwater influx into the North Atlantic during an interglacial climate state. During the last 2000 years, several centennial scale climate oscillations (e.g. the Medieval Warm Period and the Little Ice Age) were identified. In addition to these events, other, short-lived climate anomalies were observed, such as the historic St. Magdalenes flood in July 1342 AD or the unprecedented European heat and drought of 1540 AD. Some events were triggered by volcanic eruptions, such as the year without summer in 1816 AD, which was related to the Tambora eruption in 1815 AD. Several speleothems including the 8.2 ka event and the last 2000 years from the three cave systems in Germany are available. For all three caves, long-term cave monitoring programs have been set up, which is a prerequisite to understand the processes occurring in the cave systems and to interpret the proxy signals recorded in the speleothems. We will analyse both stable isotopes and trace elements in the corresponding sections of the stalagmites at very high resolution (~annual), and precisely date the samples by MC-ICPMS 230Th/U-dating. The identification of the most suitable proxies for reconstruction of past short-term extreme events will be performed using a quantitative forward modelling approach based on meteorological and the cave monitoring data. The combination of precisely dated high-resolution multi-proxy records and a quantitative forward modelling approach provides a solid base in order to (i) identify the most suitable proxies for reconstruction of past short-term extreme events and (ii) compare specific events in different speleothems. This will allow the determination of the timing, duration and structure of the events.