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

该提案的目的是评估洞穴沉积物重建过去（短暂）极端气候阶段和事件的潜力，例如特别低的温度，极端的降雨量或非常高的风速。这种极端事件很少发生，但往往造成巨大破坏，可能对有关地区的人口和生态系统造成严重后果。更好地了解这些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，这对于为人口的后果作出适当安排至关重要。洞穴沉积物提供了精确的日期与近年度决议多代理记录，因此有很大的潜力，如档案等事件。然而，在洞穴上方的含水层中，记录在洞穴沉积物中的代理信号在一定程度上被平滑。因此，需要评估不同洞穴系统和洞穴沉积物替代物对重建过去极端事件的敏感性。本建议的重点是8.2 ka事件和最近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期间淡水大量涌入北大西洋的影响。在过去的2000年里，几个百年尺度的气候振荡（如中世纪温暖期和小冰期）被确定。除了这些事件，还观察到其他短暂的气候异常，例如公元1342年7月历史性的圣抹大拉洪水或公元1540年前所未有的欧洲炎热和干旱。有些事件是由火山爆发引发的，如公元1816年的无夏之年，与公元1815年的坦博拉火山爆发有关。德国三个洞穴系统的洞穴沉积物包括8.2 ka事件和最近2000年的洞穴沉积物。对于所有三个洞穴，长期的洞穴监测计划已经建立，这是一个先决条件，以了解发生在洞穴系统中的过程，并解释记录在洞穴沉积物的代理信号。我们将分析石笋的稳定同位素和微量元素在相应的部分在非常高的分辨率（~每年），并精确地定年样品的MC-ICPMS 230 Th/U-定年。将根据气象和洞穴监测数据，采用定量正向建模方法，确定最适合重建过去短期极端事件的替代物。精确定年的高分辨率多代理记录和定量正演模拟方法相结合，提供了坚实的基础，以便（一）确定最合适的代理重建过去的短期极端事件和（二）比较特定的事件在不同的洞穴沉积物。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.