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

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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.