Assessing the variability of precipitation during the Holocene from stalagmite records

Stalagmites can be dated very precisely with Th/U. The growth rate of stalagmites is generally in the range between 30 and 100 μm year. Stable isotopes sampled at a resolution of 50-100 μm yield information with a resolution ranging from a sub-decadal to centennial scale. Precipitation determines the growth periods of the stalagmites and the stable isotope signal is mainly a proxy for the intensity of precipitation. Stable isotopes in Holocene stalagmites from Central Germany (S. Niggemann, Bochum) record the intensity of winter precipitation in the past, because it is mainly winter precipitation that contributes to ground water formation. From the records of two stalagmites we reconstruct several periods of reduced winter precipitation during the last 5,000 years. These periods are recorded as kinetic enrichment of d18O proportional to enrichment of d13C. They are apparently correlated with the intensity of the sun, derived from D14C in tree rings. Meteorologists find that at present drier winters in Central Europe are related to a NAOindex, whereas NAO+ index corresponds to wet and mild winters. If this rule applies also in the past, our results suggest that periods of enhanced sun activity favored NAO+ conditions in Central Europe and vice versa also during the past 5,000 years. Spannagel Cave in the Central Alps is another area in Europe that we are studying intensively (C. Spoetl, Innsbruck). Three Holocene stalagmites cover the time period over the last 5,000 years and partly overlap each other. The stable isotope records show no significant correlation between d13C and d18O suggesting that kinetic effects are not significant. The precisely-dated isotopic composition of stalagmite SPA12 is then translated into a high-resolution record of atmospheric temperature at high elevation during the past 2,000 years. Temperature maxima during the Medieval Warm Period between 800 and 1300 AD are about 2C higher than the minima in the Little Ice Age and slightly higher than present-day values. The good correlation of this record with D14C suggests that solar variability was a major driver of climate in Central Europe during the past 2 millennia. The temperature reconstruction from SPA 12 shows a pattern similar to other climatic archives from the Northern Hemisphere including Greenland ice cores, sea-surface temperatures (SST) from the Bermuda Rise, as well as to the reconstruction of glacier advances and retreats in the Alps.