Rapid climate change during the last ice-age cycle

The term ice age is usually associated with arctic temperatures and huge ice masses. What is even more relevant from a paleoclimatological point of view are the dynamics which characterized these long glacial periods: analyses primarily of ice cores from Greenland have demonstrated that ice ages were not uniformly cold and dry, but interrupted by many warmings which lasted between a few centuries up to several thousands of years. Most importantly, the onset of these warm phases (or interstadials) was abrupt, certainly within decades, perhaps even as fast as a few years; the end of these warm phases, however, was gradual. A total 25 interstadials have been identified in the Greenland ice of the last glacial cycle alone and their forcing remains one of the big unknowns in the study of the Earth`s climate system. A major challenges in this respect is the accurate timing of these climate changes. This is precisely the goal this grant proposal. Earlier work has shown that traces of these enormous climate swings can be detected in a completely different area, locally even without gaps, i.e. dripstones (speleothems) in karst caves. The big advantage of this "climate archive" as compared to polar ice is their precise chronology. This project will examine speleothems from caves of the Eastern and Western Alps, as previous studies by our research team at the University of Innsbruck have shown that alpine caves are particularly suited as ice age "climate archive". The traces of past climate will detected primarily using the stable isotopes of oxygen in the calcite of these inorganic carbonate deposits. The precise dating relies on the radioactive decay of the trace elements uranium and thorium and these measurements will be performed in the world-leading isotope laboratory at the University of Minnesota. Furthermore, innovative methods will be applied to reconstruct past temperature changes. This research will be carried out in collaboration with experts from Germany, Great Britain, the United States, and Denmark, and is exposed to provide calibration points for the Greenland ice cores through a comparison with accurately dated alpine speleothems, and will provide quantitative information about speed and magnitude of glacial-age climate change in the Alps.

Rapid and high-amplitude climate shifts occurred repeatedly during the last glacial period (Dansgaard-Oeschger cycles) and are among the most dramatic examples of climate change in the most recent history of the Earth. Key to a better understanding of these events is a precise chronology which is difficult to obtain from polar ice cores, where these events were first identified. We therefore studied stalagmites from caves along the northern rim of the Alps, because previous research has shown that this region is particularly sensitive to climate change and the isotope signal recorded in these cave carbonates provides a very close match of the same signal in Greenland ice cores. Our study confirmed the striking similarity of the isotope curve from the Alpine region with the curve from Greenland - an icon of climate change - underscoring the close climatic relationship between these two regions. We improved our existing record (NALPS) and filled gaps. In addition, we extended this record to 35,000 years before present. We also pushed our glacial record back in time and established a high-precision record of the Last Interglacial. The new composite, albeit partly incomplete, climate curve reveals the full dimension of large-scale climate fluctuations in Central Europe between 135,000 and 35,000 years before present and, given its high accuracy and precision, allows to discuss issues of leads and lags in the global climate system during times of major reorganisations.