Accurate time scales for climate archives from European tree-ring chronologies in the Late Glacial - Extension and consolidation of Swiss and German pine chronologies back to 14000 BP

• Applicants: Dr. Gerhard Helle; Dr. Bernd Kromer; Dr. Willy Tegel
• Subject Area: Palaeontology
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 264059065

Annually resolved and absolutely dated tree-ring chronologies are important paleo-environmental proxy archives, because robust master chronologies are available for many different regions around the globe. The unique dating accuracy has a strong impact on many fields of application, such as paleoclimatology and paleoecology, but also archeology and radiocarbon dating. Here, we strive to consolidate and extend the worldwide longest continuous tree-ring width chronology from Hohenheim/Zurich, which currently reaches back to 12 500 before present (BP). An exceptional discovery of 256 individual pine trees within the town of Zurich in 2013 (herein referred to the Binz material), for which first radiocarbon dates now suggest a time window between 14 000 and 11 000 BP, implies strong hope to fill the existing gaps in the Late Glacial tree-ring chronology around 12 500 BP. If successful, the worldwide longest, absolutely dated and continuous tree-ring record would be extended by almost two millennia until around 14 000 BP, thus covering a particularly interesting climatological transition from the Last Ice Age into the Early Holocene - a period for which proxy evidence is generally scarce. Achieving this task, however, requires joint forces across an international Swiss-German collaboration, which will in addition to the dendrochronological ring width and density measurements also generate corresponding high-resolution radiocarbon (14C) dates as well as stable isotope (13C and 18O) records. The proposed multi-parameter approach will not only support and strengthen the chronology development process typically based on ring width measurements alone, but particularly also our palaeoenvironmental understanding of the Late Glacial period surrounding the Younger Dryas, a period during which rapid climatic shifts likely provide a natural analogue to the most recent anthropogenic change.The new multi-parameter tree-ring archive will allow extending the tree-ring-based terrestrial radiocarbon calibration curve for more than 2 000 years into late glacial times improving considerably radiocarbon dating accuracy for archaeologists and geosciences. In combination with several available marine radiocarbon records and complementary radioisotopic records from polar ice cores (10Be, 36Cl), an precise and highly resolved calibration curve will also provide information about changes of solar activity, as well as evidence for trends and extremes at the putative transition of generally colder to warmer climatic conditions, associated with rapid changes in the hydrological cycle. In addition, decadal to centennial 14C variations in tree-rings will be compared to the mirror image of 10Be in polar ice cores, thus anchoring the ice core time scale to the tree-ring scale. Consideration of the high-resolution stable isotopes (13C and 18O) from the same trees will further help us to capture the full range of late glacial temperature and precipitation variability.

• DFG Programme: Research Grants
• International Connection: Switzerland
• Participating Person: Dr. Lukas Wacker