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Improving Late Glacial European tree-ring chronologies for accurate climate archive dating - Consolidation and extension of the Swiss-German pine chronology back to 14,000 BP

Improving Late Glacial European tree-ring chronologies for accurate climate archive dating - Consolidation and extension of the Swiss-German pine chronology back to 14,000 BP

Annually resolved and absolutely dated tree-ring chronologies are important paleo-environmental proxy archives, because they can cover several thousands of years and robust master chronologies are available for many different regions around the globe. Moreover, the unique dating accuracy has a strong impact on many fields of application, including paleoclimatology and paleoecology, but also archaeology and radiocarbon dating. Here, we strive to a) consolidate and b) 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 253 individual pine trees within the town of Zurich in 2013 (herein referred to as the Binz material), for which first radiocarbon dates now suggest a time window roughly between 14,000 and 11,000 BP, implies strong evidence to fill the existing gaps in the Late Glacial tree-ring chronology around 12,500 BP. If indeed 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 remarkable task, however, requires joint forces across an international Swiss-German collaboration, which will in addition to ample new dendrochronological ring width and density measurements also generate a unique record of corresponding high-resolution radiocarbon (14C) dates as well as stable isotope ratios (d13C and d18O). The herein 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 further allow extending the highly rewarded (tree-ring-based) terrestrial radiocarbon calibration curve for more than 1,500 years into late glacial times improving considerably radiocarbon dating accuracy for archaeologists and geological sciences. In combination with several available marine radiocarbon records and complementary radio-isotopic records from polar ice cores (10Be, 36Cl), an exceptionally precise and highly resolved calibration curve will also reveal historical information about changes in and levels of solar activity, as well as mounting evidence for trends and extremes at the putative transition of generally colder to warmer climatic conditions, associated with rapid changes in the Earth's 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, therefore anchoring the ice core time scale to the tree-ring scale. Employment of the proposed high-resolution stable isotopes (d13C and d18O) from the same trees will further help us to more accurately capture the full range of synaptic-scale late glacial temperature and likely even also precipitation variability.

People

  • PIs: Lukas Wacker and Ulf Büntgen
  • Co-PIs: Kerstin Treydte, Gerd Helle, Bernd Kromer, Daniel Nievergelt, Willy Tegel, Michael Friedrich
  • PhDs: Maren Pauly, Frederick Reinig, Adam Sookdeo

In situ subfossil pine (Pinus sylvestris)

In situ subfossil pine (Pinus sylvestris) excavated in Zurich, Switzerland. Surrounded by a homogeneous clay package, this exceptionally well-preserved trunk contains more than 350 tree rings and has been radiocarbon dated to ~13,200 years BP, thus falling into the Late Glacial - Early Holocene transition.



Header image: Ectomycorrhizal fungi that live in symbiotic association with their host plants are key components of the Earth's terrestrial ecosystem. The beautiful fruiting body of the edible green-cracking Russula (Russula virescens (Schaeff.) Fr.), a highly valuable and tasty mushroom of the temperate European mixed forest zone, represents one out of 273 different mycorrhizal species that grow in the Swiss fungus reserve "La Chanéaz".