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Department of Geography


Extra-terrestrial evaluation of global-scale tree-ring dating in the first millennium CE

Tree ring-based temperature reconstructions, representing the backbone of high-resolution palaeoclimatology, provide useful long-term perspectives on climate change. A recent dispute regarding the potential misdating of tree-ring width chronologies from conifer species growing near their thermal distribution limit, due to ‘missing’ rings, has raised questions about the reliability of tree-ring chronologies as annually resolved and absolutely dated proxy archives. Consequently, the debate introduces doubt on the validity of tree ring-based temperature reconstructions. The claim of ‘missing’ tree rings, caused by exceptional summer cooling following large volcanic eruptions, is based on experimental results of a cambial growth model, used to estimate tree growth during intervals of low temperatures, as simulated by a forced climate model. Although this experiment has received substantial criticism, there has not yet been confirmation of the dating accuracy in temperature-sensitive ring width chronologies using independent geochemical markers. At the same time, recent astrophysical evidence suggests the existence of two uniquely rapid boosts in the atmospheric 14C content that occurred in 775 and 994 CE.

To objectively investigate the so-called ‘missing ring’ hypothesis, the COSMIC initiative will, for the first time ever, compile a global collection of wood samples from around 35 millennial-long tree-ring chronologies that comprise different material from living trees as well as historical timbers from roof and wall structures in old buildings and subfossil remains preserved in peat bogs, mires, lakes and glacial moraines. These datasets, covering the intervals 770-780 and 990-1000 CE, were often utilized for climate reconstructions prior to the period of ample documentary evidence, and provide an ideal test case to evaluate the individual dating precision of the various tree-ring records prior to the last millennium. In fact, we will measure the 14C to 12C isotopic ratios of the dendrochronologically dated rings of each wood sample from 770-780 and from 990-1000 CE to detect and to describe the putative global signature of the extra-terrestrial 775 and 994 radiocarbon pulses.


PIs: Ulf Büntgen, Lukas Wacker

Partners: Global consortium

Funding: Swiss National Science Foundation (SNF) and ETH Zurich Ion Beam Physics Lab

Mini Carbon Dating System (MICADAS; Ionplus)

The Mini Carbon Dating System (MICADAS; Ionplus) at the Laboratory of Ion Beam Physics (LIP), ETH Zurich, Switzerland.