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
Final Report Abstract
This project resulted in unique progress in several fields: a) The European tree-ring chronology was extended with annual certainty back to 12.314 BP years BP (before AD 1950), and with a low uncertainty of +-8 years back to 14.226 BP. This by far the longest tree-ring chronology world-wide. b) The annual 14C data set of 1705 samples between 13.100 and 11.900 BP, measured in this project, is the longest consecutive data set of annual resolution within the range of the 14C clock. It improves the resolution of the 14C calibration by an order of magnitude in this age range. c) The 14C time series shows the strongest variation in 14C production over the past 14.000 years, coincident with the onset of the Younger Dryas, and mirrored in the production of 10Be, the sister cosmogenic isotope to 14C. This observation confirms the occurrence of a very strong 'Grand Minimum' of solar activity. d) Resolution and precision of the 14C data set of this project allowed the reconstruction of the amplitude variation of the offset between the atmospheric 14C level in the Northern and Southern hemisphere. The observed increase of this amplitude in the first half of the Younger Dryas confirms model results involving reduced North Atlantic Ocean circulation and increased mixing in the Southern ocean. e) The stable isotope chronology from southern France revealed a distinct increase in inter-annual variability of sourcewater isotopes (δ18Osw-tree), with three major downturn phases of increasing magnitude beginning at 12 740 cal BP. The observed variation most likely results from an amplified intensity of North Atlantic (low δ18Osw-tree) versus Mediterranean (high δ18Osw-tree) precipitation. This marked pattern of climate variability is not seen in records from higher latitudes and is likely a consequence of atmospheric circulation oscillations at the margin of the southward moving polar front. We see three fields of applications, in addition to the ones covered by the publications of the project: a) The intensive collaboration of dendrochronologists and 14C physicists resulted in a robust and reliable chronology building, which may act as a model for future extensions of tree-ring chronologies in the past. b) The observed variations in 14C production, along with similar signals in 10Be in ice cores, will provide a unique record of solar variability to the solar physics community. c) Climate reconstructions from tree-ring stable isotopes have shown signals in different higher frequency domains than recorded by other proxies. On the other hand, low frequency signal do not seem well preserved in the tree-ring series. Deuterium measurements on tree-ring cellulose may give additional insight.
Publications
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(2016). "Decadally Resolved Lateglacial Radiocarbon Evidence from New Zealand Kauri." Radiocarbon 58(4): 709-733
Hogg, A., J. Southon, C. Turney, J. Palmer, C. B. Ramsey, P. Fenwick, G. Boswijk, U. Büntgen, M. Friedrich, G. Helle, K. Hughen, R. Jones, B. Kromer, A. Noronha, F. Reinig, L. Reynard, R. Staff and L. Wacker
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(2017): A guideline for sample preparation in modern tree-ring stable isotope research. - Dendrochronologia, 44, pp. 133-145
Schollaen, K., Baschek, H., Heinrich, I., Slotta, F., Pauly, M., Helle, G.
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(2017): Vom Monitoring zum Klimaarchiv : Sauerstoffisotope in der Paläoklimatologie . - System Erde, 7, 1
Plessen, B., Helle, G.
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(2018). "New tree-ring evidence for the Late Glacial period from the northern pre-Alps in eastern Switzerland." Quaternary Science Reviews 186: 215-224
Reinig, F., D. Nievergelt, J. Esper, M. Friedrich, G. Helle, L. Hellmann, B. Kromer, S. Morganti, M. Pauly, A. Sookdeo, W. Tegel, K. Treydte, A. Verstege, L. Wacker and U. Büntgen
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(2018). "Subfossil trees suggest enhanced Mediterranean hydroclimate variability at the onset of the Younger Dryas." Scientific Reports 8(1): 13980
Pauly, M., G. Helle, C. Miramont, U. Büntgen, K. Treydte, F. Reinig, F. Guibal, O. Sivan, I. Heinrich, F. Riedel, B. Kromer, D. Balanzategui, L. Wacker, A. Sookdeo and A. Brauer
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(2019): A high yield cellulose extraction system for small whole wood samples and dual measurement of carbon and oxygen stable isotopes. - Chemical Geology, 504, pp. 53-65
Andreu-Hayles, L., Levesque, M., Martin-Benito, D., Huang, W., Harris, R., Oelkers, R., Leland, C., Martin- Fernández, J., Anchukaitis, K. J., Helle, G.
