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A Late-glacial and Holocene record of climatic change from a Swiss peat humification profile

Institute of Geological Sciences, Baltzerstrasse 1–3, University of Berne, CH-3012 Berne, Switzerland; fiona.roos{at}geo.unibe.ch

W. O. van der Knaap

J. F.N. van Leeuwen

Institute of Plant Sciences, Altenbergrain 21, University of Berne, CH-3013 Berne, Switzerland

W. Shotyk

Institute of Environmental Geochemistry, University of Heidelberg, Im Neuenheimer Feld 236, D-69120 Heidelberg, Germany

Colorimetric measurements of alkaline extracts from two Swiss peat cores have provided a complete 14500-year-long record of peat humification, a proxy of effective precipitation. Peat from the cold Younger Dryas (11050–9550 cal. bc) was well preserved despite low levels of precipitation. A particularly dry period, peaking at c. 7100 cal. bc, is indicated by well-decomposed peat. Peat from c. 6750–4250 cal. bc shows a low degree of decomposition, indicating a wet bog surface despite relatively warm temperatures and therefore indicating high levels of precipitation. A sharp transition to higher levels of decomposition c. 4450–3750 cal. bc indicates a major transition to a drier bog surface. Subsequently, peat humification generally decreases towards the end of the deeper profile (c. cal. ad 1050), indicating a gradual return to wetter conditions. This gradual decrease is punctuated by periods of particularly low humification which appear to be due to shifts to higher levels of effective precipitation from c. 2500 to 1350 cal. bc, c. 1050 to 550 cal. bc, centered around 150 cal. bc, and from c. cal. ad 550 onwards. Anthropogenic influences appear to have affected peat humification at the site at least since the Middle Ages. This study indicates that humification in colder regions/time periods could be more affected by temperature than precipitation and vice versa.

Key Words: Peatlands • peat humification • decomposition • colorimetry • palaeoclimate proxy • effective precipitation • Lateglacial • Holocene • Switzerland

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