Radiocarbon dating of fossil wood remains buried by the Piancabella rock glacier, Blenio Valley (Ticino, southern Swiss Alps): Implications for rock glacier, treeline and climate history

Fossil wood stem remains of larch (Larix decidua) found 1 m below the surface at the base of the front of the Piancabella rock glacier (46°27′02″N, 9°00′07″E, 2480 m a.s.l.) had a conventional age range of 845 ± 50 14C y BP (UZ‐5545/ETH‐34417), corresponding to a calibrated calendar age range of 1040–1280 AD (790 ± 120 cal BP) with a statistical probability of 95.4 per cent. Based on geomorphological, climatological and geophysical observations, we infer that (1) the treeline in the Medieval Warm Period was about 200 m higher than in the middle of the 20th century, which corresponds to a mean summer temperature as much as 1.2°C warmer than in AD 1950, and (2) that ice within this rock glacier is probably several centuries old and so predates recent climatic events such as the Little Ice Age. Copyright © 2009 John Wiley & Sons, Ltd.