Minimal Extension Phases of Unteraarglacier (Swiss Alps) During the Holocene Based on 14C Analysis of Wood

Abstract

Tree trunks and wood fragments in minerotrophic fen peat that accumulated as the result of a jökulhlaup in the outwash plain of Unteraarglacier were radiocarbon-dated using conventional beta -counting. Different pretreatment methods were tested on two wood samples to determine the reliability of our dates. We dated the wood compounds after extended acid-alkali-acid treatment, as well as extraction of cellulose and lignin. The results of the samples Picea (B-6687) and Pinus cembra (B-6699) show insignificant differences of <1 sigma. The 14C dates represent retreat of Unteraarglacier due to warmer and/or drier phases in the Holocene compared to modern climate conditions. The glacier was at least several hundred meters smaller in extent than today ca. 8100-7670 BP, 6175-5780 BP, 4580-4300 BP, 4100-3600 BP and 3380-3200 BP. The 14C dates suggest a ca. 2000-yr cyclicity of tree growth in the area covered by the present Unteraarglacier. The most intense warm and dry period occurred between 4100 BP (probably extending back to 4580 BP) and 3600 BP, with growth of fen peat between 3800 and 3600 BP attributed to wetter conditions.