MINIMAL EXTENSION PHASES OF UNTERAARGLACIER (SWISS ALPS) DURING THE HOLOCENE BASED ON C-14 ANALYSIS OF WOOD

Tree trunks and wood fragments in minerotrophic fen peat that accumula ted as the result of a jokulhlaup in the outwash plain of Unteraarglac ier 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 wall as extraction of cellulose and lig nin. The results of the samples Picea (B-6687) and Pinus cembra (B-669 9) show insignificant differences of < 1 sigma. The C-14 dates represe nt retreat of Unteraarglacier due to warmer and/or drier phases in the Holocene compared to modern climate conditions. The glacier was at le ast 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 C-1 4 dates suggest a ca. 2000-yr cyclicity of tree growth in the area cov ered by the present Unteraarglacier. The most intense warm and dry per iod occurred between 4100 BP (probably extending back to 4580 BP) and 3600 BP, with growth of fen peat between 3800 and 3600 BP attributed t o wetter conditions.