Research Paper Radiocarbon wiggle-match dating of proglacial lake sediments – Implications for the 8.2 ka event Anne Hormes a, * , Maarten Blaauw b , Svein Olaf Dahl c , Atle Nesje d , Goran Possnert a a Ångstromlaboratory, Uppsala University, 75120 Uppsala, Sweden b School of Geography, Archaeology and Palaeoecology, Queen’s University, Belfast, Northern Ireland, UK c Department of Geography, University of Bergen, Breiviksveien 40, 5045 Bergen, Norway d Department of Earth Science, University of Bergen, Alle´gaten 41, 5007 Bergen, Norway article info Article history: Received 6 August 2008 Received in revised form 28 November 2008 Accepted 5 December 2008 Available online 8 January 2009 Keywords: Radiocarbon wiggle-match dating Norway Holocene Glacier variations 8.2 ka event 9.2 ka event Nedre Hervavatnet Fannaråkbreen Jotunheimen abstract The problem of insufficient age-control limits the utilisation of the 8.2 ka BP event for modelling freshwater forcing in climate change studies. High-resolution radiocarbon dates, magnetic susceptibility and lithostratigraphic evidence from a lake sediment core from Nedre Hervavatnet located at Sygnefjell in western Norway provide a record of the early Holocene. We use the method of radiocarbon wiggle- match dating of the lake sediments using the non-linear relationship between the 14 C calibration curve and the consecutive accumulation order of the sample series in order to build a high-resolution age- model. The timing and duration of Holocene environmental changes is estimated using 38 AMS radio- carbon dates on terrestrial macrofossils, insects and chironomids covering the time period from 9750 to 1180 cal BP. Chironomids, Salix and Betula leaves produce the most consistent results. Sedimentological and physical properties of the core suggest that three meltwater events with high sedimentation rates are superimposed on a long-term trend with glacier retreat between 9750 and 8000 cal BP. The lake sediment sequence of Nedre Hervavatnet demonstrates the following: only a reliable high-resolution geochronology based on carefully selected terrestrial macrofossils allows the reconstruction of a more refined and complex environmental change history before and during the 8.2 ka event. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Reviews of Holocene millennial- and centennial climate vari- ability, including the 8.2 ka event, have revealed that different archives and proxies do not always react synchronously (Mayewski et al., 1996; Rohling and Paelike, 2005; Schmidt and Jansen, 2006). The major problem of age-control creates a challenge when comparing records from different regions (Guilderson et al., 2005; Schmidt and Jansen, 2006; Blaauw et al., 2007b). Accurate age- models are the backbone for the comparison of climate signals from different paleoarchives. Tree-rings (Becker and Kromer, 1993; Muscheler et al., 2004) and ice cores (Flu ¨ ckiger et al., 2002; Ras- mussen et al., 2006; Vonmoos et al., 2006) eventually have an annual resolution. Marine sediments, lake sediments and peat bog deposits attain a decadal resolution (Eicher, 1976; Hajdas et al., 1995; Gulliksen et al., 1998; Shotyk et al., 1998; von Grafenstein et al., 1998; Bond et al., 2001; Bondevik et al., 2001; Blaauw et al., 2004; Mauquoy et al., 2004; Wolfe et al., 2004; Bondevik et al., 2006; Kylander et al., 2006). Isotope records from stalagmites and glacier reconstructions might be used on a centennial resolution (Karle ´n, 1982; Nesje et al., 1991; Nesje and Kvamme, 1992; McDermott et al., 1999; Hormes et al., 2001; Holzhauser et al., 2005; Humlum et al., 2005; Jo ¨ rin et al., 2006; Vollweiler et al., 2006). The resolution of pollen and macrofossil records is depen- dent on their stratigraphic context and might vary quite consider- ably (Brown et al., 1992; Rose ´ n et al., 2001; Wohlfarth et al., 2006). There is good evidence for abrupt climatic changes in the different records, although, it remains difficult to assess whether these are in-phase or out-of phase based on proxy records with weak age-control. We focus on the two most important challenges for high-quality age-models – the choice of material to be dated avoiding contam- ination problems and the construction of reliable high-resolution age-models. The application of AMS to dating terrestrial macrofossils is highly important, reducing potential contamination problems encountered with bulk sediment samples or humic acid extractions by either younger or older carbon sources (Olsson,1986; MacDonald et al., 1987; Bjo ¨rck and Wohlfarth, 2001; Blaauw et al., 2004). * Corresponding author. The University Centre in Svalbard, Pb 156, 9171 Long- yearbyen, Norway. Tel.: þ47 79026453. E-mail address: anne.hormes@unis.no (A. Hormes). Contents lists available at ScienceDirect Quaternary Geochronology journal homepage: www.elsevier.com/locate/quageo 1871-1014/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.quageo.2008.12.004 Quaternary Geochronology 4 (2009) 267–277