JOURNAL OF QUATERNARY SCIENCE (2004) 19(3) 241–249 Copyright ß 2004 John Wiley & Sons, Ltd. Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jqs.833 Holocene tephra horizons at Klocka Bog, west-central Sweden: aspects of reproducibility in subarctic peat deposits JONAS BERGMAN, 1 * STEFAN WASTEGA ˚ RD, 2 DAN HAMMARLUND, 1 BARBARA WOHLFARTH 2 and STEPHEN J. ROBERTS 3 1 GeoBiosphere Science Centre, Quaternary Sciences, Lund university, Sweden 2 Department of Physical Geography and Quaternary Geology, Stockholm University, Sweden 3 Department of Geography, University of Edinburgh, Scotland Bergman, J., Wastega ˚rd, S., Hammarlund, D., Wohlfarth, B. and Roberts, S. J. 2004. Holocene tephra horizons at Klocka Bog, west-central Sweden: aspects of reprodu- cibility in subarctic peat deposits. J. Quaternary Sci., Vol. 19 pp. 241–249. ISSN 0267-8179. Received 25 October 2002; Revised 5 November 2003; Accepted 6 December 2003 ABSTRACT: This paper presents one of the most extensive Holocene tephra records found to date in Scandinavia. Microtephra horizons originating from Icelandic eruptions were recorded in two ca. 2 m thick peat profiles at Klocka Bog in west-central Sweden. Five of the microtephra horizons were geo- chemically correlated to the Askja-1875, Hekla-3, Kebister, Hekla-4 and Lairg A tephras respectively. Radiocarbon-based dating of these tephras broadly agree with previously published ages from Ice- land, Sweden, Germany and the British Isles. The identification of the Lairg A tephra demonstrates a more widespread distribution than previously thought, extending the usefulness of Icelandic Holocene tephrochronology further north into west-central Scandinavia. Long-lasting snow cover and seasonal wind distribution in the lower stratosphere are suggested as factors that may be responsible for fragmentary tephra deposition patterns in peat deposits of subarctic Scandinavia. Copyright ß 2004 John Wiley & Sons, Ltd. KEYWORDS: tephra; tephrochronology; Holocene; Klocka Bog; Sweden. Introduction Tephrochronology is a powerful tool for relative and absolute dating of Quaternary deposits (Westgate et al., 1992; Sarna- Wojcicki, 2000). The high-resolution Holocene tephrochro- nology of Iceland is of particular value for constraining and cor- relating the timing and duration of short-term climatic and palaeoecological events in the North Atlantic region (e.g. Eirı ´ksson et al., 2000a, b). Over the past few decades glass particles, originating from Icelandic volcanic systems, have been identified in Holocene peat sequences and lake sediments throughout Scandinavia (e.g. Persson, 1966, 1971; Boygle, 1998; Zille ´n et al., 2002; Wastega ˚rd, in press). Here we present new evidence from Klocka Bog, an ombrotrophic peat deposit in west-central Sweden. The tephras detected include several of the most important Holocene tephra isochrones in the North Atlantic region. As part of pioneering tephrochronological investigations in central Scandinavia, Persson (1966, 1971) sampled a peat sequence at Klocka, and detected two ash layers of Icelandic origin that possibly originated from the O ¨ raefajo ¨ kull (AD 1362); (Thorarinson, 1958) and Hekla-4 or Kebister eruptions (ca. 4200 and 3800 cal. yr BP, respectively). Persson’s identifi- cations were made on the basis of refractive index measure- ments of the glass particles, supported by conventional radiocarbon dating. Our renewed sampling of the site has revealed an unprecedented set of tephras including the Lairg A tephra (Dugmore et al., 1995a; Pilcher et al., 1996; Hall, 2003), not previously recorded in Sweden. In addition, this paper highlights depositional problems encountered in tephro- chronological studies of peat deposits. The results from Klocka Bog contribute to the ongoing mapping of north-west European tephra distributions as chronological marker horizons within Quaternary stratigraphy, and these time markers open new possibilities for comparison and correlation of multi-proxy data from terrestrial, marine and ice-core archives. Site description Klocka Bog (63  18.5 0 N, 12  29.0 0 E, surface area ca. 260 ha) is a gently sloping bog-fen complex protruding into Lake A ˚ nnsjo ¨n, situated at 526 m a.s.l. in the province of Ja ¨mtland, west-central Sweden (Fig. 1; Lundqvist, 1969). The peat deposit is surrounded by coniferous forest (mainly Picea * Correspondence to: Jonas Bergman, GeoBiosphere Science Centre, Quaternary Sciences, Lund University, Sweden. E-mail: jonas.bergman@geol.lu.se