Research paper An automated method for varve interpolation and its application to the Late Glacial chronology from Lake Suigetsu, Japan Gordon Schlolaut a, * , Michael H. Marshall b , Achim Brauer a , Takeshi Nakagawa c , Henry F. Lamb b , Richard A. Staff d , Christopher Bronk Ramsey d , Charlotte L. Bryant e , Fiona Brock d , Annette Kossler f , Pavel E. Tarasov f , Yusuke Yokoyama g, h , Ryuji Tada g , Tsuyoshi Haraguchi i Suigetsu 2006 project members 1 a Section 5.2: Climate Dynamics and Landscape Evolution, German Research Centre for Geosciences (GFZ), Telegrafenberg, 14473 Potsdam, Germany b Institute of Geography and Earth Sciences, Aberystwyth University, SY23 3DB, UK c Department of Geography, University of Newcastle, Newcastle-upon-Tyne NE17RU, UK d Oxford Radiocarbon Accelerator Unit (ORAU), Research Laboratory for Archaeology and the History of Art (RLAHA), University of Oxford, Dyson Perrins Building, South Parks Road, Oxford OX1 3QY, UK e NERC Radiocarbon Facility - Environment (NRCF-E), Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride G75 0QF, UK f Institute of Geological Sciences, Palaeontology, Freie Universität Berlin, Malteserstrasse 74-100, Building D, 12249 Berlin, Germany g Department of Earth and Planetary Sciences, Faculty of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan h Ocean Research Institute, University of Tokyo,1-15-1 Minami-dai, Nakano-ku, Tokyo 164-8639, Japan i Department of Geosciences, Osaka City University, Sugimoto 3-3-138, Sumiyoshi, Osaka 558-8585, Japan article info Article history: Received 7 February 2012 Received in revised form 26 June 2012 Accepted 16 July 2012 Available online 1 August 2012 Keywords: Varves Interpolation Suigetsu LGIT Chronology Sediment core 14 C calibration abstract The Lake Suigetsu sediment has been recognised for its potential to create a wholly terrestrial (i.e. non- reservoir-corrected) 14 C calibration dataset, as it exhibits annual laminations (varves) for much of its depth and is rich in terrestrial leaf fossils, providing a record of atmospheric radiocarbon. Microscopic analysis revealed that the varve record is curtailed due to the incomplete formation or preservation of annual laminae, necessitating interpolation. The program for varve interpolation presented here analyses the seasonal layer distribution and automatically derives a sedimentation rate estimate, which is the basis for interpolation, and applies it to complement the original varve count. As the interpolation is automated it largely avoids subjectivity, which manual interpolation approaches often suffer from. Application to the Late Glacial chronology from Lake Suigetsu demonstrates the implementation and the limits of the method. To evaluate the reliability of the technique, the interpolation result is compared with the 14 C chronology from Lake Suigetsu, calibrated with the tree-ring derived section of the IntCal09 calibration curve. The comparison shows that the accuracy of the interpolation result is well within the 68.2% probability range of the calibrated 14 C dates and that it is therefore suitable for calibration beyond the present tree-ring limit. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Varved (annually laminated) sediments are palaeo- environmental archives that at the same time allow the construc- tion of high precision age models, potentially down to a seasonal resolution (Brauer et al., 1999). However, a common problem is the occurrence of incompletely varved sections. Changes in the depo- sitional environment may interrupt varve formation or result in partially indistinct records (Zolitschka et al., 2000), which therefore require interpolation. Commonly, interpolation is carried out manually, using sedimentation rate estimates from neighbouring, well varved sections. The main error source of this conventional interpolation approach is that sedimentation rates in compromised intervals (i.e. intervals with an incompletely developed varve record) and well varved intervals can be different. Also, the conventional interpolation cannot be applied to sediment profiles that do not show well varved intervals. The new approach pre- sented here is based on an automated analysis of frequency distributions of seasonal layers from the compromised interval itself and therefore avoids this main problem associated with conventional varve interpolation. Moreover, since the interpolation * Corresponding author. Tel.: þ49 331 288 1355; fax: þ49 331 288 1302. E-mail address: gosch@gfz-potsdam.de (G. Schlolaut). 1 For full details see: www.suigetsu.org. Contents lists available at SciVerse ScienceDirect Quaternary Geochronology journal homepage: www.elsevier.com/locate/quageo 1871-1014/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.quageo.2012.07.005 Quaternary Geochronology 13 (2012) 52e69