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University of Groningen Improving the Time Control of the Subboreal University of Groningen Improving the time control of the Subboreal/Subatlantic transition in a Czech peat sequence by 14C wiggle-matching Speranza, A.; Plicht, J. van der; Geel, B. van Published in: Quaternary Science Reviews DOI: 10.1016/S0277-3791(99)00108-0 IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2000 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Speranza, A., Plicht, J. V. D., & Geel, B. V. (2000). Improving the time control of the Subboreal/Subatlantic transition in a Czech peat sequence by 14C wiggle-matching. Quaternary Science Reviews, 19(16), 1589- 1604. https://doi.org/10.1016/S0277-3791(99)00108-0 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license. More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne- amendment. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Quaternary Science Reviews 19 (2000) 1589}1604 Improving the time control of the Subboreal/Subatlantic transition in a Czech peat sequence by C wiggle-matching A. Speranza! *, J. van der Plicht", B. van Geel! !Hugo de Vries Laboratory, University of Amsterdam, Kruislaan 318, NL-1098 SM Amsterdam (The Netherlands Centre for Geo-ecological Research, ICG), Netherlands "Centre for Isotope Research, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen (The Netherlands Centre for Geo-ecological Research, ICG), Netherlands Abstract To achieve an optimal time-control for a late Subboreal to early Subatlantic peat sequence from Panc\ avskaH Louka in the Czech Republic, di!erent strategies are applied to convert a series of radiocarbon dates into a calendar time-scale. The methods of selection and preparation of the samples for AMS C dating are presented. The results of calibrating single radiocarbon dates are compared with a C wiggle-match strategy. As the accumulation rate of the peat was not constant, the concentrations of arboreal pollen are used to estimate the accumulation rate changes and to correct for these changes. The resulting time-control represents the best solution for this peat sequence with the methods currently available. ( 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction animals that died during that time interval now display similar radiocarbon ages, scattering around 2450 BP. The conversion of radiocarbon dates into calendar The calibration of these radiocarbon ages into calendar ages is complicated by the nonlinearity of the calibration ages gives a probability range covering approximately curve, i.e. the presence of wiggles due to past variations in 340 calendar years, from 760 to 420 cal BC (Fig. 2). This the atmospheric C content (de Vries, 1958; Suess, 1970; lack of accuracy for calibrated results is problematic in Stuiver et al., 1998). In particular, the calibration of palaeobotanical and archaeological reconstructions if no radiocarbon dates at approximately 2500}2450 BP is other absolute dating method providing a calendar problematic due to a `plateaua (known as the `Hal- time-scale (i.e. dendrochronology, varved sequences) can lstatt-plateaua) in the calibration curve (Kilian et al., be additionally applied. A solution is given by the 1995, 2000) (Fig. 1a and Fig. 2). A decrease in solar wiggle-match strategy (van Geel and Mook, 1989), where activity caused an increase in production of C, and thus a stratigraphic sequence of C dates is matched to the a sharp rise in *C , beginning at approximately 850 cal wiggles of the calibration curve. This is analogous to (calendar years) BC (Fig. 1b). Between approximately 760 wiggle-matching of #oating tree rings to the calibration and 420 cal BC (corresponding to 2500}2425 BP), the curve (Pearson, 1986). The application of the wiggle- concentration of C returned to `normala values. These match dating strategy (WMD) can also provide evid- events are mirrored in the calibration curve as a sharp ences for a reservoir e!ect in a sequence, as demonstrated descent between 850 and 760 cal BC (2700}2450 BP) by Kilian et al. (1995) for raised bogs. * corresponding to the increase in *C * and a pla- An important application of WMD is the research on teau between 760 and 420 cal BC (2500}2425 BP) * cor- the apparent existence of a link between the decrease in responding to the decrease of the excess in C (Fig. 1). solar activity at 850 cal BC and the climatic deterioration A consequence of the decreasing atmospheric C con- occurring at the same time (Davis, 1994; Denton and centration between 760 and 420 cal BC is that plants and Karlen, 1973; Karlen and Kuylenstierna, 1996; van Geel et al., 1998, 1999; Jirikowic et al., 1993; Magny, 1993, 1999). Evidence for such a link can be the positive cor- * Corresponding author. Tel.: 0031-20-5257666; fax: 0031-20- relation between changing solar activity proxies (the cos- 5257878. mogenic isotopes C and Be) and geological climate E-mail address: [email protected] (A. Speranza). proxies. Such a relationship is feasible only when time 0277-3791/00/$- see front matter ( 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 3 7 9 1 ( 9 9 ) 0 0 1 0 8 - 0 1590 A. Speranza et al. / Quaternary Science Reviews 19 (2000) 1589}1604 Fig. 2. Example of the calibration of a radiocarbon date (2450$50 BP) around the Hallstatt plateau. The probability distribution in calen- dar years yields almost four centuries. 2. Materials and methods 2.1. Peat samples collection and preparation Fig. 1. Radiocarbon calibration curve (a) and *C detrended for the magnetic "eld (b) between 1800 cal BC and 200 cal AD. Data from the The peat bog of Panc\ avskaH Louka (5034510 N, INTCAL 98 curve (Stuiver et al., 1998). 1533250E) is located at a height of 1320 m in the Krkonos\ e Mountains (Giant Mountains), in the Czech Republic. It belongs to the complex of montane raised bogs (NeuhaK uslova et al., 1998), and at present it is control is precise. The application of WMD can provide approximately 1 km in diameter (Fig. 3). The sampled the required precision, but it requires application in those peat section represents the period from 5320$60 BP parts of the calibration curve where pronounced, charac- (GrA-6326) to the present time (1996 AD). Here we pres- teristic wiggles are present because the shape of a single ent the dating procedures and the conversion from wiggle of the calibration curve has to be recognised in the a radiocarbon to a calendar time-scale by means of sediment or peat sequence for the series of C dates to be WMD for the period between 3100 and 1900 BP. matched. This is usually an expensive strategy, as it Fluctuations in the total arboreal pollen concentration requires a great number of radiocarbon dates by AMS of mainly depend on changes in the accumulation rate of selected material (leaves, seeds and other above-ground the peat in the absence of marked human in#uence (Mid- material). deldorp, 1982). Such #uctuations can be used in the Palaeoecological analyses of a sequence from the peat wiggle-matching procedure to model a distance between bog of Panc\ avskaH Louka (Czech Republic) provided data subsequent C samples that takes into account changes on climatic change towards cooler, moister conditions at in the peat accumulation rate. We also show a relevant the Subboreal}Subatlantic transition. To reconstruct the selection of pollen and macrofossil data (peat forming phases of this climatic event, an accurate time-control plants) for the time range between 3100 and 1900 BP. The was needed. This could be achieved by using the complete micro- and macrofossil record will be published C wiggle-match dating strategy. in a future paper. A. Speranza et al. / Quaternary Science Reviews 19 (2000) 1589}1604 1591 sample was split in subsamples which were observed in water in a Petri dish. The Petri dish was divided in sectors in order to avoid overlapping with already ana- lysed parts of the subsample. A plus (#) in the curve of a taxon indicates that this taxon was present in the sample in such a low quantity that the attribution of a volume percentage was not realistic. Microfossils samples were treated with KOH and acetolysed according to the method of Faegri and Iversen (1989). The identi"cation of pollen grains was based on Moore et al. (1991). Rare taxa are indicated with a plus (#). 2.3. Preparation of the samples for radiocarbon dating The selection of macrofossils for radiocarbon dating Fig. 3. Map and location of the area. was undertaken using a binocular microscope (magni"- cations 10; and 20;). A number of samples showed traces of fossil fungal infection (mycelium). An empirical For the time interval presented, 29 samples were fungal infection coe$cient (FIC) was introduced to tenta- radiocarbon dated by AMS at the Centre for Isotope tively express the degree of fungal contamination of the Research of the University of Groningen.
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