Research paper Signal and variability within a Holocene peat bog — Chronological uncertainties of pollen, macrofossil and fungal proxies Maarten Blaauw a, ⁎, Dmitri Mauquoy b a School of Geography, Archaeology and Palaeoecology, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, UK b School of Geosciences, University of Aberdeen, Aberdeen AB24 3UF, Scotland, UK abstract article info Article history: Received 2 January 2012 Received in revised form 18 June 2012 Accepted 20 June 2012 Keywords: radiocarbon chronologies fossil proxy signal and noise raised bog peat deposits A single raised bog from the eastern Netherlands has been repeatedly analysed and 14 C dated over the past few decades. Here we assess the within-site variability of fossil proxy data through comparing the regional pollen, macrofossils and non-pollen palynomorphs of four of these profiles. High-resolution chronologies were obtained using 14 C dating and Bayesian age-depth modelling. Where chronologies of profiles overlap, proxy curves are compared between the profiles using greyscale graphs that visualise chronological uncer- tainties. Even at this small spatial scale, there is considerable variability of the fossil proxy curves. Implica- tions regarding signal (climate) and noise (internal dynamics) of the different types of fossil proxies are discussed. Single cores are of limited value for reconstructing centennial-scale climate change, and only by combining multiple cores and proxies can we obtain a reliable understanding of past environmental change and possible forcing factors (e.g., solar variability). © 2012 Elsevier B.V. All rights reserved. 1. Introduction Peat deposits from raised bogs are well-known for storing valuable information about past environmental conditions. Starting in the late nineteenth century with Rutger Sernander, distinct layers within Holo- cene peat deposits were used to infer separate climatic periods such as the Boreal, Atlantic, Subboreal and Subatlantic (von Post, 1946; Birks, 2008). Peat layers, as well as pollen stored within the peat, were used to build regional to continental-scale climatic histories at millennial time-scales (Dachnowski, 1922; von Post, 1946). Most early palaeoecological studies were done at centennial tempo- ral resolution, sub-sampling peat cores every 10–20 cm or so. Since not every cm was analysed, the records were often discontinuous (see Liu et al., 2012 for implications). However, from the 1970s on Bas van Geel and others at the Hugo de Vries laboratory (University of Amsterdam) aimed to obtain continuous and more highly resolved environmental informa- tion, and therefore started working at centimetre, or decadal resolution. They were also among the first to complement pollen analysis with that of non-pollen palynomorphs such as fungal spores and insect remains, both within pollen slides and through macrofossil analysis. Examples of such studies include that of Wietmarscher Moor (van Geel, 1972) and the well-replicated site of Engbertsdijksveen (Fig. 1; Table 1). To enable placing these decadal resolution fossil proxy data in their context (e.g. temporal comparisons with other time series such as that of past solar activity), precise chronologies were needed. Through close collaborations with the radiocarbon laboratory at Groningen University, an investigation was made to determine how peat cores could be dated at very high temporal resolution. Dense series of bulk peat or macrofossil remains were 14 C dated and then matched onto centennial to decadal scale wiggles of the 14 C calibration curve (wiggle-match dating; van Geel and Mook, 1989). Later studies aimed to test which peat remains would give the most reliable dates (e.g., Kilian et al., 1995, 2000; Shore et al., 1995; Nilsson et al., 2001; Blaauw et al., 2004a; Brock et al., 2011), or to quantify the chronological resolution of 14 C wiggle-match dated peat deposits (e.g., Kilian et al., 2000; Blaauw et al., 2003, 2004a, 2004b, 2007a, 2007b; Blaauw and Christen, 2005, 2011). Periods where the 14 C calibration curve (Reimer et al., 2009) shows rapidly declining 14 C ages indicate a reduced solar activity. As van Geel and Mook (1989) argued, high-resolution series of 14 C dates from peat deposits should show the same multi-decadal scale wiggles as the 14 C calibration curve, and thus changes in solar activity could be inferred di- rectly from these wiggles. This prompted van Geel et al. (1996, 1998, 1999) to investigate temporal links between changes in solar activity and climate variability as recorded within the peat deposits. A major drop in 14 C ages (in the calibration curve as well as in high-resolution 14 C sequences from peat bogs) starting around 2800 cal BP (calendar years before present, where present is AD 1950) was interpreted by van Geel et al. (e.g. 1996, 1998, 1999) as a decline in solar activity. This decline occurred at the same time as a major transition from highly decomposed peat to much less decomposed peat in northwest Europe- an bogs (e.g., Kilian et al., 1995), an event interpreted to have been caused by a shift to a colder and more humid climate in the region. Also archives in other regions recorded a climate change around this time (e.g., van Geel et al., 1996, 1998; Speranza et al., 2002; Chambers et al., 2007). Since the climatic shift occurred at the same time as a Review of Palaeobotany and Palynology 186 (2012) 5–15 ⁎ Corresponding author. Tel.: +44 28 9097 3895. E-mail address: maarten.blaauw@qub.ac.uk (M. Blaauw). 0034-6667/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.revpalbo.2012.06.005 Contents lists available at SciVerse ScienceDirect Review of Palaeobotany and Palynology journal homepage: www.elsevier.com/locate/revpalbo