The methodological basis for fine-resolution, multi-proxy reconstructions of ombrotrophic peat bog surface wetness MATTHEW J. AMESBURY, KEITH E. BARBER AND PAUL D. M. HUGHES BOREAS Amesbury, M. J., Barber, K. E. & Hughes, P. D. M. 2011 (January): The methodological basis for fine-resolution, multi-proxy reconstructions of ombrotrophic peat bog surface wetness. Boreas, Vol. 40, pp. 161–174. 10.1111/ j.1502-3885.2010.00152.x. ISSN 0300-9483. The need for Holocene peat-based palaeoclimatic records of increased temporal resolution has been widely iden- tified in recent research. The often rapid growth rates of ombrotrophic bogs, when combined with fine-resolution (i.e. millimetre-scale) sampling, provide an as yet largely unexploited potential to derive sub-decadal palaeocli- matic data from this proxy-archive. However, multi-proxy, fine-resolution analyses require changes to standard methodologies, and the application of sampling techniques that are new to peat-based palaeoclimate research. A peat sampler was custom-built to allow precise and replicable millimetre-scale subsampling. Subsequent metho- dological testing revealed that, irrespective of sample thickness (i.e. resolution), halving the standard sample vo- lume used for plant macrofossil (from 4 cm 3 to 2 cm 3 ) and testate amoebae (from 2 cm 3 to 1 cm 3 ) analyses and the sample weight used for peat humification analysis (from 0.2 g to 0.1 g dried peat) did not affect the interpretation of the results. A contiguous 1-mm sampling resolution for plant macrofossil analysis was also tested, but it was found that contiguous 5-mm samples provided a more reliable background record to fine-resolution testate amoebae and peat humification analyses. Based on these findings, a standardized and systematic methodological approach was developed, using the custom-built peat slicer to take millimetre-scale samples that provide enough sample material for both testate amoebae and peat humification analyses to be performed at 1-mm resolution. This approach will facilitate the testing of the palaeoclimatic reliability of multi-proxy, fine-resolution peat-based records. Matthew J. Amesbury (e-mail: m.j.amesbury@gmail.com), Keith E. Barber and Paul D. M. Hughes, Palaeoecology Laboratory (PLUS), School of Geography, University of Southampton, Highfield, Southampton SO17 1BJ, UK; received 25th April 2009, accepted 12th February 2010. Anthropogenically induced climate change is now widely recognized as a major global environmental and political issue (IPCC 2007). Consequently, the role of palaeoclimatology in providing a detailed view of past atmospheric variability has become increasingly im- portant as debates around current and future climate change have intensified, and there is an increasing need to study past climate variability at sub-decadal resolu- tion. Annually, in some cases seasonally, resolved sources of Holocene palaeoclimatic data exist in tree rings (Briffa 2000), ice cores (Alley 2000; Johnsen et al. 2001), corals (Sun et al. 2005), speleothems (Fleitmann et al. 2004) and varved lake sediments (Prasad et al. 2006). These have been widely exploited to provide the high-quality baseline data required for the study of ra- pid climate shifts and to test the latest generation of climate models (Valdes 2003; Schneider & Mastrandrea 2006; Goosse et al. 2008). Ombrotrophic peat bogs are another well-established source of palaeoclimatic data and have been studied globally (e.g. McGlone & Wilmshurst 1999; Barber 2006; Charman et al. 2006; Hughes et al. 2006; Cham- bers et al. 2007), leading to both qualitative and quan- titative reconstructions of past bog surface wetness (BSW), which can be interpreted as reflecting past cli- matic variables (e.g. Barber & Langdon 2007; Charman 2007). When peat-based palaeoclimatic research was in its infancy, Aaby (1976) observed that raised peat bogs acted as biological low-pass filters, reflecting only long- term climatic tendencies. Now, however, more than 30 years later, decadally resolved studies are com- mon (Barber & Charman 2003), and furthermore, the often rapid growth rates of ombrotrophic bogs (10 years cm 1 is common in northwest Europe), when combined with fine-resolution (i.e. millimetre- scale) sampling, provide an as yet largely unexploited potential to derive sub-decadal palaeoclimatic data from this proxy-archive. Alley & A ´ gu´stsdo´ttir (2005) stated that in all palaeoclimatic records, when bio- turbation or other diffusive processes are sufficiently small and sampling is sufficiently intensive, an anomaly of any desired age can be found. However, the relia- bility of fine-resolution peat-based records has not been widely tested (but see Joosten & de Klerk 2007a) and will depend on a number of methodological, tapho- nomic and ecological issues. To date, peat-based palaeoclimatic research has re- constructed primarily the broad climatic fluctuations of the Holocene. Although some studies have focussed on individual events or shorter time-slices within this peri- od (e.g. Blackford & Chambers 1991; van Geel et al. 1996; Anderson et al. 1998; Barber et al. 2000; Mau- quoy et al. 2002b), many have aimed to provide re- constructions for all, or a large part of, the Holocene (e.g. Hughes et al. 2000; Barber et al. 2003; Langdon et al. 2003; Blundell & Barber 2005). This has necessi- tated an approach utilizing a relatively wide sampling interval, relating in real time to samples being taken DOI 10.1111/j.1502-3885.2010.00152.x r 2010 The Authors, Journal compilation r 2010 The Boreas Collegium