The methodological basis for fine-resolution, multi-proxy reconstructions of ombrotrophic peat bog surface wetness

The need for Holocene peat-based palaeoclimatic records of increased temporal resolution has been widely identified 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 palaeoclimatic 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 methodological testing revealed that, irrespective of sample thickness (i.e. resolution), halving the standard sample volume used for plant macrofossil (from 4 cm3 to 2 cm3) and testate amoebae (from 2 cm3 to 1 cm3) 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