Fine-resolution peat-based palaeoclimate records of the late-Holocene

Abstract

The need for peat-based palaeoclimatic studies of increased temporal resolution has been identified in recent research and forined the basis of this thesis. Four ombrotrophic bogs were studied along an oceanic to continental climate transect in north-west Europe. Selected late-Holocene abrupt climatic deteriorations were identified at coarse resolution and time-slices over each of these were investigated at 2- 5 mm sample resolution using peat hurnification, testate amoebae and plant macrofossil analyses. Age-depth models based on radiocarbon dating, tephrochronology and spheroidal carbonaceous particle analysis were applied to each fine-resolution zone. By quantifying the error inherent in the age-depth models, it was confirmed that in the majority of cases, the sampling resolution used equated to sub-decadal resolution. Therefore an assessment of whether the fine-resolution results could be confidently interpreted as reflecting sub-decadal palaeoclimatic change was possible. In order to facilitate this approach, novel sampling techniques were developed and changes to standard methodologies applied. A custom-built peat slicer enabled uniform millimetre-scale slicing of frozen peat samples. Sample sizes for each of the three methods of analysis were halved after testing confirmed that this did not effect the interpretation of the palaeoclimatic record derived. It was concluded that the multi-proxy, fine-resolution results could be confidently interpreted as sub-decadal resolution palaeoclimatic data, although careful interpretation was deemed essential since some datasets were problematic in some respects. For example, the extent to which the individual records co-varied within the fine-resolution zones was variable and there was a lack of correspondence between some results from adjacent cores. In addition, a lack of contemporaneity between fine- resolution zones of the same event between sites and uncertainty in the absolute dating of the fine-resolution changes meant that the climatological conclusions relating to each abrupt event were limited, although there was evidence of palaeoclimatic changes that occurred over ca. 5- 20 years, indicating that the events studied may have been more abrupt than suggested in previous peat-based research. Fine-resolution hurnification results were subjected to spectral analysis and exhibited a dominant Periodicity of between 8 and 13 years, suggesting a link to the ca. 11 year Schwabe sunspot cycle. In order to maximise potential temporal resolution and produce reliable sub- decadal palaeoclimatic data in future research, it was recommended that peat-based studies should obtain the best possible chronological control, focus on sites with high species diversity and rapid accumulation, employ the methodological advancements developed in this thesis and perform replicate coring to assess intra-site differences in microtopography. Site specific factors should be considered above degree of continentality in the selection of sites for future research.

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