Was there a '4.2 kyr event' in Great Britain and Ireland? Evidence from the peatland record

Roland, T.P. (2012) Was there a '4.2 kyr event' in Great Britain and Ireland? Evidence from the peatland record. University of Exeter, College of Life and Environmental Sciences, Doctoral Thesis.

Abstract

Palaeoenvironmental and archaeological data from several regions around the world show evidence of a multi-centennial climatic event occurring approximately 4200 cal yr BP. Abrupt climate change (ACC) events in the early-Holocene were dominated by meltwater pulse events associated with the final stages of deglaciation, a mechanism unlikely to have driven subsequent ACC events in the mid- and late-Holocene. A study of the ‘4.2 kyr event’ therefore provides an opportunity to study an ACC event in the context of environmental conditions comparable to those of the modern day, thus providing valuable lessons for the future. Whilst the climatic change and/or impact of the 4.2 kyr event is clear in certain regions, such as western Asia, more work must be done to disentangle the timing and magnitude of change at this time in other regions, including northwest Europe. A more comprehensive reconstruction of the event’s spatial and temporal variability will help determine the likely drivers of this event. Presented here are the results of a multi-proxy examination of two peat sequences from Sluggan Moss and Fallahogy Bog in the North of Ireland. A range of palaeohydrological proxy analyses have been undertaken, including: peat humification, plant macrofossil and testate amoebae analyses. Furthermore, stable isotopic analysis (13C and 18O) of Sphagnum ?-cellulose was included to determine whether this novel technique can, as a proxy for changing atmospheric circulation and/or bog surface wetness, contribute to our understanding of the nature and/or cause of the 4.2 kyr event. The chronological resolution of these sequences is exceptionally high, with radiocarbon dating supplemented by the excellent tephrochronology of the region. Together, these high-resolution palaeoecological and stable isotopic records provide the best opportunity to examine this event in northwest Europe, in terms of their potential for climatic sensitivity and chronological constraint. After inter-site comparison, plant macrofossil and peat humification records were found to be climatically complacent. Testate amoebae records, however, were regionally coherent and were subsequently combined to produce a regional climatic record. From this, it was concluded that there was no compelling evidence to support the existence of a 4.2 kyr event in Great Britain and Ireland. In addition, data suggested that peat-based stable isotopic analysis cannot currently be accepted as a robust proxy for past palaeohydrological change. It is proposed that a lack of biomechanical understanding and standardised methodology is significantly hindering the potential of the technique’s application in peat-based palaeoclimatic studies.

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