Testing the use of bomb radiocarbon to date the surface layers of blanket peat.

Abstract

The recently formed surface layers of peatlands are archives of past environmental conditions and can have a temporal resolution considerably greater than deeper layers. The low density and conditions of fluctuating water table have hindered attempts to construct chronologies for these peats. We tested the use of the radiocarbon bomb pulse to date recently accumulated peat in a blanket mire. The site was chosen because the peat profiles contained independent chronological markers in the form of charcoal-rich layers produced from known burning events. We compared chronologies derived from accelerator mass spectrometry (super 14) C analysis of plant macrofossils against these chronological markers. The bomb (super 14) C-derived chronologies were in broad agreement with the charcoal dating evidence. However, there were uncertainties in the final interpretation of the (super 14) C results because the pattern of (super 14) C concentration in the peat profiles did not follow closely the known atmospheric (super 14) C record. Furthermore, samples of different macrofossil materials from the same depth contained considerable differences in (super 14) C. Suggested explanations for the observed results include the following: i) minor disturbance at the site, ii) in-situ contamination of the (super 14) C samples by carbonaceous soot, and iii) differential incorporation of plant material during blanket peat growth.