Challenges in dating blanket peat and implications for understanding its initiation in Ireland

Abstract

Blanket peat is widespread in maritime extra-tropical environments. Prehistoric land-use activity was traditionally invoked as the stimulus of blanket peat initiation in the British Isles, but recently, climate has been viewed as the driver of peat formation. Understanding of the timing and thus cause of blanket peat initiation is, however, confounded by uncertainties that primarily pertain to dating well-humified peat deposits. Here, we seek to address challenges in dating blanket peat with a view to better understanding its initiation in Ireland. Through a study of blanket peat profiles from five sites in the Mourne Mountains, Northern Ireland, we show that radiocarbon ages from different peat fractions are younger than contemporaneous cryptotephra ages by several centuries, probably due to the translocation of humic acids and root material down sediment profiles. Peat initiation was, therefore, dated in the Mourne Mountains using tephrochronology, and reveals initiation centred on ~8700 BP, ~7900–6800 BP and ~3500 BP. Reanalysis of Irish basal peat ages emphasises climate as the driver of blanket peat from ~7500 BP, but highlights that its development was time-transgressive at intra- and inter-regional scales. We conclude that blanket peat is a natural feature of the Irish landscape and highlight the uncertainties of radiocarbon dating blanket peat deposits.