Establishing tephrostratigraphic frameworks to aid the study of abrupt climatic and glacial transitions: a case study of the Last Glacial-Interglacial Transition in the British Isles (c. 16-8 ka BP)

Distally dispersed tephra layers have become an important tool in the investigation of palaeoenvironmental and archaeological records across the globe. They offer possibilities for the synchronisation and improved chronological control in those records to which they can be traced and hence contribute to an improved understanding of the pattern and timing of environmental and archaeological change during periods of rapid climatic adjustment. However, their use as robust isochronous markers for synchronising records is frequently compromised by uncertainties relating to stratigraphical context, precise chronology and chemical composition. Here we collate and review the tephrostratigraphical information dating to the Last Glacial-Interglacial Transition (LGIT; c. 16-8 ka BP) in the British Isles based on published and unpublished records obtained from 54 sites. Based on details of their stratigraphic position, chronology and chemical composition, we propose that 26 individual eruption events may be represented in this collective record which spans the LGIT. The great majority of these eruptives can be traced in origin to Iceland, but we also report on the recent discoveries of ultra-distal tephra from the North American Cascades range, including for the first time the Mount St Helens J Tephra at a site in southern Ireland. These particular ultra-distal discoveries have resulted from a reinterpretation of older data, demonstrating the potential importance of ‘unknown’ analyses in older tephra datasets. The outcome of this review is a comprehensive but provisional tephrostratigraphic framework for the LGIT in the British Isles, which helps to focus future research on parts of the scheme that are in need of further development or testing. The results, therefore, make an important contribution to the wider European tephrostratigraphic framework, while adding new discoveries of transcontinental isochronous tephra markers.