A new tephrochronological record of a raised bog in eastern lowland Scotland

Abstract

Cryptotephras have been widely used as a chronological tool for studying past environmental change, but many temporal and spatial gaps remain in our knowledge of the distribution of cryptotephra records. Here, last millennium cryptotephras were identified and analysed for the first time in eastern lowland Scotland. Six tephra layers were identified in six replicate short peat cores at Bankhead Moss, a raised bog in Fife, eastern lowland Scotland. Geochemical and stratigraphic correlations indicate that the tephras originate from Icelandic and Alaskan sources. We make firm correlations to Askja 1875 and WRAe, a broad correlation to Mount Churchill with the possibility of Lena tephra being inferred from its estimated timing, and uncertain correlations of three tephra layers of Icelandic origin, considering the mixed nature of these three tephra layers under the potential influence from post-depositional reworking and multiple volcanic sources, e.g. Hekla, Öræfajökull and Katla. This is the first secure record of the Askja 1875 tephra in the British Isles, which significantly extends its known spatial distribution and suggests a more complex dispersal pattern of this tephra than previously thought. Persistent presence of shards throughout parts of the peat sequences may reflect post-depositional movement of tephra shards within the peat, reworking from surrounding landscape, and/or sparse fallout from other eruptions. Our records indicate that any single peat core from this site gives a good approximation of the overall tephrostratigraphy, but there is considerable spatial variation in tephra concentrations between cores. Age-depth models for the six cores based on cryptotephras, spheroidal carbonaceous particle (SCP) counts, and radiocarbon dates likewise vary between cores, showing a pattern consistent with peat accumulation in a domed raised bog. These spatial differences in tephrostratigraphy highlight the value of a multiple-core approach in palaeoenvironmental peatland research.