Towards an Early Holocene Tephrochronology for the Faroe Islands: Methodology and first results

Sammanfattning: The uncertainties regarding future climate change have put considerable notice to the climate variability following the Late Glacial-Holocene transition (ca. 13-9 ka BP) in the North Atlantic region as well as the forcing mechanisms behind climate changes. Much attention has focused on short climate events in order to understand the mechanisms that drove these changes but also to identify the leads and lags in the climate system. Chronological uncertainties for these events remain but an accurate chronological framework for the North Atlantic region would enhance possibilities to solve some of the chronological questions.Tephrochronology uses volcanic ash from a volcanic eruption which creates a marker horizon in marine and lake sediments, peat bogs and glacier ice as the ash is spread over large areas. These time-parallel markers allow precise correlations between archives. The purpose of this thesis is to improve and refine the Early Holocene tephrochronological framework with focus on dating and identification of new and previously known tephra horizons on the Faroe Islands, especially around the climatic events of the Preboreal Oscillation (11,300-11,100 cal. yr BP), the Erdalen events (10,100-10,050 and 10,000-9800 cal. yr BP) and the 9.3 ka BP event. A second goal is to develop the methodology of tephrochronology for finding cryptotephra (not visible by the eye) horizons in lacustrine sediments.The findings of eight tephra horizons spanning ca. 11,350 to 9700 cal yr BP where three are known from other locations in Europe show the potential of tephrochronology for linking records across the North Atlantic region. Refined ages for the Askja-S and Hässeldalen tephra were obtained from an age model built on eight AMS radiocarbon ages with the Saksunarvatn ash as a constrained age. The results from using XRF ITRAX core scanner to locate tephra in lacustrine sediments illustrate that high concentrations of basaltic tephra could be captured but not lower concentrations of rhyolitic shards.