Abstract:

Tephrochronology is a precise dating method that uses volcanic ash horizons to correlate and date geological and archaeological records. Even sedimentary basins located far from volcanic sources can receive cryptotephra, microscopic volcanic ash particles invisible to the naked eye. While the presence of tephra is well documented in many European archives, little is known about its dispersal into Greenlandic lake sediments.

This research investigates the presence of volcanic ash in a sediment core from GRISO Lake in southern Greenland, collected in collaboration with the University of Copenhagen. A multi-step laboratory protocol was used to isolate and concentrate tephra particles. Among these steps, Loss on Ignition at 550 °C (LOI₅₅₀) played a key role. The objective was to assess whether low organic matter content, as indicated by LOI₅₅₀ values, correlates with high ash concentrations across the core, which was sampled at a high resolution of 1 cm.

To test this relationship, Spearman rank correlation analyses were performed. At the scale of the full core (first 140 cm), the correlation was weak and not statistically significant (rho = 0.14, p = 0.10). However, localized tests around visible tephra peaks (±2 cm) showed stronger inverse correlations, particularly at 24 cm depth (rho = –0.97, p = 0.0048). These results suggest that while LOI₅₅₀ is not a reliable indicator of tephra content at the whole-core scale, it may be a useful screening tool to help identify cryptotephra-rich layers when combined with other scanning and geochemical techniques.

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