Correlation of Seismic Data and Sediment Cores From the Seabed in the Medieval Harbour at Avaldsnes, Norway

This interdisciplinary study demonstrates the successful integration of non-destructive geophysical methods and sediment core analyses for mapping the seabed in the historical harbour at Avaldsnes in south-west Norway. In the Medieval Period, this was a royal manor, with the harbour as a central hub for the Hanseatic League in the 14th to 15th centuries. The use of an Autonomous Surface Vehicle (ASV) mounted with two distinct sub-bottom profiler (SBP) systems facilitated the acquisition of high-resolution seismic data, providing efficient imaging of the seafloor and subsurface layers. Sequence of fifteen sediment cores allowed for the description and dating of stratigraphy and the depositional environment. In combination, these methods provided a multidimensional understanding of the distribution of subsea sediments in the harbour, while preserving most of the archaeological context. The analysis revealed organic-rich sediments, primarily consisting of fine detritus gyttja, accumulated over the last 1700 years, trapping certain archaeological features. Deposition of the soft sediments likely commenced due to a lower relative sea level, possibly accompanied by intensified land-use and harbour activity. The study identified several minor anomalies in the seismic data, potentially representing artefacts of archaeological importance. An anomaly of significant size might correspond to a buried shipwreck or harbour structure. By providing a comprehensive understanding of sediment dynamics and human-environment interactions in the harbour, the research contributes to the preservation and management of an important cultural heritage site.