A Submerged and Buried Mesolithic Site off Svanemøllen Harbor, Copenhagen, Denmark: Acoustic Detection (Human-Altered Lithic Detection) and Verification by Means of Coring

Teledyne Chirp III high-resolution seismic data were acquired over a three-year period at a water depth of 6.0–9.0 m, with a clear concentration of acoustic “haystack” features, in the dredged Svanemøllen Harbor, Copenhagen. The recordings show haystacks related to preserved shallow basins and rivers in the paleo-coastal setting. Eleven short vibrocores were retrieved below these pronounced haystacks and a sandy interval, underlain by clayey till and overlain by harbor mud, which represent the basin configuration. Two cores contained four pieces of knapped flint in the sandy interval (statistical density of around 230 pieces per square meter), while the remaining cores did not reach the desired depth. Finite Element (FE) modeling revealed that the small pieces of knapped flint were resonant and that the acoustic impedance of the flint was high. The Svanemøllen Harbor site is a hitherto unknown buried Stone Age site, and this is the first time ever that an unknown submerged, buried Stone Age site has been acoustically detected (using Teledyne Chirp III), verified by means of coring and modeled using FE modeling. The Innomar and Geopulse data acquired at the site did not register any haystacks. Due to the global sea level rise after the Last Glacial Maximum, a significant part of the world’s submerged Stone Age sites must be expected to be buried in seafloor sediments.