A submerged and buried Mesolithic site off the Svanemøllen Harbour, Copenhagen, Denmark: acoustic detection (HALD) and verification through coring

Abstract

Teledyne Chirp III high resolution seismic profiles have through three years been recorded at an approximately waterdepth of 6.0-9.0 m with 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 pronounced haystacks and a sandy interval, underlain by clayey till and overlain by harbor silt, represent the basin configuration. Two cores contained 4 pieces of knapped flint in the sandy interval (statistically density of around 230 pieces per square meter), while the remaining cores did not reach the desired depth. Finite Element (FE) modeling reveals that small pieces of knapped flint resonance and that the acoustic impedance of the flint is high. Svanemøllen Harbour site is a hitherto unknown buried Stone Age settlement and this is the first time that such a site has been acoustically detected (Teledyne Chirp III), verified by drilling and modelled by FE. Innomar and Geopulse data acquired at the site did not register haystacks. Due to the relative sea level rise a significant part of the submerged Stone Age sites must worldwide be expected to be buried in the seafloor sediments.