Early Holocene Landscape Development and Baltic Sea History Based on High-Resolution Bathymetry and Lagoonal Sediments in the Hanö Bay, Southern Sweden

Abstract

The Baltic basin has experienced extensive water-level fluctuations since the last deglaciation. During two occasions of lower than present water levels, c. 11,700–10,200 and 9800–8000 cal BP, areas along the present-day coast of the Hano Bay in south-eastern Sweden were exposed and pine-dominated forests were established. Around the mouth of the Verkean River at the Havang site, remains of this landscape occur in the form of organic-rich lacustrine deposits and well-preserved stumps and trunks of pine trees, reaching depths of 21 m and distances from the present coastline of around 3 km. This study aims at refined reconstructions of the dynamic Early Holocene environment and shore-level displacement to increase the understanding of how Mesolithic people exploited the landscape. Stratigraphic analyses were performed on a sediment sequence obtained from an organic-rich deposit situated at 8.3 m water depth, aided by detailed bathymetric surveys. Radiocarbon dates obtained from the 3.6 m long sequence, supported by pollen stratigraphic correlation, indicate deposition during the period 9000–8600 cal BP with an unusually high sediment accumulation rate. As indicated by a consistently high organic matter content, stable C/N ratios and a general lack of coarse mineral matter, the sediments were deposited in a low-energy environment. Our preliminary interpretation is that the organic-rich deposit was formed in a highly productive oxbow lake, connected via a shallow threshold to the Verkean River, only allowing fine-grained, fluvially transported particles to reach the depositional environment. As indicated by numerous Mesolithic artefacts in the area, the dynamic landscape at the Havang site with its rich fishing waters and access to fresh water must have been attractive to Mesolithic hunter-gatherers. People had to adapt to the changing water levels and climatic conditions during the Early Holocene, and traces of their presence are preserved as a consequence of the accumulation of organic-rich fluvial deposits around the river mouth.