11. Drowned Forests in the Gulf of Gdańsk (Southern Baltic) as an Indicator of the Holocene Shoreline Changes

This chapter presents a newly discovered locality of tree stumps occurring in situ at the bottom of the Gulf of Gdańsk. It focuses in particular on the age of the stumps and characterization of the palaeoenvironment, i.e. the nature of the plant communities in which the trees grew and also on their position in relation to the palaeo sea level. Tree stumps occurring in situ on the sea floor along with peat deposits are the most reliable indicators of sea level changes. The site is located about 6–7 km NE of the entrance to the Gdańsk harbour, in water depth of 16–17 m. The thickness of marine sand at the site is from a few to a dozen centimetres. Below the sand, gyttja with peat intercalations and wood fragments occur. Sixteen fragments of alder trunks and one oak trunk’s fragment were extracted. Radiocarbon ages of the tree trunk fragments are 7,920 ± 50 BP, 7,940 ± 40 BP, 7,960 ± 40 BP and 8,000 ± 50 BP. The age of gyttja, according to pollen analyses, is of early Atlantic period. The characteristic forest composition of that time was the broad deciduous forest with oak (Quercus), elm (Ulmus) and lime (Tilia). The climate was characterized by good thermal and moisture conditions, which is confirmed by the presence of pollen grains of mistletoe (Viscum) and ivy (Hedera). The obtained data about the time of accumulation of the investigated sediments indicate that the sea level at that time was about 19–20 m lower than at present.