Drowned Forests in the Gulf of Gdansk (Southern Baltic) as an Indicator of the Holocene Shoreline Changes - The Baltic Sea Basin - page 221

slope inclines from 0.5 ◦ to 1.5 ◦ , locally to 2.5 ◦ . The shallows are separated from
the deeper parts of the gulf by slopes 30-35 m deep and inclined 6-12 ◦ in some
places. The sea bed in the deep water part of the Gulf of Gdansk is completely flat.
Hummocky glacial relief is cropping out only very locally. In the southern part of the
Gulf of Gdansk, late Glacial and early and middle Holocene deltaic deposits occur
at depths up to 60 m (Ejtminowicz 1982 , Uscinowicz and Zachowicz 1993 ) . The
drowned part of the Vistula Delta, with an area of about 700 km 2 , was formed during
the early and middle Holocene when the water level was lower than at present.
The site of tree stumps and fallen trunks occurring in situ at the bottom of the
Gulf of Gdansk was discovered by the Polish Central Maritime Museum in 2006. In
September 2007, the site was investigated by the German expedition on board of r/v
“Professor Albrecht Penck” within the frame of the “SINCOS” project (e.g. Harff
et al. 2005 ) , in cooperation with Polish Geological Institute - National Research
Institute.
The site is located about 6-7 km NE of the entrance to the Gdansk harbour, in
water depths of 16-17 m on the submerged part of the Vistula Delta (Fig. 11.1 ) .
The first step of the investigation was a sidescan-sonar survey of the area with
a size about 1.3 × 1.8 km. A dual-frequency digital sidescan sonar with a towed

Fig. 11.1 Location of the area and reconstructed shoreline position at the beginning of the Atlantic
period and maximum extent of the Vistula Delta