Abstract The Baltic Sea is a semi-enclosed intracontinental sea of approximately 418 500 km 2 , surrounded by Scandinavia and the lowlands of Central and Eastern Europe. Its catchment area is about four times larger than the area of the sea itself. The Baltic Sea has an average depth of around 50 m, and is connected to the Atlantic Ocean via the shallow and narrow Danish Straits. A characteristic feature of the Baltic Sea is thermohaline stratification, in particular the occurrence of a permanent halocline. The northern part of the Baltic Sea is situated within the Precambrian Baltic Shield, whereas the southern part lies on the East European Platform. A small SW part lies on the Palaeozoic West European Platform. During the Pleistocene period, Scandinavian ice sheets advanced on the area of the present Baltic Sea several times, resulting in damage to the bedrock and a deepening of the Baltic Basin. The present-day Baltic Sea had its beginnings in the retreat of the last Scandinavian ice sheet, which melted approximately 15.5–14.5 ka ago in the area of the southern part of today's Baltic Sea. The Quaternary cover of the seabed in the area of the whole Baltic Sea is formed from Pleistocene sediments of glacial, glaciofluvial and limnoglacial origin, as well as from sediments of Holocene marine accumulation. In the southern part of the Baltic, during the Holocene, the sea constantly encroached upon the land, destroying Pleistocene sediments. In the northern part, as a result of uplift of the land and regression of the sea, Pleistocene glacial and glaciofluvial deposits, as well as early Holocene Baltic sediments, are being eroded. In the Baltic Sea, sandy and gravelly sediments are present above the pycnocline, while muds have been deposited below the pycnocline.