Driving forces and determinants of barrier coast evolution in the Holocene observed on the southern coast of the Baltic Sea

Coastal barriers account for approximately one-eighth of the world’s coastline. Barriers are the most common landform type in the southern part of the Baltic Sea area. Despite the long history of research, the issue of barrier coast evolution remains unresolved. The topic of this research is to determine the conditions under which the barrier coast evolved in the Holocene and to explain the local, different histories of its development. A 35 km long stretch of the coastal zone in the eastern Pomeranian Bay (southern Baltic) was explored using boreholes, seismoacoustic and GPR profiling, as well as radiocarbon and OSL dating, biostratigraphic studies and lithological analysis. Three main groups of deposits were identified: barrier subsoil deposits, barrier deposits (marine and aeolian sand, as well as interdune peat) and Rega River delta deposits. In the early Northgrippian (~8000 yr b2k), the coastline was located from about 2 to 12 km north of its present position. In the period 8000–6000 yr b2k, the coastline migrated southwards (landwards), initially at a rate of up to 22 m/yr and later up to 2 m/yr. The main driving forces at that time were climate warming and rapid sea level rise. When the Holocene transgression ceased, there were three different histories of the barrier coast development in the study area: a barrier that was still transgressive, a barrier that evolved from transgressive to progradational, and a barrier that evolved from transgressive trough progradational to transgressive again. The main determinants of these different histories were the lithology and relief of the barrier subsoil (accommodation space) and the time-varying amount of sand available for barrier formation, which varied in different parts of the study area.