Submarine De Geer Moraines in the Kvarken Archipelago, the Baltic Sea

Publisher Summary The Kvarken Archipelago is located in the European epicontinental basin, the Baltic Sea. The Baltic Sea is one of the largest brackish water bodies in the world. The Kvarken area, between Finland and Sweden, is the narrowest part of the Gulf of Bothnia. It forms a submarine sill (25 m) that separates the Bothnian Sea in the south from the Bothnian Bay in the north. The majority of the Kvarken Archipelago is very shallow (0–25 m) and shoaly, with ∼7,000 islands and islets. Glacioisotatic land uplift rate is ∼8.0–8.5 mm/year. The boulder-rich De Geer moraines are the most characteristic geomorphic features within the area, creating a unique, washboard-like submarine landscape. Because the area is a transition zone of salinity levels at critical levels to both marine and limnic species, the diversity of marine life is poor. The local bladder wrack, Fucus radicans , is characteristic of hard bottoms in the shallow areas with salinity up to 4.5‰. The region has undergone several glaciations during the past approximately 3 million years, which has resulted in periods of repeated glacial erosion and sediment accumulation. During the latest glaciation, the Kvarken Archipelago was located close to the center of the Weichselian ice sheet, which reached a thickness of approximately 3 km during the glacial maximum. The seafloor morphology of the Kvarken area is characterized by broad-scale geomorphic features including mounds, plains, basins, and some sea valleys (holes). However, the seafloor bathymetry follows mainly the surface of the bedrock, and the relief of the area is relatively low.