Major Seas of the World

Baltic Sea

The Baltic Sea is located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Northern Europe, Eastern Europe and Central Europe, and the Danish islands. It drains into the Kattegat by way of the Öresund, the Great Belt and the Little Belt. The Kattegat continues through the Skagerrak into the North Sea and the Atlantic Ocean. The Baltic Sea is artificially linked to the White Sea by the White Sea Canal and to the North Sea by the Kiel Canal.

Subdivisions
The northern part of the Baltic Sea is known as the Gulf of Bothnia, of which the northernmost part is the Bay of Bothnia or Bothnian Bay. The more rounded southern basin of the gulf is called Bothnian Sea and immediately to the south of it lies the Sea of Åland. The Gulf of Finland connects the Baltic Sea with St Petersburg. The Gulf of Riga lies between the Latvian capital city of Riga and the Estonian island of Saaremaa.
The Northern Baltic Sea lies between the Stockholm area, southwestern Finland and Estonia. The Western and Eastern Gotland Basins form the major parts of the Central Baltic Sea or Baltic proper. The Bornholm Basin is the area east of Bornholm, and the shallower Arkona Basin extends from Bornholm to the Danish isles of Falster and Zealand. In the south, the Bay of Gdansk lies east of the Hel peninsula on the Polish coast and west of Sambia in Kaliningrad Oblast. The Bay of Pomerania lies north of the islands of Usedom and Wolin, east of Rügen. Between Falster and the German coast lie the Bay of Mecklenburg and Bay of Lübeck. The westernmost part of the Baltic Sea is the Bay of Kiel. The three Danish straits, the Great Belt, the Little Belt and The Sound (Øresund), connect the Baltic Sea with the Kattegat bay and Skagerrak strait in the North Sea. The confluence of these two seas at Skagen on the northern tip of Denmark is a visual spectacle visited by many tourists each year.

Geologic history
The Baltic Sea somewhat resembles a riverbed, with two tributaries, the Gulf of Finland and Gulf of Bothnia. Geological surveys show that before the Pleistocene instead of the Baltic Sea was a wide plain around a big river called the Eridanos. Several glaciation episodes during the Pleistocene scooped out the river bed into the sea basin. By the time of the last, or Eemian interglacial (MIS 5e), the Eemian sea was in place.
From that time the waters underwent a geologic history summarized under the names listed below. Many of the stages are named after marine animals (e.g., the Littorina mollusk) that are clear markers of changing water temperatures and salinity. The factors that determined the sea’s characteristics were the submergence or emergence of the region due to the weight of ice and subsequent isostatic readjustment, and the connecting channels it found to the North Sea-Atlantic, either through the straits of Denmark or at what are now the large lakes of Sweden, and the White Sea-Arctic Sea.

Geophysical data
The Baltic Sea is a brackish inland sea, the largest body of brackish water in the world. The fact that it does not come from the collision of plates, but is a glacially scoured river valley, accounts for its relative shallowness.

Dimensions
The Baltic sea is about 1610 km (1000 miles) long, an average of 193 km (120 mi) wide, and an average of 55 m (180 ft, 30 fathoms) deep. The maximum depth is 459 m (1506 ft), on the Swedish side of the center. The surface area is about 377,000 km² (145,522 sq mi) and the volume is about 21,000 cubic km (3129 cubic miles). The periphery amounts to about 8000 km (4968 miles) of coastline.

Hydrography
The Baltic Sea flows out through the Danish straits; however, the flow is complex. A surface layer of brackish water discharges 940 cubic km per year into the North Sea. Due to the difference in salinity, a sub-surface layer of more saline water moving in the opposite direction brings in 475 cubic km per year. It mixes very slowly with the upper waters, resulting in a salinity gradient from top to bottom, with most of the salt water remaining below 40 to 70 m deep. The general circulation is counter-clockwise: northwards along its eastern boundary, and south along the western one.(

Salinity
The Baltic Sea's salinity is much lower than that of ocean water (which averages 3.5%, or 35 parts per thousand), as a result of abundant freshwater runoff from the surrounding land; indeed, runoff contributes roughly 1/40th its total volume.(Alhonen 88) It varies from 0.1% in the north to 0.6-0.8% in the center. Below 40-70 m, it can be as much as 1.5-2.0%.