The Baltic Sea is a large, semi-enclosed body of brackish water located in Northern Europe. It is one of the world’s largest inland seas. Its unique position, nearly enclosed by surrounding landmasses, has given it a distinct ecological character. This location has also made the sea historically and economically significant, serving as a major maritime corridor for trade across the region.
Defining the Geographical Boundaries
The Baltic Sea is positioned north of Central Europe, nestled between the Scandinavian Peninsula (west) and the North and Central European Plain (south and east). Its long axis stretches approximately 1,600 kilometers from eastern Denmark toward the Arctic Circle. The sea is bordered by nine countries, including Sweden, Finland, Russia, Estonia, Latvia, Lithuania, Poland, Germany, and Denmark.
The sea is divided into several major subdivisions and gulfs. The northernmost extension is the Gulf of Bothnia, located between Sweden and Finland. The Gulf of Finland stretches eastward toward St. Petersburg, Russia, and the Gulf of Riga is situated between Latvia and Estonia. The total surface area of the Baltic Sea covers approximately 377,000 square kilometers.
The Unique Oceanic Connection
The connection between the Baltic Sea and the global ocean system is restricted. This flow occurs through a series of narrow, shallow channels known collectively as the Danish Straits. The three main channels are the Great Belt, the Little Belt, and the Øresund (The Sound), which is shared between Denmark and Sweden.
These straits lead the water southwestward into the Kattegat, a sea area situated between Denmark and Sweden. From the Kattegat, the water flows into the Skagerrak, which separates Norway from the Jutland peninsula. The Skagerrak then opens directly into the North Sea, an arm of the Atlantic Ocean. The shallowness of sills within the Danish Straits, such as the Darss Sill and the Drogden Sill, severely limits the volume of water exchange.
Key Physical Characteristics
Due to the restricted exchange with the open ocean and the large influx of fresh river water, the Baltic Sea is the world’s largest body of brackish water with low salinity. Salinity is highest near the Danish Straits (around 15 parts per thousand) but decreases dramatically farther north and east, dropping to less than 2 parts per thousand in the innermost gulfs.
This density difference creates a strong permanent halocline, a layer where salinity rapidly increases with depth, preventing the mixing of water layers. The Baltic Sea is a relatively shallow basin, with an average depth of about 55 meters, though the maximum depth reaches 459 meters in the Landsort Deep. Additionally, the northern and eastern parts of the sea experience seasonal ice cover during the winter months.