How do waters entering from the Baltic Sea affect circulation in the North Sea?

The Baltic Sea influences the North Sea primarily through the exchange of water via the Kattegat and the Skagerrak straits.1

Because the Baltic Sea receives significant freshwater input from rivers and has low evaporation rates, its surface waters are remarkably fresh. This creates a consistent surface outflow of lower-salinity water from the Baltic into the North Sea. Conversely, this exchange system facilitates a deeper countercurrent of denser, saltier water that flows from the North Sea into the Baltic.2

This interaction is a key component of the region's hydrology, as the Baltic's restricted connection to the North Sea prevents the full mixing of these water masses, maintaining the Baltic's low salinity levels. While the North Sea is characterized by tidal currents, the Baltic is largely sheltered from them, meaning the circulation between the two is driven more by these density-driven flows and wind patterns than by the tidal forces dominant in the North Sea.2