Why is seawater near Norway less salty than seawater off Great Britain?

Seawater near Norway is less saline than the water off the coast of Great Britain primarily due to the influence of less-saline water entering the North Sea from the Baltic Sea through the Skagerrak.1

While Atlantic waters with higher salinity levels (exceeding 35 parts per thousand) enter the North Sea through the English Channel and the region between the Shetland Islands and Norway, the circulation pattern creates a basin where salinity is generally lower off the Norwegian coast. Additionally, the salinity of coastal waters is frequently influenced by the dilution of seawater with fresh water from river runoff. In the North Sea, large quantities of fresh water enter the basin from major rivers such as the Rhine and the Thames, further contributing to variations in salinity levels across the region.12