An abrupt change in winds that may radically affect the coasts and deep sections of the Baltic Sea

Abstract

We explore long-term variations in the properties of waves in the Baltic Sea and geostrophic air-flow over this water body. Records of visual wave observations from 1946 to 2012 at 8 observation sites at the eastern coast of the Baltic Sea reveal a multitude of changes. A substantial decrease in the wave heights took place until about 1970, and considerable decadal variations occurred since then. The coherence between annual average wave heights at different locations was lost at the end of the 1980s. A rotation of the usual wave approach direction by almost 90° was identified at one location. We then couple this data with a reconstruction of wave fields and wave-driven sediment transport for 1970 to 2007. The reconstruction is based on adjusted geostrophic winds from the Swedish Meteorological and Hydrological Institute. The simulated net potential sediment transport along the eastern coast of the sea reveals a major change at the end of the 1980s. This change is associated with an abrupt turn of the geostrophic air-flow over the southern Baltic Sea by ~40° since 1987. This change may serve as an alternative explanation for a radical decrease in the frequency of major inflows of saltier, oxygen-rich water into the Baltic Sea since the mid-1980s.