Modeling the exchange of the Baltic Sea from the meridional atmospheric pressure difference across the North Sea

The large Baltic Sea estuary has a hampered exchange with the ocean because of the topographical constriction of the transition area. Understanding the mechanisms controlling the deep water renewal and possible climatic dependencies are of primary concern in order to understand past and future changes of the Baltic Sea. In the present paper, century long time series have been used to investigate the interrelations between observed air pressure, sea level, and salinity in period bands relevant to North Sea-Baltic Sea water and salt exchange. Strong linear relations between the north-south air pressure difference across the North Sea and the sea level in the Kattegat were found for oscillations in the 35-200 days period band. In the same period band the surface salinity of the Kattegat covaries with variations of the Baltic sea level because of movement of the horizontal salinity gradient in Kattegat related to filling/emptying of the Baltic. Using the statistical dependencies, a model of the Baltic sea level, and a simple gradient model for the Kattegat salinity, we simulated the occurrences and strengths of large high-saline inflows to the Baltic with the north-south air pressure difference across the North Sea as the only forcing. The water exchange between Kattegat and the Baltic Sea have been calculated from 1902 to 1998. The computed inflow conforms with previous estimates and with observed changes seen in the Baltic Sea deep water. It is suggested that this simple model can be used to analyze the sensitivity of the Baltic Sea to climate change.