An analysis of the salt water inflow into the Baltic in 1975 to 1976

Time series measurements from light vessel and coastal stations in the transition area of the Kattegat and the Baltic Sea are analyzed for the period August 1975 to March 1976. The data consist of daily sampled salinities from different depth levels and daily means of sea levels, surface current, and wind, respectively. The purpose of this paper is to examine the dynamics of the mass- and salt-transport during a major salt water inflow.The principal conclusions of this paper are that

1)	the dynamics of the barotropic water exchange between the Kattegat and the Baltic Sea resembles that of a Helmholtz-resonator with a geostrophically controlled flow in the connecting channel;
2)	the water exchange is forced by both the east component of the windstress over the North Sea and the windstress component in 30o true over the Baltic Sea;
3)	the salinity in the upper layer of the Kattegat is governed by a permanent weak salt flux directed from the bottom to the surface layer and the outflow of less saline Baltic water into the upper layer of the Kattegat whereas the salinity of the Belt Sea is advected by the local currents along the main channel;
4)	the most favorable conditions for a major salt inflow are initially a mean sea level of the Baltic lowered by about 30 cm followed by west winds steadily increasing over the following several ten days. Moreover, the hitherto used definition of a major salt water inflow is discussed and an improved definition is proposed.