Deep-water exchange and mixing properties in the Baltic Proper were an
alysed on the basis of temperature and salinity data measured during t
he period 1970-1990. The data were analysed applying basic model conce
pts as the conservation principles, the two-layer approach and the geo
strophic flow assumption. The renewal of the deep water in the Baltic
Proper consists of inflow from upstream basins. The inflowing dense wa
ter is diluted by surface water and on a 20-year average increased by
a factor of 4, when entering from the Kattegat into the Landsort Deep.
Three main mixing zones were localized. Firstly, the Belt Sea and the
Sound, where the deep-water inflow increases by 79%; secondly, the Ar
kona Basin, where vertical mixing causes the increase of deep current
volume flow by an average of 53%; and thirdly, in the Stolpe Channel,
where the turbulent entrainment adds an average of 28% to the deep cur
rent. Applying the geostrophic flow model on salinity data, time serie
s of deep current flow rates were calculated. The model was calibrated
by 20-year mean flows calculated from conservation principles. The ef
fective sill depths were introduced as calibration coefficients. It wa
s found that the geostrophic flow model described deep-layer flows in
the Bornholm Channel well, but the flow rate was underestimated in the
Stolpe Channel and overestimated in the Faro Channel. In the Stolpe C
hannel and in the Faro Channel, the deep-layer flow showed seasonal va
riations with rapid increase during the autumn and winter seasons, res
pectively.