Vol. 57, No. 1, 2022
Knudsen (1900) derived relations for water and salt when baroclinic water exchange dominates in a semi-enclosed basin. Here, are the corresponding relations for barotropic water exchange developed. With these relations at hand, the net volume and net salt exchange can be found as averages over a certain time, say a week, month, or year. These relations are applied to the barotropic water exchange in the Sound strait connecting the Baltic Sea with the Kattegat. The study covers the years 1977 to 2018. Volume in- and outflows are characterized by being of the same order of magnitude, whereas the average time for inflow and outflow is close to 35 % and 65 %, respectively. The average net volume flow is close to 50 % of the average runoff input to the Baltic Sea, suggesting the other 50 % of the runoff input is leaving through the Belt Sea strait. The seasonal net volume flow through the Belt Sea strait is estimated by closing the Baltic Sea water budget. During summer, the Sound and the Belt Sea straits show different responses to changes in runoff and Baltic Sea volume. The net volume flow through the Belt Sea strait even change sign being directed inwards during June and July on average.