Distribution, long-term development and mass balance calculation of total alkalinity in the Baltic Sea

During the 20th century, extensively hydrographic investigations had been performed in the Baltic Sea. One of the parameters that have been determined during these historic investigations of the Baltic Sea is the total alkalinity (AT). In this study, this large data set is used together with a specifically developed box model to estimate the in- and outflows of salinity and AT within the different sub-basins. The Baltic Sea receives large amounts of freshwater through river runoff, and AT can be used as a chemical signature of the runoff as its concentration depends on the mineralogy of the drainage basin. Rivers entering the southern part of the Baltic Sea are draining areas rich in limestone, therefore having higher AT than rivers entering the northern part of the Baltic Sea where granite dominates the bedrock. The mean AT in rivers entering a specific region of the Baltic Sea is achieved by the intercept of the regression line when salinity is plotted versus AT for the corresponding data. In this study, the focus is on the Gulf of Finland and the Gulf of Bothnia where the longest time series data are available. There is a common trend with an increase in AT in rivers entering the Gulf of Finland and a decrease in AT in rivers entering the Gulf of Bothnia.