Abstract
The Baltic Sea is one of the most contaminated seas by the radioactive isotope of strontium in the world; therefore the activity of ⁹⁰Sr is regularly controlled. Due to that fact, seawater samples for ⁹⁰Sr determination were collected at 16 stations located in the southern Baltic Sea between 2005 and 2010. In this period average activity of ⁹⁰Sr was 7.8 Bq m⁻³ and varied within the range from 3.0 Bq m⁻³ to 11.9 Bq m⁻³. Because the higher activity of ⁹⁰Sr was measured in the Baltic Sea than in the North Sea and rivers, inflows from the North Sea and the riverine runoff decreased ⁹⁰Sr activity in the Baltic Sea. The average ⁹⁰Sr activity in the bottom water along the offshore profile was 18% lower than that in the surface water and it was caused by an inflow of salt water from the North Sea. In the Vistula River mouth the average activity of ⁹⁰Sr in the surface water was about 15% lower than the average activity in the bottom waters. Coastal areas, relatively shallow with good mixing condition in the water column, were characterized by low variability in ⁹⁰Sr activity.