CHANGES IN DEPOSITION OF ORGANIC-MATTER AND NUTRIENTS IN THE BALTIC SEA DURING THE 20TH-CENTURY

In 1986-1990 a total of 121 surficial sediment samples were taken in the Baltic Sea. Sediment cores were taken at 29 sites down to 10-60 cm below the sediment/water interface. Loss on ignition (LOI) in surficial sediments is approximately twice as high (16.8% +/- 5.3) in the Baltic proper as in the Bothnian Sea (8.3% +/- 1.4). Comparisons with old sediment data indicate a more than 1.7-fold increase in organic matter deposition in the northern Baltic proper between the late 1920s and the late 1980s. From calculations based on annual sesquestering of carbon in laminated sediments from the Baltic proper, we estimate that carbon originating from primary production and external sources has increased 5-10-fold, and averages 9 g C m-2 yr-1 for the period of the early to late 1980s. The importance of including nutrients originating from erosion of uplifted old sediments in mass balances for nutrients in the Baltic Sea is emphasized. Increased sedimentation and changes affecting crucial processes/mechanisms in the sediment/water interface are likely to be of considerable importance for how the Baltic ecosystem reacts upon future changes in nutrients as well as pollutants.