Gross sedimentation-rates in the north sea-baltic sea transition - effects of stratification, wind energy-transfer, and resuspension
Gross sedimentation rates (GSR) were measured using sediment traps placed at different levels above die seabed (0.3, 0.5, 0.8, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0 m) at a water depth of 17 m. The traps were deployed for 1.25 year. The study was carried out at a location in die semi-enclosed Aarhus Bay, in the southwestern part of the Kattegat, which forms the transitional zone between the highly saline (32-34) North Sea and the less saline (15-20) Baltic Sea. Hydrographic conditions in the Aarhus Bay are dominated by significant changes in salinity during the year, and the water column was stratified for 80 % of the time. High GSR values were recorded near the seabed with a mean of 114.8 (g m-2 day-1) at 0.3 m above the seabed, whereas low GSR values were recorded in the upper traps with a mean of 5.5 (g m-2 day-1) at 10 m above the seabed. The density difference between surface and bottom water was used as a stratification parameter. A strong negative correlation between stratification and wind energy transfer was found. The negative correlation was due to opposite seasonal components of in- and outflow of waters increasing the density difference, i.e. in- and outflow occurred predominantly in seasons with calm wind conditions. Correlation coefficients were high and positive between wind energy and GSR 6.0 m above the seabed due to enhanced turbulent diffusion of suspended particulate matter in periods of strong winds. Resuspension of bottom sediments by surface waves also occurred, increasing GSR at all trap levels. A net sedimentation rate given by the Pb-210 method (2.5 g m-2 day-1) was low compared to the high GSR near the seabed (114.8 g m-2 day-1), this difference being primarily due to resuspension by currents and waves.
Lundhansen LC, Pejrup M, Valeur J, Jensen A (1993). Gross sedimentation-rates in the north sea-baltic sea transition - effects of stratification, wind energy-transfer, and resuspension. Oceanologica Acta. 16 (3). 205-212. https://archimer.ifremer.fr/doc/00099/21047/