Effect of waves and currents on the dynamics and seasonal variations of suspended particulate matter in the North Sea

Kurzfassung

Effect of waves and currents on the dynamics and seasonal variations of suspended particulate matter (SPM) in the North Sea is investigated by a three-dimensional Circulation and Transport Model for SPM (CTM-SPM) in 2002 and 2003, forced by waves and meteorological data. Calculated fine sediment exchange processes at the seawater–seabed interface are driven by the instant values of the shear stress velocity due to currents and waves. Modeled SPM concentrations are compared with in-situ measurements and satellite snap-shot images. As a result of the action of currents and waves, local bathymetry and the fine sediment content at the sea bottom, modeled time series shows different short-term dynamics of SPM concentrations in various locations in the North Sea. On a longer time scale, currents and waves result in different seasonal distributions of the shear stress velocity typical for the calm (April–October) and the storm (October–April) periods. Accordingly, our model calculates different seasonal distributions of SPM with the mean surface concentrations of about 2 mg l−1 in the calm and N5 mg l−1 in the storm periods. Waves lead to a higher frequency of resuspension and erosion events and increase mixing intensity in the water column during storm periods. During calm periods, SPM distribution is mainly shaped by currents. A different pattern, characterized by high SPM concentrations in off-shore areas, evolves instantly during transient storms events.