Research News
The satellite image clearly shows the clouding of the Wadden Sea through suspended sediment and the clear water of the North Sea. Photo: HZG
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Why Does the Wadden Sea Increase?
Wadden seas originate anywhere in the temperate regions, where the sea floods gently sloping areas in a tidal rhythm and thus deposits sediments. Since 2006, two scientists from the Institute of Coastal Research at the Helmholtz Centre Geesthacht and the Leibniz Institute for Baltic Sea Research investigate the phenomenon that the Wadden Sea does not mix with the open sea and that the flood tide stream transports more suspended sediment into the Wadden Sea than the ebb tide stream pulls out again.
The shallow water of the Wadden Sea is lighter than the water of the open sea, as it features a lower salt content and thus a reduced density due to rain and tributary waters. The coastal researchers now have found out that this difference in density is an essential factor in transporting suspended sediment within the mudflats.
With the ebb tide stream the lighter mudflat water is pushed over the water of the open sea. This results in a layering of the water. When the flood tide stream sets in, the heavier water from the open sea is pushed over the mudflats. Yet since the heavier water sinks down, the resultant water is not layered but mixed. The suspended sediment is raised from the ground and transported towards the coast by the flood tide flow. There the sediment settles so that the Wadden Sea increases over time.
