GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel
Tel.: 0431 600-0
Fax: 0431 600-2805
11:00 h, Hörsaal, Düsternbrooker Weg 20
Accelerated global sea level rise is obviously threatening low-lying coastal regions. The Wadden Sea of the German Bight with its extensive inter-tidal flats is among the most vulnerable coastlines in the world. That region is by definition low-lying, and a sea level rise of the order of 1 m without any natural adaptation or anthropogenic measures would permanently flood a large portion of the inter-tidal flats and would convert the unique ecosystem of the Wadden Sea to a system of coastal lagoons.
However, the sea level rise of the past millennium which amounts to about 1 m did not drown the Wadden Sea, since the inter-tidal flat level has grown with the sea level rise as well as the level of salt marshes. This means that sedimentary material had been imported into the Wadden Sea at a sufficient rate, first mainly from land (due to coastal erosion) and later exclusively from the sea, since coastal defense measures stopped sediment import from land.
This import of sediments from the sea is based on a complex suite of transport processes which will be discussed during this presentation. For this, the concept of estuarine circulation has been transferred from tidal estuaries (transition zone between fresh water and salt water in tidal rivers) to the well-mixed Wadden Sea. Models simulations and field observations demonstrate the efficiency of these baroclinic transport mechanisms acting on tidal time scales.
The major question is, up to which rate of sea level rise these sediment transport mechanisms are sufficient to prevent the tidal flats from drowning. Recent morphodynamic simulations using relatively simple (vertically integrated) models indicate that this critical rate of sea level rise is about 0.5 m per century, a value which is in the range of future climate projections. However, these models did not include several of the most important sediment transport mechanisms, and it is an urgent task to extend long-term morphodynamic models such that they also represent baroclinic processes on tidal time scales.