Joint Seminar: Tidal straining can result in persistent stratification in the German Bight

Stratification plays a major role in the functioning of coastal ecosystems. In these regions, the competition between tides, wind, and freshwater buoyancy input determines the state of stratification. Buoyancy input from river discharge increases the stratification while mixing due to tides and wind decreases it. Tidal straining, the interaction between tidal currents and horizontal density gradients, can periodically increase/decrease stratification. To understand the time scale of these processes and their impact on the German Bight hydrodynamics following an extreme discharge event, a high-resolution numerical model is used. The energy budget for the potential energy anomaly, a measure for stratification, is analyzed using the model results. Results show that the German Bight stratification is highly affected by the fortnightly spring-neap tidal cycle and the position of the river plume. If the river plume is confined to the eastern coastal region, stratification decreases significantly due to high mixing during spring tides. However, when the river plume moves towards deeper regions, tidal straining is stronger than mixing. This results in persistent stratification even during spring tides. The model results are also used to calculate the spatial variability and duration of stratification due to the extreme event, which is beneficial for future risk management.




15:15 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Fatemeh Chegini


Dian Putrasahan

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