Is the residual flow through the Marsdiep tidal inlet reversing?

The western Dutch Wadden Sea is connected to the North Sea by two main tidal inlets: the Marsdiep in the southwest and the Vlie in the northeast. Along with strong tidal currents, there is a residual flow from the Vlie to the Marsdiep. We found that the direction of this residual flow is reversing.

This residual flow has been studied since the 1970’s, with varying results for net volume fluxes. The driving mechanisms were identified as differences in tidal conditions in the main inlets, tidal rectification, and wind and atmospheric pressure. We analysed 13 years of ADCP observations collected on the ferry crossing the Marsdiep tidal inlet from 2009. The results are combined with earlier investigations covering the period 1998-2009. We find a significant trend in the magnitude of the residual volume flux, with decreasing export to the North Sea, and with occasional imports observed in recent years. We hypothesise that this trend is related predominantly to changes in North Sea tides, caused by increased strength and duration of stratification in response to global warming (Jänicke et al., 2021). With warming projected to continue, we expect the residual flow in the Marsdiep to continue to reverse to full inflow within the current decade, with potential knock-on effects for the sediment budget and ecosystem of the western Wadden Sea.

This work was published in Ocean Sci., 18, 1805–1816, 2022, https://doi.org/10.5194/os-18-1805-2022.

 

Jänicke, L., Ebener, A., Dangendorf, S., Arns, A., Schindelegger, M., Niehüser, S., Haigh, I. D., Woodworth, P., and Jansen, J.: Assessment of tidal range changes in the North Sea from 1958 to 2014, J. Geophys. Res.-Oceans, 126, e2020JC016456, https://doi.org/10.1029/2020JC016456, 2021.