About 8,000 years ago post-glacial sea level rise began to slow down from 1.25 m to 0.14 m per hundred years, allowing the Wadden Sea to emerge. The largest coherent tidal flat area of the temperate world evolved with a seaward barrier of dune islands and sandy shoals and a landward area of tidal flats and salt marshes.
The current landscape and submarine seascape is an almost complete product of the last three glacial periods and their interglacial phases, including the present one. Presumably, the past interglacial periods gave rise to coastal environments similar to the present Wadden Sea. At least, fossils indicate a marine fauna similar to the present one, and ancient cliffs and marine sediments show how far interglacial seas have transgressed into the land.
The rates of sea-level rise and sediment supply varied over time and locality, resulting in continuous dynamics in the coastal morphology of the Wadden Sea. As a result, at times parts of the coast have grown where the sea tides and waves have washed in more sediment from the adjacent offshore zone than was needed to compensate for sea level rise. At other times, the coast retreated in some places when sediment supply was unable to compensate for sea level rise. In this way, the Holocene history of sea level, climate, and depositional responses has been preserved in the stratigraphic record of the Wadden Sea.
Transgression curve of the average tidal high water in the southern North Sea. K.-E. Behre, 2004.