English Channel (Eastern) - Environment

The most outstanding oceanographic feature is the tidal current intensity (maximum speed varying between 2 and 4 knots and in some places up to 6 knots). The greatest tidal ranges and currents are found at the “narrows” in the West and at the Dover Strait in the East, where water masses flow from the Channel into the North Sea. In these areas, the strong tidal currents and associated intense bed shear stress produce pebbly bottoms, whereas in areas where bed shear stress is weaker (particularly bays and estuaries), finer sediments (mud, sand) accumulate. Combined with depth, the sediment type influences the spatial distribution of many marine species (e.g. benthic invertebrates, fish).

Lying at the boundary between a Boreal zone to the north (the North Sea) and a warm temperate zone to the south (the north-east Atlantic), water temperature varies seasonally with large amplitudes (greater than 10°C) between winter and summer. Surface and bottom temperatures are similar, illustrating the absence of a thermocline in this part of the Channel, due to shallowness, strong currents, and wind and tidal mixing. Another interesting feature of the study zone is the presence of a salinity gradient (coast to offshore) forming a "coastal river", an arm of low salinity and turbid water flowing parallel to the French coast in a south-north direction. These low salinities are the result of large inputs of fresh water from French rivers, notably the river Seine. The central waters of the eastern Channel come from the Atlantic and hence are relatively more saline.