A fjord is a very deep flooded glacial valley with steeply sloping banks. Its mouth is often closed off at a shallow threshold formed by a moraine.
Characteristics of fjord water
Because of their special topography, the waters of fjords are highly stratified:
- at the surface there is a layer of almost fresh water which is rich in oxygen and nutrients. Low in density and calm, this water mixes very little with the underlying salt water;
- deeper down there is normally saline water. The calmness of the water and the barrier provided by the threshold and the surface layer of fresh water severely limit exchanges with the adjoining sea. This water therefore remains in place for a very long time.
The dangers associated with these features
The stagnation of the deep water associated with the absence of light make this water an anoxic and oligotrophic environment. The contamination of this water by pollutants has long-lasting effects, the dilution and biodegrading of these pollutants being extremely slow.
Morphology of a typical Norwegian fjord. © Ken Douglas/Today is a good day CC by-nc-nd 2.0