Editing Fjord (section)

===Hydrology===
During the winter season, there is usually little inflow of water that is fresh. Surface water and deeper water (down to {{cvt|100|m|disp=or||}} or more) are mixed during winter because of the steady cooling of the surface and wind. In the deep fjords, there is still fresh water from the summer with less density than the saltier water along the coast. Offshore wind, common in the fjord areas during winter, sets up a current on the surface from the inner to the outer parts. This current on the surface in turn pulls dense salt water from the coast across the fjord threshold and into the deepest parts of the fjord.<ref name= Skreslet>{{Cite book |title=Fjordene og kyststrømmen |last=Skreslet |first=Stig |publisher=Møre og Romsdal naturvern |year=1980 |place=Åndalsnes; Rauma/Ulvåa på vektskåla |pages=48–54 }}</ref> Bolstadfjorden has a threshold of only {{cvt|1.5|m|||}} and strong inflow of freshwater from [[Vosso]] river creates a brackish surface that blocks circulation of the deep fjord. The deeper, salt layers of Bolstadfjorden are deprived of oxygen and the seabed is covered with organic material. The shallow threshold also creates a strong tidal current.<ref name= "Aarseth" />

During the summer season, there is usually a large inflow of river water in the inner areas. This freshwater gets mixed with saltwater creating a layer of brackish water with a slightly higher surface than the ocean which in turn sets up a current from the river mouths towards the ocean. This current is gradually more salty towards the coast and right under the surface current there is a reverse current of saltier water from the coast. In the deeper parts of the fjord the cold water remaining from winter is still and separated from the atmosphere by the brackish top layer. This deep water is ventilated by mixing with the upper layer causing it to warm and freshen over the summer.<ref>{{cite journal | first1= J.H. | last1= Simpson | first2= T.P.| last2= Rippeth| year= 1993| title= The Clyde Sea – a model of seasonal stratification and mixing| journal= Estuarine, Coastal and Shelf Science| number= 37| pages= 129–144| doi= 10.1006/ecss.1993.1047 }}</ref> In fjords with a shallow threshold or low levels of mixing this deep water is not replaced every year and low oxygen concentration makes the deep water unsuitable for fish and animals. In the most extreme cases, there is a constant barrier of freshwater on the surface and the fjord freezes over such that there is no oxygen below the surface. [[Drammensfjorden]] is one example.<ref name=Skreslet/> The mixing in fjords predominantly results from the propagation of an [[internal tide]] from the entrance sill or internal seiching.<ref>Arneborg, L., Janzen, C., Liljebladh, B., Rippeth, T., Simpson, J. H. & Stigebrandt, A. (2004). Spatial variability of diapycnal mixing and turbulent dissipation rates in a stagnant fjord basin. Journal of Physical Oceanography, 34(7), 1679–1691</ref>

The Gaupnefjorden branch of [[Sognefjord]]en is strongly affected by freshwater as a glacial river flows in. [[Velfjorden]] has little inflow of freshwater.<ref name=":0" />