Various processes (currents, features of the seabed, winds, tides, differences in salinity or temperature) create vertical mixing of the waters, thus favouring the ascent to the surface of nutrientrich waters. This produces frontal areas, associated with high phytoplankton production.
Tidal fronts separate vertically mixed coastal waters from mid-shelf waters, which are strongly stratified in summer.
Ocean fronts (such as the slope front) are closely linked to features of the seabed.
Other significant fronts are associated with low-salinity discharges, such as estuary fronts of lower density than the water at the shelf.