A type of water created by property modification in the vicinity of ocean fronts, especially during winter. Convection creates a deep surface layer containing water of nearly uniform temperature and salinity in regions that usually feature strong horizontal and vertical gradients. A Mode Water core is defined by the existence of minima in vertical gradients. Commonly used properties are temperature and potential density anomaly, with the minimum gradient layer then being known as, respectively, a thermostad or pycnostad.

The mode water sinks along isopycnal surfaces, retaining its properties since they can only be changed by mixing with the surrounding water. Since deep mixing processes are much weaker at depth than near the surface, mode waters tend to retain their characteristics for great distances as they move around the ocean basins. Their persistent properties make them excellent tracers for climate change studies since they retain a record of surface conditions at the time of their formation.

There are two general varities of mode water: subtropical mode water and subpolar mode water. Types of subtropical mode waters include:

• Eighteen Degree Water
• North Pacific Subtropical Mode Water
• North Atlantic Subtropical Mode Water
• Madeira Mode Water

• Subantarctic Mode Water
• Antarctic Intermediate Water
• Southeast Indian SAMW

• North Atlantic Subpolar Mode Water.