Fluid motion that results from the release of potential energy from one of two or more factors that determine the density of a fluid (for example, heat and salinity). Even if the density is statically stable, convection may result if one of the factors is statically unstable. There are three major types of double diffusive convection relevant to heat and mass transport in the ocean. 1) Finger modes may occur when hot salty fluid overlays cold fresh fluid so that convection results in the form of narrow cells (salt fingers) carrying salty water downward and freshwater upward. 2) Diffusive modes occur when a stable salinity field is heated from below so that convection results in the form of a series of well mixed layers separated by sharp density gradients. 3) Intrusive modes occur when there are horizontal density gradients in one of the components determining the density of the fluid even if the fluid density as a whole is horizontally uniform. This instability develops in the form of interleaving intrusions.