Any physical process that is caused by the nonlinear terms in the expression of density as a function of S (salinity) and T (temperature) measured at constant pressure.
The original meaning of cabbeling is described by considering the mixing of two fluids of similar density but different T and S. The volume of the mixture will generally be slightly smaller than the total volume of the two original fluids (contraction upon mixing). Therefore, the mixture will have a slightly higher density than the average density of the original fluids. This densification upon mixing is thought to cause the mixed fluid to flow downward, away from the zone of mixing, and so will allow new source fluids to come in contact. In situations where vertical mixing is occurring, the effects of nonlinearity are more subtle, leading to differential entrainment and upward migration of the mixing interface.