Quantifying energy barriers associated with density stratification in vertical displacements of water parcels

Density stratification affects mixing by limiting the interchange of properties along the water column. This stratification establishes barriers to the vertical displacement of water parcels, which interchange their properties between different layers of the ocean. Quantifying the intensity of these barriers, considering the direction (upward and downward) of the vertical displacement of a water parcel, is the main aim of this study. By employing the buoyancy energy required to displace a water parcel vertically, we propose the buoyancy potential energy (BPE) to analyze energy barriers in detail, describe the stability of a water parcel, and provide an objective integrated measure of stratification intensity in any vertical section of the water column. By illustrating the application of BPE in dynamical and ecological contexts, we demonstrate that it provides a complementary understanding of oceanic stratification. BPE is directly calculated from survey data, eliminating the need to diagnose turbulent processes, and has a straightforward numerical implementation. The routine application of BPE to study diverse ocean-atmosphere interaction processes (e.g., dynamical, thermodynamical, ecological, and biochemical) in which stratification plays a role can extend and enrich our understanding of them.