On the instantaneous salt mixing due to freshwater boundary fluxes

Abstract In this paper we detail the instantaneous transformation between freshwater and seawater while crossing the ocean boundary. From the kinematic boundary conditions for the seawater continuum we derive the associated flux of squared salinity and link it to an instantaneous mixing of salt (salinity variance decay) at the boundary. Within the water mass transformation framework this mixing occurs across virtual isohalines in salinity space. Our derivations complement the analytical description of seawater and clarify the demixing during freshwater removal.