Abstract
An air-sea buoyancy flux out of the ocean between the surface outcroppings of different isopycnals must be balanced by a convergence of advective and diffusive fluxes of buoyancy across those isopycnals (Walin, 1982; Tziperman, 1986; Garrett et al., 1995). For steady conditions, the diapycnal diffusive flux due to vertical mixing in the surface mixed layer is very small, so that the advective buoyancy flux dominates (Speer, 1993; Garrett et al., 1995).