Is horizontal convection really “non‐turbulent?”

Within the geophysical community Horizontal Convection (HC) has been considered irrelevant or nearly so in driving large scale overturning flows, based primarily on an inference based on a century old experiment by Sandström (1908), and on a theoretical argument that would prevent HC to sustain a true turbulent flow, the latter deemed necessary to achieve mixing. We revisit Paparella and Young's (2002) argument with the aid of DNS of HC at Rayleigh number up to 10 10 . We argue that the criterion used by these authors is overly restrictive. On the contrary, geometrical statistics show that HC possesses the characteristic of turbulent flows. The surprising result is that HC can transport very large quantities of heat and sustain large amounts of diapycnal mixing with a surprisingly small amount of dissipation. Values of diapycnal mixing and dissipation in the ocean are shown to be consistent with a HC driven ocean provided the effect of wind‐forcing are included.