How important are diapycnal mixing and geothermal heating for the deep circulation of the Western Mediterranean?

The dissipation rate of turbulent kinetic energy ε and the associated diapycnal turbulent mixing is inferred from a set of microstructure observations collected over several cruises from year 2012 to 2014. The geographical distribution of ε highlights several regions of enhanced levels of turbulence ranging from 10−9 to 10−6 W kg−1: the Sicily Channel, the Corsica Channel, and the Ligurian Sea. Elsewhere, ε was small, often below 10−10 W kg−1. Below 1300 m, geothermal heating provides three-fold more buoyancy than small-scale turbulence. Geothermal heating and turbulent diffusion provide enough buoyancy to balance 15% to 50% of a mean yearly deep water formation rate of 0.9 to 0.3 sverdrup (106 m3/s), respectively. The remaining part has to eventually overflow through the Strait of Gibraltar.