Thermodynamic efficiency of the oceans

Recent theoretical and experimental studies stemming from the work of Sandstrom seem to have definitively established that the oceans would have a very low thermodynamic efficiency if they were driven by buoyancy fluxes only (of the order of 7x10-7). What matters, however, is to determine whether the thermodynamic efficiency of the oceans depends sensitively upon the presence of the mechanical forcing of the winds and tides, and whether the latter may significantly increase it. In this study, a rigorous definition for the thermodynamic efficiency of the oceans will be introduced. The main result is that the presence of the winds and tides modifies both the Carnot efficiency and the actual efficiency. Whether the actual efficiency is increased compared to the buoyancy-driven case depends on whether turbulent mixing increases or decreases the internal entropy production due to irreversible diffusive mixing. Some simple theoretical ideas are presented to shed light on these issues, and define a path for future research.