Enhanced Mixing of Heat in the Arctic Ocean Halocline in Weakly Turbulent Conditions

In the low‐energy mixing environment of the Arctic Ocean halocline, a unique mixing mechanism of temperature is present. It consists of the formation of small‐vertical‐scale (∼1 m) intrusive features, with temperature anomalies up to ∼0.1°C, that create mean‐square vertical temperature gradients that are orders of magnitude greater than the background. This finescale temperature structure results in enhanced heat fluxes in conditions of extremely weak turbulence and is responsible for an irreversible mixing of heat into cold halocline waters. The rates of thermal variance dissipation and heat transport are comparable to turbulent mechanisms in the Arctic Ocean, such as internal wave‐driven mixing and double diffusive convection. We propose that in conditions of low turbulence, and in the presence of lateral thermal variability, the temperature field displays a self‐regulating mechanism by which it is able to enhance its finescale structure to generate enhanced mixing, thus compensating for the lack of turbulent fluxes.