The potential role of thermohaline-shear instability in turbulence production in the Bering Sea and the subarctic North Pacific

A recent linear stability analysis and a numerical simulation suggest that diffusive convection (DC), a regime of the double-diffusive convection, plays a potential role in onset of thermohaline-shear instability, implying that DC could contribute to turbulence production in the oceans. However, an existence of such a thermohaline-shear instability has not been examined in real oceans. We examine if this newly proposed instability mechanism exists in the subarctic North Pacific by analyzing our fine- and micro-scale turbulence measurement data. Vertical inversions were cautiously detected in seawater density profiles and used as a proxy for instability events for gradient Richardson number larger than the critical value of 1/4. We found that a portion of inversions were associated with active DC. Such DC-related inversions exhibited elevated levels of turbulent kinetic energy dissipation rate even for gradient Richardson number largely exceeding 1/4. Our estimate suggested that the thermohaline-shear instability contributes to roughly only 10% of the dissipation of turbulent kinetic energy in the diffusively convective layer in our observation site.

Automated summary

Research suggests that diffusive convection plays a potential role in turbulence production in the oceans, and the proposed thermohaline-shear instability mechanism also contributes to this. However, the existence of such instability in real oceans has not been confirmed. Analyzing measurement data, it was found that active diffusive convection is present in the subarctic North Pacific and affects turbulence production.