Effects of improved tidal mixing in NEMO one-degree global ocean model

Internal tides power much of the observed small-scale turbulence in the ocean interior. However, few models include a comprehensive and energy-constrained parameterization of mixing by internal tides. Here we present the impacts of three different tidal mixing schemes in 1,000-year long simulations with the NEMO global ocean model at one-degree resolution. The first scheme (Simmons et al. 2004) includes local bottom-intensified mixing at internal tide generation sites and a constant background diffusivity. The second explicitly includes both local and remote tidal mixing (de Lavergne et al. 2020), with no background diffusivity. The third scheme is identical to the second but has the added contribution of trapped (subinertial) internal tides, known to be important in polar regions. The three simulations show broadly similar circulation and stratification but significant differences in ventilation timescales. Explicit representation of remote tidal mixing strengthens the AMOC, while inclusion of trapped internal tides increases deep convection around Antarctica.