TRR181 Seminar: "Effects of improved tidal mixing in NEMO ocean model", by Casimir de Lavergne

"Effects of improved tidal mixing in NEMO one-degree global ocean model", by Casimir de Lavergne (LOCEAN, Paris, France)
Abstract
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 one 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 subinertial internal tides, known to be important in polar regions. The three simulations show broadly similar circulation and stratification but important regional differences. Explicit representation of remote tidal mixing strengthens the AMOC by 1.5 Sv. Inclusion of subinertial internal tides reduces heat reaching Antarctica by eroding Circumpolar Deep Water at southern high latitudes, and reduces the mean age of the global deep (more than 2 km) ocean by 10%. The results call for more observational constraints on polar ocean mixing, and point to multi-faceted climatic repercussions of tidal mixing representations.