Effects of Improved Tidal Mixing in NEMO One‐Degree Global Ocean Model

Abstract Diapycnal mixing in the ocean interior has diverse numerical representations in current global ocean models. These representations affect the simulated transport and storage of oceanic tracers in ways that remain little studied. Here we present the impacts of three different tidal mixing representations in thousand‐year‐long simulations with the NEMO global ocean model at one‐degree resolution. The first model experiment 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, with no background diffusivity. The third experiment is identical to the second but has the added contribution of bottom‐trapped (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 Atlantic Meridional Overturning Circulation by up to 1.5 × 10 6 m 3 s −1 . Inclusion of bottom‐trapped internal tides reduces heat reaching Antarctica by eroding Circumpolar Deep Water at southern high latitudes, and reduces the mean age of the global deep (>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.