[A-OS16] Frontiers of Ocean Mixing Research

[AOS16-10] The three-dimensional internal tide radiation and dissipation in the Mariana Arc-Trench system

*Zhenhua Xu¹ (1.Institute of Oceanology, Chinese Academy of Sciences)

Keywords:Internal tides, Mariana Trench , Mixing

Internal tides are known to be energetic in the Mariana arc, but their three-dimensional radiation and dissipation, particularly the trench-arc-basin impacts, remain unexplored. Here, the generation, propagation and dissipation of M₂ internal tides over the Mariana area are examined through a series of observation-supported high-resolution simulations. The M₂ barotropic to baroclinic conversion rate amounts to 8.35 GW, of which the two ridges contribute ~81% of the generated energy. The contribution to generation by the Mariana basin and deep trench is weak, but they are important in modulating the energy radiation and dissipation, since tidal beams can spread to these areas. Two arc-shaped Mariana ridges radiate the westward-focused, but eastward-spreading tidal beams. This is very consistent with the altimetric measurements. The resonance in the ridge center enhances the westward convergent beam, which can travel across the Palau Ridge 800 km away. In contrast, the beams propagate eastward over a limited lateral range, but can radiate and dissipate significant energy in the deep water column, even reaching the abyssal Mariana trench. The direct estimation from the model results reveals the dissipation’s multilayer vertical profile in the entire water column, and is well consistent with the finescale parameterization estimate based on vertical strain. However, the estimate of an oft-used energy balance method typically assuming a vertical structure function F(z) for the dissipation rate exponentially decaying above seafloor, is largely inconsistent with the measurements. Our findings highlight the complexity of the three-dimensional radiation path and dissipation map of internal tides in the Mariana area.