Spatial and Temporal Variability of Turbulent Mixing in the Deep Northwestern Pacific

Small‐scale turbulent mixing supplies potential energy for the upwelling of deep waters in the abyssal ocean, a key component of the global overturning circulation. This process is particularly significant in critical regions such as the Northwestern Pacific where the upwelling structure of deep waters remains poorly understood due to limited knowledge of deep ocean mixing. Here, we investigate the full‐depth spatiotemporal variability of turbulent mixing in the deep Northwestern Pacific based on hydrographic data collected over repeated surveys. Nineteen‐year‐average diapycnal diffusivity of 1.42 × 10−4 m2 s−1 is reveled in the deep Philippine Sea, indicating significantly stronger mixing compared to the stratified ocean interior. Spatially, turbulent mixing strengthens toward the bottom and intensifies westward from the open Pacific to the Philippine Sea due to rough topography. At certain mixing hotspots, enhanced mixing can penetrate up to 2,500 m above the bottom, suggesting a substantial potential for upwelling. Below 2,000 m, turbulent mixing exhibits pronounced seasonal variation that deep mixing is more intense in summer (winter) than in winter (summer) in the West Caroline Basin (the Parece Vela Basin). This spatially varying seasonality may be attributed to the inhomogeneous internal tidal energy dissipation in the Northwestern Pacific. Our study will serve to clarify the modulation of turbulent mixing to deep‐water mass transformation and circulation in the Northwestern Pacific. Plain Language Summary The global overturning circulation plays an important role in transporting and redistributing climate‐sensitive matters such as oxygen and carbon. This circulation is enclosed by the upwelling of deep waters facilitated by turbulence in the deep ocean, which mixes dense waters with the lighter waters above. In the Northwestern Pacific, a significant portion of deep waters from the Southern Ocean continuously intrudes into the Philippine Sea, rendering it a critical region for global circulation. However, the upwelling process of deep water remains largely unknown due to the limited understanding of turbulent mixing in the deep Northwestern Pacific. To fill this gap, we characterize the spatiotemporal distribution of turbulent mixing in the Northwestern Pacific based on long‐term observations during 2004–2022. We reveal that turbulent mixing here is highly enhanced by rough topography, 10 to 100 times stronger than that in the open ocean, particula