Diapycnal Upwelling Over the Kyushu‐Palau Ridge in the North Pacific Ocean

Abstract A significant portion (∼2.1 Sv, 1 Sv = 106 m3 s−1) of deep water penetrates into the Philippine Sea through the Yap‐Mariana Junction, the sole passage of the Philippine Sea below 4,000 m, and is then upwelled into shallower layers, closing regional overturning circulation. Yet, the structure and variability of this diapycnal upwelling remain poorly understood. Here, we report on a fine‐resolution hydrographic observation conducted at the most significant topographic feature in the Philippine Sea, the Kyushu‐Palau Ridge (KPR). Enhanced mixing up to O(10−2) m2 s−1 near the KPR is manifested, indicating the presence of substantial upwelling herein. Besides, the ridge‐related topography contributes more deep‐water mass transformation than abyssal basins in the Philippine Sea. This study highlights the significant role of rough bathymetry features in generating diapycnal upwelling in the North Pacific.