Ocean deoxygenation has occurred in most global oceans, threatening marine life and deteriorating marine environment. Oxygen subduction and obduction are key drivers for subsurface and interior oxygen levels. While previous research has mainly focused on interannual variations of oxygen subduction and obduction processes, their seasonal characters remain not yet clear. Herein, we analyze the seasonal and spatial characteristics of oxygen subduction and obduction across the permanent thermocline of the Pacific Ocean from 2004 to 2017 and further evaluate their dominant drivers. Our findings indicate a pronounced intensification of oxygen subduction in winter at subtropical mid-latitudes, due to increased downwelling from the subtropical gyre center. Conversely, in summer, the region of oxygen subduction extends to subpolar high-latitudes, intensified by reduced upwelling at the subpolar gyre center and contributions from lateral induction and other eddy processes. Concurrently, the average intensity of oxygen subduction in the subtropical region weakens, corresponding to reduced downwelling. Overall, wind-driven upwelling and downwelling are identified as key factors impacting seasonal variability of oxygen subduction and obduction. Our study reveals both seasonal and latitudinal characteristics of oxygen subduction and obduction, improving our understanding on future open-ocean deoxygenation trends.
 

Seasonal variability,Pacific Ocean,Deoxygenation,Subduction