Topography Effects on the Seasonal Variability of Ocean Bottom Pressure in the North Pacific Ocean

Ocean bottom pressure p B is an important oceanic variable that is dynamically related to the abyssal ocean circulation through geostrophy. In this study we examine the seasonal p B variability in the North Pacific Ocean by analyzing satellite gravimetric observations from the GRACE program and a data-assimilated ocean-state estimate from ECCOv4. The seasonal p B variability is characterized by alternations of low and high anomalies among three regions, the subpolar and subtropical basins as well as the equatorial region. A linear two-layer wind-driven model is used to examine forcing mechanisms and topographic effects on seasonal p B variations. The model control run, which uses a realistic topography, is able to simulate a basinwide seasonal p B variability that is remarkably similar to that from GRACE and ECCOv4. Since the model is driven by wind stress alone, the good model–data agreement indicates that wind stress is the leading forcing for seasonal changes in p B . An additional model simulation was conducted by setting the water depth uniformly at 5000 m. The magnitude of seasonal p B anomaly is amplified significantly in the flat-bottom simulation as compared with that in the control run. The difference can be explained in terms of the topographic Sverdrup balance. In addition, the spatial pattern of the seasonal p B variability is also profoundly affected by topography especially on continental margins, ridges, and trenches. Such differences are due to topographic effects on the propagation pathways of Rossby waves.