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


Ocean bottom pressure pB is an important oceanic variable that is dynamically related to the abyssal ocean circulation through geostrophy. In this study we examine the seasonal pB 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 pB 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 2-layer wind-driven model is used to examine forcing mechanisms and topographic effects on seasonal pB variations. The model control run, which uses a realistic topography, is able to simulate a basin-wide seasonal pB 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 pB. An additional model simulation was conducted by setting the water depth uniformly at 5000m. The magnitude of seasonal pB 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 pB 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.