Dynamic controls on surface ocean circulation

Western boundary currents are narrow, energetic flows along the western sides of ocean basins. The Gulf Stream and Kuroshio are familiar examples. They transport heat from the tropics toward higher latitudes and influence regional and global climate.

Wind, Earth’s rotation, and stratification all shape these currents. My work examines an additional control: the geometry of the ocean basin. I use theory and numerical models to isolate the effect of a basin’s aspect ratio, its north-south extent relative to its east-west width. Continental margins set the width, while the separation between wind-stress maxima helps set the north-south extent.

The models show that basin geometry can change western boundary current strength and recirculation nonlinearly. Some geometries maximize poleward transport, while basins that are too wide or too narrow have weaker recirculation. This provides a framework for comparing currents in basins with similar wind forcing but different shapes, such as the Atlantic and Pacific.

Basin geometry also matters for past climates. In simulations of the Cretaceous, tectonic changes that reshaped the Pacific are associated with weaker subtropical gyres and larger temperature contrasts between the equator and poles, consistent with independent geological proxy records. Future work could examine how geometry affects mesoscale eddies, sea-surface height variability, thermocline depth, and sea level along western boundaries.