The water and material exchange between global ocean and marginal sea is attracting immense research interest because it significantly influences the coastal hydrodynamic environment and ecosystem. Because of the steep topography associated with shelf break and strong nonlinearity of currents, the interaction between continental shore and circulation in the open ocean remains a great challenge. We first report the topographic beta spiral inferred from observations, which is generated by strong upwelling induced when strong western boundary current runs onto steep topography in coastal sea. This mechanism plays a vital role in regulating intrusion/bifurcation of western boundary currents, wherever strong western boundary current meets shelf break in the marginal sea. It can be used as a clue in predicting the intrusion path and the bifurcation pattern of strong boundary currents. Similar to Ekman spiral, topographic beta spiral is one kind of very important and common spirals in the world oceans. The topographic beta spiral may exist in many places in the world oceans wherever a strong current is not parallel to the isobaths. The topographic beta spiral provides a dynamical channel to bring the cold, oxygen-poor, and nutrient-rich deep water from the strong current to the continental shelf. Therefore, the topographic beta spiral reveals a long-term missing link between the oceanic general circulation theory and shelf dynamic theory, and it is important for understanding the links between changes in ocean climate, coastal hypoxia, and ecological perturbations. (Contact: Dr. Dezhou Yang, yangdezhou@qdio.ac.cn)

This topographic Beta Spiral theory was published in the Geophysics Research Letter (http://onlinelibrary.wiley.com/doi/10.1002/2017GL076614/full).

Topographic Beta Spiral and Onshore Intrusion of the Kuroshio Current