Intensified upwelling over a widened shelf in the northeastern South China Sea

Abstract

Observational and three-dimensional modeling studies reveal that the intensified up welling in the northeastern South China Sea (NSCS) is formed as a result of intensified upslope advection of dense deep waters that cross the middle shelf toward the inner shelf over a distinctly eastward widened shelf. The strongest advection occurs over the converging isobaths near the head of the widened shelf. As these dense deep waters advance shoreward, they are advected downstream by the quickly developed upwelling current over the inner shelf and eventually outcropped at the lee of a coastal cape. Dynamically, the shoreward cross-isobath transport over the widened shelf is geostrophically enhanced by a quasi-barotropic negative (westward) along-isobath pressure gradient force as a result of the net rate of the momentum influx and by an intensified bottom frictional transport owing to the flow confluence near the head of the widened shelf. A negative pressure gradient also exists at the lee of the coastal cape over the inner shelf and locally amplifies shoreward motion. Induced by the respective widened shelf and the coastal promontory, the along-isobath variations of cross-isobath transport in the water column over the middle and inner shelves interactively characterize intensified upwelling in the NSCS.