A Modeling Study of Nutrient Transport and Dynamics Over the Northern Slope of the South China Sea

Abstract Using observed data and results from a numerical model, we investigate the coupled physical‐biogeochemical processes that result from water exchanges between the South China Sea (SCS) and the western Pacific Ocean (WPO) and between the shelf and deep basin along the biophysically active continental slope. We study the nutrient transport and dynamics over the northern slope of the SCS where the main branch of the SCS basin circulation facilitates water exchange between the SCS and the WPO. Our results show that the nutrient flux consistently flows year‐round into the slope region from the WPO and that the along‐slope and cross‐slope transports regulate the nutrient budget in the region. The nutrient transport concentrates mainly in the upper 1,000 m and exhibits significant seasonality. We found that cross‐isobath motion is key to fueling nutrients for biological production along the slope and throughout the SCS. When the persistent westward slope current interacts with the variable sloping topography, a unique upslope/downslope nutrient transport occurs along convex/concave isobaths. Vertical turbulent mixing becomes the main nutrient source in the upper mixed layer, and vertical advection becomes the major contributor of nutrients to the subsurface layer. Biological production dominates the nutrient sink in both layers. Horizontal advection is also an important sink in winter when the slope current is the strongest due to the enhanced northeasterly monsoon and the Kuroshio intrusion. Our findings provide an insightful understanding on the critical role of nutrient transport over the slope in the overall ecosystem dynamics of the marginal SCS.