Project No: 16308319

Title: Nutrient transport and dynamics over the northern slope of the South China Sea

Principal Investigator: Dr. Zhongming LU

Co-Investigator: Prof. Jianping GAN

Abstract:

The northern continental slope in the South China Sea (NSSCS) locates west of Luzon Strait (LS) in the region adjacent to the western Pacific Ocean (WPO). The water volume exchange through the LS and nutrient concentration difference between the SCS and WPO regulate the nutrient influx and outflux in the South China Sea (SCS). The NSSCS is on the upstream of main pathway of the cyclonic (anticlockwise) circulation in the SCS and serves as a source region of the influx and outflux of nutrient for the entire SCS. NSSCS connects the deep basin and the shallow shelf and other parts of the SCS via along cyclonic circulation. The strong along-slope nutrient transport, and the cross-slope (vertical) nutrient transport due to the interaction between slope current and slope topography over the dynamical NSSCS greatly affect the nutrient source and sink for the ecosystem dynamics, biogeochemical cycling, and the marine environmental change in the SCS. The nutrient transport and ecosystem dynamics in the NSSCS are extremely complex and involve the monsoonal-forced transport, fluxes from Kuroshio intrusion through LS, internal dynamics of cross-slope transport and biogeochemical processes in the upper ocean. The mechanisms and processes that regulate the budget and fundamental nutrient dynamics over the NSSCS are still poorly understood, in which large uncertainties exist regarding to the nutrient dynamics associated with both physical and biogeochemical processes from local and remote forcing. Based on the analyses of previous studies and our piloting numerical experiment, we hypothesize that H1: the nutrient fluxes due to intrusion through the LS, the along-slope flux and the cross-slope vertical flux due to interaction between the slope current and the slope topography, fluxes across the northern, western and southern boundaries of the NSSCS zone, are the major controllers that determine the nutrient source/sink in the NSSCS; H2: unlike the episodically occurring cross-slope transport over the slopes in other parts of the oceans in the world, there is strong and persistent along-slope and cross-slope nutrient fluxes with high spatiotemporal variability in the NSSCS; H3: the interaction and feedback between diffusion, advection, biological production, and remineralization greatly define the nutrient dynamics of the NSSCS. We propose to use historical observational data and a customized three-dimensional, high-resolution coupled physical-ecosystem biogeochemical model to examine H1-H3. The model results will be used to quantify the 3-D pathways of nutrient transport and budget, identify the underlying dynamic and the ecosystem responses, and investigate their interactive linkages and potential impacts on the biogeochemical processes in the NSSCS region, the adjacent continental shelf and the entire SCS basin. The proposed study will be both regionally relevant and globally significant.