Winter Bloom and Associated Upwelling Northwest of the Luzon Island: a Coupled Physical-Biological Modeling Approach

A coupled physical-biological model was developed in order to study the mechanisms of the winter bloom in the Luzon Strait (referred as LZB). Based on a simulation for January, 2010, the results showed that the model was capable of reproducing the key features of the LZB, such as the location, inverted-V shape, twin-core structure and bloom intensity. The simulation showed that the LZB occurred during the relaxation period of intensified northeasterly winds, when the deepened mixed layer started to shoal. Nutrient diagnostics showed that vertical mixing was responsible for the nutrient supply to the upper ~40 m layer, while subsurface upwelling supplied nutrients to the region below the mixed layer. Hydrodynamic diagnostics showed that the advection of relative vorticity (can be nonlinear Ekman pumping here) primarily contributed to the subsurface upwelling. The relative vorticity advection was resulted from an offshore jet, which was associated with a northeasterly wind, flowed across the ambient relative vorticity field formed by a mesoscale dipole eddy and Kuroshio loop current.