Enhanced cross-shelf exchange by the eddies associated with plume front

Broadened width of high chlorophyll concentration band with wavy structures, patches and filaments are often observed along the western coastal next to the Pearl River Estuary over the northern South China Sea shelf during the transition period from winter to summer monsoon. Whereas, there is no such wide band in other seasons. By using a high resolution numerical model, we reveal that the complex structure and wider band of high coastal chlorophyll concentration results from the smaller scale eddies (about 20-50km in diameter) associated with buoyant plume and thermal fronts, which are roughly along the 30m and 50m isobaths, respectively. Two trains of eddies are formed along the fronts by the baroclinic instability triggered by frequently alternating wind over the fronts during the monsoon transition period. The influences of these two trains of eddies are extended in the cross-shelf direction by their interactions, and they temporally enhance the cross-shelf flow and material exchange. They serve as an efficient pathway to link the inner shelf towards the slope.