Program

There are many islands (reefs) in the South China Sea (SCS). The physical and biological properties around the islands are highly spatially variable compared to those of mainland coasts, because the shorelines are more complex with much smaller scale, and the topographies are step-shape with a much sharper slope. In this study, high-resolution (～400m) physical-biological coupled models for Xisha Islands and a Reef in Nansha region, nested within a gross-resolution (~7km) SCS model, were developed based on Regional Ocean Modeling System (ROMS) and Finite-Volume Community Ocean Model (FVCOM). In the high-resolution island models, the shorelines were redrew according to ~30m resolution satellite images, and four linear relaxation layers were used for the transition of nesting boundaries. Results show that the simulated SSH, geostrophic current and Chl-a are consistent with altimeter data and ocean color productions in their temporal and spatial patterns of the SCS, and the current vectors are well agreed with two mooring observations in Xisha and Nansha regions. Moreover, the high-resolution models reproduced more abundant sub-mesoscale phenomena, such as island wakes, compared to the gross-resolution one. For examples, cyclone-anticyclone asymmetry associated with vortex streets appeared a common structure in the lee of islands, which is also captured by the synthetic aperture radar (SAR) images. Significant daily signals in simulated hydrographic and biological variables were found at the downstream of islands, suggesting the existence of drastic and episodic vertical motions. The models can be useful for analyzing the sub-mesoscale processes, and evaluating the effects of island engineering on the physical and biological dynamics around the islands in the SCS.