Characteristics and mechanisms of coastal upwelling in the gulf of Thailand

Abstract

The characteristics and mechanisms of coastal upwelling in the Gulf of Thailand was investigated through 2 approaches; 1) Ekman transport upwelling index (UIET) and sea surface temperature upwelling index (UISST), and 2) Hydrodynamics model DELFT3D-FLOW under the influences of tide, spatially varying wind, water temperature, salinity and river discharge. The UIET indicated favorable upwelling conditions along the west coast of the GoT mostly during northeast monsoon in January and 1st inter-monsoon in March, while the favorable upwelling condition indicated by UISST was found along the east coast during southwest monsoon in August and 2nd inter-monsoon in October. The model expressed the favorable upwelling conditions along the west coast of the upper gulf and the west coast of Ca Mau Cape during northeast monsoon and southwest monsoon. Besides, the model results shown the upwelling with the obvious cooler coastal water along the west coast of the upper gulf and the central gulf and along the west coast of Ca Mau Cape during northeast monsoon and southwest monsoon, and with slightly cooler coastal water during 1st inter-monsoon in March and 2nd inter-monsoon in October. The coastal upwelling associated with UIET was different from UISST and the model simulation. The UIET indicated the wind-driven coastal upwelling directly connecting with directions of Ekman transport and wind. In contrast, the UISST was estimated using the satellite-observed sea surface temperature. Also, the upwelling found in the model simulation was generated using different forces, e.g., tide, wind, temperature, salinity, river discharge and heat. The tracked coastal upwelling in this study might be vital for fisheries resources managements and conservation, and to complete the knowledge of nutrient distributions in the Gulf of Thailand.