| Summary: | 碩士 === 國立中央大學 === 水文所 === 96 === The South China Sea (SCS) is a semienclosed basin with depth of 5000-6000 m in the central basin and less than 200 m over most of peripheral shelves. Observations obtained in the Asian Seas International Acoustics Experiment (ASIAEX) 2001 revealed vigorous internal tides in the northern SCS. The Luzon Strait is primary deep passage connecting South China Sea (SCS) to the northwest Pacific Ocean and blocked by two meridional ridges at depths. Barotropic tides propagate predominantly westward from the Pacific Ocean, impinge on two meridional ridges, and generate vigorous internal tides. A three-dimensional tide model coupled with a biogeochemical model is used to study the characteristics and energetic of internal tides excited in the Luzon Strait and their influence on the biogeochemical parameters in SCS. Historical CTD data (1999-2003) collected at the South East Asia Time-Serious (SEATS) station are analyzed to obtain the seasonal profiles of temperature and salinity as the initial fields of the model.
Results derives from numerical experiments indicate that diurnal (O1 , K1) and semidiurnal (M2 , S2) tides have a comparable energy flux emanating from the Luzon Strait. The barotropic to baroclinic energy concersion rate reaches 30% for diurnal tides and 20% for semidiurnal tides. There appears no significant seasonal variation of the baroclinic tidal energy flux. Sprin-neap variations are strong. Nearly 30% and 23% of barotropic energy are transferred to baroclinic tides during spring and neap tide. Although there is no significant seasonal variation of energetics, the horizontal phase speed and group speed of baroclnic tide is faster in summer than in winter.
In the SCS, the interaction of internal tide with abruptly changed topography like the Dongsha Plateau may enhance mixing and bring nutrients to sunlit upper layers of the ocean, fueling biological growth. The model results show that the nutrient transport induced by internal tide could support 3.5-6.6% of the daily primary productivity which is 410mgC/m2-day in the SCS.
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