呂宋海峽內潮及其強化生地化通量之數值研究

Numerical study of internal tides in the Luzon Strait and its influence on biogeochemical fluxes

丁錡樺(Chi-hua Ting)

指導教授 ： 劉康克 ； 詹森

國立中央大學/地球科學學院/水文與海洋科學研究所/碩士(2008年)

摘要

南海是一個半封閉的海域，由水深達5000-6000 m的中央海盆及水深淺於200 m的廣大陸棚區所組成。根據「亞洲聲學實驗」(ASIAEX) 2001年在南海的調查，發現南海北部有相當顯著的內潮(斜壓潮)活動。而呂宋海峽是連接南海與太平洋的主要通道，內部有呂宋島弧與恆春海脊兩座海檻地形，當正壓潮流流經此處會因為與海脊的交互作用激發強烈的斜壓潮波。本研究進一步利用三維潮汐模式耦合生地化模式去研究激發自呂宋海峽之內潮的特性與能量以及對南海生地化參數的影響。模式初始場則採用南海時間序列站(SEATS)自1999至2003年間的溫鹽深歷史資料所分析得到的季節性溫、鹽剖面。
數值實驗結果顯示季節性的水文結構差異並未造成斜壓潮能量有重要的改變，但是斜壓潮能量在大小潮間的變異則相當明顯，而全、半日斜壓潮的能量也有明顯的差異。估算正壓能量轉換成斜壓能量的百分率，半日斜壓潮約20%，全日斜壓潮30%，而混合型斜壓潮在大小潮期間分別為30%與23%。另外，研究結果尚指出冬夏兩季的斜壓潮能量雖然沒有重要的差異，但是夏季斜壓潮的水平相速度及水平群速度皆比冬季來的快。
生地化方面的模擬結果則顯現內潮遇上類似東沙島這類陡變的地形會有比較強的混合作用進而將深海的營養鹽向上傳輸至有光層中並提升生產力。模式結果指出內潮引起的營養鹽傳輸可支持整個南海初級生產力(410 mgC/m2-day)的3.5-6.6%。

關鍵字

初級生產力 ； 數值模式 ； 內潮

並列摘要

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.

並列關鍵字

primary productivity ； numerical model ； internal tide

參考文獻

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