The observation of vertical mixing induced by shoaling of internal waves at Dongsha Atoll.
| Autor: | Kai-lun Lin, 林凱倫 |
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| Rok vydání: | 2010 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 98 Internal waves have been identified as one of the most active mechanisms producing vertical mixing in continental slope and shelf waters. The major contribution of mixing are due to internal tides, however, shorter period internal waves are unlikely to be the main source of energy for mixing, especially on the inner part of the continental shelf. In this study, we observe the vertical mixing of huge internal waves in the Dongsha Atoll South China Sea. These solitary waves were originate near the Luzon Strait, propagated westward across the basin, evolving into internal solitary wave trains and dissipated at the western shallow continental shelf. The wave energy and phase speed reduced significantly during the shoaling process. Internal waves and their likely related induced mixing phenomena are analyzed based on multiple cruises of observations consisted of CTD hydrographic measurements, water samples and moored thermister strings. Data analyses show that the mixing processes are related to depths of water and the interfacial of wave. For depression wave in the deep water zone, upper layer water may push downward producing vertical mixing beyond the thermocline. The mixing usually dilutes the nutrients in the upper layer of water column. Statistics suggest that the N:P ratio is 12:1 which is lower than the standard value (16:1) indicating the region is nitrogen deficit, similar to most of the surface water in South China Sea. The depression solitons in deep water may evolved to a packet of elevation waves in the shallow water area at “turning point” of approximately equal depth of upper and lower layers. The mixing of shallow water internal waves can entrain cold nutrient rich water from the lower layer into the frequently nutrient depleted subsurface layer to enhance the local coral reef ecosystem. For example, CTD profiles (2008.5.7) before and after the passage of internal wave show large differences. The vertical density distribution has dramatic change. The column was stratified in two layers in normal condition. The internal waves perturbed the water column into stepwise multi-layer density distribution. The water at 50 m showed temperature decrease by 6 ℃, salinity increase by 23 psu, density increase by 1.8, fluorescence decrease by 0.065 μg/L etc. The MODIS chlorophyll images confirm the high concentration fertilized by the internal wave pumping near the NE region of the Dongsha Atoll. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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