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The South China Sea (SCS) is a large semi-enclosed marginal sea to the west of the tropical Pacific, and connected to the western Pacific through the Luzon Strait. The surface water circulation and hydrography in the SCS are strongly influenced by the East Asian monsoon system. The seasonal changes of the monsoon system induce changes in the mixed layer thickness, upwelling, primary production, and associated biogeochemistry. In order to understand the characteristics of the Kuroshio intrusion and the source strength of radium isotopes from the coastal zone, we carried out surface water and water column samplings for Ra-228 and Ra-226 measurements in the northern SCS and the Luzon Strait areas. The Ra isotopes were much higher in the SCS surface waters than in the open ocean surface waters because the SCS was enclosed mostly by landmasses which are known as sources of these nuclides. Higher surface water activities are seen in the northern (shelf and slope) area; lower values are observed in the southern (deep basin) area; the lowest values appear in the eastern (Luzon Strait) area. Large temporal and spatial variations were also observed probably due to the source strength of radium isotopes from the coastal zone and intrusion of the Kuroshio Current. The vertical 228Ra profiles are remarkably similar, showing high values in the surface layer and fairly uniform below about 500m depth but with an increase toward the bottom due to input from the underlying sediments. The shallow water profile on the shelf shows higher 228Ra values due to both vertical and horizontal mixing of the shelf water and additional source from the shore zone. The 226Ra profiles in the northern SCS are quite similar to those in the northwest Pacific both in pattern and magnitude, showing lowest values at the surface and an increase with depth although more scattered. 226Ra activities in the shallow water (less than 1000m depth) are higher in the northern SCS than in the northernwest Pacific Ocean, but they are quite comparable below this depth. The Ra-228/Ra-226 activity ratios of the surface water decrease from the coastal zone and estuaries toward the basin and the Luzon Strait (from 4.11 to 1.03), indicating the former as a main source area for Ra-228. The vertical 228Ra/226Ra activity ratios decrease rapidly from the surface at 2.3 to a depth of 1500m at 0.5 below which the values are less than 0.5. This pattern is similar to that of the open ocean but these values are much higher than those in the open oceans where the surface water values are 0.5 or less and the deep water values are less than 0.1. This suggests a strong input of Ra-228 relative to Ra-226 from the bottom sediments into the deep water of the semi-enclosed SCS.

Luzon Strait is the deepest channel for water exchange between the Northern South China Sea (NSCS) and the West Philippine Sea (WPS). It is important to investigate the seasonal and spatial distributions and the biogeochemical processes of organic carbon, nitrogen and phosphorus in Luzon Strait. During the summer season, the flow of Kuroshio water into the SCS through the Bashi Channel was restricted due to the prevailing southwest monsoon. However, during the winter season, the flow of Kuroshio water into the SCS through the Bashi Channel was enhanced due to the prevailing northeast monsoon. The characteristics of water types across the Bashi Channel depend highly upon the water exchange between the WPS and the NSCS. Distributions of dissolved organic carbon (DON), nitrogen (DON) and phosphorus (DOP) in the euphotic zone generally show an increasing trend from the WPS to the NSCS. The same distribution was pattern found for particulate organic carbon (POC) and nitrogen (PN). The stichomythic ratio (C/N/P) of dissolved organic matter in the euphotic layer was lower in spring than in autumn. The reason may be that the Kuroshio water flowing through the Luzon Strait is much less in spring than in autumn. The ratios of DIN/DIP were much lower than the Redfield ratio (16) suggesting a status of N-limitation in the euphotic zone. The DOC/DON ratios, however, were much higher than the Redfield ratio (6.6). These results implied that DOM might have played an important role in modulating nutrient cycling and food web dynamics in the euphotic zone of study area. The subsurface water (100-600m) of the NSCS, west of Luzon, was more enriched with POM than that of the WPS. However, the situation was reversed in the intermediate water (600-1500m). Correlations are significant between POC and Chl-a in spring and summer, suggesting that phytoplankton abundance may primarily control the distribution of POC in the euphotic zone. The DOC/POC ratio was inversely correlated with Chl-a in both spring and summer. The ratios generally decreased to a constant value as the Chl-a concentration increased to a higher level, implying a higher biological contribution for POC than for DOC. Correlations were also significant between TEP/POC and Chl-a. The ratio of TEP-C/POC in the euphotic layer showed a decreasing trend from the NSCS to the WPS, implying a significant influence of phytoplankton productivity on TEP distribution. During the study period, the integrated gross production (IGP) and integrated dark community respiration (IDCR) in the study area were in the range of 3056~7094 mg C m-2 d-1 and 3372~8901 mg C m-2 d-1 in autumn, respectively; 1740~5338 mg C m-2 d-1 and 2628~7685 mg C m-2 d-1 in spring, respectively; 2149~6110 mg C m-2 d-1 and 4391~8896 mg C m-2 d-1 in summer, respectively. During the autumn and summer season, there were no significant correlations between GP (DCR) and temperature, PAR, salinity, Chl-a, DOC and POC, possibly resented from the effect of typhoon. During the spring season without the typhoon effect, there were significant correlations between GP (DCR) and salinity, Chl-a, DOC and POC. The ratio of IGP/IDCR is an indicator of net ecosystem production, with>1 for the autotrophic system and <1 for the heterotrophic system. The ratio was <1 for all stations indicating a heterotrophic system. However, the ratio was slightly higher in autumn than in spring and summer.

The purposes of this study are to understand and compare: the distributions of the particulate and dissolved 210Po and 210Pb in the northern South China Sea and in the east and west sides of the Luzon Strait; the associated biogeochemical processes, including their mechanisms and rates involved in the area; and the disequilibrium between 226Ra and the 210Pb as observed in profiles. Seawater samples were collected from three stations in the northern South China Sea (station I, J, and F) and one station to the east of the Luzon Strait (station S5) using a Rosette sampling system during three Ocean Researcher I cruises (ORI-688 in July, 2003, ORI-707 in February, 2004, and ORI-734 in October, 2004). The dissolved 210Pb in surface water generally displays higher activities (around 14-28 dpm/100kg) relative to deep water, reflecting atmospheric input. The dissolved 210Pb profile as seen at station F displays a maximum of 26 dpm/100kg at 200 m and lower values at about 10 dpm/100kg below 1500 m. Highest value at 28 dpm/100kg was observed at S5 surface water. It is probably due to being on the path of the Kuroshio which has accumulated atmospheric 210Pb continually from the northern Equatorial Current on its way. The mean residence time with respect to particle scavenging is about 0.62 years for total 210Po within a 50 m mixed layer, and ranges between 0.34 to 1.13 years for total 210Pb in the mixed layer. 210Po is deficient relative to 210Pb in most profiles, suggesting that 210Po is more readily scavenged. The mean scavenging residence time is about 87 years for total 210Pb in the deep water at station F, and 60 years at station J. This residence time is longer than that in both the Pacific and East China Sea deep waters, i.e. a lower scavenging rate in the South China Sea. As the upwelling rate is much higher in the South China Sea than in the Pacific, it may effectively reduce the sinking rate of the sinking particulates, resulting in higher 210Pb residence time in the water columns of the South China Sea.

Internal waves are vertical displacements of stratified water which can propagate a long distance without much energy dissipation. It plays on important role in conveying nutrient from deep ocean to shallower layers, and promoting biological growth. It also affects acoustics, ocean engineering and submarine navigation. Therefore, in the last few years, many scholars have devoted the research of internal waves, especially their generation and transportation in South China Sea. This research discusses the internal wave source, through the Princeton Ocean Model (POM). There are two simulations, one has bigger grid size 3.6km for the whole Luzon Strait in the region, 118¢XE ~123¢XE 18¢XN ~22¢XN, the other has smaller grid of 1.6km, for 118.5¢XE ~123¢XE and 19.5¢XN ~21.5¢XN. The total simulation period is 25 days, The north and south bomdawes use radiation boundary condition, the east side is driven by tidal calculated from WXTide32 model, the west side also uses radiation boundary condition. Three dimensional flow field during May, 2005, is simulated temperature, baroclinic velocity distribution, baroclinic energy flux, Empirical Orthogonal Functio ns (EOF), Fast Fourior transform (FFT), buoyancy frequency and Froude number are all analyzed, The results show that, when tidal current near the Batan island has the stronger baroclinic flow downward to transmit, after through Heng-Chun ridge the baroclinic energy flux to concenter, extrapolated this time possibly produces for internal tide.

Thesis--University of Chicago. / Bibliography: l. 168-175. Also issued in print.

Thesis--University of Chicago. / Bibliography: l. 168-175.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1974. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Typescript (photocopy). / Digitized by Kansas Correctional Industries