The study investigated seasonal and spatial distributions and biogeochemical processes of dissolved and particulate organic matter in the upper layer of northern South China Sea (SCS). Concentrations of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) in the euphotic zone of northern SCS were in the range of 55-147 £gM, 2.4-9.9 £gM and 0.13-0.38£gM, respectively. A maximum concentration of DOC, DON and DOP, was found in the station close to the Pearl River due to freshwater input. The concentration of DOC decreased generally with distance away from the continent, but the ratio of DOC/TOC increased with distance primarily due to trophic dynamics. Concentrations of DOM were generally the highest in the surface layer and decreased with depth, but their C/N/P ratios increased with depth, indicating that both nitrogen and phosphorus were preferentially decomposed over carbon. Below the mixed layer, DOC degradation contributed only about 16% of AOU (apparent oxygen utilization). Inverse correlation between DOM and density was significant in the upper layer suggesting that the distributions of DOC, DON and DOP were largely controlled by vertical mixing. Inverse correlation was also significant between DOM and AOU, showing the effect of microbial decomposition on DOM in deep water. Concentrations of POC, PON and POP in the euphotic zone were in the range of 1.8-17.7£gM, 0.18-2.45£gM and 10-163 nM, respectively. Relatively high concentrations of POC, PON and POP in the surface water of inner shelf were also likely attributed to the input of the freshwater. Significant correlation between POC abundance and Chl-a suggested that phytoplankton abundance may control the distribution of POC. The ratio of ¡µPOC/¡µPON in the euphotic zone ranged from 4.57 to 7.3, implying various effects of bacteria and planktons on POM. A simple one-dimensional vertical eddy diffusion model was applied to estimate downward fluxes of DOC and POC and upward fluxes of nutrients across the boundary of euphotic layer and/or thermocline base. Total downward fluxes of organic carbon (OC) were compared with total upward nutrient-derived OC fluxes. The results suggested that additional nutrient sources in the euphotic layer were required to balance OC budgets. The ratios of DIN/DIP were much smaller than the Redifield N/P Ratio of 16:1, suggesting a status of N-limitation in the euphotic zone. The DOC/DON ratio, however, was much higher than the Redfield ratio. These results implied that DOM must play an important role in modulating nutrient cycling and food web dynamics in the euphotic layer.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0811104-152351 |
| Date | 11 August 2004 |
| Creators | Wang, Shih-Ming |
| Contributors | Jia-Jang Hung, Yu-Chia Chung, Yuh-ling Lee Chen |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0811104-152351 |
| Rights | unrestricted, Copyright information available at source archive |
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