Impacts of typhoons and winter monsoons on biogeochemical processes in the northern South China Sea
| Autor: | Szu-yu Huang, 黃思瑜 |
|---|---|
| Rok vydání: | 2014 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 102 Both satellite and field observations have shown that extreme weather events (EWEs), such as typhoons and winter storms, enhance chlorophyll a (chl a) concentrations in the South China Sea (SCS). However, detailed hydrographic and particulate organic carbon (POC) flux data are usually hard to obtain because of sampling difficulties on the sea shortly before and after an EWE. To better understand the biogeochemical responses (including concentrations of nutrients, chl a, POC and POC flux) in the SCS to the passage of typhoons and winter storms, hydrographic data were collected during the period of 13 cruises conducted from September 2012 to June 2014 by R/V Ocean Researcher III or V in the northern SCS. Floating sediment traps were used to collect sinking particles at the bottom of the euphotic zone, and the samples collected were used to estimate POC export fluxes. I analyzed seasonal variations in biogeochemical parameters and investigated the effects of typhoons and winter storms on these parameters. The results indicate that POC fluxes did not show distinct seasonal variations, the average POC flux was 48 ± 6 mg-C m−2 d−1 without EWE effects. The POC fluxes after the passage of typhoons Tembin and Soulik, and the passage of several winter storms were 78 ± 12、115 ± 16 and 95 ± 13 mg-C m−2 d−1, respectively. These values were 1.6- to 2.4-fold higher than those obtained without EWE effects. The average surface chl a concentrations in spring, autumn and winter in the northern South China Sea were 0.34, 0.10 and 0.54 μg L−1, respectively. The highest chl a concentration occurred in winter, suggesting that the strong vertical mixing and nutrient entrainment from subsurface water to the euphotic zone induced by strong wind enhance phytoplankton growth. When compared to field chl a data, we found that chl a data obtained by Moderate Resolution Imaging Spectroradiometer (MODIS) exhibited a tendency to underestimate chl a concentrations. In coastal waters, however, the MODIS chl a concentrations were overestimated. The error between field observations and satellite MODIS data may be strongly affected by dissolved organic matter and suspended particles in the water column. Therefore, satellite MODIS chl a data need to be validated using more field data. The results presented in this thesis provide clear evidence that EWEs can trigger elevated organic particle export from the euphotic zone to the deeper ocean in the northern SCS. Regarding the affected area and period (winter storm &;gt; typhoon), a winter storm seems to sequester more carbon in the ocean as compared to a typhoon. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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