碩士 / 國立中山大學 / 海洋科學系研究所 / 103 / Many natural methane seeps exist in waters offshore southwestern (SW) Taiwan. Researchers have frequently used gravity and piston corers to collect sediments and bottom seawater for estimating methane fluxes of these seeps. Due to the difficulty in positioning of the piston and gravity corers when sampling at sea, the actual sampling locations of these corers are difficult to match seeping vents detected by scientific echo sounder. Thus, the methane fluxes of the seeping vents estimated using these corers might not be representative methane fluxes of seeping vents off SW Taiwan. In this study, we used a real-time video multiple-corer that was designed by Underwater Mechatronics Lab, National Sun Yat-sen University (UML, NSYSU) to collect sediments and bottom seawater samples. This real-time multi-corer can precisely obtain sediments and bottom seawater samples on methane seeping vents. We analyzed the concentration of methane, anion, dissolved inorganic carbon and dissolved organic carbon in these samples and estimated methane and DOC fluxes, respectively.
The highest methane concentration in sediment has measured at MV1 (128,452 nM), next to TY1 (63,128 nM) and G96 (12,210 nM) in mud volcanoes area, and the methane concentration in core-top water were 59.8 to 2421.1 nM, respectively. Based on Fick’s First Law, methane flux from sediment to bottom water in mud volcanoes area, Four-way Closure Ridge (FWCR) cold seep area, and Good Weather Ridge (GWR) were 47.5 to 47883.4、95.1 to 99.1, and 119.4 to 194.1 μmol m−2 d−1, respectively. Comparison of our values from SW Taiwan and previously reported data around the world, our results are two to three orders of magnitude lower than those reported values(using ROV with benthic chamber, ca. 0.25~1226 mmol m-2 d-1) in different mud volcanoes and seeps, but higher than previously reported values (1.1~157 μmol m-2 d-1). Because the samples collected by multiple-corer were shallow, the corer did not reach the sulfate-methane interface (SMI) in this study. In addition to, the coring depth was far away from gas hydrate bearing zone. Elevated DOC concentrations at the bottom depths were found at some sites suggesting that some of DOC may come from seeps or mud volcanoes. The DOC benthic flux from sediment to bottom water were 53 to 2100 μmol m-2 d-1, which are higher than previously reported data (using normal corer, ca. 33~196 μmol m-2 d-1).
In summary, the fluxes of methane and DOC in the SW Taiwan are two and one orders of magnitude higher than those of previous studies in similar area respectively, indicating that the real-time multiple-corer can be used for more precisely obtaining sediments and bottom seawater samples on methane seeping vents.
| Identifer | oai:union.ndltd.org:TW/103NSYS5276020 |
| Date | January 2015 |
| Creators | Chia-Wei Hung, 洪家維 |
| Contributors | Chin-Chang Hung, 洪慶章 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 88 |
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