| Autor: |
Shiou Ya Wang, Ching Hui Tsai, Yen Fu Chen, Shu Kun Hsu, Hsiao Shan Lin, Song Chuen Chen, Yen Yu Cho, Chin Wei Liang |
| Rok vydání: |
2019 |
| Předmět: |
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| Zdroj: |
Terrestrial, Atmospheric and Oceanic Sciences, Vol 30, Iss 5, Pp 649-674 (2019) |
| ISSN: |
1017-0839 |
| DOI: |
10.3319/tao.2019.07.07.01 |
| Popis: |
Using echo sounders to detect gas plumes in seawater is common, especially in the context of hydrothermal circulation areas or gas hydrate-bearing cold seeps. To understand the distribution of gas plumes in the southernmost Okinawa Trough, we have conducted 13 cruises with a 38 kHz single-beam echo sounder (EK60). A total of 266 gas plumes of acoustic image, associated with the hydrothermal circulation, are detected. To estimate the near-seafloor bottom current speeds, 201 gas plumes are further used. As a result, the gas plumes around the axial depression of the Okinawa Trough generally tilt to the northeast at rising tides and high tides, suggesting a northeastward flow of the bottom current. However, the gas plumes in the Keelung continental slope tilt to the southwest at ebb tides and low tides, suggesting a southwestward flow of the bottom current. Our results significantly show a good estimation of the near-seafloor bottom currents from EK plume images in the case of lacking real observations. The directions of the bottom currents depend on semidiurnal tides. Assuming a quasi-constant speed of upward gas bubbles out of seabed, we have estimated the bottom current speeds in 6 hydrothermal circulation zones near the rifting center of the southernmost Okinawa Trough. The estimated bottom current speeds in submarine volcanic areas vary largely from 2 to 160 cm s-1, but bottom current speeds in relatively flat region are between 20 and 50 cm s-1. The large variation of the bottom current speeds in the submarine volcanic areas could be due to the variable emissions of the gases out of the submarine volcanic areas. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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