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YANG XiaoQiu*,
ZENG Xin,
SHI HongCai,et al
.0.Development progress of long-term seafloor heat flow monitoring system.Chinese Journal of Geophysics (in Chinese),(): 1-,doi: 10.6038/cjg2022P0190
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| Development progress of long-term seafloor heat flow monitoring system |
| YANG XiaoQiu 1,2*，ZENG Xin1,2，SHI HongCai3，YU ChuanHai1,2，SHI XiaoBin1,2，GUO XingWei4，WANG YingChun 5，REN ZiQiang1，SHAO Jia1,6，XU HeHua1,2，WEI XiaoDong7，CHEN Shun1,6，ZHAO Peng1,6
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| 1 Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences, Guangzhou 511458, China
2 Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
3 Guangdong Province Key Laboratory for Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China
4 Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071, China
5 College of Energy Resources, Chengdu University of Technology, Chengdu 610059, China;
6 University of Chinese Academy of Science, Beijing 100049, China
7 Key Laboratory of Submarine Geosciences, Ministry of Natural Resources and Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China |
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Abstract The shallow seas and subduction trenches are not only the main potential areas for mineral and oil & gas, but also areas where tectonic earthquakes occur frequently. The information on the shallow heat flow and deep temperature distribution is crucial for understanding the process of plate subduction and magma activity. However, due to the influence of seasons, ocean currents, undercurrents and tides in this area, the bottom water temperature variation (BTV) is large and strongly disturbs the temperature field in shallow sediments. Thus, the background heat flow unable to be obtained by conventional seafloor heat flow probes. It is an effective solution to carry out long-term observation of shallow seafloor sediment temperature variations. At present, Japanese scientists have mainly developed the Long-term Heat Flow Monitoring system (LTMS), Stand-Alone Heat Flow meter (SAHF) and Pop-up Long-term Heat Flow system (PLHF). The LTMS and SAHF systems have high reliability and success rates, but rely on underwater robots (ROV) operating platforms, which are costly and have large limitations; while PLHF system is highly independent, but risky and needs to discard temperature probe. So its overall reusability is poor. To this end, we propose a Tethered Long-term seafloor heat flow monitoring system (TLHF), and since 2013, a series of tests have been carried out in the South China Sea, Kangding shallow borehole, Xingycou Lake, and Huguangyan Lake. The results show: 1) the self-developed long-period and low-power miniature temperature loggers can continuously work for one year in an environment of 2-36℃. 2) even under the conditions of steep terrain, 1.5 knots of velocity, no dynamic positioning, etc., the mooring-type launch and recovery scheme is still feasible. 3) the temperature variation of sediment at depth of 0.25 m in Xingycou Lake is about 0.2℃ during 13 days, while the BTV in Huguagnyan Lake is up to ~ 2.5℃ during 93 days. During the process of conduction to the deep, its amplitude gradually decreases and the phase lags. That causes the direction and intensity of the heat flow to vary with change of seasons. For example, in mid-to-late October 2015, the heat flow of Xingycou Lake was -1.35 ~ -0.8 W/m2, the heat flow of Huangyan Lake was as high as 2.0 ~ 3.9 W/m2 in the winter of 2018, but it changed to -1.54 W/m2 in the spring of 2019. 4) in Zhonggu Village of Kangding City, the shallow ground temperature is high in winter (35~36℃) and low in summer (28~32℃) due to heavy rainfall in summer, and fluctuates synchronously at different depths. The surface heat flow is 0.504 W/m2 at the depth of 3~5 m, and rises to 0.901 W/m2 at the depth of 5~7 m. It is presumed to be caused by the upwelling of thermal fluid from the deep part of the Xianshuihe fault zone. 5) In Northern South China Sea, the BTV generally increases as the water depth becomes shallower. In Dongsha waters with a depth of 2600~3200 m, the BTV is only 0.025~0.053℃ during 17 days. Among them, the component with period of one day and low amplitude of 0.005~0.01℃ caused by the tide have weak disturbance to the ground temperature field of shallow seafloor sediments. In Xisha waters with a depth of about 1200 m and 850 m, the BTVs increase to 0.182℃ during 40 hours and 0.417℃ during 48 hours, respectively, and the disturbance to the shallow temperature field is no longer negligible. 6) In summer, the seafloor heat flow on the northern slope of the Taixinan Basin from 0.69 W/m2 at the shallow surface to -0.25~-0.05 W/m2 at a depth of 0.83 m. This is the result of the instability of the shallow temperature field caused by BTV.
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