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"Advanced Science and Technology at SUSTech" Series Report - Part 13

Jan 9, 2018 Research

Chinese manned submersible “Jiaolong” helps new discoveries in oceanic turbidity current studies

May 14, 2017, Shekou Port, Shenzhen. R/V "Xiangyanghong No. 9", the mother ship of China's first 7000-m manned submersible "Jiaolong", slowly docked at the terminal after returning from a research cruise in South China Sea (the second leg of the Chinese Ocean voyage 38). Among a dozen of scientists who have just successfully completed multiple research dives in “Jiaolong” is professor Jingping Xu, an oceanographer from the Department of Ocean Science and Engineering of the Southern University of Science and Technology (SUSTech).

Professor Jingping Xu has been working on the research of oceanic turbidity currents for many years. He is very appreciative of the opportunity to ride the "Jiaolong" to the seafloor thousands of meters deep, to observe and measure the turbidity currents and sediments and collect samples in the most precise way. These observations and sampling tasks are almost impossible to do by traditional ship-borne methods.

"Jiaolong" – a pride and dream come true for marine scientists

The "Jiaolong" is supported by the National High Technology Research and Development Program (also known as 863). It is the first deep submersible vehicle designed and assembled in China. It successfully completed 1000 m, 3000 m, 5000 m and 7000 m sea trials between 2009 and 2012. In June 2012, the Chinese manned diving record of 7062 meters was set in the Marianas Trench, which is also the underwater diving depth record for the world's submersibles in similar classes. The "Jiaolong" can be used in the vast area that accounts for 99.8 % of the world's ocean, which is of great significance for China to explore and utilize the deep-sea resources. It has the functions of maneuvering, hovering, precise positioning and sitting slope on deep-sea mounts, ocean ridges, basins, hydrothermal vents and other complex seabeds; fine measurements of bedforms in small areas; fixed point acquisition of samples of water, sediment, mineralogical nodules, and biological specimen and assessment of the coverage, abundance, and so on of biological and polymetallic nodules by video and photo. Scientific exploration of marine geology, marine geophysics, marine geochemistry, marine environment and marine life can all be effectively carried out on “Jiaolong”.

Understanding the "Debris Flow" on the Seafloor - the oceanic Turbidity Current

Turbidity currents, also known as undersea sediment gravity flow, which is similar to debris flows or avalanches on land, are nearbed flows driven by gravity to move a long distance along a slope and have high density, high sediment content, and high velocity. Turbidity currents are one of the most important ways to transport terrestrial sediments to the deep sea. A large oceanic turbidity current can carry more sediment than all the rivers in the world put together in a year, and the submarine sedimentary fan formed by its accumulation is one of the important reservoir potentials for oil and gas resources. Thus it is also of great significance in the study of the global carbon cycle and oil and gas exploration. Oceanic turbidity currents can also lead to major marine geological hazards, which have strong destructive power due to their high velocity, and pose a direct threat to submarine facilities such as oil and gas platforms, submarine communication cables and so on. There have been many occurrences of turbidity currents breaking submarine cables around the world, so the study of oceanic turbidity is one of the most recognized challenges in geoscience research. In the past 20 years, Professor Jingping Xu (formerly a researcher at the United States Geological Survey) has studied the mechanism, dynamics and sedimentary characteristics of the modern oceanic turbidity currents, and published a series of findings in mainstream journals of geoscience (Geology, Geophysical Research Letter, Journal of Geophysical Research, etc.). The research work in the field of investigating modern turbidity currents started relatively late in China. Most of the work is still using boreholes and seismic data to study sedimentary records of ancient turbidity currents, and there is a lack of studies on the process and geomorphological characteristics of the modern submarine turbidity currents.

Oceanic turbidity currents occur frequently in the submarine canyons. The northeastern part of the South China Sea is the best natural laboratory to study the process of modern submarine turbidity currents and its deposition, not only because of a large presence of submarine canyons in the area, but also because of the ample conditions required in producing oceanic turbidity currents: earthquakes, several typhoons every year that generate tremendous rainfalls and sediment erosions. The "global submarine canyon joint experiment program" launched jointly by Professor Jingping Xu and scientists from the United Kingdom, the United States and Europe takes the submarine canyons in the northern part of the South China Sea as one of the 5 typical experimental sites in the world, and launches field observation research of modern undersea turbidity. Manned deep diving is the most important means of such research.

"Thorough Investigation" Gets Great Discoveries

The headquarters of the second segment of the Chinese Ocean voyage 38 approved the deep submarine research project submitted by professor Jingping Xu, and provided two dives for the study of undersea turbidity current. Professor Jingping Xu and associate professor Naishuang Bi from Ocean University of China were the scientists to go down in the submersible. The two dives were carried out on May 3 and 5, 2017, in the northern part of the South China Sea, the southeast of Dongsha and the Taiwan canyon, respectively. In the nearly 13 hours of time underwater, the total voyage was nearly 10 kilometers, and included the near bottom bathymetric side scan range of 3.5 kilometers, the collection of 5 large biological samples, 20 short-column Pushcore samples obtained at all 13 stations, and HD images with full records. Professor Xu’s team is analyzing the above data and sediment samples and identifying the direct geomorphology and sedimentology evidences of the modern turbidity activity, to provide basis and guidance for the implementation of the design and a research plan for the key issues in the future research and observational studies of turbidity currents in the South China Sea and the rest of the world.  

Figure 1. Obtaining geomorphological and sedimentological evidence of turbidites

It is worth mentioning that one of the important findings of this subcategory is that the terraced terrain of the Taiwan Canyon is quite different from previous understanding. According to the dive plan, “Jiaolong” runs along the bottom of the canyon through a "terraced terrain" (cyclic step) (Zhong et al., 2015), to perform high-precision side-scans (Figure 2) and Pushcore (intubation) sampling. The most important discovery of the submersible is that the cyclic step is actually made up of two very steep secondary steps. The slope of the two secondary step landforms is 40o and 65o respectively, which is much larger than the slope previously calculated based on the multi-beam data from a shipboard survey (Zhong et al., 2015). This finding is very important for estimating the parameters such as velocity and thickness of ancient turbidity currents (Cartigny et al., 2010) that determine the sediment transport capabilities of oceanic turbidity current and the contribution to the global carbon cycle.

Figure 2. Topographic and geomorphologic characteristics collected by “Jiaolong” during a dive in Taiwan canyon

Opportunities and Challenges In Future Studies

Talking about future research, Professor Xu is equally excited and full of expectations: in 2018, the National Natural Science Foundation of China will launch a five-year key international cooperation project, which, together with British scientists, will carry out research on oceanic turbidity currents in the Manila Trench in the South China Sea and the Congo Canyon in West Africa; the "Jiaolong" and the "Xiang Yanghong No. 9" will be among the equipment to be used for this global voyage on behalf of the South University of Science and Technology in 2020. "We should take advantage of these rare opportunities to push ourselves and the world community to the frontier of knowledge such as oceanic turbidity currents, and strive to achieve our own par in advancing ocean science research in China," said Professor Xu.

Ready to embark the deep submersible "Jiaolong"

Crew members on Dive #138: Professor Jingping Xu, Pilot Shengya Zhao, co-pilot Jialing Tang

Professor Jingping Xu is presented a deep-diving certification

Scientists from the Qingdao National Laboratory for Marine Science and Technology onboard the Ocean Cruise 38



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