For the first time, scientists have discovered the presence of alkaline black chimneys in a post-arc deep-sea hydrothermal system

Recently, the reporter learned from the Institute of Oceanography of the Chinese Academy of Sciences that based on the self-developed deep-sea in-situ Raman spectroscopy detection system, scientists of the institute constructed an in-situ pH measurement method for high-temperature hydrothermal fluids, and applied it to the in-situ detection of post-arc hydrothermal systems, and then found that the in-situ pH of high-alkalinity hydrothermal fluids affected by sediments can be alkaline. The results were reported in Geophysical Research Letters, an international geoscience journal.

Image courtesy of the ocean by the laser Raman spectroscopy system for in situ detection of black chimneys in deep-sea hydrothermal areas

It is understood that alkaline hydrothermal systems are considered to be an ideal place for the origin of life on Earth, because alkaline hydrothermal environments can provide ideal ion gradient conditions for the formation of early life on Earth. However, alkaline hydrothermal vents are currently only found in white chimneys in the Lost City hydrothermal region of the Atlantic Ocean, and are alkaline hydrothermal vents also present in the widely distributed black chimney area around the world? To answer this question, it is necessary to obtain the hydrothermal pH accurately, but traditional measurement methods are difficult to meet this need, because the measurement method of sampling first and then experimental analysis inevitably changes in fluid temperature, mineral precipitation and ionization equilibrium, which affect the pH of hydrothermal fluids.

In order to solve this problem, the Institute of Oceanology, Chinese Academy of Sciences and University of Science and Technology Beijing cooperated to carry out quantitative analysis of H2S-HS- ionization equilibrium system based on the deep-sea extreme environment simulation platform, and established the Raman quantitative analysis model of H2S and HS- under high temperature and high pressure conditions and the hydrothermal in-situ pH inversion model. Taking a typical post-arc hydrothermal system as the research target, the research team carried out in situ detection by using the “Discovery” ROV equipped with the deep-sea in-situ Raman spectroscopy detection system, and successfully obtained the H2S, HS-in in-situ concentration and pH of the deep-sea black chimney hydrothermal fluid.

For the first time, the research team found that the in-situ pH value of the high-temperature nozzle can reach 6.3, which has exceeded the pH value of the neutral fluid at the temperature and pressure of the vent (5.6), showing weak alkaline characteristics, and the in-situ pH value is about 1.5 higher than the result measured at room temperature.

The study confirms that alkaline hydrothermal vents are not only present in hydrothermal regions controlled by serpentinization such as Lost City, but may also be prevalent in sediment-influenced hydrothermal regions near the continental margin.

Dr. Li Lianfu of the Institute of Oceanology, Chinese Academy of Sciences is the first author of the article, and researcher Zhang Xin is the corresponding author of the article. The research has been jointly funded by the National Natural Science Foundation of China, the Chinese Academy of Sciences Class A Strategic Pilot Project and other projects, as well as the support of the “Science” and “Discovery” ROV operation and maintenance teams. (Source: China Science News, Liao Yang, Wang Min)

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