Comparison of Phase Conditions of CO2-Rich Fluids Measured at Different Hydrothermal Fields in the Okinawa Trough Using an In Situ Deep-Sea Raman Spectrometer
Tomoko Takahashi*, Eiji Tasumi, Shotaro Tagawa, Yatsuse Majima, Junichi Miyazaki, Naoki Nishimura, Shinsuke Kawagucci, Takazo Shibuya and Ken Takai,
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引用次数: 0
Abstract
In this work, in situ liquid carbon dioxide (CO2)-rich fluid measurements using a deep-sea Raman spectrometer at different hydrothermal fields in the Okinawa Trough were performed. It was found that the water depths where the CO2 phase turned from liquid to gas ranged from 710 to 1060 m, which were deeper than the depth indicated in the phase diagram of the mixture of water (H2O) and CO2 (∼415 m), while our previous observation at the North-West Eifuku site at the Mariana Arc was consistent with the diagram. From observations with in situ Raman measurements and gas chromatography (GC) quantitative analysis of collected fluid samples, it can be assumed that the depth of the phase transition depends predominantly on the concentration of methane (CH4) and nitrogen (N2) in the fluid. The study demonstrates the ability of the Raman spectroscopic technique to be used as a real-time, on-site sensing tool for monitoring the dynamic phase transitions of CO2 and volatiles in fluids in the oceans. In addition, the apparatus reported in this work makes it possible to conduct multimodal liquid CO2-rich-fluid analysis by performing in situ continuous Raman measurements, GC analysis of the sampled fluid, and visual observation. This will lead to a better understanding of the role of CO2-rich fluids emitted from deep-sea hydrothermal fields in biogeochemical cycles and their contribution to acidification in the water column.
期刊介绍:
The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.