Carbon dioxide emitted from hydrothermal vents, as an important part of the global carbon cycle, can directly affect hydrothermal ecosystems. However, traditional chemical analysis methods cannot directly measure the concentrations of dissolved CO2 in high‐temperature hydrothermal fluids. Although in situ mass spectrometry has been applied to the measurements of deep sea, it cannot be used to detect high‐temperature fluids. In this study, an in situ Raman quantitative method for measuring dissolved CO2 suitable for a hydrothermal environment is established. The Raman relative intensity of CO2 displayed a linear relationship with increasing concentration of CO2 under the investigated conditions (up to 300°C and 40 MPa), allowing this in situ measurement method to be applied to most hydrothermal fields worldwide. Moreover, we find that the quantitative calibration curve for SO42− for high‐temperature and high‐pressure conditions is identical to that of SO42− for room temperature and atmospheric pressure. The concentrations of CO2 in mid‐Okinawa Trough hydrothermal fluids determined by in situ Raman measurement are 188.4–532.3 mmol/kg, which are about 3 times higher than those obtained by traditional sampling methods (59–198 mmol/kg). However, the concentrations of SO42− calculated from in situ Raman spectra were near zero, indicating that the in situ Raman measurement avoids hydrothermal fluids contaminated with seawater.

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Gas hydrates are usually buried in sediments. Here we report the first discovery of gas hydrates exposed on the seafloor of the South China Sea. The in situ chemical compositions and cage structures of these hydrates were measured at the depth of 1,130 m below sea level using a Raman insertion probe (RiP‐Gh) that was carried and controlled by a remotely operated vehicle (ROV) Faxian. This in situ analytical technique can avoid the physical and chemical changes associated with the transport of samples from the deep sea to the surface. Natural gas hydrate samples were analyzed at two sites. The in situ spectra suggest that the newly formed hydrate was Structure I but contains a small amount of C3H8 and H2S. Pure gas spectra of CH4, C3H8, and H2S were also observed at the SCS‐SGH02 site. These data represent the first in situ proof that free gas can be trapped within the hydrate fabric during rapid hydrate formation. We provide the first in situ confirmation of the hydrate growth model for the early stages of formation of crystalline hydrates in a methane‐rich seafloor environment. Our work demonstrates that natural hydrate deposits, particularly those in the early stages of formation, are not monolithic single structures but instead exhibit significant small‐scale heterogeneities due to inclusions of free gas and the surrounding seawater, there inclusions also serve as indicators of the likely hydrate formation mechanism. These data also reinforce the importance of correlating visual and in situ measurements when characterizing a sampling site.

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In situ Raman detection is an ideal method to determine the concentration of dissolved H 2 in deep-sea high temperature hydrothermal fluids, but studies on in situ Raman qualitative and quantitative analyses of H 2 that are suitable for detection in high temperature hydrothermal fluids are lacking. In this study, the Raman characteristics of gaseous and dissolved H 2 were researched at 0-400°C and 0-40 MPa in detail, which cover most deep-sea hydrothermal environments. The strong density and temperature dependences of the wavenumber and bandwidth of gaseous hydrogen vibrational Raman bands were observed. The interactions between the water molecules and hydrogen molecules were affected by temperature and pressure, and the opposite effect on the vibrational band of dissolved hydrogen was observed before and after reaching the critical condition of water. A high temperature and pressure quantitative analysis model suitable for in situ Raman detection of dissolved H 2 was also developed with the linear equation A H 2 ð Þ=A H 2 O ð Þ¼1:437 or 1:262 ð Þ ×C H 2 ð Þ, where A (H 2 )/A (H 2 O) is the peak area ratio of H 2 and H 2 O, and C (H 2 ) is the concentration of dissolved H 2 in mol/kg. The experimental temperature and pressure conditions did not influence the linear trend between the peak area ratio of A (H 2 )/A (H 2 O) and the concentrations of H 2 , which indicated that the calibration model can be applied to high temperature and pressure environments. KEYWORDS deep-sea, hydrogen, hydrothermal vent fluid, in situ, quantitative analysis ---This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

This paper evaluated the internal stresses of different diamond and diamondlike carbon ͑DLC͒ coatings. For the diamond coatings, the stresses were determined using micro-Raman spectroscopy and x-ray diffraction ͑XRD͒, while the stresses of DLC films were determined with bent plate method. The internal stress was related to the structural properties of the coatings. Direct current plasma jet, combustion flame, and microwave chemical-vapor deposition processes were used to prepare the diamond coatings on the tungsten carbide or molybdenum substrates, while the DLC films were deposited on the silicon wafers with filtered cathodic vacuum arc process. From the Raman spectra of the diamond coatings, the compressive internal stresses were determined, which were related to the microstructure of the coatings. The results from XRD were comparable with those obtained from micro-Raman spectroscopy. Higher compressive residual stresses in the DLC films were noticed, which were also related to their chemical bonding nature as well as their microstructures.

Deep-sea carbon dioxide (CO) plays a significant role in the global carbon cycle and directly affects the living environment of marine organisms. In situ Raman detection technology is an effective approach to study the behavior of deep-sea CO. However, the Raman spectral characteristics of CO can be affected by the environment, thus restricting the phase identification and quantitative analysis of CO. In order to study the Raman spectral characteristics of CO in extreme environments (up to 300 ℃ and 30 MPa), which cover most regions of hydrothermal vents and cold seeps around the world, a deep-sea extreme environment simulator was developed. The Raman spectra of CO in different phases were obtained with Raman insertion probe (RiP) system, which was also used in in situ Raman detection in the deep sea carried by remotely operated vehicle (ROV) "Faxian". The Raman frequency shifts and bandwidths of gaseous, liquid, solid, and supercritical CO and the CO-HO system were determined with the simulator. In our experiments (0-300 ℃ and 0-30 MPa), the peak positions of the symmetric stretching modes of gaseous CO liquid CO, and supercritical CO shift approximately 0.6 cm (1387.8-1388.4 cm), 0.7 cm (1385.5-1386.2 cm), and 2.5 cm (1385.7-1388.2 cm), and those of the bending modes shift about 1.0 cm (1284.7-1285.7 cm), 1.9 cm (1280.1-1282.0 cm), and 4.4 cm (1281.0-1285.4 cm), respectively. The Raman spectral characteristics of the CO-HO system were also studied under the same conditions. The peak positions of dissolved CO varied approximately 4.5 cm (1282.5-1287.0 cm) and 2.4 cm (1274.4-1276.8 cm) for each peak. In comparison with our experiment results, the phases of CO in extreme conditions (0-3000 m and 0-300 ℃) can be identified with the Raman spectra collected in situ. This qualitative research on CO can also support the further quantitative analysis of dissolved CO in extreme conditions.

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