Raman spectroscopy data of microbial methane hydrates around Sado Island

Published: 24 July 2023| Version 1 | DOI: 10.17632/j3mbg28hyc.1
Akihiro Hiruta


Near-seafloor gas hydrates of microbial methane were collected around Sado Island in the Sea of Japan during 1K17 and 7K18 cruises (July 2017 and September 2018, respectively) (Hiruta and Matsumoto, revised). These gas hydrate samples in piston corer were handled in same way with our previous work (Hiruta and Matsumoto, 2022). They were stored in a Dewar container with liquid-N2 and transported to onshore laboratory. These samples were CT scanned before obtaining Raman spectra (Hiruta and Matsumoto, 2022). For the CT, samples were taken out of liquid-N2 for ~20 minutes, then returned to the liquid-N2 storage. Subsamples for Raman spectroscopic analysis were prepared just before the analysis. Portions of the gas hydrate samples were crushed with a hammer to chunks of a few cm in diameter, then they were further crushed to small pieces (roughly <1cm) in a mortar storing liquid-N2. Raman spectra was obtained by a laser Raman spectroscopy (Jasco Corporation, RMP–510). Second harmonic of YAG laser (harmonic wave, 532 nm) was used. Grating was changed to 1800 gr/mm. The gas hydrate piece which was set in a chilling chamber was analyzed through glass window of the chamber. The sample was chilled to -150 degree using liquid-N2. Wide range from 1500 to 3200 cm-1 was measured. One spectra was obtained by exposing a spot (~20 μm in diameter) for 160 seconds. Although multiple measurements were conducted in most spots, single measurement was also applied to some spots. Surface of crushed gas hydrate piece was not flat. Therefore, air (mainly N2) must be included in focal plane of laser and occasionally appeared as N2 band at ~2332 cm-1. Polystyrene standard was put on glass window due to size of the chamber and measured in same conditions except for temperature. These band positions were used to calibrate spectra of gas hydrate. Related articles Hiruta, A., Matsumoto, R., 2022. Massive gas hydrates buried on Umitaka Spur in the Sea of Japan: description, origin, and significance to methane cycling in marine sediment. Geo-Mar. Lett. 42, 13. https://doi.org/10.1007/s00367-022-00735-w. Hiruta and Matsumoto, revised. Seafloor activity and deep-subsurface geology of gas hydrate areas revealed from d13C of methane-derived authigenic carbonates along the eastern margin of the Sea of Japan.



Meiji Daigaku


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