Raman spectroscopy data of massive gas hydrates at central part of Umitaka Spur
Description
Massive gas hydrates at various sediment depths in the Umitaka Spur were collected by rotary coring during the HR14 and PS15 expeditions (June to July 2014 and August to November 2015, respectively). Details for these collection and storage were described by Hiruta and Matsumoto (2022). Most of them were recovered by conventional rotary coring without a pressurizing tool. Samples were mostly collected on a deck and stored in a dewar-type container reserving liquid-N2. These samples were CT scanned before obtaining Raman spectra. For the CT, samples were taken out of liquid-N2 for ~20 minutes, then returned to the liquid-N2 storage. Details for Raman spectroscopic analysis will be described in future publications citing this dataset. 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. Near-seafloor gas hydrate samples at other areas were also measured in this way (Hiruta, 2023). These sample collections and analyses were conducted under the commission of the National Institute of Advanced Industrial Science and Technology (AIST) as a part of the methane hydrate research project funded by the Ministry of Economy, Trade and Industry, Japan (METI). 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, A., 2023. Raman spectroscopy data of microbial methane hydrates around Sado Island. Mendeley Data, V1, doi: 10.17632/j3mbg28hyc.1