Methane data in the western Arctic Ocean during 14th CHINARE

Seawater, under-ice water, and surface sediment porewater samples for methane analysis were collected in the western Arctic Ocean during the Chinese Arctic Research Expeditions onboard the R/V “Xuelong 2” from 19th July to 14th August 2024. Methane and its stable carbon isotopic signatures were measured on board by Picarro G2132i using a headspace method. For concentration calibration, standard gas mixtures with concentrations of 1.00 ppm, 2.00 ppm, and 4.00 ppm (National Institute of Metrology, China) were used to correct the methane mixing ratio in the headspace. For isotopic ratio calibration, four standard gas mixtures with known isotopic ratios (2.10 ppm, −40.0‰ and 2.80 ppm, −68.6‰, Air Liquide, French; 2.00 ppm, −42.9‰ and 1.97 ppm, −46.89‰, self-calibrated working standard) were used to generate linear calibrations for isotope ratios to correct for any transient deviations in the analyzer. The standard with the isotopic ratio of −40.00‰ was measured at the beginning and the end of sample measurements to calibrate the instrumental drift (a total of 1‰ within 30 days). Considering the complete sampling procedure, the overall total precision was better than 3.5% for δ13C-CH4 and 5% for methane concentration (in 95% of all samples) estimated in duplicate.