New technique for high-precision, simultaneous measurements of CH4, N2O and CO2 concentrations, isotopic and elemental ratios of N2, O2 and Ar, and total air content in ice cores by wet extraction

• Main Authors: Oyabu, Ikumi, Kawamura, Kenji, Kitamura, Kyotaro, Dallmayr, Remi, Kitamura, Akihiro, Sawada, Chikako, Severinghaus, Jeffrey P., Beaudette, Ross, Sugawara, Satoshi, Ishidoya, Shigeyuki, Dahl-Jensen, Dorthe, Goto-Azuma, Kumiko, Aoki, Shuji, Nakazawa, Takakiyo
• Format: Text
• Language: English
• Published: 2020
• Subjects: Dome Fuji; ice core
• Online Access: https://doi.org/10.5194/amt-2020-171; https://amt.copernicus.org/preprints/amt-2020-171/

Air in polar ice cores provides various information on past climatic and atmospheric changes. We developed a new method combining wet extraction, gas chromatography and mass spectrometry, for high-precision, simultaneous measurements of eight air components (CH 4 , N 2 O and CO 2 concentrations, δ 15 N, δ 18 O, δO 2 /N 2 , δAr/N 2 and total air content) from an ice core sample of ~60 g. The ice sample is evacuated for ~2 hours and melted under vacuum, and the released air is continuously transferred into a sample tube at 10 K within 10 minutes. The air is homogenized in the sample tube overnight at room temperature, and split into two aliquots for mass spectrometric and gas chromatographic measurements. Cares are taken to minimize contamination of greenhouse gases with long evacuation time, consumption of oxygen during sample storage by passivation treatment on sample tubes, and fractionation of isotopic ratios with long homogenization time for splitting. Precisions are assessed by analysing standard gases with artificial ice, and by duplicate measurements of the Dome Fuji and NEEM ice cores. The overall reproducibility (one standard deviation) from duplicate ice-core analyses are 3.2 ppb, 2.2 ppb and 3.1 ppm for CH 4 , N 2 O and CO 2 concentrations, 0.006, 0.010, 0.09 and 0.12 ‰ for δ 15 N, δ 18 O, δO 2 /N 2 and δAr/N 2 , and 0.67 mlSTP kg -1 for total air content, respectively. Our new method successfully combines the high-precision, small-sample and multiple-species measurements, with a wide range of applications for ice-core paleoenvironmental studies.