New technique for high-precision, simultaneous measurements of CH<sub>4</sub>, N<sub>2</sub>O and CO<sub>2</sub> concentrations; isotopic and elemental ratios of N<sub>2</sub>, O<sub>2</sub> and Ar; and total air content in ice cores by wet extraction

Abstract

Abstract. Air in polar ice cores provides unique 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 (CH4, N2O and CO2 concentrations; δ15N, δ18O, δO2∕N2 and δAr∕N2; and total air content) from an ice-core sample of ∼ 60 g. The ice sample is evacuated for ∼ 2 h and melted under vacuum, and the released air is continuously transferred into a sample tube at 10 K within 10 min. The air is homogenized in the sample tube overnight at room temperature and split into two aliquots for mass spectrometric and gas chromatographic measurements. Care is taken to minimize (1) contamination of greenhouse gases by using a long evacuation time, (2) consumption of oxygen during sample storage by a passivation treatment on sample tubes, and (3) fractionation of isotopic ratios with a long homogenization time for splitting. Precision is assessed by analyzing standard gases with artificial ice and duplicate measurements of the Dome Fuji and NEEM ice cores. The overall reproducibility (1 SD) of duplicate ice-core analyses are 3.2 ppb, 2.2 ppb and 2.9 ppm for CH4, N2O and CO2 concentrations; 0.006 ‰, 0.011 ‰, 0.09 ‰ and 0.12 ‰ for δ15N, δ18O, δO2∕N2 and δAr∕N2; and 0.63 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.

CH<sub>4</sub> and N<sub>2</sub>O fluctuations during the penultimate deglaciation

“…CH 4 and N 2 O measurements were performed with a completely revised analytical system, firstly employed during this study (comprehensive description in Appendix A). The new apparatus uses continuous extraction under vacuum, comparable to the approach of Schmitt et al (2014) or Oyabu et al (2020), combined with GC techniques to determine CH 4 and N 2 O mole fractions in air extracted from small (∼ 20 g) ice samples with a sample throughput of five to six samples per day. The instrument is equipped with a thermal conductivity detector, a flame-ionization detector, and an electron-capture detector for the quantification of air, CH 4 , and N 2 O, respectively.…”

CH<sub>4</sub> and N<sub>2</sub>O fluctuations during the penultimate deglaciation

“…The large variability observed in adjacent data points during the early part of the N 2 O record (Fig. 1) is unlikely to reflect atmospheric fluctuations given its atmospheric lifetime of 116 ± 9 years (Prather et al, 2015). Elevated concentrations and disproportionately high N 2 O variability have been observed in many instances for ice samples rich in mineral dust in both Antarctic and Greenland ice cores and are attributed to in situ production (Flückiger et al, 1999;Sowers, 2001;Flückiger et al, 2004;Spahni et al, 2005;Schilt et al, 2010aSchilt et al, , 2013Fischer et al, 2019).…”

Chronostratigraphy of blue ice at the Larsen Glacier in Northern Victoria Land, East Antarctica

“…To determine the concentrations of CH4 and CO2, a calibration line was established using TU-2008 (Tohoku University) scale standard air; for N2O, the TU-2006 scale standard air was used. More information on the standard air we used (named STD 1, 3, 5) is given by Oyabu et al (2020). Three standard air and a quadratic calibration line were used to determine GHG concentration in the NIPR, while single standard air and a linear calibration line were used to determine the GHG concentration in SNU.…”

“…After homogenizing the sample tube for a night, the gas was split into two aliquots, one for isotope analysis (1.5 ml) and the other one for greenhouse gas measurement (5 ml). The measurement process is described in more detail by Oyabu et al (2020).…”