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.
Highlights
Measurements of gas components in polar ice cores have provided valuable information on past climatic, atmospheric and glaciological changes
The extracted air is homogenized in the sample tube for one night and split into two aliquots for mass spectrometric (MS) and gas chromatographic (GC) measurements
After all the standard gas measurements, a sample tube is connected to the GC inlet by VCR, V8 is set to position 4, V10 is switched on to evacuate the inlet with a turbomolecular pump for ∼ 20 s and the VCR connection is leak-checked with P2 (JTEKT PMS-5M-2 pressure transducer)
Summary
Measurements of gas components in polar ice cores have provided valuable information on past climatic, atmospheric and glaciological changes. We present a new method developed at the National Institute of Polar Research (NIPR) to measure eight air components (δ15N, δ18O, δO2/N2 and δAr/N2; concentrations of CH4, N2O and CO2; and TAC) using a 60 g piece of ice with high precision. This method has the technical advantage of reducing the sample size without sacrificing precision. The system performance and precision are evaluated by various tests with standard gases (Sect. 4) and comparisons of our data from ∼ 100 ice-core samples (Dome Fuji, known as Valkyrie Dome, and NEEM) with published records from other laboratories
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