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
oleh: I. Oyabu, K. Kawamura, K. Kawamura, K. Kawamura, K. Kitamura, R. Dallmayr, A. Kitamura, C. Sawada, J. P. Severinghaus, R. Beaudette, A. Orsi, S. Sugawara, S. Ishidoya, D. Dahl-Jensen, D. Dahl-Jensen, K. Goto-Azuma, K. Goto-Azuma, S. Aoki, T. Nakazawa
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2020-12-01 |
Deskripsi
<p>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 (<span class="inline-formula">CH<sub>4</sub></span>, <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CO<sub>2</sub></span> concentrations; <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>15</sup>N</span>, <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>18</sup>O</span>, <span class="inline-formula"><i>δ</i></span><span class="inline-formula">O<sub>2</sub>∕N<sub>2</sub></span> and <span class="inline-formula"><i>δ</i></span><span class="inline-formula">Ar∕N<sub>2</sub></span>; and total air content) from an ice-core sample of <span class="inline-formula">∼</span> 60 <span class="inline-formula">g</span>. The ice sample is evacuated for <span class="inline-formula">∼</span> 2 <span class="inline-formula">h</span> and melted under vacuum, and the released air is continuously transferred into a sample tube at 10 <span class="inline-formula">K</span> within 10 <span class="inline-formula">min</span>. 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 <span class="inline-formula">ppb</span>, 2.2 <span class="inline-formula">ppb</span> and 2.9 <span class="inline-formula">ppm</span> for <span class="inline-formula">CH<sub>4</sub></span>, <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CO<sub>2</sub></span> concentrations; 0.006 ‰, 0.011 ‰, 0.09 ‰ and 0.12 ‰ for <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>15</sup>N</span>, <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>18</sup>O</span>, <span class="inline-formula"><i>δ</i></span><span class="inline-formula">O<sub>2</sub>∕N<sub>2</sub></span> and <span class="inline-formula"><i>δ</i></span><span class="inline-formula">Ar∕N<sub>2</sub></span>; and 0.63 <span class="inline-formula">mL<sub>STP</sub> kg<sup>−1</sup></span> 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.</p>