A method for resolving changes in atmospheric He ∕ N₂ as an indicator of fossil fuel extraction and stratospheric circulation

The atmospheric He/N2 ratio is expected to increase due to the emission of He associated with fossil fuels and is expected to also vary in both space and time due to gravitational separation in the stratosphere. These signals may be useful indicators of fossil fuel exploitation and variability in stratospheric circulation, but direct measurements of He/N2 ratio are lacking on all timescales. Here we present a high-precision custom inlet system for mass spectrometers that continuously stabilizes the flow of gas during sample–standard comparison and removes all non-noble gases from the gas stream. This enables unprecedented accuracy in measurement of relative changes in the helium mole fraction, which can be directly related to the 4He/N2 ratio using supplementary measurements of O2/N2, Ar/N2 and CO2. Repeat measurements of the same combination of high-pressure tanks using our inlet system achieves a He/N2 reproducibility of ∼ 10 per meg (i.e., 0.001 %) in 6–8 h analyses. This compares to interannual changes of gravitational enrichment at ∼ 35 km in the midlatitude stratosphere of order 300–400 per meg and an annual tropospheric increase from human fossil fuel activity of less than ∼ 30 per meg yr−1 (bounded by previous work on helium isotopes). The gettering and flow-stabilizing inlet may also be used for the analysis of other noble-gas isotopes and could resolve previously unobserved seasonal cycles in Kr/N2 and Xe/N2.

Preliminary results for stratigraphy and chronology of blue ice in Larsen Glacier, East Antarctica

<p>Among the paleoclimate archives, we may take advantage of ice cores to directly measure greenhouse compositions of ancient air. Nevertheless, ice cores from deep drilling projects recover limited amount of ice for a given time period and hence limiting the studies that need an extensive amount of ice such as trace gas isotopes. In contrast, blue ice areas (BIAs) may provide a large amount of ancient ice outcropped at the surface. However, ice flow makes the blue ice stratigraphy complicated in many areas, and accordingly makes it difficult to reconstruct a continuous stratigraphy. Recently, the oldest ice was discovered at Allan Hills BIA (about 2.7 Ma). However, the stratigraphy is not continuous for the older part. Here we show preliminary results from Larsen Glacier, East Antarctica. The Ground Penetrating Radar (GPR) results show parallel ice layers near the surface with dips of 1-5° and indicate that the ice thickness ranges of 200–400 m. δD<sub>ice</sub> of a vertical core sample matches well with that in the horizontally spaced surface ice samples. Greenhouse gas concentrations are significantly altered at shallow depths of < ~4.5 m. The δ<sup>18</sup>O<sub>atm</sub>, CH<sub>4</sub> concentration and stable isotopes of ice (δ<sup>18</sup>O<sub>ice</sub>, δD<sub>ice</sub>) indicate that the Larsen BIA cover the Last Glacial Termination at the studied sites. <sup>81</sup>Kr ages, corrected by <sup>85</sup>Kr for the modern air contamination, are less than 54 ka, supporting the ages constrained by the other chemistry data.</p>