High precision laser spectrometer for multiple greenhouse gas analysis in 1 mL air from ice core samples

Abstract. The record of past global background atmospheric greenhouse gas composition is crucial for our understanding of global climate change. The ”Beyond EPICA Oldest Ice Core” project is currently pushing the frontier of this knowledge forward by the retrieval of an ice core reaching back to 1.5 million years ago. The oldest section of this core will have been strongly thinned by glacier flow with about 15 kyr being trapped in as little as 1m thickness of ice. This reduces the available sample volume to only a few mL of air for the targeted century-scale resolution of greenhouse gas records. Under these conditions, the required accuracy for multiple greenhouse gases cannot be achieved with currently available analytical methods. Here, we present a new approach to unlocking such challenging atmospheric archives with a high-precision mid-IR dual-laser direct absorption spectrometer. The instrument is designed to simultaneously measure CH4, N2O, CO2 concentrations as well as δ13C(CO2) using discrete samples of only 1 mL STP, and it achieves a precision of 1.6 ppb, 1.0 ppb, 0.03 ppm and 0.04 ‰, respectively. Repeated measurement cycles of air samples demonstrate an excellent accuracy level, and high reproducibility of the spectroscopic and the gas handling system. In addition, this non-invasive method allows reuse of the precious gas samples for further analysis, which opens new opportunities in ice core science.