Atmospheric methane: discrete measurements for individual Greenland ice core samples via the Picarro G1301 analyzer

Methane (CH4) is considered the second most important greenhouse gas after carbon-dioxide (CO2), i.e. the second major anthropogenic climate forcing contributor. Its atmospheric concentration in ancient times can be directly reconstructed on the basis of air bubbles entrapped within the ice, analysing their chemical composition. For years, at least until 2009, traditional methods for methane measurements relied on Gas Chromatography (GC) and Mass-Spectrometry (MS). Since further, new advanced techniques as Cavity Ring Down Spectrometry (CRDS) improved the analytical instrumentation and procedure, providing faster analysis and a high accuracy even with very low concentrations (ppbv). Different extraction techniques (wet, dry and sublimation), as well as sampling methods (discrete, semi-continuous and continuous), have been implemented over time, providing an even greater resolution and reliability of measurements. The continuous method allows the highest resolution, however it cannot fully compete in the reproducibility with discrete methods, particularly due to its restriction with number of samples. I present a discrete method, developed through the Picarro G1301 analyser, to measure methane concentrations from trapped air bubbles within ice samples. These ice samples derive from the Eurocore project ice core, drilled in Central Greenland (1989) and cover a time period of about 1000 years, between 1907 and 974 AD. The results confim the atmospheric methane record published by Blunier et al. in 1993, with a pre-industrial methane level around 700 ppbv and an anthropogenic methane increase between 1750 and 1800, which most likely matches with the dawn of the industrialization. Noteworthy is the fact that, due to the complexity of the flow effect encountered during the experiments, my values are still affected by its presence. Neverthless, since it is incorporated in all measurements, including those of standards, it can be considered as constant and therefore neglected here. For more precise and accurate measurements a reliable flow correction must be further investigated.