Development of ice sublimation device for analyses of trapped trace gases in ice cores, future outlook and applications

Abstract:

Trapped air in ice cores is arguably one of the most unique paleoenvironmental records because it provides a direct archive of Earth’s past atmospheric composition. Common methods to liberate the air bubbles trapped in ice cores include melting (wet extraction) and mechanical destruction (dry extraction) of ice under vacuum. However, both methods have disadvantages. In a wet extraction, the presence of liquid water can introduce extraneous, non-paleoatmospheric gases from the reaction between the meltwater and impurities (Lee et al., 2020; Raynaud et al., 1982). In a dry extraction, friction between components (either metal with metal or metal with ice) can be a source of contamination (e.g., Nicewonger et al., 2016; Sowers et al., 1997). Furthermore, dry extraction methods suffer from relatively low air extraction efficiency and inability to fully liberate all of the gases from the ice matrix, which can be problematic for some analytes like ¹⁴CO₂ (Petrenko et al., 2016), CO₂, and potentially δ¹³CO₂ in clathrate ice (Bereiter et al., 2015). A third method to liberate air trapped in ice core bubbles is sublimation under vacuum (e.g., Wilson and Donahue, 1989; Schmitt et al., 2011). The sublimation method guarantees complete gas extraction from both the air bubbles and the ice matrix / clathrates (Bereiter et al., 2015), and should be free of problems associated with wet extraction. We present a new analytical system capable of sublimating ~1kg of ice and extracting ~100 mL STP air. This system was successfully used to measure ¹⁴CO₂ in ice from Summit, Greenland and Taylor Glacier, Antarctica. In the future, this system can be potentially used to improve the radiocarbon calibration curve (Reimer et al., 2013) in periods where tree ring data are not available. Another sublimation system, based on the ¹⁴CO₂ system, is currently being built for the purpose of analyzing methane stable isotopes.