Development and initial results of ice core CO2 extraction by sublimation for 14C analysis

Measurements of ¹⁴C of CO₂ in glacial ice cores have potential for radiometric dating of ice cores as well as for improving the radiocarbon calibration curve. Relatively large (≥ 1 kg) ice samples are required for these applications and corrections must be applied for the in situ cosmogenic ¹⁴C component. Typical methods for extraction of air trapped in bubble ice for trace gas analyses involve melting or mechanical destruction of the ice core sample. The former is undesirable for CO₂ analyses due to the high solubility of CO₂ and and contamination from carbonate dust, while the latter fails to fully release in situ cosmogenic ¹⁴C trapped in the ice crystal lattice. We present a new method for extraction of ~100 mL STP air from ~1 kg of ice via sublimation. The system was developed to be field deployable to eliminate the effects of post-coring cosmogenic ¹⁴C production during ice storage and transport. Extraneous carbon added during sample processing (≤3% of total carbon mass) and its impact on ¹⁴C are characterized by procedural test extractions performed with gas-free ice. Methodology and blank corrections are presented from measurements of ice and firn from Summit, Greenland to 130m depth (~1770AD) as well as old (>50kyr) ice recovered from the Taylor Glacer, Antarctica ablation zone. Successful measurements from this technique show promise for using sublimation to extract ice core trace gases that have proven difficult to collect via melting or mechanical methods.