Gas extraction from CFA for 81Kr dating of the Beyond EPICA oldest ice

The Beyond EPICA oldest ice is a unique climate archive, continuously reaching back to possibly 1.5 Ma. The continuity of the signals in the ice core likely allows for developing a continuous timescale, mostly based on orbital tuning with O2/N2 and δ18Oatm. The obtained timescale can then be checked for consistency with marine records, 36Cl/10Be dating and possibly with magnetic tie points from cosmogenic isotopes. Since these consistency checks have caveats, additional absolute age constraints may prove useful.The noble gas radioisotope 81Kr ( t1/2 = 229 ka ) with a dating range from 30 ka to 1.5 Ma can provide robust absolute age constraints in ice cores. Especially due to its gaseous and inert properties, its isotopic ratio is not altered by geochemical processes so that it preserves the pristine age information. 81Kr dating could provide additional absolute age constraints for the Beyond EPICA oldest ice. However, due to the high ice demand for numerous analyses on the core, there is no ice available for 81Kr analysis on discrete ice samples.We present gas extraction from the Continuous Flow Analysis (CFA) of the Beyond EPICA oldest ice for 81Kr dating. The gas has been passively collected from the overflow of the debubbler into multi-layer aluminium-foil bags, which are routinely employed for 81Kr dating of groundwater. From the continuous melting of ~3 m long core, discrete ~100 mL STP gas samples have been extracted, and subsequently analyzed offline for 85Kr and 81Kr. Modern air contamination, likely from diffusion through the gas bags during storage, has been quantified with the anthropogenic 85Kr. The contamination can be avoided by transfer of the sampled gas from bag to metal container after collection. The 81Kr age constraints that could be obtained are consistent with preliminary timescales. The presented gas extraction method is non-invasive and requires minimum equipment, potentially providing a base for usage also in future CFA campaigns.