Limitations on the Use of Atmospheric δO₂/N₂ for Ice Core Dating: Insights from the EPICA Dome C Ice Core

The measurement of atmospheric δO₂/N₂ trapped in ice is an incredible tool for ice core dating, as it is directly linked to local summer insolation. Numerous studies conducted between 2005 and 2022 have focused on determining the δO₂/N₂ composition of the EPICA Dome C (EDC) ice core. However, discrepancies between the datasets from these studies have emerged, raising questions about the potential causes of variability. Notably, inconsistencies between datasets measured years apart (e.g. 2012 vs. 2022) are investigated using newly acquired high-resolution δO₂/N₂ data in the age range from 450 to 550 ka BP. In this presentation, we present this new data together with a compilation of all available δO₂/N₂ values on the EDC ice core.

One significant factor influencing the δO₂/N₂ composition is gas loss during the storage of the ice samples, which appears to correlate with the storage temperature. Our results reveal that the storage temperature plays a critical role in preserving the δO₂/N₂ signature. Samples transported at -20°C, even for only a few months, exhibit a substantially more depleted δO₂/N₂ signature (approximately -5‰) compared to those consistently stored at -50°C. Additional factors influencing δO₂/N₂ values include the local accumulation rate and other regional conditions, for which the δD of the ice is a proxy. By comparing local summer insolation, δD of the ice, and δO₂/N₂ of the trapped air, one can distinguish the effects of orbital forcing from higher-frequency, non-orbital influences. Accurately interpreting the EDC δO₂/N₂ record is essential for the best use of this tool for the construction of the chronology of the new Beyond EPICA ice core.