Air enclosed in ice cores provides a unique archive for paleo-climate studies. Understanding the air enclosure process is essential for better quantifying the age of air trapped in the bubbles, correct for artifacts in elemental and isotopic composition of trapped species and estimate the smoothing effect associated with air enclosure for reconstruction of past atmospheric signal.
The latest deep ice core drilling project is at EastGRIP, in NorthEast Greenland, and aims to provide information of the past evolution of the North East Greenland ice Stream, along with outstanding ice quality over the Holocene Epoch, which has not been retrieved efficiently in past projects due to brittle ice issues.
As with any deep drilling project, it is necessary to characterize the air enclosure process, with a firn air campaign. Using a taylor made pumping system, air is retrieved at different depths, and analyzed.
In June 2017, and LSCE-IGE-U. Copenhagen team conducted such a firn air campaign, collecting samples for 10 laboratories across the world, from 0 to 60m depth.
In parallel to gas pumping, ice samples from the lock-in zone were evacuated on-site. They will help characterize the impact of the enclosure process on small fugitive gases like O2 for the first time.
Preliminary results indicate that the air at the base of the lock-in zone is rather young indicating a low gas-age ice-age difference, and that there is a significant temperature gradient though the firn column, indicating a recent warming trend.
This project will continue in years to come with a full analysis of the physical, chemical and gas properties of this core, in order to improve our understanding of the mechanisms driving gas enclosure processes.
Authors : Anais Orsi and Kevin Fourteau.