Collaborative Research: Window into the World with 40,000-year Glacial Cycles from Climate Records in Million Year-old Ice from the Allan Hills Blue Ice Area

This project developed the paleoclimate record from the Allan Hills blue ice area. Between about 2.8-0.9 million years ago, Earth's climate was characterized by 40,000-year cycles, driven or paced by changes in the tilt of Earth's spin axis. Much is known about the "40,000-year" world from studies of deep-sea sediments, but our understanding of climate change during this period is incomplete because we lack records of Antarctic climate and direct records of atmospheric greenhouse gas concentrations. We recovered ice extending, discontinuously, from 0.1-2 million years old. Ice was dated by measuring the 40Ar/38Ar (Argon) ratio of the trapped gases. Our discovery of old ice demonstrates that there is gas-record-quality ice from the 40,000-year world in the Allan Hills Main Ice Field. We have drilled two different sites, each overlying bedrock at ~ 200 m depth. We characterized the continuity of our cores by measuring the deuterium and oxygen isotope ratios in the ice to inform on the temperature and moisture source changes of the Allan Hills region to advance understanding of climate dynamics during these periods.