Collaborative Research: Allan HILLs Englacial Site (AHILLES) Selection

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Marine paleoclimate archives show that approximately one million years ago Earth's climate transitioned from 40,000-year glacial /interglacial cycles to 100,000-year cycles. This award will support a study designed to map the distribution of one million year-old ice in the Allan Hills Blue Ice Area, Antarctica using state-of-the-art ground penetrating radar. The Allen Hills was demonstrated to contain a continuous record of the past 400,000 years and is also the collection location of the oldest ice samples (990,000 years) yet recovered. The maps resulting from this study will be used to select an ice-core drilling site at which a million-plus year-old continuous record of climate could be recovered. Ice cores contain the only kind of record to directly capture atmospheric gases and aerosols, but no ice-core-based climate record yet extends continuously beyond the past 800,000 years. A million-plus year-old record will allow better understanding of the major mechanisms and driving forces of natural climate variability in a world with 100,000-year glacial/interglacial cycles. The project will support two early career scientists in collaboration with senior scientists, as well as a graduate student, and will conduct outreach to schools and the public.The Allan Hills Blue Ice Area preserves a continuous climate record covering the last 400,000 years along an established glaciological flow line. Two kilometers to the east of this flow line, the oldest ice on Earth (~1 million years old) is found only 120 m below the surface. Meteorites collected in the area are reported to be as old as 1.8 million years, suggesting still older ice may be present. Combined, these data strongly suggest that the Allen Hills area could contain a continuous, well-resolved environmental record, spanning at least the last million years. As such, this area has been selected as an upcoming target for the new Intermediate Depth Ice Core Drill by the US Ice Core Working Group. This drill will recover a higher-quality core than previous dry drilling attempts. This project will conduct a comprehensive ground penetrating radar survey aimed at tracing the signature of the million-year-old ice layer throughout the region. The resulting map will be used to select a drill site from which an ice core containing the million-plus year-old continuous climate record will be collected. The proposed activities are a necessary precursor to the collection of the oldest known ice on Earth. Ice cores provide a robust reconstruction of past climate and extending this record beyond the 800,000 years currently available will open new opportunities to study the climate system. The data collected will also be used to investigate the bedrock and ice flow parameters favorable to the preservation of old ice, which may allow targeted investigation of other blue ice areas in Antarctica.