Preservation of very old climate records in ice cores from Allan Hills, Antarctica

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• Edward Brook, Oregon State University
• Tuesday 23 April 2024, 12:10-13:00
• Department of Earth Sciences, Tilley Lecture Theatre.

If you have a question about this talk, please contact Dr Rachael Rhodes.

Extending the ice core record of climate and environmental parameters to time periods older than 800,000 years is a major international goal. The Center for Oldest Ice Exploration (COLDEX) is a US initiative to search for climate records covering the last 5 million years, including cores from blue ice regions where very old ice has been identified. This talk will discuss recent COLDEX results from one of these areas, the Allan Hills, in the Transantarctic Mountains region of East Antarctica. Ice cores from the Allan Hills contain discontinuous sections that date to as old as 6 Ma, and numerous samples with ages between 1 and 5 Ma, all dated with the 40Aratm technique. These samples provide constraints on a variety of past environmental variables, including greenhouse gases, mean ocean temperature, and Antarctic surface temperature, and create opportunities to explore other properties of climate and the environment beyond the 800 ka limit of the existing ice core record.

The Allan Hills cores and their glaciological setting are also unusual and complex, requiring new approaches to their interpretation. Ice flow, likely from a relatively local depositional area, traps old ice at shallow depths near the ice margin, albeit in a poorly understood manner. In most locations drilled so far, ice younger than 1 Ma is underlain by a relatively thin layer (20-40 m) of older material. Dating Allan Hills cores clearly shows age reversals indicative of folding. Deformation of dust and tephra bands at the surface, and deformation of bubbles at depth, also indicate complex ice flow. Three-dimensional mapping of electrical conductivity and isotopic measurements in large, 24-cm diameter cores clearly shows inclined layers and folding. Work to decipher these complex records is ongoing.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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• Department of Earth Sciences Seminars (downtown)
• Department of Earth Sciences seminars
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