Fidelity and stratigraphy of the Antarctic Allan Hills old ice archive from Continuous Flow Analysis

Extending ice core records beyond 800 thousand years (kyr) is a pivotal goal in paleoclimate research. The Allan Hills Blue Ice Area, East Antarctica, provides a unique opportunity to meet this objective, with recent work recovering 6-million-year-old ice. The ice in this area demonstrates several peculiarities—such as strong layer thinning and folding—that warrant an in-depth investigation of its stratigraphy and the climate record it holds. Here, we present a high-resolution multi-measurement continuous flow analysis (CFA) on the upper 69 and 46 m from two shallow ice cores from the Allan Hills to evaluate these complexities.

Our CFA analysis measured methane, water stable isotopes, and particulate dust concentrations and size fractions, allowing us to characterize their variations and to assess the fidelity of the archive, i.e., how well environmental parameters are recorded and preserved in Allan Hills ice. We quantitatively compared the data structures of each climate element to the EPICA Dome C (EDC) climate record by evaluating the correlations and data distributions of each variable. Each climate parameter exhibits a narrower range of values than the EDC core, and distinct data distribution patterns that differed both between the Allan Hills cores and compared to EDC. The data revealed interglacial biases as evidenced by an overrepresentation of warmer climate states when compared to EDC. Discrete ⁴⁰argon-dated sections from the two Allan Hills ice cores reveal age ranges from ~150-1200 kyr, with substantial age discontinuities and folding highlighting the complex stratigraphy of this ice. Our high-resolution investigation of this ice is a critical step toward better interpreting the discrete records from the Allan Hills, which extend beyond the 800 kyr continuous ice core record into the Pliocene, pushing our ice core records into unique and enigmatic parts of Earth’s climate history.