The Bipolar Ice Core Chronology: Enabling discovery through synchronized ice core timescales

On the continental ice sheets of Greenland and Antarctica snow accumulates annually and does not regularly melt, allowing ice cores to capture a wide variety of high-resolution and continuous environmental records, including atmospheric gas concentrations (for example carbon dioxide and methane), atmospheric aerosols and chemistry, and regional temperatures. But these records are only as useful as our ability to date them accurately. Currently, four separate ice core dating frameworks exist that disagree between them by up to several thousand years, which is much longer than most processes scientists want to study. This project will build a unified timescale spanning ice cores from both poles using the latest available data, improving dating accuracy and consistency. A large database of volcanic eruptions recorded in ice cores will be compiled and validated, and used to synchronize ice core timescales. The resulting open-source tools and datasets will enable researchers worldwide to make new discoveries. The award supports one graduate student at Oregon State University and one undergraduate student for an REU (Research Experiences for Undergraduates) summer internship, contributing to the development of the domestic STEM (Science, Technology, Engineering, and Mathematics) workforce. The project would ensure the continued relevance of existing U.S.-drilled ice cores, increasing scientific returns on past investments in polar science. This project will develop the Bipolar Ice Core Chronology (BICC), a synchronized timescale unifying 14 Antarctic and 8 Greenland ice cores by merging and updating four existing chronological frameworks. Synthesizing these frameworks enables more accurate age constraints, improved synchronization, and expanded coverage that includes more ice cores. The Holocene (< 11.7 ka) will be dated via bipolar annual layer counting of volcanically-synchronized ice cores, calibrated against cosmogenic nuclide variations shared with tree rings. The Pleistocene (> 11.7 ka) dating will use an established Bayesian multi-core probabilistic dating tool applied to all available age constraints. The project will evaluate roughly 14,600 volcanic tie points for their internal consistency and make the compiled database available. The work would further compile re-dated existing ice core datasets into an open, well-documented database in Python, MATLAB, and text formats. The team will analyze 150 Greenland ice core samples for methane and nitrogen isotopes to refine bipolar gas dating. The work will lead to new Antarctic temperature reconstructions based on the ice core gas age-ice age difference. Last, the project will apply ³⁶Cl/¹⁰Be radiometric dating to basal ice from Siple Dome with implications for West Antarctic Ice Sheet stability. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.