New Constraints on the Onset of Antarctic Glaciation From Combined Radiogenic Hafnium and Neodymium Isotopes

Abstract The drawdown of atmospheric CO 2 likely triggered Antarctic glaciation during the Eocene‐Oligocene Transition (34 Ma). Accurately constraining this shift from “greenhouse” to an “icehouse” climate is essential for understanding global carbon cycle dynamics. However, conventional proxies often lack the sensitivity to capture the earliest, localized phases of continental ice‐sheet development. In this study, we combined radiogenic hafnium and neodymium isotopes on marine sediments from Ocean Drilling Program Site 689D to track changes in silicate weathering regimes and isolate the enhanced physical weathering signal uniquely associated with glacial grinding. By analyzing the detrital sortable silt fraction, we identified the onset of major Antarctic glaciation between 34.06 and 34.13 Ma. Additionally, our data reveal two distinct precursor glacial events occurring earlier, at approximately 34.19 and 34.41 Ma. These findings provide a more refined chronological framework for one of Earth's most significant climate shifts.