Short-term Antarctic ice-sheet dynamics during the late Oligocene: Multi-proxy records from ODP Site 689

Paleoceanographic records spanning the Oligocene (33.9–23.03 Ma) provide insights into Antarctic ice-sheet (AIS) dynamics in a world warmer-than-today, allowing to improve future projections linked to current global warming. While the long-term evolution of Oligocene glaciations is relatively well-known, current knowledge about the short-term (i.e., orbital to suborbital scale) AIS dynamics is still limited. Here, we investigate short-term dynamics of the AIS during the late Oligocene (spanning ~26–25 Ma), using a high-resolution multi-proxy record from Ocean Drilling Program Site 689 (Maud Rise, Southern Ocean). Variations in ice volume were quantified using the stable oxygen isotope composition of seawater (δ¹⁸O_SW) inferred from benthic foraminiferal δ¹⁸O and Mg/Ca-based bottom-water temperatures. Changes in sediment provenance and weathering inputs were characterised using detrital neodymium isotopic compositions (εNd) of the sediments. The δ¹⁸O_SW record reflects a highly dynamic AIS during the late Oligocene, with glacial conditions characterised by an AIS volume larger than the modern one (up to +14%) and interglacial conditions characterised by a much smaller AIS volume (up to -29%) than today. Detrital εNd varies from -12 to -9, with less radiogenic εNd signatures generally matching higher δ¹⁸O_SW values (i.e., glacials) and vice-versa. This co-variation between an ice-volume proxy and a tracer of sediment provenance characterises crustal sequences exposure to weathering as the ice-sheet retreated. The detrital εNd record thus supports recent interpretations of a highly dynamic AIS during the late Oligocene, which is mirrored by large changes in the provenance of weathering products induced by the waning and waxing of the AIS.