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 (δ18OSW) 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 δ18OSW 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 δ18OSW 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.