Global mean sea-level fall from late Marine Isotope Stage 3 into the Last Glacial Maximum inferred from Great Barrier Reef large benthic foraminiferal assemblages

Marine Isotope Stage (MIS) 3, the period from 57 to 30 thousand years ago (ka), is critical to understand how glaciers and ice sheets advanced into the Last Glacial Maximum (LGM; 30–17 ka). Previous estimates of ice-volume changes and their equivalent global mean sea level (GMSL) during MIS 3 remain uncertain, particularly regarding the extent of Northern Hemisphere ice-sheet reduction and exact GMSL values during this period. Here we present a new GMSL record from late MIS 3 to the LGM (ca. 39–18 ka) inferred from paleo-water depth estimates of photosymbiotic large benthic foraminiferal assemblages in upper slope sediment cores from the Great Barrier Reef. The relative sea-level-based GMSL record reconstructed using a Bayesian statistical model, revealed long-term mean trends characterized by incrementally lowering sea levels divided into five periods. Late MIS 3 GMSL decreased from –101 m (average with a 95% confidence interval (CI) of –89 to –113 m) at ca. 39 ka to –119 m (average with a 95% CI of –114 to –124 m) at ca. 30 ka, then finally reached down to –137 m (average with a 95% CI of –131 to –142 m) during the LGM. A relatively steep sea-level fall into the LGM—approximately 17 m in magnitude—began at ca. 35 ka and took ca. 7000 years, implying an acceleration of large-scale ice sheet advance into the LGM.