Description: In conjunction with increasing benthic foraminiferal {delta}18O values at the Eocene-Oligocene transition (EOT; ca. 34 Ma), coarse-grained ice-rafted debris (IRD; 〉425 {micro}m) appears abruptly alongside fossil fish teeth with continentally derived neodymium (Nd) isotope ratios ({varepsilon}Nd) in Kerguelen Plateau (Southern Ocean) sediments. Increased Antarctic weathering flux, as inferred from two steps to less radiogenic {varepsilon}Nd values, coincides with two steps in benthic foraminiferal {delta}18O values. These results indicate that two distinct surges of weathering were generated by East Antarctic ice growth during the EOT. Weathering by ice sheets during a precursor glaciation at 33.9 Ma did not produce significant IRD accumulation during the first {varepsilon}Nd shift. Glacial weathering was sustained during a terrace interval between the two steps, probably by small high-elevation ice sheets. A large increase in weathering signals the rapid coalescence of small ice sheets into an ice sheet of continental proportions ca. 33.7 Ma. Rapid ice sheet expansion resulted in a suppression of weathering due to less exposed area and colder conditions. Parallel changes in Antarctic weathering flux and deep-sea carbonate accumulation suggest that ice-sheet expansion during the EOT had a direct impact on the global carbon cycle; possible mechanisms include associated changes in silicate weathering on the East Antarctic craton and enhanced fertilization of Southern Ocean waters, both of which warrant further investigation.

Description: The long-term climate transition from the Cretaceous greenhouse to the late Paleogene icehouse provides an opportunity to study changes in Earth system dynamics associated with large changes in global temperature and atmospheric CO2 levels. Elevated CO2 levels during the mid-Cretaceous supergreenhouse interval (~95–80 Ma) resulted in low meridional temperature gradients, and oceanic deposition during this time was punctuated by widespread episodes of severe anoxia termed oceanic anoxic events, resulting in enhanced burial of organic carbon in conjunction with transient carbon isotope and temperature excursions. The prolonged interval of mid-Cretaceous warmth and subsequent Late Cretaceous–Paleogene climate trends, as well as intervening short-lived climate excursions, are poorly documented in the southern high latitudes. International Ocean Discovery Program (IODP) Expedition 392 aims to drill five sites in the southwest Indian Ocean on the Agulhas Plateau and in the Transkei Basin, positioned at paleolatitudes of 65°–58°S during the Late Cretaceous (100–66 Ma) and in the new and evolving gateway between the South Atlantic, Southern Ocean, and southern Indian Ocean basins. Recovery of basement rocks and expanded sedimentary sequences from the Agulhas Plateau and Transkei Basin will provide a wealth of new data to (i) determine the nature and origin of the Agulhas Plateau and (ii) significantly advance the understanding of how Cretaceous temperatures, ocean circulation, and sedimentation patterns evolved as CO2 levels rose and fell and the breakup of Gondwana progressed. Importantly, Expedition 392 drilling will test competing hypotheses concerning Agulhas Plateau large igneous province formation and the role of deep ocean circulation changes through southern gateways in controlling Late Cretaceous–Paleogene climate evolution.