Description: The opening of the Southern Ocean gateways has been debated as a key element in the emergence of the Antarctic Circumpolar Current (ACC), crucial for the onset of global Cenozoic cooling (e.g., Sijp et al., 2014, Glob. Planet. Change 119; Voigt et al., 2013, EPSL 369/370). South of Africa, the opening was associated with the formation of several large igneous provinces (LIPs) including the Mozambique Ridge, Agulhas Plateau and the smaller Northeast Georgia Rise and Maud Rise. Plate tectonic reconstructions imply that the latter two were once part of the much greater Agulhas Plateau and were separated by subsequent rifting (Parsaglia et al., 2008, Geophys. J. Int. 174). It is debated whether and to what extent the emplacement of these large volcanic features obstructed the exchange of water masses between the Atlantic and the Indian Ocean thereby delaying the onset of the ACC. The Agulhas Plateau was drilled during recent IODP Expedition 392 (Uenzelmann-Neben, Bohaty, Childress, et al., IODP Exp. 392 Preliminary Report, 2022, in press). Igneous rocks were recovered at two sites on the southern part of the plateau (Sites U1579, U1580) and at one site near its northern edge (U1582). Preliminary (shipboard) data indicate that all sites returned tholeiitic basalts, formed by low pressure (shallow magma chamber) fractionation of mainly olivine and plagioclase (as typical for mid-ocean ridge basalts and many LIP lavas). 40Ar/39Ar dating will help to answer fundamental questions regarding the emplacement age of the plateau and its temporal-spatial evolution. Geochemical investigations of the recovered rocks will reveal the nature and source of the magmatism. The proposed project will focus on the determination of radiogenic (Sr, Nd, Hf, Pb) isotope compositions to further constrain the magma source composition for comparison with other regional and global LIP magmatism. In particular, we want to address the open question whether the Agulhas Plateau, Northeast Georgia Rise and Maud Rise magmatism can all be attributed to the same magma source and setting (“Greater Agulhas”) to test the previous plate tectonic reconstruction models. Additional questions are whether a (deep-sourced?) mantle plume initiated the magmatism and its causal relationship to the regional continental breakup and opening of ocean basins. The isotope data (in combination with the results from age dating and major/trace element geochemistry) will help to constrain the origin and impact of this regional LIP magmatism on tectonic configuration, ocean circulation, and global climate in the mid to late Cretaceous.

Description: International Ocean Discovery Program Expedition 392 drilled three sites on the Agulhas Plateau and one site in the Transkei Basin in the Southwest Indian Ocean in Ferb-March 2022 (Fig. 1). This region was positioned at paleolatitudes of ~53°–61°S during the Late Cretaceous (van Hinsbergen et al., 2015), within a new and evolving oceanic gateway between the South Atlantic, Southern Ocean, and southern Indian Ocean basins. Sedimentary and basement sequences were successfully recovered from the Agulhas Plateau sites U1579, U1580, and U1582, and a thick sedimentary sequence was recovered in the Transkei Basin at Site U1581 (Fig. 2). Drillcores from these four sites provide a wealth of new data to (1) determine the nature, origin, and bathymetric evolution of the Agulhas Plateau; (2) 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; (3) document long- and short-term paleoceanographic variability through the Late Cretaceous and Paleogene; and (4) investigate geochemical interactions between igneous rocks, sediments, and pore waters through the life cycle of the Agulhas Plateau large igneous province (LIP). Importantly, postcruise analysis of Expedition 392 drill cores will allow testing of competing hypotheses concerning Agulhas Plateau LIP formation and the role of deep ocean circulation changes through southern gateways in influencing Late Cretaceous–Paleogene climate evolution.

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.

Description: A series of organic-rich sedimentary sequences that span the Paleocene through the Campanian was recovered from the Transkei Basin during IODP Expedition 392. Preliminary analyses of their organic geochemistry reveals suites of biomarkers that reflect diverse contributions of organic matter from both marine and terrestrial sources. The characteristics of the organic matter (OM) for a range of samples have been determined by shipboard and shore-based analyses that include evaluation of OM type and maturity by Rock-Eval pyrolysis, isotopic compositions of OM and the distributions of biomarkers including GDGTs. Samples from both the Paleocene and Campanian contain series of C37 to C40 diunsaturated alkenones, including the earliest record of C38 alkadien-2-ones and C39 alkadien-3-ones [1]. A sequence of Campanian samples also reveal an abundance of C28 sterenes and steryl ethers potentially indicative of upwelling conditions [2]. Polyaromatic hydrocarbons, including coronene, are present throughout the sequence likely reflecting inputs of OM associated with paleofires [3]. Variations in the abundance of organosulfur compounds [4,5] may afford evidence for temporal changes in redox conditions within the Transkei Basin during the Campanian. These initial results provide evidence that biomarker profiling will facilitate determination of the sources of OM throughout Late Cretaceous and Paleocene and the paleoenvironmental conditions of its deposition. [1] Brassell, 2014; [2] Brassell, 2009; [3] Finkelstein et al., 2005; [4] Valisolalao et al., 1984; [5] Brassell et al., 1986

Description: A series of organic-rich sedimentary sequences that span the Paleocene through the Campanian was recovered from the Transkei Basin during IODP Expedition 392. Preliminary analyses of their organic geochemistry reveals suites of biomarkers that reflect diverse contributions of organic matter from both marine and terrestrial sources. The characteristics of the organic matter (OM) for a range of samples have been determined by shipboard and shore-based analyses that include evaluation of OM type and maturity by Rock-Eval pyrolysis, isotopic compositions of OM, and the distributions of aliphatic and aromatic biomarkers. Samples from both the Paleocene and Campanian contain series of C37 to C40 diunsaturated alkenones, including the earliest record of C38 alkadien-2-ones and C39 alkadien-3-ones [1]. Samples from a section of the Campanian (~72.5 Ma) reveal an abundance of C28 steradienes and steryl ethers potentially indicative of upwelling conditions [2]. Polyaromatic hydrocarbons within the sequence include compounds that reflect inputs of OM derived from angiosperms and paleofires [3,4]. Dominant hopanoids in the samples include -homohopane, hop-17(21)-ene, and 29-norhop-17(21)-ene, accompanied by fernenes [5], a C35 hopanoid thiophene [6] and also dammarenes [7] in Paleocene samples. These initial results provide evidence that biomarker profiling will facilitate determination of the sources of OM from the Late Cretaceous to the Paleocene in the Transkei Basin and paleoenvironmental conditions of deposition.

Description: 3.9.2. haiku captures scientific exploration and discovery as it took place in remote locales, far from the public eye. It invites audiences of all ages to engage with cores from the privileged point-of-view of researchers who were the first to see, smell and touch material from deep under the ocean floor; who, after watching the cores be split open, spent hours analyzing each centimeter. Their poems, and especially their readings of them, reveal not only the cores but also the scientists as they experience anticipation, frustration, awe, excitement and wonder. It turns out that haiku is an especially relevant way to package stories from cores of mud and rock from the Cretaceous period, which was the focus of IODP Expedition 392 to the Agulhas Plateau. An ancient poetic form consisting of 17 syllables in three lines (5-7-5), haiku compactly and powerfully captures moments of time . . . moments that, on the surface, may appear unremarkable—a frog jumping. Moments that resonate with the deep truths that emerge from paying close attention to the natural world. When introduced to the concept of 3.9.2 haiku, more than one brilliant researcher balked: “I’m no good at this. . . I can’t write poetry.” During several writing workshops conducted during the expedition, scientists began to recognize haiku as the linguistic equivalent to cores they were studying. They delighted that a dozen (or fewer) precisely packaged words could align so closely with the cores precisely drilled from the Agulhas Plateau. Each individual haiku is a gem. Strung together, they are a trove of impressions that span millennia.

Description: This presentation gives an account of the International Ocean Discovery Program (IODP) expedition 392 [Agulhas Plateau Cretaceous Climate: drilling the Agulhas Plateau and Transkei Basin to reconstruct the Cretaceous–Paleogene tectonic and climatic evolution of the Southern Ocean basin] which took place from February to April 2022. Four geological sites were drilled on the seafloor of the Agulhas Plateau and the Transkei Basin (Figure 1). A total of 28 scientists from sailed on the Joides Resolution vessel and the deepest hole drilled of four reached 994 m below the seafloor, in over 4500 m of water. The overarching objectives of Expedition 392’s recovery of rocks and sedimentary sequences were aimed at: (1) determining the nature and origin of the Agulhas Plateau; (2) advancing the understanding of how Cretaceous temperatures, ocean circulation, and sedimentation patterns evolved as CO2 levels rose and fell and the breakup of Gondwana progressed; (3) documenting long-term palaeoceanographic variability through the Late Cretaceous and Paleogene; and (4) investigating geochemical interactions between igneous rocks, sediments, and pore waters through the life cycle of a large igneous province.

Description: The Eocene-Oligocene Transition (EOT; ~34.4–33.7 Ma) was a major shift in Earth’s long-term climatic evolution, marking the cooling from the early Paleogene greenhouse to the icehouse regime that has prevailed from the Oligocene until today. However, it remains uncertain which landmasses were already covered by ice sheets during the Early Oligocene Glacial Maximum (EOGM; ~33.7–33.2 Ma), an interval of peak glaciation immediately following the EOT. The scarcity of earliest Oligocene climate records in both Arctic and Antarctic regions hitherto prevented the reconstruction of environmental conditions and ice-sheet extent during the EOGM. Such constraints, however, are critical for assessing ice–ocean–atmosphere interactions during the early stages of the Cenozoic icehouse. Here, we present the first shallow-marine drill-core record of earliest Oligocene environmental conditions in West Antarctica’s Pacific sector. It comprises marine mudstones documenting the presence of a cool-temperate Nothofagus-dominated forest situated within a marine archipelago at 73.5°S palaeolatitude. Any evidence for marine-terminating glaciers is lacking, thus no land-based ice or only small ice caps existed in West Antarctica during the EOGM. Our new EOGM temperature and topographical constraints allow for more reliable verification of a fully-coupled Earth System Model. It simulates a large East Antarctic ice sheet already during the EOGM. However, West Antarctica does not glaciate until ~26 Ma, thereby illustrating the significance of asymmetric Antarctic ice sheet response during initial Cenozoic glaciation and highlighting the importance of differential regional response for future cryospheric change.

Description: The Eocene-Oligocene Transition (EOT; ~34.4–33.7 Ma) was a major shift in Earth’s long-term climatic evolution, marking the cooling from the early Paleogene greenhouse to the icehouse regime that has prevailed from the Oligocene until today. However, it remains uncertain which landmasses were already covered by ice sheets during the Early Oligocene Glacial Maximum (EOGM; ~33.7–33.2 Ma), an interval of peak glaciation immediately following the EOT. The scarcity of earliest Oligocene climate records in both Arctic and Antarctic regions hitherto prevented the reconstruction of environmental conditions and ice-sheet extent during the EOGM. Such constraints, however, are critical for assessing ice–ocean–atmosphere interactions during the early stages of the Cenozoic icehouse. Here, we present the first shallow-marine drill-core record of earliest Oligocene environmental conditions in West Antarctica’s Pacific sector. It comprises marine mudstones documenting the presence of a cool-temperate Nothofagus-dominated forest situated within a marine archipelago at 73.5°S palaeolatitude. Any evidence for marine-terminating glaciers is lacking, thus no land-based ice or only small ice caps existed in West Antarctica during the EOGM. Our new EOGM temperature and topographical constraints allow for more reliable verification of a fully-coupled Earth System Model. It simulates a large East Antarctic ice sheet already during the EOGM. However, West Antarctica does not glaciate until ~26 Ma, thereby illustrating the significance of asymmetric Antarctic ice sheet response during initial Cenozoic glaciation and highlighting the importance of differential regional response for future cryospheric change.