Description: The transition from the Cretaceous “Supergreenhouse” to the Oligocene icehouse provides an opportunity to study changes in Earth system dynamics from a time when climate models suggest CO2 levels may have been as high as 3500 ppmv (parts per million by volume) and then declined to less than 560 ppmv. During the Supergreenhouse interval meridional temperature gradients were very low and oceanic deposition was punctuated by episodes of widespread anoxia, termed Oceanic Anoxic Events (OAEs) resulting in large scale burial of organic carbon reflected in positive delta 13C excursions. High CO2, greenhouse climate conditions are envisioned for the near future calling for action to get a better understanding of their potential impacts and dynamics. Climate models have identified significant geography-related Cenozoic cooling arising from the opening of Southern Ocean gateways, pointing towards a progressive strengthening of the Antarctic Circumpolar Current as the major cause for cooler deep ocean temperatures. Analogous arguments point to an important role for deep circulation in explaining Late Cretaceous climate evolution. The Agulhas Plateau is located in a key area for retrieving high-quality geochemical records to test competing models, e.g. to what extent and exactly when the opening of Drake Passage contributed to cooling of the deep ocean. The proposed drill sites on Agulhas Plateau and Transkei Basin are at high latitudes (65°S-58°S from 100 to 65 Ma) and within a gateway between the newly opening South Atlantic, Southern Ocean and southern Indian Ocean basins. Recovery of expanded and stratigraphically complete pelagic carbonate sequences from this region, and comparison with drilling results from Naturaliste Plateau (760-Full), will provide a wealth of new data to significantly advance the understanding of how Cretaceous temperatures, ocean circulation, and sedimentation patterns evolved as CO2 level rose and fell, and the breakup of Gondwana progressed.

Description: Twenty-first century atmospheric pCO2 concentrations will rise to levels that the Earth has not experienced for more than 30 Myr (〉500 ppm). Geological records from the Paleogene (66 to 23 million years ago, Ma) provide the means to decipher the operation of the Earth System under high pCO2 conditions, but tackling this scientifically and societally important problem requires precise integration of climate datasets across latitudes and ocean basins. Currently we lack the continuous high- resolution archives from the southern high latitudes that we need to provide comprehensive information on (sub)polar climate evolution and test competing hypothesized mechanisms of Paleogene climate change, such as the influence of atmospheric pCO2 change versus the opening of Southern Ocean tectonic gateways to deep-water circulation. Here we present the new International Ocean Discovery Program (IODP) pre-proposal 862-Pre (SW Atlantic Paleogene Climate) designed to drill a depth transect of Paleogene sites in the subantarctic South Atlantic Ocean on the easternmost tip of the Falkland Plateau (Maurice Ewing Bank and Georgia Basin). In the modern ocean, this is a critical area for deep-water mixing and communication between the Pacific and Atlantic oceans across the Drake Passage, with local bathymetry controlling the dispersal and propagation of deep- and bottom-waters throughout the Atlantic. The plan is to recover a composite of Paleogene sections spanning an extensive range of paleo-water depths (~500-4500 m) to determine the timing and variability of shallow- and deep-water connectivity across the Drake Passage and to test whether the onset of a proto-Antarctic Circumpolar Current (ACC) circulation had a direct impact on high-latitude and global climate evolution. These drillcores will thus provide crucial insight on the long-standing question of the relative influence of atmospheric pCO2 drawdown vs. Southern Ocean gateways in driving Paleogene climate evolution. The target sites are also ideally positioned to assess the relationships between local tectonic subsidence of deep-water barriers, high-latitude climate change, and the onset of bottom-water production in the Weddell Sea and northward propagation into to the deep western Atlantic - a process that, along with ACC circulation, fundamentally altered Cenozoic circulation in the Atlantic. Multi-proxy datasets from expanded hemipelagic sections will shed new light on climate change, biotic shifts, and deep-sea chemistry during the Paleogene, allowing evaluation of: (i) the magnitude of temperature change and response of high-latitude plankton groups across transient 'greenhouse' events, (ii) the initiation of southern high latitude cooling and onset of Antarctic Peninsula glaciation during the middle Eocene - early Oligocene 'greenhouse' to 'icehouse' transition, and (iii) variation in the Calcite Compensation Depth in the South Atlantic and its relation to changes in global carbon cycling. Following the positive recommendation by the Science Evaluation Panel (SEP) for IODP 862-Pre two companion seismic reflection survey and piston coring operations in the eastern Falkland Plateau region of the subantarctic southwest Atlantic Ocean have been developed. One Site Survey Investigation (SSI) cruise led by Uenzelmann-Neben (AWI, Bremerhaven) and Westerhold (MARUM, Bremen) is proposed to survey the Maurice Ewing Bank extending southward across the Falkland Trough. The complementary SSI led by Bohaty (Univ. Southampton, UK) is proposed to survey the eastern half of the region across the Georgia Basin and Northeast Georgia Rise. The collaboration between German and UK groups will feasibly provide the extensive data coverage needed to survey the entire east–west transect of drillsites to meet the scientific objectives of 862-Pre. This transect is a fundamental requirement to allow reconstruction of deep-water properties across a range of palaeo-water depths and surface- water conditions across several modern frontal boundaries.

Description: Located in a key region in the southern Indian Ocean the complex topography of the Kerguelen Plateau, one of the world’s largest Large Igneous Provinces, has a strong influence on pathways of water masses within the Antarctic Circumpolar Current (ACC) and the Antarctic Bottom Water (AABW). Topographic highs like the Williams Ridge at the Kerguelen Plateau reduce the flow of water masses leading to the deposition of thick sediment packages. Gaps and narrow passages in contrast lead to erosion and non-deposition. In the Cenozoic era significant modifications in pathways and intensity of those water masses have been caused by the tectonic development of the Kerguelen Plateau as well as the opening of the Tasman Gateway, the Drake Passage and major global climatic changes. In the Kerguelen Plateau region all of these changes are explicitly well documented in the formation of sedimentary structures, e.g. sediment drifts, supposedly at very high resolution. Studying these sedimentary structures using high-resolution seismic reflection data in combination with geological information from ODP Sites 747-751 will provide new insights into the evolution and dynamics of the ACC and AABW in the southern Indian Ocean. New high-quality seismic data from the Labuan and Ragatt Basin area, which will be collected using the German RV Sonne, will allow studying the interaction of climatic and tectonic changes of the last 66 million years and provide important information on the formation and dynamics of the Antarctic ice sheet due to the unique location of the Kerguelen Plateau. The seismic study is complemented by geological sampling to enable dating of reflections terminating at the seafloor where no ODP drill hole exist.

Description: The transition from the Cretaceous “Supergreenhouse” to the Oligocene icehouse provides an opportunity to study changes in Earth system dynamics from a time when climate models suggest CO2 levels may have been as high as 3500 ppmv (parts per million by volume) and then declined to less than 560 ppmv. During the Supergreenhouse interval meridional temperature gradients were very low and oceanic deposition was punctuated by episodes of widespread anoxia, termed Oceanic Anoxic Events (OAEs) resulting in large scale burial of organic carbon reflected in positive delta 13C excursions. High CO2, greenhouse climate conditions are envisioned for the near future calling for action to get a better understanding of their potential impacts and dynamics. Climate models have identified significant geography-related Cenozoic cooling arising from the opening of Southern Ocean gateways, pointing towards a progressive strengthening of the Antarctic Circumpolar Current as the major cause for cooler deep ocean temperatures. Analogous arguments point to an important role for deep circulation in explaining Late Cretaceous climate evolution. The Agulhas Plateau is located in a key area for retrieving high-quality geochemical records to test competing models, e.g. to what extent and exactly when the opening of Drake Passage contributed to cooling of the deep ocean. The proposed drill sites on Agulhas Plateau and Transkei Basin are at high latitudes (65°S-58°S from 100 to 65 Ma) and within a gateway between the newly opening South Atlantic, Southern Ocean and southern Indian Ocean basins. Recovery of expanded and stratigraphically complete pelagic carbonate sequences from this region, and comparison with drilling results from Naturaliste Plateau (760-Full), will provide a wealth of new data to significantly advance the understanding of how Cretaceous temperatures, ocean circulation, and sedimentation patterns evolved as CO2 level rose and fell, and the breakup of Gondwana progressed.

Description: The late Miocene-early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here, we present the first continuous late Miocene-early Pliocene (8.0-4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0-3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest mean sea-surface-temperatures (SSTs) are ~27.8±1.1°C (1 Sigma) between 6.4-5.5 Ma. The planktic foraminiferal d18O record implies a 2°C cooling between 7.2-6.1 Ma and an up to 3°C warming between 6.1-4.4 Ma, consistent with observed tropical alkenone paleo-SSTs. Diverging fine-fraction-to-foraminiferal d13C gradients likely suggest increased upwelling from 7.1-6.0 and 5.8-4.6 Ma, concurrent with the globally recognized late Miocene Biogenic Bloom. This study shows that both warm and asymmetric mean states occurred in the equatorial Pacific during the late Miocene-early Pliocene. Between 8.0-6.5 and 5.2-4.4 Ma, low east-west d18O and SST gradients and generally warm conditions prevailed. However, an asymmetric mean climate state developed between 6.5-5.7 Ma, with larger east-west d18O and SST gradients and eastern equatorial Pacific cooling. The asymmetric mean state suggests stronger trade winds developed, driven by increased meridional thermal gradients associated with global cooling and declining atmospheric pCO2 concentrations. These oscillations in equatorial Pacific mean state are reinforced by Antarctic cryosphere expansion and related changes in oceanic gateways (e.g., Central American Seaway/Indonesian Throughflow restriction).