Description: Cyclostratigraphy and astrochronology are now at the forefront of geologic timekeeping. While this technique heavily relies on the accuracy of astronomical calculations, solar system chaos limits how far back astronomical calculations can be performed with confidence. High‐resolution paleoclimate records with Milankovitch imprints now allow reversing the traditional cyclostratigraphic approach: Middle Eocene drift sediments from Newfoundland Ridge are well‐suited for this purpose, due to high sedimentation rates and distinct lithological cycles. Per contra, the stratigraphies of Integrated Ocean Drilling Program Sites U1408–U1410 are highly complex with several hiatuses. Here, we built a two‐site composite and constructed a conservative age‐depth model to provide a reliable chronology for this rhythmic, highly resolved (〈1 kyr) sedimentary archive. Astronomical components (g‐terms and precession constant) are extracted from proxy time‐series using two different techniques, producing consistent results. We find astronomical frequencies up to 4% lower than reported in astronomical solution La04. This solution, however, was smoothed over 20‐Myr intervals, and our results therefore provide constraints on g‐term variability on shorter, million‐year timescales. We also report first evidence that the g〈sub〉4〈/sub〉–g〈sub〉3〈/sub〉 “grand eccentricity cycle” may have had a 1.2‐Myr period around 41 Ma, contrary to its 2.4‐Myr periodicity today. Our median precession constant estimate (51.28 ± 0.56″/year) confirms earlier indicators of a relatively low rate of tidal dissipation in the Paleogene. Newfoundland Ridge drift sediments thus enable a reliable reconstruction of astronomical components at the limit of validity of current astronomical calculations, extracted from geologic data, providing a new target for the next generation of astronomical calculations.

Description: Plain Language Summary: The traditional cyclostratigraphic approach is to align and correlate a geologic depth‐series with an astronomical solution. However, the chaotic nature of the Solar System prevents astronomers from precisely calculating planetary motions beyond 40–50 million years ago. This in turn limits the options for geologists to use the resulting oscillations in Earth's climate system as a metronome for determining geologic time. In this study, we reversed the cyclostratigraphic approach and used the highly rhythmical sedimentary deposits from Newfoundland Ridge (North Atlantic) to back‐calculate planetary motions at ∼41 million years ago. The superior quality of the Newfoundland Ridge geoarchive originates from the combination of relatively high sedimentation rates (∼4 cm/kyr) and the time‐continuous character of our two‐site composite record between 39.5 and 42.8 million years ago. In this work, we had to first overcome considerable challenges in reconstructing the timing of sediment deposition, which we did with highly resolved geochemical measurements from two sites. We then were able to extract information on the Earth's planetary motion and on the Earth‐Moon interactions. These astronomical reconstructions based on geological data can now be used by astronomers to describe the evolution of the solar system further back in time than was previously possible.

Description: Key Points: A new precession‐based cyclostratigraphy for the middle Eocene intervals of IODP Sites U1408 and U1410. Variability in astronomical fundamental frequencies (g‐terms) on million‐year timescales is larger than previously assumed. Our precession constant estimate for 41 Ma (51.28 ± 0.56″/year) confirms earlier indicators of slower tidal dissipation in the Paleogene.

Description: National Science Foundation http://dx.doi.org/10.13039/100000001

Description: University of California http://dx.doi.org/10.13039/100005595

Description: Belgian American Educational Foundation http://dx.doi.org/10.13039/100001491

Description: https://paloz.marum.de/AstroComputation/index.html

Description: https://paloz.marum.de/confluence/display/ESPUBLIC/NAFF

Description: Much of our understanding of Earth’s past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states—Hothouse, Warmhouse, Coolhouse, Icehouse—are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics.

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: Previous scientific ocean drilling expeditions have revealed that sediments deposited in the Kerguelen Plateau region have the potential to provide an out-standing chronicle of regional and global climate changes. In particular, this area is an excellent location to monitor subantarctic and high-latitude climate dynamics and obtain far-field information documenting Antarctic climate history in a world warmer than today. Here we report first results from site survey RV Sonne cruise SO272 that sailed January 11 to March 4 2020 from Port Louis, Mauritius, to Cape Town, South Africa. During the cruise ~4000 km of high resolution seismic reflection data were recorded along 18 seismic profiles across the central and southern Kerguelen Plateau. At 11 stations sediment cores with recoveries of up to 10m were retrieved [GU1] to complement the seismic studies and provide ages of the outcropping sediment at the sea floor. Three gravity cores targeted the Labuan Basin recovering Plio-Pleistocene diatom ooze with drop stones and rhythmic changes in reflectance. Eight gravity cores targeted the Raggatt Basin with the main objective to penetrate through the upper undifferentiated layer of surface sediment and probe the below much older outcropping sediment. Carbonate rich sediments were successfully retrieved at three locations with microfossil assemblages of late Eocene age. X-ray fluorescence core scanning, benthic stable isotope and bio-stratigraphic data will be presented. Seismic and geological datasets will form the base for an IODP full proposal to drill a complete Miocene to Paleocene high latitude sediment package, build upon the #983-Pre IODP proposal.

Description: The Kerguelen Plateau, southern Indian Ocean rises up 2000 m above the surrounding seafloor and hence forms an obstacle for the flow of the Antarctic Circumpolar Current (ACC) and the Antarctic Bottomwater (AABW). The ACC is strongly deviated in its flow towards the north. A branch of the AABW flows northwards along the eastern flank of the plateau and in its path is steered by several basement highs and William’s Ridge. Seismic data collected during RV Sonne cruise SO272 image sediment drifts shaped in the Labuan Basin, which document onset and variabilities in pathway and intensity of this AABW branch in relation to the development of the Antarctic ice sheet and tectonic processes, e.g., the opening of the Tasman gateway. The eastern flank of the Kerguelen shows strong erosion of the post-mid Eocene sequences. In places, the Paleocene/early Eocene sequences are also affected by thinning and erosion. A moat can be observed along the Kerguelen Plateau flank indicating the flowpath of the north setting AAWB branch. Sediment drifts and sediment waves are formed east of the moat. Similar features are observed at the inner, western flank of William’s Ridge thus outlining the recirculation of the AABW branch in the Labuan Basin. The chronological and spatial will be reconstructed via the analysis of those sedimentary structures to provide constraints on climate and ocean circulation variability.

Description: Much of our understanding of Earth's past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states-Hothouse, Warmhouse, Coolhouse, Icehouse-are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics.

Description: Published

Description: 1383–1387

Description: 5A. Ricerche polari e paleoclima

Description: JCR Journal