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Fig. S4. Bispectra assessing phase coupling and energy transfers between frequencies in the δ 18 O data. Bispectral results over three 2-My-long intervals that correspond to (A) ∼2.4-My Eccentricity Cycle 9 (21.10 My to 19.10 My ago, (B) Cycle 10 (23.54 My to 21.54 My ago), and (C) Cycle 12 (28.30 My to 26.30 My ago; see SI Methods). Gray lines reflect the main astronomical frequencies of eccentricity, obliquity, and precession. The two panels of Fig. 2 are reproduced here (B and C) and expanded to include the interactions with the precession frequencies.
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The Antarctic ice cap waxed and waned on astronomical time scales throughout the Oligo-Miocene time interval. We quantify geometries of Antarctic ice age cycles, as expressed in a new climate record from the South Atlantic Ocean, to track changing dynamics of the unipolar icehouse climate state. We document numerous ∼110-thousand-year-...
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Knowledge of the equatorial thermocline is essential for understanding climate changes in the tropical Pacific. Multispecies planktic foraminiferal analyses provide a way to examine temperature distributions and thus the structure of the thermocline. Although the secular thermocline development has been documented back to the late Miocene, the earl...
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... This agrees with occurrence of low temperatures during eccentricity minima and obliquity minima (when glacial periods are expected to occur). Asymmetric, sawtooth-shaped cycles are typical for glacial cycles of the Late Pleistocene (Lisiecki & Raymo, 2007) and are also found in the Early Miocene, linked to prolonged ice sheet growth on Antarctica and subsequent rapid retreat (Liebrand et al., 2017). The approximately symmetrical cycles during the MCO indicate a more direct response to astronomical forcing, which is in line with a smaller Antarctic ice sheet that was restricted to the inner continent (Colleoni et al., 2018). ...
... Benthic δ 18 O records indicate that the high-latitude climate was paced by obliquity and eccentricity during the Early Miocene (Billups et al., 2004;Liebrand et al., 2016Liebrand et al., , 2017Pälike et al., 2006) and mainly by ∼100 kyr eccentricity during the Middle to Late Miocene, with a switch to dominant obliquity pacing during 2.4 Myr eccentricity minima around 14.4, 9.5, and 7.5 Ma (Holbourn et al., 2007(Holbourn et al., , 2018. Although direct comparison is difficult, this seems to agree with patterns reflected in the Lower to Middle Miocene proxy records of Site 959 ( Figure S14 in Supporting Information S1). ...
Detailed analysis of tropical climate dynamics is lacking for the Early to Middle Miocene, even though this time interval bears important analogies for future climates. Based on high‐resolution proxy reconstructions of sea surface temperature, export productivity and dust supply at Ocean Drilling Program Site 959, we investigate astronomical forcing of the West African monsoon in the eastern equatorial Atlantic across the prelude, onset, and continuation of the Miocene Climatic Optimum (MCO; 18–15 Ma). Along with previously identified eccentricity periodicities of ∼400 and ∼100 kyr, our records show that climate varied on ∼27–17 kyr, ∼41 kyr, and ∼60–50 kyr timescales, which we attribute to precession, obliquity, and their combination tones, respectively. The relative contribution of these astronomical cycles differed between proxies and through time. Three intervals with distinct variability were recognized, which are particularly clear in the temperature record: (a) strong eccentricity, obliquity, and precession variability prior to the MCO (18.2–17.7 Ma), (b) strong influence of obliquity just after the onset of the MCO (16.9–16.3 Ma) concurring with a 2.4 Myr eccentricity minimum, and (c) dominant eccentricity and precession variability during the MCO between 16.3 and 15.0 Ma. Sedimentation at Site 959 was influenced by astronomically paced variations in upwelling intensity and North African aridity related to West African monsoon dynamics. Continuously present patterns of precession imply low‐latitude forcing, while asymmetric eccentricity and obliquity imprints and strong obliquity influence suggest that Site 959 was also affected by high‐latitude, glacial‐interglacial dynamics.
... Sheet extent throughout the Oligocene (Liebrand et al., 2017), although ice-sheet extent during the late Oligocene is still unclear (Roberts et al., 2003;Hauptvogel et al., 2017;Kulhanek et al., 2019;Pollard and DeConto, 2020). ...
The Antarctic ice sheet blankets >99% of the continent and limits our ability to study how subglacial geology and topography have evolved through time. Ice-rafted dropstones derived from the Antarctic subglacial continental interior at different times during the late Cenozoic provide valuable thermal history proxies to understand this geologic history. We applied multiple thermochronometers covering a range of closure temperatures (60–800 °C) to 10 dropstones collected during Integrated Ocean Drilling Program (IODP) Expedition 318 in order to explore the subglacial geology and thermal and exhumation history of the Wilkes Subglacial Basin. The Wilkes Subglacial Basin is a key target for study because ice-sheet models show it was an area of ice-sheet retreat that significantly contributed to sea-level rise during past warm periods. Depositional ages of dropstones range from early Oligocene to late Pleistocene and have zircon U-Pb or 40Ar/39Ar ages indicating sources from the Mertz shear zone, Adélie craton, Ferrar large igneous province, and Millen schist belt. Dropstones from the Mertz shear zone and Adélie craton experienced three cooling periods (1700–1500 Ma; 500–280 Ma; 34–0 Ma) and two periods of extremely slow cooling rates (1500–500 Ma; 280–34 Ma). Low-temperature thermochronometers from seven of the dropstones record cooling during the Paleozoic, potentially recording the Ross or Pan-African orogenies, and during the Mesozoic, potentially recording late Paleozoic to Mesozoic rifting. These dropstones then resided within ~500 m of the surface since the late Paleozoic and early Mesozoic. In contrast, two dropstones deposited during the mid-Pliocene, one from the Mertz shear zone and one from Adélie craton, show evidence for localized post-Eocene glacial erosion of ≥2 km.
... These changes could explain the differences between low and high latitude assemblages. The geotectonic events such as changes in inter-ocean gateways (Osborne et al., 2014;Sijp et al., 2014;O'Dea et al., 2016;Brierley and Fedorov, 2016), the growth of high latitude continental scale ice sheets (De Schepper et al., 2015;Stein et al., 2016;Liebrand et al., 2017), and the development of major mountain belts (Ruddiman, 2013;Spicer et al., 2003;Graham, 2009;Fauquette et al., 2015). All these events combined to influenced and altered the paleogeographical pattern, the water circulation, and the chemical composition of the different regions. ...
Understanding the biostratigraphy of tropical areas during the Neogene period can be improved by studying dinoflagellate cyst events. These events have traditionally been identified through qualitative analysis. Nevertheless, to obtain consistent data on this subject, we used quantitative and probabilistic analysis of palynological data from the Southern Gulf of Mexico to identify dinoflagellate cyst events in the Neogene era. We analyzed a database of six wells, including 1,005 core and cuttings samples, a change from past qualitative analysis methods. With this quantitative approach with the RASC program, we obtained the Ranking Optimum Sequence (ROS) and compared it with ten published databases from Neogene tropical sites. The ROS identified eleven dinoflagellate species as age markers, we propose a most likely sequence of dinoflagellate cysts bioevents and define three assemblages: “Cantharellus” (Oligocene to early Miocene), “Hyalina” (Miocene), and “Patulum” (middle Miocene to Pleistocene), that can help recognize most Neogene stratigraphic stages in tropical areas. The comparison with the previous databases shows that the Gulf of Mexico and the tropical sites share 60% of the species, which enables age calibration of the optimal sequence and allows us to infer a possible provincial affinity. Additionally, we found a predominance of autotrophic dinocysts during the Neogene in tropical oceans. This trend mirrors the current abundance of gonyaulacoid cysts in tropical and subtropical areas, which has persisted since the Jurassic era.
... The Middle Oligocene Glacial Interval (MOGI) from 29 to 26 Ma is labeled, as is the Oligocene-Miocene transition (OMT). We highlight this duration of MOGI on the basis of the 1218 benthic δ 18 O record as indicated in Fig. 4; it is slightly longer than the 28 to 26.3 Ma MOGI defined by Liebrand et al. (2016Liebrand et al. ( , 2017. could yield the observed trends in marine 87 Sr / 86 Sr, is illustrated in Supplement Fig. S1 for a sample residence time of 2.5 Myr as suggested by Hodell et al. (1990). ...
The 87Sr / 86Sr of marine carbonates provides a key constraint on the balance of continental weathering and hydrothermal Sr fluxes to the ocean, and the mid-Oligocene to mid-Miocene period features the most rapid rates of increase in the 87Sr / 86Sr of the Cenozoic. Because previous records of the 87Sr / 86Sr increase with time were based on biostratigraphically defined age models in diverse locations, it was difficult to unambiguously distinguish million-year-scale variations in the rate of 87Sr / 86Sr change from variations in sedimentation rate. In this study, we produce the first 87Sr / 86Sr results from an Oligocene to early Miocene site with a precise age-model-derived orbital tuning of high-resolution benthic δ18O at Equatorial Pacific Ocean Drilling Program (ODP) Site 1218. Our new dataset resolves transient decreases in 87Sr / 86Sr, as well as periods of relative stasis. These changes can be directly compared with the high-resolution benthic δ18O at the same site. We find that slowing of the rate of 87Sr / 86Sr increase coincides with the onset of Antarctic ice expansion at the beginning of the mid-Oligocene glacial interval, and a rapid steeping in the 87Sr / 86Sr increase coincides with the benthic δ18O evidence for rapid ice retreat. This pattern may reflect either northward shifts in the Intertropical Convergence Zone precipitation to areas of nonradiogenic bedrock and/or lowered weathering fluxes from highly radiogenic glacial flours on Antarctica. We additionally generate the first 87Sr / 86Sr data from ODP Site 1168 on the Tasman Rise and Integrated Ocean Drilling Program (IODP) Site 1406 of the Newfoundland Margin during the Oligocene to early Miocene to improve the precision of age correlation of these Northern Hemisphere and Southern Hemisphere midlatitude sites and to better estimate the duration of early Miocene hiatus and condensed sedimentation.
... Global climate change near the Oligocene-Miocene boundary provides a potential mechanism for the abrupt appearance of desert conditions in the study region. Although the Oligocene is widely regarded as a period of global cooling in relationship to the opening of Drake Passage and the growth of a significant Antarctic ice sheet, climate records for latest Oligocene to early Miocene time show considerable variability (Zachos et al., 1997;Pfuhl and McCave, 2005;Liebrand et al., 2017). In South America, it is possible that such variations, potentially linked to atmospheric CO 2 , orbital forcing, or ice-climate feedbacks may have triggered increases in surface temperature that promoted aridification and protracted early Miocene eolian deposition in the retroarc region of northern and central Argentina. ...
Late Oligocene-early Miocene aridification in the retroarc foreland basin adjacent to the southern central Andes was recorded by widespread eolian conditions that
coincided with accelerated subsidence driven by the main phase of Andean tectonic loading. An extensive eolian dune system, which is rare in most foreland basins,
indicates specific conditions in terms of climate (aridity), atmospheric circulation, orography, sediment sources, dispersal patterns, and accommodation space.
Detrital zircon U-Pb geochronological results for eolian sandstones spanning 20 foreland localities in northwestern to west-central Argentina, from 22◦S to 36◦S,
reveal relatively localized Andean sources rather than regional cratonic provenance. Clastic detritus was largely derived from Phanerozoic igneous and sedimentary
rocks of the Andean magmatic arc and retroarc fold-thrust belt during initial shortening-induced uplift of hinterland regions such as the Western Cordillera, Principal
Cordillera, and Frontal Cordillera. This provenance record provides the earliest evidence for major westerly winds, transporting Andean detritus broadly eastward to
the foreland basin (with common axial northward deflections) during a climate shift marked by the latest Oligocene-earliest Miocene inception of arid conditions. In
addition to the climatic implications, independent stratigraphic data provide the basis for a compilation of sediment accumulation histories showing that eolian
deposition was synchronous with accelerated subsidence attributable to enhanced Andean shortening. We propose that accelerated Andean uplift in the latest
Oligocene-early Miocene generated rain-shadow conditions contemporaneous with increased sediment accommodation in the foreland basin, underscoring the
important influence of tectonic processes on regional climate.
... Wireline logs from closely spaced boreholes make it possible to link this astronomical framework in high resolution (<20 kyr) to the nearshore record of transgressive-regressive shoreline movements and sea-level change. The results are compared with published sea-level curves for the early Miocene (Liebrand et al. 2017) and Late Pleistocene (Spratt and Lisiecki 2016), which serve as reference examples of eustatic regimes controlled by uni-polar (Antarctic) and bi-polar glaciations, respectively. Differences in the phasing of sea-level change relative to the astronomical forcing suggest contrasting mechanisms and sources of sea-level variability under greenhouse and icehouse climates. ...
... Examples of sea-level cyclicity that can be linked accurately to eccentricity phasing are found in the icehouse regimes of the Cenozoic. The earliest Miocene, c. 18 to 22 Myr ago, exhibits a prominent 405-kyr pacing of oxygen isotope composition of benthic foraminifera, which has been attributed to ice-volume variations (Liebrand et al. 2017; for spectral estimates see Supplementary Materials, Figure S8). Correlation to astronomical solutions (Laskar et al. 2004(Laskar et al. , 2011 suggests that glacial retreat and glacioeustatic sea-level rise on the 400-kyr scale were coordinated with the rising phases of 405-kyr eccentricity (Figs. 6, 7). ...
Climate-controlled changes in eustatic sea level (ESL) are linked to transfers of water between ocean and land, thus offering a rare insight into the past hydrological cycle. In this study, we examine the timing and phase of Milankovitch-scale ESL cycles in the peak Cretaceous greenhouse, the early Turonian (~93-94 million years, Myr, ago). A high-resolution astronomical framework established for the Bohemian Cretaceous Basin (central Europe) suggests a ~400-kyr pace and a distinct asymmetry of interpreted ESL cycles. The rising limbs of ESL change constitute only 20-30% of the cycle, and are encased entirely within the falling phase of the 405-kyr eccentricity; the intervening ESL falls (≤6 m in magnitude) are more protracted, starting within 70 kyr prior to the eccentricity minima and culminating ~60 kyr after the 405-kyr eccentricity maxima. Despite similarities to the sawtooth shape of ~100-kyr glacioeustatic oscillations of the Late Pleistocene, the time scales and phasing are unparalleled in the Pleistocene icehouse. A similar, 405-kyr pace is 2 found in ice-volume variations of the early Miocene, but the timing of glacioeustatic change relative to eccentricity forcing is incompatible with the phase of greenhouse sea-level oscillations. The phasing points to major differences in the geographic location and insolation sensitivity of the key hydrological reservoirs under icehouse and greenhouse regimes. The inferred structure of greenhouse eustasy points to low-or middle-latitude water storage, likely aquifers, that charge (expand) with rising seasonality variations and discharge (contract) with declining seasonality amplitudes on the 405-kyr scale. The net volume of water transferred on these time scales is within 2.2 x10 6 km 3 , equivalent to ≤10 % of the present-day storage in the uppermost 2 km of continental crust; potential additive interference with steric eustasy, proportionally relevant during greenhouse regimes, could reduce the volumes required for continental storage.
... As such, the significant eccentricity in our records may be more likely be related to eccentricity modulation of low-latitude summer insolation through nonlinear interactions with the global carbon cycle (e.g., Palike et al., 2006;Ao et al., 2021b). Such a low-latitude origin for eccentricity has been proposed previously as a cause of eccentricity in global climate records, including those based on Cenozoic benthic foraminiferal δ 18 O records (e.g., Liebrand et al., 2017;Liebrand and de Bakker, 2019). ...
... The Oligocene climate history began with the establishment of large sustained ice sheets on Antarctica at the Eocene-Oligocene Transition (~33.6 Ma ago) 4,5 , followed by the colder but highly variable Mid-Oligocene Glacial Interval (~28-26.3 Ma) 6 . A warming climate characterised the late Oligocene warming phase (LOW) betweeñ 26.3 and 23.7 Ma 6 that was abruptly terminated by a major transient glaciation at the Oligocene-Miocene Transition (OMT; ∼23.7-22.7 Ma ago; Fig. 1a) 4,7 . ...
... Ice-proximal sedimentological records are interpreted to indicate significant, recurring obliquitypaced AIS oscillations [8][9][10][11] but stratigraphic age control in such archives is often challenging. Even in ice-distal pelagic marine sequences, where age control is typically stronger, the astronomical imprint on benthic foraminiferal oxygen isotope (δ 18 O BF ) records is enigmatic with pronounced spatial and temporal variability in both the~400-and 100-kyr eccentricity and 40-kyr obliquity cycles 6,[12][13][14][15] . A further complicating observation is that δ 18 O BF -based ice-volume reconstructions for the AIS yield sharply conflicting conclusions over the size and stability of the AIS during the LOW interval. ...
... A further complicating observation is that δ 18 O BF -based ice-volume reconstructions for the AIS yield sharply conflicting conclusions over the size and stability of the AIS during the LOW interval. Using a δ 18 O BF record from Site 1264 (South Atlantic Ocean, Fig. 2a), ref. 6 inferred episodes of high-amplitude variability in δ 18 O BF requiring waxing and waning by at least~85 to 110% of the present-day volume of the East Antarctic Ice Sheet (EAIS) oñ 100-kyr timescales with a distinct overall ice-volume decrease from about 27 to 24 Ma (Fig. 2a). In contrast, a heavily glaciated Antarctic continent from 27.8 to 24.5 Ma with ice sheets approaching or exceeding their modern-size and no indications of significant ice-sheet disintegration is invoked based on a δ 18 O BF record from Maud Rise (Antarctica; Fig. 2a) 16 . ...
The late Oligocene (~27.8–23 My ago) offers an opportunity to study past climate variability under high-CO2, warmer-than-present and the unipolar (Antarctic) glaciated state. Here, we present new high-resolution geochemical records from exquisitely well-preserved benthic foraminifera for the late Oligocene, an interval for which Antarctic ice-sheet size and stability are debated. Our records indicate four obliquity-paced glacial-interglacial cycles with ice-volume changes of up to ~70% of the modern Antarctic ice-sheet. The amplitude of ice-volume change during these late Oligocene glacial-interglacial cycles is comparable to that of the late Pliocene and early Pleistocene. Ice-volume estimates for interglacials are small enough to be accommodated by a land-based Antarctic ice-sheet but, for three of the four glacials studied, our calculations imply that ice sheets likely advanced beyond the Antarctic coastline onto the shelves. Our findings suggest an Antarctic ice-sheet vulnerable to melting driven by both bottom-up (ocean) and top-down (atmospheric) warming under late Oligocene warmer-than-present climate conditions.
... Here, we present a time series analysis of precession-scale resolution environmental magnetic records of fluvial-lacustrine sediments from the Nima Basin in the central TP to constrain the midlatitude hydrological changes, the SAM northward progression, and potential forcing mechanisms on tectonic through orbital time scales during the late Oligocene. During the late Oligocene, there is only a unipolar ice sheet on Antarctica and the Earth experienced the Late Oligocene warming event (32)(33)(34)(35). The TP experienced significant uplift during the late Oligocene (36)(37)(38)(39). ...
... Magnetic proxies with the same rhythmic variation as the lithology and color confirm the presence of changing redox conditions in terms of magnetic minerals. The significant loss of hematite in green layers (32,35,47). (E) La2010d-Ecc3L eccentricity solution (45). ...
... Antarctic ice volume reconstruction suggests that these phases correspond well in time to intervals of ice sheet expansion (Fig. 5B). Ice volume pnas.org was paced by eccentricity (35,47). Therefore, weak monsoon precipitation at the six phases on the 405-kyr timescale could be directly caused by a response to the long eccentricity-modulated precession of Earth's spin axis, or by Antarctic ice sheet expansion through interactions with the global carbon cycle (28,35,72). ...
The modern pattern of the Asian monsoon is thought to have formed around the Oligocene/Miocene transition and is generally attributed to Himalaya-Tibetan Plateau (H-TP) uplift. However, the timing of the ancient Asian monsoon over the TP and its response to astronomical forcing and TP uplift remains poorly known because of the paucity of well-dated high-resolution geological records from the TP interior. Here, we present a precession-scale cyclostratigraphic sedimentary section of 27.32 to 23.24 million years ago (Ma) during the late Oligocene epoch from the Nima Basin to show that the South Asian monsoon (SAM) had already advanced to the central TP (32°N) at least by 27.3 Ma, which is indicated by cyclic arid-humid fluctuations based on environmental magnetism proxies. A shift of lithology and astronomically orbital periods and amplified amplitude of proxy measurements as well as a hydroclimate transition around 25.8 Ma suggest that the SAM intensified at ~25.8 Ma and that the TP reached a paleoelevation threshold for enhancing the coupling between the uplifted plateau and the SAM. Orbital short eccentricity-paced precipitation variability is argued to be mainly driven by orbital eccentricity-modulated low-latitude summer insolation rather than glacial-interglacial Antarctic ice sheet fluctuations. The monsoon data from the TP interior provide key evidence to link the greatly enhanced tropical SAM at 25.8 Ma with TP uplift rather than global climate change and suggest that SAM's northward expansion to the boreal subtropics was dominated by a combination of tectonic and astronomical forcing at multiple timescales in the late Oligocene epoch.
... The differentiation of M. hypoleuca and M. officinalis is Oligocene-Miocene transition (OMT, 25~22 MA) which is a period of intense geological and historical events caused by the collision of the Indian plate and Eurasia (Zhao and Li, 2019). The rapid uplift of the Qinghai-Tibet Plateau and Himalayas, the rapid lateral sliding of the Indochina Peninsula and the strengthening of the monsoon occurred at this stage (Liebrand et al., 2017). The uplift of the Qinghai-Tibet Plateau and the Himalayas is one of the most significant meteorological and geological events in the Cenozoic era, which not only affects the structural pattern of Eurasia, but also has a profound impact on the global climate change since the Cenozoic era. ...
Magnolia hypoleuca Sieb. & Zucc, a member of the Magnoliaceae of magnoliids, is one of the most economically valuable, phylogenetic and ornamental tree species in Eastern China. Here, the 1.64 Gb chromosome-level assembly covers 96.64% of the genome which is anchored to 19 chromosomes, with a contig N50 value of 1.71 Mb and 33,873 protein-coding genes was predicted. Phylogenetic analyses between M. hypoleuca and other 10 representative angiosperms suggested that magnoliids were placed as a sister group to the eudicots, rather than sister to monocots or both monocots and eudicots. In addition, the relative timing of the whole-genome duplication (WGD) events about 115.32 Mya for magnoliid plants. M. hypoleuca was found to have a common ancestor with M. officinalis approximately 23.4 MYA, and the climate change of OMT (Oligocene-Miocene transition) is the main reason for the divergence of M. hypoleuca and M. officinalis, which was along with the division of Japanese islands. Moreover, the TPS gene expansion observed in M. hypoleuca might contribute to the enhancement of flower fragrance. Tandem and proximal duplicates of younger age that have been preserved have experienced more rapid sequence divergence and a more clustered distribution on chromosomes contributing to fragrance accumulation, especially phenylpropanoid, monoterpenes and sesquiterpenes and cold tolerance. The stronger selective pressure drived the evolution of tandem and proximal duplicates toward plant self-defense and adaptation. The reference M. hypoleuca genome will provide insights into the evolutionary process of M. hypoleuca and the relationships between the magnoliids with monocots and eudicots, and enable us to delve into the fragrance and cold tolerance produced by M. hypoleuca and provide more robust and deep insight of how the Magnoliales evolved and diversified.
