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Astronomical calculations reveal the Solar System’s dynamical evolution, including its chaoticity, and represent the backbone of cyclostratigraphy and astrochronology. An absolute, fully calibrated astronomical time scale has hitherto been hampered beyond ~50 million years before the present (Ma) because orbital calculations disagree before that age. Here, we present geologic data and a new astronomical solution (ZB18a) showing exceptional agreement from ~58 to 53 Ma. We provide a new absolute astrochronology up to 58 Ma and a new Paleocene–Eocene boundary age (56.01 ± 0.05 Ma). We show that the Paleocene–Eocene Thermal Maximum (PETM) onset occurred near a 405-thousand-year (kyr) eccentricity maximum, suggesting an orbital trigger. We also provide an independent PETM duration (170 ± 30 kyr) from onset to recovery inflection. Our astronomical solution requires a chaotic resonance transition at ~50 Ma in the Solar System’s fundamental frequencies.

New data on the foraminifers and the regional geological setting of the Trachilos sediments (NW Crete, Greece) from which Gierlinski et al. (Proc Geol Assoc 128: 697–710, 2017) described hominin-like footprints show that the published 6.05 Ma-shallow marine interpretation is incorrect. In our new interpretation, the Trachilos succession is Late Pliocene and part of a shallowing marine series that became subaerially exposed some 3 millions of years ago. Placed in a larger geological context, Crete was an island during the Late Pliocene and separated by ~ 100 km of open sea from the nearest European mainland, and therefore out of reach of Late Pliocene hominins.

Climate during the last glacial period was marked by abrupt instability on millennial timescales that included large swings of temperature in and around Greenland (Daansgard–Oeschger events) and smaller, more gradual changes in Antarctica (AIM events). Less is known about the existence and nature of similar variability during older glacial periods, especially during the early Pleistocene when glacial cycles were dominantly occurring at 41 kyr intervals compared to the much longer and deeper glaciations of the more recent period. Here, we report a continuous millennially resolved record of stable isotopes of planktic and benthic foraminifera at IODP Site U1385 (the “Shackleton Site”) from the southwestern Iberian margin for the last 1.5 million years, which includes the Middle Pleistocene Transition (MPT). Our results demonstrate that millennial climate variability (MCV) was a persistent feature of glacial climate, both before and after the MPT. Prior to 1.2 Ma in the early Pleistocene, the amplitude of MCV was modulated by the 41 kyr obliquity cycle and increased when axial tilt dropped below 23.5∘ and benthic δ18O exceeded ∼3.8 ‰ (corrected to Uvigerina), indicating a threshold response to orbital forcing. Afterwards, MCV became focused mainly on the transitions into and out of glacial states (i.e. inceptions and terminations) and during times of intermediate ice volume. After 1.2 Ma, obliquity continued to play a role in modulating the amplitude of MCV, especially during times of glacial inceptions, which are always associated with declining obliquity. A non-linear role for obliquity is also indicated by the appearance of multiples (82, 123 kyr) and combination tones (28 kyr) of the 41 kyr cycle. Near the end of the MPT (∼0.65 Ma), obliquity modulation of MCV amplitude wanes as quasi-periodic 100 kyr and precession power increase, coinciding with the growth of oversized ice sheets on North America and the appearance of Heinrich layers in North Atlantic sediments. Whereas the planktic δ18O of Site U1385 shows a strong resemblance to Greenland temperature and atmospheric methane (i.e. Northern Hemisphere climate), millennial changes in benthic δ18O closely follow the temperature history of Antarctica for the past 800 kyr. The phasing of millennial planktic and benthic δ18O variation is similar to that observed for MIS 3 throughout much of the record, which has been suggested to mimic the signature of the bipolar seesaw – i.e. an interhemispheric asymmetry between the timing of cooling in Antarctica and warming in Greenland. The Iberian margin isotopic record suggests that bipolar asymmetry was a robust feature of interhemispheric glacial climate variations for at least the past 1.5 Ma despite changing glacial boundary conditions. A strong correlation exists between millennial increases in planktic δ18O (cooling) and decreases in benthic δ13C, indicating that millennial variations in North Atlantic surface temperature are mirrored by changes in deep-water circulation and remineralization of carbon in the abyssal ocean. We find strong evidence that climate variability on millennial and orbital scales is coupled across different timescales and interacts in both directions, which may be important for linking internal climate dynamics and external astronomical forcing.

Marine sediment records from the Oligocene and Miocene reveal clear 400,000-year climate cycles related to variations in orbital eccentricity. These cycles are also observed in the Plio-Pleistocene records of the global carbon cycle. However, they are absent from the Late Pleistocene ice-age record over the past 1.5 million years. Here we present a simulation of global ice volume over the past 5 million years with a coupled system of four three-dimensional ice-sheet models. Our simulation shows that the 400,000-year long eccentricity cycles of Antarctica vary coherently with δ 13 C data during the Pleistocene, suggesting that they drove the long-term carbon cycle changes throughout the past 35 million years. The 400,000-year response of Antarctica was eventually suppressed by the dominant 100,000-year glacial cycles of the large ice sheets in the Northern Hemisphere. The precise contributions of solar forcing, the carbon cycle and glaciation to the pacing of global climate remains unresolved. Using four 3D ice-sheet models, de Boer et al. show that Antarctic ice volume and carbon-cycle dynamics varied coherently during the Pleistocene, as has been observed in the Miocene.

Recurrent deposition of organic-rich sediment layers (sapropels) in the eastern Mediterranean Sea is caused by complex interactions between climatic and biogeochemical processes. Disentangling these influences is therefore important for Mediterranean palaeo-studies in particular, and for understanding ocean feedback processes in general. Crucially, sapropels are diagnostic of anoxic deep-water phases, which have been attributed to deep-water stagnation, enhanced biological production or both. Here we use an ocean-biogeochemical model to test the effects of commonly proposed climatic and biogeochemical causes for sapropel S1. Our results indicate that deep-water anoxia requires a long prelude of deep-water stagnation, with no particularly strong eutrophication. The model-derived time frame agrees with foraminiferal δ 13 C records that imply cessation of deep-water renewal from at least Heinrich event 1 to the early Holocene. The simulated low particulate organic carbon burial flux agrees with pre-sapropel reconstructions. Our results offer a mechanistic explanation of glacial–interglacial influence on sapropel formation. Numerous theories exist regarding the evolution of a deep-water oxygen deficiency in the eastern Mediterranean Sea. Here, the authors test several popular hypotheses with a focus on the S1 event showing that long-term stagnation was necessary, preconditioned by the changes associated with the last deglaciation.

At the boundary between the Palaeocene and Eocene epochs, about 55 million years ago, the Earth experienced a strong global warming event, the Palaeocene–Eocene thermal maximum 1 , 2 , 3 , 4 . The leading hypothesis to explain the extreme greenhouse conditions prevalent during this period is the dissociation of 1,400 to 2,800 gigatonnes of methane from ocean clathrates 5 , 6 , resulting in a large negative carbon isotope excursion and severe carbonate dissolution in marine sediments. Possible triggering mechanisms for this event include crossing a threshold temperature as the Earth warmed gradually 7 , comet impact 8 , explosive volcanism 9 , 10 or ocean current reorganization and erosion at continental slopes 11 , whereas orbital forcing has been excluded 12 . Here we report a distinct carbonate-poor red clay layer in deep-sea cores from Walvis ridge 13 , which we term the Elmo horizon. Using orbital tuning, we estimate deposition of the Elmo horizon at about 2 million years after the Palaeocene–Eocene thermal maximum. The Elmo horizon has similar geochemical and biotic characteristics as the Palaeocene–Eocene thermal maximum, but of smaller magnitude. It is coincident with carbon isotope depletion events in other ocean basins, suggesting that it represents a second global thermal maximum. We show that both events correspond to maxima in the ∼405-kyr and ∼100-kyr eccentricity cycles that post-date prolonged minima in the 2.25-Myr eccentricity cycle, implying that they are indeed astronomically paced.

The Paleocene-Eocene thermal maximum (PETM) has been attributed to the rapid release of [approximately]2000 x 10⁹ metric tons of carbon in the form of methane. In theory, oxidation and ocean absorption of this carbon should have lowered deep-sea pH, thereby triggering a rapid (<10,000-year) shoaling of the calcite compensation depth (CCD), followed by gradual recovery. Here we present geochemical data from five new South Atlantic deep-sea sections that constrain the timing and extent of massive sea-floor carbonate dissolution coincident with the PETM. The sections, from between 2.7 and 4.8 kilometers water depth, are marked by a prominent clay layer, the character of which indicates that the CCD shoaled rapidly (<10,000 years) by more than 2 kilometers and recovered gradually (>100,000 years). These findings indicate that a large mass of carbon ([right-pointing double angle quotation mark]2000 x 10⁹ metric tons of carbon) dissolved in the ocean at the Paleocene-Eocene boundary and that permanent sequestration of this carbon occurred through silicate weathering feedback.

The early Eocene (56 to 48 million years ago) is inferred to have been the most recent time that Earth's atmospheric CO2 concentrations exceeded 1000 ppm. Global mean temperatures were also substantially warmer than those of the present day. As such, the study of early Eocene climate provides insight into how a super-warm Earth system behaves and offers an opportunity to evaluate climate models under conditions of high greenhouse gas forcing. The Deep Time Model Intercomparison Project (DeepMIP) is a systematic model–model and model–data intercomparison of three early Paleogene time slices: latest Paleocene, Paleocene–Eocene thermal maximum (PETM) and early Eocene climatic optimum (EECO). A previous article outlined the model experimental design for climate model simulations. In this article, we outline the methodologies to be used for the compilation and analysis of climate proxy data, primarily proxies for temperature and CO2. This paper establishes the protocols for a concerted and coordinated effort to compile the climate proxy records across a wide geographic range. The resulting climate “atlas” will be used to constrain and evaluate climate models for the three selected time intervals and provide insights into the mechanisms that control these warm climate states. We provide version 0.1 of this database, in anticipation that this will be expanded in subsequent publications.

The Cenozoic Arctic Ocean Little was known about the environmental history of the Arctic Ocean before the 2004 ACEX ocean drilling expedition. Now a 430-metre sea floor sediment core has been recovered and its analysis, reported this week, provides a 56-million-year climate record spanning the transition from a warm ‘greenhouse’ to a colder ‘icehouse’ world. Several key events are identified during the Cenozoic: surface waters during the Palaeocene/Eocene thermal maximum (55 million years ago) were much warmer than previous estimates; surface-water freshening confirms an intensified hydrological cycle about 49 million years ago; and the first ice-rafted debris occurred 45 million years ago, 35 million years earlier than was thought. The revised timings for the earliest Arctic cooling events coincide with those for Antarctica, supporting suggestions that global climate changed symmetrically about the poles. Identification of the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence shows that sea surface temperatures near the North Pole increased from roughly 18 degrees Celsius to over 23 degrees Celsius — such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. The Palaeocene/Eocene thermal maximum, ∼55 million years ago, was a brief period of widespread, extreme climatic warming 1 , 2 , 3 , that was associated with massive atmospheric greenhouse gas input 4 . Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition 5 . We show that sea surface temperatures near the North Pole increased from ∼18 °C to over 23 °C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations 6 , but the absolute polar temperatures that we derive before, during and after the event are more than 10 °C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms—perhaps polar stratospheric clouds 7 or hurricane-induced ocean mixing 8 —to amplify early Palaeogene polar temperatures.

It has long been hypothesized that climate can modify both the pattern and magnitude of erosion in mountainous landscapes, thereby controlling morphology, rates of deformation, and potentially modulating global carbon and nutrient cycles through weathering feedbacks. Although conceptually appealing, geologic evidence for a direct climatic control on erosion has remained ambiguous owing to a lack of high-resolution, long-term terrestrial records and suitable field sites. Here we provide direct terrestrial field evidence for long-term synchrony between erosion rates and Milankovitch-driven, 400-kyr eccentricity cycles using a Plio-Pleistocene cosmogenic radionuclide paleo-erosion rate record from the southern Central Andes. The observed climate-erosion coupling across multiple orbital cycles, when combined with results from the intermediate complexity climate model CLIMBER-2, are consistent with the hypothesis that relatively modest fluctuations in precipitation can cause synchronous and nonlinear responses in erosion rates as landscapes adjust to ever-evolving hydrologic boundary conditions imposed by oscillating climate regimes. Fisher et al. combine sediment geochemistry and climate modelling to reveal long-term synchrony between erosion rates and orbitally-driven climate oscillations in the tectonically-active southern Central Andes.