Between about 55.5 and 52 million years ago, Earth experienced a series of sudden and extreme global warming events (hyperthermals) superimposed on a long-term warming trend. The first and largest of these events, the Palaeocene-Eocene Thermal Maximum (PETM), is characterized by a massive input of carbon, ocean acidification and an increase in global temperature of about 5 °C within a few thousand years. Although various explanations for the PETM have been proposed, a satisfactory model that accounts for the source, magnitude and timing of carbon release at the PETM and successive hyperthermals remains elusive. Here we use a new astronomically calibrated cyclostratigraphic record from central Italy to show that the Early Eocene hyperthermals occurred during orbits with a combination of high eccentricity and high obliquity. Corresponding climate-ecosystem-soil simulations accounting for rising concentrations of background greenhouse gases and orbital forcing show that the magnitude and timing of the PETM and subsequent hyperthermals can be explained by the orbitally triggered decomposition of soil organic carbon in circum-Arctic and Antarctic terrestrial permafrost. This massive carbon reservoir had the potential to repeatedly release thousands of petagrams (10(15) grams) of carbon to the atmosphere-ocean system, once a long-term warming threshold had been reached just before the PETM. Replenishment of permafrost soil carbon stocks following peak warming probably contributed to the rapid recovery from each event, while providing a sensitive carbon reservoir for the next hyperthermal. As background temperatures continued to rise following the PETM, the areal extent of permafrost steadily declined, resulting in an incrementally smaller available carbon pool and smaller hyperthermals at each successive orbital forcing maximum. A mechanism linking Earth's orbital properties with release of soil carbon from permafrost provides a unifying model accounting for the salient features of the hyperthermals.

About 34 million years ago, Earth's climate cooled and an ice sheet formed on Antarctica as atmospheric carbon dioxide (CO2) fell below ∼750 parts per million (ppm). Sedimentary cycles from a drill core in the western Ross Sea provide direct evidence of orbitally controlled glacial cycles between 34 million and 31 million years ago. Initially, under atmospheric CO2 levels of >600 ppm, a smaller Antarctic Ice Sheet (AIS), restricted to the terrestrial continent, was highly responsive to local insolation forcing. A more stable, continental-scale ice sheet calving at the coastline did not form until ∼32.8 million years ago, coincident with the earliest time that atmospheric CO2 levels fell below ∼600 ppm. Our results provide insight into the potential of the AIS for threshold behavior and have implications for its sensitivity to atmospheric CO2 concentrations above present-day levels

At least since the middle Miocene (∼16 Ma), subduction erosion has been the dominant process controlling the tectonic evolution of the Pacific margin of Costa Rica. Ocean Drilling Program Site 1042 recovered 16.5 Ma nearshore sediment at ∼3.9 km depth, ∼7 km landward of the trench axis. The overlying Miocene to Quaternary sediment contains benthic foraminifera documenting margin subsidence from upper bathyal (∼200 m) to abyssal (∼2000 m) depth. The rate of subsidence was low during the early to middle Miocene but increased sharply in the late Miocene‐early Pliocene (5–6.5 Ma) and at the Pliocene‐Pleistocene boundary (2.4 Ma). Foraminifera data, bedding dip, and the geometry of slope sediment indicate that tilting of the forearc occurred coincident with the onset of rapid late Miocene subsidence. Seismic images show that normal faulting is widespread across the continental slope; however, extension by faulting only accounts for a minor amount of the post‐6.5 Ma subsidence. Basal tectonic erosion is invoked to explain the subsidence. The short‐term rate of removal of rock from the forearc is about 107–123 km3 Myr−1 km−1. Mass removal is a nonsteady state process affecting the chemical balance of the arc: the ocean sediment input, with the short‐term erosion rate, is a factor of 10 smaller than the eroded mass input. The low 10Be concentration in the volcanic arc of Costa Rica could be explained by dilution with eroded material. The late Miocene onset of rapid subsidence is coeval with the arrival of the Cocos Ridge at the subduction zone. The underthrusting of thick and thermally younger ocean crust decreased the subduction angle of the slab along a large segment of the margin and changed the dynamic equilibrium of the margin taper. This process may have induced the increase in the rate of subduction erosion and thus the recycling of crustal material to the mantle.

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Antarctic glaciation was abruptly established during the EoceneOligocene transition (EOT) in two ∼200-kyr-spaced phases between 34.0 Myr and 33.5 Myr ago, as recorded by the oxygen isotope composition of marine biogenic calcite 3,4,9 (δ 18 O). The first shift (EOT-1) is believed to represent a transient glaciation [10][11][12] , later followed by the establishment of a continental-scale ice sheet across the Oligocene isotope event-1 33.7 Myr ago; ref. 4). This is consistent with Northern Hemisphere ocean-sediment cores, which indicate a 60 ± 20 m relative sea level (rsl) fall across the EOT (refs 13-15). Under isostatic equilibrium conditions, the observed regression nearly corresponds to the rsl drop expected from glacioeustasy 6 . Along the Antarctic margins, however, the rsl changes accompanying the glaciation are expected to strongly deviate from the eustatic, because of large crustal and gravitational perturbations induced by the ice sheet on the deformable Earth 6 . Furthermore, strong regional rsl change gradients would be maintained long after the ice-sheet stabilization, by the flexure of lithosphere 16 . This necessitates self-consistent physical models for rsl change to compare near-field sedimentary sequences with far-field ice-sheet volume estimates.Here we evaluate the regionally varying rsl changes in response to glacial expansion and their effects on glaciomarine facies 17 around East Antarctica with a numerical model for glacial-hydro isostatic adjustment (GIA). Our model is based on the solution of the gravitationally self-consistent sea-level equation 7,8 for a prescribed Antarctic ice-sheet chronology 18 and a linear viscoelastic rheology for the solid Earth (Methods and Supplementary Information). We compare the model results with sedimentary records from the Wilkes Land Margin (Fig. 1a) The ice-sheet model employed in our GIA computations is characterized by a 2.2 Myr growth phase caused by a combination of decreasing CO 2 and orbital forcing that drives summer temperatures below the threshold for glaciation 18 but uses a new reconstruction of Antarctic topography 24 at EOT time (Methods). The ice-sheet volume at the glacial maximum corresponds to ∼69.0 m of equivalent sea level in this model, ∼14.0 m more than previous modelling results 18 , probably owing to larger Antarctic land surface 24 .We run a reference simulation (Fig. 1a-d) for an Earth model defined by an elastic lithosphere thickness (LT) of 100 km, and by a viscosity profile (RVP) that is discretized into a lower mantle (LM), a transition zone (TZ) and an upper mantle (UM) and is characterized by viscosities of 1.0 × 10 22 , 5.0 × 10 20 and 2.5 × 10 20 Pa s respectively (RVP-100 km-LT simulation). To evaluate how the GIA signal varies according to the mantle viscosity, we perform simulations for an ensemble of viscosity profiles (EVPs) characterized by viscosities varying in the range of