Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.

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Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present

[1] We present a 53-Myr stack (the “LR04” stack) of benthic δ18O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm This is the first benthic δ18O stack composed of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene We also present a new LR04 age model for the Pliocene-Pleistocene derived from tuning the δ18O stack to a simple ice model based on 21 June insolation at 65°N Stacked sedimentation rates provide additional age model constraints to prevent overtuning Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 53 Myr and in the precession band for more than half of the record The LR04 stack contains significantly more variance in benthic δ18O than previously published stacks of the late Pleistocene as the result of higher-resolution records, a better alignment technique, and a greater percentage of records from the Atlantic Finally, the relative phases of the stack's 41- and 23-kyr components suggest that the precession component of δ18O from 27–16 Ma is primarily a deep-water temperature signal and that the phase of δ18O precession response changed suddenly at 16 Ma

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A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

We present here a new solution for the astronomical computation of the insolation quantities on Earth spanning from -250 Myr to 250 Myr. This solution has been improved with respect to La93 (Laskar et al. [CITE]) by using a direct integration of the gravitational equations for the orbital motion, and by improving the dissipative contributions, in particular in the evolution of the Earth–Moon System. The orbital solution has been used for the calibration of the Neogene period (Lourens et al.  [CITE]), and is expected to be used for age calibrations of paleoclimatic data over 40 to 50 Myr, eventually over the full Palaeogene period (65 Myr) with caution. Beyond this time span, the chaotic evolution of the orbits prevents a precise determination of the Earth's motion. However, the most regular components of the orbital solution could still be used over a much longer time span, which is why we provide here the solution over 250 Myr. Over this time interval, the most striking feature of the obliquity solution, apart from a secular global increase due to tidal dissipation, is a strong decrease of about 0.38 degree in the next few millions of years, due to the crossing of the  resonance (Laskar et al. [CITE]). For the calibration of the Mesozoic time scale (about 65 to 250 Myr), we propose to use the term of largest amplitude in the eccentricity, related to , with a fixed frequency of /yr, corresponding to a period of 405 000 yr. The uncertainty of this time scale over 100 Myr should be about , and  over the full Mesozoic era.

/pdf/a-long-term-numerical-solution-for-the-insolation-quantities-4jg807k9xu.pdf

A long-term numerical solution for the insolation quantities of the Earth

We review Phanerozoic sea-level changes [543 million years ago (Ma) to the present] on various time scales and present a new sea-level record for the past 100 million years (My). Long-term sea level peaked at 100 ± 50 meters during the Cretaceous, implying that ocean-crust production rates were much lower than previously inferred. Sea level mirrors oxygen isotope variations, reflecting ice-volume change on the 10 4 - to 10 6 -year scale, but a link between oxygen isotope and sea level on the 10 7 -year scale must be due to temperature changes that we attribute to tectonically controlled carbon dioxide variations. Sea-level change has influenced phytoplankton evolution, ocean chemistry, and the loci of carbonate, organic carbon, and siliciclastic sediment burial. Over the past 100 My, sea-level changes reflect global climate evolution from a time of ephemeral Antarctic ice sheets (100 to 33 Ma), through a time of large ice sheets primarily in Antarctica (33 to 2.5 Ma), to a world with large Antarctic and large, variable Northern Hemisphere ice sheets (2.5 Ma to the present).

/pdf/the-phanerozoic-record-of-global-sea-level-change-14696qrujw.pdf

The Phanerozoic Record of Global Sea-Level Change

We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ~14.5 ka.

https://science.sciencemag.org/content/sci/325/5941/710.full.pdf

The Last Glacial Maximum.

https://physics.ucf.edu/~britt/Geophysics/Readings/G15-Evolution%20of%20obliquity.pdf

Long term evolution and chaotic diffusion of the insolation quantities of Mars

The solution for the precession and obliquity of the Earth, issued from the orbital solution La90 (Laskar 1990) is presented. This solution provides the necessary data for the computation of insolation at the surface of the Earth from −20 Myr to +10 Myr. When taking into account the tidal dissipation, this solution presents very good agreement with the 3Myr numerical integration of (Quinn et al. 1991). The main source of uncertainty in the computation of precession and obliquity of the Earth is found to arise from the changes of dynamical ellipticity of the Earth which can occur during an ice age. This change is especially important because of the existence of a resonant effect with a secular term of frequency s 6 − g 6 + g 5 resulting from the perturbations of Jupiter and Saturn

Orbital, precessional, and insolation quantities for the earth from -20 Myr to +10 Myr.

ACCORDING to Milankovitch theory1,2, the ice ages are related to variations of insolation in northern latitudes resulting from changes in the Earth's orbital and orientation parameters (precession, eccentricity and obliquity). Here we investigate the stability of the Earth's orientation for all possible values of the initial obliquity, by integrating the equations of precession of the Earth. We find a large chaotic zone which extends from 60° to 90° in obliquity. In its present state, the Earth avoids this chaotic zone and its obliquity is essentially stable, exhibiting only small variations of ± 1.3° around the mean value of 23.3°. But if the Moon were not present, the torque exerted on the Earth would be smaller, and the chaotic zone would then extend from nearly 0° up to about 85°. Thus, had the planet not acquired the Moon, large variations in obliquity resulting from its chaotic behaviour might have driven dramatic changes in climate. In this sense one might consider the Moon to act as a potential climate regulator for the Earth.

Stabilization of the Earth's obliquity by the Moon

As the obliquity of Mars is strongly chaotic[2, 5], it is not possible to give a solution for its evolution over more than a few million of years. Using the most recent data for the rotational state of Mars, and a new numerical integration of the Solar System, we provide here a precise solution for the evolution of Mars spin over 10 to 20 Myr. Over 250 Myr, we present a statistical study of its possible evolution, when considering the uncertainties in the present rotational state. Over much longer time span, reaching 5 Gyr, the chaotic diffusion prevails, and we have performed an extensive statistical analysis of the orbital and rotational evolution of Mars, relying on Laskar’s secular solution of the Solar System, based on more than 600 orbital and 200 000 obliquity solutions over 5 Gyr. The density function of the eccentricity and obliquity are explicited with simple analytical formulas. We found an averaged eccentricity of Mars over 5 Gyr of̄e = 0.0690 with standard deviation σe = 0.0299, while the averaged value of the obliquity is ε̄ = 37.62◦ with a standard deviation of σε = 13.82◦, and a maximal value of82.035◦. We find that the probability for Mars obliquity to have reached more than 60◦ in the past 1 Gyr is 63.0%, and89.3% in 3 Gyr. Over 4 Gyr, the position of Mars axis is given by a uniform distribution on a spherical cap limited by the obliquityεm̃ = 58.62◦, with the addition of a random noise allowing a slow diffusion beyond εm̃. We can also define a standard model of Mars insolation parameters over 4 Gyr with the most probable values for the eccentricity es = 0.067 andεs = 45.60◦ for the obliquity.

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F. Joutel

Papers

A long-term numerical solution for the insolation quantities of the Earth

Long term evolution and chaotic diffusion of the insolation quantities of Mars

Orbital, precessional, and insolation quantities for the earth from -20 Myr to +10 Myr.

Stabilization of the Earth's obliquity by the Moon

A New Astronomical Solution for the Long Term Evolution of the Insolation Quantities of Mars