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Modelling the effect of variations in the Earth’s orbit on climates and biomes during the major Eocene-Oligocene climate transition

By comparing the results of climate simulations from the Eocene and Oligocene eras, subjected to different configurations of the Earth's orbit, a study published in the journal Science Advances, shows the role of these orbital variations in ancient climate variability and their influence on plant cover. Scientists from IPGP, CEREGE, CNRS, Université de Paris and their colleagues identify major environmental changes in tropical zones and along certain dispersal corridors, which may have had an impact on the migration of fauna at the time.

Modelling the effect of variations in the Earth’s orbit on climates and biomes during the major Eocene-Oligocene climate transition

Publication date: 28/10/2021

Press, Research

Related teams :
Paleomagnetism

Related themes : Origins

Around 34 million years ago, the Earth shifted from a warm Eocene climate to a much colder one, leading to the establishment of a perennial polar cap in Antarctica during the Oligocene. Recent studies, based on sedimentary records with very high temporal resolution, show that this global climatic transition was punctuated by rapid local climatic oscillations of the order of a few tens of thousands of years, linked to periodic changes in the Earth’s orbit. These orbital variations, due to the Earth’s interaction with the other planets in the solar system, modify the distribution of insolation received at the Earth’s surface.

Alternating layers of sedimentary archives from the Eocene-Oligocene period, China (© N. Meijer)

This has repercussions on atmospheric and oceanic circulations, and therefore on the types of climate to which different regions of the globe are subjected. Today, these orbital variations are involved in the alternation between glacial and interglacial cycles, for example.

But the precise reconstruction of the climates of this Eocene-Oligocene transition period is complex. Indeed, for such a long time ago, the various paleo-environmental indicators available are often dated with too little precision to account for these “rapid” terrestrial orbital changes on a geological timescale. Climate reconstructions are currently based on compilations of fossils, particularly plant fossils, representing an “average” and sometimes contradictory view of the climates considered.

In a study published on October 22, 2021 in the journal Science Advances, and led by scientists from the Institut de Physique du Globe de Paris, Université de Paris, CEREGE (CNRS, Aix Marseille Université), LSCE (CNRS, Université Paris-Saclay), the Universities of Stockholm, Amsterdam, Rennes and Potsdam, they sought to assess the extent to which the failure of models and botanical compilations to take account of orbital variations biases the representation of paleoclimates of this era.

Using French models recently adapted to simulate ancient climates (the IPSL-CM5A2 earth-system model and the ORCHIDEE continental surface model), this study carried out a wide range of simulations testing different orbital configurations (changes in precession, obliquity and eccentricity parameters). These simulations enabled us to significantly improve the correspondence with botanical data available at the time, and to map the regions of the globe where vegetation was most sensitive to orbital modifications for the two periods under consideration.

These results show that, for a constant CO2 level, vegetation in the tropics could have oscillated between conditions of tropical rainforest and open shrub forest, or even desert. These local but major environmental changes are linked to the impact of precession, and to a lesser extent obliquity, on inter-tropical temperature gradients, enabling the intermittent establishment of a monsoon-type climate.

The international team also demonstrates that the combined impact of CO2 depletion and obliquity variations induces a fragmentation of bioclimatic corridors in Anatolia and Siberia. The biogeographical implications of these results are significant, as these migratory corridors linking Europe and Asia were decisive in the migration of Asian fauna towards Western Europe during the faunal dispersal event known as the Great Divide.

 

Ref: D. Tardif, A. Toumoulin, F. Fluteau, Y. Donnadieu, G. Le Hir, N. Barbolini, A. Licht, J.-B. Ladant, P. Sepulchre, N. Viovy, C. Hoorn, G. Dupont-Nivet, Orbital variations as a major driver of climate and biome distribution during the greenhouse to icehouse transition. Sci. Adv. 7, eabh2819 (2021)

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