With the aim to learn about our future, researchers from CNRS at Géosciences Rennes together with international colleagues led by Niels Meijer in the the Senckenberg Biodiversity and Climate Research Center, explore warm periods of the Earth's history.
In their study, published Monday January 29 in the journal "Nature Geoscience", they show that an increase in greenhouse gases in the atmosphere 56 million years ago led to an abrupt increase in precipitation and vegetation over Central Asia.
Today, vast treeless steppes characterize the landscape of Central Asia. The sparse rainfall that reaches the Asian interior is mostly caused by monsoon events in summer or the westerly winds of the mid-latitudes in winter and spring. "Such grassland steppes are particularly susceptible to the consequences of changes in temperature and precipitation - with all the consequences for their inhabitants such as the Saiga antelope or the endangered Przewalski's horse," explains Dr. Niels Meijer and continues: "One of the great uncertainties of global climate change is how the Asian monsoon and the regions in Central Asia shaped by it will react to future changes in climate."
Two studied fossil pollen grains: Left Ephedra, typical bush of the Asian Steppe oft he Paleogene period. Right Juglandaceae, an ancester of the walnut tree that strived during the greening event 56 million years ago in Asia. Crédits : Hanna van den Hil and Julia Gravendyck.
As part of an international research team led by Guillaume Dupont-Nivet working in the region since over two decades, Niels Meijer who worked on his PhD in Géosciences Rennes, recently focused on the hot early Paleogene period where he identified an hyperthermal event of extreme warming precisely dated 56 million years ago.
In order to reconstruct the precipitation patterns of that time, the researchers combined their expertise to develop an innovative multi-proxy approach in which they combined fossil pollen and spores with Prof. Carina Hoorn (Univ. Amsterdam) as well as geochemical data from fossil soils with Alexis Licht (CNRS-CEREGE). "During the hyperthermal event we studied, precipitation temporarily doubled due to the higher temperatures and the regional steppe was replaced by a forest landscape," Meijer describes the results and adds: "More importantly, however, we were able to use geochemical data to show that the soils dried out in winter, meaning that, contrary to expectations, most of the precipitation fell during the summer period - comparable to the modern monsoon."
Scientists attribute the unusually wet period during the "Paleocene/Eocene temperature maximum" to a far inland expansion of precipitation - so-called proto-monsoons. The global warm phase at that time was associated with a greatly increased input of greenhouse gases into the Earth's atmosphere and oceans. During this period, the global temperature rose by an average of six degrees Celsius within a few thousand years.
"The abrupt greening of the Central Asian steppe desert resulting from the monsoon climate probably also enabled the spread of new mammal species and may also have played a role in the feedbacks of the global carbon cycle", summarizes Meijer and concludes: "Our work provides paleoclimatic evidence for an abrupt and non-linear response of Asian monsoons to extreme greenhouse conditions. Although the seas and mountains of Asia 56 million years ago were very different from today, the data highlight the potential for abrupt changes in Central Asian precipitation and ecosystems under future global warming. Current warming burdens with extreme temperature and increased drought Central Asian steppe and its fragile flora and fauna, which are already endangered by anthropogenic land use. Yet more dramatic abrupt changes are expected if temperatures continue to increase".
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Extreme Eocene warmth drove proto-monsoons and desert greening far into the Asian interior
Niels Meijer1, Alexis Licht2, Amber Woutersen3, Carina Hoorn3, Faez Robin-Champigneul4, Alexander Rohrmann5, Mattia Tagliavento6, Julia Brugger1, Fanni D. Kelemen7, Andrew Schauer8, Micheal Hren9, Aijun Sun10-12, Jens Fiebig6, Andreas Mulch1,6, Guillaume Dupont-Nivet13,14
1) Senckenberg Biodiversity and Climate Research Centre (SBiK-F), Frankfurt am Main, Germany.
2) CNRS, IRD, INRAE, CEREGE, Aix Marseille University, Aix-en-Provence, France.
3) Department of Ecosystem and Landscape Dynamics (ELD), Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Amsterdam, the Netherlands.
4) Maastricht University, Faculty of Science and Engineering, Maastricht Science Programme, Maastricht, the Netherlands.
5) Institute of Geological Sciences, Freie Universität Berlin, Berlin, Germany
6) Goethe University Frankfurt, Institute of Geosciences, Frankfurt am Main, Germany.
7) Goethe University Frankfurt, Institute for Atmospheric and Environmental Sciences, Frankfurt am Main, Germany.
8) Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA.
9) Department of Earth Sciences, University of Connecticut, Storrs, CT, USA
10) Key Laboratory of Western China's Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, China.
11) Key Laboratory of Desert and Desertification, Northwest Institute of Eco-Environment
and Resources, Chinese Academy of Sciences, Lanzhou, China.
12) University of Chinese Academy of Sciences, Beijing, China.
13) Géosciences Rennes-UMR CNRS 6118, Univ Rennes, CNRS, Rennes, France.
Senckenberg Biodiversity and Climate Research Center
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IBED- University of Amsterdam
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