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Proto-monsoon rainfall and greening in Central Asia due to extreme early Eocene warmth

Nature Geoscience volume 17, pages 158–164 (2024)Cite this article

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Abstract

The dry continental interior of Asia has remained arid throughout most of its geological history, yet the future of this unique ecosystem remains unclear. Here we use palynological and isotopic records to track vegetation and moisture throughout the warm early Eocene (57 to 44 million years ago) as an analogue for extreme atmospheric CO2 scenarios. We show that rainfall temporarily doubled and replaced the regional steppe by forested ecosystems. By reconstructing the season of pedogenic carbonate growth, we constrain the soil hydrologic regime and show that most of this rainfall occurred during the summer season. This humid event is therefore attributed to an inland expansion of monsoonal moisture following the massive greenhouse gas release of the Palaeocene–Eocene Thermal Maximum as identified by a negative carbon isotope excursion. The resulting abrupt greening of the Central Asian steppe-desert would have enabled mammal dispersal and could have played a role in carbon cycle feedbacks by enhancing soil organic carbon burial and silicate weathering. These extreme Eocene proto-monsoons, albeit different from the topography-driven Asian monsoon today, highlight the potential for abrupt shifts in Central Asian rainfall and ecosystems under future global warming.

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Fig. 1: Geological setting showing hypothesized Eocene hydroclimates in Asia, including a subtropical arid belt, westerly or monsoonal domain.
Fig. 2: Palaeo-environmental reconstruction showing temperate forests replacing steppe shrubs during a negative CIE.
Fig. 3: Proxy comparison with simulated surface air temperature and precipitation in the Eocene Xining Basin.
Fig. 4: Distribution of monsoonal domains in climate model simulations.

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Data availability

Palynology counts, TOC and bulk organic δ13C, n-alkane δ13C and δ2H, XRD bulk mineralogy and carbonate δ13C, δ18O and Δ47 are available at https://doi.org/10.1594/PANGAEA.962894. The DeepMIP pre-industrial and Eocene climate model simulations are available by following the instructions at https://www.deepmip.org/data-eocene/. The weather station data from Xining and Tashkent are available at https://www.ncei.noaa.gov/products/wmo-climate-normals.

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Acknowledgements

This study was funded by an ERC consolidator grant (MAGIC 649081 to G.D.-N.) and through the VeWA consortium by the LOEWE programme of the Hessen Ministry of Higher Education, Research and the Arts, Germany. We thank R. Petschick for help with the XRD analyses as well as J. McCormack and A. Davies for suggestions on the formation of dolomite. We acknowledge R. Erkens and the following students from Maastricht University for their help in exploring the palynological samples: H. del Marmol, L. Sauerschnig, K. de Jong, A. Villagrasa, L. Licht, H. de Schrevel and B. Diana. We also acknowledge H. van den Hill (University of Amsterdam) and J. Gravendeyk (University of Bonn) for extensive sporomorph documentation. We thank H. Meyer for kindly providing organic stable isotope analyses and A. Ballian, S. Hofmann and S. Anderson for assistance with stable and clumped isotope analyses. We also thank C. Günter and U. Altenberger for their help with the SEM and CL. We are grateful to N. Barbolini, X.-J. Liu, X. Wu, Z. Wu, M. Xiao and Y. Zhang for their support with collecting the samples. We also acknowledge the efforts of the DeepMIP community and are thankful for the available climate model simulation data.

Author information

Authors and Affiliations

  1. Senckenberg Biodiversity and Climate Research Centre (SBiK-F), Frankfurt am Main, Germany

    Niels Meijer, Julia Brugger & Andreas Mulch

  2. CNRS, IRD, INRAE, CEREGE, Aix Marseille University, Aix-en-Provence, France

    Alexis Licht

  3. Department of Ecosystem and Landscape Dynamics (ELD), Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Amsterdam, the Netherlands

    Amber Woutersen & Carina Hoorn

  4. Faculty of Science and Engineering, Maastricht Science Programme, Maastricht University, Maastricht, the Netherlands

    Faez Robin-Champigneul

  5. Institute of Geological Sciences, Freie Universität Berlin, Berlin, Germany

    Alexander Rohrmann

  6. Institute of Geosciences, Goethe University Frankfurt, Frankfurt am Main, Germany

    Mattia Tagliavento, Jens Fiebig & Andreas Mulch

  7. Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Frankfurt am Main, Germany

    Fanni D. Kelemen

  8. Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA

    Andrew J. Schauer

  9. Department of Earth Sciences, University of Connecticut, Storrs, CT, USA

    Micheal T. Hren

  10. Key Laboratory of Western China’s Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, China

    Aijun Sun

  11. Key Laboratory of Desert and Desertification, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China

    Aijun Sun

  12. University of Chinese Academy of Sciences, Beijing, China

    Aijun Sun

  13. Géosciences Rennes-UMR CNRS 6118, Univ Rennes, CNRS, Rennes, France

    Guillaume Dupont-Nivet

  14. GFZ German Research Centre for Geosciences, Potsdam, Germany

    Guillaume Dupont-Nivet

Authors
  1. Niels Meijer
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  2. Alexis Licht
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Contributions

N.M., A.L. and G.D.-N. designed the study. N.M., A.L., A.W., A.R., A.S. and G.D.-N. conducted the fieldwork and collected the samples. N.M. performed the XRD and petrographic analyses. A.W., F.R.-C. and C.H. prepared and analysed the palynological samples. A.R. and M.T.H. performed the n-alkane analyses. N.M., A.L., A.J.S. and A.M. conducted the stable isotope analyses. N.M., M.T. and J.F. performed the clumped isotope analyses. J.B. and F.D.K. analysed and plotted the climate model simulation data. N.M. wrote the paper with major input from A.L., G.D.-N. and A.M. All co-authors contributed to interpreting the data and writing the paper.

Corresponding author

Correspondence to Niels Meijer.

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The authors declare no competing interests.

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Nature Geoscience thanks the anonymous reviewers for their contribution to the peer review of this work. Primary Handling Editor: James Super, in collaboration with the Nature Geoscience team.

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Extended data

Extended Data Fig. 1 Pre-industrial control simulations and weather station data from the Xining Basin.

Weather station precipitation data (https://www.ncei.noaa.gov/products/wmo-climate-normals) and pre-industrial control simulations of A) temperature and B) precipitation in the Xining Basin using the DeepMIP climate model ensemble.

Extended Data Fig. 2 Carbon isotope values versus TOC.

Soil organic matter δ13C versus Total Organic Content (TOC).

Extended Data Fig. 3 XRD.

XRD diffractograms showing the dominant peaks and bulk mineralogy of selected samples including: a dolomite bed (CjC9, as shown on Extended Data Fig. 4G; composite position: -37.1 m), a calcareous mudrock (16Cj237.5; composite position: 193 m), a calcareous mudrock from the CIE interval (18Ld-16; composite position: -31m) and a dolomitic mudrock (15Cj79; composite position: 54 m). The samples 16Cj237.5 and 18Ld-16 were used for stable and clumped isotope analyses.

Extended Data Fig. 4 Microscope and field photographs.

A) and B) Cross-polarized and cathodoluminescence image of a mudrock sample with vadose-grown calcite cement (18LD-15; Ledu section; -15 meter-level) showing silt-sized matrix with dispersed organic matter, dull luminescent micrite and some luminescent microsparite and sparite. Plane-polarized images of pedogenic nodules showing: C) Micrite matrix with floating detrital grains in 18LD+4nodB (Ledu section; 12.3 meter-level). D) Floating detrital grains with isopachous microsparite to sparite rim and micritic matrix in 18LDconglonod (Ledu section; -60 meter-level). Massive red dolomitic mudrock samples showing rhombohedral dolomite crystals in E) plane-polarized light (15CJ-111_75; Caijia section 131.25 meter-level) and F) SEM (15CJ-112_5; Caijia section; 132 meter-level). G) Greenish lacustrine mudrocks interbedded with massive dolomite beds (Caijia section; 75 meter-level), hammer for scale. H) Dolomite-filled burrow (Caijia section; 93 meter-level).

Extended Data Fig. 5 Carbonate and plant wax stable isotopes.

Stable isotope record (δ18Ocarb and δ13Ccarb) of the vadose-grown and pedogenic carbonates and δ2Hwax values of plant waxes. δ18O values of the soil water (δ18Owater) are reconstructed using the Δ47-derived temperatures. Modern-day δ18Owater values of the summer monsoon and wintertime westerlies are shown57.

Extended Data Fig. 6 Carbonate stable isotope biplot.

Stable isotope biplot of the studied calcites.

Extended Data Fig. 7 Monsoonal domains in DeepMIP climate model simulations.

Distribution of monsoonal domains in the pre-industrial control and 3x pCO2 Eocene DeepMIP simulations. Summer (MJJAS) minus winter precipitation (NDJFM) is used as a metric and regions where this difference is > 2.5 mm/day are considered monsoonal44. Red dot indicates the location of the Xining Basin.

Extended Data Fig. 8 Timing of Xining CIE compared with CENOGRID and astronomical solutions.

CENOGRID showing the evolution of benthic foraminifera stable isotope values4. The δ18O values show peak warmth of the EECO and the δ13C values show several hyperthermal events characterized by negative CIE’s. The astronomical solutions76 show the evolution of the eccentricity of Earth’s orbit. The radiometric ages bracketing the CIE in the Xining Basin are indicated.

Extended Data Fig. 9 Summer sea-level atmospheric pressure anomalies in DeepMIP climate model simulations.

Sea-level atmospheric pressure anomalies during summer (JJA) in the 6x pCO2 Eocene and the pre-industrial control simulations of the DeepMIP ensemble. Red dot indicates the location of the Xining Basin.

Supplementary information

Supplementary Data 1

Palynological counts.

Supplementary Data 2

Bulk organic data.

Supplementary Data 3

n-Alkanes.

Supplementary Data 4

MAP reconstruction.

Supplementary Data 5

XRD.

Supplementary Data 6

Carbonate stable isotope data and summary of clumped isotopes.

Supplementary Data 7

Clumped isotope data.

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Meijer, N., Licht, A., Woutersen, A. et al. Proto-monsoon rainfall and greening in Central Asia due to extreme early Eocene warmth. Nat. Geosci. 17, 158–164 (2024). https://doi.org/10.1038/s41561-023-01371-4

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