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Jurassic greenhouse ice-sheet fluctuations sensitive to atmospheric CO2 dynamics

Nature Geoscience volume 15, pages 54–59 (2022)Cite this article

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Abstract

Sea-level proxy records and palaeoclimate models suggest that globally elevated temperatures during the greenhouse climate of the Jurassic were punctuated by poorly understood, transient icehouse events. Here we investigate atmospheric CO2–ice-sheet dynamics as a case study from the Early Jurassic Pliensbachian–Toarcian transition (182.7–180.6 million years ago). Applying the C3 CO2 plant proxy to previously published fossil wood data reveals that CO2 levels during this transition ranged from 250 to 400 ppm. Previously published belemnite δ18O values suggest that sea-level low stands were equivalent to ice volumes up to two-thirds of Antarctica today. Beginning with the Toarcian ocean anoxic event, these ice sheets largely melted when CO2 reached sustained concentrations of ~500–700 ppm. Compared with the Cenozoic East Antarctic Ice Sheet and ice sheets modelled for the Middle Jurassic, Early Jurassic ice sheets exhibit minimal lags (hysteresis) between warming and cooling limbs, suggesting they were thin and located at lower latitudes and elevations with a higher temperature sensitivity to melting. These sensitivities of ice volume to CO2 provide additional constraints on climate models for application to warming transitions in both the past and future.

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Fig. 1: Early Jurassic geographic setting for the icehouse–greenhouse transition.
Fig. 2: Isotopic composition of carbon reservoirs from the Western Tethys region.
Fig. 3: Atmospheric CO2 concentration and ice-sheet indicators from the study area.
Fig. 4: Atmospheric CO2 versus sea level from Early Jurassic proxy data and from Mesozoic and Cenozoic climate models.

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Data availability

All values from wood and bulk carbonate δ13C to compute atmospheric CO2 concentrations and all values from the δ18O of belemnites for sea-level estimates were compiled from other sources as discussed in the main text and Methods section. Readers may contact L.N. if additional information is needed from this manuscript.

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Acknowledgements

We thank H. Jahren for comments that improved the clarity of the manuscript. S. Hesselbo kindly provided his previously published stable carbon and oxygen data from the Peniche study area.

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Authors and Affiliations

  1. Department of Geosciences, Baylor University, Waco, TX, USA

    Lee Nordt

  2. Department of Geological Sciences, University of Texas, Austin, TX, USA

    Daniel Breecker

  3. Department of Biology, Baylor University, Waco, TX, USA

    Joseph White

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Contributions

L.N. and D.B. designed the study. J.W. helped provide the underlying assumptions and plant physiological interpretations of the C3 plant CO2 proxy. L.N. wrote the main part of the paper in consultation with D.B. and J.W.

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Correspondence to Lee Nordt.

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Nature Geoscience thanks Michaël Hermoso and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: James Super.

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Extended data

Extended Data Fig. 1 δ18O belemnite values from the Western Tethys.

Note general congruence of data prior to the T-CIE, and greater scattering during and after. Study areas in the northern Tethys (Bulgaria72; Yorkshire, UK, plus symbol73; Yorkshire, UK, gray square74; Yorkshire, UK, orange circle75; S. France76; Belgium77; Germany78; and S. France77) were likely influenced by freshwater lowering δ18O values during the T-CIE, where because of anoxia, belemnites may have migrated to warmer surface habitats further lowering isotopic values50. Scattered δ18O values after the T-CIE are attributed to the evolution of new belemnite species adapted to different habitats in the water column50. Data from Portugal and Spain (N. Spain, gray circle23; N. Spain, blue circle22; N. Spain, red circle24; Portugal, green circles19) were influenced less by freshwater and anoxia, and used for the sea level computations.

Extended Data Fig. 2 Curve relating eustatic sea level to ice volume.

(modified from ref. 79,80,81,82). Total pre-industrial ice volume (Antarctica-AnIS + Greenland-GrIS) is ~ 34 M km3 with a sea level equivalent of 64 m (LGM – Last Glacial Maximum). Early Jurassic Atmospheric CO2 is only that from the late Pliensbachian.

Extended Data Table 1 Modern carbon isotopes of Cuprussaceae wood and bark
Full size table
Extended Data Table 2 Uncertainty calculation for the C3 Plant CO2 Proxy (CPC)
Full size table
Extended Data Table 3 Early Jurassic valley incision rates and glacio-eustasy estimates
Full size table

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Nordt, L., Breecker, D. & White, J. Jurassic greenhouse ice-sheet fluctuations sensitive to atmospheric CO2 dynamics. Nat. Geosci. 15, 54–59 (2022). https://doi.org/10.1038/s41561-021-00858-2

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