Plume magmatism and continental breakup led to the opening of the northeast Atlantic Ocean during the globally warm early Cenozoic. This warmth culminated in a transient (170 thousand year, kyr) hyperthermal event associated with a large, if poorly constrained, emission of carbon called the Palaeocene–Eocene Thermal Maximum (PETM) 56 million years ago (Ma). Methane from hydrothermal vents in the coeval North Atlantic Igneous Province (NAIP) has been proposed as the trigger, though isotopic constraints from deep sea sediments have instead implicated direct volcanic carbon dioxide (CO2) emissions. Here we calculate that background levels of volcanic outgassing from mid-ocean ridges and large igneous provinces yield only one-fifth of the carbon required to trigger the hyperthermal. However, geochemical analyses of volcanic sequences spanning the rift-to-drift phase of the NAIP indicate a sudden ~220 kyr-long intensification of magmatic activity coincident with the PETM. This was likely driven by thinning and enhanced decompression melting of the sub-continental lithospheric mantle, which critically contained a high proportion of carbon-rich metasomatic carbonates. Melting models and coupled tectonic–geochemical simulations indicate that >104 gigatons of subcrustal carbon was mobilized into the ocean and atmosphere sufficiently rapidly to explain the scale and pace of the PETM.
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All data generated or analysed during this study are provided in the online version of this article (Supplementary Data File S1) and in Extended Data Tables 1–6. The map in Fig. 1b was plotted with open source plate tectonic application software GPlates (https://www.gplates.org/; licensed for distribution under a GNU General Public License). Any new geochemical data generated in this study are also available to download via the figshare repository at: https://doi.org/10.6084/m9.figshare.19732948. Source data are provided with this paper.
More details on the computational methods and tools used for this study are available from the corresponding author upon reasonable request.
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This study was supported by a Natural Environment Research Council (NERC) grant (NE/R004978/1) to T.M.G., which also supported T.K.H. T.M.G. and T.K.H. received funding from The Alan Turing Institute under the EPSRC grant EP/N510129/1. J.L. was supported by NERC grant NE/K00543X/1 awarded to M.R.P. and T.M.G. T.M.G. acknowledges the Distinguished Geologists’ Memorial Fund of the Geological Society of London to sample the Rockall tuffs at the International Ocean Discovery Program (IODP) Bremen Core Repository (BCR). R.N.M. was supported by a National Natural Science Foundation of China grant (41888101) and a Key Research Programme of the Institute of Geology & Geophysics, Chinese Academy of Sciences (CAS), grant (number IGGCAS-201905). A.S.M. was supported by the Deep Carbon Observatory, Richard Lounsbery Foundation and MCSA Fellowship NEOEARTH, project 893615. We are grateful to the staff of the BCR, especially W. Hale, for their assistance, and to M. Cooper, A. Michalik and A. Milton (University of Southampton) for laboratory assistance. We thank G. Hincks for illustrating the Late Palaeocene northeast Atlantic ridge (Fig. 4).
The authors declare no competing interests.
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Extended Data Fig. 1 Schematic stratigraphic log of Palaeocene–Eocene volcanic and sedimentary lithofacies at DSDP Leg 81 Site 555, and the composition of tuff layers.
The corresponding plots show the major-element composition, and Mg#, of tuff layers, shown as horizontal red lines (and labelled by lithology; see also Extended Data Fig. 3a) on the log. The Mg# of a number of basalt lavas and tuffs from Harrison and Merriman99 are also shown as filled grey symbols.
Total alkali-silica (TAS) diagram (after ref. 101) showing the composition of volcanic tuffs of PETM age (approximately 700-600 mbsl; see Extended Data Fig. 2), in addition to Danish ashes of the ‘negative series’23. b, Nb versus Zr of tuffs from Site 555, shown alongside tuffs of the Danish Ash Series23 and Balder Formation in the North Sea102, and lavas from the Rockall/Hatton Bank103. The fields shown for OIB, N-MORB and Iceland rift-zones are from ref. 104. c, Incompatible element patterns of Rockall tuffs from the upper section (700-600 mbsl) normalized to primitive mantle105. The corresponding depths in the core are provided in Extended Data Table 3. For comparison, some Danish ashes (negative series) are also shown23.
Extended Data Fig. 4 Input distributions for sampled variables used in carbon outgassing simulations.
a, Fraction of CO2 present in mid-ocean ridge basalts and those of large igneous provinces (LIPs); b, Fraction of CO2 lost from the ocean crust via degassing at mid-ocean ridges; c, Fraction of CO2 lost from LIP basalt eruptions; d, Thickness of the sub-continental lithospheric mantle (SCLM); e, Width of the SCLM melting zone beneath the mid-ocean ridge system; f, Fraction of CO2 present in the SCLM. Note that the red line denotes the mean. See the Methods for further information on these variables.
143Nd/144Nd and associated εNd measurements of tuffs, lavas and hyaloclastites from DSDP Leg 81 Site 555. The sample ID number includes the site number (555), core box reference (e.g., 65-1), and the depth from the top of a given core (in cm). The 143Nd/144Nd ratios and associated εNd values are corrected to an age of 55 Ma. Also provided are published 143Nd/144Nd and associated εNd measurements from Site 555 lavas73. Errors on discrete measurements are 2 and 1 standard error (SE).
Trace element compositions by ICP-MS of selected PETM-age tuffs from Site 555. The associated recoveries of trace elements from standard reference materials are provided in Supplementary Table 2.
Distribution coefficients (D) used in the construction of Fig. 2e. Note that n = number of individual values of D.
Description of inputs used in modelling of CO2 fluxes from mid-ocean ridges, large igneous provinces (LIPs), and melting of the sub-continental lithospheric mantle (SCLM). See the Methods for further details and model description.
Description of variables used in the carbon flux simulations (Fig. 3) given best estimates of the minimum, maximum and mean for each variable, based on data and observations (see Methods). We fixed the standard deviation, SD = 0.2 x range. See the Methods for further details and model description.
Supplementary Tables 1–2.
143Nd/144Nd and associated ϵNd measurements of tuffs, lavas and hyaloclastites from DSDP Leg 81 Site 555. The sample ID number includes the site number (555), core box reference (for example, 65-1) and the depth from the top of a given core (in cm). The 143Nd/144Nd ratios and associated ϵNd values are corrected to an age of 55 Ma. Also provided are published 143Nd/144Nd and associated ϵNd measurements from Site 555 lavas73. Errors on discrete measurements are 2 and 1 standard error.
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Gernon, T.M., Barr, R., Fitton, J.G. et al. Transient mobilization of subcrustal carbon coincident with Palaeocene–Eocene Thermal Maximum. Nat. Geosci. 15, 573–579 (2022). https://doi.org/10.1038/s41561-022-00967-6