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Link to original content: https://doi.org/10.1038/nature23646
Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum | Nature
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Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum

Nature volume 548, pages 573–577 (2017)Cite this article

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Abstract

The Palaeocene–Eocene Thermal Maximum1,2 (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates3. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming1,3,4,5. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data—a proxy for seawater pH—that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event6,7. We find strong evidence for a much larger (more than 10,000 petagrams)—and, on average, isotopically heavier—carbon source than considered previously8,9. This leads us to identify volcanism associated with the North Atlantic Igneous Province10,11, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system12.

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Figure 1: Stable-isotope data from DSDP Site 401.
Figure 2: δ13C evolution and pH reconstruction based on analysis of boron isotopes in M. subbotinae from Site 401.
Figure 3: Assimilation of data from our Earth system model.

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Acknowledgements

This study was funded by a UK Ocean Acidification Research Program NERC/DEFRA/DECC grant (NE/H017518/1) to P.N.P., G.L.F. and P.F.S. (also supporting M.G.). A.R. was supported by a Heising–Simons Foundation award, and by EU grant ERC 2013-CoG-617313. E.T. was in part supported by the National Science Foundation Division of Ocean Sciences (grant no. NSF OCE 1536611). H.P. was in part supported by ERC grant 2013-CoG-617462. This study used samples provided by the International Ocean Discovery Program. We thank A. Milton at the University of Southampton for maintaining the mass spectrometers used in this study, and M. Davies at The Open University for assistance with sample preparation. We thank L. Haxhiaj and D. Nürnberg at GEOMAR Kiel and H. Kuhnert at MARUM Bremen for their help with carbon and oxygen isotope analyses.

Author information

Authors and Affiliations

  1. Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, SO17 1BJ, UK

    Marcus Gutjahr, Eleni Anagnostou & Gavin L. Foster

  2. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1–3, Kiel, 24148, Germany

    Marcus Gutjahr

  3. School of Geographical Sciences, Bristol University, Bristol BS8 1SS, UK

    Andy Ridgwell

  4. Department of Earth Sciences, University of California at Riverside, Riverside, 92521, California, USA

    Andy Ridgwell

  5. School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes, MK7 6AA, UK

    Philip F. Sexton

  6. School of Earth and Ocean Sciences, Cardiff University, Cardiff, CF10 3AT, UK

    Paul N. Pearson

  7. MARUM, Center for Marine Environmental Sciences, University of Bremen, Bremen, 28359, Germany

    Heiko Pälike

  8. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, 92037, California, USA

    Richard D. Norris

  9. Department of Geology and Geophysics, Yale University, New Haven, 06520, Connecticut, USA

    Ellen Thomas

  10. Department of Earth and Environmental Sciences, Wesleyan University, Middletown, 06459, Connecticut, USA

    Ellen Thomas

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  1. Marcus Gutjahr
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Contributions

G.L.F., P.F.S. and P.N.P. developed the concept and designed the study. M.G. and E.A. carried out the preparation of chemical samples, as well as elemental and isotopic analyses. P.F.S. performed foraminifer taxonomy and prepared foraminifer samples for the analyses. R.D.N. and E.T. supplied washed coarse-fraction samples. P.F.S. developed the age model. A.R. devised and conducted the Earth system modelling and analysis. H.P. carried out the carbon and oxygen isotopic analyses. M.G., A.R., G.L.F. and P.F.S. led the writing of the manuscript. All authors contributed to the interpretation of results and writing of the final text.

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Correspondence to Marcus Gutjahr.

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The authors declare no competing financial interests.

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Reviewer Information Nature thanks T. Bralower, K. Meissner and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figure 1 Elemental and stable-isotope cross-plots for M. subbotinae.

a–f, We screened samples for chemical consistency by checking various elemental ratios (Al/Ca, B/Ca and Mg/Ca) as well as measured δ11B and δ13C.

Extended Data Figure 2 Stable-isotope data for foraminifera and bulk carbonate.

Foraminifera-based stable-isotope compositions were generated from identical samples after splitting the δ13C/δ18O fraction from the δ11B fraction. For both foraminifera and bulk carbonate, the data are plotted against the depth of the core sample. The same data are plotted against age relative to CIE in Fig. 1.

Extended Data Figure 3 Illustration of the results of δ11B-to-pH conversion, and differences in age models.

a, We used our δ11B measurements as a proxy to calculate the evolution of pH at Site 401 during the PETM CIE, using either the borate ion47 (red) or the T. sacculifer43 (green) calibration. The age scale used follows ref. 25. b, Direct comparison of our two age models, plotting the reconstructed pH evolution of Site 401 using either the age model of ref. 57 or our preferred age model25. c, Expanded view of b.

Extended Data Figure 4 Selection of age-model tie points.

Comparison of bulk carbonate δ13C (top) and δ18O (bottom) values for Site 401 and Site 690 (ref. 25). Vertical lines show the age tie points used to derive the age model relative to the PETM CIE (see Methods).

Extended Data Figure 5 Key results of sensitivity experiments.

The figure shows the influence of uncertainties in the CIE onset duration on diagnosed total carbon release. For these idealized experiments, the CIE onset phase was assumed to occur linearly, with the decline in ocean surface dissolved inorganic carbon (DIC) δ13C (by 3.5‰) and pH (by 0.3 pH units) having a duration (Δτonset) that varied from 100 to 20,000 years; thereafter, the target pH and δ13C values were held constant until the end of the experiment (at 50,000 years). a–h, The evolution with time of these target ocean surface variables, with pH on the left-hand y axis, and δ13C(DIC) on the right-hand axis. i–p, Maximum carbon emission rate per time interval. q–x, Cumulative carbon emission per time interval in Eg of carbon. y, z, aa–af, Average emitted δ13C per time interval.

Extended Data Figure 6 Spatial and temporal evolution of mean annual surface ocean pH in the Earth system model cGENIE, shown both for the PETM and for preindustrial and future times.

a, Black line, global mean surface ocean pH values across the PETM, from experiment R07sm_Corg (these are our main pH estimates, obtained using the inorganic borate ion calibration and the RH07 age model, and including an assumption of organic carbon burial after the peak PETM). Red circles represent the annual mean pH values at Site 401 (location shown in b) in the model, taken at times in the model simulation that have corresponding δ11B-derived pH data points (see Fig. 3b; note that we do not use all of the observed data points). b, Model-projected spatial pattern of annual mean surface ocean pH at time zero (that is, PETM onset). The star shows the location of Site 401. c–f, Model-projected spatial patterns of the annual mean surface ocean pH anomaly compared with time 0, for the highlighted time points from a (5.0, 31.6, 58.2 and 71.5 kyr after onset). g, Model-projected spatial pattern of annual mean surface ocean pH in the modern ocean under pre-industrial (year 1765) atmospheric CO2 levels (278 p.p.m.). The model is configured as described in ref. 74 and driven with a CO2 emissions scenario that is consistent with RCP 6.0. h, i, Model-projected spatial pattern of the annual mean surface ocean pH anomaly compared with that for 1765, at years 2010 and 2050. The scale is as for c–f.

Extended Data Figure 7 Spatial and temporal evolution of surface sedimentary calcium carbonate content in cGENIE during the PETM.

a, Black line, global mean surface levels (in wt%) of sedimentary calcium carbonate (CaCO3) across the PETM, from experiment R07sm_Corg. White circles, times from PETM onset onwards that correspond to the δ11B-derived pH data points in Fig. 3b and Extended Data Fig. 6. The white circles do not represent ‘values’, and simply mark specific time points. b, Model-projected spatial pattern of surface sedimentary wt% CaCO3 at time zero (PETM onset). Shown are the locations of sites for which surface ocean pH has been reconstructed (see Fig. 2) and at which detailed down-core model–data comparison is carried out (Extended Data Fig. 9). c–f, Model-projected spatial patterns of the surface sedimentary wt% CaCO3 anomaly compared with time 0, for the time points highlighted in a. g, For reference, the assumed seafloor bathymetry in the model (and the locations of the four data-rich sites that are discussed in Supplementary Information).

Extended Data Figure 8 Spatial and temporal evolution of sea surface temperature in cGENIE during the PETM.

a, Black line, global and annual mean SSTs during the PETM, from experiment R07sm_Corg. Yellow circles, annual mean SST values at Site 401 in the model, at the times from PETM onset onwards that correspond to the δ11B-derived pH data points (see Fig. 3b). Blue and orange circles, δ18O- and Mg/Ca-derived SST estimates, respectively. b, Model-projected spatial pattern of annual mean SSTs at time 0. The star shows the location of Site 401. c–f, Model-projected spatial patterns of the annual mean SST anomaly compared with time 0, for the time points shown in a.

Extended Data Figure 9 Down-core model–data evaluation at four data-rich sites.

a–p, Comparisons for four Ocean Drilling Program Sites (401, 865, 1,209 and 1,263) for which surface ocean pH has been reconstructed across the PETM (Fig. 2; this study and ref. 20). q, The palaeo-locations of these sites in the cGENIE Earth system model. a–p, Model–data comparisons are made for: wt% CaCO3 (a, e, i, m); δ13C values from bulk carbonate (b, f, j, n); and surface ocean pH (c, g, k, o). Panels d, h, l and p provide an orientation in time, showing the projected evolution of atmospheric δ13C from CO2 in the model. For wt% CaCO3 and δ13C of bulk carbonate, model points (resolved at 1-cm intervals) are plotted as filled yellow circles. Model-projected pH values (global and annual means, as in Fig. 3h and Extended Data Fig. 6a) and atmospheric δ13C values for CO2 are shown as continuous red lines. In all cases, observed data values are shown as asterisks. For Sites 865, 1,209 and 1,263, the age models—employing the original relative age-model constraints20 used to convert from model-simulated sediment depths (resolved at 1-cm intervals) at each location in cGENIE—were calculated using a constant detrital flux accumulation rate. The observed data are plotted on the respective Site-690-derived age models25. Both model-based and data-based age scales are synchronized to time 0 (PETM onset; horizontal line). See Supplementary Information for details.

Extended Data Table 1 Key results from individual model runs
Full size table

Supplementary information

Supplementary Information

This file contains a detailed account about the Earth System Modelling approaches that were used and additional references. (PDF 331 kb)

Supplementary Table 1

This table contains foraminifera-based stable isotope results, relative sample ages, selected elemental ratios as well as the calculated mixed layer pH. (XLSX 59 kb)

Supplementary Table 2

This table contains bulk carbonate stable carbon and oxygen isotope results, presented alongside relative ages following our two alternative age models (see Methods). (XLSX 80 kb)

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Gutjahr, M., Ridgwell, A., Sexton, P. et al. Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum. Nature 548, 573–577 (2017). https://doi.org/10.1038/nature23646

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