Abundant Early Palaeogene marine gas hydrates despite warm deep-ocean temperatures

Journal name:
Nature Geoscience
Volume:
4,
Pages:
848–851
Year published:
DOI:
doi:10.1038/ngeo1301
Received
Accepted
Published online

Abrupt periods of global warming between 57 and 50 million years ago—known as the Early Palaeogene hyperthermal events—were associated with the repeated injection of massive amounts of carbon into the atmosphere1, 2, 3, 4. The release of methane from the sea floor following the dissociation of gas hydrates is often invoked as a source5. However, seafloor temperatures before the events were at least 4–7°C higher than today1, which would have limited the area of sea floor suitable for hosting gas hydrates6, 7. Palaeogene gas hydrate reservoirs may therefore not have been sufficient to provide a significant fraction of the carbon released. Here we use numerical simulations of gas hydrate accumulation8 at Palaeogene seafloor temperatures to show that near-present-day values of gas hydrates could have been hosted in the Palaeogene. Our simulations show that warmer temperatures during the Palaeogene would have enhanced the amount of organic carbon reaching the sea floor as well as the rate of methanogenesis. We find that under plausible temperature and pressure conditions, the abundance of gas hydrates would be similar or higher in the Palaeogene than at present. We conclude that methane hydrates could have been an important source of carbon during the Palaeogene hyperthermal events.

At a glance

Figures

  1. The gas hydrate volume fraction (Vfrac,h[equiv]Sh[phi]) with respect to depth below the sea floor at different seafloor temperatures
Tsf (Case I).
    Figure 1: The gas hydrate volume fraction (Vfrac,hShφ) with respect to depth below the sea floor at different seafloor temperatures Tsf (Case I).

    Dsf=2.0km. The total gas hydrate volume per unit seafloor area (V h, in m3m−2) is given for each curve. For the parameters see Supplementary Table S2. Note that changes in V h are not straightforward because temperature impacts multiple parameters (Supplementary Table S2).

  2. Methane production profiles with respect to depth below the sea floor at different seafloor temperatures (Case I).
    Figure 2: Methane production profiles with respect to depth below the sea floor at different seafloor temperatures (Case I).

    Dsf=2.0km. The effects of higher organic carbon input and elevated methanogenesis rates at higher sediment temperatures have been included. The black bars show the base of the GHSZ for each Tsf. The parameters (Supplementary Table S2) are the same as those in Fig. 1.

  3. Contour plots showing the ratio of total hydrate volume at seafloor temperature (Tsf) of 9[thinsp][deg]C to that at 3[thinsp][deg]C (k=Vh,9C/Vh,3C).
    Figure 3: Contour plots showing the ratio of total hydrate volume at seafloor temperature (Tsf) of 9°C to that at 3°C (k=Vh,9C/Vh,3C).

    ac, Organic carbon rain (μmolcm−2yr−1): 10 (a), 30 (b), 100 (c). k>1 means that the total gas hydrate volume is greater with warmer deep ocean water. Case I is that shown in Fig. 1. represents the ratio of sediment burial to average reaction rate at Tsf=3°C; Ntφ,3C represents the ratio of the GHSZ thickness at Tsf=3°C to the characteristic length of compaction. Seafloor depth Dsf=2.0km. For other system parameters see Supplementary Table S3.

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Affiliations

  1. Department of Chemical & Biomolecular Engineering, Rice University, Houston, Texas 77005, USA

    • Guangsheng Gu,
    • Gaurav Bhatnagar,
    • George J. Hirasaki &
    • Walter G. Chapman
  2. Department of Earth Sciences, Rice University, Houston, Texas 77005, USA

    • Gerald R. Dickens
  3. Institutionen för Geologiska Vetenskaper, Stockholms Universitet, Stockholm 106 91, Sweden

    • Gerald R. Dickens
  4. College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA

    • Frederick S. Colwell
  5. Present address: Shell International Exploration and Production, Houston, Texas 77082, USA

    • Gaurav Bhatnagar

Contributions

G.R.D. conceived the overarching hypothesis; G.B. constructed a prototype numerical model published elsewhere with insights from G.J.H, W.G.C. and G.R.D.; G.G. modified the model for this work, carried out the simulations and prepared the data, with advice and input from G.J.H, G.R.D. and W.G.C.; G.G. and G.R.D. wrote the initial manuscript; all authors contributed to subsequent revisions.

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The authors declare no competing financial interests.

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