Potential methane reservoirs beneath Antarctica

Journal name:
Nature
Volume:
488,
Pages:
633–637
Date published:
DOI:
doi:10.1038/nature11374
Received
Accepted
Published online

Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon1. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14kilometres thick2 and an estimated 21,000 petagrams (1Pg equals 1015g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model3 and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300metres in West Antarctica and 700metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.

At a glance

Figures

  1. Methane production in sub-Antarctic sediments.
    Figure 1: Methane production in sub-Antarctic sediments.

    a, A conceptual model of biogeochemical processes in a sub-Antarctic marine sediment/till complex, indicating three main zones and assuming non-frozen basal conditions. Zone A is the methane production zone (after 16kyr of glaciation), zone B is the sulphate reduction/anaerobic oxidation of methane zone (during the first 16kyr of glaciation) and zone C is the sulphide oxidation (oxic/anoxic)/nitrate reduction zone. White arrows indicate methane diffusion. In parts of the ice sheet where frozen basal conditions prevail, zone A is likely to extend to the ice/sediment interface. The graph on the left also indicates the likely evolution of sulphate concentrations in the upper part of the marine sediment/till complex over time (t values indicate arbitrary, increasing periods of time), as the sulphate pool is depleted by methane oxidation and sulphate reduction (where t = 3 is of the order of 10kyr). b, Comparison of rates of methane production (Rxn, in units of fmol CH4 per gram dry weight of sediment per hour) measured experimentally for subglacial sediments (this paper) and other anoxic environments. For comparison, we also plot Rxn values used in the modelling for two parameter sets for surface sediments (depth d = 0; grey symbols) and sediments exceeding 200m depth (pink symbols) and for v = 0.1 and v = 0.01 (where v is the reactivity parameter in the OC degradation model, with high v values indicating high organic matter reactivity). (The percentage total OC content of sediments, TOC(0,0) = 1%.)

  2. Methane hydrate+gas accumulation potential beneath the ice sheet.
    Figure 2: Methane hydrate+gas accumulation potential beneath the ice sheet.

    This indicates the sensitivity of methane hydrate+gas accumulation (‘releasable methane’) beneath the Antarctic Ice Sheet to varying TOC(0,0) and v values in the reactive continuum model under the zero flux scenario for the EAIS (a) and WAIS (b), and the maximum flux scenario for the EAIS (c) and WAIS (d). Methane hydrate+gas accumulation is calculated after 30Myr (EAIS) and 1Myr (WAIS) of simulation time. The high hydrate inventory for the maximum flux scenario reflects the greater area contribution of melting basal conditions for the WAIS and EAIS.

  3. Vertical profiles of methane solubility, dissolved methane, methane hydrate and methane gas in zero flux simulations.
    Figure 3: Vertical profiles of methane solubility, dissolved methane, methane hydrate and methane gas in zero flux simulations.

    Concentrations in a and b are normalized to the maximum methane solubility defined at the three-phase equilibrium point for methane in pore waters Ceq, methane hydrate and methane gas are reported in units of percentage of pore volume (note the different scale for the x axis). Simulations assume 30Myr (EAIS) and 1Myr (WAIS) of glaciation. The upper and lower extent of the GHSZ is indicated. Ceq is the equilibrium concentration of methane in pore waters and CCH4 is the modelled dissolved concentration of methane in pore waters.

  4. Modelled thermogenic methane accumulation beneath WAIS over 1[thinsp]Myr of glaciation under the maximum flux scenario (v = 0.1, TOC(0,0) = 1%).
    Figure 4: Modelled thermogenic methane accumulation beneath WAIS over 1Myr of glaciation under the maximum flux scenario (v = 0.1, TOC(0,0) = 1%).

    a, Vertical profiles of methane solubility (Ceq) and dissolved methane concentrations (CCH4, for a vertical advection velocity of 50mmyr−1 only) at t = 1Myr (that is, after a million years of glaciation) where concentrations are normalized to the maximum Ceq. The upper and lower extent of the GHSZ is indicated. b, Methane hydrate formed after 1Myr of glaciation and employing different vertical advection velocities (in the range 5–50mmyr−1). Zones of upward fluid flow velocities and methane fluxes for active vents (‘discrete fluxes’) versus more diffuse seepage (‘diffuse fluxes’) are indicated based upon refs 26 and 27.

References

  1. Priscu, J. et al. in Polar Lakes and Rivers (eds Vincent, W. F. & Laybourn-Parry, J.) 320 (Oxford University Press, 2009)
  2. Ferraccioli, F., Armadillo, E., Jordan, T., Bozzo, E. & Corr, H. Aeromagnetic exploration over the East Antarctic Ice Sheet: a new view of the Wilkes Subglacial Basin. Tectonophysics 478, 6277 (2009)
  3. Davie, M. K. & Buffett, B. A. A numerical model for the formation of gas hydrate below the seafloor. J. Geophys. Res. 106, 497514 (2001)
  4. Wellsbury, P., Mather, I. & Parkes, R. J. Geomicrobiology of deep, low organic carbon sediments in the Woodlark Basin, Pacific Ocean. FEMS Microbiol. Ecol. 42, 5970 (2002)
  5. Cragg, B. A. et al. Bacterial populations and processes in sediments containing gas hydrates (ODP Leg 146: Cascadia Margin). Earth Planet. Sci. Lett. 139, 497507 (1996)
  6. Colwell, F. S. et al. Estimates of biogenic methane production rates in deep marine sediments at Hydrate Ridge, Cascadia margin. Appl. Environ. Microb. 74, 34443452 (2008)
  7. Parkes, R. J. et al. Bacterial biomass and activity in deep sediment layers from the Peru margin. Phil. Trans. R. Soc. Lond. A 331, 139153 (1990)
  8. Yoshioka, H., Sakata, S., Cragg, B. A., Parkes, R. J. & Fujii, T. Microbial methane production rates in gas hydrate-bearing sediments from the eastern Nankai Trough, off central Japan. Geochem. J. 43, 315321 (2009)
  9. Kotsyurbenko, O. R. et al. Acetoclastic and hydrogenotrophic methane production and methanogenic populations in an acidic West-Siberian peat bog. Environ. Microbiol. 6, 11591173 (2004)
  10. Franzmann, P. D., Roberts, N. J., Mancuso, C. A., Burton, H. R. & McMeekin, T. A. Methane production in meromictic Ace Lake, Antarctica. Hydrobiologia 210, 191201 (1991)
  11. Smith, R., Miller, L. & Howes, B. The geochemistry of methane in Lake Fryxell, an amictic, permanently ice-covered, antarctic lake. Biogeochemistry 21, 95115 (1993)
  12. Ellis-Evans, J. C. Methane in maritime Antarctic freshwater lakes. Polar Biol. 3, 6371 (1984)
  13. Archer, D. Methane hydrate stability and anthropogenic climate change. Biogeosciences 4, 521544 (2007)
  14. Wadham, J. L., Tranter, M., Tulaczyk, S. & Sharp, M. Subglacial methanogenesis: a potential climatic amplifier? Glob. Biogeochem. Cycles 22, GB2021 (2008)
  15. Lanoil, B. et al. Bacteria beneath the West Antarctic Ice Sheet. Environ. Microbiol. 11, 609615 (2009)
  16. Boyd, E. S., Skidmore, M., Mitchell, A. C., Bakermans, C. & Peters, J. W. Methanogenesis in subglacial sediments. Environ. Microbiol. Rep. 2, 685692 (2010)
  17. Pattyn, F. Antarctic subglacial conditions inferred from a hybrid ice sheet/ice stream model. Earth Planet. Sci. Lett. 295, 451461 (2010)
  18. Maule, C. F., Purucker, M. E., Olsen, N. & Mosegaard, K. Heat flux anomalies in Antarctica revealed by satellite magnetic data. Science 309, 464467 (2005)
  19. Claypool, G. F., Lorensen, T. D. & Johnson, C. A. Authigenic carbonates, methane generation, and oxidation in continental rise and shelf sediments, ODP leg 188, sites 1165 and 1166, offshore Antarctica (Prydz Bay). Proc. ODP Sci. Results 188, 115 (2004)
  20. Tarnocai, C. et al. Soil organic carbon pools in the northern circumpolar permafrost region. Glob. Biogeochem. Cycles 23, GB2023 (2009)
  21. Houghton, R. A. Balancing the global carbon budget. Annu. Rev. Earth Planet. Sci. 35, 313347 (2007)
  22. Meyers, P. A. & Ishiwatari, R. Lacustrine organic geochemistry—an overview of indicators of organic matter sources and diagenesis in lake sediments. Org. Geochem. 20, 867900 (1993)
  23. Boudreau, B. P. & Ruddick, B. R. On a reactive continuum representation of organic-matter diagenesis. Am. J. Sci. 291, 507538 (1991)
  24. Reeburgh, W. S., Whalen, S. C. & Alperin, M. J. In Microbial Growth on C1 Compounds (eds Murrell, J. C. & Kelly, D. P.) 114 (Intercept Ltd, 1993).
  25. Etiope, G. & Klusman, R. W. Geologic emissions of methane to the atmosphere. Chemosphere 49, 777789 (2002)
  26. Torres, M. E. et al. Fluid and chemical fluxes in and out of sediments hosting methane hydrate deposits on Hydrate Ridge, OR. I: Hydrological provinces. Earth Planet. Sci. Lett. 201, 525540 (2002)
  27. Wallmann, K., Drews, M., Aloisi, G. & Bohrmann, G. Methane discharge into the Black Sea and the global ocean via fluid flow through submarine mud volcanoes. Earth Planet. Sci. Lett. 248, 545560 (2006)
  28. Boswell, R. & Collett, T. S. Current perspectives on gas hydrate resources. Energy Environ. Sci. 4, 12061215 (2011)
  29. Pollard, D. & DeConto, R. M. Modelling West Antarctic ice sheet growth and collapse through the past five million years. Nature 458, 329332 (2009)
  30. Dyke, A. S., Prest, V. K. & Narraway, J. D. in Map/Geological Survey of Canada 1702A (Geological Survey of Canada, 1987)
  31. Dickens, G. R., Paull, C. K. & Wallace, P. Direct measurement of in situ methane quantities in a large gas-hydrate reservoir. Nature 385, 426428 (1997)
  32. Barker, P. F., Camerlenghi, A. & Acton, G. D. Leg 178 Summary. Proc ODP Init. Rep. 178, 60 (1999)

Download references

Author information

Affiliations

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

    • J. L. Wadham,
    • S. Arndt,
    • M. Stibal,
    • M. Tranter,
    • J. Telling,
    • G. P. Lis,
    • E. Lawson,
    • A. Ridgwell,
    • A. M. Anesio &
    • C. E. H. Butler
  2. Department of Earth Sciences – Geochemistry, Utrecht University, 3508 Utrecht, The Netherlands

    • S. Arndt
  3. Earth and Planetary Sciences Department, University of California, Santa Cruz, California 95064, USA

    • S. Tulaczyk &
    • M. J. Sharp
  4. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton T6G 2E3, Canada

    • A. Dubnick

Contributions

J.L.W. wrote the paper and directed the work, and led the sample collection in Greenland. S.A. did the numerical modelling and contributed to manuscript preparation. S.T. assisted with the modelling and contributed to manuscript preparation. M.S. contributed to the writing of the manuscript and did experimental work. J.T. did the initial design of incubation experiments, laboratory analysis of incubation experiments, and sample collection. G.P.L. performed laboratory analysis of the incubation experiments, and did sample collection. E.L. performed laboratory analysis of incubation experiments. A.D. performed laboratory analysis of the incubation experiments. M.T. assisted with the manuscript and modelling calculations. M.J.S. added input to the incubation experiments, and did sample collection of Antarctic subglacial material. A.M.A. assisted with writing the manuscript and advised upon incubation experiments. A.R. assisted with manuscript preparation and numerical modelling. C.B. assisted with the laboratory analysis of the incubation experiments.

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to:

Author details

Supplementary information

PDF files

  1. Supplementary Information (1.1M)

    This file contains Supplementary Text, Supplementary Tables 1-6, Supplementary Figures 1-6 and Supplementary References.

Additional data