Changes in Natural Methane Emissions in a Warming World
Methane is a powerful greenhouse gas and has been an important contributor to recent global warming. There is considerable concern that, with continued warming, some potentially large natural sources of methane may become much more active, increasing the atmospheric methane concentration and providing a further positive feedback to the warming.
Bubbles of ancient air trapped in glacial ice. Photo by P.Neff
One of these possible natural sources is methane hydrates. Methane hydrate is an ice-like solid composed of H2O and CH4 that is stable at relatively low temperatures and relatively high pressures. Methane hydrates are widely distributed in ocean sediments along continental margins as well as in permafrost. The total amount of methane carbon contained in these deposits is estimated to be very large -- similar to the amount of carbon in all of the world’s oil and natural gas deposits.
The second possible natural source is thawing permafrost. Permafrost is estimated to contain a very large amount of organic carbon, with the total amount in the range similar to the carbon in methane hydrates. As permafrost thaws, this carbon could be converted to CH4 if anoxic (oxygen-free) conditions develop.
Both of these potentially large methane sources are sensitive to climate warming. Our project at Taylor Glacier, Antarctica aims to answer the question of how likely it is that these methane sources would contribute large amounts of methane to our atmosphere as warming continues. To do this, we are studying ancient air from the last time that the Earth experienced a large global warming: the last deglaciation, which occurred approximately between 18 and 8 thousand years ago. CH4 from both hydrates and permafrost would be expected to contain “old” carbon with no or relatively little 14C as compared to other methane sources. We are obtaining large samples of ancient air from the old ice of Taylor Glacier to measure 14C of methane and investigate the possible contributions from hydrate and permafrost sources.
This project is being supported by NSF Polar award PLR-1245659
Petrenko, V.V., A.M. Smith, E.J. Brook, D. Lowe, K. Riedel, G. Brailsford, Q. Hua, H. Schaefer, N. Reeh, R.F. Weiss, D. Etheridge, J.P. Severinghaus, 2009. 14CH4 Measurements in Greenland Ice: Investigating Last Glacial Termination CH4 Sources. Science 324, 506-508. http://www.sciencemag.org/content/324/5926/506
Schaefer, H., M.J. Whiticar, E.J. Brook, V.V. Petrenko, D.F. Ferretti, and J.P. Severinghaus. 2006. Ice record of delta C-13 for atmospheric CH4 across the Younger Dryas-Preboreal transition. Science, 313 (5790), 1109-1112.http://www.sciencemag.org/content/313/5790/1109