Did geologic emissions of methane play any role in Quaternary climate change?

• Published in: Global and Planetary Change
• Main Authors: Etiope, G., Milkov, A., Derbyshire, E.
• Other Authors: Etiope, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia, Milkov, A.; BP America, Exploration and Production Technology Group, Houston, Texas, USA, Derbyshire, E.; Centre for Quaternary Research, Royal Holloway, University of London, UK, Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia, BP America, Exploration and Production Technology Group, Houston, Texas, USA, Centre for Quaternary Research, Royal Holloway, University of London, UK
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2007
• Subjects: Methane; climate change; seepage; Quaternary; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases; ice core
• Online Access: http://hdl.handle.net/2122/3029; https://doi.org/10.1016/j.gloplacha.2007.08.008

The “methane-led hypotheses” assume that gas hydrates and marine seeps are the sole geologic factors controlling Quaternary atmospheric and climate changes. Nevertheless, a wider class of geologic sources of methane exist which could have played a role in past climate changes. Beyond offshore seepage, relevant geologic emissions of methane (GEM) are from onshore seepage, including mud volcanism, microseepage and geothermal flux; altogether GEM are the second most important natural source of atmospheric methane at present. The amount of methane entering the atmosphere from onshore GEM seems to prevail on that from offshore seepage. Onshore sources inject a predominantly isotopically heavy (13C-enriched) methane into the atmosphere. They are controlled mainly by endogenic (geodynamic) processes, which induce large-scale gas flow variations over geologic and millennial time scales, and only partially by exogenic (surface) conditions, so that they are not affected by negative feedbacks. The eventual influence on atmospheric methane concentration does not necessarily require catastrophic or abrupt releases, as proposed for the “clathrate gun hypothesis”. Enhanced degassing from these sources could have contributed to the methane trends observed in the ice core records, and could explain the late Quaternary peaks of increased methane concentrations accompanied by the enrichment of isotopically heavy methane, as recently observed. This hypothesis shall be tested by means of robust multidisciplinary studies, mainly based on a series of atmospheric, biologic and geologic proxies. Published On line First 4.5. Degassamento naturale JCR Journal reserved