Publication Date:
2017-04-04
Description:
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.
Description:
Published
Description:
On line First
Description:
4.5. Degassamento naturale
Description:
JCR Journal
Description:
reserved
Keywords:
Methane
;
climate change
;
seepage
;
Quaternary
;
03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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