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many regions of the Siberian Traps (Black et al ., 2011 ; Ross et al ., 2005 ); some
authors have estimated that they comprise as much as 25% of the total volume,
though this
ated (Ross et al ., 2005 ). Chapter 1 in this topic
discusses in more detail the evidence for and importance of explosive fragmenta-
tion during LIP eruptions. Explosive delivery of volatiles to the stratosphere would
strongly in
figure may be in
uence the potential climate effects of Siberian Traps magmatism.
Geologic and palaeontologic proxies for environmental conditions across the
Permian - Triassic boundary provide a key constraint on the role of volcanic forcing
during the end-Permian mass extinction. The pattern of extinction in the oceans -
where Erwin ( 1994 ) notes that extinction rates exceeded 90% at the species level -
suggests that organisms with less capacity to adapt to changes in partial pressure of
CO 2 (pCO 2 ) may have suffered preferentially (Knoll et al ., 2007 ). Terrestrial
sections record changes in the diversity and health of
floral populations. Plant
fossils directly re
ect prevailing atmospheric conditions. While the statistical
signi
cance of extinction rates among some plant populations during the
end-Permian has been disputed (Rees, 2002 ), aberrant pollen remains provide
convincing evidence for widespread atmospheric stress (Foster and Afonin,
2005 ; Visscher et al ., 2004 ). Ward et al .( 2000 ) interpret a shift in
fluvial style
as evidence for catastrophic devegetation.
20.3 Gas
flux from large igneous provinces
The
flux of gases such as CO 2 ,CH 4 ,CH 3 Cl, HCl and SO 2 governs the range and
magnitude of the climate response to volcanism. The atmospheric lifetime of CO 2
is between 10 3 and 10 5 years (Archer, 2005 ); the lifetimes of other important
volcanic and thermogenic gases are much shorter, ranging from 10 - 2 to 10 1 years
(Seinfeld and Pandis, 1997 ). Because the hiatus between eruptive events may
exceed the lifetime of many of these gases, climate forcing may occur in jolts
determined by the magnitude and duration of gas emission.
Sobolev et al . summarize the lines of evidence available to substantiate
estimates of volatile release in Chapter 10 . Based on melt inclusion data, Black
et al .( 2012 ) found that magmatic degassing from the Siberian Traps may have
accounted for the atmospheric release of 6,300 - 7,800 Gt S, 3,400 - 8,700
Gt Cl and 7,100 - 13,600 Gt F, depending on the ef
ciency of degassing. Sobolev
et al .( 2011 ) estimate that the Siberian Traps LIP could have released up to
170,000 Gt of mantle-derived CO 2 . During intrusion and thermal meta-
morphism, the reaction of rock salt layers with hydrocarbons could also have
generated
10 3 Gt CH 3 Cl.
Estimates of sulfur degassing from the Deccan Traps (Self et al ., 2008 ) and the
Columbia River
~
flood basalts (Blake et al ., 2010 ; Thordarson and Self, 1996 )
prescribe volumetric
fluxes comparable to that of the Siberian Traps (Black et al .,
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