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In contrast, evidence from the post-glacial explosive eruption histories of south-
ern Chile, Kamchatka and the Cascades shows no statistically signi
cant
enhancement in rates of volcanism following deglaciation at arc volcanoes (Watt
et al ., 2013 ). There is though a suggestion that some of the largest post-glacial
eruptions in southern Chile occurred shortly after ice retreat, consistent with
magma ponding beneath glaciated volcanoes and released once the ice has been
removed (Watt et al ., 2013 ).
Modulation of volcanic activity, and degassing, by glacial cycles may mean that
non-arc volcanoes accounted for a relatively higher proportion of global volcanic
emissions in the early post-glacial period than at present-day (Watt et al ., 2013 ).
However, the global signi
cance of these changes is still under debate. Huybers
and Langmuir ( 2009 ) suggested that global volcanic activity increased, perhaps as
much as six-fold, from 12 to 7 ka, due to enhanced eruption rates in formerly
glaciated regions. They postulated that associated increases in volcanic emissions
may have contributed signi
cantly to the post-glacial increase in atmospheric
CO 2 . However, modelling studies of the oceanic carbon cycle (e.g. Roth and Joos,
2012 )
find only a small role for volcanic forcing in post-glacial CO 2 , while a more
detailed analysis of volcanic eruption records (Watt et al ., 2013 ) shows sparser
evidence for a post-glacial volcanic
pulse ' , with a maximum two-fold increase
in global eruption rates, relative to the present day, between 13 and 7 ka. This
suggests that although volcanism may have been an important source of CO 2 in
the early Holocene, it is unlikely to have been a dominant control on changes
in atmospheric CO 2 after the LGM.
Other studies have argued that rapid post-glacial sea-level rise (Nakada and
Yokose, 1992 ) and fall (Rampino et al ., 1979 ; Wallmann et al ., 1988 ) may have
led to enhanced volcanic eruption rates (McGuire et al ., 1997 ). However, the
data needed to prove these hypotheses remain incomplete, and the evidence for
an association is still weak. More recently, Lund and Asimow ( 2011 ) have
suggested that since mantle decompression rates induced by changes in sea level
during glacial
'
interglacial cycles may approach the same order of magnitude as
those due to plate spreading, there may be signi
-
cant sea-level driven variations
in submarine magma
flux. This remains to be tested.
(iv) Perturbations to magma volatile load and the composition
of the volcanic gases emitted
Other chapters in this topic deal with major perturbations to the volatile load or
composition of
flood basalt magmatism ( Chapters 10
-
12 ) . These chapters discuss
potentially enhanced
fluxes of volatiles, for example, from the recycled oceanic
crustal component of the mantle plume (Sobolev et al ., 2011 ), and release of
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