Halogen release from Plinian eruptions and depletion of stratospheric ozone - Volcanism and Global Environmental Change - page 247

small volcanic eruptions since 2000, and encompass the stratosphere only in parts
(Kotra et al ., 1983 ; Mankin and Coffey, 1984 ; Millard et al ., 2006 ; Rose et al .,
2006 ; Hörmann et al ., 2013 ). While the Cl release from large eruptions has been
better studied (Gerlach et al ., 1996 ; Gerlach, 2004 ; Wallace, 2005 ), the release
of Br remains largely unknown. Although Br is typically more than two orders
of magnitude less abundant than Cl in volcanic gases (Bureau et al ., 2000 ), its
ef 60 times higher than for

Cl (Montzka et al ., 2011 , and references therein), if Br does reach the stratosphere.
Only recently, ground-based, aircraft and satellite measurements revealed that
small volcanic eruptions at low and high latitudes delivered reactive Br into
tropospheric and up to stratospheric levels (Bobrowski et al ., 2003 ;Millard et al .,
2006 ;Rose et al ., 2006 ; Theys et al ., 2009 ;Heue et al ., 2011 ; Hörmann et al .,
2013 ).
Model calculations of the effects of additional Br in the stratosphere strongly
indicate that Plinian eruptions represent a special case. The combination of sulfuric
acid aerosols together with elevated Br and Cl concentrations is particularly ef

ciency in halogen-catalyzed ozone destruction is ~

cient
for ozone destruction in the mid-latitude lower stratosphere, where a large fraction
of the Br-induced ozone loss is dominated by the BrO x /HO x catalytic cycle, and
BrO/ClO ratios are additionally relevant with regard to ozone loss in polar latitudes
(Salawitch et al ., 2005 ; Sinnhuber et al ., 2009 ). Halogens from Plinian eruptions
therefore seem to have a potential impact on the stratospheric ozone concentration
as well (Stolarski and Butler, 1978 ; von Glasow, 2009; Kutterolf et al ., 2013a ),
aside from heterogeneous reactions on volcanic aerosols leading to enhanced strato-
spheric ozone depletion during high Cl background levels.

16.4 The CAVA background
The Central American subduction zone is characterized by the subduction of
the Cocos beneath the Caribbean plate since the early Miocene at convergence rates
of 70

90 mm/year (Barckhausen et al ., 2001 ; DeMets, 2001 ). In the resulting CAVA,
extending

-

1400 km from Guatemala in the northwest to Panama in the southeast,
numerous felsic tephras from highly explosive Plinian eruptions have been emplaced
during the Pliocene and Holocene, where the varying magmatic compositional
diversity along the CAVA results from systematically changing subducting param-
eters (Syracuse and Abers, 2006 ;Carr et al ., 2007 , and references therein).
Quaternary, andesitic to rhyolitic highly explosive eruptions, originating
from large caldera volcanoes in the north (Guatemala and El Salvador) and
stratovolcanoes in the south (Nicaragua and Costa Rica) ( Figure 16.1 ), produced
92 widespread tephras, which occur > 20 km from the source (Kutterolf et al .,
2008 and references therein). Kutterolf et al .( 2013a ; unpublished) and Metzner

~