Environmental Engineering Reference
In-Depth Information
20.8 Ozone
The stratospheric ozone layer provides a crucial shield against incoming ultraviolet
radiation. Halogen-bearing compounds facilitate the catalytic destruction of strato-
spheric ozone through cycles that resemble:
Cl
þ
O
3
!
ClO
þ
O
2
ClO
þ
O
!
Cl
þ
O
2
.
for an observed spike in abnormal pollen during the end-Permian. Contact
metamorphism of Siberian sedimentary rocks
-
including hydrocarbon reservoir
strata and evaporates
-
may have produced abundant CH
3
Cl (Aarnes
et al
.,
2011
;
Beerling
et al
.,
2007
; Svensen
et al
.,
2009
). Beerling
et al
.(
2007
) demonstrated
that atmospheric release of suf
cient quantities of this thermogenic CH
3
Cl could
drive near-total ozone layer collapse. Volcanic HCl can also trigger ozone deple-
tion, especially when background CH
3
Cl emissions are elevated (Black
et al
.,
2014
), but water and ice in eruptive plumes help to scavenge HCl and may limit its
introduction to the stratosphere (Tabazadeh and Turco,
1993
; Textor
et al
.,
2003
).
Figure 20.4c
and
20.4d
show the distribution of ozone after several years of
volcanic HCl or thermogenic gas release. While signi
cant uncertainty accompan-
ies estimates of metamorphic gas release during the eruption of the Siberian Traps,
the presence of major evaporite and petroleum deposits in the Tunguska Basin
differentiates the Siberian Traps from other LIP eruptions. The potential for
CH
3
Cl-driven ozone collapse is thus a distinctive attribute of the Siberian Traps.
20.9 Continental weathering
The eruption of the Siberian Traps and the end-Permian mass extinction both
occurred near the onset of a major increase in seawater
87
Sr/
86
Sr (Korte
et al
.,
2003
; Korte
et al
.,
2004
). This increase in radiogenic Sr, which spans the earliest
Triassic, has been interpreted as evidence for a global increase in continental
weathering. Warmer temperatures, elevated atmospheric CO
2
, decimation of ter-
restrial vegetation, and acid rain are all potential drivers of accelerated weathering.
Flood basalt deposits may also provide an important long-term sink for CO
2
.
During weathering, the Ca contents in the basalts become available to bond with
carbonate (Dessert
et al
.,
2001
; Dessert
et al
.,
2003
). The eruption of LIPs can
create large new expanses of basaltic surface area, and chemical weathering of this
basalt may be much more ef
cient than chemical weathering of granite or gneiss
(Berner,
2006
; Dessert
et al
.,
2001
; Dessert
et al
.,
2003
). On the basis of pedogenic
carbonate measurements from the Newark Basin, Schaller
et al
.(
2012
) suggest that
