Environmental Engineering Reference
In-Depth Information
calculations (
Table 19.2
), especially for the more enriched sources. Time-
continuous simulations using box models of the open-ocean C cycle, depending
on the duration of the simulation, give slightly more C compared to simple mixing
models because they take into account the damping effects of the weathering input.
The Earth system model, which also calculates the effect of saturation state on
carbonate deposition and sea
oor dissolution, provides additional buffering cap-
acity, and thus demands even more light C input to generate a given excursion.
cation
Geologic evidence, including the extinction selectivity of heavily calci
19.4.2 Ocean acidi
ed marine
organisms with limited buffering capacity (Clapham and Payne,
2011
), the depos-
ition of carbonate-rich oolite and microbialite immediately after the extinction
event (Kershaw
et al
.,
2002
; Payne
et al
.,
2007
), the submarine carbonate dissol-
ution observed underlying the microbialite (Payne
et al
.,
2007
) and calcium
isotope constraints (Payne
et al
.,
2010
), suggests ocean acidi
cation might have
been associated with the extinction event.
Montenegro
et al
.(
2011
) presented model simulations of the end-Permian
event; surface ocean aragonite saturation values dropped below 1.15 and were
thus unsuitable for present-day reef-forming coral species (Kleypas
et al
.,
1999
).
The difference between their study and ours arises because Montenegro
et al
.
(
2011
) did not treat the ocean
is carbonate system as an open system; i.e. there is no
weathering delivery of alkalinity to the ocean to balance the burial of carbonate in
their model; they were therefore unable to capture this important component of the
oceanic response to acidi
cation.
Overall, CO
2
build-up from the larger emission scenario due to the Siberian
Traps volcanism is consistent with the ocean acidi
'
cation from the top down
shown in our model and can explain both the observed sedimentological features
and calcium isotopes. This is different from the ocean acidi
cation from bottom up
proposed for the Paleocene
Eocene thermal maximum. This occurred in an ocean
that had a better buffering capacity to changes in
p
CO
2
because of its deep-sea
CaCO
3
sediment accumulation and for which rates of emission were apparently
slower.
-
19.5 Conclusion
We
find it most likely that the Siberian Traps volcanism released CO
2
in two major
multimillennial pulses. The modeled rates of C release are dependent on the
δ
13
cation is most
severe for a plume-related CO
2
release because it requires the most total C to
C of the source and the initial saturation state. Ocean acidi
