Environmental Engineering Reference
In-Depth Information
other groups with limited ability to buffer calcifying
fluids have higher extinc-
tion rates, suggesting hypercapnia and/or ocean acidi
cation played a prominent
role in the observed extinction patterns (Knoll and Fischer,
2011
). Sedimento-
logical features, such as erosional truncations, have been found in uppermost
Permian shallow-marine carbonate deposits in South China, Turkey and Japan,
suggesting widespread submarine carbonate dissolution (Payne
et al
.,
2007
).
However, whether the observed truncation surface occurred during subaerial
exposure or submarine dissolution is controversial (Payne
et al
.,
2009
;Wignall
et al
.,
2009
).
Here we present model
cation driven by
CO
2
emission from seven distinct sources, ranging from biogenic methane
(
simulations of ocean acidi
13
C) to volcanic CO
2
(
). We invert the model by forcing the surface
ocean dissolved inorganic carbon (DIC) to conform to the prescribed
-
60
‰ δ
-
9
‰
13
C values
by adding depleted C at each time-step. Due to the uncertainty concerning the
end-Permian ocean chemistry, we explore the ocean buffering capacity for
CO
2
addition with three different initial ocean saturation states of calcite (
δ
cal
),
and quantitatively evaluate the response of the extent and pattern of ocean
acidi
Ω
cation.
19.2 Methods
19.2.1
“
Neritan
”
ocean with reef deposition
Because deep-sea calcifiers did not evolve until the mid Mesozoic, carbonates are
presumably only deposited in shallow
“
neritic
”
regions of less than 200 m depth
(Zeebe and Westbroek,
2003
). Modeling studies using reconstructed sea level,
atmospheric
p
CO
2
, [Ca
2
þ
] and weathering
flux suggest that surface ocean satur-
ation state with respect to calcite (
”
Permian ocean (Ridgwell,
2005
; Riding and Liang,
2005
). The Earth system model
we use, cGENIE, has been used in a previous study to simulate changes in the
global carbon cycle and climate during the end-Permian extinction (Cui
et al
.,
2013
). However, the mean ocean-surface saturation is not
a priori
known so
sensitivity analysis must be carried out with a range of reasonable estimates. Prior
to the perturbation, we assume an atmospheric
p
CO
2
of 2800 ppm (10
Ω
cal
) can be as high as 9
-
11 in a
“
Neritan
PAL
(preindustrial atmospheric level, 280 ppm)) as we did in a previous study
(Cui
et al
.,
2013
). This value is within the rather large range of proxy estimates
and previous assumptions concerning the generally warm, ice-free late-Permian
climate states (Cui
et al
.,
2013
). We consider three different surface saturation
states: (1)
Ω
¼
10 represents the late Paleozoic estimate based on
“
Neritan
”
calcite
Ω
¼
'
mode modeling (Ridgwell,
2005
), (2)
5 is similar to today
is value, and
calcite
Ω
¼
(3)
2.5 is used in a previous carbon-cycle modeling study on the
calcite
