Geoscience Reference
In-Depth Information
Table 3.1
Published trends (slope ± SE) in atmospheric CO
2
, surface p CO
2
, pH
T
, and [CO
3
2-
] at three time-series stations: BATS
(1983-2005), ESTOC (1995-2004), and ALOHA (1988-2009)
Station
x
CO
2
atm
p
CO
2
sea
pH
T
[CO
3
2-
]
(ppmv yr
-1
)
(μatm yr
-1
)
(unit yr
-1
)
(μmol kg
-1
yr
-1
)
BATS
1.78 ± 0.02
a
1.67 ± 0.28
a
-0.0017 ± 0.0003
a
-0.47 ± 0.09
a
1.80 ± 0.02
b
1.80 ± 0.13
b
-0.0017 ± 0.0001
b
-0.52 ± 0.02
b
ESTOC
-
1.55 ± 0.43
c
-0.0017 ± 0.0004
c
-
1.7 ± 0.7
d
1.7 ± 0.7
d
-0.0018 ± 0.0003
d
-0.90 ± 0.08
d
ALOHA
1.68 ± 0.03
e
1.88 ± 0.16
e
-0.0019 ± 0.0002
e
-0.50 ± 0.06
e
-
-
-0.0014 ± 0.0002
f
-
a
Bates ( 2007 , Table 1), simple linear i t.
b
Bates ( 2007 , Table 2), seasonally detrended.
c
Santana-Casiano et al. (2007), seasonally detrended.
d
Gonzalez-Davila et al. (2010).
e
Dore et al. (2009), simple linear i t using calculated pH
T
(full time series).
f
Dore et al. (2009), simple linear i t using measured pH
T
(partial time series).
With more spatial coverage but for only two
points in time, ocean pH
T
was measured directly on
section P16N in the North Pacii c, i rst during the
World Ocean Circulation Experiment (WOCE) in
1991 and then again in 2006. During those 15 years,
ocean pH
T
changed by -0.06 units over the upper
500 m (Byrne
et al.
2010 ). Roughly equal contribu-
tions were attributed to anthropogenic and non-
anthropogenic factors, based on standard separation
techniques relying on oxygen measurements. In the
surface layer, the anthropogenic decline in pH
T
was
0.0018 ± 0.0003 units yr
-1
, consistent with the
observed increase in atmospheric CO
2
as well as
results from the three time-series stations.
In the higher latitudes, there is a time-series sta-
tion in the Iceland Sea where seasonal measure-
ments of
C
T
and
p
CO
2
have been made since 1985.
The 1985-2008 wintertime trend in computed surface
pH
T
is 0.0024 units yr
-1
, one-third greater than at the
three lower-latitude time-series stations; simultane-
ously, surface Ω
a
declined by 0.0072 units yr
-1
while
Ω
c
declined by 0.0117 units yr
-1
( Olafsson
et al.
2009 ).
The decline in pH
T
below 1500 m in the Iceland Sea
is one-quarter of that at the surface, while Ω
a
declines
at 0.0009 units yr
−1
. The latter causes the aragonite
saturation horizon (ASH), the interface between
supersaturated waters above and undersaturated
waters below, to move upward (shoal) at a rate of
4 m yr
-1
. That shoaling exposes local seal oor previ-
ously covered with supersaturated waters to these
newly corrosive conditions at a rate of 2 km
2
d
-1
.
Although it is not possible to measure anthropo-
genic
C
T
directly, data-based techniques have been
derived to distinguish anthropogenic
C
T
from the
much larger natural background using measure-
ments of carbon system variables, oxygen, nutri-
ents, and transient tracers (e.g. Gruber
et al.
1996 ;
Sabine
et al.
2004 ; Khatiwala
et al.
2009 ). These esti-
mates have been used to evaluate how surface and
interior ocean chemistry have changed since the
beginning of the industrial era (Feely
et al.
2004 ; Orr
et al.
2005), as detailed in subsequent sections.
3.5 Future scenarios
In 2001, for the Third Assessment Report (TAR) of
the Intergovernmental Panel on Climate Change
(IPCC), a family of future emissions scenarios
was constructed and provided to the scientii c
community in the IPCC's Special Report on
Emissions Scenarios (SRES; Naki
and
Swart 2000). These SRES scenarios replaced the
earlier IS92a family used for the previous IPCC
report. They have allowed many different model-
ling groups to make consistent simulations, under
different proposed lines of human behaviour, to
project corresponding 21st century changes, and
to compare model results within the framework
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