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UNIVERSITE DE PERPIGNAN BIOPHYSIQUE ET DYNAMIQUE DES SYSTEMES INTEGRES. EA: 1947. BDSI. Revisited estimates of anthropogenic CO 2 throughout the Atlantic Ocean: a novel approach. Franck Touratier & Catherine Goyet. EA 1947 BDSI, Université de Perpignan, France. - PowerPoint PPT Presentation
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Revisited estimates of anthropogenic CO2 throughout the
Atlantic Ocean:a novel approach
Franck Touratier & Catherine Goyet
EA 1947 BDSI, Université de Perpignan, France
UNIVERSITE DE PERPIGNAN
BIOPHYSIQUE ET DYNAMIQUE DES SYSTEMES INTEGRES
How can we estimate anthropogenic CO2 in the ocean?Since anthropogenic CO2 cannot be measured at sea, two major kinds of models have been used to separate the anthropogenic signal from the bulk of TCO2: Models using back calculation techniques:
• approaches of Brewer (1978), and Chen and Millero (1979),• the C* approach of Gruber et al. (1996),• the approach of Peng et al. (1998),• the MIX approach (Goyet et al. 1999).
Ocean circulation models: 2.5D model of Stoecker et al. (1994), IPSL model (e.g. Delecluse 1994), MPI model (e.g. Maier-Reimer 1993), Hadley model (Taylor 1995), Princeton model (e.g. Sarmiento et al. 1995), …
• the CAO approach ------------------------------------------->
1. Definition of CAO (Carbon, Alkalinity, Oxygen tracer):
106 162 3 3 4 2
2 3 3 4
Respiration,decomposition
Photosynthesis
( ) ( ) ( ) 138
106 16
CH O NH H PO O
CO HNO H PO
2 122 H O
2 2 2123 1 17165 2 165
TCO O TA O
2 2165 1
131.5 2CAO TCO TA O
2 21.2 0.6CAO TCO TA O
A novel (back calculation) approach: the CAO model
CARINA database
La méthode TrOCATracer combining Oxygen, iorganic Carbon, and total
AlkalinityTouratier et Goyet (a,b; 2004)
2 21.2 0.6TrOCA TCO TA O
0 00 02 21.2 0.6TrOCA TCO TA O
‘quasi-conservatif’
‘conservatif’
0 00
2 202 2
1.2ANT
TA TA TrOCA TrOCAC TCO TCO
O O
TrOCA0 is the unknown of the system
CAO0
The form of the equation CAO0= ƒ () is first determined by using the program of e.g. Lewis and Wallace (1998). The best fit is obtained with an exponential of the form a e-
/b (r2 ≈ 1).
2 21.2 0.6CAO TCO TA O
0 89.041505.04 eCAO
0
1.2ANTCAO CAOC
The coefficients a and b are then determined by fitting the exponential function to CAO0 values computed from recent TCO2, TA, and O2 data sampled in waters from the latitude belt 20°S-40°S, and characterized by ≤ 2°C.
3. Precision of the CAO model
Prior 1991 During /after 1991
TCO2: 15 µmol kg-1 2 µmol kg-1
TA: 15 µmol kg-1 4 µmol kg-1
O2: 1.1 µmol kg-1 1.1 µmol kg-1
Potential temperature (; °C)
0 5 10 15 20 25 300
2
4
6
16
17
18
0 5 10 15 20 25 30
Err
or
(µm
ol
kg
-1)
0
5
20CAO (prior 1991)
CAO (during / after 1991)
CAO0
CO2ant (prior 1991)
CO2ant (during /
after 1991)
4. Results for the 1990s
North-south section
East-west sections
5. Results for the 1980s
North-south section
6. Anthropogenic CO2 inventories for the 1980s
Latitude
90°S
80°S
70°S
60°S
50°S
40°S
30°S
20°S
10°S EQ
10°N
20°N
30°N
40°N
50°N
60°N
70°N
80°N
90°NA
nth
rop
og
enic
CO
2 in
ven
tory
(G
t C
)
0
1
2
3
4
5
6
7Gruber et al.Chen et al.Stoecker et al.Sarmiento et al.This study (1980s)
7. Inventories for the 1980s and the 1990s
Latitude
90°S
80°S
70°S
60°S
50°S
40°S
30°S
20°S
10°S EQ
10°N
20°N
30°N
40°N
50°N
60°N
70°N
80°N
90°N
An
thro
po
gen
ic C
O2
inve
nto
ry (
Gt
C)
0
1
2
3
4
5
6
7During the 1990sDuring the 1980s
60 60
43
64
5430
9
22 68 78
44
25
42
10
37
5469
47 103
43
3861
190
157
49
216
Ne
t in
cre
as
e (
Gt
C)
-2
-1
0
1
2
8. Net increase of anthropogenic CO2 for the period 1984-1995:
??
The annual rate:
0.47 ±0.02 Gt C yr-1 0.66 Gt C yr-1
Perspectives:
We are planning to use the CAO model to estimate the concentrations of anthropogenic CO2 in other oceanic regions (Indian Ocean, Pacific Ocean), Using exactly the same observations to estimate the anthropogenic CO2, it would be useful to compare the results of the different models. The paper of Coatanoan et al. (2001), that compares the MIX and the C* approaches using data from the WOCE section I1 (northern Indian Ocean), shows that information can be gained from this kind of inter-comparison exercise. The end