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 CO 2 in the ocean ? Since anthropogenic CO 2 cannot be measured at sea, two major kinds of models have been used to separate the anthropogenic signal from the bulk of TCO 2 :  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): A novel (back calculation) approach: the CAO model

CARINA database

La méthode TrOCA Tracer combining Oxygen, iorganic Carbon, and total Alkalinity Touratier et Goyet (a,b; 2004)  ‘quasi-conservatif’  ‘conservatif’  TrOCA 0 is the unknown of the system

 The form of the equation CAO 0 = 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 (r 2 ≈ 1).  The coefficients a and b are then determined by fitting the exponential function to CAO 0 values computed from recent TCO 2, TA, and O 2 data sampled in waters from the latitude belt 20°S-40°S, and characterized by  ≤ 2°C.

3. Precision of the CAO model Prior 1991During /after 1991  TCO 2 : 15 µmol kg -1 2 µmol kg -1  TA: 15 µmol kg -1 4 µmol kg -1 O2:O2: 1.1 µmol kg -1

4. Results for the 1990s  North-south section

 East-west sections

5. Results for the 1980s  North-south section

6. Anthropogenic CO 2 inventories for the 1980s

7. Inventories for the 1980s and the 1990s

8. Net increase of anthropogenic CO 2 for the period : ? ?  The annual rate: 0.47 ±0.02 Gt C yr Gt C yr -1

Perspectives:  We are planning to use the CAO model to estimate the concentrations of anthropogenic CO 2 in other oceanic regions (Indian Ocean, Pacific Ocean),  Using exactly the same observations to estimate the anthropogenic CO 2, 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