A multiparametric linear regression technique was used for waters in the Southern Ocean to estimate the change in both &dgr;13CDIC(&Dgr;&dgr;13CDIC) and dissolved inorganic carbon (DIC) (&Dgr;DIC) between 1978 and 1998, due to the accumulation of anthropogenic CO2. The observed decrease in &dgr;13CDIC at the surface, the Suess effect, was -0.015¿0.003?yr-1 in the Sub-Antarctic Zone and -0.015¿0.003?yr-1 in the Antarctic Zone, similar to values reported for the southern Indian Ocean [Gruber et al., 1999; Sonnerup et al., 2000]. To compare the &Dgr;&dgr;13CDIC with &Dgr;DIC, we used the ratio of these two anomalies (&Dgr;RC=-&Dgr;&dgr;13CDIC/&Dgr;DIC?(&mgr;molkg-1)-1). Along the section, &Dgr;RC ranged from 0.015¿0.005 at 42¿S to 0.007¿0.005?(&mgr;molkg-1)-1 at 54¿S. The spatial variability in &Dgr;RC in the Southern Ocean reflects different timescales for processes controlling the uptake of 13C from those controlling the uptake of 12C and indicates that &Dgr;&dgr;13CDIC decouples from &Dgr;DIC poleward of the Sub-Antarctic Zone. The variations of &Dgr;RC along the section suggest that the &dgr;13CDIC anomaly is not a good predictor of the anthropogenic CO2 inventory in the Southern Ocean. Some methods for determining anthropogenic CO2 uptake both on the global and regional scale assume the penetration depths of &Dgr;&dgr;13CDIC to be the same as &Dgr;DIC, which implies a constant value for &Dgr;RC in the ocean at ~0.016? (&mgr;mol kg-1)-1 [Heimann and Maier-Reimer, 1996; Oritz et al., 2000; Bauch et al., 2000]. The use of a constant &Dgr;RC and the observed &Dgr;&dgr;13CDIC to estimate anthropogenic CO2 could lead to an underestimate in the inventory of anthropogenic CO2 for the Southern Ocean by ~50%. ¿ 2001 American Geophysical Union