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This paper describes for the first time the summer and winter distributions of sea surface δC in the Southern Indian Ocean (20°S-60°S). For this we used δC measurements from 10 cruises conducted between 1998 and 2005. For summer and winter, the highest δC values (>2‰) are observed in sub-Antarctic waters (40°S-50°S) and attributed mainly to biological activity, enhanced in the vicinity of Crozet and Kerguelen Archipelagoes. The lowest δC values are found in subtropical waters (25°S-35°S), with a minimum (<1‰) in the Agulhas Current region and in the Mozambique channel. On the seasonal scale, δC is higher during summer than during winter in all regions. The largest seasonal amplitude of variation (∼0.3‰), observed in the region 35°S-40°S, is attributed to biological activity during summer and to deep vertical mixing during winter. In subtropical oligotrophic waters, the mean seasonal amplitude of variation (∼0.15‰) is mainly explained by air-sea CO fluxes. On the interannual scale, we also identified a large negative anomaly of δC in the subtropical waters during austral summer 2002, associated to an anomalous ocean CO sink due to cold conditions during this period. [ABSTRACT FROM AUTHOR]