Sempéré¹, R., C. Panagiotopoulos¹, F. Van Wambeke¹, M. Goutx¹, M. Bianchi¹ and P. Tréguer²

¹LMM, CNRS/INSU, UMR 6117, Centre d’Océanologie de Marseille, Marseille France, Fax: + 33 (0) 4 91 82 90 51, E-mail: sempere@com.univ-mrs.fr and ²LEMAR, UMR CNRS/INSU 6539, Institut Universitaire Europeen de la Mer, Plouzane, France

Bacterial cycling of dissolved and particulate organic carbon in the Indian Sector of Southern Ocean: Results of the Antares Program

Seawater samples were collected in the Indian Sector of the Southern Ocean during October 1995 and January-March 1999, they were analysed for total organic carbon (TOC) as well as bacterial production. Sinking particles were also collected by using in situ pumps and floating sediment traps (200 m) and were studied for particulate organic carbon (POC), amino-acids like compounds and sugar composition during in vitro biodegradation experiments. We observed that clearly the biological system may shift from one system according to the season and the latitude, with both high TOC accumulation and high bacterial production associated to low export of POC or to the opposite. Biodegradation experiments indicated that exported POC was less degraded in Polar Front Zone (PFZ) than in Sub-Antarctic region (SAr) probably because of the higher temperatures and bacterial production encountered in surface SAr waters or because of the more rapid dissolution of mineral matrices in SAr area. We also found that sinking particles were also characterized by lower carbohydrate yields and C:N ratios compared to particles collected in Mediterranean Sea. Although, there is not yet a clear explanation on this point, we can note from the literature, differences in the C:N ratios of sinking POC between the Mediterranean Basin and the Indian sector of the Southern Ocean i.e.[(Mediterranean Sea : C:N ratios: 7.8-13); (Southern Indian Ocean: C:N ratios: 5.7-7.3)] as well. These results are consistent with previous investigations indicating special chemical composition of phytoplankton and/or marine particulates in Southern Ocean compared to other Oceanic Provinces.