Si-cycle in surface waters was investigated in summer 2003 during a transect conducted from south-Australia to Antarctica. Diatoms dominated the microphytoplankton. Silicic acid was depleted up to 60degreesS; a subsurface maximum of biogenic silica (= biosilica) was observed in the Permanent Open Ocean Zone. In the 100-0.01% light zone, the ratio of depth-integrated biosilica dissolution rate ( D) to depth-integrated biosilica production rate ( P) ranged between 0 to 3.1, being > 1 for 5 of our 6 stations. The biosilica dissolution was related to the percentage of dead diatoms but not to the temperature and might be, at least partially, under bacteria mediation. This study shows that during summer the Southern Ocean silicate pump can be much less efficient than usually expected. Existence of scenarios with intense surface Si-recycling in the Southern Ocean has major consequences both for modelers and paleoceanographers.