The bSiO2 ooze of the Southern Ocean (S.O) has long provided a source of discussion over how and why such thick accumulations exist underlying a region of relatively low diatom productivity. The low temperatures and high nutrient conditions of many regions of the S.O are understood to be optimal for Fragilariopsis kerguelensis, a slow growing diatom with a high silicate (Si), yet low iron requirement, thus making it a dominant species in the surface ocean of this region. The high level of silification and robust characteristics of F.kerguelensis has been hypothesised as being a main factor contributing to its persistence in the sediments of the S.O. However, specific dissolution characteristics of this species have not previously been elucidated, nor have the effects that temperature and aggregation might have in determining the diatom composition of deep ocean sediments. Laboratory experiments tested the hypothesis that the rate of bSiO2 dissolution of aggregated F.kerguelensis is lower than that of the less silicified Chaetoceros debilis. The effects of temperature and physiological stage of the cells on the dissolution rate of freshly aggregated cells was also investigated. Four experiments were undertaken; one with F.kerguelensis at 5º C, one with senescent C.debilis at 5º C, one with senescent C.debilis at 15º C, and one with exponentially growing C.debilis at 5º C. Aggregates were formed in rolling tanks and Si dissolution monitored for 4 months. bSiO2 dissolution was significantly lower for F.kerguelensis as compared to C.debilis at 5º C. Dissolution of C.debilis aggregates formed using exponentially growing cells started with a lag period of 1 week in comparison to those formed using senescent cells, and dissolution increased markedly with temperature
