Fractionation of silicon isotopes by marine diatoms during biogenic silica formation

The fractionation of silicon isotopes by three species of marine diatoms, Skeletonema costatum, Thalassiosira weissflogii, and Thalassiosira sp., grown in batch culture, is reported. Fractionation was observed for all species. The delta(30)Si value of the diatom silica and that of the initial silicic acid in the culture medium were used to compute a fractionation factor (alpha). The values of a for the three species were nearly identical, averaging 0.9989 +/- 0.0004 (s.d., n = 13), which corresponds to the production of diatom silica with a delta(30)Si value that is 1.1 parts per thousand more negative than that of the dissolved silicon utilized for growth. The fractionation factor did not vary with temperature and the consequent change in growth rate (ANOVA, p = 0.61; tested at 12 degrees, 15 degrees, and 22 degrees C with Thalassiosira sp.). The observation of fractionation of silicon isotopes by diatoms is an essential step in establishing delta(30)Si variations in biogenic silica as a potential oceanographic tracer. Copyright (C) 1997 Elsevier Science Ltd.