FRACTIONATION OF SILICON ISOTOPES BY MARINE DIATOMS DURING BIOGENIC SILICA FORMATION

The fractionation of silicon isotopes by three species of marine diato ms, 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 o f 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), whi ch corresponds to the production of diatom silica with a delta(30)Si v alue that is 1.1 parts per thousand more negative than that of the dis solved silicon utilized for growth. The fractionation factor did not v ary with temperature and the consequent change in growth rate (ANOVA, p = 0.61; tested at 12 degrees, 15 degrees, and 22 degrees C with Thal assiosira sp.). The observation of fractionation of silicon isotopes b y 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.