Text Box: Phytoplankton Ecophysiology Lab department of botany and plant pathology, oregon state university Text Box: | Home | Research | People | Contact | Links | Codes Text Box: Silicon metabolism in Diatoms and the d30Si record. Opal accumulation rates in sediments have been used as a proxy for carbon flux but there is poor understanding of the factors that may regulate the Si quota of diatoms. Natural variation in silicon isotopes (d30Si) in diatom frustules recovered from sediment cores are an alternative to opal mass for reconstructing diatom Si use and potential C export over geological time scales. Understanding the physiological factors that may influence the Si isotopic signal is vital for interpreting the d30Si of biogenic silica. We investigated the influence of pCO2 on the Si quota and Si fluxes across the cell membrane in the diatom Thalassiosira weissflogii and determined the impact that pCO2 has on the isotopic fractionation of Si (e). We found that under conditions of saturating silicic acid concentration, Si quota rises in cells grown with low pCO2 (100 ppm) and that the increased quota is the result of greater retention of Si (i.e. lower losses of Si through efflux). The ratio of influx : efflux increased two fold as pCO2 decreased from 750 ppm to 100 ppm. Changes in the influx : efflux ratio should influence the d30Si of silica and could effect measures of silica dissolution made using isotope dilution techniques. The efflux of silicon is shown to significantly bias measures of silica dissolution rates determined by isotope dilution, but no effect on the fractionation factor e was observed. The latter effect suggests that silicon isotopic discrimination in diatoms is set by the Si transport step rather than by the polymerization step. This observation supports the use of the d30Si signal of biogenic silica as an indicator of the percent utilization of silicic acid. Milligan, A.J., D.E. Varela, M.A. Brzezinski and F.M.M. Morel. (2004) Dynamics of silicon metabolism in a marine diatom as a function of pCO2. Limnol. Oceanog. 49: 322-329. PDF

Paleoproxies