Production of biogenic silica by spring diatoms

The radioactive isotope Si-32 was used to measure Si uptake during a spring bloom dominated by the diatom Thalassiosira nordenskioeldii. The diatoms c onverted virtually all dissolved silicic acid in the surface layer into bio genic silica. The rate of Si uptake was unsaturated in all the experiments conducted during the bloom. The half-saturation constant for Si uptake decl ined from 6-12 mmol m(-3) early in the bloom to 2 mmol m(-3) when dissolved silicic acid concentration was low. The highest specific Si-uptake rates m easured (ca. 0.3 d(-1)) were comparable to average net growth rates calcula ted from cell abundance measurements.