Incorporation of terrigenous materials into diatom frustules

Abstract

Laboratory investigation of the potential for diatoms to obtain silica from feldspars, using aluminum as a tracer. Diatoms were cultivated with and without feldspar powder. Population and concentrations of silica and TEP were measured 2-3 times per week throughout one month of cultivation. Aluminum distribution in the frustule was then measured with EPMA. The presence of feldspars seemed to cause the bloom to be spread over a larger number of days, while also inhibiting diatom growth. The total number of living and dead diatoms at the end of the experiment was approximately the same for all three bottles, implying that these two effects counterbalanced one another. TEP concentration remained almost the same for all three until day 20 of the experiment, when it began to rise. The concentration was found to be far higher for albite, and the lowest for control. TEP concentration did not increase until after the peak of the diatom bloom. Silica concentration dropped quickly in all bottles, but showed a lag in the case of albite. By the time of the diatom population peak, Si concentration was extremely low in all cases. After most diatoms had died, around day 25, it began to rise again. When the diatoms were cultivated in an environment where the dominant source of aluminum was from the powdered feldspars, their frustules revealed a higher aluminum to silica ratio in the outer layer of the frustule. Diatoms grown without added feldspars, where aluminum was therefore minimally present as a background trace element, instead showed low Al/Si values for both inner and outer layers. The mechanisms and function of this double peak remains to be examined.