Impact of post-mortem alternation on oxygen isotope values of diatom silica
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Oxygen isotope values of biogenic silica are increasingly used as proxies of paleoenvironmental conditions. A number of studies have demonstrated a strong relationship between the diatom silica and the temperature/oxygen isotope value of the formation water; however, some studies have indicated that early diagenesis of biogenic silica may alter the oxygen isotope values by several permil. Quantification of the maturation process has proven difficult since the mechanisms that drive post-mortem changes in the silica oxygen isotope values have not been well characterized. New silica maturation data from marine diatom, Stephanopyxis turris, cultured in a controlled laboratory experiment, demonstrate a rapid post-mortem decline in silica reactivity. A decrease in relative abundance of surface silanol groups coincides with a decrease in the surface charge density of freshly harvested frustules. These experiments demonstrate that rapid post-mortem alteration of biogenic silica provides a possible mechanism for alteration of oxygen isotope values in biogenic silica.