While our data are qualitatively consistent with previous evidence for pore water Al incorporation into diatom opal, our observed, roughly linear relationship between opal Al/Si and
MK0752 opal content does not agree with laboratory experiments. Koning et al. (2007) have demonstrated in both batch and flow-through experiments that the aluminum content associated with diatom frustules reaches a stable value after several weeks, and the samples exposed to water with a higher concentration of dissolved aluminum do not appear to incorporate a significantly higher amount of Al than the samples exposed to water with lower aluminum concentration (Koning et al., 2007; Table 1). Therefore, the authors argued that the number of suitable reactive surface sites on the frustules perhaps controls the uptake of Al and
chromatin the saturation of these sites prevents further Al incorporation (Koning et al., 2007). Although the concentrations of dissolved Al and Si in those experiments were representative of pore water concentrations, the reactions in the deep-sea sediments may well be more complicated and involve elements or compounds as the catalysts that were not considered in these experiments. The discrepancy may also arise from a distinction between the nature of the Al incorporation observed over several weeks to months in the laboratory and the Al incorporation mechanisms in marine sediments that apply over decades to millenia.
