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The analyses of metal contents in cleaned diatom samples from JPC17 show high aluminum to AZD5438 ratio, which are on average one order of magnitude greater than Ca, Mg and Fe. All of the measured trace metals exhibit the same patterns of variations as observed for Al among samples (Fig. 4A, B; including Mn, not shown). The Al/Si ratio measured with ICP range between 0.0034 and 0.0870, with an average value of 0.0289. Both the absolute values and the variations among samples were confirmed with EDX measurements (Fig. 4C, D). Because EDX measures the Al content of diatom frustules exclusively without the ambiguity of detrital clays, the similarity between the two again strongly suggests that the Al measured by ICP is incorporated into the biogenic silica.
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Fig. 4.
Downcore measurements of metal contents in cleaned diatom samples from JPC17 using inductively coupled plasma optical emission spectroscopy (A, B, and filled symbols in C, error bars are estimated standard deviations from the replicates) and using energy-dispersive X-ray spectroscopy (C: average value in open symbols; dashed lines indicate average value ± standard deviation of the variation among the sampling spots within each sample), as well as the comparison between the two measurements (C, D). For panel D, the plotted linear regression (solid line) and 95% confidence interval (dashed lines) include the sample with high Al/Si value (sample at 816 cm). If this sample is excluded, the linear regression of the 20 samples is Al/SiICP = 0.748 × Al/SiEDX ave., with a lower squared correlation coefficient of 0.682.