Inter-laboratory comparison of oxygen isotope compositions from biogenic silica

Abstract

Several techniques have been introduced in the last decades for the dehydration and release of O 2 from biogenic silica (opal-A) for oxygen-isotope analysis. However, only one silica standard is universally available: a quartz standard (NBS28) distributed by the IAEA, Vienna. Hence, there is a need for biogenic silica working standards. This paper compares the existing methods of oxygen-isotope analyses of opal-A and aims to characterize additional possible working standards to calibrate the d 18 O values of biogenic silica. For this purpose, an inter-laboratory comparison was organized. Six potential working standard materials were analysed repeatedly against NBS28 by eight participating laboratories using their specific analytical methods. The materials cover a wide range of d 18 O values (+23 to +43 & ) and include diatoms (marine, lacustrine), phytoliths and synthetically-produced hydrous silica. To characterize the proposed standards, chemical analyses and imaging by scanning electron microscopy (SEM) were also performed. Despite procedural differences at each laboratory, all methods are in reasonable agreement with a standard deviation (SD) for d

Application of Fourier Transform Infrared Spectroscopy (FTIR) for assessing biogenic silica sample purity in geochemical analyses and palaeoenvironmental research

“…The second is the marine diatom standard PS1772-8 from the South Atlantic Ridge. Diatoms in both samples are well preserved and show no signs of diagenesis or frustule dissolution (Chapligin et al, 2011). Whereas trace levels of contamination have been detected through XRF and light microscopy in BFC mod , no impurities have been found in PS1772-8 with additional SEM, light microscopy, X-ray Diffraction (XRD) and Nuclear Magnetic Resonance (NMR) analyses confirming the purity of both samples (Chapligin et al, 2011).…”

“…5a, b). Although XRF analyses indicate small levels of contamination in BFC (Al 2 O 3 = 2.0 wt.%) compared to PS1772-8 (Al 2 O 3 = 0.09 wt.%) (Chapligin et al, 2011), using the PS1772-8 end-member only marginally reduces the difference between XRF and FTIR estimates of contamination. However, values of Residual c for PS1772-8-"Silt" are significantly lower at c. 5% for most samples, suggesting that the PS1772-8 end-member produces more accurate results with better identification of the optimal FTIR model (Fig.…”

A Review of the Stable Isotope Bio-geochemistry of the Global Silicon Cycle and Its Associated Trace Elements

“…The disparate bSiO 2 -water fractionation factors have been attributed to two primary causes: (1) methodological biased and/or incomplete removal of hydroxyl oxygen, and (2) potential alteration of δ 18 O values during bSiO 2 formation/diagenetic alteration of δ 18 O values on geologic timescales. The analytical bias has been addressed thorough an inter-laboratory comparison that showed no significant difference in δ 18 O values across a range of dehydration and analytical techniques (Chapligin et al, 2011); therefore, the only remaining source of uncertainty is in the bSiO 2 -water fractionation relationship recorded by the diatom bSiO 2 .…”

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

“…For every session of measurement, the effectiveness of the entire dehydration and IR-laser-fluorination-IRMS procedure was checked through the analysis of a working phytolith standard (MSG60) with δ 18 O = 36.90±0.78 ‰, δ 17 O = 19.10± 0.40 ‰ and 17 O-excess = −215 ± 34 per meg (n = 29). For comparison, the inter-laboratory pooled value for MSG60 is δ 18 O = 37.0 ± 0.8 ‰ (Chapligin et al, 2011). Recent measurements of the silicate reference materials UWG-2 garnet (Valley et al, 1995) and San Carlos (SC) olivine gave the following values: δ 18 O UWG−2 = 5.72 ± 0.12 ‰, δ 17 O UWG−2 = 2.95 ± 0.06 ‰, 17 O-excess UWG−2 = −68 ± 27 per meg (n = 5), δ 18 O SC = 4.95 ± 0.22 ‰, δ 17 O SC = 2.56 ± 0.12 ‰, 17 Oexcess SC = −49 ± 24 per meg (n = 3).…”