SIMS sputtering rates in biogenic aragonite: implications for culture calibration studies for palaeoenvironmental reconstruction

Abstract

We used scanning white light interferometry to view the craters produced during secondary ion mass spectrometry (SIMS) analysis of the CaCO3 skeleton of an aragonitic coral. The dimensions and volumes of craters sputtered during trace element, δ18O, δ13C and δ11B analyses were determined. Sputtering rates were ~6 µm3 nA−1 min−1 for a 16O− primary beam and ranged from ~12 µm3 nA−1 min−1 (for δ18O analyses) to ~19 µm3 nA−1 (for δ13C analyses) using a Cs+ primary beam. Sputter yields (atoms sputtered/impinging primary ions) ranged from 1.3 to 1.4 for a 16O− primary beam and from 2.5 to 4.5 using a Cs+ primary beam. Useful ion yields (ions detected/atoms sputtered), using instrument conditions typically used in geoscience applications, were of the order of 10−4 for B, Mg, Ca, Sr, Ba and C and 10−2 for O. The maximum lengths of the SIMS craters, at the sample surface, range from ~17 µm (δ13C analyses) to ~36 µm (δ11B analyses) and crater depths range from ≤3 µm (δ18O analyses) to >20 µm (δ11B analyses). These dimensions are significant in relation to accretion rates in a range of biogenic carbonates and SIMS analyses typically sample carbonate deposited over time periods of days to months depending on the organism and structure analysed. In culture calibration studies, accurate determination of the temporal resolution of the analysed volume is crucial to ensure that the entire volume reflects the culture conditions and does not include carbonate deposited prior to introduction of the organism to the culture system. Copyright © 2013 John Wiley & Sons, Ltd.