科研之友
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摘要
In this study, we show that the rate of shell precipitation in the extant planktic foraminifer Orbulina universa is sufficiently rapid that 12 h calcification periods in O-18-labeled seawater can be resolved and accurately measured using secondary ion mass spectrometry (SIMS) for in situ delta O-18 analyses. Calcifying O. universa held at constant temperature (22 degrees C) were transferred every 12 h between ambient seawater (delta O-18(w) = -0.4 parts per thousand VSMOW) and seawater with enriched barium and delta O-18(w) = +18.6 parts per thousand VSMOW, to produce geochemically distinct layers of calcite, separated by calcite precipitated with an ambient geochemical signature. We quantify the position of the Ba-labeled calcite in the shell wall of O. universa via laser ablation ICP-MS depth profiling of trace element ratios, and then measure intrashell delta O-18(calcite) in the same shells using SIMS with a 3 mu m spot and an average precision of 0.6 parts per thousand (+/- 2 SD). Measured delta O-18(calcite) values in O. universa shell layers are within +/- 1.1 parts per thousand of predicted delta O-18(calcite) values. Elemental and oxygen isotope data show that LA-ICP-MS and SIMS measurements can be cross-correlated within the spatial resolution of the two analytical techniques, and that delta O-18(calcite) and elemental tracers appear to be precipitated synchronously with no measurable spatial offsets. These results demonstrate the capability of SIMS to resolve daily growth increments in foraminifer shells, and highlight its potential for paleoceanographic and biomineralization applications on microfossils.
- 出版日期2013-4-15
