title: Nano-SIMS analysis of Mg, Sr, Ba and U in natural calcium carbonate.
abstract: Concentrations of minor (Mg and Sr) and trace (Ba and U) elements in four natural calcium carbonate samples were first analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical dissolution and calibrated against a standard dolomite. Their homogeneities were checked by in situ laser ablation (LA) ICP-MS with 10-20 spots. The carbonate samples were measured by using a high lateral resolution secondary ion mass spectrometer (Nano-SIMS NS50). A approximately 4 nA O- primary beam was used to sputter a 5-6-microm diameter crater on the sample surface, and secondary positive ions were extracted for mass analysis using an accelerating voltage of 8 kV and a Mattauch-Herzog geometry. A multi-collector system was adjusted to detect 26Mg+, 43Ca+, 88Sr+, 138Ba+, 238U16O+ and 238U16O2+ ions at the same time. A resolving power of 2500-5000 at 10% peak height was attained by an entrance slit set at 40 microm, and each exit slit at 50 microm with adequate flat-topped peaks. The observed 26Mg/43Ca, 88Sr/43Ca, 138Ba/43Ca and 238U16O2/43Ca ratios agreed well with those measured by LA-ICP-MS. Foraminifera shells were analyzed at 5-6 microm scale by Nano-SIMS. There was a large variation of the Mg/Ca ratios, up to +/- 38%, even in a single fragment of the shell, suggesting that although the ratios provide a useful paleoceanographic proxy at bulk scale, they may reflect a more complex pattern at < 10 microm scale.
authors.affiliation: Ocean Research Institute, The University of Tokyo, Nakanoku, Japan. ysano@ori.u-tokyo.ac.jp
authors.forename: Yuji
authors.initials: Y
authors.lastname: Sano
authors.forename: Kotaro
authors.initials: K
authors.lastname: Shirai
authors.forename: Naoto
authors.initials: N
authors.lastname: Takahata
authors.forename: Takafumi
authors.initials: T
authors.lastname: Hirata
authors.forename: Neil C
authors.initials: NC
authors.lastname: Sturchio
mesh_terms: D001464:Barium / Q000032:analysis*; D002119:Calcium Carbonate / Q000737:chemistry*; D004577:Electron Probe Microanalysis; D008274:Magnesium / Q000032:analysis*; D036103:Nanotechnology; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods*; D013324:Strontium / Q000032:analysis*; D014501:Uranium / Q000032:analysis*
chemical_list: D001464:Barium; D014501:Uranium; D002119:Calcium Carbonate; D008274:Magnesium; D013324:Strontium