For the solution data, sampling and isotope analysis was done in a prior study and is detailed in Britton et al.23 (link). To summarise, the second and third molars (M2 and M3) were extracted from the mandibles, brush-cleaned with water and left to dry overnight. The whole teeth were mechanically abraded to remove surficial enamel. Sampling was done on the buccal face of the anterior loph as it presented a thicker enamel, with the face removed and cleaned from adhering dentine using a tungsten carbide burr. Enamel faces were then marked for horizontal sectioning at ∼ 1.5 mm intervals, ultrasonicated in deionize water (DI H2O, 18.3 MΩ) and dried, before being cut into strips using diamond-coated superfine circular drill bits. Samples were then individually ultrasonicated in DI H2O, dried and split longitudinally with ∼ 5 mg of enamel being reserved for 87Sr/86Sr solution analysis and the remainder being retained for carbon and oxygen isotope analysis. In that study, sections were numerically assigned from the ERJ to the OS (M2-1, M2-2, M2-3,…).
Strontium was isolated from enamel in clean laboratory facilities at the Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology (MPI-EVA), Leipzig, Germany using a modified version of the method from Deniel and Pin28 (link) described in detail in Copeland et al.34 (link). The following description of the analytical procedure is reproduced from Britton et al.23 (link), and is also presented there in full. The ∼ 5 mg samples were dissolved in 1 ml 14.3 M high purity HNO3 then evaporated to dryness. The obtained residue was then re-dissolved in 1 ml 3 M HNO3 before loading into pre-conditioned columns containing Sr Resin (Eichrom Technologies, Lisle, IL, USA), being passed through three times. Strontium was then eluted using ultrapure deionized water (18.2 MΩ), dried and re-dissolved in 3% HNO3 and analysis of 87Sr/86Sr ratios was undertaken using a Thermo Fisher Neptune™ (MC-ICP-MS). All the acids solutions used in the procedure were purified through a PicoTrace double-distilled sub-boiling distillation system. The subsequent 87Sr/86Sr measurements on standards and samples were corrected for interferences from krypton (Kr) and rubidium (Rb) and normalized for instrumental mass bias to 88Sr/86Sr = 8.375209 (exponential law). Analysis of the international strontium isotope standard NIST SRM987 (National Institute of Standards and Technology, Gaithersburg, USA) during each analytical session was used for external normalisation of data (long-term 87Sr/86Sr value = 0.710273 ± 0.000033 (2σ) (n = 97)). All 87Sr/86Sr values reported here were adjusted so SRM987 = 0.71024072, involving a data correction factor of − 0.00002. Strontium concentrations of the enamel samples were determined using the method described in34 (link), which is accurate to within ± 31 ppm.
Strontium was isolated from enamel in clean laboratory facilities at the Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology (MPI-EVA), Leipzig, Germany using a modified version of the method from Deniel and Pin28 (link) described in detail in Copeland et al.34 (link). The following description of the analytical procedure is reproduced from Britton et al.23 (link), and is also presented there in full. The ∼ 5 mg samples were dissolved in 1 ml 14.3 M high purity HNO3 then evaporated to dryness. The obtained residue was then re-dissolved in 1 ml 3 M HNO3 before loading into pre-conditioned columns containing Sr Resin (Eichrom Technologies, Lisle, IL, USA), being passed through three times. Strontium was then eluted using ultrapure deionized water (18.2 MΩ), dried and re-dissolved in 3% HNO3 and analysis of 87Sr/86Sr ratios was undertaken using a Thermo Fisher Neptune™ (MC-ICP-MS). All the acids solutions used in the procedure were purified through a PicoTrace double-distilled sub-boiling distillation system. The subsequent 87Sr/86Sr measurements on standards and samples were corrected for interferences from krypton (Kr) and rubidium (Rb) and normalized for instrumental mass bias to 88Sr/86Sr = 8.375209 (exponential law). Analysis of the international strontium isotope standard NIST SRM987 (National Institute of Standards and Technology, Gaithersburg, USA) during each analytical session was used for external normalisation of data (long-term 87Sr/86Sr value = 0.710273 ± 0.000033 (2σ) (n = 97)). All 87Sr/86Sr values reported here were adjusted so SRM987 = 0.71024072, involving a data correction factor of − 0.00002. Strontium concentrations of the enamel samples were determined using the method described in34 (link), which is accurate to within ± 31 ppm.
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