Crossing the Borders: New Methods and Techniques in the Study of Archaeological Materials from the Caribbean

Tracing Human Mobility with 87 Sr/ 86 Sr / 219
then dissolved in 2 to 3 drops of concentrated HN03 and dried down. This step was
repeated. The residue was dissolved in 0.5 ml 3N HN03, and this solution was centrifuged
for 4 minutes at 12,000 rpm to remove any possible nonsoluble constituents
(none were visible in any of the samples). The upper 90 percent of the solution
was then transferred to a Strontium Spec resin chromatography column
for strontium extraction, according to standard procedures (Heumann and Davies
2002). Strontium isotope ratios were determined on the FinniganMat 262 RPQ
Plus thermal ionization mass spectrometer at the Free University Amsterdam. Statistical
analysis of the collected data was done using SPSS 12.0.
Measurement Accuracy
Blanks
Laboratory blanks yielded 80 to 500 pg of strontium. The higher value is typical
for the samples measured at the end of 2005 and is due to the use of a batch of
Strontium Spec of substandard quality. The blank strontium is derived from the
Strontium Spec resin used in column extraction and to a lesser extent from laboratory
chemicals. It has an 87 Sr/ 86 Sr of ~0.7075. On a 200 ng sample this amounts
to 0.25 percent of the total strontium present. The presence of this contaminating
strontium decreases the accuracy of our measurements on typical ( 87 Sr/ 86 Sr =
0.7091) samples by 0.001 percent (one unit in the fifth decimal place). This error is
approximately equal to the analytical error and is therefore negligible compared to
the natural variation in 87 Sr/ 86 Sr, so no blank correction has been applied.
Standards
NBS 987 is used to assess measurement accuracy. Standard analyses over 2003
yielded mean 87 Sr/ 86 Sr of 0.710245 ± 8 (n = 7), whereas analyses over 2005 yielded
mean 87 Sr/ 86 Sr of 0.710241 ± 4 (n = 8). The means are equal within error to the
long- term mean of 0.710243 ± 9 (n > 200) so no correction has been applied to
samples measured during different analytical periods.
Results
The mean strontium isotope ratios for the samples are presented in Table 15.1, and
the individual results for the human and rice rat enamel samples are listed in Table
15.2. The mean 87 Sr/ 86 Sr of human enamel is 0.708989 and is lower than the mean
found for the soil and rice rats. The mean values found for the human enamel
samples are similar for all types of dentition. There is, for example, no significant
difference between strontium isotope ratios in permanent incisors and premolars
(ANOVA, f = 0.132, n = 49, p = 0.88).
Two well- preserved teeth have been sampled in multiple spots to determine
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