Assessing the preservation of biogenic strontium isotope ratios (87Sr/86Sr) in the pars petrosa ossis temporalis of unburnt human skeletal remains: A case study from Saba

Rationale:Strontium isotope (87Sr/86Sr) analysis of skeletal remains has become apowerful tool in archaeological studies of human migration and mobility. Owing to itsresistance to post-mortem alteration, dental enamel is the preferred samplingmaterial used for 87Sr/86Sr analysis in bioarchaeological provenance research,although recent studies have demonstrated that cremated bone is also generallyresistant to diagenesis. This paper presents the results of a pilot study exploring thepotential of unburnt petrous bone (pars petrosa) as a reservoir of biogenic(diagenetically unaltered) strontium, as the otic capsule or bony labyrinth within thepetrous bone is extremely dense and is thought to be unable to remodel after early childhood, potentially providing an alternative for dental enamel.

Methods:From an individual from a colonial-era (18th century) site on the island of Saba in the Caribbean for whom previous enamel 87Sr/86Sr results had indicatednon-local origins, multiple locations (n=4) on the petrous were sampled andmeasured for strontium isotope composition. Saba (13 km2) has been extensively mapped for baseline strontium isotopes (n=50) with 87Sr/86Sr varying from ca 0.7065 to 0.7090, where as enamel 87Sr/86Sr (n=3) ranged from 0.7104 to 0.7112.

Results:All four petrous87Sr/86Sr ratios (0.7111–0.7122) are consistently andconsiderably higher than the local bioavailable range, and very similar to the enamel 87Sr/86Sr. These results provide initial evidence that unburnt petrous bones maypreserve biogenic strontium, at least in this specific burial context.Conclusions:While more research in diverse burial conditions is needed to validatethis observation, if confirmed, it would have broader implications for sampleselection strategies in bioarchaeological studies using the strontium isotope method.