Stable strontium isotopic ratios from archaeological organic remains from the Thorsberg peat bog

Strontium isotope evidence for a trade network between southeastern Arabia and India during Antiquity

Cotton (Gossypium sp.), a plant of tropical and sub-tropical origin, appeared at several sites on the Arabian Peninsula at the end of the 1st mill. BCE-beginning of the 1st mill. CE. Its spread into this non-native, arid environment is emblematic of the trade dynamics that took place at this pivotal point in human history. Due to its geographical location, the Arabian Peninsula is connected to both the Indian and African trading spheres, making it complex to reconstruct the trans-continental trajectories of plant diffusion into and across Arabia in Antiquity. Key questions remain pertaining to: (1) provenance, i.e. are plant remains of local or imported origin and (2) the precise timing of cotton arrival and spread. The ancient site of Mleiha, located in modern-day United Arab Emirates, is a rare and significant case where rich archaeobotanical remains dating to the Late Pre-Islamic period (2nd-3rd c. CE), including cotton seeds and fabrics, have been preserved in a burned-down fortified building. To better understand the initial trade and/or production of cotton in this region, strontium isotopes of leached, charred cotton remains are used as a powerful tracer and the results indicate that the earliest cotton finds did not originate from the Oman Peninsula, but were more likely sourced from further afield, with the north-western coast of India being an isotopically compatible provenance. Identifying the presence of such imported cotton textiles and seeds in southeastern Arabia is significant as it is representative of the early diffusion of the crop in the region, later to be grown extensively in local oases.

Strontium isotope ratios of human hair from the United States: Patterns and aberrations

RATIONALE

Strontium isotope ratios (⁸⁷ Sr/⁸⁶ Sr) of hair may be a valuable tool to estimate human provenance. However, the systematics and mechanisms controlling spatial variation in ⁸⁷ Sr/⁸⁶ Sr of modern human hair remain unclear. Here, we measure ⁸⁷ Sr/⁸⁶ Sr of hair specimens from across the USA to assess the presence of geospatial relationships.

METHODS

Ninety-eight human hair specimens were collected from salon/barbershop floors in 48 municipalities throughout the conterminous USA. [Sr] and ⁸⁷ Sr/⁸⁶ Sr ratios were measured from hair using quadrupole and multi-collector inductively coupled plasma mass spectrometers, respectively. The [Sr] and ⁸⁷ Sr/⁸⁶ Sr ratios of hair were compared with the measured [Sr] and ⁸⁷ Sr/⁸⁶ Sr ratios of tap waters from the collection locations. In addition, the ⁸⁷ Sr/⁸⁶ Sr ratio of hair was compared with the modeled ratios of bedrock and surface waters.

RESULTS

Hair color was independent of the ⁸⁷ Sr/⁸⁶ Sr ratio, but related to [Sr]. The ⁸⁷ Sr/⁸⁶ Sr ratios of hair and leachate were not statistically different and were positively correlated; however, in several hair-leachate pairs, the ratios were conspicuously different. The ⁸⁷ Sr/⁸⁶ Sr ratios of both hair and leachate were linearly correlated with tap water. The ⁸⁷ Sr/⁸⁶ Sr ratio of hair was also significantly correlated with the modeled ratio of bedrock and surface waters, although the ⁸⁷ Sr/⁸⁶ Sr ratio of hair was most strongly correlated with the measured ratio of tap water.

CONCLUSIONS

The ⁸⁷ Sr/⁸⁶ Sr ratio of hair is related to the ratio of tap water, which varied geographically. The ratio of hair provided geographic information about an individual's recent residence. Differences in the ⁸⁷ Sr/⁸⁶ Sr ratios of hair and hair leachate may be concomitant with travel and could potentially be used as a screening tool to identify recent movements.