Reconstruction of travel history using coupled delta super(18)O and super(87)Sr/ super(86)Sr measurements of hair

Rationale Oxygen isotope ratios ( delta super(18)O values) of hair largely reflect features of regional hydrology while strontium isotope ratios ( super(87)Sr/ super(86)Sr) are thought to reflect bedrock geology; combination of both isotope signatures may provide greater capacity for determining provenance and reconstructing travel history of an organism. To test this hypothesis, we compared the O-Sr isotope profiles of hair from domestic horses with known residency histories. Methods Tail hairs were collected from a pair of horses pastured together for a period of 16 months, one of which lived in a different location for the 8 months prior. Hair samples were washed with solvents to remove external contaminants prior to sequential sampling for delta super(18)O and super(87)Sr/ super(86)Sr analysis via TC/EA-IRMS and MC-ICP-MS, respectively. Hair digests were concentrated and analyzed employing low-flow natural aspiration to measure super(87)Sr/ super(86)Sr. Results Tail hair from the control and transported horses had mean delta super(18)O values of 11.25 plus or minus 1.62 ppt and 10.96 plus or minus 1.53 ppt, and mean super(87)Sr/ super(86)Sr of 0.7101 plus or minus 0.0006 and 0.7109 plus or minus 0.0020, respectively. The delta super(18)O and super(87)Sr/ super(86)Sr profiles for the control and transported horses were indistinguishable when they were pastured together. The super(87)Sr/ super(86)Sr profiles were significantly different during the period that the horses were living apart, while the delta super(18)O values were indistinguishable during that period. Conclusions By comparing the O-Sr isotope profiles of a control and transported horse, we investigated isotopic signal(s) potentially useful for reconstructing travel histories via high-resolution sequential sampling along single strands of tail hair. Improved analytical capabilities allowed for extremely low Sr abundance samples to be analyzed for super(87)Sr/ super(86)Sr and proved capable of resolving a horse's movement between distinct regions.