Table 1.
Metadata on the four deceased undocumented border crossers.
Table 2.
Isotope results of the four deceased undocumented border crossers.
Fig 1.
Sulfur isoscape generated by regression kriging.
A: Cross-validation between measured and predicted δ34S values using a Generalized Linear Model (GLM) regression using distance to the coast, longitude, latitude and country as predictors. RMSE = Root Mean Square Error. The red line is the best-fit linear model. δ34Shair-obs values correspond to the measured δ34S values in human hair B: Variogram of the GLM regression residuals. Red line is a Gaussian model fit using simple kriging. C. Cross-validation between measured and predicted δ34S values using GLM regression kriging. RMSE = Root Mean Square Error. The red line is the best-fit linear model. δ34Shair-obs values correspond to the measured δ34S values in human hair D. Map of δ34S in hair of resident humans across North America with locations of collection sites from residents (including individuals from this study as well as published data) [38, 44]. Coastlines and country boundaries are from http://www.naturalearthdata.com/. The R scripts to generate these figures are available in S1 and S2 Scripts. Data are available in S1 Database.
Fig 2.
Hydrogen isoscape generated in the assignR package.
A: Map of δ2H in hair of residents from North America with locations of collection sites from residents (including individuals from this study as well as published data) [33, 37, 55]. Coastlines and country boundaries are from http://www.naturalearthdata.com/. B: Calibration equation between modeled δ2H in precipitation and hair from North American residents (including individuals from this study as well as published data). The R script to generate these figures is available in S2 Script. Data are available in S2 Database.
Fig 3.
Quality evaluation of hydrogen, sulfur and dual-isotope probability maps.
Plots were generated using the QA function in the assignR package. A. Proportion of the study area excluded from the assignments as a function of probability threshold. Higher values indicate a potential for more specific assignments. B. Proportion of validation samples correctly assigned as a function of the probability threshold. If accurate posterior probabilities are estimated for each sample, these values should fall along the 1:1 line. C. Proportion of validation samples correctly assigned as a function of the area quantile, providing an integrated measure of assignment sensitivity. D. The distribution of odds ratios for the known origins of the validation samples relative to random quantifies the strength of isotopic support for one location relative to another. Higher odds ratios indicate more specific assignments. The R script to generate these figures is available in S2 Script.
Fig 4.
Probabilistic maps of provenance for deceased undocumented border crossers estimated from δ2H and δ34S values for bulk hair.
Locations where the human remains were discovered, are indicated by white circles. Locations where the remains are thought to have originated, based in independent evidence, are marked with red circles. Colours on the maps depict the predicted probability of origin based on isotopic evidence. Coastlines and country boundaries are from http://www.naturalearthdata.com/.The R script to generate these figures are available in S2 Script. Data are available in S1 Table and Table 2.
Fig 5.
Isotope values in Mr. Halifax’s hair profile (complete data per hair segment available in the S2 Table).
A. δ15N values; B. δ13C values; C. δ2H values; D. δ34S values. Dashed lines define isotopic lines used for dual isotope probability maps in Fig 6. The R script to generate this figure is available as S2 Script. Data are available in S2 Table. Due to the difficulty in aligning the hair of Mr. Halifax, the timeframe represented by hair length is more elastic than usual [11, 36]. We used an approximate hair growth rate of 1cm per month for visualization.
Fig 6.
Isotope-based probabilistic maps of provenance for Mr. Halifax estimated from δ2H and δ34S values for different representative hair segments.
Locations where the human remains were discovered (Halifax, NS) are indicated by red points. Colours on the maps depict the predicted probability of origin. Coastlines and country boundaries are from http://www.naturalearthdata.com/.The R script to generate these figures is available in S2 Script. The data are available in S2 Table.