Fig. 1

Study region and DHP174 (Dempster Highway Peatland, near 174 km marker) site. a Regional map showing the DHP174 site (red star) and GNIP (Global Network of Isotopes in Precipitation) sites (1) Mayo and (2) Whitehorse; b the local δD_precip-temperature regression line calibrated with Mayo GNIP data (circles; excluding any leverage points marked with a square, see Methods); the validation r² reflects the performance of the calibration model in predicting Whitehorse GNIP δD_precip (crosses); the validation r² in brackets excludes extreme outlier residuals >2.5× the interquartile range (see Supplementary Fig. 1 for δ¹⁸O_precip-T line); c lithostratigraphy and position of the two core profiles (~50 m lateral distance); d overhead and e DEM oblique view of the study site—Google Earth and DigitalGlobe satellite images—with points marking the upper (red) and lower (yellow) core site locations; and f ground-level photograph from the peatland edge looking southwest across the disturbed surface