a, Calculated U/Th ages, relative to the date of subsample preparation for U and Th analyses, in thousands of years (ky) before 1950 CE (BP), plotted as burnt orange closed circles versus stalactite depth. Depth refers to distance from stalactite tip, increasing towards the cave ceiling; zero mm is the youngest calcite subsampled for δ18Oc. Error bars depict ± 2σ analytical uncertainty of U/Th analyses. The line and shaded envelope shows the median, and 10th to 90th percentile distributions of our age model, respectively; estimated by fitting N = 1,000 splines in the Bchron software package4. b, 232Th versus depth, exhibiting consistent, low32part-per-billion concentrations irrespective of sample depth. c, A histogram and Gaussian KDE of 232Th concentrations highlight the narrow distribution of232Th values.