The dataset includes speleothem U-Th ages used to reconstruct climate in southeastern Alaska during the past ~3,500 years. Speleothem WB-21-5-A was collected in Wishbone Cave (55.774 N, -133.191 E; 420 m.a.s.l.) and speleothem WA-21-6-A was collected in Walkabout Cave (55.776° N, 133.195° W; 350 m.a.s.l.) on May 21, 2022 and June 21, 2022, respectfully. The data collection was completed between September 2021-March 2022. U-Th ages were measured on a ThermoFisher Neptune Plus multi-collector inductively coupled plasma mass spectrometer.

U decay constants: l238 = 1.55125x10-10 (Jaffey et al., 1971) and l234 = 2.82206x10-6 (Cheng et al., 2013).Th decay constant: l230 = 9.1705x10-6 (Cheng et al., 2013). d234U = ([234U/238U]activity – 1)x1000d234Uinitial was calculated based on 230Th age (T), i.e., d234Uinitial = d234Umeasured x el234xT. Corrected 230Th ages assume the initial 230Th/232Th atomic ratio of 4.4 ±2.2 x10-6. Those are the values for a material at secular equilibrium, with the bulk earth 232Th/238U value of 3.8. The errors are arbitrarily assumed to be 50%.** B.P. stands for “Before Present” where the “Present” is defined as the year 1950 CE.