Eight samples of monospecific planktic foraminifera of Neogloboquadrina pachyderma (sin.) with a weight of 4–6 mg were picked from the >125‐μm size fraction and measured in the Beta Analytic Radiocarbon Dating Laboratory. Conventional accelerator mass spectrometer (AMS) 14C ages were calibrated to calendar ages using Calib 8.20 with the Marine20 calibration curve (Heaton et al., 2020) and the ΔR of 350 ± 40 years according to the reservoir age of the far NW Pacific equal to 900 years (Max et al., 2012). The resultant AMS 14C data along with other time points were used for age model construction.