a: Measured at the Keck Carbon Cycle Accelerator Mass Spectrometry Facility (UCIAMS), Earth System Science Department, University of California, Irvine, USA.b: All raw radiocarbon dates were converted to 2Sigma calendar ages with the CALIB 7.1.0 software using the MARINE13.14C calibration dataset (Reimer et al., 2013) without a further adjustment for a regional 14C reservoir age (DeltaR, deviation from the average global reservoir age of about 400 years).c: 2Sigma enclosing 95.4% of probability distribution.