Calibration of Multiple Tree-Ring Blocks and Its Implication on the Debate of Minoan Eruption of Santorini Around 17th–16th Century Bce

Abstract

The Minoan eruption of Santorini, Greece, is an important and often-debated chronological marker in contexts of the Eastern Mediterranean region. Among various age estimates of this event, one based on wiggle-matching of radiocarbon (14C) dates from an olive branch found in Santorini by Friedrich et al. (2006) has been widely discussed. Calibrated age estimates based on wiggle-matching of these 14C ages have been changing with improvements in the 14C calibration curve. As also shown earlier, calibration of average 14C age of multiple tree rings dated together should not be done using a single-year calibration curve. Since recent calibration curves include many single-year 14C datasets, a different approach should be considered to calibrate the average 14C age of block of multiple tree rings. Here we have demonstrated the use of multiple moving average (MA) calibration curves for calibrating the sequence of four 14C ages reported for the Santorini olive branch. The resultant calibrated ages for the Minoan Eruption are relatively younger than previous estimates and range from the late-17th century BCE to mid-16th century BCE date.

Problems of Dating Spread on Radiocarbon Calibration Curve Plateaus: The 1620–1540 BC Example and the Dating of the Therasia Olive Shrub Samples and Thera Volcanic Eruption

“…This stable isotope record seems to exhibit a spring (start) to a summer or later peak to fall/winter (end) δ 13 C signal for each year and thus demonstrates photosynthesis and growth each year and across the later spring through autumn and not only at the different partial periods reported in Raj et al (2023b). For example, the 1964 δ 13 C record seems to have a largely symmetical shape and mid-year peak as does 1965, directly contrary to the claimed very different claimed growth periods from the radiocarbon 'matching' stated in Raj et al (2023a). Therefore, the only conclusion is that the calendar timescale placements/associations reported in Raj et al (2023b: Fig.…”

“…lower 14 C ages on the earlier portions of slopes and raised 14 C ages on the later portions of slopes), but not create a parallel calendar-shifted curve (as shown e.g. for the period 1620-1600 BC in the moving average curve of Raj et al 2023a: Fig. 1).…”

“…2) for the wood portions used for the 14 C measurements are likely not secure. Raj et al (2023a) argue that, since the original Thera olive (TO) samples comprised blocks of wood containing a number of growth increments or likely years, then the radiocarbon dates obtained should be calibrated against a moving average calibration curve of similar chronological resolution (not that this is strictly known for such olive wood samples-see above). The difference is relatively small.…”