Fig. 2.

A shows annual ¹⁴C ages (radiocarbon years B.P.) from two calendar-dated tree-ring series [North American bristlecone pine (29) and Irish oak (30)] and the Mediterranean Gordion juniper series (positioned so the end ring of the whole sequence, which extends beyond the analyzed period, is at 745 BC) relative to the IntCal13 calibration curve. Data marked AA and ETH were collected at the University of Arizona and Eidgenössische Technische Hochschule Zurich radiocarbon laboratories, respectively. We note that these closely agreeing annual data seem to indicate that uncalibrated radiocarbon dates from pre-Thera contexts in the range from 3350 to 3310 ¹⁴C years B.P. could calibrate anywhere between c. 1620 and 1540 BC. An improved recalibration of such samples will be possible following the release of the IntCal20 curve, which will combine carefully screened annual data for this period from multiple laboratories using a different statistical method than was used for IntCal13. For this reason, we do not attempt to more closely compare curve shape between the annual data and the IntCal13 curve in this study. B shows the annual ¹⁴C ages in A converted to $\mathrm{\Delta }$¹⁴C (21) to emphasize patterns used to synchronize the floating chronology. Visual matching of the small-scale data feature shown for all growth locations at c. 1528 BC (arrow) further confirms the χ² result. The feature at c. 1548 BC is present only in the juniper data but if replicated in this material, could indicate a localized disturbance in the carbon cycle.