#date calibration

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A graffito scratched with charcoal on a wall being repaired when Vesuvius erupted. The inscription is read as "XVI K[alends] Nov in[d]ulsit pro m... esurit[ionis]" translated as "16 days before the first of November he gratified ... hunger." Being written in charcoal it could not have been exposed to much weathering before it was protected by volcanic ash.

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The dating of the Mediterranean Bronze Age eruption of Thera on Santorini has for a number of years largely relied on the radiocarbon dating of a scorched olive branch found at the base of the eruption deposit.  Several recent reports have had a bearing on the interpretation of that evidence.

The International Calibration Working Group, formed in 2002, has produced a revised calibration curve for 14C dating named IntCal-20.  A calibration curve is necessary because although the rate of radioactive decay is constant once the 14C is taken up by a tree from CO2 in the air, the atmospheric concentration of radioactive 14C can vary with the rate at which it is produced in the air by solar and cosmic radiation or diluted by environmental releases of stable carbon dioxide from more ancient deposits. The calibration depends on 12,904 measurements of 14C in accurately dated tree rings and dissolved gas in ice core layers. The revised calibration curve is presented in a number of research papers in the August 2020 issue of the journal Radiocarbon. This revised calibration curve changes the dating of the olive branch evidence (as originally reported) to two windows, late-17th-century B.C.or early to mid-16th century B.C.

However, the reliability of that olive branch evidence itself was called into question in a 2018 report published in (Nature) Scientific Reports, vol. 8, article:11841, “Radiocarbon analysis of modern olive wood raises doubts concerning a crucial piece of evidence in dating the Santorini eruption.”

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Annual radiocarbon record indicates

16th century BCE date for the Thera eruption

Science Advances  15 Aug 2018: Vol. 4, no. 8, eaar8241 http://advances.sciencemag.org/content/4/8/eaar8241

Abstract

The mid-second millennium BCE eruption of Thera (Santorini) offers a critically important marker horizon to synchronize archaeological chronologies of the Aegean, Egypt, and the Near East and to anchor paleoenvironmental records from ice cores, speleothems, and lake sediments. Precise and accurate dating for the event has been the subject of many decades of research. Using calendar-dated tree rings, we created an annual resolution radiocarbon time series 1700–1500 BCE to validate, improve, or more clearly define the limitations for radiocarbon calibration of materials from key eruption contexts. Results show an offset from the international radiocarbon calibration curve, which indicates a shift in the calibrated age range for Thera toward the 16th century BCE. This finding sheds new light on the long-running debate focused on a discrepancy between radiocarbon (late 17th–early 16th century BCE) and archaeological (mid 16th–early 15th century BCE) dating evidence for Thera.

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Santorini Minoan eruption (1613 ± 7 BCE)

much larger than originally believed

https://www.volcanodiscovery.com/santorini/minoan-eruption/size.html