The olive branch chronology stands irrespective of tree-ring counting.
Friedrich, Walter L. ; Kromer, Bernd ; Friedrich, Michael 等
Cherubini et al. (above) question the reliability of identifying
annual growth increments in olive trees, and therefore voice caution
against the result of the wiggle-match of the four sections of a branch
of an olive tree to the [sup.14]C calibration curve. Friedrich et al.
(2006) were well aware of the problematic density structure of olive
trees, and therefore assigned rather wide error margins of up to 50 per
cent to the ring count. This still resulted in a late seventeenth
century BC youngest date for the modelled age range of the outermost
section of wood (95.4% probability). One can even remove any constraint
from ring counting altogether and model the four radial sections as a
simple ordered sequence, in which only the relative position is used as
prior information, in other words that outer sections are younger than
inner ones in a radial section. The model
Sequence()
{
Boundary("S");
R_Date("innermost section", 3383, 11);
R_Date("2nd section", 3372, 12); R_Date("3rd section", 3349, 12);
R_Date("outermost section", 3331, 10); Boundary("E");
};
yields 1609 cal BC (95.4%) as the minimum age of the outermost
section (IntCall3; Reimer et al. 2013). The 95.4% range is 1656-1609 cal
BC (modelled using OxCal v.4.2 (Bronk Ramsey 2009)).
Secondly, Cherubini et al. essentially limit their discussion of
the dispute between the historical Egyptian chronology and natural
scientific dating methods to the literature published only to the year
2010, and ignore important subsequent contributions. For instance
Hoflmayer (2012: 444) concludes that "Theran pumice in eastern
Mediterranean contexts and White Slip pottery on Thera and in the Levant
have been found to be inconclusive", because of an unknown interval
between eruption (pumice)/production (ceramics) and deposition; hence
this evidence must be considered a terminus ante quem. Kutschera et al.
(2012) find a similar offset of about a century between a stratified
series of [sup.14]C dates from Tell el-Dab'a and the archaeological
dating of the site's sequence, far away from any potential
C[O.sub.2] of volcanic origin. They observe that the generally good
agreement between [sup.14]C dating and the Egyptian historical
chronology (Bronk Ramsey et al. 2010) cannot be quoted here, because the
eighteenth and seventeenth centuries are not covered in that model
(Kutschera et al. 2012: fig. 7). Manning and Kromer (2012) present an
extensive discussion of the statistical robustness of the set of single
year samples from the Akrotiri volcanic destruction level, contrary to
the statement of Cherubini et al. claiming 'wide disparities in the
underlying measurements', and they discuss the potential effect of
small volcanic C[O.sub.2] contributions to the samples used in the data
sets, as proposed by Soter (2011). They find that even allowing for a
subjective selection of a 'low-date clump' the 'likely
date for the Santorini volcanic eruption horizon lies, in round terms,
in the last three decades of the seventeenth century BC'. Cherubini
et al. refer to a 'date range for the eruption of 1525-1490 BC
proposed by numerous other radiocarbon studies' (our italics), but
these studies simply do not exist. There is instead a robust body of
[sup.14]C dates based on reliable sample material and secure contexts
which favours the late seventeenth century BC and does not run beyond
1520 cal BC.
[FIGURE 1 OMITTED]
Hence while we agree with Cherubini et al. that caution is
justified with respect to annual ring counting of olive trees, we can
nevertheless show that simply assuming a growth pattern sequential in
time, without any reference to ring counting, still constrains the date
of the eruption to the late seventeenth century BC. Cherubini et al.
postulate that the olive branch could have been dead or polluted by old
C[O.sub.2]. These arguments too can be ruled out by the following
observations. The fact that the age of the outermost olive section
agrees well with the ages of the short-lived samples from Akrotiri
renders it extremely implausible that the olive branch had been dead for
a substantial number of years prior to the time of the eruption.
Furthermore the olive tree and a second one next to it were found in the
pumice in living position (Figures 1 & 2), and under each tree,
olive leaves were found testifying that the trees were still alive when
buried (Pfeiffer 2003; Friedrich 2009).
[FIGURE 2 OMITTED]
The unique role of the [sup.14]C sequence obtained from the olive
branch in the chronology dispute is that the strength of the Bayesian
approach (combining prior information with [sup.14]C dates) allows the
ambiguity of the [sup.14]C calibration of single dates, leading to a low
but statistically relevant probability in the sixteenth century even at
highest precision, to be resolved. At the same time, Cherubini et al.
ignore important progress in the discussion about the Santorini eruption
in recent years, which negates various of their other statements.
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Walter L. Friedrich (1), Bernd Kromer (2), Michael Friedrich (2,3),
Jan Heinemeier (4), Tom Pfeiffer (5) & Sahra Talamo (6)
(1) Department of Geoscience, Aarhus University, Hoegh
Guldbergsgade 2, DK-8000Aarhus, Denmark
(2) University of Heidelberg, Institute of Environmental Physics,
Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany
(3) Institute of Botany, Hohenheim University, D-70593 Stuttgart,
Germany
(4) Accelerator Mass Spectrometry 14 C Dating Centre, Department of
Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark
(5) VolcanoDiscovery, Kronenstrasse 2, Troisdorf53840, Germany
(6) Max Planck Institute for Evolutionary Anthropology, Department
of Human Evolution, Deutscher Platz 6, D-04103 Leipzig, Germany
