Hermione Wrote:

> Oh ... So ... it seems that it would be incorrect
> to draw any particular connection between the
> dating of the Latvian fortress and the
> AD
> 774/5 Miyake event. (which perhaps might
> not have taken place ... ?) after all ...
>

Actually the opposite. What the paper is saying is that when they previously did a wiggle match using IntCal13 the felling date for the wood was given as somewhere in the vicinity of the 775-784s. Therefore one would think that there was a pretty good chance that the 774/5 miyake event would be recorded by the wood, especially since the event appears in wood from across the globe. If you find the tree rings with that event, and count outwards to the bark you can then date get the felling date for the wood. The researchers therefore looked for it where they expected it to be somewhere in the 10 or so rings from the outside of the wood they looked at a decade worth of wood, but couldnt find it.

Then came the new IntCal20 calibration curve, which has more single year radiocarbon measurements in it around the decades of the 774/5 Miyake event. When they performed the same wiggle match calibration as before using IntCal20 they got felling date in the 830s. Given this result, it meant that the 774/5 Miyake event should be recorded in the wood around 60 or so rings from the outside. When they then took a look at this region of wood they found teh Miyake event which allowed them to get an exact felling date of AD 835 for the wood.

So it was the IntCal13 calibration curve that was telling them the wood was older than it actually was, and so misdirecting them in finding the Miyake event.

What I am finding interesting is that this is now the second known occasion where we find that the IntCal13 (and previous iterations) have given dates that are too old. In the search of the date for the bronze age eruption of Thera, the radiocarbon dates obtained using the IntCal13 (and previous) curve are all too old in comparison dates calibrated using the single year measurement portion of the IntCal20 curve.

So the AD 774/5 Miyake event did happen, and is recorded in global tree rings (in both hemispheres). What is of significance is that this event is showing an issue with the IntCal13 and prior iterations of the calibration curves. Whether this is a systematic issue still needs to be seen, and the way to find out is by achieving the ultimate goal to have a single year measurement for every point in future calibration curves, which should not only detect other Miyake like events, but should also make the radiocarbon calibration method more accurate, and has teh potential to imporve our chronological understanding of archaeological sites and/or events.

Jonny

The path to good scholarship is paved with imagined patterns. - David M Raup