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Hi Kristin,

I can see where some confusion lies. In our paper we have revised the GICC05 timescale (which was constructed from three ice cores-Dye3, GRIP and NGRIP-and to complete the circle, mapped back on to each individual ice core, and also onto the NEEM ice core in 2013) back to around 2000 BC. This is the same timescale which in 2015 we showed had a 7 year error during most of the 1st millennium AD. Shortly after our 2015 paper, Sigl et al (2015) confirmed this error in the the GICC05 timescale using data from the NEEM core back to around 500 BC. In actual fact the offset changes within this 2500 year period as seen in the solid line in the figure below (and the extrapolated dashed line in the BC era)



So while the offset in the GICC05 timescale had been directly identified and corrected in the first millennium BC (and extrapolated, back to around 500 BC by synchronising events seen in NEEM with NGRIP) it had not yet been corrected before that. Hence why we show a 14 year offset back to around 2000 BC as we are just continuing our 2015 paper as well as, in a way, continuing the above diagram. The difference though is that in our recent paper we are comparing the ice cores with tree rings, the latter being absolutely dated and without any error or offsets, whereas Sigl et al in their extrapolated portion are comparing ice cores with ice cores, and so can only look at a relative offset between those two ice cores rather than an absolute offset between an ice core and an absolute calendar date. That is to say, there is a possibility that the new NEEM ice core chronology may have had errors in it too in the BC error, but how would you know?

As it stands if you look at our Table 1 and compare the GRIP off sets with respect to tree-rings, and the offset between the NEEM and GICC05 NGRIP core in Sigl et al's data in the above graph you will see that the agreement is very good back to 500 BC. So it looks as if the new NEEM timescale back to 500 BC is very good.

I dont know much about the geological evidence, but the eruption does seem to be a powerful eruption in the terms of volume of displaced rock it is considered 7 on the Volcanic Explosive Index scale. It is considered one of teh largest, if not THE largest eruption of the Holocene. While it was a large eruption, what I think the actual debate about it is, was it a large sulphur producer or not. As I mentioned above up to around 1990 it was considered to not produce a lot of sulphur (relatively speaking), but then the ice core workers told volcanologists that their yield estimates didn't match their ice core signal (which we now know is likely to be Aniakchak), and so the volcanologists went away and did more measurements of the Theran rock deposits, and so found more. Below are three pages from Mike Baillie's "A slice through time" book (everyone should buy a copy, as it is a must to read, and written in 1995, there are some sections in it that are simply prophetic!) which discusses the sulphur yield issue around 1989-1990. Start at Volcanological evidence.

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Jonny

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Subject Views Written By Posted
When did Thera erupt? Probably not in the 17th century BC. 1040 JonnyMcA 18-Feb-19 15:20
Re: When did Thera erupt? Probably not in the 17th century BC. 100 Susan Doris 18-Feb-19 17:42
Re: When did Thera erupt? Probably not in the 17th century BC. 99 JonnyMcA 19-Feb-19 15:41
Re: When did Thera erupt? Probably not in the 17th century BC. 96 Susan Doris 20-Feb-19 06:16
Re: When did Thera erupt? Probably not in the 17th century BC. 86 Aine 21-Feb-19 20:18
Re: When did Thera erupt? Probably not in the 17th century BC. 79 JonnyMcA 22-Feb-19 11:19
Re: When did Thera erupt? Probably not in the 17th century BC. 92 Eddie Larry 18-Feb-19 22:12
Re: When did Thera erupt? Probably not in the 17th century BC. 83 Vanya 22-Feb-19 11:17
Re: When did Thera erupt? Probably not in the 17th century BC. 81 JonnyMcA 22-Feb-19 11:34
Re: When did Thera erupt? Probably not in the 17th century BC. 117 Vanya 22-Feb-19 12:20


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