In my last post, I described a rather primitive emulation of a long period proxy temperature reconstruction by Marcott et al, going back to 11300 BP. I tried first using the published dates, and got a fairly unsurprising result, similar to the paper, except that it lacked a recent spike visible there. Then I tried using the modified dates of Marcott et al, and got s generally similar result, except for a very large initial spike.
I have found a rather trivial reason for this, but I'm not sure what to make of it. At least one proxy sheet in the spreadsheet, proxy 65 RAPID-12-1K, had some junk in a block of numbers well down from the main data block. These are in the data columns E:G, which are, respectively, published date, temperature, and Marcott date. Update, 64 and 68 have similar junk.
My program read those as data, and for some proxies it considerably affected the interpolation. The reason for the difference is that for published dates, the extra numbers seemed to be dates beyond 11300, which did no harm. But in col G, the Marcott dates, they were small numbers, and interpreted as early years.
When I fixed this, and read only numbers in the consecutive data block, the numbers were much more reasonable, although a spike remained.
I don't know if a corresponding issue may have affected the paper. I would doubt it, although it would explain the discrepancy between the thesis version and the Science paper.
Update I have posted an active viewer for the individual proxies.
Update - I have made some minor changes to the plots:
1. I changed the anomaly base from 5800-6200 BP to 4500-5500. The period I initially used was from Fig S26, but the latter is the right one. I don't think it made a perceptible difference
2. Romanm at CA noted some spurious zeroes in proxy 62. These caused the earlier dip at about 9000.
3. I improved the y-axis alignment of the combined plots.
Here are the plots. Firstly the new plot with published dates, which is not much changed:
Then the plot with Marcott revised dates. This has a still considerable spike, but less than before:
And here are the two orange curves solo:
The new spike is less than before, and less than for Marcott et al. But it still represents a change caused by dating, and I'm looking into the reasons. I think it may be particular proxies; theree are two main contributions.
One is from, 44: Mount Honey on Campbell Island, has the early part of the date range rather compressed - about 30yr intervals go to about 10 years. The temperatures themselves are unremarkable, but the trends increase.
The other comes from two proxies which have large negative anomalies, but which disappear from the early years on redating. These are 54: OCE326-GGC30 and 58: Flarken Lake. In both cases, re-dating moves the date back 100 and 150 years respectively. In both cases there had been substantial cooling over many centuries.