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There must be some kind of error. The formula clearly indicates the more 13C in a sample the higher the δ 13 value. But the text somehow describes the opposite. Also the sentences are wrong: "Measured δ 13 C values for marine plankton range from −10‰ to −31‰" should be written like this: "Measured δ 13 C values for marine plankton range from −31‰ to -10‰". Or am I missing something here?? --22.214.171.124 (talk) 14:24, 3 November 2013 (UTC)
Can you give an example of where the text seems to contradict the formula? It's a confusing area and I may have made mistakes in the text. I agree on switching the order of the terms and will do that later today if you don't do it first; I thought it would look odd that way but in fact it's misleading to have it the way it currently is. Mike Christie (talk - contribs - library) 14:37, 3 November 2013 (UTC)
The problem is caused by the term "fractionation". Does it mean a higher or lower δ 13 value? If it means a higher value, the text is wrong, e.g. "Under these conditions, fractionation is reduced, and at temperatures above 14°C the δ 13 C values are correspondingly higher, reaching −13‰. At lower temperatures CO 2 becomes more soluble and hence more available to the marine organisms; fractionation increases and δ 13 C values can reach −32‰." Here the δ 13 value decreases (from -13 to -32‰) but the fractionation increases, that's quite strange. I would say that more fractionation means a higher δ 13 value, so the δ 13 value should go up from -32 to -13‰. Actually I just checked the mathematical formula but I'm no biologist, so I won't edit the article. --126.96.36.199 (talk) 18:12, 3 November 2013 (UTC)
Just a hint: the formula is not "delta"-negative (e.g. y = -x), it just contains a "-1" that makes the absolute value negative (e.g. y = x - 1), but not the changements of the value (see @derivation). So an increase in 13C always means an increase in δ 13. And since we are in negative numbers, we get such an increase e.g. from -32 to -13. It's quite similar to the negative values of the decibel unit. Hope this helps. By the way, the trick with any mathematical equation is to draw it in the cartesian coordinate system, then you'll immediately understand it...and after a while you can draw it in your head. Math is so easy if only the teacher would understand to teach math the same as it was invented by Descartes, Leibniz et al: Just by drawing. We should learn to draw functions at the age of 10, then we'd all be mathematical geniouses at 20. ;) --188.8.131.52 (talk) 18:36, 3 November 2013 (UTC)
Fractionation refers to 13C being taken up in a process less readily than 12C, so if there is more fractionation in a process, the result is less 13C, or a more negative (lower) value for δ13C. When fractionation is reduced, 13C is taken up faster, and there is more of it, so the δ13C is higher. -13‰ is a higher value than -32‰, so I think the confusion stems partly from having the ranges written the wrong way round, as you pointed out. I've fixed that -- does that help?
Clearly this is a difficult paragraph to follow, so I'll think about ways to rewrite it more clearly. Mike Christie (talk - contribs - library) 22:10, 3 November 2013 (UTC)
Taylor, in Radiocarbon Dating page 133, refers to the calibration curves of Seuss from 1967 and 1970. Akin, in Science-based Dating in Archaeology, p. 67, says that the first results were in the 1970 paper. Does anyone have access to the 1967 paper to see if there is a calibration curve in it or just the raw data? The 1967 paper is "Bristlecone pine calibration of the radiocarbon time scale rom 4100 BC to 1500 BC", in Radiocarbon Dating and Methods of Low-Level Counting, Vienna, International Atomic Energy Agency, pp. 143–150. The 1970 paper, for comparison, is "Bristlecone-pine calibration of radiocarbon time 55200 BC to present", in Radiocarbon Variations and absolute chronology, edited by I.U. Olsson, Stockholm, Almqvist & Wiksell, pp. 303–312. Thanks for any info on these. Mike Christie (talk - contribs - library) 18:31, 1 January 2014 (UTC)
The 1967 paper seems to be very rare, see here. The 1970 paper is easy to get, but do you have it already? Zerotalk 05:37, 4 January 2014 (UTC)
I don't have it and would be interested in seeing it, if it's easy to get. For one thing, it might provide an internal reference to the 1967 paper that would make it clear whether the graph appeared there first. Mike Christie (talk - contribs - library) 13:24, 4 January 2014 (UTC)
I'll get it soon. Meanwhile, if you ask for the 1967 paper at WP:REX you might get lucky. Btw, you have mail. Zerotalk 19:43, 4 January 2014 (UTC)
Does anyone have access to Speleothem Science by Fairchild and Baker? I can see enough of it on Google Books to guess that it would be a good source for how speleothems have been used to extend calibration curves, and for the accuracy of the most recent work which has helped in extending the INTCAL curves. Mike Christie (talk - contribs - library) 00:52, 2 January 2014 (UTC)
Send me mail (link at my home page). Zerotalk 06:11, 4 January 2014 (UTC)
I just removed a mention of a statistical critique of current methods of deriving calibrated dates from radiocarbon dates. I contacted the paper's author, Douglas Keenan, who told me there has been no response to the paper in the peer-reviewed literature. The paper looks like it might be a significant contribution but I don't think we can include it here until there is more discussion of the result in reliable sources. Mike Christie (talk - contribs - library) 16:56, 3 January 2014 (UTC)
While I'm not proposing to put it back at the moment, I question your justification. The paper itself is in the peer-reviewed literature and I don't see why waiting for a published response is required. That is not a standard criterion in wikipedia. Zerotalk 01:01, 4 January 2014 (UTC)
Fair enough. Here's what I was thinking. The paper argues that one of the key modern statistical techniques is flawed. The rest of the community appears to be continuing to use that technique without paying any attention to the criticism. Including mention of a single paper that has drawn no response despite a significant claim seems to me to be undue weight; there are thousands of papers each year that relate to radiocarbon, and I think it's best to include only topics that are covered in secondary sources. Once the decision is made to cover the topic then papers can be cited but this is a claim with no coverage at all as far as I can tell. In addition, it's not yet clear how dramatic the effect is -- the real impact seems likely to be on Bayesian analysis but the paper doesn't give examples of Bayesian analysis giving different results. (I plan to ask Keenan about that, and may be able to get a data set from an archaeologist I know to try running it through his analysis, but of course nothing I get back will count as an RS.) Mike Christie (talk - contribs - library) 04:18, 4 January 2014 (UTC)
FYI for other editors, here's what I think are the next steps on the article.
Finish revising the calibration section -- needs some more details on the process of developing calibration curves, and on how they are used -- simple intercepts, probabilistic methods, and Bayesian analysis for multiple data points.
Add a section on archaeological practice -- the secondary sources spend a good deal of time discussing how radiocarbon dating is useless without good field practice to ensure association of the sample with the context to be dated.
Add a section giving some examples of how radiocarbon dates have had a dramatic impact on the field, leading to a significant revision in understanding. The Chauvet Cave is one I would like to cover and maybe a couple of others. I would eliminate the list of examples; it's better to have a short list and discuss their impact.
Once that's done, do a pass through for consistency and make sure the article is balanced.
Review for what can be cut and moved to subarticles -- the article is really too long as it now stands. Create the subarticles and shrink the main article by summarizing them.