Hello everyone, Roy kindly pointed out that the paper I referenced used uppercase D14C, not lowercase d14C. The reference trail from that paper leads to the Stuiver and Polach (1977) paper referenced here. I also just confirmed with the person doing the analysis that they use the 13CO2 correction for their reported values, so a definition including that update would be:
enrichment_of_14C_in_air_expressed_as_uppercase_delta_14C (Canonical unit: 1e-3) 'Isotopic enrichment of 14C, often called d14C or delta14C (lower case delta), is a parameterisation of the 14C/12C isotopic ratio in the sample with respect to the isotopic ratio in a reference standard. It is computed using the formula (((14C/12C)sample / (14C/12C)standard) - 1) * 1000. The quantity called D14C, or Delta14C (upper case delta) is d14C corrected for isotopic fractionation using the 13C/12C ratio as follows: D14C = d14C - 2(dC13 + 25)(1+d14C/1000). If the sample is enriched in 14C relative to the standard, then the data value is positive. Reference: Stuiver, M. and H.A. Polach, 1977, Discussion reporting of 14C data, Radiocarbon, Volume 19, No. 3, 355-363, doi: 10.1017/S0033822200003672. The reference standard used in the calculation of delta14C should be specified by attaching a long_name attribute to the data variable. "C" means the element carbon and "14C" is the radioactive isotope "carbon-14", having six protons and eight neutrons and used in radiocarbon dating.' My first email was based on an incorrect understanding of the issues involved. I was too eager to join the discussion I neglected my due diligence in understanding. Sorry for the confusion. I will be more careful in the future. Daniel On 02/21/2019 07:52 AM, Alison Pamment - UKRI STFC wrote: > Dear Roy, > > On reflection, I think you're right that it is better not to put the > reference standard into the definition. One could argue that, even if > everyone is currently using the same reference material, it is still an > experimental detail and therefore doesn't belong in either the standard name > or its definition. Using a different reference would change the value of > (14C/12C)standard) in the first formula, but not the formula itself, so the > standard name would apply to all Delta14C measurements. As you say, > experimental details should be specified using long_name and/or comment > attributes. That would be consistent with our usual approach to standard > names while providing a means of recording the precise details of how the > data values were calculated. > > Here's the revised version (including the addition of our standard sentence > about 14C that was accidentally omitted last time): > enrichment_of_14C_in_air_expressed_as_uppercase_delta_14C (Canonical unit: > 1e-3) > 'Isotopic enrichment of 14C, often called d14C or delta14C (lower case > delta), is used to calculate the fossil fuel contribution to atmospheric > carbon dioxide using isotopic ratios of carbon. It is a parameterisation of > the 14C/12C isotopic ratio in the sample with respect to the isotopic ratio > in a reference standard. It is computed using the formula (((14C/12C)sample / > (14C/12C)standard) - 1) * 1000. The quantity called D14C, or Delta14C (upper > case delta) is d14C corrected for isotopic fractionation using the 13C/12C > ratio as follows: D14C = d14C - 2(dC13 + 25)(1+d14C/1000). If the sample is > enriched in 14C relative to the standard, then the data value is positive. > Reference: Stuiver, M. and H.A. Polach, 1977, Discussion reporting of 14C > data, Radiocarbon, Volume 19, No. 3, 355-363, doi: 10.1017/S0033822200003672. > The reference standard used in the calculation of delta14C should be > specified by attaching a long_name attribute to the data variable. "C" means > the element carbon an d "14C" is the radioactive isotope "carbon-14", having six protons and eight neutrons and used in radiocarbon dating.' > > Best wishes, > Alison > > ----------------------------------------------------------------------------------------------------------- > Alison Pamment Tel: > +44 1235 778065 > NCAS/Centre for Environmental Data Analysis Email: > [email protected] > STFC Rutherford Appleton Laboratory > R25, 2.22 > Harwell Oxford, Didcot, OX11 0QX, U.K. > > From: Lowry, Roy K. <[email protected]> > Sent: 20 February 2019 19:30 > To: Pamment, Alison (STFC,RAL,RALSP) <[email protected]>; > [email protected] > Subject: Re: [CF-metadata] New standard name for 14CO2 > > Dear Alison, > > I would suggest that if the reference standard isn't included in the Standard > Name then I wouldn't put it into the definition. I don't like the idea of > having narrower semantics in the definition compared to the name. How about > putting a recommendation that the standard be specified in the long name into > the definition? > > Cheers, Roy. > > I have now retired but will continue to be active through an Emeritus > Fellowship using this e-mail address. > > ________________________________________ > From: CF-metadata <mailto:[email protected]> on behalf of > Alison Pamment - UKRI STFC <mailto:[email protected]> > Sent: 20 February 2019 16:40 > To: mailto:[email protected] > Subject: Re: [CF-metadata] New standard name for 14CO2 > > Dear Katherine, Roy, Jonathan, Daniel, > > Thank you all for the very clear and interesting discussion - I have learned > a lot from reading all your comments and the various references. It seems > that we are inching towards agreement on: > enrichment_of_14C_in_air_expressed_as_uppercase_delta_14C (Canonical unit: > 1e-3). > > Certainly it is shorter and more readable if we don't include the reference > standard in the name itself. I suggest that we include it in the definition > for completeness, but leave it out of the name. In future, if someone were to > propose a similar quantity based on a different standard we could add more > detail into the names and turn the original one into an alias. However, the > references I have looked at seem to indicate that the same international > standard has been in use since the 1950s, so it isn't something that changes > on a regular basis. > > Based on Roy's suggested definition, other comments in the discussion, and > text used in the definitions of existing standard names, we would have > something like the following: > 'Isotopic enrichment of 14C, often called d14C or delta14C (lower case > delta), is used to calculate the fossil fuel contribution to atmospheric > carbon dioxide using isotopic ratios of carbon. It is a parameterisation of > the 14C/12C isotopic ratio in the sample with respect to the isotopic ratio > in a reference standard, in this case the radiocarbon absolute reference > standard, Oxalic Acid I. It is computed using the formula (((14C/12C)sample / > (14C/12C)standard) - 1) * 1000. The quantity called D14C, or Delta14C (upper > case delta) is d14C corrected for isotopic fractionation using the 13C/12C > ratio as follows: D14C = d14C - 2(dC13 + 25)(1+d14C/1000). If the sample is > enriched in 14C relative to the standard, then the data value is positive. > Reference: Stuiver, M. and H.A. Polach, 1977, Discussion reporting of 14C > data, Radiocarbon, Volume 19, No. 3, 355-363, doi: 10.1017/S0033822200003672.' > > Does that sound okay? > > Best wishes, > Alison > > ----------------------------------------------------------------------------------------------------------- > Alison Pamment Tel: > +44 1235 778065 > NCAS/Centre for Environmental Data Analysis Email: > mailto:[email protected] > STFC Rutherford Appleton Laboratory > R25, 2.22 > Harwell Oxford, Didcot, OX11 0QX, U.K. > > > Hi Jonathan and Roy, > > > I do not feel there is need to mention the reference material. Oxalic Acid > has been agreed upon as the primary reference material and any other > reference materials are all traceable to the primary standards for > radiocarbon analysis. > > Thanks, > > Katherine > > On 16/02/2019, 16:04, "CF-metadata on behalf of Jonathan Gregory" > <mailto:[email protected] on behalf of > [email protected]> wrote: > > Dear Roy > > I went for "big" because it's shorter and a bit more amusing. If we have > "uppercase" it would also be OK - no need for _ in the middle of it, I > think. > > Yes, it would be good to hear an authoritative view on whether there is > more > than one standard in use. > > Best wishes > > Jonathan > > ----- Forwarded message from "Lowry, Roy K." <mailto:[email protected]> > ----- > > > Date: Fri, 15 Feb 2019 15:24:06 +0000 > > From: "Lowry, Roy K." <mailto:[email protected]> > > To: Jonathan Gregory <mailto:[email protected]>, > "mailto:[email protected]"; > > <mailto:[email protected]> > > Subject: Re: [CF-metadata] New standard name for 14CO2 > > > > Dear Jonathan, > > > > I am almost happy with 'big_delta14C', but would prefer > 'upper_case_delta14C'. > > > > I still feel that unless explicitly told otherwise by a domain expert > the reference standard needs to be there. As I mentioned in a previous > posting there have been multiple 14C standards used over the past 40 years, > although I cannot say for certain whether more than one is in current use. > > > > Cheers, Roy. > > > > > > I have now retired but will continue to be active through an Emeritus > Fellowship using this e-mail address. > > > > ________________________________ > > From: CF-metadata <mailto:[email protected]> on behalf > of Jonathan Gregory <mailto:[email protected]> > > Sent: 15 February 2019 15:00 > > To: mailto:[email protected] > > Subject: Re: [CF-metadata] New standard name for 14CO2 > > > > Dear all > > > > Thank you for the clarifications. Actually I still do not understand > what the > > normalisation does, but evidently it's a well-defined procedure. > > > > I'm in favour of precision, of course, when there is a danger of > ambiguity. > > Roy proposes > > > > > enrichment_with_respect_to_radiocarbon_absolute_reference_standard_of_14C_in_carbon_dioxide_in_air_expressed_as_D14C > > > > I would like to ask if we could make it > > > > enrichment_of_14C_in_carbon_dioxide_in_air_expressed_as_big_delta14C > > > > That is: (a) Do we have to mention the reference standard? Katherine > does not > > specify this. Is there more than one standard in use? If so, we do need > to > > include it, I agree. (b) It seems clearer to me to spell out delta than > to > > put just D. (c) I appreciate that the small-delta version is obsolete > but we > > can't rule out it being needed sometime (or perhaps a similar > distinction is > > in actual use with other isotopes?), and I think it would be unreliable > to > > distinguish two standard names just because one had a small d where the > other > > had a big D. If we ever need the small-delta version we can put > small_delta. > > > > Best wishes > > > > Jonathan > > > _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
