Hello Jonathan,
It is definitely the mass of 13C atoms that we want, not the 13C plus oxygen atoms that it was attached to prior to becoming part of the biomass.
Some examples of the broader use of "A_expressed_as_B" (in which the amount of A cannot generally be inferred from A):
mass_fraction_of_particulate_organic_matter_dry_aerosol_particles_expressed_as_carbon_in_air
mole_concentration_of_mesozooplankton_expressed_as_nitrogen_in_sea_water
atmosphere_moles_of_anthropogenic_nmvoc_expressed_as_carbon
mole_fraction_of_nox_expressed_as_nitrogen_in_air
For comparison (where A is a molecule or ion, and B an atomic component):
sinking_mole_flux_of_calcite_expressed_as_carbon_in_sea_water
surface_downward_mass_flux_of_carbon_dioxide_expressed_as_carbon
There are 270 standard names using "expressed_as", and those using it in the narrow sense are, I think, a small fraction. There are a large number like the nox/nitrogen example in which A refers to a collection of related molecules, and many more in which A is biological organism or organic process.
regards,
Martin
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Jonathan Gregory <j.m.gregory at reading.ac.uk>
Sent: 24 April 2018 17:16
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] PMIP (including 1 or more that originated in C4MIP) Standard Names: Carbon and Nitrogen terms
Dear Martin
Tricky! I'm not sure that is better. Yes, I think you've correctly described
why I'm uncomfortable. Could you give other examples of this expanded use of
expressed_as, for comparison?
What do we actually want to mean with these new GPP names? Is it just the mass
of 13C atoms in the GPP? Or is it the mass of all C atoms in molecules which
contain (at least) one 13C atom? It seems not so clear to me in "biomass" as
in CO2, where there is only one C atom.
Best wishes
Jonathan
----- Forwarded message from Martin Juckes - UKRI STFC <martin.juckes at stfc.ac.uk> -----
> Date: Tue, 24 Apr 2018 15:21:22 +0000
> From: Martin Juckes - UKRI STFC <martin.juckes at stfc.ac.uk>
> To: Jonathan Gregory <j.m.gregory at reading.ac.uk>
> CC: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] PMIP (including 1 or more that originated in
> C4MIP) Standard Names: Carbon and Nitrogen terms
>
>
> Hello Jonathan,
>
>
> I think the usage of "expressed_as" has crept into new areas, while remaining consistent with the definition as given in the standard names. The current help text says "It means that the quantity indicated by the standard name is calculated solely with respect to the B contained in A, neglecting all other chemical constituents of A", what you are implying is a more restrictive interpretation with some understanding that "A_expressed_as_B" is an alternative representation of A (as surface_downward_mass_flux_of_carbon_dioxide_expressed_as_carbon would be, for most climate modellers, a simple multiple of surface_downward_mass_flux_of_carbon_dioxide [if the latter existed in the standard name table]). There are a number of terms in the standard name table for which this additional implication does not hold.
>
>
> Looking at the existing names I noticed there construction "content_of", which cannot be used directly here, but might be helpful, as in "vegetation_mass_content_of_13C". For the gpp terms we can't use "content", but could perhaps replace it with "flux": gross_primary_productivity_of_biomass_mass_flux_of_13C.
>
>
> This would require, I think, a change of the existing term gross_primary_productivity_of_biomass_expressed_as_carbon to gross_primary_productivity_of_biomass_mass_flux_of_carbon
>
>
> Would that be an improvement?
>
>
> regards,
>
> Martin
>
> ________________________________
> From: Jonathan Gregory <j.m.gregory at reading.ac.uk>
> Sent: 24 April 2018 15:28
> To: Juckes, Martin (STFC,RAL,RALSP)
> Cc: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] PMIP (including 1 or more that originated in C4MIP) Standard Names: Carbon and Nitrogen terms
>
> Dear Martin
>
> Yes, I see what you mean, but nonetheless it seems odd to me. Is it normal
> to express GPP as mass of 13C? For example, this would be like expressing
> anthropogenic CO2 emissions as 13C. If 13C is about 1% of all the C in fossil
> fuels (I don't know what % it is - this is just an example), that means we'd
> say fossil fuel emissions containing 9 Gt of C per year could be "expressed as"
> 90 MtC of 13C per year. It seems more natural to me to say that 90 Mt per year
> of 13C are contained in the emissions of CO2.
>
> What you propose is consistent and logical, and I haven't managed to work out
> why it sounds strange.
>
> Best wishes
>
> Jonathan
>
> On Tue, Apr 24, 2018 at 01:47:29PM +0000, Martin Juckes - UKRI STFC wrote:
> > Date: Tue, 24 Apr 2018 13:47:29 +0000
> > From: Martin Juckes - UKRI STFC <martin.juckes at stfc.ac.uk>
> > To: Jonathan Gregory <j.m.gregory at reading.ac.uk>,
> > "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> > Subject: Re: [CF-metadata] PMIP (including 1 or more that originated in
> > C4MIP) Standard Names: Carbon and Nitrogen terms
> >
> > Dear Jonathan,
> >
> >
> > It is a logical extension, I believe, in the existing usage in terms such as "gross_primary_productivity_of_biomass_expressed_as_carbon", for which the help text states: "The phrase "expressed_as" is used in the construction A_expressed_as_B, where B is a chemical constituent of A. It means that the quantity indicated by the standard name is calculated solely with respect to the B contained in A, neglecting all other chemical constituents of A", i.e. the new terms are meant to refer to the mass of 13C/14C which is contained in the biomass.
> >
> > regards,
> > Martin
> >
> > ________________________________
> > From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Jonathan Gregory <j.m.gregory at reading.ac.uk>
> > Sent: 24 April 2018 13:35
> > To: cf-metadata at cgd.ucar.edu
> > Subject: [CF-metadata] PMIP (including 1 or more that originated in C4MIP) Standard Names: Carbon and Nitrogen terms
> >
> > Dear Martin
> >
> > Thanks for the new proposals.
> >
> > > gross_primary_productivity_of_biomass_expressed_as_13C
> > > gross_primary_productivity_of_biomass_expressed_as_14C
> >
> > These don't seem quite right to me. They imply you can express the *entire* GPP
> > as kg of 13C or 14C. Does it means the mass of 13C or 14C in the GPP?
> >
> > Best wishes
> >
> > Jonathan
> > _______________________________________________
> > CF-metadata mailing list
> > CF-metadata at cgd.ucar.edu
> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
----- End forwarded message -----
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