Dear All, Some additional information on 'chorophyll-a fluorescence' in observational oceanography. As John says, strictly speaking fluorescence is the amount of radiation within a given waveband resulting from excitation. It could also be expressed as a dimensionless parameter that is the ratio of the radiation generated over the amount of excitation energy (sometimes called fluorescence yield).
Over the years, I have come across many types of in-situ fluorometers used to estimate chlorophyll-a in seawater. Many of these deliver a parameter called 'chlorophyll-a fluorescence'. Over the years I have encountered this manifesting itself as raw voltages or ADC counts but these days these raw measurements have some sort of internal algorithm applied to produce a measurement that is linearly related to the chlorophyll-a concentration in units such as ug/l. I think this is what Elodie wishes to describe semantically in CF. If so, one solution would be to use existing chlorophyll-a concentration Standard Names with a qualification that it is an uncalibrated measurement in the long name. Any other suggestions? As for alkalinity, whilst John's viewpoint holds from a modelling perspective there is a strong voice in the observational marine science community for alkalinity measurements having units of Equivalents per kilogram (dimensionality mol/kg) which cannot be interconverted with sufficient precision to mol/m3 using factors based on in-situ density (other factors come into play such as temperature of measurement etc.). Consequently, I support Elodie's request. The current standard name with dimensionality mol/m3 is sea_water_alkalinity_expressed_as_mole_equivalent, so the new name would be better as sea_water_alkalinity_per_unit_mass_expressed_as_mole_equivalent rather than just sea_water_alkalinity_per_unit mass. Cheers, Roy From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of John Dunne - NOAA Federal Sent: 05 December 2016 20:45 To: Elodie Fernandez <elodie.fernan...@mercator-ocean.fr> Cc: cf-metadata@cgd.ucar.edu; Fernando Manzano Muñoz <fmanz...@puertos.es> Subject: Re: [CF-metadata] New standard_names for ocean biogeochemistry A couple of questions... 1) Regarding the request to add Chlorophyll_a fluorescence, the proposed unit is kg/m3, but shouldn't fluorescence have radiation units (i.e. Watts/m2)? I was not aware that any of the proposed CMIP models treated fluorescence explicitly, but if that were the case, it would seem like converting to chlorophyll_a volumetric mass units would seem to me redundant with the existing chlorophyll_a metric. 2) Regarding the request to add a variable for alkalinity in mass units to augment the current one volumetric units, this would seem redundant for models using the Boussinesq Assumption and thus a single reference density. For non-Boussinesq models, one should be able to approximate this with sea_water_potential_density (rhopoto), but I acknowledge that this would make the global integral not exact... Are non-Boussinesq models being planned? If so, adding alkalinity as a mass-based variable would also then beg the question as to which tracers should be posted in both units (e.g. DIC) - how much is the request expected to be expanded? Cheers, John On Mon, Dec 5, 2016 at 3:38 AM, Elodie Fernandez <elodie.fernan...@mercator-ocean.fr<mailto:elodie.fernan...@mercator-ocean.fr>> wrote: Dear all, We would like to suggest the addition of two new standard_names for ocean biogeochemistry: - mass_concentration_of_chlorophyll_a_fluorescence_in_sea_water unit: kg m-3 definition: Mass concentration means mass per unit volume and is used in the construction mass_concentration_of_X_in_Y, where X is a material constituent of Y. A chemical species denoted by X may be described by a single term such as 'nitrogen' or a phrase such as 'nox_expressed_as_nitrogen'. Chloropyll fluorescence is a proxy for Chlorophyll concentration measuring re-emitted light from light absorption. Chlorophylls are the green pigments found in most plants, algae and cyanobacteria; their presence is essential for photosynthesis to take place. There are several different forms of chlorophyll that occur naturally. All contain a chlorin ring (chemical formula C20H16N4) which gives the green pigment and a side chain whose structure varies. The naturally occurring forms of chlorophyll contain between 35 and 55 carbon atoms.Chlorophyll fluorescence is mainly emitted from the Chlorophyll a pigment. I believe there are no standard_names yet for fluorescence. The definition was built from the mass_concentration_of_chlorophyll_a_in_sea_water definition. - sea_water_alkalinity_per_unit_mass unit: mol kg-1 definition: sea_water_alkalinity_per_unit_mass is the total alkalinity (including carbonate, nitrogen, silicate, and borate components). A standard name already exists for alkalinity expressed as mol/m3, sea_water_alkalinity_expressed_as_mole_equivalent, but none exist for mol/kg. Best regards, Elodie _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu<mailto:CF-metadata@cgd.ucar.edu> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ________________________________ This message (and any attachments) is for the recipient only. NERC is subject to the Freedom of Information Act 2000 and the contents of this email and any reply you make may be disclosed by NERC unless it is exempt from release under the Act. 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