Standard names: *Organic Mercury - mole_concentration*

[EDescourvieres]

Proposer's name: Emmanuelle DESCOURVIERES (on behalf of NECCTON and Copernicus Marine Service).

We would like to propose new standard_names for product Mercury. This data is developed in the framework of the NECCTON project as potential new products for Copernicus Marine Service.

Date: 12 January 2026.

Term:

1- mole_concentration_of_organic_mercury_in_phytoplankton

2- mole_concentration_of_organic_mercury_in_zooplankton

3- mole_concentration_of_organic_mercury_in_sea_water

4- mole_concentration_of_organic_mercury_in_fish

5- mole_concentration_of_organic_mercury_in_phycosphere

6- mole_concentration_of_particulate_organic_mercury_in_sea_water

7- mole_concentration_of_dissolved_organic_mercury_in_sea_water

Description:

As there is no CF definition for "Organic mercury" yet, and similarly to #297, I suggest:

• "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury (MeHg), monomethylmercury (MMHg), dimethylmercury (DMHg), ethylmercury (EtHg)).

In the same way, i would like to suggest:

• "Phycosphere" refers to the microenvironment surrounding phytoplankton cells
• "Dissolved organic mercury" refers to mercury that is covalently bonded to carbon (organic forms) and are present in water in dissolved form, often occuring as ionic species (e.g., methylmercury, CH₃Hg⁺; ethylmercury, C₂H₅Hg⁺), or as complexes with dissolved molecules (e.g., mercury bound to dissolved organic matter, Hg–DOM).

1: Mole concentration means number of moles per unit volume, also called "molarity", and is used in the construction mole_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'. "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury (MeHg), monomethylmercury (MMHg), dimethylmercury (DMHg), ethylmercury (EtHg)). "Phytoplankton" are algae that grow where there is sufficient light to support photosynthesis.

2: Mole concentration means number of moles per unit volume, also called "molarity", and is used in the construction mole_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'. "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury (MeHg), monomethylmercury (MMHg), dimethylmercury (DMHg), ethylmercury (EtHg)). "Zooplankton" means the total zooplankton population, with components such as mesozooplankton, microzooplankton and miscellaneous zooplankton.

3-4: Mole concentration means number of moles per unit volume, also called "molarity", and is used in the construction mole_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'. "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury (MeHg), monomethylmercury (MMHg), dimethylmercury (DMHg), ethylmercury (EtHg)).

5- Mole concentration means number of moles per unit volume, also called "molarity", and is used in the construction mole_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'. "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury (MeHg), monomethylmercury (MMHg), dimethylmercury (DMHg), ethylmercury (EtHg)). "Phycosphere" refers to the microenvironment surrounding phytoplankton cells.

6: Mole concentration means number of moles per unit volume, also called "molarity", and is used in the construction mole_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'. Particulate means suspended solids of all sizes. "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury (MeHg), monomethylmercury (MMHg), dimethylmercury (DMHg), ethylmercury (EtHg)).

7: Mole concentration means number of moles per unit volume, also called "molarity", and is used in the construction mole_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'. "Dissolved organic mercury" refers to mercury that is covalently bonded to carbon (organic forms) and are present in water in dissolved form, often occuring as ionic species (e.g., methylmercury, CH₃Hg⁺; ethylmercury, C₂H₅Hg⁺), or as complexes with dissolved molecules (e.g., mercury bound to dissolved organic matter, Hg–DOM).

Units (If applicable): nmol mg-3

Thank you for your help

[github-actions]

Thank you for your proposal. These terms will be added to the cfeditor (http://cfeditor.ceda.ac.uk/proposals/1) shortly. Your proposal will then be reviewed and commented on by the community and Standard Names moderator.

[JonathanGregory]

Dear Emmanuelle

Thanks for these proposals. Are they really mole concentration? If so, the units should be mol m-3, not mol kg-1.

There are plenty of existing names for mole_concentration_ofX_in_sea_water, and _in_phycosphere would be fine too, I think. Moles per unit volume of phytoplankton, zooplankton and fish makes sense, but CF standard names haven't previously used biological entities as a "medium". Have I understood correctly, that you mean e.g. per cubic metre of fish? Do you have to specify whether it's the volume of fish in water or dried fish, for example, or any other parameters about it?

I've commented in #297 about organic mercury.

Cheers

Jonathan

[EDescourvieres]

Hello @JonathanGregory

Apologies for the confusion, the units are nmol m-3 and represent mole concentrations.

Yes, that's correct. I mean the surface area dependent on an ecosystem functional so here surface area of phytoplankton, zooplankton and fish, and therefore in per m3. I do not think that it is necessary to add more detail.

Best regards,

Emmanuelle

[JonathanGregory]

@EDescourvieres. OK, we can understand fish as a bulk medium! It's a novelty for standard names. In your reply above, you say "surface area", though. Did you mean "volume" there? Thanks.

[EDescourvieres]

Hello @JonathanGregory

That's a good question, thank you for bringing it up. I mean volume here.

Best regards,

Emmanuelle

[JonathanGregory]

To summarise, the proposal is for a number of names of the form mole_concentration_of_[X_]organic_mercury_in_Y, canonical unit mol m-3, such as mole_concentration_of_organic_mercury_in_fish, which means the number of moles of Hg (in some organic form) per cubic metre of fish. That's all fine then.

[taylor13]

To be sure, is the concentration the moles per cubic meter of fish or moles per cubic meter of water in which the fish is found? If I were doing budget studies, I think I'd like to keep track of the moles in the water volume (including the fish volume in that water), not in the individual constituents of that water volume. Thus I would consider a cubic meter of sea water including the volume occupied by fish, particulates, organisms of various kinds, etc., and then report the moles of mercury found in the fish or in the particulates, or in the organisms of various kinds. For ocean budget studies, I wouldn't care about the concentration of mercury within fishes, within particulates, or within organisms.

We should also clarify whether mole_concentration_of_organic_mercury_in_sea_water is the moles per cubic meter of seawater (including the moles in such things as fish and iincluding the volume of the fish when determining the concentration). For example, does the concentration in sea water include the mercury in fish and in particulate organic matter found in that volume of sea? If so, do we also need a name for mercury in sea_water excluding the mercury in all the other "things" found in the sea water?

[JonathanGregory]

@taylor13. I had the same uncertainty as your first paragraph but I understood from Emmanuelle's replies that it really means per cubic metre of fish i.e. the volume contained by the skin of the fish. As to your second question, this is something we could ask in other cases as well. For example, in mole_concentration_of_bacteria_expressed_as_carbon_in_sea_water, does the volume of sea water include the volume of the bacteria? In that case, I expect it must do, because you would first measure the volume of sea water containing bacteria, and then measure many moles of bacterial carbon is contained in it by some method that does not respect the integrity of the bacteria or measure their volume, I guess. If that is true, we should also understand sea_water as a medium which contains a certain content of fish. But I guess the volume fraction occupied by fish is rather small, so perhaps it doesn't matter.

[EDescourvieres]

Hello @JonathanGregory and @taylor13,

Yes by mole_concentration_of_organic_mercury_in_fish, I mean mole of organic mercury per cubic meter of fish. To be more precise, mole concentration of organic mercury in fish bioaccumulated by bioconcentration (which is defined as the passive uptake of dissolved Hg2+ through the cell membrane of a functional ecosystem) and biomagnification (which is the sum of active uptake and release through feeding) (Bieser et al. 2023).

Bieser, J., Amptmeijer, D. J., Daewel, U., Kuss, J., Soerensen, A. L., & Schrum, C. (2023). The 3D biogeochemical marine mercury cycling model MERCY v2. 0–linking atmospheric Hg to methylmercury in fish. Geoscientific Model Development, 16(9), 2649-2688.

For the second point, i am not certain whether “in seawater” includes organisms or not. However, i agree with Jonathan that, if they are included, their contribution is likely negligible, as the volume fraction occupied by fish is very small. If you consider it necessary, I can contact the data producers.

Best regards,

Emmanuelle

[eileenhertwig-dkrz]

Hello @EDescourvieres,

I have now added all 7 proposed new standard names to the CF standard name editor. Please check if everything looks fine:

1. mole_concentration_of_organic_mercury_in_phytoplankton: https://cfeditor.ceda.ac.uk/proposal/5793/
   "Mole concentration" means number of moles per unit volume, also called "molarity", and is used in the construction "mole_concentration_of_X_in_Y", where X is a material constituent of Y. A chemical species or biological group denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_as_nitrogen". "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury (MeHg), monomethylmercury (MMHg), dimethylmercury (DMHg), ethylmercury (EtHg)). Phytoplankton are algae that grow where there is sufficient light to support photosynthesis.
   Unit: mol m-3

2. mole_concentration_of_organic_mercury_in_zooplankton: https://cfeditor.ceda.ac.uk/proposal/5794/
   "Mole concentration" means number of moles per unit volume, also called "molarity", and is used in the construction "mole_concentration_of_X_in_Y", where X is a material constituent of Y. A chemical species or biological group denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_as_nitrogen". "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury, monomethylmercury, dimethylmercury, ethylmercury). "Zooplankton" means the total zooplankton population, with components such as mesozooplankton, microzooplankton and miscellaneous zooplankton.
   Unit: mol m-3

3. mole_concentration_of_organic_mercury_in_sea_water: https://cfeditor.ceda.ac.uk/proposal/5795/
   "Mole concentration" means number of moles per unit volume, also called "molarity", and is used in the construction "mole_concentration_of_X_in_Y", where X is a material constituent of Y. A chemical species or biological group denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_as_nitrogen". "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury, monomethylmercury, dimethylmercury, ethylmercury).
   Unit: mol m-3

4. mole_concentration_of_organic_mercury_in_fish: https://cfeditor.ceda.ac.uk/proposal/5796/
   "Mole concentration" means number of moles per unit volume, also called "molarity", and is used in the construction "mole_concentration_of_X_in_Y", where X is a material constituent of Y. A chemical species or biological group denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_as_nitrogen". "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury, monomethylmercury, dimethylmercury, ethylmercury).
   Unit: mol m-3

5. mole_concentration_of_organic_mercury_in_phycosphere: https://cfeditor.ceda.ac.uk/proposal/5797/
   "Mole concentration" means number of moles per unit volume, also called "molarity", and is used in the construction "mole_concentration_of_X_in_Y", where X is a material constituent of Y. A chemical species or biological group denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_as_nitrogen". "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury, monomethylmercury, dimethylmercury, ethylmercury). "Phycosphere" refers to the microenvironment surrounding phytoplankton cells.
   Unit: mol m-3

6. mole_concentration_of_particulate_organic_mercury_in_sea_water: https://cfeditor.ceda.ac.uk/proposal/5798/
   "Mole concentration" means number of moles per unit volume, also called "molarity", and is used in the construction "mole_concentration_of_X_in_Y", where X is a material constituent of Y. A chemical species or biological group denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_as_nitrogen". "Particulate" means suspended solids of all sizes. "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury, monomethylmercury, dimethylmercury, ethylmercury).
   Unit: mol m-3

7. mole_concentration_of_dissolved_organic_mercury_in_sea_water: https://cfeditor.ceda.ac.uk/proposal/5799/
   "Mole concentration" means number of moles per unit volume, also called "molarity", and is used in the construction "mole_concentration_of_X_in_Y", where X is a material constituent of Y. A chemical species or biological group denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_as_nitrogen". "Dissolved organic mercury" refers to mercury covalently bonded to carbon (organic forms) present in water in dissolved form, often as ionic species (e.g., methylmercury CH₃Hg⁺, ethylmercury C₂H₅Hg⁺) or complexes with dissolved organic matter (Hg–DOM).
   Unit: mol m-3

Don't you think it might be helpful to add something to the description of _in_fish to make clear that you only mean per volume of fish and not seawater containing fish?

Best regards,
Eileen

[EDescourvieres]

Dear @eileenhertwig-dkrz,
I have contacted the producers regarding the definition of in_fish, and I will get back to you as soon as I receive their response.
Best regards,
Emmanuelle