[CF-metadata] Silicate vs. dissolved inorganic silicon

James Orr James.Orr at lsce.ipsl.fr
Fri Mar 24 09:46:06 MDT 2017

Dissolved inorganic phosphorus in seawater takes several forms, with 
phosphate (P043-) being only one of them.  Furthermore, PO43- is not 
even the most abundant form at normal seawater pH.  Rather it is HPO42- 
(hydrogen phosphate). Oceanographers do often refer to phosphate but 
what they really taking about is total dissolved inorganic phosphorus 
(the sum of all inorganic forms).

The seawater system for dissolved inorganic silicon is simpler because 
we only need to consider two forms: silicic acid (Si(OH)4) and silicate 
(SiO(OH)3-). The former is more abundant than the latter in seawater.

It is best then to refer to
- total dissolved inorganic phosphorus rather than phosphate and
- total dissolved inorganic silicon rather than silicate.

For more insight see the last figure in the OMIP-BGC protocols paper 
in the CMIP6 special issue at




On Fri, 24 Mar 2017, Lowry, Roy K. wrote:

> Dear All,
> If one makes the assumption that all the silicon and phosphorus atoms not associated with organic ligands are
> in a single chemical form associated with oxygen in solution then what Martin says is correct. In my
> experience I have never known anybody challenge this assumption and I cannot think of any other anions
> incorporating P and Si. Consequently, I would agree that whilst there is a theoretical semantic difference
> between the members of each Standard Name pair I would agree that this could be ignored and they could be
> considered synonyms.
> Note, this only holds true as these are MOLE concentrations. The MASS concentration of inorganic phosphorus
> is very different from the MASS concentration of phosphate as the oxygen atoms have mass.
> If the decision is taken to take action on this then I would recommend that the 'inorganic_silicon' and
> 'inorganic_phosphorus' names be than ones to be converted to aliases. This is based on common terminology
> usage in the oceanographic community.
> Cheers, Roy.
> Please note that I partially retired on 01/11/2015. I am now only working 7.5 hours a week and can only
> guarantee e-mail response on Wednesdays, my day in the office. All vocabulary queries should be sent to
> enquiries at bodc.ac.uk. Please also use this e-mail if your requirement is urgent.
> _____________________________________________________________________________________________________________
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of martin.juckes at stfc.ac.uk
> <martin.juckes at stfc.ac.uk>
> Sent: 24 March 2017 08:48
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] Silicate vs. dissolved inorganic silicon  
> Hello Alison, others,
> the standard name list includes both
> (1) mole_concentration_of_dissolved_inorganic_silicon_in_sea_water and (2)
> mole_concentration_of_silicate_in_sea_water
> The definition of the first says that "dissolved inorganic silicon" means silicate ions in solution. Both
> have units of "mol m-3". It looks to me as though they are describing the same thing. If this is true, should
> one be demoted to the alias of the other? If they are different, what is the difference?
> The same question applies to mole_concentration_of_dissolved_inorganic_phosphorus_in_sea_water and
> mole_concentration_of_phosphate_in_sea_water.
> regards,
> Martin
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