[CF-metadata] Sea water pH values: at standard or in-situ conditions?

James Orr James.Orr at lsce.ipsl.fr
Fri Jun 9 01:08:54 MDT 2017

All ocean modelers report pH at in situ conditions. Some ocean observers report 
pH corrected to 25°C, but when doing so they often call that pH25. Many ocean 
observationalists report in situ pH, for example from data collected on buoys or 
ARGO floats equiped with pH sensors.

Would it make sense to define pH25 as another CF variable in addition to the 
current pH variable (in situ pH)? These variables may be considered as different 
as in situ temperature and potential temperature.



On Thu, 8 Jun 2017, Lowry, Roy K. wrote:

> Hi John,
> Totally agree with you about the confidence level and what people SHOULD be doing. 
> However, I am uncomfortable with CF becoming a tool to force those who have quoted at standard conditions and
> used the existing Standard Name rework their data. However, should a formal approach from a
> recognised authority in the carbonate chemistry community be made to CF then my comfort level might rise
> somewhat. Then it is they who is forcing the change, not CF.
> 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
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> _____________________________________________________________________________________________________________
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of John Dunne - NOAA Federal
> <john.dunne at noaa.gov>
> Sent: 08 June 2017 18:58
> To: Matthias Tuma
> Cc: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] Sea water pH values: at standard or in-situ conditions?  
> Hi Matthias,
> I'm going to have to go with in-situ, unless someone can correct me otherwise.  I'm 86.33% confident,
> however.  I have been looking at Jim Orr's documentation
> (http://www.geosci-model-dev-discuss.net/gmd-2016-155/gmd-2016-155.pdf), and it cites:
> Biogeochemical protocols and diagnostics for the CMIP6 ...
> www.geosci-model-dev-discuss.net
> Biogeochemical protocols and diagnostics for the CMIP6 Ocean Model Intercomparison Project (OMIP) James C.
> Orr 1, Raymond G. Najjar 2, Olivier Aumont 3, Laurent Bopp ...
> Dickson, A. G., Sabine, C. L., and Christian, J. R.: Guide to best practices for ocean CO2 measurements, ,
> PICES Special Publication 3, 191
> pp., http://aquaticcommons.org/1443/, 2007.
> [Guide_all_in_one.pdf]
> Guide to best practices for ocean CO2 measurements ...
> aquaticcommons.org
> Item Type: Monograph or Serial Issue Title: Guide to best practices for ocean CO2 measurements: Personal
> Creator/Author:
> which gives the calculations for pH on the total scale in SOP6a and SOP6b as a function of insitu T as a
> variable.  Also, I would argue from an environmental science perspective that we *should* be posting the
> insitu variable.
> Hope that helps! John
> On Thu, Jun 8, 2017 at 5:56 AM, Matthias Tuma <mtuma at wmo.int> wrote:
>       Hello all,
>       we had a question come up for the "sea_water_ph_reported_on_total_scale" standard name: it
>       appears that for some communities, in particular on the measurement side, pH would regularly be
>       reported only after first having converted to its equivalent at standard conditions (25C, 0dbar).
>       In other communities, pH would most regularly be reported at in-situ conditions (temperature and
>       pressure at actual measurement spot).
>       While we assume that the CF conventions would implicitly assume values to be reported at in-situ
>       conditions (i.e., the latter variant), my two questions are:
>       1) whether someone can confirm this, to be 100% certain?, and
>       2) whether adding a few according clarifying words to the description would be seen as useful?
>       Thanks and best,
>       Matthias
>       --
>       Matthias Tuma
> WCRP Junior Professional Officer
> c/o WMO
> 7bis, avenue de la Paix
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> Fax: +41 22 730 8036
> Email: mtuma at wmo.int
> http://www.wcrp-climate.org
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