Apologies for coming to the party so late on this one folks.. I do believe that before progressing on changing the units for any of these variables, there needs to be a consideration/revisitation of what is currently in place.
Back in 2011 when the TEOS-10 standard names were proposed we spent a fair amount of time attempting to clean up the mess that was (and is) salinity and “units”. For historians, there’s a full trail of the discussions available at http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2011/022581.html and linked messages previous and subsequent. For this reason 3 “historical” salinities were proposed and accepted (along with a bunch of other quantities) which included “sea_water_knudsen_salinity”, “sea_water_cox_salinity” and “sea_water_practical_salinity” which were intentionally added to attempt to give some context in how “salinity” had been measured through time. For each of these quantities, there is considerable descriptive text included in order to put these quantities into perspective: sea_water_knudsen_salinity: Knudsen Salinity, S_K, is defined unitless as a mass fraction per mil (0/00) or "parts per thousand", and was calculated from the titration of inorganic salts from a sample of sea water after a commission to study the problem of determining salinity and density was initiated by the International Council for the Exploration of the Sea (ICES) in 1899. S_K was the standard salinity measure until S_C (Cox Salinity) was established in 1967. Since the work of Knudsen (1901), chlorinity is converted into Knudsen Salinity using S_K = 0.030 + 1.805 Cl. This type of salinity was called simply "salinity" from 1901 to 1966. From the 1960s on, electrical conductivity began to be used to estimate the Knudsen Salinity, rather than chemical titration. Knudsen Salinity was replaced by Cox Salinity in 1967 which was in turn replaced by Practical Salinity, S_P, in 1978. Conversion of Knudsen Salinity to Practical Salinity follows S_P = (S_K - 0.03) * (1.80655 / 1.805). Reference: Knudsen, 1901; Thomas et al., 1934 doi: 10.1093/icesjms/9.1.28; Lyman, 1969 doi: 10.4319/lo.1969.14.6.0928; Wooster et al., 1969 doi: 10.4319/lo.1969.14.3.0437; Lewis, 1980 doi: 10.1109/JOE.1980.1145448; Millero et al., 2008 doi: 10.1016/j.dsr.2007.10.001. There are standard names for the precisely defined salinity quantities sea_water_cox_salinity, S_C (used for salinity observations between 1967 and 1977), sea_water_practical_salinity, S_P, sea_water_absolute_salinity, S_A, sea_water_preformed_salinity, S_* and sea_water_reference_salinity. Salinity quantities that do not match any of the precise definitions should be given the more general standard name of sea_water_salinity. sea_water_cox_salinity: Cox Salinity, S_C, is defined unitless as a mass fraction per mil (0/00) or "parts per thousand". S_C was the standard salinity measure from 1967 until Practical Salinity, S_P, was established with PSS-78 (1978). Chlorinity, Cl, is calculated from the conductivity of a sea water sample and since the work of the Joint Panel for Oceanographic Tables and Standards (JPOTS; 1966) is converted into Cox Salinity using S_C = 1.80655Cl. This type of salinity was called simply "salinity" from 1967 to 1978. Cox Salinity was replaced by Practical Salinity in 1978. Cox Salinity is converted to Practical Salinity following S_P = S_C, however the accuracy of this is dependent on whether chlorinity or conductivity was used to determine the S_C value, with this inconsistency driving the development of the Practical Salinity Scale 1978 (PSS-78). Reference: Cox et al., 1967 doi: 10.1016/0011-7471(67)90006-X; Lyman, 1969 doi: 10.4319/lo.1969.14.6.0928; Wooster et al., 1969 doi: 10.4319/lo.1969.14.3.0437. There are standard names for the precisely defined salinity quantities sea_water_knudsen_salinity, S_K (used for salinity observations between 1901 and 1966), sea_water_practical_salinity, S_P, sea_water_absolute_salinity, S_A, sea_water_preformed_salinity, S_* and sea_water_reference_salinity. Salinity quantities that do not match any of the precise definitions should be given the more general standard name of sea_water_salinity. sea_water_practical_salinity: Practical Salinity, S_P, is defined on the Practical Salinity Scale of 1978 (PSS-78) and is calculated from the electrical conductivity of sea water (as well as temperature and pressure). Officially S_P is dimensionless so that, while convenient, and while it is common practice, it is not officially sanctioned to say S_P = 35 psu. Often authors use PSS-78, as in S_P = 35 PSS-78. If salinity was measured using remote sensing techniques and not conductivity, then it is recommended that additional metadata (calibration/validation information) be described in the variable comment attribute. This name should be used to describe salinity observations made from 1978 onwards (Practical Salinity is the salinity quantity stored by national data centres for post-1978 observations). The only exception to this is where the observed salinities are definitely known not to be recorded on the Practical Salinity Scale. There are also standard names for the precisely defined salinity quantities sea_water_knudsen_salinity, S_K (used for salinity observations between 1901 and 1966), sea_water_cox_salinity, S_C (used for salinity observations between 1967 and 1977), sea_water_absolute_salinity, S_A, sea_water_preformed_salinity, S_*, and sea_water_reference_salinity. Salinity quantities that do not match any of the precise definitions should be given the more general standard name of sea_water_salinity. Reference: www.teos-10.org; Lewis, 1980 doi:10.1109/JOE.1980.1145448 We need to be a little careful with any changes, as sea_surface_salinity which is now measured by satellite has been calibrated back to in-situ measurements which themselves align to PSS-78 (as do all ongoing measurements that are being and will be stored in oceanographic databases now and in the future). Cheers, P
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