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.75179 γData Representations:Metadata requirements of TEOS-10and Absolute Salinity AnomalyThe working group strongly recommends thatoceanographers continue to report salinity to nationaldatabases as Practical Salinity, determinedon the Practical Salinity Scale of 1978 (suitablyupdated to ITS-90 temperatures as described inappendix E of the TEOS-10 manual).There are three very good reasons for continuingto store Practical Salinity rather than Absolute Salinityin such data repositories:1. Practical Salinity is an (almost) directly measuredquantity whereas Absolute Salinity is generallya derived quantity. Practical Salinity is directlycalculated from measurements of conductivity,temperature and pressure, whereas AbsoluteSalinity is derived from a combination of thesemeasurements plus other measurements andcorrelations that are not yet well established.Practical Salinity is preferred over the measuredin situ conductivity value because of its conservativenature with respect to changes oftemperature and pressure, or dilution with purewater.2. It is imperative that confusion is not createdin national databases where a change in thereporting of salinity may be mishandled atsome stage and later be misinterpreted as areal increase in the ocean’s salinity. This secondpoint argues strongly for no change in presentpractice in the reporting of Practical Salinity innational databases of oceanographic data.the density of Standard Seawater) should beconverted to corresponding numbers of PracticalSalinity for storage. The practice of storingone type of salinity in national databases (PracticalSalinity, S P ) but using a different type ofsalinity in publications (Absolute Salinity, S A )is analogous to the present practice withtemperature; in situ temperature (t) is storedin databases (since it is a measured quantity)but the temperature variable that is used inpublications is a calculated quantity: potentialtemperature under EOS-80 or conservativetemperature under TEOS-10.3. The algorithms for determining the best estimateof Absolute Salinity of seawater withnon-standard composition are immature andwill undoubtedly change in the future, sostoring Absolute Salinity in national databasesis not recommended. Storage of an intermediatevalue, the Reference Salinity, (S R , definedto give the best estimate of Absolute Salinityof Standard Seawater), would also introduceconfusion in the stored salinity values withoutproviding any real advantage over storingPractical Salinity. Values of Reference Salinityobtained from suitable observational techniques(for example, by direct measurement ofDr Steve Rintoul and Stephanie Barrett, CSIRO.9