Parameters Codes, Units, and Conversions

Following a recommendation of the Intergovernmental Oceanographic Commission (IOC) endorsed by its eleventh Session in Mexico City, March 1979, measured parameters should be labeled by GF3 codes (IOC, 1987, Unesco, 1996). Table 20.4 provides a selected list of most relevant GF3 codes used at lOW. Codes consist of four letters indicating the quantity, followed by four letters describing the measurement method, device, or unit. 

TABLE 20.2 Recent Numerical Values of Selected Fundamental Constants 

TABLE 20.3 Freezing Point, tf, and Temperatnre of Maximum Density, Zmi), for Brackish Seawater of Reference Composition (Millero et al., 2008) with Absolute Salinity, Sa, between 0 and 25 g/ kg. Computed from the lAPWS Formulations for Water (lAPWS, 1996) and Ice (lAPWS, 2006) and the Saline Gibbs Function (Feistel, 2007). Theoretical Values below the Freezing Points are in Brackets 

In Table 20.4, the abbreviation psu, short for practical salinity unit, indicates salinity expressed in the Practical Salinity Scale of 1978 (PSS-78) as a dimensionless quantity. The term psu is not an official unit (Unesco, 1985 Siedler, 1998) but is in widespread use and is particularly helpful to distinguish, say, a given salinity value from absolute salinity in g/kg. Before 1978, salinity was computed from chlorinity, CL by the Cox scale, 5= 1,80655 xCZ (Mamayev et al, 1991), The recommended numerical conversion factor between the PSS-78 salinity and the Cox salinity is 1, Cox salinity is usually expressed in parts per thousand, ppt, %o, or g/kg. None the less, it is lower by about 0.5% than the absolute salinity of seawater in grams of dissolved substance per kilogram of seawater, which in turn is not exactly known but can be estimated sufficiently well (Millero et al., 2008), see Section 20.2.1. 

The International Temperature Scale of 1990 (ITS-90) is in effect since January 1, 1990, (Mamayev et al., 1991). For oceanographic applications, a simple conversion formula (Saunders, 1990 Mamayev et al, 1991 Feistel and Hagen, 1995) is sufficiently accurate for theconversionbetween ITS-90 temperatures (tgo) and the former IPTS-68 temperatures (tgg), as 

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