6
F. J. Millero
The mean molecular weight (Mr) of sea salt is given by:
Mr = "LniMi = 62·793
(1.4)
These equations can be converted into functions of the salinity (S) using the approximate relationship:
S (%0) = 1.80655 CI(%o)
(1.5)
The composition of the major components of sea water is summarized in Fig. 1.4.
The major sea salts include NaCI, Na2S04' MgCl2 and MgS04. The concept of salinity
is discussed in more detail in the next section.
1.1.2
The Concept of Salinity
Salinity (S) was originally conceived as a measurement of the mass of dissolved salts
in a given mass of sea water (the weight fraction in parts per thousand, ppt, %0). The
experimental determination of the salt content of sea water by drying and weighing
presents some difficulties. At the temperatures necessary to drive off the last traces of
H20, the bicarbonates and carbonates are decomposed to oxides (M02, where M = Na
or K), and some halides are lost when heating to dryness (HCI and HBr). One can prevent the loss of HCI by adding NaF before evaporation (Morris and Riley 1964). This
led earlier researchers to use indirect methods to measure the salinity. A complete
chemical analysis of sea water is the only reliable way to determine the true salinity of
sea water (Sr)' This method, however, requires too much time, and cannot be used for
routine work. The early work related the true salinity to chlorinity:
Sr = a CI(%o}
(1.6)
where a = 1.8056 (Dittmar 1884) and 1.8148 (Lyman and Fleming 1940), which can be
compared to the values of 1.8154 (Table 1.1). Earlier researchers suggested that CI(%o}
could be used as a measure of salinity. Measurements of the chlorinity and evaporation salinity gave:
S (%0) = 0.030 + 1.805 CI(%o)
(1.7)
For approximately 65 years, this formula was used in oceanography to determine
salinity to an accuracy of 0.01%0 in S. "Normal" sea water of known CI(%o) (prepared
for years in Copenhagen and now in Wormley, England) was used to calibrate the titration methods use to determine CI. Measurements of the physical properties of sea
water such as density as a function of Cl(%o) could be used to calculate physical properties from CI measurements made at sea. The intercept was due to the use of Baltic
Sea waters that have an input of river salts (Ca(HC0 3 h) and little chloride. Since the
salts of different rivers can vary, the intercept can vary for each estuarine system. The
salinity of sea water can be determined by measuring a number of physical properties (listed below along with the estimated errors in salinity).
F. J. Millero
The mean molecular weight (Mr) of sea salt is given by:
Mr = "LniMi = 62·793
(1.4)
These equations can be converted into functions of the salinity (S) using the approximate relationship:
S (%0) = 1.80655 CI(%o)
(1.5)
The composition of the major components of sea water is summarized in Fig. 1.4.
The major sea salts include NaCI, Na2S04' MgCl2 and MgS04. The concept of salinity
is discussed in more detail in the next section.
1.1.2
The Concept of Salinity
Salinity (S) was originally conceived as a measurement of the mass of dissolved salts
in a given mass of sea water (the weight fraction in parts per thousand, ppt, %0). The
experimental determination of the salt content of sea water by drying and weighing
presents some difficulties. At the temperatures necessary to drive off the last traces of
H20, the bicarbonates and carbonates are decomposed to oxides (M02, where M = Na
or K), and some halides are lost when heating to dryness (HCI and HBr). One can prevent the loss of HCI by adding NaF before evaporation (Morris and Riley 1964). This
led earlier researchers to use indirect methods to measure the salinity. A complete
chemical analysis of sea water is the only reliable way to determine the true salinity of
sea water (Sr)' This method, however, requires too much time, and cannot be used for
routine work. The early work related the true salinity to chlorinity:
Sr = a CI(%o}
(1.6)
where a = 1.8056 (Dittmar 1884) and 1.8148 (Lyman and Fleming 1940), which can be
compared to the values of 1.8154 (Table 1.1). Earlier researchers suggested that CI(%o}
could be used as a measure of salinity. Measurements of the chlorinity and evaporation salinity gave:
S (%0) = 0.030 + 1.805 CI(%o)
(1.7)
For approximately 65 years, this formula was used in oceanography to determine
salinity to an accuracy of 0.01%0 in S. "Normal" sea water of known CI(%o) (prepared
for years in Copenhagen and now in Wormley, England) was used to calibrate the titration methods use to determine CI. Measurements of the physical properties of sea
water such as density as a function of Cl(%o) could be used to calculate physical properties from CI measurements made at sea. The intercept was due to the use of Baltic
Sea waters that have an input of river salts (Ca(HC0 3 h) and little chloride. Since the
salts of different rivers can vary, the intercept can vary for each estuarine system. The
salinity of sea water can be determined by measuring a number of physical properties (listed below along with the estimated errors in salinity).