Afi r s ti m p r e s s i o n
11
ocean water is well mixed over geological time scales. This motivates to define
the salinity S and the water fraction W as
S =
1
m
n−1
k=1
m k ; W =
m n
m
,
(1.2)
such that all mass fractions can be expressed as c k = λ k S, k =1, ···,n− 1 with
λ k =
m k
n−1
l=1 m l
→
n−1
k=1
λ k =1; S + W =1.
(1.3)
In this way, seawater can be considered as a two-component liquid (water and
salt) in which there is only one independent variable, the salinity S.
In early times, the salinity was determined from samples of seawater through
titration of chloride ions (Cl − ) and the use of the constant relationship between
chloride content Cl and salinity S,givenby
S =1.806 Cl.
(1.4)
Nowadays one determines the salinity through the electrical conductivity of a particular seawater sample which is much more accurate than the titration method.
For the open ocean, a typical value of the salinity is 35 gram of salt per kg of
seawater, also indicated as S =3 5ppt (parts per thousand). Often the Practical
Salinity Unit (psu), defined as the ratio of the conductivity of the sample and a
standard NaCl solution, is used as a measure of the salinity; values in psu hardly
differ from those in ppt (S ppt =1.004867S psu ).
1.3.2. The surface distribution of temperature and
salinity
A still often used climatology of temperature and salinity data is the Levitus and
Boyer multivolume ocean atlas (Levitus and Boyer, 1994; Levitus et al., 1994).
This multivolume atlas presents global, objectively analyzed fields of major ocean
parameters on a one-degree latitude-longitude grid for selected standard depth
levels from the sea surface to 5500 m depth. Work to date includes quality control
of historical in-situ temperature, salinity, oxygen, phosphate, nitrate, and silicate
data and the preparation of one-degree latitude-longitude mean fields for each of
these parameters. A more modern data set is from Gouretski and Koltermann
(2004) and these data can be conveniently inspected and plotted using the Ocean
Data View software (http://odv.awi-bremerhaven.de/).
From the Gouretski and Koltermann (2004) data, the mean sea surface temperature of the ocean is plotted in Fig. 1.4a. At mid-latitudes, the temperature
at the western part of each basin is substantially warmer than that at the eastern
side. At high latitudes in the Atlantic Ocean, the water in the Norwegian Sea is
11
ocean water is well mixed over geological time scales. This motivates to define
the salinity S and the water fraction W as
S =
1
m
n−1
k=1
m k ; W =
m n
m
,
(1.2)
such that all mass fractions can be expressed as c k = λ k S, k =1, ···,n− 1 with
λ k =
m k
n−1
l=1 m l
→
n−1
k=1
λ k =1; S + W =1.
(1.3)
In this way, seawater can be considered as a two-component liquid (water and
salt) in which there is only one independent variable, the salinity S.
In early times, the salinity was determined from samples of seawater through
titration of chloride ions (Cl − ) and the use of the constant relationship between
chloride content Cl and salinity S,givenby
S =1.806 Cl.
(1.4)
Nowadays one determines the salinity through the electrical conductivity of a particular seawater sample which is much more accurate than the titration method.
For the open ocean, a typical value of the salinity is 35 gram of salt per kg of
seawater, also indicated as S =3 5ppt (parts per thousand). Often the Practical
Salinity Unit (psu), defined as the ratio of the conductivity of the sample and a
standard NaCl solution, is used as a measure of the salinity; values in psu hardly
differ from those in ppt (S ppt =1.004867S psu ).
1.3.2. The surface distribution of temperature and
salinity
A still often used climatology of temperature and salinity data is the Levitus and
Boyer multivolume ocean atlas (Levitus and Boyer, 1994; Levitus et al., 1994).
This multivolume atlas presents global, objectively analyzed fields of major ocean
parameters on a one-degree latitude-longitude grid for selected standard depth
levels from the sea surface to 5500 m depth. Work to date includes quality control
of historical in-situ temperature, salinity, oxygen, phosphate, nitrate, and silicate
data and the preparation of one-degree latitude-longitude mean fields for each of
these parameters. A more modern data set is from Gouretski and Koltermann
(2004) and these data can be conveniently inspected and plotted using the Ocean
Data View software (http://odv.awi-bremerhaven.de/).
From the Gouretski and Koltermann (2004) data, the mean sea surface temperature of the ocean is plotted in Fig. 1.4a. At mid-latitudes, the temperature
at the western part of each basin is substantially warmer than that at the eastern
side. At high latitudes in the Atlantic Ocean, the water in the Norwegian Sea is