Chemical Oceanography
Earlier sections in this Handbook have discussed the ways in which the properties of water affect the chemistry of fresh water and the hydrological cycle. In this section we will examine the ways in which sea water differs from fresh water, how these diff
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Earlier sections in this Handbook have discussed the ways in which the properties of water affect the chemistry of fresh water and the hydrological cycle. In this section we will examine the ways in which sea water differs from fresh water, how these differences affect the reactions occurring in sea water, and how these reactions are further affected by the addition of compounds resulting from man's activities. Properties of Sea Water
The properties of sea water are in general determined by the properties of water. The anomalous latent heats of fusion and vaporization, the high heat capacities, and the high boiling and freezing points, all properties resulting from the great degree of structure present in liquid water and which serve to make water a most unusual liquid, are also present in sea water. What makes sea water different from either fresh water or the various non-marine salt waters, such as the Dead Sea or the Great Salt Lake, is the constancy of composition of its salt content. Sea water is a medium of moderately high (-·"0.7 M) ionic strength. The relative composition of its Table 1. Major ions of sea water Cations
g/kg atS = 35%0
Anions
g/kg atS = 35%o
Na+ Mg2+ Ca2+ K+ sr+
10.77 1.29 0.412 0.399 0.0079
c.-
19.354 2.712 0.067 0.0013
so~-
Br-
p-
O. Hutzinger, The Natural Environment and the Biogeochemical Cycles © Springer-Verlag Berlin Heidelberg 1980
P. J. Wangersky
52
major constituents (Table 1) is constant enough so that the determination of one major component allows us to calculate the amounts of the other components present in the sample. Because of the accuracy and reproducibility of the measurement, the quantity usually chosen for measurement has been the chlorinity, a measure of the halide content of the sample. The analytical method normally used was the Mohr titration with silver nitrate, using potassium chromate as the indicator. Chlorinity was defined in terms of the atomic weight of silver, as the mass in grams of silver needed to precipitate the halogens in 328.5233 g of sea water, and was commonly expressed in parts per thousand (%o). The salinity, the grams of sea salt present in 1 kg of sea water after drying according to a specified technique, could then be calculated from the chlorinity by a relationship determined by an International Commission in 1899. This technique for measuring salinity is seldom used now; instead, the salinity is calculated from the conductivity of the sea water, a technique as accurate as the Mohr titration and considerably faster. However, since much of the older work was presented in terms of salinity and chlorinity, by definition the two units are related by the equation S(%o)= 1.80655 Cl (%o). The relationship between salinity and conductivity at any temperature to be found in the oceans can be derived from the International Oceanographic Tables [1]. The units in which salinity and chlorinity are expressed are currently under review, and within the next few years will be revised to conform to ISO usage. The total range of salinity in the o
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