Exergy evolution of the mineral capital on earth - circe

26 THE GEOCHEMISTRY OF THE EARTH. KNOWN FACTS
Table 2.4. Volume <strong>of</strong> Oceans and Seas. Adapted from [85]
Name Volume, M km 3
Atlantic Ocean
without marginal seas 324,6
with marginal seas 354,7
Pacific Ocean
without marginal seas 707,6
with marginal seas 723,7
Indian Ocean
without marginal seas 291
with marginal seas 291,9
Arctic Ocean 17
Mediterranean Sea and Black Sea 4,2
Gulf <strong>of</strong> Mexico and Caribbean Sea 9,6
Australasian Central Sea 9,9
Hudson Bay 0,16
Baltic Sea 0,02
North Sea 0,05
English Channel 0,004
Irish Sea 0,006
Sea <strong>of</strong> Okhotsk 1,3
Bering Sea 3,33
The world ocean 1.370
sources after <strong>the</strong> process <strong>of</strong> desalination and as chlorine and bromine sources 2 . Never<strong>the</strong>less,
its salinity avoids seawater to have more economic uses than <strong>the</strong> o<strong>the</strong>r
types <strong>of</strong> water reservoirs mentioned before. In fact it is frequently considered to be
a drain ra<strong>the</strong>r than a resource.
2.4.1.1 The composition <strong>of</strong> <strong>the</strong> sea
Despite <strong>the</strong>ir overall size, <strong>the</strong> oceans are sufficiently uniform to make description
<strong>of</strong> <strong>the</strong>ir chemical nature relatively straightforward. Studies have shown that <strong>the</strong>
relative compositions <strong>of</strong> major components: N a + , M g2+ , Ca2+ , K + , Cl − , SO −2
4 ,
Sr 2+ , HBO −
3 , CO2−
3 , B(OH) 3, B(OH) −
4 , F − <strong>of</strong> seawater were constant [69], [37],
[264] and [224]. The first six ions make up 99,4% <strong>of</strong> <strong>the</strong> dissolved salts (see table
2.5). Most <strong>of</strong> <strong>the</strong> chemicals in <strong>the</strong> ocean are brought from <strong>the</strong> water <strong>of</strong> rivers,
which in turn receive <strong>the</strong>m from rocks <strong>of</strong> <strong>the</strong> crust that have suffered <strong>the</strong> process
<strong>of</strong> wea<strong>the</strong>ring. An average composition <strong>of</strong> river waters given by Livingstone [197] is
listed in table 2.8. It is remarkable <strong>the</strong> difference between river and ocean chemical
compositions. The explanation <strong>of</strong> that relies on <strong>the</strong> residence time <strong>of</strong> <strong>the</strong> ions. Most
abundant ions found in seawater have residence times <strong>of</strong> above one million years
[137]. The salinity <strong>of</strong> ocean water is about 35 parts per thousand by mass, but
2 See sections 3.4.16 and 3.4.10 for more details.