Geology Reference
In-Depth Information
CHAPTER 4
Chemistry of the Oceans
STEPHEN J. DE MORA
International Atomic Energy Agency, Marine Environment Laboratory,
4 quai Antoine 1
er
, MC 98000, Principality of Monaco
4.1 INTRODUCTION
The World Ocean is a complex mixture containing all the elements, albeit
in dilute amounts in some cases. Seawater contains dissolved gases and,
apart from some exceptional environments, is consequently both well
oxygenated and buffered at a pH of about 8. There are electrolytic salts,
the ionic strength of seawater being approximately 0.7, and many organic
compounds in solution. At the same time, there is a wide range of
inorganic and organic particles in suspension. However, these comforta-
ble distinctions become quite confused in seawater because some mole-
cules present in true solution are sufficiently large to be retained by a filter.
Moreover, surface adsorption allows particles to scavenge-dissolved ele-
ments and accumulate coatings of organic material from solution. Some
elements, particularly those with biochemical functions, may be rapidly
removed from solution. Concurrently, reactions involving geological time
scales are proceeding slowly. Yet despite this apparent complexity, many
aspects of the composition of seawater and chemical oceanography can
now be explained with recourse to the fundamental principles of chem-
istry. This chapter serves to bridge the gap between those with environ-
mental expertise and those with a traditional chemical background.
4.1.1 The Ocean as a Biogeochemical Environment
A traditional approach utilised in geochemistry, and now also in envi-
ronmental chemistry, is to consider the system under investigation a
reservoir. For a given component, the reservoir has sources (inputs) and
sinks (outputs). The system is said to be at equilibrium, or operating
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