94
E. Pelizzetti . P. Calza
The possible photolysis of abundant hydrophobic and largely particulate monoand polyunsaturated fatty acids in the marine environment is of biogeochemical interest. Numerous pathways are known for such molecules once liberated from cells,
and they are the suspected precursors of some humic and fulvic acid components.
Finally, there is evidence that the surfaces of algae (living and dead) are active in
some photoprocesses. Heat-killed and ascorbate-washed cells also promote the reaction, so although the cells are living, the process does not appear to be metabolic. Similar effects have been seen for various other organophosphorus compounds.
3.3.2.4
Organic Compounds in Sea Water
Although the concentration of organic matter in the oceans is less than 0.01% of the
total amount of salts, these compounds are important modifiers of many of the biological and chemical reactions that take place in the sea. They provide a nutritional
and energy base for micro and macroorganisms, have a major impact on the speciation of many metals by such processes as complexation and adsorption, and are precursors of fossil fuels such as petroleum and oil shale. These organic compounds can
also provide growth promoters and inhibitors that may control phytoplankton succession.
The source of most of the organic compounds in sea water is from primary production in the euphotic zone. Part of the organic matter from photosynthesis is partially metabolized in order to satisfy the energy requirements of phytoplankton. Much
of the organic matter is consumed by organisms, but a significant amount is decomposed at the surface, while 1 to 12% of the annual production remains as a refractory
fraction, quite resistant to biological and chemical transformations. The residence time
of this residual dissolved organic matter in the sea has been estimated by Williams
and Druffel (1987) to be 1310 yr for surface and 6240 yr for deep dissolved organic
matter. Most of this residual organic carbon consists of humic substances. The other
sources of input of organic matter to sea water, in addition to primary productivity by
marine plankton, include terrestrial input by rivers and by the atmosphere, excretion
by marine organisms and the resuspension of organic matter from marine sediments.
The direct addition of organic matter due to oil spills is an additional source.
In aquatic systems, it is traditional to divide organic matter into two major categories: dissolved and particulate (DaM and paM). paM includes those species that will
be retained by a glass fibre filter of 0.45 jlm.
Dissolved organic carbon (DOC) is about 50% of the DaM, and likewise particulate organic carbon (PaC) is about 50% of the value of paM. The concentration of
dissolved organic carbon in sea water is typically significantly greater than that of pac.
Seasonal variations of DOC and pac occur primarily in shallow waters and are similar to the variations in primary productivity. At depths below a few hundred metres,
the average DOC is 40 jlM, while the average pac is 0.8 jlM (Millero 1996). The pac
frequently goes through a maximum in the oxygen minimum zone. Some have suggested that this is a result of sinking particulate material having a density similar to
water at a depth of 500 to 1000 m. The oxygen minimum is thus a result of bacteria
oxidizing this material in this zone. The dissolved and particulate organic carbon, nitrogen and phosphorus levels in surface, deep, and coastal waters are compared to the
levels at the oxygen minimum. The coastal levels are higher than those in surface wa-
E. Pelizzetti . P. Calza
The possible photolysis of abundant hydrophobic and largely particulate monoand polyunsaturated fatty acids in the marine environment is of biogeochemical interest. Numerous pathways are known for such molecules once liberated from cells,
and they are the suspected precursors of some humic and fulvic acid components.
Finally, there is evidence that the surfaces of algae (living and dead) are active in
some photoprocesses. Heat-killed and ascorbate-washed cells also promote the reaction, so although the cells are living, the process does not appear to be metabolic. Similar effects have been seen for various other organophosphorus compounds.
3.3.2.4
Organic Compounds in Sea Water
Although the concentration of organic matter in the oceans is less than 0.01% of the
total amount of salts, these compounds are important modifiers of many of the biological and chemical reactions that take place in the sea. They provide a nutritional
and energy base for micro and macroorganisms, have a major impact on the speciation of many metals by such processes as complexation and adsorption, and are precursors of fossil fuels such as petroleum and oil shale. These organic compounds can
also provide growth promoters and inhibitors that may control phytoplankton succession.
The source of most of the organic compounds in sea water is from primary production in the euphotic zone. Part of the organic matter from photosynthesis is partially metabolized in order to satisfy the energy requirements of phytoplankton. Much
of the organic matter is consumed by organisms, but a significant amount is decomposed at the surface, while 1 to 12% of the annual production remains as a refractory
fraction, quite resistant to biological and chemical transformations. The residence time
of this residual dissolved organic matter in the sea has been estimated by Williams
and Druffel (1987) to be 1310 yr for surface and 6240 yr for deep dissolved organic
matter. Most of this residual organic carbon consists of humic substances. The other
sources of input of organic matter to sea water, in addition to primary productivity by
marine plankton, include terrestrial input by rivers and by the atmosphere, excretion
by marine organisms and the resuspension of organic matter from marine sediments.
The direct addition of organic matter due to oil spills is an additional source.
In aquatic systems, it is traditional to divide organic matter into two major categories: dissolved and particulate (DaM and paM). paM includes those species that will
be retained by a glass fibre filter of 0.45 jlm.
Dissolved organic carbon (DOC) is about 50% of the DaM, and likewise particulate organic carbon (PaC) is about 50% of the value of paM. The concentration of
dissolved organic carbon in sea water is typically significantly greater than that of pac.
Seasonal variations of DOC and pac occur primarily in shallow waters and are similar to the variations in primary productivity. At depths below a few hundred metres,
the average DOC is 40 jlM, while the average pac is 0.8 jlM (Millero 1996). The pac
frequently goes through a maximum in the oxygen minimum zone. Some have suggested that this is a result of sinking particulate material having a density similar to
water at a depth of 500 to 1000 m. The oxygen minimum is thus a result of bacteria
oxidizing this material in this zone. The dissolved and particulate organic carbon, nitrogen and phosphorus levels in surface, deep, and coastal waters are compared to the
levels at the oxygen minimum. The coastal levels are higher than those in surface wa-