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Chemical Oceanography, 4th Edition
in surface seawater below the microlayer. The chemical composition of the organic matter
in the seawater microlayer is not yet well known, but appreciable quantities of macromolecule species similar to humic substances constitute a major fraction of the DOC and POC
at this interface. Mono- and polysaccharides as well as fatty acids have also been isolated
from surface microlayers.
The transfer of organic material across the air–sea interface can be accomplished by
either wet (liquid) or dry (gas or solid) deposition, although these categories are sometimes
difficult to effectively separate from each other. For example, when liquid deposition takes
place (rainwater), the dissolved gases and particulate material in rainwater are simultaneously deposited. Williams (1975) has estimated that 2.2 × 10 14 gC yr –1 is a reasonable estimate for the amount of organic carbon contributed to the oceans by rainfall. This figure is
similar in value to the amount of organic carbon input by rivers (3.3 × 10 13 moles C yr –1 ×
12 gC L –1 mole C = 4.0 × 10 14 gC yr –1 ). Hunter and Liss (1977) pointed out that this flux of
organic carbon into the oceans may not represent a net input because of the input of marine
organic matter into the atmosphere by the bursting of bubbles in whitecaps and breaking
waves. Bubble bursting ejects a significant amount of organic matter from the seawater
microlayer into the atmosphere, and rising bubbles also harvest organic matter from subsurface waters. Thus, it is possible that a significant portion of the organic matter transferred to the sea from the atmosphere by rain is organic matter recycled from seawater.
Much of this organic material is lipid material that is concentrated in surface seawaters.
Other recent studies of marine aerosols have found that the organic matter in the aerosols was dominated by waxes of terrestrial origin. Peltzer and Gagosian (1989) reported
that four lipid compound classes (aliphatic hydrocarbons, fatty alcohols, fatty acid esters,
and fatty acid salts) all indicate a terrestrial vascular plant source for organic matter isolated from atmospheric samples collected from the tropical North Pacific. Their results
indicated that these aerosol lipids originate from wind erosion of soils and direct emission
from vegetation, and that the major fluxes to seawater result from rain rather than from
dry deposition.
However, definite net fluxes of organic matter from the atmosphere to seawater have
been established for anthropogenic substances such as DDT and polychlorinated biphenyls (PCBs). DDT is a chlorinated hydrocarbon pesticide that was used extensively following World War II. It is no longer used in the United States because it is extremely persistent
and tends to accumulate in food chains. PCBs are also very persistent in the environment, and until the manufacture of these compounds was discontinued in 1977, they were
used industrially as plasticizers, in paints, and as coolants and transformers. Hunter and
Liss (1977) estimated that 10% and 0.5% of the total annual production of PCBs and DDT,
respectively, are transported into the world’s oceans through atmospheric– seawater fluxes.
PCBs and DDT are extremely widespread in the marine environment and have been found
in the tissues of many marine organisms.
9.4.1.3 Additional Sources of Organic Matter
In addition to the sources of organic matter described, marine organisms are often considered an “internal source” of organic matter by the excretion of metabolites and the release
of substances on the death and decay of cells. However, marine organisms, except for the
case of primary producers, are not really sources of organic matter but are essentially
transformers that modify the organic substances that enter the marine environment by the
processes discussed. Another internal source of marine organic matter that must be con-
Chemical Oceanography, 4th Edition
in surface seawater below the microlayer. The chemical composition of the organic matter
in the seawater microlayer is not yet well known, but appreciable quantities of macromolecule species similar to humic substances constitute a major fraction of the DOC and POC
at this interface. Mono- and polysaccharides as well as fatty acids have also been isolated
from surface microlayers.
The transfer of organic material across the air–sea interface can be accomplished by
either wet (liquid) or dry (gas or solid) deposition, although these categories are sometimes
difficult to effectively separate from each other. For example, when liquid deposition takes
place (rainwater), the dissolved gases and particulate material in rainwater are simultaneously deposited. Williams (1975) has estimated that 2.2 × 10 14 gC yr –1 is a reasonable estimate for the amount of organic carbon contributed to the oceans by rainfall. This figure is
similar in value to the amount of organic carbon input by rivers (3.3 × 10 13 moles C yr –1 ×
12 gC L –1 mole C = 4.0 × 10 14 gC yr –1 ). Hunter and Liss (1977) pointed out that this flux of
organic carbon into the oceans may not represent a net input because of the input of marine
organic matter into the atmosphere by the bursting of bubbles in whitecaps and breaking
waves. Bubble bursting ejects a significant amount of organic matter from the seawater
microlayer into the atmosphere, and rising bubbles also harvest organic matter from subsurface waters. Thus, it is possible that a significant portion of the organic matter transferred to the sea from the atmosphere by rain is organic matter recycled from seawater.
Much of this organic material is lipid material that is concentrated in surface seawaters.
Other recent studies of marine aerosols have found that the organic matter in the aerosols was dominated by waxes of terrestrial origin. Peltzer and Gagosian (1989) reported
that four lipid compound classes (aliphatic hydrocarbons, fatty alcohols, fatty acid esters,
and fatty acid salts) all indicate a terrestrial vascular plant source for organic matter isolated from atmospheric samples collected from the tropical North Pacific. Their results
indicated that these aerosol lipids originate from wind erosion of soils and direct emission
from vegetation, and that the major fluxes to seawater result from rain rather than from
dry deposition.
However, definite net fluxes of organic matter from the atmosphere to seawater have
been established for anthropogenic substances such as DDT and polychlorinated biphenyls (PCBs). DDT is a chlorinated hydrocarbon pesticide that was used extensively following World War II. It is no longer used in the United States because it is extremely persistent
and tends to accumulate in food chains. PCBs are also very persistent in the environment, and until the manufacture of these compounds was discontinued in 1977, they were
used industrially as plasticizers, in paints, and as coolants and transformers. Hunter and
Liss (1977) estimated that 10% and 0.5% of the total annual production of PCBs and DDT,
respectively, are transported into the world’s oceans through atmospheric– seawater fluxes.
PCBs and DDT are extremely widespread in the marine environment and have been found
in the tissues of many marine organisms.
9.4.1.3 Additional Sources of Organic Matter
In addition to the sources of organic matter described, marine organisms are often considered an “internal source” of organic matter by the excretion of metabolites and the release
of substances on the death and decay of cells. However, marine organisms, except for the
case of primary producers, are not really sources of organic matter but are essentially
transformers that modify the organic substances that enter the marine environment by the
processes discussed. Another internal source of marine organic matter that must be con-