420
Chemical Oceanography, 4th Edition
in plants and have 4 to 36 carbon anions. The term fat is normally applied to solid glycol esters and oils and liquid glycol esters. Fats and oils are esters (–COOR) of glycerol
(HO–CH 2 –CHOH–CH 2 –OH) and fatty acids (RCOOH). The term lipid refers to fats, oils,
and fat- soluble compounds. Nonvolatile fatty acids have concentrations between 10 and
200 μg L –1 and typically account for 1% of the DOC. Less is known about the concentrations
of hydroxy [RC(OH)COOH], dicarboxylic [RCOOH], and aromatic acids (C 6 H 6 –COOH) in
the marine environment. Most of the fatty acids arise from the hydrolysis of triglycerides
(triacylglycerols) during the degradation of detrital organic matter. Triglycerides comprise
a major fraction of the lipid component of plant and animal storage tissue, and the fatty
acids account for approximately 90% of the weight of triglycerides. Thus, fatty acids are a
major component of lipids derived from the degradation of organic matter.
9.4.3.5 Humic Substances
Humic substances are complex mixtures of individual compound classes and tend to be
quite resistant to extensive microbial degradation. They are precursors of the geopolymeric material known as kerogen (dispersed organic matter found in sedimentary rocks
and insoluble in organic solvents, mineral acids, and bases). Petroleum is produced from
the geochemical maturation of kerogen derived primarily from aquatic organisms. Since
humic substances consist of a mixture of plant and animal debris at various stages of
decomposition, the chemical composition will vary with source of input and environment
of deposition. Humic substances have been studied by soil and water chemists for many
years because of the important roles they play with respect to water quality, soil fertility,
and soil porosity and their association with both inorganic and organic nutrients and pollutants through complexation and adsorption processes. In seawater, the concentration of
humic substances ranges from 60 to 600 μg C/ L, which accounts for 10 to 30% of the DOC
of seawater.
Early studies of marine humic substances described the isolation of “gelbstoff,” a
yellowish- brown acid material that could be extracted from seawater with organic solvents.
Humin is both acid and base insoluble. Humic and fulvic acids are typically extracted
together into a basic solution (0.5 M NaOH), and the humic acids are precipitated out by
acidification of the solution (addition of HCl to a pH of 2.0 or the use of an ion- exchange
resin in the H + form), leaving the acid- soluble fulvic acid fraction in solution. Humin is
chemically very similar to humic acid but is more tightly bound to the inorganic soil and
sediment constituents. Humic substances consist of approximately 40 to 60% carbon, 30 to
45% oxygen, 1 to 5% nitrogen, and 2% or less sulfur. Humic acids tend to be richer in
carbon and poorer in oxygen than fulvic acids. Historically, the chemical compositions of
humic substances from various environments were studied by wet chemical and instrumental methods of analysis. The major structural components include aliphatic chains
with varying degrees of branching, aromatic rings, phenolic, hydroxyl, methoxyl, and carboxylic acid groups.
9.4.3.6 Steroids
Steroids are related to the terpenoids, which are built of five carbon atom isoprene units
(CH 2 CHCH 3 CHCH 2 ). Steroids (Table 9.10) are classified according to their principal functional groups. Cholesterol, for example, is classified as a sterol because it contains an alcohol group (ROH). All steroids have the same carbon skeleton (Table 9.10), typically have 27
Chemical Oceanography, 4th Edition
in plants and have 4 to 36 carbon anions. The term fat is normally applied to solid glycol esters and oils and liquid glycol esters. Fats and oils are esters (–COOR) of glycerol
(HO–CH 2 –CHOH–CH 2 –OH) and fatty acids (RCOOH). The term lipid refers to fats, oils,
and fat- soluble compounds. Nonvolatile fatty acids have concentrations between 10 and
200 μg L –1 and typically account for 1% of the DOC. Less is known about the concentrations
of hydroxy [RC(OH)COOH], dicarboxylic [RCOOH], and aromatic acids (C 6 H 6 –COOH) in
the marine environment. Most of the fatty acids arise from the hydrolysis of triglycerides
(triacylglycerols) during the degradation of detrital organic matter. Triglycerides comprise
a major fraction of the lipid component of plant and animal storage tissue, and the fatty
acids account for approximately 90% of the weight of triglycerides. Thus, fatty acids are a
major component of lipids derived from the degradation of organic matter.
9.4.3.5 Humic Substances
Humic substances are complex mixtures of individual compound classes and tend to be
quite resistant to extensive microbial degradation. They are precursors of the geopolymeric material known as kerogen (dispersed organic matter found in sedimentary rocks
and insoluble in organic solvents, mineral acids, and bases). Petroleum is produced from
the geochemical maturation of kerogen derived primarily from aquatic organisms. Since
humic substances consist of a mixture of plant and animal debris at various stages of
decomposition, the chemical composition will vary with source of input and environment
of deposition. Humic substances have been studied by soil and water chemists for many
years because of the important roles they play with respect to water quality, soil fertility,
and soil porosity and their association with both inorganic and organic nutrients and pollutants through complexation and adsorption processes. In seawater, the concentration of
humic substances ranges from 60 to 600 μg C/ L, which accounts for 10 to 30% of the DOC
of seawater.
Early studies of marine humic substances described the isolation of “gelbstoff,” a
yellowish- brown acid material that could be extracted from seawater with organic solvents.
Humin is both acid and base insoluble. Humic and fulvic acids are typically extracted
together into a basic solution (0.5 M NaOH), and the humic acids are precipitated out by
acidification of the solution (addition of HCl to a pH of 2.0 or the use of an ion- exchange
resin in the H + form), leaving the acid- soluble fulvic acid fraction in solution. Humin is
chemically very similar to humic acid but is more tightly bound to the inorganic soil and
sediment constituents. Humic substances consist of approximately 40 to 60% carbon, 30 to
45% oxygen, 1 to 5% nitrogen, and 2% or less sulfur. Humic acids tend to be richer in
carbon and poorer in oxygen than fulvic acids. Historically, the chemical compositions of
humic substances from various environments were studied by wet chemical and instrumental methods of analysis. The major structural components include aliphatic chains
with varying degrees of branching, aromatic rings, phenolic, hydroxyl, methoxyl, and carboxylic acid groups.
9.4.3.6 Steroids
Steroids are related to the terpenoids, which are built of five carbon atom isoprene units
(CH 2 CHCH 3 CHCH 2 ). Steroids (Table 9.10) are classified according to their principal functional groups. Cholesterol, for example, is classified as a sterol because it contains an alcohol group (ROH). All steroids have the same carbon skeleton (Table 9.10), typically have 27