419
Primary Production in the Oceans
surface waters and decreased to 25% in deep waters. These results indicate that carbohydrates are more abundant and reactive in the oceans than previously thought.
9.4.3.2 Amino Acids and Proteins
Proteins are present in all living cells and often account for over 50% of the bulk weight of
organisms. They serve as a component of the structure of the cell and as metabolic regulators and are instrumental in motion and defense. Proteins are made up of amino acids
linked by peptide (amide) bonds. Although a wide variety of proteins exists, they are composed of a rather small number of amino acids. Since the nitrogen composition of proteins
is nearly constant (16%), the nitrogen concentrations are used as a way of determining the
protein content of living material. The concentration of amino acids in seawater ranges
from 20 to 250 μg L –1 and makes up 2 to 3% of the DOC. Amino acids are organic acids in
which the alpha carbon of the –COOH group is replaced by an –NH 2 group. They have
the general formula (RCHNH 2 COOH), where R is a functional group that differs for each
amino acid. Free amino acids make up a small fraction of the organic carbon compounds
present in living cells. Combined amino acids are found in dissolved, colloidal, and particulate matter. Free amino acids are also produced enzymatically by the hydrolysis of
peptides and proteins in seawater by bacteria.
9.4.3.3 Hydrocarbons
Hydrocarbons make up less than 1% of the DOC in seawater and contain carbon and hydrogen in the chemical formula C n H m . They have concentrations between 1 and 50 μg L –1 , with
an average of 10 μg L –1 . Hydrocarbons are frequently classified as low (C 14 )
molecular weight. Methane (CH 4 ) is the simplest hydrocarbon and is found in all natural
waters. Its concentrations range from 10 to 100 μgL –1 . The biological production of methane
is of interest because it is a useful fuel and also a greenhouse gas that has doubled in the
atmosphere since 1900.
Hydrocarbons are classified as saturated, unsaturated, and aromatic. Saturated hydrocarbons (paraffins or alkanes) are quite stable. Unsaturated hydrocarbons contain one or
more double bonds (C=C). The most common found in seawater are alkenes or olefins. An
unsaturated hydrocarbon with two double bonds is called a diene, with three it is called
a triene, and so on. Isoprene is a diene that is a component of many plants and animals
and is often referred to as one of nature’s building blocks. Many complex hydrocarbons
can be broken down into isoprene units, which is called the “isoprene rule.” Terpenes are
isoprenoids that are found in the essential oils of plants. They have a regular head- to- tail
arrangement of isoprene units. Aromatic hydrocarbons contain at least one benzene ring
(six carbon atoms arranged in a ring with alternating single and double bonds, e.g., C 6 H 6 ).
They are considered to be derived mainly from abiotic processes such as the pyrolysis of
organic matter at high temperatures (e.g., forest fires and fossil fuel combustion).
9.4.3.4 Carboxylic Acids
Carboxylic acids have at least one carboxylic group (–COOH). Amino acids discussed previously and fulvic and humic acids also contain a –COOH group but are discussed
separately because of their unique behavior. The other carboxylic acids of importance in
the marine environment include fatty acids such as stearic acid [CH 3 (CH 2 ) 16 –COOH] and
palmitic acid [CH 3 –(CH) 2 –COOH]. Fatty acids are found as fats in animals and waxes
Primary Production in the Oceans
surface waters and decreased to 25% in deep waters. These results indicate that carbohydrates are more abundant and reactive in the oceans than previously thought.
9.4.3.2 Amino Acids and Proteins
Proteins are present in all living cells and often account for over 50% of the bulk weight of
organisms. They serve as a component of the structure of the cell and as metabolic regulators and are instrumental in motion and defense. Proteins are made up of amino acids
linked by peptide (amide) bonds. Although a wide variety of proteins exists, they are composed of a rather small number of amino acids. Since the nitrogen composition of proteins
is nearly constant (16%), the nitrogen concentrations are used as a way of determining the
protein content of living material. The concentration of amino acids in seawater ranges
from 20 to 250 μg L –1 and makes up 2 to 3% of the DOC. Amino acids are organic acids in
which the alpha carbon of the –COOH group is replaced by an –NH 2 group. They have
the general formula (RCHNH 2 COOH), where R is a functional group that differs for each
amino acid. Free amino acids make up a small fraction of the organic carbon compounds
present in living cells. Combined amino acids are found in dissolved, colloidal, and particulate matter. Free amino acids are also produced enzymatically by the hydrolysis of
peptides and proteins in seawater by bacteria.
9.4.3.3 Hydrocarbons
Hydrocarbons make up less than 1% of the DOC in seawater and contain carbon and hydrogen in the chemical formula C n H m . They have concentrations between 1 and 50 μg L –1 , with
an average of 10 μg L –1 . Hydrocarbons are frequently classified as low (
molecular weight. Methane (CH 4 ) is the simplest hydrocarbon and is found in all natural
waters. Its concentrations range from 10 to 100 μgL –1 . The biological production of methane
is of interest because it is a useful fuel and also a greenhouse gas that has doubled in the
atmosphere since 1900.
Hydrocarbons are classified as saturated, unsaturated, and aromatic. Saturated hydrocarbons (paraffins or alkanes) are quite stable. Unsaturated hydrocarbons contain one or
more double bonds (C=C). The most common found in seawater are alkenes or olefins. An
unsaturated hydrocarbon with two double bonds is called a diene, with three it is called
a triene, and so on. Isoprene is a diene that is a component of many plants and animals
and is often referred to as one of nature’s building blocks. Many complex hydrocarbons
can be broken down into isoprene units, which is called the “isoprene rule.” Terpenes are
isoprenoids that are found in the essential oils of plants. They have a regular head- to- tail
arrangement of isoprene units. Aromatic hydrocarbons contain at least one benzene ring
(six carbon atoms arranged in a ring with alternating single and double bonds, e.g., C 6 H 6 ).
They are considered to be derived mainly from abiotic processes such as the pyrolysis of
organic matter at high temperatures (e.g., forest fires and fossil fuel combustion).
9.4.3.4 Carboxylic Acids
Carboxylic acids have at least one carboxylic group (–COOH). Amino acids discussed previously and fulvic and humic acids also contain a –COOH group but are discussed
separately because of their unique behavior. The other carboxylic acids of importance in
the marine environment include fatty acids such as stearic acid [CH 3 (CH 2 ) 16 –COOH] and
palmitic acid [CH 3 –(CH) 2 –COOH]. Fatty acids are found as fats in animals and waxes