CHAPTER 2 . Marine Organic Geochemistry: A General Overview
2.2.5
Uncharacterized Organic Material
Although amino acids, carbohydrates and lipids constitute the major biochemicals in
living organisms, they are usually present in macromolecular matrices that are not fully
amenable to molecular-level analyses by currently-available analytical techniques.
Analyses of cultured plankton provide wide ranges of the proportions of organic carbon present as these biochemical classes (Fig. 2.19), although in most cases all three
compound classes were not analysed simultaneously in the same samples. Comprehensive molecular-level analyses of amino acids, carbohydrates, pigments and lipids
in particulate material in the equatorial Pacific (Wakeham et al.1997a) determined that
about 84% of DC in plankton could be accounted for (Fig. 2.19), mainly as amino acids. Pigments, while important light-harvesting biochemicals in photosynthetic organisms, were relatively minor constituents of DC. The remaining 16% of DCwas not characterized by the molecular techniques used, but might include nucleic acids, uronic
acids, and amino sugars. The fraction of characterizable DC decreases, and as a consequence the fraction of uncharacterizable material increases, with the extent of diagenesis in the ocean. In the interior of the ocean, only about 30% of DC could be characterized, while in sediments the fraction of characterized DC dropped still further to
less than 20%.
Plankton
Shallow
traps
Deep
traps
Surface
sediment
o
f.-.---. . . . . . . ~ I
I I
I
,
_
Amino acids
o Carbohydrates
D
Li ids
'\ ,
\
20
40
60
80
100
Organic carbon (%)
Fig. 2.19. Ranges of amino acid, carbohydrate and lipid contributions to DC in plankton, shallow sediment traps deployed near the base of the euphotic zone, deep traps in the mesopelagic and bathypelagic
zones, and deep-sea surface sediments. Lines correspond to average fractions of organic carbon represented by amino acid, carbohydrate, lipid, and uncharacterized material in the equatorial Pacific as reported by Wakeham et al. (1997b). References - plankton: Degens and Mopper (1976); Smetacek and
Hendrikson (1979); Tanoue et al. (1982); Wefer et al. (1982); Cowie and Hedges (1984,1996); Parsons et al.
(1984); Montani and Okaichi (1985); Sargent and Henderson (1986); Tanoue and Handa (1987); Cowie
and Hedges (1992); shallow traps: Wakeham et al. (1993, 1984a,b); Lee and Cronin (1982,1984); Hedges
et al. (1988); Cowie and Hedges (1992); deep traps: Lee and Cronin (1984); Wefer et al. (1982); Ittekkot
et al. (1984a,b); Wakeham et al.1984b; Miiller et al. (1986); Wakeham and Lee (1989); Haake et al. (1992);
sediments: Whelan (1977); Farrington and Tripp (1977); Tanoue and Handa (1987); Venkatesan et al. (1987);
Steinberg et al. (1987)
2.2.5
Uncharacterized Organic Material
Although amino acids, carbohydrates and lipids constitute the major biochemicals in
living organisms, they are usually present in macromolecular matrices that are not fully
amenable to molecular-level analyses by currently-available analytical techniques.
Analyses of cultured plankton provide wide ranges of the proportions of organic carbon present as these biochemical classes (Fig. 2.19), although in most cases all three
compound classes were not analysed simultaneously in the same samples. Comprehensive molecular-level analyses of amino acids, carbohydrates, pigments and lipids
in particulate material in the equatorial Pacific (Wakeham et al.1997a) determined that
about 84% of DC in plankton could be accounted for (Fig. 2.19), mainly as amino acids. Pigments, while important light-harvesting biochemicals in photosynthetic organisms, were relatively minor constituents of DC. The remaining 16% of DCwas not characterized by the molecular techniques used, but might include nucleic acids, uronic
acids, and amino sugars. The fraction of characterizable DC decreases, and as a consequence the fraction of uncharacterizable material increases, with the extent of diagenesis in the ocean. In the interior of the ocean, only about 30% of DC could be characterized, while in sediments the fraction of characterized DC dropped still further to
less than 20%.
Plankton
Shallow
traps
Deep
traps
Surface
sediment
o
f.-.---. . . . . . . ~ I
I I
I
,
_
Amino acids
o Carbohydrates
D
Li ids
'\ ,
\
20
40
60
80
100
Organic carbon (%)
Fig. 2.19. Ranges of amino acid, carbohydrate and lipid contributions to DC in plankton, shallow sediment traps deployed near the base of the euphotic zone, deep traps in the mesopelagic and bathypelagic
zones, and deep-sea surface sediments. Lines correspond to average fractions of organic carbon represented by amino acid, carbohydrate, lipid, and uncharacterized material in the equatorial Pacific as reported by Wakeham et al. (1997b). References - plankton: Degens and Mopper (1976); Smetacek and
Hendrikson (1979); Tanoue et al. (1982); Wefer et al. (1982); Cowie and Hedges (1984,1996); Parsons et al.
(1984); Montani and Okaichi (1985); Sargent and Henderson (1986); Tanoue and Handa (1987); Cowie
and Hedges (1992); shallow traps: Wakeham et al. (1993, 1984a,b); Lee and Cronin (1982,1984); Hedges
et al. (1988); Cowie and Hedges (1992); deep traps: Lee and Cronin (1984); Wefer et al. (1982); Ittekkot
et al. (1984a,b); Wakeham et al.1984b; Miiller et al. (1986); Wakeham and Lee (1989); Haake et al. (1992);
sediments: Whelan (1977); Farrington and Tripp (1977); Tanoue and Handa (1987); Venkatesan et al. (1987);
Steinberg et al. (1987)