CHAPTER 2 • Marine Organic Geochemistry: A General Overview
2.2.6
Dissolved Organic Matter
Dissolved organic matter (DaM, <0.2 !lm) is one of the largest reservoirs of organic
nitrogen and carbon in the ocean. On average, this reservoir contains 600 Gt C (Williams and DruffeI1987). Dissolved organic carbon (DOC) is typically enriched in the
surface mixed layers of all oceans compared to the deep sea. This enrichment appears
to be related to production of soluble material by phytoplankton. Chemical analysis
of DaM has resulted in a low proportion of small, rapidly cycling organic compounds
(amino acids, amines, sugars, etc.). The majority of DaM is made of resistant components of unknown chemical structure.
Between 25-30% of seawater DaM is of molecular weight >1000 D (UDOM 5 ). Proton NMR of UDOM produces similar spectra regardless of the sampling site. Thus,
carbohydrates account for 55% of the total carbon in UDOM, whereas acetate and lipids account for 7 and 6% of the carbon, respectively (Aluwihare et al. 1997). Polysaccharide linkage analysis of samples from the North Atlantic and Pacific Ocean resulted
in 40% of terminal sugars, 40% of sugars linked without branching, and 20% of the
sugars cross-linked with one branch point. That observation, plus the relative fixed
ratio of biochemicals found in UDOM, indicated that the pool is a mixture of acyloligosaccharides in which carbohydrates, acetate, and lipids are linked in a common
macromolecular structure. The source of UDOM appears to be phytoplankton release
(Aluwihare et al. 1997).
15N CPMAS 6 NMR spectra of UDOM from the Pacific Ocean showed a single peak at
260 ppm in surface and deeper samples (100, 375 and 4000 m), corresponding
to the resonance of amide nitrogen (McCarthyet al.1997).Although the amide fraction
makes about 80% of the nitrogen, <10% of the nitrogen was identified as amino acids.
Other nitrogen forms may contribute to UDOM. Some of the potential can-didates are
"pyrrol-like" nitrogen such as purines, pyrimidines, porphyrins, as well as melanoidins
(complex condensates of sugars and amino acids) (McCarthy et al. 1997).
Acknowledgements
We would like to thank A. Gianguzza and the organizing committee of the International
School on Marine Chemistry for the invitation to participate in this event. S. Pantoja
was supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic
Institution, with funding provided by the Johnson Foundation.
References
Allard B, Templier J, de Leeuw JW (1998) Artifactual origin of mycobacterial bacteran. Formation of
melanoidin-like artifactual macromolecular material during the usual isolation process. Org.
Geochem 26:691-703
Aluwihare LI, Repeta DJ, Chen RF (1997) A major biopolymeric component to dissolved organic carbon in surface seawater. Nature 387:166-169
5 UDOM, ultrafiltered dissolved organic matter. The fraction of DOM isolated with ultra-filters of
nominal pore size of -1 nm (-1000 daltons).
6 CPMAS, cross-polarization magic-angle-spinning.
2.2.6
Dissolved Organic Matter
Dissolved organic matter (DaM, <0.2 !lm) is one of the largest reservoirs of organic
nitrogen and carbon in the ocean. On average, this reservoir contains 600 Gt C (Williams and DruffeI1987). Dissolved organic carbon (DOC) is typically enriched in the
surface mixed layers of all oceans compared to the deep sea. This enrichment appears
to be related to production of soluble material by phytoplankton. Chemical analysis
of DaM has resulted in a low proportion of small, rapidly cycling organic compounds
(amino acids, amines, sugars, etc.). The majority of DaM is made of resistant components of unknown chemical structure.
Between 25-30% of seawater DaM is of molecular weight >1000 D (UDOM 5 ). Proton NMR of UDOM produces similar spectra regardless of the sampling site. Thus,
carbohydrates account for 55% of the total carbon in UDOM, whereas acetate and lipids account for 7 and 6% of the carbon, respectively (Aluwihare et al. 1997). Polysaccharide linkage analysis of samples from the North Atlantic and Pacific Ocean resulted
in 40% of terminal sugars, 40% of sugars linked without branching, and 20% of the
sugars cross-linked with one branch point. That observation, plus the relative fixed
ratio of biochemicals found in UDOM, indicated that the pool is a mixture of acyloligosaccharides in which carbohydrates, acetate, and lipids are linked in a common
macromolecular structure. The source of UDOM appears to be phytoplankton release
(Aluwihare et al. 1997).
15N CPMAS 6 NMR spectra of UDOM from the Pacific Ocean showed a single peak at
260 ppm in surface and deeper samples (100, 375 and 4000 m), corresponding
to the resonance of amide nitrogen (McCarthyet al.1997).Although the amide fraction
makes about 80% of the nitrogen, <10% of the nitrogen was identified as amino acids.
Other nitrogen forms may contribute to UDOM. Some of the potential can-didates are
"pyrrol-like" nitrogen such as purines, pyrimidines, porphyrins, as well as melanoidins
(complex condensates of sugars and amino acids) (McCarthy et al. 1997).
Acknowledgements
We would like to thank A. Gianguzza and the organizing committee of the International
School on Marine Chemistry for the invitation to participate in this event. S. Pantoja
was supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic
Institution, with funding provided by the Johnson Foundation.
References
Allard B, Templier J, de Leeuw JW (1998) Artifactual origin of mycobacterial bacteran. Formation of
melanoidin-like artifactual macromolecular material during the usual isolation process. Org.
Geochem 26:691-703
Aluwihare LI, Repeta DJ, Chen RF (1997) A major biopolymeric component to dissolved organic carbon in surface seawater. Nature 387:166-169
5 UDOM, ultrafiltered dissolved organic matter. The fraction of DOM isolated with ultra-filters of
nominal pore size of -1 nm (-1000 daltons).
6 CPMAS, cross-polarization magic-angle-spinning.