Characterization of the Semi-Labile Polysaccharide Fraction of Marine Dissolved Organic Matter

Approximately 20-25 percent of marine dissolved organic carbon (DOC) occurs as a family of structurally related polysaccharides that display a remarkable uniformity in chemical characteristics across ocean basins, and between fresh and marine waters. A specific subset of the polysaccharides produced by marine microbes, DOC-polysaccharides are distinct in that they resist microbial degradation and therefore accumulate to very high concentrations in seawater, sequestering a significant amount of carbon, nitrogen, and phosphorus in the process. Acid hydrolysis of DOC-polysaccharides only recovers between 10-15 percent of the total carbohydrate as monosaccharides. Treatment with acid degrades the remaining 85-90 percent of the DOC-polysaccharide to uncharacterizable material. The distribution of monosaccharides that are recovered does not agree with properties derived from elemental analyses and ¹³C nuclear magnetic resonance spectroscopy of the total polysaccharide fraction. To more fully understand the structural features that may make DOC polysaccharides so resistant to microbial degradation, we developed an approach to selectively degrade polysaccharides to oligosaccharides, which can be more fully characterized by spectral and molecular level analyses. From the distribution and sequence of sugars in DOC-oligosaccharides, we are working to reassemble the structure of DOC polysaccharides.