A MAJOR BIOPOLYMERIC COMPONENT TO DISSOLVED ORGANIC-CARBON IN SURFACESEA-WATER

Organic carbon dissolved in sea water is an important component of the global carbon cycle(1). Concentrations of dissolved organic carbon (D OC) in the ocean's surface mixed layer are at least twice those in the deep sea(2,3), because of the production of soluble carbon compounds by marine algae in the euphotic zone(4,5). But very little is known ab out the chemical composition of DOC, and the connection between photos ynthetic production and DOC accumulation is not well understood(6,7). Here we report the chemical characterization of macromolecular DOC at several sites in the Atlantic and Pacific oceans. Neutral sugars, acet ate and lipids show similar distributions, suggesting that these const ituents are linked together in a common macromolecular structure. Chem ical linkage patterns between the oligosaccharide portions of dissolve d organic matter subjected to ultrafiltration are highly specific, wit h little variation between ocean basins. We show that laboratory cultu re experiments on the decomposition of algal exudate produce macromole cular organic matter with similar compositions and linkage characteris tics. We propose that a significant fraction of DOC in sea surface wat er consists of structurally related and biosynthetically derived acyl oligosaccharides that persist after more labile organic matter has bee n degraded.