How the nature of dissolved organic matter might affect the analysis of dissolved organic carbon

Abstract

A discrepancy exists between the low concentrations of dissolved organic carbon (DOC) in seawater measured by ‘standard’ techniques, such as wet-chemical oxidation, UV photo-oxidation, and dry high-temperature combustion, and the relatively high concentrations measured using new catalyzed, high-temperature combustion methods. One of the factors that could help explain this discrepancy is the nature of the DOC being analyzed. Because little is known about the structure of the bulk of DOC, here we will discuss DOC sources, how sources could affect structure, and how structure as well as chemical factors and sampling procedures might affect analysis of DOC. One likely reason for the discrepancy between the standard and new methods is the presence of a fraction of DOC not previously measured by the standard techniques. This ‘new’ DOC could consist of refractory, large, highly cross-linked macromolecular organic material, possibly colloidal in nature. Material that incorporates sulfur or specific organic structures which inhibit wet-chemical oxidation or photo-oxidation could also be present. Other possible materials present that might explain the discrepancy are those that are prone to incomplete oxidation because they form unreactive compounds during standard oxidation procedures.