Production of biologically refractory dissolved organic carbon by natural seawater microbial populations
Carbon from glucose and leucine added at natural concentrations to seawater was biologically transformed to higher molecular weight (mol. wt) dissolved materials that persisted through 6 months of incubation. At the end of incubation, the amount of carbon in high mol. wt dissolved fractions was approximately equal to the amount of carbon incorporated into particulate fractions. In tests of their resistance to biological utilization, only 1-17% of the high mol. wt materials were respired when re-incubated with seawater microbial populations, whereas 40-75% of the monomers were respired over the same time span. In situ transformations of biologically available carbon may be an important source of refractory dissolved organic carbon in the oceans.