13C/12C composition of marine dissolved organic carbon

The stable isotopic composition of marine dissolved organic carbon (DOC) was measured with a high temperature, sealed tube combustion technique. The δ13C values of DOC (DO13C) were approximately −22‰ for all samples that were collected (1) in a monthly survey conducted in Woods Hole Harbor, (2) in a spatial survey across Georges Bank during a spring bloom period, and (3) in depth profiles near Bermuda, Georges Bank and in the eastern Equatorial Pacific. The DO13C values were uniform in waters of varying DOC content, including low DOC deep waters and high DOC surface waters, indicating little overall isotopic fractionation during formation and degradation of marine DOC. The −22‰ DO13C values are similar to those observed for average marine particulate and sedimentary organic material, and exclude a large contribution from −27‰ terrestrial DOC to ocean pools.