Dynamics of dissolved organic carbon (DOC) in oceanic environments
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Crossflow ultrafiltration techniques and a hightemperature combustion (HTC) method were used to investigate the distributions and fluxes of dissolved (DOC) and colloidal organic carbon (COC) in the Gulf of Mexico and in the Middle Atlantic Bight. Concentrations of DOC in both regions decreased from 80 uM in surface waters to 45 M in deep waters and showed large vertical gradients in the subsurface layer. The vertical distributions of DOC were oceanographically consistent. A conservative mixing behavior of DOC was observed in slope waters, and water mixing processes were important factors in controlling the distribution of DOC in the ocean. Calculated downward fluxes of DOC are comparable to those measured for particulate organic C. Size fractionation results revealed that COC (1 kDa0.2 m) comprised 4050% of the total DOC in seawater off Cape Hatteras, while it comprised 3040% in the Gulf of Mexico. Highmolecularweight COC10 (10 kDa0.2 m) represented 410% of the total DOC in both study areas. Concentrations of COC1, COC3, and COC10 and their percentages in the total DOC decreased from nearshore to offshore and from surface to deep waters. The COC fractions seem to partition in a predictable way in seawater, with DOC concentration as a master variable. On average, 47% of the total DOC was in the COC10 fraction, 714% was in the 310kDa fraction, and ~24% was in the 13kDa fraction, leaving 55 65% in the <1kDa fraction.
