Sea-trials of three different methods for measuring non-volatile dissolved organic carbon in seawater during the JGOFS North Atlantic pilot study

In 1989 the shipboard comparison of three different methods for measuring concentrations of dissolved organic carbon (DOC) resulted in reasonable agreement, with differences likely as a result of a combination of calibration offsets and general instability of the instruments at sea. Typical concentrations were about 80-140 µmol in the upper 1000 m of the water column, with a tendency towards higher values (100-150 µmol) in the surface waters. These elevated surface water levels are below the 200-300 µmol values recently reported for the Atlantic and the Pacific Oceans. In 1990 the small dataset obtained with a further modified High Temperature Combustion instrument showed similar trends. Within the analytical error there is no significant offset between two HTCO methods and one wet oxidation technique