Dynamics of DOC in the Norwegian Sea inferred from monthly profiles collected during 3 years at 66°N, 2°E

Water samples were collected monthly for 3 years at 66°N, 2°E in the Norwegian Sea, 250 nautical miles off the Norwegian coast. Concentrations of dissolved organic matter were measured with high temperature catalytic oxidation. DOC varied from 53 μmol C 1−1 to 149 μmol C 1−1 among all the samples collected. Blank readings from MilliQ water were less than 9.3 μmol C 1−1; these values were not subtracted. In the 0–50 m layer DOC concentration was on average 1.2 times greater than in deep water. In the upper 50 m, annual variation was pronounced, with an increase in DOC concentration in spring and summer of variable timing and magnitude, and a less variable decrease in DOC concentration starting in August-September. The rates of increase were in the range 0.16–0.26 μmol C 1−1 d−1. During 1992 we measured a pulse of DOC at depths between 400 and 800 m. The concentration increased consistently at a rate of 0.14–0.16 gmol 1−1 day−1 during 1 year. This change presumably was caused by advection, because these waters are well below the photic zone. Within our resolution limit, changes in the deep water from 1000 to 2000 m were hardly detectable and not related to annual cycles.