Monthly profiles of DOC, mono- and polysaccharides at two locations in the Trondheimsfjord (Norway) during two years

Profiles of water samples were collected monthly during 2 years at two locations from the Trondheimsfjord on the Norwegian coast. Concentrations of dissolved organic carbon (DOC) were measured with high temperature catalytic oxidation, and carbohydrates were measured using the 2,4,6-tripyridyl-s-triazine (TPTZ) method. The concentration of DOC below 50 m depth was very similar at both stations and averaged 80 μM C. At the summer maximum, the concentration of DOC in the surface water was 2.3–2.7 times higher than the water below the photic zone at the Inner station, and two times higher at the Central station in the fjord. During autumn the DOC concentration decreased in the surface layer at both locations from mid August until the winter minimum was reached in February–March. Average values of total dissolved carbohydrates at different depths varied from 11–33 μM C, and total carbohydrate-C averaged 19–21% of the DOC in the surface samples, and 15–16% of the DOC in the deeper samples, which indicate that carbohydrates are a significant constituent of DOC in the Trondheimsfjord. Dissolved carbohydrates accumulated in the productive season at both stations and maximum concentrations appeared during spring and summer. The level of monosaccharides was fairly constant at approximately 5–6 μM C below the euphotic zone, whereas polysaccharides showed more varying concentrations at all depths. Carbohydrates and DOC correlated positively.