Dissolved organic carbon on Georges Bank

Dissolved organic carbon (DOG) in sea water from Georges Bank was measured by a high temperature combustion/direct injection (HTC/DI) technique during the spring bloom period in April 1993. Concentrations in surface waters (72-85 mu M) and deep waters (54-56 mu M) were similar to DOC concentrations measured in the oligotrophic north-west Atlantic Ocean by a number of other investigators by various techniques. Although surface values for Chl-alpha concentrations ranged from 2 to 5 mu g l(-1), NO3- ranged from 3 to 9 mu M and particulate organic carbon (POC) concentrations ranged from 1.0 to 10 mu M, DOC concentrations only varied by <18%. DOC was slightly higher (similar to 5 mu M) in the highly productive central bank region than in surrounding stratified surface waters. Relatively constant stable carbon isotopes ((DOC)-C-13 = -22.0 +/- 0.5 parts per thousand) could not be used to identify a source for these small variations. Slight decreases of DOC (5-12 mu M) and dissolved organic nitrogen (DON) (0.5-1.0 mu M) in filtered sea water kept in the dark was observed over six months, suggesting the presence of a small, labile pool of dissolved organic matter in addition to a large, more refractory reservoir of DOC (similar to 70 mu M) during the spring bloom period on Georges Bank.