Dissolved organic carbon on Georges Bank

Dissolved organic carbon (DOC) 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 μM) and deep waters (54–56 μM) 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-a concentrations ranged from 2 to 5 μg l−1, NO3− ranged from 3 to 9 μM and particulate organic carbon (POC) concentrations ranged from 1.0 to 10μM, DOC concentrations only varied by <18‰ DOC was slightly higher (∼5 μM) in the highly productive central bank region than in surrounding stratified surface waters. Relatively constant stable carbon isotopes (DO13C = −22.0 ± 0.5 could not be used to identify a source for these small variations. Slight decreases of DOC (5–12μM) and dissolved organic nitrogen (DON) (0.5–1.0 μM) 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 (∼70 μM) during the spring bloom period on Georges Bank.