Marginal seas provide a globally important interface between land and interior ocean where organic carbon is metabolized, buried or exported. The trophic status of these seas varies seasonally, depending on river flow, primary production, the proportion of dissolved to particulate organic carbon and other factors. In the Strait of Georgia, about 80% of the organic carbon in the water column is dissolved. Organic carbon enters at the surface, with river discharge and primary production, particularly during spring and summer. The amount of organic carbon passing through the Strait (approximately 16x10(8) kg C yr(-1)) is almost twice the standing inventory (approximately 9.4x10(8) kg C). The organic carbon that is oxidized within the Strait (approximately 5.6x10(8) kg yr(-1)) presumably supports microbial food webs or participates in chemical or photochemical reactions, while that which is exported (7.2x10(8) kg yr(-1)) represents a local source of organic carbon to the open ocean.