A sediment and organic carbon budget for the greater Strait of Georgia

Recent efforts to construct global ocean budgets for carbon have recognized the importance of continental margins. In this study, we constructed budgets for the Strait of Georgia, a temperate, North American west coast basin that receives the inflow of one of the world’s major rivers. Drawing from published and unpublished data, we have estimated the magnitude of the various sources and sinks of fresh water, sediment and organic carbon. The Fraser River is the dominant source of fresh water and particles to the strait, contributing approximately 73% of the 158 109m3 year 1 of water and 64% of the 30 109 kg year 1 of particles. Other rivers supply most of the remainder, while rain, groundwater and anthropogenic sources of water and particles are negligible in comparison. Fresh water escapes the Strait of Georgia through Juan de Fuca Strait, but particulate inputs are approximately balanced by sedimentation within the greater Strait of Georgia, implying almost complete trapping of particles. Dissolved and particulate organic carbon are derived mainly from in situ primary production (855 106 kg year 1) and from the Fraser River (550 106 kg year 1). Other rivers contribute 200 106 kg year 1 of organic carbon, and anthropogenic sources (ocean dumping, sewage, pulp mills and aquaculture) a further 119 106 kg year 1. Particulate organic carbon is predominantly buried (428 106 kg year 1) or oxidized (90 106 kg year 1) in the sediments of the strait. About 70% of the organic carbon that enters or is produced in the strait is dissolved. Most of the dissolved organic carbon is oxidized within the strait (784 106 kg year 1), but the remainder (400 106 kg year 1) is exported to the Pacific Ocean. Although the particulate organic carbon budget by itself implies net autotrophy, dissolved organic carbon oxidation may make the Strait of Georgia slightly net heterotrophic.