Spatio-temporal variability of the CO₂ system on the Scotian Shelf

Abstract. Relative to their surface areas, coastal oceans and continental shelves host a disproportionately large fraction of ocean productivity. The Scotian Shelf is a biologically productive coastal region of the Northwestern Atlantic Ocean. This subpolar region is influenced by the outflow of the St. Lawrence Estuary system and acts as an annual source for atmospheric CO₂. As part of the Atlantic Zone Monitoring Program, dissolved inorganic carbon (DIC), total alkalinity, and surface CO₂ partial pressure measurements were made throughout the Scotian Shelf in 2007. A shelf-wide assessment of the spatio-temporal variability of the inorganic carbon system was made relying on observations in April and September. Between these periods, biological production results in a significant drawdown of inorganic nutrients and DIC in the surface mixed-layer, while hydrographic controls also influence seasonal changes in DIC. Net community production (NCP) over the spring and summer seasons was estimated on the basis of inorganic carbon data. We find significant spatial variability in NCP with the largest values in the Southwestern Browns Bank region and a general trend of increasing NCP with distance offshore. A bulk seasonal carbon budget suggests that along-shore and cross-shelf transport may result in the export of subsurface DIC from this region.