As part of the Atlantic Zone Monitoring Program, dissolved inorganic carbon (DIC), total alkalinity, and nitrate 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 spring (April) and autumn (October). Over the 6-month period, a combination of biological production, surface dilution, and air–sea CO2 exchange resulted in seasonal decreases in surface DIC of up to 70 μmol kg−1 and subsurface (between 50 and 100 m) increases of DIC on the order of 50 μmol kg−1 on the inner shelf. The regional mean surface water pH was roughly 7.8 in spring and increased to greater than 8.0 in autumn; subsurface pH was approximately 7.6 throughout the region and a seasonal decrease, attributed in part to the respiration of organic matter at depth, was observed. The surface aragonite saturation state increased from less than 2.0 to a maximum of 3.2 between spring and autumn; the region as a whole exhibited relatively low saturation states, however values approaching 1.0 were only observed in the Cabot Strait at depths below 100 m. Winter-to-spring and winter-to-autumn deficits in surface inorganic carbon and nitrate were used to estimate net community production (NCP) throughout the region. The nitrate-based estimates of NCP using the autumn observations were significantly lower (0.1 to 0.3 mol C m−2 month−1) than the carbon-based estimates (0.1 to 0.8 mol C m−2 month−1) at most stations. The cumulative autumn NCP based on nitrate (0.4 to 1.9 mol C m−2 over 6 months) was up to 50% lower than the cumulative NCP based on inorganic carbon deficits (0.5 to 4.7 mol C m−2 over 6 months), suggesting that continued biological production through the summer season occurs in nitrate-depleted waters.
net community production, carbon uptake, nitrate drawdown, ocean acidification