Source or Sink? A Modeling Study of Inorganic Carbon Cycling on the Scotian Shelf

Continental shelves account for a large proportion of global primary production, and potentially a disproportionate fraction of the carbon dioxide (CO₂) flux between atmosphere and ocean. The continental shelf pump hypothesis proposes that continental shelves at high latitudes act as net sinks of atmospheric CO₂. However, direct measurements on the Scotian Shelf, off eastern Canada, indicate that this shelf region acts as a net source of CO₂ to the atmosphere. The mechanisms underlying this deviation from the continental shelf pump mechanism are poorly understood. We employ a biogeochemical model of the northwestern North Atlantic continental shelf, and aim to improve our understanding of processes influencing air-sea CO₂ flux, and transport and transformation of inorganic carbon on the Scotian Shelf. Numerical models are useful tools for investigating the complex interactions of processes affecting carbon cycling. Models can help interpret sparse measurements through mechanistic representations of the relevant processes. Our model is initialized for total inorganic carbon and total alkalinity, and extensively compared against observations from the region, including data from the Atlantic Zone Monitoring Program (AZMP) cruises and global databases from Global Ocean Data Analysis Project (GLODAP) and Carbon Dioxide Information Analysis Center (CDIAC). Using the validated model, we perform a series of tests to explore the role of key processes contributing to the observed carbon fluxes on the Scotian Shelf.