Source or Sink? A numerical modeling study of inorganic carbon fluxes on the Scotian Shelf
Presenter: Krysten Rutherford, Dalhousie University
Abstract: Continental shelves are thought to be disproportionately affected by climate change and are a large contributor to global air-sea CO2 fluxes. Additionally, it is often reported that low latitude shelves act as net sources of CO2 to the atmosphere whereas mid- and high-latitude shelves act as net sinks of CO2. Here, we focus on the Scotian Shelf, a mid-latitude shelf in the northwest North Atlantic. Whether the Scotian Shelf acts as a source or sink of CO2 is controversial in the literature. Here a high-resolution regional model is employed to explore shelf-wide pCO2 variability and better understand what processes are underlying the regional air-sea CO2 fluxes. Seasonally, surface pCO2 on the Scotian Shelf is strongly tied to the large drawdown in Dissolved Inorganic Carbon (DIC) during the spring bloom, and temperature effects associated with warming from 0oC in winter to nearly 20oC in summer. Spatially, pCO2 on the Scotian Shelf is relatively uniform, except for coastal upwelling events during the summer which lower nearshore pCO2 in the surface water. The model agrees with regional observations and reproduces seasonal patterns of pCO2. On the Scotian Shelf, the model simulates net annual outgassing of CO2 from the ocean, which is in contrast to the global pattern. Passive dye tracers are used to qualitatively diagnose the dominant transport pathways in the model and their effect on CO2 dynamics. This analysis suggests that the Scotian Shelf is highly influenced by cold, DIC-rich Arctic-originating water that is warmed as it travels, thus becoming oversaturated with CO2 and feeding outgassing from the ocean.