Source or Sink? A modeling study of inorganic carbon cycling on the Scotian Shelf

Abstract

The Scotian Shelf, located in the highly dynamic northwestern North Atlantic along the eastern Canadian seaboard, has been the focus of much debate as previous studies have yielded conflicting estimates of air-sea CO2 flux on this mid-latitude shelf. To resolve these inconsistent estimates of air-sea CO2 flux, a quantitative understanding of the underlying carbon transport mechanisms is needed. The Continental Shelf Pump (CSP), which is thought to apply to mid- to high-latitude shelves, posits that the effective transport of carbon from these shelves to the subsurface open ocean creates a sustained sink of CO2. In contrast, the Scotian Shelf behaves as a sustained source of CO2 to the atmosphere, and knowledge about the regional transport mechanisms that could be driving this net outgassing of CO2 has been lacking. My thesis contributes to a better understanding of the observed CO2 flux on the Scotian Shelf, and how it may change in the future. First, I introduce an analysis of dye and age tracers to quantify transport timescales and pathways in a numerical model of the northwestern North Atlantic. Secondly, I present a validation of the inorganic carbon component of the model, and evaluate spatial and temporal variability of the simulated air-sea CO2 flux. Then I use the dye tracers in the carbon model to determine what transport mechanism is underlying the observed air-sea CO2 flux. Lastly, I show future model projections to illustrate how a changing climate may affect carbon transport, air-sea flux, and pH on the northwestern North Atlantic shelf.