Elucidating Coastal Ocean Carbon Transport Processes: A Novel Approach Applied to the Northwest North Atlantic Shelf

Abstract

A latitudinal pattern in coastal air-sea CO2 flux has emerged where mid-and high-latitude shelves act as net sinks and low-latitude shelves as net sources to the atmosphere. Regional studies, however, report the mid-latitude Scotian Shelf (SS) at the eastern Canadian seaboard acts as a large source of CO2, contradicting several global syntheses. Here, we combine observations and a regional biogeochemical model to explain, for the first time, how this net outgassing of CO2 is sustained. We employ a novel approach using passive dye tracers to estimate how carbonate properties change along dominant transport pathways. We show that cold, carbon-rich subpolar North Atlantic water is a dominant endmember that warms and combines with low alkalinity (TA), carbon-deplete freshwater from the Gulf of St. Lawrence, becoming oversaturated with CO2 on the SS. Our approach explicitly considers the 3-dimensional nature of coastal ocean transport processes and should be applied to other shelf regions.