The uptake of anthropogenic CO2 drives ocean acidification, with attendant effects on the saturation state of calcium carbonate (Ω) and marine ecosystems. Here, we examine ocean acidification within the context of large-scale water mass exchange and local physical and biogeochemical processes along a section around northern North America. Waters in the North Pacific are preconditioned by the global-scale circulation to be low Ω source waters and as they move northward across the Bering and Chukchi seas they are modified by biological activity. These waters then enter the Canada Basin and Canadian Arctic Archipelago where cooling, river discharge, sea ice formation and biological activities modify water mass characteristics further. Continuing eastward into Baffin Bay, relatively low Ω waters extend from the surface to depth due to remineralization. Changes in Ω are large along this pathway and the response of local marine ecosystems will likewise be shaped by the biogeography of species occupying a given region.