We compare total dissolved inorganic carbon (DIC) and chlorofluorocarbon (CFC) measurements in the northwest Atlantic made during the Transient Tracers in the Ocean, North Atlantic Study (TTO-NAS) in 1981 with modern measurements from a cruise in 2004. The observed changes in the DIC and CFC fields are compared to those predicted from an eddy-permitting ocean circulation model. The rapid, but time-variable, atmospheric CFC increase in relation to the relatively steady anthropogenic CO2 increase influences the relationship between the observed uptake of DIC and CFC. We demonstrate the importance of ocean mixing in the calculation of anthropogenic CO2 (Cant) based on transient tracer data by comparing our observations to a "no-mixing" scenario. We further find that the Cant is in transient steady state in the North Atlantic; that is, the Cant concentration increases proportionally over time through the whole water column in a manner that is directly related to the time-dependent surface concentration.