Coastal margins could be hotspots for acidification due to terrestrial-influenced CO₂ sources. Currently there are no long-term (>20 years) records from biologically important coastal environments that could demonstrate sea surface CO₂ fugacity (fCO₂) and pH trends. Here, multidecadal fCO₂ trends are calculated from underway and moored time series observations along the United States southeast coastal margin, also referred to as the South Atlantic Bight (SAB). fCO₂ trends across the SAB, derived from ∼26 years of cruises and ∼9.5 years from a moored time series, range from 3.0 to 4.5 µatm yr⁻¹, and are greater than the open ocean increases. The pH decline related to the fCO₂ increases could be as much as −0.004 yr⁻¹; a rate greater than that expected from atmospheric-influenced pH alone. We provide evidence that fCO₂ increases and pH decreases on an ocean margin can be faster than those predicted for the open ocean from atmospheric influence alone. We conclude that a substantial fCO₂ increase across the marginal SAB is due to both increasing temperature on the middle and outer shelves, but to lateral land-ocean interactions in the coastal zone and on inner shelf.