Multidecadal <i>f</i>CO₂ Increase Along the United States Southeast Coastal Margin

Abstract

Abstract Coastal margins could be hotspots for acidification due to terrestrial‐influenced CO 2 sources. Currently there are no long‐term (&gt;20 years) records from biologically important coastal environments that could demonstrate sea surface CO 2 fugacity ( f CO 2 ) and pH trends. Here, multidecadal f CO 2 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). f CO 2 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 f CO 2 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 f CO 2 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 f CO 2 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.