Calculations to resolve the anthropogenic component of CO2 are remarkably difficult for the
coastal ocean, where the assumptions of the various methods (Sabine and Tanhua 2010) are not met, thereby precluding a direct calculation of the effect of anthropogenic CO2 on observed trends in
coastal pH. Calculations based on mixing between an open - ocean end - member displaying the trajectories predicted from OA and the freshwater end - member are also unreliable because pH and the carbon system do not necessarily
behave conservatively within the
coastal zone and because the freshwater end - member may also shift into the future.