Influence of terrestrial inputs on continental shelf carbon dioxide

The US South Atlantic Bight (SAB) is a lowlatitude shallow continental shelf bordered landward by abundant salt marshes and rivers. Based on previously published data on sea surface partial pressure of carbon dioxide (pCO2) and new dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) data, a model analysis is presented to identify and quantify the contributions of various terrestrial carbon inputs on SAB sea surface pCO2. After removal of pCO2 variations due to annual temperature variability and air–sea gas exchange from the in situ pCO2, the temperatureand gas-exchange-corrected pCO2 (TG-corrected pCO2) is derived. Contributions from rivers, salt marshes, and the continental shelf to the TGcorrected pCO2 are then calculated. Our findings demonstrate that although additions of CO2 from within shelf waters (i.e., 1pCO2(shelf)) were the greatest of the three components and underwent the largest seasonal changes, 1pCO2(shelf) showed smaller onshore–offshore gradients than rivers and marshes. In contrast, CO2 contributions from river (1pCO2(river)) and salt marsh (1pCO2(marsh)) components were greatest closest to the coast and decreased with distance offshore. In addition, the magnitude of 1pCO2(marsh) was about three-fold greater than 1pCO2(river). Our findings also revealed that decomposition of terrestrial organic carbon was an important factor regulating the seasonal pattern of pCO2 on the inner shelf. Despite large uncertainties, this study demonstrates the importance of terrestrial inputs, in particular those from coastal wetlands, on coastal ocean CO2 distributions.