Influence of terrestrial inputs on continental shelf carbon dioxide
The US South Atlantic Bight (SAB) is a low-latitude shallow continental shelf bordered landward by abundant salt marshes and rivers. Based on previously published data on sea surface partial pressure of carbon dioxide ( pCO 2) 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 pCO 2. After removal of pCO 2 variations due to annual temperature variability and air–sea gas exchange from the in situ pCO 2, the temperature- and gas-exchange-corrected pCO 2 (TG-corrected pCO 2) is derived. Contributions from rivers, salt marshes, and the continental shelf to the TG-corrected pCO 2 are then calculated. Our findings demonstrate that although additions of CO 2 from within shelf waters (i.e., Δ pCO 2(shelf)) were the greatest of the three components and underwent the largest seasonal changes, Δ pCO 2(shelf) showed smaller onshore–offshore gradients than rivers and marshes. In contrast, CO 2 contributions from river (Δ pCO 2(river)) and salt marsh (Δ pCO 2(marsh)) components were greatest closest to the coast and decreased with distance offshore. In addition, the magnitude of Δ pCO 2(marsh) was about three-fold greater than Δ pCO 2(river). Our findings also revealed that decomposition of terrestrial organic carbon was an important factor regulating the seasonal pattern of pCO 2 on the inner shelf. Despite large uncertainties, this study demonstrates the importance of terrestrial inputs, in particular those from coastal wetlands, on coastal ocean CO 2 distributions.