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 (<i>p</i>CO<sub>2</sub>) 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 <i>p</i>CO<sub>2</sub>. After removal of <i>p</i>CO<sub>2</sub> variations due to annual temperature variability and air–sea gas exchange from the in situ <i>p</i>CO<sub>2</sub>, the temperature- and gas-exchange-corrected <i>p</i>CO<sub>2</sub> (TG-corrected <i>p</i>CO<sub>2</sub>) is derived. Contributions from rivers, salt marshes, and the continental shelf to the TG-corrected <i>p</i>CO<sub>2</sub> are then calculated. Our findings demonstrate that although additions of CO<sub>2</sub> from within shelf waters (i.e., Δ<i>p</i>CO<sub>2</sub>(shelf)) were the greatest of the three components and underwent the largest seasonal changes, Δ<i>p</i>CO<sub>2</sub>(shelf) showed smaller onshore–offshore gradients than rivers and marshes. In contrast, CO<sub>2</sub> contributions from river (Δ<i>p</i>CO<sub>2</sub>(river)) and salt marsh (Δ<i>p</i>CO<sub>2</sub>(marsh)) components were greatest closest to the coast and decreased with distance offshore. In addition, the magnitude of Δ<i>p</i>CO<sub>2</sub>(marsh) was about three-fold greater than Δ<i>p</i>CO<sub>2</sub>(river). Our findings also revealed that decomposition of terrestrial organic carbon was an important factor regulating the seasonal pattern of <i>p</i>CO<sub>2</sub> 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<sub>2</sub> distributions.

Abstract licence: CC BY

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