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Abstract Productive shelf seas are often considered hotspots for absorbing atmospheric CO 2 . However, the contribution of biological processes to carbon source or sink remains unclear in global large river‐dominated shelf seas. As a case study, we applied a three end‐members mixing model to quantify the contribution of biological processes (including the release of CO 2 from organic matter degradation by microbes and CO 2 uptake by phytoplankton) to the variations of air‐sea CO 2 flux (F) in the Changjiang plume‐impacted shelf area (CPS). We also established a 1‐D mass budget model to quantitatively assess the factors controlling of the partial pressure of carbon dioxide ( p CO 2 ) during seasonal transitions. Our results showed that CPS acted as a source of atmospheric CO 2 in summer (2.0 ± 13.9 mmol m −2 d −1 ) and autumn (5.4 ± 8.6 mmol m −2 d −1 ), but as a sink in winter (−6.8 ± 9.4 mmol m −2 d −1 ) and spring (−1.0 ± 4.8 mmol m −2 d −1 ). Biological processes significantly influence p CO 2 variability. It is worth noting that during the winter‐to‐spring transition, biological processes contributed 36% (the largest among the four transition periods) to the p CO 2 decrease. In the CPS, the air‐sea CO 2 flux caused by biological processes in winter, spring, summer, and autumn are 2.6 ± 4.1, −15.1 ± 22.0, 2.2 ± 8.2, and −2.0 ± 4.9 mmol m −2 d −1 , respectively, with relative contributions of biological processes to F of 13.5%, −53.9%, 5.0%, and −11.0%, respectively. These findings suggest biological uptake of dissolved inorganic carbon in global continental shelf seas significantly enhance carbon sequestration and contribute to mitigating global warming.
Wang et al. (Sat,) studied this question.