Modeling the contribution of the microbial carbon pump to carbon sequestration in the South China Sea
The two key mechanisms for biologically driven carbon sequestration in oceans are the biological pump (BP) and the microbial carbon pump (MCP); the latter is scarcely simulated and quantified in the China seas. In this study, we developed a coupled physical-ecosystem model with major MCP processes in the South China Sea (SCS). The model estimated a SCS-averaged MCP rate of 1.55 mg C m−2 d−1, with an MCP-to-BP ratio of 1:6.08 when considering the BP at a depth of 1000 m. Moreover, the ecosystem responses were projected in two representative global warming scenarios where the sea surface temperature increased by 2 and 4°C. The projection suggested a declined productivity associated with the increased near-surface stratification and decreased nutrient supply, which leads to a reduction in diatom biomass and consequently the suppression of the BP. However, the relative ratio of picophytoplankton increased, inducing a higher microbial activity and a nonlinear response of MCP to the increase in temperature. On average, the ratio of MCP-to-BP at a 1000-m depth increased to 1:5.95 with surface warming of 4°C, indicating the higher impact of MCP in future ocean carbon sequestration.
KeywordsSouth China Sea Microbial Carbon Pump Global change Numerical model
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The authors thank Dr. T Trull from University of Tasmania, Dr. E Laws from Louisiana State University, and two anonymous reviewers for their constructive input that helped to improve this paper. This work was supported by the National Basic Research Program (Grant No. 2013CB955704), the National Program on Global Change and Air-Sea Interaction (Grant No. GASI-03-01-02-05). This study was also partially supported by the SOA Global Change and Air-Sea Interaction Project (Grant No. GASI-IPOVAI-01–04), the National Natural Science Foundation of China (Grant Nos. 41630963, 41476007 & 41476005).
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