Impact of external nitrogen and phosphorus input between 2006 and 2010 on carbon cycle in China seas

Abstract

It is widely accepted that excess nutrients change the dissolved inorganic carbon (DIC) system, which drives air–sea carbon dioxide (CO2) exchanges, so the changes in the DIC system will then affect the oceans’ carbon (C) biogeochemistry cycle. This study explores the impact of external nutrient input from 2006 to 2011 on the DIC system and air–sea CO2 exchanges in four largest coastal seas in China. The result demonstrates that external nutrient input significantly facilitates the biological uptake of DIC and promotes air–sea CO2 fluxes in coastal waters. The C sink caused by nitrogen (N) and phosphorus (P) input for the Bohai Sea, the Yellow Sea, the East China Sea, and the South China Sea account for 46, 45, 11, and 59 % of the total C sink, respectively. The excess nutrient input significantly changes the DIC system and C biogeochemistry cycle process in China Ocean. Up to a certain point, these effects are positive in increasing DIC levels and enhancing air–sea CO2 exchanges. However, the DIC levels may decrease if the nutrient increase is greater than the capacity of the oceanic C system. In addition, the other impact factors, including sea level, winds, water, and air temperatures, and various human activities, such as agriculture, industry, and domestic discharge, also affect N and P transport, air–sea CO2 fluxes, and C biogeochemistry cycles.