In the past decades, China has experienced substantial economic growth and industrialization. However, the effects of vast development of China on Hg input to the nearby oceans are still unclear. In this study, the influx and isotopic compositions of Hg in four Pb-210-dated sediment cores were examined to investigate changes in Hg deposition to the marginal seas off China over a century. Nearshore cores had higher Hg influxes than offshore cores. Increases of Hg influxes started since the 1950s, which coincides with China's economic development. Dramatic historical changes in Hg isotopic composition were observed in the cores (Hg-202: -2.01 to -0.69; Hg-199: -0.16 to 0.31; n=106). Hg-202 increased from the deep to the surface layers of the cores. The offshore cores mainly showed positive Hg-199 values, but the pre-1950 samples had more positive Hg-199 values than the younger samples. The nearshore cores mainly showed negative Hg-199 values in the pre-1950s samples, but the younger samples showed Hg-199 values close to zero. A triple-mixing isotope model, used to quantify the contribution of potential Hg inputs (e.g., direct discharge of industrial Hg, soil Hg, and precipitation-derived Hg), showed clear evidence of enhanced industrial Hg inputs to the ocean margin, but slightly decreased watershed soil Hg inputs in the last few decades. The variations of watershed-derived Hg were likely caused by the construction of impoundments in major rivers of China. This study demonstrates that mercury inputs to Chinese marginal seas have been largely altered due to the industrialization and economic development of China. 

Plain Language Summary This study demonstrates that mercury inputs to Chinese marginal seas have been largely altered due to industrialization and economic development of China with enhanced industrial Hg inputs to the ocean margin, but slightly decreased watershed soil Hg inputs in the last few decades.