Terrestrial input changes and their controlling factors as revealed by the elemental geochemical evidence in the East China Sea muddy area during the last century

Abstract

Terrestrial input changes in large river-dominated marginal seas are influenced by anthropogenic and climate forces with spatiotemporal heterogeneity that has not been well clarified. In this work, based on elemental geochemical evidence of a centennial-scale sediment core from the muddy belt in the East China Sea (ECS), together with previously published organic geochemical data of the same core and selected environmental parameters, we reveal a synchronous decline in terrestrial input with enhanced anthropogenic activities after ca. 2000. The rapid decrease in 2000–2004 may be attributed to the construction of dams such as the Three Gorges Dam (TGD). During the pre-TGD period, the terrestrial input maintained stable high values (except for a distinct peak in 1965), which coincided with enhanced chemical weathering, stable annual temperature, increased precipitation, and strong East Asian winter monsoon (EAWM) driven by climatic factors. After ca. 2000, anthropogenic activities gradually became the dominant controlling factor on terrestrial input variations. In addition, significant coastal erosion recorded by Al/Si ratios during 2000–2004 and intensified nearshore eutrophication captured by δ15N values from 1950 to 1985 are linked to the construction of the TGD and increased fertilizer usage, respectively. Overall, our findings provide vital insights into modern processes using inorganic and organic geochemical proxies in marginal seas. Notably, terrestrial input and related geochemical parameters in representative cores from north to south in this region show considerable spatiotemporal variations, requiring further investigation into their underlying causes.