Sedimentary record off the Yangtze River estuary and its response to typhoons and human activities over the past 70 years

Abstract

The muddy area off the Yangtze River estuary serves as an archive that can be investigated to unravel the impacts of environmental changes and human activities. However, in the context of increasing human activity and global climate change, it is unclear how the sedimentary records in this area respond to these changes. Radionuclide activity, magnetic susceptibility, grain size, clay minerals and chemical elements of samples in a sediment core (T1) collected off the Yangtze River estuary were analyzed in this study to identify the sediment provenance and elucidate the impacts of typhoon events and human activities on the sedimentary records over the past 70 years. Based on the analyses of clay minerals, Cr/Th vs. Sc/Al, element ratios, and correlations between grain size and magnetic susceptibility, sediments at 44–90 cm were mainly derived from the Yangtze River, while sediments at 0–44 cm were influenced by the Yangtze River, old Yellow River, and relict sand. Since AD 1950, the mineralogical–geochemical compositions of sediments in core T1 have significantly altered, which was attributed to typhoon events and human activities. Before 2003, typhoon activity influenced the frequency of sand layer deposition, which was related to El Niño-Southern Oscillation (ENSO) variations. However, following the operation of the Three Gorges Dam in 2003, the relationship between typhoon event records and ENSO was disrupted. Human activities have affected the sedimentary records of typhoon events off the Yangtze River estuary. This study emphasizes that sediments at the edge of the muddy area off the Yangtze River estuary can serve as good records of typhoon events, but the influence of human activities should be considered when studying the relationship between typhoon activity and climate change, especially during the past several decades.