Sr and Nd isotopic compositions and their significance of surface sediments in the Yangtze River Estuary and its adjacent seas

The Yangtze River Estuary is a vital hub linking the land and the ocean. Due to its complex topography, abundant terrestrial materials, and close association with human activities, it has attracted extensive attention from researchers. MethodsFocusing on the surface sediments in the Yangtze River Estuary and its adjacent seas, this study systematically analyzed the geochemical behavior of Sr and Nd isotopes as well as trace elements. ResultsThe results showed that the sediments in the Yangtze River Estuary and its adjacent seas were mainly composed of terrestrial materials, dominated by sediments from the Yangtze River Basin, with a portion originating from the ancient Yellow River delta. In the river-sea mixing zone, Nd was significantly enriched due to colloidal coagulation, while complex hydrodynamic conditions resulted in finer sediment particle sizes, and Sr exhibited noticeable depletion. Through analysis using the stable isotope mixing model in R (SIMMR), it was found that the contribution of sediments from the middle and lower reaches of the Yangtze River to the surface sediments in the sea-land interaction zone increased. Sediments from the upper reaches of the Yangtze River have been largely trapped by dam construction, which has turned the river channels in the middle and lower reaches from a sediment "sink" into a sediment supply "source", thereby increasing their contribution to the sediments in the estuary and its adjacent seas. Nevertheless, sediments from the upper reaches of the Yangtze River still dominated the composition of sediments in the estuary. Objective and ConclusionThe findings reveal the sedimentary environment and source-sink processes in the Yangtze River Estuary and its adjacent seas, providing crucial information for elucidating the surface material cycling process and exploring the evolution of the marine environment.