Stable Barium Isotope Dynamics During Estuarine Mixing
Zhimian Cao, Xinting Rao, Yang Yu, Christopher Siebert, Ed C. Hathorne, Bo Liu, Guizhi Wang, Ergang Lian, Zhibing Wang, Ruifeng Zhang, Lei Gao, Gangjian Wei, Shouye Yang, Minhan Dai, Martin Frank
Abstract
Abstract Stable barium isotopes are a potential proxy for riverine inputs into the ocean that reflect monsoon variability and climate change. However, dissolved Ba isotope (δ 138 Ba DBa ) geochemistry in river estuaries, a dynamic land to ocean transition zone, has rarely been systematically examined to date. Here, we show that significant Ba isotope fractionation occurs at near‐zero salinities in the Yangtze and Pearl River Estuary, whereas conservative mixing dominates δ 138 Ba DBa distributions beyond low salinities, which are well predicted by an ion exchange model. Elevated δ 138 Ba DBa in the river endmember results from preferential removal of light Ba isotopes by adsorption to fluvial particles. Subsequently, δ 138 Ba DBa rapidly drops to minimum signatures at increased salinities indicating particle desorption of isotopically light Ba. Nevertheless, the apparently conservative δ 138 Ba DBa ‐salinity relationship beyond the low‐salinity minimum in both estuaries provides a modern calibration for using Ba isotopes as a proxy for paleosalinity and river water inputs into the ocean.