Stable Barium Isotope Fractionation in Pore Waters of Estuarine Sediments

Abstract

Estuaries form the transition from freshwater to coastal marine environments and act as efficient reactors for many riverine trace elements before they reach the open ocean. While the formation of authigenic mineral phases in anoxic estuarine sediments enhances the removal of some trace elements, early diagenetic reactions can also release trace elements back into the water column via reductive processes (e.g., of manganese (Mn) and iron (Fe) oxides) or dissolution of barium (Ba) bearing solid phases (cf.,

Diagenesis Decreasing the Mo Isotopic Composition in Estuarine Systems: Implications for Constraining Its Riverine Input to Ocean

“…Cao et al. (2023) observed that most Mn/Al and Fe/Al ratios in PRE sediment cores fall below the global crustal averages reported by Rudnick and Gao (2014) and Taylor and McLennan (1985), with the exception of Fe/Al ratios at stations P06 and A09. These ratios exhibit a distinct decrease from the lower to the upper sediment layers, especially at upstream stations P03, P06, and A03.…”

“…Cao et al. (2023) noted elevated Mn and Fe levels in pore water, indicative of a suboxic zone in the upper 8–10 cm, characterized by the reduction of nitrate, manganese, and iron. Similarly, Hong et al.…”

“…Previous studies have documented hypoxic or suboxic conditions throughout the basin (Dai et al., 2006; B. He et al., 2010, 2014; X. Li et al., 2018; Su et al., 2017; Y. Zhao et al., 2020), facilitating geochemical exchange reactions between sediment and water (Cao et al., 2023; Hong et al., 2018). The hypoxia generally arises from a combination of eutrophication‐induced high biological productivity and restricted water exchange (Dai et al., 2006; B.…”

“…The pore water chemistry in PRE sediments offers more direct evidence. Cao et al (2023) noted elevated Mn and Fe levels in pore water, indicative of a suboxic zone in the upper 8-10 cm, characterized by the reduction of nitrate, manganese, and iron. Similarly, Hong et al ( 2018) also reported higher pore water concentrations of Mn and Fe compared to the overlying bottom water, suggesting a release of these elements from the pore to the bottom water.…”