Copper and zinc isotopes reveal redox-driven nutrient cycles in the Mesoproterozoic ocean

During the Mesoproterozoic, ocean redox conditions varied significantly across different regions, creating a complex and heterogeneous redox pattern. However, the drivers of this variability and its effects on nutrient cycling remain debated. To better understand these processes, we studies samples from the Hongshuizhuang Formation in North China using Cu and Zn isotopes, TOC, TS, and major and trace elements. The results show that dynamic redox environments are associated with variations in Cu and Zn isotopes, redox-sensitive element concentrations and nutrient-related ratios such as TOC, Ba/Al, C/P and P/Al. These findings suggest that high organic matter export enhanced sulfate reduction, which led to a dynamic euxinic environment. In turn, these redox changes may influence nutrient cycling in the paleo-ocean. Such feedbacks between redox state and nutrient cycling may help explain the heterogeneous ocean patterns observed in the Mesoproterozoic ocean.