Balancing the oceanic Zn isotope budget: The key role of deep-sea pelagic sediments

Oxygenated deep-sea pelagic sediments with Fe-Mn−oxide particles represent a key oceanic oxic sink for transition metals in the modern ocean. However, the isotopic composition of authigenic Zn in the pelagic zone remains poorly constrained, which hampers our understanding of the global budget of Zn isotopes. Here, we analyzed the Zn isotopic compositions of two deep-sea pelagic sediment columns collected from the Pacific Ocean. The results show that authigenic Zn in deep-sea sediments is primarily hosted by the Fe-Mn (oxyhydr)oxides. The light Zn isotopic signatures (δ⁶⁶Zn: −0.02‰ to 0.34‰, n = 42; computed as the per mille deviation of the ⁶⁶Zn/⁶⁴Zn ratio from the JMC-Lyon standard) observed in deep-sea sediments are completely different from the previously assumed values of ∼1.0‰ based on the Zn isotopic compositions of Fe-Mn crusts and nodules. Based on this observation (Zn flux of deep-sea sediments = 5.3 × 10⁸ mol yr⁻¹), we propose a new, balanced global budget for Zn isotopes.