Reevaluating the Global Oceanic Copper Isotope Budget: The Critical Role of Deep‐Sea Pelagic Sediments

Abstract Understanding the oceanic Copper (Cu) budget is essential for tracing nutrient pathways, interpreting ancient sediment records, and assessing global environmental changes. However, the global oceanic Cu cycle remains imbalanced, largely due to insufficient studies on the flux and isotopic composition of authigenic Cu in oxic pelagic sediments. Here, we present the Cu isotopic compositions of pelagic sediments collected from the western (non‐hydrothermal area) and eastern South (hydrothermal area) Pacific Ocean. These results indicate that authigenic Cu in pelagic sediments is primarily hosted by iron‐manganese (oxyhydr)oxides. The isotopic composition of authigenic Cu in pelagic sediments (0.01‰ ± 0.13‰, 2SD) is considerably lighter than the previously assumed value of ∼0.3‰, which was based on the Cu isotopic compositions of iron‐manganese crusts and nodules. Using these new isotopic constraints, together with a newly calculated Cu flux to pelagic sediments of 15.2 × 10 8 mol yr −1 , we propose a new, balanced oceanic budget for Cu isotopes. This study precisely defines the flux and isotopic composition of the largest oceanic Cu sink, placing new constraints on the marine Cu cycle.