Oxygen minimum-zone expansion controls critical metal enrichment and growth rates in a ferromanganese crust from the central Pacific Ocean

Hydrogenetic ferromanganese crusts (FMCs) rich in critical metals [e.g., cobalt (Co), nickel (Ni), and rare-earth elements plus yttrium (REY)] are known as promising mineral resources for the transition to a net-zero carbon emission future. The oxygen minimum zone (OMZ) has an important influence on the formation of FMCs, but its controlling mechanism for the enrichment of critical metals in FMCs is poorly constrained, hindering a fuller understanding of and exploration for critical metal-rich FMCs. The studied FMC (~2000 m depth) collected just below the oxygen minimum zone (OMZ; ~300-1000 m depth) in the central Pacific Ocean records the OMZ expansion during FMC formation; key evidence of this is changes in the size of the positive Ce anomaly and positive shifts in δ15N values. Our data indicate that OMZ expansion reduces FMC growth rates over time, with texture transitions from dendritic to botryoidal. The OMZ expansion contributes to an increase in Mn oxides with Co and Ni enrichment and a decrease the Fe oxyhydroxides and REY content. Our findings underscore the pivotal role of global OMZ expansion in influencing the growth dynamics of FMCs and the accumulation of critical metals, which is crucial for understanding the enrichment and cycling of critical metals in the deep ocean.