Fate of copper complexes in hydrothermally altered deep-sea sediments from the Central Indian Ocean Basin

•Deep-sea mining may increase bioavailability and Cu flux to the global ocean.•Cu associate with Fe-oxide phases of hydrothermally altered marine sediments.•Stability of non residual Cu-Sediment complexes can be higher than Cu-EDTA complexes.•Deep-sea sediments from CIB do not significantly contribute to the global Cu flux.

The current study aims to understand the speciation and fate of Cu complexes in hydrothermally altered sediments from the Central Indian Ocean Basin and assess the probable impacts of deep-sea mining on speciation of Cu complexes and assess the Cu flux from this sediment to the water column in this area. This study suggests that most of the Cu was strongly associated with different binding sites in Fe-oxide phases of the hydrothermally altered sediments with stabilities higher than that of Cu-EDTA complexes. The speciation of Cu indicates that hydrothermally influenced deep-sea sediments from Central Indian Ocean Basin may not significantly contribute to the global Cu flux. However, increasing lability of Cu-sediment complexes with increasing depth of sediment may increase bioavailability and Cu flux to the global ocean during deep-sea mining.

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