Insights Into a Correlation Between Magnetotactic Bacteria and Polymetallic Nodule Distribution in the Eastern Central Pacific Ocean

The Clarion–Clipperton Fracture Zone (CCFZ) in the eastern central Pacific Ocean is the world's largest area for potential deep-sea polymetallic nodule mining and is attracting increased scientific and commercial interest. Recent studies indicate that biogenic magnetite, generated intracellularly by magnetotactic bacteria (MTB), can carry a biogeochemical remanent magnetization in polymetallic nodules, although whether biogenic or physical-chemical processes are responsible for nodule formation remain poorly constrained. Here, we report a combination of magnetic, electron microscope and geochemical analyses on seafloor surface sediments from the eastern CCFZ to understand the spatial distribution of biogenic magnetite and possible relationships between MTB and polymetallic nodules. Experimental results indicate that sedimentary magnetic minerals from the northern and southern regions are dominated by detrital (eolian loess and volcanic material) and biogenic magnetic minerals (magnetosomes), respectively. Sediments from the intermediate region contain both detrital and biogenic magnetic minerals. Quantitative first-order reversal curve-principal component analysis indicates that biogenic magnetite has the highest concentration in the intermediate CCFZ region, coincident with the highest polymetallic nodule density. Combined with previous research, we speculate that MTB growth on the CCFZ seafloor is driven mainly by local redox conditions. Manganese nodule surfaces are rich in organic biofilms, which results in a relatively thick oxic-anoxic transition zone in high-abundance manganese nodule regions, which generates an optimal microenvironment for both MTB growth and magnetite biomineralization. This study provides new clues for understanding the ecological distribution of MTB and the biogeochemical remanent magnetization recorded by biogenic magnetite in deep-sea sediments.