The unexpected role of magnetic microbes in deep-sea mining

Polymetallic nodules are potato-sized formations on the ocean floor that are rich in minerals such as nickel, cobalt and manganese. Their concentration of rare and economically important minerals has made these nodules the focus of controversial deep-sea mining ventures.

There are several hypotheses about how nodules develop, but most agree that they form when metallic components in seawater slowly precipitate to the seafloor. Several studies suggest that microorganisms also play a role in nodule growth. The nodules tend to contain biogenic magnetite, the fossil remains of magnetotactic bacteria, which have magnetic organelles that act like tiny compass needles.

In a study published in the Geophysical Research Journal: Solid EarthResearchers examined the relationship between bacteria abundance and the distribution of polymetallic nodules in the Clarion-Clipperton Fracture Zone (CCFZ), an environmental management zone south of Hawaii managed by the International Seabed Authority. The CCFZ could be an economically vital region for the thriving deep-sea mineral exploration industry.

The authors analyzed seafloor sediments collected during a research cruise in 2013. They used a vibrating sample magnetometer to determine magnetic properties, electron microscopes to identify minerals based on electron diffraction, and spectroscopy techniques (which test how materials absorb and emit light and other radiation). for testing rare earth elements.

The results revealed three distinct origins of the magnetic minerals in the samples: wind-blown dust, volcanoes and bacteria. Wind-borne sediments were likely carried into the region by mid-latitude westerly winds and northeast trade winds, as indicated by decreasing magnetite concentrations from north to south and east to west in the CCFZ. Volcanic magnetite results from the erosion of Antarctic bottom waters from the Line Islands and the Hawaiian chain.

The greatest abundance of biogenic magnetite, the type associated with bacteria, coincided with the highest densities of polymetallic nodules in the CCFZ. The results led the authors to hypothesize that the nodules produce carbon-rich, oxygen-poor microenvironments that support bacteria and encourage biomineralization of magnetite nanocrystals. In turn, the bacteria help promote the growth of nodules.

The results provide new insights into the formation of polymetallic nodules and the ecological distribution of magnetotactic bacteria, with implications for possible deep-sea exploration.

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.