Controls on the distribution of rare earth elements in deep-sea sediments in the North Atlantic Ocean

Deep-sea sediments can contain relatively high concentrations of rare earth elements and yttrium (REY), with a growing interest in their exploitation as an alternative to land-based REY resources. To understand the processes that lead to enrichment of the REY in deep-sea sediments, we have undertaken a detailed geochemical study of sediments recovered from the Atlantic Ocean, on a transect along ~24°N that includes the deep Nares Abyssal Plain and the Canary and North America Basins. Total REY concentrations (ΣREY) range from 7.99 to 513ppm, and total concentrations of the heavy REY (Eu - Lu) range from 0.993 to 56.3ppm. REY concentrations are highest in slowly accumulating pelagic red clays, especially in samples that contain ferromanganese micronodules. Factor analysis reveals that hydrogenous Fe- and Mn-(oxyhydr)oxides are the primary REY carrier phase in the red clays. In situ analysis of individual micronodules confirms that they have high ΣREY (up to 3620ppm). REY concentrations are higher in micronodules that have a hydrogenous source, characterised by higher Fe/Mn, compared to micronodules that have a diagenetic source. The ΣREY content of North Atlantic deep-sea sediments is ~4 times lower than in Pacific deep-sea sediments. We calculate that the area of seafloor required to extract ~10% of the global annual REY demand is ~100km2, assuming removal of the upper 1m of sediment.