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 ($Σ$REY) range from 7.99 to 513 ppm, and total concentrations of the heavy REY (Eu - Lu) range from 0.993 to 56.3 ppm. 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 $Σ$REY (up to 3620 ppm). 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 $Σ$REY 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 {\~{}} 100 km2, assuming removal of the upper 1 m of sediment.