Brine Pool Microbes Enrich Metalliferous Sediments in Salt Giant Basins

We report the discovery of an extinct deep‐sea brine pool in the Red Sea's Hume Deep, providing evidence that rift‐shoulder pools are ephemeral on millennial timescales, and that the microbially‐enriched metalliferous deposits produced during the pool's active phase persist into the stratigraphic record. Now devoid of brine, the Hume Deep retains signatures of activity, including a well‐preserved Lagerstätte death assemblage, seafloor staining consistent with past inhabitation by extremophile microbes, and enrichment of metals associated with their metabolisms. Elemental analyses of seafloor sediments demonstrate that the high metal concentrations in the Hume Deep match those of the active NEOM brine pool, situated 90 km north. In the NEOM pool, metagenomics and metatranscriptomics, coupled with scanning electron microscopy and energy‐dispersive spectroscopy, suggest that microbes drive metal enrichment via microbe‐mineral interactions up to 117× higher than background values. These results suggest a role for microbial processes in metalliferous sediment formation in deep‐sea brine pools. Uranium‐thorium dating suggests the Hume pool was last active between two and 16 thousand years ago. We propose that rift‐shoulder brine pools fill and drain in response to tectonically controlled hydrothermal circulation. Our findings suggest that: (a) microbes inhabiting ancient Red Sea brine pools radically enhanced the metalliferous content of the stratigraphy within and above the basin's Miocene evaporites, and (b) that the elemental composition of other salt giant basins might have been similarly microbially mediated. With implications for understanding early life on Earth, our results provide a framework for interpreting deep‐sea metal enrichments in modern and ancient extremophile environments.