Microbes living in oxygen-free brine pools at the bottom of the Red Sea enrich seafloor sediments with metals at up to 117 times normal levels, and the traces outlast the pools themselves by millenniums, scientists reported last month.
The study, published in the journal AGU Advances, describes what its authors call an extinct brine pool in the Hume Deep, a depression about 1,370 meters down in the northern Red Sea rift. No brine remains, but the basin holds a well-preserved assemblage of dead organisms and staining of the seafloor consistent with past inhabitation by extremophile microbes. “The only component lacking from this site is the brine itself,” the researchers wrote.
For comparison, the team, led by Morgan I. Chakraborty, analyzed sediments from the active NEOM brine pool, 90 kilometers to the north in the Gulf of Aqaba and about 1,770 meters deep. The metal concentrations in the lifeless Hume Deep matched those of the living NEOM pool. Gene sequencing, electron microscopy and chemical analysis of the NEOM sediments pointed to microbes as the concentrators, enriching metals through their interactions with minerals at up to 117 times background values.
Uranium-thorium dating indicates the Hume pool was last active between 2,000 and 16,000 years ago. The authors propose that such rift-shoulder pools fill and drain in cycles, driven by tectonically controlled hydrothermal circulation, which would make any single pool a temporary feature on geological time scales.
That fits the strangeness of the pools themselves. “You’d expect diffusion to dilute the pools and yet they seem to last a very long time somewhere on the order of thousands of years,” one Hacker News commenter, areoform, wrote of active ones. “It’s not immediately obvious to me how the physics of these pools functions.”
The metals in question, manganese, copper, iron, potassium and molybdenum, include several in demand for clean-energy technologies, and the authors wrote that the findings could inform future resource exploration. Modern Red Sea pools cover less than 0.1 percent of the 440,000-square-kilometer basin, by their calculation. But the study argues that pools were far larger and more numerous when “salt giant” basins like the Red Sea first formed and later reflooded, so microbes may have helped set the metal content of ancient deposits far beyond one basin.
The bigger claim reaches back billions of years. Sharp rises of manganese in ancient oceans, long read as signatures of oxygen, may in some cases record microbial activity instead, the authors wrote. Their work, they argue, gives researchers a new framework for spotting traces of early life in the chemistry of ancient rocks.