It’s been known since the 1990s that microbes can live trapped in ocean sediments for millions of years, but until now it’s been a mystery how these organisms make a living.
To find out, scientists collected mud-dwelling bacteria from 11 spots, each tens of meters below the seafloor of the North Pacific Gyre, a circular current that encompasses much of the Pacific.
The gyre “just turns round and round like a huge closed pot, without exchanging much water with the rest of the ocean,” said study leader Hans RÃ¸y, a geomicrobiologist at Aarhus University in Denmark.
As a result, vast swaths of ocean around the gyreâ€”and the sediments belowâ€”are among Earth’s most nutrient starved.
Probing the mud with oxygen sensors, RÃ¸y’s team found that the deep-sediment bacteria are consuming oxygen at extremely sluggish rates. What’s more, the team discovered the microbes are living off the same supply of organic carbon that got trapped along with them.
“They left the surface world when the dinosaurs walked the planetâ€”and they are still eating the same lunch box that they got back then,” RÃ¸y said.
And they’re not alone: Such microbes may be the most common organisms on the planet, making up about 90 percent of Earth’s single-celled life, recent research suggests.