Existing estimates say about one thousand billion tons of carbon are stored in living organisms, of which 30 percent are in single-cell microbes in the ocean floor and 55 percent in land plants, but that number needs revising, the study published in the Proceedings of the National Academy of Science said.
A research team led by Jens Kallmeyer of the GFZ German Research Center for Geosciences said only about 4 billion tons are stored in subseafloor microbes, reducing the total amount of carbon stored in living organisms by about a third.
Previous estimates were based on drill cores taken close to shore or in very nutrient-rich areas, researchers said.
"About half of the world's ocean is extremely nutrient-poor," Kallmeyer said. "For the last 10 years it was already suspected that subseafloor biomass was overestimated.
"Unfortunately there were no data to prove it."
Kallmeyer, with colleagues from the University of Potsdam and the University of Rhode Island, collected sediment cores from areas that were far away from any coasts and islands and found there were up to one hundred thousand times less cells in sediments from open-ocean areas, dubbed "deserts of the sea" due to their extreme nutrient depletion, than in coastal sediments.
"Our new results show the need to re-examine the other numbers, as e.g. the amount of carbon in deep sediments on land," Kallmeyer said.