Estimates of the total mass of all life on Earth should be reduced by about one third, based on the results of a study by Robert Pockalny, David C. Smith, and Steven D’Hondt of  the University of Rhode Island’s Graduate School of Oceanography and colleagues in Germany.

According to previous estimates, about one thousand billion tons of carbon is stored in living organisms, of which 30 percent is in single-cell microbes in the ocean floor and 55 percent reside in land plants. The researchers have now revised the number downward. Instead of 300 billion tons of carbon in subseafloor microbes, they estimate these organisms contain only about 4 billion tons. This reduces the total amount of carbon stored in living organisms by about one-third.

“Previous estimates of microbial biomass in the ocean sediments were hindered by a limited number of sample locations preferentially located in near-shore, high-productivity regions,” explained Rob Pockalny, URI associate marine research scientist. “With support from the National Science Foundation, we were able to obtain samples from the middle of the Pacific Ocean in some of the lowest productivity regions in the ocean.”

Earlier estimates were based on drill cores that were taken close to shore or in very nutrient-rich areas. The research team collected sediment cores from a total of 57 sites in the South Pacific Gyre, the North Pacific Gyre, and the eastern equatorial Pacific Ocean – areas that were far away from any coasts and islands. The six-year work showed that there were up to 100,000 times fewer cells in sediments from open-ocean areas, which are dubbed “deserts of the sea” due to their extreme nutrient depletion, than in coastal sediments.

With these new data, the scientists recalculated the total biomass in marine sediments and found drastically lower values. The new findings contribute to a better picture of the distribution of living biomass on Earth.

The research was published recently in the Proceedings of the National Academy of Sciences. The abstract is available at http://www.pnas.org/content/early/2012/08/14/1203849109.abstract

The related URI press release is available at this link.

Photo: David C. Smith, Robert Pockalny, Steven D’Hondt