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Previous
estimates about the total mass of all life on our planet have to be
reduced by about one third. This is the result of a study by a German-US
science team published in the current online issue of Proceedings of
the National Academy of Science (PNAS).
According
to previous estimates about one thousand billion tons of carbon are
stored in living organisms, of which 30% in single-cell microbes in the
ocean floor and 55 % reside in land plants. The science team around Dr.
Jens Kallmeyer of the GFZ German Research Centre for Geosciences and
University of Potsdam has now revised this number: Instead of 300
billion tons of carbon there are only about 4 billion tons stored in
subseafloor microbes. This reduces the total amount of carbon stored in
living organisms by about one third.
Previous estimates were based on drill cores that were taken close to shore or in very nutrient-rich areas.
“About
half of the world’s ocean is extremely nutrient-poor. For the last 10
years it was already suspected that subseafloor biomass was
overestimated,” explains Dr. Jens Kallmeyer the motivation behind his study. “Unfortunately there were no data to prove it.”
Large Piston Corer of the Woods Hole Oceanographic Institution on the research vessel R/V Knorr. Up to 40 m of sediment core can be obtained with this device. Credit: GFZ, Jens Kallmeyer |
Therefore,
Kallmeyer and his 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. The six-year work showed that
there were up to one hundred thousand times less 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 these new, drastically lower values.
Despite
of the high logistic and financial efforts for marine drilling
operations there are more data of the abundance of living biomass in the
sea floor than of their abundance on land.
“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 states.
Research
on the “deep biosphere“ is still in the fledgling stages; this is life
that can be found in a kilometer deep inside the Earth’s crust. The new
findings contribute to a better picture of the distribution of living
biomass on Earth.
Global distribution of microbial abundance and biomass in subseafloor sediment
