By Alaina G. Levine
In my continuing mission to better understand what’s going on “down there”, specifically in the sediments under the sea in the planet’s basement, an exciting finding has caught my eye. According to a new paper published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), there is a heck of a lot less life on Earth as we know it. For the first time, scientists have been able to create a clear map that predicts how many microbes are in subseafloor, which puts the estimate of Earth’s total number of microbes to be 50-78% lower, and consequently the total number of living biomass on the planet to be 10-45% lower, than previously believed.
As Steve D’Hondt, a co-author of the paper and professor in the Graduate School of Oceanography at the University of Rhode Island, recently told me, he and his team made the potentially game-changing discovery in an innovative manner – they demonstrated that the number of cellular creatures is linked to “everyday” processes in the ocean, that in turn are affected by surface activity. Specifically, D’Hondt and his colleagues recognized that there is a “strong correlation” between the number of microbes and sedimentation rate and distance from shore. By analyzing and factoring in sedimentation rates, distance to shore, and other factors like sea-surface chlorophyll concentration, they estimate that there are 2.9×10(to the 29) microbes living in the subseafloor.
In 1998 Whitman et al wrote that the predicted number of subseafloor microbes was around 35.5×10(to the 29). But as D’Hondt explained, Whitman and his group took samples from six sites that were in upwelling zones that contained an abundance of organic matter. More organic matter means there is more food for the little critters to enjoy, and thus one finds more cells in these areas. He also assumed the same depth of sedimentation everywhere. So according to the authors of this new paper, Whitman’s estimates were naturally skewed.
This new method takes into account that the sedimentation rates are not the same everywhere, and using statistical analysis offers the first clear map of the global distribution of subseafloor cells, predicting how many microbes actually live “down there”. These results and the method employed have more potential significant consequences – they can possibly be used to obtain a better estimate of the amount of carbon buried in the subseafloor, thus giving scientists a better grasp on the extent of, and subseafloor contribution to, the global carbon cycle, says D’Hondt.
A. Geographic distribution of sedimentation rate. B. Geographic distribution of distance from shore. C. Geographic distribution of integrated number of cells (derived from b, m and sediment thickness). Dot colors indicate numbers of cells calculated for actual sites (log10 cells/km2)
Alaina G. Levine is a freelance science writer, professional speaker, corporate comedian, and President of Quantum Success Solutions, a leadership and career consulting enterprise. She can be contacted through her website at www.alainalevine.com.