Global distribution of microbial abundance and biomass in subseafloor sediment

TLDR

Subseafloor sedimentary microbial distribution and its drivers remain largely unexplored globally. We find that subseafloor microbial abundance varies by five orders of magnitude, correlates strongly with sedimentation rate and distance from land, and estimate a global total of 2.9 × 10²⁹ cells (~4.1 Pg C, ~0.6 % of Earth’s biomass), roughly equal to seawater and soil totals but far lower than prior estimates, implying a 50–78 % reduction in Earth’s total microbial count and a 10–45 % reduction in total living biomass.

Abstract

The global geographic distribution of subseafloor sedimentary microbes and the cause(s) of that distribution are largely unexplored. Here, we show that total microbial cell abundance in subseafloor sediment varies between sites by ca. five orders of magnitude. This variation is strongly correlated with mean sedimentation rate and distance from land. Based on these correlations, we estimate global subseafloor sedimentary microbial abundance to be 2.9⋅10 29 cells [corresponding to 4.1 petagram (Pg) C and ∼0.6% of Earth’s total living biomass]. This estimate of subseafloor sedimentary microbial abundance is roughly equal to previous estimates of total microbial abundance in seawater and total microbial abundance in soil. It is much lower than previous estimates of subseafloor sedimentary microbial abundance. In consequence, we estimate Earth’s total number of microbes and total living biomass to be, respectively, 50–78% and 10–45% lower than previous estimates.