“…Yet, current knowledge of the pelagic microbial community structure of the dark ocean, the largest biome in the biosphere, is based on a pool of samples collected at specific locations (DeLong et al, 2006;Martín-Cuadrado et al, 2007;Brown et al, 2009;Galand et al, 2010;Agogué et al, 2011;Eloe et al, 2011;Quaiser et al, 2011;Smedile et al, 2012;Wang et al, 2013;Wilkins et al, 2013;Ganesh et al, 2014) (Supplementary Figure S1) and thus are dwarf in comparison with the analyses of upper ocean microbial communities, which have indeed been assessed at global scales Yooseph et al, 2007;Zinger et al, 2011;Sunagawa et al, 2015). Whereas the deep ocean is often considered to be a rather uniform environment, the connectivity of pelagic microbial communities may be reduced by the limited mixing between water masses (Agogué et al, 2011;Hamdan et al, 2013) or modulated by advection (Wilkins et al, 2013) imposing limitations on the dispersion of marine microbes in this low-turbulence environment.…”