Spatial Distribution of the Subseafloor Life: Diversity and Biogeography

Marine subsurface sediments that cover more than two-thirds of the Earth harbor remarkable numbers of microbial cells. Subseafloor microbial activities may affect global biogeochemical cycles; however, our knowledge of the deep-subseafloor biosphere remains very limited. Recent molecular ecological studies have shown that subseafloor microbial communities are predominantly composed of yet -uncultivated, -uncharacterized bacteria and archaea with great phylogenetic diversity. Some phylogenetic groups are commonly detected in global marine sediments regardless of location and depth, and environmental factors such as sedimentological, geochemical, and geophysical characteristics probably control their activities, biomass, and community structures. This chapter reviews emerging patterns of microbial diversity in deeply buried marine sediments and discusses the potential ecological roles and distribution of microbial communities.