Abstract
The discovery of the marine “deep biosphere”—microorganisms living deep below the seafloor—is one of the most significant and exciting discoveries since the ocean drilling program began more than 40 years ago. Study of the deep biosphere has become a research frontier and a hot spot both for geological and biological sciences. Here, we introduce the history of the discovery of the deep biosphere, and then we describe the types of environments for life below the seafloor, the energy sources for the living creatures, the diversity of organisms within the deep biosphere, and the new tools and technologies used in this research field. We will highlight several recently completed Integrated Ocean Drilling Program Expeditions, which targeted the subseafloor deep biosphere within the crust and sediments. Finally, future research directions and challenges of deep biosphere investigation towards uncovering the roles of subsurface microorganisms will be briefly addressed.
Highlights
The ocean covers around 70% of the earth surface, and it represents the largest water mass on Earth and the largest aqueous habitat for microbial life
We introduce the history of the discovery of the deep biosphere, and we describe the types of environments for life below the seafloor, the energy sources for the living creatures, the diversity of organisms within the deep biosphere, and the new tools and technologies used in this research field
For more detailed discussion of the deep biosphere, the reader is referred to several recent reviews [13,14,15,16,17]
Summary
The ocean covers around 70% of the earth surface, and it represents the largest water mass on Earth and the largest aqueous habitat for microbial life. Recent studies demonstrated that the biogeographic patterns of hydrothermal vent microorganisms are shaped primarily by large variations of geochemical compositions of hydrothermal fluids, the H2 concentrations [30] These hydrothermally-driven water-rock reactions are a fundamental component of global geochemical cycles and are critical for understanding exchanges and fluxes between the crust and the oceans. The North Pond and Juan de Fuca Ridge flank studies of young oceanic crust will provide a useful contrast to the aged oceanic crust sampled during Expedition to the South Pacific Gyre (crustal ages of >100 Ma) and Expedition to the Louisville Seamounts (crustal ages >70 Ma) Comparisons of these investigations will document first-order patterns of basement habitability and potential microbial activities at a global scale [45]
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