Illuminating subseafloor ecosystems using microbial tracers

The use of microorganisms as tracers of the physical, chemical, and biological nature of otherwise inaccessible environments is explained and this concept applied to the subseafloor at mid-ocean ridges. Hyperthermophilic microorganisms found in low-temperature fluids can be used as tracers of the characteristics of subseafloor environments. These organisms show that the subseafloor at mid-ocean ridges tapped by these low-temperature fluids contains a microbial ecosystem and has physical and chemical characteristics consistent with a mixture of end-member hydrothermal fluid and seawater. Other subseafloor environments examined using microorganisms include crust that has experienced eruptions and sedimented ridges. Novel hyperthermophilic organisms cultured from subseafloor environments indicate that there are physicochemical habitats that are unique to the subseafloor.