[rsa4046]

Deep sea chemosynthetic communities, sustained by cycling and release of hydrothermal vent fluids on the seafloor (discovered in the 1970s), are quite unlike anything living at or close to ocean surface, where primary production is sustained by phytoplankton [0]. And bacteria have been found even in extremely deep boreholes [1].

Cold seep chemotrophy exists on the sea floor as well, fueled by reduced gases such as methane, other hydrocarbons (e.g. Gulf of Mexico). But in these seeps, the source of organic carbon may have ultimately come from the sea surface environment.

[0] https://www.whoi.edu/know-your-ocean/ocean-topics/ocean-life... [1] https://www.mdpi.com/2075-1729/10/1/2/htm