Dead bodies of biota constantly shower in deep sea. These do contain energy & is used by many forms like saprotrophs, deep sea fish, epifauna & infauna. There are deep sea currents which are again a natural source of energy. There are hydrothermal vents which constantly give out a mixture of gases in which chaemosynthetic bactria proliferate. read more
For deep sea brine pools the source of the salt is the dissolution of large salt deposits through salt tectonics. The brine often contains high concentrations of methane, providing energy to chemosynthetic extremophiles that live in this specialized biome. read more
The three main sources of energy and nutrients for deep sea communities are marine snow, whale falls, and chemosynthesis at hydrothermal vents and cold seeps. Marine snow The upper photic zone of the ocean is filled with particle organic matter (POM) and is quite productive, especially in the coastal areas and the upwelling areas. read more