These
reservoirs are mainly in poorly explored regions
where little geophysical data has been acquired and / or they are so
deep that they defy established methods used to identify hydrocarbons from their geophysical signatures.
The marine biota also redistribute carbon: marine organisms grow organic tissue and calcareous shells in surface waters, which, after their death, sink to
deeper waters,
where they are returned to the dissolved inorganic carbon
reservoir by dissolution and microbial decomposition.