Adjective : suboceanic oil. ,suboceanic plants.    From Dictionary.com. 

Such an explosion, indescribable in its fury, might in the end raise the height of the subocean island a foot.    From Wordnik.com.  [Hawaii]

And then one day, at the northwest end of the subocean rupture, an eruption of liquid rock occurred that was different from any others that had preceded.    From Wordnik.com.  [Hawaii]

The subocean connections would be deep sea cables in the least vulnerable position, and it may be added that the system would possess an advantage peculiar to a globe-encircling line of telegraph-each point touched would be telegraphically connected with every other point by two distinct routes extending in opposite directions.    From Wordnik.com.  [Our Empire Cables] Reference