bathyal zone vs sea bottom

bathyal zone and sea bottom both are nouns.

Word	Noun	Adjective	Verb	Adverb
bathyal zone	Yes	No	No	No
sea bottom	Yes	No	No	No

As nouns, sea bottom is a hypernym of bathyal zone; that is, sea bottom is a word with a broader meaning than bathyal zone:

bathyal zone: the steep descent of the seabed from the continental shelf to the abyssal zone
sea bottom: the bottom of a sea or ocean

Other hypernyms of bathyal zone include Davy Jones's locker, Davy Jones, ocean bottom, ocean floor, sea floor, seabed.

bathyal zone (noun)	sea bottom (noun)
the steep descent of the seabed from the continental shelf to the abyssal zone	the bottom of a sea or ocean