also: うなぞこ
noun
bottom of the ocean; seafloor; seabed
Refers to the physical bottom of the sea or ocean. Common in scientific, geographical, and everyday contexts.
海底にはまだ多くの謎が残っている。
Many mysteries still remain on the ocean floor.
その船は海底に沈んだ。
The ship sank to the bottom of the sea.
noun-modifying (irregular)
undersea; submarine
Prenominal use, modifying nouns to mean 'under the sea' or 'submarine'. Common in compound terms like 海底ケーブル (submarine cable) or 海底火山 (submarine volcano).
海底ケーブルがインターネット通信を支えている。
Submarine cables support internet communication.
海底火山の噴火で新しい島ができた。
A new island was formed by the eruption of a submarine volcano.