海かい面めん下か

noun, noun which may take the genitive case particle 'no'

below sea level; undersea; beneath the waves

Refers to the area or state of being under the surface of the sea. Often used in scientific or descriptive contexts.

• その島しまの一いち部ぶは海かい面めん下かにある。

  Part of the island is below sea level.

• 海かい面めん下かの地ち形けいを調ちょう査さする。

  Survey the undersea topography.