Submarine endures choppy area (8)
I believe the answer is:
undersea
'submarine' is the definition.
(submarine means under the sea)
'endures choppy area' is the wordplay.
'choppy' indicates anagramming the letters (choppy implies disruption).
'area' becomes 'a' (maths abbreviation).
'endures' anagrammed gives 'underse'.
'underse'+'a'='UNDERSEA'
(Other definitions for undersea that I've seen before include "Beneath the surface of the ocean" , "in salt water" , "Where bed is" , "Below marine surface" , "Beneath the oceans" .)