Where marine life will never be happy (2,3,2,3,5)
I believe the answer is:
on top of the world
'happy' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for on top of the world that I've seen before include "happy" , "as a successful North Pole expedition?" , "Delighted" , "In seventh heaven" , "as a polar bear, but not as a penguin?" .)