Ocean temperature reveals position (4)
I believe the answer is:
seat
'position' is the definition.
(I know that seat is a more specific form of position)
'ocean temperature' is the wordplay.
'ocean' becomes 'sea' (synonyms).
'temperature' becomes 't' (abbreviation).
'sea'+'t'='SEAT'
'reveals' acts as a link.
(Other definitions for seat that I've seen before include "Constituency; location" , "MP's place in parliament" , "Take one and sit" , "Box ---, position of advantage" , "Somewhere to sit" .)