Salty expanses (4)
'salty expanses' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for seas that I've seen before include "Bodies of salt water" , "Red and Black are" , "Oceans" , "Aegean and Mediterranean, say" , "Red and Dead" .)
(Other definitions for oceans that I've seen before include "Large seas" , "Southern Indian" , "Vast bodies of water" , "Large amounts (of water)" , "Arctic and Indian" .)