Reportedly bound to sea change (4)
I believe the answer is:
tide
'change' is the definition.
(I know that tide is a type of fluctuation)
'reportedly bound' is the wordplay.
'reportedly' shows a homophone (sound like).
'bound' becomes 'tied' ('tie' can be a synonym of 'bind').
'tied' is a homophone of 'TIDE'.
'to sea' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tide that I've seen before include "Periodic flow" , "It ebbs and flows" , "Powerful trend of events" , "turning point" , "Current, ebb" .)