Traverse cold Antarctic sea (5)
I believe the answer is:
cross
'traverse' is the definition.
('cross' can be a synonym of 'traverse')
'cold antarctic sea' is the wordplay.
'cold' becomes 'c' (eg on taps).
'antarctic sea' becomes 'ross' (Ross Sea).
'c'+'ross'='CROSS'
(Other definitions for cross that I've seen before include "tangelo for one" , "Maybe mule" , "Go to the other side" , "something to bear" , "Short punch in boxing" .)