Marsh bird from intensely cold North (7)
I believe the answer is:
bittern
'marsh bird' is the definition.
(I've seen this before)
'intensely cold north' is the wordplay.
'intensely cold' becomes 'bitter' (I've seen this before).
'north' becomes 'n' ('N' can be a synonym of 'north').
'bitter'+'n'='BITTERN'
'from' is the link.
(Other definitions for bittern that I've seen before include "Source of boom" , "Compact tawny-brown heron with nocturnal habits and a booming cry" , "Bird with a booming cry" , "found hidden in reed-beds" , "Booming marsh bird" .)