From about 16 to 22 mins (use link below):
www.bbc.co.uk/iplayer/episode/b07l1zvw/forces-of-nature-with-brian-cox-3-the-moth-and-the-flame

Mike

I've found halocline absolutely fascinating to watch, but only experienced it from a DSRV. It took all the pilot's skill not to bounce off it during the descent and not to porpoise on the way back up up again after the dive with a full load on board.